MODELING EXPOSURES to POLY- and PERFLUOROALKYL SUBSTANCES (PFASs) in AQUATIC BIOTA and HUMANS
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AbstractPoly- and perfluoroalkyl substances (PFASs) are a class of persistent anthropogenic chemicals widely used in consumer products. Exposure to PFASs has been associated with a suite of health effects including immunotoxicity, metabolic changes, and developmental disorders. However, the dominant exposure pathways for humans are still poorly understood. The overarching goal of this dissertation is to characterize present and future exposure risks associated with PFASs with a focus on populations that rely heavily on marine foods.
Chapter 2 characterizes the changes in composition of PFASs in pilot whale muscle from 1986-2015 to learn how changes in emissions are affecting the marine environment. We observe that all PFASs have continued to increase with the exception of the perfluorooctanesulfonate (PFOS) precursor, perfluorooctanesulfonamide (FOSA). We combine a simple environmental partition model with a bioaccumulation model to show that changes in pilot whale FOSA were driven by declines in atmospheric FOSA in polar and subpolar regions around 2000. These results help explain the large declines in PFOS exposure for species that metabolize FOSA, including seafood consuming human populations.
Chapter 3 compares temporal trends of PFASs in serum from Faroese children with those in the pilot whales they consume between 1985-2013 to gain insight into how changes in the marine environment are influencing human exposures. Principal component analysis identified three distinct groupings of PFAS exposure, one of which is associated with seafood consumption. Toxicokinetic models parameterized with individual hair mercury levels showed that PFAS exposures from seafood has become increasingly important (53% of PFOS in 2012) despite a decline in whale consumption in recent years. We infer that even in a major seafood
consuming population, declines in legacy PFAS exposure after 2000 were achieved by the rapid phase out of PFASs in consumer products.
Chapter 4 investigates the role of phospholipids and proteins in predicting the distribution of PFASs across different pilot whale organs in order to better understand the mechanisms of bioaccumulation. We show that phospholipids are highly predictive of the distribution of the longest-chained PFASs (PFDS, PFTA, PTriA) and that this association dampens with shorter length. Protein levels were moderately correlated with most compounds. These patterns are generally consistent with experimental membrane-water and protein-water partitioning coefficients and points to two distinct and competing mechanisms of accumulation for this class of ionic organic compounds.
Together, these chapters provide insight into the timescales and mechanisms of transport, accumulation, and elimination of PFASs in biological systems directly contributing to improved exposure assessment for these compounds.
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