Environmental assessment of lead with spatial gradient in the Lake Biwa-Yodo River basin of Japan: The development of distributional multimedia model

Abstract

A distributional multimedia model was developed based on one-box model and applied to the Lake Biwa-Yodo River basin in Japan to assess the risk of heavy metal lead. As a useful approach to evaluate the environmental risks, the one-box model could predict the lead concentration by assuming the target area as a homogenies box and calculating mass balance between four environmental media. However, the homogeneity of such wide area assumed by the one-box model is inappropriate. The result of one-box model was not accurate, which cannot show the spatial distribution of pollutants or show the internal transfer of pollutants over time. In this study, the distributional model improved the previous model by incorporating spatial gradients, internal advections and finer meshes. The model was applied to the region from 1957 to 2016 based on the amount of pollutant emission data from the Ministry of Economy's official report, measured meteorological data from the Japan Meteorological Agency, land-use data from the Ministry of Transport, and the river discharge of the hydrology model. The calculated lead concentrations were compared to the observed concentrations at several monitoring stations. The results of this study indicated that the simulated concentration had a gradient inside the region. The area near the emission point and downstream of the river showed relatively high concentrations. For any location, the pollutant concentration is affected by direct emissions, and by adjacent areas due to wind and river discharge. The sediment and water media accumulated more pollutants, and the atmospheric concentration was underestimated in the major pollutant discharge area. This was attributed to underestimation of the distribution of lead emissions in urban areas.

Keywords

• Environmental risk
• Risk assessment
• Multimedia model
• Spatial gradient
• Lead