Impact of a Hydrocarbon Surfactant on the Retention and Transport of Perfluorooctanoic Acid in Saturated and Unsaturated Porous Media

Abstract

The transport and retention behavior of perfluorooctanoic acid (PFOA) in the presence of a hydrocarbon surfactant under saturated and unsaturated conditions was investigated. Miscible-displacement transport experiments were conducted at different PFOA and sodium dodecyl sulfate (SDS) input ratios to determine the impact of SDS on PFOA adsorption at solid–water and air–water interfaces. A numerical flow and transport model was employed to simulate the experiments. The PFOA breakthrough curves for unsaturated conditions exhibited greater retardation compared to those for saturated conditions in all cases, owing to air–water interfacial adsorption. The retardation factor for PFOA with a low concentration of SDS (PFOA–SDS ratio of 10:1) was similar to that for PFOA without SDS under unsaturated conditions. Conversely, retardation was greater in the presence of higher levels of SDS (1:1 and 1:10) with retardation factors increasing from 2.4 to 2.9 and 3.6 under unsaturated conditions due to enhanced adsorption at the solid–water and air–water interfaces. The low concentration of SDS had no measurable impact on PFOA air–water interfacial adsorption coefficients (K ia) determined from the transport experiments. The presence of SDS at the higher PFOA–SDS concentration ratios increased the surface activity of PFOA, with transport-determined K ia values increased by 27 and 139%, respectively. The model provided very good independently predicted simulations of the measured breakthrough curves and showed that PFOA and SDS experienced various degrees of differential transport during the experiments. These results have implications for the characterization and modeling of poly-fluoroalkyl substances (PFAS) migration potential at sites wherein PFAS and hydrocarbon surfactants co-occur.

Estimation of Transport Parameters of Perfluoroalkyl Acids (PFAAs) in Unsaturated Porous Media: Critical Experimental and Modeling Improvements

“…Several of the CD method studies also indicate some degree of solid-phase partitioning. ,,,,, The competition between solid-phase sorption and air–water interfacial sorption is another possible reason why drainage-based studies consistently observe lower K ia values than equilibrium values predicted by the Freundlich model. Competitive sorption will need to be considered for field sites, where the presence of organic matter, , nonaqueous phase liquids (NAPLs), , solid sorbents, − and competing sorbates ,, could cause a reduction in the equilibrium partitioning of PFAAs to the air–water interface.…”

Retention of PFOS and PFOA Mixtures by Trapped Gas Bubbles in Porous Media

“…42,47−49 PFAS retention at air− water interfaces at these higher concentrations may be less than at lower concentrations, depending on the sensitivity of the air−water partitioning coefficient to PFAS concentration and its applicability at lower concentrations. 24,27,29 Each experiment consisted of five steps (illustrated in Figure S1). First, the nonreactive tracer was pumped through the water-saturated sand pack.…”

“…PFAS partition to air–water interfaces because of their surfactant properties. ,, The extent of partitioning is proportional to the air–water interfacial area, which generally increases with decreasing water saturation. , Previous studies conducted using PFOS and PFOA over a range of water saturations have shown that 50–80% of total retention in sand can be attributed to the air–water interface. , Air–water interfacial adsorption has also been shown to depend on ionic strength of the background solution, chain length, functional headgroup, and PFAS concentration. − Although some studies have used batch experiments or surface tension measurements to investigate air–water adsorption, recent studies have focused on transport experiments. ,,− These transport experiments have demonstrated less retention than predicted using a Freundlich isotherm (rather than a Langmuir isotherm), particularly for PFOA, and that the discrepancy between predicted and measured retention increases with decreasing PFAS concentration …”

Per‐ and Polyfluoroalkyl Substances (PFAS) in Subsurface Environments: Occurrence, Fate, Transport, and Research Prospect

“…SDS refers to sodium dodecyl sulfate. The multi‐process mass‐transfer models, including Brusseau 2020 (a–b) (Brusseau, 2020), Brusseau 2021 (c–d) (Brusseau et al., 2021) (Guo et al., 2020), and (e–f) (Ji et al., 2021) can describe the transport behaviors of PFAS under saturated and saturated porous media. Copyrights: 2020 Elsevier, 2021 Elsevier, and 2021 American Chemical Society (reproduction with permission).…”