Dissertation Defense

Per- and polyfluoroalkyl substances (PFAS) are synthetic chemicals valued for their stability that are now recognized as globally persistent pollutants. In the United States, legacy PFAS have been largely phased out since the early 2000s and replaced with shorter chain alternatives designed to be “safer”. Despite having a shortened fluorinated backbone, “next generation” PFAS have not consistently demonstrated the decreased bioaccumulation or toxicity that they were designed to achieve. This dissertation sought to understand the ecological risk posed by one next generation compound, perfluorohexanesulfonic acid (PFHxS) to early life stage (ELS) red drum (Sciaenops ocellatus), an estuarine sportfish whose larvae develop in highly variable coastal habitats. These fish spend a large part of their initial life history in estuaries, habitats known for high turnover rates and fluctuations in multiple abiotic conditions, including salinity.  Due to continuous use and numerous contributing sources, PFAS are continuously released into the environment, with the majority detected at relatively low concentrations compared to freshwater habitats. This dissertation also investigated the influence of salinity and dissolved organic carbon (DOC) on the fate and transport of PFAS with specific consideration for PFHxS. Results showed that PFHxS is more likely to remain soluble in the water column at salinities up to 45ppt compared to PFOS. Knowing that PFHxS can persist in the water column more readily, this dissertation next assessed whether the presence of low concentrations of PFHxS would increase the risk of ELS red drum mortality under simultaneous exposure to elevated salinities. Concentrations as low as 1 µg/L were sufficient to cause significant reductions to hatch success and 48-hr survival at 35 ppt and 39 ppt. Lastly, this dissertation analyzed differentially expressed genes (DEGs) to determine how exposure to PFHxS influenced molecular pathways involved in stress response, development, and osmoregulation. Overall, this dissertation provides insight into the fate of PFHxS in estuarine habitats and demonstrates toxicity under realistic estuarine conditions and with environmentally relevant concentrations. The results herein contribute critical data utilizing multi-stressor approaches, assessment of sublethal endpoints, and the integration of molecular endpoints to assess ecological risk in vulnerable early life stages of an estuarine sportfish.