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Toxicology

Organophosphate insecticides (OPs) are among the oldest of the synthetic pesticides and are currently the most widely used class of insecticides. Although French chemist, Jean Louis Lassaigne, first synthesized OPs from the reaction of phosphoric acid and alcohol in 1820, it was not until the 1930s that Gerhard Schrader, a German chemist, discovered their insecticidal properties.
The OPs do not accumulate in the body because they are rapidly metabolized and excreted. They also undergo a number of metabolic reactions in mammals. Malathion, for instance, is quite susceptible to hydrolysis by esterases and so has very low mammalian toxicity. Parathion, on the other hand, contains an aromatic phosphate ester group that is more resistant to enzymatic hydrolysis.
OPs inhibit the activity of acetylcholinesterase (AChE), which is a neurotransmitter in mammals. Normally, acetylcholine (ACh) is rapidly broken down following its release by a group of enzymes known as cholinesterase. OPs, or their metabolites, can compete with acetylcholine for its receptor site on these enzymes, thus blocking the breakdown of ACh.
Although OPs are a significant occupational hazard to agricultural workers, residues on food products normally do not result in exposures sufficient to lead to toxic symptoms in humans.

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