| Summary: | The extraction of gold from arsenopyrite at Giant Mine, near Yellowknife, generated arsenic trioxide between 1940 and 2004. This contamination went beyond the immediate mining sites via emission to the atmosphere and subsequent deposition on soils and lakes. At present, the extent of this legacy is poorly known. Yellowknife is in the subarctic area, one of the most rapidly warming areas in the world. As climate warms, the permafrost melts and the decomposition rates for organic matter accelerates. This increases the load of dissolved organic matter, promotes greenhouse gas emissions and increases the mobility of contaminants in the water. The objectives of this research project were to determine the extent and history of arsenic contamination in eight lakes along an 80 km transect northwest from the mine, using the sediments as an environmental archive. Because arsenic is mobile in sediment, the mobility of arsenic and its possible remobilisation in water were assessed. The water content (porewater) of sediment samples was analysed by inductively coupled plasma mass spectrometry (ICP-MS) for metals and metalloids. Acid volatile sulfides (AVS) were analysed by ultraviolet-visible spectroscopy after extractions. Comparison of the concentration profile obtained for different elements allows speculating on the reactions that occur in the sediment. Finally, inverse diagenetic modelling was performed to determine arsenic reaction rates and the fluxes. This information was then used to discriminate between natural and anthropogenic arsenic sources, and to quantify its mobility in sediments and its probabilities of remobilization to lake water.
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