Environmental pollution by insecticides and its impact on biosphere
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Pesticides are biologically active chemicals used for pest control. But their spectrum of activity often extends far beyond the pests and justifies the more applicable term ‘biocide’.
Pesticides are widely distributed by natural means but, unlike such natural pollutants as dusts, they tend to retain much of their biocidal activity for fairly long periods.
Huge amounts of different kinds of poisonous agricultural chemicals are being used these days and the whole biosphere is being increasingly poisoned and polluted as a consequence.
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Many of these chemicals and pesticides are known to persist for long periods in the environment and their concentration builds up geometrically as they are transferred to different stages of the food-web.
Serious cases of fish mortality have occurred following the leaching of poisonous biocides from agricultural fields to nearby rivers or streams after rainfall. One such well-documented case that attracted considerable public attention in America, was a case of large-scale fish kill in the lower Mississippi river in which five million fish died.
Careful investigations indicated that the fish had died as a consequence of dumping of Endrin-rich agricultural wastes and runoff into a tributary of the Mississippi river at Memphis.
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The widespread use of DDT as an insecticide has also aroused considerable concern in recent years and some countries have already legally banned its use.
Agroecosystems are specially vulnerable to the wide range of pesticides applied to maximise growth of crops. Residues of various weedicides and insecticides often accumulate in agricultural soils more rapidly than they are degraded. Insecticides are designed to kill insects and in many cases, they may not be toxic to plants.
In contrast, some herbicides differ from insecticides in killing both desirable species as well as the intended target. Their impact may not be limited directly to the plant community or agricultural crop but they may also act indirectly through effects on such soil microbes as nitrogen fixing blue-green algae and bacteria. This in turn may impair the growth and production of higher plants.
The impact of such chemical wastes as phenols, acids, metals, etc., applied to soil can also be fairly high and may range from selection towards tolerant species to complete destruction of vegetation and also soil sterilization.
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Extensive researches in the USA have established widespread distribution of DDT residues through food chains in several lakes. Residues were detected in shallow and deep water mud samples, crustaceans, whitefish, duck, ring-billed and herring gulls and other fauna. Both DDT and Dieldrin have seen shown to pass from mother to offspring through the placenta in mice and certain other animals, possibly including man. Residues of Dieldrin, Endrin, DDT and DDE have been detected in all major river basins in the United States. It is also believed that the declining percentage of immature biro in the American bald eagle population is due to DDT and other hard biocides.
The following are some general properties of pesticides or their residues:
(1) They often strike not only the intended pests but also several nontar- get organisms.
(2) Many of them persist and cannot be disposed off.
(3) They may cause such unintended effects as resistance, faunal displacement and other population changes.
(4) They may be carried to places far removed from the points of application or origin, and water is a very effective medium for their dispersal.
(5) Their concentration and magnification in biological systems may- lead to certain unexpected or untoward results.
Most of our pests are basically created in four ways (Rudd, 1971): (a) certain species of plants or animals may be selectively propagated; (b) many species are moved from one place on earth to another either intentionally or unintentionally; (c) a reduction in biological diversity often takes place either intentionally or accidentally; and (d) living organisms may adapt to changed environment and, in the case of pest, ‘biological weeds’ can be evolved.
Quite often a pest in one land is not a pest in its native land since its translocation to a remote place (mostly by man) means that its natural predators and parasites are left behind, thereby permitting its numbers to increase enormously in the new habitat.
Pesticides are widely distributed by natural means but, unlike such natural pollutants as dusts, they tend to retain much of their biocidal activity for fairly long periods.
Huge amounts of different kinds of poisonous agricultural chemicals are being used these days and the whole biosphere is being increasingly poisoned and polluted as a consequence.
ADVERTISEMENTS:
Many of these chemicals and pesticides are known to persist for long periods in the environment and their concentration builds up geometrically as they are transferred to different stages of the food-web.
Serious cases of fish mortality have occurred following the leaching of poisonous biocides from agricultural fields to nearby rivers or streams after rainfall. One such well-documented case that attracted considerable public attention in America, was a case of large-scale fish kill in the lower Mississippi river in which five million fish died.
Careful investigations indicated that the fish had died as a consequence of dumping of Endrin-rich agricultural wastes and runoff into a tributary of the Mississippi river at Memphis.
ADVERTISEMENTS:
The widespread use of DDT as an insecticide has also aroused considerable concern in recent years and some countries have already legally banned its use.
Agroecosystems are specially vulnerable to the wide range of pesticides applied to maximise growth of crops. Residues of various weedicides and insecticides often accumulate in agricultural soils more rapidly than they are degraded. Insecticides are designed to kill insects and in many cases, they may not be toxic to plants.
In contrast, some herbicides differ from insecticides in killing both desirable species as well as the intended target. Their impact may not be limited directly to the plant community or agricultural crop but they may also act indirectly through effects on such soil microbes as nitrogen fixing blue-green algae and bacteria. This in turn may impair the growth and production of higher plants.
The impact of such chemical wastes as phenols, acids, metals, etc., applied to soil can also be fairly high and may range from selection towards tolerant species to complete destruction of vegetation and also soil sterilization.
ADVERTISEMENTS:
Extensive researches in the USA have established widespread distribution of DDT residues through food chains in several lakes. Residues were detected in shallow and deep water mud samples, crustaceans, whitefish, duck, ring-billed and herring gulls and other fauna. Both DDT and Dieldrin have seen shown to pass from mother to offspring through the placenta in mice and certain other animals, possibly including man. Residues of Dieldrin, Endrin, DDT and DDE have been detected in all major river basins in the United States. It is also believed that the declining percentage of immature biro in the American bald eagle population is due to DDT and other hard biocides.
The following are some general properties of pesticides or their residues:
(1) They often strike not only the intended pests but also several nontar- get organisms.
(2) Many of them persist and cannot be disposed off.
(3) They may cause such unintended effects as resistance, faunal displacement and other population changes.
(4) They may be carried to places far removed from the points of application or origin, and water is a very effective medium for their dispersal.
(5) Their concentration and magnification in biological systems may- lead to certain unexpected or untoward results.
Most of our pests are basically created in four ways (Rudd, 1971): (a) certain species of plants or animals may be selectively propagated; (b) many species are moved from one place on earth to another either intentionally or unintentionally; (c) a reduction in biological diversity often takes place either intentionally or accidentally; and (d) living organisms may adapt to changed environment and, in the case of pest, ‘biological weeds’ can be evolved.
Quite often a pest in one land is not a pest in its native land since its translocation to a remote place (mostly by man) means that its natural predators and parasites are left behind, thereby permitting its numbers to increase enormously in the new habitat.
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