Soil Dissipation ~(14)CET-751 (Pyraflufen-ethyl) in Bare Ground in California: High Specific Activity Radiolabeled Test Substance and Small Plot Design Afford Excellent Method To Measure Field Dissipation

摘要

Field soil dissipation studies to support EPA registration of pyraflufen-ethyl (ET-751) were conducted in small outdoor plots (3 * 20 feet) under cotton growing conditions in California using [pyrazole-5-~(14)C] labeled test substance applied at 13.4 g/acre (33.2 g/ha). Use of radiolabeled ET-751 afforded a limit of quantification (LOQ) of <0.001 parts per million (ppm) for soil total radioactive residues (TRR) determinations and extracted metabolite residues. The t_(1/2) for ET-751 was <1 day due to rapid hydrolysis to the free acid (E-1). The latter reached its maximum (0.0193 ppm) in 0-3 inch soil segments after 6 hours, but this was short lived (t_(1/2)～14 days) and residues fell to <0.010 ppm by 14 DAY. Other identified metabolites were formed from E-1 or ET-751 by reductive cleavage, O-methylation and/or N-demethylation reactions. Each of the latter metabolites was detected at 0.010 ppm in 0-3 inch soil extracts. At least two unidentified polar metabolites (designated U-1 and U-2) were also detected. U-2 contained at least two components, which had chromatographic properties similar to unknown polar metabolites detected in parallel soil photolysis or aerobic soil studies. None of the 3-6 inch soil segments contained TRR > 0.010 ppm. TRR in lower soil segments were 0.010 ppm. A maximum of 0.0025 ppm E-1 was detected in 3-6 inch soil extracts (14 DAT) and U-2 reached 0.0038 ppm in 28 DAT 3-6 inch soil. By 359 DAT all metabolite residues were 0.001 ppm, or less, in 0-3 inch and 3-6 inch soil extracts. The degradation of parent and formation of known metabolites in the dissipation study and a parallel aerobic soil metabolism study was similar both qualitatively and quantitatively.