Radium analysis in natural waters remains a current challenge in the field of radiological monitoring, as well as for environmental concerns. A new Ra-selective grafted resin was developed in the present work; a calix[4]arene derivative functionalized with a crown-6 ether and two synergistic carboxylic groups serves as the selective chelating agent, while the support consists of SiO2. Its properties were investigated in the laboratory by coupling experimental data with a modelling approach. The resin was shown to be efficient for Ra within the pH range typical of natural waters (similar to 6-8). Its affinity for Ra was significantly higher than for other alkaline earth cations, although it remained sensitive to salt loading. This trend was confirmed by batch sorption tests conducted with both synthetic aqueous media and various natural water samples. The proposed resin appears promising for radium extraction and pre-concentration from natural waters.

Understanding the behavior of contaminants in soils and their transport in water is crucial. This study focuses on the mobility of uranium (U) in a buried contaminated sediment layer, deposited in a wetland 70 years ago by the first U mining activities in France. U mobilization is kinetically limited in the contaminated layer with a small fraction of labile U as deduced from laboratory desorption-based studies and in situ studies performed by DET (Diffusive Equilibration in Thin films)/DGT (Diffusive Gradients in Thin films) passive sampler data monitored over time. The smart-Kd approach, combined with a comprehensive system characterization, identified this labile fraction as U(VI) primarily adsorbed on 2:1 clay minerals, which is in line with X-ray Absorption Spectroscopy (XAS) data. The inert fraction was found to correspond to U minerals and adsorbed U(IV) and U(VI) species exhibiting desorption hysteresis. Combining laboratory and field studies, this multiscale approach allows to connect molecular processes to operational Kd(labile) parameters.

Background: The release to the environment of natural radionuclides like 226Ra due to human activities have raised concerns about human and ecosystem exposure. 226Ra's resemblance to calcium and involvement in biological processes accentuate the importance of understanding its geochemical behavior and migration pathways. Soil and sediment pore waters provide valuable information but have proved to be challenging to analyze, requiring to push the limits of current sample preparation and detection methods often not scaled for low concentrated microvolumes of samples. A more efficient and accurate analytical method is therefore needed to get reliable data to support hydro-geochemical modeling. Results: We describe here a novel comprehensive approach for accurate 226Ra quantification in pore waters of a wetland located downstream of the former Rophin uranium mine. In order to highlight the migration of 226Ra between the different soil layers, microvolumes of soil pore waters were in situ sampled up to 50 cm depth employing Diffusive Equilibrium in Thin-Films (DET) probes. The workflow included spiking DET extracts with an in-house 228Ra tracer, specific solid-phase extraction with 50 mg of AnaLig Ra-01 (R) resin, and elution fraction calcination. This process eliminated interferences and simplify the analysis matrix. Quantification relied on isotope dilution after measurement by ICP-MS hyphenated to a desolvator module and to a microsampler (150 mu L injection). The resulting 1 cm-high-resolution profile revealed unusual 226Ra enrichment with depth, signs of Ra mobility from the solid contamination source. These elements are essential for assessing 226Ra distribution coefficients across soil horizons and subsequent wetland remobilization considerations. Significance and novelty: This first methodological advance for 226Ra constitutes a significant step to understand 226Ra behavior i.e., to quantify its activity level, fluxes inside of wetland soils or at the interface overlying waters/sediments. Its potential extension to studies involving other elements underscores its broader applicability in environmental research. The findings contribute to evidence-based decision-making for environmental protection and management, aiding in the preservation of ecological integrity and human health.

This paper presents a quantitative characterisation of the fracture openings obtained in triaxial shear tests on several cement mortar samples. The comparison was carried out on three samples with various apertures using different methods of semi-destructive and non-destructive characterisation: optical microscopy, scanning electron microscopy, X-ray computed tomography, digital volume correlation and the 14 C-polymethylmethacrylate method. The fracture aperture distribution results are in good agreement between the different methods. Although the opening results obtained are comparable, the most advantageous method was considered to be XRCT profile analysis based on the size of the target area studied and the specific characteristics of each technique.

Although many studies have explored the responses of living organisms or ecosystems exposed to radioelements from human activities, very few studies have focused on the characterization of microbial biodiversity and the adaptations developed in environments characterized by natural, chronic and old radioactivity. Radioactive mineral springs are insulated ecosystems that have barely evolved in the last centuries. They therefore offer exceptional windows on the history of life on earth. Within the framework of the TIRAMISU project (biodiversiTy In RAdioactive MIneral Springs of the aUvergne region), biologists, ecologists, geologists, physicists, radiochemists and sociologists explore if and how natural ionizing radiation can be an “abiotic driver” impacting the diversity and structuring of microbial communities in food webs exposed to this radiation for long periods.

An in situ methodology combining DET and DGT probes was applied in a wetland soil, downstream of a former uranium mine (Rophin), to evaluate metal resupply by calculating the R ratio (R - [U](DGT)/[U](pore water)) from a high resolution and large (75 cm) soil profile. Our study confirms its applicability in soil layers with varying properties; only soil layers with low water content or coarse texture appear to be limiting factors. For soil profiles, DET provides new insights of the distribution of Uranium as soluble species (free ions, small inorganic complexes,.) along the pore water profile, whereas DGT highlights the presence of other "DGT labile" species. The pairing of DET and DGT, plus the calculation of the R, highlights two U behaviors in combining results from red-ox sensitive elements (Mn, Fe). First, in the organic topsoil layer, an increase in [U](DET) and [U](DGT) at 3-4 cm reflects the desorption of U probably trapped onto Fe- and Mn-oxohydroxides in a DGT-labile form. However, the resupply from soil to pore water is close to a diffusion only case (R < 0.2) meaning that a portion of U is certainly tightly bound by OM in soil as non-labile species. Second, a peak in [U](DGT) perfectly corresponding to the former mine deposit layer signifies the presence of U under DGT-labile species. Moreover, a maximum R value of 0.87 demonstrates the near complete resupply of U from a labile fraction in this layer, as opposed to other elements like Pb. (C) 2021 Elsevier Ltd. All rights reserved.

Global climate warming disproportionately affects high-latitude and mountainous terrestrial ecosystems. Warming is accompanied by permafrost thaw, shorter winters, earlier snowmelt, more intense soil freeze-thaw cycles, drier summers, and longer fire seasons. These environmental changes in turn impact surface water and groundwater flow regimes, water quality, greenhouse gas emissions, soil stability, vegetation cover, and soil (micro)biological communities. Warming also facilitates agricultural expansion, urban growth, and natural resource development, adding growing anthropogenic pressures to cold regions' landscapes, soil health, and biodiversity. Further advances in the predictive understanding of how cold regions' critical zone processes, functions, and ecosystem services will continue to respond to climate warming and land use changes require multiscale monitoring technologies coupled with integrated observational and modeling tools. We highlight some of the major challenges, knowledge gaps, and opportunities in cold region critical zone research, with an emphasis on subsurface processes and responses in both natural and agricultural ecosystems.

Uranium mining activities expose uranium ore and mine tailings to the surface environment, where the release of radionuclides is facilitated by weathering at rates exceeding those typically found in nature. Therefore, close to former uranium mining sites, radionuclides and especially uranium concentrations in water may surpass local background levels. The methodology proposed herein, entails coupling, gamma-ray mapping, water sampling and chemical analyses including DGT (Diffusive Gradient in Thin Film) measurements, provides new insights into describing the environment of the La Commanderie site (France). Gamma-ray mapping allows identifying water seepage, output from a waste rock pile, as a potential pathway for radionuclides into the environment. Water seepage monitoring has shown: a low pH value (4.2), high sulfate content (179 mg.L-1) and high uranium concentrations of up to 436 μg.L-1. These recordings indicate that an acid mining drainage (AMD) process is occurring inside or under the oxidized parts of the waste rock pile. Monitoring data over three flow periods revealed the release of the highest uranium concentrations during a high-flow period downstream of the site, which is compliant with local regulations. The AMD process is also responsible for the release of significant amounts of Fe, Mn and As within the immediate environment in both dissolved and particulate forms. Changes in dissolved oxygen concentration and redox potential during low flow periods, modify the speciation of Fe (in AMD waters) which acts as a scavenger for other elements such as As, Mn and U. The use of DGT under environmental conditions, and specifically AMD waters, seems to be relevant in comparison to filtered spot water sampling strategies. Moreover, based on DGT measurements, the dissolved part of the released uranium is considered as labile with concentrations above the environmental standards for freshwater organisms.

Cement-based materials are key components in radioactive waste repository barrier systems. To improve the available knowledge base, the European CEBAMA (Cement-based materials) project aimed to provide insight on general processes and phenomena that can be easily transferred to different applications. A bottom up approach was used to study radionuclide retention by cementitious materials, encompassing both individual cement mineral phases and hardened cement pastes. Solubility experiments were conducted with Be, Mo and Se under high pH conditions to provide realistic solubility limits and radionuclide speciation schemes as a prerequisite for meaningful adsorption studies. A number of retention mechanisms were addressed including adsorption, solid solution formation and precipitation of radionuclides within new solid phases formed during cement hydration and evolution. Sorption/desorption experiments were carried out on several anionic radionuclides and/or toxic elements which have received less attention to date, namely: Be, Mo, Tc, I, Se, Cl, Ra and 14C. Solid solution formation between radionuclides in a range of oxidation states (Se, I and Mo) with the main aqueous components (OH−, SO4−2, Cl−) of cementitious systems on AFm phases were also investigated.

Alteration experiments involving intermediate level nuclear waste (ILW) glass in contact with hardened cement paste (HCP) were performed to assess its behavior under simulated repository conditions. Batch experiments were conducted at 20 °C and 50 °C in several artificial cement pore water (ACW) samples (pH from 10 to 13), in the presence of HCP (CEM-I, CEM-V and low pH), with a ratio of glass surface to volume of solution of 8000 m-1 and a ratio of mass of HCP to volume of solution of 10 g L-1. Glass alteration rates increase up to ∼4 × 10-2 g m-2 d-1 with pH in contact with HCP, notably with CEM-I. This value decreases by 2 orders of magnitude in low pH cement solution and also for residual alteration rates. The effect of calcium on glass alteration was observed, mainly in Ca(OH)2 saturated solution, with an incubation effect on the release of Si in solution. Experimental data were successfully modeled with the PhreeqC geochemical code. Glass and HCP samples were characterized via SEM/EDX and micro-Raman studies. This work showed that vitrified glass exhibits good performance in terms of low alteration rates (∼10-4 g m-2 d-1), the absence of secondary phases, and the formation of a gel layer at the surface, when in contact with low pH conditions (in the presence or absence of low pH HCP).

An original methodology to quantitatively explore exchangeability of hydrogen isotopes in carbohydrate molecules is proposed. To access the speciation of organically bound hydrogen isotopes, isotopic exchanges were carried out under a soft path regime in the vapor phase at 20 degrees C with set (D,T/H) vapor pressure ratios. When steady states were reached, the fraction of exchangeable hydrogen of microcrystalline cellulose, alpha-cellulose and wheat grains were obtained and ranged from 13 to 31% (versus a theoretical value of 30%). In cellulose, and more specifically in microcrystalline cellulose, the molecular hydrogen bonds as well as the different conformations of the network seemed to decrease the hydroxyl groups of glucose units available for isotopic exchange. On the contrary, the assumed enzymatic hydrolysis of the constitutive molecules of wheat starch into low-molecular weight carbohydrate molecules enhanced the exchangeable pool. An average value of the activity between non-exchangeable organically bound tritium (NE-OBT) and non-exchangeable organically bound hydrogen was calculated for wheat grains, ((T)(H)) (NE) = 0.55 +/- 0.03 Bq.g(-1) of hydrogen atoms. (C) 2017 Elsevier Ltd. All rights reserved.

As a first step in developing better molecular scale understanding of the effects of organic additives on the adsorption and mobility of radionuclides in cement under conditions of geological nuclear waste repositories, two complementary approaches, wet chemistry experiments and molecular dynamics (MD) computer simulations, were applied to study the sorption behaviour of two simple model systems: gluconate and uranyl on calcium silicate hydrate phases (C-S-H) - the principal mineral component of hardened cement paste (HCP). Experimental data on sorption and desorption kinetics and isotherms of adsorption for gluconate/C-S-H and U(VI)/C-S-H binary systems were collected and quantitatively analysed for C-S-H samples synthesised with various Ca/Si ratios (0.83, 1.0, 1.4) corresponding to various stages of HCP aging and degradation. Gluconate labelled with C-14 isotope was used in order to improve the sensitivity of analytical detection technique (LSC) at particularly low concentrations (10(-8) -10(-5) mol/L). There is a noticeable effect of Ca/Si ratio on the gluconate sorption on C-S-H, with stronger sorption at higher Ca/Si ratios. Sorption of organic anions on C-S-H is mediated by the presence of Ca2+ at the interface and strongly depends on the surface charge and Ca2+ concentration. In parallel, classical MD simulations of the same model systems were performed in order to identify specific surface sorption sites most actively involved in the sorption of gluconate and uranyl on C-S-H and to clarify molecular mechanisms of adsorption. (C) 2017 Elsevier Ltd. All rights reserved.

This work is carried out in the frame of a radioecological monitoring of anthropogenic tritium from upstream and downstream of several nuclear power plants along the Loire River to its estuary. This paper studies the variation of anthropogenic tritium species in the Loire River system from upstream to the mouth of the estuary. Tritiated water (HTO and HTO in sediment pore water) and organically bound tritium (OBT) forms were analysed after dedicated pre-treatments. The collected environmental samples consist in (i) surface-sediment and core samples from the river floor, (ii) surface and water column samples. A maximum 3H activity concentration of 26±3Bq·L−1 in the Loire River estuary is obtained whereas an environmental background level around 1Bq·L−1 is determined for a non influenced continental area by anthropogenic activities. The European follow-up indicator used as a screening value is 100Bq·L−1. The conservative tritium behaviour was used in order to characterize the tidal regime and river flow influences in the mixing zone of the Loire River estuary. Furthermore, OBT levels and total organically carbon (TOC) content are explored. Finally, ratios of OBT relative to HTO in sediment pore water in surface-sediment and core samples are also discussed.