Enrichment of uranium, arsenic, molybdenum, and selenium in sediment cores from boreal lakes adjacent to northern Saskatchewan uranium mines

Abstract

Assessment of flux rates and concentrations of potentially toxic elements in sediment cores from 5 lakes adjacent to the McClean Lake uranium mines in northern Saskatchewan (impact lakes) compared to results from a set of 5 upwind and distant lakes (reference lakes) clearly indicated enrichment of several elements in lakes close to the mining operations. The flux of uranium to the sediments of the 5 impact lakes was significantly higher post-1960 from the mean pre-1960 background conditions by 1.5 to 23 times. Flux rates of arsenic, molybdenum, and selenium also indicated significant enrichment from background conditions in the majority of the impact lakes. In contrast, large and significant increases in flux only occurred in 1 of the 5 reference lakes for arsenic. The highest levels of enrichment were found in the 3 lakes either in closest proximity to the tailings management facility, waste-rock piles, or downstream from the treated effluent management system. High flux rates and concentrations of elements such as arsenic and vanadium in both the reference lakes and in pre-mining samples of the impact lakes indicated that potentially toxic elements can occur naturally in this region. Sediment core analyses of elemental flux and concentration in both reference lakes and pre-1960 conditions in the impact lakes provided an estimate of natural background conditions. Our data suggest that the McClean Lake mine may be a source for the enrichments of toxic elements in the lakes in close proximity to the mining operations.