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(243) Biological and chemical analysis of esterase inhibiting pesticides in rainwater. Hamers, Timo1, Koeman, Jan1, Murk, Albertinka1, 1 ABSTRACT- Over the past few years, high concentrations of pesticides have been reported in Dutch rainwater. Organophosphate (OP) and carbamate insecticides form an important part of the complex mixture of airborne pesticides, because they are toxic to a broad spectrum of species and are efficiently washed out from the atmosphere by wet deposition, due to their relatively polar character. To determine the integrated esterase inhibiting potency of the pesticides present in the rainwater (expressed as ng dichlorvos-equivalents (DEQ) per liter), extracts from rainwater samples collected at different sites were tested in a newly developed microtiter esterase inhibition assay (Hamers et al., Toxicol. Sci. 58(2000): 60-67). In addition, the bioassay results were compared to the calculated esterase inhibiting potency based on chemically analyzed concentrations 31 OP and carbamate insecticides in the same samples. For the individual insecticides dichlorvos and pirimiphos-methyl, maximum concentrations were observed that exceeded the EC50 for Daphnia (190 and 80 ng/l, respectively), suggesting that pesticides in rainwater pose a risk to aquatic organisms. Good correspondence (r>0.8) was found between the measured and calculated esterase inhibiting potency of the rainwater extracts. A maximum esterase inhibiting potency equivalent to 1.4 Key words: esterase inhibition, organophosphate, carbamate, rainwater |
g dichlorvos per liter was measured in a sample collected in an area with intense horticultural activities in June. This DEQ concentration is almost 2000 times higher than the maximum permissible concentration of dichlorvos set for Dutch surface water, whereas it exceeds the EC50 for Daphnia by a factor 7.The high DEQ concentration was attributed to elevated concentrations of dichlorvos, mevinphos, pirimiphos-methyl and methiocarb. The bioassay enables a direct assessment the esterase inhibiting potency of all individual compounds present in the complex mixture of rainwater pollutants, even if they are unknown or present in concentrations below the detection limit. Therefore, they are valuable tools for prescreening and hazard characterization purposes.