Pesticides and their metabolites in groundwater : a field investigation from south east England

Contamination of groundwater by pesticides has brought increased environmental concern over the past decade although there is currently no requirement for water supply organisations to measure pesticide metabolites. Previous work on diuron has shown that metabolites are a major component of the residual compounds found in soil and groundwater following normal application. This scoping study expands on previous work carried out at the experimental plot scale to the catchment scale. Groundwater has been sampled for diuron and its metabolites from 11 sites across a catchment in south east England during the autumn of 2003. High concentrations of diuron have previously been detected in the catchment and a number of sources are possible. Diuron was found on 91% of occasions, DCPMU and DCPU on 82% of occasions, and DCA was found in more than a third of the samples. In 6 of the study sites, more than 50 % of the total diuron and degradation products was composed of the metabolites. Concentrations of diuron and its metabolites were commonly found at significant levels throughout the catchment. From such a small ‘one-off’ sampling it is not possible to determine the likely source of the herbicide although regular analysis of the groundwater quality together with analysis of the soils and unsaturated zone, would give evidence of the likely scale of the problem.