Potentially toxic elements pose significant and long-term human health risks in river basin districts with abandoned gold mines

Gold (Au) mining area is known to be one of the major sources of toxic elements; however, the potential risks of toxic elements from abandoned Au mines to the surrounding river basin districts and human exposure pathways to toxic elements need to be clarified. In this study, the distribution and mobilities of nine toxic elements (As, Cd, Cu, Pb, Sb, Zn, Cr, Ni and V) in Kesennuma City, Tohoku Region in Japan, a typical Au-mining district with several river basins, were studied through a geochemical survey (including element total concentrations and water-/acid-leaching concentrations determinations, as well as GB calculations), and environmental assessment on these elements in soil, river sediment, and river water samples from the study area. The contamination evaluation by index of geo-accumulation (I_geo) and enrichment factor (EF) suggested that As, Cu, Ni and Sb enrichments were greatly observed in the vicinity of the abandoned Au mines; moreover, calculated GB upper values for Cu in the river sediment surpass that of Tohoku Region. It has been found in this study that each element has particular mobility, which eventually influences its exposure pathway to humans. For instance, As in soil and sediment poses adverse non-carcinogenic risks and unacceptable carcinogenic risks to especially children mainly through groundwater ingestion. To minimize the potential risks associated with exposure to toxic elements in Au-mining districts, effective risk management measures should be implemented around river system by Au-mining companies even after their long-time closures, based on the consideration of each element’s mobility.