New insights into U(VI) sorption onto montmorillonite from batch sorption and spectroscopic studies at increased ionic strength.

The influence of ionic strength up to 3 mol kg-1 (background electrolytes NaCl or CaCl2) on U(VI) sorption onto montmorillonite was investigated as function of pHc in absence and presence of CO2. A multi-method approach combined batch sorption experiments with spectroscopic methods (time-resolved laser-induced fluorescence spectroscopy (TRLFS) and in situ attenuated total reflection Fourier-transform infrared spectroscopy (ATR FT-IR)). In the absence of atmospheric carbonate, U(VI) sorption was nearly 99% above pHc 6 in both NaCl and CaCl2 and no significant effect of ionic strength was found. At lower pH, cation exchange was strongly reduced with increasing ionic strength. In the presence of carbonate, U(VI) sorption was reduced above pHc 7.5 in NaCl and pHc 6 in CaCl2 system due to formation of aqueous UO2(CO3)x(2-2x) and Ca2UO2(CO3)3 complexes, respectively, as verified by TRLFS. A significant ionic strength effect was observed due to the formation of Ca2UO2(CO3)3(aq), which strongly decreases U(VI) sorption with increasing ionic strength. The joint analysis of determined sorption data together with literature data (giving a total of 213 experimental data points) allowed to derive a consistent set of surface complexation reactions and constants based on the 2SPNE SC/CE approach, yielding log K°≡SSOUO2+ = 2.42 ± 0.04, log K°≡SSOUO2OH = -4.49 ± 0.7, and log K°≡SSOUO2(OH)32- = -20.5 ± 0.4. Ternary uranyl carbonate surface complexes were not required to describe the data. With this reduced set of surface complexes, an improved robust sorption model was obtained covering a broad variety of geochemical settings over wide ranges of ionic strengths and groundwater compositions, which subsequently was validated by an independent original dataset. This model improves the understanding of U(VI) retention by clay minerals and enables now predictive modeling of U(VI) sorption processes in complex clay rich natural environments.

An integrated approach combining soil profile, records and tree ring analysis to identify the origin of environmental contamination in a former uranium mine (Rophin, France).

Uranium mining and milling activities raise environmental concerns due to the release of radioactive and other toxic elements. Their long-term management thus requires a knowledge of past events coupled with a good understanding of the geochemical mechanisms regulating the mobility of residual radionuclides. This article presents the results on the traces of anthropic activity linked to previous uranium (U) mining activities in the vicinity of the Rophin tailings storage site (Puy de Dôme, France). Several complementary approaches were developed based on a study of the site's history and records, as well as on a radiological and chemical characterization of soil cores and a dendrochronology. Gamma survey measurements of the wetland downstream of the Rophin site revealed a level of 1050 nSv.h-1. Soil cores extracted in the wetland showed U concentrations of up to 1855 mg.kg-1, which appears to be associated with the presence of a whitish silt loam (WSL) soil layer located below an organic topsoil layer. Records, corroborated by prior aerial photographs and analyses of 137Cs and 14C activities, suggest the discharge of U mineral particles while the site was being operated. Moreover, lead isotope ratios indicate that contamination in the WSL layer can be discriminated by a larger contribution of radiogenic lead to total lead. The dendroanalysis correlate U emissions from Rophin with the site's history. Oak tree rings located downstream of the site contain uranium concentrations ten times higher than values measured on unaffected trees. Moreover, the highest U concentrations were recorded not only for the operating period, but more surprisingly for the recent site renovations as well. This integrated approach corroborates that U mineral particles were initially transported as mineral particles in Rophin's watershed and that a majority of the deposited uranium appears to have been trapped in the topsoil layer, with high organic matter content.

Spectroscopic identification of ternary Cm-carbonate surface complexes.

The influence of dissolved CO(2) on the sorption of trivalent curium (Cm) on alumina (gamma-Al(2)O(3)) and kaolinite was investigated by time resolved laser fluorescence spectroscopy (TRLFS) using the optical properties of Cm as a local luminescent probe. Measurements were performed at T < 20 K on Cm loaded gamma-Al(2)O(3) and kaolinite wet pastes prepared in the absence and presence of carbonate in order to pictorially illustrate any changes through a direct comparison of spectra from both systems. The red-shift of excitation and emission spectra, as well as the increase of fluorescence lifetimes observed in the samples with carbonate, clearly showed the influence of carbonate and was fully consistent with the formation of Cm(III) surface species involving carbonate complexes. In addition, the biexponential decay behavior of the fluorescence lifetime indicated that at least two different Cm(III)-carbonate species exist at the mineral-water interface. These results provide the first spectroscopic evidence for the formation of ternary Cm(III)-carbonate surface complexes.

Effects of water supplementation with selenium and vitamin E on growth performance and blood selenium and serum vitamin E concentrations in weanling pigs.

OBJECTIVE: To determine effects of supplementation of drinking water with selenium and vitamin E on blood selenium and serum vitamin E concentrations, growth performance, and water intake of pigs. DESIGN: Prospective controlled study. ANIMALS: 228 weanling pigs. PROCEDURE: In experiments 1 and 2, pigs were given drinking water supplemented with selenium and vitamin E, and blood selenium and serum vitamin E concentrations were measured. In experiment 3, growth performance and water intake were measured in pigs that received supplemented water for 2 or 5 weeks and in control pigs. RESULTS: In experiment 1, blood selenium concentrations were significantly increased after 7 days of supplementation, and serum vitamin E concentrations were significantly increased after 1 and 7 days of supplementation, compared with baseline concentrations. In experiment 2, blood selenium concentrations were not significantly different between treated and control pigs, and serum vitamin E concentrations were significantly increased on day 7. In experiment 3, gain-to-feed ratios were significantly higher for pigs supplemented with selenium and vitamin E for 5 weeks, but other differences were not detected. CLINICAL IMPLICATIONS: Supplementation of drinking water with selenium and vitamin E may improve the selenium and vitamin E status of weanling pigs by increasing selenium and vitamin E intake.

Bovine luteinizing hormone (LH) isoforms and amounts of messenger ribonucleic acid for alpha- and LH beta-subunits in pituitaries of cows immunized against LH-releasing hormone.

Ovariectomized beef cows were actively immunized against LHRH to test the hypothesis that decreased stimulation of gonadotropes would alter the distribution of LH isoforms and amounts of mRNA for subunits of LH in the pituitary. Eight long-term (3 yr) ovariectomized beef cows were randomly assigned to one of two treatments: immunization against LHRH conjugated to human serum globulin (n = 4) and nonimmunization (control, n = 4). Mean concentration of serum LH in cows immunized against LHRH (1.0 +/- .83 ng/ml) was less (p = 0.01) than in control cows (5.0 +/- 0.83 ng/ml). Amounts of alpha- (p = 0.13) and LH beta-subunit (p = 0.10) mRNA tended to be reduced in cows immunized against LHRH compared to control cows. However, weight of the anterior pituitary and concentrations of LH in this gland did not differ (p = 0.90) among cows from the two groups. Pituitary extracts were chromatofocused on pH 10.5-7.0 gradients, and concentrations of LH in eluent fractions were determined by RIA. Extracts of all pituitaries resolved into nine isoforms (designated A through H and Z beginning with the most basic form). Only isoform F (mid-alkaline elution, pH = 8.8) was influenced by treatment (p = 0.05). Cows immunized against LHRH had a greater relative amount of isoform F (42.1 +/- 1.4%) than controls (37.2 +/- 1.4%). In summary, immunization of cows against LHRH altered 1) circulating concentrations of LH, 2) amounts of mRNA for the subunits of LH, and 3) distribution of intrapituitary LH isoforms without changing the concentrations of LH in the anterior pituitary.