Effect of microplastics on the photodegradation of high-consumption drugs under simulated sunlight: The critical role of aging and reactive oxygen species

• Evaluation of PP, PLA, and PET MPs as photosensitizers for everyday drugs. • The complex mixture of selected drugs has never been investigated before. • Examination of the MP aging degree on the photodegradation of the targeted mixture. • Evaluation of ROS generated by MPs in the degradation process of the model drugs. The main aim of this study was to examine the effect of polypropylene (PP), poly(ethylene terephthalate) (PET), and poly(lactic acid) (PLA) microplastics (MPs) on the photolytic degradation of a mixture of seven commonly used pharmaceuticals under simulated solar irradiation (SSL). The target mixture included four common antibiotics (metronidazole, trimethoprim, indomethacin, isoniazid), two non-steroidal anti-inflammatory drugs (diclofenac, ketoprofen), and one antihypertensive drug (valsartan). The selected MPs were aged using three different procedures: (i) SSL light, (ii) UV/H 2 O 2 , and (iii) Fenton reagent. The effect of MPs mass concentration was examined using only the pristine MPs, while the aging effect was evaluated for the three different aged MPs for each polymer type. The results demonstrated that the presence of MPs generally accelerates the photolytic degradation of the drugs, and increasing their concentration further enhances the reaction rate. Aging of the MPs also appeared to enhance the photodegradation of the selected pharmaceuticals. Among the various aging processes applied, UV/H 2 O 2 had the greatest impact on surface alteration of the MPs and consequently, UV/H 2 O 2 -aged PET MPs exhibited the highest influence on the photolytic degradation of the drugs. To gain a deeper understanding of the mechanism behind the photolytic degradation of the examined pharmaceuticals, a systematic characterization of pristine and aged MPs was conducted using Fourier transformed infrared spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), and Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) techniques, which detected the formation of oxygen containing groups on the MPs’ surfaces. Finally, scavenger experiments were also conducted to explore the formation and role of reactive oxygen species (singlet oxygen, superoxide anions, and hydroxyl radicals) in the degradation of the target compounds.