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Photochemical Chain Scissions Enhance Polyethylene Glycol Biodegradability: From Probabilistic Modelling to Experimental Demonstration
Summary
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.