pesticide,insecticide,pollution

PESTICIDES AS A SOURCE OF

POLLUTION AND CONTROL MEASURES

 Introduction

In  1995, world pesticide consumption reached 2.6 million metric

tons of “active ingredients”, the biologically active chemicals at the heart

of commercial pesticide formulations, with a market value of $38 billion

(US dollars). Roughly 85% of this consumption was used in agriculture.

India is currently the largest manufacturer of pesticides and the second

largest producer of agrochemicals in Asia.

The use of pesticides (insecticides, fungicides, herbicides) in

India is increasing at the rate of 2 to 5% per annum. The pesticide

demand is close to 90,000 MT per annum. The per capita consumption is

600 gm per hectare as compared to 10-12 kg/ha in developed economies.

Yet, the problem of pesticide use has assumed serious proportions in

India because of the non-uniform use of the plant protection chemicals in

different regions, cropping systems and crop and indiscriminate use and

misuse and abuse of these chemicals. Obviously, there is a mismatch

between pesticide use and cropped area. Cotton, rice, fruits and

vegetables, which account for less than 35 per cent of the cropped area,

consume 84 per cent of the pesticides. On the other extreme, wheat,

coarse cereals, millets and pulses contributing to 54 per cent of the

cropped area consume only 3per cent of the pesticides used. Insecticide

(73%) dominates the market, followed by herbicide (14%) and fungicide

(11%). Although it is expected that herbicide will grow faster in the

future, insecticides will continue to dominate the market. Cotton, rice

and wheat growers account for almost 70% of pesticide consumption,

and the states consuming more in the decreasing order are Andhra

Pradesh, Punjab, Karnataka and Gujarat.

  Pesticides were considered as panacea to contain pestilence on

crops. This attitude led to a phenomenal growth of pesticide use in

agriculture. The pesticides upset natural balance and ecosystem and also

affect the field workers. If the residues go undetected, the consumer may

also be affected. Pesticides residues in soil, water, environment, foods

etc, are of serious environmental concern.

  Insecticides 

In almost all the soils that have been surveyed for insecticide

residues in India, the most common chemical, and the one that is found

in the largest amounts is DDT, followed by HCH and dialdrin. In a study

in Punjab, out of 106 soil samples, 91 were found contaminated with

insecticide residues. The highest level of 0.08 mg/g DDT-R was found in

cotton growing areas, which is four times its permitted level of 0.02

mg/g. The presence of cholinesterase inhibitors in 19% soil samples

indicated contamination with organophosphates and carbamate

insecticides. Data collected by Acharya N.G. Ranga Agricultural

University Scientists over years indicated presence of high and toxic

amounts of pesticide residues in food grains fruits, vegetables, milk and

milk products, eggs, soils, water etc. (Table 7.1). Even human breast

milk is reported to contain pesticide residues.

Pesticide residues in food items, which are on the increase, have

become a matter of threat to man. Even small quantities of these residues

ingested daily along with food can build-up high levels in the body fat.

The long-term effects of these residues in the human body include

carcinogenicity, high infant mortality and varied metabolic and genetic

disorders. The major source of dietary intake of DDT residues is through

milk and milk products followed by oils and fats, in both vegetarian and

non-vegetarian diet. The dietary intake of HCH is also mainly through

milk and milk products followed by meat and eggs for the nonvegetarian

diet, whereas it is through cereals followed

by milk

and milk

products

in vegetarian diet

 Pesticide residues identified in various

food, fodder and feed items

Pesticide

Items of food having residues of toxic levels

HCH RiCe , milk, eggs, tomato, carrot, cucumber, onion, radish, brinjol,

okra, bitter,

gourd, green chillies, dry chilles, chillinpowder, rice bran, rice straw,

water samples,

rice growing soils

Certain brands of cooking oils, milk, milk products like skimmed milk,

milkpowder, 

butter, cheese, every day whiteners

Poultry feed-maize, cakes, bran, fish, feed mix

Livestock feed-eggs, fish, corn cakes, wheat+jowar+groundnut cake 

DDT Cooking oil, milk, butter, maize, fish, feed mixture, eggs, human breast

milk,

livestock feed

Monocr

otophos

Cyperm

ethrin

Quinolp

hos

Tomato, onion, cooking oil (one brand)

Cooking oil (certain brands)

Fish, cooking oil (one brand)

Aldrin Maize, fish, feed mix, livestock feed, eggs, human breast milk

Endosul

phan

Livestock concentrated feed, fish

Source: Rao (1994)

  The reactions, movements and degradation of insecticides affect

the persistence of these chemicals in soils and determine the risk of soil

pollution. The relative mobility of pesticides in soils is given in Table 7.2

(Jayraj, 1997). Large number of pesticide compounds have a mobility

class value of 1 indicating their high immobility. This group includes

compounds such as phorate, parathion, ethlon, zineb, benomyl, paraquat,

trifluralin, heptachlor, endrin, aldrin, chlordane, toxaphene, DDT, etc.

Some of these are already banned for use in agriculture. The commonly

used herbicides such as atrazine, alachlor, propachlor, simazine, prpanil,

diuron, etc, have moderate to high immobility indicating greater

persistence in soil. When the pesticides are used repeatedly in each crop

season and those applied to soils, which are poor in organic matter and

microbial biodiversity, the chemicals are bound to accumulate for longer

periods of time causing much environmental pollution and yield

depressions, the biochemical degradationby soil organisms is the single

most important mechanism that can remove insecticides from the soil.

Before pesticides are completely inactivated, they may adversely affect

the functioning of non-target microbes  and other forms of life inhabiting

the soil. They may also be taken up by the plants or get translocated in

the aquatic system by leaching or run-off, thus contaminating the

plankton, fish, invertebrate and other form of life using the pesticide

contaminated water.

 . Relative mobility of pesticides in soils

DECREASING ORDER

Dalapon, Chloramben

Picloram,2,4-D

Propachlor, Atrazine, Simazine, Ipazine, Alachlor, Ametryne,

Propazine

Propanil, Diuron, Azinphosmethyl, Diazinon

Lindane, Phorate, Parathion, Ethinon, Isodrin, Benomyl, Dieldrin,

Paraquat, Trifluralin, Heptachlor, Endrin, Aldrin, Chordane,

 Toxaphene, DDT

Fungicides

 The residues of fungicides based on the inorganic

compounds of sulphur copper, and mercury accumulate in soil

because the heavy metals contained in them are irreversibly

adsorbed on soil colloids. Under certain conditions, toxicity from

the accumulation of copper and sulphur containing fungicides

may render the soil useless for growing crops and cause

significant yield depressions. Depressing effect of fungicides on

the nodule formation and yields of groundnut were also reported.

 Herbicides

  In intensive and diversified cropping rotation systems, the

herbicide applied to one crop may persist in the soil at

concentrations high enough to damage the subsequent sensitive

crops. Under Indian conditions, when a herbicide dose of 0.5 to

2.0 kg/ha is applied, it results in a buildup of residues in the

range of 0.25 to 1.0 mg/g/, which is safely below the potential

residual effect. But the same herbicide when applied repeatedly it

starts building undesirable residues in the soil. For example,

fluchloralin, metabenzthiazuron and atrazine were detected in

amounts that could adversely affect not only other crop plants

but also several processes in soil leasing to inefficient nutrient

management and in turn, reduced crop yields. The herbicide, 2,

4-D, restricts the growth of azotobacter, Lindane applied at

normal rates considerably reduces the number and weight of

nodules in groundnut.

Control measures to reduce pesticide pollution

• Application of easily decomposable organic matter

• Use of large quantities of organic manures

• Raising high N cover crops

• Growing of crop plants that a tendency to accumulate the

pesticide

• Follow soil management practices leading to increased

leaching of pesticides

• Adoption of biological control methods

• Use of biochemical pesticides

• Need based plant protection

 Biopesticides and bioherbicides

 Biological control is defined as applied natural control

wherein man intervenes to improve the efficiency of natural

enemies including parasites, predators, and pathogens of pest

species by introductions, conservation, or augmentation to

maintain pest populations below economically injurious levels.

 Biological control by means of entomopathogens and

other microbial pest control agents involves the application of

microorganisms on to the crop for ingestion by insect’s pests or

directly on the noxious insects, fungus or weed with the

objective of destroying the, these bio control agents include

bacteria, protozoa, fungi, viruses and nematodes.

Biopesticdes

Biopesticides also known as biological pesticides are certain

types of pesticides dervived from such materials as animals,

bacteria, and certain minerals. These are an important group of

pesticides that can reduce pesticide risks.

 Characteristics of Bio-pesticides

• Have a narrow target range and a very specific  mode of

action

• Are slow acting

• Have relatively critical application times

• Suppress, rather than eliminate, a pest population

• Have limited field persistence and short shelf life

• Are safer to humans and the environment than

conventional pesticides

• Present no residue problems 

Advantages of using bio-pesticides

• Biopesticides are inherently less harmful than

conventional pesticides 

• Biopesticides are designed to affect only one specific pest

or, in some cases, a few target organisms, in contrast to

broad spectrum, conventional pesticides that may affect

organisms as different as birds, insects, and mammals

• Biopesticides often are effective in very small quantities

and they decompose quickly thereby resulting in lower

exposures and largely avoiding the pollution problems

caused by conventional pesticides

• When used as a component of integrated pest

Management (IPM) programs, biopesticides can greatly

decrease the use of conventional pesticides while crop

yields remain high

• To use biopesticides effectively; however, users need to

know a great deal about managing pests

 Microbial pesticides

Microbial pesticides contain a microorganism (bacterium,

fungus, virus. Protozoon or algae) as the active ingredient. They

suppress pests by 

• Producing a toxin specific to the pest;

• Causing a disease;

• Preventing establishment of other microorganisms through

competition; or

• Other modes of action

An example of microbial pesticide is Bacillus thuringiensis ot Bt.

Bacillus thuringiensis is a naturally occurring soil bacteria that is

toxic to the larvae of several species of insects but non-toxic to

non-target organisms. Bacillus thuringiensis can be applied to

plant foliage or incorporated in to the genetic material of crops

eg. Bt cottons. Bacillus thuringiensis as discovered is toxic to the

caterpillars (larvae) of moths and butterflies. Several strains of Bt

have been developed and now strains are available that control

fly larvae. These can be used in controlling mosquitoes and black

flies. Microbial pesticides need to be continuously monitored to

ensure they do not become capable of harming non-target

organisms, including humans. Other examples of microbial

pesticides include the following:

• Bacillus thuringensis against caterpillars of Heliothis,

Earias, Spodoptera etc

• Pseudomonas fluoroscenes against Pythium spp.,

Rhizoctonia spp., Fusarium spp.

• Nematodes like Green commandoes and Soil commandoes

against caterpillars & grubs

• Nuclear Polyhedrosis Virus(NPV)

• Trichoderma virdi against many common diseases of

vegetables and spices

• Weevils Neochitina eichorniae & N bruchi against water

hyacinth

• Beetle Zygogramma biocolorata against Parthenium

 Biochemical pesticides

These are naturally occurring substances that control pests by

non-toxic mechanisms. (Conventional pesticides, by contrast, are

synthetic materials that usually kill or inactivate the pest).

Biochemical pesticides include substances that interfere with

growth or mating, such as growth regulators, or substances that

repel or attract pests, such as pheromones. Pheromones are often

used to detect or monitor insect populations, or in some cases, to

control them.

 Bioherbicides

 The biological control of weeds involves the use of living

organisms such as plant pathogens, insects and mites,

herbivorous fish, nematodes, other animals and competitive

plants to limit their infestation. The objectives of biological

control are not eradication, rather the reduction and, regulation of

weed population below the levels of economic injury. A

successful bio-agent is host specific, rapid destroyer of the target

weed, effective on several taxa of the weed in question,

adjustable to new environment and easy to multiply. Biological

control of weeds has had a long and successful record in the

United States and several other countries.

  “A bioherbicide is a plant pathogen used as a weed control

agent through inundative and repeated application of its

inoculums or by augmentation of natural, seasonal disease levels

through small releases of inoculums. The bioherbicide can

provide an effective, safe and viable method of weed control”. A

list of bioherbicides is presented in Table 7.3.

A bioherbicide can often live in the environment and wait for the

next growing season when there will be more weeds to infects.

This reduces the farmer’s cost of applying herbicides year after

year. A new range of bioherbicides may essentially allow

farmers to replace or reduce the expensive chemical herbicides

that they now use. They also allow farmers to get rid of weed

that interfere with their crop’s productivity without threatening

the environment.

PHEROMONE TRAP

Bracon hebetor larval parasitoid

Trichogramma sps

Biological Weed Control

Siam weed affected and its 

growth stunted by Gall Fly - an 

example of successful bio-

control of invasive weeds 

Hyles euphorbiae 

(adult)

Parthenium  Beetle, 

Pallister Beetle 

(Zygogramma 

bicolorata

 Registered and approved bioherbicides

since 1980

Biohebicide Kind of bioagent Target weed Crop

Devine

Phytophthora

palmivora

Morrenia odorata

Citrus groves

Collego

Colletorichum

gloeosporioides

sp. Aeschynomene

Biomal

Colletorichum

gloeosporioides

sp. Malvae

Biopolaris

Bipolaris

sorghicola

Biophos

Streptomyces

hygroscopicus

Comperico

Xanthomonas

campestris

Biochon

Chondrostereum

purpureum

Emmalocera

spp.

Aeschynomene

virginica

Rice

Malva pusilla

Various row

crops

Sorghum

halopense

General vegetation 

Rice & Wheat

Poa annua

Golf course

turfs

Prunus serotina

Forests

Stem boring moth

Echinocloa spp

Rice & Wheat

Tripose

Plant pathogen

Rumex spp.

Rice & Wheat

Uromyces

rumicis

Plant pathogen

Rumex spp.

Rice & Wheat

Gastrophysa

viridula

Bactra

verutana 

Beetle

Rumex spp.

Rive & Wheat

Shoot boring moth

Cyperus rotundus

Rice & Wheat

 The most common reason given for the limited

commercial interest is that the market size for biocontrol agents

is typically small and the market is often too regional, and

consequently the financial returns from biocontrol agents are too

small for big industries. The potential to use a bioherbicide in

diverse crops and against several weeds might create commercial

interest in this technology.

    ***