Carbon isotopic fractionation during reductive dehalogenation of chlorinated ethenes by metallic iron

Highly chlorinated ethenes are resilient under aerobic conditions, but are known to degrade in reducing systems through biotic and abiotic reductive dehalogenation. Reductive dehalogenation of chlorinated ethenes by zero valent iron was recently shown to occur in both natural and engineered systems. The study reported in this paper was aimed at determining the magnitude and direction of the carbon isotopic fractionation of chlorinated ethenes during reductive dehalogenation by metallic iron. Large isotopic shifts were observed during the reaction duration for each of the solvents, where delta(13)C values of PCE, TCE and c-DCE shifted by 24 parts per thousand, 12 parts per thousand and 24 parts per thousand, respectively, after 80-90% consumption. The fact that these large changes in isotopic composition can occur during reductive dehalogenation has significant implications for monitoring the progress of zero valent iron remediation, and perhaps other remediation technologies. If chlorinated ethenes from contaminated sites can be analyzed for carbon isotope composition at any given point of an engineered remediation program, our results indicate that the efficacy of remediation can be assessed quantitatively. (C) 1999 Elsevier Science Ltd. All rights reserved.