Determination of pesticides and chronic test with Daphnia magna for rainwater samples.

Pesticides contained in rainwater were investigated in June and July 2001 in Yokohama. Although there were few farms and rice paddies near the sampling point, insecticides (fenitrothion and dichlorvos) and fungicides (chlorothalonil and futhalide) were detected by GC-MS and GC-FPD analysis. The maximum concentrations of dichlorvos and fenitrothion were 0.22 microg/L and 0.15 microg/L, respectively. Chronic tests with Daphnia magna were then conducted on two rainwater samples. Test solutions for these chronic tests were prepared by solid-phase extraction. In the case of the rainwater sampled on 25 July, the survival rate of D. magna was 100% after 21 days and no differences were found between the control and sample with regard to the average total number of live offspring produced per parent animal. However, a similar test with rainwater sampled on 14-15 June showed a marked toxic effect, since all the test animals were dead within 2 days. It is concluded that rainwater containing pesticides is an important ecological factor for freshwater plankton.