Assessment of MTBE biodegradation in contaminated groundwater using 13C and 14C analysis: Field and laboratory microcosm studies

► Carbon isotope fractionation for MTBE varies with dissolved oxygen concentration. ► Carbon isotope fractionation can underestimate MTBE biodegradation at plume fringes. ► Fractionation factors must be for specific biodegradation mechanisms and conditions. ► Specific microbial populations influence carbon isotope fractionation in groundwater.