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 été menée sur les dépôts de sédiments de crue retrouvés dans les gorges du Gardon (Languedoc). Le plomb-210, le césium-137 et l’analyse géochimique des sédiments contaminés par les mines ont été utilisés pour reconstruire l’histoire des dépôts de crue. Cette approche a été combinée avec l’historique des crues du Gardon depuis 1890 pour affiner l’approche géochronologique. Au niveau de la cavité GG et de la terrasse GE les analyses ont permis d’illustrer les mécanismes d’érosion-redéposition pouvant perturber les séquences de sédiments. Les enregistrements des dépôts de sédiments de crue sont complets sur la terrasse GE située à 10 m au-dessus du lit mineur à partir de 1958, et incomplets auparavant. Sur la période 1880-1958, 25 crues ont eu un débit suffisant (>1450 m3/s) pour recouvrir la terrasse, alors que l’on recense seulement 5 à 6 crues depuis 1958 (pour un débit de submersion supérieur à 1700 m3/s). L’augmentation progressive du débit de submersion et la fréquence moindre d’inondation de la terrasse ont pu permettre sur la période récente la stabilisation de la couche de surface par la végétation et limiter l’érosion lors de crues importantes. Les enregistrements semblent complets dans la cavité GG située à 15 m au-dessus du lit mineur. La fréquence moindre de submersion à ce niveau plus élevé peut expliquer une meilleure stabilisation des dépôts de crue, rendus moins vulnérables à l’érosion. La datation au radiocarbone a été testée même si elle ne permet pas de dater avec précision les dépôts de crue des derniers siècles. 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 s’expliquer par une remobilisation/déstockage de charbons de bois anciens. Les datations radiocarbone sur graines donnent de meilleurs résultats, car issues d’une production annuelle, plus facilement décomposable et moins sujette à des dépôts intermédiaires. Au final, il apparaît que la technique de datation par radiocarbone sur des charbons de bois retrouvés dans les séquences sédimentaires n’est pas fiable, alors qu’elle est la plus pratiquée en paléo-hydrologie. L’utilisation combinée du plomb-210, du césium-137, de l’analyse géochimique des sédiments et des informations sur les crues historiques a permis de discriminer et de dater les différents dépôts de crue de ce dernier siècle dans la cavité 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 5 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

Anisotropic Solid Texture Synthesis Using Orthogonal 2D Views

International audienc

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 (40–100 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 (δ123Sb) in the CRMs ranged between −0.52 ± 0.06‰ (2 sd) and 0.40 ± 0.03‰ (2 sd) relative to an in-house isotopic standard solution (SPEX). The external reproducibility was evaluated at 0.05‰ (2 sd) for δ123Sb, based on replicated measurements of independently digested and purified CRMs. CRMs GSD-3, SDO-1 and BCR-176R exhibited δ123Sb 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 (δ123Sb = 0.00 ± 0.05‰, Sb Fisher Scientific® and PlasmaCAL-1, SCP Science®), while a δ123Sb value of 0.62 ± 0.02‰ was measured for the third one (PlasmaCAL-2, SCP Science®). This raises the importance of choosing a common isotopic standard solution to compare already published and future Sb isotope data

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 east–west 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 (δ11B). B concentrations range from 3.5 ppb to 14 ppb and δ11B values range from +30.5‰ to +45‰. Mean annual values are 6 ppb and +41‰, respectively. A clear relationship is observed in precipitation samples between δ11B 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 δ11B of +45–50‰ 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 80–90% 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 δ11B values of rivers are consistent with δ11B 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

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