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International audience; The biodegradation of hexachlorocyclohexanes (HCHs) is known to be accompanied by isotope fractionation of carbon (13C/12C), but no systematic studies were performed on abiotic degradation of HCH isomers by iron (II) minerals. In this study, we explored the carbon isotope fractionation of α-HCH during dechlorination by FeS nanoparticles at different pH values. The results of three different experiments showed that the apparent rate constants during dehalogenation of α-HCH by FeS increased with pH. The lowest apparent rate constant value α-HCH during dehalogenation by FeS was 0.009 d−1 at pH value of 2.4, while the highest was 1.098 d−1 at pH 11.8. α-HCH was completely dechlorinated by FeS only at pH values 9.9 and 11.8, while the corresponding apparent rate constants were 0.253 d−1 and 1.098 d−1, respectively. Regardless of the pH used, the 1,2,4-trichlorobenzene (1,2,4-TCB), 1,2-dichlorobenzene (1,2-DCB), and benzene were the dominant degradation products of α-HCH. An enrichment factor (εC) of −4.7 ± 1.3‰ was obtained for α-HCH using Rayleigh model, which is equivalent to an apparent kinetic isotope effect (AKIEC) value of 1.029 ± 0.008 for dehydrohalogenation, and of 1.014 ± 0.004 for dihaloelimination, respectively. The magnitude of isotope fractionation from this study suggests that abiotic isotope fractionation by FeS must be taken into account in anoxic sediments and aquifers contaminated with HCH isomers, when high concentrations of FeS are present in the above-mentioned anoxic environments.

International audience; Short-chain chlorinated paraffins (SCCPs) are under regulation through the European Water Framework Directive and were recently classified as POPs. Consecutively, the increasing use of middle-chain chlorinated paraffins (MCCPs) becomes of growing concern. Knowledge on the occurrence of chlorinated paraffins (CPs) is still scarce particularly in water phase. To achieve sufficient method sensitivity, the passive sampling approach, acting as a relevant alternative to usual grab sampling, has been considered only very recently for the monitoring of CPs in water. The present work aimed at determining the diffusion coefficients in silicone (D s) and the silicone-water partition coefficients (K sw) of various CP groups, having different chlorine contents and carbon chain lengths, in four commercial CP mixtures. Log D s (-10.78 to-10.21) was found to vary little and to be high for the groups of CPs studied. Thus, their uptake in silicone is controlled by the water boundary layer, which allows to consider the release of performance and reference compounds for infield estimation of the sampling rate. Moreover, CPs partitioned strongly towards silicone rubbers. Both the chlorination degree and the carbon chain length of CPs cause large uncertainties in the partitioning between silicone and water (log K sw between 4.85 and 6.30), indicating that instead of an average value, differentiated K sw should be used to estimate aqueous CPs more accurately. Even so, the probable influence of chlorine atoms position on polarity and partitioning may be an argument for favoring sampling in the kinetic stage.

International audience; Position-specific isotope analysis by Nuclear Magnetic Resonance spectrometry was employed to study the 13C intramolecular isotopic fractionation associated with the migration of organic substrates through different stationary phases chromatography columns. Liquid chromatography is often used to isolate compounds prior to their isotope analysis and this purification step potentially alters the isotopic composition of target compounds introducing a bias in the later measured data. Moreover, results from liquid chromatography can yield the sorption parameters needed in reactive transport models that predict the transport and fate of organic contaminants to in the environment. The aim of this study was to use intramolecular isotope analysis to study both 13C and 15N isotope effects associated with the elution of paracetamol (acetaminophen) through different stationary phases and to compare them to effects observed previously for vanillin. Results showed very different intramolecular isotope fractionation profiles depending on the chemical structure of the stationary phase. The data also demonstrate that both the amplitude and the distribution of measured isotope effects depend on the nature of the non-covalent interactions involved in the migration process. Results provided by theoretical calculation performed during this study also confirmed the direct link between observed intramolecular isotope fractionation and the nature of involved intermolecular interactions. It is concluded that the nature of the stationary phase through which the substrate passes has a major impact on the intramolecular isotopic composition of organic compounds isolated by chromatography methods..

International audience; This study aimed at investigating whether stable isotopes can be used to monitor the progress of volatile organic compounds (VOCs) volatilization from contaminated sediment during venting. Batches of a dry aquifer sediment were packed into stainless steel HPLC columns, humidified with distilled water and later contaminated by either liquid toluene or propan-2-ol. The VOCs were then volatilized by a stream of gas at room temperature, and the concentrations and stable isotope ratios of gaseous VOCs were recorded by isotope-ratio mass spectrometry. During early stages of volatilization of toluene, the isotope ratios Δδ13C shifted to more negative values by about −3 to −5‰ and the Δδ2H by more than −40‰, while the concentration remained at or near initial saturated vapor concentration. Depletion of the isotope ratios in the gas was explained by the vapor-liquid fractionation process, which is amplified by successive self-partitioning steps of gaseous VOC into remaining liquid VOC. For propan-2-ol the carbon isotope shift was negative like for toluene, whereas the H shift was positive. Hydrogen bonding in the liquid propan-2-ol phase causes a normal vapor-liquid H isotope effect which was described already in classical literature. The isotope shifts in the present experiments are larger than previously reported shifts due to phase-change processes and reach the magnitude of shifts usually observed in kinetic isotope fractionation.

International audience; Stable isotopes have been widely used to monitor remediation of environmental contaminants over the last decades. This approach gives a good mechanistic description of natural or assisted degradation of organic pollutants, such as methyl tert-butyl ether (MTBE). Since abiotic degradation seems to be the most promising assisted attenuation method, the isotopic fractionation associated with oxidation and hydrolysis processes need to be further investigated in order to understand better these processes and make their monitoring more efficient. In this study, position-specific isotope effects (PSIEs) associated with permanganate oxidation and acid hydrolysis of MTBE were determined using isotope ratio monitoring by 13C Nuclear Magnetic Resonance Spectrometry (irm-13C NMR) combined with isotope ratio monitoring by Mass Spectrometry (irm-MS). The use of this Position-Specific Isotopic Analysis (PSIA) method makes it possible to observe a specific normal isotope effect (IE) associated with each of these two abiotic degradation mechanisms. The present work demonstrates that the 13C isotope pattern of the main degradation product, tert-butyl alcohol (TBA), depends on the chemical reaction by which it is produced. Furthermore, this study also demonstrates that PSIA at natural abundance can give new insights into reaction mechanisms and that this methodology is very promising for the future of modeling the remediation of organic contaminants.

Several remediation techniques are available to treat source zones with Non-Aqueous Phase Liquids (NAPLs). Despite hundreds of treated sites, it is still quite difficult to estimate the potential efficiency of a treatment technique under a given context. In the literature, numerous papers deal with the potential limitations of one remediation technique at a laboratory scale or in the field, but only a few studies compared two or more different techniques. Thus, the objective of this chapter is to compare different treatment techniques in the same solid matrix and under the same conditions at three different experimental scales: batch, columns, and metric pilot tank experiments. The chosen techniques are among the most common ones, i.e., oxidation, sparging, surfactant flushing, and low-temperature thermal treatment. These four techniques were applied first at the batch and column scale in order to assess their potential efficiency under well-controlled conditions. These experiments are mandatory for choosing the best oxidant, the activating agents for this oxidant, the best concentration, and the determination of the limiting factors which can be encountered. All these lab experiments allowed a selection of favorable conditions for testing four techniques at the pilot scale. These treatment techniques were tested in the same configuration, in tanks of one cubic meter volume, filled with sand and emplaced sources containing a toluene/decane mixture as representative of a NAPL phase. The major findings of this study are: (1) Thermal treatment was the most efficient remediation technique; (2) Dissolution issues reduced the efficiency of the three other techniques; (3) Heterogeneity in the tanks caused a decrease in the removal efficiency for all treatments compared to efficiencies obtained at the column scale; (4) Density effects, which were not encountered at the column scale, caused problems for oxidant injection in the tanks; (5) Removal techniques that are equal for mass-based removal goal were quite different in lowering the dissolved contaminant flux from the system. Therefore, the ranking of techniques based on mass removal may not be appropriate and be replaced by a flux reduction selection; and (6) A need to perform experiments at three experimental scales is evidenced: batch studies allow sufficient variations in experimental conditions, the column experiments permitted the optimization of surfactant and oxidant injection, whereas tank experiments allow studies under heterogeneous flow conditions.

International audience; BIOCHLOR is a well-known simple tool for evaluating the transport of dissolved chlorinated solvents in ground-water, ideal for rapid screening and teaching. This work extends the BIOCHLOR model for the calculation of stable isotope ratios of carbon and chlorine isotopes in chioroethenes. An exact solution for the three-dimensional reactive transport of a chain of degrading compounds including sorption is provided in a spreadsheet and applied for modeling the transport of individual isotopes C-12,C-13, Cl-35, Cl-37 from a constant source. The model can consider secondary isotope effects that can occur in the breaking of C-Cl bonds. The model is correctly reproducing results for delta C-13 and delta Cl-37 modeled by a previously published 1-D numerical model without secondary isotope effects, and is also reproducing results from a microcosm experiment with secondary chlorine isotope effects. Two applications of the model using field data from literature are further given and discussed. The new BIOCHLOR-ISO model is distributed as a spreadsheet (MS EXCEL) along with this publication. (C) 2016 Elsevier B.V. All rights reserved.

Tracing the origin of iron-cyanide complexes in the environment is important because these compounds are potentially toxic. We determined the stable isotopic compositions of cyanide-carbon (CCN) and cyanide-nitrogen (NCN) in 127 contaminated solids and 11 samples of contaminated groundwater from coal carbonization sites, blast furnace operations, and commercial cyanide applications. Coal-carbonization-related cyanides had unique high mean δ(13)CCN values of -10.5 ± 3.5‰ for the solids and -16.1 ± 1.2‰ for the groundwater samples, while the values for blast furnace sludge (-26.9 ± 1.5‰), commercial cyanides (-26.0 ± 3.0‰), and their corresponding groundwaters were significantly lower. Determination of δ(13)CCN is a promising tool for identifying the source of cyanide contamination. However, for coal carbonization sites, historical research into the manufacturing process is necessary because a nonconventional gas works site exhibited exceptionally low δ(13)CCN values of -22.7 ± 1.7‰. The δ(15)NCN values for samples related to coal carbonization and blast furnaces overlapped within a range of +0.1 to +10.3‰, but very high δ(15)NCN values seemed to be indicative for a cyanide source in the blast furnace. In contrast, commercial cyanides tend to have lower δ(15)NCN values of -5.6 to +1.9‰ in solids and -0.5 to +3.0‰ in the groundwater.

International audience; Position-specific isotope effects (PSIEs) have been measured by isotope ratio monitoring C-13 nuclear magnetic resonance spectrometry during the evaporation of 10 liquids of different polarities under 4 evaporation modes (passive evaporation, air-vented evaporation, low pressure evaporation, distillation). The observed effects are used to assess the validity of the Craig-Gordon isotope model for organic liquids. For seven liquids the overall isotope effect (IE) includes a vapor-liquid contribution that is strongly position specific in polar compounds but less so in apolar compounds and a diffusive IE that is not position-specific, except in the alcohols, ethanol and propan-1-ol. The diffusive IE is diminished under forced evaporation. The position-specific isotope pattern created by liquid-vapor IEs is manifest in five liquids, which have an air-side limitation for volatilization. For the alcohols, undefined processes in the liquid phase create additional PSIEs. Three other liquids with limitations on the liquid side have a lower, highly position-specific, bulk diffusive IE. It is concluded that evaporation of organic pollutants creates unique position-specific isotope patterns that may be used to assess the progress of remediation or natural attenuation of pollution and that the Craig-Gordon isotope model is valid for the volatilization of nonpolar organic liquids with air-side limitation of the volatilization rate.

International audience; Isotopic fractionation of pollutants in terrestrial or aqueous environments is a well-recognized means by which to track different processes during remediation. As a complement to the common practice of measuring the change in isotope ratio for the whole molecule using isotope ratio monitoring by mass spectrometry (irm-MS), position-specific isotope analysis (PSIA) can provide further information that can be exploited to investigate source and remediation of soil and water pollutants. Position-specific fractionation originates from either degradative or partitioning processes. We show that isotope ratio monitoring by C-13 NMR (irm-C-13 NMR) spectrometry can be effectively applied to methyl tert-butylether, toluene, ethanol and trichloroethene to obtain this position-specific data for partitioning. It is found that each compound exhibits characteristic position-specific isotope fractionation patterns, and that these are modulated by the type of evaporative process occurring. Such data should help refine models of how remediation is taking place, hence back-tracking to identify pollutant sources. (C) 2015 Elsevier Ltd. All rights reserved.

International audience; We aim at predicting the effect of structure and isotopic substitutions on the equilibrium vapour pressure isotope effect of various organic compounds (alcohols, acids, alkanes, alkenes and aromatics) at intermediate temperatures. We attempt to explore quantitative structure property relationships by using artificial neural networks (ANN); the multi-layer perceptron (MLP) and compare the performances of it with multi-linear regression (MLR). These approaches are based on the relationship between the molecular structure (organic chain, polar functions, type of functions, type of isotope involved) of the organic compounds, and their equilibrium vapour pressure. A data set of 130 equilibrium vapour pressure isotope effects was used: 112 were used in the training set and the remaining 18 were used for the test/validation dataset Two sets of descriptors were tested, a set with all the descriptors: number of C-12, C-13, O-16, O-18, H-1, H-2, OH functions, OD functions, C=O functions, Connolly Solvent Accessible Surface Area (CSA) and temperature and a reduced set of descriptors. The dependent variable (the output) is the natural logarithm of the ratios of vapour pressures (ln R), expressed as light/heavy as in classical literature. Since the database is rather small, the leave-one-out procedure was used to validate both models. Considering higher determination coefficients and lower error values, it is concluded that the multi-layer perceptron provided better results compared to multi-linear regression. The stepwise regression procedure is a useful tool to reduce the number of descriptors. To our knowledge, a Quantitative Structure Property Relationship (QSPR) approach for isotopic studies is novel. (C) 2014 Elsevier Ltd. All rights reserved.

The enrichment factor (e) is a common way to express Isotope Effects (IEs) associated with a phenomenon. Many studies determine e using a Rayleigh-plot, which needs multiple data points. More recent articles describe an alternative method using the Rayleigh equation that allows the determination of e using only one experimental point, but this method is often subject to controversy. However, a calculation method using two points (one experimental point and one at t0) should lead to the same results because the calculation is derived from the Rayleigh equation. But, it is frequently asked “what is the valid domain of use of this two point calculation?” The primary aim of the present work is a systematic comparison of results obtained with these two methodologies and the determination of the conditions required for the valid calculation of e. In order to evaluate the efficiency of the two approaches, the expanded uncertainty (U) associated with determining e has been calculated using experimental data from three published articles. The second objective of the present work is to describe how to determine the expanded uncertainty (U) associated with determining e. Comparative methodologies using both Rayleigh-plot and two point calculation are detailed and it is clearly demonstrated that calculation of e using a single data point can give the same result as a Rayleigh-plot provided one strict condition is respected: that the experimental value is measured at a small fraction of unreacted substrate (f < 30%). This study will help stable isotope users to present their results in a more rigorous expression: e ± U and therefore to define better the significance of an experimental results prior interpretation.

11th International Symposium on Applied Isotope Geochemistry (AIG), French Geol Survey, Orleans, FRANCE, SEP 21-25, 2015; International audience; The common practice of measuring the change in isotope ratio for the whole molecule using isotope ratio measurement by mass spectrometry leads to the loss of significant information of potential interest, since it is the position-specific fractionation which most closely reflects the effect of physicochemical processes. We have shown for MTBE, a common ground water contaminant, that isotopic quantitative C-13 NMR spectrometry can be effectively applied to obtain this position-specific data. It is found that different characteristic position-specific isotope fractionation patterns are introduced by different types of evaporative process or by oxidative degradation. (C) 2015 Published by Elsevier B.V.

A diesel fuel contaminated aquifer in Menziken, Switzerland was treated for 4.5 years by injecting aerated groundwater, supplemented with KNO3 and NH4H2PO4 to stimulate indigenous populations of petroleum hydrocarbon (PHC) degrading microorganisms. After dissolved PHC concentrations had stabilized at a low level, engineered in situ bioremediation was terminated. The main objective of this study was to evaluate the efficacy of intrinsic in situ bioremediation as a follow-up measure to remove PHC remaining in the aquifer after terminating engineered in situ bioremediation. In the first 7 months of intrinsic in situ bioremediation, redox conditions in the source area became more reducing as indicated by lower concentrations of SO24‾ and higher concentrations of Fe(II) and CH4. In the core of the source area, strongly reducing conditions prevailed during the remaining study period (3 years) and dissolved PHC concentrations were higher than during engineered in situ bioremediation. This suggests that biodegradation in the core zone was limited by the availability of oxidants. In lateral zones of the source area, however, gradually more oxidized conditions were reestablished again, suggesting that PHC availability increasingly limited biodegradation. The total DIC production rate in the aquifer decreased within 2 years to about 25% of that during engineered in situ bioremediation and remained at that level. Stable carbon isotope analysis confirmed that the produced DIC mainly originated from PHC mineralization. The total rate of DIC and CH4 production in the source area was more than 300 times larger than the rate of PHC elution. This indicates that biodegradation coupled to consumption of naturally occurring oxidants was an important process for removal of PHC which remained in the aquifer after terminating engineered measures.

The anaerobic biodegradation of hydrocarbons at mineral oil contaminated sites has gathered increasing interest as a naturally occurring remediation process. The aim of this study was to investigate biodegradation of hydrocarbons in laboratory aquifer columns in the absence of O2 and NO&#1753, and to calculate a mass balance of the anaerobic biodegradation processes. The laboratory columns contained aquifer material from a diesel fuel contaminated aquifer. They were operated at 25°C for 65 days with artificial groundwater that contained only SO24&#175 and CO2 as externally supplied oxidants. After 31 days of column operation, stable concentration profiles were found for most of the measured dissolved species. Within 14 h residence time, about 0.24 mM SO24&#175 were consumed and dissolved Fe(II) (up to 0.012 mM), Mn(II) (up to 0.06 mM), and CH4 (up to 0.38 mM) were produced. The alkalinity and the dissolved inorganic carbon (DIC) concentration increased and the DIC became enriched in 13C. In the column, n-alkanes were selectively removed while branched alkanes persisted, suggesting a biological degradation. Furthermore, based on changes of concentrations of aromatic compounds with similar physical–chemical properties in the effluent, it was concluded that toluene, p-xylene and naphthalene were degraded. A carbon mass balance revealed that 65% of the hydrocarbons removed from the column were recovered as DIC, 20% were recovered as CH4, and 15% were eluted from the column. The calculations indicated that hydrocarbon mineralization coupled to SO24&#175 reduction and methanogenesis contributed in equal proportions to the hydrocarbon removal. Hydrocarbon mineralization coupled to Fe(III) and Mn(IV) reduction was of minor importance. DIC, alkalinity, and stable carbon isotope balances were shown to be a useful tool to verify hydrocarbon mineralization.

In this paper, four treatment techniques commonly applied to Volatile Organic Compounds (VOC) removal from soil are compared in column experiments with pure sand containing a residual Light Non-Aqueous Phase Liquid (L-NAPL) contamination. Oxidation is tested through the injection of Fenton reagent, with persulfate, and combined with sparging with the injection of ozone. Surfactant treatment was conducted at low flow rates with Tween®80. Sparging was conducted by air injection but at a low flow rate of 1 mL min−1. Finally several columns were thermally treated at a temperature of 80 °C. The results showed high removal (>90%) for all techniques used, although only thermal treatment on BTEX (Benzene, Toluene, Ethylbenzene and Xylenes) reached 100% efficiency. The main limiting factors of each technique were: (i) for oxidation, the solubility of the substance limited the removal; (ii) for surfactant both the solubility in the surfactant and the type of surfactant are important; (iii) for sparging, the main factors are contaminant vapor pressure and porous media grain size; (iv) for thermal treatment, the limitation arises from the contaminant vapor pressure and the medium hydraulic conductivity. A comparison with literature data shows that the results are consistent with most of the studies conducted on one technique.

The study focuses on the effect of volatilization, diffusion, and biodegradation on the isotope evolution of volatile organic compounds (VOCs) in a 1.06 m long column filled with alluvial sand. A liquid mixture of 10 VOCs was placed at one end of the column, and measurements of VOC vapor concentrations and compound-specific isotope ratios (δ13C) were performed at the source and along the column. Initially, the compounds became depleted in 13C by up to −4.8‰ along the column axis, until at 26 h, uniform isotope profiles were observed for most compounds, which is expected for steady-state diffusion. Subsequently, several compounds (n-pentane, benzene, n-hexane) became enriched in 13C throughout the column. For the same compounds, a significant decrease in the source vapor concentration and a gradual enrichment of 13C by up to 5.3‰ at the source over a period of 336 h was observed. This trend can be explained by a larger diffusive mass flux for molecules with light isotopes compared to those with a heavy isotope, which leads to a depletion of light isotopes in the source. The isotope evolution of the source followed closely a Rayleigh trend and the obtained isotope enrichment factor corresponded well to the ratio between the diffusion coefficients for heavy and light molecules as expected based on theory. In contrast to diffusion, biodegradation had generally only a small effect on the isotope profiles, which is expected because in a diffusion-controlled system the isotope shift per decrease of mass flux is smaller than in an advection-controlled system. These findings open interesting perspectives for monitoring source depletion with isotope and have implications for assessing biodegradation and source variability in the unsaturated zone based on isotopes.

International audience; The relationship between the strength of the intermolecular interaction in liquid and the position-specific 13C fractionation observed during distillation was investigated. A range of molecules showing different intermolecular interactions in terms of mode and intensity were incorporated in the study. Although it had previously been suggested that during evaporation the diffusive 13C isotope effect in the thin liquid layer interfaced with vapor is not position-specific, herein we show that this is not the case. In particular, the position-specific effect was demonstrated for a series of alcohols. Our hypothesis is that intermolecular interactions in the liquid phase are the source of position-specific 13C fractionation observed on the molecule. A clear trend is observed between the 13C isotope effect of the carbon bearing the heteroatom of chemical function and the relative permittivity, the solvent hydrogen-bond acidity and the solvent hydrogen-bond basicity, while only a weak trend was observed when using the 13C content of the whole molecule. Furthermore two families of products appeared when using the hydrogen-bond acidity parameter for the correlation by distinguishing H-acceptors and H-donors molecules to those H-acceptors only. This strongly reinforces the hypothesis of an important role of the 13C positioned close to the interaction center.

International audience; Compound-specific isotope analysis (CSIA) is a state-of-the-art analytical tool that can be used to establish and quantify biodegradation of pollutants such as BTEX compounds at contaminated field sites. Using isotopes of two elements and characteristic Lambda values (A) in dual-isotope-plots can provide insight into reaction mechanisms because kinetic isotope effects (KIEs) of both elements are reflected. However, the concept's validity in the case of reactions that show strong isotope fractionation needs to be examined. The anaerobic ethylbenzene degradation pathway of Aromatoleum aromaticum is initiated by the ethylbenzene dehydrogenase-catalyzed monohydroxylation of the benzylic carbon atom. Measurements of stable isotope ratios revealed highly pronounced hydrogen fractionation, which could not be adequately described by the classical Rayleigh approach. This study demonstrates the nonlinear behavior of hydrogen isotope ratios caused by anaerobic ethylbenzene hydroxylation both mathematically and experimentally, develops alternative dual plots to enable the comparison of reactions by considering the reacting atoms, and illustrates the importance of the stereochemical aspects of substrate and product for the quantification of hydrogen fractionation in an enzymatic reaction. With regard to field application, proposals for an improved CSIA evaluation procedure with respect to pronounced hydrogen enrichment are given.

International audience; This study compared four treatment techniques for the removal of a toluene/n-decane as NAPL (Non Aqueous Phase Liquid) phase mixture in identical 1 cubic meter tanks filled with different kind of sand. These four treatment techniques were: oxidation with persulfate, surfactant washing with Tween80®, sparging with air followed by ozone, and thermal treatment at 80 °C. The sources were made with three lenses of 26 × 26 × 6.5 cm, one having a hydraulic conductivity similar to the whole tank and the two others a value 10 times smaller. The four techniques were studied after conditioning the tanks with tap water during approximately 80 days. The persulfate treatment tests showed average removal of the contaminants but significant flux decrease if density effects are considered. Surfactant flushing did not show a highly significant increase of the flux of toluene but allowed an increased removal rate that could lead to an almost complete removal with longer treatment time. Sparging removed a significant amount but suggest that air was passing through localized gas channels and that the removal was stagnating after removing half of the contamination. Thermal treatment reached 100% removal after the target temperature of 80 °C was kept during more than 10 d. The experiments emphasized the generation of a high-spatial heterogeneity in NAPL content. For all the treatments the overall removal was similar for both n-decane and toluene, suggesting that toluene was removed rapidly and n-decane more slowly in some zones, while no removal existed in other zones. The oxidation and surfactant results were also analyzed for the relation between contaminant fluxes at the outlet and mass removal. For the first time, this approach clearly allowed the differentiation of the treatments. As a conclusion, experiments showed that the most important differences between the tested treatment techniques were not the global mass removal rates but the time required to reach 99% decrease in the contaminant fluxes, which were different for each technique.; This study compared four treatment techniques for the removal of a toluene/n-decane as NAPL (Non Aqueous Phase Liquid) phase mixture in identical 1 cubic meter tanks filled with different kind of sand. These four treatment techniques were: oxidation with persulfate, surfactant washing with Tween80®, sparging with air followed by ozone, and thermal treatment at 80 °C. The sources were made with three lenses of 26 × 26 × 6.5 cm, one having a hydraulic conductivity similar to the whole tank and the two others a value 10 times smaller. The four techniques were studied after conditioning the tanks with tap water during approximately 80 days.The persulfate treatment tests showed average removal of the contaminants but significant flux decrease if density effects are considered. Surfactant flushing did not show a highly significant increase of the flux of toluene but allowed an increased removal rate that could lead to an almost complete removal with longer treatment time. Sparging removed a significant amount but suggests that air was passing through localized gas channels and that the removal was stagnating after removing half of the contamination. Thermal treatment reached 100% removal after the target temperature of 80 °C was kept during more than 10 d.The experiments emphasized the generation of a high-spatial heterogeneity in NAPL content. For all the treatments the overall removal was similar for both n-decane and toluene, suggesting that toluene was removed rapidly and n-decane more slowly in some zones, while no removal existed in other zones.The oxidation and surfactant results were also analyzed for the relation between contaminant fluxes at the outlet and mass removal. For the first time, this approach clearly allowed the differentiation of the treatments. As a conclusion, experiments showed that the most important differences between the tested treatment techniques were not the global mass removal rates but the time required to reach 99% decrease in the contaminant fluxes, which were different for each technique.

International audience; Source delineation of hydrocarbon contaminated sites is of high importance for remediation work. However, traditional methods like soil core extraction and analysis or recent Membrane Interface Probe methods are time consuming and costly. Therefore, the development of an in situ method based on soil gas analysis can be interesting. This includes the direct measurement of volatile organic compounds (VOCs) in soil gas taken from gas probes using a PID (Photo Ionization Detector) and the analysis of other soil gases related to VOC degradation distribution (CH4, O-2, CO2) or related to presence of Light Non-Aqueous Phase Liquid (LNAPL) as Rn-222. However, in widespread heterogeneous formations, delineation by gas measurements becomes more challenging. The objective of this study is twofold: (i) to analyse the potential of several in situ gas measurement techniques in comparison to soil coring for LNAPL source delineation at a heterogeneous contaminated site where the techniques might be limited by a low diffusion potential linked to the presence of fine sands and silts, and (ii) to analyse the effect of vertical sediment heterogeneities on the performance of these gas measurement methods. Thus, five types of gases were analysed: VOCs, their three related degradation products O-2, CO2 and CH4 and Rn-222. Gas measurements were compared to independent LNAPL analysis by coring. This work was conducted at an old industrial site frequently contaminated by a Diesel-Fuel mixture located in a heterogeneous fine-grained aquifer. Results show that in such heterogeneous media migration of reactive gases like VOCs occurs only across small distances and the VOC concentrations sampled with gas probes are mainly related to local conditions rather than the presence of LNAPL below the gas probe. Rn-222 is not well correlated with LNAPL because of sediment heterogeneity. Oxygen, CO2, and especially CH4, have larger lengths of diffusion and give the clearest picture for LNAPL presence at this site even when the gas probe is somewhat distant. (C) 2016 Elsevier B.V. All rights reserved.

Analytical models were developed that simulate stable isotope ratios of volatile organic compounds (VOCs) near a point source contamination in the unsaturated zone. The models describe diffusive transport of VOCs, biodegradation and source ageing. The mass transport is governed by Fick's law for diffusion, and the equation for reactive transport of VOCs in the soil gas phase was solved for different source geometries and for different boundary conditions. Model results were compared to experimental data from a one-dimensional laboratory column and a radial-symmetric field experiment, and the comparison yielded a satisfying agreement. The model results clearly illustrate the significant isotope fractionation by gas-phase diffusion under transient state conditions. This leads to an initial depletion of heavy isotopes with increasing distance from the source. The isotope evolution of the source is governed by the combined effects of isotope fractionation due to vaporization, diffusion and biodegradation. The net effect can lead to an enrichment or depletion of the heavy isotope in the remaining organic phase depending on the compound and element considered. Finally, the isotope evolution of molecules migrating away from the source and undergoing degradation is governed by a combined degradation and diffusion isotope effect. This suggests that in the unsaturated zone, the interpretation of biodegradation based on isotope data must always be based on a model combining gas-phase diffusion and degradation., 11 pages, 6 figures

The purpose of this work was to develop a coupled hydrological and chemical model that can simulate time-dependent concentrations of pesticides and their degradation products in shallow coastal water bodies of variable volumes. The model was applied to simulate the exposure of two herbicides, oxadiazon and MCPA, in three interconnected lagoons which form the coastal wetlands of the Camargue. These shallow lagoons and adjacent marshes are of international importance for the preservation of biodiversity. The chemical fugacity and reactivity are modeled in these complex ecosystems as in classical fate models for well-mixed lakes, but additionally water exchanges between the lagoons, seawater intrusion, variable evaporation rates and fluctuating water volumes of the lagoons are incorporated. Analytical solutions for coupled differential equations for the water volumes of the lagoons, the salinities, and the concentrations of pesticides were derived and evaluated using the software Maple. The model was calibrated using salinity data and was able to simulate measured concentrations of oxadiazon and MCPA and two subsequent degradation products of MCPA in the main lagoon in Camargue. Interestingly, model simulations differed from real observations in the two smaller lower lagoons, and the model served tracking so far unknown entry paths of herbicides into these lagoons.

In this comment, we revisit equations concerning the analytical solutions presented by Gutierrez-Neri and co-workers for reactive transport for a pollutant undergoing core and fringe degradations. We state that a correction needs to be made in Eq. (9) of the work of Gutierrez- Neri et al. in order that the equation follows closely previous work published by J. Bear (in 1-D) and P.A. Domenico (in 3-D). Furthermore we derive alternative solutions for Eqs. (13)–(16) which separate more clearly the first-order reaction and the instantaneous reaction. It is shown that the corrected solution agrees better with the results from the numerical model than the previous solution. An improvement is also made by giving a solution which avoids negative concentrations. Furthermore, the corresponding solution for the electron acceptor reacting with the pollutant is given.

Microcosm experiments were conducted to quantify carbon isotope fractionation during aerobic biodegradation of n-alkanes (from C3 to C10) and monoaromatic hydrocarbons in unsaturated alluvial sand. In single compound experiments with n-alkanes, the largest enrichment factor was obtained for propane (−10.8 ± 0.7‰). The magnitude of the enrichment factor decreased with increasing number of carbon atoms from propane to n-decane (−0.2 ± 0.1‰). This trend can partly be explained by the decreasing probability that a 13C is located at the reacting site in the molecule with increasing chain length. After correcting for the presence of non-reacting positions, a chain length dependence of the calculated apparent isotope effect persisted. This observation suggests that transport and binding steps before the actual reaction step become increasingly rate limiting with increasing chain length. For aromatic compounds tested individually, the enrichment factor was the largest (−1.4 ± 0.1‰) for benzene (B), followed by toluene (T) (−0.8 ± 0.1‰) and m-xylene (X) (−0.6 ± 0.1‰). Enrichment factors for BTX were systematically smaller than for n-alkanes with equivalent number of carbons, which is likely related to different biodegradation mechanisms. The study demonstrates that significant carbon isotope fractionation occurs during aerobic biodegradation of n-alkanes and aromatic compounds under unsaturated conditions and that the magnitude of isotope enrichment is linked to molecule size and molecule structure.

International audience; In forensic environmental investigations the main issue concerns the inference of the original source of the pollutant for determining the liable party. Isotope measurements in geochemistry, combined with complimentary techniques for contaminant identification, have contributed significantly to source determination at polluted sites. In this work we have determined the intramolecular C-13 profiles of several molecules well-known as pollutants. By giving additional analytical parameters, position-specific isotope analysis performed by isotope ratio monitoring by C-13 nuclear magnetic resonance (irm-C-13 NMR) spectrometry gives new information to help in answering the major question: what is the origin of the detected contaminant? We have shown that isotope profiling of the core of a molecule reveals both the raw materials and the process used in its manufacture. It also can reveal processes occurring between the contamination site `source' and the sampling site. Thus, irm-C-13 NMR is shown to be a very good complement to compound-specific isotope analysis currently performed by mass spectrometry for assessing polluted sites involving substantial spills of pollutant. (C) 2015 Elsevier B.V. All rights reserved.

A field experiment was conducted in Denmark in order to evaluate the fate of 13 volatile organic compounds (VOCs) that were buried as an artificial fuel source in the unsaturated zone. Compound-specific isotope analysis showed distinct phases in the 13C/12C ratio evolution in VOC vapors within 3 m from the source over 114 days. At day 3 and to a lesser extent at day 6, the compounds were depleted in 13C by up to -5.7% per hundred with increasing distance from the source compared to the initial source values. This trend can be explained by faster outward diffusion of the molecules with 12C only compared to molecules with a 13C. Then, the isotope profile leveled out, and several compounds started to become enriched in 13C by up to 9.5% per hundred with increasing distance from the source, due to preferential removal of the molecules with 12C only, through biodegradation. Finally, as the amount of a compound diminished in the source, a 13C enrichment was also observed close to the source. The magnitude of isotope fractionation tended to be larger the smaller the mass of the molecule was. This study demonstrates that, in the unsaturated zone, carbon isotope ratios of hydrocarbons are affected by gas-phase diffusion in addition to biodegradation, which was confirmed using a numerical model. Gas-phase diffusion led to shifts in delta(13)C >1% per hundred during the initial days after the spill, and again during the final stages of source volatilization after >75% of a compound had been removed. In between, diffusion has less of an effect, and thus isotope data can be used as an indicator for hydrocarbon biodegradation.

A microcosm study was conducted to investigate the degradation of mono- and polyaromatic hydrocarbons under in situ-like conditions using alluvial sediments from the site of a former cokery. Benzene, naphthalene, or acenaphthene were added to the sediments as (13)C-labeled substrates. Based on the evolution of (13)C-CO(2) determined by gas chromatography isotope-ratio mass spectrometry (GC-IRMS) it was possible to prove mineralization of the compound of interest in the presence of other unknown organic substances of the sediment material. This new approach was suitable to give evidence for the intrinsic biodegradation of benzene, naphthalene, and acenaphthene under oxic and also under anoxic conditions, due to the high sensitivity and reproducibility of (13)C/(12)C stable isotope analysis. This semi-quantitative method can be used to screen for biodegradation of any slowly degrading, strongly sorbing compound in long-term experiments.

International audience; Spills of chloroethenes (CEs) at industrial and urban sites can create groundwater plumes in which tetrachloro- and trichloroethene sequentially degrade to dichloroethenes, vinyl chloride (VC) and ethene, or ethane under reducing conditions. For detoxification, degradation must go beyond VC. Assessments based on ethene and ethane, however, `` are difficult because these products are volatile, may stem from alternative sources, can be further transformed and are not always monitored. To alternatively quantify degradation beyond VC, stable carbon isotope mass balances have been proposed where concentration-weighted CE isotope ratios are summed up and compared to the original source isotope ratio. Reported assessments, however, have provided not satisfactorily quantified results entailing greatly differing upper and lower estimates. This work proposes an integrative approach to better constrain the extent of total chloroethene degradation in groundwater samples. It is based on fitting of measured concentration and compound-specific stable carbon isotope data to an analytical reactive transport equation simulating steady-state plumes in two dimensions using an EXCEL spreadsheet. The fitting also yields estimates of degradation rates, of source width and of dispersivities. The approach is validated using two synthetic benchmark cases where the true extent of degradation is well known, and using data from two real field cases from literature. (C) 2015 Elsevier BM. All rights reserved.

International audience; A pipeline transporting crude-oil broke in a nature reserve in 2009 and spilled 5100 m(3) of oil that partly reached the aquifer and formed progressively a floating oil lens. Groundwater monitoring started immediately after the spill and crude-oil recovery by dual pump-and-skim technology was operated after oil lens formation. This study aimed at documenting the implementation of redox-specific natural attenuation processes in the saturated zone and at assessing whether dissolved compounds were degraded. Seven targeted water sampling campaigns were done during four years in addition to a routine monitoring of hydrocarbon concentrations. Liquid oil reached the aquifer within 2.5 months, and anaerobic processes, from denitrification to reduction of sulfate, were observable after 8 months. Methanogenesis appeared on site after 28 months. Stable carbon isotope analyses after 16 months showed maximum shifts in delta C-13 of +4.9 +/- 0.22 parts per thousand for toluene, +2.4 +/- 0.19 parts per thousand for benzene and +0.9 +/- 0.51 parts per thousand for ethylbenzene, suggesting anaerobic degradation of these compounds in the source zone. Estimations of fluxes of inorganic carbon produced by biodegradation revealed that, in average, 60% of inorganic carbon production was attributable to sulfate reduction. This percentage tended to decrease with time while the production of carbon attributable to methanogenesis was increasing. Within the investigation time frame, mass balance estimations showed that biodegradation is a more efficient process for control of dissolved concentrations compared to pumping and filtration on an activated charcoal filter. (C) 2015 Elsevier B.V. All rights reserved.

The natural attenuation of volatile organic compounds (VOCs) in the unsaturated zone can only be predicted when information about microbial biodegradation rates and kinetics are known. This study aimed at determining first-order rate coefficients for the aerobic biodegradation of 13 volatile petroleum hydrocarbons which were artificially emplaced as a liquid mixture during a field experiment in an unsaturated sandy soil. Apparent first-order biodegradation rate coefficients were estimated by comparing the spatial evolution of the resulting vapor plumes to an analytical reactive transport model. Two independent reactive numerical model approaches have been used to simulate the diffusive migration of VOC vapors and to estimate degradation rate coefficients. Supplementary laboratory column and microcosm experiments were performed with the sandy soil at room temperature under aerobic conditions. First-order kinetics adequately matched the lab column profiles for most of the compounds. Consistent compound-specific apparent first-order rate coefficients were obtained by the three models and the lab column experiment, except for benzene. Laboratory microcosm experiments lacked of sensitivity for slowly degrading compounds and underestimated degradation rates by up to a factor of 5. Addition of NH3 vapor was shown to increase the degradation rates for some VOCs in the laboratory microcosms. All field models suggested a significantly higher degradation rate for benzene than the rates measured in the lab, suggesting that the field microbial community was superior in developing benzene degrading activity.

Soil-gas monitoring is a widely used tool to observe the migration of volatile organic compounds (VOCs) at contaminated sites. By combining this technique with natural gradient tracer methods, diffusive contaminant fluxes can be measured in situ, and non–aqueous phase liquid (NAPL) can be detected and roughly quantified. This work describes the new approach and its application at a field site in Denmark with an emplaced NAPL contamination. Soil-gas probes with a low dead volume were installed at 1-m depths in the sandy vadose zone, and a small volume of gas containing conservative and partitioning tracers was injected. Soil-gas samples were withdrawn subsequently during 1 to 4 h and analyzed simultaneously for VOCs and tracers. Tracers detected the NAPL reliably, and the combined data allowed for a close delineation of the source zone. The calculated NAPL saturation deviated by up to a factor of 3 from the analyses of soil cores. Better agreement was found by taking the NAPL composition into consideration, which is, however, generally unknown at the actual field sites. In addition, the tracers were also used to estimate effective diffusion coefficients in situ, which varied by a factor of 2 between various locations. From these data, diffusive contaminant vapor fluxes were quantified without additional laboratory experiments or the use of empirical relationships. The new approach yields a better site investigation with a few additional measurements.

Modeling the gas exchange flux between soil and the atmosphere, risk assessment, and the evaluation of remediation strategies at contaminated sites require the knowledge of gas-phase diffusivities in the subsurface. We review methods to measure the tortuosity factor or the effective gas-phase diffusion coefficient in situ. The strong dependency of these parameters on the structure and volume of the air-filled pore space in the subsurface calls for an accurate and robust in situ measurement. A variety of approaches have been proposed during the last decades, each based on the observation and interpretation of gaseous tracer diffusion in near-surface soils or the deeper vadose zone under various initial and boundary conditions. We briefly describe the conceptual basis and experimental setup of each method and give insight into error propagation. We then discuss 115 effective diffusion coefficients D e compiled from the original method papers and applications. In situ methods and laboratory measurements on undisturbed soil cores yield comparable results. The Penman relationship, D e/ D m = 0.66θa, sets an upper limit for the field-determined effective diffusion coefficient in the case of uniform porosity. The Moldrup relationship, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(D\_{\mathrm{e}}/D\_{\mathrm{m}}\ =\ \mathrm{{\theta}}^{2.5}\_{\mathrm{a}}/\mathrm{{\theta}}\_{\mathrm{t}}\) \end{document}, originally proposed for sieved and repacked soils, gave the best predictions of several porosity-based relationships, but the relative deviation between observed and predicted D e can be substantial. Therefore, the application of such a relationship for the site-specific modeling of gas-phase diffusion should be justified with in situ measurements, especially in heterogeneous environments.

Petroleum products involve mixtures of different volatile organic compounds (VOCs) that may represent a risk for groundwater after a spill to the unsaturated zone. However, the majority of the published approaches and codes for unsaturated zone modeling handle only either a single or a limited number of compounds in order to cope with the complexity of processes involved in VOC attenuation. This work aimed at simulating complex VOC scenarios using a grouping procedure, which results in the definition of a small number of effective pseudospecies with carefully specified effective properties. Grouping criteria are developed for a hypothetical scenario that involves a mixture of seven VOCs with properties covering a wide range of values. These criteria are assessed through a comparison of group-based calculations with rigorous calculations using the individual components. Groups of species with similar solubility resulted in concentration profiles that compared very satisfactorily with the rigorous results. The approach is validated with data from a large-scale lysimeter experiment. The simulation results compare satisfactorily with the experimental data for several days and for the vast majority of the mixture components. The agreement was significantly improved when temporally varying solubility values were used, justified by the difference in the compound volatility and the concomitant alteration of the VOC mixture composition with time.

Chlorofluorocarbons (CFCs) are synthetic halogenated volatile organic compounds that have been manufactured since 1930 and can be detected analytically in water in pg L−1 concentrations. The use as tracers for age dating of pristine groundwater has been summarized by previous review articles, where occasional failure of the CFC age-dating technique caused by local CFC contamination in excess of the equilibrium with modern air was reported. This article summarizes the worldwide occurrence of CFCs in groundwater with a focus on contaminated aquifers. CFC data from 24 aquifers and two regions on four continents are compiled. In 10 aquifers, contamination in more than 20% of samples with either CFC-11, CFC-12, or CFC-113 is reported. Pathways of CFC input to groundwater such as local atmospheric pollution, river water infiltration, landfills, and industrial solvent spills are discussed. The aerobic and anaerobic biotransformation reactions and natural attenuation processes of CFCs in aquifers are also reviewe...

International audience; Various industrial processes and anthropogenic activities in urban areas induce a release of metals, metalloids and organic pollutants. Phytoremediation of co-contaminated waters in constructed wetlands is a promising solution for reducing the impact on natural environments. In order to improve the design and management of constructed wetlands, more knowledge is needed concerning the effect of organic pollutants on plant metal and metalloid uptake. In this study, the effects of a mixture of organic pollutants commonly found in industrial effluents (hydrocarbons, polycyclic aromatic hydrocarbons, anionic detergent) on the uptake of ten metals and metalloids (MM), i.e. Al, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn, by five helophytes having a wide European distribution were studied. Main effects of plant species and pollutant conditions on metal uptake and interactions between factors were determined by a statistical treatment of a microcosm experiment. Overall, the order of element uptake in plants was Fe > Al > Mn > Cr, Ni, Zn, > Cu > As, Cd, Pb, which was consistent with relative concentrations in the rhizosphere environment of microcosms. Larger amounts of metals were retained in belowground biomass of plants than in aboveground parts. Statistical analysis showed that organic pollutants enhanced the accumulation of Mn in whole plants and the retention of Fe in belowground parts, while they reduced the accumulation of Cd, Ni, and Zn in whole plants and the retention of Cu in belowground parts. For the other MM (Al, As, Cr, Pb), effects were variable, depending on the plant species. Among the five plants tested, Carex cuprina generally removed the highest quantities of MM, which was the result of both a high metal accumulation capacity and high biomass production. Nevertheless, no significant proportion of the MM total loading could be removed in plants aboveground parts. (C) 2014 Elsevier Ltd. All rights reserved.

8th International-Association-of-Hydrological-Sciences Groundwater Quality Conference (GQ), Univ Florida, Gainesville, FL, APR, 2013; International audience; After a crude oil spill caused by a broken pipeline in 2009 to a gravel aquifer in southern France, degradation processes under various redox conditions progressively established, but at rates that predict a long life-time of the source under natural attenuation after partial source removal. In this study, we aimed at identifying the rate-limiting factors for each redox condition, with special emphasis on phosphate as limiting nutrient. The study was conducted in laboratory microcosms assembled with material collected on site: sediments, water from monitoring wells, oil and microbial sludge. Redox conditions were promoted by adding electron acceptors (either oxygen, nitrate, limonite (FeO(OH)), cryptomelane (K(Mn4+, Mn2+)(8)O-16), or sulfate). For each condition, the role of phosphate was studied by repeated additions for up to 290 days. The results showed a very strong stimulation of aerobic and denitrifying rates of oil degradation by phosphate, provided that oxygen and nitrate were repeatedly supplied. Phosphate caused also a marked stimulation of methanogenic degradation, and a relatively small stimulation of metal reduction. These anaerobic processes started only after marked lag phases, and phosphate shortened the lag phase for methanogenic degradation. Degradation of aromatic and aliphatic hydrocarbons with less than 8 carbons, including benzene, was confirmed even under unstimulated conditions. It is concluded that degradation rates at the site are limited by both, availability of electron acceptors and availability of phosphate needed for promoting microbial growth. (C) 2014 Elsevier B.V. All rights reserved.

Chlorinated phenols (CP) are frequently found as harmful soil contaminants. Depending on the environment, CP may persist for extended periods of time. The influence of environmental factors on the degradation of 2,6-dichlorophenol (2,6-DCP) in unsaturated soil was examined using Ralstonia basilensis RK1 as inoculum for bioaugmentation. The disappearance of 2,6-DCP in soil microcosms was caused by bacterial mineralization. This was proved using U-{sup 14}C-labeled 2,6-DCP. After 5 days of incubation, 61% of the initial activity was detected as {sup 14}Co{sub 2}, while only 20{degree} of the radioactivity remained in the soil, and 2,6-DCP was not detected. The relative importance of individual factors and possible two-factor interactions was assessed using a fractional-factorial experimental design. The following individual factors were identified as important. 2,6-DCP concentration, temperature, inoculum size, and the presence of an additional substrate. The strongest factorial interaction was observed between bacterial inoculation and 2,6-DCP concentration. For practical reasons, the influence of oxygen, organic matter, and the age of the contamination were not included in the factorial design; however, these factors were analyzed separately and found to significantly affect the biodegradation of 2,6-DCP. The findings of this study are important for the design of bioremediation techniques as well as the predictionmore » of natural attenuation.« less

This study presents a stepwise concept to assess the in situ microbial mineralization of petroleum hydrocarbons (PHC) in aquifers. A new graphical method based on stable carbon isotope ratios (δ13C) was developed to verify the origin of dissolved inorganic carbon (DIC). The concept and the isotope method were applied to an aquifer in Studen, Switzerland, in which more than 34,000 liters of heating oil were accidentally released. Chemical analyses of ground water revealed that in this aquifer locally, anaerobic conditions prevailed, and that PHC mineralization was linked to the consumption of oxidants such as O2, NO2-, and SO42- and the production of reduced species such as Fe2+, Mn2+, HSS and CH4. However, alkalinity and DIC balances showed a quantitative disagreement in the link between oxidant consumption and DIC production, indicating that chemical data alone may not be a reliable assessment tool. δ13C ratios in DIC have been used before for bioremediation assessment, but results were reported to be negatively influenced by methanogenesis. Using the new graphical method to display δ13C data, it was possible to identify anomalies found in methanogenic monitoring wells. It could be shown that 88% of the DIC produced in the contaminated aquifer originated from microbial PHC mineralization. Thus, the new graphical method to display δ13C ratios appears to be a useful tool for the assessment of microbial hydrocarbon mineralization in a complex environment.

During the in situ bioremediation of a diesel fuel-contaminated aquifer in Menziken, Switzerland, aquifer material containing weathered diesel fuel (WDF) and indigenous microorganisms was excavated. This material was used to identify factors limiting WDF biodegradation under denitrifying conditions. Incubations of this material for 360 to 390 d under denitrifying conditions resulted in degradation of 23% of the WDF with concomitant consumption of NO{sub 3}{sup {minus}} and production of inorganic carbon. The biodegradation of WDF and the rate of NO{sub 3}{sup {minus}} consumption was stimulated by agitation of the microcosms. Biodegradation was not stimulated by the addition of a biosurfactant (rhamnolipids) or a synthetic surfactant (Triton X-100) at concentrations above their critical micelle concentrations. The rhamnolipids were biodegraded preferentially to WDF, whereas Triton X-100 was not degraded. Both surfactants reduced the surface tension of the growth medium from 72 to

Engineered in situ bioremediation is an economically and ecologically sound technology for the clean-up of contaminated soils and aquifers. However, a successful bioremediation requires solid evidence for the detoxification of the contaminants, preferably proven by complete mineralization. This paper discusses a stepwise evaluation leading to the demonstration of successful engineered in situ bioremediation. Five major evaluation steps assess whether: (1) the contaminants can be mineralized by the indigenous microbial population (2) the mineralization rates can be increased (3) the remediation concept can be simulated under continuous flow conditions (4) the increase of mineralization rates can be achieved at the field site (scale-up), and (5) complete mineralization to harmless end products is achieved at the field site. For these evaluations, the applicability of four experimental approaches (field investigations, laboratory aquifer columns, microcosms and microbial cultures) and the relevance of various microbiological or chemical monitoring parameters are discussed. The evaluations are illustrated using a specific engineered in situ bioremediation of a diesel fuel-contaminated aquifer in Menziken, Switzerland. The case study demonstrates that microbiological and chemical monitoring parameters as well as field tracer studies and stable carbon isotopes should be combined for the unequivocal evaluation of engineered in situ bioremediation.

International audience; In isotope geochemistry, the Rayleigh equation describes the evolution of isotope ratios in a parent compound as a function of reaction progress, and associated equations describe isotope ratios in an instantaneous product and an accumulated product. The Rayleigh equation is commonly used for fitting fractionation factors of processes undergoing kinetic isotope fractionation such as biochemical reactions. This work extends the equations associated with the Rayleigh equation for describing the isotope ratios in intermediate products in a chain of reacting species degrading with first-order kinetics. A general solution is presented for decay chains of any length, and explicit examples are presented for the biodegradation of a substrate or a mixture of substrates through 3 intermediate products to a final product. Applications of these analytical solutions for the fitting of enrichment factors for intermediate compounds in laboratory experiments are demonstrated with a spread-sheet. This avoids separate experiments to measure each intermediate product. The utility of the equations for the assessment of slopes in dual isotope plots is furthermore illustrated, and limitations of its use are critically discussed. (C) 2013 Elsevier Ltd. All rights reserved.

International audience; The appearance of agriculture in urban areas improved the health-iness of the diet of people by enabling their consumption of fresh vegetables and fruits. This study assessed the level of fertility, and the impact of the cropping system and of the exploitation time on the physicochemical properties and the pseudo-total and EDTA-extractable metals contents of the vegetable soils of urban garden of in Libreville (Gabon). The results indicated a low fertility of the cultivated soils. The metal contents in the open field cultured soils were generally different from the soils cultured under shelters. Except Al that could be toxic for cultivated vegetables, the soil properties and metal element concentrations decreased significantly with time in the open field soil, while they did not vary in open shade cultured soils. The pseudo-total cadmium concentration was below the detection limit in all soils. Multivariate analysis showed that Al, Fe and Pb were of lithogenic origin, while Cu, Zn and Mn were of anthropogenic origin.

A diesel fuel-contaminated aquifer in Menziken, Canton of Aargau, Switzerland, was in situ bioremediated from 1989 to 1994 by adding O2, NO−3 PO3−4, and NH+4 through an infiltration well. After a remediation time of 3.5 years, aquifer material from the contaminated zone was excavated and found to contain >106 hydrocarbon-degrading microorganisms/g and 1.15 ± 0.15 mg/g weathered diesel fuel comprizing mainly isoprenoid alkanes and an unresolved complex mixture (UCM) of unknown components. Samples of this material were incubated for up to 470 days in aerobic and anaerobic microcosms. The microbial activity was determined by measuring the production of inorganic carbon and the consumption of O2 and NO−3. The degradation of the weathered diesel fuel was quantified by infrared spectroscopy and by capillary gas chromatography. In aerobic microcosms, all isoprenoid alkanes and most of the UCM were biodegraded as long as a nitrogen source was present. The O2 consumption could be stimulated by adding KH2PO4 and by elevating the temperature to 22° C. In anaerobic microcosms with KNO3, NO−3 was consumed, inorganic carbon was produced, and the isoprenoid alkanes and the UCM were partially metabolized. In some selected microcosms, the NO−3 consumption rate was stimulated by adding external substrates such as toluene, o-xylene, m-xylene, p-xylene, n-alkanes, or fatty acids. Mineralization of toluene, naphthalene, and hexadecane to CO2 under denitrifying conditions was confirmed by using [14C]-labelled substrates.

Microbial cultures enriched from a diesel fuel-contaminated aquifer were able to grow on p-xylene under denitrifying conditions. The oxidation of p-xylene to CO2 was coupled to the reduction of NO3-. The enrichment cultures also grew on toluene and m-xylene, but they did not degrade benzene, ethylbenzene, and o-xylene.

Various numerical reactive transport models were developed in the last decade to simulate plumes of pollutants in heterogeneous aquifers. However, these models remain difficult to use for the non-specialist, and the computation times are often long. Users who need to fit several model parameters to match predictions with field data in heterogeneous aquifers may be discouraged by the time needed to run the simulations. The objective of this paper is to provide a set of approximations that allow performing almost instantaneous calculations for transport of redox-reactive pollutants, the most common examples being benzene, toluene, ethylbenzene and xylenes (BTEX). The approach relies on two major tools: (i) the use of flux tubes (FT), a variant of stream tubes that include dispersion, and (ii) sequential superposition of the reactions (Mixed Instantaneous and Kinetics Superposition Sequence (MIKSS)). The calculation of transport is uncoupled from the calculation of reactions. The superposition principle has been used previously for the analytical solution of a bimolecular reaction of an electron donor with an acceptor and is here extended to more than one dissolved electron acceptor reacting with more than one donor. The approach is furthermore improved by including limitations of the kinetic reactions according to the availability of the reactants and by combining kinetic and instantaneous reactions. The results computed with this approach are compared to three well known numerical models (RT3D, PHT3D, PHAST) for various test cases including uniform, slightly diverted or highly irregular flow fields and several reaction schemes for BTEX. The FT-MIKSS solution gives nearly the same results as the other models and proved to be very flexible. The major advantage of the FT-MIKSS solution is fast computation times that are generally 100 to 1000 times faster than other numerical models. This approach might be a useful tool during the long fitting procedure of field data, which may be followed by one single run of a classical numerical model using the best-fit parameters.

The aim of this study was to conceive a reactive transport model capable of providing quantitative site-specific enrichment factors for fractionation in 13 C isotopic content during sorption. As test compound the model treats vanillin, for which the 13 C isotopic content at natural abundance at each of the 8 carbon positions can be measured by quantitative 13 C nuclear magnetic resonance spectrometry. This technique determines the isotope ratios with a resolution better than ±1‰ (0.1%) at each carbon position. Site-specific isotope fractionations were recorded in chromatography column experiments with silica RP-18 as stationary phase. The one dimensional reactive transport model accounted for the sorption/desorption behavior of 8 individual 13 C-isotopomers and one 12 C-isotopomer of vanillin and reproduced satisfactorily the bulk (average over the whole compound) fractionation observed during elution. After model calibration, the enrichment factors were fitted for each carbon site where a significant fractionation was recorded. To show the interest of such a transport model for environmental studies, the model, extended to three dimensions, was exploited to simulate reactive transport in an aquifer. These results show that significant 13 C isotope fractionation is expected for 4 out of 8 13 C-isotopomers in vanillin, and illustrate that bulk isotope ratios measured by conventional compound specific isotope analysis and mass spectrometry would hardly document significant isotope fractionations in vanillin. It is concluded that modeling of site-specific isotope ratios in molecules is a priori feasible and may help to quantify unknown processes in the environment.

Processes controlling the nitrogen (N) exchange between water and sediment in eutrophic Lake Sempach were studied using three different independent methods: benthic flux chambers, interstitial water data and hypolimnetic mass balances. The sediments released NH 4 + (1.1–16.1 mmoles m−2 d−1), NO 2 - (0.1–0.4 mmoles m−2 d−1) and dissolved organic N (

Data interpretation of the Porewater Chemistry (PC) experiment at the Mont Terri Rock Laboratory has led to unexpected observations of anaerobic microbial processes which caused important geochemical perturbations of the Opalinus Clay water in the borehole. The increases of acetate to 146 mg C/L, of DIC to 109 mg C/L and of CH4 to 0.5 mg C/L were unexpected and could not be explained without the presence of a C source in the system. The organic C fuelling the observed microbial activity was until then unknown. Leaching tests were performed on several polymers used for the fabrication of the PC equipment to identify the source of organic matter (OM). Polyethylene (PE) appears to be very inert and does not release detectable concentrations of dissolved organic C (DOC) (

Radioactive fallout from the burning Chernobyl nuclear reactor provided a pulsed release of 137 Cs to Lake Sempach at the beginning of May 1986. The time-dependent removal of 137 Cs from the water column into the sediments has been investigated by analyzing water samples, settling particles and sediment cores. A flux balance has been established to determine and to quantify the removal processes in the epilimnion and hypolimnion of Lake Sempach. Between May 1986 and March 1988, removal residence times of 137 Cs averaged 150 days in the epilimnion and 280 days in the hypolimnion. 137 Cs accumulated in the hypolimnion during stratification and its scavenging from the hypolimnion into the sediments was the rate-limiting step of the overall process of removing 137 Cs from the water column. Resuspension of sedimentary 137 Cs occurred during circulation periods in winter. Scavenging by settling particles was the dominant removal process of 137 Cs in epilimnion and hypolimnion. Sediment trap fluxes of 137 Cs and 210 Pb linearly correlated with increasing particle fluxes up to a maximum of about 2.5 g m−2 d −1 . Higher particle fluxes, likely due to calcite precipitation, did not enhance removal fluxes and scavenging efficiency for these nuclides. The distribution coefficient for the partition of 137 Cs between lake water and settling particles, K d , was determined to 7.0 ± 1.0 sx 10 4 cm 3 g −1 for epilimnetic particles and to 5.3 ± 1.1 × 10 4 cm 3 g −1 for hypolimnetic particles. The distribution coefficient for 210 Pb was estimated to 1.1 × 10 6 cm 3 g −1 . The possibility of postdepositional mobility of Chernobyl and nuclear weapons 137 Cs and natural 210 Pb in sediments was proved.