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History
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The use of pesticides began in the 18th century & the first synthetic pesticide
chemical appeared in the latter part of the 19th century, but the most important
phase of their development occurred in the past five decades.
In U.S., the use of arsenical & botanically derived insecticides led the field until
the middle 1940s when the synthetic organic insecticide chemicals began a remarkable
rate of growth; now, synthetic chemicals dominate the field, greatly outstanding
other types of insecticide chemicals.
In the last two decades, much effort has been on the development of organophosphorus
chemicals, compounds which inhibit Cholinesterase & certain aliesterases in insects,
mites & mammals. While many of these are highly toxic, such chemicals remain in
or on the plants for a relatively short time, their effective period varying from
several hours to a few days. Also, most of these compounds are metabolized in mammals
to harmless products in a day or so. As a result, organophosphorus compounds have
a favourable chronic toxicity pattern to man & useful animals tissues, including
milk.
In the past decades, emphasis has been on the development of carbamate - type &
thionophosphate - type insecticide chemicals. The carbamates generally inhibit cholinesterase,
metabolize rapidly in mammals & show very little propensity for storage in meat
& milk. Much work has been done & is still being done, to elucidate the biochemistry
of these two types of insecticide chemicals, especially their fate in insects &
mammals.
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