[en] In biological sample microanalysis, a mass-normalisation method is commonly used as a quantitative index of elemental concentrations determined by particle-induced X-ray emission (PIXE). The organic mass can either be determined using particle backscattering spectrometry (BS) or scanning transmission ion microscopy (STIM). However, the accuracy of quantitative microanalysis in samples such as cultured cells is affected by beam-induced loss of organic mass during analysis. The aim of this paper is to compare mass measurements determined by particle BS or by STIM. In order to calibrate STIM and BS analyses, we measured by both techniques the thickness of standard foils of polycarbonate (3 and 6 μm), Mylar[reg] (4 μm), Kapton[reg] (7.5 μm) and Nylon[reg] (15 μm), as well as biological samples of mono-layered cultured cells. Non-damaging STIM analysis of samples before PIXE irradiation is certainly one of the most accurate ways to determine the sample mass, however, this requires strong experimental handling. On the other hand, BS performed simultaneously to PIXE is the simplest method to determine the local mass in polymer foils, but appears less accurate in the case of cultured cells

[en] Scanning transmission ion microscopy (STIM) imaging of living cultured cells has been carried out using a proton external-beam with the nuclear microprobe of Bordeaux-Gradignan. STIM could be performed in air atmosphere after passage of a focused proton beam through a 150 nm thick silicon nitride window. Energy loss STIM images were obtained with a spatial resolution in the micrometer range and enabled the identification of sub-cellular ultrastructures

[en] N-myc oncogene amplification is one of the most established prognostic factors in neuroblastoma (NB), a young children solid tumor. Amounts of ferritin, an iron storage protein, are abnormally increased in serum of patients with advanced stage disease. N-myc amplified NB cells can synthesize zinc metalloenzymes allowing tumor invasion and metastases formation. The aim of this study was to find a relationship between N-myc amplification and trace metals in human neuroblasts. Coupling PIXE and RBS techniques, nuclear microprobe allowed to analyze elemental distributions and to determine trace metal concentrations within cultured neuroblasts characterized by various degrees of N-myc amplification. They were compared to trace metal distributions and concentrations in tumor xenograft models of human NB, after injection of cells from the same lines in athymic nude mice. Our data allowed to establish a relation between trace metal contents and mechanisms of NB oncogenesis, amplified cell lines representing more aggressive phenotypes of the disease. They should be confirmed by analysis of cultured neuroblasts and tumors issued from a non-amplified cell line transfected with the N-myc oncogene

[en] Transferrin (Tf), the iron binding protein of vertebrates serum, is known to be synthesized by oligodendrocytes (Ols) in the central nervous system. It has been postulated that Tf is involved in Ols maturation and myelinogenesis. This link is particularly important in the understanding of a severe human pathology: the multiple sclerosis, which remains without efficient treatment. We generated transgenic mice containing the complete human Tf gene and extensive regulatory sequences from the 5^' and 3^' untranslated regions that specifically overexpress Tf in Ols. Brain cytoarchitecture of the transgenic mice appears to be normal in all brain regions examined, total myelin content is increased by 30% and motor coordination is significantly improved when compared with non-transgenic littermates. Tf role in the central nervous system may be related to its affinity for metallic cations. Normal and transgenic mice were used for determination of trace metals (iron, copper and zinc) and minerals (potassium and calcium) concentration in cerebellum and corpus callosum. The freeze-dried samples were prepared to allow proton-induced X-ray emission and Rutherford backscattering spectrometry analyses with the nuclear microprobe in Bordeaux. Preliminary results were obtained and carbon distribution was revealed as a very good analysis to distinguish precisely the white matter region. A comparison of metallic and mineral elements contents in brain between normal and transgenic mice shows that iron, copper and zinc levels remained constant. This result provides evidence that effects of Tf overexpression in the brain do not solely relate to iron transport

[en] Chemical studies have shown that doxorubicin, a well-established anticancer agent, is a powerful iron chelator and the resultant iron-drug complex is an efficient catalyst of the conversion of hydrogen peroxide to the highly reactive hydroxyl radical. However, the intracellular complexation of doxorubicin with iron is still debated. Using nuclear microprobe analysis (NMPA), we previously observed in human ovarian cancer cells exposed to 20 μM iodo-doxorubicin (IDX) that iodine and iron cellular distributions were spatially correlated, suggesting a mechanism of intracellular iron chelation by the anthracycline compound. Because maximal plasma drug concentrations in patients are expected to be around 5 μM, NMPA and X-ray absorption near edge spectroscopy (XANES) experiments for iron speciation analysis were performed on cultured cells exposed to pharmacological doses of 2 μM IDX or doxorubicin

[en] Preconception exposure to certain chemicals may increase risk of tumors in offspring, especially with regard to occupational metals such as chromium. However, the mechanism of chromium trans-generation carcinogenicity remains unknown. Using scanning proton X-ray microanalysis we have been able to detect chromium in testicular tissue sections from mice treated by intraperitoneal injection of 1 mmol/kg CrCl₃. Chromium concentration was about 5 μg/g dry mass in average, but higher concentrations were found within the limiting membrane of the testes, the tunica albuginea. In addition, synchrotron radiation X-ray fluorescence measurements, with microscopic resolution, clearly demonstrated the presence of chromium in the tunica albuginea but also within isolated cells from the interstitial connective tissue

[en] The retina as well as other tissues needs iron to survive, but modifications in iron metabolism have also been suggested to contribute to cerebral neurodegenerative diseases. Our study was intended to investigate iron distribution in the retina of normal rats and Royal College of Surgeons (RCS) rats affected by hereditary degeneration of the photoreceptors at different developmental stages (35, 45 and 55 days after birth). Iron (Fe) distribution was determined by proton induced X-ray emission (PIXE) microanalysis on retinal sections and compared to other tissues (cornea, liver, spleen) and to other elements (Cu, Zn, Ca). Elemental concentrations were determined in different retinal layers especially the photoreceptors, which are progressively altered and disappear in the RCS rats. Iron is unevenly distributed throughout the rat retina. The highest concentration is observed in the choroid and the retinal pigmented epithelium and in the inner segments of photoreceptors. Iron content is lower in the outer segments but still significant. It increases during both the development and the disease at the level of the segments. This last localised iron increase can result in an overproduction of free radicals and be correlated with the photoreceptor cell loss. The distributions of other elements (Cu, Zn, Ca) revealed interesting temporal progressions

[en] Pyrometallurgy of uranium and plutonium in chloride and fluoride molten salts is now intensively studied while little attention is given to the long-lived fission product technetium, which is one of the most hazardous nuclear wastes. Regarding the study of the speciation of technetium-99 in the course of pyrochemical reprocessing of spent nuclear fuel, now considered the most probable alternative approach to reprocessing of spent MOX and high burn-up nuclear fuel, EXAFS measurements were performed at the Rossendorf Beamline (ROBL) on the samples simulating radioactive wastes generated by pyrochemical reprocessing, prepared at UMR5084. During pyrometallurgical spent fuel reprocessing, technetium can remain in the fused salt or enter (depending on the applied temperatures, reagents and oxidative or reducing potentials) either the sedimented phase, contaminating Pu-enriched phase or the electrodeposited U phase. The Tc phase could not be detected by means of X-ray diffraction either in the sediment or in the deposit. The Tc phase is finely dispersed and X-ray amorphous. There are some data showing that technetium in such matrix forms not only a hexagonal but also a metastable cubic lattice with higher chemical reactivity. Therefore, it is very important to develop methods of analyses like EXAFS that allow to determine the Tc speciation in such samples. Our results show that under conditions when chlorine or oxygen could be formed or injected into the melt, Tc can also form several oxides, oxychlorides and chlorides of different but rather high volatility, turning on an important polluting risk linked to gas-off. The available EXAF spectra of technetium species are fragmentary and do not present the whole of the species possible under pyrometallurgy conditions. Some recent studies gave indications on the presence of unknown Tc chloride complexes. It was of high importance to carry out synthetic work to supply a large set of technetium compounds in the closed containers which met the security and quality demands, radioactivity level, special requirements on sample size, thickness and sample homogeneity for EXAFS measurements. Based on this set of reference samples, which include technetium metal, different technetium halogenides, oxo-halogenides, oxides and pyro-metallurgically-formed sediments, Tc chemical forms responsible for Tc accumulation in fused salts, deposits or gas-off depending on if the applied reprocessing conditions are studied by means of XANES and EXAFS. The EXAFS data obtained for technetium hexa-halides are in good agreement with literature. For lower oxidation states of technetium including oxides, chlorides and metal state, further EXAFS study both of reference compounds and of simulated radioactive wastes is necessary. (authors)

[en] The sorption of technetium by powdered and polished mineral stibnite Sb₂S₃ has been investigated in simulated and natural underground waters from the Meuse/Haute-Marne region (France). The sorption by powdered stibnite has been found to be complete under both aerobic and anaerobic conditions in batch experiments. The sorption rate is higher in the absence of oxygen than under aerobic condition. Increasing the temperature from 30 C to 60 C results in a rise of the sorption rate by 9.1 and 27 times under anaerobic and aerobic conditions, respectively. The observed differences in sorption kinetics in the presence and in absence of oxygen are explained by the interaction of oxygen with sulfide ion in aerobic conditions and by the reduction of technetium(VII) by iron(II) and by other impurities present in natural water and in the mineral, and by the subsequent sorption of Tc(IV) on stibnite under anaerobic conditions. The sorption on a polished mineral surface resulted in the formation of a technetium film, probably Tc₂S₇, with a thickness of 1-3 μg Tc/cm² pH 3-6 and 4-12 μg Tc/cm² at 9-12. The simultaneous formation of stibnite colloids with adsorbed technetium occurs at pH 9-12. The study of the technetium film on the mineral by proton induced X-ray emission analysis showed it to be at least one order of magnitude thinner on the SiO₂ impurities than on the main Sb₂S₃ component and the iron impurities. (orig.)

[en] Full text of publication follows: Technetium is one of the most mobile long-lived radioactive element accumulated as fission product in spent fuel of nuclear power plants. In spite of its low radioactivity (less than 0,001 % of total radioactivity of spent nuclear fuel) now, technetium-99 will contribute for the main part of β- activity in total radioactivity of modern wastes of nuclear fuel cycle in 500 years, when cesium- 137, strontium-90 and others short-lived radionuclides will be disintegrated. The research on the behavior of technetium in natural waters is basic for the elaboration of methods for sorption and immobilization of this radioelement by some engineer barriers, which have to be constructed between radioactive waste storage and environment. Principal technetium species in water in oxic conditions is pertechnetate ion Tc^VIIO₄^-, which is weakly sorbed by majority of minerals and rocks. The sulfide-containing minerals stibnite Sb₂S₃ and pyrrhotite FeS are known to be fairly good sorbents for Tc(VII) from natural waters; pyrite FeS₂ is weakly sorbent. Technetium (VII) adsorption on stibnite at different temperatures has not yet been studied. We have shown at 90 deg. C a 98-99% sorption of Tc(VII) on stibnite powder during only 4 hours agitation; only 5% sorption on pyrite in the same aerobic conditions. The interactions of Tc(VII) (1,2.10^-4)M with mineral stibnite Sb₂S₃ have been investigated in aqueous solutions at pH 3-12 at room temperature in aerobic conditions. A decrease of Tc concentration in the solution, the formation of a technetium film (probably Tc₂S₇) on the stibnite surface and the presence of colloidal technetium particles in the solution have been observed during contact with stibnite. We have shown that sorption of Tc(VII) on stibnite is effective at pH 3-7 but at pH >8, Tc₂S₇ adhesion on the mineral is reduced and an important part of Tc sulfur is present in a colloidal brown solution. On stibnite polished surface samples, we observed some SiO₂ impurities areas (from ten to hundred μm diameter) on which technetium adsorption would be very different. First experiments with the nuclear microprobe set-up in Bordeaux have confirmed that technetium film is more dense on stibnite areas than on SiO₂ or other impurities. This technique can be informative for this type of research. (authors)