The Risk Posed by Pesticides and Contaminant Mixtures to Freshwater Mussels (Unionidae) in Ontario

Nearly 70% of North American unionids are at risk due to impacts from waterborne contaminants. Few studies have compared the sensitivity of toxicological endpoints assessed after chemical exposures. The main goal of this thesis was to assess the risk posed by waterborne contaminants to different life stages of mussels. To ensure a rigorous evaluation, I first compared the sensitivities of three toxicity endpoints after chemical exposure, which were not significantly different. Toxicity tests performed across three life stages showed in general that the tested pesticides do not pose a risk to mussels in Ontario streams. However, the effects of some ubiquitous waterborne contaminants and selected binary mixtures demonstrated a relatively greater risk to mussels. This thesis provided critical toxicological data on the risk posed by waterborne contaminants to the different life stages of Ontario-sourced mussels, which will assist in developing water quality guideline, recovery strategies, and risk assessments.