Isolating the AFFF Signature in Coastal Watersheds Using Oxidizable PFAS Precursors and Unexplained Organofluorine

Water supplies for millions of U.S.
individuals exceed maximum
contaminant levels for per- and polyfluoroalkyl substances (PFAS).
Contemporary and legacy use of aqueous film forming foams (AFFF) is
a major contamination source. However, diverse PFAS sources are present
within watersheds, making it difficult to isolate their predominant
origins. Here we examine PFAS source signatures among six adjacent
coastal watersheds on Cape Cod, MA, U.S.A. using multivariate clustering
techniques. A distinct signature of AFFF contamination enriched in
precursors with six perfluorinated carbons (C6) was identified in
watersheds with an AFFF source, while others were enriched in C4 precursors.
Principal component analysis of PFAS composition in impacted watersheds
showed a decline in precursor composition relative to AFFF stocks
and a corresponding increase in terminal perfluoroalkyl sulfonates
with < C6 but not those with ≥ C6. Prior work shows that
in AFFF stocks, all extractable organofluorine (EOF) can be explained
by targeted PFAS and precursors inferred using Bayesian inference
on the total oxidizable precursor assay. Using the same techniques
for the first time in impacted watersheds, we find that only 24%–63%
of the EOF can be explained by targeted PFAS and oxidizable precursors.
Our work thus indicates the presence of large non-AFFF organofluorine
sources in these coastal watersheds.