Citation:

Ruyle, B., C. Thackray, J. McCord, M. Strynar, K. Mauge-Lewis, S. Fenton, AND E. Sunderland. Reconstructing the Composition of Per- and Polyfluoroalkyl Substances in Contemporary Aqueous Film-Forming Foams. Environmental Science & Technology Letters. American Chemical Society, Washington, DC, 8(1):59-65, (2021). https://doi.org/10.1021/acs.estlett.0c00798

Impact/Purpose:

Aqueous film-forming foams (AFFF) are complex mixtures often formulated for application in fire suppression and commonly use per- and polyfluorinated alkyl substances (PFAS), which are a chemical class of significant concern to the EPA. The components of the complex mixture are of significant importance due to potential exposure to persistent PFAS with unknown toxicity, and an understanding of the contents of modern AFFF formulations can inform environmental screening of impacted media. This manuscript applies non-targeted mass spectrometry to characterize the nature of PFAS chemicals in a selection of AFFF materials and then applies a combination of total fluorine measurements, extractable organic fluorine measurements, total oxidizeable precursor assays, and targeted PFAS measurements to codify the amount of fluorine containing substances in the mixtures, as well as cross-validate the identifications from the non-targeted analysis as being "complete" inventories of the PFAS in the mixtures. This approach represents a way to provide bounded search space for characterizing unknown or uncharacterisized PFAS in multimedia samples.

Description:

Hundreds of public water systems across the United States have been contaminated by the use of aqueous film-forming foams (AFFF) containing per- and polyfluoroalkyl substances (PFAS) during firefighting and training activities. Prior work shows AFFF contain hundreds of polyfluoroalkyl precursors missed by standard methods. However, the most abundant precursors in AFFF remain uncertain, and mixture contents are confidential business information, hindering proactive management of PFAS exposure risks. Here, we develop and apply a novel method (Bayesian inference) for reconstructing the fluorinated chain lengths, manufacturing origin, and concentrations of oxidizable precursors obtained from the total oxidizable precursor (TOP) assay that is generally applicable to all aqueous samples. Results show virtually all (median 104 ± 19%) extractable organofluorine (EOF) in contemporary and legacy AFFF consists of targeted compounds and oxidizable precursors, 90% of which are 6:2 fluorotelomers in contemporary products. Using high-resolution mass spectrometry, we further resolved the 6:2 fluorotelomers to assign the identity of 14 major compounds, yielding a priority list that accounts for almost all detectable PFAS in contemporary AFFF. This combination of methods can accurately assign the total PFAS mass attributable to AFFF in any aqueous sample with differentiation of gross precursor classes and identification of major precursor species.

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