休廃止鉱山流域でのカワニナに対する重金属の影響

Abstract

The effects of closed mine-effluent on the freshwater snail, Semisulcospira bensoni, were studied in the Sasu River in the Tsushima Islands. Concentrations of Cd, Pb, and Zn were consistently higher in soft parts of the snails from the Sasu River than in those from the Se River as a control river in the Tsushima. The same trend was observed for the concentrations in the shells. The snails collected at the lower reaches of the Se River were placed in cages at the lower reaches of the Sasu River and of the Se River itself for a month. The mortalities of the snails thus placed were significantly higher in the Sasu River than in the Se River. Though remarkably high concentrations of heavy metals in the attached substance mainly composed of algae were detected in the Sasu River, those in the Se River seemed to be as low as in other non-polluted rivers. The heavy metals were not detected in the water of the Se River, while a certain amount of heavy metals was found in those of the Sasu River. The Zn concentration was relatively high. These results suggest that S. bensoni is a useful monitoring organism for the assessment of heavy metals pollution, and the snails may be affected by heavy metals through the food (attached algae) as well as by the ambient water.