Abstract

On six sites in the "polder Bleiswijk", an area used for glasshouse agriculture situated south-west of Bleiswijk, samples of surface water have been taken monthly during the period May 1990-April 1991. These samples were investigated for the presence of 32 pesticides and related substances, and for cholinesterase inhibition, a sumparameter. A total of 22 compounds was found in one or more samples. Endosulfan-sulphate and gamma-HCH were found in all the water samples that were analysed. Ecologically safe values have been exceeded one or several times for 16 of the 22 compounds. For 12 out of 16 compounds the safe value was exceeded in all cases that the compound was present in a sample. The values "algemene milieukwaliteit" given in the "Derde Nota Waterhuishouding" have been exceeded for 5 compounds viz. aldicarb, dichlorvos, alpha-endosulfan, endosulfan-sulphate and gamma-HCH. For dichlorvos this value was exceeded in all cases that the compound was present in a sample.