Application of short-term bioassay guided chemical analysis for water quality of agricultural land run-off

The effect of agricultural land run-off on the water quality of Lake Kojima , Japan, was investigated using a short-term bioassay-guided chemical analy sis. Water samples were collected for 1 year starting from June 1995 to Jun e 1996. Toxicity of the dissolved and adsorbed extracts in the water sample s was evaluated using the Daphnia immobilization test and the concentration s of pesticides and putative toxic substance in the extracts were determine d by high performance liquid chromatography. Most of the dissolved extracts caused immobilization of the test Daphnia magna at low concentrations duri ng the period of paddy pesticide application. Some extracts were found to c ontain pesticides such as dymron, mefenacet and flutolanil, but their conce ntrations were too low to have a toxic effect on the daphnia. An unknown to xic compound, Peak C, was isolated from some river water samples, but it pr oduced only a relatively weak toxicity to Daphnia. To better understand the impact of agricultural run-off on a receiving water body, the relationship between the observed toxicity and the concentrations of pesticides and Pea k C in the water samples was studied both temporally and spatially. (C) 199 9 Elsevier Science B.V. All rights reserved.