Landfill aging enhances chlorinated organophosphate adsorption on microplastics: Mechanistic insights and elevated risks for biodegradable polymers.

Landfill aging generates microplastics (MPs) that migrate via leachate and interact with chlorinated organophosphate flame retardants (Cl-OPFRs). However, the adsorption mechanisms under landfill conditions remain poorly understood. This study combined experimental batch adsorption with density functional theory (DFT) calculations, frontier molecular orbital (FMO) analysis, and interaction region indicator (IRI) to elucidate the adsorption behavior of Cl-OPFRs onto both petroleum-based MPs (PMPs) and biodegradable MPs (BMPs) before and after simulated mechanical-thermal aging. Aging induced 28-45% particle size reduction and selective surface oxidation of PMPs, while BMPs underwent pronounced depolymerization and fragmentation. These physicochemical changes significantly enhanced the adsorption capacity of all MPs for Cl-OPFRs. Notably, aged BMPs exhibited substantially greater increases (up to 27.63%) compared to PMPs (up to 13.30%). Mechanistically, van der Waals forces, halogen bonding, and π-H interactions governed adsorption onto polar MPs, while hydrophobic interactions dominated for non-polar polyethylene. Furthermore, aging elevated the ecological risk quotient of MP-Cl-OPFR complexes, particularly for BMPs and more hydrophobic Cl-OPFRs, with risk increases reaching 24.53%. These findings demonstrate that landfill aging critically enhances the vector role of MPs (especially biodegradable types) for Cl-OPFRs, offering essential mechanistic insights for improved risk assessment and management strategies in landfill-affected ecosystems.