Mechanistic insights into electrolyte-PFAS interfacial interactions through molecular simulations and experimental...

Understanding how electrolytes modulate the interfacial behavior of per- and polyfluoroalkyl substances (PFAS) is critical for predicting their environmental fate and guiding remediation strategies. In this study, we systematically investigated the surface activity and interfacial partitioning of four PFAS regulated in U.S. and European drinking water standards, along with a C4 PFAS, in the presence of eight inorganic salts representing diverse cationic and anionic identities. Surface tension results were modeled using the Szyszkowski equation, extended with mean ionic activity (a*) to unify electrolyte effects. This framework was found to effectively capture short-chain PFAS behavior, but parameter fitting for long-chain species produced highly variable values, reflecting ion-specific effects and model limitations. Multivariate analysis, including principal component analysis and clustering, revealed distinct patterns governed by PFAS chain length and ion type. Density functional theory simulations provided molecular-level insight, showing that cations modulate interfacial adsorption through electrostatic binding, orbital polarization, or co-localization effects depending on hydration properties and electronic structure. These findings highlight the limitations of conventional activity-based models for long-chain PFAS and underscore the need to incorporate specific ion effects into interfacial transport models. Our integrated experimental-computational framework advances mechanistic understanding of PFAS-electrolyte interactions and offers new perspectives on their air-water interfacial behavior. These findings have important environmental implications, as electrolyte composition in natural and engineered waters may significantly alter PFAS interfacial accumulation, transport, and aerosolization potential. Incorporating specific ion effects into predictive models may improve the assessment of PFAS fate in water treatment systems and contaminated aquatic environments.