title: Quantification of biotransformation of chlorinated hydrocarbons in a biostimulation study: added value via stable carbon isotope analysis.
abstract: Stable carbon isotope analysis of chlorinated aliphatic compounds was performed at an in situ biostimulation pilot test area (PTA) at a site where 1,2-dichloroethane (1,2-DCA) and trichloroethene (TCE) were present in groundwater. Chlorinated products of TCE reductive dechlorination (cis-dichloroethene (cDCE) and vinyl chloride (VC)) were present at concentrations of 17.5 to 126.4 micromol/L. Ethene, a potential degradation product of both 1,2-DCA dihaloelimination and TCE reductive dechlorination was also present in the PTA. Emulsified soybean oil and lactate were added as electron donors to stimulate anaerobic dechlorination in the PTA. Stable carbon isotope analysis provided evidence that dechlorination was occurring in the PTA during biostimulation, and a means of monitoring changes in dechlorination efficiency over the 183 day monitoring period. Stable carbon isotope analysis was also used to determine if ethene production in the PTA was due to dechlorination of TCE, 1,2-DCA, or both. Fractionation factors (alpha) were determined in the laboratory during anaerobic biotransformation of 1,2-DCA via a dihaloelimination reaction in four separate enrichment cultures. These alpha values (as well as the previously published ranges of alpha for the dechlorination of TCE, cDCE and 1,2-DCA) were used, along with isotopic values measured during the pilot test, to derive quantitative estimates of biotransformation during the pilot test. Dechlorination was found to account for 10.7 to 35.9%, 21.9 to 74.9%, and 54.4 to 67.8% of 1,2-DCA, TCE and cDCE concentration loss respectively in the PTA. Stable carbon isotope analysis indicates that dechlorination of 1,2-DCA, TCE and cDCE were all significant processes during the pilot test, while ethene production during the pilot test was dominated by 1,2-DCA dihaloelimination. This study demonstrates how stable carbon isotope analysis can provide more conservative estimates of the extent of biotransformation than do conventional protocols. In addition, in a complex mixed plume such as this, compound specific isotope analysis is shown to be one of the few methods available for clarifying dominant biotransformation pathways where breakdown products are non-exclusive (i.e. ethene).
authors: Stable Isotope Laboratory, Department of Geology, University of Toronto, Toronto, ON, Canada.
authors: Sarah K
authors: SK
authors: Hirschorn
authors: Ariel
authors: A
authors: Grostern
authors: Georges
authors: G
authors: Lacrampe-Couloume
authors: Elizabeth A
authors: EA
authors: Edwards
authors: Leah
authors: L
authors: Mackinnon
authors: Cory
authors: C
authors: Repta
authors: David W
authors: DW
authors: Major
authors: Barbara
authors: B
authors: Sherwood Lollar
mesh_terms: D001711:Biotransformation; D002247:Carbon Isotopes; D006843:Hydrocarbons, Chlorinated / Q000378:metabolism*; D019344:Lactic Acid / Q000378:metabolism; D013024:Soybean Oil / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000378:metabolism*; D014881:Water Supply
chemical_list: D002247:Carbon Isotopes; D006843:Hydrocarbons, Chlorinated; D014874:Water Pollutants, Chemical; D019344:Lactic Acid; D013024:Soybean Oil