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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
    Accès libre
    Perchloroethene source delineation using carbon-chlorine isotopic analysis: field investigations of isotopic signature variability / Perchlorethen-Quellendifferenzierung mittels Kohlenstoff-Chlor-
    (2015-12)
    Badin, Alice 
    ;
    Schirmer, Mario 
    ;
    Wermeille, Christiane
    ;
    Hunkeler, Daniel 
    When dealing with contaminated sites, identifying the source of contamination is critical for regulatory purposes. For chlorinated ethenes, previous studies have shown that dual carbon-chlorine (C-Cl) stable isotope analysis could be a key to address this issue as isotopic signatures vary between manufacturers and therefore, supposedly between sources. A successful application of this method relies on the assumption that different sources in the field will also show different signatures. Since the solvents used in the past are no longer available, this study aimed at investigating the extent of applicability of C-Cl stable isotope measurements for source identification based on field investigations. Ten sites which covered all of Switzerland and various sectors employing perchloroethene (PCE) were chosen. Differences were observed between some sites, suggesting that this method could be successfully applied. Other sites showed very similar isotopic signatures, indicating that this method applicability is site-specific. Additionally, the isotopic signature variability between sites was less significant than between the values previously reported for solvents from various manufacturers from North America. It was also confirmed that PCE reductive dechlorination should be considered when applying C-Cl isotope analysis for source identification. © 2015, Springer-Verlag Berlin Heidelberg.
  • Publication
    Accès libre
    Identification of chlorinated solvents degradation zones in clay till by high resolution chemical, microbial and compound specific isotope analysis
    (2013)
    Damgaard, I
    ;
    Bjerg, P.L
    ;
    Baelum, J
    ;
    Scheutz, C
    ;
    Hunkeler, Daniel 
    ;
    Jacobsen, C.S
    ;
    Tuxen, N
    ;
    Broholm, M.M
    The degradation of chlorinated ethenes and ethanes in clay till was investigated at a contaminated site (Vadsby, Denmark) by high resolution sampling of intact cores combined with groundwater sampling. Over decades of contamination, bioactive zones with degradation of trichloroethene (TCE) and 1,1,1-trichloroethane (1,1,1-TCA) to 1,2-cis-dichloroethene (cis-DCE) and 1,1-dichloroethane, respectively, had developed in most of the clay till matrix. Dehalobacter dominated over Dehalococcoides (Dhc) in the clay till matrix corresponding with stagnation of sequential dechlorination at cis-DCE. Sporadically distributed bioactive zones with partial degradation to ethene were identified in the clay till matrix (thickness from 0.10 to 0.22 m). In one sub-section profile the presence of Dhc with the vcrA gene supported the occurrence of degradation of cis-DCE and VC, and in another enriched δ13C for TCE, cis-DCE and VC documented degradation. Highly enriched δ13C for 1,1,1-TCA (25‰) and cis-DCE (−4‰) suggested the occurrence of abiotic degradation in a third sub-section profile.Due to fine scale heterogeneity the identification of active degradation zones in the clay till matrix depended on high resolution subsampling of the clay till cores. The study demonstrates that an integrated approach combining chemical analysis, molecular microbial tools and compound specific isotope analysis (CSIA) was required in order to document biotic and abiotic degradations in the clay till system.
  • 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
    Evaluating the fate of chlorinated ethenes in streambed sediments by combining stable isotope, geochemical and microbial methods
    (2009)
    Abe, Yumiko
    ;
    Aravena, Ramon
    ;
    Zopfi, Jakob 
    ;
    Parker, Beth
    ;
    Hunkeler, Daniel 
    The occurrence of chlorinated ethene transformation in a streambed was investigated using concentration and carbon isotope data from water samples taken at different locations and depths within a 15×25 ms tudy area across which a tetrachloroethene (PCE) plume discharges. Furthermore, it was evaluated how the degree of transformation is related to groundwater discharge rates, redox conditions, solid organic matter content (SOM) and microbial factors. Groundwater discharge rates were quantified based on streambed temperatures, and redox conditions using concentrations of dissolved redox-sensitive species. The degree of chlorinated ethene transformation was highly variable in space from no transformation to transformation beyond ethene. Complete reductive dechlorination to ethane and ethene occurred at locations with at least sulfate-reducing conditions and with a residence time in the samples streambed zone (80 cm depth) of at least 10 days. Among these locations, Dehalococcoides was detected using a PCR method where SOM contents were >2% w/w and where transformation proceeded beyond ethene. However, it was not detected at locations with low SOM, which may cause an insufficient H2 supply to sustain a detectably dense Dehalococcoides population. Additionally, it is possible that other organisms are responsible for the biodegradation. A microcosm study with streambed sediments demonstrated the potential of VC oxidation throughout the site even at locations without a pre-exposure to VC, consistent with the detection of the epoxyalkane:coenzyme M transferase (EaCoMT) gene involved in the degradation of chlorinated ethenes via epoxidation. In contrast, no aerobic transformation of cDCE in microcosms over a period of 1.5 years was observed. In summary, the study demonstrated that carbon isotope analysis is a sensitive tool to identify the degree of chlorinated ethene transformation even in hydrologically and geochemically complex streambed systems. In addition, it was observed that the degree of transformation is related to redox conditions, which in turn depend on groundwater discharge rates.