Biological and chemical analysis of the toxic potency of pesticides in rainwater

A newly developed method for measuring the integrated esterase inhibiting p otency of rainwater samples was applied in practice, and the results are co mpared to the toxic potency calculated from concentrations of 31 organo-pho sphate (OP) and carbamate pesticides, out of a total of 66 chemically analy zed pesticides. In addition, the general toxic potency of the rainwater sam ples was evaluated in a microtiter luminescence assay with Vibrio fischeri bacteria. Rainwater samples were collected over four consecutive 14-day per iods in both open and wet-only samplers. The esterase inhibiting potency of the open rainwater samples (expressed as ng dichlorvos-equivalents/l) corr esponded well with the chemical analyses of the rainwater samples collected by both types of samplers (r=0.83-0.86). By far, the highest esterase inhi biting potency was found in a sample collected in an area with intense hort icultural activities in June, and was attributed to high concentrations of dichlorvos, mevinphos, pirimiphos-methyl and methiocarb. The esterase inhib iting potency of this sample was equivalent to a dichlorvos concentration o f 1380 ng/l in the rainwater, which is almost 2000 times higher than the ma ximum permissible concentration (MPC) of dichlorvos set for surface water i n Netherlands. Maximum individual concentrations of dichlorvos and pirimiph os-methyl even exceeded the EC50 for Daphnia, suggesting that pesticides in rainwater pose a risk for aquatic organisms. Not all responses of the lumi nescence-assay for general toxicity could be explained by the analyzed pest icide concentrations. The bio-assays enable a direct assessment the toxic p otency of all individual compounds present in the complex mixture of rainwa ter pollutants, even if they are unknown or present at concentrations below the detection limit. Therefore, they are valuable tools for prescreening a nd hazard characterization purposes. (C) 2001 Elsevier Science Ltd. All rig hts reserved.