Towards a fingerprint of aqueous film-forming foam (AFFF) as source of PFAS across environmental compartments

The use of Aqueous film-forming foams (AFFF) is a major emission source of per- and polyfluoroalkyl substances (PFAS). This review explores whether fingerprints of AFFF contamination can be identified. We examine the composition of AFFF formulations and whether the physicochemical properties of AFFF-related PFAS differ from those of other PFAS. We then compare the distribution patterns of PFAS in various environmental compartments at AFFF-impacted sites. Either PFOS or 6:2 FTS congeners usually dominate formulations, depending on the production method. PFHxSAm, a potential precursor to FHxSA and PFHxS, was also found to be relevant in AFFFs produced via electrochemical fluorination. The analysis of the chemical descriptors suggests that AFFF-related PFAS are constitutionally similar, regardless of the manufacturing process. On average, PFOS accounts for 75% of the total content of the most detected PFAS in soils, while 6:2 FTS and its congeners were dominant where exclusively telomerisation-based AFFF were applied. PFHxS, PFHxA and PFOA were the next most detected compounds. Groundwater shows a lower median share of PFOS (50%), a higher occurrence of short chain PFCA and PFSA and a larger range of concentrations. These findings rely on surveys primarily targeting a limited number of compounds. In a few cases, FHxSA, its related compounds, and 6:2-FTAB accounted for a large fraction of total analyzed PFAS in affected sites. This review marks a significant step forward in identifying fingerprints of AFFF-PFAS contamination, and it highlights the need to expand the analytical panel in environmental monitoring at AFFF-impacted sites.