Metabolism of isoproturon in soils originating from different agricultural management systems and in cultures of isolated soil bacteria

To assess the biodegradation pathway of the phenylurea herbicide isoproturon [N-(4-isopropylphenyl)-N', N'-dimethylurea] in soils, acetone extracts of the herbicide and its metabolites in four soils originating from different agricultural management systems were analyzed by HPLC. Furthermore, the metabolite pattern in media of mixed and pure cultures of bacteria isolated from these soils was investigated after 14 days of incubation with isoproturon. After 56 days of soil incubation with [ring-U-C-14-]-labelled isoproturon, polar metabolites represented up to 80% of the total integrated area. In addition to the main metabolite monodesmethyl-isoproturon, 2-OH-isoproturon, 2-OH-monodesmethyl-isoproturon, 2-OH-didesmethyl-isoproturon, and didesmethyl-isoproturon were also identified in soil extracts. In mixed bacterial cultures, 1-4.2% of the total integrated area corresponded to polar metabolites within 14 days, whereas in pure bacterial cultures only negligible amounts of degradation products were found. Based on this extensive characterization of metabolites, a concise model for the pathway of isoproturon degradation in soils is suggested.