Field and experimental measurements of antimony flux from lake sediments contaminated by gold mining

Abstract

Processes that control the environmental fate of antimony (Sb) in aquatic ecosystems remain poorly characterized. This study investigated Sb flux from lake sediments of Yellowknife Bay (Great Slave Lake, Northwest Territories, Canada), which were contaminated by gold mining operations. Sediment Sb fluxes were measured in the field by short term (2-6 day) incubations of intact sediment cores and in the laboratory by incubating bulk sediment over a longer 30-day period. Antimony diffused from sediment to overlying water in 17 of 28 cores (61%) from Yellowknife Bay. Overlying water and surface sediment remained oxic during the measurements. When detected, sediment Sb fluxes were relatively low (10-279 µg/m²/day) and were positively correlated with sediment Sb concentrations (0.7-47 µg/g). The Sb mineralogy of Yellowknife Bay sediments (characterized in a companion study) likely also played a critical role in the spatial pattern of Sb fluxes. Other environmental factors, specifically season, temperature, organic matter content, and iron or manganese concentrations of sediment did not explain Sb flux. Porewater Sb concentrations were low (0.2-9.6 µg/L), and porewater depth profiles were not related to solid-phase Sb concentration, suggesting limited post-depositional mobility within sediments. Laboratory incubation of mixed bulk sediments showed higher Sb fluxes of 185-1555 µg/m²/day over the course of a 30-day experiment. Temperature warming from 7 to 22 °C did not enhance the Sb flux. Higher Sb fluxes in the laboratory versus field measurements may have been due to (i) more Sb in the laboratory sediments (~160 µg/g), and (ii) oxidative dissolution of stibnite and Sb sulfosalt minerals that were previously stable in deeper anoxic sediments but disturbed and exposed to oxygen during laboratory manipulation. This study found Sb can diffuse from mining-contaminated sediments to overlying water under oxidizing conditions, with a flux related to the solid-phase Sb concentration and the mineralogy of Sb present.