Danish wells contaminated with pesticides

The Danish newspaper Jyllands Posten carried the leaked interim results of the research, which show high levels of 2.6-dichlorobenzamide – known as BAM, a metabolite of a herbicide, dichlobenil. Figures released by the Geological Survey of Denmark and Greenland show BAM concentrations above the drinking water limits in 10% of Denmark’s 90,000 privately-owned wells.

In 1998, the Danish Government initiated the Pesticide Leaching Assessment Programme, an intensive monitoring exercise aimed at evaluating the leaching risk of pesticides under field conditions. The objective is to improve the scientific foundation for decision making in the assessment of pesticides for registration in Denmark and, specifically, to analyse whether pesticides applied in accordance with current regulations leach to the groundwater at levels exceeding the maximum allowable concentration of 0.1µg/l.

The results of early monitoring showed that although many pesticides did not leach from the topsoil around their target crops, there were significant exceptions. Two degradation products of metribuzin (desamino-diketo-metribuzin and diketo-metribuzin) were found to leach from the root zone in concentrations exceeding the maximum permitted concentration of 0.1µg/l.

Leaching was most pronounced with desamino-diketo-metribuzin, which was detected in concentrations as high as 2.1µg/litre. As these degradation products have not yet reached downstream monitoring wells, the GSDG was not able to assess their impact on groundwater quality.

However, at two sandy sites, the survey found that previous application of pesticides had caused marked groundwater contamination. Degradation products of metribuzin, particularly diketo-metribuzin, were detected at a maximum concentration of 0.33µg/litre at one site and 0.5 µg/l at the other.