Ecotoxicity assessment of the aquatic environment around Lake Kojima, Japan

Abstract

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 ecotoxicological study on the aquatic environment around Lake Kojima, a man-made lake located in the southwest of Japan. Lake Kojima receives its chemical inputs mainly from two rivers that flow through various agricultural and industrial areas. For ecotoxicity screening, surface water and sediment samples were collected 4 times in 1993 from 16 preselected sites. Then, the solutes in the filtered surface water were concentrated by ODS resin, and the organic chemicals in the suspended solids (SS) and sediments were extracted by acetone. A battery of five ecotoxicity tests (agar plate test using bacteria and yeast, algal growth inhibition test, Daphnia magna immobilization test, and root elongation test using lettuce seeds) was used to assess these extracts. The results show that the surface water extracts had a lethal effect on D. magna, the 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 detected by these ecotoxicity tests. Attempts also were made to identify the putative ecotoxic chemicals in the collected samples. Elementary sulfur was identified as one of the major toxicants in the sediment extracts that were inhibitory to the yeast growth. Moreover, samples of surface water around Lake Kojima, collected weekly from June to September in 1994, were found to contain three pesticides and were toxic to D. magna. But the concentration of the pesticides detected was too low to cause daphnia immobilization. It is believed that the toxicity of the water extracts was mainly due to the combined toxic effect of natural and man-made components. © 1996 by John Wiley & Sons, Inc.