Soil incubations. Incubation of the unreacted PEGs (i.e., t0 solution) resulted in a small maximum in mineralization rates of ~ 0.035 % 13 C h -1 after 20 hours, after which mineralization rates decreased to low and approximately constant values of ~ 0.0005 % 13 C h -1 over the rest of the incubation (Figure ). The low final 13 CMineralized = 1.25 % after 150 days of incubation (Figure ) revealed that the PEG molecules with MWs around 6200 Da did not readily biodegrade in this soil. Incubation of PEGs from the reacted solutions showed higher initial normalized mineralisation rates that reached global maxima also after approximately 20 hours of incubation. The mineralization rates increased with increasing •OH reaction time to values of 0.17 % 13 C h -1 for the most reacted PEGs (i.e., t3 solution). After approximately 4 days of incubation, the •OH-reacted PEGs showed a second, smaller maximum in normalized mineralization rates which increased from 0.012 % 13 C h -1 for the t1 sample to approximately 0.024 % 13 C h -1 for the t3 sample. At this point, cumulative mineralization extents reached 4, 6, and 8 % for the t1, t2, and t3 samples, respectively, while it was below 0.1 % for t0 sample (Figure ). The mineralization rate subsequently decreased for all reacted PEGs to values between ~ 0.002 % 13 C h -1 (t1 solution) and 0.007 % 13 C h -1 (t3 solution). Distinct increases in the mineralization extents of treated PEGs were observed at around 40 days of incubation resulted from wetting of the soil to re-adjust its water content (Figure ) and are further discussed below. Final mineralization extents after 150 days of incubation increased with increasing reaction of PEGs with •OH from CMineralized = 20 ± 0.8, to 34 ± 3.2, and 45 ± 0.3 % for the t1, t2 and t3 samples, respectively (Figure ). Given that 13 CO2 was still formed when incubations were terminated, higher final extents would have been obtained if the soil incubations had been continued beyond 150 days. Quantification of CNon-Mineralized in the soils closed mass balances on total added 13 C for all soil incubations (i.e., mass balances between 97 ± 2 % and 104 ± 4 % of C added; Figure ).