Aerobic soil metabolism of metsulfuron-methyl

Abstract

A laboratory study was conducted to determine the degradation rates and identify major metabolites of the herbicide metsulfuron-methyl in sterile and non-sterile aerobic soils in the dark at 20°C. Both [phenyl-U-14C]- and [triazine-2-14C]metsulfuron-methyl were used. The soil was treated with [14C]metsulfuron-methyl (0.1 mg kg−1) and incubated in flow-through systems for one year. The degradation rate constants, DT50, and DT90 were obtained based on the first-order and biphasic models. The DT50 (time required for 50% of applied chemical to degrade) for metsulfuron-methyl, estimated using a biphasic model, was approximately 10 days (9–11 days, 95% confidence limits) in the non-sterile soil and 20 days (12–32 days, 95% confidence limits) in the sterile soil. One-year cumulative carbon dioxide accounted for approximately 48% and 23% of the applied radioactivity in the [phenyl-U-14C] and [triazine-2-14C]metsulfuron-methyl systems, respectively. Seven metabolites were identified by HPLC or LC/MS with synthetic standards. The degradation pathways included O-demethylation, cleavage of the sulfonylurea bridge, and triazine ring opening. The triazine ring-opened products were methyl 2-[[[[[[[(acetylamino)carbohyl]amino]carbonyl]amino] carbonyl]-amino]sulfonyl]benzoate in the sterile soil and methyl 2-[[[[[amino[(aminocarbonyl)imino]methyl] amino]carbonyl]amino]sulfonyl]benzoate in the non-sterile soil, indicating that different pathways were operable. © 1999 Society of Chemical Industry