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Microwave-activated oxidation to replicate polyethylene plastic environmental fragmentation and contaminant release pathways
Summary
Scientists used a lab technique to fast-forward the sun-and-weather aging process that breaks down plastic, revealing that as plastic degrades, it doesn't just crumble into tiny particles—it also releases metals like titanium, chromium, iron, and calcium that were mixed into the plastic during manufacturing. This matters because it shows that aging plastic is a two-in-one health concern: it sheds both physical microplastic bits and hidden chemical additives at the same time, meaning current safety assessments that focus on just one or the other may be underestimating the full exposure risk to people and the environment.
The environmental degradation of polyethylene (PE) plastic is commonly described as a slow fragmentation process, generated by radical oxidation induced by sunlight, followed by gradual release of additives. Here, we challenge this view by applying a microwave-activated hydrogen peroxide (MW/H₂O₂) system able to reproduce key oxidative signatures observed during polyethylene weathering and allows study of particle release and additive release. We show that micro- and nanoplastics form concurrently, driven by early oxidative embrittlement and the development of surface cracks linked to structural heterogeneity. ATR-FTIR and depth-resolved O-PTIR spectroscopy reveal pronounced chemical transformations at the PE surface (including hydroxyl, and carbonyl groups formation) that trigger crystallinity changes, plastic swelling, and enhanced susceptibility to mechanical fracture. Using multimodal chemical analysis (µ-XRF, ICP-MS), we reveal selective migration of metallic additives (Ti, Cr, Fe, Ca), with surface enrichment directly correlated to the oxidation state of PE. Correlative analysis demonstrates that additive migration is promoted by surface oxidation and microstructural weakening, with Fick law modeling yielding diffusion coefficients up to 1.4 × 10⁻ 11 m² s⁻¹. These results provide mechanistic insight into how aged plastics act as dynamic vectors for particulate and chemical contaminants, highlighting the need to integrate additive release into environmental risk assessments.