Use of chronic tests with Daphnia magna for examination of diluted river water

River water sampled in May and June 2000 was subjected to chronic tests with Daphnia magna to investigate the harmful effects of pesticides; then test animals were raised in reconstituted water (Elendt M-7) containing a solid-phase extract prepared from river water using polystyrene cartridges. The solid-phase extract was present in reconstituted water at a concentration equal to that in river water. Test animals died within 1–4 days in the reconstituted water containing the extract. On the other hand, these harmful effects were not realized if reconstituted water containing the extract was diluted several times. Assays were made using 53 kinds of pesticides as standards to investigate toxicity, and several pesticides were detected in the river water by GC–MS, GC, and HPLC. Two insecticides (fenitrothion and dichlorvos) affected D. magna significantly, because harmful effects were observed in chronic tests using reconstituted water to which the appropriate levels of pesticides had been added. Additionally, these results also indicate that factors other than the two insecticides may be involved in the harmful effects.