Predicting Interfacial Tension and Adsorption at Fluid–Fluid Interfaces for Mixtures of PFAS and/or Hydrocarbon Surfactants

Abstract

Many per- and polyfluoroalkyl substances (PFAS) are surface-active and adsorb at fluid–fluid interfaces. The interfacial adsorption controls PFAS transport in multiple environmental systems, including leaching through soils, accumulation in aerosols, and treatment methods such as foam fractionation. Most PFAS contamination sites comprise mixtures of PFAS as well as hydrocarbon surfactants, which complicates their adsorption behaviors. We present a mathematical model for predicting interfacial tension and adsorption at fluid–fluid interfaces for multicomponent PFAS and hydrocarbon surfactants. The model is derived from simplifying a prior advanced thermodynamic-based model and applies to nonionic and ionic mixtures of the same charge sign with swamping electrolytes. The only required model inputs are the single-component Szyszkowski parameters obtained for the individual components. We validate the model using literature interfacial tension data of air–water and NAPL (non-aqueous phase liquid)–water interfaces covering a wide range of multicomponent PFAS and hydrocarbon surfactants. Application of the model to representative porewater PFAS concentrations in the vadose zone suggests competitive adsorption can significantly reduce PFAS retention (up to 7 times) at some highly contaminated sites. The multicomponent model can be readily incorporated into transport models to simulate the migration of mixtures of PFAS and/or hydrocarbon surfactants in the environment.

Impact of Variable Water Chemistry on PFOS-Goethite Interactions: Experimental Evidence and Surface Complexation Modeling

“…Perfluorooctanesulfonate (PFOS) is a perfluorinated surfactant containing a fluorinated backbone with multiple carbon–fluorine bonds attached to a sulfonate headgroup. It was manufactured for decades and nowadays, even if its production has been ceased in most countries, is present at elevated concentrations in diverse environmental matrices, such as soil and sediments, − surface waters, , seawater, , and groundwater. − For instance, high PFOS concentrations, ranging from μg/L up to mg/L, have been measured in groundwater source zones and plumes, which were transported downgradient from hot-spot contaminated sites such as fire-training areas and manufacturing plants. − Given the severe toxic effects associated with PFOS exposure − and the mobility of this compound across different environmental compartments, − understanding the factors controlling PFOS fate and transport has become an issue of compelling interest and concern.…”

Anomalous Adsorption of PFAS at the Thin‐Water‐Film Air‐Water Interface in Water‐Unsaturated Porous Media

“…(2021) has an impurity of 4%. The uncertainties in the measured surface tension data due to small differences in different experiments (despite that they have the same overall conditions) are discussed in prior studies (e.g., Guo et al., 2023). The fitted parameters K 1 , K 2 , and Γ m are summarized in Table 1.…”

The Dynamics of Per- and Polyfluoroalkyl Substances (PFAS) at Interfaces in Porous Media: A Computational Roadmap from Nanoscale Molecular Dynamics Simulation to Macroscale Modeling

“…Hence, the resulting Darcy models in the literature are highly dependent on the conditions of the laboratory, pilot, and field studies to characterize the transport phenomena. As PFAS molecules show complex behavior at the nanoscale, any Darcy scale model derived based on existing data sets and measurements may produce misleading information in variant cases. ,, For instance, a very common simplifying assumption used in Darcy scale models is that intermolecular interactions are negligible at fluid–fluid interfaces. , Such an assumption is usually justified through an empirical relationship between surface excess and the bulk solution concentration of PFAS . However, it is known that surface active compounds (experimental data only available for non-PFAS long-chain hydrocarbon surfactants) at fluid–fluid interfaces behave uniquely and often show thermodynamically counterintuitive behavior during mass transfer. ,, Such information cannot be captured through the macroscale experiments performed to build an empirical relationship.…”

“… 15 , 18 , 56 For instance, a very common simplifying assumption used in Darcy scale models is that intermolecular interactions are negligible at fluid–fluid interfaces. 67 , 68 Such an assumption is usually justified through an empirical relationship between surface excess and the bulk solution concentration of PFAS. 13 However, it is known that surface active compounds (experimental data only available for non-PFAS long-chain hydrocarbon surfactants) at fluid–fluid interfaces behave uniquely and often show thermodynamically counterintuitive behavior during mass transfer.…”