and sediment. The formation of PEG molecules with lower MW (including the abovementioned oxidized PEG variants) due to •OH-induced chain scissions is hypothesized to result in enhanced biodegradability. This hypothesis was tested by incubating aliquots of the unreacted PEG solution (i.e., t0 = 0 min) and the three reacted PEG solutions (i.e., UV/H2O2 treatmemt times t: t1 = 15 min, t2 = 30 min, and t3 = 45 min of reaction) in triplicate in a reference soil and sediment. The use of C-labelled PEGs enabled the selective quantification of PEG mineralization to 13 CO2 (i.e., CMineralized) over the course of the incubations, as well as the total non-mineralized PEG-added 13 C (i.e., CNon-Mineralized) that remained in the soil and sediment at the end of the incubations.