Degradation and mineralization of nano - molar concentrations of the 2 herbicide dichlobenil and its persistent metabolite 2 , 6 - dichlorobenzamide 3

ion wells (29). Not only the pesticides themselves are monitored, selected stable metabolites 8 are also included and often these are detected more frequently than the pesticide itself (3). The most 9 commonly encountered pesticide residue in Danish groundwater is 2,6-dichlorobenzamide (BAM). 10 BAM is a metabolite produced from partial degradation of the benzonitrile herbicide 2,611 dichlorobenzonitrile (dichlobenil) (1,9,16) and is often highly persistent in the environment. 12 Dichlobenil is a broad-spectrum herbicide mostly used on non-agricultural areas as well as in plant 13 nurseries and fruit orchards. This herbicide was banned for use in Denmark in 1997, but BAM is 14 still the main pesticide residue in Danish groundwater, with 19.7% of the abstraction wells analyzed 15 in 2003 having detectable BAM concentrations and 8.1% of the wells containing BAM 16 concentrations exceeding the EC threshold limit of 0.1 μg l for drinking water (3). Similar results 17 have been reported in 2003 in a monitoring program from Sweden (13) and BAM has additionally 18 been detected in groundwater in the Netherlands, Germany and Italy (18,42,44). 19 A potential for partial degradation of the herbicide dichlobenil to BAM has been measured in 20 various soils and subsurface sediments, with estimated half-lives ranging from 106 – 2079 days 21 (6,8,16,41). Also 2,6-dichlorobenzoic acid, another known metabolite from dichlobenil, has been 22 measured in dichlobenil-treated soils (8,24) and in groundwater samples (3,18). Two additional 23 AC CE PT ED on O cber 2, 2017 by gest ht://aem .sm .rg/ D ow nladed fom