Desorption of Poly- and Perfluoroalkyl Substances from Soil Historically Impacted with Aqueous Film-Forming Foam

AbstractBench-scale experiments were performed to measure and evaluate the desorption kinetics of poly- and perfluoroalkyl substances (PFAS) from a vadose zone soil exposed decades ago to aqueous film-forming foams (AFFFs). Desorption kinetics in the shallow zone (0.03–0.9 m below ground surface) that contained an elevated organic carbon (OC) content, and in an underlying deep zone (0.9–2.4 m below ground surface) that contained a relatively low OC content, were evaluated for a wide range of anionic and zwitterionic compounds. Results showed that, for a given perfluorinated chain length, the head group impacted desorption. For the low-OC deep soil, desorption equilibrium generally occurred rapidly (within 48 h), indicating that mass transfer limitations were minimal. However, for the high-OC shallow soil, less-hydrophobic and short-chained compounds (including C