Degradation of Isouron in Three Upland Soils in Taiwan

Abstract

Degradation of isouron in soil fitted the first-order kinetics with half-lives of 42 to 203 days under various conditions in the laboratory experiments. Close correlations between the degradation rate and the soil moisture and temperature were observed. Under laboratory condition, the half-lives of isouron in autoclaved (148 to 208 days) and nonautoclaved soils (58 to 70 days) showed that soil microbes played an important role in the degradation. Under model field conditions, the half-life was about 90 days in sandy loam. One unknown metabolite (VIII), six degradation products, namely 3-(5-tert-butyl-3-isoxazolyl)-1-methylurea (II), 3-[5-(1, 1-dimethyl-2-hydroxyethyl)-3-isoxazolyl]-1, 1-dimethylurea (III), [3-(5-tert-butyl-3-isoxazolyl)] urea (IV), 3-[5-(1, 1-dimethyl-2-hydroxyethyl)]-1-methylurea (V), 3-[5-(1, 1-dimethyl-2-hydroxyethyl)-3-isoxazolyl] urea (VI), and 3-amino-5-tert-butylisoxazole (VII) were identified by autoradiography and mass spectrometry.