Mise au point d'un dispositif expérimental pour l'analyse du retrait-gonflement des sols argileux

International audienceThe paper presents a new experimental device, which can be incorporated in an Environmental Scanning Electron Microscope (ESEM). It allows to measure simultaneously the evolution of the surface strain of clayey aggregates and the evolution of their water content. The initial state of samples is in powder form, what allows making a complete cycle of wetting-drying in 24 hours, faster than the classic tests at the mesoscopic scale. The obtained results seem dissociate homogeneous and/or 'industrial' clays than heterogeneous natural clays with the evolution of their surface strain and their water content. These observations allow to envisage concrete applications such as the correlation of the collapses of a massif with the profiles of evolution of the water content (function of the depth) or the optimization of the choice of bentonites used for the sealings of the storages of radioactive waste.L'article présente un nouveau dispositif expérimental, pouvant être incorporé dans un Microscope Electronique àABalayage Environnemental (MEBE). Il permet de mesurer simultanément l'évolution de la déformation surfacique d'agrégats argileux et l'évolution de leur teneur en eau. L'état initial des échantillons est sous forme de poudre, ce qui permet d'effectuer un cycle d'humidification-séchage complet en 24 heures, soit beaucoup plus rapide que les essais classiques à l'échelle mésoscopique. Les résultats obtenus semblent permettre de dissocier les argiles homogènes et/ou " industrielles " des argiles naturelles hétérogènes par l'évolution de leur déformation surfacique et de leur teneur en eau. Ces observations permettent d'envisager des applications concrètes telles que la corrélation des tassements d'un massif aux profils d'évolution de la teneur en eau (fonction de la profondeur) ou l'optimisation du choix des bentonites utilisées pour les scellements des stockages de déchets radioactifs

Apport d'un nouveau dispositif pour améliorer l'estimation du retrait-gonflement des argiles

National audienceThe paper presents a new experimental device, developed in an Environmental Scanning Electron Microscope (ESEM), allowing to measure simultaneously the evolution of the surface strain of clayey aggregates and the evolution of their water content. The initial state of samples is in powder form, what allows making a complete cycle of wetting-drying in 24 hours, unlike the classic tests in the mesoscopic scale. The obtained results can be correlated in the profiles of evolution of the water content according to the depth workbenches in situ.L'article présente un nouveau dispositif expérimental, développé dans un Microscope Electronique à Balayage Environnemental (MEBE), permettant de mesurer simultanément l'évolution de la déformation surfacique d'agrégats argileux et l'évolution de leur teneur en eau. L'état initial des échantillons est sous forme de poudre, ce qui permet d'effectuer un cycle d'humidification-séchage complet en 24 heures, à la différence des essais classiques à l'échelle mésoscopique. Les résultats obtenus peuvent être corrélés aux profils d'évolution de la teneur en eau en fonction de la profondeur établis in situ

Effect of non-ageing and ageing ceria nanoparticles suspensions on fresh water micro-algae

When assessing the hazards properties of nanomaterials in the environment, the main research challenges are numerous. Firstly, determining if nanomaterials are more or less toxic than the bulk forms of the same materials and the extent to which toxicity is governed or influenced by the physico-chemicals properties of the nanoparticles. Secondly, it appears necessary to study the effect of nanomaterials and nanoparticles throughout their life cycle including both initial forms and physico-chemically modified form (i.e. aggregated or agglomerated forms) resulting from an ageing process. Our work focused on the effect of commercial ceria nanoparticle (nCeO2) suspensions, towards freshwater micro-algae assessing the effect nCeO2 suspensions with different agglomeration/aggregation state obtained by using an artificial ageing process. Both ageing and non-ageing nCeO2 suspensions were fully characterized using dynamic light scattering (ZetaSizer, Malvern Instruments) or laser diffraction (MasterSizer, Malvern Instruments) and transmission electron microscopy (TEM). In addition, the interaction between NPs and algae were investigated using flow-cytometry and environmental scanning electron microscope technique (E-SEM).The results obtained showed that the algae growth inhibition was similar after exposure to non-ageing or ageing nCeO2 suspensions. The results obtained from flow-cytometry and E-SEM proved that the ceria NPs are able to tightly entrap the algae cells, which could in part contribute to the effect recorded. Those results also support the fact that aggregation or agglomeration has a few influences when focusing on the standardized algae ecotoxicity test. Moreover by comparison to our previous studies performed with other ceria suspensions, it was shown that the primary particle size and consequently the particle surface area is a relevant parameter in assessing the ecotoxicity of nanoparticles

Biodistribution and clearance of instilled carbon nanotubes in rat lung

<p>Abstract</p> <p>Background</p> <p>Constituted only by carbon atoms, CNT are hydrophobic and hardly detectable in biological tissues. These properties make biokinetics and toxicology studies more complex.</p> <p>Methods</p> <p>We propose here a method to investigate the biopersistence of CNT in organism, based on detection of nickel, a metal present in the MWCNT we investigated.</p> <p>Results and conclusion</p> <p>Our results in rats that received MWCNT by intratracheal instillation, reveal that MWCNT can be eliminated and do not significantly cross the pulmonary barrier but are still present in lungs 6 months after a unique instillation. MWCNT structure was also showed to be chemically modified and cleaved in the lung. These results provide the first data of CNT biopersistence and clearance at 6 months after respiratory administration.</p

Assessing metals bioaccessibility to man in human health risk assessment of contaminated site

International audienceSoil ingestion is a significant exposure pathway to Man for sites contaminated with heavy metals. In France, risk assessments on polluted soils currently consider the total soil metal content for calculation of the dose exposure to Man. However several studies done on animals showed that this assumption was not accurate as the total soil metal content was not available for absorption though the gastro-intestinal system. The fraction that is actually entering the systemic circulation is the bioavailable fraction and was shown to be dependent on the solid metal distribution (Casteel et al., 2001; Henningsen et al., 1998). Measurement of metal bioavailability can be done using animals (pigs and monkeys) having similar digestive conditions than Humans. However these experiments are costly and can be ethically problematic. These last years, both North American and European scientists developed chemical tests to measure the bioaccessible fraction of the soil metals. These tests are based on two or three steps extraction method that simulates the extraction of the metal by the digestive fluxes (saliva, gastric and intestinal conditions). These fractions were shown to be correlated to the bioavailable fraction for some metalloids (arsenic) or metals (lead). The bioaccessible fraction of metal is then used to correct the soil metal total concentration. This data can be used to improve the estimation of the external fraction of the contaminant that is available for absorption through the digestive tract. The objectives of this paper are to give a short overview of the methods available in the literature to assess the soil metal bioaccessibility, focusing on the tests developed by the European BARGE working group. One of these tests is then used on four soils sampled on a residential area on which soils are strongly contaminated with lead. Results of bioaccessibility are then discussed regarding the soil solid phase repartition of this metal using Tessier sequential extractions. Finally, a theoretical human health risk assessment is then carried out considering both the total and the bioaccessible lead fraction. Impact of bioaccessibility in terms of management of contaminated sites is then discussed

Analyse au niveau microscopique du comportement hydrique d'agrégats argileux

National audienceThe paper presents analyses performed in a microscopic level on Romainville clay. They were performed with an Environmental Scanning Electron Microscope (ESEM) by imposing wetting-drying cycles with long enough duration steps to reach hydric equilibrium state. The first observations show a kinetic onstituted by two successive phases and more important surface strain at high values of relative humidityL'article présente des analyses menées à l'échelle " microscopique " sur l'argile verte de Romainville, dans son état naturel. Elles ont été réalisées dans un Microscope Electronique à Balayage Environnemental (MEBE). Des cycles d'humidification-séchage ont été imposés, par paliers d'une durée suffisamment longue pour que l'équilibre hydrique soit atteint. Les premières observations montrent une cinétique constituée de deux phases successives et des déformations surfaciques plus importantes aux fortes humidités relative

Analyse aux échelles micro et macroscopique des mécanismes de déssicsation et de gonflement des sols argileux

National audienceAnalysis of the physico-chemical mechanisms at the local or microscopic level during the shrinkage or the swelling of clayey materials is an essential step for the understanding and the characterisation of the sensitivity of soils towards such phenomena (shrinkage and swelling). In order to better understand such mechanisms, experimental analyses are yet performed at different scales, but mainly at a microscopic level using an Environmental Scanning Electron Microscope (ESEM). This apparatus allows the analysis of some features of the behaviour or physical properties of various clay "samples" subjected to controllable hygrometry conditions. In this research, two natural clays, Greek montmorillonite, homogeneous, and Romainville clay, heterogeneous, are analysed in a powder state. These two clays are submitted to wetting/drying cycles in the ESEM chamber. Homogeneous clay has a large swelling and a full destructuration due to wetting and saturation of the powder in water. The heterogeneous clay is studied in the context of relations between spatial scales (microscopic and macroscopic). We observed that the rate of swelling measured at the microscopic level (ESEM) is of the same order of magnitude as that measured at the macroscopic scale (oedometer free swelling tests).L'analyse des mécanismes physico-chimiques à l'échelle locale ou microscopique lors du retrait et du gonflement des matériaux argileux est une étape indispensable pour la compréhension et la caractérisation de la sensibilité de certains sols ainsi que leur prédisposition vis-à-vis des phénomènes de retrait et de gonflement. Afin de mieux comprendre ces mécanismes, des analyses expérimentales sont menées à différentes échelles, mais principalement à une échelle microscopique en utilisant un Microscope Electronique à Balayage Environnemental (MEBE). Ce dernier permet l'analyse de certains aspects du comportement ou les propriétés physiques de différents " échantillons " d'argiles soumis à des conditions d'hygrométrie contrôlées. Dans cette étude, deux argiles naturelles, la montmorillonite grecque, homogène, et l'argile verte de Romainville, hétérogène, sont analysées sous forme de poudre. Ces deux argiles sont soumises à des cycles d'humidification/séchage dans la chambre du MEBE. L'argile homogène présente un gonflement important et une déstructuration totale suite à l'humidification et la saturation de la poudre en eau. L'argile hétérogène est étudiée dans le cadre de rapports entre échelles spatiales (microscopiques et macroscopiques). On observe que le taux de gonflement mesuré à l'échelle microscopique (MEBE) est du même ordre de grandeur que celui mesuré à l'échelle macroscopique (essais de gonflement libre à l'oedomètre)

Spéciation des métaux Pb, Zn, Cd dans les poussières en suspension dans l'air ambiant par extractions chimiques et pae ESEM-EDS automatisé

To evaluate the toxicity, the biodisponibility and the environmental behaviour of metals like Pb, Zn , Cd in ambient air dust, it is necessary to determine the speciation of these elements, i.e their main physico-chemical species. A chemical extraction procedure has been defined and optimized for pure species of Pb, Zn and Cd (sulfate, sulphur, carbonate and oxide).Pour évaluer la toxicité, la biodisponibilité et le comportement dans l'environnement des métaux Pb, Zn et Cd, il est nécessaire de connaître leur spéciation, c'est à dire de déterminer leurs principales espèces physico-chimiques. Dans ce but, un protocole d'extractions chimiques a été défini et optimisé pour des espèces pures (sulfates, sulfures, carbonates et oxydes)

Behaviour of ceria nanoparticles in standardized test media - influence on the results of ecotoxicological tests

International audienceThe main objectives of this work were to establish the behaviour of a ceria nanopowder in different ecotoxicological media commonly used in standardized aquatic ecotoxicity tests and consequently to assess the acute and chronic ecotoxicity in two microinvertebrates: Daphnia magna and Ceriodaphnia dubia and in a freshwater green algae: Pseudokirchneriella subcapitata. Different approaches to disperse the ceria nanoparticles (i.e. stirring, use of probe sonication, addition of humic acids) were tested and the influence on the biological endpoints was investigated. Despite the agglomeration phenomena observed in all the tested media, the results obtained indicated higher stability in the lower ionic strength media with addition of humic acid (2 mg.L-1, TOC). No acute toxicity were observed with D. magna, whatever the dispersal method performed and the nCeO2 concentration tested (up to 1000 mg.L-1), as no acute toxicity was recorded with C. dubia following exposure to the stirring suspensions. On contrary, acute toxicity was recorded in C. dubia with EC50 values comprise between 11.9 and 25.3 mg.L-1 using the probe sonicated suspension with or without humic acids addition. Significant chronic effect on the reproduction capability was also recorded in C. dubia. The estimated EC10 values were comprised between 2.1 and 2.9 mg.L-1. Focusing on P. subcapitata, despite the different agglomerate size recorded in the tested media at the end of the exposure periods, results obtained were similar. Adverse effect on algal growth around 5 mg.L-1 were reported (mean EC10 = 4 +- 1.8 mg.L-1). Those results suggested the needed for standardized testing protocol concerning the aqueous media used or the sample preparation for laboratory testing