Microbial degradation of isoproturon and related phenylurea herbicides in and below agricultural fields

The phenylurea herbicides are an important group of pesticides used extensively for pre- or post-emergence weed control in cotton, fruit and cereal crops worldwide. The detection of phenylurea herbicides and their metabolites in surface and ground waters has raised the awareness of the important role played by agricultural soils in determining water quality. The degradation of phenylurea herbicides following application to agricultural fields is predominantly microbial. However, evidence suggests a slow degradation of the phenyl ring, and substantial spatial heterogeneity in the distribution of active degradative populations, which is a key factor determining patterns of leaching losses from agricultural fields. This review summarises current knowledge on the microbial metabolism of isoproturon and related phenylurea herbicides in and below agricultural soils. It addresses topics such as microbial degradation of phenylurea herbicides in soil and subsurface environments, characteristics of known phenylurea-degrading soil micro-organisms, and similarities between metabolic pathways for different phenylurea herbicides. Finally, recent studies in which molecular and microbiological techniques have been used to provide insight into the in situ microbial metabolism of isoproturon within an agricultural field will be discussed.