Evaluation of mercury concentration in the lake biwa-yodo river basin by a one-box multimedia model and model sensitivity on the experimentally determined water-sediment partition coefficient

Considering the environmental damage caused by mercury, evaluating mercury concentrations in four environmental media, namely the atmosphere, water, soil, and sediment, is necessary. Available data on mercury emissions and computational modeling were used for this evaluation. Evaluating the sensitivity of the model for the water-sediment partition coefficient was another objective of this study. Recorded consumption and emission data of mercury were used to calculate the total annual emission amounts from 1959 to 2009 for the Lake Biwa-Yodo River basin of Japan, which was selected as the study site for this study. Laboratory-scale batch-shaking experiments were carried out to evaluate the partition coefficient of mercury between the aqueous and solid phase using soil, sediment, and sand samples. The experimentally determined partition coefficient was then incorporated into the one-box multimedia model. Mercury concentrations in this study site were calculated based on the calculated annual mercury emission data. The sensitivity of the model calculations on the partition coefficient was studied by comparing the calculated concentrations from different partition coefficient values with observed data. Calculated concentrations of mercury in all four environmental media were within the range of observed concentrations, and the performance of the model was validated. The results showed the accumulation of mercury in soil and sediment, and in the last 30 years, the mercury concentration has been constant, except in the atmosphere. Variations in atmospheric mercury concentrations were observed. Calculated concentrations for the representative partition coefficients for different soil types were compared with the environmental monitoring data. Improvements in the model performance due to the incorporation of an experimentally evaluated partition coefficient were confirmed. Thus, it was concluded that the one-box multimedia model could reliably calculate the environmental mercury concentrations based on the emission data. The sensitivity of the model was improved by using the experimentally evaluated partition coefficient value of mercury. Experimental evaluation of the other parameters used in the model calculations would further improve the model.