Numerical evaluation of mercury concentration by using a distributional multimedia model in the Lake Biwa-Yodo River Basin, Japan

A distributional multimedia model was developed and applied to the Lake Biwa-Yodo River Basin in Japan to reproduce the mercury level in different environmental media. This model was developed based on a Level III steady-state fugacity model, and the space was divided into four environmental media (atmosphere, water, soil, and sediment). The mass transfer of Hg in this model consists of emission, deposition, sedimentation inside one medium, and advection between different media. The dissolution rate and ion exchange equilibrium have also been considered. We estimated Hg emissions in the Lake Biwa-Yodo River Basin from 1957 to 2009 based on the Pollutant Release and Transfer Registry (PRTR) system and the domestic usage of Hg in Japan. The distribution of emission was based on land data, including industrial land area, industrial location, and proportion of the population. The calculated and observed Hg concentrations were compared to evaluate the model. At both large scale and small scale, results showed that the distributional model could predict Hg concentrations in all environmental media. Sediment and soil media showed the accumulation of Hg by showing the higher concentrations than that of other media. In terms of geographical distribution, the urban area and downstream of the river showed high Hg concentrations owing to high Hg emissions. The Hg concentration in the atmosphere was affected by the transboundary pollution. Thus, the distributional multimedia model could reliably calculate the environmental Hg concentration and be utilized in environmental monitoring and management.