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Hunkeler, Daniel

Nom
Hunkeler, Daniel
Affiliation principale
Fonction
Professeur ordinaire
Email
daniel.hunkeler@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/142

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  • Publication
    Métadonnées seulement
    Monitoring oxidation of chlorinated ethenes by permanganate in groundwater using stable isotopes: Laboratory and field studies
    (2003)
    Hunkeler, Daniel 
    ;
    Aravena, Ramon
    ;
    Parker, Beth
    ;
    Cherry, John
    ;
    Diao, X
    Permanganate injection is increasingly applied for in situ destruction of chlorinated ethenes in groundwater. This laboratory and field study demonstrates the roles that carbon isotope analysis can play in the assessment of oxidation of trichloroethene (TCE) by permanganate. In laboratory experiments a strong carbon isotope fractionation was observed during oxidation of TCE with similar isotopic enrichment factors (-25.1 to -26.8 parts per thousand) for initial KMnO4 concentrations between 67 and 1250 mg/L. At the field site, a single permanganate injection episode was conducted in a sandy aquifer contaminated with TCE as dense nonaqueous liquid (DNAPL). After injection, enriched delta(13)C values of up to +204% and elevated Cl- concentrations were observed at distances of up to 4 m from the injection point. Farther away, the Cl- increased without any change in delta(13)C of TCE suggesting that Cl- was not produced locally but migrated to the sampling point. Except for the closest sampling location to the injection point, the delta(13)C rebounded to the initial delta(13)C again, likely due to dissolution of DNAPL. Isotope mass balance calculations made it possible to identify zones where TCE oxidation continued to occur during the rebound phase. The study indicates that delta(13)C values can be used to assess the dynamics between TCE oxidation and dissolution and to locate zones of oxidation of chlorinated ethenes that cannot be identified from the Cl- distribution alone.
  • Publication
    Métadonnées seulement
    Isotopic and geochemical assessment of in situ biodegradation of chlorinated hydrocarbons
    (2003)
    Kirtland, Brian
    ;
    Aelion, Marjorie
    ;
    Stone, Peter
    ;
    Hunkeler, Daniel 
    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, O-2, and CO2 concentrations were analyzed using gas chromatography over 114 days at the Savannah River Site. delta(13)C of CHC and delta(13) C and C-14 of vadose zone CO2, sediment organic matter, and groundwater dissolved inorganic carbon (DIC) were measured. Intermediate metabolites of TCE and CT accounted for less than or equal to10% of total CHCs. delta(13)C of cis-1,2-dichloroethylene (DCE) was always heavier than TCE indicating substantial DCE biodegradation. C-14-CO2 values ranged from 84 to 128 percent modern carbon (pMC), suggesting that plant root-respired CO2 was dominant. C-14-CO2 values decreased over time (up to 12 pMC), and contaminated groundwater C-14-DIC (76 pMC) was substantially depleted relative to the control (121 pMC). C-14 provided a direct measure of complete CHC mineralization in vadose zone and groundwater in situ and may improve remediation strategies.
  • Publication
    Métadonnées seulement
    Carbon isotopes as a tool to evaluate the origin and fate of vinyl chloride: Laboratory experiments and modeling of isotope evolution
    (2002)
    Hunkeler, Daniel 
    ;
    Aravena, Ramon
    ;
    Cox, Evan
    Accumulation of vinyl chloride (VC) is often a main concern at sites contaminated with chlorinated ethenes and ethanes due to its high toxicity. Since there can be several possible sources of VC and ethene at such sites, assessing the origin and fate of VC can be complicated. Aim of this study was to evaluate carbon isotope fractionation associated with various anaerobic processes that lead to the production of VC and ethene in view of using isotopes to evaluate the origin and fate of these compounds in groundwater. Microcosms were constructed using sediments and groundwater from a contaminated site and amended with potential precursors for VC and ethene production. In the microcosms with dichloroethene isomers, sequential reductive dechlorination was observed, and isotopic enrichment factors of -19.9+/-1.5%,for cis- 1,2-dichloroethene -30.3+/-1.9%o for trans-1,2-dichloroethene, and -7.3+/-0.4%o for 1,1,1-dichloroethene were obtained. In microcosms with chlorinated ethanes, 1,2-dichloroethane (1,2-DCA) and 1,1,2-trichloroethane (1,1,2-TCA) were predominantly transformed by dichloroelimination to ethene and VC, respectively, and enrichment factors of -32.1+/-1.1%o for 1,2-DCA and -2.0+/-0.2%o for 1,1,2-TCA were observed. Except for 1,1,2-TCA, a strong C-13 enrichment in each of the potential precursor of VC was observed, which opens the possibility to trace the origin of VC based on the isotope ratio of potential precursors, Furthermore, it was possible to model the isotope evolution of VC present as substrate or intermediate product as a function of time. The study demonstrates that carbon isotope ratios can potentially be used for qualitative and possibly quantitative evaluation of the origin and fate of VC at sites with complex contaminant mixtures.