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.
