| Summary: | This thesis describes studies and research conducted as part of the development, standardization, and validation of a new laboratory protocol for measuring the bioaccumulation of sediment-associated contaminants in freshwater organisms. The test species used in this method are the oligochaete Lumbriculus variegatus, the mayfly nymph Hexagenia spp., and the juvenile fathead minnow Pimephales promelas. Bioaccumulation methods in the literature were critically reviewed to properly guide the development and standardization of methods. This enabled data gaps to be addressed and the conditions and exposure techniques of the new method to be standardized, properly justified, and based on experimental evidence. Method development included the investigation of the effect of the density of organisms on bioaccumulation in the three test species. The importance of standardizing loading density to total organic carbon (TOC) in sediment was demonstrated, as was the appropriateness of using a ratio of TOC to organism dry weight of 27:1 as a standard loading density for the different test species. To validate the new method and assess the relative effectiveness of the three test species for accumulating different contaminants, a variety of field-contaminated sediments were tested, representing a range of contaminants, levels of contamination, and physical properties of sediment. It was observed that differences in bioaccumulation between the three species may, but do not always, exist, and can vary with contaminant and sediment type. It was also demonstrated that estimates of bioaccumulation, such as biota-sediment accumulation factors (BSAFs), can be species- and site-specific, supporting the need and use of standardized bioaccumulation methods and test species to facilitate comparisons across sites or over time. Comparisons of laboratory- and field-based estimates of bioaccumulation further validated the new laboratory method. Good agreement was observed between laboratory and field estimates for fish, while bioaccumulation was higher in laboratory-exposed invertebrates compared to mussels caged in situ. The laboratory method generally overestimated the relative bioavailability of contaminants compared to the field, but provides a conservative estimate of bioaccumulation. A kinetic study investigated the uptake and elimination of PCBs in the three test species and demonstrated that a 28-d test duration was a sufficient standard for both invertebrate species to reach steady-state concentrations. There was conflicting evidence of whether steady-state concentrations were truly reached in the fish and uncertainty remains as to the appropriateness of a 28-d test for these organisms, for which additional testing is necessary.
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