| Abstract
| - Vinyl chloride (VC) is a carcinogenic contaminantcommonly found in groundwater. Much research hasfocused on anaerobic reductive dechlorination of VC, andrecently on aerobic VC degradation. In this study, thestable carbon isotope enrichment factor associated withaerobic VC assimilation was determined for Mycobacteriumsp. strains JS60, JS61, and JS617 and Nocardioides sp.strain JS614. The enrichment factors ranged from −8.2 ±0.1 to −7.0 ± 0.3 ‰ and did not change as a functionof biomass concentration. The measured enrichment factorsfor aerobic VC degradation were smaller than thosereported for anaerobic VC degradation. Enrichment factorscan also be expressed in terms of kinetic isotope effects(KIEs), 12k/13k, which result from the difference in reactionrates of bonds containing light and heavy isotopes. TheKIEs for aerobic VC degradation (1.01 ± 0.001) were smallerthan those for anaerobic VC degradation (1.03 ± 0.007).From the perspective of bond breakage during a chemicalreaction, the larger KIE associated with anaerobic VCdegradation as compared to aerobic VC degradation agreeswith KIE theory. This theory predicts that larger fractionationscan be expected in reactions where heavier atoms areinvolved (i.e., C−Cl bond for anaerobic versus CC foraerobic) and in reactions involving large changes in vibrationalfrequencies of the molecule between its ground stateand transition state (i.e., C−Cl cleavage versus CCepoxidation). The significant fractionation observed duringaerobic VC degradation suggests that stable carbonisotope measurements may be used as a tool to distinguishbetween biodegraded and nonbiodegraded VC.
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