physical properties, structure, and shape of radioactive cs from the fukushima daiichi nuclear power...

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Journal of Environmental Radioactivity xxx (2014) 1e6

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Journal of Environmental Radioactivity

journal homepage: www.elsevier .com/locate/ jenvrad

Physical properties, structure, and shape of radioactive Cs from theFukushima Daiichi Nuclear Power Plant accident derived from soil,bamboo and shiitake mushroom measurementsq

Nobuo Niimura a,*, Kenji Kikuchi a, Ninh Duc Tuyen a,1, Masakazu Komatsuzaki b,Yoshinobu Motohashi c

a Frontier Research Center for Applied Atomic Sciences, Ibaraki University, 162-1 Shirakata, Tokai, Naka, Ibaraki 316-1106, JapanbCenter for Field Science Research and Education, College of Agriculture, Ibaraki University, 3-21-1 Chuou, Ami, Inashiki, Ibaraki 300-0393, JapancCountermeasure Department on Radiation, Takahagi City Hall, Kasuga 3-10, Takahagi, Ibaraki 318-8511, Japan

a r t i c l e i n f o

Article history:Received 21 September 2013Received in revised form21 December 2013Accepted 21 December 2013Available online xxx

Keywords:SoilReagent solutionAutoradiographyRadioactive cesiumGranular FukushimaDaiichi Nuclear Power Plant

q This is an open-access article distributed undeCommons Attribution-NonCommercial-No Derivativemits non-commercial use, distribution, and reproductthe original author and source are credited.* Corresponding author. Tel.: þ81 29 352 3240; fax

E-mail addresses: [email protected] (N. Niac.jp (K. Kikuchi), [email protected] (N.D. Tuac.jp (M. Komatsuzaki), [email protected] (Y.

1 Present address: Centre for Nuclear TechniqueHochiminh City, Vietnam.

0265-931X/$ e see front matter � 2013 The Authorshttp://dx.doi.org/10.1016/j.jenvrad.2013.12.020

Please cite this article in press as: Niimura,Nuclear Power Plant accident derived from(2014), http://dx.doi.org/10.1016/j.jenvrad.2

a b s t r a c t

We conducted an elution experiment with contaminated soils using various aqueous reagent solutionsand autoradiography measurements of contaminated bamboo shoots and shiitake mushrooms todetermine the physical and chemical characteristics of radioactive Cs from the Fukushima Daiichi NuclearPower Plant accident. Based on our study results and data in the literature, we conclude that the active Csemitted by the accident fell to the ground as granular non-ionic materials. Therefore, they were notadsorbed or trapped by minerals in the soil, but instead physically adhere to the rough surfaces of the soilmineral particles. Granular Cs* can be transferred among media, such as soils and plants. The physicalproperties and dynamic behavior of the granular Cs* is expected to be helpful in considering methods fordecontamination of soil, litter, and other media.

� 2013 The Authors. Published by Elsevier Ltd. All rights reserved.

1. Introduction

Discharge of radioactive Cs (134Cs and 137Cs, termed Cs*) fromthe Fukushima Daiichi Nuclear Power Plant (FDNPP) accidenttriggered by the earthquake and tsunami on 11 March 2011contaminated a wide area of northeastern Japan (Kinoshita et al.,2011; Yasunari et al., 2011; Yoshida and Takahashi, 2012; Ohkuraet al., 2012). Because the Cs* has been found to be non-water-soluble, it has been very difficult to decontaminate contaminatedareas (Ohnuki and Kozai, 2013; Kozai et al., 2012). To elucidate thedynamics of transfer of Cs* between soil and flora as well as to

r the terms of the CreativeWorks License, which per-

ion in any medium, provided

: þ81 29 287 7872.imura), [email protected]), [email protected]).s, 217 Nguyen Trai, 1 Dict,

. Published by Elsevier Ltd. All righ

N., et al., Physical propertiessoil, bamboo and shiitake

013.12.020

ensure that uncontaminated food is protected against futurecontamination by Cs*, it is critical to establish the physical prop-erties, structure, and shape of the Cs*. Modern techniques ofstructural analysis such as X-ray crystallography and fluorescentanalysis could be used for these purposes, but require minimumpicograms or nanograms of Cs* (about 1010 atoms of pure Cs*).Spatial concentrations, distributions, and depth profiles of Cs* havebeen measured to estimate doses (Kato et al., 2012; Tanaka et al.,2012). Those studies determined that the highest concentrationof Cs* in the soil wasw105 Bq/kg (Tanaka et al., 2012), equivalent tow2.3 � 10�10 mole/kg. Large-scale equipment is required to collectpure Cs* in the amount required for these experiments fromcontaminated soil. Even if the experimentally required amount ofCs* could be collected, the radiation level would be on the order ofGBqeTBq, which would be challenging to handle in a typical lab-oratory. Therefore, they tend to use materials that include Cs, butwhich do not originate from the FDNPP accident. However, wemust carefully consider whether these materials are appropriatelyrepresentative.

Kaneyasu et al. collected Cs* in aerosols 47 days after the FDNPPaccident at Tsukuba and measured the activity size distributions of

ts reserved.

, structure, and shape of radioactive Cs from the Fukushima Daiichimushroom measurements, Journal of Environmental Radioactivity

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N. Niimura et al. / Journal of Environmental Radioactivity xxx (2014) 1e62

134Cs and 137Cs in the aerosols (Kaneyasu et al., 2012). They foundthat the activity median aerodynamic diameters in the first sample(28 Aprile12 May) were 0.54 and 0.53 mm, respectively, and thosein the second sample (12e26 May) were both 0.63 mm. The activitysize distributions of these radiocesium samples were similar to themass size distribution of non-sea-salt sulfate but not to that of soils(Kaneyasu et al., 2012). The results indicated that the Cs* emittedfrom the FDNPP accident may have been granular, which isconsistent with autoradiography images of contaminated plantleaves using imaging plates (IP) (Sakamoto et al., 2012; Nakajimaet al., 2012). Black spots were observed on the contaminatedleaves; the origin of the black spots may have been granularradioactive materials such as Cs*. In particular, images showingblack spots on the leaves of tall cedar trees indicated that the Cs*fell on the leaves directly from the sky. Therefore, the Cs* likely alsofell to the ground as granular radioactive materials. Very recently,Adachi et al. have reported that the shape of the Cs* collected usingaerosol sampler was found to be spherical by a scanning electronmicroscope (Adachi et al., 2013).

In contrast, it has been stated that the Cs* that fell on the groundwas adsorbed and trapped in soil minerals, explaining why the Cs*was not soluble in water. There have been many previous reportsthat radioactive and/or non-radioactive Cs is adsorbed into soilminerals (Tamura and Jacobs, 1989; Sawhney, 1970; Comans et al.,1991; Westrich et al., 1995; Ejeckama and Sherriff, 2005; Saiersand Hornberger, 1999; Ohnuki, 1994; Singh and Tandon, 1977;Hasany and Chaudhary, 2005). However, these papers were pub-lished before the FDNPP accident, and according to the mechanismdescribed for Cs adsorption into the soil minerals, the Cs shouldexist in an ionic or atomic state.

After the FDNPP accident, there were also several reports thatthe Cs* was adsorbed into the soil minerals (Kogure et al., 2012;Kozai et al., 2012; Ohnuki and Kozai, 2013). For example, Kogureet al. carried out x-ray diffraction and high-resolution transmissionelectron microscopy experiments of the Cs ions trapped in newvermiculite clay. They showed that “ionic Cs” was fixed in thecenters of hexagonal rings in the upper and lower silicate tetra-hedral sheets (Kogure et al., 2012). However, they used commer-cially available CsNO3 for the Csþ ions in the samples (Kogure et al.,2012). It is not yet clear whether the Cs* emitted from the FDNPPwas actually in an ionic state and thus, the experiment of Kogureet al. may not have simulated actual conditions. Ohnuki et al.studied the adsorption behavior of radioactive Cs by non-micaminerals, including kaolinite and 5 other minerals. For the Cs,they used commercially available radioactive and non-radioactiveCsCl. This type of radioactive Cs and normal Cs are present in wa-ter in an ionic state andwould be expected to be adsorbed into non-mica minerals (Ohnuki and Kozai, 2013). This experiment was alsonot intended to simulate the behavior of the Cs* emitted from theFDNPP accident. Kozai et al. examined the Cs* fallout on soilscollected in Fukushima, Japan and characterized them withdesorption experiments using appropriate reagent solutions (Kozaiet al., 2012). They used contaminated soils containing Cs* emittedfrom the FDNPP accident, but analyzed all the obtained dataassuming that the Cs* was adsorbed into the matrix of the soilminerals.

Because there are reports that the Cs* was in the form of anaerosol (Kaneyasu et al., 2012) and was observed as black spots inIP autography images (Sakamoto et al., 2012; Nakajima et al.,2012), additional experiments are required to determinewhether the Cs* has been adsorbed into soil minerals. Based onthe IP autoradiography of the leaves of tall trees (Sakamoto et al.,2012) and the activity size distributions of the aerosols (Kaneyasuet al., 2012), we may assume that granular Cs* fell onto the trees aswell as on the ground. The physical and chemical characteristics of

Please cite this article in press as: Niimura, N., et al., Physical propertiesNuclear Power Plant accident derived from soil, bamboo and shiitake(2014), http://dx.doi.org/10.1016/j.jenvrad.2013.12.020

the Cs* need to be examined using soils contaminated with Cs*from the FDNPP accident and moreover, we must considerwhether the Cs* is present inside or outside the soil minerals,because it has not yet been clarified whether granular Cs* can beadsorbed into soil minerals. Therefore, in this study, we charac-terized the desorption behavior of Cs* in soil from the FDNPPaccident using various reagent solutions. In addition, we consid-ered autoradiography results for soils, plants, and other materialsto determine the dynamic behavior of Cs*.

2. Experimental

2.1. Water washing of soils contaminated by the FDNPP accident

Contaminated soils from the playground of a primary school inFukushima prefecture were collected on 5 May 2012. The place ofthe primary school is indicated in the map as shown in Fig. 1.Twenty grams of soil were immersed in 30 ml water while stirringat 200 rpm for 3 h at 20 �C and filtered through a 0.5 mmmesh filter.The radioactivities of the soil residues and filtrates were measuredby a Ge-semiconductor detector, (CANBERRA GC4020: Energy res-olution at 1.33 MeV is smaller than 2.0 keV.) termed Ge-measurement below.

2.2. Washing of soils contaminated by the FDNPP accident with Csþ

ion excess aqueous solution

After water washing, 20 g of the soils were immersed in 30 ml0.1 M CsNO3 aqueous solution while stirring at 200 rpm for 3 h at20 �C and filtered through a 0.5 mm mesh filter. The radioactivitiesof the soil residues and filtrates were measured using Ge-measurement.

2.3. Washing of soils contaminated by the FDNPP accident withvarious reagent solutions

After water washing, 10 g of the soils were immersed in 30 ml ofvarious aqueous solutions, including HCl (1 M), H2SO4 (1 M),CH3COOH (1 M), (NH4)2SO4 (1 M), NH4Cl (1 M) while stirring at200 rpm for 3 h at 20 �C and filtered through a 0.5 mm mesh filter.The radioactivities of the soil residues and filtrates were measuredusing Ge-measurement.

2.4. Autoradiography of contaminated soils, bamboo shoots, andshiitake mushrooms with imaging plates

The distributions of Cs* in soils, bamboo shoots, and shiitakemushrooms contaminated by the FDNPP accident were measuredusing imaging plates (IPs; BAS-SR 2040, 200 mm wide � 400 mmlong). The IPs were inserted into 12 mm thick aluminum foil. Thesamples were placed on 12 mm thick aluminum foil and sand-wiched by IPs. The samples and IPs were stored in a shielding houseconstructed of lead bricks, a 0.5 mm thick Cd sheet, and 200 mmthick water layer for shielding from environmental radiation(gamma rays and neutron beams). The environmental radiationbackground was reduced to 0.004 mSv/h from 0.103 mSv/h. IPreadings were conducted with a Fuji Film BAS-2500, termed IPmeasurement.

Shiitake mushrooms were harvested at a cultivation field inYokokawa, Takahagi about 84 km south of the FDNPP on 14November 2012. Bamboo shoots were harvested from a bambooforest in Nihonmatsu, about 30 km west of the FDNPP on 19 May2012. The places of Yokokawa and Nihonmatsu are indicated in themap (Fig. 1). Although Yokokawa locates at 80 km south fromFDNPP, the deposition densities of total of cesium �134 & 137 at


Fig. 1. Map of the area where the samples used in the experiment were collected (Airborne monitoring results, 2012).

Table 1Cs* radioactivities of the filtrates and filtration residues, and percent transfer of Cs*to solution after washing with various reagent solutions.

Solvent Filtrate (Bq/g) Residue (Bq/g) Transitionrate (%)134Cs

(604.66 keV)

137Cs(661.64 keV)

134Cs(604.66 keV)

137Cs(661.64 keV)

HCI 0.63 � 0.03 1.38 � 0.04 20.6 � 0.2 44.3 � 0.4 7H2SO4 0.64 � 0.03 1.24 � 0.04 6.40 � 0.1 13.7 � 0.2 11(NH4) 2SO4 0.22 � 0.01 0.46 � 0.02 23.6 � 0.3 49.3 � 0.4 2NH4Cl 0.16 � 0.01 0.32 � 0.02 14.8 � 0.2 31.1 � 0.2 1CH3COOH ND (<0.03) ND (<0.02) 38.0 � 0.4 81.5 � 0.7 0

N. Niimura et al. / Journal of Environmental Radioactivity xxx (2014) 1e6 3

Yokokawa are reported as 30e60 kBq/m2 as shown in the map(Airborne monitoring results, 2012).

3. Results

3.1. Water washing of soils contaminated by the FDNPP accident

After water washing, 134Cs (604.66 keV) and 137Cs (661.64 keV)radioactivities in the filtrate were not detected (<1.2230� 10�2 Bq/g) and detected at 1.6996�10�2� 3.6946� 10�3 Bq/g, respectively,and those of the soil residues were 1.7097� 8.9696� 10�2 Bq/g and3.3697� 10� 1.2204�10�1 Bq/g, respectively. The percent transferof 134Cs and 137Cs to water was 0 and 0.05% respectively; thus, 134Csand 137Cs in soils contaminated by the FDNPP accident can beregarded as insoluble in water.

3.2. Washing of soils contaminated by the FDNPP accident with Csþ

ion excess aqueous solution

After washing the soils with 0.1M CsNO3 aqueous solution, 134Cs(604.66 keV) and 137Cs (661.64 keV) radioactivities in the filtrateliquid were 1.4618 � 10�1 � 9.2687 � 10�3 Bq/g and3.34501 � 10�1 � 1.3525 � 10�2 Bq/g, respectively. The percenttransfer of 134Cs and 137Cs to solution was 0.8% and 0.6%, respec-tively; thus, 134Cs and 137Cs in soils contaminated by the FDNPPaccident can be regarded as nearly insoluble in 0.1 M CsNO3aqueous solution. Therefore, the possibility that 134Cs and 137Csreleased by the FDNPP accident were not trapped in soils as indi-cated by the previous X-ray diffraction and high-resolution trans-mission electron microscopy experiments is very low.

3.3. Washing of soils contaminated by the FDNPP accident withvarious reagent solutions

After washing the soils with various reagent solutions, the Cs*radioactivities of the filtrates and the filtration soil residues and thepercent transfer of Cs* to the solutions are shown in Table 1. The Cs-


137/Cs-134 ratio of the Cs* from the FDNPP accident is reported thatmost of the ratio of atmospheric concentration of Cs-134 to that ofCs-137 was found between 0.9 and 1.1 from 15 March to 7 April2011. The Cs-137/Cs-134 ratios of the Cs* were obtained in July 2013between 1.93 and 2.09 from Table 1, and these values were in goodagreement with those of Ohkura et al.’s report by considering thehalf-life of Cs-137/Cs-134. The Cs* was soluble in strong acid solu-tions such as HCl (1 M) and H2SO4 (1 M), but not in weak acid so-lutions such as CH3COOH (1 M). The Cs* was slightly soluble incertain salt solutions such as (NH4)2SO4 (1 M) and NH4Cl (1 M).

3.4. Autoradiography of contaminated soils, bamboo shoots, andshiitake mushrooms using imaging plates

Fig. 2 shows an IP image of the soil, exhibiting many black spots.The soil has been treated in various ways as indicated in figurecaptions. The IP image of each was found to be almost similar andthis indicates that the existing form of Cs* in the soil depends onneither the size of soil nor washing of soil. Figs. 3 and 4 showphotographs of portions of a bamboo shoot and their correspond-ing IP images, respectively.

The bamboo shoot body was cut vertically and horizontally.There were no black spots on the body in the IP image. However,there were black spots in the skin and litter images. The Cs* on thesurface of the bamboo skin was likely transferred from the litter


Fig. 2. IP images of several kinds of contaminated soils. (a) Raw soil, (b) after sieving of soil with a diameter of 0.5 mm or less, (c) after sieving of soil with a diameter of 0.5e4 mm,(d) after sieving of soil with a diameter of 4 mm or more, (e) washing soil, (f) after sieving of washing soil with a diameter of 0.5 mm or less, (g) after sieving of washing soil with adiameter of 0.5e4 mm, and (h) after sieving of washing soil with a diameter of 4 mm or more.


when the bamboo shoots sprouted through the litter and touchedto the Cs* on the liter.

Figs. 5 and 6 show photographs of shiitakemushrooms and theircorresponding IP images, respectively. One black spot on the lamellaof the shiitake mushrooms (Fig. 6(a1)), several black spots on theoutside of the cross section of the log (Fig. 6(b2)) and many blackspots on the end face of the mushroom-cultivating log (Fig. 6(b1))were observed in the IP images, respectively. However, there wereno black spots inside the mushroom-cultivating log. Therefore, TheCs* on the lamella of the shiitakemushrooms did not come from theinside of the log, but it was likely transferred from the surface of themushroom-cultivating log when the shiitake mushrooms emergedand touched to the Cs* on the surface of the log.

4. Discussion

4.1. Nature of the 134Cs and 137Cs released from the FDNPP accidentin the soil

It has previously been reported that Cs can be trapped andadsorbed into soil minerals. Kogure et al. determined the crystalstructure of minerals capturing Cs by transmission electron

Fig. 3. Photographs of (a) the body of a bamboo shoot, (b) the outer skin of a bambooshoot, (c) soil, and (d) litter.


microscopy and x-ray diffraction (Kogure et al., 2012) and Ohnukiet al. showed that radioactive Cs could be trapped in several kindsof minerals (Ohnuki and Kozai, 2013). However, the Cs used assamples in these experiments were ions, such as Csþ or 134Csþ and137Csþ, which did not originate from the FDNPP accident (Kogureet al., 2012; Ohnuki and Kozai, 2013). We agree that ionic Csþ

such as 134Csþ and 137Csþ can be captured by minerals. Cs trappedas ionic Csþ in minerals would need to be dissolved in aqueoussolution containing excess amounts of non-radioactive Csþ toachieve chemical equilibrium between the minerals and theaqueous solution. For example, Ohnuki et al. showed that ionic134Csþ and 137Csþ dissolved in CsCl solution were captured inminerals. However, as stated in Section 3.2, the 134Cs and 137Cs inthe soils contaminated by the FDNPP accident were nearly insol-uble in 0.1 M CsNO3 aqueous solution. This indicates that the 134Csand 137Cs in the contaminated soils would not be available to beadsorbed into soils, in contrast to previous results. It appears thatthe 134Cs and 137Cs were not in ionic states, but were in the form ofvery small grains when they were released from the FDNPP. It isessential that 134Cs and 137Cs be in an ionic state to be trapped intosoil minerals, as supported by the structure determined by Kogureet al., in which they showed that “ionic Cs” was fixed at the centers

Fig. 4. IP images of (a) the body of a bamboo shoot, (b) the outer skin of a bambooshoot, (c) soil, and (d) litter, as shown in Fig. 3.


Fig. 5. Photographs of (a1) lamella, (a2) stipe of the shiitake mushroom, and (a3)pileus, respectively, and (b1) an end face of the log, and (b2) a cross section of the logon which the mushrooms are cultivated, respectively.

Fig. 6. IP images of (a1) lamella, (a2) stipe of the shiitake mushroom, and (a3) pileus,respectively, and (b1) an end face of the log, and (b2) a cross section of the log onwhich the mushrooms are cultivated, respectively, as shown in Fig. 5.

N. Niimura et al. / Journal of Environmental Radioactivity xxx (2014) 1e6 5

of hexagonal rings in the upper and lower silicate tetrahedralsheets (Kogure et al., 2012). The reason of the different results be-tween ours and theirs is as follows: We have used the Cs* emittedfrom FDNPP as samples in our experiment of the IP autoradiog-raphy and solubility assessment. There were no evidences that theCs* emitted from FDNPP was ionic. On the other hand, Ohnuki et al.and Kogure et al. have used commercially available radioactive CsCland commercially available CsNO3, respectively, both of whichweresoluble in water and the Cs used in their experiments were in ionicstates.

4.2. Structure and shape of the radioactive Cs from the FDNPPaccident

Based on the activity size distributions of 134Cs and 137Cs inaerosols (Kaneyasu et al., 2012), the results of a scanning electronmicroscope of the Cs* aerosols (Adachi et al., 2013), and the IPimages taken of contaminated plant leaves (Sakamoto et al., 2012)and soils, bamboo shoots, and shiitake mushrooms (Figs. 2, 4 and6), the shape of the radioactive Cs from the FDNPP accident isgranular and around 1 mm in diameter, based on the activity sizedistributions of the aerosols (Kaneyasu et al., 2012; Adachi et al.,2013). The IP image spots seen in soils, on the plant leaves,bamboo shoots, and shiitake mushrooms are interpreted as gran-ular substances containing Cs* (hereinafter referred to as “granularCs*”). It appears that the granular Cs* can easily adhere physically totiny hollows on the surfaces of soil mineral particles, plant leaves,and other materials. The size of the granular Cs* might be expected


to be equivalent to the size of the black spots on the IP images;however, this is not necessarily the case. The IP image is affected bythe positional resolution of the imaging plate detector (50 mm,much larger than the size of the granular Cs*) as well as the opticsof the autoradiography system, which are rather complex.

4.3. Chemical and physical properties of the granular Cs*

The actual microscopic and atomic scale structure of the gran-ular Cs* has not yet been clarified. Its chemical properties wereexamined through solubility measurements with various reagentsolutions (see Section 3). The granular Cs* is soluble in strong acidsolutions such as HCl (1 M) and H2SO4 (1 M), but not in weak acidsolutions such as CH3COOH (1 M). The granular Cs* is also slightlysoluble in certain salt solutions such as (NH4)2SO4 (1 M) and NH4Cl(1 M). This might suggest that the granular Cs* consist of Cs as wellas NH4

þ and SO42�, which were reported as Cs* aerosol components

by Kaneyasu et al. (2012).Solubility measurements in other reagent solutions are planned

for future research to assist in determining the microscopic andatomic scale structure of the granular Cs*.

Some physical properties of the granular Cs* can be inferredfrom the IP measurements of the bamboo shoots and shiitakemushrooms. The black spots observed in the IP images are



interpreted as granular Cs*. It appears that the granular Cs* is easilytransferred from litter to bamboo shoots and from the surface of thelogs used for cultivation of the shiitake mushrooms as interpretedin section 3.4. Therefore, the Cs* grains are very small (around 1 mmin diameter), light, and physically adhere to soils and so on, and canbe easily transported to other places or media. As a matter of fact,we had several experiences that granular Cs* on shiitake mush-rooms and bamboo shoots have been wiped off with a cloth.

The granular Cs* was insoluble in water as indicated in Section3.1. If the Cs* were trapped and captured in soil minerals, it wouldnot be as easily transported.

It has been confirmed that radioactive Cs is present withinvarious plants to look like in the ionic states. We have not yetknown how the water-insoluble granular Cs* becomes soluble andionic, but this would be the next important subject, because once itbecomes soluble and ionic, this ionic Cs* would become available toand absorbed into plants. Such soluble and ionic Cs* might also betrapped and adsorbed into the soil minerals over time.

The physical properties and dynamic behavior of the granularCs* is expected to be helpful in considering methods for decon-tamination of soil, litter, and other media.

5. Conclusions

Based on our observed IP images of Cs* taken of contaminatedsoils, bamboo shoots and shiitake mushrooms, and the activity sizedistribution of Cs* in aerosols, Cs* emitted by the FDNPP accidentfell onto the ground and plant surfaces in a granular form (around1 mm in diameter). Since the granular Cs* is not soluble in water,and it does not become ionic Cs, it cannot be trapped into soilminerals, but physically adheres to the rough surfaces of soil min-eral particles. This has been confirmed by the experiment that the134Cs and 137Cs in the soils contaminated by the FDNPP accidentwere nearly insoluble in 0.1 M CsNO3 aqueous solution. This meansthat the 134Cs and 137Cs in the contaminated soils would not beavailable to be adsorbed into soils. Since it is soluble in strong acidsolutions and slightly soluble in certain salt solutions such as(NH4)2SO4 (1 M) and NH4Cl (1 M), these might suggest that thegranular Cs* consist of Cs as well as NH4

þ and SO42�. Since Cs*

physically adhere to soils and so on, it can be transferred amongmedia, such as soils and plants. The physical properties and dy-namic behavior of the granular Cs* is expected to be helpful inconsidering methods for decontamination of soil, litter, and othermedia. Moreover the reason why the granular Cs* emitted by theFDNPP accident are non-water soluble should be elucidated fromthe microscopic and atomic scale structural aspects, and the pro-cess how the water-insoluble granular Cs* become soluble andionic in the soils and then are absorbed into plants should also beclarified in the future important subjects.

Acknowledgments

We thank Dr. S. Ishiyama of the Japan Atomic Energy Agency andMakino Co. Ltd. for providing contaminated soils.


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http://dx.doi.org/10.1038/srep02554

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physical properties, structure, and shape of radioactive cs from the fukushima daiichi nuclear power...

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