Mise au point de techniques analytiques pour la spéciation du sélénium dans les boues de stations d'épuration d'eaux résiduaires urbaines

Les stations d'épuration d'eaux résiduaires sont une des étapes du cycle du sélénium dans l'environnement et contribuent à sa redistribution dans le milieu naturel. Très peu étudié jusqu'à présent dans ces milieux, le sélénium n'en est pas moins un élément très important du point de vue écotoxicologique, sa teneur dans les boues de stations d'épuration destinées à l'épandage agricole faisant par ailleurs l'objet d'une norme.Nous avons mis au point des techniques permettant la détermination spécifique de l'élément total dans ce type d'échantillon, par minéralisation classique ou assistée par micro-ondes et dosage par Voltamétrie de Redissolution Cathodique Différentielle Pulsée (DPCSV) et Spectrométrie d'Absorption Atomique ElectroThermique (ETAAS). Le contrôle qualité a été effectué sur deux échantillons certifiés fournis par le Bureau Communautaire de Référence (BCR) : la boue CRM 145 R et la boue CRM 007.Cependant, lorsqu'on parle de risque toxicologique, il est important de s'intéresser à la détermination des différentes formes sous lesquelles cet élément peut être présent. Nous avons pour cela réalisé des extractions parallèles (spéciation de phases) du sélénium contenu dans les boues afin de déterminer quel pourcentage du sélénium total est réellement et potentiellement disponible pour les végétaux lors d'un épandage sur sol agricole. La spéciation d'espèces a été brièvement abordée dans le but de déterminer les teneurs en Se(IV) et Se(VI), espèces les plus toxiques.The great effort undertaken for about twenty years to improve the quality of surface waters has led to the construction of numerous waste water treatment plants, generating an increasing amount of sludge. Waste water and sludge treatment processes represent an important point in the hydrological cycle at which the disposal of substantial quantities of trace elements to the environment may be regulated. From the law on waste recovery and disposal in 1975 to the European guideline about wastes in 1991, the priority has been given to waste recovery and recycling. With increasing pressure to ban all sludge dumping at sea, and considering the prohibitive costs of land-filling and incineration, there is a great tendency to dispose of sludge on land (40% in 1988 to 60% in 1992).Although numerous studies have demonstrated the intrinsic value of sludge for soil amendment, given its nitrogen, phosphorus and homogeneous organic matter content, evidence has accumulated in recent years that numerous environmental problems can arise because of the presence in sludges of high amounts of certain trace elements (potentially toxic to plants and to human beings and liable to be concentrated along the food chain), among which selenium is particularly interesting.Selenium presents a complex case, as it is also an essential element for living organisms (including humans). The amendment with sewage sludge is sometimes used to increase the selenium content in crops, and afterwards in cattle, when there is a proven lack of this element in a given place. Nevertheless the boundary between essentiality and toxicity is relatively narrow and is expressed at trace levels. It is thus particularly important to survey the selenium concentrations encountered in sewage sludge, especially as guidelines and regulations concerning these data will probably be strengthened. Presently, in France, sludge must not contain more than 200 mg Se·kg-1 dry weight and must not be used on soils containing more than 10 mg Se·kg-1 dry weight (AFNOR U 44-041 norm). This norm concerns only the total amount of selenium contained in sludge and does not take into account the different species (organic and inorganic Se(-II), Se(0), Se(IV) and Se(VI)) that could be present.First of all we had to develop methods for the classical and microwave-assisted wet digestion of sewage sludge, and the determination of their total selenium concentration by Differential Pulse Cathodic Stripping Voltammetry (DPCSV) and ElectroThermal Atomic Absorption Spectrometry (ETAAS). Quality assurance involved the analysis of two BCR (Community Bureau of Reference) certified sewage sludge reference materials (CRM 145 R and CRM 007) and the different techniques were then applied to natural samples from a representative French sewage treatment plant located in the city of Tarbes (South-West of France). The mixture HNO3-H2O2-H2O led to the best results for the digestion and analysis of certified samples, caused few problems for the analysis by DPCSV and ETAAS, and was therefore retained. The decrease of the digestion duration obtained by the use of microwaves was particularly interesting (from one to three days on a hot plate to less than one hour by the Microdigest 301 (PROLABO, France)), and reproducibility was also acceptable (between 3 and 10%). Concentrations obtained for the sewage sludge from the Tarbes treatment plant were very much lower than those for NF U 44-041: 1.08±0.11 mg Se·kg-1 dry weight.However knowledge of speciation, that is to say the determination of the different physicochemical forms of selenium present in a given medium, is necessary when speaking of the toxicological risk represented by an element. The mobility of selenium and its toxicity to the biosphere are related to its association with various sludge or soil constituents as well as to its total concentration. "Soft" or partial extraction techniques are necessary when the aim of the study to determine trace element speciation. The extractants used must separate selenium from the matrix without inducing any loss or change in the partitioning of individual chemical species. In parallel extractions the mechanisms involved for each extractant must correspond to processes occurring in nature and are then associated with special fractions of selenium: soluble, exchangeable, "oxidizable", and "mineral" fractions .Parallel extractions with three types of extractants were chosen for this study and applied first to CRM 007: warm water (soluble fraction), ammonium phosphate-citric acid (soluble + exchangeable fraction) and sodium hydroxide (soluble + exchangeable + "oxidizable" fraction). The soluble, exchangeable, "oxidizable" and "mineral" fractions represent respectively : 11%, 14%, 39% and 36%. The same procedure was then applied to natural samples from Tarbes giving the following results: 36% soluble, 22% exchangeable, 42% "oxidizable". The sodium hydroxide extraction procedure allowed us to extract the entire Se content of this sludge (1.07±0.03 mg Se·kg-1 dry weight), showing that all the selenium present is potentially available after agricultural land application. It was then possible in this fraction to deal with the species speciation of selenium by the mean of a separation of inorganic and organic species on an Amberlite CG-400 resin and a specific analysis by DPCSV. Se(IV) and Se(VI) represent respectively between 30 and 40% and between 2 and 20% of total selenium in the sludges from Tarbes

Insulin therapy during pregnancy in women with type 1 diabetes

Течение и исходы беременности при СД1 зависят от компенсации СД. Наиболее эффективным методом достижения целевой гликемии при беременности является интенсивная, в том числе помповая, инсулинотерапия с использованием аналога инсулина ультракороткого действия ? новорапида. Применение инсулина ультракороткого действия позволяет также значительно снизить частоту гипогликемических состояний

Radiation Tolerance of Single-Sided Microstrip Detector with Si3N4Si_{3}N_{4} Insulator

The ALICE Collaboration is investigating the radiation tolerance and operation of silicon microstrip detectors for the inner tracking system. Detectors with and without an additional layer of Si3N4 insulator were made in one set, using the same thickness of SiO2 insulator. Measurements were made on both types of detectors after irradiation with 20 MeV electrons, using doses up to 2Mrad. The additional Si3N4 layer allows a coupling capacitor breakdown voltage larger than 100 V and capacitor yield larger than 99 percent. However, the leakage current for detectors with double layer insulator is about 20 nA per strip while the leakage current for the single layer SiO2 insulated detectors is only 0.5 nA. The 20 nA leakage current leads to 450 electrons noise when the ALICE 128C electronics with a peaking time of 1.4 microseconds is used. At a 1 nA leakage current the noise is 100 electrons. The ENC for an input capacitance of 5 pF is 300 electrons. Since all detectors show an increased leakage current after irradiation, the difference between the single and duoble layer insulation detectors becomes negligible when doses of the order of several hundreds of krad are applied

Isomeric pair 95m,gNb{^{95\rm m,g}\rm{Nb}} in photonuclear reactions on nat^{\rm nat}Mo at end-point bremsstrahlung energy of 35-95 MeV

The ${^{\rm nat}\rm{Mo}}(\gamma,x\rm np)^{95\rm m,g}$Nb photonuclear reaction was studied using the electron beam from the NSC KIPT linear accelerator LUE-40. Experiment was performed using the activation and off-line $\gamma$-ray spectrometric technique. The experimental isomeric yield ratio $d(E_{\rm{\gamma max}}) = Y_{\rm m}(E_{\rm{\gamma max}}) / Y_{\rm g}(E_{\rm{\gamma max}})$ was determined for the reaction products $^{95\rm m,g}\rm{Nb}$ at the end-point bremsstrahlung energy $E_{\rm{\gamma max}}$ range of 35-95 MeV. The obtained values of $d(E_{\rm{\gamma max}})$ are in satisfactory agreement with the results of other authors and extend the range of previously known data. The theoretical values of the yields $Y_{\rm m,g}(E_{\rm{\gamma max}})$ and the isomeric yield ratio $d(E_{\rm{\gamma max}})$ for the isomeric pair $^{95\rm m,g}\rm{Nb}$ from the ${^{\rm nat}\rm{Mo}}(\gamma,x\rm np)$ reaction were calculated using the partial cross-sections $\sigma(E)$ from the TALYS1.95 code for six different level density models $LD$. The comparison showed a noticeable excess (more than 3.85 times) of the experimental isomeric yield ratio over all theoretical estimates. At the investigated range of $E_{\rm{\gamma max}}$ the theoretical dependence of $d(E_{\rm{\gamma max}})$ on energy was confirmed - the isomeric yield ratio smoothly decreases with increasing energy.Comment: 9 pages, 9 figures, 1 tabl

Interstrip resistance of a semiconductor microstrip detector

In this work the interelement (interstrip) resistance of the microstrip detector is studied. A few detectors with a different construction are investigated. The dependence of the interstrip resistance on the dose of detector irradiation with electrons is obtained. The possibility of application interstrip resistance measurement for the determination of the good strip yield is shown

Combination of electron energy-loss spectroscopy and energy dispersive x-ray spectroscopy to determine indium concentration in InGaN thin film structures

We demonstrate a method to determine the indium concentration, x, of In x Ga1-x N thin films by combining plasmon excitation studies in electron energy-loss spectroscopy (EELS) with a novel way of quantification of the intensity of x-ray lines in energy-dispersive x-ray spectroscopy (EDXS). The plasmon peak in EELS of InGaN is relatively broad. We fitted a Lorentz function to the main plasmon peak to suppress noise and the influence from the neighboring Ga 3d transition in the spectrum, which improves the precision in the evaluation of the plasmon peak position. As the indium concentration of InGaN is difficult to control during high temperature growth due to partial In desorption, the nominal indium concentrations provided by the growers were not considered reliable. The indium concentration obtained from EDXS quantification using Oxford Instrument ISIS 300 x-ray standard quantification software often did not agree with the nominal indium concentration, and quantification using K and L lines was inconsistent. We therefore developed a self-consistent iterative procedure to determine the In content from thickness-dependent k-factors, as described in recent work submitted to Journal of Microscopy. When the plasmon peak position is plotted versus the indium concentration from EDXS we obtain a linear relationship over the whole compositional range, and the standard error from linear least-squares fitting shows that the indium concentration can be determined from the plasmon peak position to within Δx = ± 0.037 standard deviation

Photonuclear reactions cross-sections at energies up to 100 MeV for different experimental setups

In experiments on the electron linac LUE-40 of RDC "Accelerator" NSC KIPT, the flux-averaged cross-sections $\langle{\sigma(E_{\rm{\gamma max}})}\rangle_{\rm{exp}}$ of photonuclear reactions ${^{100}\rm{Mo}}(\gamma,n)^{99}\rm{Mo}$, ${^{27}\rm{Al}}(\gamma,x)^{24}\rm{Na}$, ${^{93}\rm{Nb}}(\gamma,n)^{92m}\rm{Nb}$, ${^{93}\rm{Nb}}(\gamma,3n)^{90}\rm{Nb}$, and ${^{181}\rm{Ta}}(\gamma,n)^{180g}\rm{Ta}$ were measured using the $\gamma$-activation technique. The theoretical flux-average cross-sections $\langle{\sigma(E_{\rm{\gamma max}})}\rangle_{\rm{th}}$ were computed using the partial cross-section $\sigma(E)$ values from the TALYS1.9-1.95 codes and bremsstrahlung $\gamma$-flux calculated using GEANT4.9.2. Two different experimental setups were used in the experiments: an aluminum electron absorber and a deflecting magnet to clean the bremsstrahlung $\gamma$-flux from electrons. A comparison of the flux-average cross-sections measured for two experimental setups was performed. The possibility of using the reactions ${^{100}\rm{Mo}}(\gamma,n)^{99}\rm{Mo}$, ${^{27}\rm{Al}}(\gamma,x)^{24}\rm{Na}$, ${^{93}\rm{Nb}}(\gamma,n)^{92m}\rm{Nb}$, ${^{93}\rm{Nb}}(\gamma,3n)^{90}\rm{Nb}$, and ${^{181}\rm{Ta}}(\gamma,n)^{180g}\rm{Ta}$ as monitors of the bremsstrahlung $\gamma$-flux for the energy range 30-100 MeV was investigated.Comment: 8 pages, 6 figures, 1 tabl

Production of 180m{^{180\rm{m}}}Hf in photoproton reaction 181{^{181}}Ta(γ,p)(\gamma,p) at energy EγmaxE_{\rm{\gamma max}} = 35-95 MeV

The production of the $^{180\rm{m}}\rm{Hf}$ nuclei in the photoproton reaction ${^{181}\rm{Ta}}(\gamma,p)$ was studied at end-point bremsstrahlung energies $E_{\rm{\gamma max}}$ = 35-95 MeV. The experiment was performed at the electron linear accelerator LUE-40 NSC KIPT with the use of the $\gamma$ activation and off-line $\gamma$-ray spectroscopy. The experimental values of the bremsstrahlung flux-averaged cross-sections $\langle{\sigma(E_{\rm{\gamma max}})}\rangle_{\rm{m}}$ for the ${^{181}\rm{Ta}}(\gamma,p)^{180\rm{m}}\rm{Hf}$ reaction were determined, and at $E_{\rm{\gamma max}} > 55$ MeV obtained for the first time. The measured values, also as the literature data, are significantly exceed the theoretical flux-averaged cross-sections $\langle{\sigma(E_{\rm{\gamma max}})}\rangle_{\rm{th}}$. The $\langle{\sigma(E_{\rm{\gamma max}})}\rangle_{\rm{th}}$ values were calculated using the cross-section $\sigma(E)$ computed with the TALYS1.95 code for six different level density models. A comparative analysis of the calculated total cross-sections for the reactions ${^{181}\rm{Ta}}(\gamma,p)^{180}\rm{Hf}$ and ${^{181}\rm{Ta}}(\gamma,n)^{180}\rm{Ta}$ was performed. It was shown that the photoproton $(\gamma,p)$ to photoneutron $(\gamma,n)$ strength ratio is consistent with the estimates based on the isospin selection rules and the value from the $(e,e'p)$ experiment.Comment: 9 pages, 4 figures, 2 table

Structure and chemical bonds in reactively sputtered black Ti–C–N–O thin films

The evolution of the nanoscale structure and the chemical bonds formed in Ti–C–N–O films grown by reactive sputtering were studied as a function of the composition of the reactive atmosphere by increasing the partial pressure of an O2+N2 gas mixture from 0 up to 0.4 Pa, while that of acetylene (carbon source) was constant. The amorphisation of the films observed by transmission electron microscopy was confirmed by micro- Raman spectroscopy, but it was not the only effect associated to the increase of the O2+N2 partial pressure. The chemical environment of titanium and carbon, analysed by X-ray photoemission spectroscopy, also changes due to the higher affinity of Ti towards oxygen and nitrogen than to carbon. This gives rise to the appearance of amorphous carbon coexisting with poorly crystallized titanium oxynitride. The evolution of the films colour is explained on the basis of these structural changes.Fundação para a Ciência e a Tecnologia (FCT) - PTDC/CTM/69362/2006, SFRH/BPD/27114/2006CRUP (Acção Integrada Luso-francesa N° F-2307) and the GRICES/CNRS collaboration (Proc. 4.1.1 França