Heavy-Metal Ions\nControl on PFAS Adsorption on Goethite\nin Aquatic Systems

Per- and polyfluoroalkyl substances (PFAS) are ubiquitous\nenvironmental\ncontaminants that often co-occur with heavy metals. Despite their\nprevalence, the mobility of PFAS in complex, multicomponent systems,\nparticularly at the molecular scale, remains poorly understood. The\nvast diversity of PFAS and their low concentrations alongside anthropogenic\nand natural substances underscore the need for integrating mechanistic\ninsights into the sorption models. This study explores the influence\nof metal cations (Cu(II), Cd(II), and Fe(II)) on the adsorption of\nfour common PFAS (PFOA, PFOS, PFDA, and GenX) onto goethite (α-FeOOH),\na common iron (oxyhydr)oxide in both aquatic and terrestrial environments.\nPFAS adsorption was highly dependent on the PFAS type, pH, and metal\nion concentration, with a surface complexation model effectively predicting\nthese interactions. Cu(II) and Cd(II) enhanced PFOS and PFDA adsorption\nvia ternary complexation while slightly reducing PFOA and GenX adsorption.\nUnder anoxic conditions, Fe(II) significantly increased the adsorption\nof all PFAS, showing reactivity greater than those of Cu(II) and Cd(II).\nAdditionally, natural organic matter increased PFAS mobility, although\nmetal cations in groundwater may counteract this by enhancing PFAS\nretention. These findings highlight the key role of metal cations\nin PFAS transport and offer critical insights for predicting PFAS\nbehavior at oxic–anoxic environmental interfaces.