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Adsorption behaviors and mechanisms of azithromycin on degradable and non-degradable microplastics aged with UV/sodium percarbonate
Summary
Scientists found that when microplastics (both regular plastic and "eco-friendly" biodegradable plastic) get weathered by sunlight and cleaning chemicals used in wastewater treatment, their surfaces become rougher and chemically altered, making them up to 4 times better at soaking up azithromycin, a common antibiotic that surged in use during COVID-19. This matters because these antibiotic-loaded microplastics could act as carriers, potentially transporting drugs through water systems and the environment in ways that aren't fully understood yet, including possibly contributing to antibiotic resistance or human exposure down the line.
The frequent detection of azithromycin (AZI) in wastewater treatment plants (WWTPs) during the COVID-19 has raised concerns. However, the interaction between degradable microplastics (MPs) and AZI under ultraviolet/sodium percarbonate (UV/SPC) influence remains unclear. This study investigated the aging of polylactic acid (PLA) and polyethylene (PE) under UV/SPC and their subsequent adsorption behaviors and mechanisms towards AZI. SEM results indicated that UV/SPC reduced the average particle size and increased the surface roughness of both PE and PLA. FTIR and XPS analyses revealed that UV/SPC broke C H bonds on the PE surface, forming C O and C O bonds, while in PLA, C O bonds decreased and C O bonds increased. The adsorption capacities of aged PE (APE) and PLA (APLA) for AZI increased to 3.68 and 5.39 mg/g, compared to 1.44 and 1.28 mg/g for pristine MPs. Adsorption kinetics indicated that chemical adsorption dominated the process for APE and APLA. The intra-particle diffusion model suggested that aging primarily enhanced the surface adsorption process. Thermodynamic analyses indicated homogeneous monolayer adsorption onto APE and APLA. Optimal adsorption occurred at pH 5, while Pb, humic acid, and Na⁺ inhibited adsorption. FTIR analysis indicated that AZI adsorption onto APE primarily involved C H, C O, and C O bonds, while adsorption onto APLA primarily involved O-C=O, C H, and C O bonds. XPS analysis revealed that AZI adsorption onto APE mainly involved C H and C O bonds, while adsorption onto APLA mainly involved O-C=O bond. This study provided a theoretical basis for understanding the interactions among traditional PE, biodegradable PLA, and AZI under UV/SPC treatment in WWTPs.