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

Schaefer, Charles E.; Nguyễn, Duc Tung; Christie, Emerson; Shea, Stefanie; Higgins, Christopher P.; Field, Jennifer A.

doi:10.1061/(asce)ee.1943-7870.0001846

Cited by 41 publications

(37 citation statements)

References 22 publications

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“…PFAS transport within AFFF-impacted surface soils is slowed by a combination of sorption to soil components, retention in nonadvective regions, as well as accumulation at water–solid, air–water, and air–NAPL interfaces. ,− PFAS sorption on soils is mediated by nonionic (i.e., van der Waals or hydrophobic interactions) and electrostatic interactions. , For example, electrostatic interactions with negatively charged soil constituents are likely responsible for higher soil–water partitioning coefficients of zwitterionic and cationic PFASs relative to anionic PFAAs. − , In addition, while the importance of rate-limited sorption/desorption to PFAS transport is increasingly appreciated, previous studies under controlled conditions have either been limited to a small number of PFAAs or have not used field-collected soils which have been in contact with AFFF for the decadal time scales typical of impacted field sites. ,,− …”

Section: Introductionmentioning

confidence: 99%

Release of Per- and Polyfluoroalkyl Substances from Aqueous Film-Forming Foam Impacted Soils

Maizel

Shea

Nickerson

et al. 2021

Environ. Sci. Technol.

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Per- and polyfluoroalkyl substances (PFASs) are highly mobile in the saturated subsurface, yet aqueous film-forming foam (AFFF)-impacted source zones appear to be long lasting PFAS reservoirs. This study examined the release of over one hundred anionic and zwitterionic PFASs from two AFFF-impacted surface soils under saturated conditions with packed soil columns. Perfluoroalkyl acids (PFAAs) were released more rapidly than their polyfluorinated precursors, while anionic PFASs that were present in partially uncharged states were released more slowly than PFASs that were present entirely as anions, as were zwitterionic PFASs with terminal cationic functional groups when compared with analogous zwitterions with only anionic terminal groups. Nonideal transport was observed in both per- and polyfluorinated classes, as soil column effluent concentrations of slowly released PFASs increased by up to 107-fold with sustained artificial groundwater flow. A flow-interruption experiment suggested the influence of rate-limited desorption on diverse PFAS classes, including PFAAs with as few as four perfluorinated carbons. These results suggest that during infiltration the slow, rate-limited desorption of anionic and zwitterionic PFAA precursors may result in these compounds comprising an increasingly large fraction of the remaining PFASs in AFFF-impacted surface soils.

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Section: Introductionmentioning

confidence: 99%

Release of Per- and Polyfluoroalkyl Substances from Aqueous Film-Forming Foam Impacted Soils

Maizel

Shea

Nickerson

et al. 2021

Environ. Sci. Technol.

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“…As summarized in recent critical reviews, , retardation of nonpolymeric PFAS within vadose zone soils is a complex combination of multiple retention mechanisms and processes. Specific to the anionic perfluoroalkyl acids (PFAAs) of primary regulatory interest relevant to legacy AFFF formulations, these include hydrophobic interactions with the organic carbon (OC) fraction in soil, electrostatic interactions with the surfaces of variable-charged clay minerals including iron (Fe) and aluminum (Al) oxides and hydroxides to include potential irreversible chemisorption, and fluid–fluid (e.g., air–water) interfacial accumulation resulting in retardation from a “surface excess”. − Laboratory experiments further suggest that PFAA transport in soil is complicated by rate-limiting kinetics attributable to diffusive fluxes into and out of the OC matrix and associated hydrophobic solid-phase interactions, nonlinear (i.e., concentration-dependent) sorption to both solids and air–water interfaces, , and significant desorption hysteresis − resulting at least in part from biphasic porosity domains (highlighting the importance of diffusive fluxes) within natural soils. , In general, PFAS transport through unsaturated soil is “nonideal” even at environmentally relevant concentrations, and studies have suggested that kinetic models with these multiprocess retention mechanisms may be prerequisites for simulating transport under field conditions. , The various soil retention processes and their kinetics, interactions thereof, and potential confounding effects from the accumulation of PFAAs in soil as a result of polyfluorinated precursor transformation are the subject of much ongoing research …”

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confidence: 99%

The Case for Direct Measures of Soil-to-Groundwater Contaminant Mass Discharge at AFFF-Impacted Sites

Anderson

2021

Environ. Sci. Technol.

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Many entities around the world are initiating massive field campaigns to characterize the environmental distribution of per- and polyfluoroalkyl substances (PFAS), particularly at aqueous film-forming foam (AFFF) impacted sites where historic point-source discharges occurred at the ground surface. Concurrently, many regulatory agencies are publishing criteria used in practice to define the “nature and extent” of PFAS-impacted environmental media. Specific to the soil-to-groundwater transport pathway protective of the groundwater ingestion end point, these soil criteria (or screening values) are to date exclusively based on the traditional approach used for hydrophobic organics with a number of simplifying assumptions. Research has clearly contradicted these assumptions, yet alternative methodologies have yet to emerge from the literature. This Perspective provides a rationale for why alternative approaches are critically necessary and proposes the application of lysimetry as a practical solution to accurately assess PFAS transport within unsaturated vadose zone soils. Ultimately, there is an urgent need to justify soil remediation on the basis of groundwater protection and to prioritize remedial efforts in order to optimize limited fiscal resources.

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“…The difference in PFAS leachability suggests that soil textural class may play a role and the sandy soils tend to leach out most of the PFAS (65%–99%) they retain. Whether such a trend can be generalized to other soils needs caution, as soil properties could greatly influence the desorption of nonanionic PFAS from soils (Nguyen et al, 2020; Schaefer et al, 2021; Xiao et al, 2019).…”

Section: Resultsmentioning

confidence: 99%

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

et al. 2021

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Technologies applicable at a field scale to mitigate soil and groundwater pollution by per-and polyfluoroalkyl substances (PFAS) due to the release of aqueous film-forming foams are urgently needed. We demonstrate that modified bentonite clays as soil amendments can effectively reduce the leaching of PFAS from impacted soils. In batch experiments, the significant decrease (95%-99%) of leachable anionic PFAS, including perfluorooctane sulfonate, perfluorohexane sulfonate, and perfluorooctane carboxylate, was achieved in 1-4 days at a clay dosage as low as 0.5% w/w. A significant decline of leachable cationic and zwitterionic PFAS (70%-99%) was also observed. The clays performed the best in immobilizing PFAS anions, while granular activated carbon was effective in preventing PFAS cation leaching. Hardwood biochar had minor or negligible effects on any PFAS. The study provides strong evidence to support using modified clays as part of mitigation or remediation strategies to prevent PFAS from mobilizing on a field scale. K E Y W O R D Saqueous film-forming foams (AFFFs), groundwater remediation, modified clays, per-and polyfluoroalkyl substances (PFAS)

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

Cited by 41 publications

References 22 publications

Release of Per- and Polyfluoroalkyl Substances from Aqueous Film-Forming Foam Impacted Soils

Release of Per- and Polyfluoroalkyl Substances from Aqueous Film-Forming Foam Impacted Soils

The Case for Direct Measures of Soil-to-Groundwater Contaminant Mass Discharge at AFFF-Impacted Sites

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

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