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Molecular characteristics and plastic additives in dissolved organic matter derived from polystyrene microplastics: Effects of cumulative irradiation and microplastic concentrations
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This study investigated how ultraviolet light breaks down polystyrene microplastics and releases dissolved organic matter, including plastic additives, into the surrounding water. Greater UV exposure produced more complex chemical mixtures with higher levels of potentially toxic compounds. The findings are important because sunlight-driven breakdown of microplastics in the environment may release harmful chemicals into water sources that people use for drinking and recreation.
Microplastic-derived dissolved organic matter (MP-DOM), released during ultraviolet-induced aging of microplastics (MPs), has emerged as a critical yet underexplored topic regarding the environmental impacts of MPs. However, the effects of irradiation intensity on the release and molecular diversity of MP-DOM, including plastic additives, remain poorly understood. In this study, the photoaging processes of polystyrene MPs (PS-MPs) were simulated under varying cumulative irradiation (irradiation intensity × irradiation duration) and PS-MPs concentrations (1 - 5 g/L). The PS-derived DOM (PS-DOM) was characterized using fluorescence spectroscopy, Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS), and liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS). After 21 days of irradiation, the amount of leached PS-DOM ranged from 7.76 to 39.40 mg-C/g. Cumulative irradiation significantly accelerated PS-MPs aging and PS-DOM leaching (p < 0.001). Initially, these processes proceeded slowly until the cumulative irradiation exceeded 75 kWh/m. Beyond this threshold, PS-MPs exhibited substantial size reduction, increased oxidation, and enhanced PS-DOM leaching. FT-ICR MS analysis revealed that PS-DOM contained 30.1 %-31.8 % unique components compared to natural organic matter, with greater degradability at lower PS-MPs concentrations. Furthermore, LC-HRMS identified 13 oxidation products and 25 plastic additives in PS-DOM, with their amounts decreasing as PS-MPs concentrations increased, from 17.05 to 3.24 mg/g and 4.88 to 1.85 mg/g, respectively. Notably, lower PS-MPs concentrations resulted in greater cumulative irradiation per unit mass, intensifying PS-DOM leaching, enhancing degradability, and increasing plastic additives release. This study highlights the environmental implications of per unit cumulative irradiation on MP-DOM leaching and its molecular composition, providing insights into its ecological risks and potential impacts on aquatic systems.
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