Roberto D. Pérez

Association between As and Cu renal cortex accumulation and physiological and histological alterations after chronic arsenic intake.

Arsenic (As) is one of the most abundant hazards in the environment and it is a human carcinogen. Related to excretory functions, the kidneys in humans, animal models or naturally exposed fauna, are target organs for As accumulation and deleterious effects. Previous studies carried out using X-ray fluorescence spectrometry by synchrotron radiation (SR-microXRF) showed a high concentration of As in the renal cortex of chronically exposed rats, suggesting that this is a suitable model for studies on renal As accumulation. This accumulation was accompanied by a significant increase in copper (Cu) concentration. The present study focused on the localization of these elements in the renal cortex and their correlation with physiological and histological As-related renal effects. Experiments were performed on nine male Wistar rats, divided into three experimental groups. Two groups received 100 microg/ml sodium arsenite in drinking water for 60 and 120 consecutive days, respectively. The control group received water without sodium arsenite (< 50 ppb As). For histological analysis, 5-mum-thick sections of kidneys were stained with hematoxylin and eosin. Biochemical analyses were used to determine concentrations of plasma urea and creatinine. The As and Cu mapping were carried out by SR-microXRF using a collimated white synchrotron spectrum (300 microm x 300 microm) on kidney slices (2 mm thick) showing As and Cu co-distribution in the renal cortex. Then, renal cortical slices (100 microm thick) were scanned with a focused white synchrotron spectrum (30 microm x 30 microm). Peri-glomerular accumulation of As and Cu at 60 and 120 days was found. The effects of 60 days of arsenic consumption were seen in a decreased Bowmans space as well as a decreased plasma blood urea nitrogen (BUN)/creatinine ratio. Major deleterious effects; however, were seen on tubules at 120 days of exposition. This study supports the hypothesis that tubular accumulation of As-Cu may have some bearing on the arsenic-associated nephrotoxicological process.

Immunotoxicological effects of arsenic bioaccumulation on spatial metallomics and cellular enzyme response in the spleen of male Wistar rats after oral intake

Arsenic (As) is a worldwide environmental contaminant, which compromises immunity and causes various associated disorders. To further investigate its immunotoxicity, male Wistar rats were exposed to 100ppm of sodium arsenite (inorganic AsIII) in drinking water for 2 months. Given that metals are significant immune regulators, their content and distribution were analysed in spleen tissues, to then evaluate subsequent changes of redox enzyme responses in spleen parenchyma cells (splenocytes). X-ray fluorescence spectrometry demonstrated As accumulation in both white and red pulps (p<0.005), and As-related pulp-dependent modifications of the content of Cu, Ca, Zn and Fe (p<0.01). Correlational path analysis revealed direct effects of As on their spatial distribution (Cu: -0.76, Ca: -0.61, Zn: 0.38; p<0.02). As-exposed splenocytes showed ɣ-glutamyltranspeptidase inhibition, peroxidase induction, and variable responses of nitric oxide synthase (p<0.05). Concanavalin A-treated splenocytes (T cell mitogen) were more susceptible in vitro to these As-related enzymatic changes than those treated with lipopolysaccharide (B cell mitogen) (p<0.05). The study thus established the impact of As bioaccumulation on metallic spatial homeostasis in the spleen, and then identified enzymatic dysfunctions in splenocytes. This suggested that arsenic disrupts biometal-dependent immune pathways and redox homeostasis, with mitogen exposure modifying the toxicological response.

New spectrometer for grazing exit x-ray fluorescence

Among the x-ray fluorescence techniques using energy dispersive systems, the excitation in the total reflection regime is becoming widespread. This technique may be applied to surface analysis if the fluorescent radiation emitted by the sample is measured as a function of the grazing incidence angle. The main limitation in performing this sort of analysis is the need to use a monochromator, which notably reduces the incident flux of radiation. Besides, the method requires the radiated surface to be perfectly smooth and polished and to have a total length of some centimeters. A similar technique known as grazing exit x-ray fluorescence presents certain advantages and is easier to implement. By this method, fluorescent photons in terms of the grazing exit angle are detected. In this work, a spectrometer for performing surface analysis at grazing exit is described, the different experimental situations are analyzed, and some measurements performed with this device are shown.

Depth Profiling Nano-Analysis of Chemical Environments using Resonant Raman Spectroscopy at Grazing Incidence Conditions

Both X-ray total reflection and X-ray Raman scattering techniques were combined to discriminate chemical environments in depth-profiling studies using an energy dispersive system. This allowed, for the first time, to resolve oxidation state on surface nanolayers with a low-resolution system. Samples of pure Cu and Fe oxidized in tap water and salty water, respectively, were studied in the Brazilian synchrotron facility using monochromatic radiation and an EDS setup. The measurements were carried out in total reflection geometry with incident energy lower and close to the K absorption edge of both elements. The results allowed observing the presence of very thin oxide layers, usually not observable with conventional geometries of irradiation. They also permit the identification of the compound present in a particular depth of the sample with nanometric, or even subnanometric, resolution using a low-resolution system.

Bromate Determination by X-Ray Fluorescence (XRF) to Identify Pre-Baking Potassium Bromate Addition in Bread

Wavelength-dispersive x-ray fluorescence (WDXRF) was applied to determine bromate (Br) as an indication of pre-baking bromate addition in bread. The proposed methodology needed a minimum sample preparation procedure because it was carried out directly on solid samples. The calibration of Br in bread obtained showed low detection limit and high sensitivity to distinguish precisely Br concentrations greater than natural Br. The excellent performance of the present methodology would be useful to identify pre-baking bromation in bread, which can be used to help set up a programme to control bromation in bread. Application of this methodology to bakery control caused an important reduction of bromate use in province of Córdoba, Argentina.

Mathematical model for evaluation of surface analysis data by total reflection XRF

The general problem of an electromagnetic wave moving through a stratified medium appears naturally in all the techniques associated with surface analysis by total reflection. It is a consequence of the theoretical models that describe that describe the physical processes involved in these techniques. This problem has been extensively studied owing to its importance in optics. The mentioned techniques are known as grazing incidence x-ray fluorescence (GIXRF) and grazing exit x-ray fluorescence (GEXRF). In this work, the electric field in a stratified medium was calculated using basic mathematical tools. The model uses a matrix approach to take advantage of well-known mathematical results (such as Hessenbergs matrix properties). In this way, the model optimizes and facilitates the data analysis in GIXRF measurements and GEXRF experiments. The simplicity of the formalism admits approximations of the electric field, which allow a better understanding of the experimental data in both techniques. The model was used to analyze experimental data on silicon wafers with surface layers of different elements, showing excellent results.

Surface analysis by total-reflection X-ray fluorescence

Abstract This work shows the feasibility of surface analysis though the detection of characteristic fluorescent radiation in the total-reflection regime. A theoretical formalism to correlate surface parameters with X-ray fluorescence intensities from multiple-layer samples was developed. Experimental measurements were performed in the Microanalysis Station of the Frascati National Laboratory, Italy. The samples were Si wafers with surface layers of different thicknesses of Cr. The angular dependence of the Kα fluorescent intensity emitted by Cr was recorded with a Si(Li) detector, and the obtained data were fitted to the correspondent theoretical expression. Our results agreed very well with the values measured during sample fabrication. Diffusion processes of the surface layer into the substrates were also considered. They were analysed assuming a middle layer between the surface layer and the substrate.

XRF analysis of arsenic uptaking in mice organs and tissues

Abstract In this work, an investigation on the levels of uptaken arsenic in different organs and tissues of mice was carried out. Mice were given water, doped with 100 μg/ml of As2O3, during a period of a week. The Energy Dispersive X-Ray Fluorescence (EDXRF) technique was used for the measurements; the external standard (calibration curve) and the internal standard (addition) methods were used to obtain concentrations. These methods were used in order to minimize matrix effects (which in many cases are complex and prone to errors) and to allow an easy calculation of As concentrations. The average concentrations obtained here were: 3.9 μg/g for liver, 13 μg/g for pre-stomach, 21 μg/g for esophagus, 2.9 μg/ml for blood, and 42 μg/ml for urine.

L-subshell Coster-Kronig yields measured with synchrotron radiation

Abstract The synchrotron photoionization method was applied to measure L -subshell Coster-Kronig yields. This method is based on the capability of tuning the energy of the synchrotron photons producing a selective subshell ionization. Two foil samples of Yb and Ta were irradiated and their characteristic spectra were recorded. Data were analyzed using a new formalism (based on a matrix representation) for expressing X-ray fluorescence intensities involving Coster-Kronig transitions. The results obtained in this work are f 12 = 0.249 ± 0.021, f 13 = 0.408 ± 0.055 and f 23 = 0.186 ± 0.040 for Yb, and f 12 = 0.168 ± 0.039, f 13 = 0.322 ± 0.072 and f 23 = 0161 ± 0.053 for Ta. These data are very reliable and represent a valuable information for spectroscopists, considering the lack of data for L -shell parameters.

Calibration Method for Confocal X-Ray Microanalysis with Polychromatic Excitation

To apply the fundamental parameters method at the confocal setup the knowledge of the sensitivity of the spectrometer is required which depends on the characteristics of two X-ray lenses: one in the excitation channel and another in the detection channel. For the particular case of polychromatic excitation, the theory shows that the focalization properties of the excitation lens for all incident energies affect the X-ray fluorescence intensity. Therefore the traditional calibration method based on the measurement of standard samples becomes unstable since the number of required fitting parameters is too high. To reduce these parameters a previous characterization of the excitation lens by a simulation program was employed giving rise to a simplified confocal setup calibration. The developed calibration method was applied for a confocal spectrometer implemented in the Brazilian Synchrotron Radiation Source (LNLS) with white beam. The experimental parameters of the sensitivity were obtained from depth profile analysis of several pure thin films. The calibrated confocal setup was used to quantify reference standards in order to validate the calibration procedure. Our results for elemental concentrations show relative errors less than 15% for the quantitative analysis of a light matrix reference standard.