Extractable Organofluorine Mass Balance Analysis of Aqueous Film-Forming Foam-Impacted Soils: Sample Pretreatment and a Combination of Target Analysis and Suspect Screening

The application of aqueous film-forming foams (AFFFs) has caused considerable per- and polyfluoroalkyl substances (PFAS) pollution in the environment. Soil serves as a long-term source of PFAS for the adjacent groundwater and surface water, but the lack of extractable organofluorine (EOF) mass balance data in the AFFF-impacted soils may lead to an underestimation of PFAS contamination. This study analyzed ten surface soil samples from three AFFF-impacted sites in Sweden, using alkaline extraction followed by acidic extraction. The alkaline and acidic fractions were subjected to further cleanup and analyzed separately for target, suspect screening, and EOF analysis to evaluate the extraction efficiencies of different PFAS in the soil samples and reveal PFAS remaining unknown in the AFFF-impacted soils. Total target PFAS concentrations ranged from 33.0 to 2.40 × 10⁴ ng/g dry weight. Thirty-six PFAS were identified using suspect screening. Considerable amounts of zwitterionic and cationic PFAS (up to 58%) were identified in the acidic extraction fraction, while >95% of anionic PFAS were found in the alkaline extraction fraction. EOF mass balance analysis was conducted on AFFF-impacted soils for the first time. The high proportion of unexplained organofluorine (up to 65%) indicated the necessity for future investigation of the unknown PFAS in AFFF-impacted soils to comprehensively understand their fate and risk.