Here is a compilation of notes on Pesticides. After reading these notes you will learn about: 1. Meaning of Pesticides 2. Classification of Pesticides 3. Magnification 4. Mode of Action 5. Hazards od Pesticides to Human Life 6. Behaviour of Pesticides in Soil.
Contents:
- Notes on the Meaning of Pesticides
- Notes on the Classification of Pesticides
- Notes on the Magnification of Pesticides
- Notes on the Mode of Action of Pesticides
- Notes on the Hazards od Pesticides to Human Life
- Notes on the Behaviour of Pesticides in Soil
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Note # 1. Meaning of Pesticides:
Pesticides include chemicals which protect crops from insects (insecticides), weeds (herbicides), disease causing microorganisms (fungicides and bactericides), mites (acaricides), nematodes (nematicides), and rodents rodeotacides). Pesticides also include chemicals that control pests directly hazardous to animals and human beings, particularly vectors-such as mosquitoes, flies, fleas, ticks and lice that transmit diseases.
Pesticides are chemicals used to control harmful organisms in the everyday life of modern man. These have become essential tools to the agriculturist and the urbanite alike.
The urbanite depends on pesticides for control of algae in swimming pools, weed control in his lawns, flea powder for pets, sprays for controlling a host of garden and lawn insects and diseases, household sprays for ants and cockroaches, aerosols for flies and mosquitoes, soil and wood treatment for termite protection, rodent baits for occasional mice or rats, insecticide treatment of woolens, as dry cleaners for clothes and repellants to keep away mosquitoes while fishing and camping.
More than 1,170 pesticides are registered today with U.S. Environmental Protection Agency out of which 425 are herbicides, 335 are insecticides and 410 are fungicides. They are sold in more than 32,700 products or formulations. In India alone 1/2 kg. of pesticide is used every year by every man, woman and child to feed, clothe and protect them.
A present 10,000 species of insects, 600 weed species, 1500 plant diseases and 1500 species of nematodes are injurious to some degree to men, plants and animals. The use of chemicals to control pests has been in vogue for centuries and these chemicals are called pesticides.
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The greatest benefit of the use of pesticides has been that millions of human lives have been saved from yellow fever, encephalitis, malaria and other insect borne diseases. Pesticides have also protected food from pest damage.
The three major problems which limit the continued usefulness of pesticides are:
(1) Some pest organisms have developed resistance to chemicals.
(2) Some pesticides are not readily biodegradable and tend to persist for years in the environment (in water and soil both). These chemicals move to other parts of the environment.
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(3) The detrimental effects of chemicals on organisms other than the target pests. Soil flora and fauna may be adversely affected. Birds and fish tend to consume these chemicals in their body tissue in some cases to toxic levels.
Today India is passing through “Agricultural Revolution” or “Green Revolution”. During the past few years, there has been considerable increase in agricultural production due to high yielding varieties of seeds and use chemicals, fertilizers and insecticides.
According to Central Food Technological Research Institute, Mysore as much as 50% of our food is lost due to pests and parasites and for this loss major responsibility is that of insects. Hence to save this 50% loss of food, we are struggling very hard and the only ray of hope is the use of insecticides. The first synthetic insecticides which came in use are only 80-85 years old e.g. D.D.T. was discovered in Switzerland in 1930.
“All the chemical compounds which kill insects, harm them, interfere in their reproduction and normal life cycle are called pesticides.”
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The problem of these toxic pesticides requires the attention of research workers, public health authorities and the government, as these are hazardous not only to human health, animals, fruits and vegetables but to the economy as a whole.
The recommended limits (26) for pesticides in drinking water are given in Table 1.
Pesticides pollute the water because they produce many chemical species as given in Table 2. They also increase BOD, COD and total solids in water.
District Meerut has an area of 5944 sq. km with a population of 27, 23, and 441. Industrialization is going on at a very fast pace in this area with more prospects of expansion in near future.
The most established industries in the region include Electra, Light Carts, Diwan Rubber Industries, Saru Steel and Alloys, Dayal Fertilizers, Mawana Sugar Works, Daurala Sugar Works, Daurala Distillery, Daurala Chemicals, Modi Rubber Ltd. etc. Due to discharge of effluents and emissions from these and number of other industries the problem of air, water and soil pollution in this region has assumed serious proportions.
Note # 2. Classification of Pesticides:
Pesticides can be classified into following groups:
(a) Insecticides
(b) Fungicides
(c) Herbicides
(d) Fumigants
(e) Antibiotics
(f) Rodenticides and
(g) Nematicides
For the first time these are used in larger quantities and are, therefore, more likely to contaminate soils.
Description of Pesticide with Chemical Groups:
(a) Insecticiddes used to kill insects:
Chlorinated hydrocarbons: BHC, Ethylene dichloride, Toxaphene, Endrin, DDT, Aldrin, Dialdrin
Organophosphates: Diazinon, Parathion, Melathion, Dimethoate, Manazon, Systox.
Carbamates: Sevin
(b) Fungicides:
Fungicides are chemicals used to kill fungi, bacteria and viruses.
Mercurials: Ceresan
Dithiocarbamates: Ferbam, Ziram, Maneb, Thiram
Others: S, SO2, Copper Sulphate, Copper Oxychloride, Copper Zinc Chromates, Cuprous Oxide, Basic Copper Sulphate
(c) Herbicides:
Herbicides are used to kill weeds without harming the crop.
Aliphatic acids: Trichloroacetic acid, 2, 2, 2-dichloropropionic acid
Phenylureas: Monuron, Diuron, Fenuron, Linuron
Carbamates: Isopropyl carbanilate, isopropyl m-chlorocarbanilate
Dinitroanilines: Dipropalin, Benefin, Trifluralin
Bipyridyliums: Paraquat, Diquat
(d) Fumigants:
Are highly volatile, small moleculed fungicides that have fumigant action e.g., Methyl bromide, trichloronitromethane, methyl isothiocyanate.
(e) Antibiotics:
The antibiotic fungicides are substances produced by micro-organisms which destroy other micro-organisms such as penicillin, tetracyline and chloramphenicol.
(f) Rodenticides:
Are the chemicals which damage small mammals specially rodents like rats, mice etc., which damage man’s dwellings, his stored products, and his culivated crops like-Phosphorus, coumarins, organochlorines etc.
(g) Nematicides:
Are the chemicals which kill or harm nematodes (round worms that live in soil or water) such as halogenated hydrocarbons, organophosphates, isothocyanates.
Note # 3. Magnification of Pesticides:
When magnification of some of the pesticides takes place biological, the process is known has biological amplification. Several pesticides such as DDT and other chlorinated hydrocarbons have persistent effectiveness of their residual deposits. The biologial amplification takes place in sequence of an Eltonian pyramid.
For example, if the concentration of DDT in a water body such as pond is say, 3.0 × 10-6 ppm, it will amplify to 1.5 × 10 when it reaches the top of Eltonian pyramid, represented by large fish. If this fish is consumed by a person, the presence of heavy dose of DDT will disturb the functioning of blood molecules and hence lead to illness.
The bioamplificaiton of DDT is about 107 times the original residue. Hence it is called as ecopoisonous circulation of DDT.
Note # 4. Mode of Action of Pesticides:
By mode of action we mean the way in which a chemical acts upon the system of an insect to cause its death. Chemical poisons affect the normal functions of specific cells and tissues in the same way as is the case with higher animals. Generally, the chemical processes in insects are affected by abnormal functioning of their organs.
The insecticides can be divided into four groups based on their mode of action:
(i) Protoplasmic poisons
(ii) Respiratory poisons
(iii) Physical poisons and
(iv) Nerve poisons
(i) Protoplasmic poisons:
Chemicals like lead arsenate, sodium arsenite etc. kill all types of cells by poisoning them and by precipitating protein.
(ii) Respiratory poisons:
The fumigants like hydrocyanic acid gas, ethylene dibromide, methyl bromide and ethylene dichloride kill the insects by inactivating the respiratory enzymes (oxidases, peroxidases, reductases etc.).
(iii) Physical poisons:
These poisons kill by some physical action such as excluding air, for example, silica dusts and charcoal dust.
(iv) Nerve poisons:
DDT, malathion, parathion etc. may be classed together as nerve poisons. DDT initiates high nervous excitation and causes the release of excessive amounts of neuroactive substance. When it is produced in large amounts, it becomes toxicant and disrupts normal nerve functions.
Melathion causes tremours, convulsion, muscle paralysis and finally death.
Note # 5. Hazards of Pesticides to Human Life:
Due to widespread use of chemicals, the food consumed by man today is contaminated with chemicals. With rain it is washed down into the rivers causing pollution of water. These poisonous chemicals are stored in the fatty tissues of human body and it is estimated that about 5-27 ppm of DDT compound is found in tissues of persons living in the countries where DDT is widely used.
The accumulation of chemicals in human body is found to be harmful for health causing diseases like hypertension, tumour, cancer, lukemia, sterility etc. Some chemicals even damage the liver Endrin, penetrate percutaneously (through the skin) and produce toxic effects.
The highly toxic organophosphrous compounds are supposed to break down quickly in nature. Recently the accidental release of an insecticide into river Rhine killed millions of fish before it could be controlled.
The pesticides reach our body indirectly through vegetables, eggs etc.
The chart is given in Table 4 below:
A total of more than 812 samples collected from various sources such as farmers’ houses, FCl godowns and markets of Delhi, Hyderabad, Mysore, Patna and Ludhiana were analysed. Thirty five percent samples were found to contain residues of DDT, BHC, malathion or captan.
A table showing contamination of food samples is given below (table-5).
DDT has also been found in the bodies of human beings in different countries (Table 6). People are known have died after eating food contaminated with pesticides.
In Turkey 320 deaths occurred by eating seed grams containing hexachlorobenzene, 18 deaths in Columbia by eating flour contaminated with parathion. About 690, 185, 139, 1503 and 889 cases of poisoning were recorded in health and agricultural departments of Maharashtra, Bihar, Karnataka, Madras and West Bengal. The pesticides were parathion, endrin and diazinon.
Note # 6. Behaviour of Pesticides in Soil:
Plants sprayed with pesticides become toxic. However, the toxicity of pesticides is not permanent. Soon after they are applied on a crop, pesticides start breaking down because of the action of plants enzymes or environmental factors such as light, temperature and wind.
After sometimes, the concentration of pesticide decreases below maximum reducible limit (MRL), a level of pesticide residue considered safe for daily consumption.
During application, some of the pesticides fall on the ground, contaminating the soil. The pesticides are detoxified in the soil by adsorption and degradation. However, their presence in the soil for a long time could adversely affect its fertility, besides contaminating nearby water bodies.
The harmful effects of a pesticide depend on its toxicological properties and the degree of exposure of human beings to the pesticide residue. Many of these chemicals are deadly not only to the intended or particular organisms, but also to other life forms, including man.
Some can be accumulated by lower organisms (aquatic micro-organisms, etc.) and increase in concentration successively going up the food chain until toxic concentrations are consumed by higher animals (birds, mammals). This increase in concentration up to the food chain is called biological magnification.
When pesticides are added to soil, they act in the following ways:
(i) The chemical may be adsorbed by soil.
(ii) They may move downward through the soil in liquid or solution form and may be lost by leaching.
(iii) They may vaporise and be lost to into atmosphere without chemical change.
(iv) They may undergo chemical reactions within or on the surface of the soil.
(v) They may be broken down by soil micro-organisms.
