Chlorimuron dissipation in water and soil at 5 and 25 degrees C

Chlorimuron, 2-[[[(4-chloro-6-methoxy-2- pyrimidinyl)amino]carbonyl]amino]sulfonyl]benzoic acid ethyl ester, was added to water (pH 7.5, hardness = 110 mg of CaCO3/L) and soil (sandy loam, pH 5.2) to determine the rates of dissipation at 5 and 25 degrees C. Radioactivity of both pyrimidine- and phenyl-14C-labeled chlorimuron was quantitatively recovered from water after incubation for 112 days. Greater than 85% of the radioactivity was recovered from the soil treatments after 56 days of incubation. Extractable radioactivity in the soil decreased with time. The rate of degradation of chlorimuron in water followed zero-order kinetics (R2 0.95). Less than 7% of the chlorimuron degraded at 5 degrees C, and the slope of the zero-order constant did not differ from zero. Half-life for chlorimuron in water at 25 degrees C ranged from 388 to 725 days, depending upon treatment. Dissipation of chlorimuron appeared to be greater in light than dark treatments. In soil, chlorimuron dissipation was described by first-order kinetics and half-life ranged from 17 to 22 days. Probable degradation products (saccharin, ethyl benzoate sulfonamide, and pyrimidine amine) in soil and water were identified in the methanol eluate by thin layer chromatography. Ethyl benzoate sulfonamide and pyrimidine amine are hydrolysis products of chlorimuron. Less than 1% of the radioactivity from water was evolved as carbon dioxide. Three to 5% of the radioactivity was evolved as carbon dioxide from the nonsterile soil treatment. Temperature appears to be a significant factor affecting chlorimuron dissipation in soil and water. Light may also enhance chlorimuron dissipation in water