<p>Lately, a group of chemical compounds, per-polyfluoroalkyl substances (PFAS), has been attracting attention due to their discovery in the environment as well as the risk they pose to human life, the environment, and groundwater. PFAS exhibit various physicochemical properties, which make them useful in a variety of industries and products, adding to their pervasiveness. These compounds have been used in various products over the years and have, therefore, accumulated in the environment. One of the most investigated PFAS compounds is PFOS (perfluorooctane sulfonic acid). To date, there are still many unanswered questions regarding the fate and transport of PFAS in unsaturated zones and how the underlying groundwater is affected. This is due to the PFAS's ability to partition, bioaccumulate, and biotransform and due to its indestructibility due to the strong C–F bond. This, coupled with their toxic effects on humans and biota, leads to concerns regarding their fate and consequences to the ecosystem. In this paper, the fate and transport of PFAS (specifically PFOS) in both saturated and unsaturated zones in the soil environment are investigated through numerical modeling using the finite-difference method. This study looks at the effect of transport processes (advection, diffusion, and adsorption) on the fate of PFAS in soil and groundwater. After the model was developed, a grid sensitivity analysis was carried out to determine the sensitivity of the model against the spatial and temporal discretization (i.e., selection of time, <InlineEquation ID="IEq1"> <EquationSource Format="TEX">$dt$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="italic">dt</mi> </mrow> </math></EquationSource> </InlineEquation>, and space, <InlineEquation ID="IEq2"> <EquationSource Format="TEX">$dz$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="italic">dz</mi> </mrow> </math></EquationSource> </InlineEquation>). The results show negligible (i.e., < ± 1%) error margin and sensitivity to <InlineEquation ID="IEq3"> <EquationSource Format="TEX">$dt$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="italic">dt</mi> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq4"> <EquationSource Format="TEX">$dz$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="italic">dz</mi> </mrow> </math></EquationSource> </InlineEquation> within the selected range. Multiple scenarios were then investigated using the model to understand the fate and transport of PFAS in both vadose and saturated zones to qualitatively verify the results.</p>

Investigating PFAS Interface Interactions through Vadose and Saturated Zones Using a PFAS Transport Model

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2025年6月21日

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Md Khorshed Alam,
Pierrette Iradukunda,
Arvin Farid

摘要

Lately, a group of chemical compounds, per-polyfluoroalkyl substances (PFAS), has been attracting attention due to their discovery in the environment as well as the risk they pose to human life, the environment, and groundwater. PFAS exhibit various physicochemical properties, which make them useful in a variety of industries and products, adding to their pervasiveness. These compounds have been used in various products over the years and have, therefore, accumulated in the environment. One of the most investigated PFAS compounds is PFOS (perfluorooctane sulfonic acid). To date, there are still many unanswered questions regarding the fate and transport of PFAS in unsaturated zones and how the underlying groundwater is affected. This is due to the PFAS's ability to partition, bioaccumulate, and biotransform and due to its indestructibility due to the strong C–F bond. This, coupled with their toxic effects on humans and biota, leads to concerns regarding their fate and consequences to the ecosystem. In this paper, the fate and transport of PFAS (specifically PFOS) in both saturated and unsaturated zones in the soil environment are investigated through numerical modeling using the finite-difference method. This study looks at the effect of transport processes (advection, diffusion, and adsorption) on the fate of PFAS in soil and groundwater. After the model was developed, a grid sensitivity analysis was carried out to determine the sensitivity of the model against the spatial and temporal discretization (i.e., selection of time, $dt$ $dt$ , and space, $dz$ $dz$ ). The results show negligible (i.e., < ± 1%) error margin and sensitivity to $dt$ $dt$ and $dz$ $dz$ within the selected range. Multiple scenarios were then investigated using the model to understand the fate and transport of PFAS in both vadose and saturated zones to qualitatively verify the results.