L’Amiante dans la Marine nationale : matrice emploi-exposition

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Distribution and geochemical behaviour of antimony in the Gironde Estuary A first qualitative approach to regional nuclear accident scenarios

International audienceAntimony (Sb) is a highly toxic trace element for which environmental biogeochemical cycles are still relatively poorly known, especially in coastal aquatic systems. In addition, Sb is a fission product in nuclear power plants (NPPs), presenting non-negligible decay and consecutive exposition rates over short to mean terms (i.e., 125Sb isotope half-life of 2.76 years). Understanding the environmental behaviour and fate of natural stable isotopes and combining this with intrinsic properties of the respective radionuclides (e.g. half-life) is essential to predict the environmental fate and potential dispersion of radioisotopes before accidental NPP events. In the present work, the distribution and geochemical behaviour of stable Sb are determined for the first time in the highly turbid Gironde Estuary. Both dissolved and particulate concentrations along the estuarine salinity and turbidity gradients were quantified during low, intermediate and high freshwater discharges. Results clearly suggest that long residence times within the salinity and turbidity gradients favour the observed non-conservative, additive behaviour of Sb. Distribution coefficients (log10 Kd ≈ 3.5–4.4 l kg− 1) indicate that in the Maximum Turbidity Zone (MTZ; SPM ~ 1000 mg l− 1) ~ 90% of total Sb occurs in the particulate phase, compared to only ~ 10% in the less turbid portions of the estuary (SPM ≤ 100 mg l− 1). We propose a first/broad qualitative approximation (scenarios) to possible behaviour and dispersion of Sb radionuclides in case of accidental release from the Blayais NPP located on the Gironde Estuary. Our results suggest that the hydrological situation and the position of the MTZ during a potential accident can be primordial to residence time and distribution pathways in the estuary. We estimate that (i) high river discharge and a downstream position of the MTZ may favour Sb radionuclide adsorption onto particles, implying long (months to years) residence times in the estuary and a high risk of seasonal upstream transport into the city of Bordeaux, whereas (ii) under low discharge conditions, dissolved Sb species will predominate implying rapid transport and higher dispersion along the coast. © 2016 Elsevier B.V

New computation for a better estimation of the annual dissolved metal net fluxes. The case of the cadmium in the Gironde estuary

Despite major management efforts initiated in 1987 and 2007 and decreasing emissions in the Gironde watershed, cadmium (Cd) levels in oysters from the downstream Gironde estuary are still higher to the consumption limit (5 mg/kg, dw, EC). Dissolved Cd concentrations were measured in surface water collected in the Gironde estuary during nine cruises (2014 – 2015). The obtained theoretical (Cdd0) concentrations and the daily net Cdd fluxes, using the Boyle’s method, confirm a decadal stepping decrease of the Cd pollution corresponding to that observed in the oysters from the long term national monitoring for priority contaminants at the estuary mouth. As this observation invalidates the previous estimating methods for estimating annual net Cdd fluxes, we propose an original empirical model applicable for the four last decades. This model is based on four exponential functions with defined boundaries for low water discharges. Each of them is representative of one distinct situation of Cd pollution in the watershed relative to major remediation processes implemented in the last four decades. These results allow to develop a direct estimation of the annual net Cdd fluxes only based on the data of the annual mean discharge. Thus, this study demonstrates the strength of the field research in geochemistry to obtain a better quantification of the exportation of dissolved bioavailable pollutants from the continental watersheds to the coastal ocean.Malgré d’importants efforts d’aménagement initiés en 1987 et 2007 et la diminution consécutive des émissions issues du bassin versant de la Gironde, les teneurs en cadmium (Cd) présentent dans les huîtres de l’aval de la Gironde restent supérieures à la norme de consommation (5 mg/kg, p.s., CE). Des concentrations en cadmium dissous ont été mesurées dans les eaux de surface collectées dans l’estuaire de la Gironde au cours de neuf campagnes océanographiques (2014–2015). Les concentrations théoriques en cadmium dissous (Cdd0) et les flux nets journaliers de Cdd ont été obtenus, selon la méthode de Boyle. Ils confirment une diminution de la pollution en Cd par paliers décennaux, correspondant à celle observée dans les huîtres girondines grâce au réseau national de surveillance des contaminants prioritaires. Cette observation invalidant les précédentes méthodes d’estimation des flux nets annuels, nous proposons un modèle empirique original appliqué aux quatre dernières décennies et basé sur quatre fonctions exponentielles tronquées. Chaque fonction est représentative d’une situation distincte de la pollution du bassin versant relative aux principaux processus de remédiation entrepris au cours des quatre dernières décennies. Les résultats nous ont permis de proposer un abaque de quantification des flux nets annuels de Cdd utilisant uniquement les données de débit moyen annuel. Ainsi, cette étude démontre l’efficacité de la géochimie de terrain pour obtenir une meilleure quantification de l’exportation de polluants dissous et biodisponibles, des bassins continentaux vers l’océan côtier

Nouveau modèle analytique pour une meilleure estimation des flux nets annuels en métaux dissous. Cas du cadmium dans l’estuaire de la Gironde

International audienceNouveau modèle analytique pour une meilleure estimation des flux nets annuels en métaux dissous. Cas du cadmium dans l'estuaire de la Gironde New computation for a better estimation of the annual dissolved metal net fluxes. The case of the cadmium in the Gironde estuar

Estuarine dissolved speciation and partitioning of trace metals: a novel approach to study biogeochemical processes

Estuaries are complex systems involving numerous biogeochemical gradients and processes that influence the behavior of trace metals. Lead (Pb), cadmium (Cd), and copper (Cu) speciation and partitioning were studied in the Gironde Estuary (SW France), using a multi-method approach in which data from innovative sensors and laboratory-based techniques were combined. For the first time in this system, the so-called dynamic fractions of the target metals (dissolved forms that are potentially bioavailable) were recorded on-board through voltammetry using unique antifouling gel-integrated microelectrode arrays (GIME) incorporated in a submersible sensing probe (TracMetal). Trace metals in the operationally defined dissolved <0.2 μm and <0.02 μm fractions, as well as complexed with suspended particles (collected after centrifugation) were quantified through sampling/laboratory-based techniques. High spatial resolution trace metal concentrations were monitored along the salinity gradient (S = 0.10 to S = 34.0) together with master bio-physicochemical parameters providing robust cruise-specific information on how well-known abiotic and biotic processes control the Gironde estuarine trace element partitioning, (i.e. conservative behavior, addition/removal). Combining conventional methods with GIME measurements showed: (i) the dominance of Cd dynamic species in the intra-estuarine total dissolved fraction (up to 90%), (ii) the importance of small colloids as trace metal carrier phases, desorbing and complexing dynamic fractions of Pb and Cu, and (iii) the potential influence of photo-redox processes remobilizing Pb under their dynamic forms (up to 80%). Data also suggest trace metal release/sorption by phytoplankton with an increase of dissolved Cu concentrations in the riverine branch, as well as Cu and Cd particulate concentrations showing higher levels towards productive coastal waters. This complete approach allowed to monitor key estuarine biogeochemical processes and highlighted the valuable use of the TracMetal to record subtle variations of potentially bioavailable dissolved metal fractions

CBCT guided adaptive radiotherapy for cervix cancer Uncertainty of the choice of the plan of the day

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