Sorption of sulfamethoxazole onto six types of microplastics

Microplastics and sulfamethoxazole (SMX) are ubiquitous in aquatic environment. In this study, we investigated the sorption of SMX onto six types of microplastics (polyamide (PA), polyethylene (PE), polyethylene terephthalate (PET), polystyrene (PS), polyvinyl chloride (PVC) and polypropylene (PP)). The sorption rate and mass transfer steps of SMX was studied by using the phenomenological kinetics models. The effect of pH and salinity on SMX sorption was examined. The results showed that the sorption of SMX onto microplastics reached equilibrium within 16 h. The external mass transfer was the slowest sorption step. The linear and Freundlich isotherms fitted well the sorption equilibrium data. PA had the highest sorption capacity (2.36 mg g^-1 at SMX concentrations of 12 mg L^-1), with high distribution coefficient (K_d) value (284 L kg^-1). The K_d values of PE, PS, PET, PVC, and PP ranged from 22.2 to 30.9 L kg^-1. The sorption capacity of SMX decreased with increase of pH and salinity in the solution.