Surface soil PFAS mixtures dominated by PFOS: Prioritization for ecotoxicity testing and ecological risk assessment at current and former US Air Force Bases

Abstract Per- and polyfluoroalkyl substances (PFAS) detection at military installations where current and historical aqueous film-forming foam (AFFF) use has occurred drive a need for empirical derivation of environmentally relevant PFAS mixtures to facilitate toxicity testing and risk assessment efforts. We applied a formalized prioritization method to a large dataset of PFAS concentrations in surface soil at AFFF-affected sites on active and former U.S. Air Force installations. Our approach revealed several observations about PFAS at these sites. First, perfluorooctane sulfonate (PFOS) occurred most commonly and often at the highest concentration across the PFAS measured. Second, two to three PFAS contributed 86% to 91%, respectively, of the sum PFAS in any given site-specific mixture. Third, after PFOS, the most common and high concentration PFAS among target analytes were perfluorohexane sulfonate (PFHxS), perfluorooctanoic acid (PFOA), perfluorooctanesulfonamide (PFOSA), and/or perfluorohexanoic acid (PFHxA), in that order. Site-specific PFAS mixtures are approximately 5% to 12% PFHxS, PFOA, PFOSA, and PFHxA behind approximately 82% PFOS. Another observation relevant to future sampling is the high concentration but inconsistent prevalence of the 6:2 and 8:2 fluorotelomer sulfonates (FTSs). An uncertainty that could also be addressed through future sampling is the detection of less abundant or yet unmeasured PFAS that have unknown or poorly characterized toxicological potency. These results support the continued importance of efforts to understand effects and exposure of PFOS but highlight the need to consider other PFAS such as PFHxS and fluorotelomers in exposure and effect estimations to support ecological risk assessments and ecotoxicological testing of PFAS mixtures.