Aging dominated effects of environmental microplastics on the sorption and toxic potential of typical pharmaceutical

Co-occurrence of pharmaceuticals and microplastics (MPs) can induce the combined toxicity, causing high risks to aquatic ecosystems. The interactions among co-occurring pollutants are important for their accurately risk assessment, but understanding on their interactions remains limited, especially aged MPs (A-MPs). Therefore, this study focused on sorption behaviors of typical pharmaceuticals (naproxen (NAP), bezafibrate (BZF), and sulfamethoxazole (SMX)) in three MPs before and after aging (polystyrene (PS), polyethylene terephthalates (PET), and polyethene (PE)), and the combined toxicity was also explored. Results showed that aged MPs have 24.3-131.1 % higher sorption of pharmaceuticals than virgin MPs, with capacity closely related to their types. Specifically, aged PET, aged PS, and aged PE MPs present the largest sorption for NAP (2.037 mg g^-1), BZF (2.877 mg g^-1), and SMX (2.118 mg g^-1) in pure water, respectively (pH = 7.0, T = 25 °C). Site energy distribution analysis revealed that π-π interactions contribute a major for sorption of NAP and BZF by MPs, whereas hydrogen bonding mainly contributes for sorption of SMX. Characterization and theoretical calculations verified the results, indicating aging promotes π-π interactions between A-MPs and NAP or BZF, but enhances the hydrogen bonds between A-MPs and SMX and thus resulting a decreased toxicity of SMX on typical algae Dunaliella salina. These findings provide deeper insights on the regulating of real MPs on pharmaceutical risks in aquatic environment.