Pesticides in surface water in the "Westland"

On ten sites in the "Westland", an area used for glasshouse agriculture situated sout-west of The Hague, samples of surface water have been taken monthly during the period july 1989 - april 1990. These samples were investigated for the presence of 79 pesticides and related substances, and for cholinesterase inhibition, a sumparameter. A total of 40 compounds was found. Two of these 40 compounds, desethyl-atrazin and desisopropyl-atrazin, could not be evaluated ecotoxicologically due to lack of data. Indicative Maximum Acceptable Risk Levels (MAR's) have been exceeded one or several times for 24 of the 40 compounds. For 4 compounds, dichlorvos, mevinphos, parathion-ethyl and pyrazophos, the indicative MAR's have been exceeded a factor of more than 100, in one or more cases. For aldicarb-sulfoxide, cyanazin, malathion and triazophos, indicative MAR's have been exceeded a factor of more than 100, in one or more cases. For 16 out of the 40 compounds that were found, the indicative MAR was exceeded in all cases that the compound was present in a sample. The values "Kwaliteitsdoelstelling 2000" given in the "Derde Nota Waterhuishouding" have been exceeded for 11 compounds. For diazinon, dichlorvos, malathion, mevinphos, parathion-ethyl, pyrazophos and triazophos this value was exceeded in all cases that the compound was present in a sample. Compared to the results of the 1988/ 1989 program, there is a slight increase in the average number of times that pesticides are found in a sample. However, the percentage of values that exceed the indicative MAR has not increased much.HIM