The water-sediment interactions for Hyalella azteca exposed to uranium-spiked or contaminated sediments and different overlying water chemistries

Abstract

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.