@article {579,
	title = {Assessing in situ mineralization of recalcitrant organic compounds in vadose zone sediments using delta(13)C and (14)C measurements},
	journal = {Journal of Contaminant Hydrology},
	volume = {76},
	year = {2005},
	note = {883lpTimes Cited:11Cited References Count:52},
	month = {Jan},
	pages = {1-18},
	abstract = {Few techniques exist to measure the biodegradation of recalcitrant organic compounds such as chlorinated hydrocarbons (CHC) in situ, yet predictions of biodegradation rates are needed for assessing monitored natural attenuation. Traditional techniques measuring O(2), CO(2), or chemical concentrations (in situ respiration, metabolite and soil air monitoring) may not be sufficiently sensitive to estimate biodegradation rates for these compounds. This study combined isotopic measurements ((14)C and delta(13)C Of CO(2) and delta(13)C of CHCs) in conjunction with traditional methods to assess in situ biodegradation of perchloroethylene (PCE) and its metabolites in PCE-contaminated vadose zone sediments. CHC, ethene, ethane, methane, O(2), and CO(2) concentrations were measured over 56 days using gas chromatography (GC). 613C of PCE, trichloroethylene (TCE) and cis- 1,2-dichloroethylene (DCE), delta(13)C and (14)C of vadose zone CO(2) and sediment organic matter, and delta(13)C, (14)C, and deltaD of methane were measured using a GC-isotope ratio mass spectrometer or accelerator mass spectrometer. PCE metabolites accounted for 0.2\% to 18\% of CHC concentration suggesting limited reductive dechlorination. Metabolites TCE and DCE were significantly enriched in (13)C with respect to PCE indicating metabolite biodegradation. Average delta(13)C-CO(2) in source area wells (-23.5parts per thousand) was significantly lower compared to background wells (- 18.4\%o) indicating CHC mineralization. Calculated CHC mineralization rates were 0.003 to 0.01 mg DCE/kg soil/day based on lower (14)C values Of CO(2) in the contaminated wells (63\% to 107\% modem carbon (pMC) relative to the control well (117 pMC). Approximately 74\% of the methane was calculated to be derived from in situ CHC biodegradation based on the (14)C measurement of methane (29 pMC). (14)C-CO(2) analyses was a sensitive measurement for quantifying in situ recalcitrant organic compound mineralization in vadose zone sediments for which limited methodological tools exist. (C) 2004 Elsevier B.V All rights reserved.},
	issn = {0169-7722},
	doi = {10.1016/j.jconhyd.2004.07.007},
	author = {Kirtland, B. C. and Aelion, C. M. and Stone, P. A.}
}
@article {957,
	title = {Isotopic and geochemical assessment of in situ biodegradation of chlorinated hydrocarbons},
	journal = {Environ Sci Technol},
	volume = {37},
	year = {2003},
	note = {Kirtland, Brian CAelion, C MarjorieStone, Peter AHunkeler, DanielengResearch Support, Non-U.S. Gov{\textquoteright}tResearch Support, U.S. Gov{\textquoteright}t, Non-P.H.S.2003/10/04 05:00Environ Sci Technol. 2003 Sep 15;37(18):4205-12.},
	month = {Sep 15},
	pages = {4205-12},
	abstract = {Currently there is no in situ method to detect and quantify complete mineralization of chlorinated hydrocarbons (CHCs) to CO2. Combined isotopic measurements in conjunction with traditional chemical techniques were used to assess in situ biodegradation of trichloroethylene (TCE) and carbon tetrachloride (CT). Vadose zone CHC, ethene, ethane, methane, O2, and CO2 concentrations were analyzed using gas chromatography over 114 days at the Savannah River Site. delta13C of CHC and delta13C and 14C of vadose zone CO2, sediment organic matter, and groundwater dissolved inorganic carbon (DIC)were measured. Intermediate metabolites of TCE and CT accounted for < or = 10\% of total CHCs. Delta13C of cis-1,2-dichloroethylene (DCE) was always heavier than TCE indicating substantial DCE biodegradation. 14C-CO2 values ranged from 84 to 128 percent modern carbon (pMC), suggesting that plant root-respired CO2 was dominant. 14C-CO2 values decreased over time (up to 12 pMC), and contaminated groundwater 14C-DIC (76 pMC) was substantially depleted relative to the control (121 pMC). 14C provided a direct measure of complete CHC mineralization in vadose zone and groundwater in situ and may improve remediation strategies.},
	issn = {0013-936X (Linking)},
	doi = {10.1021/es034046e},
	author = {Kirtland, B. C. and Aelion, C. M. and Stone, P. A. and Hunkeler, D.}
}
