Biodegradation of the phenylurea herbicide isoproturon and its metabolitesin agricultural soils

Degradation of the phenylurea herbicide isoproturon (3-(4-isopropylphenyl)- 1,1-dimethylurea) and several phenylurea and aniline metabolites was studie d in agricultural soils previously exposed to isoproturon. The potential fo r degradation of the demethylated metabolite 3-(4-isopropylphenyl)-1-methyl urea in the soils was much higher compared to isoproturon. In the most acti ve soil only 6% of added C-14-labelled isoproturon was mineralised to C-14( 2) within 20 days while in the same period 45% of added C-14-labelled 3-(4- isopropylphenyl)-1-methylurea was mineralized. This indicates that the init ial N-demethylation may be a limiting step in the complete mineralization o f isoproturon. Repeated addition of 3-(4-isopropylphenyl)-1-methylurea to t he soil and further subculturing in mineral medium led to a highly enriched mixed bacterial culture with the ability to mineralize 3-(4-isopropylpheny l)-1-methylurea. The culture did not degrade either isoproturon or the dide methylated metabolite 3-(4-isopropylphenyl)-urea when provided as sole sour ce of carbon and energy. The metabolite 4-isopropyl-aniline was also degrad ed and utilised for growth, thus indicating that 3-(4-isopropylphenyl)-1-me thylurea is degraded by an initial cleavage of the methylurea-group followe d by mineralization of the phenyl-moiety. Several attempts were made to iso late pure bacterial cultures degrading 3-(4-isopropylphenyl)-1-methylurea o r 4-isopropyl-aniline, but they were not successful.