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Future
status of pesticides development
By Dr Sohail Ahmed
Maximum productivity and efficiency in agriculture will depend
on the development and the use of improved practices, such as
growing varieties with disease-and-insect resistance ,
application of proper kinds and amounts of fertilizers,
efficient use of water, and labour-saving machinery and
equipment. But these advantages will be lost without the use
of crop protecting chemicals.
 There
are pest problems today for which no satisfactory control
methods exist to replace the use of chemicals, and pesticides
will be the most dependable weapons of the applied biologist
unless and until more acceptable techniques can be developed.
The chronological evidence, from the discovery of the DDT to
the present day pyrethroid insecticides and similar
development in many other potent, selective and safe
pesticides, has shown not only increased production and
consumption but awareness and sense of judgment about hazards
and risks as well.
At present, the developing countries are using relatively
little in the way of chemicals to control pests in the
majority of crops. In developed countries the use of crop
protecting chemicals have played a major role in the increased
and more efficient production of food because pesticides have
provided immediate effective control at practical and
affordable costs.
Many people, when considering chemicals, including pesticides,
fail to distinguish between the toxicity and hazard. Toxicity,
on the one hand, refers to the ability of a chemical to cause
poisoning when administered in adequate quantity through
specified routes.
Hazard on the other hand means the probability that a
substance will cause harm in the circumstances of usage. Two
distinct types of toxic effects (acute and chronic) can be
observed from many poisons.
Since, for any one poison, there may be little or no relation
between either the mechanism of these two kinds of toxic
action or the magnitude of the concentrations which evoke
them, the two effects must be carefully distinguished.
An acute toxic response is one, which occurs shortly after
application of a single dose of the poison. It is determined
by the intrinsic toxicity of the substance to the organism and
can often be traced to some specific disruptive effect at the
biochemical level.
A chronic effect, on the other hand, is one, which sometimes
occurs when an organism is exposed to repeated small and
non-lethal doses of poison over a considerable period of time.
Most pesticides are not highly dangerous materials.
Occupational pesticide poisoning is uncommon, most cases being
due to accidental or intentional ingestion of large amounts.
Safety problems are mainly confined to a few very highly
poisonous substances that are so effective or so economical
that at present they are unlikely to be supplanted. The hazard
of a pesticide varies with its mode of formulation (e.g.,
solution, emulsion, powder, gas, granule, pellet, etc.), and
with its mode of application, which may be by dispersal as a
spray, dust, smoke, gas, incorporation in soil, or by release
from aircraft.
Many people may confuse accidents caused by direct exposure to
chemicals with the possible hazards presented by pesticide
residues in air, water and food. There is no evidence that our
drinking water supplies and food are contaminated to a level
that would be injurious to masses.
Pesticides have made possible a greater abundance and variety
of agricultural products at far less cost to the consumer than
would otherwise be the case. They have been a major
contributor to the upsurge in agricultural productivity over
the past three decades.
But from this productivity came the great surpluses, and the
farmers' temporary gains from increased efficiency have often
been erased by lower prices. In another vein, the use of
pesticides to eradicate disease-carrying insects throughout
the world has sharply reduced the death rate and thus has been
a substantial factor in the population explosion.
The concept of the benefit-risk equation has a compelling
logic which all accept in principle. But going from principle
to practice always is attended with disagreement and conflict.
This occurs because a diverse society generates a diverse
range of material and aesthetic interests and values. Conflict
occurs even though all concur with the ultimate goal of the
promotion of the public good.
Although, all of us are consumers and all have a stake in an
expanding and prosperous economy, our attitudes on pesticides
and their regulation differ; the wildlife conservationist and
the chemical manufacturer approach the subject from different
perspectives, the housewife buying vegetables and fruits at
the market has different concerns than the farmer who grows
the food.
The public debate over pesticides is but one facet of a wider
debate that reflects a greater sensitivity to the fundamental
questions raised by the continuing and accelerating pace of
man's modification of his total environment.
Pesticides are but one factor and we are increasingly aware
that our environment is being altered, perhaps even more
dramatically, by air and water pollution from sources other
than pesticides, atomic fallout, and the population explosion.
It is not generally known that without the aid of pesticides,
without the technology of the agricultural chemical industry,
we would not have a large exportable surplus. We would in
fact, be barely able to feed our present population - and
certainly not in the manner to which it has become accustomed.
Pollution is assuming alarming proportions all over the world,
and looks like becoming one of the major problems of our time.
Pesticides are only a small part of alarming proportions of
pollution all over the world but an important one.
All reasonable efforts must be made to reduce these dangers as
far as possible. It is fair to add that investigations to date
have not shown any significant damage to any form of life on
planet for which pesticides can clearly be held responsible.
Critics of persistent chemicals as influenced by Rachael
Carlson mythical approach have not fully addressed alternates
originated as a result of public outcry. One such example is
remarkable advancement to research on biopesticides.
Biopesticides are certain types of pesticides derived from
such natural materials as animals, plants, bacteria, and
certain minerals. For example, canola oil and baking soda have
pesticidal applications and are considered biopesticides. At
the end of 2001, there were approximately 195 registered
biopesticide active ingredients and 780 products.
Biopesticides fall into three major classes:
(1) Microbial pesticides consist of a microorganism (e.g., a
bacterium, fungus, virus or protozoan) as the active
ingredient. Microbial pesticides can control many different
kinds of pests, although each separate active ingredient is
relatively specific for its target pest[s].
For example, there are fungi that control certain weeds, and
other fungi that kill specific insects. The most widely used
microbial pesticides are subspecies and strains of Bacillus
thuringiensis, or Bt. Each strain of this bacterium produces a
different mix of proteins, and specifically kills one or a few
related species of insect larvae.
While some Bt's control moth larvae found on plants, other
Bt's are specific for larvae of flies and mosquitoes. The
target insect species are determined by whether the particular
Bt produces a protein that can bind to a larval gut receptor,
thereby causing the insect larvae to starve
(2) Plant-Incorporated-Protectants (PIPs) are pesticidal
substances that plants produce from genetic material that has
been added to the plant. For example, scientists can take the
gene for the Bt pesticidal protein, and introduce the gene
into the plant's own genetic material.
Then the plant, instead of the Bt bacterium, manufactures the
substance that destroys the pest. The protein and its genetic
material, but not the plant itself, are regulated by the EPA.
(3) Biochemical pesticides are naturally occurring substances
that control pests by non-toxic mechanisms. Conventional
pesticides, by contrast, are generally synthetic materials
that directly kill or inactivate the pest.
Biochemical pesticides include substances, such as insect sex
pheromones, that interfere with mating, as well as various
scented plant extracts that attract insect pests to traps.
Because it is sometimes difficult to determine whether a
substance meets the criteria for classification as a
biochemical pesticide, the EPA has established a special
committee to make such decisions.
The DAWN
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