2,6-Dichlorobenzonitrile (dichlobenil) is an herbicide used primarily in non-agricultural areas. It is commercially available under names such as Prefix, Barrier, Casoron, Dyclomec and Norosac. Although dichlobenil does not readily leach to groundwater, it is quickly metabolized to 2,6-dichlorobenzamide (BAM). Due to high water solubility and low sorption affinity in soil (Albrechtsen et al., 2001), the very persistant BAM has been detected in groundwater samples at levels which exceed current regulations (Porazzi et al., 2005).
The first step in the microbial degradation of dichlobenil in previously exposed soils involves hydrolysis of the nitrile group to the benzamide. Further hydrolysis of the amide to a carboxylate is found to be much slower. Reductive dechlorination occurs both prior to, and after amide hydrolysis resulting in ortho-chlorobenzoate (Holtze et al., 2007). This last compound has several known biodegradation pathways.
The following is a text-format Dichlobenil pathway map. An organism which can initiate the pathway is given, but other organisms may also carry out later steps. Follow the links for more information on compounds or reactions. This map is also available in graphic (8k) format.
2,6-Dichlorobenzonitrile Aminobacter sp. O-1 | | | nitrile hydratase | v 2,6-Dichlorobenzamide / \ / \ amidase / \ 2,6-dichlorobenzamide / \ reductive dehalogenase / \ v v 2,6-Dichlorobenzoate 2-Chlorobenzamide \ / \ / 2,6-dichlorobenzoate \ / amidase reductive dehalogenase \ / \ / v v to the 2-Chlorobenzoate -----> Benzoate Pathway | | | 2-chlorobenzoate | reductive dehalogenase | v Benzoate | | v to the Benzoate Pathway
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