Formation of Environmentally Persistent Free Radicals on Microplastics under Light Irradiation

• Published in: Environmental science & technology Vol. 53; no. 14; pp. 8177 - 8186
• Main Authors: Zhu, Kecheng, Jia, Hanzhong, Zhao, Song, Xia, Tianjiao, Guo, Xuetao, Wang, Tiecheng, Zhu, Lingyan
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 16.07.2019
• Subjects: Aging; Chain scission; cleavage (chemistry); Contaminants; Decay rate; Ecosystems; Electron paramagnetic resonance; electron paramagnetic resonance spectroscopy; environmental science; Fourier transforms; Free radicals; gel chromatography; Hazards; Infrared analysis; Infrared spectroscopy; Irradiation; Light irradiation; lighting; Liquid chromatography; Microplastics; NMR; Nuclear magnetic resonance; nuclear magnetic resonance spectroscopy; Organic chemistry; Phenol formaldehyde resins; Phenols; photoaging; Photoelectron spectroscopy; Photoelectrons; Plastic pollution; poly(vinyl chloride); Polyethylene; Polyethylenes; Polystyrene; Polystyrene resins; polystyrenes; Polyvinyl chloride; Reactive oxygen species; Reflectance; Resonance; Spectroscopy; Spectrum analysis; X ray photoelectron spectroscopy
• ISSN: 0013-936X; 1520-5851; 1520-5851
• DOI: 10.1021/acs.est.9b01474

Microplastics (MPs) are presumed to be inert during aging under ambient conditions. In this study, four types of virgin MPs, including polystyrene (PS), phenol-formaldehyde resin (PF), polyethylene (PE), and polyvinyl chloride (PVC), were aged under simulated solar light irradiation. Surprisingly, several environmentally persistent free radicals (EPFRs), which are considered to be a type of emerging contaminant, were detected on the irradiated PS and PF, rather than PE and PVC, by electron paramagnetic resonance (EPR) spectroscopy. Depending on the photoaging duration time, the characteristic g-factors of the EPFRs produced on PS and PF were 2.0044–2.0049 and 2.0043–2.0044, respectively. The generated EPFRs on PS and PF decayed rapidly at the initial stage and then slowly disappeared with the elapsed aging time. Analyses by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance (NMR), and gel permeation chromatography (GPC) suggested that MPs might experience chemical chain scission, O2/H2O addition, and EPFR formation under the light irradiation. Accompanying with the formation of EPFRs, reactive oxygen species, such as O2 •– and •OH, were also observed. The findings provide a novel insight to evaluate the potential hazards of MPs to organisms and ecosystems.