Sulfur-Containing Persistent Free Radicals and Reactive Species on Photoaged Microplastics: Identification and the Formation Mechanism

Abstract

The elemental composition may affect the persistent free radical (PFR) and reactive species (RS) formation associated with photoaging microplastics; however, a relevant study is still lacking. This study systematically investigated the formation, evolution, and types of PFRs and RS on sulfur-containing microplastics (S-MPs) under simulated sunlight. Electron paramagnetic resonance detection and power saturation curve analysis isolated three different PFRs on each photoaging poly(phenylene sulfide) (PPS) and polysulfone (PSF). Combining the results of characterization and density functional theory calculation, these observed PFRs on the irradiated S-MPs were classified as oxygencentered radicals with an adjacent S atom (namely, thio−oxygen radicals), oxygen-centered and sulfur-centered radicals, where the thio−oxygen radicals on PPS were benzenethiol-like radicals, and oxygen-centered radicals and sulfur-centered radicals on PSF that were identified as benzenesulfonic-like radicals and phenyl sulfonyl-like radicals, respectively. Moreover, potential precursor molecule fragments of PFRs on the photoaging S-MPs, including p-toluenesulfinic acid and benzenesulfonic acid, were detected by pyrolysisgas chromatography/mass spectrometry and liquid chromatography-mass spectrometry. Interestingly, reactive sulfur species (SO 3 •−) was also observed on irradiated S-MPs in addition to reactive oxygen species, which was mainly derived from the reaction of • OH and sulfonyl radicals. These results have implications for assessing the potential risks of atmospheric S-MPs.

Unrecognized Role of Organic Acid in Natural Attenuation of Pollutants by Mackinawite (FeS): The Significance of Carbon-Center Free Radicals

“…To identify the ROS potentially produced, the EPR technique was applied using DMPO as a spin-trapping agent. − As displayed in Figure a,b, the variable EPR spectral features indicate that various types and abundances of radicals are produced in both pure FeS and FeS/OA systems. In the pure OA system, no signals were detected by EPR, which emphasized that OA alone cannot contribute to the production of ROS (Figure S12).…”

Photoaged Tire Wear Particles Leading to the Oxidative Damage on Earthworms (Eisenia fetida) by Disrupting the Antioxidant Defense System: The Definitive Role of Environmental Free Radicals

“…The distance between the lamp and the samples was 150 mm. This lamp consistently provided a UVA intensity of 4.82 ± 0.32 mW/cm 2 , which is comparable to the intensity of natural sunlight (4.36 mW/cm 2 ) . The reactor temperature was maintained at 20 °C by using a temperature control system during the photoaging process.…”

“…ECOSAR software (Version 2.2) was used to predict the lethal toxicity of each organics from the leachate to the earthworm. The EPFRs, hydroxyl radicals ( • OH), and superoxide radicals (O 2 •– ) of TWP samples were detected by electron paramagnetic resonance (EPR, Bruker EMXmicro-6/1/P/L, Karlsruhe, Germany). , The details for the methods of the above characterizations are provided in Text S3 and S5–S8.…”

“…This lamp consistently provided a UVA intensity of 4.82 ± 0.32 mW/cm 2 , which is comparable to the intensity of natural sunlight (4.36 mW/cm 2 ). 28 The reactor temperature was maintained at 20 °C by using a temperature control system during the photoaging process. To ensure uniform illumination, the TWP samples were flipped every 8 h. On days 5, 10, 15, 20, 25, and 30 of irradiation, samples were removed for EPFRs and reactive oxidative species (ROS) analyses.…”

“…) of TWP samples were detected by electron paramagnetic resonance (EPR, Bruker EMXmicro-6/1/P/L, Karlsruhe, Germany). 28,29 The details for the methods of the above characterizations are provided in Text S3 and S5−S8.…”