| Abstract
| - Stable carbon isotopic analysis has the potential toassess biodegradation of chlorinated ethenes. Significantisotopic shifts, which can be described by Rayleighenrichment factors, have been observed for the biodegradationof trichloroethlyene (TCE), cis-dichloroethylene (cDCE),and vinyl chloride (VC). However, until this time, no systematicinvestigation of isotopic fractionation during perchloroethylene (PCE) degradation has been undertaken. In addition,there has been no comparison of isotopic fractionation bydifferent microbial consortia, nor has there been acomparison of isotopic fractionation by consortia generatedfrom the same source, but growing under differentconditions. This study characterized carbon isotopicfractionation during reductive dechlorination of the chlorinatedethenes, PCE in particular, for microbial consortia fromtwo different sources growing under different environmentalconditions in order to assess the extent to which differentmicrobial consortia result in different fractionationfactors. Rayleigh enrichment factors of −13.8‰, −20.4‰,and −22.4‰ were observed for TCE, cDCE, and VC,respectively, for dechlorination by the KB-1 consortium. Incontrast, isotopic fractionation during reductive dechlorination of perchloroethylene (PCE) could not always beapproximated by a Rayleigh model. Dechlorination by oneconsortium followed Rayleigh behavior (ε = −5.2),while a systematic change in the enrichment factor wasobserved over the course of PCE degradation by two otherconsortia. Comparison of all reported enrichment factorsfor reductive dechlorination of the chlorinated ethenes showssignificant variation between experiments. Despite thisvariability, these results demonstrate that carbon isotopicanalysis can provide qualitative evidence of the occurrenceand relative extent of microbial reductive dechlorination ofthe chlorinated ethenes.
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