Linking physiological mechanisms and the chronic impacts of bioaccumulated metals in aquatic organisms

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This research program addresses the physiological mechanisms of chronic sublethal Ni and Cu toxicity in rainbow trout, from initial disruption of homeostasis to final acclimation. Investigations will follow the physiological disruption that occurs as metals are taken up from the water into various tissues (gills, liver, kidney, muscle) and, as the concentration of metal in tissues increases, distinguish between cellular defense systems that can detoxify and store (or eliminate) the metal and cellular elements that react with and are damaged by accumulated metal. A method of partitioning bioaccumulated metal into distinct cellular pools representing potentially toxic forms of metal and detoxified forms will be linked to physiological responses. A suite of physiological responses will be assessed (e.g. immune function, stress response, vitamin A metabolism, respiratory function, ion regulation and generation of reactive oxygen species (ROS)). It is hypothesized that the primary disruptions will be in ion homeostasis and in the generation of reactive oxygen species (ROS) and that these will occur in a biphasic manner during exposure, first ion homeostasis then ROS. Under this hypothesis, the uptake of metal early in the exposure is expected to disrupt ion regulation (Cu interfering with Na and Ni with Mg). This is predicted because data from studies on the physiological effects of acute metal exposure show impacts on ion regulation. In the second phase of the exposure significant amounts of metal will have permeated into cells and as concentrations rise, detoxification mechanisms will be overwhelmed and ROS will be generated. The prediction in this case is that ROS induced pathophysiology will be directly related to increases in the subcellular fraction of metal in the toxic pool. Ni and Cu are expected to show contrasting results related to ion regulation and tissue bioaccumulation but similarities in the cellular partitioning and generation of ROS. The studies are designed to understand the physiological responses, damage repair and adjustments in fish as they acclimate to metal exposure; the data will be of socio-economic relevance to better manage the impacts of metals in the environment.