Accumulation of vinyl chloride (VC) is often a main
concern at sites contaminated with chlorinated ethenes
and ethanes due to its high toxicity. Since there can be
several possible sources of VC and ethene at such sites,
assessing the origin and fate of VC can be complicated. Aim
of this study was to evaluate carbon isotope fractionation
associated with various anaerobic processes that lead
to the production of VC and ethene in view of using isotopes
to evaluate the origin and fate of these compounds in
groundwater. Microcosms were constructed using sediments
and groundwater from a contaminated site and amended
with potential precursors for VC and ethene production. In
the microcosms with dichloroethene isomers, sequential
reductive dechlorination was observed, and isotopic
enrichment factors of −19.9 ± 1.5‰ for cis-1,2-dichloroethene,
−30.3 ± 1.9‰ for trans-1,2-dichloroethene, and −7.3 ±
0.4‰ for 1,1-dichloroethene were obtained. In microcosms
with chlorinated ethanes, 1,2-dichloroethane (1,2-DCA)
and 1,1,2-trichloroethane (1,1,2-TCA) were predominantly
transformed by dichloroelimination to ethene and VC,
respectively, and enrichment factors of −32.1 ± 1.1‰ for 1,2-DCA and −2.0 ± 0.2‰ for 1,1,2-TCA were observed.
Except for 1,1,2-TCA, a strong 13C enrichment in each of
the potential precursor of VC was observed, which opens
the possibility to trace the origin of VC based on the
isotope ratio of potential precursors. Furthermore, it was
possible to model the isotope evolution of VC present as
substrate or intermediate product as a function of time. The
study demonstrates that carbon isotope ratios can
potentially be used for qualitative and possibly quantitative
evaluation of the origin and fate of VC at sites with
complex contaminant mixtures.