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Accelerated Oxidative Aging of Microplastics and Its Effect on Copper Sorption Behavior
Summary
Scientists exposed common plastics (like those in water bottles and food containers) to harsh chemical treatments similar to those used in wastewater treatment plants, mimicking how microplastics age in the environment. Surprisingly, whether the plastic was "weathered" or fresh didn't change how much copper it could stick to and carry around—meaning aged microplastics are just as capable as new ones of ferrying metal contaminants into water supplies and potentially our bodies. This matters because it shows we can't assume that breaking down or aging microplastics makes them safer.
Microplastics (MPs) in wastewater treatment plants are exposed to oxidative conditions during disinfection and advanced oxidation processes (AOPs), which can alter morphology and surface chemistry and influence interactions with coexisting contaminants. Here, accelerated chemical oxidation was simulated using heat-activated potassium persulfate (K2S2O8) and sodium hypochlorite (NaOCl) to examine the oxidative aging of MPs made from polyethylene (PE), polyethylene terephthalate (PET), and polypropylene (PP). Changes in particle morphology and surface chemistry before and after oxidant treatment were characterized using scanning electron microscopy (SEM) for morphological analysis and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy for chemical characterization. Carbonyl formation, an indicator of polymer oxidation, was evaluated using the carbonyl index (CI). Both oxidants induced surface morphological defects and carbonyl functional groups in the MPs, with CI increasing with degradation time. The CI trends suggest that MP oxidation varies with polymer type and oxidant. The effect of oxidative aging on MP sorption capacity was also investigated using copper ions as a model inorganic constituent. Although oxidative aging introduced oxygen-containing functional groups, no statistically significant differences in copper sorption were observed between pristine and oxidized MPs, indicating that MPs can act as vectors for copper regardless of their degree of surface oxidation.