Co-transport of antimony with pristine/reduced PBAT microplastics in porous media: Insights into transport forms and interfacial interaction

Microplastics (MPs) and antimony (Sb), key components of electronic waste, pose an emerging environmental challenge through co-exposure in anaerobic subsurface environments, yet their co-transport mechanisms remain unclear. The adsorption and co-transport of Sb(V) in association with pristine and reduced polybutylene adipate terephthalate (PBAT), a representative biodegradable microplastic, were investigated through batch adsorption and column experiments under variable chemical conditions. The adsorption results indicate that reduction aging enhances the surface roughness and pore structure of PBAT, which provides more adsorption sites for Sb(V) and thereby increasing PBAT's sorption capacity for Sb(V). Co-transport results indicate that the lower mobility of PBATs compared with Sb(V) inhibits the mobility of Sb(V) by decreasing the transport of bound Sb(V). Conversely, Sb(V) increased the recovery rate of PBATs by 20.81–26.71% through the synergistic effect of stronger electrostatic repulsion mediated by bound Sb(V) and interfacial repulsion from free Sb(V). Furthermore, high ionic strength and divalent cations weaken intermolecular electrostatic repulsion through electrostatic shielding, thus inhibiting the co-transport of PBATs and Sb(V) in porous media. The retention of reduced PBAT and Sb(V) in porous media is promoted by low molecular weight organic acids, with effects dependent on acid type. These findings highlight the critical role of MPs properties and their affinity for Sb(V) in determining their distribution and fate in the subsurface.