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Kinetic study of microplastic reactivity with hydroxyl radicals: Insights into photochemical fate and transformation products
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Sunlight and natural chemical reactions in water can slowly break down common plastics like polyethylene and polypropylene (found in bags, bottles, and packaging), but this process also creates new byproducts, including smaller plastic fragments and other chemical compounds. This matters because it shows that microplastics don't just sit unchanged in the environment—they transform into other substances over time, and scientists still need to figure out whether these breakdown products are more or less harmful to human health than the original plastic.
Plastic pollution in the form of microplastics (MPs) poses a significant environmental threat, due to the widespread dispersion and persistence of these materials in aquatic ecosystems. This study investigates the reactivity of polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC) MPs with hydroxyl radicals (HO • ) through a kinetic competition method, using sodium benzoate (NaBz) as a reference compound with selective HO • reactivity. Photosensitization by NaNO 3 under UV-B irradiation was employed as known HO • source. The first-order reactivity constants for PE and PP MPs were (μ ± σ) k PE = (6.58 ± 4.99) × 10 4 s −1 and k PP = (6.24 ± 2.98) × 10 4 s −1 , respectively. On the other hand, the reactivity of PVC MPs was influenced by reactions with organic compounds leached from the plastic material. Long-term photodegradation experiments revealed some small morphological changes in PE and PP MPs as a result of photoaging. The process also produced low molecular weight organic compounds, including short-chain carboxylic acids, and indicates that the presence of anions such as acetate and (in the case of PVC) chloride is associated with the photodegradation processes of the investigated MPs. FTIR spectroscopy suggested the presence of carbonyl groups, associated with oxidation of the polymer chains and the possible presence of plastic additives. Transformation products (TPs) were elucidated, indicating dechlorination processes for PVC MPs and/or the organic compounds they carried, and hydrogen abstraction, primary oxidation, dehydrogenation, and oxidative cleavage for PE and PP MPs.
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Investigations into the Reactivity of Microplastics in Water
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Researchers investigated how hydroxyl radicals — naturally occurring reactive molecules in water — chemically transform microplastics, finding that radiation-generated radicals can break plastic bonds and alter their surface properties. Understanding microplastic chemical reactivity in water is important for predicting how environmental degradation changes their biological effects.
Fate and environmental behaviors of microplastics through the lens of free radical
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Researchers reviewed how free radicals influence the fate and environmental behavior of microplastics, including surface degradation, chemical release, and changes in crystallinity and water affinity. The study found that while free radicals can cause weathering and fragmentation of microplastics in the environment, high concentrations of free radicals with strong oxidation potential can also be harnessed to effectively degrade microplastic pollutants.
Contribution of free hydroxyl radical to the formation of micro(nano)plastics and release of additives during polyethylene degradation in water
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Researchers found that hydroxyl radicals generated from hydrogen peroxide in water significantly accelerate the degradation of polyethylene and the formation of micro- and nano-sized plastic particles. The study, conducted over 620 days, demonstrates that naturally occurring reactive oxygen species in aquatic environments may contribute to the generation and spread of secondary microplastics.
The fate of microplastics in the environment: Systematic studies to determine release rates of secondary micro- and nanoplastics and water-soluble organics induced by photolysis and hydrolysis
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Researchers conducted systematic studies on the photolytic and hydrolytic degradation of microplastics using three photolysis protocols and multiple polymer types to determine release rates of secondary micro- and nanoplastics and water-soluble organics, providing mechanistic data needed for environmental fate and risk assessment.
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