The water-sediment interactions for Hyalella azteca exposed to uranium-spiked or contaminated sediments and different overlying water chemistries
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In comparison with other metals such as Cd, Cu, Pb, Ni, and Zn, little is known about uranium (U) toxicity to Hyalella azteca. There is even no national U water or sediment quality guideline yet for the protection of aquatic life in Canada, despite Canada being home to some of the biggest U producers in the world. In this context, the aim of this research was to determine the toxic effects of U concentrations in the water and sediment to H. azteca, and if these relationships can be modelled. This thesis demonstrated that U bioaccumulation was mainly via the water phase rather than the sediment phase. It showed that U bioaccumulation measurements in H. azteca were more reliable indicators of U toxicity than U concentrations in the water or sediment. A water-bioaccumulation saturation model was satisfactory at describing this relationship. Overlying water chemistry was found not only to influence U bioaccumulation and toxicity in the H. azteca but also the desorption of U in the sediment into the overlying water. A water-sediment partitioning saturation model was also satisfactory at explaining these interactions. Both body size and gut-content had an overall effect on U bioaccumulation in H. azteca exposed to water-only U concentrations in soft water. A saturation model was used not only to estimate the effect of gut-content on U bioaccumulation, but to predict the uptake and elimination rate constants for H. azteca exposed to water-only U concentrations. A field study was conducted to determine if the saturation models developed and applied in the laboratory could be used in the field to quantify U bioavailability, bioaccumulation and toxicity to H. azteca. Unfortunately, U concentrations in the water and sediment were below concentrations needed to validate these models. However, toxicity, not related to U concentrations in the field, was observed at some field sites. Overall this thesis not only encourages more work on U toxicity to H. azteca, but provides significant data and models to be used by risk assessors and regulators in the development of U water and sediment quality guidelines in the protection of aquatic environments in Canada.