Microbial Degradation and Detoxification of Pollutants 9783110743623, 9783110743272

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Maulin P. Shah (Ed.) Microbial Degradation and Detoxification of Pollutants

Sustainable Water and Wastewater Treatment

Edited by Maulin P. Shah

Volume 2

Microbial Degradation and Detoxification of Pollutants Edited by Maulin P. Shah

Editor Dr. Maulin P. Shah Enviro Technology Limited Industrial Waste Water Research Lab Opp. Champapuri Jain Mandir A/103 Satsang Park Ankleshwar 393002 India

ISBN 978-3-11-074327-2 e-ISBN (PDF) 978-3-11-074362-3 e-ISBN (EPUB) 978-3-11-074370-8 ISSN 2747-4208 Library of Congress Control Number: 2022946975 Bibliographic information published by the Deutsche Nationalbibliothek The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the Internet at http://dnb.dnb.de. © 2023 Walter de Gruyter GmbH, Berlin/Boston Cover image: smirkdingo/iStock/Getty Images Plus Typesetting: Integra Software Services Pvt. Ltd. Printing and binding: CPI books GmbH, Leck www.degruyter.com

Contents List of contributing authors

VII

Priyadarshini Dey, Krishna Murthy T.P., Gangaraju Divyashri, Abhikhya Raghavendra, Akanksha Singh, Aishwarya Girish, Aliya Shaik, Anushka Amarnath Poola, Deeksha Krishnamoorthy Gopinath, Prithvi Prabhu, Rucha Konety, Sahana Kumar, Shreeya Kumaresan Bioremediation of organic and inorganic contaminants by microbes 1 Bedabrat Barooah, Kritika Sharma, Garima Kaushik Role of microbial enzymes in degradation of personal care products present in environmental matrices 21 Abel Inobeme,, Charles Oluwaseun Adetunji, John Tsado Mathew, Stanley Okonkwo, Mutiat Oyedolapo Bamigboye, Alexander Ikechukwu Ajai, Emmanuel Afoso, Jonathan Inobeme Advanced nanotechnology for the degradation of persistent organic pollutants 51 Abel Inobeme, Charles Oluwaseun Adetunji, Stanley Okonkwo, Mutiat Oyedolapo Bamigboye, Alexander Ikechukwu Ajai, Jonathan Inobeme, John Olusanya, Emmanuel Afoso Fate and occurrence of microplastic and nanoplastic pollution in industrial wastewater 73 Karthik Vijayarangan, Gladstone Christopher Jayakumar, Bindia Sahu An insight on chemicals used in the leather industry 99 Sonia Sethi, Samvida Bioaugmentation: approach for treating wastewater

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Aditya Amrut Pawar, Shilpa Sharma Advanced nanotechnology for the degradation of persistent organic pollutants 135 Dipankar Roy, Sreyashi Paul, Medha Basu, Arup Kumar Mitra Removal of heavy metal pollutant from electroplating industry through bioaugmentation 159

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Contents

Mary Isabella Sonali J., Veena Gayathri Krishnaswamy Use of microalgae for the removal of emerging contaminants from wastewater 189 Rajalakshmi Sridharan, Veena Gayathri Krishnaswamy Microplastics in the ecosystem and methods to identify them

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Tanya Gupta, Debatri Chakraborty, Angana Sarkar Microbial enzymes and role in bioremediation of environmental pollutants: prospects and challenges 217 Priyanka Role of nanotechnology for the degradation/removal of toxic pollutants from wastewater 239 Rahul Patwa, Daisy Das, Garima Kaushik Fate and occurrence of microplastic and nanoplastic pollution in industrial wastewater 251 Atun Roy Choudhury, P. Sankar Ganesh, Saikat Dutta, T.S. Sasi Jyothsna, Prasenjit Mondal, Anaya Ghosh, Debkumar Chakraborty, Nagati Amulya A comparative assessment of co-digestion of organic municipal solid waste and slaughterhouse waste 277 Index

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About the series

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List of contributing authors Chapter 1 Priyadarshini Dey Department of Biotechnology Ramaiah Institute of Technology Bengaluru, Karnataka India Krishna Murthy T.P. Department of Biotechnology Ramaiah Institute of Technology Bengaluru, Karnataka India Gangaraju Divyashri Department of Biotechnology Ramaiah Institute of Technology Bengaluru, Karnataka India Abhikhya Raghavendra Department of Biotechnology Ramaiah Institute of Technology Bengaluru, Karnataka India Akanksha Singh Department of Biotechnology Ramaiah Institute of Technology Bengaluru, Karnataka India Aishwarya Girish Department of Biotechnology Ramaiah Institute of Technology Bengaluru, Karnataka India Aliya Shaik Department of Biotechnology Ramaiah Institute of Technology Bengaluru, Karnataka India

https://doi.org/10.1515/9783110743623-203

Anushka Amarnath Poola Department of Biotechnology Ramaiah Institute of Technology Bengaluru, Karnataka India Deeksha Krishnamoorthy Gopinath Department of Biotechnology Ramaiah Institute of Technology Bengaluru, Karnataka India Prithvi Prabhu Department of Biotechnology Ramaiah Institute of Technology Bengaluru, Karnataka India Rucha Konety Department of Biotechnology Ramaiah Institute of Technology Bengaluru, Karnataka India Sahana Kumar Department of Biotechnology Ramaiah Institute of Technology Bengaluru, Karnataka India Shreeya Kumaresan Department of Biotechnology Ramaiah Institute of Technology Bengaluru, Karnataka India Chapter 2 Bedabrat Barooah Department of Environmental Science Central University of Rajasthan Bandarsindri Kishangarh Ajmer, Rajasthan India

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List of contributing authors

Kritika Sharma Department of Life Sciences Hemchandracharya North Gujarat University Patan, Gujarat India

Mutiat Oyedolapo Bamigboye Department of Chemical Sciences Kings University Odeomu Nigeria

Garima Kaushik Department of Environmental Science Central University of Rajasthan Bandarsindri Kishangarh Ajmer, Rajasthan India

Alexander Ikechukwu Ajai Department of Chemistry Federal University of Technology Minna Nigeria

Chapter 3 Abel Inobeme Department of Chemistry Edo University Iyamho PMB 04 Auchi Edo State 312101 Nigeria Charles Oluwaseun Adetunji Applied Microbiology Biotechnology and Nanotechnology Laboratory Department of Microbiology Edo University Iyamho PMB 04 Auchi Edo State Nigeria John Tsado Mathew Department of Chemistry Ibrahim Badamasi Babangida University Lapai Lapai Niger State 911101 Nigeria Stanley Okonkwo Department of Chemistry Osaka Kyoiku University Osaka Japan

Emmanuel Afoso Department of Biochemistry University of Benin Benin City Nigeria Jonathan Inobeme Department of Geography Ahmadu Bello University Zaria Nigeria Chapter 4 Abel Inobeme Department of Chemistry Edo University Iyamho PMB 04 Auchi Edo State 312101 Nigeria Charles Oluwaseun Adetunji Applied Microbiology Biotechnology and Nanotechnology Laboratory Department of Microbiology Edo University Iyamho PMB 04 Auchi Edo State Nigeria Stanley Okonkwo Department of Chemistry Osaka Kyoiku University Osaka Japan

List of contributing authors

Mutiat Oyedolapo Bamigboye Department of Chemical Sciences Kings University Odeomu Nigeria Alexander Ikechukwu Ajai Department of Chemistry Federal University of Technology Minna Nigeria Jonathan Inobeme Department of Geography Ahmadu Bello University Zaria Nigeria John Olusanya Department of Chemistry Federal University of Technology Minna Nigeria Emmanuel Afoso Department of Biochemistry University of Benin Benin City Nigeria Chapter 5 Karthik Vijayarangan CLRI Regional Centre Jalandhar Punjab India Gladstone Christopher Jayakumar Centre for Academic and Research Excellence CSIR-Central Leather Research Institute Chennai Tamil Nadu India and Department of Leather Technology Anna University Chennai Tamil Nadu India

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Bindia Sahu Centre for Academic and Research Excellence CSIR-Central Leather Research Institute Chennai Tamil Nadu India and Department of Leather Technology Anna University Chennai Tamil Nadu India Chapter 6 Sonia Sethi Dr. B. Lal Institute of Biotechnology Malviya Industrial Area Malviya Nagar Jaipur Rajasthan India Ms. Samvida Dr. B. Lal Institute of Biotechnology Malviya Industrial Area Malviya Nagar Jaipur Rajasthan India Chapter 7 Aditya Amrut Pawar Department of Biological Sciences and Engineering Netaji Subhas University of Technology Dwarka New Delhi India Shilpa Sharma Department of Biological Sciences and Engineering Netaji Subhas University of Technology Dwarka New Delhi India

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List of contributing authors

Chapter 8 Dipankar Roy Postgraduate Department of Microbiology St. Xavier’s College Kolkata West Bengal India

Chapter 10 Rajalakshmi Sridharan Department of Biotechnology Stella Maris College Affiliated to University of Madras Chennai Tamil Nadu India

Sreyashi Paul Postgraduate Department of Microbiology St. Xavier’s College Kolkata West Bengal India

Veena Gayathri Krishnaswamy Department of Biotechnology Stella Maris College Affiliated to University of Madras Chennai Tamil Nadu India

Medha Basu Postgraduate Department of Microbiology St. Xavier’s College Kolkata West Bengal India

Chapter 11 Tanya Gupta Department of Biotechnology and Medical Engineering National Institute of Technology Rourkela Odisha India

Arup Kumar Mitra Associate Professor Department of Microbiology St. Xavier’s College Kolkata West Bengal India

Debatri Chakraborty Department of Biotechnology and Medical Engineering National Institute of Technology Rourkela Odisha India

Chapter 9 Mary Isabella Sonali J. Department of Biotechnology Stella Maris College Affiliated to University of Madras Chennai Tamil Nadu India

Angana Sarkar Department of Biotechnology and Medical Engineering National Institute of Technology Rourkela Odisha India

Veena Gayathri Krishnaswamy Department of Biotechnology Stella Maris College Affiliated to University of Madras Chennai Tamil Nadu India

Chapter 12 Priyanka Department of Chemistry Indian Institute of Technology Roorkee Roorkee Uttarakhand India

List of contributing authors

Chapter 13 Rahul Patwa Bernal Institute University of Limerick Limerick V94 T9PX Ireland

Saikat Dutta Environmental Consultancy Ramky Enviro Services Private Limited Hyderabad Telangana India

Daisy Das Department of Fuel, Minerals and Metallurgical Engineering Indian Institute of Technology (Indian School of Mines) Dhanbad 826004 Jharkhand India

Sasi Jyothsna T.S. Environmental Consultancy Ramky Enviro Services Private Limited Hyderabad Telangana India

Garima Kaushik Department of Environmental Science Central University of Rajasthan NH-8 Bandar Sindri Ajmer 305817 Rajasthan India Chapter 14 Atun Roy Choudhury Department of Biological Sciences Birla Institute of Technology and Science Pilani Hyderabad Campus Hyderabad, Telangana India and Chadwick’s FSM Laboratory Banka BioLoo Limited 56, Nagarjuna Hills Road Punjagutta Hyderabad Telangana India Sankar Ganesh P. Department of Biological Sciences Birla Institute of Technology and Science Pilani Hyderabad Campus Hyderabad, Telangana India

Prasenjit Mondal Department of Chemical Engineering Indian Institute of Technology Roorkee Hobbies Club Road Roorkee Uttarakhand India Anaya Ghosh Department of Chemical Engineering National Institute of Technology Durgapur Mahatma Gandhi Rd A-Zone Durgapur West Bengal India Debkumar Chakraborty School of Environmental Science and Engineering Indian Institute of Technology Kharagpur Kharagpur West Bengal India Nagati Amulya Department of Chemical Engineering Indian Institute of Technology Roorkee Hobbies Club Road Roorkee Uttarakhand India

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Priyadarshini Dey✶, Krishna Murthy T.P., Gangaraju Divyashri, Abhikhya Raghavendra, Akanksha Singh, Aishwarya Girish, Aliya Shaik, Anushka Amarnath Poola, Deeksha Krishnamoorthy Gopinath, Prithvi Prabhu, Rucha Konety, Sahana Kumar, Shreeya Kumaresan

Bioremediation of organic and inorganic contaminants by microbes Abstract: Rapid industrial development coupled with the increase in human population has led to rampant discharge of hazardous inorganic chemicals (heavy metals) and organic pollutants such as dyes, pesticides, and pharmaceutical compounds into the environment, resulting in an imbalanced ecosystem. This review focuses on the bioremediation of contaminated ecosystems by different microorganisms such as algae, bacteria, and fungi and tries to arrive at a mechanism for contaminant removal from the environment. The efficiency of removal of these harmful contaminants depends on the type of microorganisms used for bioremediation (algae, bacteria, and fungi) and mode of removal of contaminants (biosorption or bioaccumulation). Here, the recent developments in the field of bioremediation of organic and inorganic contaminants have been summarized.

1 Introduction Small- and medium-scale enterprises such as electrical appliances manufacturing, battery, electroplating, printing, steel processing, and leather are important economic sectors in developing countries like India. However, these small and medium scale enterprises are a cause for environmental pollution and are responsible for the release of massive volumes of hazardous organic and inorganic contaminants into the environment. These industries are less stringent in terms of treating the wastewater, prior to the release to the different water bodies such as rivers that form the point

Note: All authors contributed equally. ✶ Corresponding author: Priyadarshini Dey, Department of Biotechnology, Ramaiah Institute of Technology, Bengaluru, India, e-mail: [email protected]. Krishna Murthy T.P., Gangaraju Divyashri, Abhikhya Raghavendra, Akanksha Singh, Aishwarya Girish, Aliya Shaik, Anushka Amarnath Poola, Deeksha Krishnamoorthy Gopinath, Prithvi Prabhu, Rucha Konety, Sahana Kumar, Shreeya Kumaresan, Department of Biotechnology, Ramaiah Institute of Technology, Bengaluru, India

https://doi.org/10.1515/9783110743623-001

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sources of contamination [1]. These contaminants ultimately bioaccumulate in the food chain of the ecosystem and cause various life-threatening diseases [2, 3]. A few select hazardous contaminants, which would help in understanding their remediation process, have been described briefly. Organic pollutants are aromatic compounds, chlorinated hydrocarbons, pesticides, textile dyes, phenolic compounds, and pharmaceutical compounds that are discharged into the wastewater from industries such as pharmacy, pesticides, textile, and petrochemical processing units [4–6]. Dyes are a group of unsaturated organic compounds that absorb light (chromophore) and emit color from the visible region. Majorly, the textile industries release dyes such as triphenylmethane dyes, anthraquinone dyes, phthalocyanine dyes, xanthene dyes, azo dyes, polymethine dyes, and indigoids. These dyes are responsible for the high salinity, high pH, high turbidity, and higher color density that result in contamination of the water bodies and, therefore, it is pertinent to remediate these dyes because of their high tectorial values, where even a discharge of less than 1 ppm of a dye into the water bodies brings about substantial variations in the chemical and physical characteristics of water. The prevalence of color decreases the solubility of oxygen as a result of high chemical oxygen demand and causes imbalance in the ecosystem [7–9]. The dyes are classified according to their color, as per their chromophore structure, and on the method of application. Chromophores are a group of atoms in the dye that impart color, based on their structure. The dyes belonging to the chromophore include azo dyes, cyanine dyes, xanthene dyes, nitro dyes, quinione-imine dyes, indigoid dyes, acridine dyes, oxazine dyes, anthraquinone dyes, triarylmethane dyes, phthalein dyes, triphenylmethane dyes, nitroso dyes, nitro dyes, and diarylmethane dyes. Also, dyes can be categorized as per their industrial applications as disperse dyes, direct dyes, reactive dyes, vat dyes (known for color and wet fast property), basic dyes (having positive charge on an NH4+ group or delocalized charge on the dye cation), acid dyes (having (SO3H and COOH group on the dye, sulfur dyes (known for being high molecular weight), azo dyes, and mordant dyes. These dyes are a potential threat to mankind for causing respiratory problems and skin diseases, and thus, removal from the environment becomes pertinent [10]. Pesticides are chemicals used to control weeds, insects such as mosquito, microbes (bacteria and fungi), and pests. The extensive usage of pesticides particularly for high agricultural yield has resulted in increased pollution of air, water, and soil. Besides the pesticides are lipophilic, have long half-life, and are easily transportable. Thus, this intensifies the chances of contamination and persistence of the pesticides, even after several years of application. The pesticides are classified based on chemical nature, for example, organochlorines and organophosphate, based on application such as in agriculture, public health, etc., as well as based on target organisms used, namely, herbicide, insecticide, or fungicide. Further, it is important to understand the chemical structures of

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pesticides, as different mixtures of pesticides with similar chemical structure do not produce the additive toxic effect. The toxicity level of the pesticide that contain a secondary chemical also changes, which influences the toxicokinetics of the pesticide [11]. Pesticides based on chemical nature are organochlorines (DDT, chlorobenziate, lindane, methoxychloro, aldrin, chlordane, and endosulfan); organophosphate (parathion, caumphos, dichlorovas, phosphomidon, malathion, and trichlorofan); carbamates; pyrethroids; phenyl amides (carbanilates, acylanilide, toluidines, and acetamide); phenoxy alkonates [2,4-D-(2,4-dichlorophenoxy acetic acid), 2,4,5-T (2,4,5-trichloro phenoxy acetic acid)]; trazines, benzoic acid, and phthalimides. These pesticides cause chronic health damage such as impairment to the nervous system and endocrine disorders. Hence, removal of these pesticides becomes of paramount importance [12]. Pharmaceutical compounds are released into the environment mainly via municipal wastewater. Many of the pharmaceutical compounds do not metabolize completely in the human bodies and, as a consequence, are released with the urine and feces excretions into the sewage system. Further, untreated wastewater from the hospitals and pharmaceutical industries also release it to municipal wastewater [13]. These hazardous pharmaceutical compounds include organic pollutants (antibiotics, anti-inflammatories, lipid regulators, antidepressants, reproductive hormones, beta-lactamides, analgesics, steroids, cytostatic agents, etc.) and heavy metals such as cadmium, lead, chromium, nickel, and mercury. These pharmaceutical compounds, after entering the water bodies, pose risk to the aquatic life and also human beings, even when present in small quantities [14]. Inorganic contaminants such as heavy metals are discharged from numerous industries like batteries, fertilizer, preservatives, electroplating, textile, and pesticides, and are perpetually released into the water bodies [2, 15]. Heavy metals such as arsenic, mercury, cadmium, chromium, copper, nickel, lead, and zinc are a major group of lethal pollutants due to their recalcitrant nature. Heavy metals are categorized as elements that have atomic weights between 63.5 and 200.6 and density higher than 5.0 g/cm3 [16]. Heavy metals cannot be biodegraded and, hence, accumulate in the ecosystem and are carcinogenic [17]. These inorganic as well as the organic pollutants are priority contaminants that pose peril to the environment. Thus, several physical and chemical methods have been employed to remediate these contaminants. These methods include membrane filtration, adsorption, chemical precipitation, electrochemical treatment technologies, ion-exchange, coagulation–flocculation, and floatation. Some of the disadvantages of these physicochemical methods include sludge formation, low selectivity of contaminants, and high cost. Thus, microorganisms are a natural and economical substitute for the physicochemical remediation process. To overcome the disadvantages of the physicochemical treatments of organic and inorganic contaminants, a large section of researchers have explored microbes like algae, bacteria, and fungus as bioremediators [18–32]. However, most of the studies have focused on the biosorption method of contaminant removal that employs inactive

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form of the microbes. Only a fraction of the investigations used actively growing microbes that comprised of contaminant sequestration by production of enzymes for bioaccumulation. Active cells sustain themselves via continuous metabolic uptake of the contaminants, while biosorption is a metabolically passive process that involves binding of contaminants on the surface of cell [33]. Moreover, bioaccumulation of contaminants by growing active cells can bypass the requirement of harvesting, processing, and drying of biomass before usage [34].

2 Mycoremediation Mycoremediation (remediation with the use of fungi) has shown to be a very sustainable technique. Fungi can be said to be more effective bioremediators than the unicellular organisms, due to their robust morphology and multifaceted metabolic ability. They are able to survive in different habitats, thereby facilitating easy colonization. Fungi are able to colonize stably within freshwater and marine habitats. They are efficient in metabolizing numerous organic compounds and use the obtained product for survival, without any extra need for nutrition. Fungi are a lucrative option, as they produce unique enzymes that are able to carry out complex chemical reactions. Their well-developed enzymatic system allows them to grow well on a variety of substrates, both natural and synthetic. They secrete higher rates of a variety of extracellular enzymes that can degrade the substrate into smaller molecules, so that it can be absorbed and metabolized within the cell. Using these enzymes for the treatment, removal, and detoxification of environmental pollutants has generated great interest owing to their high efficiency [35]. An additional advantage of using fungus as bioremediator is that the growth of mycelia maximizes the mechanical contact with the contaminant, due to enhanced cell-to-surface ratio [36]. Thus, fungus aids in the removal/breakdown of different recalcitrant organic pollutants, such as petroleum hydrocarbons, halogenated organic compounds, polycyclic aromatic hydrocarbons, dyes and pesticides, and heavy metals and provide a solution to tackle the contamination in different ecosystems [37–40].

3 Fungal remediation of organic and inorganic compounds The enzymes produced by fungi have low specificity for different contaminants, which allows them to metabolize many constituents of diverse pollutants, which are structurally unlike. For example, Phanerochaete chrysosporium, a crust fungus, degrades many toxic chemicals such as xylene, toluene, benzene, ethylbenzene

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organochlorines, PAHs, nitroaromatic compounds, pesticides, synthetic polymers, and even mixtures containing all of these. The major categories of enzymes that actively contribute towards the degradation of toxic organic compounds are essentially seen to fall into three categories of extracellular oxidoreductases, cell bound enzymes, and transferases [41]. Extracellular oxidoreductases: This category of enzymes, namely, laccases, peroxidases, and tyrosinases allows fungal strains and its isolates to grow and survive on recalcitrant substrates such as lignocelluloses, which cannot be effectively degraded by bacteria. This makes the use of the fungal enzymes advantageous. Laccases are coppercontaining enzymes that essentially catalyze polymerization and depolymerization processes mainly produced in Ascomycetes and Basidiomycetes. These can be employed in various decolorization and detoxification processes of recalcitrant compounds in wastewater effluents and other hazardous components that are water and soil pollutants. A novel fungal strain Peroneutypa scoparia oxidized the dye Acid Red 97 to its metabolites, naphthalene 1,2-dione and 3-(2-hydroxy-1-naphthylazo) benzenesulfonic acid, with the help of enzyme laccase. The dye degradation was up to 75% within 6 h [42]. The enzyme laccase secreted by Pycnoporus sanguineus CS43 was also responsible for the removal of pharmaceutical compounds diclofenac (50%), β-naphthol (97%), and 2,4-dichlorophenol (71%) within 8 h and 5,7-diiodo-8-hydroxyquinoline (78%) within 3.5 h from initial concentrations (10 mg/L), in simulated media. This fungal strain also removed 53% of all the above pharmaceutical compounds from the actual groundwater sample from northwestern parts of Mexico [43]. Tyrosinase is another copper-containing enzyme that oxidizes phenols and chlorinated phenol compounds. Peroxidases like lignin and manganese peroxidase enzymes that can oxidize pollutants and convert them into nonhazardous products with a high redox potential [13]. A non-white fungus Penicillium simplicissimum was studied for its decolorization of the triphenylmethane dyes of crystal violet (98.7%), methyl violet (97.5%), malachite green (97.1%), and cotton blue (96.1%) within 2 h, with initial concentration of the dyes at 50 mg/L. The enzymatic analysis for biodegradation of dyes revealed the involvement of the enzymes, manganese peroxidase, tyrosinase, and triphenylmethane reductase [44]. Cell-bound enzymes: Numerous toxic compounds and pollutants are able to pass through the fungal cell membrane, that is, they are permeable, and once inside, they are catabolized through several intracellular cell bound enzymes present within the fungi. The pollutants essentially undergo degradation through the fungal metabolism pathways, until they are mineralized. Cytochrome P450 is an intracellular heme-containing monooxygenase. They play an effective role in the degradation of dioxins and oxidation of organic compounds. White rot fungus, Phanerochaete chrysosporium, is well known to use this enzyme for degradation of xenobiotic compounds [45]. Another white rot fungus, Trametes versicolor, metabolized the pesticide fipronil, which is used for flea/tick treatment and transformed to products of

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hydroxylated fipronil sulfone and glycosylated fipronil sulfone, with the help of enzyme cytochrome P450. Thus, when the fungus was exposed to the cytochrome P450 inhibitor 1-aminobenzotriazole, the production of the fipronil metabolites decreased. Furthermore, understanding the pesticide transformation products is crucial, as pesticide specificity for targets can be lost through structural changes [46]. Transferases: This is a miscellaneous group of enzymes, for example. aromatic nitroreductases and quinone reductases that transfer functional groups and transform the hazardous pollutants into nonhazardous end products. They are seen to degrade those compounds of pollutants containing hydroxyl groups by transforming them into conjugates. These can then either be stored, fixed. or secreted into the natural environment in the inactive form of the conjugate. thereby rendering them harmless [41]. A white-rot fungus Phanerochaete chrysosporium was used in the degradation of the compound, imidacloprid, belonging to the neonicotinoid group of pesticides. The pesticide degradation was determined by quinone redox cycling. Degradation rate was enhanced in the presence of gallic acid mediator. At initial pesticide concentration of 10, 20, 30 mg/L and presence of 100 μM Mn2+,100 μM Fe3+, 300 μM of oxalate, and 500 μM of gallic acid, imidacloprid was degraded to 97.37%, 82.0%, and 73.52%, respectively [47]. Apart from enzymes, fungi also contain lipids, polysaccharides, and pigments, such as melanin that aid in binding of heavy metals. Similarly, hydroxyl, phenolic, carbonyl, carboxyl, and methoxyl groups play important roles in binding to the oxygenbinding sites that are present in the cell wall components, as melanins and phenolic polymers [48]. In a study, five fungal strains (Beauveria bassiana 4580, Paecilomyces fumosoroseus 4099, Aspergillus fumigatus PD-18, Aspergillus terreus AML02, and Aspergillus terreus PD-17) were compared for removal of 30 mg/L mixture of metals (5 mg/L each of cadmium, chromium, copper, nickel, lead and zinc) in simulated composite media. It was observed that the uptake of metals differed, even at the variety level of fungal species [19]. Further, an entomopathogenic fungus, Beauveria bassiana 4,580 was studied in detail for its multiple metal combination as well as individual metal bioaccumulation. The ability of the fungus for removal of 100 mg/L of individual metals (Zn2+, Cu2+, Cd2+, Cr6+, and Ni2+) varied, when the same heavy metals were present in a 30 mg/L mixture [49]. Thus, the uptake of metals by the fungus is influenced by the combination of metals in a mixture. In a study, a white rot fungus, Phanerochaete chrysosporium, was studied for its biosorption potential. The fungus was reinforced with intracellular mineral scaffold and displayed high biosorption potential for the metals, Cd2+ and Pb2+. Here, the biosorption process was divided into three phases: surface adsorption phase (fast), transfer phase from external to internal (slow), and phase of reaching equilibrium [50]. In another study, low cost biosorbents were prepared from fungal biomasses of Penicillium chrysogenum and Aspergillus ustus, which successfully removed Cu2+,

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Cd2+, and Pb2+ with mean concentration 2.6–234 µg/L in the wastewater samples from northern, eastern, and western Saudi Arabia [51].

4 Phycoremediation Phycoremediation is the method of the degradation or biotransformation of wastewater toxins by utilization of algal species. Algae have been recognized to feed on different types of wastewater pollutants dispensed through domestic, agricultural, and industrial sources. Algae are prokaryotic (cyanobacteria) or eukaryotic microorganisms with increased adaptability to harsh environmental conditions that include variable pH, temperature, and low nutrient levels. The mechanism of adaptation to extreme conditions can be explained by spontaneous gene mutations or physiological adaptation [52]. Algae can grow in unicellular form or as colonies. Algal species can grow autotrophically or heterotrophically. Photosynthetic algae-containing chlorophyll can sequester carbon dioxide from the atmosphere and utilize it for growth, thereby alleviating the increased levels of this greenhouse gas. Studies show that the use of microalgal–bacterial consortium ends up in a synergistic interdependence that is helpful in treatment where bacteria release carbon dioxide, and oxygen is provided by algae. This is considered essential in a treatment process due to the reduction in oxygen supplementation. The potential mechanisms associated with microalgal–bacterial systems may be photodegradation, biodegradation, volatilization, biosorption, and bioprecipitation [53–55]. Thus, algae have the natural ability to take up nutrients, accumulate heavy metals, and degrade organic contaminants. Phycoremediation of inorganic contaminants: The main mechanism involved in phycoremediation of heavy metals is biosorption. In biosorption, contaminants in contact with algal biopolymers/biomaterials are adsorbed. Biosorption offers flexibility in design and operation. It also reduces the use of chemical reagents and prevents the production of secondary sludge as in the case of chemical adsorbents. One of the major advantages of biosorption in an industrial scenario is the recovery of metal ions. Besides, this process is eco-friendly and economic. There are mainly two types of biomasses involved in phycoremediation: active algal biomass (AAB) and passive algal biomass (PAB). Usually, the actively growing cells of AAB are not preferred for biosorption, as they require nutrients for growth. AAB cells might not grow well in high toxic contaminant environment. On the other hand, PAB is preferred for biosorption, as they do not require any nutrients. PAB cells can adsorb heavy metal ions on cell wall surfaces. They are polymer aggregations, which are capable of binding heavy metals. Other advantages of the passive algal biomass include that they can treat large volumes of contaminants in a short time. They have high specificity and selectivity to metal ions and can purify mixed wastes by removing many metals. Further,

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nonviable algae are the preferred choice as biosorbents, as the process is metabolismindependent and involves the binding of metal ions onto the cell wall. Nonviable algae can be easily obtained, and the cost of preparation of microalgal biosorbent is low [18]. Heavy metal bioremediation is affected by biotic and abiotic factors. Some of the biotic factors are species of algae used, biomass concentration, tolerance of algae to the toxic environment, volume, and size of biomass. Some of the abiotic factors are pH, hardness, salinity, temperature, and ionic strength. The advantages of biosorption depend on the type of algal biomass that is chosen. Two of the most important categories of algae used for bioremediation are microalgae and macroalgae [56]. Microalgae are a group of organisms that are photosynthetic and can assimilate carbon, nitrogen, and phosphorous. They can specifically take up certain heavy metals in trace amounts that are required for their growth and metabolism. Some of these metals are boron, cobalt, and copper. They require these metals for enzymatic processes and metabolism of cells. The uptake of these metals occurs because of hormesis phenomenon, wherein low doses of certain agents can be stimulatory or beneficial, but higher doses of the same can be toxic. Other metals like arsenic, cadmium, and chromium are toxic to microalgae, even in small amounts [57, 58]. During photosynthesis, the microalgae form peptide bonds, which can bind heavy metal ions to form organometallic complexes. These complexes are taken to vacuoles, in order to maintain the concentration of metal ions in cytoplasm. This neutralizes the toxic effects of heavy metals. The complexes with pollutants are formed due to the presence of reactive groups with active binding sites. The suspended and dissolved solid contents are reduced due to flocculation, and thus, total dissolved solids and total suspended solids are reduced from wastewater. Microalgae adopt various strategies for protection against heavy metals. They can immobilize heavy metal ions, regulate the genes, and exclude and chelate ions, and so on [59]. There are two steps involved in bioremediation by microalgae. The initial step is fast, extracellular, and passive adsorption called as biosorption. It is followed by slow intracellular positive diffusion and accumulation. This is called as bioaccumulation. The cell wall of the microalgae has various components like polysaccharides, lipids, organic proteins, and monomeric alcohols. Other components present in the cell wall are laminarin and carboxyl groups that bind to the heavy metals. They can attract anionic and cationic species of heavy metals. Biosorption of heavy metals on the cell surface is a rapid process. It can take place by various mechanisms such as covalent bond formation with heavy metals and ionic exchange of heavy metal cations. Bioaccumulation is a much slower active transport of heavy metals across the cell membrane and into the cytoplasm. This is followed by diffusion and binding with internal binding sites of phytochelatins, glutathione, and so on. Microalgae can synthesize antioxidant and nonantioxidant enzymes for counteracting the free radicals formed during adsorption. Superoxide dismutase (SOD) is an antioxidant enzyme. It acts as the first line of defense against superoxide anion. It degrades superoxide to hydrogen

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peroxide and oxygen. Another antioxidant enzyme, catalase, degrades hydrogen peroxide into water and oxygen. Cysteine, a nonenzymatic antioxidant, acts as a precursor for phytochelatins, glutathione, metallothioneins, and so on. It acts as an indicator to produce various antioxidants. Along with glutathione, ascorbic acid helps in managing reactive oxygen species (ROS) [57]. However, a few challenges are associated with the microalgal bioremediation are that other microorganisms can contaminate the process. There might be variation in the nutrients and high solid content. The harvesting of biomass is also difficult. Thus, microalgal strains should be effectively screened for favorable characteristics, such as that they should have high tolerance to heavy metal pollutants and should be able to grow rapidly, should be stable, should have high carbon dioxide sequestration ability, and have fewer nutrient requirements. This can increase specificity and robustness of the strains. The preferred microalgae for removal of heavy metals are Chlorella and Scenedesmus species [57, 60]. Macroalgae or marine algae are also promising bioremediators. They are widely available, and do not require special conditions for growth, and also have high productivity. To retain metal ions, only a few simple preparation stages are needed. The cultivation of marine algae is easy. Macroalgae have various functional groups in their cell structure that bind easily to heavy metals. However, they have low mechanical resistance and can be used only for a short duration. This is disadvantageous for industrial applications. As in microalgae, the cell wall surface of marine algae also contains functional groups that bind to toxic metal ions from aqueous media. The interaction of heavy metal ions and functional groups determines the efficiency of uptake of heavy metals. This interaction is affected by various factors such as dissociation degree of functional groups, speciation, number of binding sites in macroalgae, and the type of heavy metals. Further, it is necessary to find optimal conditions for efficiency of biosorption process. The elementary process that occurs in desorption of toxic heavy metals is of ion-exchange type. Thus, the marine algae biomass can be used for another round of the process. But the efficiency of biosorption reduces as the number of cycles increase. After 6–8 cycles, biomass is not efficient for biosorption. This is usually due to irreversible degradation of structure of biomass. It can also be due to incomplete desorption of toxic heavy metals. These disadvantages act as important limitations in practical industrial scenario. Desorption lowers the cost of removal of heavy metal ions from aqueous media. Chemical reagents that can be used for desorption are mineral acids, inorganic salts, and complexing agents like EDTA. The use of marine algae biomass in advanced treatment of wastewater with heavy metal ions could be an efficient solution for industrial effluent treatment. Commonly used macroalgal species for bioremediation are Ulva lactuca and Spirogyra spp [61, 62]. In a novel study, two macroalgae, Sargassum muticum and Ulva lactuca and two microalgae, Arthrospira platensis and Chlorella vulgaris, were used as passive

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bioremediators for the heavy metals Ni2+, Zn2+, Cd2+, and Cu2+.The heavy metals were amended singly and in combination in the range (10–150 mM). The algal biomass containing metals were then subjected to hydrothermal liquefaction biorefinery approach that yielded products such as bio-crude oil (aqueous phase), solid residue, and gas [63].

5 Phycoremediation of organic contaminants Bioadsorption by microalgal cells is facilitated when compounds are passively and nonmetabolically adsorbed onto the algal cell wall components, or onto the extracellular polysaccharides (EPS) that are secreted by the algal cell into the neighboring environment. The ability of an emerging organic contaminant to adsorb onto algal cell surfaces depends on the chemical structure of the organic contaminant. Cationic organic contaminants that are hydrophobic are attracted actively to the algal cell via electrostatic interactions, while organic contaminants that are hydrophilic are repelled. Further, the amount of organic contaminants adsorbed by algae depends on its cell surface area and chemistry. The algal cell surface contains variety of functional groups, namely, hydroxyl, carboxyl, or sulfate that differs in specificity and affinity for the emerging organic compounds via several chemical processes such as chelation, microprecipitation, surface complexation reactions, ion exchange reactions, and adsorption reactions. These processes, in turn, depend on the physical and chemical properties of the surrounding environment, that is, redox, pH, temperature, and so on [60] Phenanthrene (PHE) and fluoranthene (FLA) are two of the commonly found highly toxic organic polyaromatic hydrocarbons (PAHs). Hong et al. [64] carried out studies on PHE and FLA biodegradation, by making use of the algal species Skeletonema costatum and Nitzschia sp. The breakdown potential of S. costatum was lower than that of Nitzschia sp. FLA breakdown by the two species was found to be a slower process, suggesting the probability of FLA being the more recalcitrant compound. Greater efficiency of the two algal species was observed in the degradation of FLA-PHE mixture than in PHE or FLA alone. This indicated the possibility of stimulation of degradation in the presence of both PAHs. When PAHs are internalized into microorganisms, they undergo degradation due to triggering of a series of enzymatic reactions on the aromatic rings by the oxygen atoms incorporated by green algae. The end product would either be cisdihydrodiols or phenols [65]. Further, Cruz-Uribe et al. [66] used sterilized plantlets obtained from green algae, Acrosiphonia coalita and red algae, Porphyra yezoensis and Portieria hornemannii, to degrade 2,4,6-trinitrotolune (TNT). The three species were found to remove TNT by 20% from marine water, and they shared a

Bioremediation of organic and inorganic contaminants by microbes

11

comparable metabolic pathway of degradation, where the reduction of TNT to 2-amino-4,6-dinitrotoluene and 4-amino-2,6-dinitrotoluene takes place. Other than removing contaminants, algal biomass can produce various valueadded products. Some of these products are bioethanol, biohydrogen, biodiesel, and electricity. In the current environmental scenario, it is imperative to use bioremediators that not only remove wastes but also produce byproducts that are useful to mankind. The various limitations associated with the use of algae for bioremediation can be overcome by using genetic engineering, proper screening mechanisms, and use of relevant physical and chemical methods, along with algal biomass [56].

6 Bacterial bioremediation Bacterial bioremediation is a process wherein growth of bacteria is stimulated by the use of contaminants as a source of food and energy. Generally, contaminants treated using bacterial bioremediation process include solvents, pesticides, oil, and other petroleum products [67]. They rely on the bacterial population that live naturally in soil and groundwater. Bacteria digest these contaminants and change them into small amounts of water and gases, namely, carbon dioxide and ethene. Bioremediation process can further be improved by the addition of extra bacterial population to the site, and this process is termed as bioaugmentation. The process can be applied in place of contamination (in situ) or offsite of contamination (ex situ) [67, 68]. Proper conditions (temperature and nutrients) dictate the effectiveness of the bioremediation process. In situ bioremediation is often slow and it seems difficult to optimize and control process parameters affecting the overall process [67]. However, engineered bioreactors are considered to provide optimum conditions for the growth of bacteria and degradation of contaminants. Airlift, packed, stirred tanks, and partitioning phase reactors are designed for bioremediation process [69–71]. Bacterial bioremediation of heavy metals is proven successful when consortia of bacterial strains are used, instead of a single strain [72]. Bacterial bioremediation works best under aerobic conditions; however, anaerobic conditions may also permit bacterial degradation of recalcitrant molecules [73]. Bacterial bioremediation of recalcitrant, lignin, and organopollutants encompasses the participation of different intracellular and extracellular enzymes [74].

7 Factors affecting bacterial bioremediation The factors affecting the bacterial bioremediation process include: (a) the ability of bacterium/bacterial consortia to degrade the contaminants; (b) the availability of contaminants to the bacterium/bacterial consortia; and (c) environmental factors, namely, soil type, nutrients, pH, temperature, the presence of oxygen, and/or other

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electron acceptors [75]. The physicochemical properties of the contaminants and the metabolic characteristics of the bacterium determine the possible interaction during the bioremediation process. Growth and activity of the bacteria are affected by soil structure, pH, temperature, moisture, chemical structure, and concentration of the contaminant. Biodegradation occurs in a wide range of pH; however, pH 6.5 to 8.5 is generally optimal for aquatic and terrestrial bioremediation systems [76].

8 Bacterial bioremediation of heavy metals Persistent exposure to heavy metals results in the onset of lethal diseases including keratosis, gangrene, cancer, diabetes, and cardiovascular disorder. Different bacterial species involved in the bioremediation process include Pseudomonas putida, Pseudomonas fluorescence, Bacillus jeotgall, Escherichia coli, Enterobacter spp., and Arthrobacters spp. (Table 1). Table 1: Bioremediation of heavy metals using bacteria. Bacterial species

Metal ion

Biosorption capacity

References

Pseudomonas putida

Zinc (Zn)

. mg/g

Green-Ruiz et al. []

Bacillus jeotgali

Zinc (Zn)

. mg/g

Green-Ruiz et al. []

Arthrobacter spp.

Chromium, Cr(VI)

. mg/g

Hasan and Srivastava []

Pseudomonas fluorescence

Chromium, Cr(VI)

. mg/g

Uzel and Ozdemir []

Pseudomonas spp.

Chromium, Cr(VI)

 mg/g

Ziagova et al. []

Enterobacter spp. J

Copper, Cu(II)

. mg/g

Lu et al. []

The mechanism through which bacteria bioremediates heavy metals is given in Figure 1. The complete mechanism is not fully understood. However, the mechanism is broadly classified, depending on bacterium metabolism, as (i) metabolism dependent, wherein metal ions are transported across the cell membrane [82]; and (ii) metabolism independent, wherein metals are bound to the cell walls [83]. According to the metal location site, the mechanism is further classified as (i) extracellular precipitation/accumulation: (ii) cell surface precipitation/sorption; and (iii) intracellular accumulation. A study by Kang et al. [84], investigated the synergistic effect of bacterial mixtures, namely, Enterobacter cloacae KJ-46, Viridibacillus arenosi B-21, E. cloacae KJ47, and Sporosarcina soli B-22 on bioremediation of heavy metals, namely, Cd, Pb, and Cu. Their results demonstrated the greater efficiency of bacterial consortia than using single strain with remediation efficiencies of 85.4% for Cd, 98.3% for Pb, and

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5.6% for Cu. Ghodsi et al. [85], reported the adsorption ability of Bacillus macerans (60%), Corynebacterium (vitaromen) (43%), and Bacillus megaterim (38%) for arsenite after 48 h of growth were 60%, 43%, and 38%, respectively. Transport across membrane Metabolism dependent

Bioremediation Mechanism

Metabolism independent

Intracellular adsorption Precipitation

Complexation

Extracellular adsorption

Ion-exchange

Cell surface adsorption/ precipitation

Bioremediation Mechanism

Physical adsorption

Figure 1: Mechanism of bacterial bioremediation process.

Ameen et al. [86] were successful in isolating and characterizing a metal-resistant lactic acid bacterium from Alexandrian Mediterranean Seacoast, Egypt. The isolated strain was found to be Lactobacillus plantarum MF042018 and showed higher degree of resistance for chromium and nickel, up to 100 and 500 ppm, respectively. Furthermore, Klebsiella and Enterobacter have proven their potential for bioremediation of soil contaminated with lead, arsenic, and cadmium [87].

9 Conclusion Microbial bioremediation is proven to be a safe method to remove toxic metal contaminants from the environment. Particularly, bacteria offer great potential in the clean-up of the environment. However, the bioremediation process will only be successful through the employment of bacterium/bacterial consortium capable of remediating and tolerating toxicity of heavy metals.

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[63] Piccini M, Raikova S, Allen MJ, Chuck CJ. A synergistic use of microalgae and macroalgae for heavy metal bioremediation and bioenergy production through hydrothermal liquefaction. Sustainable Energy Fuels 2018, 3(1), 292–301. https://doi.org/10.1039/C8SE00408K. [64] Hong Y-W, Yuan D-X, Lin Q-M, Yang T-L. Accumulation and biodegradation of phenanthrene and fluoranthene by the algae enriched from a mangrove aquatic ecosystem. Mar Pollut Bull 2008, 56(8), 1400–05. https://doi.org/10.1016/j.marpolbul.2008.05.003. [65] Lika K, Papadakis IA. Modeling the biodegradation of phenolic compounds by microalgae. J Sea Res 2009, 62(2), 135–46. https://doi.org/10.1016/j.seares.2009.02.005. [66] Cruz-Uribe O, Cheney DP, Rorrer GL. Comparison of TNT removal from seawater by three marine macroalgae. Chemosphere 2007, 67(8), 1469–76. https://doi.org/10.1016/j. chemosphere.2007.01.001. [67] Tekere M, Tekere M. Microbial Bioremediation and Different Bioreactors Designs Applied. In: Biotechnology and Bioengineering, IntechOpen, 2019. https://doi.org/10.5772/ intechopen.83661. [68] Jeon CO, Madsen EL. In situ microbial metabolism of aromatic-hydrocarbon environmental pollutants. Curr Opin Biotechnol 2013, 24(3), 474–481, https://doi.org/10.1016/j. copbio.2012.09.001. [69] Pino-Herrera DO, Pechaud Y, Huguenot D, Esposito G, van Hullebusch ED, Oturan MA. Removal mechanisms in aerobic slurry bioreactors for remediation of soils and sediments polluted with hydrophobic organic compounds: An overview. J Hazard Mater 2017, 339, 427– 449. https://doi.org/10.1016/j.jhazmat.2017.06.013. [70] Gargouri B, Karray F, Mhiri N, Aloui F, Sayadi S. Application of a continuously stirred tank bioreactor (CSTR) for bioremediation of hydrocarbon-rich industrial wastewater effluents. J Hazard Mater 2011, 189(1), 427–434, https://doi.org/10.1016/j.jhazmat.2011.02.057. [71] Chikere CB, Okpokwasili GC, Chikere BO. Monitoring of microbial hydrocarbon remediation in the soil. 3 Biotech 2011, 1(3), 117–138, https://doi.org/10.1007/s13205-011-0014-8. [72] Ojuederie OB, Babalola OO. Microbial and plant-assisted bioremediation of heavy metal polluted environments: A review. Int J Environ Res Public Health 2017, 14(12), Article 12, https://doi.org/10.3390/ijerph14121504. [73] Karigar CS, Rao SS. Role of microbial enzymes in the bioremediation of pollutants: A review. Enzyme Research 2011, 2011, 1–11, https://doi.org/10.4061/2011/805187. [74] Vidali M. Bioremediation. An overview. Pure Appl Chem 2001, 73(7), 1163–1172, https://doi. org/10.1351/pac200173071163. [75] Abatenh E, Gizaw B, Tsegaye Z, Wassie M, Abatenh E, Gizaw B, Tsegaye Z, Wassie M. the role of microorganisms in bioremediation- a review. Open J Environ Biol 2017, 2(1), 038–046, https://doi.org/10.17352/ojeb.000007. [76] Omokhagbor Adams G, Tawari Fufeyin P, Eruke Okoro S, Ehinomen I. Bioremediation, biostimulation and bioaugmention: A review. Int J Environ Bioremed Biodegrad 2015, 3(1), 28–39, https://doi.org/10.12691/ijebb-3-1-5. [77] Green-Ruiz C, Rodriguez-Tirado V, Gomez-Gil B. Cadmium and zinc removal from aqueous solutions by Bacillus jeotgali: PH, salinity and temperature effects. Bioresour Technol 2008, 99(9), 3864–3870, https://doi.org/10.1016/j.biortech.2007.06.047. [78] Hasan SH, Srivastava P. Batch and continuous biosorption of Cu2+ by immobilized biomass of Arthrobacter sp. J Environ Manage 2009, 90(11), 3313–3321, https://doi.org/10.1016/j. jenvman.2009.05.005. [79] Uzel A, Ozdemir G. Metal biosorption capacity of the organic solvent tolerant Pseudomonas fluorescens TEM08. Bioresour Technol 2009, 100(2), 542–548, https://doi.org/10.1016/j. biortech.2008.06.032.

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[80] Ziagova M, Dimitriadis G, Aslanidou D, Papaioannou X, Litopoulou Tzannetaki E, LiakopoulouKyriakides M. Comparative study of Cd(II) and Cr(VI) biosorption on staphylococcus xylosus and pseudomonas sp. In single and binary mixtures. Bioresour Technol 2007, 98(15), 2859– 2865, https://doi.org/10.1016/j.biortech.2006.09.043. [81] Lu W-B, Shi -J-J, Wang C-H, Chang J-S. Biosorption of lead, copper and cadmium by an indigenous isolate Enterobacter sp. J1 possessing high heavy-metal resistance. J Hazard Mater 2006, 134(1), 80–86, https://doi.org/10.1016/j.jhazmat.2005.10.036. [82] Bankar A, Nagaraja G. Chapter 18 – Recent Trends in Biosorption of Heavy Metals by Actinobacteria. In: Singh BP, Gupta VK, Passari AK., eds. New and Future Developments in Microbial Biotechnology and Bioengineering. Elsevier, 257–275, 2018, https://doi.org/ 10.1016/B978-0-444-63994-3.00018-7. [83] Ahalya N, Ramachandra TV. Biosorption of heavy metals. Res J Chem Environ 2003, 7, 8. [84] Kang C-H, Kwon Y-J, So J-S. Bioremediation of heavy metals by using bacterial mixtures. Ecol Eng 2016, 89, 64–69. https://doi.org/10.1016/j.ecoleng.2016.01.023. [85] Ghodsi H. Investigation of bioremediation of arsenic by bacteria isolated from contaminated soil. Afri J Microbiol Res 2011, 5(32), https://doi.org/10.5897/AJMR11.837. [86] Ameen FA, Hamdan AM, El-Naggar MY. Assessment of the heavy metal bioremediation efficiency of the novel marine lactic acid bacterium, Lactobacillus plantarum MF042018. Sci Rep 2020, 10(1), Article 1, https://doi.org/10.1038/s41598-019-57210-3. [87] González Henao S, Ghneim-Herrera T. Heavy metals in soils and the remediation potential of bacteria associated with the plant microbiome. Front Environ Sci 2021, 9, https://www.fron tiersin.org/articles/10.3389/fenvs.2021.604216.

Bedabrat Barooah, Kritika Sharma, Garima Kaushik✶

Role of microbial enzymes in degradation of personal care products present in environmental matrices Abstract: Personal care products are a prominent in the modern society due to their extensive use by people every day across the globe. They are defined as chemical substances formulated artificially using natural as well as synthetic ingredients with the aim of protecting or enhancing the physical appearance of a person. Personal care products are usually considered similar to pharmaceuticals via the universal term PPCPs (Pharmaceutical and Personal Care Products). Despite their relevance, however, PPCPs have been found to contain or produce several harmful chemicals that can cause adverse effects on the environment as well as on the consumers of such products. These harmful substances include heavy metals, such as mercury and chromium, aromatic hydrocarbons such as derivatives of benzene, estrogen and its derivatives, and so on. Such chemicals can give rise to severely harmful health conditions, such as cancer, infertility, and neurotoxic effects. Therefore, there is a need for suitable methods for the removal of such hazardous substances. To achieve this removal, research has been conducted in several study areas. Microorganisms are the major focus of such research since they can produce numerous enzymes that can biodegrade the hazardous chemicals and thus achieve bioremediation or the sequestration of harmful chemical constituents so that they do not adversely affect the consumer or the environment in general. In addition, such enzymes are preferred to physical or chemical alternative methods of removal since enzymes are highly specific and effective and they usually do not produce wastes such as used filters, toxic by-products, and so on. In addition, they can be manufactured on a large scale due to the recombinant DNA technology and genetic engineering. Hence, they can be used extensively without the need for highly elaborate measures of waste collection, treatment, sequestration, removal, and disposal. In addition, enzymes that can biodegrade harmful chemicals were investigated in genera such as Arthrobacter so that remediation of the environment may be achieved.

✶

Corresponding author: Garima Kaushik, Department of Environmental Science, Central University of Rajasthan, Bandarsindri, Kishangarh, Ajmer, India, e-mail: [email protected] Bedabrat Barooah, Department of Environmental Science, Central University of Rajasthan, Bandarsindri, Kishangarh, Ajmer, India Kritika Sharma, Department of Life Sciences, Hemchandracharya North Gujarat University, Patan, India

https://doi.org/10.1515/9783110743623-002

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Bedabrat Barooah, Kritika Sharma, Garima Kaushik

1 Introduction Personal care products (PCPs) may be described as synthetically manufactured materials intended for commercial utility that serve by maintaining or enhancing the physical appearance and personal hygiene of consumers. They are essential in modern societies around the globe, more specifically in urban communities. The commonest among such products are produced to protect or improve the skin of individual users, and include products such as: i. Soaps and shampoos ii. Skin lotions iii. Sunscreen lotions iv. Body oils v. Therapeutic products vi. Lip care balms vii. Foot creams viii. Moisturizers and conditioners These products are also described as cosmetics. The word originates from the Greek word “kosmeticos,” which means “to adorn.” Assorted beauty products, predominantly utilized by women, constitute the vast majority of cosmetic products in the global market. The current estimated value of the cosmetic industry is around 20 billion dollars, globally. This market size is also projected to increase in the immediate future, with a vast increase in demand observed in the past few years, as shown below (Figure 1). The value of PCPs is directly related to demand, which arises due to the immense utility offered by PCPs on a daily basis. Therefore, there exists a great need to find alternative sources of products that can achieve the same utilities provided by PCPs. In addition, the synthetic constituents of PCPs are cheap to produce on a mass scale, which presents a particular problem with regards to finding alternative components that can replace such constituents without rendering the process of manufacturing PCPs impractical or cost-intensive. This may be solved by utilizing constituents that are easy to extract or can be produced on a very large scale. If this is not found to be a feasible possibility, components that can perform similar functions as the synthetic components, but at much lower and cost-effective quantities, need to be formulated. For instance, microbial products may be utilized due to their high specificity and potential for action at very low quantities. There exists a tendency to consider both pharmaceuticals as well as personal care products as similar entities such that they are collectively referred to as PPCPs (pharmaceutical and personal care products). This may be due to the relevant constituents being somewhat similar in both types of products, with minor differences between the two. In addition to the constituents, the effects elicited by the toxic

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Role of microbial enzymes in degradation of personal care products

Growth Trend of PCP in the Global Market (2004–2017) 6

4.9

5

5

5 4.6

4.6

Annual Growth Rate (%)

4.2 4

3.8

4

3.6

3.4 3

3.9

3.8

2.9

2

1

1

0 Year

Figure 1: Market trend of PCPs (source: STATISTA GmbH, Hamburg, Germany).

chemicals present in the products are also quite similar in mechanism. Hence, the preventive or corrective measures employed would be similar in both situations. In cosmetics, certain chemicals can lead to several adverse effects, including cancer, reproductive and neurological harm, and developmental delays. Cosmetic chemicals enter the body through the skin, inhalation, ingestion, and internal use, and pose the same risks as food chemicals. In addition to the risks posed by intentionally added ingredients, cosmetics can be contaminated with heavy metals, including arsenic, cadmium, lead, mercury, and nickel. Some chemicals that are used in personal care products pose risks at very low doses, and can interfere with the hormone system. The introduction of PPCSs into the environment occurs through several mechanisms. For instance, wastewater effluents from sewage treatment plants and large animal farms have been identified to be major sources discharging these emerging contaminants into the surrounding water bodies. That is because many pharmaceuticals and supplements are made with higher concentrations of chemical compounds than what the bodies of humans or animals can process. Humans and animals process the chemicals to varying degrees. In some cases, humans ingest 95% of the active ingredient. In other cases, it is closer to 5%. Either way, portions of these chemicals are unused by the body and are excreted as waste or disposed of

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Bedabrat Barooah, Kritika Sharma, Garima Kaushik

into water bodies or via sewage. In addition, several hormones are eliminated from the human body, which can further contaminate the surrounding abiotic environment that subsequently influences the biotic components of the environment in drastic ways. One of the ways by which the harmful components of PCPs can be effectively removed is the use of appropriate microbes. Microorganisms, being living organisms that are ubiquitous on earth, are capable of performing natural metabolic processes that can be applied to biodegradation of hazardous chemicals. Microbial degradation refers to a form of bioremediation that involves the microbial conversion of hazardous chemicals to less toxic or more useful forms in the environment or in the laboratory. Knowledge of the genetic mechanisms involved in this process is instrumental in determining procedures that can be applied to bioremediation. In terms of regulation, the commercial aspects of PCPs enable certain considerations to be awarded to the most prominent brands so long as the corresponding permissible limits are met. Thus, certain regulatory entities exist that are responsible for enforcing the relevant norms and rules required to be followed by the industry, as shown in Figure 2. The federal FDA, the EPA, and the Consumer Product Safety Commission (CPSC) have broad authority to ensure the safety of chemicals in consumer products. Such organizations are responsible for regulating the chemical constituents of various commercial products, including cosmetics and other PPCPs. They also ban certain chemicals from the market after determining their adverse effects on human health and safety as well as for the preservation of the environment.

PPCP Regulation (USA) Food and Drug Administration (FDA) US Environmental Protection Agency (USEPA) Consumer Product Safety Commission (CPSC)

Pharmaceuticals

Central Drug Standards Control Organization (CDSCO)

Drug Controller General of India (DCGI)

Food Safety and Standard Authority of India (FSSAI)

Food Safety and Standards Regulations (2016)

PPCP Regulation (India)

Nutraceuticals

Figure 2: PCP regulation (source: Global Regulatory Partners, Inc.).

Opposition to such oversight has been observed. For instance, in the USA, Congress has tried to modernize legislation but has experienced opposition since the early 1950s. Since 2015, the FDA has been conferred the power of regulation to a certain extent, without the interference of cosmetic companies. However, certain other companies have proven to be roadblocks to the effective regulation methodologies undertaken by the relevant authorities. In addition, certain products have even shown

Role of microbial enzymes in degradation of personal care products

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trace amounts of heavy metals such as mercury. The presence of heavy metals leads to high toxicity in the environmental matrices that are exposed to such products. Due to the nature of such products and their toxic constituents, bioaccumulation of toxicants occur in the external environment, which eventually results in the degradation of various essential components of the environment as a whole; subsequently leading to detrimental effects on human beings and other forms of life.

2 Process of PCP production The protocols involved in the manufacture of personal care products consist of several major steps. These are devised in order to enable optimum efficiency of processing such that the manufacturing unit always operates at the highest possible productivity. The major steps involved in PCP production (source: Devex PLM System, Selerant), as shown in Figure 3, are as follows:

Innovation

Formulation Regulation Commercialization Product

Product Launch

Figure 3: Process of PCP production (source: Devex PLM System, Selerant).

2.1 Innovation The process of actual manufacturing is preceded by the creation of novel concepts, often by R&D, that is, the research and development division. The marketing department is usually responsible for the collection of data pertaining to the demands of the customer base, which subsequently forms the foundation upon which novel innovative ideas are built. The incoming marketing requests are subsequently incorporated into novel strategies that lead to new formulae to improve preexisting

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Bedabrat Barooah, Kritika Sharma, Garima Kaushik

products or to develop completely new concepts for new products that are designed to meet the demand of specific niches in the vast market.

2.2 Formulation The various requirements necessary to fulfill the innovative novel concept under consideration must be formulated. Consequently, the numerous raw materials required for the formulation process are procured. Generally, the raw materials needed for production are sourced in-house or manufactured by the brand itself. However, certain essential ingredients may be sourced from an external agency via different marketing connections or channels, which increases the cost of production. Once the ingredients are collected, the process of formula trials commences, which involves testing multiple ratios and proportions of ingredients until the appropriate combination of constituents of the product is attained. The formula trials are followed by testing the stability of the drug or cosmetic product over an adequate duration of time and under various conditions that simulate the eventual use of the product after its introduction into the market. Simultaneously, the process of quality assessment (QA) is also carried out in conjunction with the track stability tests, wherein the objective is to render the product feasible for commercial use. In the pursuit of this objective, numerous targets are set in categories such as optimum productivity, cost-effectiveness, meeting the standards set by regulatory bodies, and so on.

2.3 Regulation This step is essential for the purposes of enabling the brand to grow and introduce the product into the market to as large a population size as possible. To that end, regulatory consultants are employed by the brand or a collaborative effort is carried out in order to find the optimum strategies to ensure that the product being introduced complies with the regulatory standards. In addition to meeting the regulatory benchmarks, statements from the relevant authorities like INCI (International Nomenclature of Cosmetic Ingredients) are obtained after filing reports containing all the required information about the active ingredients and the other agents present in the product. Any claims filed must also be forwarded in appropriate formats to the relevant authorities. The process of certification as well as the Safety Data Sheet (SDS) must be validated. This includes aspects of standardization and documentation, followed by issuance of the relevant certification.

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2.4 Commercialization The protocol of regulation is followed by commercialization, which basically involves aspects such as producing the appropriate label information for the product. Subsequently, the packaging of the product is devised, keeping the standards of the market under consideration. This enables ease of introduction of the product into the active customer base in a staggered manner. The product is usually introduced to a sample of the population, and based on user feedback, the product can be optimized for commercial utility in various market niches around the globe. This is also accompanied by the activity of advertising so as to expose a major part of the customer base to the relevant product. This is done toward the end of the product life cycle since it is highly cost-intensive and, as such, a heavy investment should only be made once the guarantees of product commercialization, such as valid certification and satisfactory regulatory standards, are fulfilled.

2.5 Launch of the finished product The final step involves the actual introduction of the product into the active market. Based on the feedback provided by the sample user base, multiple departments establish a collaborative and cumulative strategy to enable efficient marketing and advertising of the product to the wider community. Firstly, the product is introduced to a relatively local or confined customer base or population size. This enables an effective way of gauging the general perception of the public to the product, which can be used to improve the product, as necessary. This is then followed by the consequent staggered introduction of the product into an even wider user base, which is done in conjunction with appropriate advertising and marketing strategies, which may involve several different avenues, including various platforms on social media. The final product is usually officially launched at a larger event to ensure maximum public awareness for the launch of the product.

3 Properties of PCPs With regards to PCPs, the constituents include several synthetically produced chemicals that may be potentially harmful to consumers. Therefore, a cumulative set of properties may not be feasible. However, the individual toxicants have certain distinct properties that contribute heavily toward conferring toxicity to the constituent, leading to adverse conditions in users and proving to be devastating to the environment as well. These toxicants may arise as a result of prolonged reaction of certain active ingredients with the common environmental conditions. The

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Bedabrat Barooah, Kritika Sharma, Garima Kaushik

reactions consequently result in several by-products that can give rise to a varied array of detrimental health effects on the human body as well as to the external environment, at large. The health of the users being impaired also leads to negative press for the brand itself, causing major impacts elsewhere, such as employees being laid off, affecting the aspects of unemployment and the general economy as well. The toxicants associated with the personal care products include: i. Caffeine ii. Mercury and other trace heavy metals iii. Triclosan iv. Meta- and ortho-phenylenediamine v. Quaternium 15 vi. Formaldehyde and its derivatives vii. Estrogen derivatives viii. The long-chain per- and polyfluoroalkyl substances (PFAS) ix. Methylene glycol x. Isobutyl and isopropyl parabens xi. Dibutyl and diethylhexyl phthalates xii. Synthetic copolymers xiii. Dyes and other coloring agents The toxic properties of each constituent differ, based on the specific product under consideration. However, certain properties associated with the general constituents, as shown in Table 1, demonstrate their potential for toxicity. Table 1: PCP toxicant properties. S. no. PCP toxicant

Major toxic property

    

Circadian rhythm disruption Poisonous Hormone analogues Cell dehydration Disruption of metabolism

       

Caffeine Dyes and coloring agents Estrogen derivatives Formaldehyde derivatives Long-chain per-/poly-fluoroalkyl substances (PFAS) Mercury m-/o-Phenylenediammine Methylene glycol Quarternium- Synthetic copolymers Triclosan Isobutyl/isopropyl parabens Dibutyl/diethylhexyl phthalates

Heavy metal toxicity Skin deterioration Cell dehydration Fertility impairment Poisonous Thyroid hormone disruption Cell toxicity-inducing Sex hormone disruption

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Pan et al. [1] investigated the sorption properties of PPCPs in order to establish a comparative basis for the study of different products and their associated effects pertaining to toxicity. To this end, an expansive analytical protocol was devised to measure various aspects of the products so as to ascertain the appropriate parameters that serve as an effective foundation for the relevant conclusions. The focus was kept on soils, and the relevant interactions of the compounds with minerals and other soil components were scrutinized thoroughly. A comparison with Hydrophobic Organic Contaminants (HOCs] was also included. In addition, the interactions in different phases were compared, and relevant inferences were drawn. Yong et al. [2] examined gemfibrozil, octylphenol, bisphenol A, triclosan, and carbamazepine on three soil types. The results facilitated numerous significant inferences regarding the potential of sorption as an effective and efficient means of control or degradation of PPCPs and the associated chemical compounds. The inferences were facilitated by the Freundlich adsorption isotherm, which describes the connection between gas pressure and the quantity of the gas adsorbed onto a solid surface. The equations associated with the aforementioned isotherm dictate the quantitative estimates found, and consequently, the inferences indicate that the properties of sorption, chirality, and so on help in finding ways to sequestrate such toxicants from the environmental matrices since most of the compounds that contribute to the various detrimental effects are in fact aromatic hydrocarbons or their derivatives and analogues. Certain other properties may also contribute in unforeseen ways to the toxicity profiles of PCP constituents. Sanganyado [60] analyzed the chirality of the active ingredients of PCPs that can lead to several adverse conditions rendered within the environmental matrices wherein they are introduced or present. Such compounds are found in polycyclic materials such as perfumes. Several interconnected properties associated with the compounds were also elaborated so as to ascertain a comprehensive framework of the properties of the PCPs and their larger implications upon the environment. In addition, certain PCP components have well-studied structures. For instance, the structure of quaternium-15 has been extensively elucidated upon, as shown below [Source: National Center for Biotechnology Information [3] (Figure 4). The compound is halogenated and, as such, may dissociate in an aqueous environment and contribute to an altered pH, thereby impacting the homeostasis of the respective ecosystem.

4 Environmental fate of PCP constituents The chemicals associated with PCPs can end up in various environmental matrices, leading to several adverse toxic effects that can have larger implications on the environment at large. The fate of different constituents depend on the product, since

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Bedabrat Barooah, Kritika Sharma, Garima Kaushik

Cl

H

H

N+

N N

N Figure 4: Structure of quaternium-15 (source: National Center for Biotechnology Information [3]).

varying products reach differing locations, based on methods of disposal employed. In addition, the products originate from different sites, and based on their natures, they may differ with respect to their transportation strategies and their intended purposes. The products also differ based on their shelf lives, which lead to certain products being discarded en masse relatively quickly, while others find themselves being utilized for years on end. This also indicates that the constituents present in products with shorter shelf lives accumulate in larger quantities in the respective environmental matrices. If such constituents happen to be non-biodegradable, the ecosystem can be affected in a more prolonged and severe manner. Kot-Wasik et al. [4] investigated the effects of certain components of PPCPs in a general review, citing several inputs or sources, in conjunction with the relevant trends observed with regard to pharmaceuticals as well as para-pharmaceuticals. In addition, the elucidation of the important metabolites and their effects on various environmental matrices was also elaborated upon and analyzed. The general consensus dictated that the constituents found their way to several major environmental matrices, and were capable of accumulating and extending their toxic effects to multiple trophic levels of different ecosystems. The sources of such constituents were also found to be very common, which could be a cause for concern. Bendz et al. [5] insinuated that pharmaceutically active compounds, that is, PhACs may persist in environmental matrices for a very long period of time, with the implication of products being metabolized to a greater extent in humans not translating perfectly to the persistence in aqueous environments. Antioxidants and constituents such as caffeine were also studied, with a specific view on their persistence in the environment. The compounds that are found to be easily metabolized in the human body may be considered to be low risk in terms of their persistence in the harsher environmental conditions. However, this simplistic perspective is

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challenged by findings. Therefore, there exists a need to establish novel approaches to ensure that PhACs and similar compounds present in PCPs that seem to be easily metabolized or degraded by bodily secretions and hormones may actually persist for longer durations in prominent environmental matrices. Beghin et al. [6] exposed a certain sample size of fish in a river to a particular mixture of environmentally relevant drugs or pharmaceuticals. The findings can be utilized to establish similar inferences for PCPs as well. Various parameters associated with the immune and nervous systems as well as detoxification mechanisms in the fish bodies were analyzed. One of the most prominent of these was the lysozyme activity. In addition, serotonin levels in the brain also indicate the extent of the impact of the constituents on the nervous system, particularly the cerebral cortex and the associated sites. This can aid in establishing a frame of reference to compare various products and their respective toxicity profiles. Certain strategies may also be devised in order to accomplish the protection of environmental matrices from the contaminants. Certain contaminants of emerging concern (CECs) can prove highly detrimental to the integrity of the environment. Kwon & Lee [7] constructed a contraption with the purpose of enabling the removal of CECs from major environmental matrices by utilizing a membrane bioreactor (MBR) that can effectively sequestrate the contaminants associated with PPCPs. In addition, the efficiencies of MBRs were also compared to expedite the process of improvement, to attain higher standards of effectiveness. Multiple factors and parameters associated with the MBRs were analyzed, including the retention times of entities, such as sludge as well as the hydraulic operational components. Bilal et al. [38] studied triclosan, which is a toxicant prevalent in various products that can eventually find its way to environmental matrices and cause several adverse conditions to the individual environmental matrices via different routes, as depicted in Figure 5. The points of entry into various environmental matrices can be present in disposal sites for different products, based on the methods of disposal and their specific natures and physicochemical properties. For instance, landfills are the locations where several commonly used PCPs are disposed. The leachate formed in such locations can contaminate the adjacent area, rendering the soil infertile and causing adverse phytotoxic effects as well. In addition, constituents that enter aqueous environments can contaminate the ecosystems by many routes of impact, such as altering the pH, thereby causing high alkalinity and proving toxic to several multitudes of aquatic forms of life. This, consequently, has a discernible impact on species biodiversity. The major toxic waste is treated at WWTPs or such other facilities. However, the treated waste can retain certain toxicants that are extremely difficult to degrade by conventional means, which necessitates the prospect of other avenues such as microbial enzymes. The treated materials confined to water or soil may eventually return to the trophic levels connected to consumers and wreak havoc in numerous ways.

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Triclosan Synthesis

Pharmaceuticals and Personal Care Products

Household and SportsRelated Products

Consumer Solid Waste

Effluents

Landfill (Leachate)

Wastewater Treatment Plant (WWTP)

Miscellaneous Utilities

Sludge (Biosolid)

Treated Water

Figure 5: Routes of entry of triclosan into environmental matrices [38].

5 Phytotoxicity of PCPs The diverse range of components present in various classes of PCPs can produce a multitude of adverse effects within the environmental matrices wherein they are present. One of the most significant aspects of the impact of PCPs on the environmental matrices includes the relatively immediate deterioration of the local floral species in the region. The phytotoxic aspect of PCP constituents is an imperative basis of estimation of the potency of the compounds with regard to their cumulative action on plants and microflora present in the different matrices of the environment. The efficient study and documentation of the phytotoxicity of such compounds and their derivatives can prove instrumental in establishing a sound strategy to devise corrective as well as preventive measures for the purposes of protection and enhancement of the environment. In addition to protection, the strategies can act as the foundation upon which multiple prediction models can be formulated, thereby enabling the possibility of extrapolating existing data on known compounds toward their associated analogous compounds or their derivatives. This may be considered similar to the manner in which novel viral strains are created in order to expedite the process of finding vaccines for viral diseases that are yet to emerge in society, thus serving as a premonition for future calamitous adversities. The phytotoxic effects of commonly used household products are of paramount significance since they are abundantly found and can easily find their way into the vast majority of terrestrial as well as aquatic ecosystems. The significance of such phytotoxic effects is perhaps most prominent and dangerous in edible plant species

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as they are consumed by the mass public and, therefore, pose a substantial threat to the health and safety of the people in all communities. For instance, cucumbers are a prominent species of edible vegetables sold in the market and the PCP constituents can induce a multitude of detrimental effects, such that the generation of biosolids and other forms of toxic waste material [8]. The major routes of entry of toxicants into the vascular tissues of plants usually involve the roots, as opposed to the leaves or other surfaces. The significant inhibitory effects of the toxicants include several important metabolic and cellular pathways. The pathways are inhibited via different avenues, but the standard route seems to be the inhibition of essential enzymes involved in several varied cellular processes. For instance, glutathione peroxidases may be targeted specifically, usually involving the selenium cofactors, and the enzyme inhibition severely impairs optimal functioning of the individual cells, leading to a wide range of detrimental conditions induced, such as reduced growth and development, and seed infertility. As a matter of fact, phytotoxicity must be considered through the perspective of relevant factors such as the duration of exposure, intensity, frequency, and environmentally relevant quantities. In addition to the conventional paradigms that dictate the phytotoxicity caused by PCPs on plants, certain components may affect in different ways. For instance, dibutylphthalate (DBP) functions as a phytotoxicant by targeting parameters such as chlorophyll synthesis, lipid membrane integrity, as well as antioxidant capabilities [9]. Most of the biochemical parameters that influence the growth and development of plants are adversely affected by toxicants like quaternium-15 and triclosan. The mechanism of PPCP uptake influences the phytotoxicity, with the ease of transport directly affecting the amounts and the intensity of cellular toxicity in the tissues of the plant [45]. It usually begins with the transport of PPCP from the manufacturing or consumption units, which may include individual households and livestock. They are rendered as biosolids before ending up in the soil where the separate components are absorbed or translocated via the plant roots into the vascular tissues of the plants before they are bioconcentrated [10]. As shown in Figure 6, the alternative routes involve consumption by human users and the eventual involvement of WWTPs where the majority of the PPCP mixtures are treated and disposed. The mixtures can accumulate within the various environmental matrices, usually involving the soil. Additional studies focused on other aspects of phytotoxicity brought about by PCPs. The products usually cause enhanced absorbance or uptake by the plant roots, with certain constituents stimulating the translocation capabilities [11]. The accumulation of toxic chemicals within the plant tissues may manifest further in other appendages, thereby leading to increased phytotoxicity. This can further impact larger aspects of the environmental matrices and transfer to other matrices as well.

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PPCP

Consumer Base

Livestock

Households Biosolids and Animal Waste

WWTP Public Sector Phytoextraction

Bioconcentration

Translocation

Uptake by plant roots Soil Matrices

Figure 6: Mechanism enabling PPCP phytotoxicity [10].

6 PCP toxicity in users Toxicants can affect all aspects of the environment, including higher trophic levels of an ecosystem, usually occupied by human beings. Some of the significant effects related to the toxicological aspect of various PCP constituents are as follows:

6.1 Endocrine disruptors Snyder et al. [12] examined the capacity of chemical constituents of PPCPs to act as EDCs (endocrine-disrupting compounds). The mechanisms through which these compounds interact with the endocrine system were determined. In addition, the chemical homologues of certain hormones were considered and the chemical constitution of PPCPs was analyzed and compared with the structures of common human hormones. DDT (Dichlorodiphenyltrichloroethane), aromatic compounds like octylphenols, bisphenol-A, and derivatives of estrogen such as estradiol were of particular significance in the research conducted and were found to be present

Role of microbial enzymes in degradation of personal care products

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as impurities and trace elements in common PPCPs such as skin care products. The compounds may also end up in soil and water, consequently entering the food chain and eventually reaching the higher trophic levels occupied by human beings. Effects of such compounds such as infertility were determined. In addition, methods to contain such compounds were studied. For instance, in order to remove hazardous chemicals from water, various filtration techniques were analyzed that included ozonation, chlorination, activated carbon adsorption, and, of course, biotransformation. In addition, cosmetics in the market may also have unforeseen adverse effects on the endocrine hormones in the body, which may be associated with cofactors and other necessary cellular components, without which the normal functioning of the cell is severely impaired [13].

6.2 Formaldehyde toxicity Certain toxic compounds have been investigated so as to gauge their possible mechanisms of action. For instance, Quaternium-15, the structure of which was elucidated upon earlier, is believed to produce many toxic effects due to its nature as a releaser of formaldehyde molecules [14]. The formaldehyde (HCHO) molecules may undergo several subsequent reactions, mediated by cellular enzymes such as transferases and oxidoreductases. The molecules may consequently be converted to several derivatives such as paraformaldehyde. These compounds may also act analogous to certain enzymes or metabolites and travel into cells via transmembrane channels located in the cell membranes. They may then combine with cellular proteins or other biomolecules to produce a multitude of toxic effects that propagate throughout the body. It is also within the realm of possibility that formaldehyde may be released as an indirect consequence of the PCP component disrupting a separate pathway via inducing deficiencies in optimal levels of particulate enzymes and hormones, leading to many adverse conditions, not limited to dermatitis [15]. As such, there is an urgent need to find solutions to formaldehyde toxicity, especially in children, as they are more susceptible to the medical conditions caused by excess levels of toxicants such as the aforementioned derivatives of aromatic hydrocarbons among others.

6.3 Effects on the reproductive system Henrotin et al. [16] scrutinized the possible hazards faced by workers operating in sectors pertaining to occupational health. One of the most prominent effects includes disorders related to the reproductive system. This might involve important enzymes associated with fertility and the reproductive processes in the body. It may disrupt standard sexual cycles and impede the optimal maintenance of normal levels of several hormones related to the reproductive system such as estrogens. As a

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matter of fact, certain compounds present in PCPs, such as triclosan, act as hormone analogues, most commonly inhibiting estrogen found in the body [17]. This can lead to cases of reduced fertility as well as even sterility or loss of reproductive function in some situations. The compounds may differ in the extent of the effects shown as well as the mechanisms by which they bring about the effects. For instance, certain compounds target the cofactors of enzymes by competing for the binding sites or the active sites of enzymes, whereas other compounds may inhibit the mRNA molecules, preventing transcription and, therefore, leading to the respective proteins remaining untranslated, causing disruption to the normal cellular functionality. Laws et al. [18] studied the effects of PCP constituents on sexual wellness and reproductive systems as well as their related effects on hormones belonging to various organ systems, including the endocrine and reproductive systems. Hlisníková et al. [19] elaborated upon the probable effects of specific compounds, namely, phthalates on the sexual and reproductive system functionality of test specimens. Several enzymes, such as P450 and HSD, in addition to cofactors and other conditions were found to be impacted substantially by phthalates and their associated derivatives. The enzymes can also act as a form of negative feedback, once inhibited. This is mainly due to the fact that each enzyme forms a part of a cascade of reactions that occur, as shown in Figure 7. This is also linked to other cellular pathways, which on first glance, may not seem to have any bearing on the compound under consideration. However, receptors such as the LH (luteinizing hormone) as well as FSH (Follicle Stimulating Hormone) receptors are instrumental in ensuring the optimal functioning of processes such as folliculogenesis, oogenesis, and so on. If such processes are impaired, the long-term implications are sterility, decreased expression of sexual characteristics and loss of virility, among others. In addition to the above conditions, premature ovarian failure (POF), testicular dysgenesis syndrome (TDS), and such other adverse effects may be caused, which can lead to consequent impacts upon the hypothalamic–pituitary–gonadal (HPG) axis, which can then impair several cascading reactions such as the MAPK cascade, and finally result in apoptosis or the death of the cell.

6.4 Damage to the urinary tract The PCP components may contribute to medical issues or conditions that lead to the deterioration of the urinary tract in individuals. One of the ways by which the levels of certain parabens, phthalates, and other chemicals can be gauged is via analyzing the urine of individuals in a sample of the population [20]. The levels usually are consistent and indicate the effects of PCP constituents in the body via disruption of mechanisms such as the ADME (absorption distribution metabolism elimination) process that is responsible for ensuring that a potential toxicant (usually

Role of microbial enzymes in degradation of personal care products

37

Phthalate Exposure

Pre-Natal & Post-Natal Ontogenesis

Post-Natal Ontogenesis

Puberty

POF

Folliculogenesis and oogenesis

TDS

Cancer

Spermatogenesis

HPG Axis

Steroidogenesis

MAPK NF-kB PI3K/Akt

NR

Genes Regulating Reproduction

Peptide Receptors

Cell Proliferation & Apoptosis

Figure 7: Effects of phthalates on the reproductive system [19].

derived from pharmaceutical drugs) is efficiently removed from the body so as not to accumulate and cause harm to the individual. A source of concern is that the observation suggests a higher retention of toxicants in women and children, which yields information about the differential aspect of metabolism based on sex as well as age in addition to several other factors.

6.5 Dermatological conditions PCP components can also induce many dermatological complications. The severity of such complications usually depends on factors such as the sensitivity of the skin of an individual, genetic predisposition to certain specific ailments as well as the presence of other compounds in conjunction with the actual PCP constituent. Roden [21]

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studied the role of preservatives in the compounds sold in the market. Parabens and other constituents of PCPs are present to increase the shelf life of products. However, they can give rise to many unpredictable health effects pertaining to the skin, such as allergic reactions upon microbial spoilage [44]. This can lead to further problems and may even prove fatal in some cases. This produces the notion that the compounds should be regulated further and also emphasizes the need to devise corrective and preventive measures in order to reduce the occurrence of such health adversities.

6.6 Mutagenicity, teratogenicity, and cancer Perhaps the most significant and life-threatening medical condition that can be induced by PCP toxicants is cancer. The key mechanism by which the PCP toxicants bring about such a condition is generally by targeting the ligands, receptors, and factors associated with apoptosis and cell signaling pathways in the body. For instance, certain common cosmetic skincare products, if applied excessively, may lead to the risk of developing breast cancer as well as tumor formation in the endometrium [22]. Other forms of cancer may also be caused as a result of exposure to various types of cosmetics and other personal care products. The mutagenicity is also influenced by certain products. Connor et al. [23] observed the significance of specific biocides, namely, Kathon 886 and Kathon CG with respect to mutagenicity and toxicity. These biocides were found to exist in certain cosmetic products and possessed varying levels of mutagenicity due to their structural components, that is, heterocyclic isothiazolinones. These were found in various types of products, ranging from shampoos to lotions. The mutagenicity might also translate to teratogenicity if the relevant cellular mechanisms and pathways are impaired. This could lead to severe physiological problems in the body, often proving fatal to the victims.

7 Microbial degradation of PCPs PCP dominance in the market compels the pursuit of modern technologies, formulations, and corrective measures that may enable the protection of important environmental matrices from contamination via PCP toxicants. This may involve physical, chemical, as well as biological methods of removal.

7.1 Limitations of physicochemical methods With regard to the mentioned objective of remediation, certain physical methods of toxicant removal have been extensively studied, which involve techniques such as

Role of microbial enzymes in degradation of personal care products

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filtration and irradiation. In addition to physical methods, several chemical methods have also been analyzed, often in the form of biochemical techniques that exploit specific important types of reactions, such as conjugation and methylation [24]. However, it has been observed that both physical and chemical methods of toxicant removal or sequestration have many limitations; the major ones being that they are often not highly effective and produce large quantities of by-products that can also be harmful to the environment or pose the threat of pollution, due to which they need to be efficiently disposed. In addition, certain chemicals and filters are quite expensive and can be somewhat difficult to transport and store. These deficiencies or demerits also include the limitations of sizes that physical filters can sequestrate, and the relatively lower activity of chemical catalysts, as opposed to enzymes.

7.2 Relevance of biological methods The most prevalent solution to the problem posed by physicochemical methods is through the use of biological entities, mainly microbial metabolites and enzymes. Larger biological forms are not feasible for industrial and commercial utility due to cost, storage, maintenance, and other logistical complications. Therefore, enzymes are commonly used as they act as biological catalysts and have a high specificity towards certain toxic molecules such as triclosan and phthalates. In addition, they are otherwise inert in nature, only reacting with the specific substrate, that is, the toxicant. Hence, they seldom produce harmful by-products and may actually reduce the PCP constituents from toxic forms into relatively less toxic or nontoxic forms, thereby simplifying the disposal process. Such properties are also compounded by the use of microbes as bioreactors as they can be bioengineered to produce large quantities of such enzymes, either intracellularly or extracellularly, depending on the need. They can be utilized to form so-called eco-remedial systems [25] that can perform a significant role in the preservation and enhancement of the health of an ecosystem and the different environmental matrices within. Certain significant chemicals and formulations that constitute PCPs have been considered below:

7.3 Detergent degradation Certain consortia of fungi and other microbes have also been observed to have the capacity to biodegrade specific toxicants present in PCPs. For instance, a particular strain of the fungal species Mucor racemosus was found to be capable of degrading the toxicants specific to detergents [26]. The metabolites that achieve biodegradation

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Bedabrat Barooah, Kritika Sharma, Garima Kaushik

generally contain various types of microbial enzymes. The most prevalent enzymes that have been found to perform very efficiently in this regard include laccases and other oxidoreductases, peroxidases, and transferases. In order to perform at peak efficiency, laccases require certain metabolites and conditions of pH, temperature, and other factors [49]. The enzymatic activity was also impacted by factors such as the microbial strain under consideration, contact time with the toxicant, and the external cellular environment.

7.4 Triclosan degradation Several studies have been carried out in the field of triclosan degradation due to its potency as an environmental toxicant. It can also act as a biocide or a pesticide. However, its presence in relatively common products such as toothpaste tubes can implicate its ubiquitous nature in the modern society, and hence abundance in the waste generated. There is, therefore, an urgent need to devise efficient strategies to ensure its removal from the matrices where it may reside, including water and soil. Chen et al. [27] performed triclosan degradation by utilizing axenic microbial cultures. The sources included wastewater, which enables the efficient practical application of such techniques in WWTPs, where a concentrated mixture of various chemical waste, derived from nearby households and other sources, can be found. In addition, enzymes such as laccase are utilized to degrade the compound. Common techniques to degrade such toxicants usually involve various consortia of microorganisms, including algae, fungi, and bacteria. As shown in Table 2, the degradation parameters and efficiencies may differ, based on factors such as pH and concentration. In addition, certain by-products may be produced as a result of degradation by the microbial enzyme isolate. These by-products are, for the most part, relatively inoffensive to the environmental matrices where the reactions happen to occur. The concentrations of various compounds simulated in most studies are usually environmentally relevant so as to maintain a realistic approach to the tests conducted and, consequently, obtain relevant and viable results. Arboleda et al. [28] analyzed different strains of the white rot fungi (WRF], namely, G. stipitatum as well as L. swartzii. Their capacity to degrade bisphenol-A as well as triclosan was investigated via utilizing 250 U/L of the enzyme laccase in the enzyme solution derived from the strains. As shown in Table 3, the efficiency of the enzyme extracts was found to be very satisfactory and the potential for further application was concluded to be quite high. The experiment involved introduction of the enzyme extract into a 5 mg/L solution of the toxicants and allowing a contact period of 6 h, after which observations were noted and the respective inferences were drawn. Regression studies were carried out to validate the findings of the experiment, with respect to the variables inherent to the test. Another interesting

Role of microbial enzymes in degradation of personal care products

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Table 2: Degradation of triclosan via microbial cultures [27]. Conditions of exposure

Triclosan removal efficiency References

pH

Matrix

Triclosan conc. (mg/L)

.

In nitrogen-rich medium



Most of the triclosan was converted to by-products by day 

Hundt et al.,  []

.

In static cultures of eight ligninolytic fungal strains

.

Triclosan was degraded within  days

Cajthaml et al.,  []

, , , 

In simulated wastewater and semisynthetic media (A. versicolor)

, ., ., .

Simulated wastewater = .%; Semi-synthetic media = .%

Taᶊtan and Dӧnmez,  []

 to  Enzyme-catalyzed oxidation by laccase (Trametes versicolor)

.

Conversion rate = –% (with enzyme dose was increased from .– U/L)

Kim and Nicell,  []



By enzyme solution from WRF (Coriolopsis polyzona)



% triclosan was removed after either a  or an  h treatment

Cabana et al.,  []



In aqueous system with laccase from Ganoderma lucidum

.

.% removal within  h

Murugesan et al.,  []

.

Laccase immobilized on vinylmodified poly(acrylic acid)/SiO nanofibrous membranes



% removal within  h

Xu et al.,  []

% removal within  h

By free laccase 

In  mL brown glass tubes with  U/mL laccase and – mg/L humic acid



t/ for initial enzyme activity (, , , , ,  U/ mL) = [, , , , ,  min)

Dou et al.,  []

observation made during the study was that the strain that achieved high degradation of one toxicant was less efficient in degrading the other. However, the efficiency of degradation was relatively high in most cases, suggesting the adequately relevant application of such enzymatic concoctions in future practical scenarios. In addition to such fungal enzymatic extracts, other sources have also been utilized to achieve similar results. Lee et al. [29] indicated that a bacterial isolate found in wastewater, namely, a Sphingopyxis strain (KCY1) was able to degrade triclosan to a certain extent via dechlorination, with an accompanying stoichiometric release of a

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Bedabrat Barooah, Kritika Sharma, Garima Kaushik

Table 3: Degradation of triclosan by laccase extract from fungal strains [28]. Coded variable

Triclosan degradation efficiency (%)

X

X

G. stipitatum

L. swartzii

      −    −     − −

   −  −  −         −

 . .  . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

few chloride molecules. The enzyme detected in the cell extract and consequently postulated to perform a role in the process of triclosan degradation was catechol 2,3-dioxygenase. The reduction potential of such enzymes may be a contributing factor, in conjunction with the specificity of the respective binding and active sites.

7.5 Octocrylene degradation Suleiman et al. [30] worked on octocrylene (molecular formula: C24H27NO2), which is an integral constituent of sunscreens. It serves as an absorber of potent UV radiation, which is the primary function of sunscreens, thereby rendering octocrylene as an essential component in such products. It can also perform the function of emulsifier, when combined with the stabilizer, avobenxone. However, the compound can also be hazardous to the user if it is allowed to accumulate, and can also be toxic to the environment upon disposal. Techniques such as GC-MS and LC-MS allowed the efficacy analysis of a specific microbial metabolite with regard to the degradation of octocrylene. The microbial species utilized for the experiment were Mycobacterium agri and Gordonia cholesterolivorans. As shown in Figure 8, the samples incubated with the test organism (M. agri) showed a decrease in octocrylene concentration (19.1%), indicating a substantial extent of degradation. In addition, the ubiquitous nature of

Role of microbial enzymes in degradation of personal care products

43

4000

3500 Concentration of Octocrylene (mg/L)

3000

2500

2000 Control

Incubated with M. agri

(Samples Tested) Figure 8: Octocrylene degradation using M. agri (reprinted from [30]).

M. agri enhanced the prospect of its utilization in the future as a viable means of bioremediation.

7.6 Application of enzyme immobilization in environmental matrices The most significant aspect of the information discerned in studies such as those mentioned above is the practical application in the various environmental matrices wherein toxicants are present. For instance, triclosan found in PCPs can eventually end up in water bodies after disposal. These matrices contain various reactive chemicals and adverse physical conditions. Enzymes, in their native forms, can be easily denatured by external factors such as acids or reactive agents present in the vicinity or by physical parameters like heat. Thus, in order to utilize the enzyme solutions in such matrices, the technique of immobilization is used extensively, which also helps maintain enzyme stability and reusability, among the other desirable qualities.

8 Future prospects The prospect of bioremediation through the utilization of microbial enzymes depends heavily on the efficiency of the protocol employed. As such, technological and academic advances are essential in finding novel strategies in order to enhance the effectiveness of the existing techniques or devising new bioremediation methods [47].

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This may involve mutually beneficial relationships between plants and microbial entities, such as certain endophytes as well as rhizobial species. The added benefits of such enzymes or biological metabolites include the fact that they degrade the toxicant to neutral or harmless forms as well as promote the growth and development of the affected species via enhancing specific enzymes [31], thereby accomplishing the additional goal of remediation by enabling corrective mechanisms in the tissues of the damaged individual specimens. Additionally, certain biotechnological advancements such as rDNA technology can be applied in conjunction with the eco-remedial systems so that the efficacy of the strategies is enhanced significantly. This involves the utilization of genomic markers, restriction endonucleases, as well as various shuttle or expression vectors to accomplish both cloning as well as gene expression. This results in increased quantities of clones containing the remedial enzymes obtained from genetically modified microbial specimens or recombinants, as they are commonly referred to. PCP constituents are highly diverse. Personal care products are found to contain several different kinds of compounds that can combine to produce previously unforeseen and unpredictable results. One such result includes the prospect of developing probiotics by utilizing PCPs [32]. Probiotics are increasing in relevance with the advent of new and modern technologies, with their obvious benefits to health driving the need to improve upon the potency of preexisting probiotics. One of the unlikeliest of sources of such materials may be found in PCPs that are designed to be somewhat edible or, at the very least, ingestible, without the threat of toxicity. However, certain challenges may arise with the possibilities of other constituents in the PCP to elicit adverse reactions, such as allergies and inducing toxicity through indirect means. Therefore, the need for a greater extent of research in the area might lead to promising results in the near future. One of the major organs of the human body that is often affected by PCP toxicants is the skin, which contains several species of microbes, acting as a sort of microbiome [33]. These species perform various roles, such as maintaining an acidic skin pH that acts as a deterrent and preventing the growth of pathogenic cultures. The microbiota involved in such functions have been investigated and their relevant properties analyzed so that future advances in this field of study may enable the integration or incorporation of samples of such useful microflora into skincare products, thereby enhancing the structural and functional integrity of the individual user’s skin and preventing many common ailments or infections by pathogenic microbes by utilizing preexisting microbes and reinforcing their efficacy via the use of fortification. Sectors pertaining to the preservation of the environmental matrices offer prime opportunities to establish new and improved strategies to sequestrate toxicants such as sulfonated or halogenated surfactants [34]. One of the future prospects for research includes the aspect that deals with respiration and fermentation that are enabled by multiple microbial species. The enzymes and other metabolites may be extracted in

Role of microbial enzymes in degradation of personal care products

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different ways, depending on whether the secondary metabolite products are intracellular or extracellular [42]. Volarić et al. [35] analyzed the heavy metal toxicity aspect of PCP constituents and the consequent effects on the future scenario. The findings suggested the scope of bioremediation as an efficient means of curbing the toxicity caused by metals. Specifically, the use of microbes as bioreactors, in addition to secondary metabolite production and improved extraction techniques, can help accomplish the removal of toxicants from different environmental matrices. Parameters such as bioavailability and ion persistence also help ascertain the extent of the effects caused by the toxicants [43]. In addition, certain consortia of microorganisms exhibit high levels of tolerance [61] or resistance to toxicity and act as effective barriers to contamination [59]. In addition to heavy metals, the focus has also been placed on investigating the specific routes through which the toxicants are inadvertently concentrated before being exposed to the various environmental matrices, such as through WWTPs, wherein the wastewater and activated sludge [48] generated can prove toxic to adjacent soil acquifers [45]. Girijan & Kumar [36] considered the relatively practical approaches of utilizing microbial species to act on wastewater generated from sources exposed to PCPs, and analyzed the efficacy of the remedial techniques. This provides an opportunity for improving the techniques involved so that the future prospect of bioremediation is realized to an even greater extent by influencing factors such as cost, time, and resources. In the case of rural areas, in particular, advances in such spheres of study may prove highly beneficial and suggests a greater potential for substantial practical application, which is the ideal goal of research in the first place. The estimated value of the technologies employed in the cosmetic and personal care product sectors indicate that there exists a substantial scope for devising novel machinations to achieve better results, a large part of which is impacted negatively by the cost of treatment and regulation of the products, in general. Hence, techniques that aid in the remediation of toxicants like mercury and triclosan can enable profits to be enhanced, thereby proving to be a substantial incentive for brands to invest in such strategies [46]. The trends that are followed with regards to remediation techniques have been studied and compared temporally in order to establish a baseline or reference [39] so as to form postulated theories and concepts that can enhance the scope of bioremediation of toxicants such as heavy metals [57]. Heavy metals are a significant aspect of research in the field since they can have an immense impact on various aspects of the environment at relatively trace or low quantities. Thus, the advances made in this respect will enable the establishment of a largely positive future in terms of phytotoxicity as well as detrimental effects on public health and safety. Finally, one of the major alternative approaches to improve the situation pertaining to PCPs and the prevention of contamination [41] of the environment is to improve the extent of regulations imposed on the industry [37]. Regulations are founded upon federal laws, with the legislation acting as the tool to achieve the goals of protection and enhancement of the environment in general [50]. The legislative tool is utilized by

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specific regulatory agencies that are specific to the country under consideration, with certain agencies such as the US-EPA and FDA wielding more authority than others. The logistics of operating such organizations compel the personnel to function in a streamlined manner in terms of efficiency, with rigid guidelines to be followed based on the situation under consideration [40].

9 Conclusion Personal care products fulfill an important role in modern people’s everyday lives. They mainly comprise cosmetics, in addition to toothpaste, sunscreen, as well as other products designed to enhance or protect one’s physical appearance. Personal care products contain various chemical compounds that may have unforeseen adverse effects on the environment as well as on the health and safety of the customer or user. As such, there is an urgent need for the prevention and control of hazardous chemicals associated with personal care products. The compounds may differ in nature and cause adverse health effects in numerous ways. They can affect both terrestrial as well as aquatic ecosystems and, consequently, enter the food chain via soil or water and cause harm to human beings. Examples of compounds that may pose a serious health risk to human beings as well as animals include aromatic hydrocarbons, bisphenol-A, phthalates and their derivatives, DDT, polyethylene glycols (PEGs), triclosan and other antibiotics or antibacterial agents, and heavy metals such as lead, nickel, cadmium, mercury, and so on. Microorganisms can be utilized as a means of degradation of chemical compounds present in personal care products. Biological methods of degradation (such as the use of microbial enzymes) are preferred to physical and chemical methods due to factors such as cost and creation of harmful by-products or waste material. The major research breakthroughs in this field involve reducing the cost of the separation process via use of cheaper sources of the relevant enzymes. For instance, various consortia of fungi as well as bacteria (e.g., Pseudomonas putida and Arthrobacter sp. SPG) are explored for use in degrading specific components of PPCPs such as indole derivatives, aromatic hydrocarbons (present in fragrances or perfumes), and triclosan. Various tests and experiments are carried out in order to ascertain the efficacy of the microbial enzymes being utilized. These include GC-MS, LC, and first-order kinetics. As discussed earlier, one of the most revealing methods to efficiently determine the relevant results is to plot numerous curves using the appropriate physical quantities or values so as to extrapolate and determine the significant results. In addition, emphasis may be placed upon immobilization to enhance enzyme reusability as well as on rDNA technology so as to enable the synthetic preparation of relevant microbial enzymes and secondary metabolites in the future via processes similar to those used to produce insulin and antibiotics, on a global scale.

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Abel Inobeme✶, Charles Oluwaseun Adetunji, John Tsado Mathew, Stanley Okonkwo, Mutiat Oyedolapo Bamigboye, Alexander Ikechukwu Ajai, Emmanuel Afoso, Jonathan Inobeme

Advanced nanotechnology for the degradation of persistent organic pollutants Abstract: Environmental contamination by different groups of compounds has become more concerning, in recent times, due to the alarming increase as well as the deleterious effects of these contaminants. Persistent organic pollutants (POPs) is a major class of these contaminants and based on the Stockholm Convention, 21 members of this class were identified with a view to limiting their production. Most of the known POPs have been reported to show resistance to natural degradation processes. POPs are released into the environment through various natural and anthropogenic means. These compounds result in health concerns due to some of their properties, such as bioaccumulation, transportability over long range, and tendency of degradation into carcinogenic compounds. They are released into the environment through various means including industrial discharge, pesticide application, and fertilizers, among others. Various technologies have been explored for the degradation of POPs, and each of these approaches has its inherent limitations. Nanotechnology has been identified as one of the most powerful tools for the management of POPs through remediation and degradation processes. Nanotechnology makes available various materials: nanoparticles, nanocomposite, carbon nanotubes, and quantum dots, among others, for use in the degradation of contaminants. This paper highlights the application of nanotechnology as a tool in the

Acknowledgments: The authors are sincerely grateful to their various universities for giving them enabling environment for this review. ✶ Corresponding author: Abel Inobeme, Department of Chemistry, Edo University Iyamho, PMB 04, Auchi, Edo State-312101, Nigeri, e-mail: [email protected]; [email protected], ORCID Id: https://orcid.org/0000-0002-9373-5828/ Charles Oluwaseun Adetunji, Applied Microbiology, Biotechnology and Nanotechnology Laboratory, Department of Microbiology, Edo University Iyamho, PMB 04, Auchi, Edo State, Nigeria John Tsado Mathew, Department of Chemistry, Ibrahim Badamasi Babangida University Lapai, Niger State 911101, Nigeria Stanley Okonkwo, Department of Chemistry, Osaka Kyoiku University, Osaka, Japan Mutiat Oyedolapo Bamigboye, Department of Chemical Sciences, Kings University, Odeomu, Nigeria Alexander Ikechukwu Ajai, Department of Chemistry, Federal University of Technology Minna, Nigeria Emmanuel Afoso, Department of Biochemistry, University of Benin, Nigeria Jonathan Inobeme, Department of Geography, Ahmadu Bello University Zaria, Nigeria

https://doi.org/10.1515/9783110743623-003

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degradation of POP, thus making a provision for an updated review of various kinds of POPs, their sources, different nanomaterials that have been employed for the degradation of these pollutants, and advantages of nanotechnology. An attempt is also made at examining the various mechanisms involved in the degradation of these contaminants.

1 Introduction Persistent organic pollutants (POPs) are poisonous chemicals that are majorly produced through anthropogenic means such as during manufacturing, application, and discarding of some organic substances. A number of these chemicals were manufactured industrially for disease as well as pest control, industrial use, and crop production. A few POPs, including polychlorinated biphenyls and pesticides are deliberately manufactured, despite the fact that others like furans and dioxins are accidental by-products of manufacturing processes or released during the incineration of organic chemicals [1]. Over the years, various kinds of POPs have been released into the environment, most of which have tendencies of persisting and bioaccumulation in living tissue, as they are conveyed over long distances into new habitants, resulting in harmful effects on man and the ecosystem. This group of compounds is also known to show strong resistance to natural processes involved in degradation of pollutants. Though the POPs show resistance to some degradation processes within the environment, some microorganisms have been reported to degrade some of these compounds to less harmful simpler products [2]. Various methods had been applied for treating POPs, and most of the methods have their inherent limitations including cost of operation, impact on environment, removal efficiency, and doses of contaminants that can be removed, among others. Different approaches like adsorption, degradation through photocatalytic means [3], ozonation, and membrane filtration processes have been used by various researchers alongside engineered microorganisms, in the treatment of POPs. Studies have also reported the use of bioaugmentation and phytoremediation in the degradation of polycyclic aromatic hydrocarbons and several other organic contaminants [4]. There are other techniques that were also employed in the elimination of POPs, which were, however, limited by their effectiveness in removing only trace amounts. Processes involved during the removal of the contaminants from the environment were mainly physical, chemical, biological, and electrochemical methods. Some these methods were of concern, as they solve the problems but also pose other ones to the environment. In some studies, degradation of POPs was done biologically, through the use of laccase that are multi-copper proteins for the bioremediation of chlorophenols and polycyclic aromatic hydrocarbons [5]. Due to the inherent limitations of the existing approach, the use of advanced nanotechnology becomes promising, due to the unique properties of various kinds of

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nanomaterials that can be employed in this approach. Nanotechnology involves the utilization of nanoparticles within a range of 1–100 nm, and this is now relevant in all areas of studies, including material science, engineering, chemistry, and physics, among others. Nanoparticles have also been documented to be useful in the degradation of various POPs, due to some their unique properties such as structural, optical, electromagnetic, thermal, and mechanical, giving them unique advantages for several applications, including their use as nanomembrane, nanoadsorbent, and nanosensor devices [6]. Nanomaterials are synthesized through different methods such as hydrothermal, solvothermal, sol-gel and green synthesis [7]. Nanomaterials are quick in reaction, primarily as a result of their minute dimensions and relatively larger surface area; they are able to remove compounds from their aqueous media, have remarkable semi conductor properties, efficient thermal conductivity, chemical stability, and catalytic potentials [8]. Nanomaterials have characteristic physiochemical and magnetic properties, with specificity to target the desired pollutants. Nanoadsorbents, nanometals, and nanometal oxides, photocatalytic catalysts are examples of nanomaterials that have been employed in the degradation of POP [8]. Nanotechnology can be employed in making the environment clean, which other methods have not been able to do. Green synthesis of nanoparticles for degradation of POPs has been reported, using various environmental substrates: Gum tragacanth, Cassia fistula plant, moringa oleifera, and orange peels [9]. Total elimination of POPs can be achieved through application of advanced nanotechnology, which is proven to be highly efficient for removal of various organic and inorganic pollutants. In some of the investigations, researchers used advanced nanotechnology tools independently, while others integrated this approach with some other existing techniques, for better results. The increasing investigations on the utilization of nanotechnology in the degradation of POPs has attracted global interest as a result of its potential use that covers various fields like medicine and food technology and therefore, the potential for possible utilization in the transformation of the traditional methods of remediation. The use of advanced nanotechnology for the removal of POPs from the environment is addressed in this chapter.

2 Sources of POPs and types of POPs Due to their inert chemical nature and resilience, POPs are widely used in various materials such as fire suppressants, surfactants, flame retardants, agents of heat transfer, and pesticides. They are also known to contain dioxins, which are formed accidentally during industrial processes. Despite attempts to reduce or eliminate the use of such POPs, their use remains widespread, due to their significance in a variety of industries. Some of the major POPs of remarkable concern are discussed:

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2.1 Pentachlorophenol (PCP) and polybrominated diphenyl ethers (PBDEs) PBDEs are used as additives; they are added to plastic to reduce combustion, prevent fire outbreak and also delay the spread of fire. They are also used by construction companies, in electrical equipment (televisions, monitor, computer, and fax machine), and in the healthcare industry with a consumption rate of over 1.5 million; tons hence, they are ubiquitous and used widely [10] reported the presence of 21 PBDEs compounds in soil in concentration ranges of 5.3–22,110 μg/kg, with mean values of 2,283 μg/kg. The contaminants were produced from the burning of electronic wastes in a closed incinerator in South China. During manufacture of PBDEs, they can escape into the air, water, and soil. Daso et al. discovered 2,2,4,4,5, 5-hexabromobiphenyl in Capetown, South Africa, and the source was landfill leachate [11]. Figure 1 gives the structures of some PCP and PBDEs. Br

Br

Br

Br

Br

Br

Br

Br O

Br

Br

2,4,4-tribromo congener

Br

Br

Br

Br

Br

Br 2,2,4,4,5,6-hexabromo congener

2,2,4,4,6-pentabromo congener Br Br Br

O Br

Br O

O

O Br

2,2,4,4-tetrabromo congener

Br

Br

2,2,4,4,5,5-hexabromo congener

Figure 1: Structures of some penta-chlorophenol (PCP) and polybrominated diphenyl ethers (PBDEs).

2.2 Polycyclic aromatic hydrocarbon (PAHs) Polycyclic aromatic hydrocarbons (PAHs) are produced during incomplete combustion processes of fossil fuels, organic wastes, volcanic eruption, and forest fires [12]. Dispersal of PAHs in air brings about environmental pollution. When PAHs react with various radicals such as nitrate, ozone, and hydroxyl, toxic compounds are produced. They are classified as persistent organic pollutants, because they are ubiquitous and have a long-range of transport [13]. PAHs have an adverse effect on human

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health due to their mutagenic and carcinogenic effects, reduce adult population, and affect the weight of babies at inception [12], cognitive development in children, and causes obesity, and oxidative stress [14]. Naphthalene is one of the simplest members of the PAHs. It is a toxic air pollutant found outdoor and indoor, in chemical industries, during burning of biomass, oil combustion, fumigants, cigarette smoking, and so on [15]. Its molecular formula is C10H8, with boiling and melting points of 80.5 and 218 °C, respectively; it is semivolatile with a vapor pressure of 0.087 mmHg at 25 °C. It is the most volatile member of PAHs. Naphthalene is ingested through water, diet, and by inhalation. A high exposure has been found during bush burning and workers in industries with a high use of naphthalene, especially in the production of mothball.

2.3 Organochlorine pesticides (OCPs) OCPs are used to remove pests in agriculture, homes, and in the environment. It has helped the agricultural sector have an increase in the yield of crops and has also helped in the eradication of carriers of diseases in the environment [16]. But when OCPs are applied, they affect nontargeted areas. Due to their ability to dissolve in oil and fats, they attach themselves to fatty tissues in terrestrial animals and humans, causing risks like neurological damage, cancer, disruption of endocrine system, suppression of immune system, and death. Their lipophilic property makes them stable in the environment through accumulation in water, sediments, soil, and plants [17]. Dchlorodiphenyl trichloroethane T is used to eradicate the malarial vector and also to control pests in crop; chlorinated cyclodienes are used in the farm to control insects and to control mosquitoes and tsetse flies that causes malaria and sleeping sickness (African Trypanosomiasis) while hexachlorobenzene, chlorinated benzene, is a fungicide used in seed treatment to control fungal diseases in wheat [17]. Structures of some OCPs are given in Figure 2.

2.4 Halogenated polycyclic aromatic hydrocarbons (Cl-PAHs and Br-PAHs) These are halogenated compounds derived from PAHs. They are a group of compounds that has one or more halogen as a substituent on the ring [18]. These include the chlorinated and brominated PAHs, generally written as Cl-PAHs and Br-PAHs, respectively. Their toxicity is similar to that of dibenzo-p dioxins compounds [19]. Their formation in the atmosphere occurs through various routes, but primarily during incomplete burning processes, and they are also found as undesired by-products

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Cl

Cl

Cl

Cl

Cl dichlorodiphenyltrichloroethane (DDT) Cl

Cl

dichlorodiphenyldichloroethylene (DDE) Cl

Cl

Cl

Cl

Cl

Cl

Cl

Cl

dichlorodiphenyldichloroethane (DDD)

Cl Hexachlorocyclohexane (HCH)

Cl Cl

Cl

Cl

Cl Cl

Hexachlorobenzene (HCB) Figure 2: Structures of organochlorine pesticides (OCPs).

during the production of different chlorinated products. The Cl-PAHs are reported to initiate the aryl hydrocarbon receptor, thereby resulting in toxic effects on body tissues [20]. Cl-PAHs have also been reported to be found in waste water, atmosphere, and during combustion of polyvinyl compounds. When iron ore undergoes the thermal agglomeration process, natural gas and coal are used as a carbon source, and this forms organic contaminants; also, plastics feedstock in the iron ore can provide halogens, and hence, Cl-PAH and Br-PAH are formed [21]. Through natural processes such as chemical and photochemical reactions like ozone formation and photography, where there is smog formation (reaction of nitrogen oxides and volatile organic compounds with sunlight) these compounds are also produced. Researchers have discovered Cl-PAHs and Br-PAHs in different parts of the ecosystem, like in the Tibetan Plateau; Photochemical reactions and anthropogenic sources were identified to be sources of the pollutants; different variants of halogenated PAHs were reported. In Pearl River Estuary, halogenated PAHs were present

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significantly, and the source of this pollutant was found to be the river, waste incineration, and emission from automobiles; they are transported when suspended on particulate matters [19].

2.5 Polycyclic chlorinated biphenyl (PCBs) PCBs are synthetic organic compounds, having a general formula of Cl2H(10n)Cln, where n is the number of chlorine atoms within the range of 1–10. They are used as plasticizers and as flame retardants in plastic material added to improve specific qualities like flexibility, pliability, stretchability, durability, and elasticity. They can be used as hydraulic and heat exchange fluids and can also be applied as lubricants in transformers and capacitors [22].

3 Impact of POPs on the environment and health Pollution from POPs has emerged as a significant threat to the environment and health of humans and other organisms. The effects of persistent organic contaminants on the atmosphere are becoming a hot topic among scientists. POPs are long-lasting chemicals that accumulate in living things and can function as endocrine disruptors or carcinogens, if exposed to them for long periods of time. Persistent organic contaminants may be passed from mother to child via breast milk and placenta, posing long-term and immediate health risks. Two crosssectional investigations were performed in villages in Mexico’s Sinaloa and Sonora states, where high levels of persistent organic contaminants were discovered all through human and environmental monitoring. In the first sample, persistent organic contaminants were measured in the serum of 60 fertile, aged people. In the second study, the concentrations of persistent organic contaminants in breast milk were measured in a pooled sample of 50 women. These findings can be used to determine possible levels of persistent organic contaminants exposure in the most vulnerable stages of life, as well as to assess concentration patterns in the process of removing these compounds [23]. Due to concerns about their harm to habitats and human health, the majority of POPs found, to date, have been banned or limited around the world. However, even long-banned POPs can still be found in the environment; others are still in use and are being directly emitted; and new POPs could be discovered, about which we have no knowledge [24]. Due to the deleterious effect of this group of compounds, methods for their analysis must be of high sensitivity, so as to be able to reach the lowest limits of detection required for environmental safety and health concerns [25]. POPs can be

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found in raw food. Exposure to these toxins has been linked to endocrine destruction, cardiovascular disease, diabetes, cancer, immune and birth defects, and reproductive system dysfunction [26]. Several of these compounds usually have poor solubility in water, bioaccumulate in food chains, and have also been connected to various health challenges in either wildlife or humans. The existence of likely compounds in aquatic and terrestrial food chains is applicable to some of the concerned by means of both environmental protection as well as human health for the reason that various usual biological effects [23].

4 Recent methods for removal of POPs from environment Various remediation approaches have been put forward, recently, for the removal and degradation of POPs from the environment [27].

4.1 Membrane filtration technologies Membrane filtration approach is a reliable strategy for the treatment and degradation of POPs. A membrane refers to a narrow interphase lying between two phases in adjacent positions, thereby acting as a semipermeable barrier through the regulation of the transport of materials between the two compartments. The principle involved in the treatment of POPs using membrane technology is unique and is based on the transport selectivity of the membrane. The use of membrane has the advantage that it does not require the use of various additive agents unlike some other approaches; it is simple to maintain and design and can be carried out at a low temperature. Upscaling and downscaling processes associated with membrane technology for treatment of POPs as well as integration into other processes during reactions or separation are easy [28]. The major disadvantages include frequent backwashings (which induce higher operational costs), membrane fouling/scaling, and investment costs [29]. To achieve degradation of POPs, combinations of ultrafiltration/ microfiltration and nanofiltration/ reverse osmosis are usually needed. The successful utilization of membrane processes depends on various factors such as type of molecules, material composition, membrane selection, wastewater characteristics, and the interactions between the membrane and pollutants [30]. The mechanism of nanofiltration is based on retaining the POPs, while letting water pass through the selective barriers. Nanofiltration uses porous membranes with pore sizes of 1–2 nm. The separation is based on a mechanism of spherical exclusion. A typical membrane used for nanofiltration is made of thin film composite

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having a loose layer of polyester, which is responsible for the provision of structural support, an ultra thin topmost layer, and a layer that is similar to an ultra filtration membrane. The ultra filtration membrane is made of polyester material, which is responsible for retaining the total POPs dissolved [31]. The POPs are adsorbed on the surface of the membrane, bringing about an enrichment on the membrane and a rise in the chemical potential, which enhances the movement through the membrane toward the stream of permeate, thereby lowering the rejection [27].

4.2 Ozonation approach The degradation of POPs using ozone basically involves two reaction routes: the first involves the direct reaction by the ozone, while the second is the indirect pathway involving the hydroxyl radicals (OH*) that are produced during the reaction of ozone. Ozone reacts selectively with the POPs having moieties that are deficient in electrons such as activated aromatics, deprotonated amines, and olefins. The major source of hydroxyl radicals is the POPs. The radicals are formed from the side reaction involving ozone and a specific class of POPs such as those that are derivatives of phenols and amines [32]. The hydroxyl radicals are characterized by less selectivity and react quickly with a broad range of POPs, making the indirect reaction pathway more beneficial for the degradation of the POPs. The hydroxyl radicals ensure the efficient breakdown of the POPs into smaller inorganic compounds [33]. The degradation of POPs during ozonation is dependent on the rate constant of the reaction for the POPs with the hydroxyl and ozone. The reaction rate is also affected by pH of the media. Protonation can bring about a decrease in the rate of the reaction by several times [34]. Several factors such as the amount of POPs susceptible to degradation, availability of the hydroxyl radicals, presence of stimulating agents, and turbidity in aquatic environment can affect the degradation potential of the hydroxyl radicals, significantly [35]. In spite of the advantages provided by the treatment of POPs using ozone, it has inherent limitations which include cost of treatment, toxicity, and high cost of sustenance. In addition, the efficiency of ozone, in this regard, is relatively poor in waste water media having a high chemical oxygen demand, high carbon contents, and remarkably high biological oxygen demand [36].

5 Role of nanotechnology in degradation of POPs Nanotechnology is increasingly playing a vital role in proffering innovative and effective remediation to a vast range of environments polluted with POPs [37]. Removal of

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high doses of POPs from the environment was reported to be more efficient when using various integrated technologies based on nanoparticles utilization [38]. The remediation of various contaminants including chlorinated compounds, hydrocarbons, organic compounds, and heavy metals have been actualized in recent years, through the application of carbon nanotubes, nanocomposites, quantum dots, and nanofibers. There are different nanotreatment approaches, which have shown high efficiency in the degradation and treatment of POPs, such as heterocyclic compounds, polychlorinated biphenyls, DDT, and polyhdroxylalkanoates [39].

5.1 Use of nanotubes One of the most reliable and efficient means for the removal of organic contaminants such as bioaerosol is the air filtration technique that involves the use of carbon nanotubes, and silver and copper nanoparticles, through ventilation mechanisms. Several studies have documented the potential of silver nanoparticles in removing bioaerosols during the process of air filtration. The efficiency of this technique is affected by factors such as relative humidity, dosage of the nanotubes, duration of exposure, and concentration of the contaminants [40]. Nanomaterials are valuable adsorbents suitable for the removal of various POPs from the environment. Their kinetics of absorption is highly favorable for the removal of POPs due to their surface chemistry, surface active groups, numerous adsorption sites, and short intraparticle distance [41]. For most available studies, POPs were removed using various kinds of carbonaceous materials. Nanomaterialbased adsorbents have better potential than activated materials. The nanoparticles could be modified and adapted or integrated with other materials for composite formulation, which could improve their efficiency in the remediation of POPs from the environment. Their high permeability, low mass, and tinny pore sizes make them suitable for the process of filtration.

5.2 Use of nanofibers Nanofibers have been reported to have unique potential in the removal of POPs from waste water and other environmental matrices. The polymeric composite membrane made of nanofiber could be fabricated through the use of electrospinning method. This is an efficient and reliable approach for the formation of ultra fine nanofibers using various materials such as metals, ceramics, and polymers having a diameter of 20–2,000 nm [42]. Electrospun nanofibrous layers have broad surface areas and fine pores which are turnable. They also have high liquid flux, which is the reason behind the interest of industries and researchers in investigating their possible use in micro filtration

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and ultra filtration. Findings from studies show that membranes made of nanofibers are capable of removing small particles of micron sizes from waste water, without detectable fouling, making recovery of the membrane from cleaning easy [43]. Electron spun nanofabers can readily be modified and adapted for special use as membrane for the removal of organic contaminants and heavy metals during the process of filtration, through the introduction of some functional groups [41]. Synthesis of nanospore membrane makes use of various natural and synthetic polymers, which includes polyvinyl fluoride, polyacrylonitrile, and polypropylene, which are effective in the treatment of wastewater pollutants of micro sizes. Nanofibers have a stable absorption when compared to tubes and particles, owing to their loose structures. Nanofibers produced from semiconducting materials and titanium dioxide have photocatalytic ability for the degradation of industrial pollutants and various dye compounds [42]. Composite nanofiber membranes were found to have up to 95% efficiency in the degradation of micropollutants [44].

5.3 Metal nanoparticles and composites Titania (TiO2) nanocatalysts have an established potential in the removal of pollutants from soil, waste water, and other environmental matrices. TiO2 nanoparticles are proposed to be both complementary and supplementary to the existing water treatment technologies, by means of transformation or destruction of harmful chemical wastes to inoffensive end products such as H2O and CO2. Several studies have explored the removal of POPs using various kinds of nanocomposites with emphasis on their synthesis, application, and modifications for water treatment purposes [45].

6 Mechanisms involved in removal of POPs using nanotechnology 6.1 Adsorption mechanism Physical and chemical properties of POPs such as polarity, molecular weight, nature of functional groups, and surface charges have also been used in their removal from environmental matrices through the process of adsorption, in integration with nanotechnology [46]. Various kinds of nanoparticles have played a vital role in this regard, including nanosilica and nanocelluloses, among others (Figure 3). Adsorption is a surface phenomenon that occurs on the surface of the nanoadsorbent material. The mechanism of adsorption involves the attachment of the molecules of

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Fire suppressants

Surfactants Flame retardants

Pesticides Presistent Organic Pollutants (POPs)

Organic wastes

Industrial processes

Nanofibres

Quantum dots

Role of Nanotechnology in degradation of POPs

Carbon nanotubes

Metal NPs

Metal oxide NPs

Figure 3: Schematic representation of source of POPs and their degradation using different nanomaterials.

sorbate onto the surface of the sorbents, through interactions at molecular level as well as the diffusion of the molecules of sorbate into the interior of the adsorbent material. The process of adsorption is affected by various factors such as the dose of adsorbent, temperature, contact time, pH, and surface morphology. The chemical structure and concentration of the sorbate also affect the process. Different adsorbent materials have been employed in the removal of POPs from the environment. The results on adsorption studies for POPs are usually explained using various kinetic and thermodynamic models [47].

6.2 Photocatalytic degradation mechanism Semiconductor photocatalysis integrated with nanomaterials could be applied to decompose numerous organic contaminants in open air, in the presence of aqueous media, by means of solar energy. Photocatalysis is another primary mechanism involved during the breakdown of POPs. This primarily involves the use of ultra violet rays for the production of photo charges that can be effectively transferred to any surface, thereby bringing about the mineralization of the POPs into simple inorganic materials [48]. Generally, during this process, electrons (e–) and holes (h+) are formed on the surface of the photocatalytic substance such as titanium oxide on

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irradiation with UV [49]. Various types of reactive species such as hydroxyl radicals (OH*) and active oxygen (O2*) are then generated from the interactions between the holes and electrons with oxygen and water: e− + O2 ! O2 ✶ h+ + H2 O ! OH✶ + H The mineralization process of the POPs into simple inorganic substances that are more environmentally friendly such as water and carbon dioxide continues through the reaction of the hydroxyl radicals generated with the POPs. These processes also involve the shortening of chains and dehalogenation processes, until the final products of degradation are formed. There are several semiconducting materials that are employed as photocatalysts for this process, which is as a result of some of their unique properties such as stability to chemicals, electronic properties, and low cost [50]. More recently, various researchers have attempted to modify the crystalline structures of some materials with a view to boosting their use in the degradation of POPs. One of the most commonly used and efficient semiconductors for POPs degradation is titanium oxide. Modified forms of this compound have also been produced with higher efficiencies, through the use of ultrasound-assisted electronic deposition approach. Modified structures have been synthesized by combining other semiconductor materials with ultrasoundassisted electronic deposition methods [51]. Also, heterogeneous photocatalysts have also been shown to play a vital role during the elimination of xenobiotics in waste water that has high hydrophilicity. The efficiency of the catalyst used in degradation of POPs is affected by factors such as size, surface morphology, and pore volume [52]. In a related study, a TiO2 aerogel nanofiber for quick photocatalytic degradation of methylene blue solution was prepared by means of a superficial hydrothermal technique. The complexes aerogel can be considered as a portable as well as green photocatalyst, for the reason that it was promising in wastewater treatment application as a result of its good high photocatalytic stability and activity under solar irradiation and ultraviolet light [53].

7 Recent studies on use of nanotechnology in degradation of POPs Li et al., [53] in their work, synthesized cerium oxide nanocomposites for the degradation of organic contaminants through facile synthetic approach. The reaction was carried out for a duration of 90 min, and the degradation efficiencies was observed to range from 93.3–100%. The nanoparticles were reused about six times, without a significant change in the efficiency of degradation.

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Munir et al. (2020) used CuFe2O4/Bi2O3 nanocomposite to degrade methylene blue, an organic dye pollutant. The magnetic property of the prepared nanoparticle made it easy to separate it from dye, and it was very stable, making it reusable. The recycling experiment was done three times, and there was no decrease in its efficiency, with a value as high as 91% within 3 h of degradation exercise [54]. Alfred et al. [55] prepared solar-active clay-TiO2 nanocomposites through biomass-assisted synthesis, and this was utilized for the removal of ampicillin, a pharmaceutical contaminant, from water, and the efficiency of the nanocomposites was 100%. The nanocomposites were reused five times and still had about 90% efficiency; the degradation was fast, which gave a high removal capacity. In a related work, Rodrigo et al. [56] reported the degradation of chlorobenzoic and chlorophenoxy in an acidic medium electrochemically, using the peroxi-coagulation approach integrated with nanomaterials. In this approach, electro-oxidation and anodic oxidation using hydrogen peroxide were adopted for the mineralization of the contaminants into smaller substances such as water, carbon(IV) oxide, and inorganic ions. During the anodic oxidation step, radicals, mostly of hydroxyl group, were formed on the top of the overvoltage anode, on oxidation of water. Fahiminia et al. [57] investigated the production of copper nanoparticles (CuNPs) using photocatalytic approach and assessed their efficiency in degrading 4-nitrophenol in aqueous environment and the usability potential. Huang et al. [58] synthesized graphene-based copper nanocomposite, (rGO@Cu2O/BiVO4) using different copper oxide doping and investigated its potential in degradation of sulfamethoxazole compounds in waste water. Liu et al. [59] used graphene-modified nanosheet with titanate (G/A/TNS) for the photocatalytic breakdown of sulfamethazine and reported 96% efficiency in removal of the contaminants from waste water. Park et al. [60], in a related study, investigated the photocatalytic degradation of perfluoro octanoic acid, using TiO2 nanotubes with graphene oxide on the titanium sheet. They reported high removal efficiency. Akhil et al. [61] investigated ZnO nanoparticles alongside various capping agents such as polyvinyl alcohol, gelatin, and ethylene glycol, using coprecipitation technique for their preparation. This was used to assess the photocatalytic breakdown of methylene blue in the presence of UV light. The ZnO NPs were found to have the highest photocatalytic activity. Huaccallo et al. [62] investigated the potential of magnetic magnetite/carbon nanotube in degradation of diclofenac in waste water treatment plant, waste water from hospital, and surface water. They recorded the highest removal after 8 h of the treatment.

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Table 1: Use of various nanomaterials in the degradation of POPs. Nanomaterials

POPs degraded

References

FeO/SiO nanocrystals

Insecticide O,O-diethylO[-isopropyl--methylpyridimidinyl] phosphorothioate (diazinon)

[]

Electrospun carbon nanofiber [CNF-CNT]

Ulfamethoxazole and atrazine

[]

Carbon nanofibers with MgO and AlO nanoparticles

Diazinon pesticide

[]

Polystyrene nanofibers

Pesticides (atrazine, atrazine desisopropyl, atraton, carboxin, linuron, and chlorpyrifos)

[]

Acid-modified polyacrylonitrile nanofibers

Polyhexamethylene guanidine hydrochloride (PHGC)

[]

Multiwalled carbon nanotubes

Methylene blue and atracine

[]

PET-based activated carbons and Fe composite precursor

Phenol and congo red

[]

CNTS

,-Dichlorobenzene

[]

Single-walled and multiwalled CNTs

Trihalomethanes

[]

Clay–TiO nanocomposites

Ampicillin in water

[]

Multiwalled CNTs

Chlorophenols, herbicides, and DDTs.

[]

TiO nanoparticles

Polychlorinated biphenyls (PCBs), benzenes, and chlorinated alkanes

[]

TiO nanoparticles

Microcystins

[]

CuFeO/BiO nanocomposite

Methylene blue

[]

Multiwalled CNTs functionalized with Fe nanoparticles

Benzene and toluene

[]

Nitrogen- and Fe(III)-doped TiO nanoparticles

Azo dyes and phenol

[]

Cerium zirconium oxide nanocomposite

Sulfonamide

[]

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8 Conclusion and future trends This chapter has discussed the role of advanced nanotechnology in the degradation of persistent organic pollutants (POPs) comprehensively. It examined the sources and distribution of POPs in the environment. The impact of these compounds on human health and the environment at large was also discussed. Most recent studies on various kinds of nanomaterials that have been employed in the degradation of POPs were also explored. Advanced nanotechnology is the most attractive approach for the removal of these contaminants due to the various advantages of this technique over other conventional approaches, which include nontoxicity of nanoparticles, high sorption potential for contaminants, ease of removal and possible recycling, and ease of preparation using various green approaches, among others. Degradation of POPs using advanced nanotechnology is a promising and novel area for present and future investigations. Novel approaches for synthesis of these nanomaterials, which form the backbone of the technology, can be further explored. Modification of the surface morphology of the nanomaterials and integration with other modern approaches would further enhance the efficiency of nanotechnology in degradation of POPs and other emerging organic and inorganic contaminants. Further investigations are necessary for detailed comprehension of some of the mechanisms involved in degradation of POPs, using novel nanocomposites.

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Abel Inobeme✶, Charles Oluwaseun Adetunji, Stanley Okonkwo, Mutiat Oyedolapo Bamigboye, Alexander Ikechukwu Ajai, Jonathan Inobeme, John Olusanya, Emmanuel Afoso

Fate and occurrence of microplastic and nanoplastic pollution in industrial wastewater Abstract: The presence of plastic waste at micro- and nanolevels in the environment has become a burning global issue in recent times. Various researchers have therefore positioned environmental pollution by microplastic (MP) and nanoplastic (NP) as a serious pollution threat. Industrial wastewater has been identified as a major source of these contaminants, while global plastic production has also been reported to have skyrocketed. The presence of these contaminants in marine and freshwater ecosystem has been well documented. Hence, MP and NP have been labelled as emerging contaminants that are capable of posing significant threat to human health, global economy, and general aesthetics. Plastic pollutants are nonbiodegradable and hence are capable of remaining in the environment for a long period. This review examines thoroughly the occurrence, sources, environmental distribution, and the fate of MP and NP in the environment. The paper also highlights the impact of these contaminants on the aquatic ecosystem and human life. Finally, an attempt is also made at exploring the strategies for their removal and degradation.

Acknowledgments: The authors are sincerely grateful to their various institutions for providing them with the enabling environment for this review. ✶

Corresponding author: Abel Inobeme, Department of Chemistry, Edo University Iyamho, PMB 04 Auchi, Edo State 312101, Nigeria, e-mail: [email protected]; [email protected], ORCID Id:https://orcid.org/0000-0002-9373-5828/ Charles Oluwaseun Adetunji, Applied Microbiology, Biotechnology and Nanotechnology Laboratory, Department of Microbiology, Edo University Iyamho, PMB 04 Auchi, Edo State, Nigeria Stanley Okonkwo, Department of Chemistry, Osaka Kyoiku University, Osaka, Japan Mutiat Oyedolapo Bamigboye, Department of Chemical Sciences, Kings University, Odeomu, Nigeria Alexander Ikechukwu Ajai, John Olusanya, Department of Chemistry Federal University of Technology Minna, Nigeria Jonathan Inobeme, Department of Geography, Ahmadu Bello University Zaria, Nigeria Emmanuel Afoso, Department of Biochemistry, University of Benin, Nigeria https://doi.org/10.1515/9783110743623-004

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1 Introduction Plastics are vital items that are found everywhere due to their usefulness in different areas: in telecommunications, automotive, agriculture, packaging, medical world, industrially, as toys, clothing, electronics, and so on; thus, their high rate of usage has lead to increase in their global production to about 360 million tons in 2018 [1]. Plastics are basically organic polymers of high molecular mass and are made of various monomeric constituents as well as several additives. They are usually synthetic, most commonly derived from petrochemicals and nonbiodegradable compounds [2]. They are applied in numerous areas and are vital, in that they help to make our lives easier, cleaner, and enjoyable. Plastic waste materials are spread by air to water bodies and after about 600 years, they naturally degrade or by UV action into small particles called microplastics (MPs) of diameters less than 5 mm, which degrade to nanoplastics (NPs) [3] of diameters between 1 and 100 mm, making these smaller particles available to organisms and animals, which eventually gets to humans, who are at the top of the food chain. In 2013, the production of plastic was said to have reached about 299 million tons, which was a 3.9% rise against that of 2012. The European Union (EU), United Kingdom, and Germany are the largest producers of plastic-based waste, recovering 80% and 26% of their production, respectively [4]. Most of the environmental plastic is nonbiodegradable and are present as waste for a long time, while some end up in the ocean. Various types of plastics exist; polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), polystyrene (PS), and the type with heteroatoms; polyurethanes (PU) and polyethylene terephthalate (PET), making their mode of degradation into MPs and NPs different [5]. The general polymeric compositions of different plastics materials at a global scale are as follows: polystyrenes (7%, used in packaging), polyamides (1%, a component of nylon), polypropylenes (23%, packaging, food containers and textiles), polyethene (bags and microbeads packaging) containing 15% HDPE, 17% low-density PE, for plastic bags, packaging, microbeads, polyethylene terephthalates (7%, for plastic and synthetic fibers), and others, which include poly(methyl)methacrylates (PPMA, 1%, for synthetic glass) and polycarbonates (1%, for synthetic glasses and plastic bottles [6]. Environmental contamination by NPs and MPs has become an issue of concern in recent times. MPs generally refer to fragments of plastics that are below 5 mm in diameter, based on international standards [7]. According to the definition proposed by Gigault et al. [8], NPs are fragments