Bench-scale experiments were performed to assess uptake of poly- and perfluoroalkyl substances (PFAS), both single compounds and mixtures, at the air–water interface. The focus was on evaluating uptake at field-relevant PFAS concentrations (<2 × 10–4 mol m–3 or 0.1 mg L–1), assessing the impacts of various PFAS mixtures, and quantifying the impacts of background NaCl concentrations. Both interfacial tension measurements and direct quantification of PFAS mass sorbed at the air–water interface in water films were used to evaluate PFAS interfacial partitioning. Results showed that a Freundlich-based model, rather than a Langmuir-based model, described perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) interfacial uptake. At lower and field-relevant PFOS and PFOA concentrations, the Langmuir-based model underpredicted interfacial uptake by up to several orders of magnitude. The interfacial partition coefficient, k aw, increased as PFAS concentrations decreased. Results also showed that the interfacial tension and interfacial uptake of PFAS mixtures were (within a factor of 2) predicted based on the single solute systems assuming ideal dilute behavior. Furthermore, the addition of NaCl at concentrations of up to 0.01 M increased PFOS uptake by less than a factor of 2 at field-relevant PFOS concentrations. The results presented herein have important implications for PFAS migration in unsaturated soils as well as for remedial technologies that rely on PFAS interfacial sorption, particularly at field-relevant PFAS concentrations.

Rapid small-scale column tests (RSSCTs) are often employed in laboratory testing to determine contaminant treatment effectiveness by anion-exchange resins (AERs) or granular activated carbons (GACs) in a short timeframe compared to pilot testing. RSSCTs are performed by reducing the AER or GAC particle size via grinding, allowing for increased mass transfer and water throughput. However, the scaling factors between ground and unground resins for perfluoroalkyl acids (PFAAs), specifically for waters with elevated natural organic carbon levels, remain uncertain. Bench-scale column experiments were performed to evaluate the applicability of employing RSSCTs for removal of PFAAs from groundwater with elevated naturally occurring organic carbon using ground and unground AERs and GACs. For both the AERs and the GAC, PFAA migration through the columns was well-described by the Thomas model. A constant diffusivity model was appropriate for describing transport. For GAC and one of the AERs tested, the inclusion of near-surface adsorption was accounted for by scaling the equilibrium sorption capacity to r –0.5.