80 ENVIRONMENTAL SCIENCE
PESTICIDES: ENVIRONMENTAL PROBLEM
Use of Pesticides
Until 1940’s the following chemicals were used to control pests:
(1) Elements fungicides (S, Cu, Hg, organomercury) against fungal diseases.
(2) Copper sulphate, sodium aresenite and ferrous sulphate against weeds.
(3) Nature insecticides e.g. pyrethrum and nicotine, against beetles and aphids.
(4) Tar oil, petroleum, etc., against and red spider mite eggs.
(5) Lead arsenate against caterpillars.
Even these chemicals were sparingly used. The applications to cereals used to be confined
to seed treatment with organomercury to kill-borne pathogens.
The organochlorine insecticides and herbicides became quite widespread in the mid and
late 1950s and a large variety of these dangerous compounds were being used in the 1960s
in USA, UK, and other developed countries. The British Govt. approved over 150 chemicals
for use as pesticides/herbicides by 1970.
THE HAZARDOUS METHODS OF PESTICIDE APPLICATION
The main method of pesticide application on a large scale is the ‘Aerial Drift Spray”. It is
a highly inefficient and wasteful, capital-intensive technique. A close study shows its nature:
(1) More than 40 per cent of applied pesticide is normally out of the target area.
(2) 15 per cent is out of the target crops.
(3) 40 per cent near the target insect.
(4) 75 per cent is not in contact with it.
(5) It is estimated that the insect through contact, inhalation and ignition absorbs less
than one of the total applied pesticide.
(6) Only about 0.3 per cent of the applied insecticides appear to be absorbed by aphids
on bean contours and 0.02 per cent by myriads on cocoa. The wasteful use is
magnified by the practice followed by farmers who apply pesticide according to the
pre-set schedules prepared by manufacturers. Indeed the actual use of pesticides
by many advanced country farmers may safely be cut by 30 to 50 per cent with no
adverse effect on crop production in case pesticides are applied only when necessary
and in relation to specific pests.
The following are some general properties of pesticides or their residues:
(1) They often strike the intended pests as well as several off.
(2) Many of them continue to persist and cannot be disposed off.
(3) They may cause unintended effects like resistance, faunal displacement and other
population changes.
(4) They may be carried to places fare removed from the points of application or origin.
(5) Their concentration and magnification in biological systems may lead to certain
unexpected or untoward result.