Measuring stable isotope fractionation of carbon, hydrogen, and other elements by Compound Specific Isotope Analysis (CSIA) is a new, innovative approach to assess organic pollutant degradation in the environment. Central to this concept is the Rayleigh equation which relates degradation-induced decreases in concentrations directly to concomitant changes in bulk (= average over the whole compound) isotope ratios. The extent of in situ transformation may therefore be inferred from measured isotope ratios in field samples, provided that an appropriate enrichment factor (ebulk) is known. This ebulk value, however, is usually only valid for a specific compound and for specific degradation conditions. Therefore, a direct comparison of ebulk values for different compounds and for different types of reactions has in general not been feasible. In addition, it is often uncertain how robust and reproducible ebulk values are and how confidently they can be used to quantify contaminant degradation in the field. To im...

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A new concept linking observable stable isotope fractionation to transformation pathways of organic pollutants.

Stable isotope fractionation analysis as a tool to monitor biodegradation in contaminated acquifers.

Area 6 at Dover Air Force Base (Dover, DE) has been the location of an in-depth study by the RTDF (Remediation Technologies Development Forum Bioremediation of Chlorinated Solvents Action Team) to evaluate the effectiveness of natural attenuation of chlorinated ethene contamination in groundwater. Compound-specific stable carbon isotope measurements for dissolved PCE and TCE in wells distributed throughout the anaerobic portion of the plume confirm that stable carbon isotope values are isotopically enriched in 13C consistent with the effects of intrinsic biodegradation. During anaerobic microbial reductive dechlorination of chlorinated hydrocarbons, the light (12C) versus heavy isotope (13C) bonds are preferentially degraded, resulting in isotopic enrichment of the residual contaminant in 13C. To our knowledge, this study is the first to provide definitive evidence for reductive dechlorination of chlorinated hydrocarbons at a field site based on the δ13C values of the primary contaminants spilled at the s...

Stable carbon isotope evidence for intrinsic bioremediation of tetrachloroethene and trichloroethene at area 6, Dover Air Force Base

https://www.pure.ed.ac.uk/ws/files/8536865/PDF_Gilfillan_et_al._2008_GCA.....pdf

The noble gas geochemistry of natural CO2 gas reservoirs from the Colorado Plateau and Rocky Mountain provinces, USA

Carbon isotope fractionation during dechlorination of chlorinated ethenes was investigated using a methanogenic microbial enrichment culture. Subcultures were amended with trichloroethene (TCE), cis-1,2-dichloroethene (cis-DCE), and vinyl chloride (VC), respectively. Carbon isotope ratios and concentrations of reactants and of all dechlorination products were monitored during two experiments. All dechlorination steps were accompanied by significant isotope fractionation. The isotope ratios of the reactants were described with a Rayleigh type model, and the following enrichment factors (eP/R) were obtained: −6.6 and −2.5‰ for dechlorination of TCE, −14.1 and −16.1‰ for dechlorination of cis-DCE, and −26.6 and −21.5‰ for dechlorination of VC. Isotope and mass balances suggested that ethene (ETH) was degraded. In additional experiments with ETH as reactant, ETH became enriched in 13C as its concentration decreased indicating the cultures were capable of degrading ETH. The average value for the enrichment fac...

/pdf/carbon-isotope-fractionation-during-microbial-dechlorination-28fzn66qwb.pdf

Carbon Isotope Fractionation during Microbial Dechlorination of Trichloroethene, cis-1,2-Dichloroethene, and Vinyl Chloride: Implications for Assessment of Natural Attenuation

P. MacKenzie

Papers

Contrasting carbon isotope fractionation during biodegradation of trichloroethylene and toluene: Implications for intrinsic bioremediation