In-situ speciation measurements and bioavailability determination of plutonium in natural waters of a karst system using diffusion in thin films (DGT) techniques

Nuclear activities of 1945-1975 have released in the environment significant amounts of radioactive elements. Three main sources contributed to contamination with plutonium: nuclear weapon tests, discharges from nuclear facilities and nuclear accidents. Global atmospheric fallout has marked pristine environments with trace amounts of 239Pu and 240Pu. Plutonium is an alpha-particle emitter with long half life and it is dangerous when incorporated in the organism. The amount of Pu which can be assimilated by living organisms depends on its chemical form and on local physico-chemical characteristics of the environment. To study the bioavailability of plutonium in aquatic environments, we developed a technique of diffusive gradients in thin films (DGT), which allows measuring free and labile Pu species only, diffusing through a thin layer of a polymer gel. DGT devices exposed in freshwaters in the mineral Venoge spring and organic-rich Noiraigue Bied brook have demonstrated that the major fraction of Pu in these waters is fully available for biouptake. Similarly, the ultrafiltration technique has shown that in both mineral and organic-rich water the major fraction of Pu is found in the dissolved phase. Laboratory experiments using the DGT technique revealed a relatively high dissociation rate constant for Pu complexes with natural organic matter, suggesting that such complexes in natural environment can contribute to biouptake of Pu by aquatic organisms. Sequential elution of Pu from different compartments of aquatic mosses (Venoge) and plants (Noiraigue) indicated that the major fraction of Pu was co-precipitated with calcite on their extracellular parts. The development and testing of the DGT technique for Pu measurements in the frame of this project paves the way for further applications of DGTs to study the bioavailability and speciation of Pu in contaminated and marine environments. -- Les activités nucléaires des années 1945-1975 ont relâché dans l'environnement d'importantes quantités d'éléments radioactifs. Trois sources principales ont contribué à la contamination par le plutonium: les essais d'armes nucléaires, les rejets des installations nucléaires et les accidents nucléaires. Les retombées atmosphériques globales ont marqué l'environnement avec des traces de 239Pu et 240Pu. Le plutonium est un émetteur de particules alpha de longue période et il est dangereux lorsqu'il est incorporé dans l'organisme. La quantité de Pu pouvant être assimilée par les organismes vivants dépend de sa forme chimique et des caractéristiques physico-chimiques locales de l'environnement en question. Pour étudier la biodisponibilité du plutonium dans les milieux aquatiques, nous avons développé une technique du gradient de diffusion en couche mince (DGT), qui permet de mesurer seules les espèces libres de Pu, capables de diffuser à travers une mince couche d'un gel polymère. Les dispositifs DGT exposés dans les eaux douces de la source de la Venoge et du Bied de Noiraigue, riche en matière organique, ont démontré que la majeure fraction de Pu dans ces eaux est entièrement disponible pour l'assimilation biologique. De même, la technique d'ultrafiltration a démontré que dans l'eau minérale et dans l'eau riche en matière organique, le Pu se trouve principalement dans la phase dissoute. Des expériences de laboratoire utilisant la technique DGT ont révélé une constante de dissociation relativement élevée pour des complexes de Pu avec la matière organique naturelle, ce qui suggère que ces complexes en milieu naturel peuvent contribuer à l'accumulation de Pu par les organismes aquatiques. L'élution séquentielle de Pu de différents compartiments de mousses aquatiques (Venoge) et de plantes (Noiraigue) a montré que la majeure partie du Pu a été co-précipité avec la calcite sur leurs parties extracellulaires. Le développement et l'application de la technique DGT pour les mesures de Pu dans le cadre de ce projet ouvre la voie à de nouvelles applications de DGTs pour étudier la biodisponibilité et la spéciation du Pu dans des environnements marins contaminés. -- The speciation and the bioavailability of trace elements in the aquatic environments are the key limiting factors defining the toxic effects to the aquatic biota. Radioactive elements found in the environment arouse particular interest since they can exert radiotoxic effects at low concentrations, yet insufficient to show any chemotoxic effects. Plutonium (Pu) is a heavy artificial radionuclide of particular concern due to its long half-life and alpha- particle emission. Assessing the speciation and the bioavailability of Pu in natural waters is essential in order to predict its environmental risks. The overall goal of this research work was to develop the technique of the diffusive gradients in thin films (DGT) for in-situ bioavailability measurements of Pu. We first aimed to determine the diffusion coefficients (D) of Pu in the diffusive polyacrylamide (PAM) gel. Afterwards, we intended to test in laboratory experiments the feasibility of the DGT technique for Pu measurements, using Chelex resin as a binding phase. The positive outcome of the initial experiments with Pu allowed us to expand the application of the DGT technique to further studies on the molecular interactions of Pu with natural organic matter (NOM) and on the mobility of Pu in +IV and +V oxidation states. To measure the bioavailable fraction of Pu in natural waters, DGT samplers with large surface area were fabricated and deployed in two, chemically distinct, karstic freshwater environments. The results of DGT measurements were complemented with ultrafiltration technique, providing the distribution of Pu between colloid-bound and truly dissolved fractions. Finally, the determination of Pu in different compartments of aquatic mosses and plants enabled us to integrate all the results into a model of Pu speciation in karstic freshwater environments. The determination of diffusion coefficients of Pu in solutions of different chemical composition demonstrated that the mobility of Pu species in natural waters depends on the content of natural colloids and natural organic matter. Diffusion experiments yielded higher diffusion coefficients for Pu in the simple buffered solutions, compared to solutions containing Pu in the presence of fulvic or humic substances. Similarly, the diffusion of Pu was less restrained in water from a mineral spring, compared to the Pu diffusion in organic-rich water. Enriching natural waters with colloids by ultrafiltration also reduced the diffusion coefficients of Pu. The effects of the redox speciation of Pu were also quantified using the DGT technique. As demonstrated, Pu (V) was more mobile compared to Pu (IV) in both raw buffered solutions and in the presence of humic substances. The interaction of Pu with natural organic matter results in the formation of soluble complexes, altering its speciation in natural waters. The rate of dissociation of these complexes determines the fraction of free Pu, available for biouptake. Multiple DGT devices with different diffusive layer thicknesses were used to estimate the dissociation constant, kdis, of Pu-NOM complexes and the extent of their contribution to the biouptake of Pu. Using a mathematical dynamic model, we found a relatively high kdis for Pu-NOM complexes (kdis 7.5 × 10-3 s-1), suggesting that in the organic-rich natural waters Pu is fully available for biouptake. The findings obtained in laboratory experiments were thereafter confirmed in the field studies. DGT samplers deployed in the mineral water of the Venoge spring (NOM < 1 mg L-1) measured the major fraction of Pu as bioavailable. In the organic-rich water (NOM = 15 mg L-1) of the Noiraigue Bied brook the fraction of free Pu was lower compared to the Venoge spring. However, the DGT devices with thicker diffusive gel layer accumulated twice as much Pu, as expected from the theory for labile complexes. This indicated that the dissociation of soluble Pu-NOM complexes in this water contributed to the uptake of Pu. The distribution of Pu eluted from different compartments of the aquatic mosses and plants demonstrated that the major fraction of Pu is co-precipitated with calcite on the leaves surfaces. Pu concentrations determined in the mosses (Fontinalis antypiretica) from the Venoge spring suggest that Pu is possibly found in a chemical form similar to a soluble uranyl-carbonate complex in water; this complex can further co-precipitate with calcite when CO2 is degassing from the water. Aquatic plants (Phragmites australis) in the Noiraigue Bied brook contained even a greater fraction of Pu within the calcite. However, the presence of organic matter at high concentration can complex Pu and contribute to a higher biouptake of Pu in this water since the diffusion and dissociation of the Pu-NOM complexes will create additional flux to the plant

Speciation and Bioavailability Measurements of Environmental Plutonium Using Diffusion in Thin Films.

The biological uptake of plutonium (Pu) in aquatic ecosystems is of particular concern since it is an alpha-particle emitter with long half-life which can potentially contribute to the exposure of biota and humans. The diffusive gradients in thin films technique is introduced here for in-situ measurements of Pu bioavailability and speciation. A diffusion cell constructed for laboratory experiments with Pu and the newly developed protocol make it possible to simulate the environmental behavior of Pu in model solutions of various chemical compositions. Adjustment of the oxidation states to Pu(IV) and Pu(V) described in this protocol is essential in order to investigate the complex redox chemistry of plutonium in the environment. The calibration of this technique and the results obtained in the laboratory experiments enable to develop a specific DGT device for in-situ Pu measurements in freshwaters. Accelerator-based mass-spectrometry measurements of Pu accumulated by DGTs in a karst spring allowed determining the bioavailability of Pu in a mineral freshwater environment. Application of this protocol for Pu measurements using DGT devices has a large potential to improve our understanding of the speciation and the biological transfer of Pu in aquatic ecosystems

A DGT Technique for Plutonium Bioavailability Measurements.

The toxicity of heavy metals in natural waters is strongly dependent on the local chemical environment. Assessing the bioavailability of radionuclides predicts the toxic effects to aquatic biota. The technique of diffusive gradients in thin films (DGT) is largely exploited for bioavailability measurements of trace metals in waters. However, it has not been applied for plutonium speciation measurements yet. This study investigates the use of DGT technique for plutonium bioavailability measurements in chemically different environments. We used a diffusion cell to determine the diffusion coefficients (D) of plutonium in polyacrylamide (PAM) gel and found D in the range of 2.06-2.29 × 10(-6) cm(2) s(-1). It ranged between 1.10 and 2.03 × 10(-6) cm(2) s(-1) in the presence of fulvic acid and in natural waters with low DOM. In the presence of 20 ppm of humic acid of an organic-rich soil, plutonium diffusion was hindered by a factor of 5, with a diffusion coefficient of 0.50 × 10(-6) cm(2) s(-1). We also tested commercially available DGT devices with Chelex resin for plutonium bioavailability measurements in laboratory conditions and the diffusion coefficients agreed with those from the diffusion cell experiments. These findings show that the DGT methodology can be used to investigate the bioaccumulation of the labile plutonium fraction in aquatic biota

An investigation of aspects of radiochemical purity of ^99mTc-labelled human serum albumin nanocolloid.

Nanocolloidal human serum albumin radiolabelled with <sup>99m</sup> Tc provides a diagnostic radiopharmaceutical for sentinel node lymphoscintigraphy. NanoHSA (Nanotop), a commercially available kit, enables the simple preparation of this radiopharmaceutical via reconstitution with pertechnetate eluted from a generator. Thin-layer chromatography is widely used for determining radiochemical purity in clinical nuclear medicine. Quality control methods recommended by the manufacturer were sometimes reported to yield variable results. Therefore, we proposed and evaluated three alternative thin-layer chromatography methods for the quality control of [ <sup>99m</sup> Tc]Tc-NanoHSA from a commercially available kit. The radiochemical purity of [ <sup>99m</sup> Tc]Tc-NanoHSA determined with all methods was reproducible and met the requirements of the SPC and the European Pharmacopoeia (≥ 95%). Our quality control using iTLC-SG chromatographic paper in methyl ethyl ketone mobile phase identified only free pertechnetate as impurity, resulting in > 99% RCP. The quality control using iTLC-SG in 85% methanol or iTLC-SA in 0.9% NaCl identified an additional small fraction of a hydrophilic impurity, resulting in 95-97% RCP. Glucose was identified as a potential <sup>99m</sup> Tc-carrying hydrophilic species contributing to hydrophilic impurities. Our quality control of [ <sup>99m</sup> Tc]Tc-NanoHSA with non-polar mobile phase tended to underestimate the amount of hydrophilic impurities, although without compromising the final quality of the radiopharmaceutical. Alternative TLC methods using aqueous mobile phases enabled a more accurate determination of hydrophilic impurities

Influence of bias voltage on the microstructure and physical properties of magnetron sputtered Zr–Si–N nanocomposite thin films

e report an investigation concerning the influence of ion bombardment on the nanostructure and physical properties of Zr–Si–N nanocomposite thin films. The films were deposited by reactive magnetron sputtering from individual Zr and Si targets. The Si content was varied by changing the power applied to the Si target. The increase of ion bombardment energy was obtained by applying a negative potential Ub = − 150 V to the substrate. The evolution of the film texture, grain size and lattice constant was mapped out using X-ray diffraction measurements. Zr–Si–N films deposited at a substrate temperature Ts = 510 K with a bias voltage of Ub = − 150 V exhibit less pronounced columnar structure with small crystallites having various orientations. The maximum nanohardness of 39 GPa is reached for the films at about 2.5 at.% Si, 8 nm grain size and 0.3 Si surface coverage. The increased energy of ionic species reaching the substrate when a negative bias voltage is applied seems to have the opposite effect to that of increasing substrate temperature: reduced SiNx coverage on the ZrN nanocrystallites

WC/a-C nanocomposite thin films: Optical and electrical properties

WC/amorphous carbon (a-C) thin films were deposited by dual magnetron sputtering from individual WC and graphite targets. The influence of film composition and microstructure on the optical and electrical properties was investigated. As evidenced by x-ray photoelectron spectroscopy and grazing angle x-ray diffraction measurements, the WC/a-C films are composite materials made of hexagonal W2C and/or cubic beta-WC1-X nanocrystallites embedded in (a-C) matrix. The optical properties were studied by spectroscopic ellipsometry and the electrical resistivity was measured by the van der Pauw method between 20 and 300 K. Both the optical and the electrical properties of the WC/a-C films are correlated with the chemical composition and microstructure evolution caused by a-C addition. The optical properties of W2C/a-C and beta-WC1-x/a-C films with a-C content <= 10 at. % are explained by modeling their dielectric functions by a set of Drude-Lorentz oscillators. Further increase in a-C content leads only to the formation of beta-WC1-x/a-C nanocomposite structures and their optical properties progressively evolve to those of a-C single phase. The electrical resistivity as a function of the temperature of all the films exhibits a negative temperature coefficient of resistivity. Theoretical fitting using the grain-boundary scattering model shows that the transport properties are mainly limited by the grain size and electron mean free path parameters

Radionuclides in the Environment in Switzerland: A Retrospective Study of Transfer from Soil to the Human Body.

Natural radionuclides are ubiquitous in the environment. In addition, artificial radionuclides are present in the Swiss environment after the fallout of the nuclear bomb tests of the 1950s and 1960s, after the accident of the Chernobyl nuclear power plant, or after authorized discharges from the Swiss nuclear power plants and research centres. These radionuclides can create a radiological hazard to the environment and humans because of the increased risk of cancer due to the ionizing radiation they produce. Here we show that some of these radionuclides have made their way from the air or the soil to the human body, where they target mostly the skeleton. However, the activity levels of 90 Sr, 239 Pu and 240 Pu, 226 Ra and 210 Pb/ 210 Po found in the human body remain very low and do not represent a public health issue at the current body burden

In hospital cardiac arrest: a role for automatic defibrillation.

INTRODUCTION: Sudden cardiac death (SCD) survival decreases by 10% for each minute of delay in defibrillation, however, survival rates of 98% can be achieved when defibrillation is accomplished within 30s of collapse. Recently, a fully automated external cardioverter-defibrillator (AECD) was approved by the FDA for in-hospital use. The AECD can be programmed to automatically defibrillate when a life threatening ventricular arrhythmia occurs. The purpose of this study was to assess the potential impact of in-hospital AECDs on the critical time to defibrillation in monitored hospital units. METHODS: Mock emergency (n = 18) were conducted using simulated ventricular fibrillation in various monitored units. Observers were stationed to record the time staff responded to the arrhythmia, and the time to shock. These times were compared to an AECD protocol that defibrillates automatically in an average of 38.3 s from onset of arrhythmia (n = 18). RESULTS: Staff versus AECD response time to arrhythmia (s) was 76.3 +/- 113.7 (CI 19.8-132.8) versus 7.6 +/- 0.6 (CI 7.3-7.9). Staff versus AECD time to shock was 169.2 +/- 103.1 (CI 117.9-220.4) versus 38.3 +/- 0.7 (CI 37.9-38.6). P-values are CONCLUSION: The use of AECDs on monitored units would significantly reduce the critical time to defibrillation in patients with SCA. We anticipate this would translate to improved survival rates, and better neurologic outcomes