Coumaphos toxicity

U.S. Environmental Protection Agency, Pesticide Fact Sheet Number207 Coumaphos. Office of Pesticides and Toxic Substances, Washington, DC, pp. 5-19, 1989. 

Coumarin insecticides usually contain the coumarin molecule with an 0,0-diethyl phosphate or 0,0-diethyl phosphothionate radical, e.g. Potasan, (0,0 diethyl-0-(4-methyl-7-coumaryl)phosphothionate) (111) Coumaphos, (0,0 diethyl-0-(3-chloro-4-methyl-7-coumaryl) phosphothionate (112) Haloxon, (0,0-diethyl-O-(3-chloro-4-methyl-7-coumaryl) phosphate (113). The mode of action of these compounds combines the toxic properties of coumarin moiety with the action of the organophosphorus compounds. The latter acts by inhibiting the esterase enzyme systems in the insects, particularly cholinesterase, probably by phosphorylation of the active site of the enzyme. 

Instability of the toxicant under conditions of use may affect the toxicity. Thus, the organophosphate insecticide coumaphos may decompose in dipping vats to form poto-san, which has increased toxicity to cattle. 

Matrix bound coumaphos and trichlorfon and encapsulated toxicants containing ethyl and methyl pirimiphos, permethrin, and diazinon were found to be ineffective against the fire ant. However, the ineffectiveness was not due to the controlled release mechanism but rather the ability of the ant to filter particles in its infrabuccal pocket in its head. Particles as small as 0.88 microns can be filtered and never come in contact with internal parts. 

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