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Photoaging of Microplastics in the Presence of Minerals
Summary
Sunlight breaks down plastic litter into microplastics faster when it's mixed with natural minerals like clay found in coastal sand and mud, according to new research—meaning plastic pollution on beaches and shorelines may fragment into smaller pieces more quickly than lab tests in plain water suggest. This matters because smaller microplastic fragments are more likely to be ingested by marine life and eventually end up in the food we eat, so understanding how coastal environments speed up this breakdown helps scientists better predict and manage plastic pollution's real-world impact.
This work investigated the photoaging behaviors of polyethylene (PE) and polypropylene (PP) microplastics in the presence of natural minerals, using a simulated intertidal environment as a model. The results showed that UV radiation promoted microplastics oxidation and generated oxygen-containing polar groups. Due to the lower dissociation energy of tertiary carbon atoms in the polymer backbone, the degree of photo-oxidation of PP was higher than that of PE (e.g., the carbonyl indices in the UV+clay group were 7.70 and 0.54, respectively). Furthermore, natural minerals adsorbed onto microplastics surfaces to form a mineral-plastic composite layer, in particular, clay minerals specifically acted as the primary promoter of oxidation, whereas the effect of sand was less dramatic. This indicates that microplastics degradation in realistic mineral-rich coastal environments is more severe than in bulk water. This study revealed the accelerated aging mechanism driven by environmental minerals, providing theoretical support for the scientific management of plastic pollution in complex marine systems.