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

The environmental fate of [C-14] flupyrsulfuron-methyl, a sulfonylurea herb icide, was investigated in soil and aquatic systems. The major degradative pathways in both systems were contraction of the sulfonylurea bridge follow ed by intramolecular rearrangement (at pH > 7) or sulfonylurea bridge hydro lysis (at pH < 7). Hydrolysis was a first-order reaction and was pH- and te mperature-dependent. Flupyrsulfuron-methyl was degraded rapidly at 25 degre es C in pH 5, 7 and 9 sterile buffers with half-lives of 44, 12 and 0.42 da ys, respectively. At pH 7 and 9, sulfonyl bridge contraction and rearrangem ent was the major degradative mechanism; at pH 5 the sulfonylurea bridge wa s also hydrolysed. Unique photodegradation products were formed at pH 5 and pH 7 but, in general, hydrolysis was faster than photolysis at all three p H values. Aerobic aquatic metabolism involved biphasic degradation of the herbicide ( DT50, 3-6 days), degradation being faster in the aerobic aquatic systems th an in sterile buffers. Degradation in aerobic soils was rapid, both in the laboratory (DT50 8-26 days) and in the held (DT50 6-11 days, DT50 35-123 da ys). In laboratory studies the rate of degradation in soil reduced with dec reasing temperature (rate at 10 degrees C half that at 20 degrees C) but wa s unaffected by soil water content (50% vs 70% maximum water holding capaci ty). The compound was degraded in flooded anaerobic soils (DT50 33 days). Flupyrsulfuron-methyl was weakly absorbed to soils, there being a linear re lationship between adsorption and soil organic carbon content. Following ap plication of [C-14] flupyrsulfuron-methyl to bare field soil the radioactiv ity moved little, with very little radioactivity found in soil below 60 cm from the surface. (C) 1999 Society of Chemical Industry.