Risks associated with consumption of bivalves from PFAS-affected aqueous film-forming foam sites

To understand the significance of bivalve consumption as an exposure route for per- and polyfluoroalkyl substances (PFASs), the presence of PFASs in bivalve tissues at PFAS-affected sites and bivalve specific bioaccumulation metrics are needed. Case studies from aqueous film-forming foam (AFFF)-affected sites indicated concentrations of perfluorooctanesulfonic acid (PFOS) in bivalves exceeded potentially applicable bivalve tissue screening levels for human consumers of bivalves; however, screening levels for wildlife consumers of bivalves (birds and mammals) were not exceeded. However, PFAS exposure to human and wildlife via bivalve consumption is lower than via fish consumption based on fish case study data. For example, PFOS dietary exposure to humans via bivalve consumption was predicted to be 3 to 10 times lower than exposure via fish consumption. In addition to differences in bivalve and fish consumption rates, a main reason for this observation is that PFASs are less bioaccumulative in bivalves than in fish, as indicated in a review of bivalve PFAS laboratory studies. Bioaccumulation of PFASs in bivalves is directly related to perfluoroalkyl chain length. For example, for freshwater bivalves, a significant relationship was found between log-transformed bioaccumulation factors (BAFs) and chain length (Log10BAF, L/kg wet weight = 0.65 × (number of perfluorinated carbons) -4.6; r2 = 0.91). For sites at which bivalves are exposed to PFASs, the consumption of bivalves by humans and wildlife may be an important exposure pathway. However, at most AFFF sites with both bivalve and fish consumption exposure pathways, PFAS exposures associated with fish consumption will likely drive risk management.