ENVIRONMENTAL SCIENCE : NATURAL RESOURCES 81
PROBLEMS CREATED BY THE PESTICIDES APPLICATION
Pesticides widely distributed by natural means but they tend to retain much of their
biocidal activity for fairly long periods. On account of the use of different kinds of poisonous
agriculture chemicals the whole biosphere is being increasingly poisoned and polluted. Many
of these chemicals and pesticides are known to persist for long periods in the environment.
Their concentration builds up geometrically as they are transferred to different stages of the
food web.
Harms caused by the use of pesticides are as under:(1) Harm to Fish
Serious cases of fish mortality have occurred following the leaching of poisonous biocides
from agricultural fields to nearby rivers or streams after rainfall. Great concern was shown
on a case of large-scale fish kill in the lower Mississippi river in U.S.A. wherein five million
fish died. Careful investigation indicated that the fish had died due to dumping of Endrin-
rich agriculture wastes and runoff into a tributary of the Mississippi River the Memphis.
The widespread use of DDT as an insecticide has also aroused considerable concern in
recent years. As a result, some countries have already legally banned its use.
(2) Harm Caused by the Herbicides
Residues of various weedicides and insecticides often accumulate in agricultural soils
rapidly. Insecticides are designed to kill insects. As such they may not be toxic to plants. On
the contrary to it, some herbicides differ from insecticides in killing both desirable species
as well as the intended target. They may adversely affect such soils microbes as nitroes
fixing blue-green algae and bacteria. This, in turn, may impair the growth and production
of higher plants.
(3) Damage to the Extent of Complete Destruction of Vegetation
The impact of some chemical wastes as phenols, metals etc. applied to soil may go to
the extent of complete destruction of vegetation and also soil sterilization.
Table 2.7
Relative Distribution of Aldrin & D1-2 Ethylhexyl Phythalate (Dehp) in a Model
Ecosystem (Condensed from Metcalf, 1974)Concentration (ppm equivalents) in
Water Algae Snail Mosquito FishALDRIN
Aldrin 0.00005 1.95 2.23 0.157
Dieldrin 0.0047 16.88 52.4 1.1 28.0
Polar metabolites 0.004 0.015 0.097 0.004
Unknown 0.0004 0.585 2.05 0.612
Value 3140
(Contd.)