Assessing the speciation and the biogeochemical processes affecting the mobility of selenium from a geological repository of radioactive wastesto the biosphere

In the scope of the studies carried out on the geological disposal of radioactive wastes, it is essential to assess the migration behaviour of long lived radionuclides as a function of the physicochemical conditions (pH, redox potential, temperature, pressure, ...), the nature of the host rocks and the chemical composition of the underground waters. In this study, we have considered the case of selenium which is an element of importance because of its long lived under its $^{79}$Se isotope. 
A review is first performed on the behaviour of selenium from available studies in natural systems in considering particularly the inorganic Se forms. Later on, these results are transposed to the physicochemical conditions occurring in the vicinity of a geological repository. The most stable forms in this context would be Se(-II), Se(0) and Se(IV). Several parameters can govern the mobility of these Se species such as the pH, the potential of the water and the presence of solid phases containing iron, manganese or aluminium (oxy)hydroxides on which Se(IV) can be sorbed. Selenide and selenite mobility can also be retarded by precipitation reactions. This is particularly true for Se(-II) in presence of iron(II) and sulfides. The hypothetical presence of microorganisms is also considered because of its importance on the fate of the Se species

Production and use of reference materials for environmental analyses: conclusions of a workshop

International audienceReference materials (RMs) play a vital role for the verification of the quality control of environmental analysis. The increasing requirements imposed to environmental control laboratories call for greater co-operation among RM producers and end-users to better define future production strategies. It is recognised that the present system is unlikely to be able to cope with the increasing demand for certified and non-certified RMs within the forthcoming years. These issues were discussed in the framework of a workshop funded by the M&T programme of the European Commission, which brought together RM producers, certification experts and end-users. This report summarises the round-table discussions and expert recommendations

Development of analytical procedures for the determination of hexavalent chromium in corrosion prevention coatings used in the automotive industry

cited By 12International audienceThe European directive 2000/53/EC limits the use of Cr(VI) in vehicle manufacturing. Although a maximum of 2 g of Cr(VI) was authorised per vehicle for corrosion prevention coatings of key components, since July 2007 its use has been prohibited except for some particular applications. Therefore, the objective of this work was to develop direct analytical procedures for Cr(VI) determination in the different steel coatings used for screws. Instead of working directly with screws, the optimisation of the procedures was carried out with metallic plates homogeneously coated to improve the data comparability. Extraction of Cr(VI) from the metallic parts was performed by sonication. Two extraction solutions were tested: a direct water extraction solution used in standard protocols and an ammonium/ammonia buffer solution at pH 8.9. The extracts were further analysed for Cr speciation by high-performance liquid chromatography (HPLC) inductively coupled plasma (ICP) atomic emission spectrometry or HPLC ICP mass spectrometry depending on the concentration level. When possible, the coatings were also directly analysed by solid speciation techniques (X-ray photoelectron spectroscopy, XPS, and X-ray absorption near-edge structure, XANES) for validation of the results. Very good results between the different analytical approaches were obtained for the sample of coating made up of a heated paint containing Zn, Al and Cr when using the extracting buffer solution at pH 8.9. After a repeated four-step extraction procedure on the same portion test, taking into account the depth of the surface layer reached, good agreement with XPS and XANES results was obtained. In contrast, for the coatings composed of an alkaline Zn layer where Cr(VI) and Cr(III) are deposited, only the extraction procedure using water allowed the detection of Cr(VI). To elucidate the Cr(VI) reduction during extraction at pH 8.9, the reactivity of Cr(VI) towards different species of Zn generally present in the coatings (metallic Zn and zinc oxide) was studied. The results showed that metallic Zn rapidly reduces Cr(VI), whereas this reaction is less evident in the presence of zinc oxide. Water was then retained for coatings containing metallic Zn. © 2008 Springer-Verlag