Decrease of Herbicide Bromobutide and its Debromo Metabolite in Paddy Field Soil during 24 weeks After Application

Variations in concentrations of herbicide bromobutide (RS)-2-bromo-N-(alpha,alpha-dimethylbenzyl)-3,3-dimethylbutyramide, and its metabolite bromobutide-debromo, N-(alpha,alpha-dimethylbenzyl)-3,3-dimethylbutyramide were investigated in soils from three paddy fields used for rice farming at 24 weeks after application. The bromobutide concentration was maximum within 24 h after application. That of bromobutide-debromo was maximum within 5-7 days of application. Each gradually decreased to below detection limits at 12-22 weeks after application. Bromobutide was detected up to 76-104 days after application in the paddy soils, whereas bromobutide-debromo was detected up to 125 days after application. The bromobutide composition was higher than 90 % within 6 days of application, decreasing to less than 5 % by 125 days of application. The decrease of bromobutide amount in the soil was inferred as the first-order reaction. The bromobutide half-life was calculated as 12-21 days (16 days mean) during 18-104 days following application.