Search

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; Soils and groundwater are often contaminated by complex organic mixtures also called Non Aqueous Phase Liquids (NAPLs). Several techniques such as drilling, monitoring of soil gas or injection of tracers are traditionally used to quantify NAPLs in aquifers but are complex to perform. The use of natural soil gas such as 222Rn could be an easy and cheap alternative. This method requires the knowledge of the radon NAPL-water partitioning coefficients (Kn-w.). Once spilled on soil, NAPL will undergo degradation (evaporation, effects of sun light among others) and this degradation could impact the Kn-w. This study aims at investigating the partitioning coefficients of complex NAPLs such as commercial diesel fuel and gasoline in relation to degradation such as evaporation and UV-degradation. For that purpose, batch experiments and GCMS investigations were carried out. The results show different Kn-w for the commercial diesel fuel (60.7 ± 6.1) and gasoline (37.4 ± 5.6). The results also show different Kn-w behaviors in relation with degradation. Degraded diesel fuel display opposite Kn-w values (74.8 ± 7.5 and 25.1 ± 2.5 for UV degraded and evaporated diesel fuel, respectively), compared to fresh one. Degraded gasoline shows no significant variations of the Kn-w compared to fresh one. The molecular investigation reveals the removal of the most volatile fraction for the evaporation treatment, whereas UV-degradation do not have pronounced effects on the chromatogram pattern. For the gasoline molecular investigation, no difference is observed between the treatments excepted a very slight removal of the lightest compounds under evaporation. These results show that NAPL degradation have effects on the Kn-w for diesel fuel and no significant effects for gasoline, at least with these degradation paths. This Kn-w variation will have in fine effects on 222Rn activity interpretation and NAPL subsurface quantification.

International audience; Groundwater contamination by chlorinated hydrocarbons is a worldwide problem that poses important challenges in remediation processes. In Italy, the Legislative Decree 152/06 defines the water quality limits to be obtained during the cleanup process. In situ bioremediation techniques are becoming increasingly important due to their affordability and, under the right conditions, because they can be more effective than conventional methodologies. In the initial feasibility study phase, the numerical modeling supports the reliability of each technique. Two different codes, BIOCHLOR and PHREEQC were discussed and compared assuming different field conditions. Isotopic Fractionation-Reactive Transport Models were then developed in one synthetic and one simple field case. From the results, the two codes were in agreement and also able to demonstrate the Monitored Natural Attenuation processes occurring at the dismissed site located in Italy. Finally, the PHREEQC model was used to forecast the remediation time frame by MNA, hypothesizing a complete source cleanup: a remediation time frame of about 10–11 years was achieved by means of natural attenuation processes.

In multi-elemental compound-specific isotope analysis the lambda (Λ) value expresses the isotope shift of one element versus the isotope shift of a second element. In dual-isotope plots, the slope of the regression lines typical reveals the footprint of the underlying isotope effects allowing to distinguish degradation pathways of an organic contaminant molecule in the environment. While different conventions and fitting procedures are used in the literature to determine Λ, it remains unclear how they affect the magnitude of Λ. Here we generate synthetic data for benzene δ2H and δ13C with two enrichment factors eH and eC using the Rayleigh equation to examine how different conventions and linear fitting procedures yield distinct Λ. Fitting an error-free data set in a graph plotting the δ2H versus δ13C overestimates Λ by 0.225%⋅eH/eC, meaning that if eH/eCis larger than 22, Λ is overestimated by more than 5%. The correct fitting of Λ requires a natural logarithmic transformation of δ2H versus δ13C data. Using this transformation, the ordinary linear regression (OLR), the reduced major-axis (RMA) and the York methods find the correct Λ, even for large eH/eC. Fitting a dataset with synthetic data with typical random errors let to the same conclusion and positioned the suitability of each regression method. We conclude that fitting of non-transformed δ values should be discontinued. The validity of most previous Λ values is not compromised, although previously obtained Λ values for large eH/eC could be corrected using our error estimation to improve comparison.

International audience; In order to observe the relationships between the temporal variations of CO2 surface fluxes and the CO2 soil gas transport in soil profile before and during rainfall events, two experiments were conducted in a controlled natural environment at different time periods. These experiments consisted in injecting pure CO2 in a lysimeter at 160 cm depth and simulating heavy rainfall event at its surface for 2 weeks. During the whole experiments, CO2 soil gas concentrations and surface fluxes were continuously monitored. These measurements showed that the flux measured through the flux chamber were consistent with the concentration profiles. During simulated rainfall events, the concentrations and fluxes showed a clear change linked to the presence of water on the top of the water profile. The results clearly show a significant decrease of CO2 flux to atmosphere induced by rainfall infiltration and consequential wash-out of the CO2 present in the soil.

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.

International audience; The potential of LNAPL delineation by 222Rn soil-gas monitoring in a chemically heterogeneous vadose zone was investigated in this study based on laboratory (batch and columns) experiments and numerical modelling. An enhanced version of the MIN3P reactive transport code was used to simulate Rn transport in both uncontaminated and NAPL-contaminated vadose zones and results were validated against analytical solutions and laboratory experiments. Results show that 222Rn activity profiles are mainly controlled by porous media 222Rn production, vadose zone fluid saturations and especially the type and distribution of NAPL in contaminated areas. The results also show that decreases in 222Rn activity and variations in activity gradients provide evidence for the presence and saturation of NAPL. This study demonstrates that LNAPL delineation via 222Rn gas surveys at contaminated sites works best, if gas measurements extend as deep as possible and include regions where 222Rn activity decreases due to elevated NAPL content. In addition, collection and analysis of depth-discrete gas samples allows the characterization of vertical NAPL distribution based on the 222Rn activity gradient. The determination of 222Rn production in the unsaturated zone, as well as water capillary pressure curves are of key importance in enabling the discrimination of an uncontaminated from a NAPL-contaminated area.

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.

BIOSCREEN is a well-known simple tool for evaluating the transport of dissolved contaminants in groundwater, ideal for rapid screening and teaching. This work extends the BIOSCREEN model for the calculation of stable isotope ratios in contaminants. A three-dimensional exact solution of the reactive transport from a patch source, accounting for fractionation by first-order decay and/or sorption, is used. The results match those from a previously published isotope model but are much simpler to obtain. Two different isotopes may be computed, and dual isotope plots can be viewed. The dual isotope assessment is a rapidly emerging new approach for identifying process mechanisms in aquifers. Furthermore, deviations of isotope ratios at specific reactive positions with respect to “bulk” ratios in the whole compound can be simulated. This model is named BIOSCREEN-AT-ISO and will be downloadable from the journal homepage.

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; 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.

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.

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.

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; 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.

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.

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; 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.

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 aim of this work was to extend and to validate the flux tube-mixed instantaneous and kinetics super-position sequence approach (FT-MIKSS) to reaction chains of degrading species. Existing analytical solutions for the reactive transport of chains of decaying solutes were embedded in the flux-tube approach in order to conceive a semi-analytical model that allows fast parameter fitting. The model was applied for chloroethenes undergoing reductive dechlorination and oxidation in homogeneous and heterogeneous aquifers with sorption. The results from the semi-analytical model were compared to results from three numerical models (RT3D, PH3TD, PHAST). All models were validated in a homogeneous domain with an existing analytical solution. In heterogeneous domains, we found significant differences between the four models. ET-MIKSS gave intermediate results for all modelled cases. Results were obtained almost instantaneously, whereas other models had calculation times of up to several hours. Chloroethene plumes and redox conditions at the Plattsburgh field site were realistically modelled by FT-MIKSS, although results differed somewhat from those of PHT3D and PHAST. It is concluded that it may be tedious to obtain correct modelling results in heterogeneous media with degradation chain reactions and that the comparison of two different models may be useful. FT-MIKSS is a valuable tool for fast parameter fitting at field sites and should be used in the preparation of longer model runs with other numerical models. (C) 2012 Elsevier Ltd. All rights reserved.

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.

A field study on the runoff of pesticides was conducted during the cultivation period in 2004 on a hydraulically isolated rice farm of 120 ha surface with one central water outlet. Four pesticides were studied: Alphamethrin, MCPA, Oxadiazon, and Pretilachlor. Alphamethrin concentrations in runoff never exceeded 0.001 microg L(-1). The three other pesticides were found in concentrations between 5.2 and 28.2 microg L(-1) in the runoff water shortly after the application and decreased thereafter. The data for MCPA compared reasonably well with predictions by an analytical runoff model, accounting for volatilization, degradation, leaching to groundwater, and sorption to soil. The runoff model estimated that runoff accounted for as much as 18-42% of mass loss for MCPA. Less runoff is observed and predicted for Oxadiazon and Pretilachlor. It was concluded that runoff from rice paddies carries important loads of dissolved pesticides to the wetlands in the Ile de Camargue, and that the model can be used to predict this runoff.

11th International Symposium on Applied Isotope Geochemistry (AIG), French Geol Survey, Orleans, FRANCE, SEP 21-25, 2015; International audience; This work describes position-specific isotope effects (IE) measured by iq C-13-NMR during the evaporation of 8 different liquids of different polarities under 4 evaporation modes (passive evaporation, air-vented evaporation, low pressure evaporation and distillation). The observed effects are used to assess the question whether for carbon isotopes in organic liquids the use of the Craig-Gordon isotope model is valid. It is shown for five liquids that the overall IE include vapour-liquid IE which are strongly position-specific in polar compounds and less specific in apolar compounds, and a diffusive effect for which is not position-specific. The diffusive effect is diminished under wind and low pressure. After evaporation, the position-specific isotope pattern created by liquid-vapour IE is still quite reasonably preserved in these five liquids, which have, like water, an air-side limitation for volatilisation. Three other liquids in this study with limitations rather or fully on the liquid side differed from this pattern. It is concluded that evaporation of organic pollutants creates a unique position-specific isotope pattern that may be used to assess the progress of remediation or natural attenuation, and that the Craig-Gordon isotope model is valid for the volatilization of organic liquids with air-side limitation of the volatilization rate. (C) 2015 The Authors. Published by Elsevier B.V.