76 research outputs found
A multidating approach applied to historical slackwater flood deposits of the Gardon River, SE France
A multidating approach was carried out on slackwater flood deposits, preserved in valley side rock cave and terrace, of the Gardon River in Languedoc, southeast France. Lead-210, caesium-137, and geochemical analysis of mining-contaminated slackwater flood sediments have been used to reconstruct the history of these flood deposits. These age controls were combined with the continuous record of Gardon flow since 1890, and the combined records were then used to assign ages to slackwater deposits. The stratigraphic records of terrace GE and cave GG were excellent examples to illustrate the effects of erosion/preservation in a context of a progressively self-censoring, vertically accreting sequence. The sedimentary flood record of the terrace GE located at 10 m above the channel bed is complete for years post-1958 but incomplete before. During the 78-year period 1880-1958, 25 floods of a sufficient magnitude (> 1450 m3/s) have covered the terrace. Since 1958, however, the frequency of inundation of the deposits has been lower:only 5 or 6 floods in 52 years have been large enough to exceed the necessary threshold discharge (> 1700 m3/s). The progressive increase of threshold discharge and the reduced frequency of inundation at the terrace could allow stabilisation of the vegetation cover and improved protection against erosion from subsequent large magnitude flood events. The sedimentary flood record seems complete for cave GG located at 15 m above the channel bed. Here, the low frequency of events would have enabled a high degree of stabilisation of the sedimentary flood record, rendering the deposits less susceptible to erosion. Radiocarbon dating are used in this study and compared to the other dating techniques.Eighty percent of radiocarbon dates on charcoals were considerably older than those obtained by the other techniques in the terrace. On the other hand, radiocarbon dating on seeds provided better results. This discrepancy between radiocarbon dates on charcoal and seeds is explained by the nature of the dated material (permanent wood vs. annual production and resistance to degradation process). Finally, we showed in this study that although the most common dating technique used in paleoflood hydrology is radiocarbon dating, usually on charcoal preserved within slackwater flood sediments, this method did not permitus to define a coherent age model. Only the combined use of lead-210, caesium-137, and geochemical analysis of mining-contaminated sediments with the instrumental flood record can be applied to discriminate and date the recent slackwater deposits of the terrace GE and cave GG.Une approche par datations multiples a Ă©tĂ© menĂ©e sur les dĂ©pĂŽts de sĂ©diments de crue retrouvĂ©s dans les gorges du Gardon (Languedoc). Le plomb-210, le cĂ©sium-137 et lâanalyse gĂ©ochimique des sĂ©diments contaminĂ©s par les mines ont Ă©tĂ© utilisĂ©s pour reconstruire lâhistoire des dĂ©pĂŽts de crue. Cette approche a Ă©tĂ© combinĂ©e avec lâhistorique des crues du Gardon depuis 1890 pour affiner lâapproche gĂ©ochronologique. Au niveau de la cavitĂ© GG et de la terrasse GE les analyses ont permis dâillustrer les mĂ©canismes dâĂ©rosion-redĂ©position pouvant perturber les sĂ©quences de sĂ©diments. Les enregistrements des dĂ©pĂŽts de sĂ©diments de crue sont complets sur la terrasse GE situĂ©e Ă 10 m au-dessus du lit mineur Ă partir de 1958, et incomplets auparavant. Sur la pĂ©riode 1880-1958, 25 crues ont eu un dĂ©bit suffisant (>1450 m3/s) pour recouvrir la terrasse, alors que lâon recense seulement 5 Ă 6 crues depuis 1958 (pour un dĂ©bit de submersion supĂ©rieur Ă 1700 m3/s). Lâaugmentation progressive du dĂ©bit de submersion et la frĂ©quence moindre dâinondation de la terrasse ont pu permettre sur la pĂ©riode rĂ©cente la stabilisation de la couche de surface par la vĂ©gĂ©tation et limiter lâĂ©rosion lors de crues importantes. Les enregistrements semblent complets dans la cavitĂ© GG situĂ©e Ă 15 m au-dessus du lit mineur. La frĂ©quence moindre de submersion Ă ce niveau plus Ă©levĂ© peut expliquer une meilleure stabilisation des dĂ©pĂŽts de crue, rendus moins vulnĂ©rables Ă lâĂ©rosion. La datation au radiocarbone a Ă©tĂ© testĂ©e mĂȘme si elle ne permet pas de dater avec prĂ©cision les dĂ©pĂŽts de crue des derniers siĂšcles. Sur la terrasse GE, 80% des dates au carbone 14 sur charbon de bois sont beaucoup trop vieilles par rapport aux autres techniques de datation, ce qui peut sâexpliquer par une remobilisation/dĂ©stockage de charbons de bois anciens. Les datations radiocarbone sur graines donnent de meilleurs rĂ©sultats, car issues dâune production annuelle, plus facilement dĂ©composable et moins sujette Ă des dĂ©pĂŽts intermĂ©diaires. Au final, il apparaĂźt que la technique de datation par radiocarbone sur des charbons de bois retrouvĂ©s dans les sĂ©quences sĂ©dimentaires nâest pas fiable, alors quâelle est la plus pratiquĂ©e en palĂ©o-hydrologie. Lâutilisation combinĂ©e du plomb-210, du cĂ©sium-137, de lâanalyse gĂ©ochimique des sĂ©diments et des informations sur les crues historiques a permis de discriminer et de dater les diffĂ©rents dĂ©pĂŽts de crue de ce dernier siĂšcle dans la cavitĂ© GG et la terrasse GE
Direct determination of trace elements in powdered samples by in-cell isotope dilution femtosecond laser ablation ICPMS
A method has been developed for the direct and simultaneous multielement determination of Cu, Zn, Sn, and Pb in soil and sediment samples using femtosecond laser ablation inductively coupled plasma mass spectrometry (fs-LA-ICPMS) in combination with isotope dilution mass spectrometry (IDMS). The in-cell isotope dilution fs-LA-ICPMS method proposed in this work was based on the quasi-simultaneous ablation of the natural abundance sample and the isotopically enriched solid spike, which was performed using a high repetition rate laser and a fast scanning beam device in a combined manner. Both the sample preparation procedure and the total analysis time have been drastically reduced, in comparison with previous approaches, since a unique multielement isotopically enriched solid spike was employed to analyze different powdered samples. Numerous experimental parameters were carefully selected (e.g., carrier gas flow rate, inlet diameter of the ablation cell, sample translation speed, scanner speed, etc.) in order to ensure the complete mixing between the sample and the solid spike aerosols. The proposed in-cell fs-LA-ICP-IDMS method was tested for the analysis of two soil (CRM 142R, GBW-07405) and two sediment (PACS-2, IAEA-405) reference materials, and the analysis of Cu, Zn, Sn, and Pb yielded good agreement of usually not more than 10% deviation from the certified values and precisions of less than 15% relative standard deviation. Furthermore, the concentrations were in agreement not only with the certified values but also with those obtained by ICP-IDMS after the microwave-assisted digestion of the solid samples, demonstrating therefore that in-cell fs-LA-ICP-IDMS opens the possibility for accurate and precise determinations of trace elements in powdered samples reducing the total sample preparation time to less than 5 min. Additionally, scanning electron microscope measurements showed that the aerosol generated by in-cell fs-LA-ICP-IDMS predominantly consisted of linear agglomerates of small particles (in the order of few tens of nanometers) and a few large spherical particles with diameters below 225 nm
Bioaccumulation and Toxicity of Organic Chemicals in Terrestrial Invertebrates
Terrestrial invertebrates are key components in ecosystems, with crucial roles in soil structure, functioning, and ecosystem services. The present chapter covers how terrestrial invertebrates are impacted by organic chemicals, focusing on up-to-date information regarding bioavailability, exposure routes and general concepts on bioaccumulation, toxicity, and existing models. Terrestrial invertebrates are exposed to organic chemicals through different routes, which are dependent on both the organismal traits and nature of exposure, including chemical properties and media characteristics. Bioaccumulation and toxicity data for several groups of organic chemicals are presented and discussed, attempting to cover plant protection products (herbicides, insecticides, fungicides, and molluscicides), veterinary and human pharmaceuticals, polycyclic aromatic compounds, polychlorinated biphenyls, flame retardants, and personal care products. Chemical mixtures are also discussed bearing in mind that chemicals appear simultaneously in the environment. The biomagnification of organic chemicals is considered in light of the consumption of terrestrial invertebrates as novel feed and food sources. This chapter highlights how science has contributed with data from the last 5Â years, providing evidence on bioavailability, bioaccumulation, and toxicity derived from exposure to organic chemicals, including insights into the main challenges and shortcomings to extrapolate results to real exposure scenarios
A single-step purification method for the precise determination of the antimony isotopic composition of environmental, geological and biological samples by HG-MC-ICP-MS
International audienceAntimony isotopes have been recently used as geochemical tracers for archeological or environmental purposes. The purification of antimony in samples with a low Sb concentration and a complex matrix is a critical step to measure the 123Sb/121Sb ratio by hydride generation coupled to a multi-collector inductively coupled plasma mass spectrometer (HG-MC-ICP-MS). A single-step purification method based on the use of thiol-functionalized mesoporous silica powder (TSP) was developed to separate antimony from other elements. A low amount of Sb (40â100 ng) is required thanks to low procedural blanks (<1 ng Sb) and an efficient removal (98.7% on average) of potential interfering elements (including As, Cd, Co, Cr, Cu, Fe, Ni, Pb, Se, and Sn). The method was validated on fourteen Certified Reference Materials (CRMs) including environmental materials (sediments and soils), biological materials (plants, human blood and urine), rocks and anthropogenic materials (fly ash, road dust and polyethylene). Antimony was recovered at 100 ± 7% and no isotopic fractionation occurred during the procedure. The isotopic composition of Sb (ÎŽ123Sb) in the CRMs ranged between â0.52 ± 0.06â° (2 sd) and 0.40 ± 0.03â° (2 sd) relative to an in-house isotopic standard solution (SPEX). The external reproducibility was evaluated at 0.05â° (2 sd) for ÎŽ123Sb, based on replicated measurements of independently digested and purified CRMs. CRMs GSD-3, SDO-1 and BCR-176R exhibited ÎŽ123Sb values similar to previous measurements by Rouxel et al. (2003). In addition, three pure standard solutions of Sb were measured against the in-house isotopic standard solution. Two of them were isotopically similar (ÎŽ123Sb = 0.00 ± 0.05â°, Sb Fisher ScientificÂź and PlasmaCAL-1, SCP ScienceÂź), while a ÎŽ123Sb value of 0.62 ± 0.02â° was measured for the third one (PlasmaCAL-2, SCP ScienceÂź). This raises the importance of choosing a common isotopic standard solution to compare already published and future Sb isotope data
Mesure ponctuelle des rapports isotopiques du Strontium par LA-MC-ICP-MS : couplage laser Femtoseconde-MC-ICPMS Neptune
Nd isotopic compositions of eastern Mediterranean sediments: tracers of the Nile influence during sapropel S1 formation?
Nd isotopic composition of Eastern Mediterranean sediments are used to investigate the influence of Nile flux variations during the formation of the youngest sapropel S1. Four box cores located on an eastâwest transect (around 35°N) at increasing distance from the Nile source were studied. Nd(0) signatures were measured in the lithogenic (alumino-silicate residue) fraction and the authigenic/biogenic (carbonates, organic matter and Fe, Mn oxyhydroxides) fraction of the sediment after 1 M HCl leaching. The Nd(0) profiles of the residual fraction show more radiogenic values in the sapropel layers than in the adjacent sediments. These profiles follow the Gaussian-shaped Ba/Al profile shape which defines S1. The Nd(0) variations can be related to changes in the proportions of two continental sources of particulate material: Nile particles and Saharan aerosols. A simple mixing model reveals that the contribution of Nile particulates to the sediments increases relative to Saharan aerosols during sapropel formation, indicating a higher Nile discharge and a decrease in eolian input at that time. For the cores located closest to the Nile fan, the Nd(0) signatures of the leachable fraction are always higher in the sapropel layer (?5 to ?4) than in the adjacent sediments (~?6). The sapropel layer Nd(0) values increase with decreasing distance to the Nile towards values close to the Nile particulates. All the results obtained on the leachable fraction point towards a massive input of Nile freshwater during S1 deposition
Boron isotopes in precipitation: Experimental constraints and field evidence from French Guiana
International audiencePrecipitation samples collected during one year in French Guiana were analyzed both for boron concentrations and isotopic compositions (ÎŽ11B). B concentrations range from 3.5 ppb to 14 ppb and ÎŽ11B values range from +30.5â° to +45â°. Mean annual values are 6 ppb and +41â°, respectively. A clear relationship is observed in precipitation samples between ÎŽ11B and NO3/B ratio, indicating that boron in rainwater originates from two sources. The first source is seawater. Experiments carried out in order to understand the volatilization of boron from solutions of seawater strongly suggest that the heavy component in rainwater samples is boron evaporated from seawater. We show that boric acid is preferentially evaporated and 11B preferentially lost. At seawater pH, we predict a seawater-derived atmosphere having a ÎŽ11B of +45â50â° that corresponds to the 11B enriched end-member found in the rainwater samples of French Guiana. The second source of boron in French Guiana rainwater is less constrained but strong arguments favor a main contribution of a biomass-derived component. We propose the release of boron by biomass burning as the most likely second source. We estimate the contribution of the dissolution of marine gaseous B to French Guiana precipitation at about 80â90% of the total B in rainfall.Finally, our results show that (i) most of the dissolved boron in the coastal rivers of French Guiana originates from atmospheric inputs and (ii) the ÎŽ11B values of rivers are consistent with ÎŽ11B values of yearly averaged rainwater. We demonstrate in this study the potential use of boron isotopes as tracers of the biomass burning and stress the importance of investigating boron isotopes in biomass
ĂlĂ©ments traces et espĂšces majeures dans les prĂ©cipitations d'Afrique : concentrations et sources
Determination of Ra-226 concentrations in seawater and suspended particles (NW Pacific) using MC-ICP-MS
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Reyss, J. L. Riotte, J. Freydier, R. 2 ELSEVIER SCIENCE BV AMSTERDAM MAR CHEMWe report vertical profiles of radium-226 (Ra-226) concentrations determined in seawater and suspended particles collected in the North-West Pacific using Multi Collector-Inductively Coupled Plasma Mass Spectrometry (MC-ICP-MS). Dissolved Ra-226 concentrations were determined in small size water samples (between 110 and 250 ml volume) with a precision usually better than 5% (internal error, two standard error, 2 sigma(m)) using a chemical protocol slightly modified compared to previous studies that provides a chemical recovery of 90%. The Ra-226 activities thus obtained are in good agreement with the Ra-226 activities determined using low-background gamma spectrometry. In this work, we report the first Ra-226 activities determined in marine suspended particles using MC-ICP-MS. We thus show that this method is very useful to determine Ra-226 concentrations in suspended particles that have been poorly studied up to now because they display very low Ra-226 activities (i.e. two orders of magnitude lower than the Ra-226 activity in seawater). Such a sensitive method can thus be used to build high-resolution vertical profiles of dissolved and particulate Ra-226 activities, which would allow us to better understand the impact of biology on the oceanic Ra cycle. (C) 2011 Elsevier B.V. All rights reserved
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