Interactive effects of trace metals in freshwater fish

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The vision of my research program is to better understand the physiological processes that govern the uptake, metabolism and toxicity of trace metals and their interactions in aquatic organisms, particularly fish. In natural environments, aquatic organisms are often exposed to elevated levels of trace metals due to anthropogenic activities. Some of these trace metals such as copper, zinc and selenium are essential for life, but can cause adverse effects when their concentrations exceed the threshold levels in the body. Other trace metals such as cadmium, lead and arsenic have no known biological functions, and tend to accumulate in the body and cause toxicity even at low exposure concentrations. To date, much of the emphasis in research characterizing the toxic consequences of metal exposure to aquatic organisms has been focused on single metals. However, in the contaminated aquatic ecosystems, organisms are almost always exposed to multiple metals. Trace metals when present in mixture may, however, interact with each other via shared routes of uptake and/or metabolic cross-talk, leading to antagonistic or synergistic toxicity in fish. The research outlined in this proposal has two major objectives. First, I will investigate the molecular and physiological mechanisms responsible for species- and life stage-specific sensitivity to trace metals and metal-mixtures in fish, using three ecologically distinct Canadian freshwater species (rainbow trout, white sturgeon and fathead minnow). Sensitivity to trace metals differs among these fish species and also among life stages of the same species, however the mechanisms responsible for these differences are largely unknown. Sturgeons are of especial interest in this context as they are endangered species and extremely sensitive to trace metals, especially at their early life stages. Second, I will examine how the metabolic interactions between essential and non-essential metals (selenium vs. cadmium/arsenic) affect the physiological performance of juvenile fish, using a model metal-sensitive species, rainbow trout. This study will also focus on understanding how these metabolic interactions are modulated by the exposure level (low to high) and chemical forms of trace metals (inorganic and organic). Overall, this research will generate fundamental knowledge on the physiological consequences of exposure to metal-mixtures in fish, at various life stages. Such knowledge will ultimately help to develop more effective approaches for the protection of Canadian freshwater ecosystems.