Study of Pollution Sources of Zinc in Lake Shinji Based on Zinc Isotope Ratio in Sediment

Abstract

In Lake Shinji, an increase in Zn concentration has been observed in the upper layer of sediment after about 1970. The clarifying of the pollution sources of Zn in the lake is important for assessing the impact of Zn transported from the China continent on the aquatic environment in Japan. In this study, to obtain knowledge on the pollution sources of Zn in Lake Shinji, we measured the δZn of a sediment core. Moreover, we measured the δZn of aerosols collected in Hirado City, Nagasaki Prefecture, which has been strongly affected by air pollutants from the China continent. It was difficult to explain the δZn values (+0.11±0.14 (2σ) ‰) of anthropogenic Zn, which were estimated from the Zn concentration and δZn in the sediment core, on the basis of the contribution of aerosols with negative δZn values (-0.08±0.20 (2σ) ‰). In contrast, the δZn values (+0.05–0.08‰; literature data) of treated water from sewage treatment plants and runoff on receiving water in urban areas were similar to those of anthropogenic Zn in the lake. These suggest that Zn pollution in Lake Shinji is primarily attributable to the discharge of effluent such as treated water from sewage treatment plants and runoff on receiving water in urban areas; thus, the contribution of Zn from the China continent is small. This may be attributable to the release of large amounts of Zn into the environment, because Zn is used in large quantities in various products.