Capturing the Organic Fluorine in Aqueous Film-Forming Foam (AFFF)-Impacted Groundwater: Suspect Screening, Extractable Organofluorine, and the Total Oxidizable Precursor Assay

Abstract The widespread use of aqueous film–forming foam (AFFF) for firefighting and firefighter training has led to extensive per- and polyfluoroalkyl substance (PFAS) contamination in the environment, yet the mass budget for PFASs in AFFF-impacted groundwater across diverse sites remains uncertain. Here, we integrated targeted analysis, high-resolution mass spectrometry (HRMS)-based suspect screening, extractable organofluorine (EOF), and the total oxidizable precursor (TOP) assay to evaluate total organic fluorine in 23 groundwater samples collected from 12 AFFF-impacted sites. Across all samples, total targeted PFAS concentrations ranged from 0.35 to 980 μg/L, and the highest summed PFAS concentrations, including suspect PFASs, reached 1,000 μg/L. EOF levels ranged from 5.9 to 670 μg F/L. Targeted PFASs explained 0.82–93% of the EOF (median: 44%), whereas targeted and suspect PFASs contributed 0.82–100% (median: 50%). Targeted PFASs together with oxidizable precursors quantified by the TOP assay accounted for 5.7–100% of the EOF (median: 54%). Importantly, the majority of EOF (>50%) could be explained by targeted and suspect PFASs or precursors from the TOP assay in groundwater where EOF concentrations were high (e.g., ≥50 μg F/L). These results demonstrate that combining suspect screening, EOF, and the TOP assay provides a more comprehensive assessment of PFAS contamination in AFFF-impacted groundwater, while the unresolved organofluorine indicates the presence of unidentified fluorinated compounds not captured by current workflows.