rates shown for the first 20 days of incubation). Thereafter, mineralization rates continuously decreased to low values around 0.002 % 13 C h -1 at 20 days. Time-integration of the mineralization rates yielded the cumulative mineralization extent of 13 CMineralized = 66 ± 3 % of the initial PEGs at the end of the incubation after 150 days (Figure ; t0). Similar to the incubation of unreacted solutions, incubation of the three reacted PEG solutions showed maxima in mineralization rates at around 6 days of incubation with values varying between 0.8 and 1 % 13 C h -1 . However, incubations of the three reacted PEG solutions showed an additional maximum in mineralization rates at 2 days of incubation with rates increasing from 0.1 % 13 C h -1 for t1 to approximately 0.3 % 13 C h -1 for t3. These peaks in mineralization rates likely corresponded to microbial utilization of low MW PEG molecules formed through reaction with