Photon Factory Activity Report 2005 #23 Part B (2006)
Biological Science

9A/2004G084

XAFS and distribution analysis of selenium in human oral mucosa
1Motohiro UO*1, Kiyotaka ASAKURA2, Takao KOHGO1, Fumio WATARI1
Graduate
School of Dentistry, Hokkaido Univ. Kita-ku, Sapporo, Hokkaido, 060-8586, Japan
2
Catalyst Research Center, Hokkaido Univ. Kita-ku, Sapporo, Hokkaido, 001-0021, Japan

Introduction
Selenium (Se) is an essential element in humans. It is
important not only as a cofactor in enzymes but also indetoxification of heavy metals such as mercury. The
relationship between the level of Se and heavy metals,
especially mercury (Hg) and silver, had been studied[1].
A positive correlation between Se and Hg in blood wasreported. As the detoxification mechanism, the formationof Hg-selenoprotein complex was suggested. However,the distribution of Se in the areas surrounding heavy
metals in the human body has not yet been studied,because of its low concentration.
In this study, X-ray scanning analytical microscopy(XSAM) and fluorescence XAFS were employed todetermine the selenium distribution in the human oral
mucosa containing metallic dental restoratives.
Materials and Methods
Two oral mucosa excised from two different patients,
which contained particle like foreign bodies, weresubjected to XSAM and XAFS analyses. These
specimens were excised for pathological diagnosis forpigmentation. The specimen was fixed and embedded inparaffin by the conventional method. The embedded
tissue blocks were subjected to elemental distribution
analysis using XSAM (XGT-2000V, Horiba, Japan). The
distribution images were integrated 100 times.
The XAFS spectra were measured at BL-9A of thePhoton Factory. The specified area of the specimen whereSe was enriched was analyzed. The XAFS spectra of theSe K-edge were measured in a fluorescent mode using a
multi element solid-state detector (Camberra). I0 signals
were monitored using an N2 filled ionization chamber.
Results and Discussion
Figure 1 shows the transmission X-ray image andS, Hg, Ag and Se distribution images of the specimen
with XSAM. The S distribution image shows theshapes of specimens. In the transmission X-rayimage, spot-like untransparent parts were found. Inthese untransparent spots, Hg and Ag were observed.
Dental amalgam consists of Ag-Sn-Cu alloy powder
and mercury. The foreign bodies in specimen A wereconsidered to be dental amalgam. Se was existed in
the vicinity of the Hg and Ag localized spots. Usually,
Se is not detected in the tissue by XSAM image
because of its low concentration. Therefore, Se
localization would be caused by the existence of Hgand Ag. Figure 2 shows Se K-edge XANES spectraof the part indicated by arrows in the Se distribution
images in Figure 1. Yamamoto reported that theabsorption edge of Se shifts toward higher energy

202Users' Reportwith the increase of valence of Se[2]. The absorption
edges of the spectra of the mucosa was slightly
shifted to higher energy than that of metallic Se andthere is shoulder structure at 12.66 KeV. Thissuggests the Se in those specimens would be mostly
in the low-valence state (nearly zero) and there
would be some variety in the valency of Se.
In this study, the localization in the vicinity ofdental amalgam which contained Hg and Ag wasclearly visualized using XSAM and their chemical
states were estimated using XAFS[3].

Figure 1. Elemental distribution images of dental
amalgam-like particles in human oral mucosa.

Figure 2. Elemental distribution images of dental
amalgam-like particles in human oral mucosa.
References[1] M. Molin et al., Acta Odontol. Scand., 48, 189 (1990)[2] T. Yamamoto et al., Yokosuka Res. Rep., W03034,
1 (2004)[3] M.Uo et al, Chem. Lett., 25, 66 (2006)*uo@den.hokudai.ac.jp