English Abstract In 1989 several groundwater wells below agricultural
land, used for potato-, maize- and flowerbulb culture, as well as uncropped
land has been sampled and analysed for pesticides. Below vulnerable soil
types as well as less vulnerable soil types which are representative for an
average Dutch sandy soil several pesticide residues have been found. Since
the start of this sampling program in 1988, 25 differend organic compounds
are residues of 15 pesticides. Nine of them are allowed in groundwater
protection areas: atrazine, amitrol, diuron, dichlobenil, dinoseb,
ethoprophos, maneb/zineb, metamitron and metam-sodium, while the other six
are not allowed in groundwater protection areas: aldicarb,
1,3-dichloropropene, bentazon, dimethoate, metolachlor and simazine. The
highest concentrations were found for transformation products of pesticides
and admixtures. In particular transformation products are a threat for the
quality of groundwater and drinking water supply.
