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Thullner M.,Helmholtz Center for Environmental Research | Fischer A.,Helmholtz Center for Environmental Research | Fischer A.,Isodetect Company for Isotope Monitoring | Richnow H.-H.,Helmholtz Center for Environmental Research | Wick L.Y.,Helmholtz Center for Environmental Research
Applied Microbiology and Biotechnology | Year: 2013

Biodegradation of contaminants is a common remediation strategy for subsurface environments. To monitor the success of such remediation means a quantitative assessment of biodegradation at the field scale is required. Nevertheless, the reliable quantification of the in situ biodegradation process it is still a major challenge. Compound-specific stable isotope analysis has become an established method for the qualitative analysis of biodegradation in the field and this method is also proposed for a quantitative analysis. However, to use stable isotope data to obtain quantitative information on in situ biodegradation requires among others knowledge on the influence of mass transfer processes on the observed stable isotope fractionation. This paper reviews recent findings on the influence of mass transfer processes on stable isotope fractionation and on the quantitative interpretation of isotope data. Focus will be given on small-scale mass transfer processes controlling the bioavailability of contaminants. Such bioavailability limitations are known to affect the biodegradation rate and have recently been shown to affect stable isotope fractionation, too. Theoretical as well as experimental studies addressing the link between bioavailability and stable isotope fractionation are reviewed and the implications for assessing biodegradation in the field are discussed. © 2012 Springer-Verlag Berlin Heidelberg. Source

Imfeld G.,CNRS Hydrology and Geochemistry Laboratory of Strasbourg | Kopinke F.-D.,Helmholtz Center for Environmental Research | Fischer A.,Helmholtz Center for Environmental Research | Fischer A.,Isodetect Company for Isotope Monitoring | Richnow H.-H.,Helmholtz Center for Environmental Research
Chemosphere | Year: 2014

The application of compound-specific stable isotope analysis (CSIA) for evaluating degradation of organic pollutants in the field implies that other processes affecting pollutant concentration are minor with respect to isotope fractionation. Sorption is associated with minor isotope fractionation and pollutants may undergo successive sorption-desorption steps during their migration in aquifers. However, little is known about isotope fractionation of BTEX compounds after consecutive sorption steps. Here, we show that partitioning of benzene and toluene between water and organic sorbents (i.e. 1-octanol, dichloromethane, cyclohexane, hexanoic acid and Amberlite XAD-2) generally exhibits very small carbon and hydrogen isotope effects in multistep batch experiments. However, carbon and hydrogen isotope fractionation was observed for the benzene-octanol pair after several sorption steps (δδ13C=1.6±0.3‰ and δδ2H=88±3‰), yielding isotope fractionation factors of αC=1.0030±0.0005 and αH=1.195±0.026. Our results indicate that the cumulative effect of successive hydrophobic partitioning steps in an aquifer generally results in insignificant isotope fractionation for benzene and toluene. However, significant carbon and hydrogen isotope fractionation cannot be excluded for specific sorbate-sorbent pairs, such as sorbates with π-electrons and sorbents with OH-groups. Consequently, functional groups of sedimentary organic matter (SOM) may specifically interact with BTEX compounds migrating in an aquifer, thereby resulting in potentially relevant isotope fractionation. © 2014 Elsevier Ltd. Source

Zhang N.,Helmholtz Center for Environmental Research | Bashir S.,Helmholtz Center for Environmental Research | Qin J.,Helmholtz Center for Environmental Research | Schindelka J.,Leibniz Institute for Tropospheric Research | And 6 more authors.
Journal of Hazardous Materials | Year: 2014

A systematic investigation of environmentally relevant transformation processes of alpha-hexachlorocyclohexane (α-HCH) was performed in order to explore the potential of compound specific stable isotope analysis (CSIA) to characterize reaction mechanisms. The carbon isotope enrichment factors (eC) for the chemical transformations of α-HCH via direct photolysis, indirect photolysis (UV/H2O2), hydrolysis, electro-reduction or reduction by Fe0 were quantified and compared to those previously published for biodegradation. Hydrogen abstraction by hydroxyl radicals generated by UV/H2O2 led to eC of -1.9±0.2‰ with an apparent kinetic carbon isotope effect (AKIEC) of 1.012±0.001. Dehydrochlorination by alkaline hydrolysis yielded eC of -7.6±0.4‰ with AKIEC of 1.048±0.003. Dechlorination either by homolytic bond cleavage in direct photolysis (eC=-2.8±0.2‰) or single-electron transfer in electro-reduction (eC--3.8±0.4‰) corresponded to AKIEC of 1.017±0.001 and 1.023±0.003, respectively. Dichloroelimination catalyzed by Fe0 via two-electron transfers resulted in eC of -4.9±0.1‰. AKIEC values assuming either a concerted or a stepwise mechanism were 1.030±0.0006 and 1.015±0.0003, respectively. Contrary to biodegradation, no enantioselectivity of α-HCH was observed in chemical reactions, which might be used to discriminate chemical and biological in situ transformations. © 2014 Elsevier B.V. Source

Thullner M.,Helmholtz Center for Environmental Research | Thullner M.,University Utrecht | Centler F.,Helmholtz Center for Environmental Research | Richnow H.-H.,Helmholtz Center for Environmental Research | And 2 more authors.
Organic Geochemistry | Year: 2012

Compound specific stable isotope analysis (CSIA) has been established as a viable tool for proving, characterizing and assessing degradation of organic pollutants within contaminated aquifers. The fractionation of stable isotopes during contaminant degradation leads to observable shifts in stable isotope ratios which can serve as an indicator for in situ pollutant degradation and allow for a quantitative assessment by means of the so-called Rayleigh (distillation) equation.This review highlights the recent developments of the Rayleigh equation approach for quantifying in situ degradation of organic pollutants in contaminated aquifers. The advantages and limitations of the Rayleigh equation approach are discussed and suggestions for improvements are given. Concepts are provided to estimate the uncertainty due to errors or variability of input parameters and how to deal with such uncertainty. Moreover, the applicability of the Rayleigh equation approach is evaluated regarding the heterogeneity and complexity of groundwater systems. For such systems, the review discusses the relevance of non-destructive processes, which affect the concentration (e.g., dispersive mixing) and potentially also the stable isotope ratio of contaminants (e.g., sorption, volatilization), and the resulting implications for the Rayleigh equation approach. © 2011 Elsevier Ltd. Source

Bashir S.,Helmholtz Center for Environmental Research | Fischer A.,Helmholtz Center for Environmental Research | Fischer A.,Isodetect Company for Isotope Monitoring | Nijenhuis I.,Helmholtz Center for Environmental Research | Richnow H.-H.,Helmholtz Center for Environmental Research
Environmental Science and Technology | Year: 2013

Carbon isotope fractionation was investigated for the biotransformation of γ- and α- hexachlorocyclohexane (HCH) as well as enantiomers of α-HCH using two aerobic bacterial strains: Sphingobium indicum strain B90A and Sphingobium japonicum strain UT26. Carbon isotope enrichment factors (εc) for γ-HCH (εc = -1.5 ± 0.1‰ and -1.7 ± 0.2‰) and α-HCH (εc = -1.0 ± 0.2‰ and -1.6 ± 0.3‰) were similar for both aerobic strains, but lower in comparison with previously reported values for anaerobic γ- and α-HCH degradation. Isotope fractionation of α-HCH enantiomers was higher for (+) α-HCH (εc = -2.4 ± 0.8 ‰ and -3.3 ± 0.8 ‰) in comparison to (-) α-HCH (εc = -0.7 ± 0.2‰ and -1.0 ± 0.6‰). The microbial fractionation between the α-HCH enantiomers was quantified by the Rayleigh equation and enantiomeric fractionation factors (εe) for S. indicum strain B90A and S. japonicum strain UT26 were -42 ± 16% and -22 ± 6%, respectively. The extent and range of isomer and enantiomeric carbon isotope fractionation of HCHs with Sphingobium spp. suggests that aerobic biodegradation of HCHs can be monitored in situ by compound-specific stable isotope analysis (CSIA) and enantiomer-specific isotope analysis (ESIA). In addition, enantiomeric fractionation has the potential as a complementary approach to CSIA and ESIA for assessing the biodegradation of α-HCH at contaminated field sites. © 2013 American Chemical Society. Source

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