X-ray fluorescence with synchrotron radiation to elemental analysis of lead and calcium content of primary teeth

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Abstract

Primary teeth were analyzed by micro-SRXRF. The aim of this study was to determine the elemental distribution of lead and calcium in different regions of primary incisor of children living in a notoriously contaminated area (Santo Amaro da Purificação, Bahia State, Brazil). The measurements were performed in standard geometry of 45° incidence, exciting with a white beam and using a conventional system collimation (orthogonal slits) in the XRF beamline at the Synchrotron Light National Laboratory (Campinas, Brazil).

Introduction

Pollution of the environment by lead affects human health. Particularly young children are at risk because lead adversely affects neuropsychological development (Bellinger et al., 1987; Needleman et al., 1974, Needleman et al., 1979). Whole blood lead test is the most common biomarker of lead exposure and is used in most epidemiological studies, but the amount of lead decreases in blood 40 days after the exposure to lead (Rabinowitz et al., 1974) and therefore, cannot be considered as a reliable biomarker for past exposures (Needleman et al., 1979).

Some studies have shown that superficial enamel lead concentration is related to the individual's environmental exposure to lead (de Almeida et al., 2007, de Almeida et al., 2008; Gomes et al., 2004), and enamel has been proposed as a biomarker of lead exposure. However, there are many important differences between enamel and dentine, and there is scarce information on the distribution of lead in enamel. When this information is available, enamel may become an important biomarker of exposure to lead, with the important advantage of its accessibility (it is exposed in the mouth).

The intention of this work is to perform in vitro L-shell XRF measurements of Pb in deciduous teeth using X-ray synchrotron radiation as excitation source. X-ray fluorescence was performed utilizing a synchrotron source due to the superior brightness, tunability of X-rays, increased signal-to-noise ratio, and smaller spot sizes achievable compared to conventional XRF analysis. So, the outstanding features of synchrotron radiation were exploited to investigate the Pb and Ca distribution in enamel on a microscopic scale.

The application of different analytical techniques to the determination of the microdistribution of trace elements in biomedical samples at low concentrations has previously been performed with proton induced X-ray emission (PIXE), conventional energy dispersive X-ray fluorescence (EDXRF) and laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) (Bellis et al., 2008; Lobinski et al., 2006; Magalhães et al., 2006). However, many of these approaches suffered from a number of limitations and drawbacks especially in terms of spatial resolution and requirements for sample preparation. Recent developments in synchrotron radiation source provide the impetus for XRF studies, with detection limits and spatial resolution being improved (Lombi and Susini, 2009).

The advent of dedicated synchrotron facilities allows the exploitation of the particular qualities of synchrotron radiation as a research tool. An inherent advantage of this method is its multielement detection capability, which enables the detection of different elements simultaneously. A further advantage of this method is that it is non-destructive, allowing staining and histopathological examination of the measured samples after the elemental analyses. The improvement of the lateral resolution of brilliant X-ray microbeams induced numerous applications of micro-XRF in biomedical and environmental studies (Anjos et al., 2004; Farquharson et al., 2008; Hu et al., 1995; Martin et al., 2004; Ide-Ektessabi et al., 2004). Special attention is paid to the remarkable opportunities provided by using synchrotron radiation in elemental analysis. An extended review about micro-XRF can be found at Szalóki et al. (2006).

Therefore, this study aimed at determining the spatial distribution of lead and calcium in the enamel and dentine of primary teeth donated by children living in an area notoriously contaminated with lead. Emphasis was placed on the very superficial enamel and dentin, since such comparison is essential to understand how valuable the information on enamel's lead concentration is in comparison to the information on lead concentrations found in dentine.

Section snippets

Experimental set-up

The determination of the elemental composition was performed using SRmicrobeams at the X-ray Fluorescence beamline (XRF) at Synchrotron Light National Laboratory (LNLS), in Campinas, Brazil. The measurements were performed in standard geometry, the fluorescence spectrum was recorded with a SiLi detector in air atmosphere. The white beam of a bending magnet source is focused by a fine conical capillary capable to achieve 20 μm spatial resolution. An optical microscope is used in order to select

Results and discussion

The sample was positioned in the image plane within an accuracy of 0.5 μm with a 3 axis (x, y, z) remote-controlled stage. The sampling time for each data point is 12 s which allowed samples to be scanned at acceptable time (approximately 6 h). Automatic 2D scans were performed and element distribution maps were obtained with a matrix size of 41×40 pixels resulting in an area of 2.05×2.0 mm. Selected areas of the crown of each sample were analyzed by bidimensional (x, y) scanning. The scan pattern

Conclusions

From this preliminary work we can conclude that XRF analysis using SR microbeams is capable of identifying changes in element distribution in single teeth slices which leads to developing of a new monitoring method. Lead contamination of enamel and dentine of primary incisor of children was investigated by SRXRF microprobe. In summary, significant high Pb level was observed in the surface enamel. Moreover, Pb/Ca intensity decreases from surface enamel to circumpulpal dentin. The ability of

Acknowledgments

We would like to acknowledge Dr. Carlos Alberto Perez for helping during the analysis at the XRF beamline and Anibal Araújo Alves Peixoto, for helping during collect of teeth. This research was partially supported by the Synchrotron Light National Laboratory (LNLS/CNPq), Brazil. This study was also supported by FAPESP and CNPq.

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