Enhanced Extraction of AFFF-Associated PFASs from Source Zone Soils

Abstract

Poly-and perfluoroalkyl substances (PFASs) derived from aqueous film-forming foam (AFFF) are increasingly recognized as groundwater contaminants, though the composition and distribution of AFFF-derived PFASs associated with soils and subsurface sediments remain largely unknown. This is particularly true for zwitterionic and cationic PFASs, which may be incompletely extracted from subsurface solids by analytical methods developed for anionic PFASs. Therefore, a method involving sequential basic and acidic methanol extractions was developed and evaluated for recovery of anionic, cationic, and zwitterionic PFASs from field-collected, AFFF-impacted soils. The method was validated by spike-recovery experiments with equilibrated soil-water-AFFF and analytical standards. To determine the relative importance of PFASs lacking commercially available analytical standards, their concentrations were estimated by a novel semiquantitation approach. Total PFAS concentrations determined by semiquantitation were compared with concentrations determined by the total oxidizable precursor assay. Finally, the described method was applied to two soil cores from former fire-training areas in which cations and zwitterions were found to contribute up to 97% of the total PFAS mass. This result demonstrates the need for extraction and analysis methods, such as the ones presented here, that are capable of quantifying cationic and zwitterionic PFASs in AFFF-impacted source zone soils.

Field-Scale Demonstration of PFAS Leachability Following In Situ Soil Stabilization

“…The PFASs were extracted from soil using a triple methanol rinse, and sonication or other extraction methods may have been more appropriate. 77 While this challenges the precise interpretation of the mass balance, a comparison on an order of magnitude basis showing 10 5 ng total PFAS associated with the pre- and postleached soil versus 10 2 –10 3 ng total PFAS observed in the composite leachates strongly suggests that chemical stabilization decreases PFAS leachability into groundwater as well as extractability with methanol rinse. The calculated percentage of PFHxS, PFOS, PFHxA, and PFOA leachability demonstrates that in comparison to the soil-only control from the batch testing, stabilizers reduced the leachability of these PFAAs ( Figure 3 ).…”

Multidimensional simulation of PFAS transport and leaching in the vadose zone: impact of surfactant-induced flow and soil heterogeneities

“…We recognize that foc in the first meter below the land surface may be much greater than the foc employed in the present study. Additionally, more complex sorption processes such as electrostatic interactions may lead to enhanced solid-phase adsorption in particular for cationic and zwitterionic PFAS (Barzen-Hanson et al, 2017;Mejia-Avendaño et al, 2020;Nickerson et al, 2020;Xiao et al, 2019). Under these conditions, our simulations would overestimate PFAS leaching.…”

Modified clays reduce leaching of per‐ and polyfluoroalkyl substances from AFFF‐contaminated soils

“…Polyfluoroalkyl compounds containing one or multiple ionizable groups that were detected at relatively high concentration included AmPr-FHxSA (zwitterion, 17-4111 ng/g), TAmPr-FHxSA (zwitterion, 109-3098 ng/g), FHxSA (anion, 91-545 ng/g), FOSA (anion, 81-366 ng/g), TAmPr-FOSA (zwitterion, 17-206 ng/ g), and AmPr-FOSA (zwitterion, 1.2-145 ng/g). Their detection was expected, as studies have recently reported such nonanionic PFAS to make up a large fraction of fluorosurfactants in AFFF formulations (Adamson et al, 2020;Nickerson et al, 2020). The charge status of these compounds also varies widely, determined by one or multiple ionizable groups, as well as the permanently charged quaternary ammonium group (see Scheme 1).…”

“…In many instances, PFAS are directly discharged into soils with little or no treatment, and thereby leaching from soils contributes to the PFAS load in groundwater and surface water. The elevated levels of PFAS are widely observed in the soil, water, sediment, and wildlife samples geographically relevant to the impacted sites, even when the discharges of AFFFs are discontinued for years (Barzen‐Hanson et al, 2017; Nickerson et al, 2020).…”

“…Previous investigations mainly focused on anionic PFAS, mainly PFCAs and PFSAs (USEPA, 2019), while the significant presence of the nonanionic compounds needs to be addressed as well. Particularly, cationic and zwitterionic PFAS can make up a significant fraction of the total PFAS load in impacted soils (Nickerson et al, 2020). Despite various challenges to study nonanionic PFAS, e.g., the incomplete understanding of their environmental behaviors, increasingly available chemical standards make it possible to address such a portion of nonanionic PFAS to developing soil remediation strategies (Mejia- Avendaño et al, 2017).…”