Critical role of dissolved and particulate phosphorus in controlling the fate of polystyrene nanoplastics in porous media

The different forms of phosphorus (P) (dissolved P (inorganic P (orthophosphate, PO₄) and organic P (phytic acid, PA)) and particulate P (nanohydroxyapatite, nHAP)) influenced the transport and fate of nanoplastics. This study investigates the fate of polystyrene nanoplastics (PS) in porous media under the individual and combined effects of different forms of P. It was shown that under the effect of different P forms, the migration rate of PS was: PS-PA + nHAP > PS-PA > PS-PO₄ > PS > PS-PO₄ + nHAP > PS-nHAP, which indicated that PO₄ alleviated the inhibitory effect of nHAP on the transport of PS, while coexistence of PA and nHAP produced significant synergistic facilitation effect on the transport of PS. The results of various characterization techniques, classical or extended Derjaguinee-Landauee-Verweyee-Overbeek (DLVO/EDLVO) theory, and density function theory (DFT) calculations revealed that the adsorption of PO₄ increased the negative electronegativity of the heterogeneous aggregates of PS and nHAP, alleviating the inhibitory effect of nHAP on the transport of PS by enhancing electrostatic repulsion. And PA was adsorbed on the surfaces of nHAP and PS, respectively, increasing the electrostatic interaction and steric effect between PS and the media, which synergistically promoted the transport of PS. Among them, the steric effect between PS and nHAP after adsorption of PA was the main factor for synergistic promoted PS transport. This study provides theoretical support for the development of predictive models for nanoplastic transport in phosphorus-rich environments and risk management strategies.