Research Group for Interfacial Reaction Field ChemistryGroup Leader: Bernd Grambow
Members: Naofumi Kozai, Fuminori Sakamoto, Kazuya Tanaka, Qianqian Yu, Toshihiko Ohnuki

The research objectives of this group are to explore novel
chemical reactions of aqueous species of elements including
actinides at liquid-solid interfaces on minerals, cells ofmicroorganisms, and their hybrid system and elucidate thosereaction mechanisms in order to contribute to environmental
chemistry, actinide chemistry, and waste treatment. Using ourknowledge and experience on minerals and microorganisms, wehave worked on contamination of the environment withradionuclides by the Fukushima Daiichi Nuclear Power Plant
accident.
In the year of 2015, we studied 1) reactions of lanthanides in abinary system where cells of fungi oxidize Mn(II) andconsequently MnOx forms [1], 2) profiles of 137Cs in sediments
deposited after the the Fukushima Daiichi Nuclear Power Plant(FDNPP) accident [2], and 3) bacterial dissolution of 137Cs fromthe soil contaminated by the FDNPP accident [3].
Mn(II)-oxidizing fungus releases biomolecules combine
specifically with tetravalent lanthanides
Microorganisms have high sorption capabilities forlanthanides. They sorb lanthanides on their cell surfaces andsometimes precipitate lanthanides as phosphate on the cellsurfaces. The effect of their biological response on lanthanides
migration in the environment is however yet to be clarified.
Acremonium strictum KR21-2 is a Mn(II)-oxidizing fungus.
This fungus was cultured in a nutrient medium containingMn(II)SO4. The concentration of Mn(II) in the aqueous phasedecreased with increasing number of cells and black particles(MnOx) precipitated during the culture. When lanthanides wereintroduced to the nutrient medium before the culture of cells,
most of the lanthanides were sorbed on cells in 24 h, and thenCe was preferentially desorbed. The desorbed Ce increased withincreasing precipitation of MnOx. Most of the desorbed Ce wasassociated with a biomolecule produced by the active fungus. Xray absorption near edge structure (XANES) analysis suggested
that the Ce associated with the biomolecule was in thetetravalent oxidation state. The Ce-binding biomolecule was notassociated with any other trivalent lanthanides tested or with Fe.
The biomolecule had an apparent molecular weight of c.a. 4700
Dalton in size, and it contains saccharides that differed fromthose non-nuclide-specific organic substances released fromresting cells. When trisodium citrate and lanthanides wereintroduced to the nutrient medium before the culture of cells,
neither desorption of Ce nor release of this biomolecule
occurred. When citrate was present, the sorption of lanthanides
on cells decreased with increasing the concentration of citrate.
This result strongly suggests that the release of the biomolecule
was stimulated by the sorption of lanthanides on the fungus cells.
This would be an adaptive response of fungi to lanthanides.
Depth distribution of radioactive cesium in sediments
deposited on a sandbar after the FDNPP accident
The sediments deposited on a sandbar from the surface to 20
cm in depth was collected in the Abukuma River to elucidate thehistory of 137Cs derived from the FDNPP accident. The
concentrations of 137Cs in the size-fractioned sediment samples
and bulk sediment samples were analyzed. The deepest
sediment layer (18-20 cm) contained the highest concentrationof 137Cs, which indicates that soils with a lower 137Csconcentration were transported and deposited on the sediment
having a higher 137Cs concentration (Fig.1). The upper sedimentlayer with a lower 137Cs concentration might have beentransported from upstream areas, which suggests a decrease of
the radioactivity level in the provenance areas of the sediments.
The three sediment layers at 4-6 cm, 16-18 cm and 18-20 cm
had similar grain size compositions and similar relations
between grain size and concentration of 137Cs although theconcentrations of bulk 137Cs were different from each other.
Therefore the decrease in 137Cs concentration in the bulk of theupper layers is not due to the change in the grain size
composition but due to a decrease in the radioactivity in thecatchment area. These results demonstrate that sediment layers
deposited on a sandbar retaine the cumulative history of thefluvial transport of radiocesium after the FDNPP accident.

Fig. 1 Concentrations of 137Cs in sediments deposited on asandbar in the Abukuma River
Bacterial dissolution of 137Cs from the soil contaminated by
the FDNPP accident
An endemic Japanese deciduous tree, Eleutherococcus
sciadophylloides (Franch. et Sav), accumulates highconcentrations of 137Cs and Mn from soil. Root endophytic
bacteria were isolated from this tree and their siderophore
production was evaluated via chrome azurol S (CAS) Fe and
CAS Al assays. Among the isolated 463 strains, 107 (23.1%)
strains produced siderophores. Using eight strains that showed
high siderophore production, desorption of 137Cs, Mn, Fe and Al
by the bacterial culture filtrates from 137Cs-contaminated soil
collected in Fukushima was examined after decomposing thesoil organic matter using hydrogen peroxide. The desorption of137
Cs and Mn was concomitant with desorption of Al and Fe anddecrease of pH. These results strongly suggest that the root
endophytic bacteria of E. sciadophylloides produce thesiderophores that solubilize 137Cs and Mn in the rhizosphere,
making the solubilized 137Cs and Mn ions easier for this tree toabsorb from the rhizosphere.
References[1] Q. Yu et al., Geochim. Cosmochim. Acta, 174, 1, (2016).
[2] K. Tanaka et al., J. Environ. Radioactiv., 150, 213 (2015).
[3] K. Yamaji et al., J. Environ. Radioactiv., 153, 112 (2016).