PROJECT SUMMARY/ABSTRACT – PROJECT 1 EXPOSURE Hundreds of U.S. sites are contaminated by poly- and perfluoroalkyl substances (PFAS), which have been associated with deleterious impacts on immune function, metabolism, and endocrine health. Project 1 of the Sources, Transport, Exposure, and Effects of PFAS (STEEP) Center (P1–Exposure) provides a critical link between the biomedical and engineering projects by focusing of PFAS exposure sources of concern near contaminated Superfund sites (air, water, and fish). P1–Exposure directly addresses the SRP mandate to “...develop methods and resources to detect hazardous substances and assess the risks they pose to human health” through the development of novel mechanistic and statistical tools to support PFAS exposure assessment and innovative environmental measurements in collaboration with P4–Detection using a suite of analytical techniques to close the PFAS mass budget. P1–Exposure research is essential to the overall STEEP II goals to “Assess the distribution, transformation and bioaccumulation of PFAS and “Engage new and established stakeholders across multiple sites.” Most prior work has focused on a limited suite of PFAS analytes, transport through aqueous media, and drinking water as the main vector of exposure. However, abundant polyfluoroalkyl precursors that degrade into terminal PFAS have been detected in environmental samples, atmospheric deposition is increasingly recognized as a major PFAS transport pathway, and contaminated seafood is another important vector for human exposure. The central hypothesis of P1–Exposure is that environmental PFAS exposures have been substantially underestimated due to large quantities of undetected polyfluoroalkyl precursors present in air, water, and biota. Aims 1 and 2 will investigate the propensity of PFAS precursors for bioaccumulation in aquatic food webs using field research in Cape Cod, MA, downstream of AFFF- contaminated sites. New knowledge of PFAS bioaccumulation mechanisms from field research and collaboration with P3–Mechanisms will be formalized in a mechanistic food web model, compared to traditional SRP contaminants of concern (polychlorinated biphenyls and methylmercury), and applied to understand time trends in seafood exposures for Faroese children in P2–Critical Effects. Aim 3 will develop modeling tools for characterizing atmospheric source-receptor relationships for PFAS across the contiguous U.S. Aim 4 will enhance a statistical approach for predicting private wells likely to have PFAS contamination in the states of MA, MI, and NJ. P1–Exposure research will be conducted in partnership with many stakeholders including the Mashpee-Wampanoag Tribe on Cape Cod, MA in partnership with CEC and state program managers and scientists in MA, MI, and NJ. All modeling and data management practices for new measurements and model output will be supported by STEEP’s DMAC. P1–Exposure research and engagement with multiple states will provide ample train...