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Sulfur-Containing Persistent Free Radicals and Reactive Species on Photoaged Microplastics: Identification and the Formation Mechanism
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Researchers identified sulfur-containing persistent free radicals and reactive species on photoaged microplastics for the first time, revealing that sulfur in the polymer composition promotes radical formation during UV aging with implications for environmental toxicity.
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 oxygen-centered 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 pyrolysis-gas chromatography/mass spectrometry and liquid chromatography-mass spectrometry. Interestingly, reactive sulfur species (SO3•–) 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.
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This review examines how microplastics generate long-lasting free radicals as they age in the environment through exposure to sunlight and chemical reactions. These environmentally persistent free radicals (EPFRs) on aged microplastics can cause oxidative stress and damage to living cells, adding a previously underappreciated layer of toxicity beyond the physical harm caused by the plastic particles themselves.
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Aging Process of Microplastics in the Aquatic Environments: Aging Pathway, Characteristic Change, Compound Effect, and Environmentally Persistent Free Radicals Formation
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This review summarizes how microplastics age and transform in aquatic environments through oxidation, weathering, and fragmentation. Researchers documented changes in particle size, crystallinity, and surface chemistry during the aging process, and found that aged microplastics may interact synergistically with other environmental pollutants. The study also describes how photoaging generates environmentally persistent free radicals that could pose additional toxicity concerns.
Elucidating the role of overlooked environmentally persistent free radicals and reactive chlorine species on photoaged chlorine-containing microplastics: New insights into formation mechanisms and health risks
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Researchers investigated the formation of environmentally persistent free radicals and reactive chlorine species on photoaged chlorine-containing microplastics like PVC and PVDC. The study revealed previously overlooked chemical transformations during microplastic aging that may pose additional health risks beyond the physical presence of the plastic particles themselves.
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