Stable Isotope Evidence for Biodegradation of Chlorinated Ethenes at a Fractured Bedrock Site

• Published in: Environmental science & technology Vol. 39; no. 13; pp. 4848 - 4856
• Main Authors: Chartrand, Michelle M. G, Morrill, Penny L, Lacrampe-Couloume, Georges, Sherwood Lollar, Barbara
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.07.2005
• Subjects: Applied sciences; Bedrock; Biodegradation; Biodegradation of pollutants; Biodegradation, Environmental; Biological and medical sciences; Biotechnology; Carbon; Carbon Isotopes - analysis; Carcinogens; Chlorine Compounds - metabolism; Decontamination. Miscellaneous; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Environment and pollution; Environmental Monitoring - methods; Ethylenes - metabolism; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Geological Phenomena; Geology; Groundwater pollution; Industrial applications and implications. Economical aspects; Isotopes; Pollution; Pollution, environment geology; Reproducibility of Results; Soil and sediments pollution; Soil Pollutants - metabolism; Biodegradation; Isotopic analysis; Bedrock; Bioaugmentation; Nonaqueous phase liquid; Organic solvent; Decontamination; Investigation method; Chlorine Organic compounds; Water pollution; Bioremediation; Carbon 13; Fracturing; Ground water; Ethylene(trichloro)
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es048592z

Stable carbon isotope analysis of chlorinated ethenes and ethene was performed at a site contaminated with trichloroethene (TCE), a dense non-aqueous phase liquid (DNAPL). The site is located in fractured bedrock and had variable groundwater hydraulic gradients during the study due to a local excavation project. Previous attempts to biostimulate a pilot treatment area at the site resulted in the production of cis-1,2-dichloroethene (cis-DCE), the first product of reductive dechlorination of TCE. Cis-DCE concentrations accumulated however, and there was no appreciable production of the breakdown products from further reductive dechlorination, vinyl chloride (VC) and ethene (ETH). Consequently, the pilot treatment area was bioaugmented with a culture of KB-1, a natural microbial consortium known to completely reduce TCE to nontoxic ETH. Due to ongoing dissolution of TCE from DNAPL in the fractured bedrock, and to variable hydraulic gradients, concentration profiles of dissolved TCE and its degradation products cis-DCE, VC, and ETH could not convincingly confirm biodegradation of the chlorinated ethenes. Isotopic analysis of cis-DCE and VC, however, demonstrated that biodegradation was occurring in the pilot treatment area. The isotope values of cis-DCE and VC became significantly more enriched in 13C over the last two sampling dates (in one well from −17.6‰ to −12.8‰ and from −22.5‰ to −18.2‰ for cis-DCE and VC, respectively). Quantification of the extent of biodegradation in the pilot treatment area using the Rayleigh model indicated that, depending on the well, between 21.3% and 40.7% of the decrease in cis-DCE and between 15.2% and 36.7% of the decrease in VC concentrations can be attributed to the effects of biodegradation during this time period. Within each well, the isotope profile of TCE remained relatively constant due to the continuous input of undegraded TCE due to DNAPL dissolution.