Microfiber Pollution 9789811941856, 9811941858

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Sustainable Textiles: Production, Processing, Manufacturing & Chemistry

R. Rathinamoorthy S. Raja Balasaraswathi

Microfiber Pollution

Sustainable Textiles: Production, Processing, Manufacturing & Chemistry Series Editor Subramanian Senthilkannan Muthu, Head of Sustainability, SgT and API, Kowloon, Hong Kong

This series aims to address all issues related to sustainability through the lifecycles of textiles from manufacturing to consumer behavior through sustainable disposal. Potential topics include but are not limited to: Environmental Footprints of Textile manufacturing; Environmental Life Cycle Assessment of Textile production; Environmental impact models of Textiles and Clothing Supply Chain; Clothing Supply Chain Sustainability; Carbon, energy and water footprints of textile products and in the clothing manufacturing chain; Functional life and reusability of textile products; Biodegradable textile products and the assessment of biodegradability; Waste management in textile industry; Pollution abatement in textile sector; Recycled textile materials and the evaluation of recycling; Consumer behavior in Sustainable Textiles; Eco-design in Clothing & Apparels; Sustainable polymers & fibers in Textiles; Sustainable waste water treatments in Textile manufacturing; Sustainable Textile Chemicals in Textile manufacturing. Innovative fibres, processes, methods and technologies for Sustainable textiles; Development of sustainable, eco-friendly textile products and processes; Environmental standards for textile industry; Modelling of environmental impacts of textile products; Green Chemistry, clean technology and their applications to textiles and clothing sector; Eco-production of Apparels, Energy and Water Efficient textiles. Sustainable Smart textiles & polymers, Sustainable Nano fibers and Textiles; Sustainable Innovations in Textile Chemistry & Manufacturing; Circular Economy, Advances in Sustainable Textiles Manufacturing; Sustainable Luxury & Craftsmanship; Zero Waste Textiles.

R. Rathinamoorthy · S. Raja Balasaraswathi

Microfiber Pollution

R. Rathinamoorthy Department of Fashion Technology PSG College of Technology Coimbatore, India

S. Raja Balasaraswathi Department of Fashion Technology National Institute of Fashion Technology Bengaluru, India

ISSN 2662-7108 ISSN 2662-7116 (electronic) Sustainable Textiles: Production, Processing, Manufacturing & Chemistry ISBN 978-981-19-4184-9 ISBN 978-981-19-4185-6 (eBook) https://doi.org/10.1007/978-981-19-4185-6 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore

Foreword

Have you ever noticed how soft and thin your favorite t-shirt becomes after years of wearing and washing? Do you have a pair of jeans whose knees are thin and white with wear? How much lint have you collected from a dryer lint trap? Our clothing and home textiles do not maintain their integrity over time and tiny pieces of fiber broken off of these items are found up and down rivers, near shore and offshore, at high latitudes and low, atop mountains and ocean trenches, even in the bodies of creatures of all sizes in the form of microfiber pollution. With microfiber pollution, from our clothing and home textiles as well as other sources, plaguing our air, water—both fresh and salt water, and terrestrial environments, the need for knowledge and solutions is urgent. To date, however, the subject has suffered from a somewhat narrow perspective with a focus on washing machines and wastewater treatment plants and information delivered in the form of individual articles both peer-reviewed (which is great for credibility but difficult for people outside of academia to access), and in popular media (which is accessible but can be unpredictable from a credibility standpoint). If the problem were confined to just washing machines whose effluent is treated by municipal wastewater treatment plants, I am not sure this book would be necessary. But, we do know that while washing machines and WWTPs are extremely important to understanding, preventing, and reducing microfiber pollution, by no means do they tell the whole story. There is a large amount of very recent research that shows microfiber pollution to be complex and multifaceted. This latest wave of work investigates textiles themselves, as well as the forces exerted upon them during their lifecycle—manufacturing processes, wearing, washing, drying, and, finally, the difficult question of our clothing and home textiles’ end of life. That is where this book comes in. Dr. R. Rathinamoorthy and S. Raja Balasaraswathi are leaders in the field at the forefront of textile research and understanding. Their knowledge of textile production and focus on microfiber pollution make them uniquely qualified to produce exactly what is needed in the form of this incredibly thorough and informative book. The problem of microfiber pollution is in need of solutions. These solutions will come from a variety of sectors that are part of the textile industry on the whole. v

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The more diverse these solutions, the more likely this problem can be controlled and contained. Getting the right information to this diverse group of professionals, engineers, researchers, and innovators is essential. This book, in its thorough investigation of textiles and microfiber pollution, has the power to do what hasn’t been done to date. By bringing such a breadth of up-to-date information on this topic together, this book has the power to reach people in multiple disciplines and industries. It can serve as a central source for cutting-edge information about the problem. And, as such, this book and especially the people reading it have the power to move our collective understanding of microfiber pollution in a direction that produces solutions—upstream and downstream of consumers, that help us collectively get ahead of this problem and keep microfiber pollution out of our lakes, rivers, and one, big, shared ocean. For a clean ocean, Rachael Z. Miller Founder Rozalia Project for a Clean Ocean, Co-inventor/CEO Cora Ball

Preface

Microplastic is one of the emerging pollutants in the world. Though different origins were reported to release these particles, textiles and apparel are noted to be major contributors to microfibers. Microfibers are a subclass of microplastics, classified by the name of fiber due to their higher length to diameter ratio. Though the awareness of microplastic contamination increased in the past couple of years, the awareness among the public is still meager. Researchers have listed synthetic textile material as one of the major contributors to microfibers, due to their higher consumption per capita. A higher disposable income and cheaper clothing materials have often been reported as the reason for increased clothing consumption in the current decade. The microfiber emission from textiles is noted at every stage of the material lifecycle from the manufacturing, use, and disposal phase. Due to their increased environmental impact and human health-associated issues, the research on mitigation of such pollutants is the need of the hour. In this aspect, this book consolidated the information from a textile technologist viewpoint, to address a general audience, how and where the microfiber issue arises, and what is the core reason for the development of such microfibers from textile. The first chapter of the book outlines the different types of anthropogenic materials and their sizes. The chapter also details the sustainability issues associated with the textile industry, by correlating the microplastic and microfiber emission at different stages. The second chapter of the book details the fundamental mechanism of microfiber release from the textile structure, where the latter part of the chapter mainly addresses the methods and technologies adopted to characterize the microplastics/microfiber size, color, and other properties. The third chapter of the book further details in depth on the various manufacturing process, including yarn, fabric, and their physical and mechanical characteristics by relating microfiber emission from textiles. This chapter addresses the knit, woven, and non-woven fabrics and their microfiber release behaviors. The fourth chapter of the book mainly focuses on the textile laundry process. The effect of various laundry parameters, laundry equipment, and external parameters on the microfiber emission during domestic laundry was described. The second section of Chap. 4

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details the municipal wastewater treatment plant and its role in microfiber release and subsequent environmental pollution. Chapter 5 of the book highlights the impact of microplastic pollution on different environments, namely the atmosphere, marine area, terrestrial environment, glaciers, and mountains. Further, the impact of such contamination on various animals and humans was detailed in this chapter. The last chapter of the book (Chap. 6) summarizes the potential mitigation strategies that can be adapted to control or reduce microplastic emissions, mainly addressing the textile and microfiber mitigation strategies. The chapter also deals with current regulations and norms developed across the world to control and monitor these evolving microplastics. We strongly believe that this book will be a convenient material for researchers who are interested in microplastics, especially microfiber pollution or mitigation studies. The details discussed in the content and also the issues addressed in each chapter will enable researchers to work further and help in finding a suitable solution to address this issue. The authors have confidence that this book will serve as a path for the betterment of the environment, society, and lifestyle. Coimbatore, India Bengaluru, India

R. Rathinamoorthy S. Raja Balasaraswathi

Acknowledgement

In the first place, we thank the Almighty for giving the opportunity to write this book. We are very much thankful to the researchers from various parts of the world who have worked in the area of microplastic and microfiber pollution as their research was very helpful for us in writing this book. We would like to place on record, our sincere thanks to everyone who was directly or indirectly involved in this book coming to shape. We would like to thank Dr. Subramanian Senthilkannan Muthu, Series Editor, Springer Publications, for being inspirational and instrumental in developing this book. We also would like to thank Andrea Ferris, CEO, Intrinsic Advanced Materials, LLC., for providing research data related to biodegradable polyester fibers. The data provided by her was indeed very useful for us to write this book. We also would like to thank Rachael Z. Miller, Founder/CEO—Cora Ball, and Founder—Rozalia Project for a Clean Ocean, for spending her valuable time in writing foreword for this book. As authors, we would also like to thank our college management and authorities for providing us with the necessary infrastructure. Last but not the least, we render our special thanks to our family members for their continuous moral support and understanding during this project.

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Contents

1 Microfiber Pollution—A Sustainability Issue . . . . . . . . . . . . . . . . . . . . . . 1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Plastics, Microplastics, and Microfibers . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Textile fiber Production and Consumption . . . . . . . . . . . . . . . . . . . . . . 1.4 Contribution of Textile and Apparel Industries to Microplastic Pollution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Microfiber Shedding of Textile Materials—Mechanism and Analysis Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Mechanism of Microfiber Shedding from Textile Materials . . . . . . . 2.3 Causes of Microfiber Shedding from Textile Materials . . . . . . . . . . . 2.4 Microfiber Detection in the Ecosystem . . . . . . . . . . . . . . . . . . . . . . . . 2.4.1 Sample Collection and Conditioning . . . . . . . . . . . . . . . . . . . . 2.4.2 Microplastic Particle Extraction . . . . . . . . . . . . . . . . . . . . . . . . 2.4.3 Characterization of Microfibers . . . . . . . . . . . . . . . . . . . . . . . . 2.5 Techniques and Test Methods to Analyze the Microfiber Shedding from Apparel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5.1 Textile Sample Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5.2 Washing Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5.3 Filtration Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5.4 Quantification Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5.5 Characterization of Fibers Shed from the Textile Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5.6 Quality Assurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5.7 Other Innovative Techniques in Microfiber Analysis . . . . . .

1 1 3 7 9 10 15 19 19 20 23 26 27 28 28 29 29 35 38 40 46 48 49

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2.6 Microfiber Shedding from Textile Materials Other Than Apparels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

52 61 61

3 Factors Influencing Microfiber Shedding—Role of Textile and Apparel Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 3.2 Fiber Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 3.2.1 Structural Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 3.2.2 Mechanical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 3.2.3 Moisture-Related Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 3.2.4 Chemical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 3.2.5 Role of Elastane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 3.3 Yarn Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 3.3.1 Type of Yarn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 3.3.2 Yarn Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 3.3.3 Mechanical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 3.3.4 Yarn Production Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 3.4 Fabric Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 3.4.1 Fabric Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 3.4.2 Fabric Geometry and Structural Parameters . . . . . . . . . . . . . . 86 3.4.3 Physical and Mechanical Properties . . . . . . . . . . . . . . . . . . . . . 89 3.5 Textile Processing and Finishing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 3.5.1 Preparatory Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 3.5.2 Dyeing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 3.5.3 Finishing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 3.6 Apparel Production Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 3.6.1 Cutting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 3.6.2 Sewing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 3.7 Aging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 3.8 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 4 Domestic Laundry—A Major Cause of Microfiber Shedding . . . . . . . 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Influence of Washing Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1 Laundry Duration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.2 Laundry Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.3 Mechanical Agitation and Water Volume . . . . . . . . . . . . . . . . 4.2.4 Water Hardness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Influence of Washing Additives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.1 Use of Detergents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.2 Use of Softener . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4 Influence of Washing Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.1 Top and Front Load Washing Machines . . . . . . . . . . . . . . . . .

107 107 108 109 110 111 114 114 114 117 120 121

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4.4.2 Household and Laboratory Washing Machines . . . . . . . . . . . 4.4.3 Hand Washing Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5 Effect of Repeated Laundry on Microfiber Release . . . . . . . . . . . . . . 4.6 Impact of Drying Method/Laundry Dryer . . . . . . . . . . . . . . . . . . . . . . 4.7 Estimation of Microfiber Release from Domestic Laundry Worldwide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8 Wastewater Treatment Plant (WWTP) as a Secondary Source of Microfiber Pollution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8.1 Impact of WWTP Effluent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8.2 Impact of WWTP Sludge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

121 122 123 125

5 Impact of Microfiber/Microplastic Pollution . . . . . . . . . . . . . . . . . . . . . . 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Microfibers in the Atmosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3 Microfiber in the Marine Environment and Its Impact on Aquatic Life Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4 Microfibers in Freshwater Systems and Their Impact . . . . . . . . . . . . 5.5 Microfibers in Human Food (Chain) Samples . . . . . . . . . . . . . . . . . . . 5.5.1 Contamination in Salt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5.2 Drinking Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5.3 Contamination in Milk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5.4 Contamination in Honey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5.5 Other Food Items . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.6 Microfiber in Polar Ice Caps/Glaciers . . . . . . . . . . . . . . . . . . . . . . . . . . 5.7 Impact on Human . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.8 Microfiber Interaction with Other Pollutants . . . . . . . . . . . . . . . . . . . . 5.9 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

151 151 152

6 Microfiber Pollution Prevention—Mitigation Strategies and Challenges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 Production Stage—Modification of Source (Textile Materials) . . . . 6.2.1 Surface Finishing of Textile Materials . . . . . . . . . . . . . . . . . . . 6.2.2 Improving Degradability of Synthetic Fibers . . . . . . . . . . . . . 6.2.3 Bio-based Alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3 Consumption Stage—Modification of Cause (Domestic Laundering) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.1 Use of Washing Additives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.2 Washing Aids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4 Disposal Stage—Waste Management System . . . . . . . . . . . . . . . . . . . 6.4.1 Wastewater Treatment Plants . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.2 Techniques for Microfiber Removal in Water Bodies . . . . . .

128 132 132 137 145 145

155 161 165 165 168 175 177 178 179 182 187 191 192 205 205 206 206 212 214 215 215 219 224 224 226

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6.5 Management of Microfiber Wastes—Conversion into Sustainable Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.6 Consumer Awareness on Microfiber Pollution . . . . . . . . . . . . . . . . . . 6.7 Efforts Made by Different Brands and Organizations . . . . . . . . . . . . 6.8 Government Regulations and Laws for Microfiber Pollution Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.9 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

232 233 235 237 238 238

About the Authors

Dr. R. Rathinamoorthy is working as an Associate Professor in the Department of Fashion Technology, PSG College of Technology, Coimbatore, India, since 2009. He has a Google h-index of 16 and a Scopus h-index of 11 with more than 850 citations. He had completed his Ph.D. in “Studies on Odour Formation Characteristics of Textiles” in 2016. Recently, he received the “Young Achiever Award” for the year 2019 by the Institute of Engineers India (IEI), coimbatore Chapter. In 2017, he received a national-level award, “Young Engineer award for the year 2016-17” by the Institute of Engineers India (IEI), Kolkata, West Bengal, India. He had published 20 national and 69 international research articles in various refereed and non-refereed journals, and presented several international conference papers and national seminars. He had also published 7 books and 28 book chapters with various international publishers like Springer Verlag, Springer Nature, Springer Singapore, and Elsevier publishers. S. Raja Balasaraswathi is doing Master’s in Fashion Technology at the National Institute of Fashion Technology (NIFT), Bengaluru, India. She completed her Bachelor’s degree in Fashion Technology in 2021 at PSG College of Technology, Coimbatore, India. She has received the “Best Outgoing Student—2021” from PSG College of Technology. She has been doing research in the area of Microplastics/Microfibers Pollution since 2019. She received “Dr. APJ Abdul Kalam Young Research Fellowship—2020” from Terre Policy Centre, Pune, India, for the project “Surface Modification of Synthetic textiles to reduce Microfiber Shedding”. She has also received “The Student Project of the year award 2021”, for the project titled “Mitigation of Microfiber Shedding from Synthetic Textiles” from the Institute of Scholars, Bangalore, India. She has been presented with “Best Project Award—2021” for the project “Microfiber Pollution: Analysis of Textile Parameters and Mitigation Strategy” from PSG Tech Alumni Association, Coimbatore. She had published 10 research articles in the field of Microfiber pollution in International Journals and contributed 3 book chapters on Microfiber pollution. She also presented papers and posters at 9 International conferences and 1 national conference.

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Chapter 1

Microfiber Pollution—A Sustainability Issue

1.1 Introduction The concept of sustainability has started holding a significant part in almost every sector in the world. Sustainability, as per the UN definition, is “meeting the needs of the present without compromising the ability of future generations to meet their own needs” [1]. Sustainability has been embraced from different perspectives as it can result in healthy habitat for all with the assurance of a future for all [2]. Hence, researchers and stakeholders of different fields have started addressing the sustainability issues in their own areas and trying to adopt sustainable development goals to ensure environmental, societal, and economical sustainability in their respective fields. The textile and fashion industry, being one of the most polluting industries, has enough problems that can make the industry unsustainable. The environmental footprint of the textile and fashion industry is more concerning. Every part of the supply chain of the industry starting from raw material production to disposal has an adverse impact on the sustainable aspects. 60% of the materials being used in the industry are plastic-based, which can negatively impact the environment. With that, the industry contributes around 10% of global pollution [3]. Moreover, the industry is more chemical-based which consumes 23% of chemicals produced worldwide. Textile and Fashion industries consume a huge quantity of water for the production of raw materials, especially cotton, and for textile processing. The sad reality is that the fashion industry consumes 1.5 trillion liters of water every year, whereas 750 million people in the world have no access to drinking water [4]. One-fifth of the toxic chemicals that are polluting the world’s water system is contributed by the textile industry which uses a huge volume of water for different processing steps of textile materials [5]. Almost all the dyes which are being used are synthetic, and 200,000 tons of dyes are entering the water bodies through effluent [4]. Apart from dyeing, the tanning process of leather manufacturing is also a greater matter of concern. In Bangladesh, every year, around 7.7 million liters of wastewater are being released from tanneries that contain high levels of chromium [6]. This makes the © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 R. Rathinamoorthy and S. Raja Balasaraswathi, Microfiber Pollution, Sustainable Textiles: Production, Processing, Manufacturing & Chemistry, https://doi.org/10.1007/978-981-19-4185-6_1

1

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1 Microfiber Pollution—A Sustainability Issue

fashion industry share 20% of global industrial wastewater pollution [7]. Currently, the fashion industry contributes 8–10% of global carbon emissions, which would reach 26% by 2050 if the same trend continues [8]. Since the textile and fashion industries have a significant impact on the environment as well as society, they will greatly affect the World’s Sustainable Development. The Sustainable Development Goals (SDGs) framed by United Nations (UN) to promote sustainability in different areas also pay special attention to the textile and fashion industries. It has been committed to integrating the SDGs framed by the UN in the fashion industry to address the issues related to the production and consumption of clothing. SDGs for Better Fashion mainly concentrate on creating awareness of the importance of sustainability by engaging with students, companies, and consumers to align their sustainability initiatives [9]. By understanding the role of the fashion sector in SDGs, the United Nations agencies and the allied organizations have initiated “The United Nations Alliance for Sustainable Fashion” which can contribute to the SDGs by coordinating the UN bodies which are promoting the projects and policies in the field of fashion that accelerates the achievement of SDGs [10]. Several other initiatives are made to ensure sustainable development in the fashion industry. “2020 Circular Fashion System Commitment” was made by the Global Fashion Agenda to make a commitment toward a circular fashion system by the implementation of design strategies for cyclability. It promotes the collection and reselling of used garments and other fashion products and also the market of fashion products made out of recycled post-consumer textile fibers [11]. The other initiative by the Waste & Resources Action Programme is the “Sustainable Clothing Action Plan (SCAP) 2020 Commitment”. This framework focuses on reducing carbon, water, and waste in the industry by reinventing design, production, reuse, recycling, and extending the durability of clothing [11]. The textile and fashion industries are having various sustainable issues which all should need special attention while seeking sustainable development. And several organizations have made various initiatives that can lead to a sustainable industry. Microplastic and Microfiber pollution which is being addressed recently by different environmentalists and researchers as a threatening issue is one of the problems of the Textile and Fashion Industry. Hence, it is crucial to address the issue from the viewpoint of the industry. This book enlightens the issue of Microfiber pollution in the context of Textile and Apparel Industries. Since the standardization of terms and definitions is not well established, different terms and units are being used currently. This chapter details the definition of microplastics and microfibers in terms of their size, shape, and also their classifications. Moreover, in the later section, the chapter insists on the importance of textile materials and their contribution to global microfiber pollution.

1.2 Plastics, Microplastics, and Microfibers

3

1.2 Plastics, Microplastics, and Microfibers Plastics are a greater concern for decades because of the serious hazards associated with them starting from the raw material to disposal. Plastics hold a significant place in the market and the global plastic market size is getting increased, with an expected growth rate of 3.4% from 2021 to 2028 [12]. India alone generates an average of 5.6 million tons of plastics annually, making it one of the biggest plastic consumers in the world [13]. The unbeatable versatility of plastics made them fit for a wide variety of applications. The increased usage ends up in a huge amount of plastic waste. Being a non-biodegradable material, these plastic wastes remain in the environment and act as a pollutant with huge potential to create an adverse impact on the environment. A significant increment in plastic trash has been noted with the use of single-use plastics which forms 40–50% of total annual plastic production [14, 15]. In 2020, the United Nations Environment Programme (UNEP) has reported that around 75–199 million tons of plastic waste are currently present in the ocean with the estimation of plastic emissions getting tripled by 2040 [16]. The whack of plastics on the ecosystem is a matter of higher concern. Those living organisms which are based on the environment which is polluted by plastics are found to be affected by plastics. Various reports have revealed the contamination of aquatic lives like seals, whales, dolphins, seabirds, fish, crabs, etc. by plastics and their impact [17]. It can affect the animals both physically and biologically. Researchers reported sea turtles with plastic straws and plastic forks struck their nostrils [18]. A report by Oceana claimed that around 1800 marine mammals in the US waters were found with plastics that are either swallowed or get entangled. They have also claimed that the ingestion of plastics contributes to death [19]. Moreover, the exposure of plastic wastes to weathering makes them break down and form microplastics which can have an even more serious impact because of the lack of traceability of such smaller particles. Being very small in size, the pathway of microplastics to the ecosystem is much easier; they can be even found in our food plates. In that essence, the term ‘Microplastic’ is getting more attention and recently research is being made on this area. Microplastics are the form of plastics that are categorized based on the size of the plastic particles. The particles which are plastic in nature, however, the size being very small will be considered microplastics. As per the definition supported by National Oceanic and Atmospheric Administration (NOAA), microplastics are plastic particles less than 5 mm in size and can be of a wide range of sizes without any lower limit [20]. However, a few researchers have categorized these plastic particles based on their sizes as mesoplastics, microplastics, mini-microplastics, and nano plastics [21]. This size-based classification of microplastics varies from researcher to researcher. Yet, most of the reports claimed plastic particles less than 5 mm as microplastics. Figure 1.1 summarizes the terms used in different pieces of the literature for plastic particles of different sizes. From this, it is evident that the size range is not yet standardized for microplastic particles.

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1 Microfiber Pollution—A Sustainability Issue

Fig. 1.1 Size-wise categorization of plastic particles [21, 27, 28, 29, 30, 31, 32, 33, 34]

1.2 Plastics, Microplastics, and Microfibers

5

Secondly, based on the source of origin, microplastics can be of two types, namely primary microplastics and secondary microplastics. The former is the particles that are produced in such smaller sizes intentionally for specific applications, whereas the latter is originated from the larger plastic pieces due to degradation or fragmentation which could happen with internal and external causes [22]. Cosmetics, personal care products, cleaning agents, and paint and coatings are some of the consumer products which contain primary microplastics [23]. Synthetic fibers which are released during washing will be considered under primary source as they are intentionally produced in such smaller sizes [21, 24]. Moreover, tire dust, plastic granules from artificial turf, and other materials are also remarkable sources of primary microplastics [24]. On the other hand, secondary microplastics are generated due to the mismanagement of plastic wastes in the environment. Plastic containers, plastic bottles, plastic bags, and synthetic ropes which are disposed of can release microplastics over degradation under exposure to sunlight, UV radiation, tides and waves (in the case of the marine environment), and abrasion with other materials. It has been reported that a 1 sq. cm polystyrene sample can release 1.26 × 108 plastic particles/ml when they are exposed to visible and ultra-violet light at 30 °C for 56 days [25]. Similar nature of microplastic generation was noted with Low-Density Polyethylene, Polypropylene, and polystyrene samples when they are exposed to agitated water with pebbles [26]. Though both types (primary and secondary) of microplastics have a similar impact on the environment, this kind of classification based on the source/origin is very important in the case of making regulatory norms where the “polluter pays” principle can be applied so that the polluter can bare the impact of the pollution [27]. Apart from the size and sources, microplastics can be of different shapes. In the case of primary microplastics, they can be produced in different shapes and sizes according to the applications. However, in the case of secondary microplastics, as they are generated due to the degradation of the larger particles, they can take a wide range of shapes and surface appearances. Hence, based on the appearance of the particles, microplastics have been categorized into foams (sponge or foam-like appearance), pellets (spherical pieces), fragments (irregularly shaped pieces), fibers (strand or filaments), films (thin sheet or membrane-like pieces), and lines (fiber-like strands with the same thickness along the length with sharp ends) [21, 35]. Figure 1.2 depicts the appearance of different forms of microplastics. This categorization and standardization of microplastic particles and their types are essential as they can help in backtracking and identifying the source of such particles. In addition to this, the microplastic particles which are being found in the environmental samples can be analyzed and categorized based on their colors and polymer types [36, 37, 38, 39]. While considering the term ‘Microfibers’, it can have different perceptions in the textile and fashion industries. Microfibers are the finer fibers that are of linear density less than 1 denier. The diameter of these fibers is generally half of the diameter of fine silk fibers, one-third of the diameter of cotton, and one-quarter of the diameter of fine wool fiber. The polymer type varies as viscose, acrylic, polypropylene, polyamide, and polyester, out of which polyester and polyamide are the most popular considering microfibers [40]. This innovation has a vast range of applications because of its ultimate properties such as lightweight, wrinkle resistance, shape retention, pilling

6

1 Microfiber Pollution—A Sustainability Issue

Fig. 1.2 Classification of microplastics based on sources, shapes, and structure [21]

resistance, greater absorption, and greater thermal insulation, over the conventional fibers [40, 41]. These microfiber fabrics/cloths are more popular in different fields of applications including cleaning (cleaning towels, microfiber mops, microfiber scrubbers, etc.), home textiles (carpets, curtains, bedspreads), sports wears, and also in technical textiles [42]. However, in another context, microfibers are the fibers that are shed or separated or detached or disentangled from the textile surfaces and enter the environment as smaller particles [43]. These microfibers can be originated from clothing, personal care products like wet wipes, sanitary products, home furnishings like carpets, and other fibrous materials [44, 45, 46, 47, 48]. The generation of these fibers, that is, the detachment from the fibrous surface can be caused by external actions whose detailed mechanism is discussed in Chap. 2. These fibers can be natural, synthetic, or semi-synthetic [49]. Another important parameter for a particle to be microfiber is its length to diameter ratio. By considering the size, shape, and composition, Liu et al. defined microfibers as thread-like structures including both natural and artificial origins whose length ranges from 1 µm to 5 mm with a diameter less than 50 µm which results in a length to diameter ratio of more than 100 [50]. Synthetic microfibers can be considered microplastics because of their smaller size and synthetic nature. Though the synthetic microfibers alone are categorized under microplastics, the natural microfibers can also have an impact on the environment

1.3 Textile fiber Production and Consumption

7

Fig. 1.3 Detailed understanding of Microplastics and Microfibers

with the additives or chemicals that are imparted during the manufacturing process. Hence, these microfibers, irrespective of natural or synthetic, are notified as anthropogenic litter in the environment [51, 52, 53, 54]. Figure 1.3 depicts the detailed understanding of microplastics and microfibers.

1.3 Textile fiber Production and Consumption Fiber forms the basic element of any textile material. The level of microfiber pollution in the environment can be closely tied to the consumption and production of textile materials. Around 24 million tons of textile fibers (including natural and synthetic fibers) were produced in 1975, which increased nearly five-fold in the year 2020. It has been estimated that global fiber production will face a drastic increment of 34% in 2030 in comparison with 2020 and will reach 146 million tons [55]. However, in between, the COVID-19 pandemic can have an impact on this fiber production. The textile fiber production which was facing an increment in subsequent years found to be decreased from 111 million tons in 2019 to 109 million tons in 2020 [56]. Although both natural and synthetic fibers are hugely demanded in the market, the market of synthetic fibers superseded natural fibers in the 1990s [57]. Synthetic fibers hold about 62% of total global fiber production out of which Polyester is the most dominant fiber with a share of 52% [55]. Cotton, a cellulosic fiber, is the most commonly used fiber among natural fibers, and it is expected that the consumption of cellulosic fibers will increase to 5.4 kg per capita by the year 2030. Though cotton is comprised of 90% of cellulose, it is estimated that it could not satisfy the demand for cellulosic fibers. And there comes the development of man-made cellulosic fibers/regenerated fibers [57]. Diverse types of fibers are produced in different ways, and they account for a significant share of global fiber production. Figure 1.4 depicts the production of

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1 Microfiber Pollution—A Sustainability Issue

Fig. 1.4 Contribution percentage of different textile fibers in global fiber production [56]

different types of textile fibers and their contribution to global fiber production in the year 2020 according to the Textile Exchange Report [56]. The report clearly shows that fossil-based fibers are more dominant. Though sustainable fiber production like recycled fibers was greatly insisted on, their real-time contribution is critically slow and it could not match the speed of conventional fibers [56]. The apparel market is the major user of textile fibers apart from other applications. The consumption of apparel has increased greatly when compared to earlier days. For instance, in 2014, the consumption of apparel was 60% higher than what was consumed 14 years back in 2000 [58]. The emergence of the fast fashion trend can be a notable reason for the increase in the consumption of apparel. Every year, around 100 billion garments are being made globally; the fashion brands started to adopt fast fashion models where the cost and quality of the materials were reduced which in turn can encourage more purchases and rapid disposals [59]. The major driving factors that correspond to the increase in the apparel market include an increase in the per capita income, a shift in preference for branded products, adoption of a luxury lifestyle among consumers, and rapidly changing fashion trends [60]. This pattern of large production and consumption also results in a huge volume of waste generation. It has been estimated that 85% of the total textiles produced in a year which can be worth around $ 450 billion end up in waste, and that every second, clothes equivalent to one garbage truck are burned or dumped in landfills [58, 59]. A report has revealed that an average of 35 kg/year/person of textile wastes are being generated in the US [4]. This increased level of production, consumption, and disposal of textile materials can also contribute to increasing the level of microfiber pollution in the environment as the textile materials are contributing to microfiber pollution to a greater extent.

1.4 Contribution of Textile and Apparel Industries to Microplastic Pollution

9

1.4 Contribution of Textile and Apparel Industries to Microplastic Pollution Textiles and apparel whose production and consumption are rising in recent decades are contributing more to the microplastic as well as microfiber pollution. Though several sources including synthetic tires, plastic pellets, road markings, city dust, etc. have been noted by researchers, the major source of microplastic pollution is identified as Synthetic Textiles [22]. During the entire lifecycle of textile materials (manufacturing stage, consumption stage, disposal stage), they are capable of releasing smaller fibers into the environment which can result in microfiber pollution or microplastic pollution in the case of synthetic fibers. The dominance of textile and apparel industries in causing microfiber/microplastic pollution is evident when the researchers observed the particles found in the contaminated environment to resemble the fibers used in textile and apparel products [61]. Studies have analyzed the microplastic contaminants found in different environments in terms of their surface appearance, shape, size, color, and polymer composition to backtrack their source of origin. The shape observation has revealed that the dominant type is fibers irrespective of the type of samples which is studied. The researchers who reported the dominance of fibers in the atmospheric fallout over fragments and films have pointed out that the clothes and other textile materials are the potential sources of fibrous contamination, whereas the others like fragments and films could be generated out of plastic bags or other plastic materials. Moreover, Expanded Polystyrene products were noted as the source of microplastics which are in the form of foams [62]. Similarly, the important role of textile materials was reported by other researchers. They found that among different types of microfibers identified, rayon was the most dominant which held a contribution of 57.8%. Since rayon is most commonly used in clothing, furnishing, and sanitary products, it can be correlated that textile materials were the source of such contamination [63]. The other research which analyzed the deep-sea sediments also reported a huge level of regenerated cellulose fibers in the sample which is then followed by polyester and acrylic fibers. They have correlated the types of clothes being washed in the surrounding area with the fibers in the contaminated area and found a direct link [64]. Ambrosini et al. who examined the microplastic contamination in the glaciers also reported that the clothes and other textile materials which are being used by the tourists could be the potential source of such contaminations [65]. The prevalence of microplastic particles in the farmlands was also related to the wastewater discharge from the residential areas around the farmlands. The effluent of domestic laundry in the wastewater discharged from the households might be the potential source of microplastics [66]. In the oceanic atmosphere, researchers reported a higher contribution of fibrous particles (88.89%) over fragments (11.11%). Moreover, the polymer identification revealed a higher contribution of Polyethylene Terephthalate (PET). From this, it can be evidenced that the textile industry is the major contributor as it is the major user of PET than any other industry [67]. In similar research, where the indoor and outdoor air were analyzed for microfiber contamination, higher contamination was noted in the indoor air samples

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1 Microfiber Pollution—A Sustainability Issue

than in outdoor and the researchers claimed that the textile materials which are used for the home furnishing were the potential reason for higher contamination in the indoor samples [47]. From different studies, it can be made out that the fibers are the dominant form of microplastics found in the environment and these fibers originated from the textile materials. Table 1.1 consolidates different studies which have pointed out the supremacy of microfibers in different environmental and living organism samples.

1.5 Conclusion The basic understanding of microplastics and microfibers has been detailed in this chapter. The plastic particles which are mostly less than 5 mm in size are considered microplastics which can take different sources of origin and morphological structures. Microfibers are the small fibers that are detached from the textile materials and these can be natural or synthetic. However, synthetic microfibers can be considered microplastics due to their poor degrading property over natural fibers. The chapter summarized the consumption level of different textile materials and spotlighted their correlation with microfiber pollution. Moreover, the contribution of the textile and apparel industry to microplastic pollution has been evidenced by the summary of various literature which observed the microplastic contamination of different parts of the ecosystem. It clearly showed that fibrous particles share a major part, whereas other forms like fragments, foams, pellets, and spheres are comparatively lesser. Based on the morphological structure and polymer compositions, it was strongly claimed that those fibrous materials originated from textile materials. As a whole, this chapter provides an overview of microplastic and microfiber pollution and the importance of the textile and apparel industry to address the issue as they are the major pollutants.

[69]

Surface water of Estuary

Yangtze Estuary

particles/cu.m

particles/cu.m

4137.3 ± 2461.5

Arctic waters, south and southwest of Svalbard, Norway

Sub-surface water of Sea

particles/cu.m

particles/bird

–

Unit of measurement

2.68

0.34

Arctic waters, south and southwest of Svalbard, Norway

East China Sea

Coastal Water

Surface Water of Sea

Yangtze Estuary

Estuary

[37]

Huangpu River

Rivers

–

22.8

Suzhou River

Rivers

Gastrointestinal Tract of 17 Shanghai Terrestrial birds

Shanghai

City Creek

[36]

Total particles detected

[68]

Name/Location

Sample/Study area

References

Table 1.1 Dominance of microfibers in microplastic contaminated environments Fragments

Film

Pellet

79.10

95.00

87.72

37

66

81

85

88

–

4.90

12.28

57

24

11

6

7

9.10

< 0.1

–

4

9

2

4

4

–

–

–

2

1

6

5

1

Percentage of contribution (%)

Fibers

11.60

–

–

–

Granules

0.20

–

–

–

(continued)

Spherules/Beads

1.5 Conclusion 11

[74]

[73]

[72]

Asaluyeh, Iran

Asaluyeh, Iran

West Pacific Ocean

Street Dust—Microplastic

Oceanic Atmosphere

Shanghai

Farmland—Shallow Soil

Street Dust—Microrubber

Shanghai

Farmland—Deep Soil

Shanghai

Shanghai

Atmosphere—Aerial

Shanghai

Atmosphere—Upper

Atmosphere—Ground

[39]

China

Dhanushkodi

Beach Sands

20 species of Medicinal Animals

Tuticorin

Beach Sands

East China Sea

Mumbai

Surface water of Sea

Beach Sands

Name/Location

Sample/Study area

[71]

[70]

References

Table 1.1 (continued)

particles/kg (mg/kg)

45 ± 12 (1.05 ± 0.01)

0.06 ± 0.16 particles/cu.m

–

items/kg

–

items/kg

84.75 ± 13.22

–

65.75 ± 13.92

–

–

particles/kg (mg/kg)

181 ± 60 (2.75 ± 0.03)

–

particles/cu.m particles/kg (mg/kg)

0.167 ± 0.138 220 ± 50 (3.54 ± 0.01)

Unit of measurement

Total particles detected

Fragments

Film

Pellet

60

36.00

–

53.33

37.62

77.78

23.08

72.09

84.68

51

83.20

31

61

–

37.58

28.30

22.22

53.85

26.74

15.32

–

–

–

14

6.67

33.76

–

–

9

2.10

–

–

2.12

0.32

–

–

–

Percentage of contribution (%)

Fibers

8

–

–

0.00

23.08

1.16

–

40

14.70

Granules

1

–

74

–

-

–

–

0

(continued)

Spherules/Beads

12 1 Microfiber Pollution—A Sustainability Issue

Surface Water

[75]

192

182

items/liter

items/kg

– 21.4

62.8

71.8

53.9

89.2

84.5

29.54

Swat River, Pakistan

–

–

–

68.3

90.1

River Water—Urban Stations

River Sediments—Urban Stations

[78]

River Kelvin, Glasgow, UK

–

–

Fragments

Film

Pellet

47.72

61

58.01

10.6

12.5

27.6

5

5.9

16.1

6.8

10

6

3.81

–

11.25

8

–

–

–

2.9

25

16

17

1.3

–

–

–

–

–

–

Percentage of contribution (%)

Fibers

17

Bank Sediments

[77]

Skaneateles Lake, New York

Onondaga Lake, New York

Simcoe Lake, Canada

particles/fish

particles/sq.m/day

Unit of measurement

River Sediments—Non-Urban Stations

Surface Water

[76]

Sediments

Gastrointestinal Tract of 10 Coastal Waters, 1 to 15 species of Fishes Southwest of Plymouth, UK

[63]

Dongguan City, 36 ± 7 China

Atmospheric Fallout

Total particles detected

[62]

Name/Location

Sample/Study area

References

Table 1.1 (continued)

–

–

–

–

–

–

–

–

Granules

–

–

1.25

5.71

–

–

11.5%

–

(continued)

Spherules/Beads

1.5 Conclusion 13

Tributaries Water—Non-Urban Stations

17.4

26.1

items/litre

Tributaries Water—Urban Stations

92

14.28

Tributaries Sediment—Non-Urban Stations

21.73

items/kg

Tributaries Sediment—Urban Stations

202

35.82

Fish Schizothorax plagiostomus—Non-Urban Stations

items/fish

Fragments

Film

Pellet

21.73

32.6

36.23

49

24.41

55.22

48

13.04

15.21

4.34

3

3

3.5

5.3

21.73

30.43

33.08

38

6

26

15.15

Percentage of contribution (%)

Fibers

46.51

153

Unit of measurement

Fish Schizothorax plagiostomus—Urban Stations

Total particles detected 17

Name/Location

River Water—Non-Urban Stations

Sample/Study area

[–] means not specified/not applicable

References

Table 1.1 (continued) Granules

Spherules/Beads

14 1 Microfiber Pollution—A Sustainability Issue

References

15

References 1. Sustainability (2022) United Nations. https://www.un.org/en/academic-impact/sustainability, Accessed 16 April 2022 2. Why is Sustainability Important? BluGlacier. https://bluglacier.com/why-is-sustainability-imp ortant/, Accessed 16 Apirl 2022 3. UN Helps Fashion Industry Shift to Low Carbon (2018) United Nations, climate change. https:// unfccc.int/news/un-helps-fashion-industry-shift-to-low-carbon, Accessed 16 April 2022 4. What’s wrong with the fashion industry? Sustain your style. https://www.sustainyourstyle.org/ en/whats-wrong-with-the-fashion-industry, Accessed 24 April 2022 5. Chavero ST (2017) The unsustainability of fast fashion. Datatèxtil 36 6. Tannery Operations Chromium Pollution (2011). https://www.worstpolluted.org/projects_rep orts/display/88, Accessed 24 April 2022 7. Drew D, Yehounme G (2017) The apparel industry’s environmental impact in 6 graphics. World Resource Institute, 2017. https://www.wri.org/insights/apparel-industrys-environmental-imp act-6-graphics, Accessed 24 April 2022 8. Ellen MacArthur Foundation (2017) A new textiles economy: redesigning fashion’s future. http://www.ellenmacarthurfoundation.org/publications, Accessed 24 April 2022 9. SDGs for Better Fashion (2022) Sustainable development goals. https://sustainabledevelop ment.un.org/partnership/?p=28041, Accessed 24 April 2022 10. UN alliance for Sustainable Fashion (2022) https://unfashionalliance.org/, Accessed 24 April 2022 11. Wu JX, Li L (2020) Sustainability initiatives in the fashion industry. In: Fashion industry—an itinerary between feelings and technology. https://doi.org/10.5772/intechopen.87062 12. Plastic Market Size, Share & Trends Analysis Report By Product (PE, PP, PU, PVC, PET, Polystyrene, ABS, PBT, PPO, Epoxy Polymers, LCP, PC, Polyamide), By Application, By End-use, By Region, And Segment Forecasts, 2021–2028, 2021. https://www.grandviewres earch.com/industry-analysis/global-plastics-market, Accessed 24 April 2022 13. Laskar N, Kumar U (2019) Plastics and microplastics: a threat to environment. Environ Technol Innov 14. https://doi.org/10.1016/j.eti.2019.100352 14. Senapati MR (2021) Why plastic piling in oceans post COVID-19 needs urgent attention. DownToEarth. https://www.downtoearth.org.in/blog/environment/why-plastic-piling-inoceans-post-covid-19-needs-urgent-attention-79547, Accessed 16 April 2022 15. Moore C (2022) Plastic pollution. Britannica. https://www.britannica.com/science/plastic-pol lution, Accessed 16 April 2022 16. Chacko S (2021) Plastic pollution in aquatic systems may triple by 2040: UNEP. DownToEarth. https://www.downtoearth.org.in/news/environment/plastic-pollution-in-aquatic-sys tems-may-triple-by-2040-unep-79822, Accessed 16 April 2022 17. How plastic pollution is affecting seals and other marine life 2017 World Animal Protection. https://www.worldanimalprotection.org.in/news/how-plastic-pollution-affectingseals-and-other-marine-life, Accessed 16 April 2022 18. Robinson NJ, Figgener C (2015) Plastic straw found inside the nostril of an olive ridley sea turtle. http://www.seaturtle.org/mtn/archives/mtn147/mtn147 19. Sharpless A (2022) CEO Note: plastic is choking, strangling, and drowning endangered ocean animals in U.S. waters. Oceana. https://oceana.org/blog/ceo-note-plastic-choking-stranglingand-drowning-endangered-ocean-animals-us-waters/, Accessed 16 April 2022 20. N. Marine Debris Program (2015) Laboratory methods for the analysis of microplastics in the marine environment: recommendations for quantifying synthetic particles in waters and sediments 21. Crawford CB, Quinn B (2017) Microplastic pollutants. Elsevier 22. Boucher J, Friot D (2017) Primary microplastics in the oceans: a global evaluation of sources. IUCN, Gland, Switzerland, p 43. https://doi.org/10.2305/IUCN.CH.2017.01.en

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23. van Wezel A, Caris I, Kools SAE (2016) Release of primary microplastics from consumer products to wastewater in the Netherlands. Environ Toxicol Chem 35(7). https://doi.org/10. 1002/etc.3316 24. Wang T et al. (2019) Emission of primary microplastics in mainland China: Invisible but not negligible. Water Res. 162. https://doi.org/10.1016/j.watres.2019.06.042 25. Lambert S, Wagner M (2016) Characterisation of nanoplastics during the degradation of polystyrene. Chemosphere 145. https://doi.org/10.1016/j.chemosphere.2015.11.078 26. Efimova I, Bagaeva M, Bagaev A, Kileso A, Chubarenko IP (2018) Secondary microplastics generation in the sea swash zone with coarse bottom sediments: laboratory experiments. Front Mar Sci 5(SEP). https://doi.org/10.3389/fmars.2018.00313 27. Hartmann NB et al. (2019) Are we speaking the same language? recommendations for a definition and categorization framework for plastic debris. Environ Sci Technol 53(3). https:// doi.org/10.1021/acs.est.8b05297 28. Tech T (2021) Uniform size classification and concentration unit terminology for broad application in the Chesapeake Bay Watershed 29. GESAMP (2015) Sources, fate and effects of microplastics in the marine environment: a global assessment. International Maritime Organisation, London 30. Ryan PG, Moore CJ, van Franeker JA, Moloney CL (2009) Monitoring the abundance of plastic debris in the marine environment. Philos Trans Royal Soc B: Biol Sci 364(1526). https://doi. org/10.1098/rstb.2008.0207 31. Costa MF, Ivar Do Sul JA, Silva-Cavalcanti JS, Araújo MCB, Spengler Â, Tourinho PS (2010) On the importance of size of plastic fragments and pellets on the strandline: a snapshot of a Brazilian beach. Environ Monit Assess 168(1–4). https://doi.org/10.1007/s10661-009-1113-4 32. Wagner M et al. (2014) Microplastics in freshwater ecosystems: what we know and what we need to know. Environ Sci Europe 26(1). https://doi.org/10.1186/s12302-014-0012-7 33. Belišová N, Staˇnová L, Kuˇcera J, Púˇcek O, Mackuˇlak T (2020) Washing processes and their effect of the release of microplastics to the environment, Konferencia mladých vodohospodárov. https://www.shmu.sk/File/KMO/BelisovaN_Washing_processes_ and_their_effect_release_microplastics_environment.pdf 34. Moore CJ (2008) Synthetic polymers in the marine environment: a rapidly increasing, long-term threat. Environ Res 108(2). https://doi.org/10.1016/j.envres.2008.07.025 35. Magni S et al. (2019) The fate of microplastics in an Italian wastewater treatment plant. Sci Total Environ 652. https://doi.org/10.1016/j.scitotenv.2018.10.269 36. Luo W, Su L, Craig NJ, Du F, Wu C, Shi H (2019) Comparison of microplastic pollution in different water bodies from urban creeks to coastal waters. Environ Pollut 246. https://doi.org/ 10.1016/j.envpol.2018.11.081 37. Lusher AL, Tirelli V, O’Connor I, Officer R (2015) Microplastics in Arctic polar waters: the first reported values of particles in surface and sub-surface samples. Sci Rep 5. https://doi.org/ 10.1038/srep14947 38. Karthik R et al. (2018) Microplastics along the beaches of southeast coast of India. Sci Total Environ 645. https://doi.org/10.1016/j.scitotenv.2018.07.242 39. Liu K, Wang X, Fang T, Xu P, Zhu L, Li D (2019) Source and potential risk assessment of suspended atmospheric microplastics in Shanghai. Sci Total Environ 675:462–471. https://doi. org/10.1016/j.scitotenv.2019.04.110 40. Hosseini Ravandi SA, Valizadeh M (2011) Properties of fibers and fabrics that contribute to human comfort. In: Improving Comfort in Clothing. https://doi.org/10.1533/9780857090645. 1.61 41. Srinivasan J (2010) Engineering finer and softer textile yarns. Techn Textile Yarns. https://doi. org/10.1533/9781845699475.1.185 42. Fibre2Fashion (2013) Going ‘supernatural’ with microfibers. Fibre2Fashion. https://www.fib re2fashion.com/industry-article/7019/going-supernatural-with-microfibers, Accessed 16 April 2022 43. Rathinamoorthy R, Raja Balasaraswathi S (2020) A review of the current status of microfiber pollution research in textiles. Int J Cloth Sci Technol 33(3). https://doi.org/10.1108/IJCST-042020-0051

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44. Quinn P (2021) Wet wipes: keeping them out of our seas (and sewers). Friends of the Earth. https://friendsoftheearth.uk/sustainable-living/wet-wipes-keeping-them-out-ourseas-and-sewers, Accessed 10 Aug 2021 45. McGoran A (2019) Microplastic pollution and wet wipe ‘reefs’ are changing the River Thames ecosystem. The conversation. https://theconversation.com/microplastic-pollution-and-wetwipe-reefs-are-changing-the-river-thames-ecosystem-119400, Accessed 10 Aug 2021 46. Wet wipes and sanitary products found to be microplastic pollutants (2020). https://www. labmanager.com/news/wet-wipes-and-sanitary-products-found-to-be-microplastic-pollutants23118, Accessed 10 Aug 2021 47. Dris R et al (2017) A first overview of textile fibers, including microplastics, in indoor and outdoor environments. Environ Pollut 221:453–458. https://doi.org/10.1016/j.envpol.2016. 12.013 48. Alipour S, Hashemi SH, Alavian Petroody SS (2021) Release of microplastic fibers from carpetwashing workshops wastewater. J Water Wastewater. https://doi.org/10.22093/wwj.2020.216 237.2980 49. Athey SN, Erdle LM (2022) Are we underestimating anthropogenic microfiber pollution? a critical review of occurrence, methods, and reporting. Environ Toxicol Chem 41(4). https:// doi.org/10.1002/etc.5173 50. Liu J, Yang Y, Ding J, Zhu B, Gao W (2019) Microfibers: a preliminary discussion on their definition and sources. Environ Sci Pollut Res 26(28):29497–29501. https://doi.org/10.1007/ s11356-019-06265-w 51. Liu J et al. (2021) Microfiber pollution: an ongoing major environmental issue related to the sustainable development of textile and clothing industry. Environ Develop Sustain 23(8). https://doi.org/10.1007/s10668-020-01173-3 52. González-Pleiter M et al. (2020) Fibers spreading worldwide: microplastics and other anthropogenic litter in an Arctic freshwater lake. Sci Total Environ 722. https://doi.org/10.1016/j.sci totenv.2020.137904 53. Pedrotti ML et al. (2021) Pollution by anthropogenic microfibers in North-West Mediterranean Sea and efficiency of microfiber removal by a wastewater treatment plant. Sci Total Environ 758. https://doi.org/10.1016/j.scitotenv.2020.144195 54. Roblin B, Ryan M, Vreugdenhil A, Aherne J (2020) Ambient atmospheric deposition of anthropogenic microfibers and microplastics on the Western Periphery of Europe (Ireland). Environ Sci Technol 54(18). https://doi.org/10.1021/acs.est.0c04000 55. Fernández L (2021) Production volume of textile fibers worldwide 1975—2020. Statista. https://www.statista.com/statistics/263154/worldwide-production-volume-of-textilefibers-since-1975/, Accessed 22 April 2022 56. Preferred Fiber and Material, Market report (2021) Textile exchange. https://textileexchange. org/wp-content/uploads/2021/08/Textile-Exchange_Preferred-Fiber-and-Materials-MarketReport_2021.pdf, Accessed 24 April 2022 57. Felgueiras C, Azoia NG, Gonçalves C, Gama M, Dourado F (2021) Trends on the cellulosebased textiles: raw materials and technologies. Front Bioeng Biotechnol 9. https://doi.org/10. 3389/fbioe.2021.608826 58. McFall-Johnsen M (2020) These facts show how unsustainable the fashion industry is. World Economic Forum. https://www.weforum.org/agenda/2020/01/fashion-industry-carbon-unsust ainable-environment-pollution/, Accessed 22 April 2022 59. Hosey M (2020) The unsustainable growth of fast fashion. https://thinksustainabilityblog.com/ 2020/04/14/the-unsustainable-growth-of-fast-fashion/, Accessed 22 April 2022 60. Apparel Market—Growth, Trends, Covid-19 Impact and Forecasts (2022—2027). https://www. mordorintelligence.com/industry-reports/apparel-market, Accessed 22 April 2022 61. Browne MA et al (2011) Accumulation of microplastic on shorelines woldwide: Sources and sinks. Environ Sci Technol 45(21):9175–9179. https://doi.org/10.1021/es201811s 62. Cai L et al. (2017) Characteristic of microplastics in the atmospheric fallout from Dongguan city, China: preliminary research and first evidence. Environ Sci Pollut Res 24(32). https://doi. org/10.1007/s11356-017-0116-x

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63. Lusher AL, McHugh M, Thompson RC (2013) Occurrence of microplastics in the gastrointestinal tract of pelagic and demersal fish from the English Channel. Marine Pollut Bull 67(1–2). https://doi.org/10.1016/j.marpolbul.2012.11.028 64. Sanchez-Vidal A, Thompson RC, Canals M, de Haan WP (2018) The imprint of microfibres in Southern European deep seas. PLoS One 13(11). https://doi.org/10.1371/journal.pone.020 7033 65. Ambrosini R, Azzoni RS, Pittino F, Diolaiuti G, Franzetti A, Parolini M (2019) First evidence of microplastic contamination in the supraglacial debris of an alpine glacier. Environ Pollut 253:297–301. https://doi.org/10.1016/j.envpol.2019.07.005 66. Chen Y, Leng Y, Liu X, Wang J (2020) Microplastic pollution in vegetable farmlands of suburb Wuhan, central China. Environ Pollut 257. https://doi.org/10.1016/j.envpol.2019.113449 67. Wang X, Li C, Liu K, Zhu L, Song Z, Li D (2020) Atmospheric microplastic over the South China Sea and East Indian Ocean: abundance, distribution and source. J Hazardous Mater 389. https://doi.org/10.1016/j.jhazmat.2019.121846 68. Zhao S, Zhu L, Li D (2016) Microscopic anthropogenic litter in terrestrial birds from Shanghai, China: not only plastics but also natural fibers. Sci Total Environ 550. https://doi.org/10.1016/ j.scitotenv.2016.01.112 69. Zhao S, Zhu L, Wang T, Li D (2014) Suspended microplastics in the surface water of the Yangtze Estuary system, China: first observations on occurrence, distribution. Mar Pollut Bull 86(1–2):562–568. https://doi.org/10.1016/j.marpolbul.2014.06.032 70. Tiwari M, Rathod TD, Ajmal PY, Bhangare RC, Sahu SK (2019) Distribution and characterization of microplastics in beach sand from three different Indian coastal environments. Marine Poll Bull 140. https://doi.org/10.1016/j.marpolbul.2019.01.055 71. Lu S et al. (2020) Prevalence of microplastics in animal-based traditional medicinal materials: widespread pollution in terrestrial environments. Sci Total Environ 709. https://doi.org/10. 1016/j.scitotenv.2019.136214 72. Liu M et al (2018) Microplastic and mesoplastic pollution in farmland soils in suburbs of Shanghai, China. Environ Pollut 242:855–862. https://doi.org/10.1016/j.envpol.2018.07.051 73. Abbasi S et al. (2019) Distribution and potential health impacts of microplastics and microrubbers in air and street dusts from Asaluyeh County, Iran. Environ Poll 244. https://doi.org/10. 1016/j.envpol.2018.10.039 74. Liu K et al. (2019) Consistent transport of terrestrial microplastics to the ocean through atmosphere. Environ Sci Technol 53(18). https://doi.org/10.1021/acs.est.9b03427 75. Felismino MEL, Helm PA, Rochman CM (2021) Microplastic and other anthropogenic microparticles in water and sediments of Lake Simcoe. J Great Lakes Res 47(1). https://doi. org/10.1016/j.jglr.2020.10.007 76. Driscoll C, Markley L (2022) Microplastic pollution in Onondaga and Skaneateles lakes in central New York, New York State Water Resources Institute https://wri.cals.cornell.edu/sites/ wri.cals.cornell.edu/files/shared/2019_Driscoll_Final.pdf, Accessed on 24 April 2022 77. Blair RM, Waldron S, Phoenix VR, Gauchotte-Lindsay C (2019) Microscopy and elemental analysis characterisation of microplastics in sediment of a freshwater urban river in Scotland, UK. Environ Sci Pollut Res. https://doi.org/10.1007/s11356-019-04678-1 78. Khan L et al (2022) Exploration of microplastic pollution with particular focus on source identification and spatial patterns in riverine water, sediment and fish of the Swat River, Pakistan. RSC Adv 12(16):9556–9566. https://doi.org/10.1039/d2ra00319h

Chapter 2

Microfiber Shedding of Textile Materials—Mechanism and Analysis Techniques

2.1 Introduction The increased level of contribution of textile materials to microfiber pollution urges the need for a profound understanding of microfiber release from textile materials. Researchers have reported that the mechanical and chemical actions on the textile materials lead to the fibers shedding from the surface of the material. These fibers being smaller in size (less than 5 mm) are categorized as microfibers [1]. Researchers have reported the ubiquity of microfibers in a diverse range of our ecosystem, starting from deep oceans, and seashores to the food items which we are consuming [2–7]. It has been reported that around 1,500,000 trillion microfibers have been deposited in the ocean bed [8]. In 2011, Browne et al. found microfibers in the sea shorelines and reported similarities between the fibers found in the seashores and those found in the domestic sewages. This alarmed the domestic laundering of textile materials as the major source of microfibers that are found in the environment [9]. Following this, researchers started to analyze the microfiber release from textile materials during domestic laundering [10, 11]. Researchers adopted different analysis techniques that help in replicating the domestic laundering to understand the microfiber shedding behavior of textile materials. Though various research works have been seen in this area, various contradictions were noted between the results of different researchers. While Napper et al. reported the release of 496,030 microfibers from a 6 kg wash load of polyester fabrics, Yang et al. reported 13,960 ± 2406 microfibers shed from one square meter of polyester fabric which comes around 110 g [10, 12]. These variations in the measurements were highly attributed to the different methods of analysis which vary in terms of sample preparation, washing methods, and quantification techniques adopted. Thus, various researchers have initiated the progress toward defining a standard protocol to analyze the microfiber shedding from textile materials that are more likely to simulate real-time conditions [13, 14]. Furthermore, in successive analyses, it was very clear that domestic laundering alone does not completely influence the microfiber shedding of textiles, whereas other intrinsic cues like properties © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 R. Rathinamoorthy and S. Raja Balasaraswathi, Microfiber Pollution, Sustainable Textiles: Production, Processing, Manufacturing & Chemistry, https://doi.org/10.1007/978-981-19-4185-6_2

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of textile materials were also involved in the microfiber shedding which has been evident from the difference in the microfiber shedding of different fabrics under similar washing conditions [13, 15]. This arises the need for a detailed analysis of the microfiber shedding mechanism from the textile materials under different conditions. This chapter details the exhaustive mechanism of microfiber shedding from textile materials based on the literature. Besides, various methods which are taken on by different researchers in analyzing and quantifying microfiber shedding were also discussed elaborately.

2.2 Mechanism of Microfiber Shedding from Textile Materials The detachment or fall-off of loosely packed or fractured fibers from the surface structure of textile materials is known as fiber shedding. Since the size of those fibers are being at the micro-level, the phenomenon is often termed microfiber shedding. Irrespective of fiber material (natural or synthetic fibers), all textile materials tend to shed microfibers [16]. Fibers on the surface of the textile materials can get damaged or fractured due to the external stresses applied during different phases of textile materials. These damaged fibers can later get disentangled from the surface as microfibers. Starting with the production process, there will be huge mechanical actions exerted on the fibers during the yarn manufacturing process. This can make the fibers get cut or damaged which results in the formation of shorter fibers. Being shorter, these fibers will just embed on the yarn structure without any well-built attachment to the surface [17]. Also, during the spinning process, the comparatively longer fibers get to move toward the core of the structure whereas the short fibers will be on the surface which can easily slip from the structure [18]. Moreover, fibers are noted to get severely damaged in different production stages. It has been reported that when the polyester fibers are undergone the carding process during yarn manufacturing, surface distortion and cracks were noted on the fibers [19]. In addition, the wet processing of textile materials can also cause the chemical deterioration of fibers on the surface [19]. These loosely packed and damaged fibers that emerged during the manufacturing process can easily get released from the surface structure of the material over subsequent external actions like washing and wearing. Apart from the inherent nature of textile materials that are developed during the production process, microfiber shedding can be enhanced during other external actions during the wearing and domestic laundering of textile materials. During usage of textile materials, there will be chances for the fibers to get broken as there will be small repeated loading which can also create damage as a single excessive force [19]. There will be frictional tension acting on the fabric while usage which can also lose the fibers from the structure and enables them to release from the fabric [20]. Domestic laundering during the user phase can cause both mechanical and chemical action on the textile materials which can subsequently cause fiber damage. It has been reported

2.2 Mechanism of Microfiber Shedding from Textile Materials

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Fig. 2.1 a Microscopic image of the surface of knitted fabric, b Fuzz formation on the surface due to abrasion, and c Microfibers shed from the fabric

that domestic laundry can cause huge damage to the fabrics than any other actions to which the textile materials are subjected in their lifetime [21]. The fiber damage is not limited to fiber breakage. The damage could also be splitting and peeling based on the forces acting on it [19]. Though the loose packing and damage of fibers lead to the release of short fibers from the textile surface, this phenomenon of microfiber shedding happens with step-by-step changes on the surface. Fuzz formation, that is the protrusion of fibers on the surface, has been noted as the first and foremost step in microfiber shedding. When the surface of the fabrics is exposed to any abrading action, the abradant will act on the fiber surface which is exposed and pull it to open up, thereby, forming a fuzz. This protrusion is not only limited to the short or loosely packed fibers. The fibers whose both ends are strongly held to the structure could also be snagged during abrasion and can form fuzz or protrusion [22]. This fuzz formation step happens mostly in the dry state due to the wear and tear of fabrics [23]. Figure 2.1b shows the fuzz formation on the surface of the fabric due to abrasion compared to a normal fabric in Fig. 2.1 a. This fuzz formation property varies from one fabric to other fabrics which often depends on the friction, shape, thickness, and stiffness of the fibers as well as the hairiness and breaking strength of the yarn structure [16]. These protruded fibers can easily get broken under mechanical actions, especially during domestic laundry, and release as microfibers as shown in Fig. 2.1c [16], whereas in the case of cellulosic fibers, there may be an additional step called fibrillation after the fuzz formation [16]. Fibrillation is the localized separation of fibers at the surface where a single fiber will be split into microfibers longitudinally. This happens mainly in the wet state [24]. Synthetic textiles being hydrophobic, the swelling and fibrillation will not happen as in cellulosic fibers [16]. Fiber breakage after the fibrillation step could also lead to the release of microfibers. Studies have also related microfiber shedding behavior with the pilling tendency of the fabric since the fuzz formation is the major cause of pill formation also. Researchers have also reported that fabrics with higher pilling resistance tend to shed lesser fibers [10, 12]. The pill wear-off, that is, the detachment of pills from the surface was related to shedding [25]. However, pill formation is not necessary to happen for microfiber shedding to take place. After fuzz formation, the protruding fibers can get

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detached from the surface before entangling themselves to form pills [25]. This was evinced by the results of the researchers that showed a different level of shedding from different fabrics which were found to have good pilling grade (pilling grade scale—5) [15]. Moreover, while analyzing the mechanism of pilling, the protruding fibers get entangled and are held on the surface [26], whereas, in shedding, the fibers get released from the surface which shows how the microfiber shedding phenomenon differs from the pilling tendency of textile materials. For instance, it can be more clearly understood that polyester fibers have a higher pilling tendency found to have lesser shedding than cellulosic fibers. The higher tenacity of polyester fibers helps to hold the pills and rarely releases the fibers, whereas the cellulosic fibers can readily release fibers [26]. This clearly shows that the fuzz formation step greatly influences the microfiber shedding and not the pilling tendency. Figure 2.2 illustrates the mechanism of microfiber shedding from textile materials. Though all the textile materials shed microfibers, the amount/rate of microfiber shedding of different materials is highly influenced by intrinsic cues as well as external factors. Hence, it is important to understand the influence of different properties of textile materials as well as the external environment in which the textile materials are exposed to understand the microfiber shedding behavior of textile materials.

Fig. 2.2 Mechanism of microfiber shedding from textile materials

2.3 Causes of Microfiber Shedding from Textile Materials

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2.3 Causes of Microfiber Shedding from Textile Materials Based on the mechanism of microfiber shedding, it is very clear that microfiber shedding of textile materials happens when they are subjected to external forces which damage the fiber surface, and subsequently, the fabric surface releases fibers. Figure 2.3 illustrates the different actions that could potentially damage the surface and cause microfiber shedding from the textile materials. Domestic Laundering Domestic laundering is the most common method of cleaning clothes after wearing them. Due to the regular usage of garments, the clothes tend to get stained. Besides removing dirt and stain, laundering is also important to remove odor and provide freshness to wear the garment for the next use. In common, laundering of textiles involves saturation of fabrics with water, agitation of fabrics under laundry additives like detergents, rinsing of fabrics, and drying [21]. Hence, there will be both mechanical and chemical actions on the fabric surface. This shows that domestic laundering could be a potential cause that can damage the fibers and result in microfiber shedding. This was confirmed by the similarities between the microfibers found in the sewage plants and the clothing materials that are laundered in the nearby residential areas [9]. Plenty of researchers have explored the microfiber shedding behavior of textiles during domestic laundering of textiles since it has been reported as the major cause of microfiber pollution in the environment. Researchers have reported that around 34.8% of microplastics in the environment originated from the domestic laundering of synthetic textiles [27], and it has been noticed that around 2.2 million tons of microfibers are entering the ocean every year due to laundering [28]. It has been reported that the material types being washed, methods of washing (hand laundering, machine laundering), washing conditions like temperature, duration, spin cycle, and the type of additives used have a great influence on the microfiber shedding of textile material [29–33]. The increased mechanical agitation can damage the fibers compared to all other factors. Similarly, there will also be chemical action of detergents and other additives like bleaches and softeners. Moreover, exposure to

Fig. 2.3 Different exposure conditions causing Microfiber Shedding from apparel

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this mechanical and chemical agitation for a longer duration at a higher temperature can make the fiber damage severe which further results in microfiber shedding. Researchers have claimed that a domestic wash load (6 kg of fabrics) can release up to 18,000,000 microfibers in a single wash [10], whereas the other researcher reported 114 ± 66.8 mg of fibers to release from one kilogram of fabrics being laundered. These findings show the higher magnitude of microfiber release from the domestic laundering [33]. It has been estimated that 62 kg of microfibers can be released per week in Australia due to the domestic laundering of fabrics. It has to be noted that this level of microfiber release estimation is only from 1% of total washing machines used in the world [34]. Laundry effluent from an average household can release 533 million microfibers every year which is almost equal to 135 g [35]. With the increasing impact of domestic laundering on microfiber shedding, different laundry aids and filters are being commercialized with the aim of preventing the release of microfibers into the environment [36]. Further, domestic laundering of textiles should be analyzed with foremost importance for microfiber shedding mitigation because the microfibers released during domestic laundry can directly enter the water bodies without any proper precautionary measures as people all over the world have the practice of washing clothes but not all of them are aware of microfiber shedding during laundering. Textile Processing Textile wet processing has a significant part in the textile manufacturing process. During this process, fabrics are subjected to different chemicals that are meant to impart expected, desirable properties to the fabrics. Various processes including scouring, bleaching, dyeing, and printing involve the usage of a variety of chemicals. The application process also involves physical activity as in the domestic laundry which can possibly lead to the release of microfibers from the textile material. Moreover, most of the processes are performed with the presence of different acids, alkalis, and oxidants at relatively higher temperatures which can possibly cause damage to the fiber structure and accelerate shedding [37]. This was supported by the microfibers found in the effluent of different textile processing industries. Researchers have initially analyzed the effluent from printing and dyeing industries in China for microfiber contamination. They have examined different textile mills for microfibers in the effluent and backtracked their source by comparing the processes that are being performed in different mills. It has been found that the different processing conditions, the complexity of chemicals used in those processes, and the raw materials have an influence on microfiber shedding. They have reported that preparation steps in the printing of rayon fabric such as steaming of fabrics under high temperature and pressure, and successive soaping and rinsing with surfactants and clean water exert physiochemical actions on fabrics that lead to microfiber shedding [37]. The other researchers have analyzed the effectiveness of effluent treatment plants in preventing microfibers to enter water bodies. The results reported that the microfibers are not completely removed in the treatment plants and have estimated that around 4.89 × 108 microfibers enter the water body every day from the textile processing industry which could reach 1.78 × 1011 microfibers per year. In addition

2.3 Causes of Microfiber Shedding from Textile Materials

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to this, the FTIR analysis of microfibers in the effluent showed that only 23% of fibers were identified as natural fibers whereas the rest were synthetic [38]. Similarly, other researchers reported around 361.6 ± 24.5 microfibers to be present per liter of effluent coming out of a typical textile processing mill [39]. The microfiber shedding of textile materials during wet processing was confirmed by the identification of microfibers in the effluent from the processing industries. However, the individual processes and their effects on the microfiber shedding characteristics of textile materials were not explored. The microfiber shedding during these wet processing steps should be given utmost importance, as these processes are carried out at an industrial scale which is expected to release an extremely higher level of microfibers than the domestic laundry process. Moreover, these processes like scouring and soaping in printing or dyeing preparations are similar to domestic laundry but at a stronger level, and thereby tend to cause higher shedding than in domestic laundry. Even after effective effluent treatment processes (85–99%), the microfibers in the effluent are 10–10,000 times higher than those found in the sewage treatment plants [37]. The effluent treatment plants should be enhanced in order to mitigate the microfiber’s emission into the environment. Moreover, the process parameters should also be revised that helps in reducing microfiber shedding during different wet processing steps. Abrasion during wearing During the wearing of garments, they are subjected to abrasion under different conditions which are suspected to damage the fibers and aid the release of microfibers. Researchers who have reported microfibers in the atmospheric air at different time frames noticed a difference in the microfiber composition such as cotton, wool, acrylic, polyester, and polyamides. The usage of different clothing in different seasons was reported as the reason for different fiber compositions in the atmospheric microfibers as these fibers match the clothing requirement of that particular season. This confirms that the wearing of clothing itself leads to microfiber shedding [40]. Different ways for the fabrics to get abraded while wearing can be seen. There will be fabric-to-fabric abrasions when rubbing of lining over main fabrics and rubbing of pocket fabric on body fabric happen. While sitting or doing other actions, there will be friction between fabric and those external objects. Moreover, there will be flexing, stretching, and bending of fibers while the wearer moves or performs any action which can also cause fiber slippage as well as fiber breakage due to inter-friction between fibers [41]. This friction and fiber damage during wearing can cause microfiber shedding from textile materials. In this aspect, researchers have analyzed the microfiber shedding due to the wearing of textile materials. They have reported that the microfiber shedding during wearing hugely depends on the material type. The complexity of the mechanism of fiber release from the textile material during wearing is comparatively lesser than that in washing as there will be multiple influencing factors [42]. Moreover, these abrasions can also lead to fiber fatigue and fibrillation which can lead to the release of fibrils that are smaller than the fibers. These fibrils are small enough to get inhaled by humans [43]. Since these microfibers released during wearing could end up in

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the atmosphere, they have the risk of human exposure. Moreover, detailed research that could replicate the day-to-day activities of the wearer and the resultant abrasion or frictional effect on clothing is needed for a better understanding of microfiber shedding due to the wearing of textile materials. Fragmentation and photodegradation When the textile materials get disposed of after usage, there will be a release of microfibers due to the degradation of the materials. The exposure of textile materials to the external environment can lead to fragmentation of larger textile materials due to the combined action of chemical and physical forces like photodegradation and abrasion leading to the release of smaller fragments from the textile materials. In the case of synthetic textile materials, these smaller fragments will remain in the environment as they are non-biodegradable. The fiber properties like polymer type, density, size as well as the environment influence the rate or level of fragmentation [44, 45]. The increased rate of garment disposal without proper waste management strategies increases the seriousness of the issue as the garments are randomly disposed of in the environment where they can be subjected to the abovementioned physiochemical actions. Researchers have reported degradation and fragmentation of non-woven fabric, made-of-polypropylene fibers over exposure to UV light and natural weathering which supports the microfiber release due to fragmentation [46, 47]. It has been evident that the surfaces of the polyamide and polyester fibers were noted to have holes and pits when they are exposed to sunlight [45]. When the materials are exposed to light, there will be chemical changes in the fiber polymer due to the formation and destruction of covalent bonds. This leads to a decrease in the molecular weight that subsequently results in decreased tensile strength, elasticity, and elongation at break. The deterioration of these properties weakens the fibers and leads to shedding. Moreover, photochemical degradation can happen in both the crystalline and non-crystalline regions of the fibers. Exposure to light can increase the flaws in the surface of the fibers that promote fiber breakage [48]. The thing that has to be noted here is that fibers are getting fragmented which results in the formation of micro or nano-sized particles. This will further complicate the detection and analysis of such particles. Thus, a detailed analysis of microfiber release from the textile materials when they are under a sun-exposed environment after the disposal has to be performed in detail.

2.4 Microfiber Detection in the Ecosystem As reported by various researchers, microfibers are found in different environments as well as the entire ecosystem. Researchers have found microfibers in water bodies, sea sediments, agricultural fields, food items, and tissues of several living organisms [2–4, 7, 49]. For detection of microfibers in these different areas, the following steps were followed, namely i. Sampling, ii. Isolation of microplastic particles in the samples, and iii. Characterization of microfibers. This section of the chapter

2.4 Microfiber Detection in the Ecosystem

27

highlights the detection techniques employed for identifying microfibers in different circumstances.

2.4.1 Sample Collection and Conditioning The sample collection method and conditioning protocol vary with the samples to be analyzed. Generally, while collecting environmental samples like soil, sediments, and water, researchers sampled different areas as well as at different time frames. Atmospheric air: For analysis of microfibers in the atmosphere, the vacuum suction system has been used for sampling [40, 50]. The air vacuum system with a plankton net with a pore size of 1.5 µm has been used for sampling air. Once the suction is done, the filters were sealed immediately to avoid further contamination which can be taken for analysis [40]. Water samples (River water, Sea water, and Industry Effluents): Grab sample protocol has been employed for the collection of water samples [7]. In this method, a cleaned sampler made of metal was immersed in the sampling sites which are naturally filled. Then these samples from the sampler were decanted to another container of lower volume (1 L sampled from 3 L) and taken for further analysis [7, 37]. Soils and sediments: For analysis of soils, researchers have sampled shallow as well as deep soils. Deep (soil at 3–6 cm from the surface) and Shallow (soil at 0–3 cm from the surface) samples were categorized with the help of calipers. Soil samples are generally dried before analysis. Researchers dried the soil samples at 70 °C for 24 h [4]. While collecting deep sediments from rivers, samples were taken at a depth of 10 cm and for preservation, Ethanol has been used [6]. Tissues of Living Organisms: While collecting samples of aquatic organisms like zooplanktons and lugworms, they were collected in different parts of the study area with the help of conical nets [3, 49]. In order to avoid the miscalculation of fibers originating from the nets, researchers have used nylon nets that do not match with other microfibers identified. The samples were conditioned and stored in a 70% alcoholic solution. For further analysis of microfiber contaminations, the specimens were dried by substituting absolute ethanol as a solvent which can lead to critical point drying [3], whereas a few researchers conditioned samples by freezing them until the next analysis [51]. Food Items: For table salt analysis, samples were taken from different packages of the same brand of salt. Initially, the samples will be dissolved in deionized water and filtered in order to separate the insoluble particles. These particles will be taken forward for microplastic particle extraction and analysis [2]. In the case of vegetables and fruits, they were blended after peeling and the water content was removed and dried by heating [52]. For liquid samples like milk, honey, and beverages, the samples were initially diluted (1:1 ratio) with distilled water and then taken for additional analysis [53].

28

2 Microfiber Shedding of Textile Materials—Mechanism …

2.4.2 Microplastic Particle Extraction To extract microplastic particles from the collected samples, the removal of other constituents and contaminants is needed. Researchers have used the density separation method for isolating plastic particles from carbon-based particles, plant tissues, and others. This was commonly adopted to isolate plastic particles in almost all types of samples including sediments, soil, glaciers, and table salts. In this method, the samples were treated with NaI or NaCl solutions under ultrasonic waves or simply stirred and kept idle to settle down particles. Zinc chloride solution was also used under centrifugation at 4000 rpm for the density separation process [40]. Then the supernatant solutions that have floating particles will be used for analysis. Generally, this step will be done two to three times for the complete isolation of microplastic particles [2, 4, 5]. For the removal of other digestible organic matters, the chemical degradation method has been employed. Researchers have used 30% of hydrogen peroxide solution and potassium hydroxide solution for the degradation of organic materials in the samples of soil and table salt, respectively [2, 4, 40]. It has to be noted that hydrogen peroxide was effective in reducing chromaticity due to dyes and pigments while particularly analyzing effluents from textile dyeing industries [37]. Moreover, researchers have used Fenton’s reagent of iron (II) sulfate during the process which can enhance the rate of digestion [54].

2.4.3 Characterization of Microfibers After extraction of microplastic particles in the filter surface, these particles were visually examined with the help of microscopes including a stereomicroscope, and a scanning electron microscope. The visual examination helps in the categorization of microparticles such as fibers, fragments, foams, films, and granules based on their morphology [2]. In addition, the characterization of microparticles was analyzed with the help of Fourier Transform Infra-Red (FTIR) Spectroscopy and Raman Spectroscopy which helps in identifying the chemical compositions of the microfibers [2–4]. Raman Spectroscopy provides advantages over FTIR analysis as the latter is not effective in identifying microfibers less than 20 µm [3]. Pyrolysis Gas Chromatography–Mass Spectrometry (GC/MS) is yet another technique used for the identification of microplastics in environmental samples. With the help of indicator ions which are the specific decomposition products of a particular polymer, GC/MS identifies and quantifies the microplastic particles [51]. Apart from this, microfibers were identified based on the pre-observation of the textile fibers microscopy manual. Surface gloss, shadows under different light sources, particle diameter, and aspect ratio were analyzed to identify and characterize the microfibers in the samples [40].

2.5 Techniques and Test Methods to Analyze the Microfiber …

29

2.5 Techniques and Test Methods to Analyze the Microfiber Shedding from Apparel The microfiber shedding rate of different apparel during domestic laundry has been analyzed by adopting different techniques due to their dominance in microfiber release. Since no described standard particularly analyzes the microfiber detachment rate from a fabric under defined external conditions, especially domestic laundering, different researchers have used different analytical methods that closely resemble real-time washing. Every method followed by the researchers had its own merits and demerits. This section details the different sampling methods, washing simulation, filtration techniques, and microfiber quantification protocols that are followed by different researchers who have investigated the microfiber shedding behavior of apparel during domestic laundry.

2.5.1 Textile Sample Preparation Most of the laboratory-scale studies use fabric swatches rather than the entire garment. The dimension of fabric swatches varied with the instruments that are being used for the simulation of domestic laundry; larger dimensions were used while using commercial washing machines [11, 12, 34, 55], whereas smaller fabric swatches were used in the case of laboratory-scale laundry machines [13, 16, 29, 56]. Based on the objective of the study, fabrics with different fiber compositions, fabrication methods, and finishes have been chosen by the researchers. A few researchers produced their own fabrics for analysis [18, 56–58], whereas, in most of the studies, the materials were sourced from different manufacturers and so the material compositions and the textile characteristics were confirmed by Fourier Transform Infra-Red Spectroscopy (FTIR) and Scanning Electron Microscope (SEM) analysis, respectively [12, 30, 42, 59]. This analysis can further help in the identification of fibers shed from the sample. While analyzing the microfiber shedding with fabric swatches, fabric edges become a matter of concern. The open edges can have cut fibers, and these can result in the release of more fibers. However, these edges will be sealed in the whole garment. Hence, while using fabric swatches, edges were generally sealed by sewing or hemming [10, 12, 16, 29, 34, 55, 57, 60]. For edge finishing, monofilament sewing threads are preferred to avoid microfiber release from the sewing threads [14]. A few researchers have also used laser cutters and ultrasonic welders to prevent fiber loss by sealing the edges [13, 33, 56]. In a study, textile glues were used to seal the folded edges [61]. While using whole garments, this process can be exempted as there will be no open edges in the garment. The other preparation process which holds a significant role is pre-washing/cleaning. The samples are generally pre-washed before the analysis of microfiber release. This process is usually done to remove any dirt or dust particles that are often considered non-fabric particles on the surface of the samples. Moreover, this process also removes any superfluous fibers that stick to the surface

30

2 Microfiber Shedding of Textile Materials—Mechanism …

of the samples as well as temporary textile auxiliaries and other loosely bound polymeric materials that emerged during the manufacturing process [12, 34, 61]. This step in the sample preparation is very important so that the final rinse water will have only the fibers that are shed from the textile material itself during the washing process [17]. Vacuuming of fabrics was also employed as one of the pre-cleaning methods. The fabric samples were vacuumed at a slow pace (15 cm/s) in order to remove any other foreign contaminants [13]. Table 2.1 consolidates sample forms and preparation methods which have been followed by various researchers who have analyzed the microfiber shedding from textile materials. While analyzing the sample preparation methods processed by different researchers, the most common difference found between studies is the sample dimension. Though sample sizes varied with the washing instrument type, the standard sample size for a particular washing method has not been adapted. It can be seen that the researchers using similar washing apparatus used different sample dimensions [13, 56, 60]. Secondly, in the pre-cleaning method, a few researchers followed simple washing of fabrics with water [12], however, others followed a wash cycle which is very similar to the actual laundry cycle [56, 57]. The standardization of pre-cleaning is very essential because the level of cleaning depends on this process. Moreover, these processes can probably damage the surface besides removing the unwanted contaminants. When considering the edge finishing process, there comes a wide variety of sewing methods. The sewing thread and characteristics of stitches like SPI were not detailed properly. The variation in sewing threads and stitch types can affect the results as they do have an impact on the microfiber shedding [60]. Researchers who developed a protocol for reliable quantification of microfiber shedding reported that to avoid the influence of microfibers released from the edge of the fabric sample, it is suggested to use lockstitch instead of overlock stitch to finish the edge of the fabric swatch [14]. Aging Simulation of samples While estimating the microfiber shedding during normal household laundering, it is important to consider the aging of the material. Since the garments which are being laundered in the households are used ones, the microfiber shedding of a new unused fabric/garment cannot imitate real-time laundry. Hence, for a closer resemblance of real-time household laundry, a few researchers have simulated aged fabrics and analyzed the microfiber shedding. For simulating the aged effect of fabrics and garments, researchers adopted different methods. A researcher simulated aged jackets by continuously washing a new jacket for 24 h in a washing machine with cold water without a spin cycle. This simulates the aging of material after its lifetime of laundering and the researchers termed it as ‘killer wash’ [62]. In contrast, the other researcher created the aged effect by means of the repolishing process. The fabrics were repolished in a sander, where the fabrics were abraded against an abrasive belt (dimension—75 mm × 457 mm) of 60 grains for 1 s [58]. For real simulation, researchers have also collected real-time consumer clothing from households and used it for microfiber shedding analysis [33, 63].

Garment and blanket

Kärkkäinen and Sillanpää [64]

Periyasamy [65]

Tian et al. [66]

Rathinamoorthy and Raja Balasaraswathi [31]

Kelly et al. [32]

Cai et al. [60]

Galvão et al. [67]

Lant et al. [33]

Fontana et al. [68]

2

3

4

5

6

7

8

9

10

Other preparation processing of samples

Cleaned with vacuum cleaner

Pre-washed and dried in atmospheric conditions

–

Fabric

Garment

Garment

–

–

–

High efficiency top loading machines

Front load washing machines

(continued)

Sourced for 3 min and tumble tried Bosch washing machine

Sourced from U.K. households

–

Edges were covered with overlock GyroWash sewing and double-folded sewing

10 cm × 4 cm

Fabric

Front load washing machine

–

–

Tergotometer

Garment

Laser cut edges to prevent fiber loss

Hand laundering

Launder-ometer

Hand laundering

Top load washing machine

Front load washing machine

Front load washing machine

Top load washing machine

Instrument used for laundry

5 cm × 5 cm

10 cm × 10 cm Edges hemmed with SNLS

–

–

–

66 cm × 66 cm Fabric edges were covered by double-hemming

Sample size

Fabric

Fabric

Garment

Garment

Fabric

Vassilenko et al. [55]

1

Form (Fabric/Apparel)

References

S. No.

Table 2.1 Sample preparation methods

2.5 Techniques and Test Methods to Analyze the Microfiber … 31

Fabric

Garment Garment

Fabric Fabric Fabric

Frost [57]

De Falco et al. [42]

Belišová et al. [69]

Berruezo [13, 16, 29, 31, 57, 58, 60, 70, 71]

Choi et al. [72]

˙Ilkan and Gündo˘gdu [18]

Gkirini [20]

Zambrano et al. [16]

Belzagui et al. [73]

De Falco et al. [30]

11

12

13

14

15

16

17

18

19

20 Garment

Garment

Fabric

Garment

Form (Fabric/Apparel)

References

S. No.

Table 2.1 (continued) Other preparation processing of samples

Heat cutting to stabilize edges

10 cm × 4 cm

–

–

–

Pre-washed five times

Edges finished with 100% polyester thread Fabrics were pre-washed

4 in × 4 in 1.8 kg

Garments are pre-washed

–

Pre-cleaning using vacuum cleaner

Overlocked with white polyester thread

–

5.5 cm × 5.5 cm –

–

Pre-washed in washing machine

–

–

10 cm × 10 cm Edges were finished with 100% polyester thread Pre-washed under actual laundry conditions

Sample size

(continued)

Bosch washing machine

Front load washing machine

Top load washing machines

Launder-Ometer

Front load washing machine

GyroWash

Washing machine

Linitest apparatus

Laboratory model washing machine (Camry CR8052)

Bosch washing machine

Launder-Ometer

Instrument used for laundry

32 2 Microfiber Shedding of Textile Materials—Mechanism …

Fabric

Fabric

Blanket Fabric

Fabric

Garment

Haap et al. [61]

Yang et al. [12]

McIlwraith et al. [74]

Erkoc et al. [75]

Jönsson et al. [13]

Claire O’Loughlin [34]

Lamichhane, 2018 [63]

22

23

24

25

26

27

28

Fabric (cut and welded to form a bag)

Garment

Cesa et al. [59]

21

Form (Fabric/Apparel)

References

S. No.

Table 2.1 (continued)

–

75 cm2

17 cm × 9 cm

–

Gently shaken to remove superfluous fibers

Edges were overlocked and hem-stitched

Cutting and welding are done by ultrasonic methods

Fabrics are vacuumed at 15 cm/s pace

Washing machine

(continued)

Washing machine

Front load washing machine

GyroWash

Stone laundering

Rotawash

30 cm × 30 cm –

Pulsator and Platen Laundry Machine Top load washing machine

Pre-washed with filter water

Edges were finished with cotton thread –

129.5 cm × 170.2 cm

150 cm × 60 cm

Edges were sealed with textile glues

Pre-washed as per EN ISO Labomat 15797:2004; also cleaned with lint roller

8.5 cm × 16.5 cm

Top load mini washing machine

Instrument used for laundry

–

Other preparation processing of samples

–

Sample size

2.5 Techniques and Test Methods to Analyze the Microfiber … 33

Fabric Fabric

Fabric

De Falco et al. [29]

Roos et al. [70]

Hernandez et al. [17]

Hartline et al. [76] and Bruce et al. [62]

Pirc et al. [11]

Napper and Thompson [10]

Åström [58]

Browne et al. [9]

30

31

32

33

34

35

36

37

Other preparation processing of samples

GyroWash

Linitest apparatus

GyroWash

Instrument used for laundry

–

–

Pre-washed in Wascator Front load washing machine

GyroWash

10 cm × 10 cm Laser cut edges to prevent fiber loss

Front load washing machine Front load washing machine

–

120 cm × 70 cm

Top load washing machine

Front load washing machine

20 cm × 20 cm Edges hemmed with cotton thread

–

Pre-washed with a short rinse cycle Washtex-P Roaches Edges were finished with white thread

Samples were made into bag with ultrasonic welding

Pre-washing/Vacuuming/rolled with sticky garment roll

Edges sewed with cotton threads

Pre-washed in Wascator

–

25 cm × 7 cm

–

9 cm × 9.3 cm

10 cm × 10 cm Edges cut with laser cutter to reduce fiber loss from edge

Sample size

[–] means that the particular specification is not applicable or has not been mentioned by the researcher

Blanket and Garment

Fabric

Fabric

Blanket

Garment

Fabric

Almroth et al. [56]

29

Form (Fabric/Apparel)

References

S. No.

Table 2.1 (continued)

34 2 Microfiber Shedding of Textile Materials—Mechanism …

2.5 Techniques and Test Methods to Analyze the Microfiber …

35

2.5.2 Washing Methods After the preparation of samples, the fabrics were undergone a washing process that imitates real-time domestic laundry. A range of washing methods was adopted that not only mimic the household laundry but also facilitate the microfiber shedding analysis. Washing Instruments When the washing methods were taken into account, different washing instruments were used in different studies. To replicate domestic laundry, researchers have used commercially available washing machines [9–11, 62, 76] as well as laboratory-scale laundry instruments [13, 29, 56, 58, 70] as reported in Table 2.1. Though it seems only two broad categories (laboratory-scale and domestic-scale), there are various types of instruments used in each category. In the case of domestic washing machines, front load and top load washing machines have been used. Moreover, the model and make of washing machines used varied from one study to another. This can greatly influence the results. When it comes to laboratory-scale washing, researchers have used GyroWash, Linitest apparatus, Tergotometer and Launder-Ometer for analysis which are very similar in operation [13, 16, 29, 31, 32, 57, 58, 60, 70, 71]. The detailed exploration of both kinds of washing instruments can reveal that both have limitations of their own. In the aspect of samples, domestic laundry machines can accommodate garments as well as fabrics in larger quantities which can mimic real-time washing whereas, in the case of laboratory-scale instruments, only fabric swatches of smaller dimensions can be used. At the same time, the other thing to be noted with sample collection is that in the case of domestic washing machines, while making experiments, the load has to be maintained at 3–5 kg which leads to the requirement of the huge volume of sample fabrics when repeated testing has to be made [14]. However, laboratory-scale instruments use small fabric swatches, which require comparatively lesser fabrics while going for different parameters or multiple replicates analysis. In maintaining washing conditions, the use of laboratory-scale washing machine gives the advantage of adjusting the washing parameters like water volume, temperature, washing duration, and mechanical agitation (number of steel balls) as per the requirement of the analysis, and the full control will be in the hands of analyst. This parameter controllability will help to understand the microfiber shedding in both domestic and industrial washing conditions with the same washing instrument [29]. On the other hand, while using domestic washing machines, the control of washing parameters depends on the settings of the machine. The water volume, duration, and temperature were set as per the wash cycle chosen [63]. Hence, the control over the washing parameters will be lesser when compared to laboratoryscale washing instruments. Moreover, these wash cycle settings will also vary from one model to other models of washing machines. The other major concern to be noticed here is washing effluent. The effluent from the domestic washing machines is very high which varies from 20 to 150 L based

36

2 Microfiber Shedding of Textile Materials—Mechanism …

Fig. 2.4 Benefits and shortcomings of washing instruments used for microfiber shedding analysis

on the washing machine model and wash cycle settings which can create complications with the filtration process. Though sampling has been made from such a huge volume, reliability will be a concern [14]. However, this will not be an issue in the laboratory-scale washing instruments as there will be only a lesser volume of wash effluent. The next major concern with the large-scale laundry machines is the traceability of microfibers settled in the washing drums and pipelines. There are chances for the microfibers to get deposited in the pipelines which will remain underestimated as these pipes are sealed [14]. Though an empty wash load has been run to remove any residual fibers [29, 56, 57, 60], the effectiveness of the cycle to remove all the residues is a matter of worry. Contrarily, in laboratory instruments, the containers can be thoroughly washed after each experiment and the removal of residues can be ensured. Figure 2.4 highlights the strengths and shortcomings of laboratory and domestic washing machines. When comparing the washing instruments, laboratory-scale washing instruments, GyroWash was noted to have better reliability and reproducibility of the microfiber shedding results which was proven by the intraand inter-laboratory analysis as per the standard ASTM E691-18 [14]. Apart from these washing instruments, researchers have also developed protocols to imitate the hand laundering of textiles which is also one of the most commonly adopted ways of cleaning clothes in the household [31, 66]. Fabric swatches were soaked in detergent solution and then rubbing and beating has been done. The fabrics soaked in the detergent solution were rubbed against a washboard a specified number of times (90 times) and wrung to remove excess water [66], whereas the other researchers have done rubbing and beaten fabrics with plastic rods for a specified period (15 min) [31]. Washing Parameters The adjustment of washing parameters including the water volume, washing temperature, and washing duration is another key point in emulating the domestic washing process. While working with laboratory-scale washing machines, researchers have performed washing as per the color fastness to wash testing protocol according to the standard ISO 105-C06 because this replicates domestic washing [18]. This testing follows a standard liquor volume (1:150), temperature (40 °C), duration (45 min),

2.5 Techniques and Test Methods to Analyze the Microfiber …

37

detergent level (4 gpl), and mechanical agitation (number of steel balls—10 steel balls of 6 mm diameter) to replicate domestic laundry [17, 29, 31, 60, 71]. Most of the researchers followed this standard to simulate domestic laundry for microfiber shedding analysis. Another standard AATCC Test Method 135–2015 has also been used by researchers who replicate domestic washing to check the dimensional stability of fabrics. As per this standard, the wash liquor volume, duration, and detergent concentration were maintained as 150 mL, 16 min, and 1.47 gpl [16, 57]. However, these conditions were altered as per the research requirements. While analyzing the effect of each parameter on the microfiber shedding behavior of fabrics, the washing conditions were adjusted appropriately. For industrial-scale washing simulation, temperature, washing duration, and the number of steel balls were altered as 75 °C, 60 min, and 25 steel balls, respectively [29]. In laboratory-scale washing, after washing, a few researchers adopted the rinsing process. After taking the samples from the wash containers, the cylinders, as well as the fabrics, were carefully rinsed with distilled water [13]. Researchers have rinsed the fabric samples up to five times [56]. While in the case of domestic washing machines, short cycles, as well as normal cycles, were used. The studies have used the SuperQuick program where the duration, temperature, and spinning speed were at a minimum level in order to save energy and time (15 min; 30 °C; 600–1000 rpm) [11]. However, longer washing programs were also adopted which extend up to 75 min [10]. Moreover, researchers chose wash cycles based on the textile materials being washed [34]. Studies that analyzed the microfiber shedding of different clothing and house linens set temperatures (20– 60 °C) based on the material composition. Washing duration is often calculated by the washing machine as per the wash cycle [67]. The other researchers have used a ‘synthetic’ program which was maintained at 40 °C for 107 min running at a spin rate of 1200 rpm [30]. Since the microfiber shedding of a textile material can get gradually decreased over subsequent wash cycles, a few researchers have washed the fabrics multiple times to determine the number of wash cycles required for stabilization of microfiber shedding, and further quantifications were made at the wash cycle where the shedding started to get stabilized [73]. Studies have used ultrapure water for washing. This has been done to prevent external fiber contamination [18], whereas others have used normal tap water [12, 18]. While using tap water in washing, the external contamination is generally quantified using a control filter paper with the residue without a sample. Subtracting the fibers in the control filter paper from the sample filter paper will give the actual number of fibers shed from the fabric [18]. Usage of Detergents and other additives Detergents are one of the unavoidable additives during washing that facilitate the removal of dirt and stains. Hence, while simulating domestic laundry, the detergents can’t be ignored. Researchers have used commercially available liquid detergents as well as powdered detergents [11]. When considering the composition of detergents, only a few researchers have mentioned the compositions and reported that the used detergents had C12–15 pareth-7, sodium laureth sulfate, potassium cocoate, and

38

2 Microfiber Shedding of Textile Materials—Mechanism …

TEA-Cocoate [56]. Linear alkylbenzene sulfonic acid (LAS) has also been used as an alternative for detergents in washing as it is the main surfactant ingredient in most of the commercially available detergents [60, 77]. The most commonly used concentration of detergents in laboratory-scale washing varied as 1.47 g per liter and 4 g per liter as per the standards AATCC Test Method 135–2015 and ISO 105C06, respectively [16, 29, 56, 57]. While washing in large-scale washing machines, 7 mL–150 mL of liquid detergents are used based on the load capacity and the detergent manufacturers’ recommendation [13, 17, 67]. When the impact of detergent concentration was analyzed, the level of detergents was varied [56]. The use of detergents was purposely avoided by a few researchers as they can clog the filter and make the filtering process tedious [62]. A few other additives like bleaches and softeners were also used in a few studies to analyze their impact on microfiber shedding [29, 67].

2.5.3 Filtration Process Once the washing has been done, the wash effluents were collected in sterilized containers to avoid contamination. Generally, plastic, glass, and stainless steel containers were used after sterilization for collecting the wash effluents [13, 16, 74]. Then these effluents were filtered using different filtration techniques for further quantification and analysis of microfibers shed from the textile materials. Effluent sample collection for filtration When the washing has been done with domestic washing machines, the amount of effluent released will be relatively higher (in a range of 20–30 L) [73, 74]. Filtering such a huge volume of effluent will make the process time-consuming. Thus, researchers sampled small quantity of effluent from the actual effluent released from the washing machines. Generally, the sample for filtration will be collected after stirring the total effluent collected. Stirring of effluents can be done with glass rods [74], whereas it can also be enhanced with a hose at the bottom of the container having the effluent [73]. This stirring can facilitate the uniform and homogeneous distribution of fibers in the effluent [63]. Based on the total quantity of effluent, the sample quantity will be decided. Researchers have also sampled the effluent for filtration in a step-by-step process where a huge volume of effluent will be sampled initially (10 L out of 22 L) from which further a small volume (three 10 mL samples out of 10 L) will be taken for filtration process [73]. The other researchers sampled 250 mL of the homogeneous mixture out of 30 L which is then sampled to 50 mL for filtration [59]. This step-wise procedure makes the sampling more efficient. Moreover, while working in the large-scale washing, normally, the effluents were initially filtered with filters of larger pore size which facilitates the quick removal of lint of larger size in the huge volume of wash effluent. After this step, the effluents were sampled and filtered using filters of smaller pore sizes [74].

2.5 Techniques and Test Methods to Analyze the Microfiber …

39

Filtration Techniques and filter Specifications Once the sampling of wash effluent has been made, the sampled effluent will be filtered using different filtration systems. Researchers have simply filtered the effluent through the filters [31], whereas a few others used vacuum pump or air suction pump that facilitates the filtration process [18, 63, 78]. The vacuum filtration method was most commonly adopted by various researchers to make the filtration process efficient [79]. Vacuum Filtration apparatus generally comes with filters and a vacuum. Researchers developed a vacuum filtration apparatus made of a filtering funnel, filters, filtering base, clam, filtering flask, and vacuum [63]. The vacuum pump will help in faster and more effective filtration. Researchers have also set up a two-step filtration system. In this setup, the filtering column is comprised of a sequence of two filters with varied pore sizes. Filters with larger pore sizes will be at the top of the sequence, where fibers of larger sizes will be separated. The smaller fibers which got escaped in the first filter will be caught in the second filter which is of smaller pore size. A two-step filtration column was developed by a researcher with two filters of pore sizes 333 µm and 20 µm. The two filters were kept at 30 inches gap in the filtration column [62]. The other researchers used 100 µm and 5 µm pore filters for two-step filtration [70] whereas nylon mesh filters of 60 µm and 20 µm were firstly used and then a Polyvinylidene Fluoride filter of 5 µm was used for the final filtration step by other researchers [30]. This filter helps to analyze the difference in the size of microfibers released from the textile material under different conditions and also prevents the clogging of the filter surface with more fibers. In a few cases of domesticscale washing, filters were attached to the discharge pipes of the machines to collect the fibers which were further washed in distilled water and filtered using filter papers [16, 34]. Researchers found that filtering the total volume of effluent in a single filter leads to overlapping of fibers in the filter surface which will affect the counting method. Hence, they have tried the dilution method. In this method, after the collection of effluent samples, they were diluted to a 1:10 ratio, and then the total diluted volume is divided among more than one filter. The dilution resulted in a homogeneous distribution of fibers in the filter surface, and splitting the sample effluent (cascade filtering) in more than one filter (8 filters) reduced the number of fibers per filter. This simplified the counting process as there will be no overlapping or aggregation of fibers on the filter surface [67, 73]. This also helps in reducing the difficulty in fiber identification during manual counting [17]. In different filtration processes, the samples were normally stirred to accelerate the filtering process [63]. Fluxing of water in the filtration system at 70 °C was also done to reduce the excess amount of detergent on the surface of the filter, particularly while using a powdered detergent for washing [29]. The other important consideration in filtering is the filter material and pore size. A wide variety of filter materials including nylon, cellulose, stainless steel, and PTFE have been used. Nylon mesh filter bags are the most commonly used filters for microfiber analysis [62, 73, 80]. Hydrophobicity of the filter materials was highly desired as they should not alter the weight of fiber mass due to moisture regain

40

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[14]. Glass fiber filters were found to provide better efficacy with its reduced moisture regain property along with the three-dimensional multi-layered matrix structure which stops the fiber migration in a better way [14]. The pore size of the nylon meshes that are used in microfiber filtration ranges from 20 to 333 µm. Generally, the pore sizes were chosen based on the applications. While analyzing the microfiber release from a drying vent, researchers have chosen a pore size that could filter the microfibers at the same time without affecting the airflow. In that case, medium pore sizes (100 µm) worked well [79]. The filter material and the pore size used by different researchers for the filtration process are provided in Table 2.2. Filter drying After the filtration process, the filters will be kept in Petri dishes and stored in a closed environment to avoid contamination before quantification [73]. These filter papers are dried to remove moisture content, and it is an essential step when the quantification is done by weighing as the moisture can affect the weight of the samples. Researchers are adopting different drying conditions for the removal of moisture from the samples. Complete removal of moisture is inevitable while quantification is made by the weighing method. For removing moisture from the filters with microfiber residues, desiccants were used. The researcher used a DampRid Moisture Absorber containing calcium chloride, sodium chloride, and potassium chloride for the complete drying of the filters [62]. Other researchers have performed oven drying as well as air drying. The temperature and duration of different drying methods as followed by different researchers are reported in Table 2.2.

2.5.4 Quantification Methods The filters with the microfiber residue will be analyzed for microfiber quantification. The quantification has been made on both weight and count bases. A few researchers have estimated both the number and mass of fibers [74], whereas others found weight based on the number of fibers and vice versa [10, 29, 63]. To ensure the reliability of the microfiber quantification, researchers have performed multiple replicates (2– 4) for every sample. An average of the results of all the replicates were taken as the final value/quantity of microfiber shedding. Generally, the quantification has been normalized in terms of number/mass of fibers per unit volume of effluent [18], number/mass of fibers per unit area of fabric [73], and number and number/mass of fibers per unit mass of fabric [18, 73, 80]. Researchers have also mentioned relative mass % based on the mass of fibers shed and the initial mass of the fabric tested for microfiber shedding [11].

Vacuum filtration system

5 L sampled from Two-step 140 L filtration—column with sequence of two filters

Filter with air suction

Filters attached to discharge pipes

–

Filters are attached to discharge pipe

–

>150 mL

20 mL sampled from 68 L

–

30 mL sampled from 22 L

–

50 mL sampled from 30 L

>75 mL

–

150 mL

–

[63]

[62, 76]

[29]

[67]

[11]

[73]

[80]

[74]

[13]

[34]

[16]

Vacuum filtration system

Vacuum filtration system

Vacuum filtration system

–

Inox Filtration system with vacuum pump

Peristaltic Pump connected with Tygon tubes

Filter system

Effluent volume

References DampRid moisture absorber (desiccant) Dried at 105 °C for 30 min – Air-dried

Dried at 60 °C for 24 h SEM and stereo microscope Dried at 50 °C overnight Dried at 55 °C overnight

5 µm

12 µm 200 µm 20 µm 20 µm

Polyamide Nylon (CellMicroSiev® ) Polycarbonate (Nuclepore 10 µm Hydrophilic Membrane)

Nylon mesh

Glass microfiber filter papers

Cellulose nitrate filter paper

Membrane filters

Stainless steel

Nitrocellulose Mixed Ester Membrane

Polyvinylidene Fluoride (Durapore® )

20 µm

Dried at 105 °C overnight

1.2 µm

–

Dried at 45 °C for 24 h –

1.2 µm

(continued)

Optical microscope

Air-dried

0.65 µm

Light microscope

–

SEM and stereo microscope

Stereo microscope

Scanning electron microscope

–

–

333 µm; 20 µm

Nylon

(Nitex® )

–

Microscope

Drying method

0.45 µm

–

Pore size

Filter material

Table 2.2 Filtration method adopted by different researchers to isolate microfibers from the wash effluent

2.5 Techniques and Test Methods to Analyze the Microfiber … 41

Peristaltic Pump connected with Teflon tubes

Vacuum filtration

Peristaltic Pump connected with Tygon tubes

Vacuum filtration system

Vacuum filtration system

Vacuum filtration system

–

–

–

∼ 150 mL

–

∼ 150 mL

∼ 150 mL

–

–

20 L

–

∼ 150 mL

[12]

[56]

[30]

[60]

[57]

[77]

[17]

[59]

[32]

[31]

Vacuum filtration system

Vacuum filtration system

Filters are attached to discharge pipe

–

[10]

Filter system

Effluent volume

References

Table 2.2 (continued) Dried at 30 °C –

25 µm 5 µm

Nylon (CellMicroSiev® )

Dried at 50 °C for 24 h –

8 µm 20 µm 22 µm

Glass filter Nylon (CellMicroSiev® ) Whatman filter paper Whatman Filter paper

–

Dried at 60 °C overnight

500 µm; 63 µm

Stainless steel

11 µm

Dried for 24 h in aluminum case

0.45 µm

Whatman filter paper

(continued)

Digital microscope

–

Digital microscope

Dried at room temperature overnight

0.45 µm

Cellulose nitrate membrane

Stereo microscope

–

Dried at room – temperature overnight

1.2 µm

Whatman filter paper (GF/C)

0.45 µm

5 µm

Polyvinylidene Fluoride (Durapore® ) Cellulose nitrate membrane

Oven drying—105 °C SEM and light for 1 h microscope

60 µm; 20 µm

Light Microscope

–

1.2 µm

Optical stereo microscope

SEM and light microscope

Microscope

Nylon filter

Glass fiber filter

Polytetra-fluoroethylene

Drying method

Pore size

Filter material

42 2 Microfiber Shedding of Textile Materials—Mechanism …

Vacuum filtration system

Pump filtration system

∼ 150 mL

∼ 150 mL

–

–

30 mL out of 12 L –

[18]

[71]

[20]

[69]

[66] Glass fiber Filter

Nitrocellulose membrane

–

Glass fiber filter

Cellulose membrane

Filter material

Dried in desiccator

Dried at 105 °C for 2 h Fluorescence microscope Oven drying—60 °C for 1 h

0.22 µm 1.2 µm

Stereo microscope

Optical microscope

Dried at 105 °C for 2 h SEM

–

Microscope

50 µm

–

Drying method

1.2 µm

0.45 µm

Pore size

[–] means that the particular specification is not applicable or has not been mentioned by the researcher

Vacuum filtration system

Filters are attached to discharge pipe

Filter system

Effluent volume

References

Table 2.2 (continued)

2.5 Techniques and Test Methods to Analyze the Microfiber … 43

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Count estimation In the counting method, microscopic images of the filters were examined. Researchers have used different microscopes including Scanning Electron Microscope [29], Stereomicroscope [11, 67, 79], and Digital Microscope [17, 31] with different magnifications based on the experimental setup. For counting fibers in a filter paper, researchers have taken the micrographs of the filter surface and counted the number of fibers on the surface manually. Generally, to cover the entire filter surface, researchers had to take around 16–30 micrographs; these images were analyzed and the fibers all over the surface were counted [17, 58]. For the filters, where the number of fibers seemed to be high, researchers counted fibers in half of the filter surface and estimated the total number of fibers [58]. Later, to reduce the complication, different counting methods have been adopted. Researchers have randomly chosen a specified number of micrographs (5 squares–120 squares) in the filter surface [10, 18]. Then those selective micrographs were undergone a visual examination for the number of microfibers in each image, and the total number of fibers in the entire filter is estimated by considering the total number of squares in the filter membrane [18]. Further to make this random selection a well-defined pattern, researchers started to choose squares along the orthogonal diameter of the filters. The number of squares ranged from 21 to 30 [29, 31]. This method of choosing squares along the diameter of the filter surface was also validated by comparing it with the extended counting method where the fibers in the entire filter area were counted. The statistical comparison of these two methods has shown insignificant variation which claims that the counting method by analyzing the squares along the orthogonal diagonal is effective [29]. Figure 2.5 shows the effectiveness of the counting method as it is comparable with the extended counting method. In other counting methods, the filter surface was divided into four quadrants, and fibers in one quadrant have been counted which is then multiplied by four to estimate the fibers in the filter surface [67]. Most of the researchers have manually counted microfibers in the micrographs of the filter paper, whereas a few others used software for counting [13, 60]. Cleanliness Expert v4.9 was used by the researchers to identify the particles of size more than Fig. 2.5 Effectiveness of the counting method covering fibers along orthogonal diagonal implying no significant difference between the fibers counted using the adopted method and extended counting method (Reprinted with permission from [29])

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45

5 µm. The software has been chosen as it can identify particles based on the length– width ratio which has been set. Hence for the case of fibers, 10:1 or 20:1 was set as the length–width ratio which enables the software to identify the fibers in the filter surface and count them [13]. A semiautomatic software called FiberApp v1.51 was also used for determining the number of fibers in the filter paper as well as the length of the fibers, where the user has to manually select the starting and endpoints of the fibers which enables the automatic recording of fiber length and count [60, 77]. Moreover, the number of microfibers released from the fabrics was also calculated from the weight of the fibers released. The simple method of estimating the number of fibers from the mass of the microfibers is using Eq. 2.1. Number of microfibers =

Total weight of the microfibers in filter Weight of single fiber

(2.1)

During conversion, either from mass to count or from count to mass, the fiber size plays an important role. Fiber size, that is, length and diameter are basically taken as an average value based on the lowest and higher values of the fibers that are found on the filter surface [62]. Usually, the microscopic images of the microfibers are analyzed using ImageJ software for the measurement of the length and diameter of the fibers [18, 29, 62]. Mass estimation The simple method of weight quantification is weighing the dried filters with residues and reducing the weight of the filter paper (Eq. 2.2). This will give the weight of the residue [63]. The weighing procedure will be usually done repeated times for reliability. Weight of Microfiber released = Weight of the filter paper with residue − Weight of the filter paper

(2.2)

The weight of microfibers shed from the fabrics was also estimated based on the number of microfibers counted. By specifying fiber length, fiber diameter, and fiber density, the mass of the microfibers was estimated from the number of microfibers as in Eq. 2.3 [10, 29]. Grams of microfiber/kg fabrics = 1000 × N × (π ×

D2 × L)ρ 4

(2.3)

The other method where the mass of the microfibers was estimated was based on the L* values. L* values are the luminosity indices that determine the correlation of the perceived lightness of an object in a specified illuminant. The images of the filter surfaces were examined using DigiEye® software which calculates the RGB values

46

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of every pixel to estimate the L* values. By creating a calibration curve with a known mass of fibers and their corresponding L* value, the relationship between the mass of the fibers and L* values can be established. This was further used to calculate the mass of the fibers in the filter surface. The empty filter surface will be imaged and the L* value for zero mass will be recorded [32]. Although the weighing method is a simple and time-saving method, it has the risk of overestimation of fibers because while going for mass evaluation, there will be no information about the morphology of the fibers, and there is a huge chance of mistaking other particles in the filter as fibers as there will be no visualization. Dust, production residues, and contaminants may also be added while weighing the fibers [61]. Moreover, the other soluble additives such as oils and waxes in the textile fibers can also mislead the microfiber quantification in terms of mass [20].

2.5.5 Characterization of Fibers Shed from the Textile Material Apart from quantification of microfibers shed from the textile materials, it is indispensable to characterize the microfibers. The chemical, physical, and morphological properties of fibers should be analyzed which can clearly show the microfiber release mechanism from the surface of the textile materials and the cause of fiber release. Moreover, this can help in identifying the similarities between the microfibers found in the environment and those obtained under the experimental conditions. Thus, the characterization of microfibers shed from the textile materials is also given equal importance as the microfiber shedding quantification. Fiber Composition Most of the researchers analyzed fabrics made of individual fibers and compared shedding caused by fabrics made of different fibers [12, 29, 59], whereas a few others analyzed blended fabrics [30, 33, 61]. To ensure that the fibers filtered in the filter surface originated from the samples that are analyzed for microfiber shedding, ATR-FTIR spectroscopy has been widely adopted. The spectra of the textile materials and the microfibers in the filter surface were compared to characterize their functional group [65]. When blended fabrics are analyzed, the fibers that are shed from the fabric will be different fibers that need to be separated for analysis. Haap et al. have used sulfuric acid to separate the polyester and cotton while analyzing PC blends for microfiber release [61]. The filter surface having polyester and cotton microfibers was rinsed with ultrapure water and dried in a petri dish. Then the addition of 20 mL of sulfuric acid and incubation of 1 h can hydrolyze the cotton fibers leaving polyester alone. Further neutralization can be done with ammonia solution making the polyester fibers ready for further analysis [61]. Researchers have used this sulfuric acid treatment and quantified the number of fibers shed from the 50/50 PC blend using Dynamic

2.5 Techniques and Test Methods to Analyze the Microfiber …

47

Image Analysis. Results revealed the percentage of each fiber, that is, cotton (86 ± 3%) and polyester (14 ± 3%) that was shed from the PC blend fabrics [61]. Thermogravimetric analysis has also been employed for the identification of fibers shed from blends. Researchers noted single-step degradation while analyzing polyester and cellulosic fibers individually. The maximum weight loss was noted at 454 and 377 °C for polyester and cellulosic fibers, respectively, whereas, when the filters having microfibers shed from blend fabrics were examined, a two-step degradation has been noted that shows that the weight loss at the first step corresponds to the degradation of cellulosic fibers and the next step of degradation corresponds to the polyester fibers [30]. In line with this, while analyzing real-time wash load, there will be fibers of varied compositions. For the separation of these microfibers, researchers have used a similar method adopted by Haap et al. where 75% sulfuric acid has been used for the dissolution of cotton and viscose fibers. Then the filters having fibers were subsequently treated with a 5% hypochlorite solution to digest wool fibers which finally left the filters with synthetic microfibers [33]. Fiber Length Most of the researchers categorized the microfibers shed from the fabric based on their length. The classification of microfibers shed from fabrics based on length can help in understanding the effect of textile or washing parameters in damaging the fibers. Moreover, it will be more helpful while working on mitigation strategies in the aspect of targeting fibers of a particular length [74]. According to the length of the fibers, different researchers adopted different scales of measurement. Researchers have categorized microfibers as Size 1, Size 2, Size 3, Size 4, and Size 5 which denotes fibers of length 0.025 mm–0.25 mm, 0.25 mm–1 mm, 1 mm–1.75 mm, 1.75 mm– 3 mm, and = >3 mm, respectively [56]. Similarly, other researchers categorized fibers as Small category S (1000 µm). This categorization helps in the easy identification of fibers based on their length [20]. Based on the type of fiber, the length of the microfiber shed will vary. Researchers have reported while analyzing the length of fibers shed from cotton and synthetic fabrics, the majority of cotton fibers (85%) were in the range of 50–100 µm whereas synthetic fibers were in the length range of 100–500 µm (40%) as well as 50–100 µm (53%) [67]. Similarly, the length of microfibers also varied with the fiber properties; fabrics made of fibers with good elongation at break were noted to shed longer microfibers than that of poor elongation at break values [57]. Moreover, the length of fibers also varies with aging. The aged or used fabrics can shed fibers that are of a smaller length than that of new clothes [67]. This was in line with the researchers who have noticed a decrease in the length of the fibers shed in subsequent washes [73]. The other significant influencer of microfiber length has been noted as surface processing. Fabric surfaces that are processed (fleece, brushed surfaces) were found to release shorter microfibers than the unprocessed surfaces [77]. Furthermore, the cause of release also affects the fiber length. Researchers noted a higher length of fibers when they are released from the fabric to air due to wearing actions, whereas the fibers shed during the laundry are comparatively lesser [42].

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2 Microfiber Shedding of Textile Materials—Mechanism …

Fiber Surface Appearance The analysis of the surface appearance of microfibers helps in variating the causes of release of the particular fiber. For analyzing the surface morphology of microfibers, Scanning Electron Microscope (SEM) and Optical Microscope were used. The surface of fibers was found to have damage and fiber fractures were also noted. A few resembled as they are ripped off from the fiber structure [65]. The fibers that are embedded or attached to the fabric surface were found to have regular tail-end shapes, whereas the fibers that are detached due to external actions were noted to have ripped tail-ends [73]. Other researchers have analyzed the ends of microfibers shed from fabrics whose edges are finished with different methods (scissor-cut and laser-cut). They have noticed similar distorted ends in the fibers that are released from the first as well as the tenth wash cycles which shows that the nature of fiber destruction was similar even after multiple washes. Furthermore, the fibers that are shed from the laser cut samples showed molten ends [60].

2.5.6 Quality Assurance During the analysis of microfibers, there are high chances for the contamination of samples with atmospheric micro-level particles. The filtration of samples is carried out in a laminar flow chamber which can help in avoiding atmospheric contamination [67, 74]. All the materials that are used in sampling processes were thoroughly washed with Milli-Q water [67], and the surroundings were often cleaned with lintfree wipes [61]. For the mitigation of airborne contamination, ion-generating air filters were used in the work area [55]. Moreover, during analysis, there could be a possibility for the microfibers from the clothing that the analyst is wearing can lead to affect the process. Hence, cotton lab coats are used by the researchers to prevent contamination as they can be easily differentiated from the synthetic textiles used in the analysis. Mostly, white color coats are used so that it will be easy to identify and differentiate the fibers shed from the samples [29, 42]. A few other researchers used coats and gowns made of monofilament polyamide as these materials have low-lint surfaces [61]. Nitrile gloves are being worn by the analysts to avoid any other contamination [29, 30, 42]. Even after the careful assessment of microfiber shedding, researchers reported contaminant fibers up to 1.6% of total fibers collected on the filter surface [67]. Though it seems lesser, it is important to consider the level of contamination. While performing multiple replicates, microfibers from one cycle can pass on to the next cycle. To avoid that, an empty wash cycle has been carried out without fabrics between two experiments [62]. This can clean any residual fibers/particles that are left out in the washing drum as it can affect the microfiber quantification of the next experiment. Citric acid has been used in the cleaning wash cycles of domestic washing machines [11]. Figure 2.6 summarises the techniques and test methods that are being adopted to analyse the microfiber shedding from textiles.

2.5 Techniques and Test Methods to Analyze the Microfiber …

49

Fig. 2.6 Procedure for analyzing microfiber shedding from textiles during domestic laundering

2.5.7 Other Innovative Techniques in Microfiber Analysis The conventional methods of estimating and analyzing the microfibers that are being shed from the apparel are getting upgraded with new innovative techniques that help in simulating the washing process as well as estimation of microfibers in the effluent. A few techniques that are enhanced from the conventional methods discussed above are being implemented in the microfiber shedding analysis. Ultrasonication Method The Ultrasonication technique involves the passing of ultrasonic waves to a liquid medium which makes microbubbles form, grow, and get collapsed in an extremely short duration (within microseconds). Alteration of low-pressure and high-pressure waves leads to the formation and collapse of bubbles [81]. Initially, ultrasonic waves were used in the laundry for the effective cleaning of fabrics. The chaotic oscillation of acoustic bubbles that are formed by the ultrasound waves can help in the detachment of dirt molecules that are trapped between the fibers due to their interfacial thrusts and dynamic pressure gradient [82]. The method was found to provide better soil removal while causing lesser damage to the fabrics [83]. Moreover, the processing time for the ultrasonication process is lesser than that of normal washing. Ultrasonication for 1 min can yield comparable cleaning with that of normal washing in a Wascator [84]. The hybrid washing machine that combines ultrasonic vibration with the conventional washing machine can provide 15% better performance [82].

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2 Microfiber Shedding of Textile Materials—Mechanism …

Thus, the ultrasonication method can be employed as a delicate and efficient method that can remove contaminants on the surface of textile materials. In this aspect, researchers used ultrasonication techniques to estimate microfiber shedding by extracting microfibers under ultrasound waves. The experimental procedure adopted by Cai et al. for ultrasonication involves an ultrasonic probe having a frequency of 20 kHz and output power of 70 W. The tip of the probe was submerged (1 cm below the air–water interface) in the 200 mL solution of Linear alkylbenzene sulfonic acid (LAS) in which the fabric sample was immersed. The sonication was done step-wise where each step of sonication was extended up to 10 min [77]. To ensure that the ultrasonic waves have not influenced the microfiber release, they have compared the microfiber extraction with ultrasonic waves with microfiber shedding under different washing conditions and found a 3–8% reduction in the microfibers extracted using the Ultrasonication method. This shows that the method does not cause any additional release of fibers. Moreover, fabrics were also analyzed for damages and pills after ultrasonication extraction which confirms that the ultrasound waves have not created any impact on the fabric surface. Besides, the surface of the fibers was also found flawless even after multiple extractions which is confirmed by the SEM analysis [77]. Dynamic Image analysis (DIA) Dynamic Image Analysis (DIA) is an optical detection system that is often used for particle characterization that measures the size and shape of the particles either in solid state or particles dispersed in liquids which are most commonly used in the pharmacy, food, and geology industries [61, 85]. Researchers have applied the same technique to analyze the microfibers suspended in the wash effluent. For the analysis of particles dispersed in the liquid, the DIA setup uses a cuvette through which the effluent can be transported, while a high-resolution camera captures the images of the particles simultaneously. An image analysis algorithm will facilitate the morphological characterization of the particles [61]. For quantifying microfibers in the wash effluent, the effluent was stored in a beaker with an outlet pipe which allows the effluent to the cuvette of the detection system. The effluent stored in the beaker is continuously stirred to make the particles to be dispersed without being settled down. The liquid should be transported without pulsation and to control that, pulsation dampeners can be used. The measurement will be started when the liquid is flushed into the system with intermittent stirring, and once the liquid is completely drained from the cuvette the measurement will be stopped. The full width of the cuvette (4.1 cm) is divided into 11 detection frames and most of the measurements were taken in the center position of the cuvette, however, these cuvette positions can be changed in one direction. The images were captured at a frame rate of 85 fps. Researchers used Windex v.5.10.0.3 software for data interpretation which converts the images into binary images. The evaluation process included the length, straightness, convexity, and aspect ratio of the fibers suspended in the wash effluent [61]. For the quantification of microfibers count, a correlation was noted between fiber count and the measuring positions. This was done because, since only a limited volume of effluent can be detected in a single

2.5 Techniques and Test Methods to Analyze the Microfiber …

51

measurement, extrapolation has to be adopted for estimating the total number of fibers. By assuming a symmetric fiber distribution, the fiber numbers determined by the DIA were correlated with the measuring position in the horizontal axis of the cuvette to develop a quadratic curve. Based on that, the total number of fibers can be estimated [61]. The effectiveness of DIA in quantifying the number of fibers in the wash effluent was evaluated by comparing it with the conventional microscopic counting method. This revealed that both the methods can provide results with an insignificant difference. Moreover, this method (DIA) has advantages over the time-consuming manual counting method. There are possibilities for the errors in the microscopic counting method where the researcher made a subjective assessment. DIA also overcomes the basic issue of fiber overlapping in the microscopic analysis of the microfibers in the filters as here the overlapping can be eliminated [61]. Resistive Pulse Sensor (RPS) The Resistive Pulse Sensing method is a particle detection and characterization method which is based on the Coulter Principle. The improved sensitivity and throughput opened the channel for RPS in a wide variety of applications in different fields including biomedical. In this sensing method, the conductive solution acts as an electrolyte in the main channel. The ends of the main channel are applied with an electric field across the sensing orifice which is normally smaller than the main channel. When the particle passes through the orifice, it creates a resistive pulse which is then processed with the help of an amplification circuit and data acquisition device [86]. The temporary changes in the current due to the migration of particles are monitored by the sensing system that facilitates the analysis of particles [78]. Based on the magnitude of the signal, particle sizing and counting will be made [86]. Researchers have checked the possibility of applying this technique in analyzing the microfibers suspended in the liquid. The microplastic particles are released while treating tea bags in water heated to 95 °C [78]. By calibrating the RPS device with particles of known size and concentration, microplastics in the solution in which the tea bag was dipped were analyzed. The results reported around 6.52 × 103 particles/L with an average size of 21.9 µm [78]. Though it was the beginning level where the Resistive Pulse Sensors were used for the analysis of microplastic particles, the preliminary study exhibited the scope of RPS in analyzing and quantifying microfibers. However, comprehensive research have to be made in using the RPS technique for analyzing microfibers in the washing effluent. Fiber Quality Analyzer (FQA) Fiber Quality Analyzer (FQA) is commonly used for the analysis of fiber properties and morphology like length, width, coarseness, curl, and kink when they are required for quality control. The system is based on the flow cell, polarized light source, and imaging instrument. The diluted suspension of fibers will allow passing through the flow cell where the polarized light source illuminates the flowing particles which are subsequently captured by a camera. This was popularly used in the paper industry where the fibers in the pulp have to be analyzed. The flow cell through which the

52

2 Microfiber Shedding of Textile Materials—Mechanism …

suspension passes has been made with a special sheath design that can eliminate deposits. There will be three layers of current passing the flow cell where the suspension with fibers will be in the middle current and the sheath currents will be of clean and mineral-free water. The purpose of these sheath currents is to keep the fibers to be at the focal length of the camera so that images will be more perfect. The imaging system with a higher pixel resolution of 14 × 7 µm2 has been used for recording the images. In FQA, a circularly polarized light source has been used which enables visualization and measurement of two-dimensional objects [87]. In this regard, researchers have used this technique for quantification of microfibers in the washing effluents as this method can measure thousands of fibers within a short time automatically. Researchers used diluted effluent samples (50 mL of sample diluted to 600 mL) for the analysis of microfibers using FQA. The polarized light detection and the rapid image-processing system enable the orientation, quantification, and measurement of fibers in the liquid suspension [57]. Other researchers compared the effectiveness of the FQA method of fiber quantification with that of gravimetric analysis (weighing method of quantification). Their analysis showed that FQA produced a similar trend in microfiber shedding as the gravimetric analysis. However, the FQA could analyze the fibers which are large enough to detect by the system. Researchers reported that it could detect microfibers whose length was greater than 200 µm. Fibers lesser than this size will be eliminated during the measurement [16].

2.6 Microfiber Shedding from Textile Materials Other Than Apparels Though domestic laundry of apparel was found as a major source of microfiber pollution, there are a few other textile materials other than apparel that tend to release microfibers. The understanding of microfiber release from these products (Fig. 2.7) should also be given importance while aiming to mitigate microfiber pollution. This section details the systematic release of microfibers from non-apparel textile materials which are likely to pollute the environment. Face Masks Face masks made of textile materials especially non-woven fabrics were capable of releasing microfibers and were identified as one of the arising sources of microfiber pollution [46, 47, 88–92]. Face masks were initially intended for medical purposes; however, COVID-19 made the use of face masks more essential for preventing the transmission of viral infection. The use of masks and other personal protective equipment (PPE) has reached its peak after the spread of COVID-19. Apart from medical professionals, normal people were also insisted to use face masks to get protected themselves against the spread of infection. Around 88% of the world’s population was mandated to use face masks by May 2020. This ultimately ends up in huge

2.6 Microfiber Shedding from Textile Materials Other Than Apparels

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Fig. 2.7 Non-apparel Textile products contributing to microfiber pollution

demand for face masks. World Health Organization (WHO) has reported that face mask production has to be increased by up to 40% to meet the current demand [93]. While considering the post effects of mask usage, the increased consumption leads to increased disposal which is tedious to manage due to the higher level of waste generation in a short span of time. The average disposal rate of PPE is estimated as 350 items/day and 127,750 items/year [88]. The material composition and structure of these face masks increase the hazards associated with the waste. The surgical masks are generally made of polymers including polypropylene, polyurethane, polyacrylonitrile, polystyrene, polycarbonate, and polyethylene which are synthetic in nature [94]. Various researchers have reported the improper disposal of these face masks and their fate in the environment particularly on beaches and oceans [88, 95–97]. The improper management of face mask wastes can result in 150,000– 390,000 tons of plastic debris entering the oceans globally in a year [95]. This increased use of synthetic fiber-based face masks seeks immediate attention due to their potential microfiber release behavior. Researchers reported microfiber release from the face masks after their disposal [46, 47, 90–92]. The microfiber release behavior mostly depends on the inherent nature of the masks particularly the non-woven fabric structure and fiber composition as well as the external actions in the environment. Firstly, considering the inherent properties, the microfiber release differs with types of masks [89]. In the case of disposable surgical masks, the morphological nature of different layers reacts differently while analyzing microfiber release. The outer layer and the inner layer (layer in contact with the wearer’s skin) of the masks are made of spun-bonded nonwoven fabric, in which the fibers are bonded through heat, chemical, or mechanical force [98], and the binding points are often known as nodes that provide stability and strength as shown in Fig. 2.8 [90]. These structures are prone to release microfibers over usage and exposure to external actions. In these layers of the masks, the random

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Fig. 2.8 Microscopic Structure of Spun-bonded non-woven fabric layer of surgical masks

arrangement of fibers that are intertwined without proper fixation can lead to the release of fibers from the structure. The damage or fracture of nodes will happen while the fabrics are exposed to external actions. This increases the slippage of fibers from the surface [90]. The middle layer of the masks was comprised of melt-blown non-woven fabrics that are made of self-bonded fiber web. The small fiber diameters (1–5 µm) enhance the filtration with reduced pore size [98]. Compared to the other two layers, the fibers in the middle layer are expected to get damaged easily under exposure to environmental weathering because of their smaller fiber diameter. This makes the middle layer shed more microfibers than the other two layers [46]. While considering different mask types, activated carbon masks were found to release more microfibers when compared to N95 respirators, surgical masks, fashion masks, non-woven fabric masks, and cotton masks. This difference can be attributed to the material quality, that is, a poor-quality material can easily get injured and readily release microfibers [89]. However, the microfiber release could not be related to the price of the masks [92]. Secondly, exposure to the external environment influences the microfiber release behavior of the face masks. Once the masks are disposed of, they will undergo degradation. The level of degradation varies with the surroundings: slow degradation under ambient conditions whereas increased rate of degradation in the aquatic environment [88]. In this context, the microfiber release behavior of face masks in the ocean was analyzed by a researcher by simulating the ocean conditions with artificial seawater and UV irradiation. The artificially simulated conditions replicated the real-time conditions which are proven by the comparable degradation between the masks exposed to simulated and real-time conditions. A single mask can release 135,000 microfibers/day as an average when exposed to an aquatic environment with 173,000 microfibers/day as the maximum. The mechanical agitation of water and the chemical action due to UV exposure resulted in the degradation of masks and subsequent release of microfibers [47]. Similarly, the effect of different levels of mechanical stress forces in the aquatic environment on the masks was also explored. For instance, exposure to a different level of shear intensity caused a varied amount of

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microfiber release from 2.6 ± 0.7 × 103 items/mask to 2.8 ± 0.5 × 104 items/mask. The deterioration of the masks in an aquatic environment depends on the local hydrodynamic conditions [91]. Another important aspect to be noted in the aquatic environment is abrasion with sediments. When ended up in water bodies, the masks will be subjected to abrasion due to the sands and sediments. It has been reported that the microfiber release from a single mask in an aquatic environment can increase up to 90% when the abrasion due to the sand is considered [46]. Apart from the aquatic environment, another exposure condition to be noted is UV weathering. Surgical masks were found to undergo physiochemical changes when they are exposed to UV radiations/natural weathering [46]. The aging of masks under exposure to natural conditions for 2 months leads to an increment in the microfiber release up to 25,000 times. This much-fold increment in the microfiber release after natural weathering is attributed to the increase in fragility. The nodes which provide strength in the spun-bond non-woven fabric got destructed with natural weathering. Moreover, the SEM analysis of these weathered masks revealed fracture marks on the fiber surface that aid in the formation of smaller fragments. This fracture leads to the release of shorter fibers than the unweathered masks [46, 90]. While investigating the changes in chemical characteristics, exposure to UV radiations alters the chain structure of the polymer. The C–C and C–H bonds get broken down due to the energy gained from the UV radiations and result in the scission of chains. The breakage of chains leads to a reduction in the molecular weight, thereby reducing the mechanical strength. Thus, the microfiber release increases with UV exposure due to the changes in both physical and chemical properties. Moreover, the actions during the usage of masks can also cause microfiber release. It is evident from the results of researchers who compared the microfiber release from the new masks and the masks worn for a day. The significant increment from 183.00 ± 78.42 particles/mask to 1246.62 ± 403.50 particles/mask for the used masks confirms the notable damage during the usage of masks. During wear, the actions like adjusting, folding, and pulling can cause mechanical deformation that leads to fragmentation of inner materials [92]. This fragmentation and breakage during the wearing alarm the possibility of inhalation of microfibers during the wearing of masks. Researchers analyzed the probability of inhalation of microfibers while usage. Though the wearing of masks for a shorter period of time prohibits the inhalation of atmospheric microfibers, prolonged wearing results in the inhalation of microfibers originating from the mask itself [89]. The other cause of microfiber release from the mask is the disinfection process. With the problems of increased demand and waste generation, reusable masks are introduced. For reuse purpose, the masks are undergone disinfectant processes. Different disinfectant processes that are being adapted in common include simple washing, washing with detergents (laundering), UV exposure, sunlight exposure, and disinfection with alcohol or air blower [89, 90]. It is a fact that the used mask releases a greater number of fibers than the unused one. However, the different disinfection methods alter the level of increment in the microfiber release behavior of the face masks. While comparing different disinfection processes, simple washing with distilled/ultrapure water can cause lesser effect and results in lesser increment in microfiber release than all other methods of disinfection [89, 90]. The alcohol

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disinfection process and use of detergents cause more fiber damage and also accelerate the dissolution of nodes. These actions can increase the microfiber release from the masks after the disinfection process. Hence, it has been suggested that simple washing and indoor drying of masks can reduce the damage and microfiber release [89, 90]. These studies analyzed the microfiber release after the disinfection process, however, during the disinfection process itself, there are chances for the release of microfibers. For instance, laundering is one common method of disinfecting cloth masks. Like apparels, these masks can also release microfibers during the laundering process. Since cloth masks are also available in different fiber compositions and fabric structures like apparel, they have to be given more care during the laundry process. Moreover, the repeated laundering/disinfection process ends up making the material weaker, which can adversely impact the microfiber release at the disposal stage. Besides face masks, the microfiber release of other items in PPEs should also be analyzed for microfiber release behavior due to their increased usage and their characteristics are highly susceptible to release microfiber fibers like face masks. Cigarette Filters Cigarette Butts are one of the most abundantly found litter in the environment. It has been reported that cigarette butts account for 30–40% of the items collected in coastal and urban cleanups. It is a very well-known fact that these cigarette butts that are being ended up in the water bodies can release certain toxic organic compounds, including nicotine, that have an adverse impact on the aquatic organisms [99]. A cigarette filter is one of the components of a cigarette that is intended to absorb vapors and trap larger tar particles. Fiber-containing filters made of tow of continuous filaments are very common, whereas cellulose acetate filaments are the most favorable ones [100]. Generally, finer cellulose acetate microfibers whose diameter is in the range of 0.1–10 µm are being used in the cigarette filters [101]. The most desirable form of filter material is the non-woven sheet where the individual fibers are intertwined or entangled [102]. During the manufacturing process, to achieve better filtration, the fibers are arranged perpendicular to the airflow. Since some of these filaments usually get cut during the cutting operation of a double cigarette, the short fibers will be generated and deposited within the surface. This fiber-lint was expected to release from the surface during subsequent shaking or blowing [103]. These cigarette filters, having more than 12,000 fibers/filter [104], that are disposed of away after usage are one of the predominant sources of microfibers. It has been estimated that around 0.3 million tons of microfibers can enter the environment through the disposal of cigarette butts [105]. Cellulose acetate fibers are plastic-like materials that take years to get degraded in the environment. Even after 6 months, the filters were found to remain up to 95% and 83% of their original weight in the soil surface and compost, respectively [106]. In this aspect, the microfiber release from the cigarette filters in the aquatic environment was analyzed [107] as around 80% of butts on the ground end up in waterways [108]. The results showed that one single cigarette butt can lose 10% of its mass in the form of microfibers within 15 days (100 microfibers/day) of exposure to the water bodies with low wave action. Moreover, the degradability test of cellulose acetate showed that these fibers will remain in the aquatic environment

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for at least a few decades [107]. While considering the impact, in addition to various toxic elements with the leachates of cigarette butts, these microfibers increase the toxicity level. Researchers reported an increased death rate of Daphnia Magna when they are exposed to leachates of cigarette butts along with microfibers compared to the leachates without fibers [107]. However, the other researchers have reported minimal risk associated with cigarette filter microfibers than the filter toxicants while analyzing the effect on ragworms [109]. Besides the microfiber release in the disposed of stage, the fibers in the filters are expected to draw out during the puffing of the cigarettes. The fiber release from the cigarette filters during puffing was analyzed by different researchers under two conditions, namely sham smoking (un-lit cigarette) and normal smoking (lit cigarette) [102]. Researchers reported a release of 7.3–14.5 fiber lint/cigarette during puffing [103]. This can lead to the ingestion of cellulose acetate fibers by the smokers which could cause a potential impact on the smoker [104], however, it has to be noted that the aerodynamic diameter of the fibers from the filters is larger enough that could exclude from entering deep lungs and deposit on the upper airways [110]. Thus, there arises the need for intricate research on the effect of cellulose acetate microfibers that release from the cigarette filters on the environment and their potential to harm human beings. Wipes and other sanitary products Wipes are often used for hygiene purposes for personal care as well as household cleaning/disinfectant. Though these non-woven wipes come in different fibers including cotton, polyester, viscose, wood pulp, and polypropylene [111, 112], synthetic fibers are most commonly used in the manufacturing of wet wipes [113, 114]. The wet wipes which generally end up in toilets are found to create blocks in drainage and sewage systems. Moreover, not all the wipes get trapped in the sewage treatment plants, and they end up in rivers and oceans. Study reports revealed approximately 201 wipes/sq.m along the riverbank [115, 116]. In the UK, the number of wet wipes that are found on the beaches got increased by 400% in the past 10 years [117]. These wet wipes are anticipated to release microfibers into the environment [118– 120]. The prevalence of white microfibers in the sediments near wastewater treatment plants alarms the contribution of wipes and sanitary products to microfiber pollution. The research report says around 2768 fibers/kg of sediment in the sampling sites were white fibers that resemble the fibers with which the wet wipes and sanitary towels are comprised [111]. A single sheet of wet wipes can shed up to a few hundred microfibers while usage and disposal [118]. Since not all flushable wipes are biodegradable [111], these microfibers prevail in the environment for a longer period and cause adverse impacts. The microfiber release behavior of wet wipes was reported in different states including the dry and wet states. The microfiber released from wet wipes was analyzed based on their usage and disposal conditions. Wet wipes were expected to release microfibers while cleaning with them (wet state—rubbing), after immediate disposal into toilets or basins (wet state— immersion), disposal in an aquatic environment after being stored in trash cans (dry state—immersion), and disposal through waste treatment process after storing in

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trash cans (dry state—rubbing). Experiments were carried out to replicate all these possible usage and disposal conditions and microfiber release was analyzed. Both the state of the wipe and the external environmental conditions affect the microfiber release. Considering the state of the wipe, more fiber release was noted in the wet state than in the dry state. Similarly, while considering the external environment, wet wipes can shed more fibers when ended up in water bodies than rubbing against a solid matrix. The higher fiber release in the wet condition can be related to the hydrophilicity of the carboxyl group which is the main component of the polyester wet wipes. This hydrophilic nature increases the fiber release into the water bodies when the wipes are wet. The average release of microfibers from the usage of wet wipes in Europe can reach up to 133.7 trillion fibers per year with 24,000–95,000 fibers/person [118]. With this increased level of microfiber release in wet conditions, the flushing of wipes should be reconsidered as these possess the microfiber release issue in addition to the sewage blockage problems. With different ways of disposal of wet wipes in households [114], there arises the complication in the tracking of disposed of wet wipes and their fate in the environment [118]. Most of the commercially available non-flushable wipes (64%) were not tagged with the disposal instructions [111] which leads to varied unsafe disposal. While considering the microfiber pollution associated with these disposable wipes, proper guidelines should be needed to dispose of the wipes that could reduce the microfiber release. Moreover, other sanitary products including sanitary pads, baby wipes, and sanitary towels should be analyzed for their microfiber release. Home Textiles Home textiles are one vast area in the textile industry that focuses on enhancing the interiors and home furnishing. Since man-made synthetic fibers such as polyester, nylon, polypropylene, acrylic, and rayon [121] are found to have increased application in home textiles due to their more advantageous properties, there comes the necessity for investigating the microfiber release from the home textile materials. Though these home textiles are not subjected to regular washing like apparel and clothing, these also release microfibers in every possible way. Several home textile products including carpets, sofa covers, and curtains are expected to release microfibers into the atmosphere. This is evident from the higher level of microfibers in the indoor atmosphere than in the outdoor atmosphere which is attributed to the home furnishing materials. The indoor air of private apartments and offices was sampled for microfiber analysis which revealed a higher level of synthetic microfibers (33%) with polypropylene as the dominant polymer type. This could be highly correlated with the home furnishing materials including carpets, sofas, and chairs. It has been reported that the large polypropylene carpet used in the living room sampled is attributed to the higher level of polypropylene fibers in the indoor atmosphere [50]. This confirms the microfiber release risks associated with home textile products. These atmospheric microfibers can be easily inhaled by the inmates of the house. Hence, utmost importance should be given to these sources also. Moreover, the carpet washing industry has become an unignorable source of synthetic microfibers. Cleaning of carpets can release microfibers in the range of

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1,824–3,097 microfibers per square meter of the carpet. A single carpet cleaning industry can release 13 billion microfibers into the environment every year. In the carpet cleaning process, the drying method plays an important role in determining the erosion of carpets. With increased spin speed, the erosion increases, thereby increasing the microfiber release. In addition to this, the wastewater from these kinds of industries is directly ending up in rivers without further treatment which enhances the matter of contamination [122]. Fishing gears Fishing gears that include nets, ropes, and pots can be a secondary source of microfibers in the aquatic environment. The degradation and fragmentation of fishing nets lead to the release of microfibers [27]. The most accountable fibers for the manufacturing of fishing nets include nylon, polypropylene, and polyethylene [123]. The practice of disposing of old or unusable fishing nets in the sea is very common. The plastic debris that is being released into the seas and oceans due to the lost or abandoned fishing nets can reach up to 1.15 million tons. The experimental analysis revealed that textile-based fishing nets can release microfiber into the sea. The fishing nets made of textile filaments were found to release an average of 400 microfibers per gram of the fishing net [124]. The microfiber released from fishing nets can directly end up in the contamination of oceans, and these microfibers can easily enter the marine food chain. The microfiber release from fishing nets is again reinforced by the studies that analyzed the microplastic contamination of sediments of sea and oceans [125, 126]. A microplastic contamination study by Neto et al. in the sediments of Vitoria Bay in Brazil reported 0–38 particles/300 g of sediments. Microscopic analysis of collected microplastic particles revealed that 77% of the collected particles were synthetic fibers that resemble the fibers generated from the degradation of the nylon cables that are being used in fishing activities [125]. Similarly, the other researchers analyzed the microplastic contamination in the bay where mariculture has been carried out. Their results reported a higher abundance of microfibers in the area where the fishing nets are frequently used [126]. Xue et al. claimed a strong correlation (85.86%) between the polypropylene and polyethylene microfibers in the deep sediment of Beibu Gulf with the fishery activities in the area. Further, the polypropylene and polyethylene fibers collected from the sediment were compared with the fibers from purchased fishing tackle, abandoned fishing gears collected on the shorelines, and fishing gears used for the mariculture purpose with micro-Raman spectrometer identification. This confirms fishing gears as the source of microfibers found in the deep sediment [123]. Apart from seas and oceans, fishing nets and cages were found to cause microfiber pollution in rivers. Freshwater fish in the Chi River was examined for microplastic contamination and the fishes were dominantly contaminated with fibrous materials which predominantly originated from the fishing gears, fish cages, and nylon ropes [127]. Though various researchers reported the presence of microfibers resembling those in fishing nets, a detailed study on the release mechanism of microfibers from fishing nets and ropes used in fishery activities was not yet performed. With the dominant role of these fishing gears in microfiber pollution, research should be made in these areas.

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Tea Bags Commercially available tea bags use heat-sealable materials like polypropylene, nylon, rayon, or even PVC fibers on the inner side of the tea bag surface [128–130]. Though a few tea bags are mentioned as cellulose made, most of them are found to have traces of plastic fibers in them [131]. The synthetic material in the manufacturing of tea bags makes it suspectable for microfiber release. Microplastic release from the tea bags while usage was analyzed by immersing them in hot water at brewing temperature (95 °C) and 11.6 billion microplastics were reported to release from a single tea bag [128]. The other researchers analyzed the microfiber release from tea bags by treating them with hot water for 5 min. The resultant water was analyzed with a tunable three-dimensional printed microfluidic resistive pulse sensor. The analysis showed that one tea bag can release 6.52 × 104 particles/mL [78]. While comparing tea bags made of polypropylene and nylon, nylon bags were found to release microparticles, whereas no release of plastic-related particles from the polypropylene bags was noted [132]. Polymer hydrolysis at higher temperatures was noted as the reason for the degradation of the material. Nylon readily hydrolyzes and the contact with water at higher temperature causes fracture on the fiber and aids microplastic release [128]. Tea bags, being a source of direct ingestion of microplastics by human beings, should be reconsidered and their impact on human beings should also be explored [133]. Agro Textiles Mulching is a common practice in agricultural fields where the soil will be covered in order to provide a more favorable environment for plant growth. The increased soil temperature, and reduced evaporation resulting from the mulching process help in the healthy growth of plants [134]. Mulching has been done using plastic films as well as synthetic textile materials. Woven fabrics made of polypropylene are commonly used as a barrier to weed growth. These fabric mulches are found to have increased application in the horticultural food crop production, particularly berries and highvalue perennial crops due to their air and water permeability nature and durability for up to 12 years [135]. Since these are used in the outdoor fields, they can easily get degraded and release microfibers into the soil. This is supported by the researchers who reported a steady increase in the microplastic particles in the agricultural field where plastic mulching has been done over a longer period. The study revealed lower microplastics in the field where mulching has been done for 5 years than in the field where mulching was done for 24 years [136]. Though the mulching process has been suspected to be a reason for microplastic contamination, the direct analysis of mulches and their microfiber release behavior has not been investigated. While giving importance to the domestic laundering of synthetic apparel as the source of microfiber pollution, the other textile materials are being underestimated. Though synthetic clothing dominates in the microfiber release, it has been identified and analyzed by the researchers with utmost care, whereas the non-apparel products are not explored in detail which creates a knowledge gap in the examination of microfiber pollution.

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2.7 Conclusion This chapter provided a comprehensive mechanism of microfiber shedding from the textile materials which details the step-wise processes that lead to microfiber shedding and also various conditions like domestic laundering, wet processing, wearing, and photodegradation that accelerate the microfiber shedding from the textile materials. The microfiber shedding of textiles during domestic laundering was noted as the major cause, and various methods and techniques adopted by researchers to quantify the microfiber shedding behavior of textile materials were clearly detailed. The sampling methods, washing simulation methods, and microfiber quantification techniques were elaborated. The merits and demerits of those adopted techniques were compared which can provide an insight to future researchers working on analyzing microfiber shedding. The new innovative methods that help in easy and faster quantification of microfibers were also outlined. In addition to this, physical, chemical, and morphological characterization of microfibers shed from the textile materials during domestic laundering was also elaborated. Along with that, the microfiber shedding characteristics of textile materials other than apparel and clothing were also highlighted which shows the essential requirements of microfiber analysis in those areas.

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Chapter 3

Factors Influencing Microfiber Shedding—Role of Textile and Apparel Characteristics

3.1 Introduction Microfiber shedding of textile materials is happened due to external physical or chemical actions to which the materials are exposed. As detailed in Chap. 2, microfiber shedding of textile material follows a certain mechanism. It was very clear that external actions like domestic laundering [1–8], textile wet processing [9–11], abrasion during wearing [12, 13], photodegradation [14, 15] after disposal are causing the textile material to shed fibers. However, the inherent properties of textile materials will have an impact on this behavior to a greater extent. Though external actions damage the textile surface and facilitate shedding, the nature of textile materials decides how to react to those external actions. The intrinsic characteristics of textile materials can make them prone or resistant to damaging actions. The textile properties like fabric density, yarn twist, fiber size are responsible for the fiber cohesion in the structure. Improved fiber cohesion can reduce the propagation of fibers, thereby can reduce microfiber shedding. Also, the tenacity and strength of the material can restrict fiber damage to a certain degree [16]. Hence understanding such textile characteristics and their influential actions on microfiber shedding is crucial. This became obvious when researchers found different levels of shedding from different textile materials when they are exposed to the same external actions. Researchers found a significant difference in the shedding level of three different jumpers even when they are exposed to the same washing conditions. The jumpers made of Polyester/cotton blend shed 80% lesser fibers than those made of 100% synthetic fabrics [6]. Similarly, other researchers who analyzed the microfiber shedding of 50/50 P/C blended fabrics reported that among the shed fibers, the proportion of cotton fibers is higher [2]. These variations are not limited only to fiber composition; other properties like yarn type, fabric type, processing methods, mechanical properties of textile materials are also noted to play a significant role in determining the microfiber shedding behavior of textile materials. Researchers also reported variations in shedding with

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 R. Rathinamoorthy and S. Raja Balasaraswathi, Microfiber Pollution, Sustainable Textiles: Production, Processing, Manufacturing & Chemistry, https://doi.org/10.1007/978-981-19-4185-6_3

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fabric types like knits and wovens [13] and also between different structures of knit fabrics such as single jersey, interlock, and rib structures [17]. The characteristics of textile materials can vary at the fiber stage, yarn stage, and fabric stage. When we consider apparel, the variation can be found with respect to the apparel production processes too. The yarn structure, fabric structure along with the nature of mechanical stress and chemical actions to which the textile materials are subjected during the production processes like spinning, weaving, scouring, dyeing, chemical finishing should be traced to specify the microfiber release behavior of a textile material. Figure 3.1 shows different production processes in textile manufacturing and the products obtained out of each process [18]. Hence addressing all these variations in textile materials and production processes and their influence on microfiber shedding of the apparel can help in figuring out the control strategy in the manufacturing processes. Several researchers and environmentalists have suggested that understanding the role of textile characteristics in microfiber shedding is crucial and the textile materials should be designed in such a way that it sheds lesser fibers

Fig. 3.1 Overview of different forms of textile materials and their production processes

3.2 Fiber Characteristics

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[1]. Thus, this chapter enlightens the influence of different properties of textile materials including structural, physical, and mechanical properties and apparel production process on microfiber shedding behavior of textile materials.

3.2 Fiber Characteristics Fiber is the fundamental building block of any textile material. There are different types of fibers including animal fibers, plant fibers, mineral fibers, synthetic fibers, regenerated fibers that are categorized under two broad categories—Natural and Manmade fibers [19]. As per the global market report, Polyester (52%) and cotton (24%) fibers are consumed highly. However, other fibers including polyamide, polypropylene, acrylic, elastane, man-made cellulosic fibers are also being consumed globally [20]. Based on the suitability of fibers to satisfy the requirement, different fibers are being used. Each fiber has its own structural, physical, and chemical properties [19] which in turn can have an impression on the microfiber shedding behavior of the textile material.

3.2.1 Structural Properties The structure of the textile fibers can be perceived at micro and macro levels. At the micro-level, the degree of crystallinity and degree of orientation of the fibers are considered, in which the degree of crystallinity determines the three-dimensional order of polymer chains, whereas the degree of orientation determines the alignment of a polymer chain with a fiber axis. In the case of the macro level, the surface structure, shape, and size of fiber cross-sections are taken into account [21]. These structural variations among fibers can have a profound effect on the microfiber shedding behavior. Fiber Crystallinity The crystallinity of a fiber polymer is determined by how tightly or perfectly the polymer chains are aligned together [22]. The varied degree of crystallinity had showed significant variation in different properties of fibers [23, 24] and so it is expected to have an impact on microfiber shedding. A study on fabrics of the same structure with different fiber compositions was made with the aim of understanding the role of fiber characteristics on shedding. The analysis of 100% Cotton, 100% Rayon, 50/50 Polyester/Cotton, and 100% polyester revealed higher shedding in the case of cellulosic fibers and their blends than that of 100% polyester fibers [7]. In a similar study, De Falco et al. analyzed garments made of two layers of different fiber compositions (Layer 1—100% Polyester; Layer 2—50/50 Cotton/Modal). The FTIR and thermogravimetric analysis of the shed microfibers revealed more cellulosic fibers [2]. In the higher shedding trend of cellulose-based fibers, the crystallinity level

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of the fibers is noted as a key factor. Cellulosic fibers like cotton have amorphous regions between the crystalline regions in the structure. For instance, in cotton around 70% of the fiber is crystalline where the cellulose chains are tightly packed. Whereas in the remaining amorphous region, voids, spaces, and irregularities can be seen. In the case of polyester fibers, they are highly crystalline and the polyester molecules are tightly packed and held with van der Waals forces with smooth and regular surface structure [19]. The higher crystallinity and smooth surface of polyester fibers were noted as one of the aspects that make it bear the external actions and break lesser [18]. Hence, it can be stated that microfiber shedding can have an inverse relation with the degree of crystallinity, that is, the higher the crystallinity, the lesser will be the microfiber shedding. Fiber Surface and Cross-Sections Based on the origin or manufacture of the fiber, the surface structure of fibers varies widely. For instance, the fibers which are man-made can have smooth regular surfaces whereas the natural fibers will have irregular cross-sections as they occur naturally [21]. The enhanced microfiber shedding of natural fibers is attributed to these irregular surface structures. Researchers reported higher shedding in the case of nonwovens made of cotton than of those made of regenerated cellulosic fibers. While interpreting the results, even though cotton and regenerated cellulose are cellulosic fibers, regenerated fibers are made-made which in turn can have better uniformity on the surface structure [25]. Also, these surface irregularities were noted as an important characteristic in recycled fibers. Recycling has become an emerging trend in sustainable practices. Recycled fibers can show a difference in the surface of the structure which could be emerged out of the process of recycling. Hence, such variations were analyzed for microfiber shedding. Özkan and Gündo˘gdu analyzed microfiber release from knitted fabrics made of virgin polyester and recycled polyester. Fabrics made of recycled polyester showed 2.3 times higher shedding than that of virgin polyester [26]. It was determined that the structural variations in the fibers were the cause. While comparing the structural properties of the fibers, duller and more deformation in the surface was noted in the case of recycled fibers than that of virgin fibers. Figure 3.2 shows the SEM images of virgin and recycled polyester fibers where

Fig. 3.2 Surface structure of a Virgin and b Recycled polyester fibers (Reprinted with permission from [27])

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surface changes can be noted [27]. Moreover, fiber cross-sections have a significant impact on the fuzz formation behavior. As reported earlier in Chap. 2, microfiber shedding begins with the fuzz formation step. Hence, the fiber cross-section which is a function of fuzz formation can have an impact on the microfiber shedding. While comparing the fibers of round cross-section and ribbon-like structure showed that the fuzzing tendency of fibers with round cross-section is comparatively lesser [28]. Hence, this could be the reason for lesser shedding with the synthetic fibers [7] where the most common cross-section is round; whereas fibers like cotton have a ribbon-like structure [19]. Therefore, it is evident that surface uniformity and fiber cross-section have a significant bearing on microfiber shedding. A smoother, more uniform surface with fewer irregularities can demonstrate minimal microfiber shedding. However, the direct correlation of different surface structures with microfiber shedding is yet to be explored in detail.

3.2.2 Mechanical Properties In terms of mechanical properties, fibers reveal their strength in terms of their behavior when exposed to external forces such as stretch, twist, or fracture [21]. Microfiber shedding is caused primarily by external forces, so the mechanical properties of the fibers can influence the way external forces affect textile materials, thereby altering the microfiber shedding behavior. Tensile Strength/Tenacity Tensile strength of the fibers is the ability of the fiber to withstand the force which is applied longitudinally to stretch the fibers. Tensile strength and tenacity are similar except in the way that tensile strength is the force per unit cross-sectional area, whereas tenacity is the force per unit linear density of the fiber [21]. In this regard, the tenacity and tensile strength of the fibers are compared with the microfiber shedding behavior of different textile materials. Napper and Thompson, one of the pioneers of microfiber pollution research, compared the microfiber shedding of three jumpers made of different fiber compositions (100% polyester, 100% acrylic fibers, 65/35 polyester/cotton blend). The microfiber shedding of blended fibers is noted much fewer than the 100% synthetic fibers [6]. Researchers supported the results by claiming that synthetic fibers which are having higher tenacity are intentionally weakened to avoid the pills to be stuck on the fabric surface and this ended up in increased fiber release [29]. However, a detailed analysis has not been made on the fiber properties as the garments are randomly sourced whose fabric structures and production method could vary and can have upper hand over shedding [6]. In the later research work, Cesa et al. reported that cotton fabrics released higher fibers than synthetic fibers [16]. A study on the laundering of denim made of different fiber compositions revealed similar results that cotton shed higher which is followed by 60/40 cotton/polyester blend and minimum shedding was noted with 100% polyester [30]. Moreover, to support the higher release of microfibers from natural fibers than

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that of synthetic fibers, Lant et al. reported that in a consumer soiled wash load, around 96% of fibers released were natural whereas only 4% is synthetic [5]. As reported by Napper and Thompson, it can be related to the tenacity of fibers. Cotton is having lesser tenacities (18–45 g/tex) when compared to polyester (27–81 g/tex) or other synthetic fibers [19]. While researchers found a difference in the shedding of natural and synthetic fibers, Yang et al. reported differences among different synthetic fibers (100% polyamide, 100% polyester, and 100% acetate). The microfiber shedding order follows: Polyamide > Acetate > Polyester [31]. In line with this, Cesa et al. also reported Polyamide to release more fibers than polyester. The comparison among polyamide, acrylic, and polyester showed the order of shedding as Acrylic > Polyamide > Polyester [16]. The higher release from acrylic fabric is attributed to its lower tenacity than the other two fabrics [16]. Whereas other researchers reported no significant difference in shedding between nylon and acrylic fabrics that might be due to differences in the other parameters of the textile material [32]. Hence, to understand the direct effect of the tenacity of fibers on the microfiber shedding, fabrics with similar properties in all aspects except that of fibers should be analysed. Elongation at Break In tensile testing, elongation at break is expressed as a percentage of the original length at the point of failure. The influence of elongation at break in microfiber shedding is noted with recycled fibers. In the case of recycled fibers, the reduced breaking strength and elongation made the fibers shed more easily. Thermal exposure and shear degradation during the recycling processes can deteriorate the molecular chain length and the molecular weight of the polymer and so the length of fibers shed from recycled polyester is significantly shorter than that of virgin polyester [26]. Contrastingly, in the study by Roos et al., fabrics made of recycled polyester released a significantly lesser number of fibers (843 fibers in total) than virgin polyester (1890 fibers in total). This trend was obvious even when fleece fabrics made of virgin and recycled polyester are compared [33]. In line with this, Frost et al. who analyzed knitted fabrics made of virgin cotton, 80/20 virgin cotton/recycled cotton, 60/40 virgin cotton/recycled cotton reported no significant difference has been noted between virgin and recycled fibers. However, in the case of fabrics made of polyester and recycled polyester fibers, a difference has been noted. Fabrics made of 70/30 Recycled polyester/virgin polyester showed a significant reduction in shedding when compared to 40/60 Recycled polyester/virgin polyester fabrics. Here, recycled fibers were noted to shed lesser than virgin fibers [34] and contradict the previous findings. Moreover, in the case of fabrics with recycled fibers, the fibers released were significantly longer than that of virgin fibers. This is due to the higher elongation behavior of recycled fibers. Also, this attribute is claimed for the reduced shedding in the case of recycled fibers— higher elongation values make the fibers elongate rather than breaking into small fibers [34]. Similarly, Vassilenko et al. also reported an increased length of the fibers from the recycled nylon samples. In both the studies [26, 34], though contradictions were found in the terms of microfiber release from recycled fibers, the common thing that can be noted is the relationship between elongation behavior and fiber shedding.

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In the first case, breaking strength and elongation of the recycled fibers was lower than that of virgin fibers [26], whereas Frost et al. reported higher elongation with recycled fibers [34]. This difference in the elongation behavior may be attributed to the differences in the manufacturing methods of recycled fibers. However, it is very clear that fibers with better elongation at break can show reduced microfiber shedding because it makes the fibers elongate with the external force rather than break and release as microfibers. This elongation behavior is also confirmed with the length of fibers shed from the fabrics.

3.2.3 Moisture-Related Properties As microfiber shedding happens mainly during laundering, when fabrics are exposed to water, moisture-related properties of fibers such as wettability and absorbency also play an important role. While comparing two fabrics with same fabric structure and yarn type with varied fiber composition (100% Polyester knit and 50/50 Cotton/Polyester knit), significantly higher shedding can be noted with the blended fabrics which is attributed to the presence of cotton. The higher wettability of cotton can lead to a higher release of fibers. Researchers have reported that the increased hydrophilicity of cellulosic fibers over synthetic fibers makes them release a greater number of fibers. Similarly, fiber swelling in the wet state can be another reason for the higher shedding of cotton fibers. In the wet state, when the fibers swell, the mechanical forces of laundry can easily damage the fibrils and lead to increased fiber release [13]. Moreover, the fuzz formation on the swollen surface can be increased with the mechanical actions in the washing process [35]. This influence of swelling characteristics is again supported by another study where microfiber release was noted to increase with increased laundry temperature. The supporting reason provided by the researchers is that the increase in temperature can increase the swelling and thereby increases microfiber shedding [36]. Contrastingly, polyester fibers are hydrophobic in nature and do not swell in the wet state. This inherent stability of the polyester fibers can make them bear the external actions and as a result it breaks lesser [18]. Additionally, the effect of hydrophilicity is observed to be apparent in various synthetic fibers as well. While comparing polyamide, acrylic, and polyester fibers, higher shedding is noted with polyamide which can be attributed to the fact that polyamides are comparatively hydrophilic than the other synthetic fibers analyzed (Moisture regain of fibers at standard conditions—Polyamide—4% to 5%; Polyester—0.1 to 0.4%; Acrylic—1% to 2.5%) [37]. Thus, it is clear that the hydrophilic fibers are more prone to shedding than that of hydrophobic.

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3.2.4 Chemical Properties The chemical properties of the fibers cover how the fibers react chemically to the external environment. During laundry processes, reactions between the detergents and the fibers should be considered. It has been reported that polyesters being made from petroleum products, can be dissolved by the surfactants, whose objective is to solve the fat from the textile material for cleaning [38]. Even this shows how the chemical mechanism of shedding is, detailed research on the chemical properties of different fibers and their correlation with microfiber shedding has not been explored. A detailed interaction effect of synthetic textile and laundry detergents and other laundry aids is discussed in Chap. 4.

3.2.5 Role of Elastane Elastane holds an irreplaceable place in today’s textile market as it is being used in all ranges of products from high-functional sportswear to leisurewear to improve comfort properties. Incorporating elastane into fabric structures can alter the manner in which the textile material sheds. With that note, researchers analyzed different stretch fabrics of different compositions—78/22 Recycled Nylon/Elastane, 80/20 Nylon/Elastane, and 100% Polyester and reported a similar level of shedding without any significant difference [39]. However, this similar level of shedding might be achieved due to the variation in the other fiber with which the elastane is blended. Hence, to understand the obvious effect of elastane, researchers compared cotton, polyester, and cotton/polyester blends of denim with different core materials (Elastane, PET/PTT, PBT, Elastane + PET/PTT, Elastane + PBT). The shedding potential of the fabrics was noted to vary where the fabrics with Elastane + PBT as core material released more fibers irrespective of the fibers (cotton, polyester, cotton/polyester blend) which is followed by Elastane + PET/PTT and Elastane. The fabrics with core material such as PET/PTT and PBT released comparatively lesser fibers. This shows that the presence of elastane can increase the microfiber release [30]. However, detailed research on the potential characteristics of elastane that accelerate the shedding is not made. It is crucial to understand the role of elastane as its consumption is growing greatly in the textile and apparel industry. To consolidate, the role of fiber characteristics in the microfiber shedding behavior is obvious. The critical analysis of the literature revealed that cellulosic fibers are more prone to shedding than that synthetic fibers. The structural, mechanical, chemical, and moisture-related properties are known for the variations. The more crystalline region can protect the fiber from easily getting damaged by external actions. The highly crystalline structure of synthetic fibers makes them shed lesser than cotton where the crystallinity of the structure is comparatively lesser [18, 19]. Similarly, when the surface structure and cross-section are considered, the more uniform structure can shed lesser and the round cross-section helps in reducing the fuzzing tendency

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which in turn can reduce microfiber shedding [28]. In terms of mechanical properties, lower tenacity and elongation at break accelerates shedding [16, 26, 34]. While considering hydrophilicity, highly hydrophilic fibers can cause more shedding and vice versa [13]. In the case of recycled fibers, the recycling process affects mechanical properties which can alter their microfiber shedding behavior. Though each characteristic of fibers has its impact on microfiber shedding, the combined action of these characteristics will be different. For instance, if we consider the comparison of shedding among polyester, polyamide, acrylic fibers, the study revealed higher shedding in the case of polyamide fibers. However, the tenacity of polyamide fibers is much better than that of acrylic. Still, the higher hydrophilicity of polyamides made them shed more fibers. It shows that one characteristic can override the other and hence the impact level of each character is very crucial in terms of determining the shedding behavior. In general, fibers with higher crystallinity degree, uniform and smooth surface with lesser irregularities, higher tensile properties, lesser hydrophilicity can benefit the microfiber shedding reduction. As a result, at the fiber stage, the steps associated with fiber production such as polymer formation, fiber spinning, fiber drawing, and others can be carefully designed to achieve the properties that can aid in the mitigation of microfiber shedding.

3.3 Yarn Characteristics Yarn is a strand of textile fibers that are held together by inserting twists or other methods to achieve fiber cohesion that is suitable for subsequent fabrication processes like weaving, knitting, braiding, etc. [40, 41]. Yarns are being produced with different production methods based on the required end uses. The yarns can be classified into different categories namely continuous filament yarns, staple spun yarns, composite yarns, and plied yarns [41]. It is very significant to look at the characteristics of the yarn and its properties in order to determine what properties will be acquired by the fabric made from it. Consequently, these properties will also strongly affect the shedding characteristics of fabrics.

3.3.1 Type of Yarn The two types of yarn which are widely used are continuous filament yarns and staple spun yarns. In continuous filament yarns, the filaments are parallelly arranged to form the yarn, and based on the number of filaments used, it can be classified as monofilament yarn (one filament) and multifilament yarn (more than one filament). Whereas in the case of spun yarns, staple fibers are aligned together through imparting twists or other means [42]. Moreover, other classifications are also there based on structural complexity (single yarns, plied yarns, cabled yarns) and spinning preparation process (carded yarns, combed yarns, worsted yarns, woolen yarns) [42].

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There is the possibility that these types of yarns can alter the amount of microfiber shedding. Various studies have reported variations in shedding between spun yarns and filaments yarns. In most of the cases, researchers reported spun yarns made of staple fibers are noted to shed more fibers than that of filament yarns [2, 3, 7, 16, 26, 31, 43]. This could be attributed to the fact that the spun yarns will have staple fibers which are short and can easily slip out of the structure and can be released as microfibers. And so, in such cases, fiber breakage is essentially not needed for the shedding to happen, alternatively, the fibers can slip out of the structure when it is pulled or loosened. Hence, even if the fibers are stronger, they can get shed due to slippage [18]. However, in the case of filament yarn, the breakage should happen to release fibers [26]. This phenomenon of easy slippage of fibers from the spun yarns was confirmed by the surface analysis of staple and filament yarns. Kärkkäinen and Sillanpää who reported higher shedding with spun yarns than filaments have noticed raised fiber ends on the surface of fabrics made of spun yarns, whereas in the case of fabrics made of filaments, such fiber ends were not noticed and this led to the reduced shedding in the case of filaments [44]. Similarly, other researchers reported higher shedding from spun yarns (107.7 ± 14.5 ppm) than that of twisted (51.6 ± 6.9 ppm) and non-twisted (88.7 ± 24.7 ppm) filament yarns (Fig. 3.3). It has been claimed that the higher freedom in the yarn structure allows staple fibers to move freely in the spun yarn structure, thereby increases microfiber shedding [43]. This easy slippage of fibers from spun yarns was not only limited to domestic laundering. Apart from laundering, spun yarns made of staple fibers were noted to shed more fibers than filaments even in the dry state, that is, microfiber release to air [13]. This attribute can add value to the reason for higher shedding in the case of cotton than synthetic fibers as reported in Sect. 3.2. It is well known that cotton fibers are staple fibers whereas synthetic fibers are produced as filaments, however, they can be made as staple fiber if required. And hence, natural fibers can shed more than that synthetic filaments. Contrastingly, other researchers reported an insignificant difference between the microfiber shedding of spun yarns and filament yarns. This can be due to different methods (ultrasonication extraction) used to examine the microfiber shedding potential [45]. This again insists on a standard method of evaluation. When comparing monofilament and multifilament yarns, it has been reported that the yarns with more number of filaments in the structure release more microfibers. This is because due to the increased number of filaments, there are more filaments/fiber surface exposed per unit area, and therefore, microfiber shedding is facilitated [32]. In general, when the yarn type is considered, spun yarns made of staple fibers shed more fibers than that of filaments whereas, in the case of filament yarns, higher shedding can be noted with multifilament yarns where more filaments are there per unit area.

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Fig. 3.3 SEM images of different a yarn structures and b their fabric structures and c microfiber shedding behavior of different structures (Reprinted under creative commons license from [43])

3.3.2 Yarn Geometry Yarn geometry is highly important as it can have an influence over the mechanical properties and the understanding of the relationship between the geometry and mechanical properties are crucial [46]. Geometrical properties of yarns include linear density, optical diameter, twist degree, structure, imperfections, and hairiness [47]. In the same way that these properties impact mechanical properties, they can also influence microfiber shedding behavior. In this aspect, studies have linked microfiber shedding with the geometric properties of the yarn.

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Yarn Twist The twisting of fibers is done to hold the fibers together in the yarn structure. The nature of twist imparted can be varied in terms of twist direction, twist angle, twist degree, or twist level and twist multiplier in order to achieve the desired properties of yarn [41]. In the case of spun yarns, the twist highly influences the compactness of the yarn structure [42]. Moreover, the twist level determines the inter-fiber spaces and the area of exposure of fibers in the yarn structure [48]. Hence, the yarn twist has been analyzed for its relationship with shedding. De Falco et al. reported that the microfiber shedding from the yarns with a higher twist is comparatively lesser than that of those made with a lesser twist or no twist. The reason is that when the twist level is increased, the yarn structure can get tighter which can pack the fibers firmly together. As the result, the shedding got reduced [2, 13]. Similarly, while comparing two filament yarns (hard twisted and non-twisted yarns), higher shedding has been noted with non-twisted yarns. The hard twisted yarns had tightly packed filaments whereas in non-twisted yarns, the freedom of movement and higher friction among filaments causes abrasion and so higher shedding has been noted. Figure 3.3 illustrates different yarn structures along with their microfiber shedding as reported by Choi et al. [43]. Yarn twist is noted as one of the critical factors that alter the microfiber shedding to a greater level than other influencing parameters. It is expected that fabrics with low hairiness can release fewer fibers. However, while comparing two fabrics of different hairiness, higher shedding is noted with fabrics with lower hairiness. As a result, other parameters were analyzed which showed that yarn with higher hairiness had a higher twist level in that particular sample. It can be noted that the yarn twist level superseded the influence of hairiness [13]. Similarly, the influence of twist was noted to be more than the fabric structure which is detailed in Sect. 3.4.1. Yarn Count/Yarn Linear Density Yarn count or linear density is the expression of the ‘fineness’ of a yarn. Since the diameter of the yarn can vary along the length, diameter is not suitable to express the fineness of the yarn. As a result, it can either be determined by taking the mass of a known length of yarn (direct system) or by taking the length of a known mass of yarn (indirect system) [49]. With changes in the linear density of yarns, researchers reported changes in microfiber shedding. Özkan and Gündo˘gdu reported that the increased linear density can increase the microfiber shedding in the case of staple spun yarns [26]. This can be related to the fact that increasing the linear density (coarser yarns) will have more fibers in the unit cross-sectional area of the yarn structure and thereby increases shedding. However, in the case of filament yarns, the effect of linear density was noted as insignificant [26]. Whereas, other researchers who analyzed fabrics made of polyester filament yarns of different deniers reported a direct relationship between the filament denier and microfiber shedding [17]. Figure 3.4 shows the dependence of microfiber shedding on filament denier. These differences between the studies [17, 26], can be attributed to the difference in other parameters. In both the studies, in addition to yarn linear density, other parameters were also

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Fig. 3.4 Relationship between microfiber shedding and filament linear density (Reprinted with Permission from [17])

varied between the samples. Hence, for the understanding of the influence of yarn linear density, it is suggested to analyze the samples which are similar in all aspects except that of linear density. Yarn Hairiness Yarn hairiness is one of the great influencers of handle properties. Hairiness in the structure is formed either by means of protruding fiber ends or the looped fibers arched out of the yarn core [50]. Since hairiness is determined by the number of fibers protruding on the surface of the yarn, it can be related to the microfiber shedding in which fiber protrusion is the initial stage. Researchers reported that increased hairiness can increase microfiber shedding. Other researchers correlated microfiber shedding with hairiness and reported a strong positive correlation [26]. Moreover, the fibers which are released from the samples of higher hairiness are shorter which clearly shows that those are shed from the hairy structure as shorter fibers are higher in the total hairiness [26]. However, other factors like yarn strength and twist can also have an impact along with hairiness [7, 13]. The effect of yarn hairiness on microfiber shedding can be related to their effect on pilling. Though several factors influence the pilling property, yarn hairiness also has a moderate effect, that is a higher level of reduction in hairiness can result in a comparatively lesser level of reduction in pilling (46% reduction in hairiness resulted in 0.5-grade improvement in pilling resistance). While analyzing the pill formation, it has been noted that reduced hairiness reduced the pilling by means of slowing the rate of fuzz formation [51]. Hence, there is no doubt that hairiness can have an impact on microfiber shedding since fuzz formation is the first step of microfiber shedding. Though its influence can be overridden by other factors like twist and strength, hairiness still has considerable impact and hence, it is suggested that the lower hairiness can reduce microfiber shedding. Yarn hairiness is a critical quality parameter that can affect the quality of subsequent fabrics made

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out of it and hence explorations of reducing hairiness are being made [52]. However, in addition to quality, this will also benefit in terms of reducing microfiber shedding.

3.3.3 Mechanical Properties The physical properties of the yarns like breaking strength, elongation, tensile modulus are greatly influenced by the fibers being used in the yarn structure along with the yarn geometry [47]. Considering that, these physical properties can influence how microfibers are shed from a yarn. Breaking load of yarns which indicates the strength of the yarn was noted to affect microfiber shedding. Zambrano et al. reported reduced microfiber shedding while increasing the tensile-breaking load of yarns. While comparing cotton, rayon, and polyester yarns, polyester yarns were noted to have a better tensile strength in both dry and wet states. Researchers reported that the increased tensile strength could be a potential reason for reduced shedding in the case of polyester fabrics [7]. However, the direct mechanism of influence of mechanical properties of yarns on microfiber shedding will be difficult to interpret. This is because the strength of the yarn is greatly influenced by different parameters. In the case of staple spun yarns, strength can be affected by twist level—increasing twist can increase strength to a certain level after which it will start decreasing [41]. However, increasing twist levels can reduce microfiber shedding [2, 13]. This effect of twist on yarn strength makes yarn strength to influence shedding. Similarly, if we consider inter-fiber friction, increasing the inter-fiber friction can improve the strength of the yarn by reducing the fiber slippage [53]. Also, reducing fiber slippage can reduce microfiber shedding. Hence, the increase in strength reduced microfiber shedding. Hence, it is obvious that though yarn strength has an impact on microfiber shedding, the mechanism of influence is highly based on other parameters which influence the yarn strength. Other researchers reported the effect of flexural rigidity of yarns which revealed that increased rigidity will reduce their ability to absorb external mechanical actions. It was evident when the more rigid flat filament yarns without texturization shed more fibers than the texturized filament and staple yarns which showed lesser rigidity [48].

3.3.4 Yarn Production Methods For yarn manufacturing, different preparatory processes like carding, combing, drawing, etc. are being adopted and finally, the fibers are spun into yarn by different spinning technologies. It is very important to consider the stress or strain to which the fibers are subjected in each process as they can alter the microfiber shedding. During the yarn manufacturing process, the yarns are subjected to mechanical actions which in turn can damage or break the fibers. These fibers will get embedded in the yarn structure and later they will get released from the structure [18].

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Carding Carding is the process where the lap is processed to remove short fibers or impurities and provide fiber orientation [19]. During this process, fibers can be subjected to different actions, and hence, to understand the effect of carding process, researchers analyzed the microfiber shedding of sliver which is produced out of carding process. The results of Cai et al. reported that fibers extracted from the filament yarn are 40 times lower than that of from sliver [45]. Moreover, the fibers which are extracted from the sliver were of a wide range of length (80–50,000 µm) [45]. The higher fiber release from sliver is because, in the carding process, fibers are pulled, separated, and oriented by passing them between the cylinders which are rotating at different speeds [19]. During this process, the protruding fibers will get unintentional cut due to the rotating-cutting principle, and also for parallelization of the fibers, sharp edges are being used which can have a damaging effect on the fibers. These actions can possibly enhance the microfiber release during the sliver production process [45]. Also, there are chances for these damaged fibers embedded in the structure to shed after being made into yarn. Hence careful examination of carding process can prevent microfiber shedding in the later stage. Ring Spinning Ring spinning is the conventional method of spinning where the ring and traveler are being used to impart twist and form yarns [19]. The ring spinning process is suitable for making different counts. This method of spinning can yield yarn with higher tensile strength with higher twisting values and fiber cohesion [54]. If we consider these properties (better tensile strength, fiber cohesion), they can also result in reduced shedding. However, when staple fibers are made into yarn (ring-spun yarn), when the twist is inserted from outside to inside, the fiber migration will happen which is dependent on the properties of the fibers. For instance, short, coarse, and stiffer fibers migrate towards sheath whereas long, fine and flexible fibers migrate towards the core. These shorts fibers in the sheath can be easily shed while exposed to external actions [26]. Rotor Spinning Rotor spinning is an open-end spinning technique where the sliver is opened into individual fibers and then the hollow rotating rotor into which the fibers are deposited by centrifugal force will impart a twist to form yarns [19]. Yarns made of rotor spinning can release comparatively higher fibers than other techniques. This is because, in this process, the fibers are opened up with opening rollers having sharp edges, and this can lead to the formation of short fibers in the structure due to the damaging effect of sharp edges which in turn can increase the microfiber shedding from the yarn made of rotor spinning technique [45]. Moreover, yarns made of rotor spinning are comparatively lesser in strength [19]. To compare the effect of the different spinning methods on microfiber shedding behavior, researchers compared three different yarns made of ring spinning, rotor spinning, and air-jet spinning. The results showed that rotor-spun yarn released a

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higher number of fibers than others. This showed that the damaging effect of opening rollers in the rotor spinning process is very crucial. And also, in the case of ring spinning and air-jet spinning, the shorter fibers are eliminated by means of drawing and parallelization in the processing steps. This led to the reduction of short fibers in the structure of ring-spun and air-jet spun yarns [45]. Moreover, the comparative analysis of ring-spun and rotor-spun yarns revealed that ring-spun yarn can exhibit higher tenacity and better evenness in the structure than rotor-spun yarns [55]. This can also be the reason for reduced shedding in ring-spun yarn than that of rotor-spun yarns. When we examine the yarn characteristics, their impact on microfiber shedding is not negligible. Like fiber characteristics, yarn type, yarn geometry, mechanical properties of yarn were noted to have a significant impact on the shedding. Moreover, it is also noted that different yarn production techniques play an important role. When the yarn type is considered, spun yarns are noted to release more fibers than that of filaments because of their shorter fiber length which can easily slip out of the structure [2, 3, 7, 16, 26, 31]. Different geometrical properties had different effects on microfiber shedding. Yarn twist level increased the compactness and made the fibers held together in the structure and reduced microfiber shedding [2, 13] whereas hairiness showed a direct relationship, that is an increase in hairiness increased shedding [26]. The underlying mechanism showed that reduction in hairiness can slow down the fuzz formation step of microfiber shedding. Though yarn count showed a prominent effect in the case of staple spun yarns, more clarity is needed in the case of filament yarns. The mechanical properties of the yarn had a notable effect on the shedding, however, those effects could be correlated with other parameters like twist which can affect the mechanical properties of the yarn. Finally, the different spinning methods adopted for yarn productions are analyzed which showed the influence of processing steps. The sharp edges in the rollers and cylinders can damage the fibers and lead to the generation of shorter fibers that are embedded in the yarn structure which will be later released as microfibers.

3.4 Fabric Characteristics Fabrics are two-dimensional plane structures that are made up of fibers or yarns in order to provide certain characteristics, such as strength, elongation, flexibility, etc. for various applications [56]. The properties of fabrics are highly dependent on the type of fiber and yarn being used in the construction. However, a few constructional parameters like yarn per unit area, the thickness can influence the physical, mechanical and thermal properties of the fabrics [57]. This section provides a breakdown of the fabric parameters which can impact microfiber shedding.

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3.4.1 Fabric Types Fabrics are broadly classified as yarn-based fabrics and fiber-based fabrics. Yarnbased fabrics include woven fabrics (interlacement of two sets of yarns—warp and weft), knitted fabrics (inter- or intra-looping of one or more sets of yarns), braided fabrics (narrow fabrics made of the interweaving of yarns) whereas the fiber-based fabrics include nonwoven fabrics where the fibers are directly interlocked or bonded together to form fabrics without the formation of yarn [58]. These differences in the construction methods were observed to affect the microfiber shedding. A comparison of woven and knitted structures composed of 100% polyester found that knitted structures released a greater number of fibers [13]. This variation can be related to the stability difference in the structures. In general, woven structures are more stable than the knitted structures. Also, the woven structures are tighter whereas the knits are comparatively loose in structures. This stable and tight structure of the woven fabrics made them shed lesser than that of knitted structure [59]. Contrastingly, De Falco et al. reported higher fiber release from woven structure than that of knitted structure. However, they have connected this variation with the yarn structure. In the case of knitted structure, yarn is made of continuous filaments with less hairiness, whereas the woven structure had higher hairiness yarn in warp and weft [3]. Similarly, the effect of these fabric types has been observed to be superseded by the twist level of the yarn which is used in the fabrics. This was evident when the researchers reported a higher level of shedding with the woven structure which is made of yarns with lesser twists than the knitted structure which is made of yarns with a higher level of twists [13]. Non-woven fabrics are entirely different from the woven or knit structure. In the case of wovens and knits, fabrics are made of yarns that are interlooped or interlaced whereas, in the case of non-woven, the fabrics are formed by bonding of fibers by different technologies like hydroentangling, thermal bonding, and needle punching. This difference in the structure enables more free fibers in the non-woven structure without a strong attachment to the fabric structure. An average of 70% increment in shedding can be noted with non-woven when compared to knit structure (Knit—3 mg/gram of fabric; Non-woven—10 mg/gram of fabric) [25]. Hence, it is obvious that the yarn-based fabric types are more recommended for reducing microfiber shedding than the fiber-based fabrics because yarn structure can provide better compactness of fibers in the structure. Pile Fabrics and Fleece Pile fabrics are those with tufts or loops of yarn or fiber that rise above the base fabric. These fabrics can be made by weaving, knitting, knotting, or flocking [60]. Fleece fabrics are a form of pile fabrics with a deep pile that is made out of the knitting process. These fabrics are thicker having a soft nap on the surface [61]. Since pile fabrics are distinguished with their raised surface, they are expected to release more fibers during washing or other processes. Hence studies analyzed their shedding behavior to compare with non-piled fabrics. Researchers reported significantly higher

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shedding of fleece fabrics when compared to knit structures (Knit—9 ± 7 fibers/100 cm2 ; Microfleece—1177 ± 135 fibers/100 cm2 ; Fleece—1210 ± 96 fibers/100 cm2 ) [32]. Similarly, higher shedding of fleece was reported by Åström. This higher shedding with the fleece fabrics is attributed to the manufacturing process in which surface fibers are cut to give fuzzy features [38]. These cut ends can enhance the fiber release. Apart from washing, fleece fabrics were noted to release a higher number of fibers during the drying process also. The fiber release during the tumble drying process was evaluated for different fabric structures (PES-fap—100% polyester fleece fabric; PES-fnap—100% polyester fleece fabrics; PES-ss—Composite of plain weave shell fabric and fleece with a jersey as base fabric; PES-ts—100% polyester technical sports T-shirt; PES-ts1—Single jersey knitted fabric; PES-ts2—Pique knitted fabric; PA-ts—92/8 Polyamide/elastane Single jersey knitted fabric; PAN-je—100% acrylic fluffy knitted structure) and higher release was noted with PES-fnap, PES-fap, and PES-ss which are all had raised looped surfaces. Following this, the next highest release was noted with fluffy fabric structure PAN-je [44]. Similarly, the fluffy structure fabrics were noted to release more fibers in another study by Belzagui et al. [62]. Contrastingly, other researchers have reported a similar level of shedding in both fleece and mechanically treated jersey structures of polyester fabrics. However, variations can be noted between the fleece and the knit structures which are not mechanically treated [63]. To visualize the mechanism of fiber release from fleece fabrics, researchers compared the length of microfibers released with the height of piles on the surface of fleece fabrics. Two different phenomena were noted. In a double-sided fleece sample with 1000 and 2000 µm pile height, the released fibers were 1400 µm in length. Whereas in another sample where the pile heights are 900 and 800 µm, the shed fibers were around 3500 µm in length. In the first case, it is claimed that the fibers which are on the surface get damaged and released whereas in the other case, the release is due to the poor embedment of the piles and hence the longer fibers are pulled out from the surface [44]. Moreover, the raised fiber ends, raised or looped piles on the structure can be easily damaged by the external actions, and hence the shedding got accelerated. In addition to easy breakage, these raised fibers can easily get entangled together to form pills which can often wear off during the washing cycles [44].

3.4.2 Fabric Geometry and Structural Parameters Fabric geometrical properties include interlacement point, thread density, thickness which can alter the handle, elongation, crimp, density, and weight of the materials. As a result, their effect on microfiber shedding is also perceptible [64]. Weave or Knit Pattern Woven fabrics are made of different weave structures which are varied in terms of interlacement between warp and weft yarns. The weave pattern is one such critical

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factor that determines the mechanical properties of the fabrics [65]. Fabrics made of different weave structures are analyzed for their variations in microfiber shedding. Plain, Twill, and Satin weave with different weft densities were evaluated for microfiber shedding. Among the fabrics examined, the Plain weave structure released lesser whereas the Satin weave structure released a higher number of fibers during laundering [66]. The interlacing coefficient of fabrics was noted as the influencing factor. Results revealed higher the interlacing coefficient, the lesser is the microfiber shedding. Interlacing coefficient calculation of a weave structure depends on the number of binding points for a specific number of warp and weft (interlacing coefficient = number of binding points/(number of warp × number of weft)) [66]. It can be observed that the higher values of interlacing coefficient imply that the yarns are tightly held with more number of interlacements in the unit area and so the fibers that can migrate out of the structure will be lesser [66]. Similarly, knitted fabrics can be different structures which mainly includes single jersey and double jersey (Rib and Interlock). Researchers have compared variations in these knitted structures. For the purpose of comparison, all three structures were made with the same fiber composition (100% Polyester) and similar areal density (~230 GSM). The results revealed that interlock structure released a higher number of fibers which is followed by rib and single jersey whereas in the case of mass estimation, rib structures are claimed to release more fiber mass which is attributed to the fiber fineness and average length of fibers released [17]. However, analysis of other researchers on two different knit structures, single jersey and interlock reported a similar level of shedding (no significant difference has been noted) [18]. This can be related to the variations in other constructional factors and yarn types. Hence, to understand the direct influence of different knit structures, the analysis of structures made of similar yarn structures with similar constructional factors is needed. Tightness The tightness of the fabric implies how tightly the yarns in the structure are packed together. In terms of woven fabrics, this can be termed as the cover factor which is influenced by warp and weft yarn density and count whereas, in the case of knit structures, this is termed as tightness factor which is greatly determined by the yarn count, stitch density and loop length. It has been claimed that tighter fabric structure leads to increased shedding. This is attributed to the fact that the tighter structure will have a greater number of fibers in the unit area and it leads to higher shedding per unit area [32]. However, this is contradicted by the fact that when the tightness of the structure got increased, the freedom for movement of fibers got reduced and this led to the reduction in microfiber shedding with increased tightness in the structure [66]. To support this, the correlation of stitch density and tightness factor of knitted fabrics was made with microfiber shedding. With increased stitch density the fabrics are more compacted and shedding was noted to get reduced. Similarly, the tightness factor also had a strong negative correlation with microfiber shedding. Figure 3.5 shows the relationship between fabric tightness and microfiber shedding [17]. Similarly, in the case of woven fabrics, weft densities of the woven fabrics were related to the microfiber shedding. While increasing the weft density, the fibers

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Fig. 3.5 Correlation between microfiber shedding and a stitch density and b tightness factor (Reprinted with Permission from [17])

are more compactly packed in the structure. This can reduce microfiber shedding. Researchers reported microfiber shedding of plain and twill weave structure is almost doubled when the weft density is decreased from 15 to 10 picks/cm [66]. It shows that having a greater number of weft yarns in the unit area increases the compactness of the structure and reduces microfiber shedding. Thickness Fabric thickness is a crucial variable that determines different properties including fabric stiffness, drapability, air permeability, absorbency, thermal properties, etc. [67]. This critical variable is analyzed for its impact on microfiber shedding. While analyzing the 1 × 1 interlock structures of different thicknesses, the plot between

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thickness and shedding revealed an increasing trend. It has been reported that the increase in thickness indicates the presence of a greater amount of yarn or fibers in the unit area of the fabric which results in increased shedding per unit area [17]. In woven fabrics, thickness is greatly based on the fabric weave and the binding points. The fabrics which are having longer float will have higher thickness than those with small floats [68]. If it is taken in this aspect, fabrics with a longer float will have lesser binding points and so more shedding. Then it can be expected thicker fabrics to shed more fibers. Nevertheless, the impact of woven fabric thickness on microfiber shedding has yet to be analyzed directly.

3.4.3 Physical and Mechanical Properties The effect of physical and mechanical properties of the fabrics is important in the aspect of their suitability in a particular application. This section explores how those properties are critical in altering the microfiber shedding property. Areal Density The areal density of the fabrics is the weight per unit area of the fabrics. It is often indicated in grams per square meter (GSM). The areal density of the fabric increases the microfiber release. Researchers reported a positive correlation between areal density and microfiber release irrespective of the material type. For different materials (here it is—100% nylon, 100% polyester, Blends with 12% elastane), increment in the shedding has been noted with increased areal density. Figure 3.6 shows the positive interaction between areal density and microfiber release. This increment in the microfiber release with the increased density shows that fibers release is not only from the surface but also from the deeper layers of the fabrics [63]. A similar claim Fig. 3.6 Relationship between areal density and Microfiber shedding (Reprinted with Under creative commons license from [63])

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of increment with microfiber shedding with increased areal density was reported in another study [17]. However, greater contradictions have arisen with the areal density when other researchers reported that higher areal density implying more fibers per unit area cannot directly influence the microfiber shedding, as they have noted lesser fiber release from the samples which is higher in areal density [3]. Similarly, Zambrano et al. reported that fabrics of higher density (Areal density—240 g/sq m; Volume density—296 kg/cu m) released lesser fibers than the lower density fabrics (Areal density—157.66 g/sq m; Volume density—193 kg/cu m) [7, 69]. They related it with the compactness saying that higher density fabrics have higher compactness and release lesser fibers. Hence, researchers reported a relationship between structural parameters with areal density. It has been reported that the areal density of the fabrics can be increased by increasing factors such as yarn count, stitch density, tightness, and thickness. Hence, the effect of areal density will be based on these parameters in a way that if the areal density increased by increased tightness and stitch density, it is expected to reduce microfiber release with increased density, however, in the case where areal density was influenced by thickness or yarn linear density, the trend will be opposite [17]. Abrasion Resistance Abrasion resistance of the fabrics indicates how the fabric can withstand the abrasive forces during usage. Microfiber shedding can be related to abrasion resistance because the weight loss during the abrasion is determined either by the reduced thickness or by the elimination of short/loose fibers [70]. With the perception of abrasion resistance to affecting microfiber shedding, researchers drafted the relationship between abrasion resistance and microfiber release. Abrasion resistance of 4 different fabrics (100% cotton, 100% polyester, 100% rayon, 50/50 cotton/polyester) was plotted against microfiber release and the trend has been noted as increased shedding with decreased abrasion resistance [7]. A similar effect has been noted with non-woven fabrics, where the samples with higher abrasion resistance showed lesser fibers release [71]. Contrastingly, other researchers found increased shedding in the fabrics with higher abrasion resistance. Here, it has been claimed that the increased GSM increased the abrasion resistance of the fabrics, however, increased GSM can also increase the shedding in its own way. Hence, the shedding has been noted to increase with increased abrasion resistance [17]. Pilling Resistance As discussed in the mechanism of microfiber shedding, pilling can be highly related to microfiber shedding because of the initial fuzz formation step. Hence, the pilling resistance of the fabrics was compared with shedding. Researchers reported comparatively higher shedding in the case of polyamide fabrics (comparison with polyester and acetate) which showed excelled pilling resistance (Pilling grade 5) [31]. However, this can be attributed to the fiber composition. Hence, other researchers compared the pilling property of polyester knitted fabrics of different structures. The results revealed that all the samples were similar in the case of pilling resistance (Pilling

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Grade—5), but their shedding behaviors are noted to vary to a greater extent [17]. From these findings, it is clear that improving the pilling resistance of the fabrics can help in reducing microfiber shedding, however, fabrics with excellent pilling resistance can also release microfibers during subsequent processes. Fabric Strength Fabric strength is expressed as tensile strength and tearing strength in the case of woven fabrics whereas bursting strength is considered for knitted fabrics. Increasing strength can reduce microfiber shedding and it was evident in the case of fibers and yarns. However, in the terms of fabrics, the effect of fabric strength is observed to be overtaken by the structural and physical parameters. Researchers reported higher shedding in the polyamide fabrics which showed excellent tearing strength (Warp— 1310.10 ± 23.67 N; Weft–1090.92 ± 17.46 N) than polyester (Warp—446.11 ± 41.12 N; Weft—624.23 ± 47.70 N) and acetate fabrics (Warp—443.08 ± 23.67 N; Weft—1090.92 ± 17.46 N) that showed a poor tearing strength [31]. Similarly, in knitted fabrics, fabrics with higher bursting strength were noted to release more fibers than one with lower bursting strength. This is because the bursting strength can be improved with increasing GSM and extensibility of the fabrics. In a knitted structure, the extensibility can be improved with increasing loop length which again ends up in a looser structure (reduction in tightness factor) [72]. These in turn can increase the microfiber shedding with improved bursting strength. Bringing together, the fabric characteristics have their own incidence on microfiber shedding, however, these effects are comparatively lesser to fiber and yarn characteristics. Woven fabrics with their higher stable and compact structure controlled shedding than the knitted structure. But, nonwoven fabrics released significantly higher fibers due to the absence of yarn in the structure. Fabrics with piles on the surface caused higher shedding as these piles are more vulnerable to damage and can be easily ripped off from the surface. Fabric structural properties like binding points, tightness, thickness influenced shedding. The tighter structure with more binding or interlacement sites reduced shedding whereas the increased thickness increased shedding because of a greater number of fibers/yarns in the unit area. Physical and mechanical properties like areal density, strength, abrasion resistance, pilling resistance are greatly determined by the fiber composition, yarn structure, and fabric geometry. And hence, the influence of physical or mechanical properties are overridden by them which resulted in varied conclusions from different researchers.

3.5 Textile Processing and Finishing Once the yarns are made into fabrics, there are subsequent processes that can make the fabric suitable for further applications. In textile processing, the greige fabrics out of knitting or weaving processes are dyed and/or printed to impart aesthetic values. Also, several textile finishing processes are available which can improve the desirable properties of the fabrics. For the fabrics to be ready for these processes, they are

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subjected to certain preparatory processes like desizing, scouring, bleaching, etc. to remove any impurities in the fabrics [19]. These processes mostly use chemicals that can have chemical actions on the fabrics, thereby, influencing microfiber shedding. However, a few mechanical methods of finishing also affect the structural properties and affect microfiber shedding. This section details the impact of preparatory processes, textile processing, and finishing on the microfiber shedding behavior of the textile materials.

3.5.1 Preparatory Processes Preparatory processes are very important to make the fabric acceptable for further processing. These processes remove any natural or added impurities in the fabrics and enable them to absorb dyes or chemicals which are being added in the consecutive processes. There is a possibility that these processes can affect microfiber shedding and hence understanding these processes are very important. Singeing Singeing is the process where the loose fibers or yarns that are not firmly attached to the yarn or fabric surface will be burnt off under a controlled heating process. This process removes the protruding fibers and leaves the surface smooth [73]. It has been reported that since this process removes the protruding and loose fibers on the surface of the fabric, it can reduce the microfiber shedding from the fabrics [54]. However, a direct comparative analysis of fabrics undergoing singeing processes and untreated fabrics is not made. Such analysis can evident the influence of singeing process. Scouring Scouring is the process where impurities like oil, wax, etc. will be removed from the fabrics facilitating them to allow uniform penetration of dyes and other finishes. Mild concentrated sodium hydroxide is commonly used for scouring processes [19]. Researchers found the influence of the scouring process which they have adapted as a preparatory step for analyzing microfiber shedding. Polyester samples were scoured for 3 min at 40 °C with neutral soap and dried at 80 °C. While analyzing microfiber shedding of these scoured samples in consecutive wash cycles, a significant difference has not been noted in shedding between different wash cycles [74] whereas other researchers reported a gradual decrease in shedding from the first wash [6, 16, 62]. The decreasing trend is supported by the fact that at the initial stage, the loose/short fibers which are embedded in the structure get released. This shows that the scouring process can remove such embedded fibers and reduce the shedding in subsequent stages. However, this, in turn, alerts that the effluent out of scouring processes is suspected to have a greater number of microfibers. Though the preparatory processes are noted to have a mitigative effect on microfiber shedding, the direct analysis of treated and untreated samples was not

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made. Moreover, other processes like desizing and bleaching are not explored in terms of their effect on microfiber shedding.

3.5.2 Dyeing Dyeing is the colouration process where the dyes molecules are absorbed on the textile fibers in such a way that the dye remains on the fiber and resists the release back [75]. Dyeing is a very crucial process as it imparts aesthetic value to the fabric and several types of dyes are being used in the industry. During the dyeing process, fabrics are subjected to dyes, chemical additives, temperature, and agitation [19]. Ultimately, this can influence microfiber shedding. While analyzing the microfiber release behavior of textile materials at different stages (sliver, yarn, unfinished fabrics, finished fabrics), researchers reported microfiber released during the dyeing process [45]. This can also be supported by the studies which found microfibers in the effluent of dyeing and printing industries as discussed in Chap. 2 [9–11, 76]. However, apart from the processing stage, dyed samples after the process are compared with undyed samples for the effect of dyeing. This comparison showed that fibers release after the dyeing process is very much lesser than that released during the process. Figure 3.7 shows the microfiber released during the dyeing process and the subsequent extraction process of different yarns [45]. Similarly, other researchers reported an insignificant difference in microfiber shedding between dyed and undyed samples (Fig. 3.8) [69].

Fig. 3.7 Microfiber release from different textile materials during dyeing process (Reprinted with permission from [45])

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Fig. 3.8 Microfiber release from fabrics treated with different functional finishes (Reprinted with permission from [69])

Hence, it is obvious that in the case of dyeing, a higher release of microfibers is noted during the process whereas the difference between the dyed and undyed samples in terms of microfiber shedding is insignificant. Hence, in this area, more attention should be given to the effluents that are released out of dyeing industries.

3.5.3 Finishing Finishing process is often done on textile fabrics to impart aesthetic as well as functional properties to the fabrics. Conventional textile finishings are broadly categorized into chemical and mechanical finishes. Some of the commonly used finishings are analyzed by the researchers to elaborate their influence on microfiber shedding. Brushing Brushing is a mechanical process in which the fibers in the surface of the fabrics are broken with a metal brush to give a fuzzy or soft texture to the fabric surface. Researchers reported a higher release of microfibers from the surface of the fabrics which are undergone the brushing process. The two key reasons that were reported are (i) During the process of brushing, many loosely held short fibers are generated in the structure; (ii) The process can weaken the yarn structure and fabric structure which leads to more release. Moreover, the comparative analysis revealed that the surface processed fabrics showed higher release than the unprocessed fabrics in the initial washes, however, after 10 washes, the shedding of both the fabrics was similar. This clearly shows that the shorter fibers that are developed and loosely entangled in the surface of processed fabrics are released in the initial washes themselves [77]. Similar results of increased release of microfibers from the mechanically processed surface were reported by Cai et al. who analyzed microfiber release by ultrasonication extraction [45]. As a result, it is quite clear that eliminating the brushing process or avoiding the use of brushed fabrics will greatly reduces microfiber shedding.

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Durable Press A durable press finish is often given to cellulosic fabrics to improve shrinkage resistance and wrinkle recovery. Dimethyol dihydroxy ethylene urea (DMDHEU) is the conventional formaldehyde-based durable press finish. A comparative analysis revealed cotton knitted fabrics that are given durable press finish with 5% resins were noted to shed more fibers than those of untreated samples. This increased shedding is related to crosslinking behavior. To achieve the wrinkle-free effect, the easy movement of cellulose chains is restricted by crosslinking. This crosslinking can make the fabrics more brittle than before which can release more fibers due to easy breakage. Moreover, the restriction of movement of cellulose chains also reduces the tearing strength and tensile strength of the fabrics. These in turn increase the microfiber shedding of the finished fabrics. Also, these fabrics are noted to have less abrasion resistance, which can also improve the shedding behavior [69]. Water Repellent Finish Water repellency is the ability of fabrics to resist wetting [78]. The fabrics are made water repellent by deposition of hydrophobic substances on the surface of the fabrics [79]. Fluoro-polymers, fluoro-chemicals, silicones, and waxes are some of the hydrophobic substances used in the application of water repellent finish [78]. In a study, knitted fabrics made of cotton were given water repellent finish with Fluorochemical and crosslinking agent and were analyzed for microfiber release. The higher release of fibers has been noted when compared to the unfinished samples. Similar to durable press finish, here the finish molecules are cross-linked to the cellulose structure to increase the durability of the finish. This cross-linking results in decreased mechanical properties like tensile strength, tear strength, and abrasion resistance. This in turn increased the microfiber shedding [69]. Figure 3.8 shows the microfiber release from fabrics that are treated with different functional finishes. To consolidate, textile processing and finishing have a huge impact on the microfiber shedding behavior of textile materials. The preparatory processes like singeing and scouring which eliminate protruding fibers and impurities respectively remove the short fibers embedded in the fabric structure. This in turn showed reduced shedding in the subsequent processes. However, the process effluents should be handled carefully as they can carry the fibers removed from the structure. The same was noted in the dyeing process, that is, during the process, the fabrics released a greater number of fibers, however, there is no significant difference between microfiber shedding of dyed and undyed samples [69]. Mechanical finishes like brushing increased the shedding as this process intentionally creates fuzz on the surface of the fabrics. In the case of chemical finishes, the cross-linking of chemicals with the fiber structure makes them more brittle with reduced tensile properties. This resulted in increased shedding. However, in recent times, few sustainable chemical finishes are being identified to reduce microfiber shedding from the textile materials which are discussed in detail in Chap. 6. Moreover, the chemical finishing process is suspected to be the reason for the presence of non-fibrous microplastic materials in the wash effluent. Researchers noted plastic polymers like

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acrylic copolymer, polyester, polystyrene, aminoplast resin, vinyl acetate copolymers in the wash effluent of samples. These non-fibrous fragments are expected to get included during the chemical finishing processes, yet no relationship was witnessed with the reported chemical finishing of the samples. Researchers suggested that these particles may be due to the non-reported chemicals or materials that are used in the manufacturing of the samples [63].

3.6 Apparel Production Process Apparel production is the process where the two-dimensional fabrics are converted into three-dimensional garments. This process transforms the fashion design concept into a physical product. The basic production processes include cutting, sewing, and finishing processes [80]. The effect of these production processes is also very important as the apparel products are reaching the customer and shedding in the domestic laundry is happening only after all these processes. Thus, these production process parameters are analyzed for their impact on microfiber shedding.

3.6.1 Cutting In the apparel production process, cutting is a crucial process by which the fabrics are cut into individual components of a garment which are then stitched together to form the garment. A wide range of cutting methods are available in the industries with specified applications based on the fabric materials, component sizes, total quantity, etc. [81]. The significant impact of the cutting process arises because the cutting will lead to raw edges; based on the cutting methods, fabric edges will be frayed differently. This can lead to a release of fibers from the cut edge of the fabrics. Hence, the cutting method being used in the apparel industry alters the microfiber shedding of a garment to a certain extent. Cai et al. analyzed fabrics whose edges are cut with scissors and those which are laser cut. The laser-cut samples shed lesser fibers than the scissor cut. The variation is around 3–21 times increment in shedding for scissor-cut samples compared to laser cut. The length analysis claimed that the scissor-cut samples released longer fibers. In the case of scissor-cut samples, the yarns at the edge will be cut which opens up fibers in the yarn structure to release whereas, in the laser-cut samples, the yarns are melted together. Figure 3.9 shows the microscopic image of scissor-cut and laser-cut fiber ends [77]. In similar research, where the ultrasonication method of extraction has been made to quantify microfiber release, 31 times higher shedding has been noted with scissor-cut samples than that of laser-cut samples [45]. In similar research, authors compared scissor-cut samples with ultrasonic cutting and reported comparatively higher shedding in the case of scissor-cut samples when compared to ultrasonically cut samples [33]. From these results, it is clear that scissor-cut samples are more vulnerable to shedding. However, a

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Fig. 3.9 SEM images of Scissor-cut and Laser-cut fiber ends (Reprinted (adapted) with permission from [77] Copyright {2020} American Chemical Society)

comparison between laser cutting, ultrasonic cutting, and other advanced methods of cutting can highlight the method which is effective in terms of controlling microfiber shedding.

3.6.2 Sewing Sewing is the process where different garment components are assembled together by means of needle and thread. Different types of sewing machines are available which can produce different types of seams and stitches [81]. The sewing process will have the penetration of needles onto the fabrics which can damage or weaken the fibers in the structure. The needle piercing can cause the loose fibers to break off from the continuous filaments. And these fibers can easily get released during washing or any other subsequent processes [44]. This alarms the possibility of sewing operations to enhance microfiber shedding. Overlocking in the garment manufacturing process, being the most common method for finishing raw edges in apparel, is acting as one of the great accelerators of microfiber shedding of garments [77]. Researchers compared fabrics samples whose edges are finished by overlock with fabrics with raw edges. The comparative analysis revealed a greater fiber release from overlocked samples than that of fabrics with raw edges. The claim has been made that the needle penetration or cutting during the overlock sewing can cause additional damage to the fabrics, thereby enhancing the microfiber release [77]. Similarly, while analyzing the origin of the fibers shed from the fabrics, researchers reported that they are mostly released from the cut edges and also from the seam portions of the samples where

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the piercing of needles damaged the fibers [44]. However, in the sewing process, more analysis is needed in terms of different types of stitches (lockstitch, flatlock, chain stitch, etc.) and seams (plain seam, lap seams, etc.) which are widely used in the apparel manufacturing processes. Cutting and sewing processes are very much influencing factors of microfiber shedding of apparel. From the literature, it is very well understood that these processes can influence microfiber shedding; however, its higher level of influence urges more attention towards these processes. This is because around 50% to 80% of the fibers released from a sample are noted to release from the edges and only the remaining is released from the surface of the fabric [45, 77]. And hence, the modifications in the cutting and sewing process which highly concentrate on the fabric raw edges on any apparel are highly recommended for mitigating microfiber shedding.

3.7 Aging Aging of the textile materials is expected to cause major changes in the structural aspects of the fibers. Significant changes in the molecular weight, crystallinity, orientation, chemical structure of fibers can be seen with aging of materials [82]. As discussed in Sect. 3.2.1, these structural properties of the fibers are crucial in determining the microfiber shedding. In this way, aging of materials will also affect microfiber shedding. Over the usage of textile materials, they can undergo aging which can be classified as physical aging, photochemical degradation, thermal degradation, chemical attack, and mechanical stress. These different aging will have a varied effect on the properties of the textile materials [82]. To examine the effect of aging, researchers have employed different techniques to simulate aging. Almroth et al. have analyzed the effect of aging by replicating aging with the process called ‘repolishing’. In this method, fabrics are abraded with an abrasive belt of 60 grains to recreate wear and tear. The fabrics which are repolished were noted to have higher fiber release than that of new fabrics. This is because the process of repolishing damages the surface of the yarn. In addition to that, researchers also analyzed the fiber size and reported that the fibers released from the repolished fabrics are longer than those released from the new fabrics [32, 38]. Similarly, other researchers brought the aging effect by means of laundering the garments continuously for 24 h. Aged garments released 25% more fibers than those new garments. This can be related to the changes in the visual appearance of the aged jackets where the surface was noted to be frayed [83]. Whereas in another study, a significant difference in shedding is noted between aged and new garments (60% increment in aged garments) [84]. It has been reported that the fabrics which are laundered before can have rubbing actions on the surface which can enhance the migration of fibers and so the fiber release can get increased in the subsequent washings [66]. However, these aging processes cannot replicate the real-time aging of textile materials as they are worn between each wash and wearing can also affect aging process. This was evident when the researchers found a significant increment in shedding when

3.7 Aging

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the textiles are washed after wearing them for a specific period of time. In a series of wash cycles, shedding of different garments (fleece jackets, t-shirts, socks) has been noted to decrease in consequent washes from 1 to 5. After the 5th wash, the fabrics were worn for 12 h and then the 6th wash has been done. Researchers noted a sudden increment of fiber release in the 6th wash which is attributed to the frictional tension caused during the wearing of the garments. Figure 3.10 shows the variations in the surface of textile material after washing and wearing where more protrusion of fibers are noted after the 6th wash which is done after wearing [85]. This shows that wearing can have a different effect than washing. Hence, the continuous washing method adopted in the studies [83, 84] should be refined to determine the accurate effect of aging. In another study, researchers reported higher shedding with the older jackets compared to the new ones, however, no specifications of the old jackets were detailed out [86]. Though aging has a significant role in accelerating the microfiber release, aging can be different for different types of material. Hence, a deep understanding of that aspect is very much required. In that aspect, researchers analyzed four different plastic pellets namely high-density polyethylene (HDPE), high impact polystyrene (HIPS), nylon 6 and polypropylene which can generate microplastics. Though they were not textile fibers, polyester, nylon, and polypropylene polymers are highly used in textiles. Hence, understanding the microplastic generation behavior of these particles under UV exposure can give an idea of the fate of synthetic textiles that are ended in landfills. Among the 4 different polymers studied, nylon is found to be degraded easily with UV weathering. The reported reason is that nylon is highly absorbent when compared to other polymers studied. The presence of water can enhance the photochemical reactions which in turn increased the degradation of polymer and generation of microplastics [87]. The role of UV degradation on microfiber shedding is supported by the analysis of the fibers shed from the fabrics. Researchers reported two forms of fibers—loosely entangled fibers and the other one is ripped off from the surface. Researchers reported that those ripped from the fabric surface are due to the UV degradation of the fabrics which can weaken the fibers and make them rip off [62]. For effective visualization of the effect of aging on microfiber release after disposal was analyzed with non-woven fabrics that are used in surgical masks. Here, the laboratory methods of aging were replaced by real-time conditions. The fabrics

Fig. 3.10 SEM images of a unwashed fabrics, b fabrics of after 5 washes, and c fabrics after 6th wash after 12 h of wearing showing the fiber protrusion on the surface (Reprinted under creative commons license from [85])

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are exposed to natural weathering for 30 days and analyzed for their microfiber release. Microfiber shedding of aged fabrics was 70–98% higher than that of new fabric [71]. From the literature, it is evident that aging affects the microfiber shedding of textile materials. The influence of aging should be given more importance as it will continue even after the disposal of textile materials. Researches have been made in two aspects—i. Aging during usage and ii. Aging after disposal. To replicate aging during usage, repolishing [32, 38, 83, 84] and continuous washing methods were adopted whereas to simulate aging after disposal UV exposure and natural weathering have been employed [71, 87]. In all the cases, aging showed a positive correlation with microfiber shedding. However, the level of increment varied with the method being adopted as well as the material being subjected to aging. Hence, it is important to develop a standard protocol to simulate aging which is similar to that of real-time conditions including wearing, washing, drying, ironing, etc. Moreover, the difference in the aging effect has been noted with different polymers [87]. Hence, the polymers which are being widely used in the textile industries should be evaluated for their tendency to generate microfibers with aging. Figure 3.11 consolidates the influence of all textile parameters discussed and their impact on microfiber release from textiles.

Fig. 3.11 Influence of textile and apparel characteristics on Microfiber shedding

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3.8 Conclusion This chapter provided an insight on the influence of textile materials at different stages on the microfiber shedding behavior. The influence of textile properties has been interpreted at every stage of the textile materials starting from fiber to garment. It is clearly evident that at each stage, the structural, chemical, physical and mechanical properties of the textile materials either enhanced or minimized the shedding. Figure 3.11 provides the summary of different textile characteristics and their role in microfiber shedding. The fiber and yarn characteristics had been noted to have the upper hand in the influence than the fabric properties. While considering textile processing, the role of chemical and mechanical processes has been enlightened along with the significance of preparatory processes. In wet processing, attention should be given at processing stages, because microfibers are observed to release during the process. After the fabric stage, the apparel production processes were analyzed and cutting and sewing processes were reported to have a control over microfiber shedding. Finally, the aging of the materials was correlated with microfiber shedding to elucidate the mechanism of shedding throughout usage and after disposal.

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Chapter 4

Domestic Laundry—A Major Cause of Microfiber Shedding

4.1 Introduction Microfibers are the dominant microplastic type that is reported in various environments by several researchers [1–4]. Out of different sources analyzed, always textiles were identified as the important source of microfibers [1]. The domestic laundry process was reported as one of the important pathways, through that microfibers get released from the textile and enter into the environment [5, 6]. Magnusson and Norén [7] reported that the laundry process is the third major contributor of microplastic followed by tyre abrasion and artificial turfs [7]. Due to the prevailing fast fashion trend, usage and laundering of synthetic textiles significantly increased in recent times. Hence, the urgency in understanding and measuring the impact quantitatively has become the major preference among environmentalists [8]. Polyester fiber is one of the most common fibers used in fast fashion-oriented synthetic apparel. It was evident from the higher fiber consumption and to confirm this, a recent report showed a massive share of polyester (52%) in the total fiber consumption in the world [9]. The first report on microfiber pollution in the environment was documented by Browne et al. [1]. While evaluating the sediments from the sea shore and ocean beds of the different continents, the study reported a higher level of microplastics, specifically higher microfiber contamination in the analyzed location (2–31 microplastics per 250 ml). As the first researcher to report they identified the polymer type and reported that microfibers are generally originated from textiles (polyester (56%), acrylic (23%), polypropylene (7%), polyethylene (6%), and polyamide fibers (3%)). Researchers also correlated the population density and microfiber contamination in the marine environment and found a statistically significant relationship. To confirm the microfiber release from laundry, researchers analyzed the microfiber release characteristics of blankets, fleece, and shirts and found that a garment can shed more than 1900 fibers per wash. Out of all the selected garments, fleece fabrics were found to shed 180% more amount microfibers. A liter of effluent had more than 100 microfibers and thus they concluded that the washing process was the main cause © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 R. Rathinamoorthy and S. Raja Balasaraswathi, Microfiber Pollution, Sustainable Textiles: Production, Processing, Manufacturing & Chemistry, https://doi.org/10.1007/978-981-19-4185-6_4

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of the release of microfiber into the marine environment. Further, they also advised evaluating the results on a seasonal basis, as people wear more clothes in winter (700% more washing machine usage) than in summer, and hence a higher release of microfiber is possible [1]. Later on, Magnusson and Norén analyzed the municipal wastewater treatment plant in Sweden, which treats 14,000 population, and reported that the influent water had a quantity of 15,000 microplastic per cubic meter which is equivalent to 3,200,000 microplastics per hour. As most of the microplastics were removed in the treatment plant (99%), the effluent water contained 1770 microplastics per hour. A higher degree of retention of microfiber was reported in the wastewater treatment plant [7]. Later, in 2016, Napper and Thompson did a detailed analysis of the laundry process by altering different variables and reported the impact of laundry on microfiber release. Due to the improved methods and microfiber quantification process, this study predicted the higher impact of laundry. The study reported that a 6 kg of acrylic garments wash load can release up to 700,000 microfibers into the effluent [6]. These results were far higher than the previous study results [1]. Further, other research was performed on the standardization of microfiber quantification techniques. They reported through this analysis that 35% of the marine microfibers originated from domestic laundry [10]. Recently other researchers evaluated the microfiber release from real-time household laundry where 4 people used 205 clothing items with a different range of textiles. The results of the study reported that an average 6 kg wash load can emit up to 18,000,000 synthetic microfibers. In that too, a higher contribution (53%) of smaller size microfibers was reported (10–50 µm) [11]. In the last five years, the research on microfiber emission from laundry increased exponentially. In the similar manner, several research works were also done on the scientific methods to standardize the quantification techniques. In this view, this chapter is aimed to analyze the impact of individual laundry parameters on the microfiber release characteristics of the textile material. The first part of the chapter outlines the impacts of various laundry parameters under different heads namely washing parameters, machine types, washing methods, and drying methods on microfiber shedding from textile. Later, a brief discussion on the wastewater treatment plants (WWTPs) was provided, as the domestic laundry effluent mixes with sewage and aligns with municipal wastewater. On this basis, the potential impact or contribution of WWTPs and their solid and liquid discharges on microfiber/microplastic pollution in the environment are discussed. The first section of this part details the existing literature on the effluent, and WWTPs removal efficiency. The second section outlines the impact of sludge and its microfiber contamination nature.

4.2 Influence of Washing Parameters In the consumer phase, laundry is one of the important activities to maintain the textiles clean and hygienic. Despite their importance, the laundry process is noted

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Fig. 4.1 Various laundry parameters that influence the microfiber release from textiles

to show a significant impact on products’ durability and lifetime. The use of water, laundry aids, and mechanical agitation/forces applied to the fabric are considered as the factors responsible for the release of microfiber from the textiles. This section of this chapter details the various laundry parameters and their impact on the microfiber release characteristics of textiles. The common laundry parameters that are influencing the microfiber release are analyzed in this section, as provided in Fig. 4.1.

4.2.1 Laundry Duration Researchers analyzed the effect of laundry duration on the microfiber shedding characteristics of textiles. While comparing the microfiber release characteristics of textile with different laundry programs that could run for 15 and 60 min, a researcher reported no significant difference. The majority of the microfibers are released in the first 15 min of the laundry rather than the longer duration of the laundry. From these results, researchers confirmed that the trapped and entangled fibers from the manufacturing process are the major sources of microfiber released during the laundry. Hence the study concluded that in the laundry process no fiber breakages have occurred instead the plucking is happening from the fabric structure [12]. In similar research, the cold express cycle (30 min) was compared with the cotton short cycle (40 °C, 85 min). The results reported that higher temperature (than room temperature) and longer wash time reportedly increased the microfiber shedding from laundry. Researchers reported that the higher mechanical agitation in the longer washing cycle enhanced the fiber release from textile [13]. The results of Periyasamy et al. also supported the finding that an increment in the wash duration (60, 75, and 90 min) increases the microfiber shedding from the denim jeans [14].

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Another study hypothesized a higher microfiber release from textile due to the higher mechanical agitation in the longer laundry duration. When the laundry duration was extended to 8 h, microfibers released from the textile did not show a significant increment. Hence study confirmed the insignificant impact of laundry duration or mechanical action inside the washing machine on microfiber shedding [15].

4.2.2 Laundry Temperature As far as the laundry temperature is concerned, an increase in the temperature is believed to have a positive effect on the microfiber release behavior of the textile. Though many details were not discussed, the first analysis of the laundry temperature and microfiber release was documented by Napper and Thompson [6]. Later, in their study, De Falco et al. evaluated the effect of temperature (at 30 and 40 °C) on microfiber release characteristics. The study results reported a variation (increase) in the microfiber release with an increase in temperature. Though the difference is not statistically significant, it is important to consider the results [16]. At higher temperatures, the laundry process will cause hydrolysis of polyester fabric due to the alkaline nature of the detergent used. Though the study did not evaluate the individual effect of the temperature, they reported that higher temperature will result in an increment in the microfiber shedding [16]. Other researchers compared the microfiber release at 30, 40, and 60 °C. In the case of polyester fabric, a higher release of microfiber was noted at 60 °C, compared to 30 °C or 40 °C. Similar results were also reported for the acetate fabric while laundering at 60 °C. All the fabrics showed statistically significant differences in microfiber release at a higher temperature. However, at lower temperatures between 30 and 40 °C, no such impact was reported. Hence researchers suggested that washing at a lower temperature will reduce microfiber shedding from textiles [17]. While analyzing the cotton, rayon, polyester, and polyester/cotton fibers, another study reported that irrespective of the fiber type, an increase in temperature increases the microfiber release from the textiles. A higher release was reported in the cellulosic fibers compared to the polyester. This was reported that due to the swelling action caused in presence of water, the water molecule breaks the hydrogen bonding. This in turn releases higher microfibers at higher temperatures [18]. A study compared the two different programs in the European washing machines, namely, 40 °C cotton short cycle and cold express cycle. The results of the research reported that, for a similar washing load, the cold express cycle reported a 30% reduction in the total microfiber release than the 40 °C cycle. The number of microfibers released from a similar load is reduced to 129.5 ± 42.9 ppm from 181.6 ± 87.1 ppm. The results showed a statistically significant effect of laundry temperature on the microfiber release characteristics of textile [19]. Figure 4.2 represents the impact of temperature on microfiber shedding as reported by [18]. Periyasamy et al. evaluated the influence of laundry temperature on the microfiber release behavior of denim jeans. The study performed the laundry at 30, 45, and 60 °C. The results revealed an increase in the microfiber shedding with an increase in the

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Fig. 4.2 The number of microfibers generated during accelerated laundering per gram of fabric washed. Effect of temperature on the generation of microfibers, without detergent (WOD). Error bars represent the standard error (N = 4, except for Polyester at 25 °C with N = 5). Significant differences are indicated by * (p < 0.05) (Reprinted with permission from [18])

laundry temperature. The number of microfibers released is 2,877,278, 3,121,692, and 3,283,341 for 30, 45, and 60 °C respectively. Though increment in the numbers was reported, no statistical analysis was performed to understand the significance [14]. In contrast to the above results, the study performed by Hernandez et al. did not show any statistical differences in the mass of fibers released at different temperatures namely 25, 40, 60, and 80 °C. The researchers used deionized water and liquid detergent, however, no difference occurred in the microfiber mass release with higher temperatures. Researchers suggested that when the laundry was performed at a lower temperature, the synthetic textiles were not alkalized by the detergents used in the laundry, and hence less fiber damage occurs, resulting in lower microfibers [15]. As most of the researchers addressed the laundry temperature above 40 °C, other studies focused on the effect of cold temperatures below 40 °C. In another study, a similar contrary result [15] was reported by Kelly et al. [12], who measured the effect of washing temperature in the range of 15–30 °C. Hence, it can be noted that at a higher temperature, an increase in the microfiber shedding was reported however, an increment in temperature at a lower level (less than 50 °C) did not show much difference or no statistically acceptable changes in the microfiber release.

4.2.3 Mechanical Agitation and Water Volume Mechanical agitation is one of the common phenomena applied to textile materials during the laundry process. The rotating drum and steel balls in domestic and laboratory laundry machines, respectively, give mechanical action. Similarly, in the hand washing process, rubbing and beating the cloth with wooden/plastic rod was common

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to remove soil. A higher agitation in the washing leads to more microfiber shedding. A study conducted by Hartline et al. reported a higher microfiber shedding from the top load machine compared to the front load washing machine. The results suggested that the higher mechanical agitation imparted by the top load machine was the main reason for higher microfiber release [20]. The first study conducted by De Falco et al. evaluated the effect of mechanical action by varying the number of steel balls in the canisters of laboratory laundry machines. The results of the study showed that an increase in the steel ball count increased the microfiber release characteristics of the textile. Though the study did not measure the effect separately, they reported the impact of mechanical action along with laundry temperature and time [16]. Other researchers evaluated the effect of number of steel balls on the microfiber shedding of polyester textiles. The results of the study reported that an increase in the number of steel balls in the laboratory washing machine has a strong positive correlation with the increment in microfiber release from textile. The higher mechanical actions like an increase in steel ball count, a higher laundry duration, or higher agitation or mechanical beating usually damage the textiles physically. Hence, the textiles can release more fibers from their structure due to the fiber breakage caused by the mechanical forces applied [21]. Studies also correlated the increased microfiber shedding with the longer laundry cycle with mechanical agitation. Recently a study that analyzed the microfiber emission characteristics of Jeans reported a higher surface rupture of protruding fibers in the yarn structure. Hence, stated that having a higher release of microfiber is due to the longer laundry process [14]. Other researchers evaluated the detachment phenomenon of the microfiber from the textile and reported two possible scenarios. The first one is the higher microfiber emission in the initial laundry cycles due to the loose and entrapped (during manufacturing) fibers released in presence of water. The study reported that those fibers were identified with tail-ended shapes. Whereas, the other prominent shape reported is the ripped-off structure as shown in Fig. 4.3. The authors of the study claim that these detachments happened due to the mechanical forces applied to the fibers during the laundry process [22]. However, in contrast, another study reported that an 8 h continuous laundry did not shed the cumulative amount of one-hour laundry. Hence reported that other than mechanical action, other influencing parameters play a vital role in microfiber release from textile during laundry [15].

Fig. 4.3 a Microfibers with a regular end-tailed shape, and b microfibers with a ripped-off endtailed shape (Reprinted with permission from [22])

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Water volume used in the laundry process is one of the significant parameters that influence the microfiber release characteristics of textiles. The effect of water volume also varies, as the different method of laundry uses different volume of liquid in the process. The first study on the effect of the water volume of the laundry on the microfiber emission from the textile was reported by Kelly et al. [12]. The study compared different water volumes (300 and 600 ml) in the lower agitation (100 rpm) and reported a higher microfiber emission from textile. While comparing water volume and agitation, lower agitation with higher water volume released more microfibers from polyester textiles. This preferred wash cycle generally came under delicate wash cycles in European regulation and whereas in US norms, the delicate wash cycle is defined by its lower agitation and spin speed. The results pointed out that the higher water volume increased the overall hydrodynamic pressure applied to the textile which is the reason for higher shedding. This pressure applied to the fabric structure plucks the loose fibers due to the weakening of the yarn structure. It was also evident that this delicate cycle can also release more microfibers than the regular cycle, at least for the initial four washes. A delicate wash with more water volume released 800,000 microfibers higher than the normal wash. Though several researchers reported the impact of mechanical agitation increases the microfibers during the laundering of textile [23, 24], this research reported the importance of water volume [12]. The study also interpreted the results of Hartline et al., who reported the effect of the different washing machines. The results of Hartline et al. reported that the top load washing machine imparts more mechanical agitation and hence increased the microfiber release [20]. However, Kelly et al. reported the difference in water volumes in these machines (Top load consumes more water than front load) could also be a reason for higher microfiber shedding [12]. Similar research compared the different water volumes from 50 to 200 ml without altering the other laundry parameters. The results of the study reported a lower microfiber shedding at 50 ml (15.65 microfibers per sq. cm), whereas it increased to 166.6 microfibers per sq. cm at 200 mL. The statistical analysis reported a higher correlation between the microfiber release and the water volume in the laundry. The study reported that the viscous drag force applied to the polyester textile caused higher stress and released more microfiber in the higher water volume. The study showcased a significant difference in microfiber releases in terms of both count and mass [21]. Other researchers evaluated the effect of different wash load weights on the microfiber release. The study reported an increment in the microfiber release when the wash load mass reduced significantly. The higher wash load laundries shed 50% lesser microfiber than the lower load washes. The study mentioned that at the lower wash load higher water to fabric ratio was reported to impact the textiles and enhance the microfiber release. Hence the study suggested to going with a higher wash load over smaller washloads [19].

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4.2.4 Water Hardness Though water harness is one of the important parameters of the laundry process, as it influences the soaping and soil removal characteristics, studies on their impact on microfiber emission are limited. Studies performed by De Falco et al. compared the impacts of hard and distilled water on the microfiber release characteristics [16]. The results of the studies reported an increment in the microfiber shedding from textile, in presence of hard water compared to distilled water laundry. Though these changes were reported along with other few laundry parameters, researchers reported that the higher abrasive nature of the hard water on the textile was the main reason [16]. However, recently few researchers reported the impact of seawater on microfiber release from polypropylene-based tri-layer masks and reported an increment in the microfiber release [25, 26]. These studies measured the impact of seawater exposure on polypropylene nonwoven fabrics while it is improperly disposed of. They have reported that the higher density and dissolved contents in the seawater are the main reason for higher abrasiveness and relevant microfiber shedding. From the detailed results, it can be evident that each of the laundry parameters that are discussed above has its own influence. Out of all the results detailed, the impact of the water volume of the laundry appears to be a more influencing parameter, as it changes the level of interaction of the parameters largely. Several studies reported the negative impact of laundry temperature. An increment in the temperature increases the microfiber shedding and hence a lower temperature laundry is preferred for reducing microfiber shedding. The laundry duration and mechanical actions can be noted together. As the prolonged laundry process also releases microfibers similar to the shorter cycle laundry, it was evident that the impact of laundry duration is minimal. In the case of mechanical action, though the increase in mechanical action harmed the textile and increased microfibers shedding, then again, in the presence of higher water volume the effect diminished. Since many reports were not found on the effect of water hardness on microfiber shedding, a direct analysis may provide a better understanding of the impact.

4.3 Influence of Washing Additives 4.3.1 Use of Detergents The first research on the washing additives by relating it with microfiber shedding was performed by Napper and Thompson [6]. The study evaluated the microfiber release characteristics of polyester, acrylic, and polyester/cotton fabrics against different detergents namely bio-detergent, and non-bio-detergent. The results of the research demonstrated that the use of detergent has a significant impact on the microfiber release from textile. As far as the microfiber release is concerned, a higher release has been informed with the non-bio-detergents and a significantly lower amount of

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microfibers has been stated in the bio-detergent wash. The results of the control treatment (laundry without detergent) were also found to be in the range of bio-detergent results. Hence, the researcher reported use of detergents accelerates the microfiber release of synthetic textiles [6]. In a similar work, the polyester fabrics of different structures were laundered with liquid and powdered detergent, and compared with a controlled wash (de-ionized water without detergent). The results of the study showed different levels of microfiber release with liquid and powdered detergents. A significant increment was noted with samples which are washed with detergents (1273 ± 177 microfibers for liquid detergents; 3538 ± 664 microfibers for powdered detergents) than those washed without detergent (162 ± 52 microfibers). Among the detergents compared, the study reported a higher impact of powdered detergent than liquid detergent. The presence of inorganic compounds like zeolite is reported to have a strong effect on the fabric via surface friction. Further to add, the higher alkaline nature of powder detergent also impacts the fabric and generates microfiber. Hence the changes in the pH (in presence of powder detergent) and the impact of the organic content are the major differences between powdered detergent and liquid detergent. The pH shift also has a direct impact on the polyester fiber via alkalization. However, the results also reported that overdosing of detergent did not have any impact on the microfiber release characteristics of textiles [16]. The reason for the higher release of microfiber in the presence of detergent was justified by Almroth et al. [27]. The surfactant in the detergent was testified to have a higher impact on the microfiber release. The addition of detergent into the washing liquid reduces the surface tension of the liquid and thereby increases the wettability. This nature of the surfactant helps in the release of trapped fibers and broken fiber fuzz from the surface of the fabrics. As the main function of surfactant is to disperse and remove the dirt/stains from fabric, this ability of surfactant in the detergent also helps in the effective removal of microfibers from the surface of fabrics. Other researchers measured the effect of liquid detergent on the used polyester, polyamide, and acetate fabrics’ microfiber release behavior. The results exhibited a significant increment in the microfiber release of the fabric while washing with liquid detergent. Among the fiber types analyzed, a higher release was noted with amide and acetate than the polyester fiber. The researcher reported that an increment in the pH of the laundry liquid and the presence of surfactant in the detergent was the reason for the increment in microfiber release. As reported earlier, higher pH alkalize the synthetic textile and the use of surfactants causes the higher release of microfibers [17]. Similar results were also reported by analyzing the fleece and microfleece types of fabrics made of polyester, polyacrylic, and polyamide fibers. The study also revealed a higher microfiber release in presence of detergent than in the control sample [28]. The addition of detergent in the laundry increases the microfiber release by up to 86% than pure water. The study mentioned that the detergent usage loosens the textile structure for better cleaning and this might have enhanced the release of microfibers from textile [29]. Other researchers evaluated the effect of detergent use against cotton, polyester, rayon, and cotton/polyester blended fabrics and reported a statistically significant increment in microfiber release with the presence of detergent [18]. Figure 4.4 represents the effect of detergent usage on the microfiber release

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Fig. 4.4 The number of microfibers generated during accelerated laundering per gram of fabric washed. Effect of detergent used on the generation of microfibers at 44 °C. Error bars represent the standard error (N = 4, except for Polyester at 25 °C with N = 5). Significant differences are indicated by * (p < 0.05) (WOD: without detergent; WD: with detergent) (Reprinted with permission from [18])

characteristics of cotton, polyester, rayon, and cotton/polyester blended fabrics. Another study evaluated the effect of detergent on the denim material and reported that the addition of detergent increased the microfiber release from the textile. Researchers stated a higher impact of powdered detergent on the microfiber release, due to their higher chemical content and alkaline nature. The presence of detergent increased the microfiber shedding from 2,877,278 to 2,982,681 for liquid detergent and 3,275,154 to 3,743,691 for powdered detergent [14]. However, in contrast to the above studies, few researchers reported the insignificant effect of detergent or laundry additives on the microfiber release characteristics. A study measured the impact of detergent, detergent with softener treatment on microfiber shedding of fleece blankets. The study showcased a continuous reduction in the microfiber mass with an increment in the number of laundries. Hence, the researchers considered the mass after 8th–10th washes for analyzing the release behviour as long-term emission. In this case, a weight loss percentage of 0.00108% for the control sample and a weight loss of 0.00140%, 0.00124% for the laundry with detergent and detergent with softener were reported. Thus, the study exhibited an insignificant level of variation between the samples and suggested less impact of detergents [24]. Similar to this research, other studies also reported the effect of detergent as insignificant while evaluating the microfiber release characteristics against detergent pod (as per European washing conditions). The study suggested that the difference between the results of their study and previous studies might have been attributed to the type of washing machines used [19]. Like [24], this study also used domestic washing machines to

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analyze the shedding [19]. Whereas, studies that showed significant differences used laboratory-scale washing machines [15, 27]. In line with the abovementioned results, while analyzing the microfiber release characteristics of cotton, polyester, acrylic, and polyamide, Cesa et al. reported an insignificant effect of detergent [30]. Except for the cotton fiber, all synthetic textiles showed a lower microfiber release in the presence of detergent compared to the washing without detergent. In the case of synthetic material, the use of detergent increases lubrication and reduces friction, thereby reducing the microfiber emission. Whereas, in the case of hydrophilic cotton, the penetration of the detergent into fiber causes more release of fiber. However, the study did not show any significant difference in the release of microfibers with and without detergent. Researchers suggested that the effect of laundry machine type and other laundry parameters may be the reason for the difference in the results [30]. The other researcher measured the effect of liquid and powdered detergent on the microfiber release of textiles and reported that the type of detergents did not have an impact [15]. Similarly, the research of Kelly et al. also did not find the effect of detergent on microfiber release. The study measured the microfiber using tergotometer steel pots with bidirectional mechanical agitation and this might be the reason for the difference in the results. The authors also suggested the need for the further studies as their results were different from the previous results. On the other hand, study also reported that the higher microfiber release with detergent might also be an effect of steel ball in the lab-scale washing machine [12].

4.3.2 Use of Softener The use of detergent in laundry removes lubricants from the surface of the fiber and creates a hard, and scratchy surface. Thus, it creates an uncomfortable feeling for the wearer. Hence, the use of softeners in the laundry is often made to impart a soft and smooth feeling to the fabric along with fragrances. Technically, the use of softeners creates the antistatic properties on textiles by maintaining sufficient moisture in the case of synthetic textile, and thus it reduces static charge build-up [31]. Previous researchers related the pilling behavior of the textile with the use of conditioners and softeners. The use of such aids may increase the pilling characteristics of synthetic textiles [6, 32]. As the microfiber release behavior of textile is strongly connected with the pilling behavior, researchers evaluated the effect of fabric softener usage on the microfiber release characteristics. On the analysis performed against polyester, polyester/cotton blend, and acrylic fabrics, results showed an increment in the microfiber release with softener. However, the study did not conclude on the influence of fabric softener alone, instead, the combined effect with other parameters was reported [6]. A contradictory result was reported by Pirc et al. [24] while analyzing the effect of fabric softener on the microfiber release characteristics. The study reported that the use of detergent with softener did not show a significant effect on the microfiber release characteristics [24]. Another study measured the impact

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of fabric softener usage on the fleece fabric under different washing conditions as per the US and European regulations. The results of the research showed that there is no significant level of increment in microfiber release after the use of softener in both US and European conditions [19]. The impact of fabric softener treatment on the microfiber release characteristics of polyester fleece fabric is shown in Fig. 4.5 as reported by [19]. However, later researchers showed some positive effects of softener use on the microfiber release characteristics of textiles. A study analyzed the effect of softener and bleaching liquid on the microfiber release from textile. Results presented that the use of softener lubricates the fibers in the yarn and enhances the interfiber alignment within the yarn structure. Thus, it reduces the microfiber release characteristics.

Fig. 4.5 Effect of fabric softener on the microfiber release behavior of fleece fabric under a European and b USA washing conditions (Reprinted under creative commons license from [19])

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The study reported that the use of softener in the laundry process can significantly reduce the microfiber release by up to 35% than (400,000 microfiber/5 kg wash) the wash without the softener (600,000 microfiber/kg wash). However, a reverse effect was reported with the bleach. The study recommended further studies on bleaches while clearly defining the effect of softener [16]. In line with this, other researchers measured the effect of different commercial fabric softeners on the microfiber release characteristics on the rinse cycle (after wash) and during the wash cycle. The results of the research reported a microfiber release reduction of 64.71% with the use of a softener. As far as the usage is considered, using the softener during the wash cycle showed a significant reduction in microfiber release, whereas the usage during the rinse cycle did not show a significant difference in the microfiber shedding level. The high zeta potential of the polyester fabric in the wash liquor (alkaline pH) helps in the adsorption of softener on the surface and thus it protects the fiber from external force during the laundry. This was evident from the results, where softener added after laundry (rinse cycle) did not show reduction but added in the laundry showed a significant reduction. The results were similar for all the kinds of softeners used in the study. Further, the results also presented the effect of softener concentration on the microfiber release characteristics. It is noted that the softener concentration did not show any relationship with the microfiber shedding from textile and hence the study advised a lower concentration of softener by considering the negative impacts of fabric softener on fabric properties [21]. The effect of different softeners and treatment types on microfiber release characteristics of polyester textile is shown in Fig. 4.6. The use of detergent that has bleach and softener as components is also reported to show a reduction in microfiber emission from textiles [33]. A study performed by Zambrano et al. [34] with different finishes on cotton fabric showed the impact of

Fig. 4.6 Effect of different commercial fabric softeners and the usage method on microfiber shedding behavior of textiles (Reprinted with permission from [21])

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softener treatment on microfiber shedding. However, the results of the study mainly address the characteristics of cotton fabric, and no synthetic textiles were analyzed in this research. The results of the research exhibited that all the fabric released microfibers in the range of 9000–14,000 microfibers per gram of cotton fabric. Out of several finishes analyzed, a higher microfiber shedding was noted with softenertreated fabric (1.63 mg/g of fabric) than in the control sample (0.73 mg/g of fabric). Further, the research also reported that the fibers released from the softener finished fabrics are longer than those released from the control. The other finishes evaluated like durable press finish, and water repellent finish showed lower microfiber release and shorter length than softener-treated fabric. Researchers suspected that the variation in microfiber release is associated with the types of finishes imparted on textile. This was evident from the analysis of abrasion resistance properties where the softener-treated fabrics showed higher mass loss than other finishes. The use of softener in the cotton fabric generally reduces the coefficient of friction between the fibers by providing lubrication, hence, in the case of softener-treated textiles, due to higher lubrication, the fibers migrate to the surface of the textile structure and help in higher fuzz formation during laundry. Along with that, the reduction in the tensile strength and reduction in the elongation at break was also reported as the reason for higher microfiber release in the presence of softeners [34]. While analyzing the above results, it is evident that the common laundry additives like detergents and softeners are the most analyzed items concerning microfiber release from textile during laundry. As far as detergent usage is concerned, the majority of the researchers reported that the addition of powdered detergent aids in the release of more microfibers from synthetic textiles [6, 14, 16, 27, 28]. The presence of surfactant was reported to cause higher fiber release from the fabric. However, few studies reported contradicted results due to different reasons like quantification methods and types of laundry they adopted [12, 19, 24, 30]. Similarly, in the case of softener usage, some studies did not show much variation in microfiber shedding with the use of softener [6, 14]. Other researchers who counted the numbers of microfibers had reported a significant reduction in the microfiber release from textile with softener usage [16, 21]. But the studies reported the mass of microfiber showed an increment in the microfiber release along with softener usage [34]. The study itself mentioned that the higher length of the fiber release noted with the cotton fabrics and hence, the higher mass can be expected than control. Hence it can be evident from the analysis that the quantification methods adapted in the study also play a vital role in the analysis of microfiber emission characteristics of textiles.

4.4 Influence of Washing Methods As discussed in the previous section, the effect of the laundry method was reported as one of the main reasons for the difference in the microfiber release characteristics of textiles. Always there was a debate among the researchers that the use of laboratory-scale washing machines impacts more physical abrasion on the fabric

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than the household washing machines. Hence, this section addresses the effect of the type of washing machines on the microfiber release characteristics of textiles.

4.4.1 Top and Front Load Washing Machines The first study on the type of washing method on microfiber release characteristics was analyzed by Hartline et al. [20]. This study analyzed the effect of top load and front load washing machines on the microfiber release characteristics of 5 different men’s outerwear garments. The results showed that the top load washing machines can release a higher amount of microfibers (median of 1906 mg; n = 40) than the front load machines (median 229 mg; n = 30). The statistical analysis results exhibited a significant difference in the microfiber release with washing machines. Researchers suggested that the higher abrasive action in the top load machine might have caused a higher microfiber release from the apparel evaluated [20]. Later in 2020, Lant et al. [19] analyzed the effect of top load and front load washing machines on microfiber shedding. The study evaluated the microfiber release characteristics of textiles in European and American conditions. In European conditions, the study used a front load machine and in American conditions, they have used a top load machine (one traditional and one high-efficiency top load machine). The results of the studies showed that the traditional top load machines can generate a higher amount of microfiber than the high-efficiency top load machines. The study reported a reduction of 69.7% and 37.4% in microfiber release with high-efficiency top load machine respectively for the zip fleece and T-shirt. Though the study did not compare the microfiber quantity released in the European (front load) and American (Top load) conditions, the results show that American condition (both traditional and high efficient top load machines) always showed a lower shedding at laundry [19]. Similarly, Yang et al. analyzed the impact of platen and pulsator washing machines on the microfiber emission behavior of textiles [17]. The study used polyester, polyamide, and acetate fabrics in the analysis and reported that pulsator-type washing machines are more harmful to textiles in the case of microfiber shedding. Despite the higher release of microfibers from both the washing machines (in terms of mass loss), the pulsator machine showed a higher microfiber release in the range of 1.08-fold to 2.13-fold increment over the corresponding platen machine washing conditions [17].

4.4.2 Household and Laboratory Washing Machines Compared to household laundering machines, laboratory machines always impart a higher amount of mechanical action as it uses steel balls. While analyzing these issues by relating them to the microfiber release characteristics of textiles, Zambrano

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et al. reported that due to the intense mechanical actions provided by the laboratory washing machines/accelerated machines, a higher release was evident [18]. In specific, the amount of microfiber released in the accelerated washing machines was forty times higher than the household washing machines. However, there is a general agreement between the machines while the impact of fabric type and microfiber release quantity are considered. A higher correlation coefficient value of 0.8 was reported between fabric properties and laundry types (accelerated or home) indicating the dependability of the research results. On the other hand, while considering the uncontrollable parameters like large water volume usage, different water inlet, outlet paths, and complex washing compartments, the accelerated lab-scale washing machines are better for the quantification of microfibers [18]. From this view, it can be noted that, while analyzing the effect of detergent and softener usage, the type of washing machine processed had a higher impact on both the parameters. For instance, if we consider the studies that denied the impact of detergent and fabric softener on microfiber emission, they used domestic washing machines [6, 12, 19, 24, 30]. Whereas, in the other case that reported the impact of softener and detergent on microfiber release from textile mainly used laboratoryscale washing machines [16–18, 21, 27]. While considering these results, it can be interpreted that the impact of the laundry aids mainly varied depending on the mechanical action applied during the laundry. On the other hand, no such direct studies were performed as of now to quantify the difference experimentally. The absence of steel ball was often referred to as the main reason for the lower mechanical action of household laundry machines [20]. This was the main reason for the differences in the results. Hence these findings suggest the requirement for future research in this area. Further, standardizing such laundry processes will be necessary shortly as this pollution issue is emerging in a large magnitude in recent times.

4.4.3 Hand Washing Method Similar to the machine washing method, handwashing is also reported to be adapted in the laundering of textiles in several parts of the world. However, it can be seen that due to industrial advancement, a very minimal percentage of the clothes are handwashed nowadays. Hence, the number of research works that relate the process of handwashing with microfiber release characteristics is insufficient. While comparing the effect of hand wash and machine wash on the microfiber release characteristics of polyester textile, Tian et al. reported that the hand-washed polyester sample released less number of microfibers than that of machine laundry. The study used a top load washing machine from China and used it as instructed in the manual. The handwash process adapted was a consolidated detail collected from a survey. In this process, the fabric was soaked for five minutes and then transferred to laundry, where it was scrubbed 90 times with a wooden laundry board and rinsed three times before drying. The results of the research reported machine laundry can release up to 131,000 ± 168,000 n/items and in the hand laundry process with a median of 10,500 n/item

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for new clothes. Whereas, in the case of used clothes, similar results were reported with lower microfiber in handwash than the machine wash [35]. As far as the fiber length is concerned, a higher microfiber length was reported (average of 705 µm) in the case of hand wash than the machine-washed sample (average of 610 µm). This was true for both new clothes and used clothes. The researcher suggested the higher mechanical agitation in the machine wash as the main reason for higher microfiber release from textiles than the handwash. Additionally, the shorter fiber lengths in the machine laundered effluent confirm the higher mechanical agitation in the washing machine [35]. In another study, researchers used two different handwash methods to evaluate the microfiber release namely delicate and intense handwash. In both methods, the fabric was initially soaked in the water and laundered with detergent. The delicate wash used a gentle hand rubbing process whereas the intense wash used beating with a plastic rod and scrubbing with a washing brush in addition to hand rubbing. Later the fabric was rinsed, squeezed, and dried. The results of the hand wash were compared with the machine-washed (laboratory washing machine) samples. It is reported that the delicate washed samples released an average of 17.33 microfibers per square cm of fabric. Though the machine-washed samples showed a higher number of microfiber (18.06 microfibers/sq. cm) the results were statistically insignificant. In the case of the intense wash process, a significantly higher amount of microfiber (23.7 microfiber/sq. cm) was reported than machine washing. The soaking process and mechanical beating in the intense wash might be the reason for higher shedding in the handwash [21]. As not much research work was performed on this area, the results are still not comparable. As the results of previous researchers [35] highly differs from the latter research [21], the impact of the handwash must be explored further. From the analysis, we can see a large variation in the handwashing process, where one author used a small quantity of water whereas the other author used a large water volume. Similarly, imparting mechanical action is different and the quantification methods are also significantly different between the two research works. Hence, it is very hard to conclude from these studies, whether the hand wash method can reduce the microfiber shedding. We strongly suggest future research in this area and believe that the standardization of the handwashing process will be the apt solution to solve these issues. Figure 4.7 reports the factors that are influencing the microfiber release during the laundry process.

4.5 Effect of Repeated Laundry on Microfiber Release In the case of apparel, repeated laundering is a very common phenomenon. After every use or once after soiling of apparel, laundry is essential to remove soil or to maintain hygiene. Hence, repeated laundering of textiles is one of the unavoidable parameters. In this aspect, few researchers reported the effect of repeated laundry on the microfiber release characteristics. While evaluating the microfiber release characteristics, Napper and Thompson noted that for the first 3–4 washes a significant

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Fig. 4.7 Impact of different laundering parameters on microfiber shedding of textiles during laundry (Authors’ own illustration)

reduction in the microfiber weight released from textile. But after 4th wash, there is not many changes observed, hence the researcher used the quantity details obtained in the fifth wash [6]. Similarly, other researchers performed 10 consecutive laundry cycles and reported their findings agreed with the previous research [22]. In this study, researchers reported a higher microfiber release in the first three washes. It was noted that the presence of leftover and trapped fibers inside the fabric and yarn structures are the main reason. And hence, suggested that having an industrial laundry will reduce the impact in the user phase. Further, the study did not report any variations among different fibers (polyester, polyester/elastane, and acrylic) or structures (woven and knit). Cesa et al. [30] measured the effect of repeated laundry for consecutive 10 washes of cotton, polyester, acrylic, and polyamide fabrics. The results showed a declining trend in the microfiber release from the first to last wash. The results exhibited that the first three washes can shed around 53% of total microfibers from the apparel (maximum up to 76%). The lowest emission was reported with acrylic and a higher emission was reported with polyamide fabric [30]. Other researchers performed a similar kind of repeated washing on 100% polyester and cotton/polyester and

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modal/polyester blended fabric. In consecutive washes analysis, the results of 100% polyester fabric showcased a flat line after 4th–5th wash. However, microfiber release from blended fabric was noted to be strong even after 10 laundry cycles. Researchers suggested that the higher microfiber release from the blended textiles is mainly due to the presence of cellulosic fibers [23]. A decreasing trend was reported with the consecutive washes performed on 100% polyester, polyester/elastane blend, 100% polyamide, and acrylic fabrics. The emission value of the fifth wash is reported between 1.9 × 104 and 1.9 × 105 per kg [36]. Only less than 20% of the fiber was noted from the fifth wash onwards. Other researchers reported the effect of the washing cycle with 12 different polyester samples. The study performed 10 repeated washes and the results reported a reduction in microfiber emission with the increase in the wash cycle. A major release of fiber was reported in the first three cycles of washing than in the other washes. 6–120 times higher microfiber release was noted in the first wash than in the 10th wash cycle. There was a very less number of fibers released after the 10th wash which was lower than the laboratory blank sample. Similarly, the researchers also reported shorter microfibers on initial washes than on the 10th wash cycle. The study evidenced a 30–90% microfiber release in the first wash. Cotton et al. believed that even after the 6th and 8th wash there is a quantifiable amount of microfiber released from textile and hence urged to understand the mechanism of microfiber release from textile [13]. Though researchers believed that the higher initial release of microfiber from textile is due to the trapped fibers inside the structure during manufacturing, studies did not explain the variation in the release quantities among the various products [37].

4.6 Impact of Drying Method/Laundry Dryer Studies also reported that laundry dryers also can potentially shed more amount of microfibers than the washing process. A study evaluated the microfiber release characteristics of household laundry dryers in the USA. In this research, researchers used a brand new blanket, however, instead of the washing process the blankets were soaked in the water without agitation and squeezed to remove water. The wet blankets were dried using a home dryer and the study was performed at two different locations of different altitudes. The results of the study reported that an average of 404 ± 192 microfibers were collected from 14 different sampling plots of site 1 and 1169 ± 606 microfibers at site 2. The study evidenced that the lint fibers released from the dryer vent can travel up to 30 feet in the environment. Despite most of the microfibers located in the sampling sites closer to the vent, a significant reduction was noted in the microfiber count at 10, 15, and 30 feet sampling locations. The study reported that the fiber distribution is mainly dependent on the wind direction and also the type of dryer used. This was also evident from the results that the dryer at site 2 collected less lint than at site 1 due to the structure of the lint trap in the dryer. This result indicated that the household cloth dryers used in the laundry may emit a huge mass of fibers into the environment/atmosphere than the household laundry process [38].

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Fig. 4.8 Laundry dryer and microfibers obtained from the dryer filters (Images reprinted under creative commons license from [38]

Figure 4.8 represents the microfibers identified location from the household dryers as reported by [38]. Other researchers reported the drying of 100% polyester fleece fabric in a home dryer using normal day drying mode. The fabric was initially washed 5 times in a normal laundry and used for the drying experiments for 20 min as fixed in the drying program. Air-borne samples were collected and analyzed for the emission of microfibers from the dryer. The results of the research showed that for every cubic meter of the air in the room, 1.6 ± 1.8 microfibers were reported from the collected sample after normalizing the results. The average length of microfibers from the samples was reported as 764 ± 940 µm. In contrast to the previous researchers who reported that the repeated laundering process reduces the microfiber release [15, 24, 27], the results of this study reported an increase in the microfiber count in the atmosphere while increasing the laundry cycles. Though no studies reported the atmospheric microfiber contamination with the laundry process, the results were contradictory. Researchers suggested that the higher mechanical damage that occurred during consecutive laundry might be the reason for higher atmospheric microfiber in the samples that are dried after laundering repeatedly. The study suggested a 660 g polyester blanket to shed 77 mg of lint and it is 1.1 ± 0.3 × 106 fibers in the filter. It was also estimated that 54 ± 60 fibers would be released into the atmosphere which is approximately 2 fibers per cubic meter of atmospheric air. The study predicted that washing and drying one such blanket could emit 3 × 103 fibers in the atmosphere and a 6.5 kg of such load could emit 406,468 airborne fibers per wash load [39].

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Other studies also reported that tumble dryers, both household and industrial tumble dryers can emit a significant amount of microfiber into the atmosphere. As the vented air was not filtered or treated, the microfibers directly enter the environment. Though no research was performed on the industrial scale dryers and their microfiber emission, the effect is not negligible. Further to complicate the situation, the emitted microfibers will float inside the room and be inhaled directly by the residents. The study used a household tumble dryer and measured the release of microfibers. For polyester textiles 270 ± 30 microfibers were released and for cotton 165 ± 27 microfibers were released in the 15 min drying process. The study estimated that one kg of polyester fabric can emit up to 93,635 ± 17,026 microfibers and cotton fabrics can release up to 72,188 ± 11,813 microfibers in 15 min drying. The results also showed that the microfiber release from the dryer is significantly higher than the washing machine emission. It was predicted that 6–7 kg of laundry drying can release 433,128 ± 70,878 (6 kg cotton textiles) and 561,810 ± 102,156 (7 kg polyester textiles) microfibers per 15 min drying cycle. As the number of microfibers emitted into the environment, it could be potentially inhaled and ingested by living animals and humans [40]. Previously, Pirc et al. [24] evaluated the effect of washing and drying on microfiber release. By treating six 100% polyester fleece fabrics for ten subsequent washing and drying processes, they analyzed the microfiber shedding. A reduction in microfiber emission was noted with an increase in the drying cycle. Approximately 200 mg/kg of fibers were collected in the first drying which was subsequentially reduced to 61 mg/kg in the fifth wash. A mass of 34 mg/kg of fabric dried was collected in the tenth drying process [24]. Other researchers compared five different fabrics structures on the microfiber release characteristics of washing and tumble drying. As similar to laundry, an increase in the number of drying processes also showed a reduction trend in microfiber release. The quantity of the fiber released after the fifth cycle of drying was noted as a plateau. Based on the fabric type, 100% polyester fabric emitted 340– 1700 mg/kg of fabric processed. Whereas acrylic fabric released 140 mg/kg of fiber and polyamide released the least mass in the first wash with a value of 10 mg/kg of fabric. When the machine washes to tumble drying ratio was calculated, a higher ratio of more than 1 was noted for polyester and polyamide t-shirts, which represents that these fabrics emit more fibers in the laundry process. Whereas, all other samples shed more microfiber in the tumble drying process; The researcher reported that either the detachment of loose fiber on fabric surface or breaking of fibers during laundry was a major reason for higher microfiber release in the tumble drying process. The stress imparted on the fibers in the structure further forced them to break off from the fabric during the drying. A higher length of microfibers reported with polyester fleece fabric and other materials like polyamide showed to release shorter fibers [36]. The serious issue with the laundry dryer emission is that the fiber released from these processes will not end up in the wastewaters. Instead, those fibers are directly emitted into the atmosphere without any filtration. Further, the fate of the trapped fibers inside the filter is also unknown. As the customer may discard it with domestic waste or sewage it again reaches the environment in a very short time.

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4.7 Estimation of Microfiber Release from Domestic Laundry Worldwide Boucher and Friot analyzed the global impact of synthetic microfiber emission in their research report. The results of the report showed a median value of 1.5 metric tons/year of microplastic will be released into the ocean and 3.2 metric tons/year into the environment from textiles. Asia, Africa, and the middle east are the primary source of microplastics. These regions share larger synthetic clothes than the global average. At the same time, the population and wastewater treatment facility connections were also found lower, meaning that, a significant lack of facilities. Whereas, in the case of America, Europe, and Central Asia, microplastic pollution is dominated by tires as they travel a lot compared to the rest of the world. As of 2010, the per capita consumption of textiles and apparel is 11 kg (69.7 million tons globally). 60.1% of total consumption is contributed by synthetic textiles, which is approximately twothirds of total consumption. The world’s synthetic fiber consumption exponentially increased to 300% in the last decade due to their cheaper cost. Developing economies buy a large volume of synthetic clothes than developed economies with a global consumption average of 6.1 kg per capita. In the case of microfiber release from synthetic textiles are concerned, all regions of the world contribute significantly. A major contribution of 18.3% was reported from India and South Asia, followed by North America, Europe, Central Asia, and East Asia, with a contribution of 17.2%, 15.9%, 15.8%, and 15.0% respectively [41]. As the previous section detailed the different individual parameters, few studies predicted the total emission for a complete laundry to estimate the environmental impact. The complete list of such estimations was provided in Table 4.1. From the consolidation, it can be seen that the initial predictions are very low, and the total number of microfiber counts increased over time due to the development of several advanced quantification techniques and scientific approaches. The first report on microfiber emission was analyzed and reported as low as 1900 microfiber per garment per wash [1]. Due to the filter media cut-off size and other quantification processes, the microfiber count reported was low. Whereas, in the latter stage, Napper and Thompson evaluated various laundry parameters on polyester, acrylic, and polyester/cotton garments on microfiber shedding [6]. The study used improved quantification techniques to analyze the count and reported a significantly higher microfiber emission per 6 kg of (a full load of a commercial washing machine) laundry than the previous research report by Browne et al. [6]. While evaluating the microfiber shedding from textile they have reported an emission of 0.0012 wt% of total fabric used. Based on this weight, for a city with a 2 million population, they have reported an emission of 144 kg per year by considering the washing of one blanket (350 g) and one fleece jacket (500 g) per person [24]. Libaio Yang et al. compared the microfiber contamination in the laundry effluent with the typical sewage treatment plant effluent and reported 20-fold higher microfiber contamination in the laundry effluent while washing polyester fabrics than in the normal sewage treatment plant effluent. In the case of acetate fabric

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Table 4.1 Summary of global estimation of microfiber release from domestic laundry process from literature References Type of fabrics used

Parameters analyzed

Major influencing Estimated impact parameter/important findings

Type of washing Machine

• All garments released microfiber • Fleece garment shed 180% more fibers

A single garment can shed more than 1900 microfibers

[1]

Polyester blanket, fleece, and shirt

[6]

100% polyester, • Washing 100% acrylic, and temperature polyester/cotton • Use of Detergent garments • Use of softener

Polyester cotton fabric shed lower fiber than Polyester and acrylic fabric

6 kg wash load of polyester-cotton release 137,951 microfibers, polyester release 496,030 microfibers and acrylic releases 728,789 microfibers

[24]

Fleece blankets

• Use of Detergent • Use of softener • Use of washing machine • Impact of drying

Every laundry releases 0.0012% of total weight as microfiber

Washing of a blanket and Fleece jacket will release 144 kg of microfiber per year for 2 million inhabitant city

[20]

Synthetic fleece jackets

• Garment aging • Type of washing machine

The top load washing machine can release 7 times higher microfiber than the front load washing machine

• A population of 100,000 people would produce approximately 1.02 kg of fibers each day • Laundering twice a year (synthetic jackets) will release 78–428% of microfibers to sewage treatment plants

[27]

Polyester, polyacrylic and polyamide fabrics

• Use of detergent • Repeated laundry

Polyester fleece fabric can shed more amount than normal polyester fabric

Around 1m2 of fabric is used for a garment for adults and that could release approximately 110,000 fibers (continued)

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Table 4.1 (continued) References Type of fabrics used

Parameters analyzed

Major influencing Estimated impact parameter/important findings

[44]

100% polyester aged and new T-shirt

• Repeated laundry • New and aged garment

Aged garments shed A single wash can 1.6 times more release 225,000 microfibers than the microfibers new garment

[17]

100% Polyester and 100% polyamide fabric swatches

• Washing temperature • Use of detergent • Type of washing machine

[23]

100% polyester garments (Blue T-shirt and Red T-shirt)

[12]

100% polyester T-shirt

• Use of detergent • Laundry temperature • Water volume • First wash and repeated laundry

Water volume has the highest impact on microfiber release over other parameters

A delicate cycle with higher water volume release 800,000 more microfibers than a normal wash

[42]

100% polyester garments

• Textile parameters • Microfiber emission to wastewater and air

Lowest emission of microfiber noted for woven fabric with compact structure, filament yarn, and highly twisted yarn

A year of laundry release 2.98 × 108 microfibers to wastewater and 1.03 × 109 microfiber to air

[30]

Cotton, polyester, polyacrylic, and polyamide garments

• Use of detergent • Use of repeated laundry

Use of pre-wash, potential filter, and detergent can reduce up to 53% microfiber release

18.3 thousand and 12.5 thousand tons of microfibers release from cotton and synthetic garments respectively per year globally

• Acetate fabric released more fibers • Increase in temperature increased the microfiber shedding • Use of detergent increased the release • Effect of first • First wash wash and released 125.0 ± repeated laundry 32.1 mg/kg and • Fabric 124.1 ± parameters 12.4 mg/kg of microfibers for respectively Blue and red garments • Subsequent cycle showed reduction in release but no plateau achieved

1060, 929.5, and 418.6 tons per year respectively for polyester, polyamide and acetate

For every kilogram of fabric washed, 640,000 to 1,500,000 microfibers released

(continued)

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Table 4.1 (continued) References Type of fabrics used [37]

Knit and woven fabric samples with different fiber types

Parameters analyzed

Major influencing Estimated impact parameter/important findings

–

A single laundry can • An average shed > 6,877,000 household to microfibers generate 22 Fleeces and jerseys kilotons of fiber released six times per year in US more microfibers and Canada than nylon samples • Cumulative annual emission with woven in Canada and construction the U.S.A is estimated as 878 tons of microfiber

and polyamide fabric an increment of 150, and 200 fold is expected respectively. The study also predicted that 20–34.8% of the microplastics are originated from the textiles due to the higher global consumption. The researcher estimated that based on the different types of washing machines the microfiber release will vary and for a platen laundry machine, polyester, polyamide, and acetate fabric may shed 636, 660, and 232.3 tons per year respectively. In the case of pulsator laundry, it was estimated to release 1060, 929.5, and 418.6 tons per year respectively for polyester, polyamide, and acetate fabric [17]. In the case of different washing condition analyses, Lant et al. reported that due to the nature of water consumption, European washing conditions were found to shed less amount of microfiber per laundry compared to US conditions [19]. Other researchers took some assumptions on the number of washing loads per year and individual polyester clothing usage per day and predicted the microfiber emission into the washing effluent and atmospheric air. The study results exhibited that a single person can emit 2.98 × 108 microfibers to water due to the repeated washing and 1.03 × 109 to atmospheric air during wearing per year [42]. Whereas other researchers developed a model to estimate the microfiber release to the environment due to domestic laundering worldwide by considering different key factors namely the microfiber detachment rate from different textile materials, type of washing machines being used, the volume of laundry effluent released, the percentage of municipal wastewater that is being treated, the method used for the treatment. The developed model reported 0.28 million tons of microfibers to be released into the aquatic environment per year through domestic laundering of textiles worldwide [43]. Other recent studies also reported similar amounts (sometimes relatively higher) of microfiber release from the textiles samples and predicted the global impact [30, 37]. However, due to the lack of standard estimation methods and procedures, a lot of differences among the researchers were noticed. However, the impact reported by the researchers is alarming and enlightens the importance of taking necessary action globally.

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4.8 Wastewater Treatment Plant (WWTP) as a Secondary Source of Microfiber Pollution 4.8.1 Impact of WWTP Effluent As discussed in the previous section, the laundry process is one of the prominent sources of microfiber pollution in various environments. The role of municipal wastewater treatment plants (WWTP) in the microfiber emission is important as the laundry effluent reaches WWTP through sewage. Despite their higher treatment efficiency, the WWTP was unable to eliminate the microfibers completely from the effluent. Hence several researchers predicted that the effluent released from WWTPs acts as a secondary source of microfiber emission into the environment. A study that evaluated the microplastic pollution in the Columbia River has reported higher microfiber abundance in few spots of the analysis. A detailed evaluation exhibited the use of effluent from WWTP in the nearby agricultural land for irrigation purpose as the main reason for the higher abundance of microfiber in those spots [45]. Whereas other studies correlated the human population with microfiber pollution and they have reported the impact of human population density on microfiber contamination, through WWTP effluent [46]. The first research on the microplastic contamination in the WWTP effluent was performed by Talvitie et al. [47]. The study reported that the primary sedimentation process was the main process to remove microplastics from the effluent. The results of the study reported that after a significant amount of removal, the effluent water contained 8.9 plastic particles per liter of wastewater released [47]. Other researchers reported a greater reduction efficiency of WWTP (98.4%) which reduced microplastic content from 15.70 microplastic/liter in the influent to 0.25 microplastic/liter in the effluent. The study reported a higher abundance of microfiber in the wastewater treated. A major contribution of polyester followed by polyamide and polypropylene was reported [48]. Figure 4.9 represents the different pathways of microfibers in domestic laundry and industry effluent to reach the environment through WWTPs. Other researchers also reported a higher removal efficacy of the WWTP in the US. The study concluded a very minimum quantity of microplastic, approximately 1 microplastic per 1.14 thousand liters of final effluent [5]. In contrast to the previous results, a study analyzed the effluent from 17 different WWTPs and showed a release of 4.4 × 106 microplastics per day per WWTP, despite higher removal efficiency. Though the microplastic content per liter is found lower, due to the sheer amount of wastewater treated in the WWTP, a higher quantity of microplastics is released into the environment. The study also mentioned that a higher contribution of microfibers (59%) in the effluent [49]. Since most of the WWTPs evaluated in the studies used 2 step treatment methods namely, primary and secondary, the impact of the tertiary treatment process was evaluated and reported by Talvitie et al. [50]. The results of the study reported a higher removal of microplastics while using the membrane bioreactor method. Out of several methods evaluated, they mentioned the membrane method as effective in the removal of microplastic from effluent

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Fig. 4.9 Pathways of microfibers in domestic laundry and industry effluent to reach the environment

from 6.9 microplastic/liter to 0.005 microplastic/liter [50]. One of the latter research analyzed the effluent from 12 WWTPs from Germany and detailed a higher number of microplastic in the effluent (1 × 101 to 9 × 103 microplastic per m3 ) than the previous research works [51]. However, similar to other studies, these results also reported a higher contribution of microfibers than the others shapes. Gies et al. evaluated the WWTP in Vancouver, British Columbia, Canada, which treats approximately 180,044 million liters/year. The study measured the microplastic contamination in the influent, effluent, and sludge discarded. The results showed higher domination of microfibers (65.6%), followed by fragments (28.1%) and pellets (5.4%). As far as the microplastic counts are considered, the higher removal efficiency (91.7%) was reported in the primary clarification process; 31.1 ± 6.7 microplastics per liter of influent water was reduced to 2.6 ± 1.4 microplastics per liter in the effluent. The primary sedimentation and secondary treatment reduced the microplastic further and the effluent wastewater was reported to carry 0.5 ± 0.2 microplastics per liter. Out of this, 60% of the particles are fibers. Based on this data the study predicted a release of 0.1–0.3 billion microplastics/day from the WWTP that was evaluated [52]. Other researchers measured the microplastic content in the sampled wastewater from 10 different largest WWTPs in Denmark. The study reported a medium microplastic concentration of 7216/liter in the influent water and 54 particles/liter in the effluent water. The researchers reported a high variation in the microplastic count than in the literature, and this might be due to the size variation considered in the measurement or quantification. The study also reported that the suspended solids in the wastewater and microplastic contamination do not correlate. While analyzing the polymer types, polypropylene (34%) was the major polymer type reported followed by acrylic (27%), polyester, and polyethylene. As a whole, the study reported that as a sum, all WWTP effluent can release 3 tons of microplastic/year in Denmark

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alone. While correlating the population, it was reported that the Danish WWTP can emit 0.56 g of microplastic per capita per year. The removed microplastics in the WWTPs (in the form of sludge) are mainly applied to agricultural purposes (70%) and energy recovery (30%). In this aspect, it was approximately 188 tons of microplastic per year reaches the terrestrial environment [53]. Similar research was performed with the largest WWTP in Italy, which is capable of treating 400,000,000 L/day. The study analyzed both microplastic and microfiber contamination separately and reported 0.3 ± 0.1 microplastics per liter in the effluent water compared to the influent (2.0 ± 0.3 microplastics per liter). Whereas in the case of microfiber, the count is reduced to 0.10 ± 0.03 microfibers per liter from an inlet value of 0.5 ± 0.1 microfibers per liter. The total reduction efficiency of 84% was reported while comparing the influent and effluent wastewater. For the total inlet water and the given efficiency, the study estimated that the WWTP can emit approximately 160,000,000 microplastics per day. In the effluent water, the prominent shapes noted are lines (41%), films (38%), and fragments (21%). In the case of microfibers, 89% of the fibers released in the effluent are reported as polyester [54]. Another study conducted in Wuhan, China estimated the wastewater from a WWTP that mainly handles the effluent from the residential area (with a capacity of 20,000 m3 ). The study collected effluent in the different treatment processes namely inlet sample (W1), primary sedimentation outlet (W2), secondary sediment tank outlet (W3), and final effluent outlet (W4). The results reported that WWTP showed a microplastic reduction efficiency of 64.4% and the microplastic content reduced to 28.4 ± 7.0 microplastic per liter in the effluent from 79.9 ± 9.3 microplastics per liter of influent. It was noted that in the successive treatment, the size of the microplastic was reduced to 348.2 µm (at W4) from 571.5 µm (at W1). Among the total microplastics reported, a higher contribution of fibers and fragments was reported in the final effluent. As far as the polymers are concerned, polyamide was the highest contributor (54.8%) followed by polyethylene and polypropylene respectively with a contribution of 9% and 9.6%. Hence based on the findings of the study, microfiber emission from the household laundry is the main source of these polymers and fibers [55]. Effluents from 11 different WWTPs in Changzhou, China were analyzed and reported by Xu et al. [56]. The WWTPs analyzed had 52% of the water from households and 48% from the industrial processing (mainly Textile printing and dyeing wastewater, chemical industry wastewater, slaughterhouse). The results reported an average of 196.00 ± 11.89 microplastics found in the influent water and in the effluent it was reported between 3.63 ± 0.46 and 13.63 ± 2.63 microplastics per liter. All the WWTPs showed higher removal efficiency (more than 90%) in the process. Out of the total microplastics reported, fibers were the most abundant shape followed by other shapes with smaller fractions. Rayon, polyester, polypropylene, polyethylene, and polystyrene are the most common polymer types reported in the study. The domestic laundry and textile wet processing industry were reported as the main sources of microfiber contamination in the wastewater [56]. Recent research analyzed the emission of microplastic from three different WWTPs of turkey into north-eastern Mediterranean Sea. The study collected the wastewater sample from both inlet and outlet waters of all three plants for one year at one-month intervals and

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reported the microplastic contamination in the effluent. The results of the research reported a 57% of overall removal efficiency of the three WWTPs. From the total samples collected, the study reported 2584 microplastics in the influent sample and 1041 microplastics in the effluent. During the complete year of study, no distinguished pattern of removal was reported. A higher number of microplastics were reported in the summer. As a whole, 69.7% of the microplastics are reported to be microfibers. Interestingly, an increment in the number of hard plastic particles was reported in the effluent, whereas a reduction was reported in terms of microfibers. Polyethylene and polypropylene are the major polymer types reported in this study. On an average, 0.6–1.6 microplstics/liter was reported in the effluent. While several research studies appreciated the removal effeciencies of tertiary treatment process, one of the WWTPs showed a poor microplastic removal efficiency with tertiary treatment (38%) than the WWTPs with secondary treatment process. Based on the microplastic emission quantity, the study predicted that a sum of 277.3 million microplastics can be released into the Mersin bay in daily basis and it is equal to more than (>) 100,000 million microplastic per year [57]. Bayo et al. reported the wastewater removal efficiency of WWTP located in Spain. The results showed that with a 64.26% of removal rate, the final effluent contained 0.98 ± 0.27 microplastics per liter. The microfibers were reported to be the most prevailing shape (79.65%) followed by the film (11.26%) and fragment (9.09%). In the case of polymer types, polyester was the most abundant type. The study also reported that the removal efficiency of the microfibers in the WWTPs is still noted to be lower than other types of microplastics. The study reported a daily emission of 1.6 × 107 microplastics from the WWTP via effluent [58]. In a similar study conducted in Saskatoon WWTP, Saskatchewan, Canada, results showed a higher contribution of microfibers (82%) out of total microplastics found in the effluent wastewater. The effluent from WWTP contained 1.76 microplastics per liter, however, due to the large quantity of effluent discharged (80 million liters per day), the WWTP alone can release approximately 141 million microplastics/day into the water sources [59]. While analyzing the effect of different treatment processes on the microfiber removal efficiency, Xu et al. reported 51.04% and 72.82% reduction after the primary and secondary treatment processes [60]. The study reported a 51.04% and 72.82% reduction after the primary and secondary treatment processes. Where the microplastic count reduced to 349.33 ± 17.28 from 1111.33 ± 45.76 microplastics/liter after primary treatment and 226.67 ± 28.11 from 435.33 ± 58.45 microplastics/liter after secondary treatment. The tertiary process removed more than 90% of microplastics in the wastewater. The microplastic count in the final effluent was reported as 15.22 ± 4.87 microplastics per liter and concluded that the tertiary treatment process was efficient in the removal of microplastics [35]. Most recently a study analyzed three WWTPs in Danang city, Vietnam. The results showcased a higher abundance, of microplastic even after the treatment process. The effluent water contained a microplastic abundance of 138–340 microplastics/liter, in which fibers were the most found shape in both the influent and in the effluent as shown in Fig. 4.10 [61]. The study reported the dominance of polyethylene, polyester, nylon, and polypropylene polymers as a representation of textile materials. From the three

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Fig. 4.10 The occurrence of microplastic shape in the influent and effluent of three different WWTPs (Reprinted with permission from [61])

WWTPs studied the results showed emission of microplastic in the range of 3.8 × 107 to 1.5 × 10 9 microplastics per day [61]. Other studies detected a seasonal variation in the microplastic abundance on the WWTP effluent. During the two-year study, a higher microplastic content of 76–1925 microplastics per liter was reported in the dry season. Whereas in the wet season, 36–68 microplastics per liter were reported with a significant difference in the year 2019–2020. Polypropylene and polyethylene are the major polymer type reported in the study [62]. From the above-discussed results, it can be noted that though the WWTPs have a higher potential in removing established pollutions like biological and chemical oxygen demands, and dissolved and suspended solids, their effectiveness in the microplastic removal was reasonable. Out of these findings, microfiber removal efficacy was reported to be less than microplastic removal [58]. The findings of studies revealed that the fibers are found to be the major contributors that originated from textiles [7, 54, 57–59, 63]. Fragments, films, lines, and spheres are the other contributed shapes reported in the analysis [5, 7, 48, 64]. Likewise, studies reported a better removal of microplastics with the tertiary treatment process [63].

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As far as the polymer types are concerned, polyester, polypropylene, polyethylene, polyamide, and acrylic are the major contributors [58]. Meanwhile, one of the recent reviews analyzed the publications in this area up to October 2020 and found 77 suitable papers from various scholarly databases like Web of Science, Scopus, and PubMed. From this analysis, they have reported a range of 1–31,400 microplastics/liter in the influent stage, 0.2–12,580 microplastics/liter in the primary treatment outlet, 0.002–7863 microplastics/liter in the secondary treatment outlet, and 0.003– 447 microplastics/liter in the final effluent from the tertiary treatment process. The average abundance was reported as 124.04, 20.67, 5.623, and 1.9 microplastics per liter of wastewater from influent, primary, secondary, and tertiary treatments [65]. From these findings, it can be evident that after the WWTP process a large number of microplastics are released into the environment. Hence, the addition of suitable removal methods or treatment processes by considering the microplastic size and source of influent water must be a helpful solution to save the environment. Recently one of the research reports mentioned that the addition of advanced technology in the tertiary treatment system will enhance the microfiber removal efficiency. In this research, the use of the ultrafiltration method was demonstrated as a useful method for the removal of microplastics. In the conventional process, with 86.14% removal effectiveness, the WWTP effluent contained 10.67 ± 3.51 microplastics per liter. After the ultrafiltration process in the tertiary treatment, the microplastic count was reduced to 2.33 ± 1.53 microplastic per liter with 96.97% removal efficiency [66]. Hence, research on such initiatives will be of great help in saving mother nature from microplastic and microfiber pollution and their subsequent impacts.

4.8.2 Impact of WWTP Sludge In the effluent treatment process, once all the wastewater was removed, the remaining solid mass was further treated within digesters, thickeners, dewatering process, and then dried as a solid. Due to its valuable content, the sludge obtained from municipal WWTPs used in several land applications including agricultural purposes. In all the way it ends up in the terrestrial environment. As far as the dried sludge was considered, it is expected to have higher microplastic content than the effluent water, as most of the removed microplastics will be sediment in the solid waste. Hence, it is believed that the sludge is a higher contributor than the effluent. As microfiber and plastic pollution is understood in the past decade, currently very few research details are available on this matter. An extensive analysis of the microplastic contamination on the WWTP sludge was reported by Mahon et al. [67]. In this study, sludge was collected from seven different WWTPs and the microplastic content was evaluated. The results reported the presence of 4,196 to 15,385 microplastics per kilogram of dried sludge. Out of the total particles collected, 75.8% of the microplastics are microfibers followed by fragments, films, articles, and spheres. As far as the polymers are concerned, high-density polyethylene, polyester, acrylic, polyethylene terephthalate (PET), polypropylene, and polyamide were reported [67]. Another study

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collected dewatered sludge from 28 WWTPs in 11 different provinces of China and analyzed for their microplastic contamination. The results of the study reported an average of 22.7 ± 12.1 × 103 microplastic particles per kg of dry sludge. The study confirmed the presence of a higher concentration of microplastics in the sludge than in the effluent. Fibers are the most dominant type of shape reported (63%) followed by shafts (15%) and films (14%). As far as the special distribution of the microplastics are concerned, the study reported a higher microplastic concentration in the sample sites with higher population density and vice versa. The study reported that approximately, in China alone 8 million tons of dry sludge has been generated in 2015, out of which 83.6% sludge are disposed improperly and 2.6% goes as land or agricultural application. Hence, through this process approximately 1.56 × 1014 microplastics can be emitted into the environment in 2015 alone [68]. Gies et al. analyzed the WWTP in Columbia and reported that the primary sludge had higher microfiber abundance with a count of 9.7 ± 3.7 microfibers/g and other microplastics (5.2 ± 2.9 microplastics/g). The secondary sludge also had a higher fraction of fibers (3.6 ± 2.5 microfibers/g) followed by microplastics (0.9 ± 0.3 microplastics/g). In the microplastics counted, fragments and foams are the major shapes reported. Based on the analysis, this particular WWTP alone can emit 1.28 ± 0.54 trillion microplastics (per year) into the environment via primary sludge and 0.36 ± 0.22 trillion microplastics (per year) with secondary sludge. While analyzing the effluent from WWTPs, Magni et al. also evaluated the microplastic content in the dry sludge [54]. The study measured both microplastic and microfiber content in the dry sludge that was removed from WWTP. The results reported 59.5 ± 21.6 microplastics/g and 53.3 ± 48.9 microfibers/g of dry weight of sludge. Hence a total of 113 ± 57 microplastics/gram of dry sludge was reported. In the case of microplastics, films are the major contributors (51%) followed by fragments (34%) and lines (15%). Among these shapes, the acrylonitrile-butadiene polymer was the most abundant type (27%). Whereas, in the case of microfibers, 35% of total fibers represented synthetic, mainly polyester, and the remaining fibers belong to natural origin. The analyzed WWTP can release 30 tons of sludge (dry) per day and hence the WWTP can release 3,400,000,000 microplastics per day through sludge disposal. Based on the results, the study reported that the WWTP plant can release 3,560,000,000 microplastics per day [54]. A conventional activated sludge process treated effluent and sludge from China was reported for their microplastic contamination by Liu et al. [55]. The mechanical erosion and sedimentation process performed in the WWTPs helps to remove the microplastics from wastewater and hence a higher amount of microplastics entrapped inside the sludge. From the results, after 64.4% removal efficiency, the WWTP released 28.4 microplastics/liter of effluent. But the microplastic concentration in the sludge was reported to be 240.3 ± 31.4 microplastics per g of dry weight. The study reported that a major fractions of microplastics found in the sludge are fibers (56.7%) fand fragments (45.6%) [55]. In another study, one of the largest WWTP from Beijing, China was analyzed for microplastic content in their sludge. The results reported an average of 4044 ± 1359 microplastics/kg of dried sludge. Pellets and microbeads were the most abundant type noted in the sludge. If total WWTPs in Beijing can release 18 × 104 tons of

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sludge per year, then the WWTPs alone can emit 7.28 × 1011 microplastic per year into the environment. Researchers reported that 80% of the sludge is used in land applications as fertilizer. Hence approximately 5.82 × 1011 microplastics will end up there. The researchers fear that the continuous application of such sludge in the soil will alter the properties of the soil over time and it will accumulate into the deep soil via earthworms. The effects of these property changes will be reflected in the plant growth. Though complete knowledge of the microplastic impact on soil or land application is limited, it is better to avoid such contamination [69]. A study performed in Iran, evaluated the microplastic content in the sludge samples obtained from different treatment stages of WWTP namely primary settling tank (1), clarifier (2), after sludge thickener (3), after aerobic digester (4), and mechanical dewatering unit (5). The results reported that approximately, 214 ± 16, 206 ± 34, 200 ± 13, 238 ± 31, and 129 ± 17 microplastics/g of dry sludge was reported in the respective samples obtained from site 1 to 5. 85% of the total microplastic found in all the samples were reported to be fibers. Polyester, polyethylene, polypropylene, and polyamide are the dominant polymer types reported where the fibers are mostly made of polyester and polyethylene. The study compared the microplastic reduction at a different stage and reported that the dewatering process of sludge along with aerobic digestion plays a vital role in the microplastic reduction. Compared to the first stage, a 54% reduction in the microplastics was reported with the final sludge, however, based on the large volume produced it aids a large number of microplastics into the environment. The study reported the lifestyle of the people as the major source of microfibers in the sludge, as they consume large quantities of textile, the laundry, and production process result in microfiber emission. The microfiber, microplastic and cumulative particle release per day from sample sites 1–5 of the analyzed WWTP is provided in Fig. 4.11 [70].

Fig. 4.11 Number of microfibers (MFi) and microparticles (MPa) and the total number of microplastics (MPs) per gram (dry weight) of sludge sampled at different steps in the wastewater treatment plant of Sari, northern Iran (Reprinted with permission from [70])

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In another study conducted in Spain, the researchers performed the analysis throughout the year and found that the microplastic concentration in the dry sludge was higher in the summer season (May–September), with a range of 28–39 microplastics per g of dry sludge. Whereas in the rest of the season, a lower microfiber range was detected (12–22 microplastics per g of dry sludge). As far as the microplastic types are concerned, a higher contribution of fragments (57%) followed by fibers (33%) was reported, which is in contradiction with previous literature [71]. An average of 24 microplastics were found in a gram of dry sludge, and based on the amount of solid sludge generated in the WWTP, it was estimated that the plant can emit in the range of 4.23 × 107 to 9.54 × 107 microplastics per day [71]. Some researchers believed that the microplastics that ended in the WWTPs are recirculating in the WWTP process again. For instance, a study conducted by Nakao et al. showcased 12% of microplastics in the influent are recirculated inside the sewage treatment process [72]. When the researchers measured the fate of microplastics that enters the WWTP system, during the sludge treatment process, like thickening and dewatering activities, these fiber escapes through the sidestream paths and re-enters the sewage treatment process. They have reported that microfibers are the major items identified in their study. Hence the study suggested that the effective removal of such microfibers in the WWTPs treatment system will increase the microfiber removal efficiency [72]. In line with these findings, another study questioned whether all the microplastics that enter the WWTPs are accounted for. Researchers from the University of California performed a predictive analysis from the existing literature and reported that only 4% of microplastics were identified and documented, and the remaining 96% were left unaccounted for. By using the data from the US Environmental Protection Agency (EPA), the study estimated the annual treatment quantities of wastewater and bio-solids. The results of the study reported that annually in the US alone, 1570–2160 trillion microplastics enter the WWTPs and 30–47 trillion are discharged through effluents. Moreover, 1540–2110 trillion microplastics that are cleaned via the WWTP process should end up in the sludge. But the analysis exhibited that the sludges released from WWTPs accounted for only 57–89 trillion microplastics. Thus, the research team concluded that the remaining 96% of the microplastics are left without account. As per EPA data, around 51% of the sludge is applied in agricultural use as a fertilizer and this process releases 29 trillion accounted microplastics and 1030 trillion unaccounted microplastics into the landscape. Similarly, sludge is applied in landfills (22%), incineration (16%), and 11% is being disposed of or stored in the deep well. This in turn, again releases 464 trillion microplastics into the environment via landfills. Hence, even after WWTP processing and tracking, a significant amount of microplastics enter the environment unaccounted [73]. Several other research works that estimated the microplastic emission via effluent and sludge are detailed in Table 4.2. From the above-discussed results and Table 4.2, it can be seen that the awareness of the microfiber emission from the disposed of sludge increased in recent times. Though few studies reported the presence of microplastic in the WWTP effluent in the beginning [52, 84], detailed characterizations on the microfibers have been performed in the latter years [54, 85–87]. However, it can be seen that the impact

From Effluent—300 million microplastics/day From sludge—8 × 1011 microplastics/year

183 ± 84 particles/g

12.8 ± 6.3 particles/liter

Spain, 45,000 m3 /day

7.28 × 1011 microplastics/year

4044 ± 1359 particles/kg

–

Beijing, China, 1.0 million m3 /day

–

240.3 ± 31.4 microplastics/g

28.4 microplastics/liter

Wuhan City, China/20,000 m3

Microfibers

Pellets/Microbeads

Microfibers and fragments

Microplastics and microfibers

160,000,000 microplastics/day

Italy, 400,000,000 L/day 3,56,00,00,000 microplastics/day

Microfibers

22.7 ± 12.1 × 103 1.56 × 1014 particles/kg dry sludge microplastics/year

–

28 WWTPs from China 3,400,000,000 microplastics/day

Microfibers

0.03 ± 0.01 trillion microplastics/year

1.64 ± 0.76 trillion microplastics/year

0.03 ± 0.01 trillion microplastics/year

Major microplastic type

Vancour, British Columbia

Total emission from WWTP

Microplastics in sludge

Microplastics in effluent

Study location and capacity

Table 4.2 Studies that evaluated the microplastic accumulation in the environment via WWTP effluent and sludge

PET, PE, Dyed cotton, PP

PP, PE, and PA

PA, PE, PP and PVC

PP, PET, PA PE, acrylonitrile–butadiene

Polyolefin acrylic fibers, PE, PA

–

Polymer types*

(continued)

[74]

[69]

[55]

[54]

[68]

[52]

References

4.8 Wastewater Treatment Plant (WWTP) as a Secondary Source … 141

7.91 ± 0.44 microplastics/liter of activated sludge 36.3 ± 5.7 microplastics/g 8.12 ± 0.28 × 103 microplastics/day 987 microplsatics/g 5150–21,800 microplastics/kg 864 × 106 to 1020 × 106 microplastics/day

2.76 ± 0.11 microplastics/liter

30.6 ± 7.8 microplastics/liter

2.32 × 109 microplastics/liter

–

117.8–355.6 microplastics/liter

22.1 × 106 to 133 × 106 microplastics/day

0.07–0.78 items/L

New South wales, Australia 48 Million liters/day

Harbin, China

South Korea

Iran, 23,240 m3 /day

Mauritius, 2,500–59,000 m3

Australia, 65,000–150,000 m3 /day

Guilin City, Guangxi Province, China 234.7–6908.3 microplastics/kg dry weight

Microplastics in sludge

Microplastics in effluent

Study location and capacity

Table 4.2 (continued)

–

4100 × 106 to 9100 × 106 microplastics/day

–

2118 million microplastics/day

–

7.74 × 1012 microplastic/year

Sludge—11.48–12.84 million microplastics/day Effluent—107.27–116.17 million microplastics/day

Total emission from WWTP

Microfibers

Microfibers

Microfibers

Microfibers

Microfibers

Microfibers

Microfibers

Major microplastic type [75]

References

[78]

[70]

[77]

PP, PET, PAN

(continued)

[80]

PET, PE, PP, and nylon [79]

PP, PE and PA

PET and PE

PET, PP, PE, Silicon, PS

Polyesters, PA, PET, PE [76]

PET, PP, PA, PE

Polymer types*

142 4 Domestic Laundry—A Major Cause of Microfiber Shedding

9.54 × 107 microplastics/day 44.4–750.0 microplastics/kg –

97.2 microplastics/gram of dry sludge

6.98 × 106 microplastics/day

–

2.3 ± 5.6 items/L in winter and 67.6 ± 30.6 items/L in summer

–

Caravaca de la Cruz, Spain, 8,000 m3 /day

Chengdu, China

Qingdao China, 0.8–1.7 × 105 m3 /day

Devon, England 1,000 L per second

PET, PS and PA

Polymer types*

PET, PE, PA, PVA, and [83] PP

Particles and fibers

1.61 × 1010 microplastics/month

[82]

[81]

[71]

References

Rayon, PET, and chlorinated polyethylene

Particles and debris PE, PP and PS

Fragments and fibers

Major microplastic type

8.38 × 109 to 4.25 × 1010 Microfibers microfibers/day

–

1.022 × 108 microplastics/day

Total emission from WWTP

*PE—Polyethylene; PET—Polyester; PA—Polyacrylic; PP—Polypropylene; PVA—Polyvinyl acetae; PS—Polystyrene; PVC—Polyvinyl chloride

Microplastics in sludge

Microplastics in effluent

Study location and capacity

Table 4.2 (continued)

4.8 Wastewater Treatment Plant (WWTP) as a Secondary Source … 143

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4 Domestic Laundry—A Major Cause of Microfiber Shedding

of sludge realized in the last couple of years [70, 71]. Research findings revealed that microfiber is the dominant type of microplastic found in the majority of the studies that analyzed WWTP effluent and also sludge [7, 47, 49, 52, 54, 63, 54, 68, 70, 88]. Similarly, polyester, polyamide, polypropylene, and acrylic are the common synthetic fibers reported in the literature. However, it was evident while analyzing the results that there is huge variation among the research findings of different researchers detailed in this section. The variation in the reported literature was widely evident in several works of the literature analyzed. As a consolidation, other researchers reported several reasons for such variations namely, differences in sample process, sampling methods adopted, effluent filter cutoff size, quantification methods adopted, sludge treatment methods (both pre and post-treatment), and finally the processes and technologies adopted in the WWTPs [73]. Further to add, a few researchers also commented on the variation in the microfiber emission from WWTPs (via effluent and sludge) and the amount of microfiber in the influent [54, 72]. Studies also reported the impact of seasonal variation in microfiber estimation [71]. Koutnik et al. believed that such variation is obvious as no standard methods are adopted across the microplastic analysis process. The study also reported that 94% of the microplastics entered into the WWTPs are released into the environment unaccounted for due to several reasons like i. improper identification and quantification techniques; ii. fragmentation of microplastics in WWTPs and iii. biodegradation inside the WWTPs [73]. Similar results were also reported in the earlier research, which reported an increment in the microplastic content of the effluent water than the influent wastewater [64]. Hence, standardization of such analysis is important to understand the real-time impact of the microplastic that are released from the WWTPs. Other than this, a few other process parameters that have a large influence on the microplastic quantification from WWTP effluent and sludge are provided in Fig. 4.12 as reported by Koutnik et al. [73].

Fig. 4.12 Factors influencing the estimation of microplastics in the Wastewater and Sludge released from WWTPs

References

145

4.9 Conclusion This chapter consolidates the primary and secondary impact of the laundry process, mainly the domestic laundry process on the microfiber release into the environment. The first portion of the chapter outlined various laundry parameters namely, washing conditions, use of laundry aids, types of machines used, and repeated laundry process on the microfiber emission. In this process, several subfactors were detailed and their interaction with the textile material was discussed. From this analysis, it was evident that the laundry process is the main source of microfiber release from textiles, and proper control of the process parameters, for instance, use of lower temperature, a shorter laundry cycle with mild detergent will reduce the impact. The selection of front load washing machines with a lower fabric to water volume ratio also reported having a positive impact on reducing the microfiber release from the textile. The effect of water hardness was not completely analyzed, however, few laundry aids like softeners had a positive impact on microfiber release (reduction). The washing liquor, that is released from the laundry process directly passes through the public sewage and enters into the common WWTPs that treat municipal wastewaters. Hence, the second portion of this chapter outlines the impact of WWTPs effluent and solid waste on microfiber/microplastic emission. From the review process, it was evident that, though WWTPs removed a significant amount of microplastics during the treatment process, it still emits a large number of microplastics into the environment. The impact of microplastic release from wastewater and sludge was recently brought into the research process. The review also exhibited that among the different studies, the removal efficiencies of WWTPs are lower in the case of microfibers. Hence all the studies reported a higher microfiber content, as a prominent microplastic shape in the effluent and sludge discharged. The backtracking results reported domestic laundering of the textile as the major source of such fibers in the WWTPs influent. Review results also revealed a higher variation among the results reported by several researchers. Hence, implementation of standard operating procedures for research methods and quantification techniques is the much-needed research in this area which in turn can help in the implementation of regulations concerning microplastic contamination like other wastewater norms. This will help the research community to understand the real impact of laundry and WWTPs discharges on the environment.

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Chapter 5

Impact of Microfiber/Microplastic Pollution

5.1 Introduction In recent years, there is a great concern about microplastic pollution in the environment. Higher use of disposable plastic materials was identified as one of the major reasons for the development of microplastics. The use and disposal of plastics over time cause aging and the plastics break down into small debris that creates microplastics [1]. Research works already reported the presence of microplastics in open surface waters [2], on seafloor [3], deep-sea [4], and also in Polar Regions [5]. Increased use of plastic materials in every domain of industry and commercial applications increased the sources of microplastic emission. Microfiber is one of the major contributors to microplastic pollution [6]. Microfibers are plastic fibers of the same size as microplastic with a higher diameter to length ratio. These microfibers are released from synthetic textiles (for example—Polyester, Nylon, etc.) due to various reasons like degradation, mechanical abrasion, and laundry [7]. This chapter details the various impacts of these microplastics on different terrestrial environments, aquatic life, and human health. The first section of the chapter outlines the impact of microplastics and microfiber on the contamination of the atmosphere followed by the impact of microplastic on the aquatic environment, in which the marine and freshwater system and their current pollution level are discussed. A detailed discussion on its impact on various aquatic life forms and their health were also outlined. The latter part of the chapter details the impact of microplastics on various food items. In this part, the recent research findings on contamination in salt, drinking water, vegetables, seafood, and other food items were discussed. The findings of various researchers were detailed by focusing on the potential impact of microfibers and microplastics on human health. The current knowledge on human consumption and existing research data were showcased to elucidate the impending impact of microfibers on human health. The different pathways of exposure to human and their targeting parts were also presented for better understanding. The last section of the

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 R. Rathinamoorthy and S. Raja Balasaraswathi, Microfiber Pollution, Sustainable Textiles: Production, Processing, Manufacturing & Chemistry, https://doi.org/10.1007/978-981-19-4185-6_5

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chapter points out the pollution-carrying ability of the microplastics and their impact on the host environment.

5.2 Microfibers in the Atmosphere Atmospheric air pollution is always a threat to life forms including human beings. Recently, the accumulation of microplastic and microfiber-related pollution in atmospheric air increased the complexity of the problem. Due to their lower density and micro or nano size, microfibers are capable of entering the atmosphere by carrying different pollutants on their surface [8]. The main issue with the suspended microplastics and microfibers is that, they can be effectively transported over the land and ocean surfaces by wind current [9]. A study that evaluated the microplastic pollution in the indoor and outdoor locations of central France reported a higher density of microfibers in the indoor atmosphere than in the outdoor. The findings revealed an accumulation of 1.0–60.0 fibers/m3 in indoors and between 0.3 and 1.5 fibers/m3 in outdoor. Out of the total microfibers identified, 67% of the materials are cellulosic and the remaining belongs to synthetic textile. A higher proportion of microfiber indoors is attributed to the use of synthetic floor mats and drying of clothing inside the room after laundry [10]. Whereas, in the studies reported in Shanghai, slightly higher contamination was noted than in France with a mean concentration of 1.42 ± 1.42 n/m3 [11]. The study also reported the sample collection at different altitudes. A higher concentration was reported at 1.7 m above the floor level. However, an increment in altitude reduces the concentration of microfibers in the air. A large number of microplastics observed in the atmosphere are microfibers (67%), followed by fragments and granules with 30% and 3% contribution, respectively. A higher abundance of polyester fiber was noted in all locations of the study [11]. As most of the atmospheric contamination studies were performed in the land area, Kai Liu et al. evaluated the atmospheric air for microfiber contamination in the west pacific ocean for the first time. The study was analyzed using continuous sampling during a cruise and reported in the range of 0–1.37 n/m3 . The replication of the study showed a heterogeneous distribution of microplastic particles in the air. A majority of the microplastics collected were microfibers (60%) followed by granules (31%) and fragments (8%). Through polymer identification test, it was noted that the majority of the microfibers were of polyester (51%) that originated from synthetic textiles [12]. Xiaohui Wang et al. analyzed 21 different locations from the south China ocean to the eastern Indian ocean. 9 out of 21 locations surveyed showed an abundance of microfibers from 0 to 7.7 items per 100 m3 [9]. At some study locations, no microfibers were observed even though the study location is nearer to the continent. Whereas, at some study locations, it was abundantly found even though the location was far from the land area. This distribution difference was highly attributed to climatic conditions such as wind speed, direction, and rain [13]. The findings of the research reported that wind speed and pressure are the primary components that

5.2 Microfibers in the Atmosphere

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Fig. 5.1 Polymer types of particles identified in atmospheric samples. Polypropylene (PP), poly(ethylene-co-vinyl acetate) (PEVA), polyethylene terephthalate (PET), poly(ethylene-copropylene) (PEP), poly(acrylonitrile-co-acrylic acid) (PAN-AA), phenoxy resin (PR), Polyamide (PA) (Reprinted with permission from [9])

influence microfiber abundance in the atmosphere. Other metrological parameters reported in the study that influences the transport of microplastic are humidity and gust velocity. In total identified suspended particles, around 88.8% of the items are microfiber and 11.1% are fragments. All the identified fibers are made of either polyester or polypropylene polymer. Various types of polymers and the shapes noted by Xiaohui Wang et al. are provided in Fig. 5.1 [9]. When the sources for the atmospheric microplastics were analyzed, researchers reported that the sources of microfibers are mainly associated with synthetic textiles. Whereas, the fragments were associated with the packaging materials used for transport. During the transportation, the weathering process or abrasion of the material breaks down the larger plastics into smaller molecules and releases microplastics into the atmosphere [9]. A study conducted in China, (Dongguan) also showed a higher concentration of fibers over other types of microplastics (foam, film, and fragments) in the atmosphere. The deposits of microplastics were measured in the range of 175–313 particles/m2 /day with a size range of 200–700 μm. Out of the collected samples, the three most common polymeric materials were reported, namely polyester, polypropylene, and polystyrene [14]. A study conducted in central London showed a higher deposit of microfibers on the roof surface of a nine-story building. The study reported a deposition rate of 575–1008 particles/m2 /day. Out of which, a majority (92%) of the particles was classified as microfibers. Among the identified materials, the dominant polymers are polyacrylonitrile polymers (67%) followed by polyester (19%) [15]. Miri Trainic et al. evaluated the atmospheric microfiber and plastic pollution in the remote ocean–atmosphere of the North Atlantic

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Ocean for the first time. Polyester, polystyrene, and polypropylene microplastics are found abundant in the surveyed atmosphere. A greater amount of relationship between the marine plastic debris and the atmospheric microplastic content was outlined. A possible mechanism proposed by the researcher was as follows: The water movement and wind create microplastic and fiber debris layers on the surface of the water. These microplastics were transported by air bubbles that are formed on the surface of the sea. When the bubbles burst outs, the microplastics were injected into the atmosphere [16]. Figure 5.2 consolidates the previous research results of the atmospheric microfibers and plastic in terms of number per cubic meters (for suspended particles) and the number of particles per square meter per day (for fallouts on the surface) [17]. Overall, a higher concentration of microplastics was reported in the studies that addressed the urban or indoor areas compared to the oceanic environments. While comparing the multiple researcher’s results, high variability among the number of microfibers or microplastics identified was noted, and hence log scales were used to compare the results [17]. From the results of the research, it can be noted that a higher amount of microfiber pollution was reported in the indoor compared to outdoor air [10, 11, 18]. However, researchers reported that the dilution effect of the outside air is the reason for the reduced concentration of pollution [17]. Further to add the concentration of pollution in the outdoor environment is also influenced by the altitude of the sampling area. This was evident from the results of Liu et al., where a lower number of larger particles recovered at higher altitudes [11]. Though human population and concentration of air pollution were not directly related, a lower concentration of pollution was found in the oceans compared to the lands. To confirm the effect of human

Fig. 5.2 (i) Cutoff size in mm (a) and concentration in n/m3 of suspended air samples (b), (ii) Cutoff size in mm (a) and deposition rate orders of magnitude in atmospheric fallout samples in n/m2/day (b) (The orders of magnitude are shown on a logarithmic scale) (Reprinted with permission from [17])

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activity, research was performed in a university students dormitory room, lecture building corridor, and students office. The results reported that higher microplastic pollution in the office during weekdays and in a dormitory on the weekends was noted. On weekends, a three times higher concentration of microplastic fallouts was obtained in the dormitory where two students live [19]. Other researchers measured the microplastic pollution at the planetary boundary layer using the aircraft sampling method. Their results also represented a higher density of microplastic in the urban area (13.5 particles/m3 ) than in the rural areas (1.5 particles/m3 ) investigated [20]. These findings confirmed the relationship between human activity and microplastic concentration in the atmospheric air. Similarly, a higher concentration of microfiber fallout was reported during the rainfall compared to the dry seasons [10, 21, 30]. Dris et al. reported the correlation between rainfall and microfiber fallout in their studies [10]. While considering the deposition of the microfibers and plastics, it is also essential to consider the results of other researchers who have reported that these microplastics use to travel thousands of kilometers before it gets deposited [20]. Detailed documentation of the different studies on atmospheric microplastic pollution can be found in the following literature for better understanding [31, 32].

5.3 Microfiber in the Marine Environment and Its Impact on Aquatic Life Forms A marine environment is a suitable place for the aquatic life forms to thrive and live. The impact of pollutants on the marine environment is of important concern as it affects the whole ecosystem. The marine environment almost acts as a sink for all plastic litter including microplastics and microfibers. The pollutants from the land sources are transported to the aquatic source through surface runoff, various streams, sewage, and drainage systems. Pollution also occurs due to marine-related activities like fishing and aquaculture [33, 34]. The current plastic pollution was estimated to be 4.8–12.7 million tons and it will be increased by one order of magnitude at the end of 2025 [35]. The most common way of formation of microplastic in the marine system is the degradation or breaking of larger plastics into fragments and debris due to the various physical, chemical, mechanical and biological activities [36]. Several researchers reported the abundance of microplastic and microfiber all around the globe from the Arctic to the Antarctic. The research findings demonstrated the presence of microplastics in all depths of oceans from the surface water to seabed sediments [37, 38]. Out of several studies, the abundance of microplastic was noted higher in the five subtropical gyre zones [39]. Out of which, microfibers are often found in all environments abundantly due to the higher usage of synthetic textiles and washing of the same. Several recent research works reported the effect of laundry on microfiber shedding and the number of microfibers released through every laundry load [40–43]. Regardless of the knowledge we have on microfiber and its impact, the know-how on what will happen if

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the microorganisms ingest these particles and fibers is still unknown. The interesting characteristics of textile fibers are highly flexible and asymmetric in shape, and their size varies in a large range from nano and micro range to millimeters. Though the actual fibers released from the laundry or domestic sewage are of larger size, the mechanical and chemical reactions convert them into tiny fibers. Though the effect of ingestion of these particles was not clear with marine biota, few researchers measured the effect of ingestion in a controlled environment. Research results evident that the microorganisms are capable of ingesting the microfibers and microplastics [44, 45]. The researcher reported that microorganism mistakes microplastics and fibers for their food, and this is the primary reason for the ingestion [45]. The primary investigations on the impact of microplastic on the marine life forms were investigated by Brown et al. [46]. The study measured the effect of uptake of microplastics on the biological consequence and fate of the bivalve. The study results reported that upon ingestion, the microplastics are accumulated in the guts of the species. After exposure to the seawater with microplastic, the species were transferred to clean water and evaluated for their performance. Out of a total of 48 observations, the abundance of microplastic was noted high for the first 12 days and then declined. The study also stated that the microplastic particle reaches the circulatory system in 3 days [46]. Two different zooplankton species that are widely available in the North Pacific Ocean and very critical for the marine food web were analyzed for the presence of microplastics and microfibers. The study results showed there is a significant difference between the two species tested in this analysis. The study also showed that the selected zooplankton can also ingest fibers more than the length of 2000 μm. Researchers reported that the ingestion rate of the zooplankton largely depends upon different factors, namely the size of the particle, deposition in the environment meaning how similar it looks to prey, abundance, feeding mode, and anatomy of the feeding to the species. Though the study identified the ingestion of the microfibers and microplastic, the effect of those particles on the zooplankton is still not clear. However, it is very evident that the ingestion will either affect the zooplankton itself or the species that eat zooplanktons [47]. Anita et al. evaluated the effect of microplastic concentration on the mortality of Daphnia Magna in the freshwater system. Genus Daphnia is one of the most abundant freshwater zooplanktons that can be found on all continents and climate zone of the world. A higher standard deviation was noted with the results while comparing three repetitions. However, in general, increased mortality of D. Magna was reported than the control group during the 48 h exposure. During the recovery study at 24 h exposure, in a microplastic-free medium, D. Magna was allowed to grow along with algae as food. However, it was noted that they were not able to recover completely. The researcher did not find any changes in the growth length of the D. Magna, but, they can see the ingestion of microfiber in the gut of the D. Magna. The study reported that D. Magna can ingest long microfibers from 300 to 1400 μm. It was noted that the shape and size of the microfiber and particle are some of the important factors that decide the ingestion. When the microplastic abundance in the D. Magna’s gut and the mortality rate was compared, no correlation was found. The chemicals leaching out from the fibers might also cause toxicity to the microorganisms [48]. Figure 5.3 represents the presence of microplastics in the

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157

Fig. 5.3 The presence of Microplastic in the gut of D. Magna. Left panel (a, c) are photos taken on control D. Magna with no Microplastic, and the right panel (b, d) are photos from D. Magna with a gut full of Microplastic (exposed to 50 mg/L of Microplastic). Photos were taken with a light microscope (5X magnification) under bright field illumination mode (a-1, b-1) and dark field mode (a-2, b-2). Daphnids prior to H2 O2 decomposition (c-1, d-1) and the remains after decomposition (c-2, d-2) (Reprinted with permission from [48])

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gut of D. Magna. The ingestion of microfibers in Nephrops norvegicus from the Clyde Sea was analyzed and reported by Murray and Cowie [49]. The study results revealed that out of the total sampled animals, 83% of them consisted of filaments in their stomach. 62% of the animals contained tangled plastic strands in their stomach, and only the recently molted animals did not have any fibers [49]. In other study, the researcher measured the microfiber contamination of fish found in the English Channel. Out of the measured 504 fishes, 36.5% (184) fishes had synthetic polymers ingested. The results showed an average of 1.90 pieces of synthetic polymer ingested per fish. When the types of polymers were identified through FTIR analysis, around 203 pieces were identified as rayon material, which is commonly used in apparel. Other than this, 35.6% of the contaminant were polyamides, 5.1% were polyester, and a lower amount of polystyrene, low-density polyethylene, and acrylic were also found in the research. In these identified polymers, it was also reported that 68.3% were microfibers followed by 16.1% of fragments and 11.5% of beads. The study reported that the abundance of rayon might be the consequence of the indirect input from the sewage wastes into the ocean. Apart from clothing, rayon fibers are commonly used in furnishing, female hygiene products, and diapers. The fast disintegration ability of the rayon is also one of the main reasons for their abundance [50]. The abundance of the microfibers in fishes was listed in Table 5.1, as reported by [50]. Hence, the ingestion of plastic in the fishes might have occurred either as an accident during the Table 5.1 Abundance of microfibers in the different types of fishes obtained from the English channel [50] S. No.

Type of species analyzed

Total number of samples

Number of samples with plastics

Percentage (%) of species with microplastics

1

Merlangius merlangus

50

16

32

2

Micromesistius poutassou

27

14

51.9

3

Trachurus trachurus

56

16

28.6

4

Trisopterus minutes

50

20

40

5

Zeus faber

42

20

47.6

6

Aspitrigla cuculus 66

34

51.5

7

Callionymus lyra

50

19

38

8

Cepola macrophthalma

62

20

32.3

9

Buglossisium luteum

50

13

26

10

Microchirus variegates

51

12

23.5

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feeding or the fish might have misidentified the microplastics as their prey due to their size and color. However, the latter part was not experimentally proven by the researcher [51]. Au et al. analyzed the effect of microplastic ingestion with the freshwater amphipods Hyalella Azteca against the polypropylene fibers and polyethylene spheres. The study analyzed the mortality rates of amphipods on 10 days of exposure to the microfiber and microspheres. The results showed higher mortality rates in the case of microfibers compared to spheres proving microfibers are more toxic than other components. The ingestion of the microfibers also reduced the growth of the amphipods up to a level of 50% more than the control animal. The growth reduction was expected due to the clogging of microfibers in the digestive system for a longer time than the spheres or natural food. This ultimately affects the food intake and reduces growth. The study also reported that a complete egestion of microfibers was also possible for the amphipods as the study duration did not find any aggregation of fibers [52] However, no toxicity was reported in the case of polyester microfiber ingestion in D.magna and Artemia franciscana. A 48 h exposure study showed the presence of microfibers in the guts of the animals, however, no toxicity was reported. The reason for the difference is unknown, and hence, researcher suggested that the fiber size and concentration may have an influence on this [53]. When the other researcher correlated the ingestion and egestion rates of blue mussels, it was found that the fibers in the gills were expelled faster than the fibers in the digestive system. This might be the reason for the microfibers to remain in the animal for longer times [54]. In a comparative analysis, another researcher measured the ingestion ability of Asian clams (Corbicula fluminea) against different fibers. The study used six different polymers, namely polyamide, polyester, acrylic, rayon, polyester amide, and polyvinyl alcohol with different particle sizes ranging from 5 to 5000 μm. The results reported a higher intake of polyester fiber in the size range of 100–250 μm. The researcher also reported the reason as the similar morphology and size with prey items [55]. In this study, in contrast to previous research [14], other polymers including rayon were not at all taken up by the animal [55]. As most of the microfibers found in the marine environment are polyester-based that are released from domestic laundry and other usages of polyester polymers, the ingestion of polyester by clams raises a serious concern. Other researchers measured the impact of microfibers on the growth and mortality of freshwater snails (Planorbella campanulata). A higher mortality rate was observed in the exposure of polyester microfiber over control animals. A higher microfiber concentration blocks the food intake and increases mortality. Further, the study also reported a higher amount of offspring in the polyester microfiber exposure [56]. A complete egestion of microfibers was reported after three days of ingestion from the snails. However, a detailed analysis revealed the presence of fragments inside animals even after six days of exposure [57]. As far as the shrimps are concerned, very few addressed the impact of microfibers on shrimps. A study measured the impact of different shapes and sizes of microplastics on the life of shrimps (Palaemonetes pugio). The results revealed that, within 3 h of exposure, mortality was reported. More fiber deposits were noted on the gills of the animal. A higher amount of toxicity and

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mortality was noted with the microfibers than the other microplastics like beads and spheres. The main reason for the mortality was reported as the damage to organs and entanglement of fiber. A higher mortality rate was reported with the polypropylene fiber of all the sizes, however, they did not see much increment in the mortality against the polyester fiber [58]. Horn et al. measured the effect of microfiber ingestion (polypropylene fibers) on the mortality rates of Pacific mole crabs (Emerita analog). Microfiber exposure showed increased mortality with the mole crabs compared to the control animal. Further to add, the study also reported the impaired reproduction of the microfiber-exposed crabs compared to the control group and suggested that might be the biological impact of microfiber ingestion [59]. A similar study also reported the reduction in growth and food consumption of crabs when they are exposed to the food content with polypropylene microfibers [60]. On the other hand, a most recent study measured the exposure of Japanese medaka (Oryzias latipes) to suspended polyester and polypropylene fibers. The results of the study surprisingly showed no ingestion of the microfiber in the selected fish. Even if the fish intakes the microfibers, they were flushed through the gills. Hence, small structural damage to the gills was evident due to this process. The study did not report any internal organ damage or deposits of microfiber inside the fish [61]. The results of the research by Hu et al. [61] showed no impact of microfiber ingestion on fish. But in contrast to that, the effect was obvious against Zebrafish (Danio rerio). Exposure to polypropylene fiber for 21 days significantly reduced the growth of the fish and affected the body conditions of the control animals. Whereas in the gut analysis, more fibers were found than the spheres and other shapes [62]. In support of these findings, other study reported a large level of uptake of plastic debris by the fish. The number of microplastics found inside fishes ranged from 1 to 10 based on their species type [63]. Another study reported microplastic contamination in nine commercial bivalves from a fishery market in China. The results showed a microplastic concentration of 2.1–10.5 particles/g of the seafood evaluated [64]. Similarly, the microplastic abundance in the mussels were investigated and a concentration of 1.4 particles per gram was reported. Interestingly, the study showcased a higher concentration of microplastics in the pre-cooked mussels (1.4 particle/g) than in the mussels supplied alive (0.9 particles/g) [65]. The result from these studies confirms that the effect of microfibers will also vary based on the species types. From these results, it was very evident that the impact of microplastic on aquatic life forms is very significant. In specific, the effect of microfiber on aquatic life forms is toxic and mortality-oriented. If we consider the impact of these microfibers on the aquatic life forms, the primary impact can be observed as physical. The studies on the fish, crab, snail, and other species like (different) zooplankton showed physical entrapment of microfibers inside the organs, gills, and digestive systems. Though few of the evaluated animals can flush out the microfiber through different egestion methods, their impact remains significant. The entrapment of microfibers alters the food intake level and growth level, and also impairs the reproductive nature in specific cases [45]. The secondary impact of microfiber is the release of harmful chemicals associated with polymers and their production process. As there is no evaluation of this concept, still researchers believe that the toxic nature of microfibers is highly

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related to the leachability of the dyes and chemicals used in the production phase. A recent research finding also confirms that microfibers can leach the chemical additives and plasticizers into the aquatic environment even after long exposure or photo-degradation [66]. It is also necessary to conduct a separate study on the impact of leached chemicals from microfibers like dyes, pigments, additives, and lubricants. Similarly, the long-term biological impact of microfiber on the aquatic life forms is also not evaluated as most of the studies were conducted in a controlled laboratory atmosphere. Readers with an interest in this area can access the detailed report of microfibers, microplastics, and other plastic debris’s impact on different aquatic life elsewhere [67–70].

5.4 Microfibers in Freshwater Systems and Their Impact Microfiber and microplastic pollution in the marine environment is one of the highly researched areas. Several researchers reported the abundance of the microplastics and their characteristics at different locations. However, the studies on freshwater sources are minimal. Compared to the ocean, freshwater sources are smaller in size and closer to the microfiber or microplastic sources, with a higher variation in the abundance observed [71]. Lakes and rivers are the major freshwater sources and their contamination acts as a major route for marine pollution [72–74]. Studies reported a higher abundance of microfibers in the North American, Asian, and European locations [75]. The importance of microfiber and microplastic analysis in the freshwater system increases as these reservoirs act as a source of marine pollution [76]. Kapp and Yeatman measured the microplastic abundance in different parts of the Snake and Lower Columbia rivers from their origin to the endpoint. The study showed several hotspots with higher microplastic abundance ranging from 0 to 5.405 microplastics per liter. Out of several locations examined (for a length of 1735 km approximately), researcher reported a higher abundance of the microplastics in the two locations where higher agricultural activities were reported. Similarly, a higher abundance of microplastics was noted at places where the human interventions were eminent with the river. Further, in the analysis, the researcher reported that the agricultural lands located near the hotspots were used as the wastewater treatment plant effluent for irrigation [77]. Another study evaluated the abundance of microplastics from the surface water and sediments of Lake Simcoe in Canada. The study results revealed (crawl method) that out of total pollutants and microplastics recovered, 38.5% were other pollutants, 15.4% were identified as microplastics and 15.4% were unknown. The study results showed an abundance of 0.04 microplastic per liter of surface waters analyzed. In the liquid samples, polyester and polyurethane are the major polymer types that contributed to the abundance of the particle. Out of total particles recovered, 84.5% of particles were noted as fibers followed by fragments (5.9%) and fiber bundles (5.9%). Whereas in the case of the manta trawl sample method, a higher amount of microplastics (84.9%) were reported. Out of that, the most dominant polymer

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Fig. 5.4 Type of microplastics obtained from a grab water samples and b Sediment samples. The pie graphs indicate the percentage identities of the subsampled particles in each shape category as determined through FTIR and/or Raman spectroscopy (Reprinted with permission from [78])

types noted are polyethylene (41.2%) and polypropylene (21.9%). For the sediment samples, they have reported 55 microplastics per kg of dried sediments out of 372 total particles per kg. Among the identified samples, a higher contribution of microfibers (89.2%) was evident compared to fragments (5%), fiber bundles (2.5%) [78]. The types of polymer and shape of the microplastics reported in this research are provided in Fig. 5.4. Other researchers measured the microplastic abundance from Onondaga and Skaneateles lakes in central New York. They compared the effectiveness of the different sampling processes and reported that the grab method showed higher microplastics collected compared to net and bucket methods [79]. Among the collected samples, fiber-shaped particles are more abundant than the other shapes like spheres, film, foam, and fragments in both lakes. Out of the two lakes, Onondaga Lake had higher concentrations of microplastic contamination than Skaneateles Lake. Despite the abundance, Onondaga Lake showed a higher abundance of more nonfibrous morphologies like colorful spheres. Researchers reported the abundance of fiber might be related to the laundry wastewater and spheres might be related to the disposal of cosmetic products [79]. A study measured the microfiber abundance in the Dal Lake, in Kashmir, India and reported a higher abundance of microplastics and microfibers. They reported that the abundance varied based on the seasonal changes and related it to human traffic [80]. A higher abundance of microplastics (161–432 Microplastics kg−1 dry sediment) was reported in the River Kelvin in Glasgow, Scotland, UK. A major contribution of fibers (>88%) was observed from the analysis. In the analysis, researchers reported that the micro pellets identified were not microplastics, they were made of silica. However, when the fibers are considered, a higher concentration of synthetic fibers along with natural fibers was reported based

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on SEM–EDS analysis [81]. Based on the sampling location and the nonavailability of any wastewater treatment plant or other commercial household sewage discharge pipes in the location, researchers concluded that the abundance of microfibers was mainly attributed to the atmospheric deposition of microfibers [81]. In a similar study conducted in Cumberland River in Nashville, USA, researchers reported a higher abundance of microfibers than ever reported. The study showed 27.9 microfibers per liter, which is approximately 27,900 fibers per cubic meter measured. Researchers reported that the discharged water from the wastewater treatment plants might be the major cause of pollution, as they identified few plants on the river banks [82]. Peller et al., studied the presence of microfibers in the Lake Michigan watershed through the analysis of water, sediment, and air. The results of the study reported a microfiber abundance of 26 microfibers per 4 L of water (from 15 samples), collected from the shoreline of the Lake. The study reported that the higher abundance of microfiber in the lake water might be attributed to the swash action of the water and the ability of the sand to harbor it. As the wastewater treatment plants are located in the study region, researchers measured the microfiber contamination of effluent from the treatment plant. Out of two samples measured, a larger variation was reported between the samples. The first sample yielded 440 microfibers per 4 L of water, whereas the second sample showed up a huge variation with 2200 microfibers per 4 L. However, no supportive results were found to confirm the deposition of microfibers from the air. The study concluded that, through the watershed, approximately 4 billion microplastics were transported to the tributary from the lake [83]. Miller et al. reported the abundance of microfibers along the full length of Hudson River, USA. The study results showed that out of 122 samples measured, an average of 1.24 microfibers were noted per sample with a minimum length of 0.33 mm and a maximum length of 3.59 mm. Cotton (43%) and polyester (22%) are the dominant polymer types identified in the research. It is reported that throughout the river (length surveyed), no increase or decrease in the abundance was noted. Overall, around 300 million microfibers are discharged into the river, out of which, 50% of the particles were found to be plastic. Out of the sites examined, few sites showed a higher abundance of microfiber due to the presence of either wastewater treatment plants or a higher amount of human activities, in which wastewater treatment plant effluents directly discharge the microfibers into the river, whereas the microfibers released from the human activities were transported through air and deposited on the water bodies [84]. Another research evaluated the microfiber abundance in the lake of Taihu, one of the largest lakes in China. The lake is connected with many rivers, hence microplastic abundance was performed in the lake, inlet waters from the river, and the outlet water of the lake. The results revealed that the abundance of microplastic was noted as 1.635 to 8.48 items/liter in the surface water of the lake and 1.81–128.26 items/liter in the rivers. When the researchers compared the number of microplastics that came in, it was noted higher than the amount of microplastic found in the water that is released from the lake. Polyvinyl chloride, polyester, polystyrene, and polypropylene are the most common polymers identified in the study [85]. Among the studies that reported microplastics in the freshwater system, microfiber content is reported as a dominant type of pollutant by several studies. Studies performed on the river banks and lakes

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reported the wastewater from the effluent treatment plant and laundry as the main source of microfiber contamination [86]. The potential of airborne particle deposition was noted as comparatively less than these factors. As far as the microfiber abundance is concerned, polymer size, shape, and density are the internal factors. In the case of an external factor, the distribution of microplastics/microfibers is affected by winds, currents, waves, and water density [87]. Other researchers analyzed the impact of microplastics on the freshwater mussels from Saint John River, Canada. The researchers analyzed M. margaritifera, a freshwater mussel due to the abundance in the river. The results showed that 92% of the mussels evaluated had microfiber in their tissue (out of 110 mussels). On average, every mussel had 14 microfibers in it and the variation in count among the animal was also noted as higher. Out of the microfibers found in the mussels, blue color was the most ingested (44%) followed by clear, red, and black color. A negative correlation was noted between the size of the mussel and the amount of microfiber ingested. Smaller animals with soft tissue had a higher amount of microfiber than the larger animals. The study results showed the serious impact of microfiber consumption on the mussels and its potential to enter the food web [88]. Whereas other researchers measured the ingestion capacity of freshwater Asian clams. In this study, known fiber types were shredded and used for analysis. Along with the control sample, a tank with 100 microfibers per liter and 1000 microfiber per liter was prepared and clams were allowed to grow. In the case of the tank with 100 fibers/L, only polyester and polyester amide fibers were consumed by the clams. Whereas in the case of tank with 1000 fibers/L, most of the fibers were consumed by the clams. A higher abundance of polyester fiber was reported in both the tanks (0.5 fiber/g and 4.1 fibers/g in tanks with 100 fibers/L and 1000 fibers/L, respectively). This study confirmed the influence of polymer type on the ingestion ability of Asian clams [45]. In a similar study, the effect of microplastic consumption by Tubifex worms, a freshwater species was analyzed. As a first stage, the study reported the abundance of microplastics in the host sediments (mean 914 ± 844 particles per kg; 1793 ± 1275 particles/m2 ) and later from the Tubifex worms. The results of the study showcased a higher amount of microplastics (131 microplastic particles from 302 Tubifex worms) with an average of 129 ± 65.4 particles per gram of tissues, out of which, the majorly noted shape (87%) was microfibers. The extracted fibers (from Tubifex worms) had a length ranging from 55 to 4100 μm. As the Tubifex worms are one of the main food sources of many macroinvertebrates (leaches, small benthivorous fish, salmon, and trout fish), the link to the human food chain is very evident [89]. One of the important issues with the microfibers is that they do not settle or sediment like other microplastics and are highly transported in the water streams like rivers [90]. Similar to the rivers, lakes are also highly influenced by the abovementioned factors. Additionally, lakes are often known as a semi-closed system that acts as microplastic sink [91]. As far as the impact of microfibers is concerned, very similar to the marine environment, the freshwater microfibers and microplastics also have a potential impact on the aquatic biota. The complete effect of these microplastics and microfibers is not understood as of now. As microfibers are observed in

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both non-plastic and plastic nature, studies reported that a non-plastic particle will take five years to degrade, and as far as plastics are concerned, no definite time was reported. The continuous accumulation of microplastics and fibers in the water systems will give pathways to aquatic animal consumption. Due to their size and color, they mistake these fibers with their prey and consume them. It results in choking in digestive systems and reduces the population density of those species and their food chain [52, 54]. Other major concerns with the microfibers are that they act as a pollutant carrier, either from textile manufacturing (dyes, pigment, resins, etc.) or from the surrounding environments [84]. Both the non-plastic and plastic fibers tend to absorb and desorb the contaminants. Hence, during the ingestion of these particles, the toxic chemicals will mix up with the food web more readily. The impact of natural fibers is found to be more sensitive than the plastic fibers when the toxic substance sorption and desorption are considered [92]. As this chapter detailed the impact of microfibers majorly, a detailed review on the microplastics (which also includes microfibers based on length & composition) and their impact on freshwater environments can be found in the other resources [93–96]. Figure 5.5 represents the general pathways of freshwater contaminations.

5.5 Microfibers in Human Food (Chain) Samples There are a lot of research works that reported the abundance of microplastics in the water bodies and also in the aquatic animals as discussed in the previous section. Marine microplastics became a threat to life forms due to their abundance and sizes. Recent researchers showcased the impact of marine microplastic contamination on the human food chain. The following sections detail the microplastic contamination of human food items reported in the earlier research works.

5.5.1 Contamination in Salt A study collected 21 samples of salts from different brands and locations in Spain and evaluated the potential microfiber contamination. The results reported a higher abundance in the case of the well salt (115–185 microfibers/kg) and sea salt (20–280 microfibers/kg). The identified microfibers were in the range of 30 μm–3.5 mm. Particles less than 30 μm were not found in this study. When the microfibers were analyzed for their polymer types, a major contribution was noted from polyethylene terephthalate (PET), polyethylene (PE), and polypropylene (PP), with the composition of 83.3%, 3.3%, and 6.7%, respectively. Researchers reported that the higher abundance of microfibers in the salt is mainly related to aquatic microfiber pollution. The higher contamination of these salts will open the path for these contaminants to reach the human body. The study predicted that, if an average Spaniard consumes

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Fig. 5.5 The movement of microplastics (primary and secondary) throughout freshwater environments. Arrows demonstrate the fate of microplastics within lakes and rivers and the input of microplastics from atmospheric and terrestrial sources including urban and agricultural land use. The diagram highlights the numerous interactions throughout freshwater environments, including ingestion by freshwater organisms (represented by the dotted line arrows) with a final output of the majority of these microplastics (microplastic sinks being the exception) to the marine environment, whereby rivers are one of the major sources to these environments (Reprinted with permission from [96])

5 g of salt per day (as per WHO), they might be consuming approximately 510 microfibers each year [97]. Whereas other researchers evaluated the microplastic content in the 17 salt brands that were obtained from 8 different countries. The results of the research reported 1–10 microplastics per kg of salt evaluated. Out of all the brands measured, only one brand showed 0 microplastics in its content. The characterization results showed that 41.6% of the particles were plastic polymers and 23.6% were pigments. The most common polymers reported are polypropylene (40.0%) and polyethylene (33.3%) [98]. When compared to the previous research [97], this research [98] showed a lower concentration of microplastics overall. This can be justified by the filtration method used by the latter researcher [98]. The filtration media pore size was reported as one of the major causes of the lower detection of microplastics. The authors of the study [98] used 150 μm to capture microplastics, however, the major particle range was reported as 10 to 200 μm. Thus, most of the particles might have passed through

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the filter, and hence they reported lower contamination compared to the previous study [97]. Sathish et al. evaluated the microplastic contamination of fourteen different brand salts from Tamil Nadu, India. The research compared the sea and bore-well salts and reported a mean abundance of 35–72 microplastics and 2–29 microplastics, respectively. In line with the previous studies, a higher abundance of microfibers (83%) was reported followed by other fragments. The authors of the study also reported higher marine pollution as the main reason for the higher contamination of sea salt. Polyethylene (51.6%), polypropylene (25%), polyester (21.8%), and polyamide (1.6%) are noted as the major polymer types in microfibers. Based on the WHO guidelines, researchers reported that a normal human will consume 216 microplastics per year from sea salt and 48 microplastics per year from bore-well salt as per the findings of this research [99]. In India, Tamil Nadu and Gujarat are the largest edible salt producers. A study analyzed the salts produced from these states (sourced from the market) and characterized them for microplastic pollution. The results of the study reported that out of the total amount of salts examined, a higher amount of microplastics was noted in the samples obtained from Gujarat than in Tamil Nadu. A total of 662 microplastics per 200 g of edible salt was recovered from Gujarat and 413 microplastics per 200 g of edible salt were recovered from Tamil Nadu. Out of the identified microplastics, red, white, blue, black, green, and brown colored items were observed as a contaminant. When the characteristics of the particles were analyzed, a higher abundance of fibers was noted (88.5%) followed by films (4.9%) and pellet shape (2.9%). In those pollutants, polyethylene (78%) and polyester (19%) were the major polymers reported. The study reported that higher atmospheric microplastics in the edible salt-producing sites might be the reason for microfiber contamination [100]. Recent research analyzed the microplastics from Vietnam in the form of raw sea salt and fine iodate salt. The results of the study showed a mean abundance of 878 ± 101 microplastics per kg of sea salt. Out of which, 83% of the microplastics were found to be microfibers (length range: 100–900 μm) and the remaining were noted as fragments. Whereas in the case of fine iodized salts, 340 ± 26 microplastics per kg of salts were evaluated. Though a less number of microplastics were found in the iodized salt than the raw salt, microfibers with higher length (mean length: 563 ± 103 μm) were noted as a contaminant (60%). Fragments were noted as the second most contributing contaminant. The results also reported that the Vietnamese will consume more salt (10 g/day) than the WHO recommendation (5 g/day). Hence, the average microplastic consumption of an adult in Vietnam is estimated as 637– 1270 items/year in the case of Vietnam’s iodized fine salt [101]. Danopoulos et al. reviewed various studies that performed microplastic analysis on sea salts and well salts, and consolidated the findings. The results of the analysis showcased a higher variation of microplastic contamination among the salts from different sources. For example, a higher abundance of 0–1674 microplastics was found in a kg of sea salt. Whereas in the case of lake salt and well salt, it was reported as 8–432 microplates per kg and 0–204 microplastics per kg, respectively. From all types of salts, the

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review results mentioned that the values of an average human exposure will be 0– 6110 microplastics per year. A study reported the necessity of changing regulations regarding these types of contaminations and urged the need for animal or human studies to understand the potential health impacts of these contaminants [102]. Table 5.2 consolidates the literature that evaluated the microplastic contamination from salt, as reported by Danopoulos et al. [102]. One of the recent reviews analyzed the results of various researchers on the microplastic contamination of salt and valuated their findings. The review results showcased a large variation among the study and annual consumption results. The findings also reported that the cut-off size of the microplastic measurement method plays a vital role in the results, and they also proposed size correction to eliminate such errors. Detailed information on these findings can be accessed from Kim and Song [103].

5.5.2 Drinking Water Water is one of the basic needs of humans. Any form of pollution in drinking water will aid the pollutant to directly reach humans and cause health issues. With the increment in microplastic pollution issues, researchers started evaluating the contamination in all food products including drinking water. A study evaluated the microplastic contamination in the tap waters (n = 159) that were collected from various parts of the world. The results of the study mentioned an average of 5.45 microplastics/L of water evaluated. Results also showcased that water sourced from the developed countries had a higher abundance of microplastics (6.85 microplastics/L) than the less developed countries (4.26 microplastics/L). Out of the total particles analyzed, a major contribution of 93% was reported to be microfibers followed by fragments. When the overall samples were evaluated, 81% of the samples were contaminated by microplastics. From these results, the researchers also predicted that an individual adult may consume 12–16 microplastic particles per day due to the several beverages prepared by these tap waters like juices, coffee, tea, etc. [111]. Mason et al. analyzed the microplastic contamination in packaged drinking water from five continents and the brands analyzed were Aquafina, Dasani, Evian, Nestle Pure Life, San Pellegrino, Aqua (Indonesia), Bisleri (India), Epura (Mexico), Gerolsteiner (Germany), Minalba (Brazil), and Wahaha (China). The study evaluated 259 individual bottles from 11 different brands and 27 different lots for microplastic contamination. The results of the research revealed approximately 10.4 microplastic particles (>100 μm) per liter of the bottled water sample. Out of the total bottles analyzed, 7% of the bottle does not have any microplastics in them. Among the identified particles, 66% were fragments and the rest were microfibers [112]. As far as the particles smaller than 100 μm are concerned, approximately 325 particles were identified per liter of bottled water. When the larger particles are analyzed, polypropylene was identified as the major contributor. Compared to the previous study [111], the current research [112] reported twice the amount of microplastics. These findings suggest that the sources of the microplastics were different for individual cases. The study also shockingly reported

n

5 6 5

16 5

14 2 2

28 9 2

Salt sample type

Sea Lake Rock

Sea well

Sea Lake unidentified

Sea Rock Lake

678 38 245

124.06 139

46 37.5 11.8

Mean MPs/kg

2560 55 307

56.43 26.24

12.6 14.1 1.2

SD

0–13,629 0–148 28–462

0–10

50–280 115–185

16–84 8–84 9–16

Range MPs/kg

Composition per salt origin PU (25%) PE (35.3%) PP (100%) n/r n/r

PE (35%), PP (30%), PET (30%) PET (41%), PE (26%), PP (23%) PP (47%), PE (28%), Teflon (11%)

MPs size range 20 μm–5 mm

30 μm–3.5 mm 160–980 μm

100 μm–5 mm Not specified

PP (40.0%), PE (33.3%), PET (6.66%), poly-isoprene/PS (6.66%), PAN (10.0%), NY6 (3.33%)

PET (83.3%), PP (6.7%), PE (3.3%)

PE (22.9%)

Composition all samples

Table 5.2 Literature analysis of salt samples-microplastic contamination, and polymeric composition

Fragment > fiber > film

Fragment > filament > film

Fiber

Fragment > film

Shape

(continued)

[105]

[98]

[97]

[104]

References

5.5 Microfibers in Human Food (Chain) Samples 169

5400 28,900

n/r n/r

54 12

n/r

n/r n/r n/r

6 5

6 5

7 7

8

15

Sea, Italian Sea, Croatian

Sea, Italian Sea, Croatian

Sea Well

sea

Sea Lake Rock/well

9.5 12.5

10 1

Sea Rock

Mean MPs/kg

n

Salt sample type

Table 5.2 (continued)

n/r n/r n/r

n/r

13.4 9.5

n/r n/r

6.1 n/r

SD

PET and PVC PA, PP, and nylon

10–150 μm 55 μm–2 mm

n/r

170–320 70–200

35(±15)-72(±40) 2 (±1)–29 (±11)

56 (±49)–103 (±39)

550–681 43–364 7–204

45 μm–4.3 mm

n/r

4–2100 μm 15–4628 μm

1570–8230 27,130–31,680

Polyesters (~61%, PET ~ 7%), PE (~22%), PA (~16%)

PE (51.6%), PP (25%), polyester (21.8%), PA (1.6%)

n/r

n/r

PP (39.5%), PE (34.9%), PS (14.0%), polyester (4.7%), PEI (2.3%), PET (2.3%), POM (2.3%)

Composition all samples

Fragment > fiber

Fiber > fragment

Fiber

Fragment > fiber > film

Fragment > fiber

Shape

PET (27.3%), PE CP (39.5%), PET Fragment > fiber (20.5%), CP (16.3%), PE (8.5%), (18.2%) PB (8.5%) CP (43.2%), PET (11.4%), PB (11.4%) CP (58.5%), PET (9.8%), PB (4.9%), PP (4.9%)

n/r

n/r

89.7–1474.9 μm

2.5–20

Composition per salt origin

MPs size range

Range MPs/kg

(continued)

[110]

[109]

[99]

[108]

[107]

[106]

References

170 5 Impact of Microfiber/Microplastic Pollution

n

Mean MPs/kg

SD

Range MPs/kg

MPs size range

Composition per salt origin

Composition all samples

Shape

References

Reprinted under creative commons license [102]

MPs Microplastics, CP cellophane, NY6 nylon 6, PA polyamide, PAN polyacrylonitrile, PB polybutylene, PE polyethylene, PEI polyetherimide, PET polyethylene terephthalate, POM polyoxymethylene, PP polypropylene, PS polystyrene, PU polyurethane, PVC polyvinyl chloride. n - refers to the number of brands, n/r - not reported.

Salt sample type

Table 5.2 (continued)

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0–10,000 microplastics per liter of bottled water. Hence, researchers suggested that this water might have been contaminated during the bottling process itself [112]. Kankanige and Babel measured the microplastic contamination in the single-use PET- Bottled water from Thailand. The study compared the microplastic contamination in PET-bottled water with glass-bottled water. The results of the study reported higher contamination of the drinking water with microplastics. Out of those contaminations, the study mentioned a higher abundance of smaller particles (81.0 ± 3.0 p/L for 6.5–20 μm; 26.0 ± 2.0 p/L for 20–50 μm; and 12.0 ± 1.0 p/L for ≥ 50 μm) in the packaged drinking water. When the morphology of the microplastics was analyzed, a higher fraction of fibers was noted followed by fragments. Regarding the polymers, a major contribution was reported from polyethylene terephthalate (28%), Polyethylene (24.2%), Polypropylene (18.1%), and Polyamide (7.2%). While comparing the results of the glass bottle and plastic bottle, a higher concentration of microplastics were reported in plastic PET-bottled water (140 ± 19 p/L) than that in glass-bottled water (52 ± 4 p/L). Researchers suggested this higher contamination in PET bottles might be from the bottle cap and associated plastics. However, contamination in the glass bottles suggests that the microplastics enter the water from the manufacturing plant itself [113]. Similar research results were also reported by other researchers [114, 115], however, a higher number of microplastics were reported by Obmann et al. [115]. Schymanski et al. analyzed the microplastic content in the different types of drinking water packages like single-use, returnable, and glass bottles. The results of the study showcased higher microplastic contamination of all the water bottles. Among the tested samples, higher mean microfiber contamination was noted in the returnable plastic bottles (118 ± 88 particles/L) followed by glass bottles (50 ± 52 particles/L). The least contamination was noted with single-use water bottles with 14 ± 14 particles/L. When the polymers types were analyzed, a higher contribution of polyester-polyethylene terephthalate was identified. Researchers suggested that higher microfiber content in reusable bottles might have resulted from the bottle itself as it undergoes a lot of stress and strain during usage and refilling. In the case of glass bottles, the researchers related the use of bottle caps and seal as the source. However, it is also important to look into the contributing factors of the manufacturing and refilling process [114]. Other researchers evaluated the microplastic contamination from the public water fountains along 42 metro stations in Mexico. The results of the study showed a higher abundance of microplastics with a major contribution of microfibers in the collected water samples. The majority of the sampling locations had microparticles in the range of 5–10 particles/L. A very few samples from specific sites had a higher abundance in the range of 60–91 microplastics/L. The overall average of the microplastic found in the metro station fountain was noted as 18 ± 7 particles/L. The detailed analysis of the location revealed that those fountains with higher microplastics are located in commercial places. Secondly, the variation in abundance was correlated to the water filtration, transportation, and storage systems associated with those stations. Out of all the samples tested, the poly (trimethylene terephthalate) and aliphatic–aromatic copolyester accounted for major contributions as microplastics [116].

5.5 Microfibers in Human Food (Chain) Samples

173

In the most recent research from China, researchers sourced packaged drinking water from an online store (69 bottles from 23 different brands) and evaluated the microfiber content in it. The results indicated the presence of microplastic particles in all the samples tested in the range of 2–23 particles/bottle. Out of those, a major contribution was noted from PP (polypropylene), PS (polystyrene), PE (polyethylene), PET (polyethylene terephthalate), and PU (polyurethane) polymers. The researchers also reported that the higher microplastic content might be from the packaging material of the PET bottles and caps. Approximately 33.33–100% of particles were reported as fibers from 23 brands followed by fragments. The study used an equation to estimate the daily intake (EDI) of microplastics from bottled water as follows: EDI(MP/kg/d) = (C × IR)/bw. IR = ingestion rate (L/d), C = concentration of Microplastics (particles/L), and bw = body weight (Kg).

Based on the results of this study, average consumption of 16 microplastics/L was noted. The researcher reported consumption of 7.30 microplastics/kg/year/person (for children) and for adults, it was reported as 16 microplastics/kg/year/person, respectively. The consumption rate of the water was used as per the guidelines of the Chinese Nutrition Association [117]. From the literature, it was clear that most of the bottled drinking waters are contaminated with microplastics. Most of the studies reported microfiber as the dominant type of microplastic [111, 113–115], whereas one study reported microfiber as the second major contributor [112] and the other study [117] did not analyze the particle morphology. During the analysis, studies also reported that the use of packaging material, like plastic bottles and bottle caps, along with different processing, storage, and transportation containers might have resulted in such microplastic debris in the packaged water. This idealogy can also be fitted to the tap water studies, as the processing is similar except for the packaging material. However, none of the researchers evaluated these processes to confirm the claim. One of the recent researchers evaluated the effect of loosening and retightening of disposable water bottle plastic caps (without removing them) on the microplastic release behavior. The study was performed on the water bottles obtained from California, USA. Each bottle cap was opened and closed 1, 5, 10, and 15 times before the analysis. The results of the study showed that the bottle cap opening and closing increased the microplastic in water at the rate of 553 ± 202 microplastics/L/cap cycles. Figure 5.6 represents the effect of bottle cap opening and closing on the microplastic concentration of the bottled drinking water. The abrasion between the bottle cap and bottle is noted as the major reason for the microplastic generation. Hence, the researcher suggested these parameters be considered as the main factors in future studies [118]. The results of these studies were in line with the results of Winkler et al., who reported >60,000 particles on the surface of single-use PET bottle caps after 100 cap open-close cycles. However, the study did not develop any microplastic in the water when higher mechanical stress was applied to the body (from outside of the bottle) of

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Fig. 5.6 Box and whisker plot of particle counts (Microplastics/L) measured in the bottled water as a function of the total number of bottle cap open-close cycles (whiskers show the maximum and minimum values, n is the number of samples) (Reprinted under creative commons license from [118])

the disposable water bottle for 10 min [119]. The second most important aspect that was reported in the literature is the contamination of bottled water in the manufacturing stage. Hence to confirm this factor, other researchers evaluated the potential microfiber contamination in several manufacturing processes. The results reported that all the samples checked at every stage had very few microplastics with less than 1 microplastic particle per liter. Though caustic cleaning liquid contained microplastic, those particles were removed during the cleaning process (jetting). A higher amount of microplastic was detected in the bottle capping and sealing process (increased from < 1 microplastic to 317 ± 2057 microplastics per liter). Hence, the study concluded that out of all processing stages, the water bottle capping and sealing process generates higher microplastics by confirming the previous research results. When the uncapped bottle water was analyzed before the capping process, a drastic decrease in the microplastic content was noted. Cap sealing material and capping material should be tested for their abrasive natures and potential release behaviours. Moreover, the study confirmed through FTIR analysis that more than 81% of the microplastics found were made of Polyethylene material which is used in the bottle cap. These findings confirmed that the bottle cap is the main source of microfiber contamination in bottled drinking waters [120]. Figure 5.7 depicts the microplastics identified at different bottling processes. Whereas the other water types like tap

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175

Fig. 5.7 Microplastic concentrations per L mineral water along the bottling process of four bottling sites (A–D), corresponding mean (error bars indicate standard deviation) and limit of detection (LOD) s for each sample type. Reprinted under creative commons license from [120]

water and public water resources, a detailed mechanism and pathway of microplastic contamination was detailed by Oladoja and Unuabonah [121].

5.5.3 Contamination in Milk Milk and milk products contain higher dietary fat, protein, and other nutrients. Milk plays a vital role in human health in all life stages. Fresh milk is one of the highly consumed raw materials, hence contamination in fresh milk provides a serious threat to humans [122]. Currently, raw milk is filtered for pathogens and contaminants like chemical substances but not for microplastic contamination. A study evaluated 23 milk samples of 8 different brands from Mexico. The findings of the research showcased that all the samples tested from 8 brands had microplastic content in them. A total of 150 microplastics were reported with an average of 3–11 microplastics per liter of milk sample analyzed. Out of the particles evaluated, a major contribution was reported by fibers (97.5%) followed by fragments. Though a human intervention with milk production is very less, the presence of microplastics in the milk is dreadful. Researchers reported the mixing of water into the milk might have brought a significant amount of microfibers into the milk. The other sources like the addition of fat (both vegetable and butterfat) into the milk are also reported as the main source of microfibers in milk. Other than this, filtration membrane that is used for the removal of pathogens and transportation hoses in the pasteurizing facility are also reported as possible sources. However, no extensive research was done on those areas [123].

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Other researchers evaluated the microplastic content of the milk samples obtained from Switzerland. The study compared the liquid (obtained from cows in the farm) and powdered milk that was purchased from the retail showroom. The results of the study presented that all the milk samples contained microplastics. Out of all the samples measured, the lowest abundance was noted in the liquid milk sample except for raw milk from the farm where a higher abundance was noted due to the milking machine. Other than this, the type of packing was reported as the major contributor of microplastic in the milk samples. During characterization, polypropylene (PP), polyethylene (PE), polystyrene (PS), polyamide (PA), and polymethylmethacrylate (PMMA) were reported as the major contributing polymers in milk. The detailed microplastic count and their polymer types are provided in Table 5.3 [124]. Table 5.3 Number and type of microplastics detected in cow’s milk samples Milk samples

Total number Microplastic of surface 20 mm) based on their size. However, a higher concentration of microplastics was reported. Most of the microplastics reported are microfibers (42.8%) followed by the film (35%) and fragments (22.2%). Polyethylene, polypropylene, Nylon 6.6, polystyrene-butadiene-styrene, polyvinyl chloride, polystyrene, thermoplastic polyurethane, polyvinyl alcohol, and ethylenepropylene Rubber are the major polymers reported in this research [142]. Other researchers evaluated the microplastic contamination near the Rothera Research Station, Adelaide Island, Antarctic Peninsula. The study evaluated the sediments around the 7 km region of the research station and reported a higher concentration of microfiber (total of 31 microplastics) in all the locations analyzed (mean length of microfibers in the range of 2–5 mm). A higher concentration of pollution was reported in the locations near to research station and 42% of all particles examined were rayon fibers. These results suggest that the fibers are originated from textile materials. The study ensured that shipping activities and research stations are the major source of microplastic pollution in the Antarctic regions [143]. Recently, Kelly et al. analyzed the sea ice from the East Antarctic region and reported higher microplastic contamination. The study collected sea ice from different depths and analyzed the contamination of microplastics. The results reported that a total of 96 microplastics were identified with an average of 11.71 microplastics per liter. Polyethylene, polypropylene, and polyamide are the major polymer types identified with the collected samples. The researchers compared the abundance of the microplastics with other sea ices and samples collected from the Arctic region and reported comparatively a lower abundance. The distant location from the land area is considered as the main reason for the lower abundance. The study did not relate to the atmospheric transport of microplastics. However, based on the polymer types reported, the study related the fishery equipment as the main resource for these microplastic contaminations in the Antarctic region [144]. Other researchers reported the contamination in Antarctica and south ocean regions. The study reported a total of 147 microplastics and 28 out of 30 sediments showed at least one microplastic in them. The study showed a mean microplastic concentration of 1.30 ± 0.51, 1.09 ± 0.22, and 1.04 ± 0.39 microplastic per gram of sediment from the Antarctic Peninsula, South Sandwich Islands, and South Georgia, respectively. In this research, fragments were the major contributors (56%), followed by fibers (39%) and films (5%). As far as the polymers are concerned, a total of 14 polymers are reported with a major contribution from polyesters, polypropylene, polystyrene, polyurethane, polyvinyl chloride, rubber, and acrylic polymers. This study also reported fishery equipment

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as a major contributor to microplastic contamination. However, they also mentioned that not only the marine activities are the reason, but also the atmospheric transportation. Identified polyester fibers mostly resemble textile materials, hence they might have been transported through atmospheric transfer. Further, the researchers also suggested many paint pigments used in the fishing vessels, which consist of polyester, acrylic polymers, and varnishes. Those were also reported to be the main sources of microplastic pollution [145]. Other than these snow studies, many researchers evaluated the marine microplastic contamination in the seashore and seawater around the Arctic and Antarctic regions and were consolidated in the recent research [146]. From this review, it can be clearly understood that though lower contamination was reported in the Polar Regions and glaciers than in the countryside, all samples showed the prevalence of microplastic and microfiber. Most of the researchers reported the atmospheric transportation of the microplastic from populated sites as the main reason for the microplastic deposits in the remote regions of Arctic and Antarctic regions, whereas others reported the tourist activities like trekking and camping as the main source of microplastics. Also, the fishery and shipping activities are reported as one of the reasons for microplastic shedding. In summary, other than atmospheric transmission, human activities are noted as the foremost reason for the microfiber abundance in the remote polar and glacier regions.

5.7 Impact on Human Human exposure to microplastic is one of the most researched areas in recent times. Inhalation, ingestion, and skin contact are the three major pathways of microplastic exposure in humans. As the skin will not directly allow any material through it (unless otherwise there is damage), the major exposure routes reported are ingestion from food items and inhalation from the environment. Microplastic exposures to humans generally occur from primary microplastics such as cosmetics, toothpaste, scrubs, and hand washes. One of the key pathways of microplastic to reach humans is through food items. A detailed summary of recent studies that reported seafood items with microplastic contamination can be found elsewhere [147]. Further, as discussed in the previous section, studies reported higher contamination of seafood or freshwater food items with microplastics (Sects. 5.2 and 5.5). Similarly, other researchers also reported a higher concentration of microplastics specifically microfiber in other common edible items and drinking waters from taps and bottles (Sect. 5.5). Although, knowledge on microplastics and their ingestion in aquatic life, food products, and seafood existed, the information on microplastic ingestion in to human body is not explored so far. Hence, the toxic effects of microplastics and the effect of long-term exposure were not known clearly [148]. On the other hand, few studies performed on the seafood and aquatic animals reported that the identified microplastics were mostly found on the gut of the animals that were rarely consumed [149, 150]. Hence, studies reported that the possibility of that particle ending up as a human

5.7 Impact on Human

183

health hazard is very less [151]. In the meantime, another study confirmed that the microplastic exposure from seafood like mussels is comparatively very low when we compare the atmospheric airborne microplastic fallout on our regular foods [152]. Hence, the consumption of microplastic through food, either from the aquatic life forms or from the atmospheric deposit is clearly evident. Table 5.4 consolidates the various studies that reported the approximate human consumption of microplastic from edible items as reported by Pironti et al. [153]. Studies pointed out that microplastic of smaller size (less than 150 μm) can possibly get transported from the gut cavity to the circulatory system and get reached the human body. However, a larger particle will not be absorbed into the skin. But it was predicted that the maximum absorption percentage of microplastics is less than 0.3%. In the case of an internal organ, only the particles less than 20 μm will be able to penetrate and the microplastics less than 10 μm can access all organs, cell membranes, the blood–brain barrier, and the placenta [147]. One of the recent studies reported the cytotoxic effects of microplastic and nano plastics (40–250 nm) against cerebral and epithelial parts of human cells. The in-vitro analysis results supported the previous speculation on the impact of microplastic on human health [165]. The absorption of micro and nano plastic is usually absorbed through pinocytosis and vesicular phagocytic processes. In this process, the microfold cells in the Peyer’s patches were reported as the main point of the location where the micro and nano plastics will get absorbed. This system translocates these particles into the human body [166]. Other researchers evaluated the effect of microplastics on A549 lung cells and human gastric adenocarcinoma cells. The results showcased that both the cells developed inflammation and large particles have developed cytokines in the cells [167, 168]. Another study mentioned the risks associated with airborne microplastics on human health. They have reported different stages of the microplastics inside the human body after inhalation, namely (i) deposition, (ii) clearance, and (iii) inflammation and cancer. In this process, the first step after inhalation is the deposition of inhaled microplastics in the respiratory tracks and lungs. Next to the deposition, the migration of particles is reported at the regional numb nodes. In the last stages of the process, the inhaled particles result in inflammation of the cells and release cytokines, proteases, and reactive oxygen species (ROS), creating cytotoxicity. Other than the surface interaction, the absorbed nano and microplastics induce a protective response and result in inflammation and cytotoxicity. This ultimately leads to cell damage and the intercellular effect of the particle [13]. The review also reported the importance of the translocation process of inhaled microplastics and nano plastics. The translocation of microplastics may allow these particles to deposit or circulate on or into any organs based on their hydrophilicity, size, and surface charge. This will also develop severe inflammation in human organs [13]. As discussed at the beginning of this section, the impact of three different pathways of microplastics on human health was detailed by Yee et al. [169]. In their review, they have assessed the impact of inhalation, ingestion, and dermal contact of micro and nano plastic particles and their impact on the different internal parts of the human body. The pathway and their impact on the specific part are detailed in Fig. 5.8 as reported by Yee et al. [169].

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Table 5.4 Estimated intake of microplastics through inhalation, food and beverages, and packaging Sample

Origin

Estimated intake

References

Air (inhalation)

Europe (UE)

26–130 particles/day/capita 272 particles/day/capita

[13, 154]

Dust

Tehran, Iran (IR)

107–736 particles/year/capita (Adults, normal exposure) 253–2429 particles/year/capita (Adults, acute exposure) 644 particles/year/capita (Children, normal exposure) 3223 particles/year/capita (Children, acute exposure)

[155]

Seafood

Europe and American countries

518–3078 particles/year/capita

[156]

Seafood

UK, Other countries such as France, Belgium, and Spain

123 particles/year/capita (UK) 4620 particles/year/capita

[157]

Salt

Australia, France, Iran, Japan, Malaysia, New Zealand, Portugal South Africa

37 particles/year/capita

[98]

Salt

Turkey

249–302 [158] particles/year/capita (sea salt) 203–247 particles/year/capita (lake salt) 64–78 particles/year/capita (rock salt)

Salt

North Sea Salt Celtic Sea Salt Mediterranean Sea Salt Mediterranean Sea Salt Utah Sea Salt Himalayan Rock Salt Mined Hawaiian Sea Salt Ocean Baja Sea Salt Ocean Atlantic Sea Salt Ocean Pacific Sea Salt

40–680 particles/year/capita

[111]

Salt

Spain

510 particles/year/capita

[97]

Salt

China (CN)

1000 particles/year/capita

[159] (continued)

5.7 Impact on Human

185

Table 5.4 (continued) Sample

Origin

Estimated intake

References

Drinking water

Asia, USA, and Europe

3000–4000 particles/year/capita

[160]

Drinking water

America

4000 particles/year/capita (consumers of tap water) 90,000 particles/year/capita (consumers of water from plastic bottles)

[161]

Drinking water, salt, and beer

USA

5800 particles/year/capita

[111]

Milk (infant exposure)

Asia, Europe, America, Oceania, Africa

527,000 and 893,000 [162] particles/day/capita (Asia and Africa) 2,100,000 particles/day/capita (Oceania) 2,280,000 particles/day/capita (North America) 2,610,000 particles/day/capita (Europe)

Fruits and vegetables

Italy (IT)

29,600–1,416,000 particles/kg/day

[123]

Meat (food packaging)

France (FR)

0.1–515.2 mg/year/capita

[163]

Take-out containers

China (CN)

2977 particles/year/capita

[164]

Reprinted under creative commons license from [153]

The cellular intake mechanism of microplastic was reported by Yee et al. [169]. The review reported that the intake of nano and microplastic in the human body largely depends on different shapes, sizes, and surface areas of the particle. Once they are absorbed on the skin, due to their nature, particles absorb proteins from the human body and form protein corona around its outer structure. This helps those proteincovered nanoparticles to translocate to a greater extent compared to the normal nanoparticle. Further, the researchers reported that the protein corona can also alter the shape of the nanoparticles and increase cell toxicity. Finally, these protein coronacovered particles are reported in the guts of the body by accumulation. A detailed report on the cell and nano and microplastic interaction can be found elsewhere [169]. Figure 5.9 represents the various impact of microplastics on human health. Other researchers reported higher inhalation of microfibers compared to ingestion. Approximately, 3–15 times higher amounts of microfibers are inhaled by humans than the ingestion process [153]. To support this, a study reported a higher accumulation of polyester and acrylic plastic dust in the lungs of the workers, who work in the

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5 Impact of Microfiber/Microplastic Pollution

Fig. 5.8 Different pathways of microplastic absorption into humans and their potential impact on human health

plastic processing industry [170]. Out of all the methods discussed, microplastic ingestion through dermal contact was reported as a less significant route. However, a concrete estimation of the exact interaction mechanism and the real-time effect of the microplastic inside the human body was not reported. One of the recent studies measured the lifetime accumulation of microplastic in humans through statistical modeling. The researcher evaluated the intake of microplastic through two of the above-discussed mechanisms, namely ingestion through food and beverages (nine mediums) and inhalation through the atmosphere. The study used an intake of 553 particles/capita/day and 883 particles/capita/day for children and adults, respectively, and predicted the consumption using a statistical model. The results reported an accumulation of 8.32 × 103 particles/capita for children (until age 18), and up to 5.01 × 104 for adults (until age 70). The researcher considered the microplastics in the range of 1–10 μm. However, to assess the chemical toxicology, the total uptake of the chemical through these microplastics are low compared to the other contaminant exposure routes [171]. This summary of literature clearly showcases that though literature reported the potential negative impacts of microplastic on human health, the direct studies to

5.8 Microfiber Interaction with Other Pollutants

187

Inflammation Physical stress and damage

Oxidative stress Toxic effect of microplastics

Leaching of Toxic Chemicals

Apoptosis Metabolic homeostasis

Fig. 5.9 Impacts of ingested/inhaled microplastic on human health

assess the real-time impact are fewer. Studies postulated the effect of ingestion with the existing knowledge on the nanoparticles and their ingestion. Few researchers reported the potential pathways for human exposure and in-vitro cell line studies against human cells and tissues. Even the lifetime accumulation of the microplastic inside the human body was predicted and reported. However, like aquatic animals, the original effect of these ingested and inhaled particles on human health is still under study. As the studies on microplastics and microfibers are emerging exponentially, it is speculated that soon some research findings will provide a complete impact of this contaminant on human health.

5.8 Microfiber Interaction with Other Pollutants As discussed in the previous sections of this chapter, the impact of microplastics and microfibers on different environments and life forms is highly significant. In the meantime, though much research was performed, few researchers reported that microplastic also possesses the potential to carry active pollutants from different sources as a carrier [172]. It is also speculated that the microplastics either absorb

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toxic chemicals and components from the environment or it may carry chemicals in their structure itself. Researchers reported that the additives and chemicals used in the manufacturing stages of the chemicals/products act as potential pollutants in the case of microplastic debris. The key origin of microfibers is synthetic textile materials. Hence, the dyes, finishes, and additives applied during the fiber and fabric production stages are also released into the environment while the microfibers are weathered. Since the effect of microplastic ingestion on the aquatic biota and humans is uncertain, it is also suspected that the release of chemicals possesses an additional threat to life forms. Out of several speculations, the accumulation of metals like chromium, copper, lead, zinc, and nickel has been widely studied in the literature [173–175]. Hence, the chemical sorption and release characteristics of the microplastic become one of the essential areas to be explored. Recent studies confirmed the chemical sorption characteristics of microplastics. Researchers analyzed the chemical sorption nature of high-density polyethylene, polystyrene, and polystyrene carboxylate microplastics against different perfluoroalkyl substances. The results of the research revealed that the particle size of the microplastics is an important factor in deciding the sorption rate of chemicals. A particle with a smaller size showed higher chemical sorption. These findings imply that aged particles are able to carry more chemicals due to their size reduction, and at the same time, a smaller particle has a higher chance to be consumed by aquatic microorganisms. When the sorption ability was measured against both the freshwater and seawater, higher sorption was noted with freshwater. The salinity and pH variation in the seawater act as restriction factors for the higher sorption of chemicals onto the microplastics. Out of the studied microplastics, polystyrene and polystyrene carboxylate microplastics showed higher sorption characteristics than polyethylene [176]. Whereas other study results showcased that the effect of salinity was nil on chemical sorption and desorption characteristics of microplastics. In this study, researchers measured the sorption and desorption characteristics of polyvinyl chloride (PVC) and polyethylene (PE) microplastics against phenanthrene (Phe) and 4,4' -Dichlorodiphenyltrichloroethane (DTT). Out of the two chemicals, DTT showed slightly higher sorption in freshwater than Phe suggesting different interaction mechanisms with microplastics. The results exhibited that the estuaries are the key locations where the higher contaminations are possible than the rivers and marine environment. This is mainly due to the nature of estuaries, where the water kept ideal and allowed the contaminants to settle. The study also reported a higher concentration of Phe and DTT in estuaries, which represents that they were acting as link sink for microplastics originating from nearby sources. As far as the desorption is concerned, the number of chemicals desorbed from the microplastics was higher in the case of estuaries due to their longer storage time. The desorption of chemicals from microplastics after the ingestion is not known to date. However, a higher concentration of the contaminants may harm the animals and create an adverse effect ecologically [177].

5.8 Microfiber Interaction with Other Pollutants

189

Godoy et al. [178] evaluated the metal (Cd, Co, Cr, Cu, Ni, Pb, and Zn) sorption characteristics of common plastics materials, namely polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS) and polyvinyl chloride (PVC). The study results revealed that all the selected plastics sorbed the metals quickly within 5 days and obtained equilibrium. The results showed that PVC and PE exhibited a higher metal sorption capacity than PS, PP, and PET. Adsorption of 0.5 mg/g was obtained with PE, against Cr and PVC adsorbed with 0.5 mg/g of Zinc. Other polymers adsorbed lead as a major component. Co and Ni were reported to be the least adsorbed material concerning the selected polymers [178]. The adsorption kinetics of polymers largely depends upon the affinity of the metals and also the morphological, and chemical properties of the polymers [179]. The study also demonstrated the influence of microplastics’ surface properties, porosity and morphology on the sorption behavior. With respect to the salinity of the seawater, Cu and Cr showed good adsorption on PP and PVC, whereas Cr and Co adsorption seems low with PS. Hence, researchers concluded that the influencing factors are interlinked in a complicated way, and hence, they proposed the need for future research [178]. Similarly, the disposable tri-layer surgical mask is one of the most common materials used by the general public due to the pandemic restrictions. The higher amount of masks usage in the pandemic also increased the improper disposal. Many recent researchers reported that improper disposal of surgical masks is one of the most important sources of polypropylene microfiber release into the environment [180, 181]. Synthetic textiles were also identified as a key source of microfiber emission into the environment [182]. In this regard, the pollution carrying ability of microfiber released from the disposable mask was evaluated and reported as positive. The study results proved that microfibers are able to carry textile dye as a pollutant to the aquatic environment [183]. Other than the metals, microfibers and microplastics are also able to carry organic pollutants. Microplastics collected from different beaches and sea shorelines showed a higher presence of polycyclic aromatic hydrocarbons (PAHs) in them. Results of the study reported PAHs concentration ranging from 35.1 to 8725.8 ng/g of microplastics collected from the Canary Islands and in other areas like open seas close to China, Japan, and the Caribbean Sea it was reported as 1 to 9300 ng/g [184, 185]. Other researchers reported the adsorption of benzo(a)pyrene on polystyrene micro and nano plastics particles and assessed the transfer in mussels and analyzed the toxic effect in-vitro. The results showed that ingestion of microplastics showed a higher cytotoxic to hemocytes of an animal cell. Microplastic particles reduced the plasma membrane integrity and affected the phagocytic and lysosomal activities. The study confirmed the cytotoxicity of the microplastic loaded with benzo(a)pyrene and proved that micro and nanoparticles can act as a carrier of organic pollutants [186]. Various types of pollutants carried by different microplastics are listed in Table 5.5 as reported by [187]. As far as the physical properties of the microplastics are concerned, researchers found a higher contaminant with the lighter color microplastics than the dark colored ones. Similarly, higher density microplastics showed a lower concentration of PAH and PCB. The other important factor that cannot be ignored is the effect of aging

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Table 5.5 Types of pollutants carried by different types of microplastics Microplastics

Pollutants

References

Polyamide

Benzene derivative

[188]

Polybutylene adipate terephthalate

Heavy metals

[189]

Polyethylene

Lubrication oil

[190]

Polycyclic aromatic hydrocarbon

[191]

Paraquat

[192]

Polybrominated diphenyl ether

[193]

Polychlorinated biphenyl

[194]

Per- and polyfluoroalkyl substances

[195]

Perfluorooctanesulfonamide

[196]

Pharmaceuticals personal care product

[197]

Triclosan

[198]

Polyethylene terephthalate

Heavy metals

[199]

Polypropylene

Heavy metals

[192]

Polycyclic aromatic hydrocarbon

[32]

Polystyrene

Antibiotic

[200]

Cadmium

[201]

Lubrication oil

[193]

Polychlorinated biphenyl

[194]

Per- and polyfluoroalkyl substances

[202]

Perfluorooctanesulfonamide

[196]

Polyvinyl chloride

Roxithromycin

[197]

17α-Ethinylestradiol

[203]

Antibiotic

[204]

Benzene derivatives

[189]

Heavy metals

[192]

Odesmethylvelafaxine

[205]

Polychlorinated biphenyl

[206]

Perfluorooctanesulfonamide

[202]

Phenanthrene

[202]

Venlafaxine

[202]

Low-density polyethylene

Heavy metals

[184]

High-density polyethylene

Heavy metals

[207]

Reprinted under Creative commons license from [187]

5.9 Conclusion

191

or weathering. This process increases the surface area, the roughness of the surface, and porosity, and hence higher adsorption is expected after the weathering process. However, there is a debate among the researchers as few results showed a reduction in sorption after weathering [208] and others showed an increment in sorption [209]. In the case of chemical properties, composition, synthesis method, polarity, crystallinity, functional groups, and bonding type are the main factors that decide the interaction of microplastic and pollutants [187]. For instance, a particle with a higher surface area and porosity lead to higher sorption than a lower surface area. However, a smaller area resulted in faster chemical sorption on the microplastic compared to a larger surface [200]. Likewise, the affinity of the polymer and pollutant is largely influenced by the type of chemical interaction. Hence, the types of interactions like electrostatic interaction, van der Waals force, hydrophobic interaction, π–π interaction, or hydrogen bonding also influence the sorption behavior [209]. Another chemical nature that influences the sorption behavior is hydrophobicity or hydrophilicity of the pollutant and microplastics. In summary, the type of interaction is largely variable and depends upon the changing environmental conditions and the properties of the substance [187]. Researchers reported that dissolved organic matter, pH, and salinity are the main factors that influence the pollutant sorption capacity of the microplastics [187]. In which, the dissolved organic matter has a higher influence as it interacts with microplastics and alters the sorption capacity in-situ [210]. The dissolved organic matters interact with the microplastics either through a complexation process or by hydrophobic interaction. After the interaction, it competes with other sorbents and gets sorbed onto the other sorbents based on their reactivity [206]. However, against some polymers, dissolved organic matters reduced sorption and for other pollutants, it did not have any changes in the sorption [206]. Similarly, the effect of pH or salinity is also subjected to the type of polymers and pollutants in a particular environment [187]. From these analyses, the pollution carrying ability of the microplastics and fibers is evident, and still, the effect of physical, chemical, and environmental parameters was not explored as they are widely polymer and pollutant specific. Detailed information on the recent research progress in the field of microplastics as a pollution carrier [211], its effect on toxicity, bioaccumulation, degradation, and transport [212], and their impact on aquatic life forms can be found elsewhere [213].

5.9 Conclusion The ubiquity and impact of microfiber, as well as microplastic pollution, are elaborated on in the chapter. Microplastic contamination was evident in almost all the levels of the environment and atmosphere. Various studies have quantified the contamination in the atmosphere, marine environment, freshwater bodies, glaciers, etc. and analyzed the characteristics of the microplastic particles to backtrack the potential sources of the contaminants. Most of the researchers have reported human activities like laundering of clothing, tourism, fishing, aquaculture, etc. as the major reason

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for contamination. Whereas in remote areas, where the human intervention is lesser, the source of contamination is addressed as the translocation of microplastics from different locations and deposition of atmospheric microplastics. The contamination of these environments, in turn, results in the contamination of living organisms that are depending on these environments. Different aquatic organisms were noted with microplastics and the effect of microplastics on those organisms was also reported. Similarly, various food items including table salt, milk, honey, and drinking water were also found with microplastics. Moreover, due to the prevalence of microplastics in the environment, as well as the food items, human beings are getting exposed to microplastics. Through ingestion, inhalation, and dermal contact, human beings are consuming microplastics. Though the effect of these microplastics is speculated at smaller levels, a detailed study on their effect on the human body is still in need. The knowledge of the impact and hazardous nature of the microplastics is indispensable to take a step toward mitigation. Hence, the chapter provided deep insight into the current research on the impact of microplastics and also highlighted the areas to be given more attention in future research.

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Chapter 6

Microfiber Pollution Prevention—Mitigation Strategies and Challenges

6.1 Introduction The realization of the serious impact associated with microfiber pollution on the environment and eco system made the researchers and environmentalists seek different solutions for the issue. The existence of microfibers in different levels of the environment including aquatic, terrestrial, and atmosphere was evident from different researches [1–4]. Moreover, the routes of these microfibers to reach human beings and other living organisms were also clearly defined [5–7]. The impact of these microfibers made the importance of finding the solution for the issue more obvious. Being a globalized issue, various researches are being emerged in identifying the proactive solution for the issue. Environmentalists initiated the research and have reported the contribution of different sources to microplastic pollution. They had started innovating technologies that can effectively remove microplastics from the environment. However, a mitigation strategy from one viewpoint is not sufficient to solve the problem. Since the studies had revealed that textile materials are the major sources of microplastics [8], research from the textile domain is an inevitable one. Researchers have commented that the understanding of textile properties and their effect on microfiber release is very important, and altering these properties will be the long-term solution to the issue [8–10]. An environment that is free from microfibers can be achieved only by approaching different mitigation strategies at different levels. The solutions can be at different levels starting from the source level, that is, finding better alternatives for synthetic materials to creating awareness among people and implementing regulations and laws [11]. Figure 6.1 shows the interdisciplinary measures that have to be implemented for the reduction of microfiber’s impact on the ecosystem. At each level, certain limitations restrict the effective implementation of the strategies. A clear understanding of existing mitigating measures and their drawbacks is necessary to solve the issue. Hence, this chapter details various strategies that have been made at each stage that can effectively end up in mitigating microfiber pollution. Also, the challenges that are being faced in the implementation © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 R. Rathinamoorthy and S. Raja Balasaraswathi, Microfiber Pollution, Sustainable Textiles: Production, Processing, Manufacturing & Chemistry, https://doi.org/10.1007/978-981-19-4185-6_6

205

206

6 Microfiber Pollution Prevention—Mitigation Strategies …

Fig. 6.1 Different levels for implementing mitigation strategies

of such strategies have been highlighted, and this can effectively address the gap in the research area.

6.2 Production Stage—Modification of Source (Textile Materials) 6.2.1 Surface Finishing of Textile Materials Textile materials being the point source of microfiber pollution, the alteration or modification of textile materials could be the proactive solution to the problem. Since the microfibers are found to release from the surface of the textile materials, surface finishing of textile materials was sought as a proactive solution. In general, fabric finishing is one of the common processes in fabric manufacturing that aids to impart desirable aesthetic and functional properties to the fabrics. The finishing of fabrics can be either mechanical or chemical. When controlling microfiber shedding is considered, chemical finishes have been noted to have a significant impact [12– 15]. In the chemical finishing of fabrics, the finishing agents are uniformly applied over the surface with water as a medium and the subsequent drying and curing process removes the water [16]. This coating of finishing agents on the surface can possibly bind the fibers on the surface which is believed to restrict fiber slippage and detachment from the surface. Moreover, they are expected to improve the mechanical properties of the fabrics, which, in turn, helps in reducing microfiber shedding [12, 13]. Researchers have tried the application of different finishing agents and textile auxiliaries on synthetic textiles and their effectiveness in reducing microfiber shedding was analyzed [12, 13].

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Synthetic Finishes There are several synthetic finishing agents for textile materials that are being used for improving the handle and physical properties of textiles. Since these finishes were found to improve the surface properties of textiles, researchers have explored their effectiveness in altering the microfiber shedding property of the textile materials. In this aspect, Acrylic resins (Polyacril 73, Polyacril 97, and Polyacril 56 ECO), Polyurethane resins (Purlastic 8139 and Purlastic 8189), and Silicon-based resin (Polysilk-CTE) were examined for their ability to control microfiber shedding of polyester fabrics. In the preliminary study, Polysilk-CTE, a silicone emulsion that is commonly applied to improve the softness and surface smoothness of the fabric to provide a better handle, was noted to have better action against microfiber shedding. The pad-dry-cure method was implemented for the coating of Polysilk-CTE over polyester and polyamide fabrics. Polysilk-CTE treated fabrics showed a significant microfiber shedding reduction of 47.5% and 63.25% in the case of polyester and polyamide fabrics, respectively. However, reproducibility of the results became an issue in the larger-scale analysis where a larger standard deviation has been noted. This might be attributed to the difference in the process conditions between lab-scale and industrial-scale trials [15]. Moreover, the eco-friendly nature of these synthetic finishes is questionable that can again potentially lead to the problem related to sustainability. Hence, the successive researchers focused on identifying bio-based polymers to mitigate microfiber shedding. Bio-based Finishes Researchers have analyzed the effect of chitosan as a finishing agent on synthetic textiles to mitigate microfiber shedding. Chitosan, being derived from natural sources, attracted researchers as they are widely available at a low price. Various beneficial properties including non-toxicity, biocompatibility, and biodegradability made chitosan seem like a sustainable solution [15]. Moreover, chitosan has shown excellent results as an anti-pilling and anti-felting agent. Though this was effective in natural-based fibers like cotton, the researchers attempted to analyze its effect in synthetic fabrics as pilling was noted as one of the main reasons for microfiber shedding [15]. Polyester woven fabrics were treated with chitosan by two methods, namely the impregnation method and laboratory-scale padding method. The presence of finish over the fabric surface was confirmed by the reactive dyeing method, SEM analysis, and FT-IR analysis. Researchers reported a reduction of 18% and 27% in the microfiber shedding after treating with 2% and 3% chitosan solution, respectively [15]. In line with this, other researchers analyzed the effect of chitosan coating on different synthetic fabrics including polyamide, polyester, and acrylic. The study explored the effectiveness of different concentrations of chitosan solution by treating fabrics with 0.1%, 0.4%, 0.7%, and 1% of chitosan solutions. Here, the fabrics are treated with chitosan using the dip-dry method, where the fabrics are dipped in the prepared chitosan solution for one hour at 24 ºC, and then the fabrics were dried at 120 ºC for 2 h. In the case of polyester fabrics, among different concentrations,

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0.1% have not shown any significant change from the untreated sample, whereas treatment with 0.7% chitosan solution leads to a higher reduction of microfiber shedding (around 95%). While treating with lower concentrations, the chitosan dose was not enough to form a complete coating over the surface of the fabrics compared to higher concentrations. However, the poor microfiber reduction in the case of 1% chitosan concentration which is higher than 0.7% can be attributed to the nonuniform, thick layered coating due to film sagging which was evident from the SEM analysis of coated fabrics [12]. This could be the possible reason for the lesser microfiber shedding reduction efficiency of chitosan finish in the previous research as the concentration of the chitosan was maintained higher at 2 and 3% [15]. Thus, the researchers suggested that the chitosan solution of moderate concentration (0.7%) can form a uniform coating over the fabric surface leading to a reduction in the physical damage to the fibers during laundry. They have also highlighted that the uniform coating is a key factor that determines the microfiber shedding reduction. While interpreting what exactly happens during the application of chitosan over the polyester fabrics, there forms a linear bonding between the carboxyl group of chitosan and the terminal group of polyester fabric. This bond increases the tensile strength between each fiber. Moreover, the chitosan treatment leads to an increase in the stiffness of the fabric (around 58% increment than the untreated one). The penetration of chitosan leads to the stiffness increment and forms film over the surface. Moreover, the fibers are well-connected after treatment with chitosan solution. This reduces the free movement of microfibers to detach from the surface [12]. When applying the chitosan in polyamide and acrylic fabrics, a difference in the microfiber reduction efficiency has been noted (polyamide fabrics—48% reduction; Acrylic fabrics—49% reduction) when compared to polyester fabrics. That can be again related to the level of adherence of chitosan coating on the surface of the fabrics. While examining the SEM images of (polyester, polyamide, and acrylic) fabrics treated with chitosan, polyester, and acrylic fabrics were noted to have a perfect coating of chitosan on the surface before being exposed to washing. Whereas the coating was not uniform on the surface of polyamide fabrics. Further, after washing, the coating over the polyester fabrics withstood the washing, whereas chitosan coating was noted to peel off in the acrylic fabrics. This ineffective adherence of the chitosan coating over polyamide and acrylic fabrics led to minimized microfiber shedding reduction efficiency [12]. It has been noted that the difference in the reduction efficiency is not only limited to the inefficiency of chitosan to get stuck to the fabric surface, but also the application process parameters. Further exploration of different application techniques can enable the chitosan coating effective for polyamide and acrylic fabrics as effective as in polyester fabric [12]. De Falco et al. have attempted to reduce microfiber shedding of polyamide fabrics by coating them with a natural polysaccharide—pectin. For effective application of pectin over the polyamide fabrics, the researchers modified the pectin with Glycidyl methacrylate (GMA) and then the synthesized Pectin-GMA was grafted on the surface of polyamide fabrics. The main purpose of the modification of pectin with GMA was to reduce the water solubility of pectin which sought importance in the textile finishing process. When pectin is treated with GMA, a three-membered ring

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of epoxide group of GMA reacts with the carboxyl group of pectin monomer which can conceal the carboxyl group of pectin and thereby reduce the water solubility. Secondly, GMA imparts vinyl group in pectin which helps in the effective reaction of pectin with polyamide fabrics [13]. To ensure an effective uniform coating over the fabric surface, different molar ratios of Pectin-GMA and different concentrations of pectin have been tried. The SEM analysis revealed a 1:1 pectin-GMA molar ratio and 0.5 wt/v % of pectin concentration showed uniform coating of a thin layer of pectin on the surface of polyamide woven fabrics. The thinness and uniformity of the coating are highly considered to retain the handle properties of the fabric. The effectively coated polyamide samples were found to shed lesser microfibers than the untreated fabrics. Almost 90% reduction has been noted in the microfiber shedding after treatment with Pectin-GMA synthesis. In addition to this, the reduction in the fragmentation of the fibers was also noted. The fibers that are shed from the untreated samples were shorter (312 ± 222 μm) than that of fibers shed from finished samples (550 ± 384 μm). In addition to the binding of fibers within the fabric surface, the coating also increased the tearing strength of the fabric. These alterations effectively helped in reducing the microfiber shedding behavior of the fabric. Moreover, the effective durability of the coating was also proven by the morphological analysis of the samples after washing which showed the presence of coating even after washing [13]. With uniform and homogeneous coating as an essential matter in the finishing process, in other research, the Electro Fluido Dynamic (EFD) method of coating has been performed. Poly (Lactic Acid) and Poly (butylene succinate-co-butylene adipate) were used as eco-friendly finishing agents and applied to polyamide fabric by the EFD method. With this method, a fine coating of a thickness of 100–150 nm was achieved which helped in retaining the handle properties of the fabrics [14]. This fine coating of both Poly (Lactic Acid) and Poly (butylene succinate-co-butylene adipate) helped in protecting the fabric surface from the chemical and mechanical actions during washing and reduced the microfiber shedding. While considering other physical properties of fabrics, both the finishes left the hydrophobic nature of polyamide fabrics unaltered which was confirmed by the wettability contact angle [14]. When the length of microfibers shed from the finished fabrics was compared with unfinished fabrics, both untreated and Poly (Lactic Acid) treated samples showed a similar length of fibers, whereas fabrics finished with Poly (butylene succinate-co-butylene adipate) shed longer fibers. The more ductile nature of this finish acts as a protection to control fiber fragmentation. When the durability of the finishes was explored, though both the finishes withstood consecutive wash cycles, Poly (Lactic Acid) was comparatively more durable than Poly (butylene succinate-co-butylene adipate) [14]. Table 6.1 consolidates different finishing agents that are analyzed by different researchers for mitigating the microfiber shedding behavior of synthetic textiles. From the results of the literature, the chemical finishing of textile materials can be an emerging solution that can help in controlling microfiber shedding. The studies have revealed that these finishes can act as a protective layer that can prevent the textile materials from external mechanical and chemical actions. Thus, the fibers on the surface remained undamaged even when the fabrics are exposed to external actions.

Fabric composition

Polyester

Polyester

MERMAIDS 2015 [15]

MERMAIDS 2015 [15] Woven

Woven

Polyamide

De Falco et al. 2019 [14]

Polyamide

Woven

Polyamide

Woven

Knitted

Fabric structure

De Falco et al. 2018 [13]

Acrylic

Polyamide

Kang et al. 2021 [12] Polyester

References

Polysilk-CTE

3% Chitosan –

–

–

Poly (butylene succinate-co-butylene adipate) 2% Chitosan

–

Modified with Glycidyl methacrylate

–

Pre-treatment/additives

Poly (lactic acid)

Pectin

0.7% Chitosan

Coating/finishing agents

Table 6.1 Effect of different finishing agents on mitigating microfiber shedding behavior of synthetic textiles

Padding method

Impregnation method; padding method

Electro fludio dynamic method

Treated under stirred nitrogen atmosphere (100 rpm; 1 h; 50 ºC); Dried at 70 ºC for 24 h

Dip-dry method (Dip—1 h, 24 ºC; Dry—2 h; 120 ºC)

Method of application

63.25

47.5

27

18

79.1

90.8

90

49

48

95

Max. reduction %

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Moreover, these finishes form connective links between the fibers such that the fibers on the surface get well-connected with each other reducing the fiber slippage [12]. Further, researchers have also noticed increment in the fabric mechanical properties like tearing strength [13] with these finishes which can also contribute to the reduction in microfiber shedding as the fabric strength is also an important parameter that can influence the shedding behavior. Figure 6.2 illustrates the mechanism of finishes in controlling microfiber shedding. It can be seen that the finishing agent, as well as the fabric composition, has a significant effect on shedding control. The same finish cannot be applied to different fibers as their affinity toward different fibers can vary. For each type of fabric, the process conditions should be analyzed and optimized to achieve a better affinity of finish over the fabric surface. The most important thing to be considered while opting for fabric finishes is the retainment of desired properties. Application of finishes over the fabrics can affect handle as well as other surface properties of the fabrics which are essentially desired. Hence, in this aspect, researchers have reported that the uniform and thin coating of these finishes can help in preserving the handle and surface properties of the fabrics. Researchers

Fig. 6.2 Mechanism of surface finishing of textile materials in mitigating microfiber shedding

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have reported unaltered fabric hand and wettability properties of fabrics even after the application of finishes [14]. In summary, while going for surface finishing of fabrics to reduce microfiber shedding, one should consider the sustainable nature of the chosen finishing agent, the affinity of the finish on the fabric, process parameters of finish application to yield uniform coating, and the retainment or improvement of the desirable properties of the fabric. While adapting such finishing process on the industrial scale, the exposure of fabrics to a higher temperature and mechanical actions can lead to microfiber shedding during the finishing process itself [17]. Hence, this should be taken care of as precautions to control the microfibers release during finishing treatment.

6.2.2 Improving Degradability of Synthetic Fibers The biodegradability of fibers in the environment take a key role in determining the level of the adverse impact of the fibers on the environment. When the degradability of the fibers were improved, their prevalence in the environment will get shortened. It has been commented that the easy degradability of natural fibers reduces their impact on the environment, and hence the problem of shedding in the case of textile materials made of natural fibers is often perceived as negligible [18]. This extends the scope of microfiber pollution mitigation to altering of degradability of fibers. The fact to be noted is that it is possible to alter the degradability of virgin fibers when they are subjected to subsequent textile processing like fabric dyeing and finishing. The study of Lykaki et al. revealed that the biodegradability of the viscose fabrics can be inhibited by the commercial antimicrobial finish (RUCO-BAC HAS CONC, a cationic quaternary ammonium compound-based antimicrobial agent) when compared to the control viscose fabrics. The interaction between the viscose and the antimicrobial agent restricts the interaction between microbes and viscose which eventually ends up in poor degradation [19]. The other researchers also reported variation (reduction) in the biodegradability of cotton in the initial stages when they are treated with different finishes including silicone softener, durable press, water repellent, and a reactive dye [20]. Thus, while suggesting textile processing for functional or performance requirements, biodegradability should also be considered and should be balanced. Whereas in the case of synthetic fibers which are already non-biodegradable, there are chances of improvement of degradability. In this essence, improving the degradability of synthetic fibers can be one of the potential strategies for reducing the impact of microfibers on the environment. In this aspect, the polyester fibers were modified in the fiber stage itself so that they can get degraded like natural fibers under the condition of water treatment plants or landfills [10]. CiCLO® is the brand name of a patented additive technology, which can be blended with non-degradable synthetic polymers like polyester and nylon at the time of melt extrusion to greatly accelerate the rate of biodegradation in natural environments where microfibers are prolific pollutants. The main principle is that this additive creates countless biodegradable sites throughout the matrix of the plastic,

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which acts as a source of nutrients for microbes, ultimately enabling them to attack the material, build functional colonies on it, and completely mineralize it. This makes the synthetic fibers inherently biodegradable like natural fibers. Analysis of the effectiveness of the CiCLO® technology has revealed that the biodegradability rate of the CiCLO® polyester is similar to that of wool. In functional aspects, these modified synthetic fibers are almost identical to the normal synthetics in terms of aesthetics and feel. Moreover, other properties like tenacity, pilling resistance, and wickability also remain unaltered. Most importantly, CiCLO® technology is ECO-PASSPORT certified by OEKO-TEX® , which ensures that it is not harmful [43]. Figure 6.3 shows the improvement in the rate of biodegradability of CiCLO® polyester in comparison with untreated conventional polyester in wastewater treatment plant sludge, seawater, soil, and anaerobic landfill conditions. Studies were conducted by third-party labs using internationally recognized ASTM Test Methods utilizing respirometry to measure true biodegradation (not disintegration). Respirometry studies never achieve 100% because some of the carbon is converted to biomass and water. Materials achieving at least 90% are generally considered fully bio-degraded. Lab conditions like temperature, moisture, nutrient levels, and pH can be controlled. The rate and extent of

Fig. 6.3 Biodegradability of CiCLO® treated polyester in a municipal sewage sludge, b soil, c seawater, and d high solid content-landfills (reprinted with permission from CiCLO® [21])

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any inherently biodegradable materials in uncontrolled natural environments are dependent on actual conditions [21]. Comparably, another organization ‘Duvaltex’ has imparted biodegradability to recycled polyester fabrics. They have included bio-catalyst during the yarn extrusion process which encourages the anaerobic digestion of polyester fabrics in the landfills as well as the wastewater treatment plant. These polyesters can degrade at the rate of natural fibers and it has been reported that they can degrade in 1278 days when end up in landfills as per the standard ASTM D5511 [22]. However, these fabrics were found to have applications in heavy-duty upholstery that includes acoustic panels and seating applications as per the claim of the company [23]. Detailed analysis of other high-priority properties of these fabrics may enlighten its application in garments. The biodegradability of the synthetic fibers can be altered by modifying the polymer in the extrusion stage while retaining the desirable properties of the synthetic fibers. However, that modification should not bring consequences and care should be taken in that aspect. Furthermore, this improvement in the biodegradability of fibers just prevents the prevailing of fibers for a longer period which does not inhibit the impact of fibers on the environment as a whole. These fibers with improved degradability also cause potential impact during their existence period in form of pollutant carriers. Like natural and regenerated fibers which release the adsorbed/accumulated pollutants into the environment [24], these fibers also impact the environment. This point of solution can only reduce the impact period of synthetic fibers. Thus, this can only be a small step in reducing the impact level from an environmental viewpoint.

6.2.3 Bio-based Alternatives A switch to bio-based textiles—this way of solution is entirely different and one of the out-of-the-box methods; it is a long-term goal that involves huge time to be adopted by the mass market. Various bio-based textile materials are getting emerged in the textile and fashion industry which are noted as a step toward sustainability. This aspect of leaping to bio-based textile materials without toxicity can also be a path to reducing microfiber load in the environment. Sustainable fabrics that are made from microorganisms like bacteria and fungi are turning up in the industry. Some of the emerging bio-based fabrics include Bacterial Cellulose materials (ScobyTec), Mycelium materials (MycoflexTM, Bolt Threads Mylo, MycoTex), Algae materials (Algalife, Algiknit), collagen protein of yeasts (Zoa) [25]. Though these materials are found to be eco-friendly and sustainable, the commercial viability of these materials is still not convincing. Technologists are working toward the commercialization of these materials. When these materials get to hold a huge share of the market, there will be a huge change not only in terms of microfiber pollution, but also in terms of all other impacts that are created due to the conventional natural and synthetic raw materials.

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6.3 Consumption Stage—Modification of Cause (Domestic Laundering) With the upper hand of domestic laundering in accelerating the microfiber shedding of textile materials, researchers have worked on seeking solutions in the laundry process. Some of such methods and practices reported in the literature are detailed in this section.

6.3.1 Use of Washing Additives Softener The impact and influence of different washing methods and washing parameters were particularized in the previous sections which clearly showed that these washing conditions have control over the microfiber shedding of textile materials. The use of washing additives, most commonly detergents, have a negative impact on microfiber shedding as it accelerates the microfiber release from the fabric surface. However, softener, an additive that is commonly used in the laundry to keep the fabric soft and wrinkle-free is found to have a positive effect on controlling microfiber shedding during washing [26, 27]. Softeners are generally used to regain or improve the handle of the clothes particularly after laundering [28]. Detergents that are used to remove dirt and stain will be usually harsh to the fabrics which can affect the fibers as well as the fabric handle [29]. To overcome this, fabric softeners can be used that can make the fabrics smooth, soft, and flexible by acting as a lubricant that can make the wearer feel pleasing and comfortable [28]. In addition to improvement of handle and comfort properties, the use of softeners can also improve the physical properties of the clothing. The addition of softeners during the rinse cycle was noted to reduce the shrinkage of the fabrics. It can also decrease the effect of wash aging on the fabrics [28]. The elasticity of the knitted fabrics was also noted to get increased with softener action providing good fit and shape retention [29]. Researchers have reported that the use of softeners during the wash cycle can effectively reduce the microfiber shedding of textile materials. They have suggested using fabric softeners during the wash cycle rather than using them after the laundry cycle. Both the methods of softener usage (during washing and after washing) can help in providing softness and other expected handles to the fabrics, however, the usage in the laundry cycle additionally improves the microfiber shedding reduction. When the fabrics are treated with softener after the wash cycle, its effectiveness in restricting the microfiber release in the subsequent wash was noted as insignificant. This trend was noted to be similar in the case of different brands of softeners. A strong negative correlation (−93.37%) between the softener concentration and microfiber shedding has been noted at higher concentration levels (5 mL/150 mL), whereas at lower concentration levels (0.25–3 mL/L), the effect of the concentration of softener is not significant [26]. Figure 6.4 shows the reduction in microfiber shed-

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Fig. 6.4 Microfiber shedding from polyester fabrics a while using softeners during the washing cycle and after washing, b while using different concentrations of softeners during the wash cycle (reprinted with permission from [26])

ding of polyester fabrics while using softeners. Similarly, other researchers have noticed a significant reduction of 35% in microfiber shedding when the polyester textile materials are washed with softeners (approx. 4,000,000 microfibers/5 kg of polyester fabrics) compared to the fabrics that are washed simply with liquid detergents (approx. 6,000,000 microfibers/5 kg of polyester fabrics) [27]. While contemplating the mechanism behind the softener actions, researchers have reported that the softener forms a layer over the surface of the fabric which can reduce the external forces acting on the surface that potentially breaks and releases the

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fibers. This can be related to the zeta potential of the fabric surface while being in the laundry liquid. The negative zeta potential of the synthetic fabrics which is susceptible to increase negatively in the alkaline solution of the wash liquid results in higher negative charges on the surface of the fabrics. Fabric softeners that are generally cationic in nature can get easily adsorbed on the surface of the fabric which is having a high negative zeta potential [30]. This layer of softener over the fabric surface can be either monolayer or multilayer that can protect the surface from external damage during washing by acting as a lubricant and restricting the fiber release [26, 29]. This mechanism was again noted as the reason for the ineffectiveness of the softeners while used after the wash cycle. When the fabrics are rinsed, the negative zeta potential again comes to the initial value which can lead to the desorption of softeners from the surface, and hence the effectiveness of the softener will not be there in the next wash [26, 30]. Moreover, the application of softeners to the fabric surface can reduce the inter-fiber friction and facilitates the fibers to get aligned parallel in the fiber bundle. This in turn reduces the slippage of fibers from the yarn stucture or fabric surface [27]. Besides, it can also reduce the harsh handle that is emerged due to the fibrillation on the surface that is occurred during repeated laundering [29]. These effects of softener aid in reducing the microfiber shedding of the textile materials. Figure 6.5 illustrates the mechanism of softener action on the fabric surface that prevents the microfiber shedding in laundering. This positive action of softener during laundry has made softener usage one of the effective solutions for reducing the microfiber shedding of synthetic textiles. However, a few gaps and challenges in implementation can also be spotted. The studies that reported the effective utilization of the fabric softeners in mitigating microfiber shedding were comparatively lesser. More so, the available studies used only polyester fabrics for the analysis which is again analyzed in the laboratoryscale laundry. The effectiveness of the softener in the real laundering and mitigating shedding from materials other than polyester needs to be analyzed in detail. Fabric softeners are not suitable for all kinds of fabrics, for instance, softeners are not recommended for water-resistant and highly absorbent materials as they can affect the functionality of the fabrics [31]. In certain circumstances, softeners are suspected to affect the hydrophilicity of the fabrics [29]. In such cases, the use of fabric softeners will become undesirable. In addition to this, the lubrication effect of softeners can also vary with different fabric structures [28]. Hence, that should also be taken into account while analyzing the microfiber shedding reduction. However, in a few other earlier studies, even though the use of softeners reduced the microfiber shedding, the effect was noted as statistically insignificant (microfiber shedding—0.00140 wt% when washed with detergent and 0.00124 wt% when softener is included) [32]. The most important consideration that has to be made with the usage of softeners is their chemical compositions which are non-biodegradable, which, in turn, impact the environment. Quaternary ammonium compounds like di-tallowyl dimethyl ammonium salts, distearyldimonium chloride, and diethyl ester dimethyl ammonium chloride are the main ingredients that provide a softer feel to the fabrics [29, 33]. Further, phthalates and methylisothiazolinone were included as fragrance and preservative agents, respectively [33]. The emergence of biodegradable softeners should be promoted and

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Fig. 6.5 Mechanism of softener action on mitigating microfiber shedding during laundry

their effectiveness in microfiber shedding should also be evaluated while considering softener usage as a sustainable solution for the issue. Further, the use of bleaching agents in washing was also noted to reduce the microfiber shedding from the fabrics. However, the understanding of the effectiveness and mechanism behind the microfiber shedding mitigation with bleaching agents needs detailed research [27]. Detergent Additives Detergent additives are those which can be added to the detergents being used in laundering. These additives are developed to improve fiber care. After surveying different

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detergent additives available in the market, researchers tried 6 different detergent additives in the laundering of textile materials and analyzed their microfiber shedding. Polymers, namely Polyethylene glycol polyester, co-polymer of acrylic acid and dialkyldimethylammonium chloride, wax crystal, a mix of three-dimensional polymers, amino-functionalized polydimethylsiloxane, and polyalkylene glycol were used as additives of liquid detergents. The microfibers in the washing effluents were noted to get decreased with a few of these additives. Out of six polymers examined, Copolymer of acrylic acid and dialkyldimethylammonium chloride, a mix of threedimensional polymers, amino-functionalized polydimethylsiloxane, and polyalkylene glycol were noted to reduce the shedding with amino-functionalized polydimethylsiloxane as the polymer leading to a higher reduction in microfiber shedding. It has been reported that the flexibility of the Si–O–Si backbone of the polymer results in higher mobility, which, in turn, reduces the friction between the fibers. This reduced inter-friction between the fibers helps in controlling fiber damage during laundry [15]. The variation in microfiber shedding with different polymer additives concludes that not all the detergent additives can help in microfiber shedding reduction. However, identifying and using suitable additives can reduce the microfiber release from the fabrics during washing.

6.3.2 Washing Aids These are the aids that are specifically designed to control the release of microfibers into the environment that are resulted from the laundering process. Various filtration technologies were implemented both in washing drum and washing machine outlet pipes. The supreme aim of these technologies was to prevent the entering of microfibers shed from the textile materials during laundry into the environment; more specifically waterways. The products that are developed in this aspect include Cora Balls, Guppy friend Bags, LUV-R filters, PlanetCare Filters, and a few others. These products can catch the microfibers which are shed from the textiles, which can later be retrieved from these devices. These kind of products can be classified under two broad categories, namely in-drum devices and external filters. In-drum devices are those which are used inside the drum of washing machines, where the external filters are attached to the outlet pipe of the washing machines. Cora balls and laundry bags are the in-drum devices that are noted as effective in controlling microfiber shedding. Most of the coral reefs in the water bodies can trap the particles suspended in the water which was noted to improve the quality of water [34]. Rozalia Project has commercialized this concept in the form of Cora Balls, a product made of recycled and recyclable plastic, which can trap the tiny fibers that are suspended in the wash liquor and hold them on its surface during washing [35, 36]. As per the founder’s claim, the Cora balls can be used in any type of domestic washing machine and they can help in achieving a 35% reduction of microfibers in the wash effluent [36]. Different researchers have also analyzed the efficiency of Cora balls in controlling microfibers in the wash effluent. In 2019,

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Hayley et al. have analyzed the efficiency in terms of mass and count. It has been noted that the use of Cora balls during the laundering of fleece blankets resulted in a 26% reduction in the number of microfibers in the wash effluent, whereas in terms of weight, only a 5% reduction has been noted. The analysis of the length of fibers in the effluent while washing with and without Cora balls has revealed that the Cora balls are capable of capturing fibers of a wide range of lengths as the average length difference between the control and experiment was lesser [37]. In another research, the efficiency of Cora balls was analyzed while washing different synthetic textiles including polyester, acrylic, and polyester/cotton blends. The experimental analysis revealed a 31 ± 8% reduction in the microfibers in the wash effluent [38]. The slight difference between these two studies [37, 38] might be due to the different methods of analysis and microfiber quantification. However, we can see a significant reduction of microfibers in the range of 26–35%. With this notable level of efficiency, the use of Cora balls could bring a drastic change in the microfiber load in the water systems. It has been claimed that if all the households of Toronto, a city in Canada, use Cora balls during laundry, it can reduce up to 92 billion microfibers entering the environment [37]. Similarly, if 10% of US households use Cora balls, it can reduce the plastic load created by microfibers which is equivalent to 30 million water bottles in a year [35]. Another interesting fact to be noted with Cora Balls is that the use of these balls inside the washing drum also reduces the release of fibers from the fabric surface besides capturing the shed fibers [36]. However, a few limitations can be noted with Cora balls. After usage, the fibers trapped in the balls should be removed and the balls should be cleaned before using in the next cycle. This is often tedious as the fibers get entangled in the stretchy structure of the ball [39]. Secondly, the laundry bag, which is also an in-drum device, is slightly different from Cora balls in the usage mechanism. In the case of Cora balls, they are simply put inside the laundry drum, whereas while using laundry bags, the clothes are put inside the bags and then put in the washing drum. Thus, the microfibers shed from the clothes get trapped along the hem of the bags and it restricts their leaching into the wash effluent. GuppyFriend laundry Bags and Fourth Element washing bags are two different laundry bags that are made of nylon filaments with zipper closure. These bags have fine pores of size 50 μm. The nylon filaments used in the bags were untreated and undyed in order to make them free from any other additives [40]. Though the pore size is 50 μm, the bag is managed to collect fibers that are less than 10 μm in thickness. The reason behind it is that for the fibers to escape from the pores, they should poke vertically through the bag, but the water and the motion of bags and clothes inside the washing drum do not allow the fibers to stand vertically and they are always bent. This makes the fibers be retained inside the bags even though the pore size is larger than the fiber size [40]. The researchers who analyzed the effectiveness of these bags reported that the GuppyFriend Bags are more effective in capturing fibers than the Fourth Element washing bags (54% reduction in GuppyFriend Bags; 21% reduction in Fourth Element washing bags) [38], whereas other researchers evaluated the laundry bags made of monofilament nylon bags with 50 μm pore size reported 87–91% of reduction while washing fleece jackets and swimwear suits [41]. This variation in reduction efficiency shows that the shape and design of the pores as

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well as the type of garment being washed play an important role in capturing fibers in the case of laundry bags [38]. The biggest advantage of using laundry bags is that they can protect the fabrics from mechanical actions of washing since the clothes are put inside the bags. This makes the fabrics shed lesser fibers as the mechanical actions during washing influence the microfiber shedding from the fabrics [40]. This was evident from the research report which showed a significant decrement (84– 90%) in the microfibers shed from the fabric while using laundry bags (microfibers in the effluent + microfibers collected in the laundry bags) compared to microfibers shed while not using laundry bags [41]. These findings revealed that laundry bags are much more effective in controlling microfiber pollution. The other things to be considered with these bags while washing are their potency to assure the cleanliness of washing and durability. A study has claimed that the use of laundry bags does not affect the cleanliness of clothes as the clothes washed with and without bags were noted to have the same level of cleanliness [42]. The bags can withstand more than 50 washes without getting any damage which shows that these bags need not be replaced frequently [40]. Moreover, while checking the effectiveness over usage, the pore size of the laundry bags got reduced with the increase in the number of washes, which, in turn, increased the fiber capturing the potential of the bags [43]. However, a few limitations are still there. The bags are suggested to use up to 40 ºC and thus will not be suitable for the laundry cycle where the temperature is maintained at more than 40 ºC [40]. The bags are made of nylon filaments which are synthetic in nature. Further, they are also susceptible to shed microfibers [44]. However, from the manufacturer’s side, it has been reported that polyamide 6.6 is resistant to alkalis and they are tough in nature. The monofilament nature of the structure does not shed fibers [40]. Hence, detailed research on the microfiber shedding behavior of these laundry bags made of monofilament nylon should be carried out in order to analyze the reliable effectiveness of these bags in mitigating microfiber issues. The next broad category of washing machine aid is laundry filters. These filters are generally attached to the outlet pipes which can filter the fibers in the wash effluent and release effluents with fewer fibers to the sewage systems. Different filters to capture microfibers are introduced into the market which include LUV-R Lint filters, PlanetCare Filters, XFiltra™, and Filtrol 160™. The basic principle behind these filters is very simple where the wash effluent will be passed through these filters which capture the fibers as much as possible and retain them resulting in fewer or no microfibers in the effluent that are being released into the environment. However, the filter design, material, and size of pores vary from filter to filter which greatly influences their fiber catching potential. Table 6.2 consolidates the specifications of different washing aids. In a comparative analysis, researchers have reported that XFiltra™ has better fiber capturing efficiency (78%) than LUV-R lint filters (29%) and PlanetCare filters (25%). The main reason as reported by the researchers is the smaller pore size of XFiltra™ [38]. Moreover, in XFiltra™ filters, the filtration is additionally facilitated by means of a centrifugal separator which enhances the filtration and dewaters the fibers collected in the filter. This, in turn, helps in the easy removal of the fibers from the filter. However, these filters are not yet commercialized for consumers [45]. The manufacturers are firmly making talks with global washing

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Table 6.2 Properties and efficiency of laundry aids and filters Product

Type

Material

Pore size (μm)

Reduction efficiency (%)

Price ($)

Recommended cleaning frequency

Cora Balls

In-drum Device

Recycled and recyclable plastics

–

26–35

~38

Clean while tangles of fibers are seen

GuppyFriend Bags

In-drum Device

Nylon filaments

50 μm

54–91

~35

Every wash

Fourth Element Bags

In-drum Device

Nylon filaments

50 μm

21

–

Every wash

LUV-R Lint Filters

External filter

Metal mesh 285 μm; 175 μm

29–87

~140

10–15 washes

PlanetCare Filters

External filter

–

200 μm

25–80

~160

20 washes

XFiltra™

External filter

–

60 μm

78–90

–

–

Filtrol 160™

External filter

Stainless steel

100 μm

30–60

~140

8–10 washes

Steel mesh

200 μm

–

~45

3 washes

The microfiber External filter from filter girlfriend

machine manufacturers to install this product in all new washing machines [46]. The other researchers have reported the LUV-R lint filter as effective in capturing fibers up to 87% while washing polyester fleece blankets [37]. This much difference in the reduction efficiency from the other research [38] might be attributed to the difference in the type of garments used. Researchers have found that LUV-R filters are effective in capturing longer fibers [37]. Thus, the LUV-R lint filters may not be suitable while washing garments that shed shorter fibers. Though LUV-R lint filters are noted to have significant reduction efficiency, their effectiveness against different fiber lengths should be analyzed in detail. PlanetCare Filters are one of the external filters, which also showed significant filtration of 25% of microfibers in the wash effluent as reported by the research report of Napper et al. [38], whereas the manufacturers claim that it could control up to 90% of fibers in the wash effluent [47]. In this filter, the fibers will be collected in the cartridges which can be replaced after the collection of fibers as much as possible. The filters are reported to capture fibers of a wide variety of lengths ranging from 50 μm to 5 mm [48]. The interesting fact is that these cartridges can be returned to the manufacturers after 20 washes. The manufacturers themselves take care of the cleaning and enable the filters suitable for the next use. This ensures that the fibers collected in the filters are safely disposed of [49]. However, the replacement of cartridges causes recurring costs for the filters [50].

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Similarly, Filtrol 160™, which is mainly intended to filter dirt particles, hair/fur, and concrete dust from the washing effluent (89% reduction in microparticles in the effluent), was noted to have a better performance against the microfibers [51]. A study reported 30–60% reduction in the microfibers in the wash effluent when Filtrol 160™ has been used [45]. The Microfiber Filter from Girlfriend Collective is another filter made of steel mesh having a pore size of 200 μm. As per the manufacturer’s claim, the filters can capture particles whose size is as small as 72 microns. However, independent third-party testing has not been done yet to estimate the efficiency of these filters. These filters should be cleaned frequently (for every 3 washes). The specialty of this filter is that they are very less expensive when compared with other same kinds of external filters [52]. ‘Fibio’ is one of the filtering devices for washing machines that are under construction. This is mainly designed for the front load washing machines since the filters can be placed on the top of the washing machine. The design concept shows that there will be three filters of different mesh sizes which can provide better filtering efficiency. The distinctive feature of this design is that there will be an indicator that shows when the filter is clogged. This can potentially make the cleaning process efficient. Since these filters are currently in the designing stage, the efficiency and other potential drawbacks are yet to be analyzed in detail [53]. In summary, washing aids are playing a noticeable role in controlling microfiber pollution that is originated from domestic laundry. Both the in-drum devices and the external filters are noted to have significant reduction efficiency; however, both have their own limitations. Figure 6.6 depicts different washing aids along with the merits and demerits highlighted. When the in-drum and the external filters are compared,

Fig. 6.6 Merits and demerits of washing aids that mitigate microfiber pollution

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external filters are more effective than in-drum devices in terms of capturing fibers [38]. Still, external filters require additional space for installation and they are costlier than the in-drum devices. Moreover, these filters can easily get clogged by detergents and softeners [51]. Researchers have also suggested that the combined actions of both in-drum devices and external filters can result in improved reduction efficiency [38]. The most serious drawback of these washing aids is that the fibers collected in these devices should be disposed of in a proper manner. When comes to cleaning, the first thing that a normal human thinks of will be washing under a water tap. If it becomes the case while cleaning these washing aids, then the total effort of these devices will get spoiled. Hence, proper cleaning methods and the guidelines for the disposal of the collected fibers should be given more importance.

6.4 Disposal Stage—Waste Management System 6.4.1 Wastewater Treatment Plants Wastewater Treatment Plants can be the large-scale mitigation strategy for microfibers released from the domestic laundry effluent. The main intention of the wastewater/sewage treatment plant is to remove possible pollutants from the water before it ends up in the environment. Based on the application, these treatment plants can be effluent treatment plants, domestic wastewater treatment plants, and potable treatment plants [44]. The modification of domestic wastewater treatment plants can reduce the exposure of microfibers from the domestic laundry into the environment, whereas, with the modification of effluent treatment plants in textile processing industries, the microfibers released during the processing of textile materials can be controlled. These treatment plants are indeed effective in filtering microplastic particles (up to 98%). But, due to the huge volume of wastewater being treated, the microplastic particles reaching the environment even after the treatment were enormous (in effluent) [17, 54, 55]. Hence, various experiments are being done to improve the capability of wastewater treatment plants to capture microfibers. The efficiency of sewage treatment plants in trapping microfibers can be improved in two ways: 1. 2.

Identifying the process of treatment plant which significantly captures microfiber particles and improvising the particular process Identifying an intervention point and implementing an additional process in the treatment plant that can effectively capture the microfibers

Environmentalists have analyzed the different stages of wastewater treatment plants to identify the stage where the micro sized particles can be significantly captured. Their study report revealed that the grease removal stage of the treatment plant can reduce microplastic particles to a significant level (44.59%), followed by the primary settlement tanks (33.75%) [54]. In line with this, the other study on effluent treatment plants of textile dyeing units has reported that the initial stages (before the

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225

aeration process) of the treatment plant offer better seizure of microfibers. Almost 76% of the reduction of microfibers in the effluent was noted when the effluent passes through after the primary sedimentation tank before the aeration tanks [55]. These findings unleash the fact that if these initial stages of treatment were made more effective in wastewater treatment plants, then the microfiber capturing ability of the plant can be improved significantly. At the same time, lesser attention to these initial processing stages will adversely impact the microfiber emission. Similarly, in this aspect, researchers have analyzed different sections of a municipal water treatment plant and intervened in the section just before the final discharge pipe, that is, between the disinfection section and final discharge. Since certain organic and inorganic particles are noted to be visible even after the disinfection process, this point has been chosen to intervene as it can increase the efficiency of the system to retain the microfibers effectively. A specially designed filter plate has been attached at this point. While talking about the structure of the filter plates, they have balanced macrotexture with overlapping tooth-like structures. Each tooth also has smaller teeth on it which provides microstructure to the filter plate that facilitates good capture of microfibers. Further, these filter plates are oriented in a twisted C-like direction and five pairs of these filters are arranged in the system. When the water flows through plates, cross flow and vortex filtration will happen. The cross-flow filtration facilitates the larger particles to bounce off from the filter plates and vortex filtration helps in cleaning smaller particles that are trapped in the microstructure of the filter plate and create tiny cycles in the corners and edges of the macrostructure that enables the smaller particles to move toward the back of the structure. However, this intervention in the sewage plant is at the design level, the material and manufacturing process, product testing, cost factors, and in-depth analysis in terms of sustainable frameworks should be carried out [44]. The other researchers have suggested the inclusion of the air floatation process in the effluent treatment plant of textile processing industries with the perspective of lower densities of microfibers. Further, the reverse osmosis method has also been recommended; however, the higher cost of the process will stand as a barrier [17]. The wastewater treatment plant could be worthwhile in terms of capturing microfibers. The improvement of the already available process and the introduction of a new process in the treatment plant further increases the detainment of microfibers. The major concern with these plants is the huge volume of effluent being treated, which, in turn, results in a huge number of microfibers being leached into the environment. The consequential effects of these treatment plants are also a point of concern. The sludges collected from these treatment plants will have a higher concentration of microfibers that need to be treated with utmost care. These can again end up in the terrestrial environment. Zhang et al. have reported that sewage sludges can result in 4,010,000 kg/year of microplastics entering terrestrial environments across the US [56], whereas Petroody et al. claimed 129–238 microplastics/gram of sludge from the wastewater treatment plants [57]. Moreover, these sewage sludges are also being used as soil fertilizers which transfers these microplastics to the agricultural fields. It was evident from the research of Corradini et al., who analyzed the agricultural fields where sewage sludges were applied and compared them with the

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fields without sludge application. The result claims that an increase in the rate of sludge application also increases the microplastic content in the soil [58]. Thus, the proper management of sewage sludges should be essentially drafted to contribute to wastewater treatment plants fruitful.

6.4.2 Techniques for Microfiber Removal in Water Bodies Once the microfibers get released from the textile materials, they are laborious to be traced and removed from the environment. The exploration has been made in this path to find the suitability of different physical, chemical, or biological processes to cater a solution to the microfiber pollution by means of their removal from the environment. For the separation of these solid particles from the aqueous medium, techniques including adsorption, and electrocoagulation which are currently being used in different applications are examined in the aspect of microfiber filtration.

6.4.2.1

Electrocoagulation Method

Coagulation is the process where the suspended small particles in the aqueous medium get destabilized and aggregated into large complexes. In the electrocoagulation process, the electrical current is passed for coagulation to take place [59]. In this process, metal electrodes are used to produce an electric field [60]. This is a simple and innovative solution for wastewater treatment as this method eliminates the usage of chemicals and other microorganisms in the process. This method has the advantages of being cheap, energy-saving, minimal sludge, automatic, and costeffective over the traditional chemical coagulation or activated sludge processes [60]. Moreover, this method is effective in the removal of a wide variety of pollutants in wastewater of domestic sewage [61], paint manufacturing sewage [62], and bleaching effluent [63]. In this context, the laboratory-scale experimental study has reported that the electrocoagulation method can be effective in removing microplastics in the sewage effluent with a high level of efficiency ranging from 95 to 100%. The removal efficiency of the process could be greatly influenced by the different process parameters that include anode material, applied electrolyte concentration, initial pH of the solution, applied voltage intensity, and microplastic concentration. The study analyzed the removal of both fibers and granules. For the study, the polymer types of fibers (Polypropylene and Cellulose Acetate) and granules (Polymethylmethacrylate and polyethylene) were chosen to represent the actual type of polymers in the wastewater [60]. While comparing the removal efficiency of microplastic fibers and microplastic granules, the electrocoagulation method greatly removed fibers over the granules. This improved removal efficiency concerning microfibers is attributed to the larger particle size and density of fibrous particles (1–2 mm) than granules (6.3–286.7 μm) [60]. Since the type of anode material will have an upper hand on the removal efficiency, Fe and Al anodes were studied and the results revealed that

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227

Al electrodes are better in removing all types of microplastic particles over the Fe electrodes. Electrolyte concentration plays a crucial role in the treatment process as it decides the electrical energy consumption of the process in addition to the removal efficiency. Though increasing the electrolyte concentration and applied voltage can improve the removal efficiency, there is a need to optimize these process parameters as it can improve the feasibility of application on a large scale [60]. Similarly, other researchers approached the electrocoagulation method for treating laundry wastewater. The combination of ‘Fe’ and ‘Al’ electrodes was used in the process. Under the optimum conditions (pH—9; Current—2.16 A; Time—60 min), the maximum removal efficiency of 98% was noted for microfibers when compared to the control sample [64]. In a similar study, the removal of microbeads from domestic sewage water and industrial effluent was achieved up to 99% while carrying out the electrocoagulation process at optimum conditions [65]. Though researchers have reported the potency of the electrocoagulation process for microfiber removal, the convincingness of the method relies on the operation cost. In this regard, Elkhatib et al. optimized the process parameters including operation cost. The researchers have reported 98.5% microplastic removal at the cost of $0.29 for the treatment of 1 m3 of wastewater [66]. Table 6.3 consolidates the findings of research that reported the removal of microfibers from wastewater by the Electrocoagulation Method.

6.4.2.2

Adsorption

Adsorption, the simplest physical method, is highly effective in effluent treatments. In this method, molecules in the gas or solution phase can get accumulated on the solid surface which is exposed to the gas or liquid [67]. This is a surface phenomenon that relies on surface energy [68]. Being a method with lesser complexity, adsorption has been examined from the viewpoint of removing microfibers from the water bodies. Different adsorbent materials have been analyzed for the effective removal of microfibers which are discussed here. Sponge Materials Sponges are materials with a porous 3D network that are generally made of a wide variety of materials. These are more popular in the various fields of application including liquid absorption [69], oil–water separation [70], dye adsorption [71], sensors [72], and wound healing [73] because of their porous structure and higher surface area to volume ratio. More specifically, in water treatment, these sponges are holding a prominent place as they are effective in the removal of heavy metal ions and organic dyes. Researchers have started analyzing the extent of these sponges on microplastic removal. Sun et al. developed chitin-based sponges and sought their capability to remove microplastic particles. Five different chitin-based sponge materials were developed by composing Graphene Oxide (GO), Oxygen-doped Carbon Nitride (OC3 N4 ), Carboxymethyl Cellulose (CMC), and Chitosan. These sponges were tested for the removal of polystyrene (PS), amine-modified polystyrene (PS-NH2 ), and

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Table 6.3 Electrocoagulation method for removal of microplastics Reference Microplastic Polymer type form

Electrode Optimum operating conditions

Removal efficiency (%)

[64]

Microfibers

Not mentioned (wastewater samples were collected from laundry)

Fe–Al

pH—9 Current—2.16A Time—60 min

98

[60]

Granules

Polyethylene (PE)

Al

pH—7.2

98.7

Microfibers

Fe

84.6

Polymethylmethacrylate Al (PMMA) Fe

69.5

Polypropylene (PP)

Al

99.9

Fe

96.8

Cellulose acetate (CA)

99.1

Al

99.9

Fe

93.8

[65]

Microbeads

Polyethylene

Al

pH—7.5 Current density—11 A/m2 NaCl—0 to 2 gpl

99.24

[66]

Glitters

Polyester

Al

pH—4 98.5 Current density—2.88 mA/cm2

[59]

–

Polyethylene and polyvinyl chloride

Al–Fe

pH—4 Current density—20A/m2 Time—10 min

100

carboxylate-modified polystyrene (PS-COOH) microplastics. The removal efficiency of sponges that are fully made of chitin was noted as lesser for all the three types of microplastics (43.4% for PS-COOH; 70.4% for PS-NH2 ; 63.3% for PS), whereas the addition of GO and O-C3 N4 improved the adsorption of plastic particles. The main reason as outlined by the researchers is the π–π interactions between the benzene ring of polystyrene and the GO and O-C3 N4 [74]. Even after three adsorption–desorption cycles, chitin-based sponges embedded with Graphene Oxide showed higher removal efficiencies against different microplastics (72.4% for PS-COOH; 88.9% for PS-NH2 ; 89.8% for PS) [75]. As a step toward sustainability, the sponges were innovated with plant-based proteins. Oat protein sponges were prepared with oat protein isolate which is extracted from the oat flours. These sponges are synthesized by means of the chemical cross-linking method. The adsorption efficiency of these sponges particularly against microplastics was examined and the study revealed a maximum removal efficiency of 81.2% for polystyrene microplastics. The main mechanism of adsorption as reported by the researchers is that the proteins are rich in hydrophobic functional groups in their 3D structure which enables the hydrophobic interaction with the

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benzene rings of polystyrene microplastic particles. During the desorption process, these hydrophobic interactions can be broken by ethanol treatment. While considering the processing time, the sponges adsorb 38% of microplastics within 10 s of the process. Further, these bio-based sponges can be used repeatedly as their adsorption efficiency is maintained at 60% even after 4 cycles of adsorption and desorption. In the aspect of environmental friendliness, the sponges were tested for their biodegradability. The results added value to the innovation as these sponges are bio-degraded to 60% within 8 days when ended up in the soil. However, the study was restricted to polystyrene microplastics of 1 μm, and hence the adsorption of microplastics of different morphology and chemistry should be explored as the adsorption can also be greatly influenced by the particle size, functional groups, and charge of the adsorbate [76]. Though the adsorption of microplastic particles by sponge was satisfactory, the research made so far concentrated on polystyrene particles. However, this might be quite different from the microfibers of textile materials in terms of morphology and composition. Hence, the evaluation of sponges should be made from the perspective of removing microfibers that are released from textile materials. Macro Algae The prevalence of microfibers in water bodies and water-based animals is clearly evidenced by various studies as discussed in the previous chapter. From this angle, researchers investigated the accumulation of microfibers in aquatic vegetations. Peller et al. analyzed Cladophora, a macroalga, which is submerged aquatic vegetation. The microfibers often being denser than the water, can settle down in the submerged vegetation. The analysts noted 32,000–34,000 microfibers per kilogram (dry weight) of the algae samples. This accumulation is many times higher than that of microfibers found in the water or sediment which are previously reported. This paved the way for exploring the effectiveness of algae in aggregating the microfibers in the water bodies. In the experimental set-up, cotton, lycra, acrylic, and polyester microfibers were added to the water containing Cladophora and the algae were removed immediately. A sudden gathering of the microfibers by the algae has been noted. The primary thing that has to be noted here is that the sequestration of microfibers happened irrespective of the chemical compositions of the fibers. The microscopic analysis of the algae after adsorption of microfibers revealed that the microfibers are adhered to the cell wall of algae by means of intermolecular forces. Figure 6.7 shows the bio-adsorption of microfibers on the cell wall of algae. The effective adsorption of microfibers on the algae is attributed to the combination of higher surface area and chemical characteristics of algae. The surface available for adsorption in one cell of Cladophora is around 17.85 mm3 . The cell wall of the Cladophora is highly comprised of cellulose (around 70%). Moreover, the chemical composition of algae includes ulvan polysaccharides, sulfate esters, uronic acids, and glucose. This carbohydrate content adds physiochemical properties like high charge density which positively helps in the bio-adsorption process. However, the adsorption ability is noted to decrease over aging [77]. This sheds light on the scope of future technologies that can implement this natural mechanism for microfiber removal.

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Fig. 6.7 Bio-adsorption of microfibers on the cell wall of algae; a–c adsorption of acrylic fibers on the cell wall of cladophora; d adsorption of polyester fibers on the cell wall of cladophora (reprinted with permission from [77])

Magnetic Carbon Nanotubes Carbon-based nanomaterials are emerging as potential adsorbents because of their larger surface area and a huge number of active adsorption sites. Tang et al. analyzed the efficiency of Magnetic Carbon Nanotubes against the removal of polyethylene, polyethylene terephthalate, and polyamide microplastics from the aqueous medium. Microplastic removal efficiency has been reached up to 100% while the adsorption was carried out for 180 min with a minimum concentration of carbon nanotubes (5 gpl). Though all three types of microplastic polymers were effectively adsorbed by carbon nanotubes, the mechanism of adsorption varied with different polymers. While considering the adsorption of polyethylene on carbon nanotubes, hydrophobic interaction is the key as both polyethylene and carbon nanotubes are found to have hydrophobic characteristics, whereas in the case of polyethylene terephthalate, besides hydrophobic interaction, π–π interaction was noted. The carbon nanotube surfaces are highly polarized with π electron cloud and that enables the π–π interaction. In the case of polyamide, there is no chance for hydrophobic interaction to take place as polyamides are hydrophilic in nature due to the presence of amide groups. The dissociation of carboxylic groups by the polyamides in the neutral conditions develops a negative charge on the surface and the presence of Fe3 O4 on the surface of carbon nanotubes makes them positively charged which can enhance electrostatic attraction between microplastics and carbon nanotubes. Hence, here, with respect to polyamide, π–π interaction, complexation, electrostatic interaction, and hydrogenbond interactions are noted as the causes of adsorption [78]. Figure 6.8 illustrates

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Fig. 6.8 Adsorption mechanism of magnetic carbon nanotubes against different microplastic polymers

the adsorption mechanism of carbon nanotubes with different polymers. Concerning reusability, nanotubes can be reused effectively after thermal treatment at 600 ºC up to four times. The removal efficiency of the recycled nanotubes was also good which is around 80% [78].

6.4.2.3

Bioremediation

Bioremediation is the biological method where the organic matter is degraded or converted into little or non-toxic matter with the help of living organisms. Microorganisms like bacteria and fungi are often found as suitable organisms for the degradation of synthetic materials [79]. For the degradation of synthetic materials, microorganisms with higher adaptability are required which can attach to the fibers, adapt to the surroundings, and then start growing. The microorganisms can grow on these synthetic fibers by consuming the caron contents [80]. Researchers have identified different microbial, fungal, and enzymatic methods for degrading microplastics. With the scope of bioremediation for degrading microplastics, researchers isolated 22 different bacterial species (16—genera of Bacilli; 5—genera of proteobacteria; 1—genera of Actinobacteria) from mangrove soil and analyzed their effectiveness in degrading the microplastics in the mangrove forest. Out of 22 isolates, 9 were found to have the ability to degrade polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), and polystyrene (PS) microplastics in the soil. Different strains affected the different polymer types. The higher degradation (6.2%) of PE was

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achieved by B. gottheilii, whereas for PP, the highest degradation (6.4%) was noted with R. ruber. For PET and PS, the highest degradation (6.6% and 7.4%, respectively) was noted with B. cereus [81]. Apart from bacteria, fungal species also have a notable impact on degrading microplastics. Paço et al. identified Zalerion maritimum, a naturally occurring fungus in the marine environment to degrade polyethylene. They have noticed molecular changes in both fungi and microplastics which reveals the decrease in the mass and size of the plastic pellets due to the utilization of Polyethylene by the fungi for growth [82]. Similarly, researchers have reviewed the effectiveness of microbial agents on the degradation of microplastics. They have suggested in-situ analysis to examine the reliability on a real scale. Moreover, the development of functional microbial agents is recommended to tackle the issue on a large scale [83].

6.5 Management of Microfiber Wastes—Conversion into Sustainable Resources Microfibers that are collected in the filters and washing aids are having the potential to rerelease into the environment without proper disposal ways as well as alternate applications. Hence, few researches have been made on this aspect of reusing the microfibers and lint into sustainable renewable resources. Since these wastes will have a combination of different fibers, recycling these fibers will be a tedious process and hence identification of an effective method is crucial. The microfibers which took hundreds of years to degrade were found to have flammable elements which are capable of converting into biofuel. The elemental analysis of microfibers in the lint traps of cloth dryers has revealed the presence of carbon (47.5%) and hydrogen (6.44%) at higher levels, whereas a small amount of nitrogen (0.58%) and Sulfur (0.01 wt.%) contents were also noted. With these contents, microfibers can be thermally decomposed into energy products. While the carbon and hydrogen contents increase the energy value of fuel, nitrogen and sulfur content can reduce the toxic emissions during thermal treatment. The pyrolysis treatment of microfibers collected from lint traps was carried out and the findings revealed that the microfibers can be thermally decomposed into energy products with a 65% conversion rate at 400 and 600 °C and 78.4% conversion rate at 500 °C. The research reported Toluene as the major compound found in the biogas and biooil produced from the pyrolysis treatment of microfibers. It has to be noted that the successful application of this process on an industrial scale can lead to the production of 13.8 tons of oil, 21.5 tons of gas, and 9.7 tons of char annually with 120,400 dollars as estimated profit [84]. In a similar essence, the manufacturers of PlanetCare filters are looking forward to reusing these microfibers collected in the laundry process. While using PlanetCare filters, the filter cartridges are being returned to the manufacturers after usage. Thus, by collecting all the cartridges, the organization is planning to recycle them. This includes melting and reforming of these fibers which can find a notable application

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as insulation panels for washing machines. They are also researching the way to use these microfibers in car upholstery [49].

6.6 Consumer Awareness on Microfiber Pollution Public awareness is inevitable in protecting the environment from any kind of pollution where microfiber is not an exemption. Consumers should be aware of the consequences of their day-to-day wearing and washing of clothes. Most importantly while considering the usage of laundry aids and laundry additives in controlling microfiber release, their effective utilization is in the hands of consumers. Consumers should have a concern about the impact of microfibers and they should step forward to take these preventive measures. Hence, it is important to understand the level of awareness among consumers about the issue. In this regard, researchers have analyzed the common people for their consciousness of microfiber pollution. The quantitative and qualitative methods of analyses have been made with the help of questionnaires and interviews, respectively. When the microplastic contamination has been taken into account, the majority of the people (68%) were aware of it. However, the awareness about the microfibers (microfiber shedding from textiles during laundry) is comparatively lesser (37%) [53]. Similarly, Yoon and Yoo surveyed women to understand their viewpoint on microfiber release from fleece and faux fur. Out of 413 women surveyed, 304 (73.6%) were unaware of the microfiber released during the washing of these items. Moreover, most of the people who are aware of the microfiber issues are not taking any effort to adopt a solution that can reduce the emission. Out of people who are aware of the microfiber issue, only 26.6% agreed that they are making efforts to reduce the emission [85]. The other researchers analyzed the consumer’s knowledge and thoughts toward microfiber pollution by interviewing them individually. The research sampled consumers with fashion and textile science backgrounds playing different roles including students, sales assistants, and creative directors in fashion brands, and researchers. When they are asked about microfibers, most of them responded as these microfibers are the key innovation in textile industries that are developed to provide soft textures and also about their effectiveness in cleaning cloths. This shows that they had a positive opinion of microfibers. Few others could recollect microfiber pollution from the news that they came across but they do not have a clear idea about that. However, few had better knowledge about microfiber pollution as they were able to state the source of microfibers and how it becomes pollution. Though few know about microfiber pollution, they are unaware of preventive measures. The researchers from a textile science background were not convinced with the available products like Cora Balls and Guppy Friend Bags as they expect more details on the mechanism of the product and how the caught fibers will be disposed of [86]. The profound interview has revealed that people from the background textile and fashion industries have either declarative or environmental knowledge on microfiber pollution, yet the transformation of this knowledge into procedural knowledge is

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lacking. The main reason found was the communication barrier [86]. Researchers have reported that the communication should be outcome-driven which not only implies the environmental impacts due to the issue, but also address the potential solution. One of the easiest and most effective ways of bringing attention to the consumers is through care labels [86]. Since washing parameters have a huge impact on microfiber shedding, developing care labels with washing instructions that can minimize the microfiber shedding can be a worthwhile precautionary step. The current care labels focus on enhancing the durability of the garments and the gap is that they are not addressing the environmental impact of the garment. By highlighting the warning about microfiber release and the wash care instructions that minimize the microfiber release, the knowledge about the microfiber issue can be enlightened among consumers [87]. In the case of either promoting the use of already available laundry aids like Cora Balls, LUV-R filters or designing a new product should also consider the consumers’ adaptability. Here, the people were skeptical about the effectiveness of the solution. Though few were aware of the microfiber issue and came forward to use such products, they were not sure that the product or solution actually reduces the impact. Despite having scientific proof, people need to visualize or realize that the product helps in reducing microfiber pollution. For instance, when using Guppy friend bags, they were not able to see the fibers that are trapped in the bag because of its smaller size, which, in turn, makes the consumer believe that the product is not effective in capturing the fibers [53]. While considering different criteria of the product, next to visualization of effectiveness, consumers expect durability of the product, easy usage of the product that should not cause additional time. Cost is noted as the least important factor among consumers [53]. Hence, while drafting solutions for microfiber pollution at the consumer level, the awareness among people and their perspectives on the issue should be considered carefully. As a whole, the level of consumer awareness of microfiber pollution is not satisfactory. Though the level of awareness about microplastics is convincing, people are not aware that textile materials are the major source and they are causing microfiber pollution [53, 86]. On the other hand, the people who are already aware of microfiber pollution are lacking in adapting effective measures to reduce the impact. Researchers have identified ineffective communication about the issue as the key barrier and suggested focusing on output-driven communication which can enhance the idea of available solutions among the people. Care label was noted as a key tool that can bring a change in consumer behavior in terms of washing clothes, which, in turn, helps in reducing microfiber release during washing. Similarly, the preferences of consumers play an inevitable role in designing the washing aids that can significantly reduce microfiber emissions into the environment. The weightage of each criterion is in the following order: visualization of product effectiveness > product durability > easy usage without extra time being spent > cost [53].

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6.7 Efforts Made by Different Brands and Organizations Various well-known apparel brands and other non-profit organizations are working to address the issue. This involvement of different organizations is essential to mitigate the issue commercially on a large scale. Few collaborative initiatives are being emerged that can link the knowledge about microfiber pollution, thereby effective solutions can be strategized. H&M Group H&M, which is one of the leading apparel brands, understood the effect of the issue and has collaborated with different research organizations and consortiums like RISE and The Microfiber Consortium, which are working together to bring solutions to the microfiber pollution. In 2019, a project that examines the microfiber release and the management of the textile manufacturing process has been launched by H&M in association with the Kong Research Institute of Textiles and Apparel. The major aim of the research programs is to control the microfiber release by means of modifying the textile production process. In the aspect of reducing the microfiber emission in the consumer stage, H&M has started offering laundry bags that can potentially reduce the microfiber release from the fabrics during laundry. With the motive of reducing the microfiber emission in the disposal stage, they are supporting recycling technologies, which can offer responsible handling of the materials after use without letting them degrade into microfibers in the landfills [88]. Patagonia Patagonia is a renowned outdoor clothing and gear brand that often gives more importance to environmental impact and sustainable approaches. They have initiated research work in partnership with Bren School of Environmental Science and Management at the University of California and North Carolina State University to understand the influence of fiber and fabric characteristics on microfiber release [89]. They have committed to providing care instructions to the consumers purchasing synthetic garments from their store concerning microfiber release. They have also started selling GuppyFriend bags in their retail stores. In association with Tersus Solutions, a textile processing company, Patagonia is expecting to develop waterless textile processing where the microfibers can be captured in the system without being leached to the waterways [89]. The Microfibre Consortium (TMC) This consortium focuses on developing a practical solution to mitigate the microfiber release to the environment by bridging the gap between academic research with the commercial supply chain production. This aims to help retailers, brands, and manufacturers to make textile production eco-friendly. Around 70 signatories are there which comprise brands and retailers, research and manufacturers, and affiliates.

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This collaboration has set a commitment to achieving zero impact of microfiber on the environment [90]. Their roadmap for 2030 has 3 interconnected dots: i. ii.

iii.

Aligning the sector—This mainly considers drafting a clear problem statement and the goals to be achieved as per the timeline. Understanding fragmentation—This part focuses on developing test methods and standards for a better understanding of the issue which is key to finding the solution. Also, developing a knowledge hub to share the resources that can help in avoiding duplication of research and resources. Mitigating the fragmentation—This is the next step where the research on textile manufacturing has to be made to reduce fiber fragmentation. Developing mitigation strategies and enabling them to get adopted by the signatories.

The Consortium has developed a standard testing method based on color fastness test (ISO 105 C06). The test method highlights the specimen size, washing methods, filtration method, and the quantification of microfiber release. Making the testing protocol common can enhance the comparability between the results of different researchers [90]. Then they have developed the ‘Microfibre Data Portal’ in which the signatories can upload their findings related to the microfiber release which can facilitate the data analysis. ‘Microfiber Knowledge Hub’ will help the brands and retailers to get the data regarding the microfiber release effectively to understand the actions to be made [90]. This collaborative initiative can potentially bring drastic change as it is wisely addressing the gap to make the mitigation strategies commercially. Outdoor Industry Association Outdoor Industry Association (OIA), which is addressing several sustainable issues with its Sustainable Working Group (SWG), has begun to address the microfiber issue. They have initiated the ‘Microfibers Task Force’ [91]. They have categorized their work plan into two parts in which one will analyze and collect the data of sources, emissions, and risk associated with the microfibers, whereas the other part will focus on developing test methodologies and identifying innovative production processes to mitigate the problem [91]. Surfrider Foundation Surfrider Foundation, which comprises science, environmental and legal experts, serves to protect the ocean and beaches from plastic pollution. They have initiated to address microfiber pollution. As a part of that, they are committed to educating their members about the issue and also creating awareness among the general public about the issue [92]. Moreover, they focus on identifying the source and mitigating the issue. In that essence, they have collaborated with Patagonia and the Outdoor Industry Association to collect and analyze the scientific reports and coordinate to develop mitigation strategies. They also promote policies and legislation to reduce microfiber emissions [93]. Apart from these, various organizations including American Apparel and Footwear Association (AAFA), Textile Mission, American Association of Textile

6.8 Government Regulations and Laws for Microfiber Pollution Control

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Color and Chemists (AATCC), Coastal Ocean Research Institute (CORI), European Outdoor Groups (EOG) are working on providing insight to the microfiber issues and supporting the innovative practices to tackle the problem [10]. As a whole, the brands and organizations which are addressing the microfiber issue focus on three major things. Firstly, the primary research is to collect data related to microfiber sources and emissions and to develop the standard test methods for the analysis of microfiber shedding from textile materials. Secondly, working together to modify the textile production process to reduce microfiber emissions. Thirdly, communicating the issues and the mitigation strategies to the public.

6.8 Government Regulations and Laws for Microfiber Pollution Control Making regulations and laws in the view of controlling microfiber pollution is the need of the hour as only this would make the scientific solutions into effective action. Researchers have reported that the regulations should be made in washing machines, wastewater treatment plants as well as the manufacturing process of textile materials [94]. As a legislative step, France has amended the law that will be effective from January 2025. As per the law, all new washing machines should come up with filters that can catch the microfibers released from laundry [95]. To bring awareness among the people, New York State Assembly has passed a bill to amend a new title in the Environmental Conservation Law. As per the bill, synthetic clothing which are containing more than 50% synthetic fibers should be labeled with microfiber shedding caution. The bill, which got into effect by January 2021, clearly states the care instructions for each clothing type (washable; dry cleanable, and others) [96]. A similar bill that mandates the labeling has also been passed in California Legislative Assembly [97]. In addition to that, California Legislative Assembly has passed a bill that states different measures that the state board should take in terms of controlling microfiber pollution. These measures include the development and adoption of a standard method for evaluating the efficiency of residential filtration systems. A standard methodology for quantifying the microfiber release from individual garments would also be adopted in the essence of providing solutions to the clothing manufacturers in terms of reducing microfiber release. This bill also mandates the installation of a filtration system that effectively captures microfiber when a private entity uses an industrial or commercial laundry system [97]. In this manner, an act has been enacted by the General Assembly of the State of Connecticut, which emphasizes creating awareness among consumers about the issue through labels. However, here, the information was not only limited to the microfiber releasing concern of the garment, but also the care instructions that reduce the microfiber release during washing [98]. Though few regulations and laws have been noted in few legislations, it is not enough as the issue cannot be tackled with these regulations. Researchers

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have reported that a multi-national agreement should be made in addressing the issue. Since identifying the different sources and standard methodologies has been noticed as the major concern that is becoming a barrier to finding the solution, the government should come forward to fund the research for developing standard methodologies [94].

6.9 Conclusion This chapter provided insight into possible ways of mitigating microfiber pollution. The solutions are provided at different stages and levels. In the production stage, modification of textile materials has been suggested. This modification can either reduce the shedding or increases the biodegradability of the synthetic fibers. At the consumption stage, that is, during the laundering of textiles, the addition of washing additives and usage of washing aids were noted to have a significant impact in reducing microfiber pollution. After the exposure stage, different techniques including electrocoagulation, adsorption, and bioremediation were noted to have the potency to remove microfibers from the aquatic environment. They were highlighted along with the effectiveness of sewage treatment plants. Then the necessity of consumer awareness on the issue and the government regulations were elaborated because these two factors are crucial while implementing the developed mitigation strategies practically. Finally, the efforts that are being made by renowned brands and different organizations on tackling the issue were detailed. This can give a deep insight into the ongoing research works on addressing the microfiber issue globally.

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