Assessing the potential contributions of additional retention processes to PFAS retardation in the subsurface
Open accessAbstract
A comprehensive understanding of the transport and fate of per- and poly-fluoroalkyl substances (PFAS) in the subsurface is critical for accurate risk assessments and design of effective remedial actions. A multi-process retention model is proposed to account for potential additional sources of retardation for PFAS transport in source zones. These include partitioning to the soil atmosphere, adsorption at air-water interfaces, partitioning to trapped organic liquids (NAPL), and adsorption at NAPL-water interfaces. An initial assessment of the relative magnitudes and significance of these retention processes was conducted for two PFAS of primary concern, perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), and an example precursor (fluorotelomer alcohol, FTOH). The illustrative evaluation was conducted using measured porous-medium properties representative of a sandy vadose-zone soil. Data collected from the literature were used to determine measured or estimated values for the relevant distribution coefficients, which were in turn used to calculate retardation factors for the model system. The results showed that adsorption at the air-water interface was a primary source of retention for both PFOA and PFOS, contributing approximately 50% of total retention for the conditions employed. Adsorption to NAPL-water interfaces and partitioning to bulk NAPL were also shown to be significant sources of retention. NAPL partitioning was the predominant source of retention for FTOH, contributing ~98% of total retention. These results indicate that these additional processes may be, in some cases, significant sources of retention for subsurface transport of PFAS. The specific magnitudes and significance of the individual retention processes will depend upon the properties and conditions of the specific system of interest (e.g., PFAS constituent and concentration, porous medium, aqueous chemistry, fluid saturations, co-contaminants). In cases wherein these additional retention processes are significant, retardation of PFAS in source areas would likely be greater than what is typically estimated based on the standard assumption of solid-phase adsorption as the sole retention mechanism. This has significant ramifications for accurate determination of the migration potential and magnitude of mass flux to groundwater, as well as for calculations of contaminant mass residing in source zones. Both of which have critical implications for human-health risk assessments.
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PFAS molecules and precursors are involved in both hydrophobic and electrostatic adsorption to soil/sediment/SS particles and air-water interfaces, a significant PFAS retention mechanism under unsaturated conditions.
“PFAS molecules and precursors, however, are involved in both hydrophobic and electrostatic adsorption to soil/sediment/SS particles and air–water interfaces (AWI), a significant PFAS retention mechanism under unsaturated conditions.”
From Occurrence, Concentration, and Distribution of 35 PFASs and Their Precursors Retained in 20 Stormwater Biofilters (2024) · cites this paper as [40]
Section 2a (page unavailable) describes hydrophobic and electrostatic contributions to PFAS sorption by solids. Sections 2c and 6 describe air–water-interface adsorption as a potentially significant retention mechanism in unsaturated soil, with the illustrative calculation finding substantial retention for PFOS and PFOA. But Section 5a says adsorption to fluid–fluid interfaces was minimal for the precursor examined, 8:2 FTOH; the claim overgeneralizes that mechanism to precursors. (LLM, conf=0.88)
Experimental — accuracy not yet measuredThe migration and leaching behavior of PFAS in the vadose zone is expected to depend on PFAS source properties, soil properties, meteorological conditions, and other factors.
“The migration and leaching behavior of PFAS in the vadose zone is expected to depend on a variety of factors including PFAS source properties (PFAS type, source input conditions, co-contaminants), soil properties, meteorological conditions, and other factors (Brusseau, 2018; Lyu et al., 2018; Brusseau et al., 2019a, 2019b; Guo et al., 2020).”
From PFAS concentrations in soils: Background levels versus contaminated sites (2020) · cites this paper as Brusseau, 2018
One factor that can lead to enhanced retention compared to groundwater systems is adsorption of PFAS at air-water interfaces under water-unsaturated conditions.
“One factor that can lead to enhanced retention compared to groundwater systems is adsorption of PFAS at air-water interfaces under water-unsaturated conditions (Brusseau, 2018, 2019, 2020; Lyu et al., 2018; Brusseau et al., 2019a; Guo et al., 2020).”
From PFAS concentrations in soils: Background levels versus contaminated sites (2020) · cites this paper as Brusseau, 2018
PFAS are known to be retained in the subsurface through various retention processes.
“The latter is possible, as PFAS are known to be retained in the subsurface through various retention processes (Brusseau, 2018; Zhang et al., 2019).”
From Per- and polyfluoroalkyl substances (PFAS) mass flux and mass balance at an aqueous film-forming foam release site in semiarid eastern New Mexico, USA (2025) · cites this paper as Brusseau, 2018
PFAS transport in the vadose zone and groundwater reflects the balance between sorption to the surfaces of soil/sediment solids, retention at the air-water interface in unsaturated soils, and advection in the aqueous phase.
“PFAS transport in the vadose zone and groundwater reflects the balance between sorption to the surfaces of soil/sediment solids, retention at the air–water interface in unsaturated soils, and advection in the aqueous phase.25”
From Centurial Persistence of Forever Chemicals at Military Fire Training Sites (2023) · cites this paper as [25]
Precipitation leads to higher soil moisture content, which results in collapse of the air-water interface at saturation, promotes migration of surface active PFAS into the aqueous phase, and increases aquifer recharge.
“Precipitation leads to higher soil moisture content, which results in collapse of the air–water interface at saturation, promotes migration of surface active PFAS into the aqueous phase, and increases aquifer recharge.25,34”
From Centurial Persistence of Forever Chemicals at Military Fire Training Sites (2023) · cites this paper as [25]
The air-water interface can retain significant amounts of PFAAs and has been found to be the major retention mechanism of PFAAs in the subsurface.
“The air-water interface can retain significant amounts of PFAAs and has been found to be the major retention mechanism of PFAAs in the subsurface (Brusseau, 2018).”
From Perfluoroalkyl acids on suspended particles: Significant transport pathways in surface runoff, surface waters, and subsurface soils (2021) · cites this paper as Brusseau, 2018
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References 84 · Cited by 306
Research works printed but not linked: 3
- Brusseau ML 1990 Micro-scale mass transfer processes and field-scale transport of organic solutes, paper presented at International Conference on Transport and Mass Exchange Processes in Sand and Gravel Aquifers Proc. published by Atomic Energy Can. Ltd Chalk River, Canada
- Kim H Annable MD Rao PSC 2001 Gaseous transport of volatile organic chemicals in unsaturated porous media: effect of water-partitioning and air-water interfacial adsorption Env. Sci. Technol 35 4457 4462 11757601
- Vecitis CD Park H Cheng J Mader BT Hoffmann MR 2008 Enhancement of perfluorooctanoate (PFOA) and perfluorooctanesulfonate (PFOS) activity at acoustic cavitation bubble interfaces Journal of Physical Chemistry 112 16850 16857
- Authors
- Brusseau, M. L.
- Affiliations
- University of Arizona (US)
- Corresponding author
- Brusseau, Mark L.
- ORCID
- Brusseau, Mark L.
- Venue
- Science of The Total Environment
- Publisher
- Elsevier BV
- Published
- 2018-02
- Volume
- 613-614
- Pages
- 176-185
- ISSN
- 0048-9697 (ISSN-L)
- PMC
- PMC5693257
- OpenAlex
- W2754505730
- Cited by
- 306
- References
- 84
- Citations by year
- 2026: 44 · 2025: 48 · 2024: 47 · 2023: 31 · 2022: 44 · 2021: 41 · 2020: 34 · 2019: 13 · 2018: 4
- FWCI
- 8.20
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Licence
- Locations
- The Science of The Total Environment (acceptedVersion)
- PubMed (publishedVersion)
- Europe PMC (PubMed Central) (acceptedVersion)
- PubMed Central (acceptedVersion)
- Funders
- National Institute of Environmental Health Sciences (P42 ES04940)
- Topics
- Physical Sciences › Environmental Science › Environmental Chemistry › Per- and polyfluoroalkyl substances research
- Physical Sciences › Environmental Science › Environmental Engineering › Groundwater flow and contamination studies
- Physical Sciences › Engineering › Biomedical Engineering › Environmental remediation with nanomaterials
- Keywords
- PFAS, per- and polyfluoroalkyl substances, retardation, source zone, air-water interface adsorption, PFOS, perfluorooctanoic acid, fluorotelomer alcohols, vadose zone, groundwater contamination, contaminant mass flux, human health risk assessment
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