Abstract

Microplastics (MPs) have been detected in the hydrosphere, with hazardous implications in transporting coexisting water pollutants. Our knowledge about the interaction mechanisms that MPs establish with organic pollutants are still growing, which is essential to understand the adsorption properties of MPs and their relative stability with adsor-bates. Here, we used classical (force field methods) and ab-initio (density functional theory) computational chemistry tools to characterize the interaction mechanisms between Polystyrene-MPs (PS-MPs) and pharmaceuticals/personal care products (PPCPs). Adsorption conformations and energies, thermochemistry, binding, and energy decomposition analyses were performed to obtain the quantitative mechanistic information. Our results show that PS-MPs have per-manent dipoles, increasing the interaction with neutral PPCPs while repelling the charged pollutants; in all cases, a sta-ble physisorption takes place. Moreover, PS-MPs increase their solubility upon pollutant adsorption due to an increase in the dipole moment, increasing their co-transport ability in aqueous environments. The stability of the PS-MPs/ PPCPs complexes is further confirmed by thermochemical and molecular dynamics trajectory analysis as a function of temperature and pressure. The interaction mechanism of high pKa pollutants (pKa > 5) is due to a balanced contri-bution of electrostatic and dispersion forces, while the adsorption of low pKa pollutants (pKa 5) maximizes the elec-trostatic forces, and steric repulsion effects explain their relative lower adsorption stability. In this regard, several pairwise intermolecular interactions are recognized as a source of stabilization in the PS-MPs/PPCPs binding: hydro-gen bonding, pi-pi, O\\HMIDLINE HORIZONTAL ELLIPSIS pi, and C\\HMIDLINE HORIZONTAL ELLIPSIS pi, C\\ClMIDLINE HORIZONTAL ELLIPSISC\\H and C\\HMIDLINE HORIZONTAL ELLIPSISC\\H interactions. The ionic strength in solution slightly affects the adsorption stability of neutral PPCPs, while the sorption of charged pollutants is enhanced. This mechanistic information provides quantitative data for a better understanding of the interactions between organic pol-lutants and MPs, serving as valuable information for sorption/kinetic studies.