Microbial transformations of selenite by methane-oxidizing bacteria

Abstract Methane oxidizing bacteria are well known for their role in the global methane cycle and their potential for microbial transformation of wide range of hydrocarbon and chlorinated hydrocarbon pollution. Recently, it has also emerged that methane-oxidizing bacteria interact with inorganic pollutants in the environment. Here we report what we believe to be the first study of the interaction of pure strains of methane-oxidizing bacteria with selenite. Results indicate that the commonly used laboratory model strains of methane oxidizing bacteria, Methylococcus capsulatus (Bath) and Methylosinus trichosporium OB3b are both able to reduce the toxic selenite (SeO32-) but not selenate (SeO42-) to red spherical nanoparticulate elemental selenium (Se0), which was characterised via EDX and EXAFS. The cultures also produced volatile selenium-containing species, which suggests that both strains may have an additional activity that can either transform Se0 or selenite into volatile methylated forms of selenium. Transmission electron microscopy (TEM) measurements and experiments with the cell fractions: cytoplasm, cell wall and cell membrane show that the nanoparticles are formed mainly on the cell wall. Collectively these results are promising for the use of methane-oxidizing bacteria for bioremediation or suggest possible uses in the production of selenium nanoparticles for biotechnology

Selvitys energiaköyhyydestä

Termillä energiaköyhyys viitataan usein heikossa taloudellisessa asemassa olevien kotitalouksien mahdollisuuksiin selviytyä energiakustannuksista. Energiaköyhyydelle ei ole olemassa yhtä yhtenäistä määritelmää ja myös energiaköyhyyden aiheuttamiin ongelmiin vastataan erilaisin tavoin. Tässä selvityksessä tarkastellaan energiaköyhyyden merkitystä Suomessa. Selvityksessä määritellään energiaköyhyyden käsite ja kartoitetaan kuinka suurta osaa ja minkälaisia kotitalouksia energiaköyhyys voi koskea. Lisäksi selvityksessä arvioidaan miten energiaköyhyyden aiheuttamiin haasteisiin vastataan ja miten niihin olisi tarkoituksenmukaisinta vastata. Arvioinnissa otetaan huomioon muun muassa jo olemassa olevat erilaiset tukijärjestelmät, kuten erilaiset investointituet, asumismenoja alentavat ja toimeentuloa turvaavat tuet sekä energiamarkkinalainsäädäntöön sisältyvä kuluttajansuoja. Selvityksessä kuvataan myös nykytilannetta ja ratkaisukeinoja energiaköyhyyden aiheuttamiin haasteisiin eräissä muissa EU-maissa. Selvityksen mukaan energiaköyhyys koskettaa Suomessa pientä osaa kotitalouksista osana muuta köyhyyttä. Energiaköyhyyden riskiryhmänä korostuvat lähinnä taajama-alueen ulkopuolella isoissa energiatehottomissa asunnoissa asuvat pienituloiset kotitaloudet. Selvitys sisältää toimenpide-ehdotuksia ja suosituksia energiaköyhyysongelman ehkäisemiseksi ja ratkaisemiseksi

Structural Investigation of (U 0.7 Pu 0.3 )O 2-x Mixed Oxides

International audienceUranium-plutonium mixed oxide containing 30 per cent of plutonium is a candidate fuel for several fast neutron and accelerator driven reactor systems. In this work, a detailed structural investigation on sol-gel synthesized stoichiometric U0.7Pu0.3O2.00 and substoichiometric U0.7Pu0.3O2-x, using X-ray diffraction (XRD), oxygen 17 magic angle spinning nuclear magnetic resonance ((17)O MAS NMR) and X-ray absorption spectroscopy is described. As observed by XRD, the stoichiometric U0.7Pu0.3O2.00 is monophasic with a lattice parameter in good agreement with Vegard's law, while the substoichiometric U0.7Pu0.3O2-x material is biphasic. Solid solution ideality in terms of a random distribution of metal atoms is proven for U0.7Pu0.3O2.00 with (17)O MAS NMR. X-ray absorption near-edge structure (XANES) spectroscopy shows the presence of plutonium(III) in U0.7Pu0.3O2-x. Extended X-ray absorption fine-structure (EXAFS) spectroscopy indicates a similar local structure around both cations, and comparison with XRD indicates a close similarity between uranium and plutonium local structures and the long-range ordering

The Geochemical behaviour of Selenium in the Boom Clay system: A XANES and EXAFS study

In Belgium, the Boom Clay formation is studied as a reference host formation for the geological disposal of high-level and long-lived radioactive waste for more than 30 years. This formation mainly consists of mixed clay minerals (illite, interstratified illite-smectite), pyrite and immobile and dissolved natural organic matter. Since it provides good sorption capacities, very low permeability, and chemically reducing conditions due to the presence of pyrite (FeS2), the Boom clay formation itself is considered to be the main barrier preventing radionuclide migration from the geological repository. Within this concept for geological storage Se79 has been identified as one of the critical elements contributing to the final dose to man. Although the sorption and migration behaviour of Se in the Boom Clay system has been thoroughly studied, the speciation of Se in the Boom Clay system has never been identified spectroscopically. In all previous studies, the interpretation of the behaviour of Se in Boom Clay conditions has always been based on circumstantial evidence such as solubility measurements or comparison with the spectroscopically identified speciation of Se in model systems [1-3]. Based on the XANES analysis, selenite is transformed into Se0 confirming the previously proposed reduction of selenite in the Boom Clay system. Combination of the mass-balance for Se with the results from linear combination analysis of the XANES spectra provided new evidence for the sorption-reduction mechanism proposed to explain the interaction between Se(IV) and the BC solid phase [1]. In addition, evidence was found that that the fate of Se(IV) in the BC system is completely dominated by its interaction with pyrite present in the Boom Clay. The combined EXAFS analysis of Se in Se0 reference phases (hexagonal, monoclinic, Se-loaded pyrite) allowed to elucidate further details on the short-range structure of the reaction products formed upon reduction of Se(IV) with pyrite.status: accepte

Extreme multi-valence states in mixed actinide oxides

International audienc

The relationship of monodentate and bidentate coordinated uranium(VI) sulfate in aqueous solution

The coordination of U(VI) sulfate complexes has been investigated by uranium L-III-edge EXAFS and HEXS measurements with the aim to distinguish monodentate and bidentate coordinated sulfate in aqueous solution. UV-vis absorption spectroscopy has been used to differentiate the species and to determine the species distribution as a function of the [SO42-]/[UO22+] ratio. A monodentate coordination prevails in solutions with [SO42-]/[UO22+] ratio of 1, where UO2SO4 is the dominant species. Besides the dominating monodentate sulfate a small amount of bidentate sulfate could be observed, indicating that two isomers may exist for UO2SO4. With increasing [SO42-]/[UO22+] ratio the UP2(SO4)(2)(2-) species becomes the main species. The uranium atom of this species is coordinated by two bidentate Sulfate groups