ASSESSMENT OF THE SOURCES AND MOBILITY OF SELENIUM IN MINING ENVIRONMENTS

ABSTRACT: Selenium (Se) is an essential trace element for human health. It is however characterized by a very narrow tolerance band and the World Health Organization proposes a health-based guideline value of 10 ug/L for Se in drinking water. Se is bioaccumulative and its concentration can increase along the trophic chain and can reach toxic levels for fish and wildlife as well as for humans. Se concentrations in the environment mainly depend on geology, although industrial activities can cause significant Se contamination. Given its recognized toxicity, it has become a contaminant of emerging concern (CEC) for the mining industry. However, the hydrogeochemical processes controlling Se mobility in mining environments are still poorly understood. Fitting in this context, this study aims at developing novel approaches for identifying the sources and fate of Se in surface and groundwater in mining environments of the Canadian Shield. A review of the potential geogenic and anthropogenic sources of Se in mining sites is first proposed. Geochemical calculations conducted using PHREEQC are further proposed to identify the main processes likely to control Se mobility under the conditions prevailing in mine drainage and to predict the fate of Se once released in surface and groundwater. The calculations are based on data collected at a mining site of the Canadian Shield and on pre-existing data from the scientific literature. Ultimately, the study will provide a clearer understanding of Se geochemistry in mining environments and allow for proposing feasible technological approaches to mitigate Se impacts on surface and groundwater and associated ecosystems.