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

Draft genome sequence data of Microbacterium sp. strain Be9 isolated from uranium-mill tailings porewaters

Microbacterium are Gram-positive, nonspore-forming, rod- shaped bacteria inhabiting a wide range of environments in- cluding soil, water, dairy products, other living organisms, etc. Microbacterium sp. strain Be9, isolated from mill tail- ings porewaters in France, shows a remarkable behavior in presence of uranium under distinct conditions, which is the main reason for the interest in sequencing its genome. In this work, we describe the draft genome sequence of Be9, comprising 4,046,806 bp, with a G + C content of 68.10% and containing 3,947 protein-coding sequences. The prelim- inary genome annotation analysis identified some genes en- coding for resistance to antibiotics and toxic compounds like heavy metals. This draft genome has been deposited at DDBJ/ENA/GenBank under the accession PRJNA590666.Orano MiningDepartamento de Microbiología Universidad de Granad

Mobility of daughter elements of U-238 decay chain during leaching by In Situ Recovery (ISR) : New insights from digital autoradiography

In highly permeable sedimentary rock formations, U extraction by in-situ leaching techniques (ISR - In-Situ Recovery) is generally considered to have a limited environmental impact at ground level. Significantly, this method of extraction produces neither mill tailings nor waste rocks. Underground, however, the outcome for U-238 daughter elements in aquifers is not well known because of their trace concentrations in the host rocks. Thus, understanding the in-situ mobility of these elements remains a challenge. Two samples collected before and after six months of ISR experiments (Dulaan Uul, Mongolia) were studied with the help of a digital autoradiography technique (DA) of alpha particles, bulk alpha spectrometry, and complementary petrographic observation methods. These techniques demonstrate that before and after leaching, the radioactivity is concentrated in altered and microporous Fe-Ti oxides. Most of the daughter elements of U remain trapped in the rock after the leaching process. DA confirms that the alpha activity of the Fe-Ti oxides remains high after uranium leaching, and the initial secular equilibrium of the U-238 series for Th-230 to Po-210 daughter elements (including Ra-226) of the fresh rocks is maintained after leaching. While these findings should be confirmed by more systematic studies, they already identify potential mechanisms explaining why the U-daughter concentrations in leaching water are low.Peer reviewe

Mapping U-238 decay chain equilibrium state in thin sections of geo-materials by digital autoradiography and microprobe analysis

A new approach is proposed in order to spatially localize and determine the equilibrium state of natural decay chains on hand-scale geological samples, thanks to a combination of three techniques: 1) Elementary chemical mapping by microprobe; 2) Alpha autoradiograph by gaseous detectors and 3) bulk alpha particle spectrometry. The quantitative nature of alpha autoradiograph and its comparison with U chemical maps allows to locate radioactive equilibrium state in four samples. This equilibrium state was confirmed by alpha spectrometry analysis.Peer reviewe

Geochemical control on uranium(IV) mobility in a mining-impacted wetland

Wetlands often act as sinks for uranium and other trace elements. Our previous work at a mining-impacted wetland in France showed that a labile noncrystalline U(IV) species consisting of U(IV) bound to Al-P-Fe-Si aggregates was predominant in the soil at locations exhibiting a U-containing clay-rich layer within the top 30 cm. Additionally, in the porewater, the association of U(IV) with Fe(II) and organic matter colloids significantly increased U(IV) mobility in the wetland. In the present study, within the same wetland, we further demonstrate that the speciation of U at a location not impacted by the clay-rich layer is a different noncrystalline U(IV) species, consisting of U(IV) bound to organic matter in soil. We also show that the clay-poor location includes an abundant sulfate supply and active microbial sulfate reduction that induce substantial pyrite (FeS2) precipitation. As a result, Fe(II) concentrations in the porewater are much lower than those at clay-impacted zones. U porewater concentrations (0.02-0.26 mu M) are also considerably lower than those at the clay-impacted locations (0.21-3.4 mu M) resulting in minimal U mobility. In both cases, soil-associated U represents more than 99% of U in the wetland. We conclude that the low U mobility reported at clay-poor locations is due to the limited association of Fe(II) with organic matter colloids in porewater and/or higher stability of the noncrystalline U(IV) species in soil at those locations

Mobile uranium(IV)-bearing colloids in a mining-impacted wetland

Tetravalent uranium is commonly assumed to form insoluble species, resulting in the immobilization of uranium under reducing conditions. Here we present the first report of mobile U(IV)-bearing colloids in the environment, bringing into question this common assumption. We investigate the mobility of uranium in a mining-impacted wetland in France harbouring uranium concentrations of up to 14,000 p. p. m. As an apparent release of uranium into the stream passing through the wetland was observable, we examine soil and porewater composition as a function of depth to assess the geochemical conditions leading to this release. The analyses show the presence of U(IV) in soil as a non-crystalline species bound to amorphous Al-P-Fe-Si aggregates, and in porewater, as a distinct species associated with Fe and organic matter colloids. These results demonstrate the lability of U(IV) in these soils and its association with mobile porewater colloids that are ultimately released into surface water

Sulphur cycling in a Neoarchean microbial mat

Multiple sulphur (S) isotope ratios are powerful proxies to understand the complexity of S biogeochemical cycling through Deep Time. The disappearance of a sulphur mass independent fractionation (S-MIF) signal in rocks <~2.4 Ga has been used to date a dramatic rise in atmospheric oxygen levels. However, intricacies of the S-cycle before the Great Oxidation Event remain poorly understood. For example, the isotope composition of coeval atmospherically derived sulphur species is still debated. Furthermore, variation in Archaean pyrite δ34S values has been widely attributed to microbial sulphate reduction (MSR). While petrographic evidence for Archaean early diagenetic pyrite formation is common, textural evidence for the presence and distribution of MSR remains enigmatic. We combined detailed petrographic and in-situ, high-resolution multiple S-isotope studies (δ34S and Δ33S) using secondary ion mass spectrometry (SIMS) to document the S-isotope signatures of exceptionally well-preserved, pyritised microbialites in shales from the ~2.65 Ga Lokammona Formation, Ghaap Group, South Africa. The presence of MSR in this Neoarchaean microbial mat is supported by typical biogenic textures including wavy crinkled laminae, and early-diagenetic pyrite containing <26‰ μm-scale variations in δ34S and Δ33S = -0.21 ± 0.65 ‰ (±1σ). These large variations in δ34S values suggest Rayleigh distillation of a limited sulphate pool during high rates of MSR. Furthermore, we identified a second, morphologically distinct pyrite phase that precipitated after lithification, with δ34S = 8.36 ± 1.16‰ and Δ33S = 5.54 ± 1.53‰ (±1σ). We propose that the S-MIF signature of this secondary pyrite does not reflect contemporaneous atmospheric processes at the time of deposition; instead, it formed by the influx of later stage sulphur-bearing fluids containing an inherited atmospheric S-MIF signal and/or from magnetic isotope effects during thermochemical sulphate reduction. These insights highlight the complementary nature of petrography and SIMS studies to resolve multigenerational pyrite formation pathways in the geological recordPublisher PDFPeer reviewe

The H3K36me2 writer-reader dependency in H3K27M-DIPG

Histone H3K27M is a driving mutation in diffuse intrinsic pontine glioma (DIPG), a deadly pediatric brain tumor. H3K27M reshapes the epigenome through a global inhibition of PRC2 catalytic activity and displacement of H3K27me2/3, promoting oncogenesis of DIPG. As a consequence, a histone modification H3K36me2, antagonistic to H3K27me2/3, is aberrantly elevated. Here, we investigate the role of H3K36me2 in H3K27M-DIPG by tackling its upstream catalyzing enzymes (writers) and downstream binding factors (readers). We determine that NSD1 and NSD2 are the key writers for H3K36me2. Loss of NSD1/2 in H3K27M-DIPG impedes cellular proliferation and tumorigenesis by disrupting tumor-promoting transcriptional programs. Further, we demonstrate that LEDGF and HDGF2 are the main readers mediating the protumorigenic effects downstream of NSD1/2-H3K36me2. Treatment with a chemically modified peptide mimicking endogenous H3K36me2 dislodges LEDGF/HDGF2 from chromatin and specifically inhibits the proliferation of H3K27M-DIPG. Our results indicate a functional pathway of NSD1/2-H3K36me2-LEDGF/HDGF2 as an acquired dependency in H3K27M-DIPG