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Hunkeler, Daniel

Nom
Hunkeler, Daniel
Affiliation principale
Fonction
Professeur.e ordinaire
Email
daniel.hunkeler@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/142
_
0000-0003-3525-9736

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  • Publication
    Accès libre
    Carbon and Chlorine Isotope Ratios of Chlorinated Ethenes Migrating through a Thick Unsaturated Zone of a Sandy Aquifer
    (2011)
    Hunkeler, Daniel 
    ;
    Aravena, R
    ;
    Shouakar-Stash, O
    ;
    Weisbrod, N
    ;
    Nasser, A
    ;
    Netzer, L
    ;
    Ronen, D
    Compound-specific isotope analysis (CSIA) can potentially be used to relate vapor phase contamination by volatile organic compounds (VOCs) to their subsurface sources. This field and modeling study investigated how isotope ratios evolve during migration of gaseous chlorinated ethenes across a 18 m thick unsaturated zone of a sandy coastal plain aquifer. At the site, high concentrations of tetrachloroethene (PCE up to 380 µg/L), trichloroethene (TCE up to 31,600 µg/L), and cis-1,2-dichloroethene (cDCE up to 680 µg/L) were detected in groundwater. Chlorinated ethene concentrations were highest at the water table and steadily decreased upward toward the land surface and downward below the water table. Although isotopologues have different diffusion coefficients, constant carbon and chlorine isotope ratios were observed throughout the unsaturated zone, which corresponded to the isotope ratios measured at the water table. In the saturated zone, TCE became increasingly depleted along a concentration gradient, possibly due to isotope fractionation associated with aqueous phase diffusion. These results indicate that carbon and chlorine isotopes can be used to link vapor phase contamination to their source even if extensive migration of the vapors occurs. However, the numerical model revealed that constant isotope ratios are only expected for systems close to steady state.
  • Publication
    Accès libre
    Assessing chlorinated ethene degradation in a large scale contaminant plume by dual carbon–chlorine isotope analysis and quantitative PCR
    (Elsevier, 2011)
    Hunkeler, Daniel 
    ;
    Abe, Y.
    ;
    Broholm, M.M.
    ;
    Jeannotat, S
    ;
    Westgaard, C
    ;
    Jacobsen, C.S
    ;
    Aravena, R
    ;
    Bjerg, P.L
    The fate of chlorinated ethenes in a large contaminant plume originating from a tetrachloroethene (PCE) source in a sandy aquifer in Denmark was investigated using novel methods including compound-specific carbon and chlorine isotope analysis and quantitative real-time polymerase chain reaction (qPCR) methods targeting Dehaloccocides sp. and vcrA genes. Redox conditions were characterized as well based on concentrations of dissolved redox sensitive compounds and sulfur isotopes in SO24 ¯.
    In the first 400 m downgradient of the source, the plume was confined to the upper 20m of the aquifer. Further downgradient it widened in vertical direction due to diverging groundwater flow reaching a depth of up to 50 m. As the plume dipped downward and moved away from the source, O2 and NO¯3 decreased to below detection levels, while dissolved Fe2+ and SO24¯ increased above detectable concentrations, likely due to pyrite oxidation as confirmed by the depleted sulfur isotope signature of SO24¯. In the same zone, PCE and trichloroethene (TCE) disappeared and cis-1,2-dichloroethene (cDCE) became the dominant chlorinated ethene. PCE and TCE were likely transformed by reductive dechlorination rather than abiotic reduction by pyrite as indicated by the formation of cDCE and stable carbon isotope data. TCE and cDCE showed carbon isotope trends typical for reductive dechlorination with an initial depletion of 13C in the daughter products followed by an enrichment of 13C as degradation proceeded. At 1000 m downgradient of the source, cDCE was the dominant chlorinated ethene and had reached the source δ13C value confirming that cDCE was not affected by abiotic or biotic degradation.
    Further downgradient (up to 1900 m), cDCE became enriched in 13C by up to 8‰ demonstrating its further transformation while vinylchloride (VC) concentrations remained low (<1 µg/L) and ethene was not observed. The correlated shift of carbon and chlorine isotope ratios of cDCE by 8 and 3.9‰, respectively, the detection of Dehaloccocides sp genes, and strongly reducing conditions in this zone provide strong evidence for reductive dechlorination of cDCE. The significant enrichment of 13C in VC indicates that VC was transformed further, although the mechanism could not be determined. The transformation of cDCE was the rate limiting step as no accumulation of VC occurred. In summary, the study demonstrates that carbon–chlorine isotope analysis and qPCR combined with traditional approaches can be used to gain detailed insight into the processes that control the fate of chlorinated ethenes in large scale plumes.
  • Publication
    Accès libre
    Compound-Specific Chlorine Isotope Analysis: A Comparison of Gas Chromatography/Isotope Ratio Mass Spectrometry and Gas Chromatography/Quadrupole Mass Spectrometry Methods in an Interlaboratory Study
    (2011)
    Bernstein, A
    ;
    Shouakar-Stash, O
    ;
    Ebert, K
    ;
    Laskov, C
    ;
    Hunkeler, Daniel 
    ;
    Jeannottat, Simon
    ;
    Sakaguchi-Söder, K
    ;
    Laaks, J
    ;
    Jochmann, M.A
    ;
    Cretnik, S
    ;
    Jager, J
    ;
    Haderlein, S.B
    ;
    Schmidt, T.C
    ;
    Aravena, R
    ;
    Elsner, M
    Chlorine isotope analysis of chlorinated hydrocarbons like trichloroethylene (TCE) is of emerging demand because these species are important environmental pollutants. Continuous flow analysis of noncombusted TCE molecules, either by gas chromatography/isotope ratio mass spectrometry (GC/IRMS) or by GC/quadrupole mass spectrometry (GC/qMS), was recently brought forward as innovative analytical solution. Despite early implementations, a benchmark for routine applications has been missing. This study systematically compared the performance of GC/qMS versus GC/IRMS in six laboratories involving eight different instruments (GC/IRMS, Isoprime and Thermo MAT-253; GC/qMS, Agilent 5973N, two Agilent 5975C, two Thermo DSQII, and one Thermo DSQI). Calibrations of 37Cl/35 Cl instrument data against the international SMOC scale (Standard Mean Ocean Chloride) deviated between instruments and over time. Therefore, at least two calibration standards are required to obtain true differences between samples. Amount dependency of δ37Cl was pronounced for some instruments, but could be eliminated by corrections, or by adjusting amplitudes of standards and samples. Precision decreased in the order GC/IRMS (1σ ≈ 0.1%), to GC/qMS (1σ ≈0.2_0.5%for Agilent GC/qMS and 1σ≈0.2_0.9%for Thermo GC/qMS). Nonetheless, δ37Cl values between laboratories showed good agreement when the same external standards were used. These results lend confidence to the methods and may serve as a benchmark for future applications.
  • Publication
    Accès libre
    Effect of source variability and transport processes on carbon isotope ratios of TCE and PCE in two sandy aquifers
    (2004)
    Hunkeler, Daniel 
    ;
    Chollet, N
    ;
    Pittet, X.
    ;
    Aravena, R
    ;
    Cherry, J. A.
    ;
    Parker, B. L.
    Chlorinated ethenes often migrate over extended distances in aquifers and may originate from different sources. The aim of this study was to determine whether stable carbon isotope ratios remain constant during dissolution and transport of chlorinated ethenes and whether the ratios can be used to link plumes to their sources. Detailed depth-discrete delineation of the carbon isotope ratio in a tetrachloroethene (PCE) plume and in a trichloroethene (TCE) plume was done along cross-sections orthogonal to groundwater flow in two sandy aquifers in the Province of Ontario, Canada. At the TCE site, TCE concentrations up to solubility were measured in one high concentration zone close to the bottom of the aquifer from where dense non-aqueous phase liquid (DNAPL) was collected. A laboratory experiment using the DNAPL indicated that only very small carbon isotope fractionation occurs during dissolution of TCE (0.26‰), which is consistent with field observations. At most sampling points, the δ13C of dissolved TCE was similar to that of the DNAPL except for a few sampling points at the bottom of the aquifer close to the underlying aquitard. At these points, a 13C enrichment of up to 2.4‰ was observed, which was likely due to biodegradation and possibly preferential diffusion of TCE with 12C into the aquitard. In contrast to the TCE site, several distinct zones of high concentration were observed at the PCE site and from zones to zone, the δ13C values varied substantially from −24.3‰ to −33.6‰. Comparison of the δ13C values in the high concentration zones made it possible to divide the plume in the three different domains, each probably representing a different episode and location of DNAPL release. The three different zones could still be distinguished 220 m from the DNAPL sources. This demonstrates that carbon isotope ratios can be used to differentiate between different zones in chlorinated ethene plumes and to link plume zones to their sources. In addition, subtle variations in δ13C at plume fringes provided insight into mechanisms of plume spreading in transverse vertical direction. These variations were identified because of the high-resolution provided by the monitoring network.
  • Publication
    Accès libre
    Hydrogen and Carbon Isotope Fractionation during Aerobic Biodegradation of Benzene
    (2001)
    Hunkeler, Daniel 
    ;
    Andersen, N
    ;
    Aravena, R
    ;
    Bernasconi, M
    ;
    Butler, B.J
    The main aim of the study was to evaluate hydrogen and carbon isotope fractionation during biodegradation of benzene as a possible tool to trace the process in contaminated environments. Aerobic biodegradation of benzene by two bacterial isolates, Acinetobacter sp. and Burkholderia sp., was accompanied by significant hydrogen and carbon isotope fractionation with hydrogen isotope enrichment factors of −12.8 ± 0.7‰ and −11.2 ± 1.8‰, respectively, and average carbon isotope enrichment factors of −1.46 ± 0.06‰ and −3.53 ± 0.26‰, respectively. Inorganic carbon produced by Acinetobacter sp. was depleted in 13C by 3.6−6.2‰ as compared to the initial δ13C of benzene, while the produced biomass was enriched in 13C by 3.8‰. The secondary aim was to determine isotope ratios of benzenes from different manufacturers with regard to the use of isotopes for source differentiation. While two of the four analyzed benzenes had similar δ13C values, each of them had a distinct δ2H−δ13C pair and δ2H values spread over a range of 66.5‰. Thus, combined analyses of hydrogen and carbon isotopes may be a more promising approach to trace sources and/or biodegradation of benzene than measuring carbon isotopes only.
  • Publication
    Accès libre
    Monitoring Biodegradation of Methyl tert-Butyl Ether (MTBE) Using Compound-Specific Carbon Isotope Analysis
    (2001)
    Hunkeler, Daniel 
    ;
    Butler, B.J
    ;
    Aravena, R
    ;
    Barker, J.F
    Methyl tert-butyl ether (MTBE), the most common gasoline oxygenate, is frequently detected in surface water and groundwater. The aim of this study was to evaluate the potential of compound-specific isotope analysis to assess in situ biodegradation of MTBE in groundwater. For that purpose, the effect of relevant physical and biological processes on carbon isotope ratios of MTBE was evaluated in laboratory studies. Carbon isotope fractionation during organic phase/gas-phase partitioning (0.50 ± 0.15‰), aqueous phase/gas-phase partitioning (0.17 ± 0.05‰), and organic phase/aqueous-phase partitioning (0.18 ± 0.24‰) was small in comparison to carbon isotope fractionation measured during biodegradation of MTBE in microcosms based on aquifer sediments of the Borden site. In experiments with MTBE as the only substrate and a cometabolic experiment with 3-methypentane as primary substrate, MTBE became enriched in 13C by 5.1 to 6.9‰ after 95 to 97% degradation. For both experiments, similar isotopic enrichment factors were obtained (-1.52 ± 0.06 to -1.97 ± 0.05‰).
    Biodegradation of TBA, which accumulated transiently in the cometabolic microcosms, was also accompanied by carbon isotope fractionation, with an isotopic enrichment factor of -4.21 ± 0.07‰. This study suggests that carbon isotope analysis is a potential tool to trace in situ biodegradation of MTBE and TBA and thus to better understand the fate of these contaminants in the environment.
  • Publication
    Accès libre
    Carbon Isotope Fractionation during Microbial Dechlorination of Trichloroethene,cis-1,2-Dichloroethene, and Vinyl Chloride: Implications for Assessment of Natural Attenuation
    (2000)
    Bloom, Y
    ;
    Aravena, R
    ;
    Hunkeler, Daniel 
    ;
    Edwards, E
    ;
    Frape, S.K
    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 (∈P/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 factor obtained for the degradation of ETH was -3.0‰. The large carbon isotope fractionation observed in this study confirms that carbon isotope ratios are a sensitive tool for monitoring dechlorination of chlorinated ethenes to nontoxic end products.
  • Publication
    Accès libre
    Evidence of Substantial Carbon Isotope Fractionation among Substrate, Inorganic Carbon, and Biomass during Aerobic Mineralization of 1,2-Dichloroethane by Xanthobacter autotrophicus
    (2000)
    Hunkeler, Daniel 
    ;
    Aravena, R
    Carbon isotope fractionation during aerobic mineralization of 1,2-dichloroethane (1,2-DCA) by Xanthobacter autotrophicus GJ10 was investigated. A strong enrichment of 13C in residual 1,2-DCA was observed, with a mean fractionation factor α ± standard deviation of 0.968 ± 0.0013 to 0.973 ± 0.0015. In addition, a large carbon isotope fractionation between biomass and inorganic carbon occurred. A mechanistic model that links the fractionation factor α to the rate constants of the first catabolic enzyme was developed. Based on the model, it was concluded that the strong enrichment of 13C in 1,2-DCA arises because the first irreversible step of the initial enzymatic transformation of 1,2-DCA consists of an SN2 nucleophilic substitution. SN2 reactions are accompanied by a large kinetic isotope effect. The substantial carbon isotope fractionation between biomass and inorganic carbon could be explained by the kinetic isotope effect associated with the initial 1,2-DCA transformation and by the metabolic pathway of 1,2-DCA degradation. Carbon isotope fractionation during 1,2-DCA mineralization leads to 1,2-DCA, inorganic carbon, and biomass with characteristic carbon isotope compositions, which may be used to trace the process in contaminated environments.
  • Publication
    Accès libre
    Determination of Compound-Specific Carbon Isotope Ratios of Chlorinated Methanes, Ethanes, and Ethenes in Aqueous Samples
    (2000)
    Hunkeler, Daniel 
    ;
    Aravena, R
    Compound-specific carbon isotope ratio analysis is a promising tool to assess the origin and fate of organic contaminants in groundwater. The aim of this study was to develop and evaluate a reliable, fast method to determine carbon isotope ratios of chlorinated methanes, ethanes, and ethenes in aqueous samples. Direct solid-phase microextraction (dSPME) and headspace solid-phase microextraction (hSPME) were selected as extraction method and compared to headspace equilibration. For dSPME and hSPME, deviations between carbon isotope ratios in the aqueous phase and on the SPME fiber were e 0.40‰. For headspace equilibration, molecules in the gas phase were enriched in 13C compared to molecules in the aqueous phase by up to 1.46‰, in particular for chlorinated methanes. The absence of significant carbon isotope fractionation during dSPME and hSPME could be explained by the fact that both the aqueous phase and the SPME fiber coating discriminate against molecules with 13C to a similar degree, and thus no net carbon isotope fractionation occurs. If aqueous phase/gas-phase carbon isotope fractionation during headspace equilibration is taken into account, all methods, dSPME, hSPME, and headspace equilibration, provide accurate δ13C values with a similar precision. Direct SPME was the most sensitive method with detection limits as low as 130 ppb.
  • Publication
    Accès libre
    Monitoring Microbial Dechlorination of Tetrachloroethene (PCE) in Groundwater Using Compound-Specific Stable Carbon Isotope Ratios: Microcosm and Field Studies
    (1999)
    Hunkeler, Daniel 
    ;
    Aravena, R
    ;
    Butler, B.J
    The determination of compound-specific stable isotope ratios is a promising new tool to assess biodegradation of organic compounds in groundwater. In this study, the occurrence of carbon isotope fractionation during dechlorination of tetrachloroethene (PCE) to ethene was evaluated in a PCE-contaminated aquifer and in a microcosm that was based on aquifer material from the site. In the microcosm, all dechlorination steps were accompanied by carbon isotope fractionation. The largest fractionation occurred during dechlorination of cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC), resulting in a large enrichment of 13C in the remaining cDCE and VC. Stable carbon isotope ratios (δ13C) of cDCE and VC increased from -25.7 to -1.5‰ and -37.0 to -2.5‰, respectively. The δ13C of ethene was initially -60.2‰ and approached the δ13C of the added PCE (-27.3‰) as dechlorination came to completion. A similar carbon isotope pattern was observed for PCE dechlorination at the field site. Strong enrichment of 13C in cDCE and VC during microbial dechlorination may serve as a powerful tool to monitor the last two dechlorination steps, which frequently determine the rate of complete dechlorination of chlorinated ethenes at field sites undergoing intrinsic bioremediation.