Monitored natural attenuation of a complex mixture of organochlorines using compound-specific isotope analysis.

International audience(Calibri, 12pt bold) In France, chlorinated hydrocarbons represent the third most commonly detected groundwater contaminant class (19%, directly after heavy metals, 22%, and mineral‐oil hydrocarbons, 33%; Medde, 2012). The fate and behaviour of organic contaminants in aquifer systems depend on a number of physicochemical and biological processes, which may lead to natural attenuation. To apply in situ attenuation by naturally occurring or enhanced biodegradation as a cost‐effective remediation option at these sites, it becomes primordial to accurately identify and quantify ongoing biotransformation processes. Determination and quantification of these processes are crucial for contaminated site risk assessment and sustainable groundwater management strategies. Compound‐specific isotope analysis (CSIA) by online‐coupling of gas chromatography and isotope ratio mass spectrometry (GC‐IRMS) offers a versatile tool to study the origin of a pollution and/or to decipher multiple contamination sources, to verify if biodegradation of organic pollutants is occurring, to identify degradation mechanisms, and to determine the rate and extent of in‐situ biodegradation. In the last decade, compound‐specific isotope analysis (CSIA) has evolved as a diagnostic tool for contaminated site investigation and for monitoring the efficiency of intrinsic natural or enhanced remediation processes, and is now available for studying an increasing number of environmental pollutants (Elsner et al. 2012). Chemical compounds contain heavy and light stable isotopes in a certain ratio, i.e. 13 C/ 12 C, D/H, and 15 N/ 14 N. In general, molecules containing the lighter isotope react faster than those containing the heavier isotope. Bond‐breaking processes induced by microbial metabolism, can cause a large isotope fractionation leading to an enrichment of heavy isotopes in the residual fraction of the contaminant. CSIA allows interpreting these changes in the isotopic composition of individual organic compounds, thus providing a direct proxy for chemical transformations. CSIA permits qualitative and quantitative information on in situ (bio)degradation, can distinguish different reaction mechanisms, and provides additional means for source allocation and differentiation (Schmidt et al. 2004, Blessing et al. 2009, Braeckevelt et al. 2012, Negrel et al. 2012). We applied compound‐specific carbon isotope analysis (CSIA) in a remediation study to evaluate the potential of monitored natural attenuation (MNA) at an industrial site. The study site is an organochlorine production site with a long operational history and leaking facilities or accidental spills released high amounts of contaminants to soil and groundwater. A control and monitoring program of DNAPL at the study site is installed since the 80s. A hydraulical confinement separated the DNAPL source from the contamination plume that consists of lighter, more soluble chlorinated compounds, mainly PCE, TCE, DCE, TeCA, DCA, TCP and DCP. Biostimulation using acetate and H2 amendment was performed in a limited area within the plume. The aim of the present work is to demonstrate the potential of the CSIA approach for monitoring in‐situ biodegradation and for characterizing and quantifying transformation processes of chlorinated pollutants in groundwater towards the ultimate goal of an implementation of natural and/or enhanced bioremediation at the contaminated site. To this end, a total of four monitoring wells in the source zones and nine groundwater wells within the downgradient contaminant plume over several kilometres length were sampled and stable carbon isotope ratios of the aforementioned chlorinated compounds wer

Natural gas of radiolytic origin: An overlooked component of shale gas.

SignificanceNatural gas is a key fossil fuel as the world transitions away from coal toward less polluting energy sources in an attempt to minimize the impact of global climate change. Historically, the origin of natural gas produced from conventional reservoirs has been determined based on gas compositional data and stable isotope fingerprints of methane, ethane, and higher n-alkanes, revealing three dominant sources of natural gas: microbial, thermogenic, and abiotic. In our detailed synthesis of published natural gas data from a variety of unconventional hydrocarbon reservoirs worldwide, we demonstrate that there is a previously overlooked source of natural gas that is generated by radiolysis of organic matter in shales

Impact d'un traitement au H2O2 sur la biodégradation des BTEX évaluée par fractionnement isotopique du carbone stable et abondance des gènes codant des enzymes spécifiques à la dégradation des BTEX

International audienc

Komponentenspezifische Isotopenanalyse zur Aufklärung der Herkunft und des Verbleibs von organischen Schadstoffen in komplexen Grundwasserleitern

The extensive use of organic compounds has frequently caused soil and groundwater contamination. Volatile organic compounds, such as chlorinated and aromatic hydrocarbons and the semi-volatile polycyclic aromatic hydrocarbons are among the most widespread organic pollutants. The fate and behavior of such compounds in the subsurface depend on a number of physicochemical and biological processes, which may lead to ‘natural attenuation’. For the consideration of these in-situ contaminant-reducing processes as a valid remedial approach, it is necessary to attain an appropriate understanding of the key processes occurring in natural aquifers. Compound-specific isotope analysis (CSIA) with on-line gas chromatography-isotope ratio mass spectrometry (GC/IRMS) offers a versatile tool for the characterization of origin and fate of organic contaminants in environmental analytical chemistry. The aim of the present work was to evaluate and demonstrate the potential and limitations of CSIA for studying sources and fate of organic contaminants at heterogeneous and complex aquifer systems. One major drawback in the application of CSIA to field studies, is that current GC/IRMS systems are limited in their sensitivity. To overcome this limitation and to enhance method detection limits, various sample extraction and injection techniques were optimized and validated for their use in CSIA field studies. For volatile compounds, a commercially available purge-and-trap sample extractor has been technically improved to meet the specific requirements at real sites. The results obtained demonstrate the good performance of the sample preconcentration and extraction techniques applied for the compound-specific carbon isotope analysis of volatile compounds at trace concentrations. Applied to different field sites, the techniques helped to assess the potential for biodegradation according to the Rayleigh-equation. A new analytical approach, based on the injection of large sample volumes (large-volume injection, LVI) of organic extracts into a programmable temperature vaporizer (PTV) injector, has been developed and validated for the determination of compound-specific carbon isotope ratios. The PTV-LVI method was thoroughly optimized in terms of its accuracy, precision, linearity, reproducibility and limits of detection. It was shown that the technique allows to determine accurately and precisely delta13C values of semi-volatile organic contaminants at low concentrations (1-3 µg/L for aqueous or 10-20 µg/kg for soil samples) and thus expands the applicability of CSIA considerably in environmental applications. The applicability of the method was verified for delta13C determination of individual PAHs and exemplified by a source apportionment study at a creosote-contaminated site. So far, most field applications of CSIA have been limited to fairly homogeneous aquifers. To evaluate the applicability of the CSIA concept for studying the source and fate of organic contaminants and to quantify the rate of in-situ degradation in contaminant plumes even at highly complex conditions, extensive site investigations were performed at an urban, heterogeneous bedrock aquifer system. The study highlights the potential of using delta13C values of chlorinated hydrocarbons (tetrachloroethene and its transformation products) as a tracer for discriminating different contaminant sources even in the presence of biodegradation. It was shown that careful statistical evaluation and interpretation of highly precise compound specific isotope signatures, geochemical data and site-specific additional information may allow for a comprehensive site assessment under complex boundary conditions. In addition, for a plume in the southern part of this site, a reactive transport model-based analysis of concentration and isotope data was carried out to assess natural attenuation of the chlorinated ethenes in this part of the aquifer. The results provided strong evidence for the occurrence of aerobic TCE and DCE degradation. As PCE is recalcitrant at aerobic conditions, it could be used as a conservative tracer to estimate the extent of dilution. The dilution-corrected concentrations together with stable carbon isotope data allowed for the reliable assessment of the extent of in-situ biodegradation at the site. Finally, limitations of CSIA under natural field conditions and potential analytical pitfalls of the method are critically discussed and strategies to avoid possible sources of error are provided. The results of this work exemplify how CSIA can contribute for a reliable assessment of contaminated sites, even at complex contamination scenarios. Moreover, future work will significantly benefit from the method developments attained in this study.Die flüchtigen chlorierten und aromatischen Kohlenwasserstoffverbindungen, sowie polyzyklische aromatische Kohlenwasserstoffe (PAK), gehören zu den häufig nachgewiesenen organischen Schadstoffen an kontaminierten Standorten. Physikalisch-chemische und biologische Abbau- und Rückhalteprozesse in der gesättigten und ungesättigten Bodenzone können dabei die Ausbreitung der Schadstoffe verlangsamen und unter günstigen Bedingungen zu einer Begrenzung der Schadstofffahne führen. In-situ Prozesse, die zu einer tatsächlichen Minimierung der Schadstofffrachten führen, stellen dabei eine alternative Sanierungsstrategie dar, deren Anwendung allerdings ein gutes Prozessverständnis des Transport- und Abbauverhaltens der Schadstoffe im Untergrund voraussetzen. Die substanzspezifische Isotopenanalyse (CSIA) mittels gekoppelter Gaschromatographie-Isotopenverhältnis-Massenspektrometrie (GC/IRMS) stellt in der Umweltanalytik eine wertvolle Methode dar, um solche Aussagen über die Herkunft und den Verbleib von organischen Schadstoffen zu ermöglichen. Ziel der vorliegenden Arbeit war das Aufzeigen des Potentials und Grenzen der CSIA bei der Untersuchung der Herkunft und des Verbleibs von Schadstoffen an heterogenen und komplexen Feldstandorten. Die begrenzte Empfindlichkeit derzeitiger GC/IRMS-Systeme ist häufig der limitierende Faktor beim Einsatz der CSIA in Feldstudien. Um die Empfindlichkeit zu steigern im Sinne verbesserter Nachweisgrenzen, wurden verschiedene Probenextraktions- und Probenaufgabetechniken optimiert und für den Einsatz in der CSIA validiert. Für eine effizientere Extraktion flüchtiger Verbindungen konnte ein kommerziell erhältliches Purge&Trap-System im Rahmen dieser Arbeit für die speziellen Anforderungen optimiert werden. Die erhaltenen Ergebnisse zeigen, dass die hier eingesetzten Probenanreicherungs- und Extraktionstechniken effizient und zuverlässig in der substanzspezifischen Isotopenanalytik angewendet werden können. In den durchgeführten Studien konnte damit an unterschiedlichen Feldstandorten das biologische Abbaupotential anhand der Rayleigh-Gleichung abgeschätzt werden. Für weniger flüchtige Verbindungen (z.B. PAK) wurde eine neue Methode evaluiert: PTV-LVI. Diese Technik basiert auf der Injektion größerer Probenmengen (large-volume injection; LVI) in einen speziellen, temperatursteuerbaren Injektor (PTV-Injektor). Für ihre Anwendung in der Isotopenanalytik wurde diese neue Technik auf Genauigkeit, Linearität, Präzision und Reproduzierbarkeit untersucht, sowie die methodenspezifische Nachweisgrenze ermittelt. Diese Injektionstechnik (PTV-LVI) ermöglicht jetzt auch für die bisher problematischen mittelflüchtigen organischen Verbindungen verlässliche delta13C-Bestimmungen im Spurenkonzentrationsbereich und erweitert damit das mögliche Anwendungsspektrum der CSIA-Methode in der Umweltanalytik erheblich, wie am Beispiel eines Kreosot-kontaminierten Standorts gezeigt wird. Da bislang die Feldanwendung der CSIA auf relativ homogene Aquifer-Systeme beschränkt war, lag der Anwendungschwerpunkt der Methoden auf Feldstandorten mit komplexen Bedingungen und Kontaminationsgeschichte. Dabei konnte gezeigt werden, dass die über CSIA ermittelten delta13C Werte von chlorierten Kohlenwasserstoffen, in diesem Fall Tetrachlorethen und seinen Abbauprodukten, zur Identifizierung von potentiellen Verursachern (Kontaminationsquellen) herangezogen werden können, auch wenn Bioabbau eine Rolle spielt. In einem komplexen Realfall können, wie in der Arbeit am Beispiel eines geklüfteten Festgesteinsaquifer dargelegt, delta13C Werte zusammen mit geochemischen und anderen standortspezifischen Informationen zuverlässig und mit hoher statistischer Aussagekraft interpretiert werden. In einer Schadstofffahne im südlichen Bereich des Standorts wurde zudem, durch die Integration der gemessenen Konzentrations- und Isotopendaten in ein reaktives Transportmodell, das NA-Potential in diesem Teil des Aquifers quantitativ erfasst. Die Resultate zeigen den biologischen Abbau von Tri- und cis-1,2-Dichlorethen unter aeroben Bedingung am Standort an. Tetrachlorethen wird unter aeroben Bedingungen nicht abgebaut, und kann daher als konservativer Tracer zur Abschätzung des Verdünnungsgrades dienen. Die um den so erhaltenen Verdünnungsfaktor korrigierten Konzentrationen ließen in Zusammenhang mit den Isotopendaten dann eine zuverlässige Abschätzung des Bioabbaus vor Ort zu. Ausgehend von den Ergebnissen der im Rahmen dieser Arbeit bearbeiteten Standorte werden die Beschränkungen und potentielle Fallgruben der CSIA unter Realbedingungen kritisch diskutiert und Strategien vorgeschlagen, mögliche Fehlerquellen zu vermeiden. Insgesamt verdeutlichen die hier erzielten Ergebnisse, wie CSIA-Methoden zu einer erfolgreichen Standortuntersuchung, auch für komplexe Schadensfälle, beitragen können

A review on environmental isotope analysis of aquatic micropollutants: Recent advances, pitfalls and perspectives

International audienceAn increasing amount of organic micropollutants (OMPs) are detected in aquatic environments and occur in water supplies worldwide. OMPs pose a severe threat to freshwater resources and present a potential danger to ecosystems and human health, even at trace concentrations. Compound-specific isotope analysis (CSIA) is one of the key techniques for identifying the origin and fate of environmental pollutants in aquifers and for characterizing their transformation processes. Considered as relatively mature for environmental monitoring of some well-studied industrial hydrocarbons at contaminated sites, the technique still encounters many analytical challenges in the context of diffuse pollution for other organic compounds.The present review provides a comprehensive overview on the latest technical developments concerning isotope ratio analyses of OMPs such as pesticides, various industrial compounds, pharmaceuticals and personal care products (PPCPs), and nitroaromatic compounds and organic explosives (NACs/OEs). Based on a compilation of nearly 200 CSIA-studies of OMPs, we describe the analytical challenges and address common pitfalls that can be encountered in a context of diffuse pollution in wastewater, surface waters or groundwater. Our work gives an update on instrumental developments and advances in analytical approaches for CSIA-techniques for carbon, nitrogen, hydrogen, and chlorine stable isotopes. Furthermore, the review accounts for perspectives provided by associated innovations, such as sample processing for CSIA applications of the different OMPs in the context of diffuse pollution in aquatic environments

Assessing methane oxydation under landfill covers and its contribution to the above atmospheric CO2 levels : the added value of the isotope approach

International audienceWe are presenting here a multi-isotope approach (delta13C & delta18O of CO2 ; delta13C & deltaD ofCH4) to assess the methane (CH4) oxydation rate of waste under landfill covers, and its contribution to the above atmospheric CO2 levels in Sonzay (France). The isotope approach is compared to a more conventional mass balance approach. All results show that the CH4oxidation is heterogenous, with low rates in samples displaying high biogas fluxes, which was expected in clay covers presenting cracks within which CH4 rapidly circulates, and is thus not oxidised due to an insufficient residence time with methanotroph bacteria. On the other hand, at shallow depth, slightly-mobile biogas pockets are present, and are more enclined to CH4oxidation by bacteria (which explains the high oxidation rates observed at higher depth). delta13C ofCO2 measurement from air samples can also be used to identify the main sources of this molecule in the air surrounding the landfill site

Natural gas of radiolytic origin: An overlooked component of shale gas

International audienceNatural gas is an important fossil energy source that has historically been produced from conventional hydrocarbon reservoirs. It has been interpreted to be of microbial, thermogenic, or, in specific contexts, abiotic origin. Since the beginning of the 21st century, natural gas has been increasingly produced from unconventional hydrocarbon reservoirs including organic-rich shales. Here, we show, based on a careful interpretation of natural gas samples from numerous unconventional hydrocarbon reservoirs and results from recent irradiation experiments, that there is a previously overlooked source of natural gas that is generated by radiolysis of organic matter in shales. We demonstrate that radiolytic gas containing methane, ethane, and propane constitutes a significant end-member that can account for >25% of natural gas mixtures in major shale gas plays worldwide that have high organic matter and uranium contents. The consideration of radiolytic gas in natural gas mixtures provides alternative explanations for so-called carbon isotope reversals and suggests revised interpretations of some natural gas origins. We submit that considering natural gas of radiolytic origin as an additional component in uranium-bearing shale gas formations will lead to a more accurate determination of the origins of natural gas

Combining Geoelectrical Measurements and CO2 Analyses to Monitor the Enhanced Bioremediation of Hydrocarbon-Contaminated Soils: A Field Implementation

Hydrocarbon-contaminated aquifers can be successfully remediated through enhanced biodegradation. However, in situ monitoring of the treatment by piezometers is expensive and invasive and might be insufficient as the information provided is restricted to vertical profiles at discrete locations. An alternative method was tested in order to improve the robustness of the monitoring. Geophysical methods, electrical resistivity (ER) and induced polarization (IP), were combined with gas analyses, CO2 concentration, and its carbon isotopic ratio, to develop a less invasive methodology for monitoring enhanced biodegradation of hydrocarbons. The field implementation of this monitoring methodology, which lasted from February 2014 until June 2015, was carried out at a BTEX-polluted site under aerobic biotreatment. Geophysical monitoring shows a more conductive and chargeable area which corresponds to the contaminated zone. In this area, high CO2 emissions have been measured with an isotopic signature demonstrating that the main source of CO2 on this site is the biodegradation of hydrocarbon fuels. Besides, the evolution of geochemical and geophysical data over a year seems to show the seasonal variation of bacterial activity. Combining geophysics with gas analyses is thus promising to provide a new methodology for in situ monitoring

Empfehlungspapier für das körperliche Gruppentraining zur Sturzprävention bei älteren, zu Hause lebenden Menschen

Dieser Beitrag stellt eine Aktualisierung des Empfehlungspapiers der Bundesinitiative Sturzprävention für das körperliche Gruppentraining zur Sturzprävention bei älteren, zu Hause lebenden Menschen aus dem Jahre 2009 unter Berücksichtigung aktueller Evidenz dar. Das aktualisierte Empfehlungspapier zielt darauf ab, die Umsetzung ambulanter Sturzpräventionsgruppen zu fördern sowie konkrete Empfehlungen für deren Einrichtung und Durchführung auszusprechen. Die Empfehlungen beziehen sich auf die Identifikation und Ansprache der Zielgruppe für gruppenbasierte Sturzpräventionsprogramme sowie auf die Programmgestaltung und Qualitätssicherung. Hintergründe zu Finanzierung und Trainer*innen-Ausbildung werden samt einer Auflistung der in Deutschland etablierten Programme ebenfalls dargelegt.publishe