METABOLIC PATHWAYS AND RESIDUE LEVELS OF THIFENSULFURON METHYL IN SOYBEANS

Radiolabeled thifensulfuron methyl [methyl 3-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]car-bonyl]amino]sulfonyl]-2-thiophenecarboxylate], the active ingredient in Pinnacle herbicide, was applied postemergence to greenhouse-grown soybean seedlings at 8 and 16 g of active ingredient/ha (2-4 times the labeled use rate), with and without surfactant. The soybeans were grown to maturity, and the metabolic pathways and total radiolabeled residue levels were determined. The concentration of thifensulfuron methyl in soybean foliage declined with half-lives ranging from 5 to 20 days to approximately 8 ppb 30 days after treatment. The identities and concentrations of surface residues and metabolites in soybean foliage were quantitated at 0, 7, and 30 days after treatment. Radiolabeled residues in mature soybean seeds produced from these elevated application rates were extremely low and ranged from 0.4 to 1.6 ppb.