Environmental Management: Principles and practice

Pesticides
Pesticides are compounds used to kill, deter, or disable pests, for one or more of the
following purposes:
♦
to maximize crop or livestock yields;
♦
to reduce post-harvest losses to rodents, fungus, etc.;
♦
to improve appearance of crops or livestock;
♦
for disease control (human health and veterinary use);
♦
for preservation and maintenance of buildings, clothing, boats, furniture;
♦
to control weeds which hinder transport and access (road and railway use,
control of weeds and other organisms on boat hulls, in pipes and canals);
♦
for aesthetic or leisure reasons, lawn-care, garden flowers, golf courses.
Some natural pesticides are available. However, natural compounds (‘organics’)
are not necessarily harmless alternatives to synthetics: some are very toxic or
carcinogenic.
DDT was one of the first synthetic organic compounds (mainly organochlorines
or chlorinated hydrocarbons), initially synthesized in 1874, rediscovered in 1939
and adopted for louse and mosquito control during the Second World War and from
the 1950s for agricultural use. The second main group of synthetic pesticides, the
organophosphates, were discovered in the 1930s. After the 1940s other synthetic
organic compounds were developed and widely used for agriculture and public health
measures. There has been a trend to replace many of these pesticides with ‘safer’
organophosphate (e.g methyparathion), and pyrethroid insecticides and synthetic
herbicides and fungicides. Organophosphates can be more toxic than organochlorines
but are less persistent (Conway and Pretty, 1991).
The benefits claimed for pesticides are considerable, in terms of improved
harvest, reduced storage losses, human and livestock disease control. Successful
pest control commonly reduces crop and produce losses by 20 per cent or more and
improves security of harvest and storage. But it is difficult to quantify the benefits
and the risks of pesticide use—for example, in developing countries a large proportion
of what is used is applied to luxury export crops, not staples; there may also be off-
site pollution that is difficult to trace back to the pesticide use. Pests may flourish if
predators are poisoned and they survive. Pesticides are also used because consumers
demand blemish-free produce, and growers seek to ensure ripening of the bulk of a
crop at a given moment to assist gathering and processing. There have been
suggestions that, in spite of pesticides, crop losses have increased in the last few
decades—but would things have been worse without pesticides?

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Recognition that ‘safe’ pesticides caused environmental problems came by
the early 1960s, the public being alerted by by Carson (1962). DDT was found to
concentrate in the fat of higher organisms through ‘biological magnification’. By
1972 its use in the USA was banned (but not manufacture and export). Weir and
Shapiro (1981:4) publicized how the export of pesticides banned in the USA still
had an impact there through contaminated food imports. The problems associated
with pesticide use can be summarized as:
♦
poor selectivity of compounds (not narrow-spectrum, i.e. not very specific in
terms of what is killed or injured);
♦
over-use;
♦
toxicity and slow breakdown;
♦
tendency to be concentrated by foodweb;
♦
misuse or unsafe methods of application;
♦
the effects of long-term usage of pesticides on soil fertility is little known;
♦
the impact of cumulative effects on the global environment is not known.
Ideally, a pesticide should be specific, i.e. kill, disable, or deter a pest and
affect nothing else. Unfortunately, most compounds are far from specific: non-pest
organisms may be directly or indirectly affected. There are other possible impacts:
on-farm (contamination of workers, livestock, crops, soil, wildlife and groundwater);
off-farm (contamination of nearby woods, hedges, housing, streams); and global
contamination. The impacts may be short term or long term, are often indirect, and
may have cumulative (synergistic) effects. Tracing impacts (and proving liability)
from pesticide use back to the point of application can be difficult.
Much pesticide is used pre-emptively and may not be necessary. Usage
increased rapidly from roughly 1950, partly reflecting the green revolution and the
spread of modern crop varieties. About 50 per cent of all pesticide is applied to
wheat, maize, cotton, rice and soya. Most used in developing countries goes onto
plantation crops like cocoa, coffee and oil palm. Japan is probably the most intensive
user; the largest user is the USA followed by western Europe. Roughly half of known
pesticide poisonings and at least 80 per cent of fatalities have occurred in developing
countries, yet these use only 15–20 per cent of world’s pesticides (Pimbert, 1991:3).
As pesticides are costly to develop, even those acting with the best of motives
and care may be unable to test them fully, and could be reluctant to withdraw a
compound if there is some fault; they may resist developing specific pesticides (i.e
those that act on just one or a few types of pest) because it restricts sales; they may
resist giving safety advice that could cut sales; they may promote use (or the
middlemen may do so) in inappropriate situations to maximize profit. Side-effects
may only become apparent after extensive use, and pesticide developers may neglect
important pests if there are limited profits to be made from their control.
Pesticide problems can be reduced by:
♦
banning dangerous compounds;
♦
developing alternatives like biological control or integrated pest management;

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♦
restricting trade of pesticide-contaminated produce;
♦
controlling pesticide usage by monitoring, inspection and licensing to ensure
sensible procedures;
♦
developing less dangerous pesticides;
♦
controlling prices of pesticides to discourage excessive use;
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education to discourage unsound strategies;
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rotation of crops to upset pest breeding and access to food;
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hand- or non-chemical weeding;
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encouraging agencies to cut funds for pesticides;
♦
treating drinking water to remove pesticides.
Most countries have established departments responsible for reviewing pesticide
use which have powers to initiate controls, but there are still problems in disseminating
information about pesticides and their effects, in monitoring, and with political and
economic aspects of control (Ghatak and Turner, 1978; Boardman, 1986). In 1986
the FAO issued an International Code of Conduct on the Distribution and Use of
Pesticides and in 1990 got 100 countries to sign a code of conduct on pesticides. The
UNEP, WHO, OECD, ILO, EC, the Pesticides Action Network (PAN) and other
international bodies and NGOs make efforts to improve pesticide use and controls,
but in practice there is a long way to go before controls are satisfactory. Various
databases and networks are now established to assist with monitoring and control.
The FAO and WHO have set up the Codex Alimentarius Commission (‘Codex
System’) to establish food standards. One of its tasks is to check on pesticide residues
in produce (and each year to publish information to assist in this). Under GATT
agreements the Codex has increased influence over the way countries set their food
and agriculture standards (Avery et al., 1993).
Integrated pest management (IPM) should reduce the use of pesticides and
make pest control more focused. IPM involves study of the pest(s) and the context,
using approaches like participatory rural appraisal, to diagnose the best mix of crop
and pest control techniques to use. IPM must be co-ordinated with conservation,
land and water management, social and economic development, public health, etc.,
and uses pesticides only as a last resort in a judicious manner.
As with chemical pesticides, there is a need for caution over biological controls.
History has taught that control organisms may become a problem. Genetic engineering
may also be a double-edged sword. It offers alternatives to chemical pesticides but
also threatens serious problems if a dangerous trait were passed to another species,
or a modified organism ‘misbehaves’.