Investigating metal bioavailability to aquatic organisms: Biogeochemical perspectives

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Mining activities over the past century have created a significant environmental risk for aquatic ecosystems, particularly in Canada, which holds both large mineral and aquatic resources (20% of the world's surface fresh water and the world's longest coastline). It is now well-recognized that metal bioavailability (i.e. bioaccumulation and toxicity) to aquatic organisms depends on the water's physico-chemical characteristics (e.g. pH, temperature, salinity, dissolved organic matter (DOM)). Yet, the effects of some critical environmental factors on metal bioavailability remain poorly evaluated, impairing our ability to accurately assess metal's ecological risk. Despite considerable evidence that salinity affects metal bioavailability to estuarine species exposed to the full salinity gradient of natural waters (i.e. 0 35 ppt), the mechanisms of this modulation remain poorly characterized. This knowledge gap is partially due to the difficulties in deciphering the intertwined roles of water chemistry and organism physiology, which both vary with salinity. Similarly, while temperatures of natural waters typically range from 4 to 25C in temperate regions, the environmental risk of metals mostly relies on toxicological studies performed at lab ambient temperatures, i.e. around 15 20C. Yet, temperature can affect metal aqueous geochemistry and organism physiology, which can both have strong impacts on metal bioavailability. However, there have been few studies that have investigated these temperature effects on toxicological outcomes in aquatic organisms, especially in winter vs. summer scenarios. Using elements of analytical geochemistry, biochemistry, physiology and ecotoxicology, my lab will explore the mechanisms underlying the modulation of metal bioavailability to aquatic organisms with (1) salinity and (2) temperature. Notably, we will develop a new ion-exchange technique to characterize the effects of salinity on metal aqueous geochemistry, then investigate how salinity affects metal bioavailability using euryhaline phytoplankton. Furthermore, in fresh water, we will characterize the effects of temperature on metal aqueous geochemistry (notably on metal-DOM binding), then characterize metal bioavailability to winter-acclimatized vs. summer-acclimatized fish. The present research program meets a worldwide need for an improved understanding of the processes controlling the interactions of metals with aquatic organisms. Notably, we will address fundamental knowledge gaps about the mechanisms and relevance of salinity and temperature controls on metal bioavailability to aquatic organisms. Ultimately, this research will provide critically needed information to accurately predict the environmnental risk of metals, spatially and seasonally. Finally, this program constitutes a unique HQP training opportunity, where students will use interdisciplinary science to address major societal issues of interest to both the public and the private sector.