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Photochemistry of microplastics-derived dissolved organic matter: Reactive species generation and organic pollutant degradation
Summary
Researchers investigated how dissolved organic matter released from degrading polystyrene and PVC microplastics behaves when exposed to sunlight in water. They found that sunlight breaks down the aromatic compounds in this plastic-derived material and generates reactive chemical species, though at lower rates than natural organic matter. Despite this, these reactive species significantly accelerated the breakdown of co-existing pollutants, suggesting that degrading microplastics may act as unexpected natural catalysts in aquatic environments.
Dissolved organic matter (DOM) originating from microplastics (MPs-DOM) is increasingly recognized as a substantial component of aquatic DOM. The photochemistry of MPs-DOM, essential for understanding its environmental fate and impacts, remains largely unexplored. This study investigates the photochemical behaviors of MPs-DOM derived from two common plastics: polystyrene (PS) and polyvinyl chloride (PVC), which represent aromatic and aliphatic plastics, respectively. Spectral and high-resolution mass spectrometry analyses demonstrated that photoreactions preferentially targeted poly-aromatic compounds within the MPs-DOM, leading to degradation products that predominantly form N-aliphatic/lipid-like substances. This transformation is characterized by decreased aromaticity and unsaturation. Additionally, irradiation of MPs-DOM generated reactive species (RS), including triplet intermediates (DOM*) and singlet oxygen (O), with apparent quantum yields of 0.06-0.16 % and 0.16-0.35 %, respectively-values considerably lower than those for conventional DOM (1.19-1.56 % for DOM* and 1.34-1.90 % for O). Despite this, the RS generated from MPs-DOM significantly enhance the degradation of coexisting organic pollutants, such as antibiotic resistance genes (ARGs). The findings shed light on the photoinduced transformation of MPs-DOM and suggest that MPs-DOM functions as a natural photocatalyst, mediating redox reactions of pollutants in sunlit aquatic settings. This highlights its previously underestimated role in natural attenuation and aquatic photochemistry.
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