Assessing changes in the isotopic signature of contaminants is a promising new tool to monitor microbial degradation processes in the field. So far, most studies focus on complete reductive dechlorination of chloroethenes, although chloroethenes have been demonstrated to be biodegraded via sequential reductive/oxidative pathways at several contaminated sites. The objectives of our study were to (1) identify the predominating dechlorination mechanisms at a chloroethene-contaminated site; (2) assess the specific isotope enrichment factors in microcosm experiments; and (3) evaluate microbial chloroethene degradation in the field based on isotopic signatures and specific enrichment factors. Significant isotope fractionation was observed during anaerobic and aerobic chloroethene degradation. Our study demonstrates that stable isotope fractionation is suitable not only for assessing anaerobic, but also aerobic chloroethene degradation. High enrichment factors have to be considered in particular for aerobic degradation of vinyl chloride.
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