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- Aeppli, Christoph, et al.
(författare)
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Chlorine Isotope Effects and Composition of Naturally Produced Organochlorines from Chloroperoxidases, Flavin-Dependent Halogenases, and in Forest Soil
- 2013
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 47:13, s. 6864-6871
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Tidskriftsartikel (refereegranskat)abstract
- The use of stable chlorine isotopic signatures (delta Cl-37) of organochlorine compounds has been suggested as a tool to determine both their origins and transformations in the environment. Here we investigated the delta Cl-37 fractionation of two important pathways for enzymatic natural halogenation: chlorination by chloroperoxidase (CPO) and flavin-dependent halogenases (FDH). Phenolic products of CPO were highly Cl-37 depleted (delta Cl-37 = -12.6 +/- 0.9 parts per thousand); significantly more depleted than all known industrially produced organochlorine compounds (delta Cl-37 = -7 to +6 parts per thousand). In contrast, four FDH products did not exhibit any observable isotopic shifts (delta Cl-37 = -0.3 +/- 0.6 parts per thousand). We attributed the different isotopic effect to the distinctly different chlorination mechanisms employed by the two enzymes. Furthermore, the delta Cl-37 in bulk organochlorines extracted from boreal forest soils were only slightly depleted in Cl-37 relative to inorganic Cl. In contrast to previous suggestions that CPO plays a key role in production of soil organochlorines, this observation points to the additional involvement of either other chlorination pathways, or that dechlorination of naturally produced organochlorines can neutralize delta Cl-37 shifts caused by CPO chlorination. Overall, this study demonstrates that chlorine isotopic signatures are highly useful to understand sources and cycling of organochlorines in nature. Furthermore, this study presents delta Cl-37 values of FDH products as well of bulk organochlorines extracted from pristine forest soil for the first time.
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| 2. |
- Aeppli, Christoph, et al.
(författare)
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Direct compound-specific stable chlorine isotope analysis of organic compounds with quadrupole GC/MS using standard isotope bracketing
- 2010
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Ingår i: Analytical Chemistry. - Columbus, OH : American Chemical Society. - 0003-2700 .- 1520-6882. ; 82:1, s. 420-426
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Tidskriftsartikel (refereegranskat)abstract
- A method has been developed for the direct determination of the stable chlorine isotope composition (delta(37)Cl) of organochlorines that eliminates sample preparation, achieves precision comparable to earlier techniques while improving the sensitivity, and makes use of benchtop gas chromatography-quadrupole mass spectrometry instruments (GCqMS). The method is based on the use of multiple injections (n = 8-10) of the sample, bracketed by a molecularly identical isotopic standard with known delta(37)Cl, determined using off-line thermal ionization mass spectrometry (TIMS). Mass traces of two isotopologues differing by one chlorine isotope were used to calculate delta(37)Cl values. Optimization of mass spectrometry and peak integration parameters as well as method validation was achieved using tetrachloroethene (PCE), p,p'-dichlorodiphenyltrichloroethane (DDT), and pentachlorophenol (PCP), spanning a delta(37)Cl range of -5.5 to +3.2 per thousand vs SMOC. Injecting 1.6-1100 pmol resulted in standard deviations (1sigma) of 0.6-1.3 per thousand, and the delta(37)Cl results agreed with values independently measured with TIMS. The method was tested by determining the Rayleigh fractionation during evaporation of pure liquid PCE, resulting in a chlorine isotopic enrichment factor of epsilon(Cl) = -1.1 +/- 0.4 per thousand. Furthermore, position-specific delta(37)Cl analysis based on analysis of DDT mass fragments was evaluated. The GCqMS-delta(37)Cl method offers a simplified yet sensitive approach for compound-specific chlorine isotope analysis.
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| 3. |
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| 5. |
- Aeppli, Christoph, et al.
(författare)
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Use of Cl and C Isotopic Fractionation to Identify Degradation and Sources of Polychlorinated Phenols : Mechanistic Study and Field Application
- 2013
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 47:2, s. 790-797
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Tidskriftsartikel (refereegranskat)abstract
- The widespread use of chlorinated phenols (CPs) as a wood preservative has led to numerous contaminated sawmill sites. However, it remains challenging to assess the extent of in situ degradation of CPs. We evaluated the use of compound-specific chlorine and carbon isotope analysis (Cl- and C-CSLA) to assess CP biotransformation. In a laboratory system, we measured isotopic fractionation during oxidative 2,4,6-trichlorophenol dechlorination by representative soil enzymes (C. fumago chloroperoxidase, horseradish peroxidase, and laccase from T. versicolor). Using a mathematical model, the validity of the Rayleigh approach to evaluate apparent kinetic isotope effects (AKIE) was confirmed. A small but significant Cl-AKIE of 1.0022 +/- 0.0006 was observed for all three enzymes, consistent with a reaction pathway via a cationic radical species. For carbon, a slight inverse isotope effect was observed (C-AKIE = 0.9945 +/- 0.0019). This fractionation behavior is clearly distinguishable from reported reductive dechlorination mechanisms. Based on these results we then assessed degradation and apportioned different types of technical CP mixtures used at two former sawmill sites. To our knowledge, this is the first study that makes use of two-element CSIA to study sources and transformation of CPs in the environment.
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| 6. |
- Sánchez-García, Laura, et al.
(författare)
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Molecular biomarkers in the subsurface of the Salar Grande (Atacama, Chile) evaporitic deposits
- 2018
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Ingår i: Biogeochemistry. - : Springer. - 0168-2563 .- 1573-515X. ; 140:1, s. 31-52
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Tidskriftsartikel (refereegranskat)abstract
- The Late Miocene–Pliocene aged hyperarid evaporitic system of Salar Grande is a unique, halite-rich sedimentary basin in the Cordillera de la Costa of the Central Andes (Chile) whose bio-sedimentary record is poorly understood. The persistence of hyperacidity over millions of years, the hypersalinity, and the intense UV radiation make it a terrestrial analogue to assess the potential presence of organic matter in the halite deposits found on Mars. We investigated the occurrence and distribution of biomolecules along a 100-m depth drill down to the ~ 9 Ma old detrital deposits topped by La Soledad Formation (ESF). We have identified two well-defined mineralogical and geochemical units by X-ray diffractometry (XRD) and ion chromatography: a nearly pure halite down to 40 m, and a detrital one down to 100 m depth. One-dimensional GC–MS and two-dimensional GC × GC-TOF–MS gas chromatography–mass spectrometry techniques allowed us to detect a variety of lipidic compounds (n-alkanes, n-alkanols, isoprenoids, steroids, and hopanoids), and a relative abundance of functionalized hydrocarbons (n-fatty acids or n-aldehydes), mostly in the upper halite. We also detected biopolymers and microbial markers by fluorescence sandwich-microarray immunoassays. A dominant prokaryotic origin was associated with halophile bacteria and archaea, with minor contributions of lichens, macrophytes, or higher plants. The lipidic record was also imprinted by oxic (high pristane over phytane ratios) and saline (squalane, and mono-methyl n-alkanes) signatures. The vertical abundance and distribution of biomarkers in the Salar Grande was explained by a generalized effect of xeropreservation, combined with salt encapsulation in the upper halite deposits, or with protective organics-mineral interactions in the deeper detrital unit. The results contribute to the interpretation of terrestrial bio-sedimentary records of halite deposits and their association to environmental conditions. The high potential for preservation of biosignatures at Salar Grande suggests that similar evaporitic deposits in Mars should be priority targets for searching for signs of life.
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| 7. |
- Wiegert, Charline, 1980-, et al.
(författare)
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Carbon and Chlorine Isotope Fractionation During Microbial Degradation of Tetra- and Trichloroethene
- 2013
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 47:12, s. 6449-6456
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Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional compound-specific isotope analysis (2D-CSIA), combining stable carbon and chlorine isotopes, holds potential for monitoring of natural attenuation of chlorinated ethenes (CEs), in contaminated soil and groundwater. However, interpretation of 2D-CSIA data sets is challenged by a shortage of experimental Cl isotope enrichment factors. Here, isotope enrichments factors for C and Cl (i.e., epsilon(C) and epsilon(Cl)) were determined for biodegradation of tetrachloroethene (PCE) and trichloroethene (TCE) using microbial enrichment cultures from a heavily CE-contaminated aquifer. The obtained values were epsilon(C) = -5.6 +/- 0.7 parts per thousand (95% CI) and epsilon(Cl) = -2.0 +/- 0.5 parts per thousand for PCE degradation and epsilon(C) = -8.8 +/- 0.2 parts per thousand and epsilon(Cl) = -3.5 +/- 0.5 parts per thousand for TCE degradation. Combining the values for both epsilon(C) and epsilon(Cl) yielded mechanism-diagnostic epsilon(Cl)/epsilon(C) ratios of 0.35 +/- 0.11 and 0.37 +/- 0.11 degradation of PCE and TCE, respectively. Application of the obtained epsilon(C) and epsilon(Cl) values to a previously investigated field site gave similar estimates for the fraction of degraded contaminant as in the previous study, but with a reduced uncertainty in assessment of the natural attenuation. Furthermore, 16S rRNA gene clone library analyses were performed on three samples from the PCE degradation experiments. A species closely related to Desulfitobacterium aromaticivorans UKTL dominated the reductive dechlorination process. This study contributes to the development of 2D-CSIA as a tool for evaluating remediation strategies of CEs at contaminated sites.
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| 9. |
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| 10. |
- Wiegert, Charline, 1980-, et al.
(författare)
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Dual carbon chlorine stable isotope investigation of sources and fate of chlorinated ethenes in contaminated groundwater
- 2012
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 46:20, s. 10918-10925
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Tidskriftsartikel (refereegranskat)abstract
- Chlorinated ethenes (CEs) are ubiquitous groundwater contaminants, yet there remains a need for a method to efficiently monitor their in situ degradation. We report here the first field application of combined stable carbon and chlorine isotope analysis of tetrachloroethene (PCE) and trichloroethene (TCE) to investigate their biodegradation in a heavily contaminated aquifer. The two-dimensional Compound Specific Isotope Analysis (2D-CSIA) approach was facilitated by a recently developed gas chromatography-quadrupole mass spectrometry (GCqMS) method for delta Cl-37 determination. Both C and Cl isotopes showed evidence of ongoing PCE transformation. Applying published C isotope enrichment factors (epsilon(C)) enabled evaluation of the extent of in situ PCE degradation (11-78%). We interpreted C and Cl isotopes using a numerical reactive transport model along a 60-m flow path. It revealed that combined PCE and TCE mass load was dechlorinated by less than 10%, and that cis-dichloroethene was not further dechlorinated. Furthermore, the 2D-CSIA approach allowed estimation of Cl isotope enrichment factors epsilon(Cl) (-7.8 to -0.8 parts per thousand) and characteristic epsilon(Cl)/epsilon(C) values (0.42-1.12) for reductive PCE dechlorination at this field site. This investigation demonstrates the benefit of 2D-CSIA to assess in situ degradation of CEs and the applicability of Cl isotope fractionation to evaluate PCE and TCE dechlorination.
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