ECOTOXICITY ASSESSMENT OF THE AQUATIC ENVIRONMENT AROUND LAKE-KOJIMA,JAPAN

To reduce the impact of chemical substances on the aquatic ecosystem, it is essential to understand their ecotoxicological properties in the natural aquatic environment. Consequently, we conducted an ecotoxicol ogical study on the aquatic environment around Lake Kojima, a man-made lake located in the southwest of Japan. Lake Kojima receives its chem ical inputs mainly from two rivers that flow through various agricultu ral and industrial areas. For ecotoxicity screening, surface water and sediment samples were collected 4 times in 1993 from 16 preselected s ites, Then, the solutes in the filtered surface water were concentrate d by ODS resin, and the organic chemicals in the suspended solids (SS) and sediments were extracted by acetone. A battery of five ecotoxicit y tests (agar plate test using bacteria and yeast, algal growth inhibi tion test, Daphnia magna immobilization test, and root elongation test using lettuce seeds) was used to assess these extracts. The results s how that the surface water extracts had a lethal effect on D. magna, t he SS extracts suppressed algal growth, and the sediment extracts were inhibitory to the growth of yeast. A significant inhibitory effect by the sediment extracts from 4 lake sites and 3 river sites was detecte d by these ecotoxicity tests. Attempts also were made to identify the putative ecotoxic chemicals in the collected samples. Elementary sulfu r was identified as one of the major toxicants in the sediment extract s that were inhibitory to the yeast growth. Moreover, samples of surfa ce water around Lake Kojima, collected weekly from June to September i n 1994, were found to contain three pesticides and were toxic to D. ma gna, But the concentration of the pesticides detected was too low to c ause daphnia immobilization. It is believed that the toxicity of the w ater extracts was mainly due to the combined toxic effect of natural a nd man-made components. (C) 1996 by John Wiley & Sons, Inc.