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Abstract
Freshwater mussels of the order Unionoida (unionids) are among the most imperiled aquatic fauna worldwide. Numerous causes contribute to the loss of diversity and abundance of unionids, including the presence and toxicity of chemical pollutants. Mussels are often the most sensitive animals to contaminants, and routes of exposure differ depending on the stage of their complex lifecycle. Unionid ecotoxicology testing and risk assessment has largely focused on acute and chronic toxicity of metals, pesticides and nutrients on the larval and early juvenile stages. A paucity of data exists on effects of emerging contaminants such as pharmaceuticals and personal care products, and legacy compounds that persist in the environment. I propose a partial-lifecycle assay to be incorporated within a larger lifecycle assessment framework of emerging contaminants on unionids and used a persistent industrial contaminant (perfluoroalkyl sulfonate, PFOS) and an antidepressant pharmaceutical (fluoxetine) as test compounds with the assay. The partial-lifecycle test of PFOS to Lampsilis siliquoidea incorporated a 30-d exposure to larvae within the maternal marsupia, and a 24-h exposure to glochidia removed from the mother. Results revealed that exposure in marsupia caused significant reductions in initial larval viability and duration of viability at 4.5 g/L PFOS, and reduced metamorphosis success at 69.5 g/L PFOS. Exposure of larval Lampsilis fasciola to fluoxetine resulted in increased probability of metamorphosis at 1 and 100 g/L fluoxetine, suggesting importance of a seratonergic pathway in larval development or in the larvae-host interaction. Adult L. fasciola exposed to fluoxetine were more likely to display mantle-flap lures, and had greater occurrences of foot swelling beyond the shell margins. In a follow-up experiment lasting 67 d, fluoxetine was associated with increased movement rates and changes to more diurnal behavior, which could increase susceptibility to predation with in situ exposures. The results of these experiments have been successful at identifying chemical threats to unionids at concentrations below those reported in traditional acute and chronic tests. Partial-lifecycle tests may play an important role in better understanding effects of contaminants on unionid biology and may be combined with population modeling to ascertain effects of emerging contaminants on population persistence.