Photon Factory Activity Report 2004 #22 Part B (2005)
Chemistry

9A, 12C/2003G085

The XAFS study of zinc in the Yatsu tideland sediments
Masaki KATAOKA*1 and Motoyuki MATSUO2
1Graduate School of Science, The University of Tokyo,
3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan
2
Graduate School of Arts and Sciences, The University of Tokyo,
3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan
electronic state, and the component of ZnSO4-like means
Zn which has O ligand or the similar electronic state. The
ZnS-like component increased in an upper part of middlelayer in Yatsu tideland sediments, but in Kitajukkengawa
River sediments it mainly existed from the surface part,and the proportion of the ZnS-like component was high.
This difference may be explained that the surface layer ofYatsu tideland sediments exposed to the air. On the otherhand, the surface layer of Kitajukkengawa Riversediments was always covered with water, therefore thesediments become reducing condition from the surfacelayer. The high proportion of the ZnS-like component inKitajukkengawa River sediments compared with Yatsutideland caused by the difference of the surface water.
The surface water of the Yatsu tideland mainly contains
seawater which has high concentration of sulfate, whereas
the surface water of Kitajukkengawa River mainlycontains fresh water. Thus, the concentration of eachcomponent of Zn was determined by this method.
Relat ive abundance (%)

Relative abundance(%)
05001000010102020

Dept h(cm)Depth(cm)Introduction
In a brackish water area, where fresh water andseawater are mixed, the inside of the sediments becomesvery complicated system, because sedimentation rate isquite high. There is the possibility that the chemicalchange in the sediments is affected by the degree ofanthropogenic effect, which is largely different depending
on a brackish water area of suburb. Under anaerobic
environments in the sediments, the sulfate ion fromseawater is reduced, and then various sulfides have beenformed in the sediments. We have already studied thechemical state of heavy metals in the sediment of estuary
and tideland, and revealed that several heavy metals suchas iron, manganese and zinc exist in a form of sulfide [1][2]. In order to obtain the vertical distribution of zinc
sulfides, chemical state analysis of zinc by XAFS wascarried out in this study.
Experimental
We collected sediments vertically in Yatsu tidelandwhich is located at the east part of Tokyo and the tidelandis assumed to be a non-polluted place. We also collected
sediments vertically in Kitajukkengawa River which isurban river in Tokyo and the river is assumed to bepolluted by human activity. The collected sediments
were cut at every 3-5 cm length immediately, and thenporewater was extracted by pressure filtration (5 atm, N2).
Approximately 300mg of each sample was mounted in aprolene film. The X-ray absorption measurement wasmade with synchrotron radiation by using XANES
facilities on the beam line 9A and 12C. The radiation
was monochromatized by Si (111) double crystals. Thespectra were collected in fluorescence mode using Lytletype detector at room temperature.
Results and Discussion
The zinc XANES spectra of each area sediment wereobtained. The chemical states of zinc in the sediments
were divalent in whole core of each area. But, theXANES spectra of zinc were changed a little influenced
by the nearest neighbour atoms. However, the eachcomponent of Zn could not be determined from thespectrum. The partial least-squares (PLS) regression wasemployed to resolve Zn XANES spectra of sediments andquantify the species therein. For details of the PLS
method, the papers written by Kuno et al. should bereferred to [3]. Figure 1 shows vertical distribution ofeach component of Zn in the Yatsu-tideland andKitajukkengawa-river sediments. The component ofZnS-like means Zn which has S ligand or the similar

30405050

ZnSO4-like

1003040

ZnS- like

50

ZnS- likeZnSO4- likeFig. 1. The vertical distribution of two components of Zn
in the Yatsu tideland (a) and Kitajukkengawa Riversediment (b)References[1] M. Kataoka et al., PF Activity Report, 20B, 21 (2003)[2] M. Kataoka et al., J. Radioanal. Nucl. Chem., 255,283-286 (2002)[3] A. Kuno et al., J. Synchrotron Radit., 6, 667-669(1999)*kataokai@dolphin.c.u-tokyo.ac.jp

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