Aqueous film-forming foams (AFFFs) are a major source of per- and polyfluoroalkyl substance (PFAS) exposure for millions of Americans via drinking water. AFFFs contain significant fractions of known and novel PFAS precursors, which can be transformed into persistent PFASs by environmental and biological processes. Some of these precursors, such as the fluorotelomer sulfonates and perfluoroalkyl sulfonamides, have been detected previously in drinking water. There is mounting evidence that PFAS precursors contribute to unexpectedly elevated concentrations of PFAS in serum from human biomonitoring and AFFF-dosed animal studies. While information on precursor content can be gained from the TOP assay, the degree of transformation and the structures formed are not necessarily biologically relevant. To link PFAS exposure to PFAS internal dose, information is urgently needed on the extent to which novel AFFF-associated PFAS precursors are metabolized in humans. We conducted high-resolution mass spectrometry (HRMS) suspect screening analysis of real AFFF mixtures before and after incubation with mammalian liver sub-cellular fractions to track precursor degradation and formation of persistent PFAS as well as novel transformation products. We also analyzed liver tissue and serum from mice dosed with one of these AFFFs to describe the bioaccumulation and metabolism of known and novel AFFF-associated PFASs in vivo. Pronounced signals for several tentatively-identified novel substituted perfluoroalkyl sulfonates, including unsaturated, ketone-substituted, and pentafluorosulfide-substituted sulfonates, were present in liver tissue samples. Initial results from in vitro metabolic assays suggest that some sulfonamide precursors present in historical electrochemically-fluorinated foam degrade rapidly in vitro, leading to formation of PFOS and other perfluoroalkyl sulfonates. This study has implications for understanding the tissue distribution and tissue:blood ratios for novel PFASs and is an important step forward in understanding in vivo transformation of labile PFASs.

Bioaccumulation and biotransformation of PFASs using AFFF-dosed in vivo and in vitro models

ACS Fall 2021

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