Abstract

In 1990 several permanent wells, placed below agricultural land used for potato, maize and flower-bulb culture, as well as wells placed below uncropped land, have been sampled and analysed for pesticide residues. The sampling took place on vulnerable soil types as well as soil types that were expected to be less vulnerable for leaching of pesticides. Below both soil types several pesticide residues haven been found. Since the start of this sampling program in 1988, 26 different organic compounds have been detected in the wells. The compounds are residues of nine pesticides allowed for use in groundwater protection areas and six that are not allowed in these areas. The highest concen- trations were found for transformation products and admixtures. In particular transformation products are a threat for the quality of groundwater and the drinking water supply.