Degradation of isoxaben in soils and an aqueous system

The degradation of isoxaben {N-[3-(1-ethyl-1-methylpropyl)-5-isoxazolyl]-2,6-dimethoxybenzamide} was studied in soil and in an aqueous system. Soil studies were conducted in Erlenmeyer flasks (treated with 1 mug/g isoxaben) and mineralization studies in Biometer flasks (treated with 1 mug/g unlabeled and C-14-isoxaben) incubated at 23 C. Degradation in the aqueous system was performed in Erlenmeyer flasks under aerobic and anaerobic conditions incubated at 23 degreesC. Incubation mixtures were extracted at selected times and analyzed for isoxaben and degradation products by HPLC with product identification confirmed by GC-MS. After 8 weeks, 78% and 23% of the total isoxaben disappeared in nonsterile and sterile soils, respectively. After 12 weeks, approximately 1% of the labeled isoxaben was recovered as CO2 in the Biometer flask experiments; no volatile products were detected, and 5% and 33% of the total radioactivity was recovered from the nonsterile and sterile soils, respectively. In the aquatic system after 8 weeks, isoxaben had decreased from 1 mug/g to 0. 1 and 0.004 mug/g under aerobic and anaerobic conditions, respectively. Degradation products detected from the soil studies were 3-nitrophthalic acid and 4-methoxyphenol, and 3-nitrophthalic acid in the aqueous system studies. Microbial activity was considered to be a major factor in the degradation of isoxaben in this study.