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Photochemical Chain Scissions Enhance Polyethylene Glycol Biodegradability: From Probabilistic Modelling to Experimental Demonstration
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Researchers investigated how photochemical reactions with hydroxyl radicals reduce the molecular weight of polyethylene glycols (PEGs), and found that even a few chain-scission events dramatically accelerated subsequent biodegradation in soil and sediment over 150 days. The study demonstrates that abiotic photodegradation can prime water-soluble polymers for faster microbial breakdown in natural environments.
Polyethylene glycols (PEGs), a major class of water-soluble polymers (WSPs), are widely used in diverse applications which may lead to their release into the environment. This work investigates the reaction of PEGs with photochemically produced hydroxyl radicals (•OH), an important environmental oxidant, and assesses the effect of reaction-induced molecular weight (MW) decreases on PEG biodegradation dynamics in soil and sediment. Probabilistic kinetic modelling revealed a significant reduction in PEG MW after only a few •OH-induced chain scissions on initial PEG molecules. The simulation results were experimentally validated by reacting 13C-labeled PEGs (average MW = 6200 Da) with photochemically produced •OH, resulting in pronounced shifts in the size distribution of PEGs towards lower MWs with increasing reaction extents. Incubations of the initial non-reacted and three incrementally •OH-reacted PEG mixtures over a 150-day period in sediment and soil demonstrated increasing rates and extents of PEG biodegradation to 13CO2 with increasing •OH-reaction extent and thus decreasing PEG average MW. This study underscores the importance of considering the MW distributions of WSPs and their dynamic changes through biotic or abiotic chain scission reactions — showcased herein by reacting PEGs with photochemically produced •OH — in mechanistically understanding WSP biodegradability in natural and engineered receiving environments.
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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.
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Researchers exposed small polyoxymethylene pellets to terrestrial and simulated marine environments over three years, documenting surface cracking, photo-oxidation, and mass and diameter reductions of approximately 10% and 40% respectively along with generation of 100-300 micrometer fragments. UV irradiation caused smaller changes than combined heat and light exposure, as UV could not penetrate the particle interior.
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.
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Researchers studied the photo-aging of brominated epoxy resin (BER) microplastics under simulated solar irradiation in aquatic environments, finding that photodegradation caused surface oxidation, particle size reduction, increased hydrophilicity, and surface void formation. The process also generated environmentally persistent free radicals and broke C-Br bonds, indicating that covalently bound tetrabromobisphenol A undergoes transformation during photo-aging of BER microplastics.
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