Biodegradation of the Phenylurea Herbicide Isoproturon and its Metabolites in Agricultural Soils

Research paper by Sebastian R. Sørensen, Jens Aamand

Indexed on: 01 Jan '01Published on: 01 Jan '01Published in: Biodegradation


Degradation of the phenylurea herbicide isoproturon (3-(4-isopropylphenyl)-1,1-dimethylurea) and several phenylurea and aniline metabolites was studied in agricultural soils previously exposed to isoproturon. The potential for degradation of the demethylated metabolite 3-(4-isopropylphenyl)-1-methylurea in the soils was much higher compared to isoproturon. In the most active soil only 6% of added 14C-labelled isoproturon was mineralised to 14C2 within 20 days while in the same period 45% of added 14C-labelled 3-(4-isopropylphenyl)-1-methylurea was mineralized. This indicates that the initial N-demethylation may be a limiting step in the complete mineralization of isoproturon. Repeated addition of 3-(4-isopropylphenyl)-1-methylurea to the soil and further subculturing in mineral medium led to a highly enriched mixed bacterial culture with the ability to mineralize 3-(4-isopropylphenyl)-1-methylurea.The culture did not degrade either isoproturon or the didemethylatedmetabolite 3-(4-isopropylphenyl)-urea when provided as sole source of carbon and energy. The metabolite 4-isopropyl-aniline was also degraded and utilised for growth, thus indicating that 3-(4-isopropylphenyl)-1-methylurea is degraded byan initial cleavage of the methylurea-group followed by mineralizationof the phenyl-moiety. Several attempts were made to isolate pure bacterial cultures degrading 3-(4-isopropylphenyl)-1-methylurea or 4-isopropyl-aniline,but they were not successful.