Investigations into the chemistry, toxicology, mode of action and photochemical formation of some delayed toxic sulfur-containing organophosphorus triesters

Examination of a limited series of O,S,S-trialkyl phosphorodithionates revealed that very minor changes in the alkyl substituents resulted in wide changes in toxicity. However, alkaline hydrolysis rate constants did not vary significantly with changes in alkyl substituents. O,S,S-trimethyl phosphorodithioate was several fold more reactive, and more toxic to the rat, than its corresponding phosphorothioate analogue, O,O,S-trimethyl phosphorothioate. The toxicological feasibility of sulfoxidation was examined further by the peracide oxidation of O-ethyl-S-13C-methyl ethyl-phosphonothiate (I) using 13C-NMR as the monitoring tool. Several lines of evidence pointed to the formation of the sulfoxide of I. The photochemical formation of the delayed toxicants from methyl parathion, fenthion, methidathion, azinphosmethyl, malathion, temephos, chlorpyrifos-methyl, chlorpyrifos-ethyl and diazinon in measurable amounts, suggested that they might be of some toxicological significance in the environment. This photoalteration had a strong link with the numerical closeness between the spectral emissivity of the light sources and the UV λ max of the irradiated phosphorothioate insecticide as well as the magnitude of the latter's a/sub M/ values. The levels of the delayed toxicants produced following irradiations are not expect to pose acute toxic hazards to field workers dealing routinely with agricultural chemicals