The environmental fate of [ 14C ] รฝupyrsulfuron-methyl, a sulfonylurea herbicide, was investigated in soil and aquatic systems. The major degradative pathways in both systems were contraction of the sulfonylurea bridge followed by intramolecular rearrangement (at pH > 7) or sulfonylurea bridge hydrolysis (at pH AE 7). Hydrolysis was a รผrst-order reaction and was pH-and temperaturedependent. Flupyrsulfuron-methyl was degraded rapidly at 25รC in pH 5, 7 and 9 sterile buรพ ers with half-lives of 44, 12 and 0.42 days, respectively. At pH 7 and 9, sulfonyl bridge contraction and rearrangement was the major degradative mechanism ; at pH 5 the sulfonylurea bridge was also hydrolysed. Unique photodegradation products were formed at pH 5 and pH 7 but, in general, hydrolysis was faster than photolysis at all three pH values.
Aerobic aquatic metabolism involved biphasic degradation of the herbicide 3-6 days), degra-(DT 50 dation being faster in the aerobic aquatic systems than in sterile buรพ ers. Degradation in aerobic soils was rapid, both in the laboratory 8-26 days) and in the รผeld 6-11 days, 35-123 days). (DT 50 (DT 50 DT 90 In laboratory studies the rate of degradation in soil reduced with decreasing temperature (rate at 10รC half that at 20รC) but was unaรพ ected by soil water content (50% vs 70% maximum water holding capacity). The compound was degraded in รฝooded anaerobic soils 33 days). (DT 50 Flupyrsulfuron-methyl was weakly absorbed to soils, there being a linear relationship between adsorption and soil organic carbon content. Following application of [ 14C ] รฝupyrsulfuron-methyl to bare รผeld soil the radioactivity moved little, with very little radioactivity found in soil below 60 cm from the surface.