Estimating the relative magnitudes of adsorption to solid-water and air/oil-water interfaces for per- and poly-fluoroalkyl substances

Brusseau, Mark L.

doi:10.1016/j.envpol.2019.113102

Cited by 54 publications

(40 citation statements)

References 49 publications

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“…These results demonstrate that AWI adsorption is not always the dominant contributor to retention within the vadose zone at PFAS source areas. This is in contrast to recent research demonstrating AWI adsorption contributed 50-99% of PFAS retardation during unsaturated transport [23,24,30] and is generally consistent with the trends in the foc-AWI adsorption nomograph presented by Brusseau [53]. It is clear that the differences in these results are, in part, related to the differences in porous media hydraulic properties and the differences in the magnitude of solid-phase sorption associated with these media.…”

Section: Example Simulation-1d Transport Transient Flow Condition Homogeneous Profilesupporting

confidence: 88%

A Modified HYDRUS Model for Simulating PFAS Transport in the Vadose Zone

Silva

Šimůnek

McCray

2020

Water

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The HYDRUS unsaturated flow and transport model was modified to simulate the effects of non-linear air-water interfacial (AWI) adsorption, solution surface tension-induced flow, and variable solution viscosity on the unsaturated transport of per- and polyfluoroalkyl substances (PFAS) within the vadose zone. These modifications were made and completed between March 2019 and May 2019, and were implemented into both the one-dimensional (1D) and two-dimensional (2D) versions of HYDRUS. Herein, the model modifications are described and validated against the available literature-derived PFAS transport data (i.e., 1D experimental column transport data). The results of both 1D and 2D example simulations are presented to highlight the function and utility of the model to capture the dynamic and transient nature of the temporally and spatially variable interfacial area of the AWI (Aaw) as it changes with soil moisture content (Θw) and how it affects PFAS unsaturated transport. Specifically, the simulated examples show that while AWI adsorption of PFAS can be a significant source of retention within the vadose zone, it is not always the dominant source of retention. The contribution of solid-phase sorption can be considerable in many PFAS-contaminated vadose zones. How the selection of an appropriate AawΘw function can impact PFAS transport and how both mechanisms contribute to PFAS mass flux to an underlying groundwater source is also demonstrated. Finally, the effects of soil textural heterogeneities on PFAS unsaturated transport are demonstrated in the results of both 1D and 2D example simulations.

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Section: Example Simulation-1d Transport Transient Flow Condition Homogeneous Profilesupporting

confidence: 88%

A Modified HYDRUS Model for Simulating PFAS Transport in the Vadose Zone

Silva

Šimůnek

McCray

2020

Water

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“…The measurements from the aqueous‐IPTT and mass balance (aqueous) surfactant‐tracer method are in general lower than those measured by the gas‐IPTT method, especially at lower water saturations, while higher than X‐ray microtomography measurements wherein roughness‐impacted film‐associated air‐water interfaces are not accounted for (Brusseau et al, ). Air‐water interfacial area measured by aqueous‐based methods has been shown to be more representative for transport processes in the aqueous phase (Brusseau et al, ; Brusseau, ; Lyu et al, ). Saturated conductivity for the Accusand and Vinton soil were measured by Brusseau and colleagues (unpublished) and from Bagour (), respectively.…”

Section: Data and Parametersmentioning

confidence: 99%

“…The impact of fluid‐fluid interfacial adsorption on PFAS retention and transport in soil was examined initially by Brusseau (), who employed surface tension data for PFAS including two of primary concern—perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS)—and measured air‐water interfacial areas along with a comprehensive retention model to conduct a theoretical assessment. Additional surface‐tension‐based theoretical analyses of PFAS retention have since been reported (Brusseau, , ; Brusseau & Van Glubt, ; Costanza et al, ; Silva et al, ). Miscible‐displacement laboratory experiments demonstrating that adsorption of PFAS at air‐water and NAPL‐water interfaces can be an important retention process in soil and sand materials have also been reported (Brusseau et al, ; Lyu et al, ).…”

Section: Introductionmentioning

confidence: 99%

A Mathematical Model for the Release, Transport, and Retention of Per‐ and Polyfluoroalkyl Substances (PFAS) in the Vadose Zone

Guo

Zeng

Brusseau

2020

Water Resources Research

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119

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Per‐ and polyfluoroalkyl substances (PFAS) are emerging contaminants of critical concern. As surfactants, PFAS tend to accumulate at air‐water interfaces and may stay in the vadose zone for long times before contaminating groundwater. Yet not well understood, the extent of retention in the vadose zone has critical implications for risk management and remediation strategies. We present the first mathematical model that accounts for surfactant‐induced flow and solid‐phase and air‐water interfacial adsorption. We apply the model to simulate PFOS (a PFAS compound of primary concern) transport in the vadose zone at a model fire‐training area site impacted by aqueous film‐forming foam (AFFF). Air‐water interfacial adsorption is shown to have a significant impact—amplified by the low water content due to gravity drainage—total retardation factors range from 233 to 1,355 for the sand and 146 to 792 for the soil used in the study. The simulations illustrate it can take several decades or longer for PFOS to reach groundwater. Counterintuitively, the lower water content in the sand—due to stronger drainage and weaker capillary retention—leads to retardation factors greater than for the soil. Also, most PFOS is adsorbed at air‐water interfaces with only 1–2% in the aqueous phase. The implications include (1) fine‐texture materials could have lower retardation factors than sand due to higher retained water content, (2) soil PFAS concentrations are likely to be orders of magnitude higher than those in groundwater at source zones. Both implications are consistent with recent field observations at hundreds of AFFF‐impacted sites.

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“…The Freundlich isotherms for PFOS in both Accusand and Vinton were obtained from prior sorption experiments reported in Brusseau (2020) and Brusseau et al (2019a). Because no solid-phase adsorption data are available for PFPeA, we estimated the Kf and N parameters from the measured Freundlich isotherms of PFOA using the QSPR method developed by Brusseau (2019). Similarly, we used the same QSPR method to estimate the Freundlich isotherms for PFOS and PFPeA in Hayhook and high-K sand.…”

Section: Representative Pfasmentioning

confidence: 99%

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

Zeng¹,

Guo²

2021

Preprint

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PFAS are emergent contaminants of which fate and transport in the environment remain poorly understood. As surfactants, adsorption at air-water interfaces and solid surfaces in soils complicates the retention and leaching of PFAS in the vadose zone. Recent modeling studies accounting for the PFAS-specific nonlinear adsorption processes predicted that the majority of long-chain PFAS remain in the shallow vadose zone decades after contamination ceases—in agreement with many field measurements. However, some field investigations show that long-chain PFAS have migrated to tens to a hundred meters below ground surface. These discrepancies may be attributed to model simplifications such as a one-dimensional (1D) representation of the homogeneous vadose zone. Another potentially critical process that has not been fully examined by the 1D models is how surfactant-induced flow (SIF) influences PFAS leaching in multidimensions. We develop a new three-dimensional model for PFAS transport in the subsurface to investigate the multidimensional effects of SIF and soil heterogeneities. Our simulations and analyses conclude that 1) SIF has a minimal impact on the long-term leaching of PFAS in the vadose zone, 2) preferential flow pathways generated by soil heterogeneities lead to early arrival and accelerated leaching of (especially long-chain) PFAS, 3) the acceleration of PFAS leaching in high water-content preferential pathways or perched water above capillary barriers is more prominent than conventional contaminants due to the destruction of air-water interfaces, and 4) soil heterogeneities are among primary sources of uncertainty for predicting PFAS leaching and retention in the vadose zone.

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Estimating the relative magnitudes of adsorption to solid-water and air/oil-water interfaces for per- and poly-fluoroalkyl substances

Cited by 54 publications

References 49 publications

A Modified HYDRUS Model for Simulating PFAS Transport in the Vadose Zone

A Modified HYDRUS Model for Simulating PFAS Transport in the Vadose Zone

A Mathematical Model for the Release, Transport, and Retention of Per‐ and Polyfluoroalkyl Substances (PFAS) in the Vadose Zone

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

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