Per- and polyfluoroalkyl substances-driven enhancement of colloid-facilitated contaminant transport in groundwater.

Per- and polyfluoroalkyl substances (PFAS) are widely recognized soil and groundwater contaminants of global concerns. Beyond directly compromising groundwater quality, PFAS may alter the fate and transport of coexisting contaminants, posing additional ecological and human health risks. In this study, we demonstrate that PFAS elevate the risk of colloid-facilitated contaminant transport in groundwater. Specifically, perfluorooctane sulfonate (PFOS), one of the most commonly detected PFAS in groundwater, increases the mobility of three soil colloids (Entisol, Inceptisol, and Mollisol), thereby promoting the transport of decabromodiphenyl ether associated with the colloids. In contrast, perfluorooctanoic acid (PFOA), another commonly detected PFAS, has negligible impact on the co-transport of colloids and contaminants. Using quartz crystal microbalance with dissipation, atomic force microscopy, and molecular dynamics simulations, we show that despite the fact that PFOS and PFOA have very similar molecular structures, PFOS adsorbs more strongly to aquifer materials and forms aggregates on sand grains, thereby creating steric repulsion that inhibits the attachment of soil colloids. Our findings reveal a previously unrecognized risk associated with PFAS, particularly near point sources and spill sites wherein PFAS concentrations are high, and underscore the need for a deeper understanding of the structure-activity relationships governing PFAS interfacial processes.