This study systematically assesses the effects of •OH-reaction induced chain scissions on the MW distribution and subsequent biodegradability of PEGs in soil and sediment. Chain scissions of PEGs are hypothesized to enhance biodegradability due to the formed smaller PEG molecules being more readily assimilated and metabolized by microbes. We chose PEG reaction with •OH not only due to its environmental relevance but also as an illustrative example to assess the importance of WSP chain scission reactions on subsequent WSP biodegradation in natural and engineered systems. The hypothesis was tested in a three-step approach: first, we simulated •OH reaction-induced decreases in the average MW of weightdistributed PEG molecules using numerical simulations (Monte Carlo). Second, we experimentally reacted 13 C-labelled PEGs (average MW = 6200 Da) with •OH generated by H2O2 photoirradiation and tracked the resulting changes in MW distributions of the PEG molecules over time using high-performance liquid chromatography coupled to both a charged aerosol detector and a mass spectrometer (HPLC-CAD-MS). This experimental data was compared to Monte Carlo model predictions. Third, we incubated the initial and three incrementally •OH-reacted PEG molecules in a soil and a sediment and monitored biodegradation dynamics by following the formation of PEG-derived 13 CO2. This study is the first to link WSP reaction-induced chain scissions to environmental biodegradability and, building on previous studies on structural polymers,