Polystyrene nanoplastics as PFAS carriers and their interactions with zwitterionic phospholipid membranes

The co-occurrence of per- and polyfluoroalkyl substances (PFAS) and nanoplastics (NPs) poses a synergistic threat to environmental and human health, yet the molecular mechanisms governing PFAS-NP complexation and membrane interactions remain unclear. Using atomistic molecular dynamics simulations, we investigated the adsorption of neutral polytetrafluoroethylene (PTFE) and anionic perfluorinated compounds (perfluorooctanoic acid, PFOA, and perfluorooctanesulfonic acid, PFOS) on polystyrene NPs (3.1 and 6.7 nm) and their interactions with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) membranes. Polystyrene NPs act as carriers, transporting PFAS molecules to the lipid/water interface, where PFAS attachment modifies NP interfacial behavior. PFAS adsorption on the NP surface is driven by hydrophobic and fluorophilic interactions. Neutral PTFE exhibits inhomogeneous, partially penetrated adsorption, while anionic PFOS and PFOA form relatively homogeneous adsorption layers due to electrostatic repulsion among their anionic headgroups. In the POPC membrane, the exposed trimethylammonium groups with non-hydrogen-bonded water prevail over phosphate groups with hydrogen-bonded water, reducing the zwitterionic membrane's resistance to NP adsorption. Consequently, surface hydration hinders the attachment of neutral bare and PTFE-coated NPs, while anionic PFOS-coated NPs rapidly adsorb via electrostatic attraction to the positively charged POPC trimethylammonium groups, overcoming the hydration barrier. PFOA-coated NPs adsorb transiently; however, PFOA detachment exposes the NP core, weakening NP-lipid interactions and leading to NP desorption and insertion of detached PFOA molecules. The addition of 0.1 M KCl does not significantly alter the interfacial behavior of small PFAS-NP complexes.