Evaluating the Relative Importance of Polyfluoroalkyl Substances in AFFF-Impacted Soils

This multisite study analyzed depth-discrete soil samples in 12 cores (≤2 m from the ground surface) from 10 aqueous film-forming foam (AFFF)-impacted U.S. Department of Defense installations. A broad suite of per- and polyfluoroalkyl substances (PFASs) were analyzed using extraction protocols designed for source-zone soils and liquid chromatography-high resolution mass spectrometry (LC-HRMS) with targeted and semiquantitative workflows. Across all samples, 162 PFASs spanning 50 classes were identified, with both electrochemical fluorination (ECF)- and fluorotelomer (FT)-derived signatures present at nearly all sites. Class-level detection frequency analysis showed that shallow intervals (down to 30 cm below ground surface) captured most class diversity at the studied sites. Regarding total PFAS mass within a soil core, precursors frequently dominated, though several cores were perfluoroalkyl acid (PFAA)-dominated. These data indicate that reliance on the Environmental Protection Agency (EPA) Method 1633 target list alone substantially underestimated precursor mass in all 12 studied cores. Vertical profiles of PFAAs and precursors showed varying trends and correlations in concentration with depth, suggesting site-specific transport and transformation phenomena. The results of this study point toward several polyfluoroalkyl substances that may be considered for prompt investigation while also highlighting a need for detailed characterizations of diverse AFFF-impacted sites.