Sorption Properties of Peat for U(VI) and 226Ra in U Mining Areas

AbstractUnderstanding the environmental behavior of U and 226Ra is important for remediation of former mining sites and assessment of their durability. The aim of this study is to determine the sorption properties of an acidic peat for U and 226Ra, located near a former U mine. A 90% retention of U over a pH range of 3 to 10 was observed in Na- conditioned peat samples issued from the mesotelm, with a Rd between 1000 and 12000 mL/g. It seems that U sorption in peat is not only governed by organic matter. The Kd for 226Ra adsorption increases with pH from zero to 4849 mL/g. However in this mining environment, the peat bog proved to be significantly impacted by anthropogenic activities, with the presence of detrital components in the peat material that can also contribute to U and Ra sorption

Urban Stream Channel Geomorphology: Investigating the Short-Term Channel Stability and Bed-Material Transportation within a Rehabilitated Urban Stream Reach in DeKalb County, Georgia

Rivers and streams are sensitive to alterations in their watersheds and one of the greatest disturbances is from urban development. An urban stream channel in the Atlanta metropolitan area in the Georgia Piedmont was studied to establish the nature of adjustment the channel form was experiencing. This study compared a degraded channel with a channel influenced by stabilization efforts in the same stream reach, in order to investigate the behavior of channel adjustments towards a greater stability. Measurements of the short-term changes in channel cross-sectional area and bed-material volume, following a series of threshold flow events, were taken in the reach and the variation in bed sediment texture was also investigated. Results showed that channel banks were stable compared to more mobile beds and that urban effects continued to dictate sedimentation. Rehabilitation measures were aggrading channels in their reaches and were likely perpetuating the instability of upstream channels

Les sept meditations de Ste. Therese sur le pater ; Dix-Sept autres meditations

Copia digital. Valladolid : Junta de Castilla y León. Consejería de Cultura y Turismo, 2013Sign.:A-O6 ; P4

Sorption study of 226RA(II) et 238U(VI) on to peat organic matter, in mining environment

Le devenir des anciens sites miniers est un sujet de préoccupation sociétale. Afin de garantir la protection de l'écosystème ainsi qu'un impact radiologique minimal sur la biosphère, il est important de comprendre les paramètres qui régissent la migration de l'uranium (et de ses produits de désintégration, en particulier le radium 226) et d'être capable de le modéliser. Dans la nature, parmi les phases qui peuvent retenir 238U(VI) et 226Ra(II), la tourbe est connue pour avoir une forte affinité pour l'uranium VI. La tourbe sèche étant généralement composée à près de 90% de matière organique, l'objectif de cette étude est de qualifier et de quantifier la capacité d'adsorption et de désorption de la matière organique de la tourbe pour 238U(VI) et 226Ra(II). Les échantillons de tourbe prélevés à proximité de l'ancien site d'extraction d'uranium des Sagnes (Limousin, France) ont été caractérisés et ont ensuite été utilisés pour des expériences d'adsorption et de désorption en btach. Les résultats montrent que l'adsorption de 226Ra(II) sur la tourbe est supérieure à 97% pour pH>4-6 (suivant la teneur en particules détritiques dans la tourbe), ce qui correspond à des valeurs de Kd de 4500 pour 500mL/g. Quand à elle, l'adsorption de 238U(VI) est supérieure à 80% à pH>3, avec des valeurs de Kd qui atteignent 11000 mL/g vers pH 4.5. La désorption mesurée après un mois reste très faible. Contrairement aux tourbes classiques, la tourbière des Sagnes présente la particularité d'avoir une charge détritique importante (jusqu'à 50% de la masse de la tourbe sèche). L'interprétation des courbes de rétention de 238U(VI) et 226Ra(II) nécessite au préalable de discriminer à l'aide de modélisations, la contribution des différentes phases minérales présentes (oxyde de fer, phyllosilicates). Un modèle opérationnel, représentant la fraction organique comme un échangeur d'ions, a été proposé. Celui-ci permet de décrire le comportement de ces deux radioéléments sur la fraction organique de la tourbe.The environmental footprint of former uranium mining sites is a major concern for society. In order to guarantee the protection of ecosystems and thus a minimal radiological impact on the biosphere, it si important to understand and to be able to model the phenomena controlling the migration of uranium and its decay products, specially radium (226Ra) (AREVA's Envir@Mines project). In the environment, among solid phases which can retain 238U(VI) and 226Ra(II), peat is known to have relevant affinity for U(VI). Because peat is usually composed at 90 % dry weight of organic matter, the aim of this study was to qualify and quantify peat organic matter affinity for 238U(VI) and 226Ra(II). Peat samples extracted from Les Sagnes (close to a former uranium mining site in Limousin area, France) was characterized andbatch adsorption/desorption experiments were conducted. The results indicate that 226Ra(II) adsorption onto that peat is higher than 97 % for pH>4-6 (depending on the organic/mineral ratio in dry peat) corresponding to Kd values about 4500 for 500mL/g and 238U(VI) adsorption is higher than 80 % at pH>3 with Kd maximal values reaching 11000 mL/g around pH 4.5 . Only a little desorption was measured after one month.An ion exchange modelling for radium adsorption onto one type of organic matter sorption site was enough to fit the experimental adsorption Kd for the peat over the whole range of Ph . However, uranium sorption on peat can be modelled on that organic sorption site only for pH 5 to 10. From Ph 5 to 10, to explain the experimental uranium adsorption Kd values (close to 1500 mL/g), uranium sorption onto mineral phases (such as smectite and iron oxide in this study) has to be considered. An operational data set is given for both 238U(VI) and 226RA(II) sorption onto Les Sagnes peat. Unlike usual peat, peat from Les Sagnes contains more than 10 % dry weight of mineral matter. That is why it is necessary to modele sorption of those two radioelements onto mineral phases (such as smectite and iron oxide, in this study), to discriminate which part of the sorption is due to mineral phases and which one id from organic matter. An operational dataset for 238U(VI) and 226Ra(II) sorption onto Les Sagnes organic matter was determined

Regulation of resection at double strand-breaks by SIR mediated heterochromatin

L'hétérochromatine est une caractéristique conservée des chromosomes eucaryotes, avec des rôles centraux dans la régulation de l'expression des gènes et le maintien de la stabilité du génome. Comment la réparation de l'ADN est régulée par l'hétérochromatine reste mal compris. Chez Saccharomyces cerevisiae, le complexe SIR (Silent Information Regulator) assemble une fibre de chromatine compacte. La chromatine SIR limite la résection aux cassures double-brin (DSB) protégeant les extrémités chromosomiques endommagées contre la perte d'informations génétiques. Toutefois, lesquels des trois complexes de résection redondants, MRX-Sae2, Exo1 et Sgs1-Dna2 sont inhibés et par quel(s) mécanisme(s) reste à decouvrir. Nous montrons que Sir3, le facteur de fixation des histones de l’hétérochromatine de Saccharomyces cerevisiae, interagit physiquement avec Sae2 et inhibe toutes ses fonctions. Cette interaction limite notamment la résection médiée par Sae2, stabilise MRX à la DSB et augmente le Non-Homologous End Joining (NHEJ). De plus, la chromatine répressive SIR inhibe partiellement les deux voies de résection extensive médiées par Exo1 et Sgs1-Dna2 par des mécanismes distincts. L'inhibition par les SIR de la résection extensive et de Sae2 favorise la NHEJ et limite le Break-Induced Replication (BIR), prévenant ainsi de la perte d'hétérozygotie au niveau des subtélomères.Heterochromatin is a conserved feature of eukaryotic chromosomes, with central roles in regulation of gene expression and maintenance of genome stability. How DNA repair occurs in heterochromatin remains poorly described. In Saccharomyces cerevisiae, the Silent Information Regulator (SIR) complex assembles a compact chromatin fibre. SIR-mediated repressive chromatin limits Double Strand Break (DSB) resection protecting damaged chromosome ends against the loss of genetic information. However, which of the three redundant resection complexes, MRX-Sae2, Exo1 and Sgs1-Dna2 are inhibited and by which mechanism remains to be deciphered. We show that Sir3, the histone-binding factor of yeast heterochromatin, physically interacts with Sae2-mediated resection and inhibits all its functions. Notably, this interaction limits Sae2-mediated resection, delays MRX removal from DSB ends and promotes Non-Homologous End Joining (NHEJ). In addition, SIR-mediated repressive chromatin partially inhibits the two long range resection pathways mediated by Exo1 and Sgs1-Dna2 by distinct mechanisms. Altogether SIR mediated inhibition of extensive resection and of Sae2 promotes NHEJ and limits Break-Induced Replication (BIR) preventing loss of heterozygosity at subtelomeres

Keep moving and stay in a good shape to find your homologous recombination partner

International audienc

Sorption properties of peat's organic matter for U and 226^{226}Ra in mining areas

International audienceThe environmental footprint of former uranium mining activities is a major concern for AREVA who is in charge of monitoring these ancient mining sites. In order to limit the radiological impact on the biosphere we must have a good knowledge of the chemical properties controlling the migration of uranium (U) and its decay products, in particular radium ($^{226}$Ra). This present study is focused on an acidic peat land typical of those found in the vicinity of former mining sites in the Limousin region (France). Peat is a complex material which combines in various proportions, many components such as organic compounds (humic and fulvic acids, organic acids, bacteria, fungi) and mineral phases (clay minerals, oxides), each having their own specific reactivity and influence on U(VI) and $^{226}$Ra behavior.This study aims to acquire the sorption properties of U(VI) and $^{226}$Ra on natural organic matter from peat. According to the ion exchange formalism frequently used to describe the sorption behavior of clay-minerals, oxides and more generally soils, the peat sorption properties were successfully determined, i.e. the amount of sorption site types and their selectivity towards U(VI) and $^{226}$Ra. These sorption parameters would then be implemented in geochemical models used for the environmental impact assessment of mining sites

Chemical reactivity of natural peat towards U and Ra

International audiencePeat is a complex material with several organic constituents that contribute to its high capacity to retain metals. In the context of uranium mining, peat can accumulate high concentrations of uranium and its decay products such as radium. Hence, interaction with peat appears to be a key factor in the understanding of the geochemical mechanisms controlling the fate of these products. This study aims to determine the sorption properties of two trace elements, U(VI) and 226Ra, on natural organic matter from peat. The presented method was applied to both natural peat samples originating from a mining context, with various contents of organic matter (from 40 to 70pc) and detrital loads, and wetland peat with a more than 98pc composition of organic matter. In the present study, considering peat material as a sorbent, its reactivity towards metals and other contaminants can be described as that of an ion-exchanger. A relatively simple model of ion-exchange based on the sorption properties of carboxylic sites has been applied with success to describe the sorption of uranium and radium. In the general overview of the different mechanisms able to control the mobility of these radionuclides in a uranium mining context, organic matter is likely one of the main contributors to radionuclide scavenging even under oxic conditions

Histoire du peuple de Dieu, depuis son origine jusqu'a la naissance du Messie ... ou Le Texte Sacré ... de l'Ancien Testament, réduit en un corps d'histoire

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Título: Le Texte Sacré.

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