Chlorpyrifos is a crystalline organophosphate insecticide. Chlorpyrifos is moderately toxic to humans and chronic exposure has been linked to neurological effects, developmental disorders, and autoimmune disorders. Chlorpyrifos is produced via a multistep synthesis from 3-methylpyridine, eventually reacting 3,5,6-trichloro-2-pyridinol with diethylthiophosphoryl chloride. The crops with the most intense chlorpyrifos use are cotton, corn, almonds, and fruit trees including oranges, bananas and apples. Chlorpyrifos is an organophosphate, with potential for both acute toxicity at larger amounts and neurological effects in fetuses and children even at very small amounts. For acute effects, the EPA classifies chlorpyrifos as Class II: moderately toxic. The oral LD50 for chlorpyrifos in experimental animals is 32 to 1000 mg/kg. The dermal LD50 in rats is greater than 2000 mg/kg and 1000 to 2000 mg/kg in rabbits.
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