Bioaccumulation, Trophic Transfer, and Ecosystem Effects of PFAS in Freshwater Environments

Organic contaminants in the environment are of considerable concern for both ecological and human health. My dissertation evaluates how one such group of contaminants, per- and polyfluoroalkyl substances (PFAS), move through and are transferred within aquatic food webs, and whether their presence affects ecosystem functioning, energy flow, or ecosystem services. PFAS are a class of over 15,000 synthetic chemicals first produced in the 1940’s that are now widely distributed in the environment, highly resistant to degradation, and toxic in many cases. My dissertation evaluates PFAS from various perspectives ranging from uptake by algae to human health implications. First, I demonstrate that a dominant PFAS compound – perfluorooctane sulfonic acid (PFOS) – bioaccumulates in benthic algae in a concentration-dependent manner, with bioconcentration factors (BCFs) decreasing as exposure concentrations increase. This phenomenon differs from the accumulation of lipophilic compounds where BCFs are constant. These variable accumulation patterns are likely driven by the importance of active transport processes in the uptake of PFAS. Second, I refine parameters for food web models by quantifying uptake and elimination rates in the transfer of PFOS from benthic algae to invertebrate primary consumers, providing the dietary transfer quantification between these trophic levels. I demonstrate that PFOS concentrations in amphipods, a common group of freshwater invertebrates, increase in response to ingesting a contaminated food source, but not to levels that constitute bioaccumulation when exposure is limited to diet. Third, I show that PFAS impacts extend beyond the organismal level to ecosystem function by demonstrating that microbial respiration and litter decomposition are reduced downstream of a PFAS effluent. These effects were not fully replicated in a laboratory experiment, indicating that environmental conditions or PFAS profiles likely modulate these functional impacts. Fourth, I link science to regulation by measuring PFAS in the fillets of Lake Michigan sportfish that humans consume and compare concentrations to posted guidelines from state, regional, and international agencies. I conclude that weekly consumption of Lake Michigan salmonids will exceed current safe consumption guidelines in most cases. Finally, I contextualize the environmental impacts of PFAS by investigating bioaccumulation of a legacy contaminant, mercury, in freshwater turtles. I found that freshwater turtles continue to bioaccumulate mercury in their muscle and liver tissues years after remediation efforts and that these patterns are more complex than are predictable by levels in abiotic media. Overall, I demonstrate that tissue type, trophic level, habitat heterogeneity, and movement of organisms all influence bioaccumulation patterns of contaminants. Furthermore, PFAS can be transferred through the food web and lead to ecosystem-level impacts. In total, these findings underscore how contaminants persist and cycle through aquatic environments, even after implementation of regulation and remediation (as in the case with mercury). This outcome serves as a cautionary tale for PFAS, which continues to be produced, released, and cycled with limited restrictions. An urgent need exists for comprehensive PFAS regulations and remediation strategies to mitigate the long-term ecological and human health risks posed by PFAS contamination.