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Photo-Aging of Microplastics and the Effects on the Environmental Behaviors of Organic Contaminants in Aquatic Environments

Professor Cheng Gu, School of the Environment, SKLPCRR

Multiple aging pathways in the aquatic environments and the underlying transformation mechanism were described for microplastics (MPs). The polystyrene and high-density polyethylene microplastics could be altered by heat-activated K2S2O8 and Fenton treatments, thus further improving the understanding of their long-term natural aging in aquatic environments. The active oxidizing species generated in advanced oxidation processes are generally free radicals, e.g., hydroxyl radical (OH•) for Fenton and OH•/SO4• − (sulfate radical anion) for persulfate, and their high redox potentials are likely to enhance the oxidation of microplastics. In our recent study, the photo-alteration was investigated for polyvinyl chloride microplastics (PVC-MPs), and the aging reaction could be facilitated in the presence of low-molecular-weight organic acid (LMWOA) and LMWOA-Fe (III) complex under simulated and natural sunlight irradiation and ambient conditions. The OH• generated from the photolysis of LMWOA or its ferric complexes played a dominant role in enhancing PVC-MP degradation. PVC-MP surface oxidation led to the increase of the specific surface area and affinity towards water, which would further enhance the adsorption of polar contaminants on PVC-MPs and thus increase the health risk of PVC-MPs on aquatic organisms. In addition to enhancing the sorption capacity for hydrophilic antibiotics, aged PVC-MPs exhibited great potential to accelerate the hydrolysis of cephalosporin pharmaceuticals, which could be ascribed to the interfacial hydrogen-bonding interactions between β-lactam antibiotics and oxygenated PVC-MPs. The intermolecular hydrogen-bonding force was able to lower the energy gap for the hydrolytic reaction of cephalosporin antibiotics. These researches shed light on the aging reaction of microplastics and the effects on the environmental behaviors of organic contaminants in aquatic environments.