Fate and behaviour of flupyrsulfuron-methyl in soil and aquatic systems

Abstract

The environmental fate of [14C]flupyrsulfuron-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<7). Hydrolysis was a first-order reaction and was pH- and temperature-dependent. Flupyrsulfuron-methyl was degraded rapidly at 25°C in pH 5, 7 and 9 sterile buffers 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 (DT50 3–6 days), degradation being faster in the aerobic aquatic systems than in sterile buffers. Degradation in aerobic soils was rapid, both in the laboratory (DT50 8–26 days) and in the field (DT50 6–11 days, DT90 35–123 days). In laboratory studies the rate of degradation in soil reduced with decreasing temperature (rate at 10°C half that at 20°C) but was unaffected by soil water content (50% vs 70% maximum water holding capacity). The compound was degraded in flooded anaerobic soils (DT50 33 days). Flupyrsulfuron-methyl was weakly absorbed to soils, there being a linear relationship between adsorption and soil organic carbon content. Following application of [14C]flupyrsulfuron-methyl to bare field soil the radioactivity moved little, with very little radioactivity found in soil below 60 cm from the surface. © 1999 Society of Chemical Industry