English Abstract In the first half year of 1990 several permanent wells,
placed below agricultural land used for potatoe-, maize- and flowerbulb
culture, as well as uncropped land have been sampled and analysed for
pesticides. Below vulnerable as well as less vulnerable soil types several
pesticide residues have been found. Some compounds found in previous
sampling rounds were not detected although they are still used on the
fields. These are the compounds dimethoate, metamitron and metolachlor.
Since the start of this sampling program in 1988, 26 different organic
compounds have been found in these 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 concentrations were found for
transformation products and admixtures. In particular transformation
products are a threat for the quality of groundwater and drinking water
supply.
