Plant Metabolism of Dithio-Systox and Thimet12

Abstract

The plant metabolism of dithio-Systox and of Thimet was investigated by the use of P32-radiotracers. It was demonstrated that these 2 systemic compounds were initially absorbed and translocated into cotton and lemon plants at approximately equal rates, but only from about 0.5 to 0.75 times as fast as Systox thiol isomer. The predominant processes of plant metabolism for both dithio-Systox and Thimet are primarily oxidative. Following uptake of dithio-Systox by cotton, lemon, bean, or alfalfa plants, the mercaptosulfur is oxidized very rapidly to produce the sulfoxide O, O-diethyl S-ethyl-2- sulfinylethyl phosphoro-dithioate and more slowly to produce the corresponding sulfone, O, O-diethyl S-ethyl-2-sulfonylethyl phosphorodithioate. Both the sulfoxide and the sulfone are also oxidized at the thionosulfur to produce O, O-diethyl S-2-sulfinylethyl phosphorothiolate and O, O-diethyl S-ethyl-2-sulfonylethyl phosphorothiolate. At intervals of a few days to a month after application, all 4 compounds may be present in plant residues, but no dithio-Systox is found. The sequence of consecutive reactions for dithio-Systox and for Thimet in isolated cotton leaves has been plotted, and a beginning has been made in establishing the kinetics of these. Thimet behaves in a manner completely analogous to that of dithio- Systox but exhibits somewhat different rates of metabolism. Typical harvest residues of dithio-Systox metabolites are presented from experiments using this material as a direct spray for cotton plants and as a seed treatment for alfalfa. The ultimate toxic residues are present in fractional parts per million. The application of the knowledge of plant metabolism of these compounds to analytical studies by the cholinesterase method is also discussed. All the simple oxidative metabolites of dithio-Systox and Thimet have been prepared in the pure state, and their properties are recorded.