Abstract
Five dimethylphosphorothioates were tested for their toxicity to rats, potentiation of malathion toxicity in rats, inhibition of carboxylesterase in vitro, and reaction with malathion in vitro. The compounds were: potassium salts of (CH3S)2P(O)O−(I), (CH3O)(CH3S)P(O)S−(II), (CH3O)2P(O)S−(III), (CH3O)2P(S)S−(IV), and (CH3O)(CH3S)P(O)O−(V).
The dimethylphosphorothioates are not toxic to rats (up to 1 g/kg, orally), they do not potentiate malathion toxicity in rats, and do not inhibit carboxylesterase activity in vitro (up to 1 mM concentrations). However, when the S-acid diesters (II, III, IV) are incubated with malathion for several days at room temperature or for several hours at 50° C they become methylated forming the trimethylphosphorothioates OSS-trimethyl phosphorodithioate, OOS-trimethyl phosphorothioate and OOS-trimethyl phosphorodithioate respectively, which potentiate malathion toxicity. Furthermore, these same acid diesters increase the rate of isomerization of malathion into OS-dimethyl-S-(1,2-dicarbethoxyethyl) phosphorodithioate (isomalathion) particularly, diester IV.
The formation of the trimethylphosphorothioates and isomalathion from the interaction of the S-acid diesters with malathion was determined by thin layer chromatography (TLC), gas chromatography and mass spectrometry and could be detected by in vitro inhibition of carboxylesterase. TLC methods can detect 1 mg of the trimethylphosphorothioates and isomalathion per gram malathion.
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Verschoyle, R.D., Reiner, E., Bailey, E. et al. Dimethylphosphorothioates. Arch Toxicol 49, 293–301 (1982). https://doi.org/10.1007/BF00347877
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DOI: https://doi.org/10.1007/BF00347877