FATE OF RIMSULFURON IN THE ENVIRONMENT

The fate of C-14-labeled rimsulfuron in aqueous and soil environments was examined. Hydrolysis was first-order, pH-dependent, and accelerated at higher temperatures. Rimsulfuron degraded rapidly in pH 5, 7, and 9 buffer solutions (25 degrees C) with half-lives of 4.7, 7.2, and 0.4 days, respectively, primarily through contraction of the sulfonylurea bridge. Soil metabolism studies also showed rapid decomposition by bridge contraction with half-lives of 24.5 (laboratory) and 5.7 (field) days. The degradation rate and metabolic pathway did not change when aqueous solutions (pH 7 or 9) or soil was kept in the dark or exposed to light. A faster degradation rate in light-exposed pH 5 aqueous solution was observed. Rimsulfuron was moderately adsorbed on soils with high levels of clay or organic matter. Although soil TLC suggested rimsulfuron could be mobile, minimal mobility was observed under field conditions. Rimsulfuron residues (>0.01 ppm) were not observed in rotational crops grown in rimsulfuron-treated soil.