Simultaneous derivatization and trapping of volatile products from aqueousphotolysis of thiamethoxam insecticide

An aqueous photolysis study was conducted with radiolabeled thiamethoxam, 4 H-1,3,5-oxadiazin-2-imine, 3-[(2-chloro-5 -thiazolyl)methyl]tetrahydro -5-m ethyl-N-nitro, to establish the relevance of aqueous photolysis as a transf ormation process for C-14-[thiazolyl]-thiamethoxam. C-14-[thiazoly]-thiamet hoxam was applied to sterile sodium acetate pH 5 buffer solution at a dose rate of approximately 10 ppm. The resulting samples were incubated for up t o 30 days at 25 degreesC under irradiated and nonirradiated conditions. The irradiated samples were exposed to a 12-hour-on and 12-hour-off light cycl e. Volatile fractions accounted for up to an average of 56.76% of the total dose for the irradiated incubations and <0.08% for the nonirradiated incub ations. These fractions were; proposed to be a mixture of carbonyl sulfide (COS) and isocyanic acid (CONH). Verification of these components was accom plished by trapping with cyclohexylamine and formation of the thiocarbamate and the isocyanic acid derivatives. A similar method of trapping thiocarba mate metabolites was reported (Chen and Casida, 1978) where filter paper sa turated with isobutylamine in methanol was arranged to trap (COS)-C-14 and (CO2)-C-14 under a positive flow of O-2 at 25 <degrees>C. Mass spectroscopy of the derivatized components confirmed the presence of carbonyl sulfide a s the cyclohexylamine thiocarbamate and of isocyanic acid as its cyclohexyl amine derivative. Evidence from this study indicates that thiamethoxam degr ades significantly under photolytic conditions.