Deciphering the interaction of sulfamethoxazole with biodegradable versus conventional, virgin versus aged microplastics in aquatic environment.

Co-exposure of pharmaceuticals and microplastics (MPs) significantly exacerbates the aquatic environmental pollution issue. While MPs are identified as carriers of pollutants, research on the adsorption behaviors of biodegradable and conventional MPs to pharmaceuticals limited. The study investigated the adsorption behavior of conventional MPs (polystyrene and polyethylene terephthalate), biodegradable MPs (polylactic acid (PLA) and polybutylene succinate (PBS) for sulfamethoxazole (SMX). Meanwhile, changes in physical-chemical properties, including morphology, crystallinity, hydrophobicity and structures of MPs after aging (e.g., ultraviolet treatment) were investigated. Results exhibited that the oxygen-containing functional groups of MPs surface increased after ultraviolet treatment and enhanced the adsorption capacity for SMX, except for PLA. PLA exhibits the highest adsorption capacity, primarily due to its higher hydrophobicity and larger pore size. In contrast, PBS shows the lowest adsorption affinity for SMX because of its hydrophilicity and small pore size. The adsorption capacity of degradable MPs after aging is greater than that of non-degradable MPs. Electrostatic interaction and hydrophobic interaction are the main mechanisms of adsorption of virgin MPs, while hydrogen bond interaction and electrostatic interaction are the primary adsorption mechanisms for aged MPs. These results contribute to understanding the co-transport and migration of SMX and MPs in the environment, and furnish the necessary data for their ecological risk assessment.