Global Pollution and Environmental Monitoring [1 ed.] 9789350435137, 9788184880168

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Global Pollution and Environmental Monitoring

Principal H.V. Jadhav M.Sc., FIGGE

Dr. S.H. Purohit M.Sc., Ph.D., LLM, FIGGE

Imt GfIimalaya GpublishingGflouse MUMBAl. NEW DELHI • NAGPUR • BANGALORE • HYDERABAD • CHENNAI • PUNE • LUCKNOW • AHMEDABAD • ERNAKULAt.I

©Authors No part of this book shall be reproduced, reprinted or translated for any purpose whatsoever without prior permission of the publisher in writing.

ISBN

: 978-81-84880-16-8

First Edition: 2008

Published by

Mrs. Meena Pandey forHIMALA YAPUBLISHING HOUSE PVT. LTD., "Ramdoot", Dr. Bhalerao Marg, Girgaon, Mumbai - 400 004. Phones: 2386 01 70/2386 38 63, Fax: 022-2387 71 78 Email: [email protected] Website: www.himpub.com

Branch Offices: New Delhi

"Pooja Apartments", 4-B, Murari Lal Street, Ansari Road, Darya Ganj, New Delhi - 110 002. Phones: 23270392, 23278631,30180302/03/04/05/06, Fax: 011-23256286

Nagpur

Kundanlal Chandak Industrial Estate, Ghat Road, Nagpur - 440018. Phones: 2738731, 3296733, Telefax: 0712-2721215

Bangalore

No. 16/1 (Old 12/1), 1st Floor, Next to Hotel Highlands, Madhava Nagar, Race Course Road, Bangalore - 560001. Phones: 22281541, 22385461, Telefax: 080-22286611

Hyderabad

No. 2-2-1 167/2H, 1st Floor, Near Railway Bridge, Tilak Nagar, Main Road, Hyderabad - 500 044. Phone: 65501745, Telefax: 040-27560041

Chennai

No.2, Ramakrishna Street, North Usman Road, T. Nagar, Chennai - 600 017. Phones: 044-28144004/28144005

Pune

First Floor, "Laksha" Apartment, No. 527, Mehunpura, Shaniwar Peth, (Near Prabhat Theatre), Pune - 411 030. Phones: 020 - 24496323/24496333

Lucknow

C-43, Sector - C, Ali Gunj, Lucknow - 226024. Phone: 0522-4047594

Ahmedabad: 114, ·SHIL" 1st Floor, Opp. Madhu Sudan House, C.G.Road, Navrang Pura, Ahmedabad - 380 009. Phones: 09327324149,0931467413 Ernakulam

39/104 A, Lakshmi Apartment, Karikkamuri Cross Rd., Emakulam, Cochin - 622011 . Phones: 0484-2378012, 2378016, Mob- 09344199799

DTP by

Turbo Computers, Mumbai

Printed by

M.S. Printer ,Oarya Ganj, New DeihL

Contents 1.

Environmental Awareness

1

2.

Sampling Procedures

3

3.

Water

12

4.

Physical Examination of Water

27

5.

Chemical Examination of Water

30

6.

Physico-Chemical Analysis of Water

33

7.

Soil Analysis

61

8.

Instrumental Methods in Environmental Monitoring

118

9.

Radioactive Pollution

141

10.

Thermal Pollution

150

11.

Noise Pollution

155

12.

Micro-Organisms -

Environmental Impact,

164

Morphology and Enzymatic Activity 13.

Micro-biological Analysis

177

14.

Water Microbiology - Selected Tests

197

15.

Industrial Microbiology

220

16.

Soil Microbiology

222

17.

Biological Analysis

224

18.

Bacteriological Examination of Air

237

19.

Air Pollution Monitoring

239

20.

Estimation of Carbon Dioxide

258

21.

Humidity and Dew Points

260

22.

Environmental Laws - D.M.P.lE.T.A/INTERNET

262

23.

Standard References for Environmental Monitoring

284

24.

Appendix 1, 2, 3, 4, 5, 6, 7

306

- References

315

"This page is Intentionally Left Blank"

1 ENVIRONMENTAL AWARENESS Introduction Environmental awareness has to begin with the knowledge of the surroundings. The surroundings include our home, our workplace, all the people and growing plants, that live. around us. It also includes the air we breath, the water we drink, the food we consume. Nature has been very kind to us so far, in providing enough to the growing population. In the past few years there has been growing concern over the state of environment. The quality of our surrounding has declined due to exposure to industrial wastes and harmful chemicals. There is loss of Bio-diversity, changes in the climatic conditions, 'Green House' effect, depletion of ozone layer and recent happenings of Tsunamis. There is a threat to the life support system, and an increased risks for environmental accidents. The U.N. conferences have the focus on arresting this degradation, due to increase in pollution; by creating awareness through education, utilizing proper management principles on the line of conservation and strictly enforcing the environmental laws that look after the monitoring aspects of pollution control. In order"to control or monitor the pollutants present in the surroundings, i.e., air, water and soil, nature and qualities of pollutants were required to be identified. Their toxic effects and permissible limits needed to be ascertained. Fortunately, science has made enough progress in this direction. There are highly sophisticated and dependable instrumentations and techniques in use. These monitoring technologies are very reliable, accurate and less time consuming, compared with classical methods. There are sampling procedures and instruments available to carry out these operations. The pollution concentration can be accurately quantified at trace levels as parts per million (ppm) or even parts per billion (ppb). The global concern for 'Green Technology' means pollution free environment. This has been made possible by adopting new methodology. These procedures aim at reducing the waste, recycling the waste or conducting some treatment on the waste matter before it is ready for disposal. The entire technology is to become Eco-friendly. After the UN conference in 1972, our government has introduced twenty important legislations on Environmental Protection. Our Constitution under Article 21, gave us . Fundamental Freedoms' including right to life. But after introduction of Article 48 and 51 g, right to healthy life has been provided. The first talks about duty of the state towards creating proper environment and the second explains the duty of every citizen in India to protect the environment. It is worth remembering that the target in improvement must be the socio-economic position and society; for the laws have limitation in bringing about changes without active

2

Global Pollution and Environmental Monitoring

participation and support of people. The first step in this direction, is to bring awareness by incorporating as a syllabus for schools, colleges and universities. We are lucky, that with the order of the Supreme Court of India in 2004, this has been made compulsory.

a a

0

z SAMPLING PROCEDURES Introduction The analyst must take all reasonable precautions while taking samples of air, water or soil. It is necessary to take into consideration the safety aspects while dealing with harmful or poisonous materials. The procedures for sampling must be meticulously followed so also its preservation before analysis. There are statistical approaches and correct methodology. Proper care is also required during handling so that specific components of mixture are not lost or destroyed. The entire analysis is dependent on 'analytical sample'; hence the material collected must be true representative of the original bulk material. Sampling procedures depend on objectives of analysis and accessibility of sites. The size, number and location of portions of sample also influence the final result of analysis.

Theory of

Bul~

Material

The bulk is described as one that does not contain discrete, identifiable or constant units. This is dependent on number, size and site or location of the sample collection. Standard equation is as follows: 2

s

A

B

= WN = N

where

s-variance A-constant of homogeneity B-constant of segregation N-number of samples W-weight of sample

Objective of Sampling The objective of sampling is to collect a portion of material small enough in volume to be transported conveniently and handled in the laboratory while still accurately representing the material being sampled. This objective implies that the relative proportions or concentrations of all pertinent components will be same in the samples in the material being sampled and that the sample will be handled in such a way that no significant changes in composition occur before the tests are made.

Global Pollution and Environmental Monitoring

4

General Precautions (1)

Before filling, rinse sample bottle two or three times with the water being collected, unless the bottle contains a preservative or dechlorinating agent.

(2)

Depending upon the determinations to be performed, fill container (most organic determination) or leave the space for aeration mixing etc. (microbiological analysis).

(3)

Special precautions are necessary for sample containing organic compounds and trace metals. Because many constituents may be totally or partially lost if proper sampling and preservation procedures are not followed.

(4)

Important factors affecting the results are:

(5)

(a)

Presence of suspended matter or turbidity, the method chosen for its removal.

(b)

Physical and chemical changes brought about by storage or aeration.

Do not use the same sample for chemical, bacteriological and microscopic examination because methods of collecting and handling are different.

Procedure for Collection of Sa:m.ples (A)

Chain of Custody Procedure

It is essential to ensure sample integrity from collection to data reporting. This includes the ability to trace possession and handling of the sample from the time of collection through analysis and final deposition. This is referred to as chain of custody and is important in the event of litigation involving the result. Where litigation is not involved chain-of-custody procedures are useful for routine control of sample flow.

(i)

Sample· Labels

Use label to prevent sample misidentification: Gummed paper labels or tags generally are adequate. Include at least the following information: Sample Number Name of collector Date and time of collection And place of collection

(ii)

Sample Seal

Use sample seals to detect unauthorized tampering with samples up to the time of analysis. Although seal in such a way that it is necessary to break it to open the sample container. Affix seal to container before sample leaves custody of sampling personnel.

(iii)

Field Logbook

Record all information pertinent to a field surveyor sampling in a bound logbook. As a minimum include the following in the logbook: Location of sampling point, name and address of field contact; procedure of material being sampled and address etc. (iv)

Chain of Custody Record

Fill out a chain-of-custody record to accompany each sample or group of samples. The record includes the following information: Sample number, Signature of collector, date, time and address of collection, sampling type, signature of persons involved in the chain of possession and inclusive dates of possession.

5

Sampling Procedures (v)

Sample Analysis Request Sheet

The sample analysis request sheet accompanies sample to the laboratory. The collector completes the field portion of such a form that includes most of required information noted in the logbook. The laboratory portion of such a form is to be completed by laboratory, personnel and includes: Name of person receiving the sample, date of sample receipt and determinations to be performed. (vi)

Sample Delivery to Laboratory

Deliver sample to laboratory as soon as possible as practicable. Accompany sample with chain of custody record and sample analysis request sheet. (vii) Receipt and Logging of Sample In the laboratory, the sample custodian receives the sample and inspects its condit.ions and seal, reconciles label information and seals against the chain-of-custody record, assigns a laboratory number logs samples in the laboratory logbook and stores it in a secured storage room until it is assigned to an analyst. (viii) Assignment of Sample for Analysis --

The laboratory supervisor usually assigns the sample for analysis. Once in laboratory the supervisor is analyst and responsible for the care and custody. (8)

Sampling Method

(i)

Manual Sampling

Manual sampling involve no equipment but may be unduly costly and time-consuming for routine or large-scale sampling programs. (ii)

Automatic Sampling

Automatic samples can eliminate human error in manual sampling, can reduce the labour cost, may provide more frequent sampling, and are used increasingly. Be sure the automatic sampler does not contaminate sample. (C)

Sample Containers

The type of sample container used is of utmost importance. Containers typically are made of plastic or glass; but one material may be preferred over another for diff8lent kinds of samples. (D)

Number of Samples

If an overall standard deviation is known, the required number of samples may be established by the following relationship: N > (T * S/U)2 Where

=

N Number of samples S = Overall standard deviation U = Acceptable level of uncertainty T

= Student-to-statistic for a given confidence level

6 (E)

Global Pollution and Environmental Monitoring Quantity

Collect a 2-L sample for most physical.and chemical analysis. For certain determinations, Larger samples may be necessary. {F)

Safety Consideration

Because sample constituents can be toxic, take adequate precautions during sampling and sample handling. (1) Precautions may be limited to wearing gloves or may include coverS3l1, aprons. (2) Always wear eye protection when toxic vapours present. (3) Always wash han~s thoroughly before handling food. (4) If flammable organic compounds are present, take adequate precautions to prohibit smoking near samples. (5) Keep sparks, flames and excessive heat sources away from samples and sampling locations.

Sample Preservation (A)

General

Regardless of the sample nature, complete stability for every constituent never can be achieved. At best preservation techniques only retard chemical and biological changes that inevitably continue after sample collection. (B)

Sample Storage Before Analysis

(i)

Nature of Sample Changes (a)

(b)

(c)

(d)

(e)

(ii)

Certain cautions are subject to loss by adsorption on or ion exchange with, the walls of glass containers. These includes aluminum, cadmium, copper chromium, iron, lead, manganese, etc. Temperature changes quickly; pH may change Significantly in a matter of minutes; dissolved gas (oxygen, CO 2 ) may be lost. Determine temp, pH and D.O. in the field. Microbiological activity may be responsible for changes in the nitrate-nitriteammonia content, for decreases in phenol concentration and in BOD, or for reducing sulfate .to sulfide. Biological changes taking place in a sample may change the oxidation state of some constituents. The well-known nitrogen and phosphorous cycles are example of biological influence on sample composition. Zero head space is important in preservation of samples with volatile organic. Avoid loss of volatile material by collecting sample in a completely filled container. Achieve this by overfilling bottle before capping or sealing.

Time Interval BIW Collection and Analysis (I)

(a) (b)

In general, the shorter the time that elapse between collection of a sample and its analysis, the more reliable will be the analytical result. For certain physical values, immediate analysis in the field is required.

Sampling Procedures

(II)

(C)

7

It is impossible to state exactly how much elapsed time may be allowed between collection of sample and analysis; this depends upon: (a) Character of sample.

The analysis to be made. (b) {c} Conditions of storage. (III) Changes caused by growth of micro-organism are greatly retarded by keeping the sample in the dark and at a low temperature. (IV) When the interval between sample collection and analysis is large enough to produce change in either the concentration or physical state of the constituents to be measured. Preservation Techniques (i) To minimize the potential for volatization or bio-degradation between sampling and analysis, keep sample as cool as possible without freezing. (ii)

Preferably pack sample in crushed or cube ice before shipment. (a) Avoid using dry ice because it will freeze samples and may cause glass container to break. (b) Dry ice also may effect a pH change in sample. (iii) Use Chemical Preservatives only when they are shown not to interfere with the analysis being made. When they are used, add them to the sample bottle initially so that all sample positions are preserved as soon as collected. No single method of preservation is entirely satisfactory. Because a preservation method for one determination may interfere with another one. Samples for multiple determination may need to be split and preserved separately. Clearly it is impossible to prescribe absolute rules for preventing all possible changes, but to a large degree of the dependability of an analytical determination rest on the experience and good judgement of the person collecting the sample.

Conclusions •

The main purpose of collecting and examining environment samples is to assess their quality from the point of view of safety and environmental protection.

•

Samples are taken from different sources, so as to truly represent all the characteristics at the time and place of collection. • Volumetric analysis is suitable for testing acidity, alkalinity, chlorides, hardness and dissolved oxygen. • Colour comparison procedure is adopted for measuring parameters like turbidity, pH, residual chlorine, iron, sulphate, fluorides. • Various instruments are available for directly measuring turbidity, conductivity, pH, dissolved oxygen etc. Sampling is a process of obtaining a reasonable amount of material that has all the essential properties of the bulk material. The procedure depends on nature of the test material, accuracy required, cost of the product involved, the cost of the analysis and the cost of sampling. If a drug is required to be manufactured, high degree of purity of raw material is desirable, however, for chalk sticks similar degree of care is not required.

Global Pollution and Environmental Monitoring

8 Sampling includes three stages: (I) Identification of Bulk material.

(II) Collection of Gross sample. (III) Reducing it to Lab sample. Since many substances are present at only very low levels in environmental media, it is often necessary to pre-concentrate them in some manner prior to chemical analysis. This may be achieved in a wide variety of ways, dependent upon the type of sample and the nature of the analysis. The latest techniques for analysis of metals are of sufficient sensitivity for direct assay of many metals in natural waters. Where older instrumentation is employed, or for elements present at a very low abundance, a pre-concentration may be required. Where little chance of sample contamination exists, the crudest form of pre-concentration, simple evaporation to a smaller volume by heating, may be effective and has commonly been employed with fresh waters. Alternatively, a metal-chelating reagent (e.g., ammonium pyrolidine dithiocarbamateAPDC) may be added and the complexed metal extracted into a small volume of organic solvent (e.g., methyl isobutyl ketone-MIBK). The metals are thus preconcentrated by an amount equal to the ratio of volume of water sample and organic solvent, and indeed the use of organic solvents with flame atomic absorption spectrometry gives a further enhancement in sensitivity relative to analysis of aqueous samples. In other cases the metal is extracted from the organic solvent into an acid medium, which is then analysed. Metal Species Occurring in Natural Water in Relation to Size Associati.on Typical size range (nm)

1000

Metal species

free metal ions inorganic ion pairs, inorganic complexes, low molecular weight organic complexes high molecular weight organic complexes adsorbed onto inorganic colloids (or complexion by surface-adsorbed humic); associated with detritus adsorbed onto living cells; associated with mineral solids and precipitates

Example

Phase state

Pb 2+, Cu 2+ CdCllPb-fulvates

dissolved dissolved

Cu-humates

colloidal

CO- Mn02

colloidal

Pb-FeOOH

Cd-clay 2PbC03Pb(OHh

particulate

Organic compounds in both air and water may be pre-concentrated by passage of the sample through a porous organic polymer or resin where the analyte is adsorbed. Thus hydrocarbons in street air are commonly collected upon a porous polymer such as Tenax, from which they may be displaced by heating for a subsequent chemical analysis. There are two ways of sampling: Random, i.e., without any bias. This depends on the homogenity of sample. (I) (II) Non-Random or systematic sampling.

Sampling Procedures

9

This eliminates bias or prejudice. It also, requires a prior list of items in the bulk. The three states of the sample, i.e., gas, liquid and solid, all require different treatment. For comparatively it is easier to sample gaseous products (air) than solids (soil). In general, the gases are sampled based on their property of expansion, displacement and flushing. The liquids are sampled based on their homogenity as well as their fluidity and the solids are sampled with the help of different types of instruments depending on the nature of the solid material. They could be grounded, pulvarised, powdered, conned and simply divided physically. The soil samples in this category are required to be homogeneous. Distribution of pollutants in soil may not be vertical with depth but can be sidewise (spatial). There are two strategies, (one), which is expensive, require to take all care separately and analyse, whereas the (second), more time consuming, where all samples can be combined and mixed to provide single bulk. Obviously, contamination in soil samples may give misleading results. The equipment used for sampling and storage must be cleaned with acid, EDTA and ultra pure water. Soil samples are relatively stable. For preparing for analysis this sample is completely dissolved in acid mixture containing hydrofluoric acid and oxidant. Aqua regia or a mixture hydro-chloric acid and nitric acid. Use of Hydrofluoric acid is also recommended. Fusion mix like alkaline Borax can be used. For air samples there are two basic methods suggested. Grab sampling and continuous sampling. In this the vapours are removed from the air. For a certain fixed time, followed by concentration using new instrumentation. The collection efficiency in this is nearly 100%.

Types of Santple Collection for Water (A)

Grab or Catch Sample

A sample collected at a particular time and place can represent only the composition of source at that time and place. However, when the source is known to be fairly constant in composition over a considerable period of time or over substantial distance in all direction, then the sample may be said to represent a longer time period or a large volume or both than the specific points at which it was collected. In such circumstances, some sources may be represented quite well be single grab samples, e.g., some water supplies, some surface water and rarely some waster water streams. (B)

Composite Sample

In most cases, the term "Composite Sample" refers to a mixture of grab samples collected at the same sampling point at different times. Time-composite samples are most useful for observing average concentration. As an alternate to the separate analysis of a large number of samples, followed by computations of average and total result, composite samples represent a substantial saving in laboratory effort and expense. For these purposes a composite sample representing a 4-hr period is considered standard for most determinations. (C)

Integrated Samples

For certain purposes, the information required is provided best by analysing mixtures of grab samples collected from different points simultaneously or as nearly so as possible are integrated samples. An example of the need for such sampling occur in a river or stream that varies in composition across its width and depth. To evaluate average composition or total loading, use a mixture of sample representing various points in the cross-section in proportion to their relative flow. .

Global Pol/ution and Environmental Monitoring

10

Sampling (A)

Samples for Physical and Chemical Examination

Samples for physical and chemical examination should be collected in clean glass stoppered bottle made of neutral glass of capacity not less than 2 Itr. Stoppered glass bottle technically known as "Winchester Quart bottles" are suitable. Before collecting the sample rinse the bottle well three times with water filling it each time about 30%. Then fill it with the water, tie the stopper tightly down with a piece of cloth over it and seal the string. (B)

Sample for Bacteriological Examination

(a) Sample for bacteriological examination should be collected in clean sterilized bottle made of neutral glass of capacity 200-250 ml. and provided with a ground stopper having an overlapping rim. The sampling bottle should not be opened until the moment at which it is required for filling. (b) Be very careful so that nothing except the water to be analysed comes in contact with inside of the bottle or the cap. (c) The outside of the tap .or faucet at the sample point should be inspected, and if found leaking around the handle a different point must be chosen because the water might turn down outside of the tap and enter the bottle causing contamination. (d) Clean and dry the outside of the trap or faucet with sterile papers before taking the sample. (e) Allow the water to run for at least one-half of minute before collecting the sample. (f) While filling the bottle, the bottle must be held properly so that no water which contacts the hand enter into the bottle. (g) The sample must be handed over immediately to laboratory otherwise extra bacteria may develop, thus giving wrong result.

Collecting the Sample From (A) A Tap (Distribution System) (a) When the sample is to be taken from a tap in regular use, the tap should be opened fully and the water run to waste at least 2 minutes in order to flush the interior of the nozzle and discharge the stagnant water in the service pipe. (b) In the case of samples to be collected from taps which are not in regular use the tap should be sterilized by heating it. Then the tap should be cooled by allowing the water to run to waste before the sample is collected. (B) From Well Collect samples from wells only after the well has been pumped sufficiently to insure that samples represent the ground water source. Sometimes it will be necessary to pump at a specified rate to achieve a characteristics draw down, if this determines the zone from which the well is supplied. Record pumping rate and draw down. (C) River or Stream When samples are collected from a river or stream. observed result may vary with depth, stream flow and distance from shore and from one shore to another.

Sampling Procedures

11

(a) If equipment is available take an "Integrated sample" from top to bottom in the middle of the stream or from side to side at mid depth, in such a way that the sample is integrated according to flow. (b) If only a grab sample can be collected, take it in the middle of the stream and at mid-depth.

(0)

Lake & Reservoirs

Lake and reservoirs are subject to considerable variations from normal causes such as seasonal stratification, rainfall, run-fall, run off and wind. Choose location, depth and frequency of sampling depending upon local conditions and the purpose of the investigation. Avoid surface scum. (Use only representative sample for examination. The great variety of conditions under which collection must be made make it impossible to prescribe a fixed procedure).

Soil Satnpling A representative homogeneous soil sample is essential pre-requisite of any analysis. Distribution of pollutants not only change vertically with depth but also increase side ways horizontally. There are two strategies to act upon (firstly), a number of cores may be taken and analysed separately. (Secondly), all the samples can be combined and thoroughly mixed to provide a single bulk sample. The first is costly and time consuming. The second method, however, is followed with variations in concentration. The equipments of sampling soil must be cleaned with acid, EDTA and finally with Ultrapure water. Particular care must be taken for storage of samples when air dried, these are relatively stable. For purpose of extraction the extract solution should be acidised before storage. Sampling sites, depth and method to be used for the collection of soil sample, should be decided by keeping in mind the purpose of study and parameters in question. For characterisation in general, a few random samples from the study area to the depth of about 15 cm, may be sufficient. For the study of soil profiles, samples at this depth may be needed. Using spade and shovel, surface soil samples may be obtained. The samples near the root of a large tree must be avoided. Over and near civil construction sites can be avoided. Special borer samples are required to get the samples from deeper profiles. The ones collected must be retained in polythene bags and must be brought to the laboratory without delay. This is because the parameters such as redrox potential, nitrogen phosphorus content etc. must be analysed immediately. Alternatively the sample can be stored after drying at 40°C.

000

3 WATER Introduction Human civilisation reveals that water supply and civilisation are almost synonymous. Water is the most vital resource for all kinds of life on this earth. But this resource is now adversely affected both qualitatively and quantitatively by all kinds of human activities on land, in air or in water. About 97% of the earth's water supply is in the ocean, which is unfit for human consumption and other uses because of its high salt content. Of the remaining 3%, 2% is locked in the polar ice caps and only 1% is available as fresh water in rivers, lakes, streams,. etc.

Sources of Water Supply (a) Rain water (b) Surface water in the form of : (i) stream, river, brooks, (ii) Upland surface water (c) Underground water: (i)

Shallow well water

(ii) (iii) (iv)

Deep well water Springs Artesian well water.

(a) Rain water: Rain water during its passage towards ground absorbs nitrogen, oxygen, carbon dioxide, volatile acids, Ammonia Fumes, Micro-organism and dust particles with it. Rain water is generally free from mineral matter. Due to absorption of carbon dioxide it becomes slightly acidic in nature. (b) Surface water: Rain water when falls on ground, it carries vegetable matter which in turn converts into humic acid in due course. Water also carries the excreta of human and animals. This addition is dangerous as it may contain pathogenic micro-organism. Surface water may also contain algae, soil bacteria, fungi, molluccas, sponges and polyzoa. Surface water near industrial area, village, cities may also carry obnoxious minerals and poisonous materials. (c) Underground water: Sub-soil water is suspicious as it contains inorganic or organic impurities. There is also possibility of heavy populations of micro-organisms which enters from sewage water. The well water becomes hard due to presence of carbonates, chlorides, sulphates, etc.) of calcium, magnesium and sodium. There are many sources for the. water supply and each has its own type of contamination. Examination of water is essential to confirm purity, potability and wholesomeness. It is essential also for safeguard of the public health.

13

Water

Water Quality Parall1.eters The water quality parameters are roughly classified into the three categories: (I) Physical (II) Chemical (III) Biological. Following table represents the important water quality parameters: Table 3.1 Physical

Chemical

Temperature Colour Odour Conductivity Solids

Biological

Dissolved Oxygen Biological Oxygen Demand Chemical Oxygen Demand pH, Acidity Alkalinity, Ammonia, Nitrates, Nitrites, Phosphates, Sulphates, Chlorides, Silica, Hardness, Calcium, Magnesium, Heavy Metals, Sodium, Potassium Detergents, Pesticides

Turbidity Foam and Froath

Pathogenic Bacteria Coli Forms and other Bacteria Algae Viruses

Pure water is one which is colourless, free from turbidity and abnormal tests and smell. Wholesome water is that water which is free from pathogenic organism and may contain chemical within permissible limits. Following table represents the drinking water standards: Water Quality Standards in India Parameter

pH Total hardness Turbidity Chlorides (as CI) Cyanide (as CN) PAH Fluoride (as F) Nitrate (as N03) Phenols Sulphate (as S04) Manganese Mercury Iron Copper Cadmium

Standard (Revised 1975)

6.3 - 9.2 600 ppm 25 ppm 1000 ppm 0.05 ppm 0.2 ppm 1.5 ppm 45 ppm 2 ppm 400 ppm 0.5 ppm 0.001 ppm 1 ppm 1.5 ppm 0.01 ppm

Global Pollution and Environmental Monitoring

14

0.01 ppm 0.05 ppm 0.1 ppm 0.05 ppm 15 ppm 150 ppm

Selenium Chromium Lead Arsenic Zinc Magnesium

Table 3.2 : Drinking Water Standards

Ministry of Works and Housing

World Health Organisation Characteristics

PHYSICQ-CH EMICAL Turbidity, JTU Taste and odour Colour (Pt. scale) pH Total solids Total hardness (as CaC03 Magnesium Iron (Fe) Manganese Copper Chloride Sulphates (as S04) Phenolic substances Fluoride* Nitrate Zinc Mineral Oil Anionic detergents (as MBAS) Arsenic Hexavalent Chromium Cyanide Lead Selenium Cadmium Mercury PCB (ug/1) Gross Alta-activity (PCil1) Gross Beta-activity (PCi/1)

Highest Desirable

Maximum Permissible

Acceptable

5.0 Nothing 5.00 7.0-8.5 500.0

25.00 Disagreeable 50.00 6.5-9.2 1500.0

2.5 Nothing 5.00 7.0-8.5 500.0

100.0 30.0 0.1 '0.05 0.05 200.0 200.0 0.001 1.0 45.0 5.0 0.01 0.2

500.0 150.0 1.0 0.5 1.0 600.0 400.0 0.002 1.5 45.0 15.0 0.30 1.0 0.05 0.01 0.05 0.10 0.01 0.01 0.001 0.2 3.0 30.0

200.0 30.0 0.1 0.05 0.05 200.0 200.0 0.001 1.0 45.0 5.0 0.01 0.2 0.05 0.05 0.05 0.10 0.01 0.01 0.001 0.2 3.0 30.0

Cause of Rejection 10.00 Disagreeable 25.00 6.5-9.2 1500.0 600.0 150.0 1.0 0.5 1.5 1000.0 400.0 0.002 1.5 45.0 15.0 0.30 1.0 0.05 0.05 . 0.05 0.10 0.01 0.01 0.001 0.2 3.0 30.0

15

Water Bacteriological

W.H.O.

A. B.

Water entering distribution system. If disinfected Ministry of Works and Housing Coliform count in any sample of 100 ml should be zero. coliform count in any sample of 100 ml should be zero. Water in the distribution system: Water in the distribution System: (Ideally all shall satisfy all the three criteria indicated samples taken from the distribution system below: including consumers premises should be free (i) E. Coli count in 100 ml of any sample should from coliform organisms.) be zero. Since in practice it is not always possible hence following standards: (ii) Coliform organisms not more than 10 per 100 ml shall be present in any sample (i) throughout any year, 95% of the sample (iii) Coliform organisms should not be detectable in examined should not have any coliform 100 ml of any two consecutive samples or organisms. more than 50% of the samples collected for the year. (ii) E. Coli count in 100 ml of any sample should be zero. (iii) Coliform organisms not more than 10 per 100 ml shall be present in any sample. (iv) Coliform organisms should not be detectable in 100 ml of any two consecutive samples. All the values are in mg/L otherwise stated. The acceptable Fluoride concentration varies as a function of ambient temperature.

Water Santpling and its Exantination Water samples are usually collected and examined properly keeping the following objectives: Objectives: (1)

To keep the reql.lired degree of purity.

(2) (3) (4)'

To note the SUitability of a source of water for human beings and animals. To confirm the best source of water supply by comparative water analysis. To find out the suitability of the water for domestic water supply, tannery, wool washing and for slaughter house.

(5)

To check pollution in river water and investigate its sources.

(6)

To record the changes in the quality of water in wells and rivers during rainy season or drought.

(7)

To study the- effect of water on metals, e.g., reservoirs or pipes used for distribution of water.

(8)

To determine the efficiency of purifiers or softners.

(9)

To find out the variations in the characteristics of water of various levels of the deep well.

Global Pollution and Environmental Monitoring

16 (10)

To detect the source of infection during outbreak of certain diseases, e.g., cholera, dysentry, dyphtheria, Anthrex, Blackquarter, foot and mouth disease and rinderpest.

(11)

To find out the suitability of water for the use of patients of certain diseases, e.g., rheumatism and kidney disorders.

(12)

To detect any leakage in the mains, subsoil, sewage water escaping from the main.

Selection of Sampling Sites Sampling sites are important to understand the quality of water. The selection of actual sampling location in water body depends upon the character of the water system or body. In a lake or wide river many sampling sites should be selected at various corners. If the lake is stratified, three vertical samples at one site (surface, middle and bottom) shall be required. In shallow ponds only surface and bottom samples are required. In organically polluted river at least one location should be selected above the outfall of the wastes and remaining four sites should be selected downstream, representing the zone of recent pollution saprobic zone, recovery zone and clean water. STRING---t,.\ 4(-'k'--METAL RING CATGUT --.g...~ RUBBER BAND ---RUBBER ,,It':_~---RUBBER CORK

n----

t----f-+-- LONG TUBE· t-411---H--SHORT TUBE

SAMPUNG BOmE LEAD CASE

Fig. 3.1

Sampling Site Selection for Organic Polluted River If the river is polluted by inorganic pollutants then one site above and one below the point of discharge is considered for collection of water samples. Water samples must be collected by proper care by avoiding any external contamination - there should not be any error. The following factors must be considered during the collection of the samples. (i)

The collected sample should be a representative one.

(ii)

It should be collected at different times and frequencies.

(iii)

The variations in rate of flow over a period of sampling must be taken into account.

(iv) (v)

The objective and character of the laboratory analysis to be done. The use to be made from the result of analysis.

Water

17

Selection of Containers When the sample is to be analysed for organic content, green, or amber coloured bottle should be used. Dark coloured bottles are used for re~idual chlorine estimation. Polythene bottles are used for analysis of radioactive substances, corning glass ware is good for the collection of samples for bacteriological examination. Bottle should be cleaned by good quality of detergent and clean water. Rinsing of the bottle with concentrated sulphuric acid and then with distilled water several times is necessary. Stopper should be cleaned thoroughly by the same manner. Polythene bottles should be cleaned by distilled water or may be boiled in distilled water. The glass bottles are sterilized of 15 1b pressure in autoclave for 30 minutes or at 150°C in hot air over for 2 hours. Samples should be directly collected in the bottle without the help of funnel or tube, the bottle should be rinsed with water to be sampled.

Types of Safl1.ples (1) (2) (3)

(4)

Composite Sample: Sample taken from different zones and at different depth (vertically and horizontally) and then mixed together. Grab Sample: Sample taken at random from ponds and lakes. Representative Sample : Samples are taken at different times and at different frequencies. The frequency of samples depends on the population using the sample and the purpose for which water is to be used. Integrated Sample: Samples taken of regular hourly interval and all are pooled together and then a portion of it is taken for the examination.

Safl1.ple Collection Procedure (i) River and Streams: In river and stream, the sample should be collected at a point which practically represents the condition of the stream, points near the banks should be avoided. Middle zone or mid-depth is the proper place for collecting the sample, composite or integrated sample may be taken in such cases. (ii) Lakes and Ponds: Water sample should be collected from sufficient depth. Bank should be avoided. For sampling sufficient time is given to settle the disturbed clay or sand particles at the bottom so that clean water can be collected, sampling bottle should be held at the bottom. The bottle along with stopper is taken into the water in inverted position upto the depth one to two feet below the surface of water. Then the mouth of bottle is raised in slanting position and stopper is removed, so that air comes out and water easily enters in the bottle. It is allowed to fill up to three-fourth capacity. The bottle is then closed and taken out. (iii) Sample Col/ection from Deep Well: A glass bottle is taken which is properly fitted with rubber stopper. Rubber stopper is provided with two holes (Fig. 3.2). In one hole long glass tube is fixed and in another hole short glass tube. The two tubes are connected with a rubber tube of their outer ends. Due to this, assembly becomes air tight and water in the well. The rubber tube is tied by means of string. The other end is tied to a metal ring. A strong sting is also tied over the other end so as to hang the bottle for immersing into the well water. The neck of the bottle is tied with rubber band. The rubber band is passed through the metal ring. A metallic case (madi up of lead) is placed over the bottle, such bottle is lowered into the well up to the required depth. A strong jerk is given to string which pulls the

Global Pollution and Environmental Monitoring

18

connecting rubber tube. By this air comes out and water enters into the bottle. When the bubbles stop on the water surface the bottle is pulled out and fitted with stopper. (iv) Shallow well samples: The sample bottle is fixed properly to a metal sand. The bottle is sealed by a string. Another string is used to secure the stand. The stand along with the bottle is allowed to dip in well. When the bottle reaches about 7-8 feet deep from surface of water, a jerk is given to the string which holds the stopper of the bottle. Stopper is removed from bottle and air bubbles come out allowing water to enter in the bottle. Total disappearance of bubbles indicates that bottle is filled with water. The bottle is taken out from the well and it is sealed.

Fig. 3.2

Flow Measuretnent Number of methods are available to measure the flow in stream and waste water carrying pipes. (i) Bucket Method: This method is applicable when the waste water is. coming from the pipe or sewer. A bucket is easily used to fill the water from the pipe, time is recorded by stop watch. Litre in bucket x 60 T' . S d Ime In econ s (ii) Surface Float Method: A Float (any piece of plastic, wood etc.) is thrown on water surface. The time required for a float to travel a known distance is observed and average velocity is obtained by Flow (~n litres/min) =

d

V=t d is the distance, t is the time. The factor 1.2 indicates· that surface velocities are normally about 1.2 times heavier.

Water

19

Sample Handling and Preservation After

accur~te

(1)

Submitted for

(2) (3) (4 ) (5)

Submitted by Source of sample Place of Sample Sample taken in presence of

sampling the bottles are properly labelled as under: Physical I Chemical Bacteriological examination. Name of authority and address. Surface/Well/Tap/Effluent pit. Location address. Signature and name of the person with address. / Appointed

Signature of Authority (6) It is essential to protect the water sample from changes in composition and deterioration. Parameters like pH, D.O., temperature, must be recorded quickly. The following table represents the preservation technics for various parameters (Table 3.3). Preservation is essential to control the hydrolysis, biological reduction and complex formation, volatility etc. It is always suggested that analysis must be undertaken within 4 hours for same parameters and 24 hours for other, from time of collection and it must be completed, within a week.

Parameter

Table 3.3: Water Sample Preservation Mini sample Container Preservation size, ml

2

3

pH DO COD Nitrogen Ammonia

100 100 500 500

Polythene Polythene Polythene Polythene

Nitrate + Nitrite

500

Polythene

Cyanide

500

Polythene

Sulphide

500

Polythene

Phosphate Phenol

500 500

Polythene/glass Polythene/glass

Tannin and lignin Chromium, arsenic, lead, zinc, mercury E. Coli/total bacteria /acteno-mycetis

'500 500

Polythene/glass Glass/Polythene

100

GICjss bottle

4 Measure with 0-4 hrs. Add H2S04 to pH 2; refrigerate Analyze as soon as possible; add 0.8 ml conc. H2S04/L Add 40 mg HgCI2/L and refrigerate Add NaOH to pH 12 and 25 ml of 2% ascorbic acid and refrigerate . Add 1 ml. of 2N Zn (CH3 COOh and 2 ml of 1M NaOH; stir and refrigerate A.dd 40 mg HaCI2/L and refrigerate Acidify with H3P0 4 to pH 4.0 and add Ig CUS04' 5H 20 per L to inhibit bi0gegradation Analyze as soon as possible. Add 5 ml conc. HN03 Land refrigerate Sterilize the bottles in autoclave at 121°C at 15 Ib/inch 2 pressure for 15 minutes. Collect the sample in

Global Pollution and Environmental Monitoring

20

Microplankton/algae and other biological organisms

500

Glass bottie

sterilized bottle and refrigerate immediately Add 5 ml formali~ per 100 ml sample and refrigerate immediately

Characteristics of Potable Water (1)

It should be colourless, odourless and tasteless.

(2)

It should be free from turbidity and other suspended impurities.

(3)

It should be free from germs, bacteria and other pathogenic organisms.

(4)

It should not contain toxic dissolved impurities, such as heavy metals, pesticides, etc.

(5) (6)

It should have a pH in the range 7-8.5. It should be moderately soft, having hardness preferably in the range 50-100 ppm. Its hardness should not be above 150 ppm.

(7)

It should be aesthetically pleasant.

(8)

It should not be corrosive to the pipelines and should not cause any incrustations in the pipes.

(9)

It should not stain clothes.

Table 3.4 gives the WHO (World Health Organization) standards for drinking (Potable) water.

Thble 3.4 : Standards (maximum permissible limits) for drinking water as recommended by World Health Organisation (WHO) Parameters

Level WHO Standard

pH

6.5 - 9.2

BOD COD

6 10 0.05 ppm 100 ppm 0.01 ppm 0.05 ppm 0.5 ppm 1.5 ppm 1.0 ppm 0.1 ppm 0.001 ppm 150 ppm 0.5 ppm 250 ppm 0.05 ppm 45 ppm 0.2 ppm 0.01 ppm

Arsenic Calcium Cadmium Chromium Ammonia Copper Iron Lead Mercury Magnesium Manganese Chloride Cyanide Nitrate + Nitrite Polyaromatic hydrocarbons (PAH) Selenium

Water

21

Treatment of Water for Municipal Purposes The mun'icipal water supply for drinking and other domestic uses should be colourless, odourless, free from suspended impurities, free from germs, bacteria and other pathogenic organisms and should not contain harmful dissolved impurities. Therefore, the raw or impure water obtained by municipalities from sources such as rivers, lakes, wells, tube wells, etc. has to be properly treated before supplying for the domestic purpose. The various steps involved in the treatment are as follows: (1)

(2)

(3)

(4)

(5)

Aeration: The raw water is first aerated by bubbling compressed air. This removes bad odours, CO 2 , etc.} and also removes iron and manganese by precipitating them as their respective hydroxides. Settling: The water is then allowed to stand in large settting tanks. At this stage, some of the heavier impurities present in water settle down by gravity. Also, the bacteria present are partially eliminated due to the UV radiation from sun light. Coagulation: The suspended impurities present are then removed by coagulation using lime, soda ash and aluminium sulphate (or ferric alum) as the case may be. The suspended impurities are trapped by the resulting precipitate of AI(OH 3 ) and settle down at the bottom, thereby bringing about partial clarification of the water. Also, the negatively charged colloidal impurities are neutralized by the trivalent aluminium cation, followed by agglomeration and settling down by gravity. Filtration: The partially clarified water is then passed through sand gravity filters. These comprise of rectangular tanks which contain (a) a top layer (about 1 meter thick) of fine sand (b) a middle layer (0.3 - 0.5 meter thick) of coarse sand, and (c) a bottom layer (0.3 - 0.5 meter thick) of graded gravel. A series of porous drains are provided at the bottom of the gravel layer through which filtered water is collected. The slimy surface layer comprising of finely divided clay, algae, bacteria, etc. formed on the filter bed acts as an effective filtering medium which filters the finely divided residue, suspended matter and bacteria. The filters are backwashed periodically to remove the precipitated matter from the surface, so as to ensure efficient filtration. Activated carbon may be used for filtration, if the water contains odours. Chlorination: The filtered water is sterilized by chlorination (by adding chlorine pr bleaching powder) to destroy the pathogenic micro-organisms. The water is now pumped to overhead tanks for subsequent domestic distribution.

Sewage Treatment The wastewater from bathrooms, kitchens, lavatories, etc., is called Domestic Sewage. The wastes disposed from factories, laundries, laboratories, business houses, schools, hospitals, etc., also results in Sewage. The spent water from the community as a whole is called Sanitary Sewage. Sewage contains (a) Organic impurities (e.g., Urea (from urine) proteinaceous matters, detergents, biodegradable faeces, animal wastes, fats, carbohydrates, etc.) Inorganic impurities (e.g., nitrates, phosphates, detergents, surfactants, trace (b) metals, other anions and cations).

,

22

Global Pollution and Environmental Monitoring (c)

Saprophytic bacteria which are harmless and feed upon organic matter.

(d)

Pathogenic bacteria such as (i) Vibrio cholerae (which cause cholera) Shigelia dysenteria (which causes bacillary dysentery) (ii)

(iij) Salmonella typhi (which cause typhoid) Industrial wastes, wherever applicable (e) From the point of view of public health, sewage has to be properly treated.

Objectives of Sewage Treatment (i)

(ii) (iii)

Stabilization: This is the process which involves breaking down of organic matt~r with the help of bacteria into simple substances that do not decompose further. Stabilization can be accomplished with the help of aerobic or anaerobic bacteria. To render the sewage inoffensive and devoid of its nuisance value. To prevent contamination of water supplies, thereby protecting aquatic life.

Sewage Treatment Methods The extent of sewage treatment required mostly depends on the following two characteristics : (1) The content of suspended solids. (2) The biological oxygen demand (BOD) of the sewage. The following major treatment methods are generally employed : (1) .preliminary treatment: In this treatment, gross solids (e.g., large floating and suspended solid matter, grit, oil and grease) are removed by passing through screens, skimming tanks and grit chambers. Primary treatment : This step is meant to remove the remaining suspended (2) settleable solids, reduce the strength of the waste and to facilitate subsequent secondary treatment. The processes employed include sedimentation, mechanical flocculation and chemical coagulation. After this treatment, about 60% of the suspended solids, 30% COD, 35% BOD, 10% Phosphorous and 20% total nitrogen, are generally reduced. Secondary treatment: In this treatment step, the dissolved and colloidal organic (3) matter present Iii the sewage is removed by biological processes involving bacteria and other micro-organisms. These processes may be aerobic or anaerobic. They pring about the following sequential changes : (a) Coagulation and flocculation of colloidal matter. (b) Oxidation of dissolved organic matter to CO 2 , Degradation of nitrogenous organic matter to ammonia, which is t~n converted into nitrite and eventually to nitrate. (d) Reduction of BOD. The effluent from primary sedimentation tanks is first subjected to aerobic oxidation in systems such as aerated lagoons, trickling filters, activated sludge units, oxidation ditches or oxidation ponds. Then the sludge obtained in this aerobic processes, together with that obtained in the primary sedimentation tanks, is subjected to anaerobic digestion in the sludge digesters. (c)

Water

23

The sludge from the digester which contains 90 to 93% water, is de-watered in drying beds, filter presses or vacuum filters. The de-watered sludge, after chlorination, can be sent for ultimate disposal. The options available for ultimate disposal include dumping in landfills, incineration, dumping at selected sites in sea, or utilizing as a low-grade fertilizer after composting depending upon the local conditions. After secondary treatment, about 90% reduction in COD, 90% reduction in BOD, 30% reduction in phosphorous, and 50% reduction in total nitrogen, could be generally achieved. (4) Tertiary treatment: This is the final treatment meant for "polishing' the effluents from the secondary treatment processes, to improve its quality further. The main objectives of tertiary treatment processes are : (a) Removal of fine suspended solids (b) Removal of dissolved inorganic solids (c) Removal of final traces of organics, as desired (d) Removal of bacteria (e) Decrease the load of nitrogen and phosphorous in the effluents (f) Further purification of wastewater to enable its reuse. The various processes employed in tertiary treatment include: (1) Precipitation: Calcium compounds in the effluent from secondary treatment as calcium phosphate by adding lime. (2) Nitrogen Stripping: Nitrogen is present in the effluent for secondary treatment in the form of ammonia, nitrites and nitrates. Ammonia is toxic to aquatic biota. Nitrogen compounds enhance eutrophication. Ammonia in the effluenUs removed by trickling the effluent from the top of a baffle tower while it meets the air coming upwards. (3) Chlorination: The residual micro-organisms in the effluent are removed by chlorination before it is discharged. (4) Adsorption: The undesirable tastes and odours are removed by adsorption on activated charcoal. (5) Coagulation and filtration : The residual solids in the effluent are coagulated and removed by filtration. (6) Desalination: The residual dissolved inorganic impurities may be removed by ion-exchange, reverse osmosis or electrodialysis. (7) Oxidation ponds : Bacteria, particularly of faecal origin, can be removed by retaining the effluents from the secondary biological treatment plants in maturation ponds or lagoons for specific time periods. The final effluent which has very low BOD and very low suspended solids may be chlorinated before final disposal. (8) Anaerobic digestion: Using digesters, septic tanks, Imhoff's tanks. For large towns, a combination of aerobic and anaerobic treatment followed by irrigation may be ideal. The bio-gas produced in the anaerobic treatment can be used as domestic fuel. Bhawalker Earthworm Research Institute (BERI), Pune developed a process in which the waste water is passed through a vermifilter formed by enclosing earthworms and wormcasts which harbour cocoons and a variety of microflora in a specially developed medium. The impurities in the waste-water are converted into worm casts (Le., earthworm excreta)

24

Global Pol/ution and Environmental Monitoring

which have strong absorption properties. After repeated filtration, clear water is obtained. The worm casts accumulated in the vermifilter may be harvested periodically for use as a fertilizer.

Eutrophication Enrichment of a water body by nutrients is called "eutrophication." The word eutrophication originated from two greek words - 'eu' = good or well, and "trophes" = food. Eutrophication thus means "well-fed" or "nutrient-rich", The enrichment of a water body with respect to nutrients may take place because of natural sources (e.g., decomposition of plant and animal remains) or by anthropogenic sources (e.g., man-made sources like domestic, industrial or modern agricultural practices). A newly formed waterbody possesses a very low concentration of plant nutrients and hence little plant life grown in such water. Low primary production limits animal communities too. The nutrient content in it slowly increases due to surface run-offs, windborn dust and organic debris, excreta and exudates of animals which use the water. Bacteria and blue green algae fix atmospheric nitrogen. Phosphates present in the rocks and detritus at the bottom are solubilized by the micmbial activity. Thus the nutrient status of the water body gradually increases. At this stage, a moderate population of plants, animals and microbes now develops in the system, which further increases with increasing nutrient enrichment with passage of time. Eventually, dense population of plants, phytoplanktons and animals appears. At this stage, the aquatic system becomes highly productive in terms of fish, etc. On the basis of nutrient status and productivity, anaquatic systems may be classified into the following three types: (i) Oligotrophic: Water with poor nutrient status and productivity. (ii) Masotrophic : Water with moderate nutrient status and productivity. (iii) Eutrophic: Water with rich nutrient status and high productivity. Oligotrophic waters gradually turns into mesotrophic and finally to eutrophic waters. Further ageing causes over-abundance of nutrients which leads to profuse growth of rooted and floating green plants and the water body loses its aesthetic and economic value. Organic debris and silt settles at the bottom. The water becomes useless. The boundaries of the water body turn into a marsh with only a small shallow pond in the middle. Organic debris and silt finally fill the depression and what was once a lake now converts into a dry land. The accelerated or cultural eutrophication of several waterbodies is caused by human activity. Large quantities of mineral nutrients and organic matter are added to the waterbodies in the form of sewage effluents, organic wastes, agricultural run-offs, excreta and exudates of animals and humans, etc. These provide plenty of phosphates, nitrates (mostly from fertilizers applied to agricultural lands, domestic sewage, etc.) which lead to exuberant growth of algae and other water plants. A rich microbial and animal population also develops. If water from such a waterbody is to be used for domestic or industrial purposes, expensive cleaning operations will be required. The process of natural eutrophication which is generally very slow, thus gets accelerated. Silt and organic debris accumulates at the bottom and the system turns into a shallow muddy pond, then to a marsh and finally into a dry land. Thus a waterbody which could have been useful as a reservoir of fresh water and could have helped the growth of fish, etc., for hundreds of years becomes totally useless within a span of a few years only.

25

Water

Lake Washington and lake Mendota have undergone rapid eutrophication due to anthropological activities. Similarly, the recreational value of lakes in Kashmir is reduced. Nainital lake is undergoing accelerated eutrophication due to loading with sewage. Undesirable Effects of Eutrophication

(1)

Dense population of Planktonic algae develops rapidly in eutrophic waters. The water turns green. Such waters are useless' for human use because it is very difficult and expensive to remove the micro'scopic green plants. In due course of time, the entire mass of planktonic algae may die abrupty. The decaying organic matter causes bad tastes and odours. Further, the toxic chemicals released are fatal for fish, birds and other aquatic animals which causes stinking and repulsive smell. The decay and death of dense algae lead to biodegradation, cause sudden depletion of oxygen in the water, thereby destroying fish habitats and other desirable aquatic species. (2) The inability of the water body to replenish the oxygen results in suffocation and death of several aquatic organism. (3) The layer of slime produced restrict the penetration of light and prevent atmospheric regeneration of water. (4) The decaying algae, fish, Planktons and other organisms cause foul smell. (5) Anaerobic bacteria, e.g., Clostridium botulinum flourishing in such environment generated toxins which are fatal to livestock, birds, etc. (6) Pathogenic microbes, bacteria, viruses, protozoa which flourish under the prevailing anaerobic conditions may result in causing water-borne diseases such as diarrhoea, dysentery, typhoid, viral hepatitis, etc. (7) On depletion of oxygen level and on exhausting nitrate oxygen, sulphates are reduced as a last resort to yield hydrogen sulphide which results in bad smell and putrified taste of water. (8) Growth of very long filamentous weeds reduce the stream velocity and also trap solid particles along with them. In our country, Dal lake, Loktak lake, Hussain Sagar, etc., are choked due to aquatic weeds thus affecting aesthetics, productivity of fish, and utility of aquatic flora and recreational value. (9) Over fertilization results in over production of algae and diatoms which leads to clogging of filters in water treatment plants, retard water flow and affects water quality. (10) High population densities of hydrilla, potamogeton, myriphllum, ceratophyllus and other macrophytes render the water body unsuitable for any useful purpose. (11) During eutrophication, growth of very large populations of tubicid worms and midge chironomous plumosus, etc., occur, thereby causing aesthetic and economic problems for maintaining the waterbodies. (12)

Prolonged eutrophic conditions lead to "dystrophic" conditions when bog flora and large quantities of humic acid are produced while drastically reducing Plankton productivity.

(13) The filamentous algae are washed into beaches during storms and piled up. The rotting and stinking piles of organic matter render the beaches unsuitable for recreational uses such as swimming, boating and fishing.

26

Global Pollution and Environmental, Monitoring

Steps to Control Eutrophication (1)

Effective wastewater treatment and removal of nutrients like nitrogen and phosphorous before discharging the sewerage into waterbodies.

(2)

Controlling the recyeling of nutrients through harvest.

(3) (4) (5) (6)

Effective disposal of organic matter as sludge. Removal of the algal blooms by dredging. Developing phosphate-free detergents for domestic use. Adopting effective physico-hemical methods for removal of dissolved nutrients such as nitrogen and phosphorous compounds. Overcoming the temptation of over-fertilization.

(7) (8)

Controlling entrophication by applying algicides such as copper sulphate, chlorine, etc. on susceptible surface waterbodies.

DOD

4 PHYSICAL EXAMINATION OF WATER Introduction Physical Examination is the quick test and can be performed in the field to test the quality of water. Unpleasant or water with dirty smell is not liked by human beings and animals. Colourful water indicate the presence of organic matter and the presence of microorganisms. Turbidity of water is due to the presence of inorganic salts in water. Such water is not accepted by animals. Water sample is examined for physical parameter as per following manner.

Colour Pure water has pale blue-green tint in large volume. Colour of the water is examined in a Nessler Cylinder. Test artificial light. Colour should be confirmed from one foot depth. Examine 100 ml of water sample and compare with distilled water, water sample is examined by viewing vertically downward. Greenish colour of water is due to the unicellular algal flora. Yellow colour is due to the presence of organic matter or iron. Greenish yellow colour is due to presence of vegetations in water. It is advisable to filter or centrifuge the water sample to decide the colour property. Nature and colour density can be measured by Lovibondis Nessleriser. Hazen colour standards matched with Lovinbond Glasses and disc containing nine colour standards values are from 5 to O. Colour of the water provides the guideline regarding acceptance or nonacceptance of water.

Taste and Odour Taste and odour of the water is due to the presence of organic matter. The odour of water is usually related with taste. In case of fishy taste the odour is also fishy. Odours of water are caused by living and decaying aquatic organisms. Dissolution of gases like hydrogen sulphide, ammonia, chlorine etc. are also responsible for odour. Many algae also provide taste and odours to water sample. Discharge of chemical effluent into water also imparts taste and odours to water. Water sample with unpleasant taste and odour is rejected on aesthetic ground. Some colours and odours are found to be toxic. Water sample is examined for odour parameter as per the following method. Take 100 ml of water in stoppered conical flask. Sample is shaken for five minutes and then stopper is removed. It is smelled quickly to get good results. The odour test is also performed by warming the sample to about 40°C and then smelling and comparing with the smell of distilled water. Chlorinated water with phenoltraces gives very strong chloraphenol odour, water weeds such as chara, rotten hay and strew after decaying imparts fishy odour to water. Decomposition of

28

Global Pollution and Environmental Monitoring

~ewage and its contamination with well water imparts odour of hydrogen sulphide. Fungi browing on decaying vegetable matter will give a musty odour. Many fnorganic chemicals are also responsible to impart characteristic tastes. NaGI salt imparts salty taste to water. MnCI 2 , MgCI 2 , MgS0 4 , impart bitter tastes. Pleasant or palatable taste waters are acceptable. Unpleasant or unpalatable water is not acceptable. Stagnant, peaty and polluted waters are definitely unpalatable.

Turbidity Turbidity in a water may be due to either inorganic matter or organic matter. Turbidity indicates the pollution and such water never be used for drinking purposes. Turbidity in water is also caused by phytoplankton and other microscopic organism. Turbidity determination is possible by turbidometre. It works on the Tyndall effect. Here light is scattered by the particles present in the water. Turbidity is measure in JTU. As per WHO, Turbidity for drinking water must be always less than 5 JTU. Under normal condition turbidity of water is confirmed by following method. 100 ml of water sample taken in round bottom flask of 250 ml capacity. The sample is examined from oversight keeping a white paper of its background. Such sample is now compared with same amount of pure distilled water. Distilled water is normally of bright colour. Highly polluted water is dull, opalescent and distinctly turbid. Appearance of filamenous structures, muscle fibres indicates pollution. Turbid water is unfit for domestic purposes, food and beverage industries. Turbidity in water also retards the rate of photosynthesis in aquatic plants. Turbidity is removed by the method of coagulation and then filtration.

Organic Matter Presence of organic matter indicates the contamination of water with sewage water, vegetations or carcase. Such addition in water favours the growth of microorganisms making the water very dangerous. Seprophytic bacteria also grow In water containing organic matter. Presence of organic matter is tested by undertaking 50 ml of sample of water in a conical flask of 100 ml capacity and same amount of distilled water is taken in another flask. Both the samples are shaken for 5 minutes. The formation of froth or bubbles are carefully watched and compared with distilled water. The appearance of forth or bubbles if persists for some time shows the presence of organic matter. In case of distilled water the minute bubbles formed, break and disappear immediately.

Tentperature Constant turbidity with organic matter and high temperature such as 22°C to 3rC indicates serious pollution. Temperature should be recorded at the location where the sample is taken. It should be taken at different depth. Temperature of deep source is always higher than superficial water. To take proper temperature, sample bottle is placed in a thermos flask having good insulation. Temperature is recorded as soon as the sample is taken out. This indicates type and depth of source.

Reaction Acidic / Alkaline This test is important so as to safeguard the life of human and animals. Under normal conditions this test is performed by using red and blue litmus paper or pH papers. For accurate measurements pH metres are available. Sample is taken in two test tubes. Test the

Physical Examination of Water

29

two samples with litmus papers. When red litmus paper turns blue, it shows alkaline reaction and when blue litmus paper turns red, it shows acidic reaction. pH papers also indicate mode of reaction. The pH of water should be 7 to 8.5, i.e., slightly alkaline side. Highly acidic or alkaline water have action on water carrying pipes. It also provides abnormal taste of water and makes the water hard.

DOD

5 'CHEMICAL EXAMINATION OF WATER Introduction Chemical examination is a preliminary test for deciding the quality of water and its objective is to help the estimation of the quality parameters. Water containing toxic or hazardous chemicals can be straightaway eliminated. This examination also indicates about the pollution, particularly organic in nature. Such tests are carried out for the presence of non-metallic and metallic inpurities or contaminations.

Non-Metallic hnpurities or Contantinations (i) Chloride: In 5 ml of sample, a few drops of dilute silver nitrate solution is added. A white precipitate of silver chloride indicates the presence of chlorides. Roughly estimation of chloride can be done as, 10 ml of sample, add three drops of potassium chromate solution. Titrate the sample against silver nitrate solution till the samle develops brick red colour. The total content of chloride is given by the amount of AgN0 3 consumed by sample X100. (ii) Sulphate: In 5 ml of sample, few drops of dilute hydrochloric acid are added and then added 2N Barium chloride solution. A white precipitate of barium sulphate insoluble in dilute nitric acid is the result. Regular use of water containing sulphate leads to diarrhoea in human and scoor in animals. Maximum permissible level in case of drinking water is 250 ppm. (iii) Nitrite: In 5 ml of water sample, a few drops of sulphanilic acid is added and solution is well shaken. To this add few drops of alpha naphtha I amine solution. Solution is well agitated and kept for one or two minutes. A pink colour is developed indicating the presence of nitrite. Such water is unwholesome and dangerous. (iv) Nitrate: In 5 ml. of water sample add few drops of sulphanilic acid and solution is well shaken. Then add few drops of alpha naphthal amine solution. Agitate well. Then add a pinch of zinc dust and keep it for 5 to 10 minutes. Development of pink colour indicates the presence of nitrate in water. Excess of nitrate and excess of chloride indicate the sewage pollution. Presence of nitrite and nitrate also indicate the sewage pollution. Nitrate M.P.L. is 1.5 ppm. (v) Fluoride: In 5 ml of water sample, few drops of ferric chloride solution is added. Formation of white crystalline precipitate indicates the presence of fluorides. Fluoride is a potential toxin. Excess levels lead to dental dystrophy and constipation. M.P.L. is 1 ppm. Ferric chloride reagent is prepared by dissolving 10 gm of Ferric chloride in 50 to 60 ml of distilled water which makes the quantity 100 ml.

Chemical Examination of Water

31

(vi) Cyanide: In 5 ml of sample, add small amount of Ferrous sulphate. Boil the mixture for one minute and add little amount of 2N hydrochloric acid (dilute) and wait. Formation of blue precipitate indicates the presence of cyanide. (vii) Ammonia: In 5 ml of water sample add few drops of Nessler's reagent. Formation of brown or yellow or black colouration or precipitation indicates the presence of ammonia. Nessler's reagent is prepared as, (a) Dissolve 2.5 gm of HgCI2 and 2 grams of KI in 50 ml of distilled water. (b) Dissolve 10 gm of NaOH in 50 ml of distilled water. Store these two solutions in brown glass bottle and seal properly. Mix 1 + 1 Just before use. Maximum permissible level, i.e., M.P.L. of free ammonia is 0.05 ppm and for albuminoid ammonia it is 0.1 ppm. (viii) Total Solids: Weigh the empty crucible of 100 ml capacity. 50 ml of water sample is taken in crucible. Water is evaporated to dryness by using water bath. Residue is perfectly dried by placing crucible in hot air over above 120°C. Crucible is allowed to cool and weighed. If 50 ml of water sample used then: Total solid in ppm.

Wt. of solid x 1000 50 Hard water is unfit for drinking purpose. Hard waters have been found responsible for development of renal calculi, dyspesia and gastric disturbances. Its M.P.L. is 500 to 1500 ppm.

=

Qualitative Estimation of Pb, As, Cu, Fe (i) Lead: In 5 ml of water sample add few drops of potassium iodide. Formation of bright yellow preCipitate indicates the presence of lead. Precipitate of lead iodide disappears on boiling and reappears on cooling. Lead is cumulative poison. M.P.L. is 0.01 ppm. (ii) Arsenic: To the sample (5 ml) add few gms zinc metal powder or zinc metal granules and few ml. of concentrated sulphuric acid. A filter paper containing few crystals of silver nitrate are placed over the tube. Silver nitrate crystals turn yellow and then black due the liberation of arsine (ASH 3 ) gas from arsenic. Arsenic is a cumulative poison. Excess dose is intestinal irritant and nervous depressant. Drinking water should not contain even in traces . .(iii) Copper: In 5 ml of water sample add few drops of potassium ferro cyanide solution. Chocolate red coloured preCipitate indicate the presence of copper. M.P.L. is 3 ppm. (iv) Iron: In 5 ml of water sample add few drops of potassium ferrocyanide. Formation of blue colour or precipitate indicate the presence of iron. M.P.L. is 0.3 ppm.

Reagent Required for Nitrites (1) Sulphanilic Acid: Completely dissolve 1 gm of sulphanilic acid in 70 ml of hot distilled water cool, add 20 ml of 12N Hydrochloric acid and then dilute the amount to 100 ml with distilled water. (2) Naphthylamine Hydrochloride Reagent: 0.60 gm of naphthylamine hydrochloride is dissolved in distilled water. Acidify the solution by adding 1 ml of 12N hydrochloric acid. Dilute the amount to 100 ml with distilled water. Store in a cool place. Filter before use.

32

Global Pollution and Environmental Monitoring

Reagents Required for Iron and Copper Dissolve 9 gms of potassium ferrocyanide salt in 100 ml of distilled water.

Reagent for Lead Dissolve 10 gms of potassium iodide in 100 ml of distilled water.

Reagent Required for Chloride (1) (2)

Silver Nitrate Solution: Dissolve 5 gms of Silver Nitrate in one litre of dis~illed water. Potassium Chromate Solution: 5 gm of Potassium Chromate is dissolved in 100 ml of pure distilled water.

000

,.:

6 PHYSICO CHEMICAL ANALYSIS OF WATER Introduction The significance of chemical analysis depends to a large extent on the sampling programme. Samples should be collected as per the sampling procedure and preservation of the sample is also equally important. Preservation is essential to protect water samples from changes in composition and deterioration with aging due to various internal reactions. The optimum sample holding time ranges from a zero for parameters like pH, temperature and D.O., to one week for metals.

Santple Preservation It is not possible to protect a sample from change in composition. However, various additives and treatment techniques can be minimized sample deteriotion. Table 6.1: Preservatives and Preservation Methods used with Water Samples

Preservation or Technique Used Nitric acid Sulphuric acid

Sodium hydroxide Mercuric chloride

Cooling (4°C) Chemical reaction

Effect on Sample Keeps metals in solution Bactericide Formation of sulfates with volatile bases Formation of sodium salts with volatile acids Bactericide

Inhibition of bacteria, retention of volatile material Fix a particular constituent

Type of Sample for which the Method is Employed Metal-containing samples. Biodegradable samples including organic carbon, COD, oil, and grease Amides, ammonia volatile organic acids, cyanides Samples containing various forms of nitrogen or phosphorus, some biodegradable organics Micro-organism; acidity; alkalinity; BAD, organic C,P, and N; Colour; odour Dissolved oxygen determined by the Winkler method.

34

Global Pollution and Environmental Monitoring

Technique - Methodology and Paratneters (1) pH It is the scale of acidity which defines the medium of the sample. pH is the negative Log 10 of the hydrogen ion concentration. pH measurement is possible due to litmus paper, various pH papers. But the correct pH measurement is with pH meter. Method (1) Calibrate the pH meter with two standard buffer solutions of pH 4.0 and 9.2. (2) Buffers of different pH values are prepared in the laboratory as per following manner: Dissolve 10.2 gms of potassium hydrogenphthalate in water to prepare one litre of buffer solution. This buffer solution has pH 4 at room temperature. Dissolve 3.40 gms of KH 2P0 4 and 4.45 gms of Na2HP04.2H20 in distilled water and make the volume one litre. This buffer has pH 7 at room temperature. Dissolve 3.81 gms of Na2B407.1 OH 20 in water to prepare one litre of buffer solution. pH is 9.2 at room temperature. (3) Rinse the combined electrode thoroughly with deionized or distilled water and carefully wipe with filter or tissue paper. (4) Dip the electrode into sample solution, swirl the solution and wait up to 1 minute for constant reading. This is essentially a Nernst concentration cell with potentials controlled by the activities of W ions on either side of very thin glass membrane. RT aH(sarT'4'le) E = constant + -In -~~ nF aH(standard) E = constant + 0.058 pH (at 20°C)

Ag/AgCI

Reference----+--~...

Electroode KCI solution

---1--.-

Porous Plug _.--'J~~--,/

I~~=- HCI or buffer

-:.n

Glass Membrane

Fig. 6.1 A combined glass/Ag-AgCI electrode

(2) Conductivity Conductivity is measured by conductivity meter with dip-type cell. Conductivity is measured in terms of specific conductance, i.e., K. The instrument and cell are calibrated by using 0.0005 M KCI solution having conductivity 654~ Mho cm- 1 .

35

Physico Chemical Analysis of Water Specific Conductance

1 A K=-xR 1 Here R is the observed resistance of a column of electrolyte 1 cm long and cross sectional area A cm 2 . Note the temperature of the sample and find out the factor following table to convert the values at 25°C.

Temp. °C.

3 4 5 6 7 8 9 10 11 12

Factor

1.62 1.58 1.54 1.50 1.46 1.42 1.39 1.36 1.33 1.30

Temp.oC.

Factor

Temp.oC.

13 14 15 16 17 18 19 20 21

1.27 1.24 1.21 1.19 1.16 1.14 1.12 1.10 1.08

21 24 23 24 25 26 27 28 29 30

Factor

1.08 1.06 1.04 1.02 1.00 0.98 0.97 0.93 0.93 0.92

Conductivity=observed conductance x cell constant x temp. factor at 25°C.

(3)

Total Solids (TS)

Total solids are determined as the residue left after evaporation of the unfiltered water sample. (i) Take a clean and dry evaporating dish of 100 ml capacity. Weigh it accurately. Let the weight of dry crucible be "b" gm. (ii) Now take 100 ml unfiltered sample of water in evaporating dish. Evaporate the sample by placing dish on water bath or hot plate having temperature not more that 98°C. (iii) After this residue redried at 105°C in an electric oven for one hour cool it and weigh the dish. Let the Weight be "a" gm. (a-b)x106 . Total solids Mg/L = -'------'-v Here a = Final weight of the dish in gram. b = Initial weight of the dish in gram. v = Volume of water sample taken in mililitre.

(4)

Total Dissolved Solids (TDS)

Total Dissolved Solids are estimated as the residue left after the evaporation of the filtered water sample. (1) Take clean and dry evaporation dish of 100 ml capacity. Weigh it accurately. Let the weight be "b" gm. (2) Now take 100 ml of filtered sample of water in dish. Evaporate the sample by placing the dish on water bath or hot plate having temperature not more than 98°C.

Global Pollution and Environmental Monitoring

36

(3) Heat the residue at 105°C in an electric oven for one hour, cool the dish and weight it. Let the weight be "a." TDS Mg/L = (a -b)x10

6

v Here a = Final weight of dish. b = Initial weight of dish. v = Volume of sample.

(5)

Total Suspended Solids (TSS)

Determination of suspended solids is possible by taking the difference between the total dissolved solids. TSS = TS - TDS

(6)

Acidity

Acidity signifies the presence of mineral acids present in the water. Acidity is determined by titrating sample with strong base like NaOH using methyl orange or phenolphthalein as an indicator. The titration method is suitable mainly for colourless samples. Requirements

(1) Sodium hydroxide, O.05N: Prepare 0.1 N NaOH by dissolving 4.0 gm of NaOH in distilled water and make the vOlume one litre.Now dilute 5 ml of 0.1 N NaOH to one litre with distilled water. (2) Methyl orange indication: Dissolve 0.5 gm of Methy orange in one IitrQ of distilled water. (3) Phenolphthalein indicator: Dissolve 0.05 gm of phenolphthalein in 50 ml of absolute alcohol and then add 50 ml of distilled water. Method Now take 100 ml of sample in the titration flask and add 3 drops of methyl orange indicator. If the solution turns yellow it indicates the absence of methyl orange acidity. If the sample turns pink then titrate it with 0.05N NaOH. End point is pink to yellow. Let the reading be A. Now add few drops of the phenolphthalein indicator to the same sample and titrate further with 0.05N NaOH until solution acquires pink colour. Let the reading be B. Calculations Methyl orange acidity

mg/L as CaC0 3

=

AxN of NaOH x 1000 x 50 Volume of sample

Phenolphthalein acidity mg/L as CaC0 3 =

BxN of NaOH x 1000 x 50 Volume of sample

Total Acidity at pH 8.3

Physico Chemical Analysis of Water mg/L as CaC0 3 =

(7)

37

(AxB) x N of NaOH x 1000 x 50 Volume of sample

Alkalinity

Total alkanity of water samples is measured in terms of volume of sample required to neutralize the strong acid. Total alkanity is estimated by titrating the sample with strong acid like HCI or H2 S0 4 (pH 8.3) using phenolphthalein as indicator and further to pH between 4.2 to 5.4 with methyl orange. The alkalinity by using phenolphthalein indicator is called phenolphthalein alkalinity and symbolically shown as PA. Alkalinity by using methyl orange is called total alkalinity and represented as TA. Requirements

(1) Phenolphthalein indicator: Dissolve 0.5 gm of indicator in 50 ml of absolute alcohol and then add 50 ml of distilled water. (2) Methyl orange: Dissolve 0.5 gm of indicator in 100 ml of distilled water. (3) Sodium Carbonate solution O.1N: Dissolve 5.3 gms of a Na2C03 in distilled water and make the volume to one litre. (4) Hydrochloric acid 0.1 N: Add 83.4 ml of 12N HCI in water and make quantity one litre. It gives 1N HCI. Now.dilute it ten times to give 0.1N HCI (i.e., 10 to 100 or 100 to 1000 ml.) Now standardise it against sodium carbonate solution to know exact normality of HCI. Method

(1) Take 100 ml of sample in the titration flask and add 3-4 drops of phenolphthalein indicator. (2) Solution turns pink. Titrate it against standard solution of HCI until the disappearance of pink colour. Let the reading be A. (3) Now add 3-4 drops of methyl orange indicator to the same sample and continue the titration further to obtain yellow colour. Let the reading be B. (If the solution remains colourless by adding phenolphthalein it indicates PA = O. In such a case alkalinity is calculated by the use of methyl orange indicator.) Calculation

Phenolphthalein alkalinity, i.e., PA as CaC0 3 mg/L =

AxN of HCI x 1000 x 50 Volume of sample

Total Alkalinity, i.e., TA as CaC0 3 mg/L

HCI x 1000 x 50 = BxNVolume of sample

Alkalinity is due to hydroxyl ions, carbonate ions or bicarbonate ions. The following table provides the necessary information.

38

Global Pollution and Environmental Monitoring Result

OH alkalinity

C03 alkalinity

HC0 3 alkalinity

T 2P-T a a a

a 2(T-P) 2P 2P a

a a a T-2P aT

P=T P> 1/2 T -p = 1/2T P < ,1/2 T p=o

Here P stands for phenolphthalein alkalinity T = Total alkalinity

(8)

Hardness

Hardnes.s of water is not pollution parameter but indicates water quality. Hardness is due to presence of Ca++ and Mg++ ions in water. It is measured in terms of CaC0 3 Mg/L. Requirements (1) Buffer solution: Dissolve 68 gms NH 4 CI in 540 ml of concentrated ammonia and make the solution 1 litre with distilled water. This is called ammonia buffer with pH = 10. (2) Eriochrome black indicator: (i) Mix 1 gm of eriochrome black T with 100 gm pure NaCI and grind it properly. Use a pinch of indicator for each titration. (ii) 1 gm of eriochrome black T is dissolved in 75 ml of teriethanol amine and then add 25 ml of ethyl alcohol. Shake it well. Use 3 drops of indicator for each titration. (3) EDTA solution O.01M: Dissolve 3.723 gm. of disodium salt of EDTA in distilled

water and make

t~~olume

to 1 litre with distilled water. Store in polyethylene bottle.

Method (1) Take 50 ml of sample in a titration flask. (2) Add 5 ml of buffer solution. (3) Add in pinch of eriochrome black T indicator or 3 drops of liquid indicator, solution acquires wine red colour. (4) Titrate the contents against 0.01M EDTA solution. At the end point colour of the solution changes from wine red sky blue. Calculation 1 ml of 0.01M EDTA

= 1.0 mg CaC0 3

or Hardness as CaC0 3 mg/L =

(9)

Volume of EDTA required x 1000 ml of sample taken

Dissolved Oxygen (DO)

Analysis of DO plays a key role in water pollution control activities and water treatment process control. The manganese sulphate reacts with KOH or NaOH to form precipitate of manganese hydroxide which turns brown due to presence of oxygen. In strong acidic medium, Mn ions get reduced by iodide equivalent to the original concentration of oxygen in the sample. The liberated iodine is titrated with thiosulphate by starch indicator. This is called Winkler Method.

39

Physico Chemical Analysis of Water 1 Mn2+ + - O2 + 20H ~ Mn02

2

t

+ H20

Mn02 + 21- + 4H- ~ Mn2+ + 12 + 2H 20 12 + s20l- ~ 21 n + S40 6 25 ml of 0.025M Na2S203 = 1 mg - (D. 0.) Interference of oxidents can be eliminated by adding NaH 3. Requirements (1) Sodium thosulphate: Dissolve 24.82 gms of Na2S203. 5H 20 in water and make the volume to one litre with distilled water. This is 0.1 N Na2S203. 5H 20 solution. Now 250 ml of this is diluted to one litre with distilled water. (2) Alkaline azide solution: 50 gm of NaOH +13.5 gms Nal and 1 gm NaN 2 diluted to one litre. (3) Manganese sulphate solution 40%: Dissolve 80 gms of MnS04. 4H 20 in 200 ml of distilled water and filter. (4) Starch indicator: Dissolve 1 gram of starch in 100 ml warm distilled water and add few drops of formeldeyde solution as preservative. (5) Conc.H 2S0 4 (6) 40% KF (to mask Fe 3+) 2 ml 36% MnS04 + 2 ml alkaline Iodide. Method (1) Take 100 ml of water sample in 250 ml bottle. Add 2 ml of 40% MnS04 and 2 ml of alkaline iodide-azide solution. (2) Shake the content well. Bottle contains brown coloured precipitate. (3) Now add few ml of Conc. H2S0 4 to dissolve the precipitate. (4) Now add drops of starch indicator. Content acquires dark blue colour. (5) Titrate the content with sodium thiosulfate. End point disappearance of blue colour. Let reading be A. Calculation DO mg/L

=

AxO.025xax1000 V

Here V is the volume of sample taken.

(10) Biochemical Oxygen Demand (BOD) The degree of microbially mediated O2 consumption by organic pollutants in water is k.nown as Biochemical Oxygen Demand. This parameter by the quantity of O2 utilised by suitable aquatic micro-organism during 5 days' period. Requirements (1) Sodium sulphite O.025N: Dissolve 1.575 gms Na2S03 in distilled water and make the volume to 1 litre.

40

Global Pollution and Environmental Monitoring

(2) Ferric Chloride: Dissolve 0.25 gm FeCI 3 ,6H 20 in distilled water and make to volume to 1 litre. (3) Calcium Chloride: Dissolve 27.5 gms of anhydrous CaCI 2 in distilled water to prepare one litre with water. (4) Magnesium Sulphate: Dissolve 22.5 gms of MgS0 4,7H 20 in distilled water and make the volume to one litre with water. Phosphate Buffer Dissolve each 8.5 gms. of KH 2P0 4, 21.75 gms of Na2HP04 and 1.7 gms of NH 4CI and make one litre volume with water.

Method (1) Prepare aerated water in a glass container by bubbling the compressed air in distilled water for about 30 minutes. (2) Add 1 ml each of phosphate buffer, magnesium sulphate. calcium chloride and ferric chloride for each litre of dilution water mix properly. (3) Neutralize the sample to pH =7 by using 1N NaOH or 1N Hel or 1N H2S04 depending on the initial medium or pH. (4) Here the DO in the sample is likely to be exhausted, it is therefore necessary to prepare suitable dilution of the sample according to the expected BOD range. (Refer the table). (5) Made dilutions in a large container. Mix to contents thoroughly. Fill the contents in 2 BOD bottles. (6) Keep one B.O.D. bottle in BOD incubetor at 20°C for 5 days and determine to DO . level in other set immediately. (7) Now determine the D.O. level of sample, immediately after the completion of 5 days incubation. (8) Similarly for blank, take 2 BOD boUle for dilution of water. In one determine DO level and in other incubate with sample to determine DO after 5 days.

Dilutions as per B.O.D. Range (A.P.H.A. reference)

Range of BOD

Dilution %

o

6

4

12 20 60 120 300

10 20 40 100 200 400

No dilution

50

20 10 5 2

6

1200 0.5

1000 2000

3000 6000

0.2 0.1

Physico Chemical Analysis of Water

41

Method of Calculations B.O.D. = (0 0 -0 5 ) x dilution factor Do = Initial D. 0 level 0 5 = 0.0 level after 5 days One can use simple relation as 5 ml of 0.025 N Na2S203 = 1 mg L-1 0.0 (BOD Values are important as it shows survival of fish and growth of dangerous bacteria. It is more scientific than BOD. There is no necessity to correlate COD with BOD.)

(11) Chemical Oxygen Demand (COD) Chemical oxygen demand is the oxygen required by the organic substances in water system to oxidise them by a strong oxidising agent. This is a satisfactory method of determining the organic lot of a water body. The method is based on the oxidation of the matter from water sample in the presence of conc. H2S0 4 or 50% H2S0 4. The amount of unreached oxidant like K2Cr207 is then determined by the titration with std. Mohr's salt solution. Silver sulphate catalyse the oxidation of straight chain aliphatic compounds, aromatic hydrocarbons and pyridine. Mercuric sulphate avoids the interference of chlorides.

Reagents (a) K2Cr207 Solution 0.25N: Dissolve 12.300 gms of A.R. K2Cr207 in distilled water and make the volume one litre. (b) K2Cr207 0.025N: Dilute 0.25N K2Cr207 10 times (100 to 1000 ml). (c) Ferrous ammonium sulphate 0.1N: Dissolve 39.2 gms of ferrous ammonium sulphate in little amount of water then add 20 ml of conc. H2S0 4 to increase the solubility and make the volume one litre. (d) Ferrous ammonium sulphate 0.01 N: Dilute 0.1 N Ferrous ammonium sulphate 10 times (100 to 1000 ml). (e) Ferroin indicator: 1.485 gm of 1.10 phenonthroline + 0.695 gm of Ferrous Sulphate and dilute to make 100 ml solution. (f) 18N H2 S0 4, i.e., 50% H2S0 4. (g) Silver sulphate (Ag 2S0 4 solid). (h) Mercuric sulphate (HgS04 solid).

Method (1) Take 15 to 20 ml of sample in a 250 ml of COD flask (Round bottom flask with condenser). (2) Now add 25 ml. of 0.25N K2Cr207, 30 ml of sulphuric acid, 1 gm of A9 2 S0 4 and 1 gm of HgS04 (3) Now reflux the whole amount for 2 hrs. (4) Remove the flask, cool and distilled water to make final volume to about 150 ml.

42

Global Pollution and Environmental Monitoring

(5) Add 3 to 4 drops of Ferroin indicator. Solution acquires green colour. Titrate the solution until solution acquired red colour. (6) Run a Bank with distilled water using same amount of chemicals. Calculation

COD mg/L

=

(B-A) x NofFAS x 1000 x 8 ml of sample

Here B = volume of titrant with blank. A = volume of titrant with sample. Note: In case of COD less than 50 mg/L, add 10 ml of 0.025N K2Cr207' If COD more than 50 mg/L then use 0.25N K2Cr207.

(12) Chlorides Chlorides are available in all types of waters. In natural Fresh water amount of Chloride is generally very low. Chlorides are discharged into water through domestic sewage. Chloride is estimated by Mohr's method. Silver nitrate reacts with Chloride to form very slightly soluble white precipitate of AgCI. When all the chlorides precipitated as AgCI the excess drops of AgN0 3 reacts with K2Cr04 to form reddish brown coloured ppt of A92Cr04' Appearance of reddish brown tinge is the end point. Reagnets

(a) Silver Nitrate O.02N: Dissolve 3.400 gms of A.A. AgN0 3 and distilled water to make one litre of solution and keep the solution in amber coloured bottle. (b) Potassium Chromate 5%: Dissolve 5 gms of K2Cr07 in 100 ml of distilled water. Procedure

(1) Take 50 ml of water sample in 250 ml conical flask and add 2 ml of K2Cr04 solution. (2) Now titrate the solution against 0.02N AgN0 3 . End pOint is appearance of red tinge. Calculation

Chlorides, mg/L

=

AxN AgN0 3 x 1000 x 35.5 V

Here A = Volume of AgN0 3 . V = Volume of water sample or 1 ml of 0.02N AgN0 3 = 1 mg CI Level WHO standard for drinking water is 500 mg/L.

(13) Residual Chlorine It is necessary to check the effectiveness of chlorination of raw water for public water supply through estimation of free or residual Chlorine from water sample.

Physico Chemical Analysis of Water

43

Reagents

(a) KI Solid. (b) Glacial Acetric Acid. (c) Sodium thiosulfate 0.025N : Dissolve 24.8 gms of Na2S203 5H 20 in distilled water and make the volume one litre. This is 0.1 N Na2S203' Now dilute the solution 4 times (250 ml to 1000 ml). It gives 0.025N Na2S303' (d) Starch indicator. Procedure

(1) Take 50 ml of 100 ml of water sample and add 5 ml of acetic acid. pH of the solution should be between 3 to 4. (2) Add 1 to 1.5 gm of KI solid and mix thoroughly and keep the stopper bottle in dark. (3) Add starch, solution turns blue. Titrate it against 0.025N Na2S203 till blue colour just disappears. Let the reading be A. Residual Chlorine, mg/L

=

A x 0.025 x 1000 x 35.5 Volume of sample

or use the relation 1 ml of 0.025N Na2S203 = 0.4 mg. CI 2

(14) Oil and Grease Oil and grease can be estimated by extracting it in ether which is insoluble in water and can be separated by separating funnel. The residue after evaporation of petroleum ether will yield the oil grease. Reagents

(a) Sulphuric Acid 1:2: Mix one part of conc. H2S0 4 with two parts of water. (b) Petroleum Ether: Boiling range 40°C-60°C. (c) Ethyl Alcohol. Procedure

(1) Take a 100 ml of water sample in a separating funnel. (2) Add 10 ml (1 :2) H2S0 4 and 40 ml of ether to the sample. (3) Shake well and add small amount ethyl alcohol. Keep it for 5 to 10 minutes. Solution will distribute in two distinct layers. (4) Discard lower layer of sample through separating funnel. (5) Take a previously weighed dish or clean beaker and add petroleum ether layer from separating funnel. Filter if necessary. (6) Evaporate the petroleum ether on a water bath and take final weigh of dish or beaker after cooling in dessicator. Note that never heat petroleum ether on flame. Let first weight of dish or breaker is B. And final weight is A.

Global Pollution and Environmental Monitoring

44 Calculation Oil and grease, mg/L =

S-Ax106 V

Where V is the volume of sample.

(15) Calciunl Calcium is estimated by the use of EDTA as titrant and murexide as indicator. Requirements

(1) EDTA Solution O.01M: Dissolve 3.723 gms of disodium salt of EDTA in distilled water and make the volume to one litre. Store in polyethylene bottle. (2) Murexide Indicator: Mix 0.2 gms of ammonium purporet with 100 gams of pure NaCI and grind it properly. (3) Sodium hydroxide 1N: Dissolve 40 gms of NaOH in distilled water and make the volume to 1 litre with distilled water. Method (1) Take 50 ml water in titration flask. (2) Now add 2 ml of 1N NaOH solution. (3) Add pinch (200 mg) of murexide indicator. Shake it well. Content acquires pink colour. (4) Now titrate the content against 0.01 M EDTA. End point is pink colour changes to purple. Calculation Calcium, mg/L

Ax 40.08 x 1000 =----ml of sample

Here, A is the volume of EDTA required fo titration.

(16) Magnesiunl The value of Mg++ is determined by subtracting the value of calcium from total of Ca++ and Mg++. Now, estimate the amount of Ca++ by above method. Let the reading be A. {S - A)x40.08x1000 . Mg++ mg/L - ~-..:...----­ .. - ml of sample x 1.645 Mg, mg/L = Total hardness - Calcium hardness x 0.244 Where calcium hardness is Ca++ mg/L x 2.497

(17) Hydrogen Sulphide It is estimated by using Cadmium Chloride solution. Cadmium Chloride with H2 S from sample forms a precipitate. This precipitate set dissolve in acid medium in the presence of excess of iodine. In this process sulphide is oxidized to sulphur. The remaining iodine is titrated against Sodium thin-sulphate using as an internal indicator.

45

Physico Chemical Analysis of Water Requirements

(1) Sodium thiosulfate, O.25N: Dissolve 24.82 gm of Na2S203, 5H 20 in distilled water and make the volume of 1 litre with distilled water. Now dilute 250 ml of above solution to 1000 ml with distilled water. (2) Cadmium Chloride, 2%: Dissolve 2.0 gm of CdCI 2 100 ml of distilled water. (3) Iodine solution O.025N: Dissolve 3.17 gms of Iodine crystals in 50 ml of distilled water in the presence of 20 gms of potassium Iodide. After dissolution make the volume one litre with distilled water. Standardize the solution with sodium thiosulfate by using Starch indicator. (4) Hydrochloric acid 4N: Dilute concentrated HCI three times.

(5) Starch solution: Dissolve 1 gm of starch in 100 ml of distilled water and heat. Cool it and add few drops of formaldehyde soil,ltion as preservative. Method (1) (2) (3) (4) then add

Fill the stoppered bottled with sample. Avoid bubbling. Add 1 ml of CdCI 2 and shake well. Keep the bottle to settle down the yellow precipitate of CdS (At least 24 hrs.) Decant the supernatant liquid and dissolve the precipitate in 5 ml of 4N HCI and 5 ml 0.025N iodine solution.

(5) Now add few ml of starch solution.Titrate the content with 0.025N Na2S203 till dark blue colour totally vanishes. Disappearance of blue colour is the end point. (6) Perform the experiment by taking some amount of distilled water and some amount of chemicals. It is called as blank reading. Now let blank reading be 8 and back or main reading be A then, H2 S, mg/L

(8 - A)x 0.025 x 1000 x 17 = -'------''-------

ml of sample

Water out

Gas Dispersion Tube

Suction

Test Tube

(38 mm x 200 mm)

Suction Flask

Heating Mantle

Fig. 6.2 Cyanide Distillation Apparatus

46

Global Pollution and Environmental Monitoring

(18) Esthnation of Cyanide Method

(1) Take 250 ml of water sample in a distillation flask in a fume chamber. Add 50 ml of 18N H2S0 4 and 20 ml of 50% MgCI 2 .6H 20 and reflux for one hour. (2) Collect the HCN gas in 300 ml of 1N NaOH in glass washer. Now measure the CN by titration method. . Take an aliquot of the distillate, to this add 0.5 ml to 1 ml of 0.0 2% dimethylamine obenzalrhodine solution in acetone and titrate with 0.02N AgN0 3 till colour changes from canary yellow to a salmon blue. Compare against a blank under the same condition. This method is suitable if the concentration of CN exceeds 1 mg/L-1.

(19) Iron Estimation of iron is possible by colorimetrically. Ferrous iron forms orange red coloured complex with phenonthroline. Colour intensity is proportional to concentration of iron. (1) Phenonthroline solution: Dissolve 100 mg of 1-10 phenonthroline monohydrate in 100 ml distilled water by thorough stirring. Heat the solution up to 80°C by placing container on water bath. (2) Hydroxylamine hydrochloride solution: Dissolve 10 gm solid HAH in 100 ml of distilled water. Shake well. (3) Ammonium acetate buffer solution: Dissolve 250 gms of solid and make the volume to one litre with distilled water. (4) Stock solution of iron: Dissolve 1.404 gms of Ferrous ammonium sulphate in 150 ml of water by adding about 20 ml of concentrated sulphuric acid. Make the volume to one litre. (5) Standard iron solution 10 mg FelL: Take 50 ml of stock solution and dilute it to 100 ml with distilled water. Method

(1) Take 50 ml of sample of water containing iron in 250 ml conical flask. (2) Add 2 ml of conc. HCI and 1 ml of Hydroxylamine hydrochloride solution. (3) Boil the solution to 25-30 ml (reduction in volume.) (4) Cool and add 10 ml ammonium acetate buffer and 2 ml of phenolthroline solution. Solution acquires orange red colour. (5) Dilute it to 100 ml and after 10 minutes take the reading at 510 nm on spectrophotometer. (6) Prepare a standard curve in the range of 1 to 4 mg/L of iron by using various dilutions of standard solution. (7) Calculate the concentration of Fe directly from standard curve.

(20) Chro:ntiu:nt Hexavalent chromium (Cr [vi]) reacts with diphenylcarbazide in acid medium to form a red violet colour which is measured at 540 nm.

Physico Chemical Analysis of Water

47

Method (1) Take 50 ml of water sample: (10-100 Ilg Cr) in conical flask, add 5 ml of conc. HN0 3 and 10 ml 30% H2 0 2 and evaporate on a steam bath. Again add 5 ml of conc. HN0 3 and 10 ml conc. H2 S0 4 and evaporate to dense white fumes of S03. Repeat the evaporation with HN0 3 - H2 S0 4. Cool to room temperature. Slowly dilute to 50 ml with deionized water. Filter through sintered glass crucible and transfer the filtrate and washing to 100 ml volumetric flask. Make the volume to 100 ml with distilled water. (2) Take an aliquot in 150 ml conical flask. (3) Neutralize with NH 40H till alkaline using methyl orange indicator and then add 1:1 H2 S0 4 till acidic. (4) Now add 4% KMn04 solution till dark red colour persists. Boil the solution for 2 minutes. (5) Add 2 ml NaN 3 (0.5%) solution and boil till the colour fades completely. Cool and add 0.25 ml H3P0 4. (6) Transfer to a 100 ml volumetric flask. Dilute it to 100 ml with distilled water. (7) Add 2 ml diphenyl carbazide solution (0.5% in acetone) and mix thoroughly. Allow to stand for 10 minutes. (8) Measure the absorbance at 540 nm against a reagent blank carried through same procedure.

(21) Copper Estimation of copper is done by using neocuproine (2,9 dimethyl 1, 10 phenanthroline) which forms yellow solution. Spectrophotometric measurement at 457 nm. This method is valid up to 0.2 mg Cu/25 ml. Method (1) Take 100 ml sample: (20-200 Ilg Cu) in 250 ml in beaker. Add 1 ml conc. H2S0 4 and 5 ml conc. HN0 3 heat to remove S03 fumes. (2) Further add 5 ml conc. HN0 3 till the solution becomes colourless. (3) Cool and add 75 to 80 ml of distilled water and boil. Filter into 100 ml measuring flask. Make the volume 100 ml. (4) Pipette out 50 ml in separating funnel and add 50 ml distilled water. (5) Add 5 ml of hydroxyl amine hydrochloride (1 %), 10 ml (4% sodium citrate solutions and mix properly. Adjust the pH 4 to 6 and 10 ml neocuproine reagent (100 mg/100 ml) and shake for 30 seconds. (6) Withdraw CHCI 3, extract into the volumetric flask. Dilute these combined extracts upto 25 ml with CH 30H and shake well. (7) Measure the absorbance at 450-460 nm against reagent blank carried through the same procedure.

Global Pollution and Environmental Monitoring

48

(22) Merc~ry Estimation of mercury is possible by the use of mercury analyser. Requirements

(1) Stock solution of mercury: (1 ml = 1 mg of Hg). Dissolve 1.354 gm of mercuric chloride in 800 ml of distilled water and then add 2 ml of conc. HN0 3 and make the volume to one litre. (2) Standard Mercury Solution: Prepare the solution in range of 0 to 10 Ilg/L by diluting stock solution with distilled water. (3) Conc. HN0 3 . (4) Potassium per sulphate solution: Dissolve 50 gm of K2 S 2 0 a in 300 ml of distilled water and make the volume to one litre. (5) KMn04 Solution: Dissolve 50 gm of KMn04 in 300 ml of distilled water to make the volume one litre. (6) Sodium Chloride-hydroxylamine Sulphate solution: Dissolve 120 gm of NaCI and 120 gm of (NH 20HhH 2 S0 4 in distilled water to make the volume one litre. (7) Stennous Chloride solution: Dissolve 100 gm SnCI 2 in distilled water in the presence 13 ml of conc. HCI and make the volume to one litre. (8) Conc.H 2 S04 Hg Light

sO~-----------------------

KMn04 Trap

Alkali Trap

Absorptin Cell

-----0

Acid Trap

Ma~netic

Stirrer

R1 R2 R3 R4

to to to to

Detector

purify air generate Hg vapour absorb acid vapour absorb moisture

Rs to absorb Hg vapour

Fig. 6.3 Vapour Generator System of Mercury Analyser

KMn04 Trap

Physico Chemical Analysis of Water

49

Method (1) Arrange the mercury analyzer as per the instruction of working. (2) Take 100 ml sample of water in the reaction flask. (3) Add 5 ml conc. H2 S0 2 and 3 ml of conc. HN0 3 · (4) Add 15 ml conc. H2 S0 4 solution and after 15 minutes add"8 ml of K2 S2 0 a solution. Aillow the solution to warm on water bath for 2hrs (Don't Boil). (5) Now add NaCI hydroxylamine sulphate solution to destroy the colour of KMn04 (Addition until pink colour of KMn04 disappears.) (6) Add quickly 5 ml SnCI 2 and attach reaction flask to creation apparatus of the mercury analyser and record the reading. (7) Adopting the same procedure construct the standard curve using Hg solution In the range of 0 to 5 /-lg/L. Find out the concentration of Hg from the sample by the use of std. curve.

(23) Carbondioxide Free CO 2 from water sample can be determined by titrating sample with NaOH by using phenolphthalein as an indicator. Requirements NaOH 0.05N First of all prepare 1N NaOH by dissolving 40 gms of NaOH in distilled water. Make the volume to one litre. Now dilute 50 ml of 1N NaOH to one litre with water to make 0.05N NaOH. (2) Phenolphthalein Indicator. Use usual method. Method (1) Take 100 ml of water sample in titration flask and add 4 drops of phenolphthalein as indicator. By adding if the sample acquires pink colour then it indicates the abse'nce of CO 2 in water. If the sample remains colourless then titrate with 0.05N NaOH. Addition of NaOH pink colour appears. Calculations Free CO 2 mg/L

(ml x N) NaOH x 1000 x 44 = -'-------'-------Mlofsample

(24) Tannin and Lignin Waste Products of paper industry contains tannin and lignin. It imparts reddish colour to the water. The hydroxy group OH reacts with phosphomolybdotungstic acid to form a blue colour which can be measured at 600 nm. Tannin and lignin upto 9 ppm can be estimated by this method.

50

Global Pollution and Environmental Monitoring

Reagents

(1)

Phosphomolybdtungstic acid: 100 gm of Na2W04, 2H 20 + 20 gm of phosphomolybdic acid in 700 ml distilled water + 50 ml H3P0 4 +100 ml conc. HCI refluxed for 10 hours and diluted to one litre.

(2)

Carbonate tartarate reagent: 200 gm Na2C03 +12 gm sodium tartarate in 750 ml hot distilled water diluted to one litre.

Method Take 50 ml of sample in 100 ml beaker. Add 2 ml of phosphomolybdotungstic acid and 10 ml of carbonate tartarated reagent. Allow the colour to develop for 15 minutes. Measure the colour at 660 nm Spectrophotometrically.

(25) Pesticides Sample is extracted properly with 15% ethyl ether in hexane. Ether extracts are evaporated on a steam bath to small volume, i.e., 2, 3 ml and diluted with hexane to 5 ml. 5 III is injected into the gas chromatographic column at 180°C with microsyinge using Ar/CH 4 as the carrier gas at 60 mllmin. Pesticides get vapourized. They move through the column at different rates and get detected by electron capture detector. The chromatogram is given below:

(])

"0

.§ Cl.

W

a. (])

I

15

10

5

o

Retention, Time, Min

Fig. 6.4 Gas chromatographic procedure for organochlorine pesticides: column packing 5% OV-210, carrier Ar\CH 4 at 70 mllmin-1 ; Column temperature, 180°C; detector electron capture. Glass column 180 cm 4 mn (iod), solid support Gas-chrom Q (100\128 mesh).

51

Physico Chemical Analysis of Water

c:

.;;: "C

c: .;;: "C

«

Q)

"C

Qi

·x

is

UJ

oCo c: ro

a. I

25

20

15

10

o

:cu is

5

o

Fig. 6.5 Gas chromatography of organochlorine pesticides: Column packing 1.5% OV-17 + 1.95% QF-1 (liquid phase); solid support: Gas chrom (Q) 100-120 mesh glass column 180 cm x 4 mm i.di Carrier gas, Ar/CH 4 at 60 ml/min; Column temperature 200°C Detector, Electron capture.

(26) Sulphate Sulphate from water sample is precipitated as Barium Sulphate in the acidic medium. Precipitate washed, dried and weighed as BaS04. Requirements

(1) Hydrochloric Acid(1:1): Take equal amount of 12N HCI and distilled water. (2) Silver nitrate acid reagent: Dissolve 8.5 gms of AgN0 3 and 0.5 ml concentrated HN0 3 in distilled water and make the volume to 500 ml. (3) Methyl ~ed solution: Dissolve 100 mg of solid in 100 ml of distilled water. (4) Barium Chloride solution: Dissolve 100 gm of BaCI 2 , 2H 2 0 in distilled water to prepare one litre solution. Filter if necessary. Method (1) Take 50 ml of water sample and add few drops of hydrochloric acid and 100 to 150 ml of distilled water. (2) Now add few drops of methyl red solution. Solution acquires orange colour. (3) Boil the solution and then add warm solution of BaCI 2 dropwise with constant stirring until complete precipitation. (4) Digest the preCipitate on previously heated sand bath for 2 hrs. (5) Filter the supernatant liquid through whatman Filter paper No.42. Now transfer all the precipitate to the paper. (6) Wash the precipitate with hot water till it is free from Chloride radical tested by Silver nitrate solution. In the presence of Chloride AgN0 3 develops white precipitate or turbidity.

52

Global Pollution and Environmental Monitoring

(7) Dry the precipitate and ignite in a crucible at 800°C for 1 hour. Cool it and weigh the precipitate as BaS04' Calculations

S04, mg/L =

MgofBaS04 x411.5 Mlof samples

(27) Total Phosphate Method

(1)

Take 100 ml of sample in a beaker. Digest with 1 ml of conc. H2 S0 4 and 5 ml HN0 3. Evaporate to dryness. Repeat the digestion and evaporation.

(2)

Wash (leach) the residue with 5 ml of 5N HN0 3 and transfer to a 50 ml volumetric flask.

(3)

Add 5 ml of 10% ammonium molybdate and then 5 ml of 0.25% ammonium Vanadate 6N HCI. Dilute to the mark with distilled water. Shake well and wait for 10 minutes. Measure the absorbance of the yellow reaction product at 460 nm. Perform the blank reading by some steps. Prepare calibration curve using a series of standard solution of phosphates.

(4) (5) (6) (7)

That is, 220 gm KH 2 P0 4/L concentration 1 ml

= 50

/-tg P0 4.

(28) Total Nitrate and Nitrite Nitrates and nitrites are reduced to NH3 by Devarda's alloy. Alloy consists of 50% Cu, 45 AI and 5% Zn, NH3 is distilled into excess standard acid and finally estimated spectrophotometrically or titrimetrically. . Method

(1)

Take 400 ml of sample in NH3 distillation flask. To this add 50 ml of 10% NaOH and evaporate to about 200 ml.

(2)

Allow the solution to cool and then add 3 gram Devardas's alloy and 30 ml of 10% NaOH and connect the flask with a vertical condenser whose outlet dips into receiver containing 200 ml of 0.2 NH 2 S0 4. Now distill of 60°C to 80°C for one hour.

(3) (4)

Disconnect the receiver. Dilute the content of the receiver to 250 ml. Now take 5-10 ml of aliquot in 50 ml volumetric flask and adjust the pH to 4-5.

(5)

Add 2 ml of Nessler's reagent and shake well. Measure the yellow colour at 424 nm. In volumetric method the distillate directly back titrated with standard alkali, i.e., 0.2N NaOH using methyl red indicator. Use following relation to calculate the concentration of N0 3 · 1 ml of H2 S0 4 = 0.06201 gm N0 3 Here H2 S0 4 Strength is 0.2N.

Physico Chemical Analysis of Water

53

Estimation of Nitrite (Oritrite)

(1) (2) (3)

Take 30 ml sample in volumetric flask (50 ml capacity). Adjust the pH of sample to 7.0. Add 2 ml of sulphanilamide solution (Sulphanilamide reagent is prepared by dissolving 50 gm in 500 ml of 1.2N HCI). Shake and allow to stand for 15 minutes. Add 2 ml of 1 napthylamine 7 sulphonic acid solution. Dilute to 50 ml and shake well (Reagent prepared as follows: 99 mg solid in 200 ml warm water, cooled, filtered and diluted to 250 ml with glacial acetic acid). Measure within two hours the resulting purple colour at 543 nm.

(29) Estitnation of All1.ll1.onia Nessler's Method

In this method ammonia precipitated by Nessler's reagent is prepared as follows: 70 KI + 160 gm. HgCI2 + 160 gm. NaOH diluted to one litre. Shake well and filter the solution. Method

(1) (2) (3)

Take 100 ml sample and add litle NaOH to neutralize the acid. Then add 10% ZnS04 7H 20 and 1 ml of 10% NaOH stir well and filter. It removes Ca, Fe, Mn, Mg etc. Collect the filtrate and add 1 drop of 50% EDTA (disodium salt). Mix well and then add 2 ml of Nessler's reagent. Measure the resulting yellow colour at 420 nm (Spectrophotometer).

(30) Estill1.ation of Cadll1.iull1. Cadmium is estimated with the help of dithizone which forms pink to red colour. Such colour due to cadmium is extracted into CHCI 3 and measured spectrophotometrically at 518 nm. Requirements

(1) (2) (3) (4) (5) (6) (7)

(8)

Chloroform: CHCI 3 , A.A. Grade. Sodium Hydroxide 6N: 240 gms NaOH dissolved in one litre of distilled water. Hydroxylamine hydrochloride: Dissolve 20 gm NH 40H, HCI in distilled water to prepare 100 ml solution. Dithizone reagent: Dissolve 10.0 mg dithizone in one litre of chloroform. Tartaric acid solution: Dissolve 20 gm of tartaric acid in distilled water and make the volume to one litre. Sodium Potassium tartarate: Dissolve 250 gm sodium potassium tartarate in distilled water and make the volume to one litre. Sodium hydroxide potassium cyanide solution: 400 gm NaOH + 10 gm KCN dissolve in distilled water and make the volume to one litre. This is called soiution NO.1 Dissolve 400 gm +0.05 gm KCN in distilled water and make the volume to one litre. (Solution No.2). Standard cadmium solution: Dissolve 10 mg of metal in one litre water with the help of concentrated HCI.

54

Global Pollution and Environmental Monitoring

Method

(1) (2) (3)

(4)

(5) . (6) (7)

Take 200 ml of sample and evaporate to 20 ml. Adjust the pH to 2.5 with thymol blue indicator. Solution acquires yellow colour. Adjust the sample to 25 ml with distilled water. Now add the following reagents in sequence. 1 ml of hydroxylamine hydrochloride solution and 15 ml dithizone solution. Shake well for one minute. Remove the lower layer of CHCI 3 in to a second separating funnel containing 25 ml of cold tartratic acid. Add 10 ml of CHCI 3 more to the previous funnel. Shake well, and drain into the separating funnel (No.12). Shake well for 2 minutes. Remove and discard the CHCI 3 lower layer. Add 5 ml CHCI 3 , shake well and discard lower layer. Here cadmium will remain in the tartaric acid solution. Now Add 0.5 ml of hydroxylamine hydrochloride solution, 15 ml dithizone solution, 5 ml of NaOH-KOH solution II, shake well. Let the two layers separate . Filter the HCI 3 layer (lower layer) through cotton plug. Measure the intensity of colour at 518 nm. Standard curve is obtained by taking 0 (blank), 2.4,6,8,10 J,.I.g cd. Follow the same steps to take the reading. Develop yellow colour with standard Cadmium solution.

Calculat:ions Total Cd mg/L =

Bx 100 AxC

A Diss.Cd mg/L = ml of sample

Where B = J,.I.g cd from the standard curve A = ml of original sample digested C = ml portion from 100 ml total digest

(31) Estifnation of Zinc (Zn) Blue coloured complex is formed with Ziron. Colour intensity measured by a spectrophotometer. Requirements

(1)

Sodium Ascorbate: Fine Powder.

(2)

KCN solution: Dissolve 1.0 gm KCN distilled water to prepare 100 ml solution.

(3)

Stock solution of Zinc: Dissolve 100 mg of Zn (30 to 40 mesh) metal in 6N HCI (about 2 ml) make the volume to one litre.

(4) (5) (6)

Standard Zinc solution: Dilute the above solution 10 times, i.e., 10 to 100 ml. Conc. HCI. 6N NaOH: Dissolve 240 gms of NaOH is distilled water and make the volume to one litre.

(7)

Buffer solution: Prepare 1N NaOH by dissolving 40 gms of NaOH in distilled water. Now take 220 ml of NaOH and make the Volume to 600 add 38 gms KCI and 31.0 gms of basic acid and make the volume one litre. This is a buffer with pH = 9.0.

Physico Chemical Analysis of Water (8) (9)

55

Zircon reagent: Dissolve 150 mg of Zircon in 100 m! methanol (Methyl alcohol). Keep it overnight. Choral hydrate: Dissolve 10.0 gms solid into 100 ml of distilled water.

Method

Take 50 ml of sample. To this add 1 ml Conc. HCI and adjust pH with 6N NaOH. Now take 10 ml of adjusted pH sample and then add 0.5 gm Sodium ascorbate, 1 ml KCN solution (to mas Ie other metal), 5 ml buffer solution and 3 ml chloral hydrate solution and measure the colour exactly after 5 min. at 620 nm. Prepare standard curve in the range of 0 to 70 )1g Zn (0, 2, 5, 5, 10, 3D, 50, 70, )1g Zn) by taking suitable volumes of standard Zn solution and making them to 10.0 ml. Follow the sample from the step 2 onwards. Calculation

Zn, mg/L =

)1gZn mlofsample

Summary It must be pointed out that for the analysis of pollutants present in water - Titrimetry (volumetric) procedures are competent enough in most of the cases. However, some advanced and routine volumetric analytical procedures are given below for analytical reference.

Colorimetric Methods Absorption spectrophotometry is an important method for analysis of many water pollutants. Basically, absorption spectrophotometry involves the measurement of the amount of monochromatic light passing through and absorbing solution as compared to the amount passing through a blank containing everything in the medium but the analyte constituent. The transmittance of the a blank is set at 100% and the %T of the unknown solution may range from 0 to 100 depending upon sample concentration. The absorbance, A, may be defined as follows: 100 log %T = A

... (1)

and the relationship between A and the concentration of the absorbing substance, C, is given by Beer's law:

= abC

... (2) In the Beer's law relationship, a is the absorptivity, a wave-length-dependent parameter characteristic of the absorbing- substance; b is the path length of the light through the absorbing solution; and C is the concentration of the absorbing substance. A linear relationship between A and C at constant path length reveals adherence to Beer's law_ In many cases, analyses may be carried out even when Beer's law is not obeyed if a suitable calibration curve is prepared. A

Only a few substances (such as Mn04-) are able to absorb visible light strongly enough to be analysed directly. Therefore, a colour developing step is generally needed in which the analyte reacts to yield coloured species. Generally coloured species is extracted into a non-aqueous solvent for providing a more intense colour and a more concentrated solution.

Global Pollution and Environmental Monitoring

56

The details of colorimetric analyses is given for some water constituents normally analysed by this method in the following table. Selected Colorimetric Analysis of Chemical Species in Water

Chemical Species Ammonia Arsenic Boron Bromide Chlorine Cyanide Fluoride Nitrate and nitrite

Nitrogen, Kjeldahl, phenate method Phenols

Phosphate Selenium Silica Sulfide Surfactants Tannin and lignin

Reagent and·Method Alkaline mercuric iodide reacting with ammonia producing colloidal orange-brown NH 2Hg 213 absorbing between 400 and 500 nm. Reaction of arsine, AsH 3, with silver diethylthiocarbamate in pyridine forming a red complex. Reaction with curcumin forming redrosycyanine Reaction of hypobromite with phenol red to form bromphenol blue type indicator. Development of colour with o-toluidine. Formation of a blue dye from reaction of cyanogen chloride, CnCI, with Pridinepyrazolone reagent, measured at 620 nm. Decolorization of a zircornium-dye colloidal precipitate ("lake") by formation of colourless zirconium fluride and free dye. Nitrate is reduced to nitrite which is diazotized with sulphanilamide and coupled with N-(1-naphthy1)-ethylenediamine dihydrochloride to produce a highly coloured azo dye measured at 540 nm. Digestion in sulphuric acid to NW4 followed by treatment with alkaline phenol reagent and sodium hypochlorite to form blue iodophenol measured at 630 nm. Reaction with 4-aminoantpyrine at pH 10 and in the presence of potassium ferricyanide. forming an antipyrine dye which is extracted into pyridine and measured at 460 nm. Reaction with molybdate ion to form a phosphomolydate which is selectively reduced to intesely coloured molybdenum blue. Reaction with diaminobenzidine forming coloured species absorbing at 420 nm. Formation of molybdosilicic acid with molybdate followed by reduction to a heteropoly blue measured at 650 nm or 812 nm. Foramtion of methylene blue Reaction with methylene blue to form blue salt Blue colour from tungstophosphoric and molybdosphoric acids

Details have been given below for some of the more commonly used colorimetric methods applicable to chemical species found in natural waters. . Aresenic in amounts down to 1 microgram may be estimated with silver diethldithiocarbonate reagent, (C2MSh NC(S)S-Ag+. The arsenic is first of all reduced to arsine, AsH 3 , by Zinc in acidic solution. The volatile AsH 3 is collected in silver diethyldithiocarbamate reagent and the absorbance of the resulting coloured solution is then measured at 535 nm (nanometer, 1 x 109 meter). The reagent blank is used as a reference solution. Alternatively, AsH 3 can be flushed with N2 into a Hydrogen flame and measured by atomic absorption.

Physico Chemical Analysis of Water

57

Chlorine is the chemical most widely used for killing bacteria in water supplies and swimming pools. It is found as "Free Chlorine" (primary HOCI and OCn and combined chlorine (for example, as chloramines such as NH 2CI). It may be determined in both forms spectrophotometrically by reaction with O-toluidine to yield a yellow coloured substance whose absorbance could be measured at 435 nm or 490 nm. Absorbance or colour comparison is carried out at the time of maximum colour development. Free chlorine has been found to develop colour more rapidly than chlorine. Free cyanide (HCN or CN-), a very toxic water pullatant, is determined spectrophotometrically. The free cyanide is first treated with chloramine-T to convert it to cyanogen chlorine, CNCI. This compound yields a blue dye absorbing at 620 nm when reacted with pyridine-pyrazolone reagent. It is possible to determine nitrate ion spectrophotometrically at low levels by a diazotization method in which colour is developed by the reaction of sulfanilic acid, nitrous acid and N-(1-naphthyl) ethylenediamine dihydrochloride. The absorbance of the highly coloured azo dye product may be measured at 540 nm. The same basic method has been applicable to the analysis of nitrate ion after the reduction of that ion to nitrite with cadmium turnings "copperized" by reaction with CUS04 solution. If nitrite is present, it could be determined prior to the reduction of nitrate, and the nitrate then found out by difference. Detergents, specifically anionic surfactant, may be measured spectrophotometrically as "methylene blue active substance", MSAS. Methylene blue yields blue coloured salts with anionic surfactants including alkyl benzene sulphonate (ASS), linear alkylate sulfonate (LAS) and alkyl sulfates. The salt gets extracted into chloroform and the absorbance of the solution would be measured at 652 nm. A number of materials have been found to interfere with the analysis, however. Phenol and other phenolic compounds are separated from the waste waster by distilling, for example, 450 ml of 500 ml sample of the water, adding 50 ml of phenol-free water, and distilling to total collected volume of 500 ml. Colour is developed by reaction of the phenols at pH 10.0 with 4-aminoantipyrine in the presence of potassium ferricynide. The resulting antipyrine dye is extracted into chloroform and its absorbance measured at 460 nm. The method has been quite sensitive, having a detection limit of around 1 f.l.gll of phenol.

Titrifl'letric Methods Many analytical procedures for water analysis are based upon titrations. The titration procedures may be either automated or manual. Some of the titration procedures used described as follows: Acidity, may be determined simply by titration of hydrogen ion with base. Titration to the methyl orange endpoint (pH 4.5) yields the "free acidity" due to strong acids (HCI, H2 S0 4). Carbon dioxide does not appear in this category. The preferred titration practice now is to titrate with O.O~ N-H 2 S04 to pH 8.3 (phenolphthalein endpoint) or pH 4.5 (methyl orange endpiont). Titration to pH 8.3 neutralizes bases as strong as, or stronger than, carbonate ion, C0 3 2- + W ~ HC0 3While titration to pH 4.5 protonates bases weaker than COl- but as strong as, or stronger than HC0 3 :

58

Global Pollution and Environmental Monitoring Titration to the lower pH gives rise to the total alkalinity,

Free carbon dioxide may be determined by titration with standard sodium hydroxide or sodium carbonate from the methyl orange to the phenolphthalein endpoint, pH 8.3. This is corresponding to the conversion of the carbon dioxide to bicarbonate ion. Chloride ion may be titrated with silver nitrate. Ag+ + CI- ~ AgCI and the endpoint indicated by several methods. Remarkably, the Mohr's method is still used as one of the standard methods of the chloride analysis. The endpoint in the Mohr's titration has been indicated by the precipitation of the chloride. The titration of chloride can also be followed potentiometrically. Another method for the determination of chloride involves the titration of chloride with mercuric ion to form a stable mercuric chloride complex: Hg2+ + 2CI- ~ HgCI2 The titration is carried out in the pH range of 2.3 to 2.8 and diphenyl carbazone, which yields a purple complex with excess mercuric ion, has been used to indicate the equivalence point. Water hardness, a measure of the total concentration of calcium and magnesium in water, may be readily determined by EDTA titration (sodium salt). First of all the solution is buffered at pH 10.0 to maintain the EDTA in a relatively non-protonated form. A higher pH might cause the precipitation of CaC0 3 or Mg(OHh. The reaction is Ca 2+ (or Mg 2+) + y4- ~ Cay2- (or Mgy2-) and the since calcium forms more stable complexes with EDTA than magnesium, the calcium complex is formed preferentially. Eriochrome Black T finds use as an indicator, and it needs the presence of magnesium with which it yields a wine-red complex. When liberated in the free form by complexion of the magnesium with EDTA, Enrichrome Black T forms a blue solution. In order to ensure that sufficient magnesium is present in the solution for observation of the endpoint reaction, a small quantity of magnesium EDTA complex is generally added. Due to the presence of equal quantities of magnesium and complexing agent in the magnesium-EDTA complex, the volume of EDTA required for the titration does not get affected. It is also possible to calculate hardness as the total magnesium and calcium concentrations determined by atomic analysis. It is possible to determine oxygen in water by the winkler analysis, a titration method. Many variations of the basic winkler analysis are known for dissolved oxygen to avoid interferences from species such as nitric ion or ferrous ion. The first reaction in the winkler analysis involves the oxidation of manganese (II) to managanese (IV) by oxygen in a basic medium: Mn2+ + 2 OH- + 1/202 ----) Mn02 + H20 Acidification of the brown hydrated Mn02 in the presence of 1- liberates free ' 2, Mn02 + 21- + 4W ~ Mn2+ + 12 + 2H 20 The liberated iodine (actually present as the 1- 3 complex) is titrated with standard thiosulfate, 12 + 2S20~- ~ S40~- + 21using starch as an endpoint indicator. A back calculation from the amount of thiosulfate required gives the original quantity of dissolved oxygen (DO) present.

Physico Chemical Analysis of Water

59

Biochemical Oxygen Demand, BOD may be determined by the adding a microbial "seed" to the diluted sample, saturating with air, incubating for five days, and determining the oxygen remaining. The results are calculated to show BOD as mg/I of oxygen. e.g. BOD of 80 mg/I, for example, implies that the biodegradation of the organic matter in a litre of the sample would consume 80 mg of oxygen. The determination of a related parameter, chemical oxygen demand (COD), has been discussed separately. Sulphide can be determined by titration. In sewage and in most natural water it becomes necessary to free the sulphide from insoluble salts as H2 S and collect it prior to analysis. The solution to be analysed is first of all acidified with H 2 S0 4, which converts HSand most sulphides to volatile H 2 S: HS- + W~ H2 S i Then, the volatile product is collected in zinc exceeded solution: H2S + Zn 2+ + 2C 2 H30 2- ~ ZnS + 2HC 2H30 2 Following the collection of hydrogen sulphide as zinc sulphide, the collection solution is acidified with HCI and a standardized solution of iodine in K is added. Some of the iodine gets reduced to iodide by the sulphide, and the access could be titrated with standard sodium thiosulfate solution. Sulphite occurs in some industrial wastes, especially those from some kind of papermaking operations. It is most commonly used in boiler feedwaters and water used for cooling or heat transfer, where, it acts as an oxygen scavenger for removing corrosive free oxygen: 2S0~- + O 2 ~ 2S0~-

A catalyst has to be used for this reaction when it is applied to cool waters. It is to be noted that hydrazine, N2 H4 , also acts an oxygen scavenger: N2H4 + O 2 ~ 2H 20 + N2 Sulphite may be determined by titration with iodide-iodate titrant. This reagent is prepared by reacting a standard quantity of potassium iodate, KI0 3, with excess potassium iodide for producing a solution of tr~odide ion, 13, The sulphite gets oxidized by iodine: 13 + SO~- + H20 ~ 31- + SO~- + 2W in an acidic medium. Starch indicator is added and the equivalence point is indicated by appearance of the starch-iodine blue colour.

Ammonia is determined by the measurement of light absorbed after treatment of the ammonia containing solution with Nessler's reagent. Nessler's reagent is an alkaline solution of mercuric iodide in potassium iodide. It reacts with ammonia to yield and orange+brown product, which remains for a time in colloidal suspension: 2Hgl~- + 2NH3 ~ NH2Hg213 + NH; + 51The wavelength at which the absorbance of the resulting suspension is measured gets varied from 400 to 500 nm and has been found to depend upon the concentrating range of the ammonia. A calibration curve has to be prepared from standard solution treated in exactly the same manner as the unknown to avoid interferences, ammonia frequently must be distilled from a basic solution of the sample prior to the analysis.

Radioactive Pollutants With scientific advances in the area of nuclear power plant, the reaction provide energy as well as produce radio isotopes for controlling diseases, such as cancer.

60

Global Pollution and Environmental Monitoring

Nuclear waste or containments in water must also required to be analysed and monitored. Some of the methods are as follows:

(1 )

Pho~phate Coagulation: It is very effective in remaining Sr-90, other isotopes which form:'insoluble phosphates.

(2)

Electrodialysis Method : First the Colloidal metals are removed and then soluble constituents are analysed.

(3)

Adding Clay Minerals : This is effective for concentration of 1000 ppm and more. The sludge must be carefully handled.

(4)

Adding Metallic Dusts: More than 90% of the radioactive substances can be removed except C s -137 & 1-131).

(5)

Distillation : In a small scale the most effective method of removal of radioactivity from water. In addition a and

~

actvity can be monitored using Geiger Counters and Gama-camera.

000

7 SOIL ANALYSIS Int:roduct:ion It is known that soil and water are two significant capitals of mankind and natural forests are friends of rivers and factories for manufacturing soil. The soil provides homes and ideal environmental conditions for life, i.e., living insects and others. A number of specific reactions have been found to be associated with soil environment, e.g., pesticides used in agriculture, degrade over time and their movements and rate of degradations can be determined through their interaction with soil. Another example is that of disposal of waste such as municipal garbage, sewage sludge, mine tailings, toxic materials etc. from soil environment. The word 'Soil' is derived from Latin word SOLUM which means floor or ground. What is Soil for a Scientist is Rock for Geologist. is Earth for Engineers. is Land for Economists. Conceptually, studying soil means study of soil of its origin and its classification, i.e., Pedology. Whereas Edaphology is the study of soil from the point of higher plants. It deals with study of soil in relation to growth, nutrition and crops. Methods of soil analysis which are reliable are important to many facets of human activity. This is because the soil plays the main role in production of food for human and animals. The organic matter on soil is decomposed by many a micro-organisms and the biomass is mixed by soil fauna. Good soil and congenial climatic conditions for productivity are required by every nation. But with large amount of industries and other development activities the soil gets impurities from pesticides, fertilizers, particulates from power plants, smoke etc. and gets polluted. Since soil is an important component of any. environmental cycle and chemical cycle it requires proper attention. By its very nature the soil consists of 95% of inorganic matter like minerals and 50% of organic matter such as Biomass. The contaminants of waste disposal in soil comes from domestic activity, human and animals, industries and agricultural activities mining and construction activities. An estimate of the year 1990 showed that 10% of the fertile soil of the earth has been transformed by human activities, i.e., converted from forests into desert. There are 25% which are still at the risk of conversion. Volumetric computation of mineral soil (i.e., inorganic) shows 45% minerals, 5% organics, 25% earth, soil-water and soil-air.

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Global Pollution and Environmental Monitoring

Soil is a mixture of various Inorganic and Organic matter. The important inorganic matter present in it include Ca, AI, Mg, Fe, Si, K, Na with small quantities of S, Mn, Cu, Zn, Co, I and F in the form of carbonates, sulphates, chlorides, nitrates etc. The important organic material present in soil is called Humus. This contains amino acids proteins, aromatics, sugars, alcohols, fats, oils, waxes, tennin, resins, lignin etc. 'Humus' enhances the fertility of soil and it refers to organic matter found in it. This is present in the form of colloidal substances. Mineralization is the process by which humus changes into carbon dioxide, water and minerals in a cycle of complete decomposition. The organic matter in soil comes from remains of plants and animals. The organic matter do not remain in its original form for a long time. It is attacked by a variety of micro-organisms, worms and insects present in soil. The micro-organisms convert various constituents of organic matter into new substances. Some of these are very simple whereas others are highly complex substances. These conversions are known as ammonification, nitrification etc. There are large number of reasons for the organic matter to be important in soil. Some of these are as follows: (1) (2) (3) (4) (5) (6)

Organic matter binds soil particles into structural units called aggregates. The waste holding capacity increases with the organic matter. This granular soil supplies more water. It reduces surface erosion. It acts as a thermostats for the soil. It acts as source of energy for minerals.

(7) (8)

It acts as a reservoir of elements required for plant growth. It reduces soil alkalinity.

(9) (10)

It helps giving food to insects, earthworms etc. which in turn help the soil. It acts as buffering agent.

Soil water plays an important role in the growth of plants: As water is retained in pores, plants can then readily absorb. Water being excellent solvent it dissolves the nutrients required for plant growth. In fact, the soil water is great regulator of physical, chemical and biological activities in soil. Plants absorb water through leaf opening. Soil-air relationship : Air spaces found in between the soil particles hold air which constitutes the gaseous system of soil. The exchange of carbon dioxide and oxygen between soil space and aerial atmosphere is called soil aeration. The rates of the metabolic activity of the micro-organisms depend on the air and the type that is available. A well aerated soil can be boon for micro-organisms which in turn can give the soil the enhance quality that it deserves for plant growth. Thus, soils are formed through following steps: (1)

Formation of regolith (small particles) by the breaking of rocks.

(2)

The condition of organic matter resulting from the decomposition of plant and animal residues and reorganisation of these components by soil material of varying depths.

Soil Analysis

63

The role of human being (like animals and micro-organisms must be explained in disintegration of rocks. We cut the rocks to build dams, channels, roads and buildings. These activities convert bigger size rocks into smaller ones. These increases the surface area of rocks favouring chemical process that leads to decomposition of rocks and minerals. Joffe classified the factors that leads to soil formation as follows : (1)

Active Factors: Rainfall, temperature, wind, humidity, and evaporation.

Passive Factors: These are parent materials which influence aeration, texture and hence chemical characteristics. Biospheric Factors: The living organisms, speeding and modifying the physico(3) chemical processes. The process of decomposition by micro-organisms include: (2)

(1) (2)

Group 1 Group 2

Mould, Fungi and non-spore forming bacteria. Spore forming bacteria.

(3) (4)

Group 3 Group 4

Cellulose myxobacteria. Actinomycetes.

The bacteria perform the role of, sulphur, soil or Nitrogen fixation. The beneficial role of microbes are as follows: (1) (2) (3)

Change and decomposition of organic matter. Fixation of atmospheric nitrogen. Formation and development of soil.

These are also harmful. These effects of micro-organisms are as follows: (i) Denitrification Development of plant diseases (ii) (iii) Formation of toxic substances (iv) Competition for nutrients. There are following types of soil: (1) (2)

Sandy soils Clayery soils

- Size 1 to 0.05 mm. - Size less than 0.002 mm.

(3) (4) (5)

Loamy soils - Sand, silt and clay in equal amount. Sandy-loam soils - More of sand. Clay-loam soils - More of clay.

(6)

Silt-loam soils

- Sand and silt in equal amount -

not suitable for plant growth.

Physico-Chemical Analysis of Soil Soil plays a very important role as it produces food for human beings and animals. The organic matter in soil as decomposed by a host of micro organism and biomass is mixed by the soil fauna. Good soil and a congenial climate for productivity are valuable assets for the nation. But, due to human activities, soil is the receptor of many pollutants including pesticides, fertilizers, particulate matter for power plant, smoke, stacks etc. Hence, soil is an important component of environmental chemical cycle. Soil, in general, has loose texture consisting of solid mineral and organic matter, air and space. The mineral component of soil originates from the parent rock by weathering processes while the organic matter is

Global Pollution and Environmental Monitoring

64

due to plant biomass in various stages of decay as well as high population of fungi, bacteria and animals such as earthworms. A typical soil contains 5% organic matter and 95% inorganic matter.

Soil Features Soil is the receptor of large quantities of waste products - domestic, human, animal, industries and agricultural. Combustion of sulphur containing fuels emit S02 and finally leaves sulphate on the soil. Nitrates from the atmosphere are deposited on the soil. Particulate lead from automobile exhaust also settles on soil along both sides of high ways with heavy automobile traffic. High levels of Pb, Zn etc. are observed on soils near lead and zinc mines. Major phYSico-chemical characteristics of untreated wastes of some industries in water and soil are given as follows: Major Physico-chemical Characteristics of Untreated Wastes of Some Industries in Water and Soil

S.No. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.

Industry

Physico-Chemical Characteristics

Heat, heavy metals, dissolved solids and inorganic compounds. Suspended solids, high or low pH, colour, fibres, BOD, COD, high temperature, fibres, dissolved substances. Chlorides, suspended and dissolved solids, variable pH and high BOb. Rubber Industry Acids, phenols, cyanogen, low pH, alkali, lime stone, oils, fine suspended Steel Mills solids, cyanides, cyanates, iron salts, ores and coke. Sodium, organic matter, colour, high pH and fibres. Cotton Industry Oil Refineries Acids, alkalies, phenols, tarry or resinous materials and petroleum oils. Metallics, toxic cyanides, cadmium, chromium zinc, copper, aluminium Metal Plating and low pH. Iron Foundry Coal, clay, suspended solids and iron. Pesticides Aromatic compounds, acidity and high organic matter. Acids Low pH and organic content. Antibiotics Toxic organics and high acidity or alkalinity. Synthetic Drugs High suspended and dissolved organic matter including vitamins, high acidity or alkalinity. Tanneries Calcium, chromium, high salt content, colour, dissolved and suspended matter. Distilleries Very high COD, low pH, high organic matter, high suspended and dissolved solids containing nitrogen, high potassium. Organic Chemical Industry Toxic compounds, phenols, high acidity, alkalinity. Explosives Alcohol, metals, TNT and organic acids. Fertilizers High pH, high ammonia, high fluoride content, acidity or alkalinity organic matter, nitrogen, p~sphorus and potassium. Photographic Products Organic and inorganic reducing agents, silver and alkalies. Synthetic Mills Zinc, toxic substances, sulphides and high pH. Dairy Products High BOD, high suspended and dissolved organic matter. Beet Sugar High BOD, high suspended and dissolved organic matter. Fruits and Vegetables Dissolved and colloidal organic matter. Thermal Power Plants Pulp and Paper

65

Soil Analysis 23.

Peer

24. 25 26

Soft drinks Yeast Pickles Slaughter Houses

27.

High dissolved solids containing nitrogen and fermented starches and allied products. High BOD and high pH and high suspended solids. High BOD and high organic matter. High suspended solids, colour and organic matter. High suspended solids, dissolved organic matter, proteins and blood.

Fertilizers and pesticides applied to crops are largely retained by the soil. They become part of environmental cycles through sorption by soil, leaching into water etc. Pesticides undergo degradation in soil, through the processes of biodegradation, chemical degradation or photo chemical reactions. Pesticide residues on crops and food products cause long-term health hazards. Soil gets large quantity of [lUman, animals and birds excreta which constitute the major source of land pollution by biological agents. In addition to these excreta, faulty sanitation, municipal garbage, waste water of wrong methods of agricultural practices also induces heavy soil pollution. In developing western countries, intestinal parasites constitute the most serious soil pollution problems. It may be concluded that the quality of soil has an impact on public health standards through the human food chain. The environmental health aspects deserve serious attention in the near future. Soil pollution affects the physiological process inhibiting plant growth. Rapid urbanization, with the consequent increase in population of building construction, has resulted in the reduction of land for the wastes to be disposed of. Every year solid wastes are increasing tremendously all over the world, depending upon the living standards of people. Moreover, as every day passed, the garbage in the stretch corner bin spilled over sooner, than it could be emptied. Several hazardous chemicals, the mountain of wastes are ultimately dumped on the land. Modern agricultural practices pollute the soil to a large extent. Many agricultural lands have now excessive amount of plants and animals waste which are posing pollution problems. However, it is not only the increasing utilization of fertilizers but also escalated production which creates soil pollution hazards. Today the most commonly anticipated problem is the contamination of soil with toxic chemicals. Well documented constituents include Hg, CI", N0 3 ", Zn, Fe and Cd etc., which has significant effect on crop productivity. Table shows the ionic forms of various soil nutrients. Today recent researches have enabled separation of metals from garbage even when present in minute quantities. Attempts have been made to reuse plastic in cassettes of films as well as in producing high grade papers from decayed old papers etc. Nature of various pollutants in soil is shown in Table.

Table: Ionic Forms of Various Solid Nutrients Elements Macronutrients

Ions

Elements Macronutrients

Ions

Nitrogen

NH;, NO;, NO;

Zinc

Zn 2+

Phosphorus

HP04"2, H2P04" K+ Ca 2+

Copper

Cu+, Cu 2+

Manganese

Mn2+, Mn4+

Boron

BO~-, BO~-

Potassium Calcium

66

Global Pollution and Environmental Monitoring Mg2+

Chlorine

Sulphur

SO~-, SO~-

Molybdenum

Iron

Fe2+, Fe 3+

Magnesium

Table: Nature of Pollutants in Soil Source Soil

Gases CO 2

Colloids

Suspended Particles

Clay

Clay,

Fe203, AI 20 3

Sand, Silt

MnOz

Decomposed Organic Matter

S02, H2, NH 3, CH 4, CO2

Organic Waste Materials

Humus Organic Wastes

Algae, Fungi, Bacteria, Protozoa, Viruses, Ascaris etc.

Algae, Bacteria

Dissolved Cations Na+, K+, Ca 2+, Mg2+, Mn2+, C02+, Fe3+ H+, Na+, NH/,

Dissolved Anions C032-, HCO;-, OH- CI- S024 I

,

I

F-, HSO;Organic Radicals NO;-, NO~, SO~-, CI-

Soil Organisms

It is to be hoped that the environmental health and nutrition aspects of soil and its products will receive much greater emphasis in the future. So the protection of our land, which is the wide storehouse ·of all living organisms, is not a luxury but an extreme necessity.

Sam.pling and Selection of the Site - Introduction The selection of site and sample collection of soil depends on the nature of analysis. Composite sampling is the best method for soil analysis. Nutrition study requires sample collected at the depth of 10-15 cm. Borer samples are used for this purpose. Soil samples are normally collected in polyethylene bag and dispatched or transported to laboratory as early as possible. Since some parameters like pH, redox potential, organic nitrogen phosphate fraction etc. should be analysed immediately. Other parameters dried soil below 40°C is advisable (Air drying 40°C). Mechanical analysis including estimation of carbon nitrogen, sulphur, soil should be dried at 105°C. After drying the soil, ston·es and undesirable matter are removed by hand picking method. Such a soil is then groLJnd in a mortar with pestle to get uniform and powdered soil. The soil then seived by 2 mm sieve. Stainless or nylon sieves are quite useful for this objective. For the estimation of organic carbon it requires fine powder of soil and sieved through mesh sieve 0.5 mm.

Handling, Transport and Storage: Procedure Soil and sediments samples can be collected from the place in polythene bags and transported as fast as possible in the laboratory for analysis. For other parameters, the soil can be dried and stored. lfimmediate drying is not possible, the samples can be stored for short periods at low temperature. The drying temperature for soil is critical, as many constituents change with change in temperature. High temperature drying generally affects the exchangeable characteristics of clay and organic,colloids.

67

Soil Analysis

Guidelines for immediate treatment of soils are given in Table. Analysis A. B.

C.

D.

pH reduced ionic states; redox potential Organic nitrogen; phosphorus fractions; nitrate, nitrite, ammonium nitrogen, halides, Amino acids, carbohydrates, volatile fats, humus fractions. Extractions of potassium sodium calcium, magnesium, iron, manganese, zinc, copper, boron, cation, exchange capacity, Kjeldahl nitrogen Mechanical analysis, loss on ignition, total concentrations of mineral constituents, phosphorus, nitrogen, sulphur and carbon.

Treatment Analyse immediately fresh samples Analyse immediately fresh samples. Soil can be kept at low temperature for short periods. Air drying «40°C)

Drying at 105°C

SIEVING AND GRINDING Soon after drying, stones and other similar objects are picked up act repeated. The soil is ground in a mortar to break up aggregates or lumps, taking care not to break actual soil particles. The soil is then passed through a 2 mm sieve. This mesh size allows all the nutritionally important factors to pass through. Brass sieves should be avoided where copper and zinc are to be estimated. Stainless steel or nylon sieves are preferable. If very small quantity of soil is to be used for a particular analysis - as for organic carbon and calcium carbonate, it is desirable to grind more finely and pass the soil through a smaller mesh sieve of 0.5 mm. Handling, Transport and Storage

After soil and sediment samples are collected in polythene bags they are transported to laboratory as early as possible. . Estimation of Acidity

pH of the soil refers the hydrogen iron capacity of the soil. pH is due to absorption of hydrogen and metallic ions. pH is measured by pH meter directly by introducing combine glass electrode in 1:5 soil suspension. Requirements

(1) (2)

Calibrated pH meter. 1:5 soil suspension Calibration of pH meter at 4 or 7 or 9.2.

Standard buffers are available for this (for more details refer pH measurement of water sample). Prepare the 1:5 suspension of soil as per the following method. Take 20 gm of well sieved (2-4 mm sieve) soil and add 100 ml of distilled water to it. Stir well with glass rod for one hour at regular intervals. Measure the pH of this suspension by the pH meter.

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68

SOIL CHARACTERISTICS (1)

Conductivity

Conductivity refers the presence of soluble salts in the soil. Soluble or ionised species acting as carriers of current. Conductivity is measured by conductometry for 1:5 soil suspension. Requirements (1)

Conductivity meter

(2) (3)

1:5 soil suspension Thermometer

Method Prepare 1:5 soil suspension by adding 20 gms of properly sieved soil into 100 ml of distilled water. Stir the content mechanically for one hour. Measure the conductivity of the soil suspension with conductivity meter by dipping conductivity cell into soil suspension. Temperature of the soil suspension is recorded to express conductivity at 25%C (for more detail refer conductivity of water sample).

(2) Chlorides Estimation of Chloride from soil solution is carried out by Mohr's method. It involves the titration of soil solution with standard solution of AgN0 3 by using potassium Chromate as indicator. Requirements (1) (2) (3) (4)

Mechanical Stirrer Whatman Filter Paper No. 40 Vacuum Pump Bucher Funnel

(5)

Side arm Flask

Reagents (1) O.02N AgN03

:

Preserve the solution in amber coloured bottle.

(2) Potassium Chromate Solution 5% : Dissolve 5 gms of K2Cr04 in 100 ml of distilled

water. Method Prepare 1:5 soil suspension by adding 40 gms of soil in 200 ml of distilled water. Stir the content well mechanically for one hour at regular intervals. Filter the suspension through filter paper 40 placed in buchner funnel. Buchner funnel is filled with side arm flask. Filteration is facilitated by vacuum pump. Now take 50 ml of solution and add few drops of K2Cr04 indicator. Shake well. Titrate the content with standard solution of silver nitrate till solution acquires brick red colour. Calculate the percentage of Chloride as per following relation: 01 Chi 'd _ AxO.02x35.5 /0 on e 0 5 x2 Here A = Volume of AgN0 3 required.

Soil Analysis

69

(3) Estitnation of Sulphate First of all prepare the 1:5 soil suspension by adding 100 ml distilled water to 20 gm of soil. Stir mechanically for one hour. Filter the suspension through Whatman No. 40 filter paper using buchner funnel attached with vacuum assembly. Take 50 ml of soil solution and acidify with few drops of concentrated hydrochloric acid. Warm the solution. To the warm solution add dropwise with constant stirring the 2N H2 S0 4 to obtain complete precipitate of BaS04. Digest the precipitate to the paper. Wash the precipitate with hot water. Dry the filter paper and precipitate and ignite it in a crucible at 900°C for about one hour. After cooling weigh the crucible to find out the weight of BaS04. Calculation Wt of BaS0 x 411.5

S04, Mg/L

4 = --m-Io-f-s-a-'-m-p-Ie--

or %S04

mgBaS04 x 411.5 = -----''-----'----ml of soil solution x 2000

(4) Organic Matter In this method organic matter in the soil is digested with excess of potassium dichromate with concentrated sulphuric acid and finally uneased potassium dichromate is titrated with ferrous ammonium sulphate with the help of diphenlyamine indicator. Requirements

(1) (2)

(3) (4)

Diphneyl amine indicator: Dissolve 1 gm of diphenyl amine indicator in 100 ml A.R. sulphuric acid. Ferrous ammonium sulphate D.4N : Dissolve 156.85 gms of ferrous ammonium sulphate in distilled water containing at least 20 ml of concentrated sulphuric acid. Dilute the content to one litre with distilled water. Potassium dichromate 1N : Dissolve 49 gms of K2Cr207 solution in distilled water and make the volume to one litre. Phosphoric acid: Phosphoric acid, i.e., H3 P0 4 concentrated (Sp.gr.1.17).

Method (1)

Take 10 gm of properly screened soil into 500 ml conical flask.

(2)

Add 10 ml of 1 N K2Cr207 and 20 ml of concentrated H2 S04,

(3)

Keep the flask undisturbed for 30-45 minutes. It permits the essential reaction in the contents. Dilute the content to about 200 ml with distilled water and then add 5-10 ml of H3P0 4 and 1-2 ml of diphenyl amine indicator. Titrate the solution with O.4N Ferrous ammonium sulphate till solution acquires the brilliant green colour. Note the reading as A. Take the blank reading with same amount of reagents, let the reading be B.

(4) (5)

Global Pollution and Environmental Monitoring

70 Cal~ulations

% C = 3.951

(1-:)

% organic matter = % C x 1.724 Here factor 3.951 represents 75% recovery of organic matter while factor 1.724 indicates that carbon is only 60% of the organic matter.

(5) Nitrogen (IqeJdahl Digestion Method) Requirements (1) (2)

Sodium hydroxide 40% : Dissolve 40 gms of solid NaOH in 100 ml of distilled water. Boric acid + Mixed indicator: Prepare 4% solution of boric acid by dissolving 4 gm of boric acid in 100 ml of distilled water and warm the solution.

Prepare mixed indicator as per following method. Mix 0.5% alcoholic solution of bromocresol green with alcoholic solution of methyl red 0.1 % in 2:1 ratio. (3)

(4) (5)

Add 5 ml of mixed indicator in boric acid solution. Hydrochloric acid 0.1N : Dilute 12N concentrated HCI 12 times, i.e., take 8.4 ml of HCI and dilute in 100 ml with water or 84 ml diluted to one litre with water. It gives 1N HCI. Dilute 100 ml 1N HCI to one litre to give 0.1 N HCI. Catalyst: Grind together 3 gms of K2 S0 4 , 1 gram of selenium powder and 20 gms of copper sulphate. Mix thoroughly 1 part of this with 20 parts of sodium sulphate. Sulphuric acid 0.1.

Method (1) (2) (3) (4) (5)

Take 1 gm peaty or 20 gm of sandy or 10 gm normal soil properly screened into 250 ml Kjeldahl Flask. Add 25 ml of distilled water to moisten the soil. Now add 15 gm of catalyst mixture and 30 ml of conc. H2 S0 4 , Mix it gently. Heat at low heat for first 30 minutes until frothing stops completely and then heat strongly. Cont.inue the digestion until the content becomes light yellow. Heating should be at least for 1"" hour. Cool the digest and then add 75 ml of distilled water and then transfer the supernant liquid into 1 litre distillation flask. Add 100 ml 40% NaOH solution and few pieces of Zn granules.

(6)

Place 500 ml capacity flask containing 25 ml boric acid and mixed indicator below the condensor so that tip of the condensol"\ should dip into the solution. Connect the assembly and continue the distillation. Collect about 150 ml condensate. Condensate now possesses blue colour. Titrate the contents with 0.1 N HCI until colour changes brown or pink. Perform the blank reading taking same amount of Reference Chemical except sample.

Soil Analysis

71

Calc'ulations

%N

= (b -

a) x Normality of HCI x 1.4

W Here b

=

ml of HCI used with blank

a

=

ml of HCI used with sample

W

=

Weight of soil

ROLE OF NUTRIENTS NITROGEN It is the most important nutrient for plants. It is the first fertilizer element of macronutrients usually applied in commercial fertilizers. Nitrogen is very important nutrient for plants and it seems to have the quickest and most pronounced effect. It also forms a constituent of every living cell in the plant. Plants for their growth require sixteen elements, namely, carbon, hydrogen, oxygen, potassium, phosphorus, nitrogen, calcium, magnesium, sulphur, zinc, boron, copper, manganese, molybdenum, chlorine and iron. Out of these three, namely, carbon, hydrogen and oxygen are derived from air and water and so these are called natural nutrients. Nitrogen, phosphorus and potassium are consumed in large amounts by the plants for their growth and so these are called primary nutrients. Calcium, magnesium and sulphur which occur to a limited extent in all soils, are called secondary nutrients. Rest of the elements are required by the plants in minute amounts and so these are called micro nutrients. Soil takes up the nitrogen in the form of ammonium or nitrate ions and forms amino acids with carbon compounds in the complex chemical system in the plant. These amino acids are then converted into proteins and enzymes. Proteins thus formed make part of the protoplasm, while enzymes act as catalysts for various reactions taking place in the plants. Nitrogen is also a special constituent of the chlorophyll, without which photosynthesis is not possible. Nitrogen makes up 16-18% of the plant nutrients. The main sources of nitrogen are: (a) Fertilizer (b) Organic nitrogen compounds formed in the soil by recurring natural processes, and (c) Atmosphere. The natural sources are however, not sufficient for adequate plant growth and so artificial nitrogen compounds in the form of fertilizers are added to the soi'l for making the soil productive. v In fact, air contains 78% nitrogen, but plants cannot use it directly. But the plants belonging to the family of leguminoceae, can play host to a special group of nitrogen fixing bacteria such as Rhizobium. This bacteria is capable of converting atmospheric nitrogen into organic form that can be used by host plants. Some common examples of legums are pulses, soyabean, groundnut, berseem, clovers and guar. Nitrogen is not only essential constituent of protein and chlorophyll, but it is also involved in photosynthesis, respiration and protein synthesis. The most important functions of nitrogen are:

(a) Nitrogen tends primarily to encourage above ground vegetative growth and it imparts dark green colour to the plants. (b) Nitrogen regulates to a considerable extent the utilisation of potassium, phosphorus and other constituents. (c) Nitrogen promotes vegetative growth and improves the quality of the produce including fodder, leafy vegetable and food crops. (d) Nitrogen increases the tillering of cereal crops. (e) When nitrogen is present in sufficient amounts in the soil, plants acquire healthy green colour which is· neither too dark nor too light, growth of the plant is fairly rapid and crop matures normally and gives high yields.

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72

(f) Nitrogen increases the protein content of food and fodder. It also increases the plumpness of grain in the cereal crops. Abundant supply of nitrogen may, however, cause some adverse effects, which include: (a) It delays ripening by encouraging more vegetative growth. The leaves, acquire a dark green colour, become thick and leathery and in some cases crinkled. They may also become soft and shappy. The plants become more susceptible to attack of certain fungi and their resistance to disease decreases. (b) In case of cereal crops, the straw becomes weak, and the crop very often lodges and straw and grain ratio is increased. (c) Excess nitrogen deteriorates the quality of some crops such as potato, barley and sugarcane. (d) It delays reproductive growth and many adversely affect fruit and grain quality. The deficiency of nitrogen may also cause some adverse effects, which include:

(a) The plant become yellowish or light green and remains stunted. (b) The leaves and young fruits tend to drop prematurely. (c) A nitrogen deficient plant ripens prematurely and crop gives poor yield. (d) The kernels or cereals and the seed of other crops do not attain their normal size, and become shrivelled and light in weight. (e) Root growth is severely affected. (f) It delays reproductive growth, but increases profuse vegetative growth. (g) the flower bud often turns pale and sheds prematurely.

PHOSPHORUS Phosphorus is the second fertilizer element and it is essential constituent of every living cell and for the nutrition of plant and animal. It takes active part in all types of metabolism of plant. It is essential constituent of many enzymes and also structural component of membrane system of cells, the chloroplasts and the mitochondria. It is required in much lesser amounts than nitrogen. Most soils contain phosphate in the form of complex calcium phosphate, iron and aluminium complexes and organic compounds. Such sources are insoluble and so the plants can make very little use of them. It has been found that certain high. energy phosphate bonds are involved in the respiratory and photosynthesis processes. These bonds transfer energy in some of the plants metabolic processes without which the plant CQuid not live. The need of phosphorus is also necessary for the health of the plant. It is a constituent of nucleic acids, phytins and phospholipids. It is also foulld in seeds and fruits. The phosphorus has also been found to contribute to the formation of the reproductive parts in the early life of the plant, Liebig (1940) first emphasized the need for phosphates and his work led to the commercial production of phosphate fertilizers. The main functions of phosphorus include:

(a) It stimulates root development and growth in the seedling stage and hence help to establish the seedling quickly. (b) It enhances leaf development and encourages greater growth of shoots and roots. (c) It enhances the development of reproductive parts and thus brings about early maturity of crops particularly the cereals and counteracts the effect of excess nitrogen. (d) It develops resistance to certain diseases. (e) It increases the number of tiller in cereal crops and also increases the ratio of grain to straw. As a result, the yield is increased. (f) It increases the straw of cereal crops and helps in preventing the lodging. (g) It influences cell division and formation of fat and albumin. (h) It stimulates the flowering, fruit setting and seed formation and the development of roots, particularly of root crops. (i) It has a special action on leguminous crops. It induces nodule formation of such crops and rhizobial activity. In other words, it helps in fixing more atmospheric nitrogen in root nodules.

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73

Excessive phosphorus, however, has some adverse effects, which include: (a) Profuse root growth, particularly to the lateral and fibrous rootlets. (b) It develops normal growth having green leaf colour. (c) It may trace element deficiencies in some cases, particularly those of iron and zinc. (d) Unlike nitrogen, excess of phosphorus is not harmful. A deficiency of phosphorus may cause the following important adverse effects: (a) Roots and shoot growth is restricted and plants become thin and spindly. (b) Leaves may shed prematurely and there may be considerable delaying in flowering and fruiting. (c) The leaves of cereal crops become dull greyish green in colour. The deficiency is shown by slow growth and low yields. (d) Stunted growth even under abundant supply of nitrogen and potash, and premature ripening of crops. (e) The filtering of cereal crops decreases as a result of which yield becomes slow. (f) Potato tubers have shown rusty brown lessions.

POTASSIUM Potassium, the third fertilizer element acts as a chemical traffic policeman, root booster, food former, sugar and starch transporter, protein builder, breathing regulator, water stretcher and as a disease retarder, but it is effective only in presence of countrientc; such as nitrogen and phosphorus. The function of potassium is not clearly known, but it has been found that it is essential for healthy growth of plants and cannot be replaced even by closely related elements as sodium and lithium. In the plant, it either occurs as a part of the anion of organic acid or as a soluble inorganic salt in the tissues. Formation and movement of carbohydrates in plant is contributed by potassium and a deficiency of potassium quickly reduces the carbohydrate contents. The potassium content of plants ranges from about 0.5-2.5% of the dry weight. Potassium has also been found to contribute to the vigour and resistance of plants.

The important functions of potassium are given below: (a) It is an essential element for the development of chlorophyll. (b) It is essential for photosynthesis, that is, for converting CO 2 and \o/ater into sugars and for translocation of sugars and also for starch formation. Potassium is, therefore of special value for crops like sugarcane and potatoes which are rich in sugar and starch. (c) Potassium is absolutely necessary for tuber development. (d) Potassium improves the health and vigour of the plant, enabling it to withstand adverse climate conditions. (e) It increases the crop resistance to certain diseases and counteract the adverse effects of excess nitrogen. (f) Potassium is necessary for the production of best quality of grains and fruits. (g) Potash plays an important role in the production of quality vegetables. (h) It strengthens the straw of cereals and keeps the plants green. Thus it reduces lodging in cereal crops. (i) Potassium improves the quality of some crops such as tobacco, potatoes, sugarcane, vegetables and fruits. (j) Potassium also works against undue ripening influences of phosphorus. In general, potassium exerts a balancing effect on both nitrogen and phosphorus. Hence it is especially important in mixed fertilizers. (k) Potassium increases the plumpness and boldness of grains and seeds. (I) Potassium acts as an enzyme activator. (m) Potassium improves water balance, promotes metabolism and increases the production of carbohydrates.

The potassium deficiency may cause the following important effects: (a) Deficiency of potassium may cause chlorosis, i.e., yellowing of leaves and leaf scorch in the case of fruit trees. (b) Deficiency of potassium is also responsible for dying back tips of shoots. The older leaves have been found to show the deficiency symptoms

74

Global Pollution and Environmental Monitoring

earlier. (c) Potassium deficient plants show a decreased rate of photosynthesis. (d) Potassium deficient plant becomes stunted in growth with shortening of internodes and 'bushy in appearance. (e) Potato plant shows an abnormal dark green colour of foliage followed by brownish. (f) Deficiency of potash results in blackening of tubers and damage in shortage and transit.

CALCIUM Calcium acts as a plant nutrient and also as a soil amendment to correct soil acidity. It is found as a plant constituent in the cell walls of leaves in the form of calciDm pectate. Calcium is closely associated with the growth of the flowers and a deficiency of calcium also prevents normal development of buds and tips. Calcium is also found in cell sap either in the ionic form or as salts of organic acids. Application of calcium to the soils in the form of CaC0 3 corrects the soil's acidity rather than supplying a nutrient. Calcium is a structural component of chromosomes. It has been established as an essential element for plants in

1939. The main functions of calcium include: (a) It promotes root development and growth of plant because it is involved in root elongation and cell division, (b) It is helpful in translocation of sugar in the plants, (c) It enhances the nodule formation in leguminous plants and thereby rhibial activity is increased, (d) It neutralises organic acids which may become poisonous to the plants, (e) It induces stiffness of straw and (c) hence leads to the prevention of undesirable lodging of plants, (f) It is an essential cofactor, or an activator of various enzymes including lipase and apyrase. (g) It acts as a buffer in plant systems and ameliorates the toxic effects of other nutrients if they are at toxic levels in the plant. (h) The structure of soil having calcium becomes good and cation exchange capacity increases. (i) It improves the intake of other plant nutrients, especially nitrogen and trace elements such as Fe, Zn, Cu, Mn, and B by correcting the pH of the soil.

Excessive amounts of calcium, however, decrease the availability of many micronutrients. The deficiency of calcium may cause the fol/owing important adverse effects: (a) The normal growth of the plant is arrested, (b) Roots may become short, stubby and brown, (c) Its deficiency may cause soil to be acidic, (d) The acidity of saps of cells increases abnormally and it hampers the physiological function of the plant. As a result, plant suffers illness and causes the death of plant at last, (e) Leaves may become wrinkled and the young leaves of cereal crops remain folded, (f) Young leaves of terminal buds die back at the tips and margins. It should be noted that calcium deficiency resembles boron deficiency.

MAGNESIUM Magnesium acts as a carrier of phosphate and, therefore, plays an important part in the formation of phospholipids and in the synthesis of nucleoproteins. Magnesium is also a mineral constituent of chlorophyll and makes up 2.7% of the weight of chlorophyll. Several photosynthetic enzymes present in chlorophyll require magnesium as an activator. Magnesium is usually required by plants in relatively small quantities. Hence its deficiency in soil is observed later than that of.potassium. Deficiency of magnesium is removed by the magnesium already available in the soil from natural sources. Dolomitic limestone, containing MgC0 3 is used to supplement the natural supply.

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75

The main functions of the magnesium are given below: (a) Magnesium is usually required by plants for the formation of oils and fats, (b) Magnesium is helpful in the formation of chlorophyll and thus impart dark green colour to the leaves. Chlorophyll is indispensable for the photosynthesis by plants, (c) Magnesium also regulates the uptake of nitrogen and phosphorus from the soil, (d) Magnesium is capable of increasing the crop resistance to drought as well as disease, (e) It plays an important role in the production of carbohydrates, proteins, fats, (f) In oil producing crops, magnesium plays a key role in the sYfJthesis of oils and fats. Visual symptoms of deficiency of magnesium is the yellowing of the older leaves. This is called chlorosis. Acute deficiency of magnesium may cause premature defoliation. In maize, the leaves develop intravenial white strips. In cotton, they change to purple red, veins, however, remain dark green. The veins of chlorotic leaves remain green.

SULPHUR Sulphur exists in two important essential amino acids methionine and cystine, which are also the components of proteins. Sulphur has a specific role in initiating synthesis of protein. Sulphur is an important nutrient for oil seeds, sugar and pulse crops. These crops grow best on sulphur rich soil. Sulphur is an essential constituent of many proteins, enzymes and certain volatile compounds such as mustard oil. It is present in many proteins in the form of cystine and methionine which contain 26.7 and 21.5% sulphur respectively. A deficiency of sulphur decreases the plant growth accompanied by extensive yellowing of green parts. The sulphur needs of the plants are small and supplied by soil compounds, from industrial gases that distribute sulphur compounds, or from sulphates supplied in fertilizers. The main functions of sulphur include: (a) It is involved in the formation of chlorophyll. Hence it is responsible for encouraging the vegetative growth. It is not, however, the constituent of chlorophyll, (b) Sulphur is an important constituent of straw and plant stalks, (c) Pungent odour of onions and garlic is because of the presence of the sulphur compounds, (d) Sulphur promotes the nodule formation on the root of leguminous plants, (e) Sulphur also helps in increasing root growth and stimulate seed formation, (f) Sulphur is an essential element for the synthesis of certain amino acids and oils. The deficiency of sulphur may cause the following adverse effects: (a) Young leaves may turn yellow and roots and stems may become abnormally long and may also develop woodiness. (b) Nodulation in legumes may be poor and fixation of nitrogen is reduced, (c) The fruits on fruit trees may become light green, mis-shaped, thick skinned and less juicy, (d) The maturity in cereals may be delayed, (e) The older foliage may develop orange or reddish tints and may shed prematurely, (f) The stem and leaf petioles become brittle and may collapse, (g) Sulphur deficient plants produce less protein and oil. Sulphur may be called as master nutrient for oil seed production, (h) Unlike nitrogen, sulphur deficiency symptoms usually appear first on the youngest leaves and persist even after nitrogen application.

BORON It is required by plants in extremely small amounts. Its function is obscure, but accumulation of carbohydrates and water soluble amino compounds in plants efficient in boron suggests that boron is of some importance in protein synthesis.

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The main functions of boron are given below: (a) Boron makes up the calcium deficiency to certain extent, (b) It helps in the normal growth of plant and in absorption of nitrogen in soil, (c) Boron helps in root development and flower and pollen grain formation, (d) Boron plays an important role in the development and differentiation of tissues, carbohydrate metabolism and translocation of sugar in plants. The deficiency of boron causes the following important adverse effects: (a) Plant growth is retarded and the leaves turn yellow or red. (b) Boron deficiency is generally associated with sterility and malformation of reproductive 'organs, (c) Boron deficiency decreases the rate of water absorption and translocation of sugar in plants, (d) Boron deficiency symptoms vary with the kind and age of the plant, the condition of growth and the severity of the deficiency. Each crop produces its characteristic growth abnormalities associated with boron deficiency.

IRON Iron is necessary for the synthesis of chlorophyll, but it is not a constituent of chlorophyll. Iron is used by the plant in some of its respiratory enzyme systems, especially catalyse cytochrome and peroxidase. A deficiency of iron causes leaves to turn white and growth to cease. Iron deficiency is noted in the growth of citrus and in crops such as soyabeans and peanuts. In deficiency of iron, chlorosis of young leaves takes place but the veins remain green. In severe deficiency, leaves become almost pale white because of loss of chlorophyll. Under severe deficiency leaves become dry and papery and may later turn brown and necrotic. Complete leaf fall may also occur and shoots can also die. Deficiency of iron produces chlorosis in paddy and mottle leaf and chlorosis of young leaves in sugarcane. The main functions of iron are given below: (a) It takes part in the synthesis of chlorophyll and imparts dark green colour to plants, (b) Iron is essential for the synthesis of proteins present in chloroplast. (c) Iron acts as a catalyst in the activities of several enzymes. It regulates photosynthesis, respiration and reduction of nitrates and sulphates, (d) Iron plays an important role in the formation and activity of a series of respiratory enzymes.

ZINC It is believed to be involved in enzyme systems in the plant, particularly carbonic anhydrase and carboxylase. Zinc functions in enzyme systems which are necessary for important reactions in plant metabolism. Zinc is associated with iron and manganese for the synthesis of chlorophyll. The main functions of zinc are given below: (a) It is involved in the synthesis of chlorophyll, (b) It is involved in biosynthesis of plant growth hormone and in the reproduction process of certain plants, (c) It has a role to play in photosynthesis and nitrogen metabolism, (d) It is needed for seed production and rate of growth and also RNA synthesis. The deficiency of zinc may cause the following important adverse effects: (a) Intervenial chlorosis of the foliage, particularly in lower leaves, with the size reduction young leaves, (b) New leaves of maize plant emerge white in colour whIch is known white bud. (c) Shortening of internodes and stunted growth of plants, (d) Flowering, fruiting and maturity can be delayed, shoots may die off and leaves fall prematurely.

In

Soil Analysis

77

MANGANESE Manganese is an essential constituent of chlorophyll and also for the formation of oils and fats. Manganese also, influences the uptake and utilisation of other nutrients in the plants. It is an essential factor in photosynthesis, nitrogen metabolism and respiration. It is found in active regions of the plant and acts as an oxidising agent for Iron. Deficiencies of manganese usually occur in organic soils and in alkaline or highly acidic soils. The main functions of manganese are given below: (a) It helps in the synthesis of chlorophyll, because it is a part of chlorophyll, (b) Manganese acts as a catalyst in the oxidation reduction reaction within the plant tissue, (c) It also help in the protein synthesis in chloroplast. (d) It supports the movement of iron in the plants.

A deficiency of manganese leeds to chlorosis in the interveinal tissue of netveined leaves and plants. Manganese deficiency symptoms are first visible on younger leaves. Manganese deficiency may also result in disorders such as grey speck of oats.

COPPER Copper is associated with some of the plant enzyme systems, such as polyphenol oxidase and ascorbic acid oxidase. Deficiencies are generally associated with organic soils. Copper is capable of acting as electron carrier in enzyme systems which bring about oxidation reduction systems in plants. The most important functions of copper are: (a) Copper is an essential constituent of chlorophyll and helps in the synthesis of chlorophyll. (b) Copper is essential for the synthesis of vitamin-A and various other compounds in plants. (c) Copper acts as a catalyst in respiration. Thus it is involved in respiration, (d) Copper is also involved in utilisation of iron.

Copper deficiency is evident as chlorosis, withering and often distortion of the thermal leaves. Copper deficiency is induced by heavy liming and excessive application of nitrogen and phosphates. The food synthesis by the process of photosynthesis is hampered in presence of copper deficiency. Gum pockets under the bark and die back of shoots in citrus are the predominant symptoms of copper deficiency. The fruits are subjected to cracking and die back of terminal growth can occur.

MOLYBDENUM It has also been proposed to be associated with the functioning of one or more of the plant enzyme systems, especially nitrate reducing enzymes. Molybde;.num and manganese have been found to be essential for certain nitrogen transformation in microorganisms and in plants. Molybdenum has been found to be essential for the process of nitrogen fixation both symbiotic as well as non-symbiotic. Molybdenum has been found to enhance the symbiotic nitrogen fixation as well as protein synthesis. It also regulates the activities of various enzymes. The deficiency of molybdenum produces whip tail in cauliflower and downward cupping in raddish. Most of the vegetable crops are prone to molybdenum deficiency. The deficiency of molybdenum reduces the activity of the symbiotic and non-symbiotic nitrogen fixing organism. Molybdenum deficient legumes will not nodule well or fix the normal amounts of nitrogen expected of them.

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CHLORINE It is the most recent addition to the essential nutrient list. It has been observed that the deficiency of chlorine can cause wilt chlorosis (yellowing of green plants) and necrosis. Chlorine in small amounts also stimulate growth of crops like barley, alfalfa and tobacco. Chlorine is thought to be associated with the evolution of oxygen during photosynthesis. Burning of leaf tips of margin, bronzing, premature yellowing and leaf fall are the chloride toxicity symptoms.

NON-ESSENTIAL ELEMENTS Certain non-essential elements, such as sodium, silicon, aluminium etc. are also found in plants. No evidence has yet been found that meets any of the requirements for essentiality . .----------------1

Sununary \ - - - - - - - - - - - - - - - - - - ,

•

Soil is a reservoir of primary nutrients (nitrogen, phosphorus and potassium), secondary nutrients (such as sulphur, magnesium and calcium) and micronutrients (such as iron, manganese, boron, chlorine, zinc, copper and molybdenum).

•

Nitrogen plays an important role in plant development. It encourages healthy leaf, seed and tuber yield. Phosphorus stimulates early root and plant growth and increases maturity. Potassium enhances ability to resist diseases, insect attacks, and adverse weather. It also helps form and move starches, sugars and oils. It improves fruit quality too. Sulphur is involved in energy producing processes. Sulphur is also responsible for flavour and odour.

• • • •

Magnesium is a component of chlorophyll and hence that of photosynthesis. It is also important in seed production.

•

Calcium is essential for root health, growth of new roots and root hair and also for the development of leaves.

•

Iron is needed for energy transfer, plant enzyme functions, and photosynthesis.

•

Manganese helps the plants in performing the process of photosynthesis.

•

Boron is important in tissue respiration, cell division, pollination, seed production, carbohydrate synthesis and transport. Boron also regulates water intake

•

Chlorine is required only in traces. It assists metabolism. It is perhaps also involved in water regulation.

•

Zinc is essential for regulation of growth and sugar consumption. Zinc is very important in enzyme systems.

•

Copper is an essential constituent of enzymes. It also plays a role in respiration and photosynthesis.

•

Molybdenum helps convert atmospheric nitrogen to soluble nitrogen compounds. It is also essential in the formation of proteins from soluble nitrogen compounds.

•

The top 15 cm of soil contain as much as 4000 kg of live micro-organisms.

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Soil Analysis

MAIN FUNCTIONS OF MICRONUTRIENTS Out of 16 essential plant nutrients required for the development of plant growth, seven are required in much smaller amounts arid hence they are known as micronutrients. These include manganese, zinc, copper, molybdenum, boron, iron and chlorine. Multiple cropping with high yielding varieties of crop is one of the most important reasons of removal of micronutrients from the soil. In recent years, they become more important because of conserving and increasing the fertility and productivity of soil. .

Under the deficiency of micronutrients: (a) The growth of plant is hampered, (b) The plants are subjected to attack by diseases, and (c) The yield of the crop decreases accordingly. Repeated application of one trace element can induce deficiency of other elements. Micronutrients are most essential for the growth, development and reproduction of plants. Different crops need varied quantities of micronutrients in their different stages of growth. The main functions of micronutrients are given below: (a) They help in the photosynthesis of green plants, (b) They also take part in the synthesis of chlorophyll, (c) They act as catalyst in oxidation reduction reactions within the plant. The deficiency of such micronutrients may cause shedding of flowers, improper fertilization, poor, seed setting etc. (d) They are also responsible for regulating the activities of various enzymes. Some of them are essential for the synthesis of vitamin A and other compounds in the plants. (f) They help in normal growth of the plant and in the absorption of nitrogen in the soil, (g) They also help in the utilisation of nitrogen and phosphorus, (h) They maintain potassium and calcium ratio of the plants, (i) They are involved in the biosynthesis of plant growth hormone and in the reproduction process of certain plants, (j) They help in protein synthesis in chloroplast. (k) They enhance the symbiotic nitrogen fixation. (I) They are helpful in proper utilisation of nitrogen and phosphorus.

Moisture Content in Soil As the moisture content decreases the water present in the soil is held firmly but the plant roots are unable to draw water. The plant starts wilting. This is a wilting point. It is deprived as the amount of water which is held with water pressure less than 1-10 atmosphere. At this point if soil moisture potentiai'the plants give up unless the water conditions are retained. This is a temporary point. When the next stage is reached it is called permanent wilting point from which no recovery is possible. The moisture content in soil and its determination can be explained as follows:

Gravif11.etric Procedure The sample of soil in moist condition is weighed. Then it is dried in an oven at 110°C till constant weight. (about 2 hrs). From this the mass water percentage is calculated. If, W 1

dried weight. (W1 - W2 ) x 100 percentage moisture = W -

moist weight, W 2

-

2

There are other methods such as electrical conductivity which are also in use.

Soil Reaction It is very important chemical characteristics of the soil-solution. This influences physical, chemical and Biological properties of soil. It is measured as pH (i.e., Puissance de Hydrogen).

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The Wand OH- ion concentration determine whether ·it is acidic, alkaline or neutral in nature. This in turn is designated as pH value. It is the number of hydrogen ions in one litre of solution prepared in water. Since ionic concentration of water at room temperature is value of 10-7 gms ionsllitre of [W] and [OW]. The total becomes ~ [10- 7 ] [1 0-7 ] ~ 10-14 (at 25°C). This is called ionic product of water. 14 i.e., Kw = 10-14 :. -log 10 [10- ]

= 14 Hence the pH value will be pH + pOH = 14. This is further explained as follows:

1 1 and pOH log [OH-] log [H+] [OW] For pure water [W] [OH-] 1 x 10-7 gm ion per litre Thus in pure water, pH = - log [1 x 10-7 ] = - (-7) = 7 and pOH = - log [1 x 10-7 ] = - (-7) = 7 pH

=log

[W]

=log

==

=

=

So, for pure water, pH = pOH = 7. For neutral solution pH = pOH = 7. Now, pH + pOH = 7+7 = 14 or pH = 14 - pOH Thus pH of a base can be calculated using the relation pH Acidic solution

[Wi 10- 1 10-2 10-3 10-4 10-5 10-6 10-7

pH 1 2 3

4 5 6

7

Basic solution

[Wi 10-8 10-9 10-10 10-11 10-12 10-13 10- 14

Acidic solution

= 14 -

pOH. Basic solution

pH

[OH'j

pOH

[OH'j

8

10- 14

14

10-7

9 10 11 12 13 14

10-13 10-12 10-11 10-10 10-9 10-8

13 12 11 10 9 8

10-6 10-5 10-4 10-3 10- 2 10- 1

pOH 7 (Neutral) 6 5

4 3 2 1

(Neutral) It is evident that pH of neutral solution is 7. If the pH is less than 7, the solution is acidic, and if the pH is greater than 7, it is alkaline. It is also clear that if [H+] is high, its inverse expression is low. This indicates that lower the pH, the more acidic is the solution and higher the pH, the more basic is the solution. As the concentration of H+ ions in a solution is increased 10 times, its pH decreases by one unit. For example, when pH of a solution is decreased from 5 to 2, the W ion concentration is increased 10 x 10 x 10 1000 times, because for each unit of pH decreased, the H+ ion concentration is increased by 10 times. For 100 fold increase in H+ ion concentration, the pH of the solution is decreased by 2 units. For changing the pH from 2 to 4, the W ion concentration has to be decreased by 10 x 10 = 100 times. Similarly, to

=

Soil Analysis

81

increase pH of the solution from 4 to 5, the H+ ion concentration of the solution is to decreased by 10 times. If a solution has a pH of 5, it will become neutral (pH 7) , if W ion concentration is decreased 100 times (10 times for each increase in unit of pH).

=

In general, acidity of a solution increases with decrease in pH value and alkalinity Inc reases with increase in pH value. A solution is more acidic at pH = 2 than at pH = 4 as the W ion concentration in the former case (pH = 2) is 1 X 10- 2 g. ion/litre and it is 100 times as high as in the latter (pH = 4) case 1 x 10- 4 g. ion/litre) . Similarly , a solution is more alkaline at pH = 12, than at pH = 9. In the former case, the OH - ion concentration is -

x 10- 14 [H+)

X

=

10- 14

1 x 10-

12

=10x10- 2 g.ion/Litre

1 x 10- 14 and in the second case [OW) -----::= 1 x 10-5 g.ion /litre , which is less by a x 10- 9 factor of 1000. pH 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

=

J, Acid f- Neutral --7 Alkaline The extreme pH values in the above scheme roughly correspond to the W ion concentrations of 1 NHCI solution (pH ~ 0) and 1N NaOH soitJtion (pH ~ 14). Of course , more acidic solutions with pH < 0 and more alkaline solutions with pH > 14 are also possible. bu t such cases are not usually in practice and so not included in the scheme .

It is important to note that pH = 7 ·applies to a · neutral solution only at 25°C, because ionic product of water depends on the teinperature.

DETERMINATION OF pH OF

TH.~

SOIL

There are two important methods of determining pH of the soil: (1) Colour comparison method. (2) Potentiometric method.

111

COLOUR COMPARISON DETERMINATlON

or

THE SOIL pH

Kuhn's method: This is the most common method of pH determination of the soil. This method is based on the principle that when a soil suspension is shaken vigorously with very pure BaS04 , the latter flocculates the soil colloids and leaves a clear and colourless solution. If the indicator which is not absorbed by the soil is present, its colour will represent the soil reaction. The amount of BaS04 required to give a clear suspension, depends upon the colloi dal matter present. It is necessary to reduce the amount of soil used for loam and heavy soils . Kuhn's method consists is placing a layer of BaS0 4 one cm . thick at the bottom of a very dry test tube, Which is long and narrow. Then a layer of soil about 3 cm deep is placed over the BaS04 layer. Now fill the test tube to a depth of 9 to 10 cm by adding CO 2 free distilled water. Add 0.5 ml of a suitable indicator solution depending on the pH expected an d fill the test tube to 15 cm depth with water . Close the tube with a paraffin waxed cork ano shake the test tube vigorously for about 30 seconds, so that the indicator gets mixed intimate iy with the solid particles. Now allow the tube to stand. Compare the colour of the suspens io'l with lovibond colour discs. In order to select proper range of indica tors, a BOH universal indicator is used to obtain approximate pH. For this, take some soil and a little BaS04 in a flat dish and kn ead the mixture with a few drops of the indicator. Tilt the dish towards one side and note th e

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Global Pollution and Environmental Monitoring

colour of the supernatant liquid : It will show the approximate pH of the soil. It should be noted that if flocculation takes place very rapidly , the supernatant liquid may not be properly cleared . This happens when too much BaS04 is used . If suspension gets clear very slowly, then it should be presumed that too little water has been added . Lovibond comparator instrument is made of bakelite and opens like a book . It has an opal glass screen at the back and can take in two glass tubes, one containing the sample alone and the other containing the sample as well as the indicator. A circular disc, containing a set of nine standard coloured glasses , fits into the front portion and can be easily rotated in order to bring each coloured glass in front . The disc is rotated so that the colour matches with the standard from where pH is noted . There are some well known comparators which can be fitted with interchangeable discs which provide an almost complete range of permanent glass colour standards in a compact form for the more usual colorimetric tests performed in laboratory (both chemical and clinical ).

[2] POTENTIOMETRIC DETERMINATION OF pH The various potentiometric methods of measuring pH include the hydrogen electrode, antimony electrode, quinhydrone electrode and the glass electrode . The hydrogen electrode is easily poisoned and requires great skill in its manipulation . The same is true to lesser extent in case of antimony electrode . So they are rarely used. The quinhydrone electrode is not used for pH values greater than 9 or for oxidising or reducing solutions . The glass electrode is th e most useful and accurate . It can be used from pH 1 to 9.5 with the usual electrode and to pH 11 and even higher with special electrodes. It- is not easily affected by oxidising or reducing solutions , but corrections must be applied for alkali , ion effects at the higher pH values .

(A) USING HYDROGEN ELECTRODE The hydrogen gas electrode is the primary standard for pH measurements . Fig .7.1 illustrates a standard hydrogen electrode . It consists of a piece of platinum or other noble metal · which has been activated by coating the platinum surface lightly with platinum black . The coating of finely divided layer of platinum, called platinum black helps in achieving the largest possible surface area . Moreover, this activation makes the platinum electrode to catalyse readily the fundamental electrode process H2 (g) = 2H + + 2e. A bright platinum electrode or a piece of platinum mechanically activated is advantageous when solution contains organic substances Pt Eelctrode Coated with reducible by hydrogen in contact with finely divided Pt Black platinum. The platinum electrode is immersed in a solution with W ion of activity one . Hydrogen gas is bubbled across the surface of the platinum in such a manner that the electrode is continuously in contact with both solution and the gas . For the proper operation of hydrogen gas electrode pure . Fig. 7.1 The Standard hydrogen is most essential. All traces of air must Hydrogen Electrode be excluded from the electrode compartment.

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Soil Analysis

Moreover, complete saturation of the solution with hydrogen is also essential. The half cell reaction, responsible for the transmission of current across the interface is H2 (g) p

2W + 2e

Platinum does not take part in the electrochemical reaction and it acts only as the site for the transfer of electrons. The potential of the hydrogen electrode is given by,

° 2.303 RT [+ Flog H ] 2) = E (H+. H2) By convention, EO (W, H2), i.e., the standard electrode potential of hydrogen electrode is zero. Thus. E(H+. H

E(W, H2) = - 2.30: RT log [W]

= 0.0591 pH (At 25°C) In other words, potential of a hydrogen electrode depends upon the pH value of the solution with which it is in contact. The pH value of solution can be calculated by combining hydrogen electrode with a reference electrode, say, saturated calomel electrode. The combined cell may be represent~d as, Pt, H2 (1 atm), H+ (c = unknown) II KCI (satd. soln.), H9 2CI 2(s), Hg The e.m.f. of this cell can be determined potentiometrically. The e.m.f. is given by, Ecell

or

=

Eel(ri9ht) -

Eel(left)

=

E(H92CI2.

cr) -

ECH+, H ) 2

= 0.2422 - (0.0591 pH)

0.2422 0.0591

Ecell -

pH =

With the help of this equation, the pH of the solution can be calculated. It is evident from this equation that only cell e.m.f. is unknown and it can easily be calculated potentiometrically. It should be noted that under proper conditions, hydrogen electrode is reversible in its behaviour and it may act as anode or cathode, depending upon the half celf or reference electrode with which it is coupled. In one case, oxidation of hydrogen gas to hydrogen ion occurs, while in other case, the reverse reaction takes place. The potential of hydrogen electrode depends upon the following factors: (1) Concentration of hot ions in the solution. (2) Pressure of the hydrogen at the electrode surface. (3) Temperature. In order to eliminate liquid junction potential, the hydrogen electrode is coupled with the reference electrode through a salt bridge. It is, therefore, necessary to use some other electrodes, instead of hydrogen electrode. Fortunately some other electrodes are known, whose electrode potentials depend upon W ion concentration of the solutions with which they are brought in contact. These electrodes are called pH indicating electrodes.

(b) USING pH INDICATING ELECTRODES (a) Quinhydrone electrode. (b) Glass electrode. (1) Quinhydrone electrode as pH indicating electrode: This electrode was introduced by E. Billmann (1921) and is another arrangement in use for the determination of pH values. Quinhydrone is a compound of quinone and hydroquinone and in solution it is decomposed into equimolecular quantities of these substances.

84

Global Pollution and Environmental Monitoring

P C 6 H4 0 2 + C 6 H4 (OHh

C 6 H 4 0 2 , C 6 H 4 (OHh Quinhydrone (Q)

Quinone

Hydroquinone (QH 2 ) Now consider the reversible oxidation reduction of quinone and hydroquinone, C 6 H4 0 2 + 2W + 2e ::; C 6 H4 (OHh /

This is an oxidation reduction (or redox) system and the potential of an inert electrode, such as platinum, immersed in it is given by, EO -

2.303 RT I [OH 2 ] 2F og rO] fi-!+]2

(H+, Q, QH2) -

= EO (W, Q, QH 2)

_ EO

-

(H+, Q, QH2)

_ 2.303 RT log [a] [H+f 2F [OH2 ]

+

2.303 RT I [a] og-2F [OH2 ]

= 2.303RT I W F og In practice, the ratio [Q]/[QH2] is maintained constant at unity by saturating the solution with the sUbstance quinhydrone, which is an equimotecular mixture of quinone and hydroquinone. The middle term in the above equation, therefore, reduces to zero. = EO 2.303 RTI H+ E + og (H ,Q, QH2) (H+,Q, QH2) + F The standard electrode potential (reduction) of the quinhydrone electrode, i.e.,

E(H+, Q, QH ) = + 0.6996 volts. 2 Thus the above equation at 25°C becomes, E(H+, Q, QH 2) = 0.6996 - 0.0591 pH Again it is well evident from this equation that the potential of a quinhydrone electrode depends upon the pH value of the solution with which it is brought in contact. Th.~ potential of this electrode can be determined potentiometrically by connecting it with reference electrode, such as saturated calomel electrode. The complete cell is represented as, Hg, H9 2CI 2 (s), KCI (satd.) The e.m.f. of this cell is given by Ecell

0.0591. pH

or

pH

(c= unknown), Q, QH 2 , Pt

= Eel(right) - Eel(lE:ft) _ E -E

-

or

II W

(W,

Q,

QH2 )

_ (Hg C12 , CI ) 2

= (0.6996 - 0.0591 pH) - 0.2422 = 0.6996 - 0.2422 - Ecell =

0.6996 - 0.2422 - Ecell 0.0591

Thus simply measuring the e.m.f. of the cell, i.e., Ecell the pH value of the solution can be calculated.

Soil Analysis

85

The quinhydrone electrode consists of a piece of bright platinum or gold in contact with a solution containing an excess of solid quinhydrone. a slightly soluble equimolecular compound of benzoquinone and hydro,::!uinone. The quinhydrone electrode may be set up easily by adding a pinch of quinhydrone (1 gm/100 ml) to the solution. whose pH is to be determined. A bright platinum electrode is Immersed in the solution and the' quinhydrone electrode is combined in a cell with a saturated calomel electrode. The quinhydrone electrode comes to equilibrium in 1 - 5 minutes. For greater accuracy. the inert electrode is carefully cleaned with hot chromic acid and washed with water and absolute alcohol. The solution should be freed from air in order to prevent auto-oxidation. (2) Glass Electrode: The glass electrode potential charges in presence of W ions. If this observation which was made by Haber and Klerhfenslewlcz (1909) is now used as basis of a method of determining the pH of a solution, where other electrode cannot be used. The glass electrode has attained much attention in recent years. because it can be used almost in all solutions, except those which are strongly acidic or strongly alkaline. It has been observed that a potential difference exists at the interface between glass and solution containing W ions. The magnitude of this difference of potential for a given variety of glass varies with W ions concentration and at 25°C, is given by EG = EO G + 0.0591 log [W] EG = EOG - 0.0591 pH When EOG is a constant for the given glass electrode and Polen Ii meter depends upon the nature and composition of the glass, the value of EOG can be calculated by finding I PlalmumW"e the e.m.f. produced in buffer solutions of known pH values. The glass electrode consists essentially of a very third wailed glass bulb, made of a low m.p. glass of high electrical conductivity. blown at the end of a glass tube, this bulb contains an electrode IMKCI which has a constant potential, e.g., a platinum wire inverted in a solution of hydrochloric acid of definite concentration. The bulb is Fig. 7.2 Measurement of pH with Glass Electrode placed in the liquid whose pH is to be, determined. To carry out the determination of pH of a solution, the glass electrode is connected with a saturated calomel electrode acting as a reference electrode, the whole cell may be represented as: Pt: O.1N HCI I glass I Experimental soln. II KCI (satd.). Hg 2 CI 2 I Hg The e.m.f. of this cell may be calculated potentiometrically. Since the potential of the saturated calomel electrode is known, that of glass electrode can be obtained and pH value of the solution may be evaluated, by using the following equation: pH = Eg -O.2422- Ecell 0.0591

86

Global Pollution and Environmental Monitoring

The glass electrode is the most important indicator electrode for hydrogen ions and has almost completely displaced all other electrodes for pH measurements. The glasscalomel electrode system is a remarkably versatile tool for the measurement of pH under many conditions. This combination may be used without interference in solutions containing strong oxidants, reductants, proteins and gases.· The pH of viscious or even semisolid liquids can also be determined. Most glass electrodes available today respond in a nearly theoretical manner to changes of pH in the range 0-12 or even higher.

MEASUREMENT OF pH Procedure: Take 10 g of the soil and add 25 ml of distilled water. Shake the contents! well after a lapse of about 30 minutes. Dip both, glass electrode and the reference calomel electrode in the soil suspension. Connect the electrode to the pH meter, which has already been Checked with a standard buffer solution of known pH. Switch on the current and increase or decrease the resistance in the external circuit so that the potential of the electric power equalises the potential of the cell containing soil suspension and the galvanometer needle indicates at zero. DirectlY,read the pH of the soil from the scale. Nowadays, direct reading pH meters working either on mains or storage battery are 'commercially available. These give the potential and the pH on the temperature of the solution.

DETERMINATION OF LIME AND LIMING MATERIAL IN SOIL In agriculture, lime is mainly used for the correction of Soil acidity. In other ways~ lime also acts to increase the soil fertility and supplies nutritional calcium to crops and also increases the structure of heavy soils. Agricultural liming includes, oxiqe, CaO, calcium hydroxide, Ca(OHh, and calcium carbonate, CaC03. These chemical compounds are generally derived from chalk or limestone, although corresponding materials obtained from magnesium limes have also been used. Lime reactions in soil depend upon the nature and the fineness of the liming material. Lime stone can be classified as calcite (CaC03), dolomite [CaMg(C0 3h1 or a mixture of the two. Both of these limestones are sparingly soluble in pure water, but become soluble in water containing CO2. The greater the partial pressure of CO 2 in the system, the more soluble the limestone would be. Dolomite IS somewhat less soluble than calcite. CaC0 3 + H20 + CO 2 ~ Ca(HC0 3h Burnt lime or quicklime is commercially available with a known content of CaO and ground chalk or limestone is available with a definite amount of CaC0 3 present in it. A good sample of lime to be used in agriculture mainly contains CaC03. Lime or limestone should not contain much of silica or magnesium. Principle: The lime sample for agri~ultural use generaJly contains Ci110, CaSi03, MgC03, Fe203 and A1 20 3. This sample is finely ground, suspended in water and treated with a solution of cane sugar. As a result, soluble calcium sucrate, C12H22011CaO is obtained, whereas CaC03 and CaSi0 3 remain insoluble. The solution containing calcium sucrate is titrated .as CaO against a standard solution of HCI using phenolphthalein as an indicator. Reagents: (a) 0.05N HCI (b) 10% cane sugar solution which can be prepared by dissolving 100g. cane sugar (sucrose) in one litre of distiIled water. Procedure: Accurately weight 5.0 g. of the powdered sample and transfer it to a 500 ml flask. In order to prevent the possibility of caking, moisten it with 10 ml of alcohol. Add 10

87

Soil Analysis

ml of 10% solution of cane sugar and .make up the solution to volume with water. Immediately stopper the flask and shake the flask atleast for 4 hour. Now filter th.e solution through a dry filter paper into a dry beaker. Titrate 50 ml of mal filtrate with 0.05N HCI, using phenolphthalein as an indicator. 1 ml of 0.05N HCI == 0.0014 g. CaO. .

.

Calculations: Per cent of CaO in the sample =,

X xJ)'0014 x 50 x 100 50 x 5

where X is the volume of O.O~.N HCI used to titrate calcium sucrate (50 ml). Removal of silica: PlaCe 5.0 g. of the sample in a clean beaker and add a. little distilled water. Now add dilute HCI in 6rde~ to decompose the carbonate and dissolve as chloride. Most of the silica and clay settle at the bottom of the beaker in th~ form of insoluble matter. A small amount of silica, however, also passes into the solution. Hearthe contents of the beaker to a small volume and then trahsfer it to a clean 100 ml porcelain dish. Now add 10 ml of Conc. HCI and evaporate the'liquid to dryness on a water bath. Heat the dish in an air oven at about 100°C - 105°C to conve·rt hydrated silica into anhydrous insoluble form. Add another 10 ml of conc. HCI and bake at 100°C to deposit silica. Now cool the dish and add 20 ml of conc. HC!. All the contents, except silica and clay, will become soluble. Dilute with water, filter an'd wash the residue with distilled water several times to. remove excess acid associated with the residue. Removal of iron and aluminium: Add a little bromine water in order to oxidise Fe 2+ iron to Fe 3+ iron and then boil the solution to remove excess of bromine. Now add 10 g. of add NH 4 CI and then NH 4 0H to make the solution slightly alkaline. As a result, precipitates of Fe(OHh and AI(OHh are formed. Filter the solution and wash the precipitates with hot water. Dissolve the precipitates in dilute HCI and reprecipitate by adding NH 4 CI and NH 4 0H as before. Dry the precipitates in an oven. Ignite the dry precipitate and the filter paper in a muffle furnaoe and weigh the residue as Fe203 + A1 20 3.

DETERMINATION OF SILICA AND PHOSPHORUS IN SOIL In order to find the total mineral constituents of a soil it is digested, with acid or fused with Na2C03' The method of digestion with acids such as hydrochloric acid and triple acids (nitric acid, sulphuric acid and perchloric acid) is quite common, but the most popular method is the extraction with HC!. This method is universally adopted for the determination of total phosphorus, potassium, calcium, magnesium and even for many micronutrients. However, this method suffers from two main disadvantages. (a)

11 does not differentiate between different categories of minerals present and so results obtained by the analysis of HCI extract have very little practical utility.

The amount of mineral dissolved by HCI depends on various factors such as strength of the acid, time of extraction, soil to acid ratio, temperature and nature of the soil etc. So digestion with HCI is not much used now, except for the determination of phosphorus and potash. Preparation of HCI extract: Take 20 g. of air dry, soil in a 500 ml conical flask. Add 200 ml of HCI (sp. gravity 1.25) with constant stirring. Place a funnel on the mouth of the conical flask and boil gently for one hour on a sand bath or hot plate, filter the contents through Whatmann no. 50 filter paper fitted in a Buchner funnel. Wash the residue with hot (b)

88

Global Pollution and Environmental Monitoring

water containing 50 ml of HCI per litre. Washing is continued until 500 ml of the extract is obtained. Now transfer the filtrate to a 500 ml measuring flask. Cool and make up the . volume. Suppose this is solution A. Determination of acid insoluble residue: The residue remained on the filter paper is the portion of the soil that is insoluble in the acid. Transfer the residue alongwith the filter paper to a weighed crucible. Dry and ignite the residue on a strong flame or in a muffle furnace. Cool and weigh. Now calculate the percentage of acid insoluble silica and sand. Fusion with sodium carbonate: A weighed amount of the soil sample is fused with Na2C03 in a platinum crucible, and then, in order, silica, iron, aluminium, titanium, calcium and magnesium are determined. Manganese, sodium, potassium, sulphur, phosphorus and other elements are determined separately. Preparation of sample: Pass the well mixed, air dry sample through a sieve having circular holes ~ mm. in diameter. Take the sieved soil (25g.), grind in an agate mortar, and pass all of the 25g. sample through a 100 mesh bolting cloth. Because soil weight varies considerably with the air moisture, a moisture determination must be made on the air dry sample, when the sample is weighed for the major elements. Continue heating it overnight so that the separated silica may be sufficiently dehydrated. Determination of silica: Take up the residue with 15 ml of conc. HCI and add 15 ml of hot water. Filter and wash with hot water until the content is practically free from chlorides. Now evaporate the filtrate to dryness, and add 15 ml of conc. HCI and 15 ml of hot water. Filter and wash free from chlorides into a 250 ml beaker. Combine the two precipitates and ignite the mixture, slowly at first, otherwise the light feathery ,silica may be blown away by air. After complete burnout of carbon from the precipitate, ignite at the full temperature of the blast for about half an hour. When the weight becomes constant, moisten the silica with water, and then add 6 to 8 ml of strong HF, and a few drops of dilute H2S0 4 , and heat gently to dryness. Cool and the weight lost during HF treatment equals the weight of silica. Make the filtrate from silica determination to 500 ml with distilled water ar.d use this solution for other determinations. Determination of phosphorus: Take 20-50 ml of the HCI extract or sodium carbonate extract in a 50 ml porcelain glazzed dish. Evaporate on a water bath and ignite at a dull red heat. Rub with a pastle and ignite again. Extract the ignited mass with hot water and filter free from chlorides. Take the residue on the filter paper for the estimation of P205 and the extract for potash (K2 0). Digest the residue for about 30 minutes on a water bath with 30 ml of 10% H2 S0 4 al'!d filter .free from acid. It should be noted that calcium should not be present in the residue. Transfer the filtrate to a 400 ml beaker and add 5-10 ml of nitric acid and then add ammonia until a precipitate that is formed, gets dissolved on shaking. Dilute the contents to about 100 ml and warm to about 25-30°C, and place a piece of red litmus paper, which should turn blue. Now add 10% HN03 drop by drop till it just turns red again. In order to ensure complete precipitation, add sufficient amount of ammonium molybdate. Shake vigorously for few minutes and then allow the precipitate to settle for about one hour. Filter the precipitate using Whatmann filter paper no; 44 and wash the precipitate with 2% NaN0 3 solution and ice cold water. Wash the precipitate till it is free from acid. It can be tested by adding a drop of standard alkali and a few drops of phenolphthalein. The colour of the filtrate should be pink.

Soil Analysis

89

Now spread the filter paper on the sides of the beaker in which precipitation is carried out. Wash it with a jet of distilled water. Dissolve it in a known amount of 0.1 N NaOH. Titrate with 0.1 N H2 S0 4 using phenolphthalein as an indicator (the pink colour of phenolphthalein just disappears). Introduce the filter paper in the beaker and add more acid till the pink colour which reappears on addition of the filter paper disappears. The results are calculated as: 1 ml of 0.1 N NaOH 0= 0.000309 g. P2 0 5 Assuming that soil contains about 0.2% P2 0 5 , then 20 ml of 0.1 N NaOH will be sufficient to dissolve the precipitate of ammonium phosphomolybdate formed from 50 ml of HCI extract. Potassium as K2 0 in the extract is estimated by cobaltinitrite method.

DETERMINATION OF TOTAL NITROGEN IN SOIL Total nitrogen in soils varies from about 0.01 per cent to 0.03 per cent. In plants, it usually ranges from 0.2 to 4.0 per cent depending on the species, the plant part, and the age of the plant. Kjeldahl method modified to include nitrates: In this method, the soil sample is digested with sulphuric salicylic acid. As a result, organic and nitrate nitrogen is converted to ammonium sulphate and the ammonia gas is distilled into boric acid and titrated with a standard solution of sulphuric acid. Reagents: (a) Sulphuric salicylic acid is prepared by dissolving 1.0 g. of salIcylic acid In 30 ml of conc. H2 S0 4 . (b) Sulphate mixture is prepared by mixing 10 parts of K2 S0 4 • 1 part of FeS04 and 0 5 part of copper sulphate (CUS04) and the mixture is grinded to pass a 40 mesh sieve. (c) 45 per cent NaOH is prepared by dissolving 450 g. NaOH in 1 litre of distilled water. (d) 2% aqueous solution of boric acid. (e) 0.1 N standard H 2 S0 4 solution. (f) Bromocresol green methyl red indicator. (g) Dried powdered sodium thiosulphate. Prepare 0.1 per cent solution of bromocresol green by adding 2 ml of 0.1 N N·aOH per 0.8 g. of indicator. Prepare 0.1 per cent methyl red in 95 per cent alcohol (ethanol) and mix bromocresol green indicator with 25 ml of methyl red and dilute to 200 ml with C2 H5 0H. Procedure: Take 10 g. of soil which should pass through a 20 mesh sieve. Add 50 ml of sulphuric-salicylic acid and shake well. Add 5 g. of sodium thiosulphate and heat the contents gently for about 5 minutes. Avoid froathing. Cool and then add 10 g. of sulphate mixture, and digest in Kjeldahl flask at full heat. Digestion is continued for 1 hour after the solution is cleared. Cool and then add 300 ml of distilled water and fit in the distillation apparatus. Add 100 ml of 45% NaOH and a large piece of zinc. Connect to distillation head, and distill off 150 ml into 50 ml of 2% aqueous boric acid solution. Add few drops of the bromocresol green-methyl red indicator and titrate to the first faint pink colour with standard solution (O.iN) of H2 S0 4 . Blanks should be run and the titration be performed to the same end point in exactly the same manner.

90

Global Pollution and Environmental Monitoring

Calculations: Weight of soil sample Vol. of 0.1 N H2S04 used in titration Weight of nitrogen in 10 g soil

·= 10 g. = V ml =VxO.1xO.014 = 0.0014 V

Milliequivalent of nitrogen in 10 g soil

0.0014 x V x 100 10 = 0.014 x V per cent = V x 0.1 = 0.1V

Milliequivalent per cent of nitrogen in soil

= 0.1

Per cent nitrogen

= ------

V x

100

10 =V

•

= Percent nitrogen x 106 100 = 0.014 V x 104 = 140 V. Determination of nitrate nitrogen of soil: Nitrate nitrogen of soil ranges from less than 1.0 ppm to several hundred ppm. Principle: The soil extract is clarified by using copper sulphate, calcium hydroxide, and magnesium carbonate. Nitrate is determined by adding phenoldisulphonic acid with which a yellow coloured compound is formed with nitrate. Reagents: (a) 1N copper sulphate solution. (b) Calcium hydroxide powder and magnesium carbonate powder. (c) Phenoldisulphonic acid can be prepared by first dissolving 25 g. pure white phenol in 150 ml of Conc. H2S04 , Then 75 ml of fuming sulphuric acid containing about 15 per cent S03 is added and contents are heated in a boiling water bath for two hours. It is stored in brown coloured bottle. (d) Ammonium hydroxide is prepared by diluting 1 part of strong NH 4 0H with 2 parts of water. (e) Standard nitrate solution is prepared by dissolving 0.7216 g. of pure KN0 3 in I litre of water. This solution contains 100 ppm nitrogen as nitrate. (f) Silver sulphate solution (0.02N) is prepared of dissolving 3.12 g. A9 2 S0 4 in one litre water. . ppm of nitrogen in soil

D

Procedure: Place the sample of the soil in an oven at 70 C for 4 hours. Grind and pass it through a 2 mm sieve. Take 50 g. of soil in a 500 ml flask and add 250 ml of distilled water containing 5 ml of IN copper sulphate solution and shake well for 5 to 10 minutes. If the soil is not very acidic and does not give a coloured extract, add 0.4 g. of Ca(OHh and 1.0 g. of MgC03 to the soil suspension and shake for 5 minutes to precipitate copper. Filter on a dry filter paper and discard the first 20 ml of filtrate. If the soil gives a coloured extract, allow it to settle. Then decant 125 ml of the supernatant liquid into a flask and add 0.2 g. of Ca(HOh of and 0.5 g. of MgC0 3 . Shake the contents well and filter as before. Pipette out 10 ml of it in an evaporating dish and heat it to dryness. Cool and rapidly add 2 ml of phenoldisulphonic acid directly to the centre of the evaporating dish and rotate the dish in such a way that the reagent comes in contact with all the residue. Allow itto stand for 10-15 minutes and then add about 15 ml

91

Soil Analysis

of cold water and stir with a glass rod until the residue dissolves to form a solution. Now add NH 4 0H to make the solution slightly alkaline. Transfer this solution to a Nessler tube, dilute and compare with standard solution containing 1 ppm nitrogen as nitrate using a colorimeter or Nessler tube. A convenient standard can be prepared by evaporating to dryness 25 ml of a solution containing 22 ppm nitrogen as potassium nitrate. When cool, add 4.0 ml of phenoldisulphonic acid and allow it to stand for 10 minutes, and make up the volume to 500 ml. This solution contains 1 ppm of nitrogen (0.001 mg nitrogen per mI.). Develop the colour by adding just enough NH 40H to make the solution alkaline. Compare the yellow colour so developed (that of standard) with the unknown whose nitrogen content is then calculated. If the soil contains more than 15 ppm of chloride, the latter is precipitated by adding 10 ml of silver sulphate solution in the 250 ml of solution with which the solution is treated. This will remove completely 80 ppm of chloride calculated on the basis of dry soil. If the soil contains very high concentration of chloride, add solid A9 2S0 4 to the soil suspension before shaking. In the case of highly coloured sOil extract, add 1 g. of chloride free carbon black to 100 ml of the supernatant liquid and shake well for about 10-15 minutes before adding Ca(OHh and MgC0 3 to the solution. If the soil is calcareous, add 5 ml of 1N copper sulphate also to the soil extract with the carbon black in order to ensure complete removal of colloidal carbon with copper hydroxide. It should he noted that: (a) Copper sulphate and hydroxide are used for the clarification and decolonisation of the soil extract. (b) Copper is more advantageously precipitated with Ca(OHh in the cold than with Mg(OHh in the cold or with MgO. (c) MgC03 is used to remove the excess Ca(OHh

DETERMINATION OF TOTAL NITROGEN OF THE SOIL (MODIFIED METHOD) In the soil most of the nitrogen is present in organic combination and very small amount of it is present in nitrate or ammonical form. For the determination of total nitrogen Kjeldahl method is used. There are several modifications of this method, but usually the soil is digested with sulphuric acid in the presence of a mixture of potassium sulphate, ferrous sulphate and copper sulphate. As a result, ammonium salts are formed, from which ammonia is distilled with sodium hydroxide and absorbed in a known excess of 0.1 NH 2S0 4. The excess of the acid remained un neutralised can be determined by titration against a standard alkali solution using methyl red as indicator. Reagents: (a) 0.1N H2S04 and 0.1N NaOH. (b) Salt mixture containing K2S04 (10 parts), FeS04 (1 part), CuS04.5H20 (5 parts). (c) Methyl red indicator solution. (d) Salicylic acid, and (e) Sodium thiosulphate. Procedure: Take 10 g. of soil in a clean dry Kjeldahl flask and moisten it with about 10 ml of distilled water. Shake well and allow it to stand for about half an hour. Then add 35 ml of Conc. H2S04 and 10 g. of mixture of K2S04, FeS04 and CUS04. Now add 1 g. of salicylic acid and 5 g. of sodium thiosulphate (Na2S203). Heat first at a low flame and

Global Pollution and Environmental Monitormg ,

92

gradually increase the flame length. Continue digestion until the mixture is colourless or nearly colourless. Cool, and add 50 ml of water. Cool the contents under a water tap. Transfer the solution by decantation to a 800 ml distilled flask. Wash the contents of the digestion flask with water till free from acid. Do not transfer the sandy material to the distillation flask. Make up the volume to 400 ml. Now add few pieces of porcelain to prevent bumping. Distill and receive ammonia in a known volume of 0.1 N H2 S0 4 (20 ml). Titrate using methyl red as indicator. Run the blank also in the similar manner. Calculations: 1 ml of 0.1 N H 2 S04

=

14xO.1x1 1000

= 0.0014 g. nitrogen

1. Weight of soil taken for nitrogen estimation

= 10 g.

2. Volume of 0.1 N H2 S0 4 taken (Blank value) = 'j 1 ml 3. Volume of 0.1 N NaOH needed for the neutralisation of the excess acid = V 2 ml 4. Volume of 0.1N acid used for neutralising ammonia = (V1 x V 2 ) ml (V1 -V2 ) x 0.0014 x 100 5. Per cent of nitrogen in the soil = 10

DETERMINATION OF TOTAL MANGANESI= IN SOiL Principle: The manganese in the soil is oxidised with 0.1 N phosphoric acid and 0.3N nitric acid to give pArmanganate and the optical density of the latter is measured. Interference from chlorides oan be avoided by adding mercuric sulphate. Reagents: (a) Conc. HF, Conc. H2 S0 4 and 85% phosphoric acid. (b) Ammonium persulphate salt. (0) Preparation of standard manganese solution: Prepare 100 ppm solutibn from manganese by dissolving 0.100 g. in dilute nitric acid. Boil, cool and dilute to one litre. (d) Mercuric sulphate solution: Dissolve 75g. of mercuric sulphate in 400 ml of Conc. NH0 3 and 200 ml distilled watAr. Add 200 ml of phosphoric acid and 0.035 g. AgN0 3. Dilute to one litre. Procedure: Take 0.5g. of 100 mesh soil in a platinum dish and add 4.0 ml of HF and 2.0 ml of Conc. H2S04 , Heat gently on a low flame and then increase the temperature till fumes of sulphuric acid are given off. Cool the contents and add 3 ml of Conc. H2 S0 4 and again heat till the fumes of acid are given off. Cool and dilute the contents by adding 10 ml of distilled water. Take a small known portion of the solution and add 1.0 ml of Conc. phosphoric acid. Boil the mixture to a suitable small volume and cool. Add 1.0 g. ammonium persu/phate and boil for 2 to 3 minutes. Cool th~ solution and dilute to 100 ml and find its optical density (0.0.) at 525 nm in a spectrophotometer. Compare its 0.0. with a standard curve and calculate the results.

DETERMINATION OF TOTAL SULPHUR IN SOIL Principle: The organic sulphur present in soil is oxidised to sulphate by sodium peroxide followed by fusion with Na2C03 in order to decompose the soil mi~erals. The sulphate can be determined by precipitation as barium sulphate. Reagents and apparatus: (a) Granular sodium peroxide (b) An hydrous sodium carbonate (c) Cone. HCI (sp. gravity 1.184). (d) Methyl red indicator (e) 10% BaCI 2 solution (f) 95 per cent ethyl alcohol (g) Sulphuric acid, and (h) Nickel crucible. .

Soil Analysis

93

Procedure: Weigh 5 to 10 g. of air dry soil of 0.5 mm mesh into a nickel crucible and add an equal amount of anhydrous Na2C03' Mix well and then add 2 ml of water and stir the contents well to make a stiff paste. Immediately add 10 g. of sodium peroxide successively about 19. at a time, in order to prevent excessive froathing Put the crucible containing the contents in a muffle. furnace at about 400-500°C for half an hour and then increase the temperature to red heat (about 900°C) rapidly for about 10 minutes. Take out the crucibl8 from the furnace and place it sideways in a big beaker and cover with distilled water. Add 5 ml of ethyl alcohol and place it on a hot plate, and heat. Now remove the crucible along with stirring rod from the beaker. If small glassy particles still cling to the inside of the nickel crucible, then disintegrate them by adding water and boiling over a hot plate and add it to the main content. Filter by suction through a Buchner funnel into a small beaker. When n0 more liquid can be drawn through the filter, return the residue alongwith filter paper to the original beaker. add about 1 g. of Na2C03 and then 75 to 100 ml of distilled water, and heat the contents to brisk boiling. Again filter through a Buchner funnel, using suction and wash with 20 ml portions of hot water to a total of 500 ml. Make up the volume to 1 litre by adding distilled water. The amount of sulphate in the extract can then be determined gravimetrically by precipitation as Ba80 4 . Ba 2+ + 80~- = Ba80 4

137

96

233

The determination of sulphate is carried out by preCipitation of it as Ba80 4 in a hot dilute solution of the sulphate previously acidified with HCI (In order to prevent copreclpitation. i.e., the precipitation of carbonate, phosphate etc.), present as impurities in the sample. HCI also helps in the formation of coarse and easily filterable precipitate The precipitate of Ba80 4 is filtered, washed with hot water, dried and ignited to a constant weight. The percentage of sulphate can be calculated from the weight of the precipitate.

DETERMINATION OF SOLUBLE SALTS (ALKALI SALTS) IN SOIL All soils contain varying amounts of salts in the soluble form as carbonate, bicarbonate, sulphate, nitrate etc. The water soluble salts occurring upto 0.1 per cent or more in the soil usually consist of Na+, K", Ca 2+ and Mg2+ ions in association with sulphate, chloride, carbonate and bicarbonate ions. The soil may be saline and alkaline depending on the nature and quantity of salt presEfnt. . A saline soil is that for which the conductivity of saturation extract is more than 4 m. mohs/cm at 25°C and the exchangeable sodium percentage is less than 15 and pH is generally less than B.S. A saline alkali soil is one for which the conductivity of saturation extract is greater than 4 m. mohs/cm at 25°C and exchangeable sodium percentage is greater than 15. A non-saline alkali soil is that for which the conductivity of saturation extract is less than 4 m. mohs/cm at 25°C, but exchangeable sodium per cent is greater than 15. The soluble salts in soil are determined by conductivity methods. The electrical conductivity (ohms- 1 or mhos) obtained for soil solution is very small. Thus it is convenient to express them in millimhos per cm.(m.mhos/cm). Conductivity of a solution depends on various factors such as (a) Distance between the electrodes (b) Area of electrode plates (c) Nature of salt present, and (d) Temperature.

Global Pollution and Environmental Monitoring

94

Equivalent conductivity of a solution is the conductivity of a solution containing 1g. equivalent of the electrolyte when placed between the electrodes exactly 1 cm apart. Thus, Electrical conductivity Specific conductivity x V K x V

=

=

1000 x K = Molarity where V is the volume of solution containing one gm. equivalent of the solute dissolved in it. Similarly, 1000 xK

Molar conductivity

=K x V = Molarity

Where V is volume of solution containing one gm. molecular weight or one mole of solute dissolved in it. The soil suspension or paste is taken in a conductivity cell for' the determination of electrical conductivity. Modern conductivity meters are calibrated to read directly the electrical conductance with the given conductivity cell. It may, however, be possible that the electrodes in the conductivity cell are not exactly one cm. apart and may not have a surface area of one sq.cm. So the value of observed conductivity will not be equal to the specific conductivity (Which is the conductivity of one cm. cube of the solution) but a value proportional to it. It is, therefore, essential to calculate a factor for the conductivity cel/, cal/ed the cell constant, which when multiplied by the observed conductivity gives the value of specific conductivity. A O.02M solution of KCI is taken for the determination of cell constant. The specific conductivity K for 0.02 Demal KCI at 25°C has been found to be 0.002761. Thus, Cell constant K x R Specific conductivity x Resistance

=

=

Specific conductivity Observed conductivity The total soluble solids of water extracts of soils range from less th'an 100 ppm to more than 3000 ppm in the soil. Preparation of saturation extract: Prepare a saturated soil paste by adding distilled water to a sample of soil while stirring with a spatula. The soil water mixture is consolidated from time to time during the stirring process by tapping the container on the work bench. At saturation, the soil paste glistens as it reflects light, flows slightly when the container is tipped, and the paste slides freely and cleanly on the spatula almost for all soils, except for those soils which have high clay content. After mixing, the sample is allowed to stand for about an hour, and remix with water, if it loses its shine. Transfer it to Buchner funnel and withdraw the extract by using vacuum pump. For determining soluble salts in soils, the soil iS,preferably kept at the field conditions and its conductivity is measured. For this purpose soils' saturation extract is prepared as described above, and conductivity is measured. This method is, however, very laborious. It can be replaced by 1:2 soil water suspension which is extensively used now. The conductivity or the concentration of soluble salts in 1:2 soil water suspension multiplied by 2 gives the values for the original soil sample. Take 50 g. of soil sample and add 100 ml of distilled water in a conical flask and shake for about 20 hours or overnight. Filter the solution. Rinse the conductivity cell first with distilled water 'and then with soil water suspension. Place the cell in the solution in such a

95

Soil Analysis

manner that electrodes are well immersed. Balance the galvanometer or the magic eye of the conductivity meter and read directly the specific conductivity of the soil solution. If conductivity lies between 0-0.8 m. mhos, the approximate salt concentration is below 0.05 per cent. If the conductivity is between 0.8-1.6 m. mhos, the concentration of salts would be between 0.05 and 0.15 per cent, and if the conductivity lies between 1.6 and 3.2 m. mhos, the concentration of salts would be between 0.15 and 0.25 per cent. The conductivity can also be determined by making use of wheatstone bridge operated by alternating current or newer bridge employing a cathode ray tube as the null indicator. It is very important to maintain the temperature constant and apply correction. For soil extracts and solutions, a temperature conversion factor Ft , obtained from table 2, can be used for converting values to 25°C. Thus, Electrical conductivity at 25°C = Electrical conductivity at temperature t x Ft , or E.C. at 25°C = E.C. at temperature t x Ft where Ft is the correction factor at temperature t.

MONITORING OF PESTICIDES Pesticides are the chemicals which are used to kill pests, but they are also the worst enemies of the environment. Pesticides are generally classified into three main categories. (a) Herbicides, such as carbamates and triazines (b)

Insecticides, such as organochlorine and organophosphonis compounds.

(c) Fungicides, such as dithiocarbamates. Chlorinated hydrocarbon pesticides can be subdivided into alkanes, alkenes and aromatic hydrocarbons. Examples are aldrin, chlordane, DDT, BHC, dieldrin, heptachlor (PCB), lindane etc. These pesticides are generally lipophilic and have low polarity and dipole moment. They degrade in the environment slowly and their half lives generally vary from 2.0 to about 16.0 years in soil. All these pesticides generally degrade ultimately to carbondioxide and water. These compounds are neurotoxic in '1ature. Organophosphorus pesticides include parathion, malathion, dimethate, dichloros etc. They have better water solubilities and are hydrolysed in water. They have much less half lives in soil than chlorinated hydrocarbon pesticides and the maximum half life is about 40 days. Almost all these chemicals interfere with muscular function. They usually contain phosphorus in pentavalent form. Carbamates pesticides include carbaryl (sevin), baygon etc. These chemicals are relatively soluble in water and possess very short life in the environment. Their half lives generally range from 1.5 days to 30 days at the most. They readily react with water and undergo decomposition. In addition, there are some inorganic pesticides such as fungicides, which are copper, nickel, lead and arsenic salts. 2, 4 0 (2, 4 dichlorophenoxyacetic acid) and 2, 4, 5-T (2, 4, 5trichlorophenyl oxyacetic acid) are well-known herbicides. Hexachlorobe.nzene (HCB) is non-degradable. One of the main problem usually associated with application of pesticides to the soil is the presence of pesticide residues. These pesticide residues are formed as a result of degradation of the original pesticide in water or soil. In many cases, such pesticide residues are more dangerous to health than even the original pesticide. For example, DDT undergoes degradation to DOE. The degradation

Global Pollution and Environmental Monitoring

96

of pesticides can take place through various processes which include oxidation, hydroxylation, side chain oxidation, dehydrogenation, dehydrohalogenation. conjugation or metal complex formation etc. The pesticide residues can remain in biosphere as well as in lithosphere for more than 30 years, even if the use of pesticides is completely stopped now. The degradation of pesticide residues in the environment depends on a large number of factors and the rate of degradation depends on chemical nature of the pesticide and its chemiFal structure. Despite degradation, they are not completely removed and, moreover, degradation may be complete or partial. Analytical methods are now available for pesticide analysis involving study of pesticide residue, degradation products and new formulations. The most important methods used for analysis and characterisation of pesticides are: (b)

Chromatographic methods. Polarographic methods. and

(c)

Spectroscopic methods.

(a)

The most important chromatQgraphic techniques are:

(a)

Thin layer chromatography (TLC).

(b)

Gas liquid chromatography (GLC), and

(c)

High performance liquid chromatography (HPLC).

Gas liquid chromatography is capable of detecting nanogram and picogram amounts of pesticides. Thin layer chromatography is useful for qualitative as well as quantitative analysis of pesticides. For example, carbamates are best analysed by TLC in preference to GLC. The technique of GLC has widely been used in the analysis of organochlorine pesticides by making use of electron capture detector, because chlorine has a high affinity for the capture of electrons. Under normal operating conditions nanogram quantities of chlorinated pesticides can be detected. Organophosphorus pesticides are best analysed by GLC using flame ionisation detector. . Organochlorine pesticides are best detected and analysed by TLC. For example, DDT or DDE can be analysed with AgN0 3 bromophenol blue spraying reagent in TLC. The carbamate pesticides such as carbaryl and organophosphorus pesticides such as parathion and malathion can also be characterised by TLC. Volatile pesticides are generally analysed by GLC. The organochlorine pesticides and their residues may be analysed by GLC and acetonitrile may be used as the solvent. For organophosphorus pesticides. hexane is used as solvent. Polychlorinated biphenyls (PCBs) can be characterised by GLC-MS with glass capillary column. HPLC has also been employed for the analysis and characterisation of a large number of old and new pesticides. In HPLC analysis of pesticides, photqmetric and fluorometric detectors are generally used. Pesticides containing oxidisable or reducible groups are generally analysed by polarographic technique. The spectroscopic methods of analysis of pestiCides include UV-IR spectrophotometry, NMR spectroscopy and. GC-MS technique. Pesticide residues are best analysed by IR spectroscopy. Pesticide isomers can be analysed by NMR methods. Mass spectrometry is very useful for the identification of new pesticides.

97

Soil Analysis

SEPARATION AND DETECTION OF PESTICIDES BY TLC Thin layer chromatography has widely been used in the separation and detection of pesticides. Walker and Beroza have examined the separation of 62 pesticides in 19 solvent systems in the year 1963. They used silica gel G layers for chromatographing DDT, four isomers of haxachlorocyclohexane (BHC), aldrins, isodrin, dieldrin, endrin, chlordan and pentachlorophenol. They used various solvents for the purpose. For example, petroleum ether (50 - 70°e) was used to separate DDT and four isomers of BHC. Cyclohexane was used to separate aldrin from its stereoisomer isodrin, and dieldrin from its stereoisomer endrin. Aldrin am:! its isomers were detected by spraying with 0.01 N KMn04 solution. The DDT and hexachlorocyclo-hexanes were made visible by spraying first with mono-~thanolamine and then heating for 20 minutes at 100EC. This was then followed by a spray of 0.1 N AgN0 3 .- HN0 3 (10:1). The density of HN0 3 was 1.40. After the second spray the plates were exposed to UV light or sunlight.

SEPARATION OF ISOMERS OF HEXACHLOROCYCLOHEXANE (BHC OF HCH) BY TLC Benzene hexachloride (BHC), commonly known as 666 or Gammexane is an addition product of benzene with chlorine. Because chlorine atoms may attach themselves to the benzene ring in a number of ways, atleast five different isomers were known of which gamma isomer is the only isomer which has appreciable toxicity to insects and occurs from 10-40 per cent in the commercial sample of benzene hexachloride. In recent years, it has become possible to separate the gamma isomer from the other isomers. A product containing 99% gamma isomer is known as Lindane. TLC can be used for the separation of isomers of BHC. The isomers are allowed to move on a thin coating of activated silica gel G spread on a glass plate. The isomers are then detected by making use of suitable spray reagent. In the resulting chromatogram, the zones are characterised by RF values. The RF value is defined as, RF =

Distance from the starting line to the centre of the zone Distance from the starting line to the solvent front

The RF value determines the velocity of the movement of the zone relative to that of the developer front and thus identifies the isomer. The intensity of the zone may be used as measure of the concentration by comparison with standard spots. Reagents used include chloroform: cyclohexane (20: 80), AgN0 3 (IN) and Conc. HN0 3 . Suspend a known amount of silica gel G in distilled water inorder to make a slurry. The slurry is spread over a carefully well cleaned glass plate with the help of a spreader. The plate is well activated for about 30 minutes at 11 OEC in order to activate the layer of silica gel G. The sample of BHC is now dissolved in a solvent like benzene and the plate is spotted with the help of capillary tube. It is then dipped in a solvent containing 20% chloroform and 80% cyclohexane by volume. When the solvent has moved to a certain definite distance the plate is removed and dried for few minutes. The plates are now sprayed with monoethanolamine and heated to 100°C for 20 minutes. It is then sprayed with a spray reagent containing 1N AgN0 3 (10V) and Cone. HN0 3 (IV). Now spots appear at the plate. The RF values are calculated and

Global Pollution and Environmental Monitoring

98

compounds are identified from the Rf'values which, have previously been determined with help of pure isomers.

tne

BHe Isomer

RF Value

Hepta - isomer Alpha - isomer Gamma - isomer Epsilon - isomer Beta - isomer Delta - isomer

0.56 - 0.60 0.40-0.43 0.33 - 0.36 0.31 - 0.33 0.25 - 0.28 0.14-0.17

SEPARATION OF CHLORINATED PESTICIDES BY TLC The chlorinated pesticides can be chromatographed on alumina layers activat~d by heating at 200 - 220°C for about 4 hours. The mixture of pesticides is applied on the plate which is then placed in a glass tank saturated with hexane. The RF values are then calculated.

Pesticide Aldrin DDT Perth~ne

HCH or BHC Dieldrin Methoxychlor

RF Value 0.78 0.59 0.48 0.39 0.17 0.10

- 0.81 - 0.62 - 0.50 - 0.41 - 0.19 - 0.12

The detection is carried out by taking out the plates out of the glass tank and then spraying with 0.5% solution of p-dimethylamino hydrochloride made in sodium ethoxide (1g. sodium and 100 ml ethyl alcohol). In order to moisten the plates distilled water is sprayed. Now the plates are held in front of an ultraviolet lamp for 1 minute. Dirty violet to greenish spots are given by chlorinated pesticides.

SEPARATION OF ORGANO PHOSPHORUS PESTICIDES BY~LC This group of pesticides can be chromatographed on silica gel G using hexane: acetone (4 : 1) as the solvent system. The plates are sprayed with a 0.5 per cent solution of palladium chloride in dilute hydrochloric acid giving yellow spots on a faint brownish background. The RF values are given below:

Pesticide

RF Value

Diazinon Parathion Metasystox Malathion Chlorthion Fac Rogor

0.76 - 0.82 0.65 - 0.68 0.62 - 0.64' 0.52 - 0.54 0.43-0.45 0.20 - 0.26 0.04 - 0.07

99

Soil Analysis

SEPARATION OF PESTICIDES BY GLC Suppose we have to separate a mixture containing 5 c0mponents, A, B, C, 0 and:;£: tinthe column. The sample is introduced on the packing at the front end of the columnpy, means of a syringe which carries a rubber septum on the column inlet. This then evaporates and the mixture is swept though the column by the carrier gas. Those components that have a finite solubility in the stationary liquid phase, distribute themselves between this phase and the gas according to the equilibrium law. In other words, the degree of retardation of stationary liquid phase depends upon the tendency of each component to dissolve in the stationary phase. Detector Signal Each component is represented by an arrow and its tendency to dissolve Sample Injection is shown by the amount projecting into the stationary liquid. Thus the rate of movement of various components along the column depends upon their tendency to dissolve in the stationary b 5 w liquid phase. A distribution coefficient X Time favouring the solvent results in a low rate. Components having negligible Schematic Chromatogram of A Five Component Mixture solubility in the liquid phase move rapidly through the column. Ideally bell shaped elution curves are obtained. Component A in the above separation is least strongly dissolved, while component E is most strongly dissolved. The carrier gas has most effect upon the components not dissolving the stationary phase and the components are swept tl'1rough the column so that A emerges before B, which in turn emerges before C etc. A '~cord is made of the Signal which is produced by the detector. It should be noted that if same sample is again injected on to the same column under the same circumstances of temperature and carrier gas flow rate, then an identical result is obtained. If pure component B is injected instead of a mixture, the result is single peak in the same position as B. o

1

80

w

70

1 2

C/)

3

4

z 0 60 a. C/) w

a: a: ~ 0

5

50 6

O. Hexane 1. Lindane 2. Heptachlor 3. Telodrin 4 y-Chlordane 5. Endosulphan H 6. p.p' DDT

40

w

Iii' 0

30 20 10 0

o

2

4

6 8 10 120 Retention time, minutes

140

Fig. 7.3 Separation of chlorinated pesticides dissolved in hexane, using gas chromatography.

100

Global Pollution and Environmental Monitoring

Let us again consider the separation of chlorinated pesticiqes (by vapour phase chromatography or gas chromatography) dissolved in hexane using PVC, The mixture is added to one end of a glass tube containing a solid packing material coated with a high boijing, non-voJatile liquid such as silicone oil. An unreactive carrier gas such as helium is passed through the column. The components of the sample gradually separate as they continuously vapourise into the helium and either adsorb onto or dissolve in the packing. Ordinarily the more volatile components move faster and come out of the column first.

I .

1

3

~A 2

'f

5

~

V

'--v-

14

V

12

U

10

l)

I

U

8

L./"'

6

4

2

o

Fig. 7.4 Retention time (min) Gas chror:natogram of (1) Lindane (2) Heptachlor (3) Aldrin (4) Heptachlor epoxlde. and (5) Dieldrin. The separa.tion,was performed at

eo·e using a SE-30 column. The weight of each component was 0.0824 ng.

In order to measure the extremely small quantities of herbicides and pesticides present on the surface of crops and animal tissues, extremely sensitive detectors must be used. Fortunately, most effective pesticides are halogenated compounds which can be measured with excellent quantitative results by microcoulometric methods after pyrolysis of the gas chromatographic column effluents. Preparation of the sample requires some care, especially if the pesticide is to be measured in animal tissue. One of the latest detection is based on the ability of electronegative molecules to associate with electrons. Thus electron capture detector is particularly effective in detecting polynuclear aromatics, halogenated compounds, and other molecules with conjugated Systems,

Soil Analysis

101 7.506.25-

5.00-

3.75-

2.50-

rn

~

CD C.

~

a .,...

o >
icide monitoring (HPLC with UV detection nm, GLC with el,eotron capture detection and GLC with electrical conductivity detection). All the three methods detected !inuron at 200 ppb level. ~t 254

Kirkla~d' have also s~,par~ted IinurQJl,' ~i~r~n, ~OnUfQn .~J'ld, fenur~m lJsing liquid-liquid partition' ch(,omatography. A .v~riety of substituted ur~a compounds hils also been separated by using reversed phase HPLC.

Paraquat" a !Jipy~!~i.!JUITI herbicide 'was !'lnalyzed in, c!inical urin~ samples obtained from patients whti had ingeSted the cdmpound. HPLC analysis was possible by direct injection "of (10 ng) untreated (Jrih~' samples onto a c,olumn 9f alumina containing bonded ~minopropyl groups. A-methi;lilollaqueous acid eluent was used and paraquat was monitored by measuring >the DV' absorbance at 256 nm'. The same technique was also used in the separation of ,paraquat ,an~ diquat, with diquat I?ein~ ctet~ct~.d 310 nm.

at

Kawano and Coworkers have Cllso a.nflJyzed commercial paraquat formulations on . Vydac cation .exchange resin with 0.4 M.d.imethylamine in methanol as eluent. ~isenbeirs and Sieper have separated 5 phenoxyacetic. acid herbicides on a 1.5 m x 2. mm Ld. column 0.1 Perisorb A peUicular adsorbent with a mobile phase containing hexane/ acetic acid (92.5: 1.5): The substances are non-volatile and must be esterified before GLC analysis. With HPLC system the detection limit of methoxy chlorophenoxy acetic acid, was 5 ng.

A number of other herbicides such as chlorpropham (isopropyl-3-chlorocarbanilate), a non-polar herbicide and polar hydroxy metabolites (2-hydroxy-and 4-hydroxy chlorpropham) present as plant gJycosides have also been extracted and analyzed. Chlorpropham was extracted from alfaJfaroot and shoot tissue with chloroform, and the herbicide isolated by a combination of column chromatography and HPLC on carbowax - 400 with hexane/chloroform (75 : 25) e!uent.

Fungicides : Kirkland and Coworkers have used chromatography on Zipax SCX to analyse benomyl residues in soils and plant tissues after a preliminary liquid-liquid partitioning clean up step. Extraction of benomyl from soil with acidic methanol converted benomyl to methyl-2-benzimidazflle carbamate (MBC), the principal degradation product of benomyl, and MBC wa,s analyzed quantitatively. A second degradation product,' 2-aminobenzimidazole (2-AB) was eluted on the same chromatogram and Similarly quantified. Recoveries of benomyl, MBC and 2-AB from various soils averaged 92, 88 and 71 % respe~tively. Each of the

107

Soil Analysis

compounds was monitored at 50 ppb level and ethyl acetate .extraction was used for plant tissue analysis and in this manner a wide range of crops was analyzed. Kirkland also carried out I;PLC analysis of benomyl in cucumber extracts, using (a) Column packing: Zipax SCX pellicular strong cation exchanger (b) Column dimensions: 1 m x 2.1 m.m Ld. (c) Eluent: 0.025N tetra methyl ammonium nitrate / 0.025N HN0 3 (d) Pressure: 300 psi (e) Flow rate: 0.5 ml min- 1 (f) Column temperature: 60°C (g) UV Detection: 254 nm. Kirkland analysed benomylas MBC and two hydroxylated derivatives in cow's milk, faeces and tis~ues, using Zipax sex. He also used fluorimetric detection to determine benomyl in plant tissues. Fortified cucumber

Cucumber control

Gl

Ul

r::::

8. Ul

e

i

Benomy/MBC (0.05 ppm)

1001-11 njected

0

2-AB (0.10ppm)

2-AB

~

1001-11 injected

o

10

20

t 30

o

10

20

30

Time (min)

Analysis of benomyl in cucumber extracts. Column packing. Zipax SCX pellicular strong cation exchanger; column dimensions, 1m x 2.1 mm Ld; eluent, 0.025N tetramethylammonium nitrate/0.025N nitric acid; pressure, 300 psi; flow rate, 0.5 ml min"1; column temperature, 60"C; detection, UV at 254 nm.

Vita vax (5, 6-dihydro-2 methyl-I-4-oxathin-3-carboxanilide) is an anilide fungicide which produces two oxygenated derivatives on photolysis. Analysis of vitavax. alongwith two oxygenated derivatives was carried out by Wolkoff and po-workers on Bondapak C - 18/Corasil with water/aceto nitrite (80 : 20) as mobile phase. After dichloromethane extraction of a fortified sample of lake water, 20 ppb of vitavax and 5 ppb of its two photo-products were determined by HPLC using UV detection at 254 nm.

108

Global Pollution and Environmental Monitoring

The fungicide dithianone was quantitatively analyzed after extraction from apples containing the compound at levels of 0.1 ppm and 20 ppb by Eisenbeiss and sieper. Rodenticides : The warfarin [3-(a.-acetonyl benzyl)-4-hydroxy coumarin] an anticogulant rodenticide, has been analyzed by Mondy, Quick and Machin 'in animal tissues, stomach content, body fluids and feedstuffs using Corasil (( column and iso-octane/isopropanol (98 : 2) effluent. Fasco and Coworkers have also carried out HPLC studies of the analysis of warfarin and its metabolites in blood using reversed phase chromatography.

SEPARATION OF PESTICIDES BY POLAROGRAPHY Organochlorine pesticides such as aldrin, endrin, dieldrin and hexachlorocyclohexane (HCH) can be analysed on dropping mercury electrode (DME) in LiCI in isopropyl alcohol. The half wave potential (E 1I2 ) of various nitro group containing pesticides is known. 0.1 M nitric acid, acetate buffer, ammonia-ammonium chloride buffer and 0.1 M NaOH etc. are used as the supporting electrolytes. The half wave potential in these supporting electrolytes generally varies from -0.32V to -O.72V. In case of parathion pesticide, e.g., the E1/2 is -0.26V, -0.62V and +0.74V respectively in 0.1 M HN0 3 , acetate buffer and ammonia-ammonium chloride.

ANALYSIS OF PESTICIDES BY SPECTROMETRIC METHODS In these methods, the standardised adsorbents are generally required for clean up before analysis. IR methods have been used for the analysiS of various isomers of BHC. However, IR methods are less sensitive than UV methods. NMR spectroscopy is a suitable technique for the analysis of pesticides such as DDT and pesticide residues such as DOE, Carbamates, chlorinated hydrocarbons and their metabolities can be analysed by mass spectrometry. The metabolities of 2,40 have also been studied by mass spectrometry. GCMS is an excellent technique for the analysis of various types of pesticides. PCBs, lindane and 2.4,7,8-T have successfully been analysed by GC-MS technique.

MANAGEMENT OF WASTE IN SOIL Soil pollutants, such as the domestic sewage can be readily decomposed by the natural processes, i.e., by the action of micro-organisms as bacteria, fungi, protozoa and other microbes. Biodegradable municipal sewage can also be treated by artificial methods. It can also be composted where bacteria and fungus play major roles. However, serious problem~ arise with the non-biodegradable pollutants when the input into the environment exceeds the decomposition and their dispersal capacity into the soil. Moreover, there are limits to the total amount of waste that can be decomposed in a given land. If the overall limits in the biosphere are avoided then one has to preserve about 4 to 5 acres of biologically productive land and fresh water per person. India took some strides by treating the unwanted garbage and by establishing gobar gas or bio-gas plants. Septic tank, used to process the domestic sewage, is an underground sewage container made of concrete. Waste solid materials settle at the bottom of the tank and form the sludge, while the fluids flow from the tank into a system of perforated pipes. The waste stream then passes through the holes in the pipes and slowly gets filtered through the soil. SQiI microbes decompose the organic wastes. Thus the sludge which accumulates at the bottom of septic tank is slowly digested by sewage bacteria. The sludge shou~d be period~cally pumped out and hauled to a sewage treatment plant for final disposal.

Soil Analysis

109

Sludge, i.e., the solid waste which remains after sewage treatment, is treated in a sewage treatment plant. However, handling and disposal of sludge is a major problem for treatment plant operators. It sometimes requires almost 50% of the total budget, so the main worry is - where to put the ever increasing amounts of sludge? Recently a new scheme is suggested for the sewage disposal (due to acute shortage of suitable dump sites) which would certainly help in reclamation of non-productive land. Accordingly, the sludge would first ul1dergo bacterial decomposition and thereby digestion of organic matter. It would then be pumped through a 24 inch pipe to strip-mined barrens and marginal farm lands sufficiently away from the locality. The process requires only one-third of the cost of the original disposal method. Vincent Bacon, who advised this new technique, says "that land needs our sludge as much as we need the land. " Today air, water and soil, which are the three basic amenities, for living beings, have undergone a most horrible ecological disaster. The soil on which we grow our food is polluted largely by solid wastes from homes, industries and agricultural farms. Disposal of solid waste is not easy since the economy involved is quite expensive. To make the disposal of wastes more economical, recycling and re-use of materials is essential. Hence control measures include primarily the methods for the solid wastes to be reduced and to dispose it safely. Waste worries can be reduced by the following procedures: (1) Collection of wastes. (2) Disposal of wastes. (3) Recovery of resources. (1) Collection of wastes: The solid wastes have to be collected from various streets and cities to the disposal area. However, the process is very time consuming. An estimate shows that about 80% of the total cost of solid waste management is spent for collection of waste only. Transfer stations may be constructed at different places of a city so that the refuse could be taken away to the nearest stations from where it could be brought to the ultimate disposal after cramming. Wastes can also be collected with the help of pneumatic pipes. The method is more efficient for the collection and disposal of waste but more expensive and requires much labour. (2) Disposal of wastes: Dumping of solid waste is a popular and inexpensive way of getting rid of wastes. But the disposal of waste is not free from disadvantages. Landfill seems to be the possible way of waste disposal. Landfill operation, which is a biological method of treatment, involves the depositing of refuse, compacting and covering it with a soil. Industrial wastes consist mainly of suspended solids, fats, oils, organic solvents, carbohydrates, toxic metals and metallic compounds. These effluents are a potential source of soil pollution through their direct or indirect disposal on the land. So in all de'/eloped and developing countries industrial units adopt one or more of the following ways to dispose off their wastes and effluents:

(1) Treat their waste to remove suspended solids and discharging their effluents into water course. (2) Discharge untreated effluents into public sewerage system, to be processed with domestic sewage by Municipal Sewage Treatment Plants. (3) Transport the untreated wastes for land disposal sites. (4) Discharge the liquid waste into sewers and to dump the solid sludge. (5). Chemical treatment of industrial wastes such as coagulation and precipitation for removing solutes or suspensions. (6) Distillation, steam or inert gas stripping to remove low boiling wastes. (7) Screening, oxidation, flocculation and sedimentation of effluents followed by biological treatment. (8) lon-exchange, electro-dialysis or active carbon adsorption to remove highly toxic compounds before their disposal to land.

110

Global Pollution and Environmental Monitoring

(3) Recovery of resources: Useful products can be recovered from the wastes. In India, about 30% of the energy consumed by public is biological in nature. Gobar gas plants, based on anaerobic fermentation of organic wastes in the absence of air increase the heating efficiency of the cattle dung by about 20%, and produce an organic manure which is about 43% better than the dry cattle dung itself. This manure can also reduce pressure on naphtha-based fertilizers. Gobar gas, a mixture of methane, carbon dioxide and a minute quantity of other gases, is a more, cleaner fuel than the dry dung itself. Biogas.is a very good answer to the country deepening energy crisis, because it is not only the non-polluting energy source, but also provides enriched manure and improves local sanitation and health standards. Now thousands of gobar gas plants have been installed to meet the increasing demands of energy needs of rural areas and today India is the second (after China) in the extent of its biogas programmes. A limitation of biogas is, however, its dependence on cattle dung, from which it is produced through the anaerobic fermentation. A large number of government and voluntary organizations are involved in disseminating biogas technology. In advanced cities, where underground facilities exist, sewage gas may be utilized. It is a mixture of methane and carbon dioxide. This methane gas may be separated out, compressed and filled in cylinders, which can be used for heating purposes. A considerable amount of heat energy and agricultural manure may be obtained from urban trash, which is being discharged in the environment resulting in pollution and health hazards. Toxic gases (methane, hydrogen sulphide etc.) produced by anaerobic decomposition of wastes can be controlled to no more than 5% near the sites. However, compacted clays, asphaltic and plastic lines help to retain gases within the landfill. The addition of perforated pipes in gravel filled trenches with or without air pressure or suction can be used to remove unwanted gases before high concentration build up occurs within the landfill. Recycling requires one inevitable condition - separation of each waste. The volatile and semi-volatile organic chemicals can be conveniently separated using air, water or steam. Separation of liquid wastes is a simpler process. (1) Separation of volatile compounds: The technique involves the tainted water which is pumped up through a column down which flows with a current of air. This stripping removes a part of volatile contaminants. Steam can also be used instead of air. To clean soil contaminated with volatile organics, air is drawn through by creating vacuum at many holes drilled into it. The volatile organics so stripped off can then be burnt or used in manufacturing processes if they are not very complex in nature. Porous activated charcoal can effectively be used to absorb all organics. Any remaining organic component, if harmful, is inactivated by chemical treatment. (2) Separation of water soluble compounds: Water soluble organics, including inorganic soluble salts and acids can be washed off from contaminated soil or solid wastes adhered to it with water. Some organic wastes can be removed USing other solvents which dissolve them, provided that the precious solvent is easily available, cheap and is in plenty. (3) Other solid organic wastes need, however, different strategies. Most of these are reduced to a manageable waste by incineration or thermal pyrolysis. t)

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(a) Incineration: The technique involves burning of wastes to a very high temperature probably above 500°C. Incineration is most advantageous because the bulk of solid waste can be reduced to a small volume of ash. The heat so produced during incineration can be used to raise steam for turbines producing electricity. However, the process is not without drawbacks which are as follows: (i) For incineration to be successful the waste should contain enough things that burn creating no air pollution problems. (ii) Sometimes the bulk of wastes is as low in calorificcontent an indicator of their burning ability that they do not burn at al/. Disadvantages of incineration in developed countries: The problems concerning incineration in western countries is different from the developing ones. Their solid wastes are so cluttered with plastics, papers, synthetic polymers that incineration is not a problem at all. But the burning of these materials often produces smoke and toxic vapours like sulphur dioxide, hydrogen peroxide, dioxins and carbon dioxide etc. adding to the already existing air pollution. Moreover, incineration reduces only 30% of the total volume of waste. Incineration is not a solution as far as garbage disposal is concerned. Over 50% of the garbage is organic and hence it cannot be used for energy generation. Thus efforts are made to modernise composting plants. These plants can be located in radial directions with a capacity of about 500 tonnes each. The compost so formed can be sold to farmers .. Incineration of such materials also requires additional facilities that detain the toxic contents of smoke produced. Such scrubbers just prevent poisoning of air but produce a more toxic solid waste that has to be chemically treated.

(b) Thermal pyrolysis: In thermal pyrolysis, the solid wastes are heated to a very high temperature (600-BOO°C) but in a very sparse air or oxygen so that they do not burn completely but only smoulder. The pyrolysis product resembles to that of charcoal. It can be used in fuel provided that its burning does not produce any harmful gas. Rubber tyres and synthetic polymers etc., when burnt produce extremely polluting smoke posing air pollution. However, if these items are pyrolysed, they can be reduced to manageable wastes. This method does not reduce the waste bulk to a pittance like incineration. None of these methods of waste disposal are as cheap as burning dung cakes. Incineration of wastes is a very costly affair often requiring crores of rupees as investment and high technical expertise so that all trash burns without causing any further pollution. An alternative method contemplated to render organic wastes into non-toxic constituents seems to be bioremediation.

(4) Bioremedlatlon : This approach envisages hiring help from bacteria to convert toxic compounds into either useful industrial products or harmless wastes. Here solid waste is composted, similar to that of producing farm manure. The technique involves microbial help to turn municipal wastes into fertilizers or soil-reinforcing products. Liberation of gas by these is also on the anvil. Although bio-remediation is cheap but enough time consuming. Also many synthetic polymers like plastics are so novel that there exist no microbes which can degrade all of them completely. (5) Bio-technological approach: Recently the giant steps taken by bio-technology research, especially in genetic engineering, have to some extent come to help. Now several genetically engineered bacterial strains are available to decompose complex organic compounds which were considered to be non-biodegradable. Efforts are also made to synthesize such bio-degradable plastics which are easily palatable to microbes.

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(6) Controlled tipping: This remediation approach involves the use of familiar landfilling especially by controlled tipping (which can keep leachates at bay). The method is applied to a mixture of inorganic and organic solid wastes which do not budge to any other treatment. (7) Vitrification: The recent technique insitu vitrification aims at converting the solid wastes into a sort of glass in the place where they stand. To accomplish this method electrodes are inserted into the waste-heap and a very powerful electric current is passed through it. The strong heat so produced melts glass, plastic, muck, mud and other waste into a glass like solid. It can then be dumped anywhere as it leaches very little. However, in this method care is taken to prevent mingling of radio active wastes with other organic compounds, as radioactivity remains in whatever form the waste may be converted into. (8) Recycling and reuse of waste: Recycling envisages to reuse of most of the waste and reducing the bulk as well as its toxicity. Some waste components can be easily 'recycled and reused. Recycling of complex soil pollutants: The paper, plastics and petroleum products - Today it is the perennial persistence of papers, plastics and petroleum products that is the main reason behind increase in wastes. Every new bit has to be given a new place. Japan, a small country annually produces trash that could fill 125 football stadia. Of this half garbage is composed of papers. It is therefore not surprising that recycling of paper, plastic, glass, metals and organics is the main issue today. Recycling of paper: The waste can be converted into useful products. Previously recycling of old papers generated low graded papers which can only be used in manufacturing packing materials as cartons, corrugated boards etc. Presently modifications in recycling are being done to get a good quality paper for use even on a .xerox machine. Japan recycles 40% of its unwanted paper into new high grade one. Dr. Aarne Vasilind has reported that recovery of one ton of paper saves about 17 trees from the axe which are the sources of virgin paper. Although the cost of manufacturing new paper from waste paper is more than making virgin paper directly, but the waste paper problem can be solved upto some extent. Recycling of plastics: Plastics are extremely stable and app.ear difficult to treat, as they are polymers of very different molecules. Polyethylene tetra phthalate (PET), the material used in transparent plastic bottles is quite different from that of polyvinyl chloride (PVC) used in polythene bags or in sturdy pipes or buckets. Recycling PET picked from a wastedump though easy but not without risk. PET can pick up several poisonous substances from the waste-dump and slowly release them into any drink or food stored in PET bottles. Torn polythene bags can be recycled only when they are pure. Recycling PVC after retrieval from a waste dump does not produce better quality plastic. It is hard, brittle and tough. Numerous synthetic varieties as tapes, photo films, hana bags etc. are quite different in their chemistry from the plastics of buckets, bins and boats. Each variety of waste is separated according to its category and chemically restructured to recycle. Today, although many countries are recycling much of throw out glass and paper but they are hesitant to recycle plastics. Diapers too are non-biodegradable and non-recyclable. But scientists have not lost their hopes. Today researches have enabled separation of metals and their retrieval from garbage even when in minute quantities. Attempts have been made to reuse plastics in cassettes and films as well as in producing high grade paper from decayed old papers etc. Even plans to obtain a new variety of plastic by mixing various plastics in wastes, are providing fruitful results.

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Scientists are now designing a compatibilizer molecule which sticks together these different plastic molecules making the recycled plastic very durable. These 'commingled plastics' with as much gloss and sturdiness as the originals can be used in fence-posts and car-bumpers etc. Recycling of plastic in India: Plastic recycling in India does not seem to be an issue. Previously hawkers (raddiwalas) have collected everything from paper to plastics for recycling. It then can be used in making bright coloured plastic toys, hard slippers used by poor, the buckets and vessels which are easily breakable. This large-scale retrieval of burnable plastics and papers has made the Indian refuse low-calorific and non-burnable. Tin cans, scrap iron, iron-tailings are other wastes which can be usefully recycled in India. Thus the plastic recycling, which is a problem in the west, is not so in our country. Recycling of glass: Glass is a perfect recyclable product that can be used in a variety of ways. But the preparation of glass from waste glass is expensive than original glass manufacture. Recycling of metals: Recycling of metals from metallic wastes, disposed metallic cans, metallic soraps and wrecked automobiles is quite profitable and can be utilized in many other ways. Recycling of organics: Organics contained in solid wastes can be stJbjected to aerobic decomposition. The product so formed is termed as compost which acts as an excellent soil conditioner. However, in developed countries, inorganic synthetic fertilizers are cheaper and preferred over the compost manure. It is estimated that about 45 Indian smaller cities (with 4 to 5 lakh population) generate about 50,000 tonnes of municipal wastes every day. Kolkata Metropolitan District (KMD) generates daily garbage of 3,000 tonnes while its municipal wastes may rise to 912,000 tonnes in the near future. This waste created by Greater Mumbai is about 5000 tonnes which require 20,000 persons and 500 carriers to collect the garbage and to dispose them off at suitable dump sites. Delhi and Chennai produce municipal wastes of 3,000 and 1,500 tonnes per day respectively. Management of solid wastes involves the following important steps: (1) Collection of municipal wastes. (2) Applying scientific methods for the disposal of solid wastes. (3) Sorting of waste materials. (4) Dumping of non-combustible and harmless substances into dump sites. (5) Compositing organic substances which are biologically degradable. According to an estimate a town with one lakh population may generate 20, 000 tonnes of garbage and 8000 tonnes of night soils which can be converted into 18, 000 tonnes of compost manure. (6) Burning of combustible substances in specially designed incinerators such as Multiple Hearth Furnaces (MHF) and Fluidized Bed Furnaces (FBF). Pyrolysis is the best way to treat solid wastes.

NEW TECHNOLOGY FOR MONITORING (a)

Genomics: It is the molecular characterisation of species.

(b) (c)

Bioinformatics: It deals with data banks and data processing for genomics analysis. Transformation: It deals with the introduction of individual genes conferring potentially useful traits into plants, trees, livestock, and fish species.

(d)

Molecular breeding: It deals with the identification and evaluation of useful traits by use of marker assisted selection which greatly speeds up traditional breeding processes.

114 (e)

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Diagnostics: It deals with identification of pathogens by molecular characterisation, and (f) Vaccine technology : It deals with the use of modem immunology to develop recombinant DNA vaccines for improved disease control against lethal diseases of animals and fish. While genetically modified products have tremendous potential to meet the challenge of feeding the teeming world population, there is a flip side, rep~rts of which have already started coming in. Herbicide resistant crops are designed ,in such a manner that the herbicides kill associated weeds, while the crop remains unaffected. Now there is increasing scientific evidence that genes for herbicide resistance can cross over to the target weeds, defeating the very purpose of developing bioengineered varieties as the weeds also develop resistance to the herbicides designed to get rid of them. Among the well known risks associated with genetically engineered food crops are: (a) Increasing incidence of antibiotic resistance, (b) Production of toxic proteins, and (c) Human allergies. For example, a tomato with genes from peanuts might cause allergies due to peanut proteins. People with peanut allergies are normally very careful about avoiding any peanut products, but if they eat an unlabelled genetically engineered tomato, they may suffer dangerous allergic reactions that can be fatal in extreme cases. There are widespread public concerns about the potential adverse impact of genetically modified organisms (GMOs) on human health and the environment. In order to take advantage of recombinant DNA technologies without associated harm to human or ecological health, it is important that every country has in place suitable institutional structures and regulations for biosafety, bioethics and biosurveillance. New communications and computing technologies will have profound implications in everyday research activities. (a) Access to the internet will soon be universal. Thus it can provide unrestricted low cost access to information. The internet will not only facilitate interactions among scientists. but also greatly improve their ability to communicate effectively with the potential users of their research knowledge, (b) Computing makes it possible to process large-capacity data base such as libraries, remote sensing and GIS data, gene banks etc. and to construct simulation models with possible applications in ecosystem modeling, preparation of contingency plans to suit different weather probabilities and market variables. (c) The software industry is continuously providing new tools that are capable of increasing research productivity and create new opportunities for understanding complex' systems of growing conditions. (d) Remote sensing and other space satellites outputs are providing detailed geographic information useful for land and natural resources management. However, there is much to learn from the past. in terms of the ecological and social sustainability of technologies. At the same time new developments have opened up new opportunities for developing technologies which can lead to high productivity without any adverse impact on the natural resource base. Combining traditional and frontier technologies leads to the birth of ecotechnologies with combined strength in the areas of economics, ecology, equity, employment and energy. For example, in the area of water harvesting and sustainable use, there are many lessons to be learnt from the past. In the desert area of Rajasthan, drinking water is available even in areas with 100 mm annual rainfall, largely because women continue to harvest water

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In simple structures called kunds. In contrast, drinking water is scarce during summer months in some areas of the north east with an annual rainfall of 15,000 mm.

Precision agricultural farming involves a systematic approach to experimental design and agronomic practices. It requires inter-disciplinary research drawing on experience in a range of subject areas such as agronomy, plant science, genetics, soil science, entomology, meteorology, weed science, plant physiology, plant pathology, ecology and economics. Agricultural extension workers using if1formation technology will play an increasingly important role in crop production and natural resources management. Precision agriculture IS particularly valuable for increasing opportunities for skilled employment in the farm sector. For example, computer software development, equipment fabrication and sales. custom hiring of software and farm equipment. local production of biofertilizers and drip irrigation equipment and consultancy services can all provide new opportunities for unskilled workers to become skilled. Precision farming methods are to be based on scientific land and water use planning. It will require concurrent attention to natural capital stocks and nature's services. Examples of stocks include soil and nutrients, water, biodiversity, minerals, forests and oceans. Examples of nature's services are water cycles, nutrient cycles, carbon sequestration and waste recycling, agro forestry and other sustainable systems of land management need to be popularised in areas experiencing varying degrees of desertification. Sustainable agriculture in the 21st century will be based on the appropriate use of biotechnology, information technology and ecotechnology. The experience of the present century teaches us that unless technology and public policy are rooted in the principles of ecology, social and gender equity, employment generation and energy conservation and development will not be environmentally and socially sustainable~ Thus, on the one hand, we need new tools to solve the serious environmental and economic issues confronting mankind; on the other hand, are important ecological, social and ethical issues relating to the use of such tools, particularly the recombinant DNA technology. The critical areas for intervention would be: (a) Improving availability of seed/planting material of high yielding varieties, (b) Developing and promoting use of hybrids, especially for rainfed ecologies, (c) Expansion of areas under different crops and commodities through diversification of agriculture, (d) Improving productivity of crops, existing plantations and livestock, (e) Developing infrastructure for post harvest management, marketing and agribusiness, (f) Small farm mechanisation, (g) Transfer of technology through assessment and refinement continuously, and (h) Enhancement of export potential in selected areas where India has a comparative advantage. A major thrust would be needed on improved farming practices because it is through timely operations and precision farming that we will be able to tmprove the input use efficiency in future. The advent of biotechnology as a powerful tool has opened new vistas in breaking the genetic field barriers. Thanks to the advancement of science gene transfer across the board is possible. In view of emerging second generation problems affecting both the productivity and sustainability of our irrigation system, it is necessary that focus is turned on to the identification of non-sustainability indicators and addressing these through appropriate research,

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development and policy options. In this context, precision farming using the best available technologies would demand effective scientist-farmer relationship and coordination of all departmental and development agencies responsible for the supply of inputs in time. In future, the priority areas for consideration would essentially be agriculture in the rainfed areas that have an entirely different set of environmental problems arising from a combination of factors such as rural poverty, rapid population growth and inadequate dissemination of technology. In rainfed areas, a unified strategy encompassing watershed management, promotion of hybrid technology, and small farm mechanisation would be of great importance in the future. Also great thrust on promotion of technologies which could minimise the use of costly inputs and result in natural resources conservation such as Integrated Plant Nutrient Management (IPNM) and Integrated Pest Management (IPM) would be the key for an evergreen revolution. Soil is a vital natural resource, the proper use of which greatly determines the capability of life supporting system and the socio-economic development of the people by providing food, fibre, fodder and fuel for meeting the basic needs of humans and animals. However, its capacity to produce is limited and the limits to production are set by its intrinsic characteristics, agro-ecological settings and its use and management. This resource is under constant demand for industrial growth and urban expansion which would result in its shrinkage for use in agriculture. As a result of intensification of land use in areas that are naturally well endowed or can be made so by economically viable human interventions such as irrigation and drainage systems, in future, there will be a significance in land' per rural household. The future approach to the soil resource inventory and land use planning research needs to be a holistic one involving multi-disciplinary and inter-institutional programmes. Any land use strategy must consider the questions of limited soil resources and sustainability of their productivity. Because the pressure on available limited soil resources can only increase with time, effective and rational use of this resource will be the only strategy to increase future productivity on a sustainable basis. Similarly, water will be a scarce resource in the future and good quality of water wiil be available less and less for agriculture. Hence water use efficiency and on farm conservation of water becomes need of the hour. Also, strategies and technologies which could minimise the use of agricultural. chemicals such as fertilizers and pesticides will be required to be put in place on priority. Irrigated agricultural covering 48 million hectare of land area was producing about 2.5 tonnes of food grains per hectare in 1996, which is very low. There is a wide gap between the realisable potential and the actual average yield needs to be bridged. Rainfed areas occupying about 92 million hectare continue to have a productivity of about one tonne per hectare. There is a growing realisation that using modern technologies, the productivity of dryland crops can be doubled. The significant area of salt affected land (about 8 million hectare) can be made productive by adopting the soil reclamation technology. Similarly, limitations of fallow land have to be addressed and remedied.to contribute to the overall production. Shifting emphasis from commodity research towards production system research would be the key for enhanced productivity, profitability and permanency of our agriculture. Hence increased emphasis on the sustainability of production systems as practiced by the farmers through the adoption of improved technologies aiming at efficient land and water management IPM, IPNM, etc. will have to be given priority in future. For example, watershed management in rainfed agriculture and rice-wheat system in irrigated agriculture are to be addressed

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through interaction of research and development efforts as well as through plant-animal-man chain. The' extent to which the research system meets future challenges and opportunities largely depends on its state of science and technological development and capability. Biotechnology has emerged as a powerful tool to address major biotic and abiotic stress with greater precision and success. Similarly, revolution is taking place in the field of information technology. There is a need for moving upstream in frontier technologies by making use of new sciences like biotechnology, informatics, environmental sciences, geographic information system, crop modelling, bioengineering, food science and agribusiness. With globalisation, the management of NARS (National Agricultural Research Systerh) in terms of research, financial and administrative aspects cannot be ignored. Maintaining the quality of the system through appropriate institutional arrangement, management reforms, incentives, rewards, training, funding mechanisms, interfere with all the stakeholders. particularly the farmers and the private sector, increases communication and information technology are important to become not only locally efficient but also globally competitive. India is fortunate to have generated a large number of skilled staff at all levels of agricultural research system. It was mainly due to our skilled human resource that we could generate and disseminate new technologies to the field leading to overall advances in agriculture. Hence competent human resource will be the key for fufure successes. To propel Indian agriculture into the 21st century, the quality, technical skills and management of agllicultural manpower must improve in accordance with the rapidly changing national and global market needs. Emphasis in the human resource development area should be on the fol/owing important points: (a) Qualitative improvement, (b) Accreditation of universities, (c) Infrastructure development. (d) Networking, (e) Distant education, (f) Vocationalisation, (g) Women's education, (h) Inservice training, both at the national and international levels, (i) Introduction of visiting scientist scheme, (j) Recruitment in SAUs based on national eligibility test (NET), (k) Lateral entry at various levels to attract talents, (I) Links with advanced research institutions (ARls) and the international agricultural research centres, (m) Strengthening the training in educational technology, renovation, modernisation of existing hostels, libraries, classrooms, laboratory facilities, curriculum development and delivery system, (n) Promoting centres of excellence to develop multi-disciplinary teams with necessary skills, expertise and capabilities. Efforts are being made to ensure proper allocation and generation of required funds to achieve these targets. It is believed that we shall get success in our mission of having food secure India in the 21st century.

DOD

8 INSTRUMENTAL METHODS IN ENVIRONMENTAL MONITORING There are large number of techniques currently employed in Environmental analysis. They are used, depending on type of pollutants required to be analysed. While analysing the complexity of the sample required on analysis, concentration of chemical species of interest and nature of the accuracy desired are of prime importance. The selection of a technique is also dependent in advantages and limitations of individual techniques. It is important that the procedure selected must deliver the results more accurately than required by the authorities Calibration of instrumentation and purity of standards or reference material. is another important requirement of analysis. The methods are classified as follows : (1) Separation methods: GC, HPCL, Paper, TLC, etc. (2) Electro-analytical methods : Potentiometry, Conductomentry, Polarography, Voltammetry, etc. (3) Thermal methods: TG, DTA, etc. (4) Radio arJalytical methods: Neutron Activation analysis (5) Optical methods : Spectroscopy (6) Classical methods: Gravimetry, Titrimetry, etc. The following table indicates the method used, depending on the pollutant required to be identified: . Instrumental Methods for the Analysis of Environmental Pollutants Method UV-ViSible spectrorrietry

IR spectrometry Emission spectrometry Turbidimetry/Nephelometry Conductimetry

Examples of Pollutants Analysed 502, H25, NOx, NH 3, 0 3, C6h. and phenols, etc. in air. water/ soil Metal ions present in water/soil. Hydrocarbons, CO, CO2 in air Metals in suspended particulate matter,metal ions in water / soil Sulfates in water/soil 50 2, NH 3, H halide in air, ions in water

Instrumental Methods in Environmental Monitoring Coulometry Gas chromatography

GC-MS, GC-FTIR,GC-AAS and other hyphenated techniques Fluorimetry Chemiluminescence AAS I Flame photometry Ion selective electrodes HPLC/lon chromatography TLC/HPTLC/Paper chromatography Other electroanalytical methods like polarography, stripping voltametry amperometry, etc.

119

0 3, Halogens, NOx, CO in air All volatile inorganic/organic pollutants in air Iwater. Even particulates can be analysed (by using suitable columns detectors, after derivatization) Most of the volatile pollutants can be analysed undr-· suitable conditions Metals like AI, Be, etc. In water/soil NO, N0 2 in air Many metals including Pb, Hg, etc. particulates in air, water and soil Ions present in water Organic pollutants I inorganic cations and anions in water I soil Organiclinorganic pollutants in water/soil Inorganic ionic pollutants in water

The instrumental methods are discussed as follows : (1) (2)

Chromatography Mass spectrometry

(3) (4)

Hyphenated technique, e.g., GC-MS Ion-exchange techniques

(5) (6) (7)

Spectroscopy UV, visible and IR, Atomic absorption spectroscopy Flame Emission spectroscopy

(8) (9)

Electo-chemical methods Radio':analytical methods

(10)

Classical Titrimetry

[1] CHROMATOGRAPHY

Introduction These are very versatile and reliable methods and can be routinely used on large number of analytical samples. These methods are capable of analysing gases as well as Liquids. Classified as in separation technique along with solvent extraction, it gets the advantage from the moving (mobile) phase. In present times, HPCL - High Performance Liquid Chromatography, in particular is considered a must for every Quality Control Laboratory. The component of high to medium pressure of the mobile phase gives the resolving power unmatched by previous methods. The other advantage comes from its mode of operations. It can be used in various modes such as Adsorption, Partition, lon-Exchange and size-exclusion. Even normal to reverse operations can by performed. In the hypheneted mode the output of one independent method is joined with the input of another independent technique. This makes it vastly superior in terms, of efficiency and

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sensitivity. These are GC-MS, HPCL-MS where MS-mass spectroscopy, is another independent end superior technique. 'Chromatography' is the combination of two words 'Chromatos' and 'Graphicos' means 'Coloured Bands'. These are the analytical methods with mechanism of separation 'as adsorption, partition, ion exchange, size exclusion or electron static attraction. The 'chromatograms' obtained as a plot of detector response against time of evaluation or volume of mobile phase, can be interpreted with the help of number of parameters such as retention time, retention volume, length of column etc. Flow Chart G.C. Chromatographic Injector column Detector system

Computer/Integrator

~+--Oven

GC system Fig. 8.1

Liquid Chrontatography This mode was developed latter, where the mobile phase is liquid and the stationary phase is also a liquid which is immobilized on a solid support. The other methods are, paper chromatography thin layer chromatography, called classic methods which are developed further in last decade. Many new procedures, such as size exclusion chromatography and SFC have corne in recent times.

High Pressure Liquid Chrontatography High Performance (Pressure) liquid chromatography is an improvement of the c.lassical method of liquid or partition coefficient. Classical method is time consuming and tedious. This is because of the low flow rates of the liquid mobile phase which· moves down the column under the influence of gravity alone. Attempts made to increase the rate of flow of the mobile phase by using a high pressure and decreasing the column length resulted in increase the flow rate of the mobile phase the conditions have to be satisfied. First the' column packing should consist of small spherical and uniform sized particles (about 60 Ilm) so that the packing'has the optimum homogeneity and density. Second, the stationary liquid phase should be in the form of a thin uniform layer. These conditions are satisfied in high performance liquid ctlromatography. In general, three types of particles are used for column packing in H.P.L.C. Microporous particles which consist of cross linked networks. The particle diameter is about 5 to'10 Ilm. Only small molecules of the solutes are accessible in the pores of these particles. macrophorous particles with particles diameter of about 60llm. These are accessible to small as well as big solute molecules. Some particles have particle size 35 to 45 1J.ffi.'

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Instrumental Methods in Environmental Monitoring

~-------12--------~·1 ~--11,---:·~1

I

CD

U)

c: o a. U)

~ \ \

,

,,

, \

I---,/.,';Ci-::--::-::--::--=--w~----m--~~--fii-m----w;---- ----..\Time Fig. 8.2 Resolution of peaks Resolution can be improved by(1) Changing the temperature. (2) Decreasing Un" or increasing the number of theoretical plates. (3) Combination of above. High performance liquid chromatography is an efficient. highly selective method of separation. Small sample sizes can also be separated. The only condition is that a suitable immiscible solvent pair must by available. In HPCL separation is carried at room temperature. Therefore, thermally unstable SUbstances which cannot be separated by GLC can be separated. The method is also applicable for the Separation of inorganic samples. The apparatus used in high performance liquid chromatography: (1) A reservoir System for mobile phase ,(2) A high pressure pump having on output of at least 100 Psi (3) Precolumns (4) An injection system for the sample (5) The analytical column (6) A detector and recorder assembly The solvent (mobile phase) reservoir system consists of one or more glass or stainless steel vessel which contains 1 to 2 litres of solvent. Dissolved oxygen and nitrogen in the solvent are removed by pretreatment. These gases form bubbles in the analytical column and resolution of peaks is affected. Two types of elution techniq.ue are used. The single solvent is used, the separation is called isocratic elution. Separation efficiency can be increased by using two or more solvents. Such an elution is called .gradient elution. If gradient elution is used, the solvents from the reservoirs are mixed in the mixing vessel and pumped into a pre-column by means of a high pressure pump. The precolumn contain the

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122

same packing as is used in analytical column. The objectives of precolumn are (i) To saturate the mobile phase with liquid stationary phase. (ii) To remove impurities in the solvent. The experimental sample is injected into the column by means of self-sealing teflon or neoprene sodium. The analytical column consists of a stainless tube about 15 to 150 cm in length. The selection of the column packing depends on the chemical nature of the sample components and the mobile phase to be used. The column is generally surrounded by a water jacket to maintain constant temperature. The sample sets separated on the column due to components registered on a detector. The signal from the detector goes to the recorder ~nd chromatogram of the sample is obtained. The most commonly used detector is spectro photometer. Resolution : Resolution in chromatography means the degree of separation of compounds of similar character. Resolution (R) is expressed in terms of retention times and peak widths. If two peaks have peak width W1 and W2 and the respective retention times are t1 and t2 then resolution (R) of the two peaks is given by 2(12 -t1) R = W1 +W2 L------.-_----'

Sample Injection Unit

Precolumn Pressure Gauge ~....L-"_-, r-

- Analytical Column

High Pressure Pump

Mixing Vessel

,

/'

Solvent Reservoir

Recorder

Detector

Fig. 8.3 HPLC Schematic diagram The high pressure and the speed, involved in HPlC sometimes tend to mechanically remove the stationary liquid phase from the solid support. To overcome this difficulty economically bounded stationary phases have been developed. These consist of organic groups attached to silica gel. For instance, a hydrocarbon surface can be formed by the reaction of trialkyl mono chlorosilanes with the OH groups on the surface of silica gel.

123

Instrumental Methods in Environmental Monitoring

R

-Si-O

IHel1 R

I -Si-O-Si I R

I

-Si-O~

I R

-R

Such column packings are called brush type packings.

Qualitative and Quantitative Infortnation frotn Gas Chrotnatography Qualitative Analysis: The safest way of identifying sample components is by examining the column effluent by the use of mass, infra red or ultraviolet spectrometer. The combination of a mass spectrometer and gas chromatograph is ideal. When the mass spectrum and the retention characteristics agree with known materials, identification is virtually complete. In addition to the use of large instruments such as mass spectrometer, comparison of elution characteristics of an unknown mixture with those of known compounds are not readlity available. In such cases more time consuming methods have to be followed. Quantitative Analysis: The output signal from a chromatography detector as a function of time is normally fed to a data collector to provide a permanent record. This is often a recorder having as output a strip of paper on which the output signal is traced as a function of time or volume of carrier gas. Plots obtained in gas chromatography are in the form of a series of peaks. Since the signal obtained from the detector is linearly proportional to the amount of a given solute in the carrier gas, the total amount of a particular solute eluted from a column is directly proportional to the peak area. Since the proportionality constant varies for different solutes, it must be determined empirically for each substance through the use of known amount. Peaks obtained with a sample containing known amounts of substances can be called as a calibration curve. The below given figure is curve obtained with a sample containing known amounts of substances A, B, and C.

Q)

c

Ul

c: o

a.

Ul

~

"iii c:

en01 M

L

N

lime Fig. 8.4 Typical Gas Chromatogram

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As the pure carrier gas flows through the column and passes into the detector, a straight line is drawn by the pen recorder on the chart. This is the base line or zero line. At the moment M, the sample is injected into mixture by the column emerges first. When this component has passed, the properties of the gas mixture following out correspond approximately to those of the carrier gas and curve drops to the base line. Similarly peaks B and A are obtained. The distance from M to L, i.e., to the peak is the time during which the component C passes through in the column. Prior to peak C a small peak due to air is obtained. The peak height is the length of the perpendicular drawn from the top of the peak to the base line, CL. The peak area can be measured by multiplying peak height by peak half width (the width measured at the.middle of the peak height) SR. The peak area of component is proportional to the amount of that"component in the mixture. There are other physical methods available for the measurement of area under the peak. One method is use of planimeter.

[2] MASS SPECTROMETRY A mass spectrometry produces ions of the sample in High Electric Voltage and accelerates them in a magnetic field with vacuum. The entire operation is carried out in high magnetic field. The .ions move and strike the detection photographic plate in their mass to change ratios. Many instruments such as - single, double, quadruple .focussing are available with version of 'time in flight' analysis. The environmental samples in gas, liquid or solid state are introduced (after modification) and ionized using different modes such as -E.!. Electric Impact, C.!. chemical, ionization etc. The Ionization Process do not always follow a box pattern. These can be radicals short lived intermediates or the one in high energy state. For example, B + e ~ A + B + e In a typical mass spectrometer the analyte is introduced, usually in gaseous form, into the source, where it is bombarded with a stream of electrons, usually of energy 70 e V' (1e V, or electron volt, is the energy acquired by an. electron when accelerated through a potential difference of volt: 1 e V ;: 96.5 kJ mol-1 ). This causes the formation of positive ions by knocking electrons from the analyte atoms or molecules. These ions are accelerated out of the source by a high negative potentii:II, from here they travel in a high vacuum through a magnetic field which curves the path of their motion. Their kinetic energy, -mv2 (m = ion mass, v velocity) is equal to the accelerating energy where is the accelerating V voltage and e is the charge on ion. Under normal conditions most ions acquire only a single positive charge equal to the charge on an electron e. Then,

=

1 -mv 2

2

=Ve

If the ion is curved through a radius r, equating the force exerted by the magnetic field to the centrifugal force on the ion,

•

rrif

HeV=r where H is the magnetic flux density.

m

2V

e = V2

125

Instrumental Methods in Environmental Monitoring substituting for V

Neutral gas

Flament~: '\~ , "

"

J

Electron

'~am

IElectron ,--.--J trap

-,

r"'-Ion lens

,

Collimating slits

+---

1,

•

Mixed ion beam

~

Positive ions

Enlarged side view of ionisation chamber

Magnetic field to paper

Electromagnetic force Recorder

Fig. 8.5 Schematic diagram of a magnetic-focussing mass spectrometer Thus for any given value of magnetic flux density, the accelerating voltage, V can be adjusted by bringing an ion of any mass to charge ratio, m/e through radius r to the detector. In practice, the accelerating voltage can be ramped automatically to bring each ion of progressively higher mass into focus on the detector, thus generating a mass spectrum. If a monoatomic element is introduced into the mass spectrometer, it would be anticipated that only one mass peak corresponding to the atom of that element would be observed. Commonly, however, elements are a mixture of different isotopes and peaks observed corresponding to each isotope, with intensities directly proportional to their relative abundances. Please note, however, Mass Spectrometry is not classical spectroscopy.

L3] Gas Chrontatography -

Mass Spectrontetry (GC-MS)

In environmental analysis, one common application of the mass spectrometer is to identify and quantify organic compounds. A typical application might involve analysis of organic pollutants in water. These are first extracted into a solvent and then, since many individual compounds are present, injected into a gas chromatograph to give separation. The

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column effluent from the gas chromatograph is, after separation of the carrier gas, passed into the source of the mass spectrometer. A mass spectrum may then be generated corresponding to each peak in the chromatogram. A single organic compound will give a complex mass spectrum. The ion formed initially by removal of one electron from the organic compound, termed the molecular ion, is commonly inherently unstable and decays to give other charged fragments. These fragments contribute to the mass spectrum and give a pattern which is characteristic of, but rarely unique to, the particular compound. This can be helpful, since for example, all isomers of C 5 H12 will give the same molecular ion, C5 H 12 , but differences will exist between the fragmentation patterns, and hence the observed mass spectra, of the many different isomers. This may allow identification. In more extreme cases in which say, an alkanal and an alkanol have the same molecular formula, separate identification of the basis of the mass spectrum may be rather easy. Reference spectras are retained upon a computer-based memory, and comparison of experimental and reference spectras is carried out automatically to provide a tentative identification of an unknown compound. Spectra includes the mass spectra of three compounds, all of molecular weight 126, and two with an identical molecular formula, C9 H18 . It is evident that discernible differences exist in the three mass spectra. If a very high temperature plasma is used as the ion source, the mass spectrum comprises ionised atoms rather than molecular fragments. CH 3

I

CH

/

CH 2

"-CH-CH

3

I I CH 2 CH-CH 3 \C /

Cyclohexane, 1, 2, 3-trimethyl.

'-

I

1

M

C9 H18 = 126

, CH 3

I

/

CH

CH 2

"-CH-CH

3

I I CH 2 CH-CH 3 \c / '

Cyclohexanone, 4 -ethyl-

C9H18 = 126 50

100

150

200

250

300

350

400

450

500

550

Fig. 8.6 (a) Mass spectra of three compounds of identical molecular weight. (M+ molecular ion).

=

600

127

Instrumental Methods in Environmental Monitoring

Mass spectrometers are also widely used for determination of isotopic ratios of elements which may provide valuable insights into sources and environmental pathways of elements.

L4] ION EXCHANGE TECHNIQUE Ion liquid chromatography is an extension of HPLC. This technique is very good, sensitive and accurate for analyses of inorganic ions. It mainly depends upon the separation of anions on a column of anion exchange resin, according to their size and charge. Elution is by the use of dil. Na2C03/NaHC03 solution. The separated anions are then converted to the corresponding free acids by passing the eluate through a column in the W Form (cation exchange). Ion chromatography is a valuable tool to monitor mobile and stationary sources of air pollution, water pollution in potable water, ground and surface water, municipal and industrial wastes. It is a good tool in environmental field such as acid rain, automobile exhaust, drinking water, sea water, waste water. Following figures indicate acid rain sample and industrial waste water sample. CICo

.......' - - - - - 13 MIN.

------;.~

Analysis of anions in acid rain (column IC Pak Anion Eluent Borate/Gluconate buffer flow rate: 1 ml/min detector conductivy meter.)

2+

Column Radial Park C18 Cartridge 5J.l Eluent Ch30H/CH3CN Flow rate: 4 ml/min Detector : UV 254nm

Fig. 8.6 (b) Analysis of anions in acid rain (column IC Pak Anion Eluent Borate/Gluconate buffer flow rate: 1 ml/min detector conductivity meter.) Column: Radial Park C18 Cartridge 5).l Eluent: CH 30H/CH 3CN Flow rate : 4 ml/min Detector: UV 254 nm The technique is versatile and is capable of carrying any analysis of many organic species. This is because in recent times, new ion exchanging materials have been discovered. The advantage is the material is solid and the ion gets separated because of the charge exchange even when present in liquid phase. The other advantage is that the organic ion exchange material is reusable.

Ls] SPECTROSCOPY The spectroscopic techniques under the title of optical methods are based on interaction of electro-magnetic radiations. The absorption or emission of energy by the sample is dependent on the structure within the atoms and molecules. The energy is quantified as explained by quantum theory and the energy absorption is governed by Beer-Lambert's Law,

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Accordingly, when a monochromatic beam of light passes through a solution of an absorbing substance, its absorption remains constant when the concentration and thickness of absorption layer are changed in inverse proportion. The spectrometer is the device which detects the absorption or percentage transmission of light intensity, through the sample when it interacts with electro-magnetic radiation of proper intensity (energy), when clear, coloured solutions are subjected to analysis the. instrument is called colorimeter. This uses filters for selection of proper incident wave lengths. Filters are dispersing or interferometric devices. The selection is based on complementary colours. The advanced monochromotors such as prisms, grattings or grisms are fitted in costly instruments called spectrophotometers. These are of two types (i) Single Beam and (ii) Double Beam instruments.

Colorhneter Light from a source (S) passes through a collimating lens (L) and then through an adjustable diaphragm (D), by adjusting the diaphragm, the intensity of incident radiation can be altered to any required level. In some instruments, this is done by introducing a variable rheostat in the circuit of the source. Light is then incident on the filter whfch allows only a narrow band of wave length to pass through the curvette. The solvent or sample solution is placed in the cuvette (C) and the transmitted light falls on a barrier type cell (P) producing a small current. The current is read on a damped galvanometer which is calibrated to read transmittance directly. /

~

D:::~~

Filter

rI I I I I I I

s Light emission or absorpjion by atoms and molecules in the UV-visible region (- 180-700nm wavelength) is due to transitions of electrons between energy levels within the atom or molecule, Molecular UV-visible spectra may be obtained in the gas or liquid phase samples. Under these conditions, molecular absorption spectra take the form of band spectra (as opposed to line spectra), which means that absorption of light occurs continuously over a range of wavelengths, rather than at single discrete wavelengths. Analytical measurements are generality, but not exclusively, made at the wavelength of maximum absorbance, "max so as to maximize sensitivity.

r

Fig. 8.7 0.50 , - - - r - - - - - - - - - - - - - - - - - , 0.40 0.30 0.20 0.10

500 Wavelength (mm)

Fig. 8.8 UV-vislble spectra of the 1, 10phenthrollne complexes of Fe(II} and Fe(III}

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129

In environmental chemistry, UV-visible absorption spectroscopy is generally used to quantify the concentration of a substance known to be present. If as usually happens, that substance does not have convenient light absorbing properties within the UV-visible wavelength range, it is necessary to use some chemical property of the substance to make a Iightabsorbing derivatives, preferably in such a way that no other, potentially interfering light absorption derivatives of other substances are formed. Hence the derivation reaction should be specific to the analyte of interest. Figure shows the absorption spectra of equimolar concentrations of Fe (\I) and Fe (11\) as their complexes with 1, 10-phenanthroline. This is a standard method for iron analysis, usually after reduction of Fe (III) to Fe (II). The method can also be used to obtain speciation information on the oxidation state of the iron as at the Amax for Fe (II) there is little absorption, and hence little interference from the Fe (III) complex. The isobestic point, at which the two complexes have an identical absorbance, is marked; Fe (total) could be analysed at this wavelength without prior reduction of Fe (III) to Fe (II). A simple example of environmental analysis using UV-visible spectrophotometry is the assay of ozone in air by bubbling a known volume of air through neutral buffered potassium iodide solution. The effect of the ozone is to oxidise iodide to iodine, 12 : 0 3 + 2W 21- ~ 12 + H20 + O2 The iodine reacts further with potassium iodide to form the strongly absorbing triiodide iron, 13 , Which is determined by measuring its absorbance at 352 nm : 12+KI~KI3

The method is calibrated by making up standard solutions of iodine in potassium iodide and measurement of their absorbance to produce a calibration curve. Analysis of atmospheric ozone may be more reliably carried out by measurement of its UV absorption at 254 nm using a long path cell to enhance absorption this is highly accurate and is a standard reference method for ozone in air. Standard methods for analysis of many anions such as sulphate, phosphate and chloride are based upon UV-visible absorption methods. However, ion chromatography, often offers advantages in terms of sensitivity, specificity and speed of analysis, and provides a very valuable alternative procedure. Spectroscopy is widely used method in chemical and environmental laboratories.

16J

ATOMIC ABSORPTION SPECTROSCOPY

The electronic absorption spectra of atoms, unlike molecules, take the form of discrete lines of small bandwidth in the gas phase. These absorption lines are very narrow (less than 0.1 nm) and are characteristic of the analyte elements. Thus by converting an element into gas phase atoms, measurement of absorption of light at one of these characteristic wavelengths may be used to determine its concentration within a sample. The instrumental set-up atomic absorption spectroscopy (AAS) is shown. It bears much similarity to a UV-visible spectrometer and indeed operates within the same wave length range. The main difference are two-fold. Firstly, the wide spectrum light source of the UV-visible spectrometer is replaced with a hollow cathode lamp. This lamp has a cathode coated with the analyte metal, emits the characteristic resonance wavelengths of that metal at a very high intensity. Secondly, the sample cell is replaced by an atomisation unit (e.g., a flame). The preferred absorption wavelength is selected by the monochromator. The light absorption is calibrated by the use of standard solution of the analyte metal. The beam

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chopper is used to pulse the light from the lamp, and the phase-sensitive detector is synchronized with this pulsing so as 'to respond only to signal to noise ratio, and hence the sensitivity of the instrument, is enhanced. ( Several systems have been utilised to conv~rt the analyte to ground state atoms which can subsequently absorb their characteristic resonance frequencies.. The earliest atomisation units comprised flames, typically air/ethane or nitrous oxide/ethane. These operate at 18002100,K and 2300·}500 K, respectively, and hence exhibit differing atomisation efficiencies; otherwise processes within the flame are comparable. The an,alyte sQlution is aspirated into the flame and first is desblvated. The resulting aerosol is thermally dissociated leac;ling eventually to ground state atoms. Mqximum sensitivity is obtained by using tl:le flame where the atom cloud exhibits the greatest concentration. To achieve this depends upon the element concerned, the flame stoichiometry and sample matrix. For elements like chromium that tend to form very stable oxides, enhanced atomisation oc~urs within a reducing flame. Metal

Analytical

Flame

line(nm)

(pg mt1

328.1 309.3 As 193.7 422.7 Ca Cd 228.8 Co 240.7 Cr 357.9 Cu 324.7 Fe 248.3 Hg 253.6 K 766.5 Mg 285.2 Mn 279.5 Mo . 313.3 Na 589.0;589.6 Ni 323.0 Pb 283.3 Sb 217.6 Se 196.0 Sn 224.6 V 318.3;318.4;318.5 Zn 213.9

0.0009 0.30 h 0.1 0.001 0.005 0.006 0.002 0.001 0.003 0.2 0.002 0.00001 0.001 0.03 0.0002 0.004 0.01 0.03 0.07 0.16 0.04 6 0.0008

Ag AI

Graphite atomiser (ng ml- 1)"

(pg)

0.5 1

20 5 0.3 2 2 2 2000 2 0.4 2