Cesium-137 deposition and contamination ofJapanese soils due to the Fukushima nuclear accident
Teppei J. Yasunaria,1, Andreas Stohlb, Ryugo S. Hayanoc, John F. Burkhartb,d, Sabine Eckhardtb, and Tetsuzo YasunarieaUniversities Space Research Association, Goddard Earth Sciences Technology and Research, Columbia, MD 21044; bNorwegian Institute for Air Research,
P.O. Box 100, N-2027 Kjeller, Norway; cDepartment of Physics, University of Tokyo, 7-3-1 Hongo, Bukyo-ku, Tokyo 113-0033, Japan; dSierra Nevada
Research Institute, University of California, Merced, 5200 North Lake Road, Merced, CA 95343; and eHydrospheric Atmospheric Research Center,
Nagoya University, Nagoya, Aichi 464-8601, Japanaerosol ∣ dispersion modeling ∣ radioactive falloutA

catastrophic earthquake and tsunami occurred on March 11,
2011, which caused destruction in northeastern Japan andseverely damaged the Fukushima Daiichi Nuclear Power Plant(NPP). This event led to emissions of radioactive materials fromthe NPP (1), albeit at unknown and likely strongly varying release
rates (1–3). Among these materials, with a half-life of 30.1 y (4),cesium-137 (137 Cs) causes the largest concerns because of its
deleterious effect on agriculture and stock farming, and, thus,
human life for decades. Removal of 137 Cs-contaminated soils or
land use limitations in areas where removal is not possible is,therefore, an urgent issue. The Japanese government, generalpublic, and scientists have been waiting for the information of thespatial distributions of 137 Cs deposition and its soil contamination
over all of Japan.
The aerosol-bound 137 Cs can be removed from the atmosphereand brought to the surface by dry or wet deposition. Analysisof data collected after the Chernobyl accident has shown that
137 Cs adsorbed in the top soil layer can remain there for many
years (5, 6), restricting land use, e.g., for food production, ofhighly contaminated areas for a long time. To minimize the impacts on human health of soil contamination in Japan due to the
Fukushima NPP accident, spatial maps of 137 Cs deposition andconcentrations in soil are urgently needed. Sporadic sampling of
the soils in and around Fukushima prefecture has been carriedout after the NPP accident under the instruction by the Ministryof Education, Culture, Sports, Science and Technology (MEXT)
www.pnas.org/cgi/doi/10.1073/pnas.1112058108(7) and others (Table S1). However, it is impossible to fully capture the distribution of 137 Cs deposition across Japan from a limited number of in situ measurements alone. On the other hand,reliable estimates using dispersion models are also not available
because of the largely unknown source term. Not only is the total
release of 137 Cs from the damaged NPP poorly known, but also
its variation with time is even more uncertain. Although firstattempts to estimate it have been made (2) and another study
tried to estimate its deposition based on the previous study (2)over the limited areas around Fukushima prefecture with a regional chemical transport model (8), these estimates on the emission
rate are highly uncertain and the discussion on deposition over
all of Japan has not been made.
In this study we quantitatively estimate the spatial distributionof the 137 Cs deposition and its soil contamination over all ofJapan. We take relative deposition distribution patterns from a
Lagrangian particle dispersion model, FLEXPART (Materials andMethods and SI Text) (9), using a constant source term [as assumed
also in some simulations because of high uncertainty of theemission amount (10–16)]. We fuse daily varying observations of
137 Cs deposition in each Japanese prefecture (17) into the modeled deposition fields to obtain quantitative deposition estimates.
Results
Our estimate of 137 Cs deposition is made for the period between
March 20 and April 19 because no observations of 137 Cs deposition were made between March 12 and 17 and the dispersion
model did not simulate any depositions at the observation locations on March 18 and 19 (Fig. S1). Thus, our quantitative estimates do not include the first 8 d after the NPP accident, yet forthat period we provide relative contributions to the deposition. In
Fig. 1A we show the relative contribution map of the deposition
over the period when our estimate was not applicable. It showsthat before March 20, potentially contaminated air masses weremainly transported toward the Pacific Ocean and 137 Cs deposition would have occurred mostly over the ocean, except for
Fukushima prefecture and some neighboring provinces. Between
March 20 and April 19 (Fig. 1B), a much wider area was effectedby the deposition. In particular, eastern and northeastern parts ofJapan had a greater potential for 137 Cs deposition, whereas inwestern Japan the potential for 137 Cs deposition was low. Overall,however, the highest potential deposition occurred over the
Pacific Ocean, where a few observations of 137 Cs deposition exist(18), showing that winds were generally quite favorable and carried most radiation away from populated areas.
Author contributions: T.J.Y. designed research; T.J.Y., A.S., J.F.B., and S.E. performed
research; T.J.Y. and R.S.H. analyzed data; and T.J.Y., A.S., J.F.B., and T.Y. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
Freely available online through the PNAS open access option.
1

To whom correspondence should be addressed: E-mail: tyasunari@usra.edu.

This article contains supporting information online at www.pnas.org/lookup/suppl/
doi:10.1073/pnas.1112058108/-/DCSupplemental.

PNAS Early Edition ∣1 of 5ENVIRONMENTALSCIENCES

The largest concern on the cesium-137 (137 Cs) deposition and its
soil contamination due to the emission from the Fukushima Daiichi
Nuclear Power Plant (NPP) showed up after a massive quake on
March 11, 2011. Cesium-137 (137 Cs) with a half-life of 30.1 y causes
the largest concerns because of its deleterious effect on agriculture
and stock farming, and, thus, human life for decades. Removalof 137 Cs contaminated soils or land use limitations in areas where
removal is not possible is, therefore, an urgent issue. A challenge
lies in the fact that estimates of 137 Cs emissions from the Fukushima NPP are extremely uncertain, therefore, the distribution of
137 Cs in the environment is poorly constrained. Here, we estimate
total 137 Cs deposition by integrating daily observations of 137 Cs
deposition in each prefecture in Japan with relative deposition distribution patterns from a Lagrangian particle dispersion model,
FLEXPART. We show that 137 Cs strongly contaminated the soils inlarge areas of eastern and northeastern Japan, whereas westernJapan was sheltered by mountain ranges. The soils around Fukushima NPP and neighboring prefectures have been extensively contaminated with depositions of more than 100,000 and 10,000 MBq
km−2 , respectively. Total 137 Cs depositions over two domains: (i) theJapan Islands and the surrounding ocean (130–150 °E and 30–46 °N)
and, (ii) the Japan Islands, were estimated to be more than 5.6
and 1.0 PBq, respectively. We hope our 137 Cs deposition maps will
help to coordinate decontamination efforts and plan regulatory
measures in Japan.

ENVIRONMENTALSCIENCES

Edited by James E. Hansen, Goddard Institute for Space Studies, New York, NY, and approved October 5, 2011 (received for review July 25, 2011)

Fig. 1. Cesium-137 deposition maps. (A) Relative deposition contributions between March 11 and 19, showing the areas potentially effected by 137 Cs before
the start of measurements. The sums of the depositions during the period were divided by the maximum deposition in the accumulated field. (B) The same as inA, but for March 20–April 19. (C) An example of estimated daily deposition of 137 Cs on March 21. Squares in black denote the observation locations in eachprefecture (Table S2). (D) Daily accumulated rainfall on March 21 by TRMM.

From March 20, we can estimate 137 Cs deposition fields overJapan more reliably because daily observations have been madein most Japanese prefectures (17) (Table S2). For days fromMarch 20, we create deposition estimates using scaled model
values [hereafter called, deposition ratio (DR); see Materials
and Methods] from a constant source term simulation in conjunction with the measurements from the MEXTobservation network(17). An example of a three-hourly DR animation map is available in Movie S1. For periods when the simulated daily DR value
is close to zero yet deposition is observed, a threshold factor isemployed in Eq. 2 (Materials and Methods and SI Text). In suchcases, a minimum positive deposition ratio value, hereafter called
DR threshold (DRT), needs to be used to derive the scaling(Materials and Methods and SI Text). The choice of this DRT
is subjective and also effects the estimated deposition amountin our method. After performing comparisons with the observed
depositions in each prefecture (SI Text, Fig. S2, and Table S3), we
used a DRT of 0.005 for the best guess estimate of daily deposition between March 20 and April 19 (Movie S2) but we also report derived deposition estimates for other DRT values.
The simulated distribution of 137 Cs deposition is closely linked
to precipitation as shown for the case of March 21 (Fig. 1 C
and D). The highest deposition values downwind of the NPP areclearly aligned with satellite-observed precipitation by tropicalrainfall measuring mission (TRMM, 3B42 V6 product) in afrontal rain band, which causes washout of the radionuclides(Movie S2 and S3). Comparison of daily observed precipitation
fields with the estimated deposition maps shows that 137 Cs
deposition is simulated mainly when frontal rain bands pass overJapan (Movie S2). It was reported previously (19) that around
90% of the total deposition of 137 Cs occurs with precipitation.
Thus, the general agreement between observed precipitation andsimulated deposition confirms that the model captures the main
deposition events, which is also consistent with the discussion
from the study by using a regional chemical transport model (8).
The daily 137 Cs deposition was frequently detected at observatories (17) in the eastern and northeastern prefectures of Japan
from March 20. Furthermore, large increases of atmosphericradioactivity in the prefectures around Fukushima were observed(20) on March 22 (Fig. S3), probably reflecting ground shine
2 of 5 ∣www.pnas.org/cgi/doi/10.1073/pnas.1112058108

radiation from the radionuclides deposited during the rainfall
event on March 21 (Fig. 1 C and D).
Maps of the total 137 Cs deposition between March 20 and April
19 are shown in Fig. 2A. As a general characteristic, most of theeastern parts of Japan were effected by a total 137 Cs deposition of
more than 1;000 MBq km−2 . Our estimates show that the areaaround NPP in Fukushima, secondarily effected areas (Miyagi
and Ibaraki prefectures), and other effected areas (Iwate, Yamagata, Tochigi, and Chiba prefectures) had 137 Cs depositions ofmore than 100,000, 25,000, and 10;000 MBq km−2 , respectively.
Airborne and ground-based survey measurements jointly carriedout by MEXT and the US Department of Energy (DOE) (21)show high 137 Cs deposition amounts were observed northwestward and up to a distance of 80 km from Fukushima NPP. It
was estimated from the first measurement that by April 29, morethan 600;000 MBq km−2 had been deposited in the area, whichis greater than our estimate of less than 500;000 MBq km−2
(Fig. 2A), yet well within the range of uncertainty of our method(Fig. S4). Furthermore, because no observations on daily deposition were available before March 27 in Fukushima City (Fig. 2B)
and no daily deposition observations around NPP, our estimatesare expected to underestimate the total deposition in the vicinityof the NPP. In conducting sensitivity studies with DRT, our estimates provide values on the similar order of the MEXT/DOE
observations using a DRT value of 0.001 (Fig. S4).
Using an approximate relationship between 137 Cs deposition
and its topsoil concentration (22) [conversion coefficient (CC)of 53  15 kg m−2 ] (Fig. S5), we converted the estimated depositions into topsoil concentrations (Fig. 3, Movie S4, and Table S4).
We compared 137 Cs concentrations in the topsoil derived fromboth observed 137 Cs deposition values (17) and from our estimates, with direct measurements of 137 Cs concentrations in soils
and grasses with a soil-to-grass transfer factor of 0.13 (23) (SI Text
and Table S1) (Fig. 4). The MEXT deposition-based soil contamination tends to be lower than the soil- and grass-based samplings
because of the latter including the time period just after the NPP
accident. Our scaled model deposition fields agree well with boththe point measurements including the MEXT areal surveys andother available observations (Fig. 4), generally falling in the range
between the two techniques. If the soil contaminations closer to
Yasunari et al.

A
1e+06
500,000
250,000
100,000
50,00025,00010,000
5,000
2,500
1,000
500
250
100
50

40,00030,00020,000Fig. 3. The 137 Cs concentration in soil. We used DRT of 0.001 and CC of
53 kg m−2 . Outputs with 0.2° × 0.2° were interpolated to finer resolution
using cubic interpolation. The Merged IBCAO/ETOPO5 Global Topographic
Data Product (25) was used to mask out ocean area below 0 m above sea
level (a.s.l.).

10,000Niigata

Kanagawa

Tokyo

Chiba

SaitamaGunma

Tochigi

Ibaraki

Fukushima

Yamagata

Akita

Miyagi

Iwate

Aomori

Hokkaido

Selected prefectures

Total deposition of 137 Cs. (A) Gridded total 137 Cs deposition values

1.0E+03
1.0E+02
1.0E+01
1.0E+00
1.0E-01

Selected prefectures

Fukushima

Yamagata

Akita

MiyagiIwate

1.0E-02

1.0E+04
1.0E+03
1.0E+02
1.0E+01
1.0E+00
Niigata

Kanagawa

Selected prefectures

Tokyo

Chiba

SaitamaGunma

1.0E-01

Tochigi

Yasunari et al.

1.0E+04

AomoriDiscussion
There are many important agricultural regions in Japan. In
Japan, the limit for the sum of 134 Cs and 137 Cs concentrations(as total cesium) in soil is 5;000 Bq kg−1 under the Food Sanitation Law (24). Considering that about half (2;500 Bq kg−1 ) of
the total radioactive cesium deposition is due to 137 Cs, the east
Fukushima prefecture exceeded this limit and some neighboring
prefectures such as Miyagi, Tochigi, and Ibaraki are partially close

B

Case 0.1 estimate
Case 0.01 estimate
Case 0.005 estimate
Obs. from soil or grass samplings

1.0E+05

Ibarakithe Fukushima NPP are included, the observed soil contamination has a wider range of 190–310;000 Bq kg−1 with mean andmedian values of 20,575 and 5;750 Bq kg−1 , respectively. The
observations in Fukushima City give a lower range of 620–
21;000 Bq kg−1 (mean, 5;969 Bq kg−1 ; median, 4;200 Bq kg−1 ).
Our estimated distributions were within the range of the observations around the NPP, but close to the lower bound (Fig. 3 andFig. 4A). From the sporadic observations (7, 21) (Table S1) andour estimate in this study, Fukushima prefecture as a whole ishighly contaminated, especially to the northwest of the NPP, withsoil 137 Cs concentrations above 1;000 Bq kg−1 throughout theeast prefecture from our estimate (Fig. 3). Neighboring prefectures are less contaminated, but 137 Cs concentrations there arestill above 250 Bq kg−1 in most of the areas. Thus our approachprovides a necessary estimate of deposition beyond the immediate area of the Fukushima prefecture, where monitoring activities
are less intensive.

Estimated from depositions (MEXT)
Case 0.05 estimate
Case 0.007 estimate
Case 0.001 estimate

Hokkaido

Fig. 2.
for the period March 20–April 19 using our reference DRT value of 0.005.
Outputs with 0.2° × 0.2° were interpolated to finer grid using cubic interpolation. Squares in black denote the observation locations in each prefecture (Table S2). (B) Comparisons between total observed depositions for theperiod March 20–April 19 and estimates at the grid point of each observatory
location (Table S2) in the selected prefectures, using different DRT values
to derive the scaling factor for the model output. Orange, gray, and black boxes
denote no observation (Miyagi) and missing observations (Yamagata, between
March 29 and April 3; Fukushima, before March 27 and April 4), respectively.

A

Cs137 concentration-1
in soil [Bq kg ]0

Fig. 4. Atmospheric, soil, and grass observation-based Cs-137 concentrations, and estimates based on the scaled model output and for different
DRT values used for the scaling. (A) Comparisons in northern prefectures.
Aomori and Miyagi prefectures had no 137 Cs detections on the daily deposition data and no measurements, respectively. The minimum value in Yamagata prefecture is no detection and no lower error bar is shown. (B) The sameas in A, but around Kanto area. Lower and upper error bars denote minimum
and maximum concentrations using CC of 68 and 38 kg m−2 based on Fig. S5,
respectively. Orange, gray, and black boxes denote no observation (Miyagi)
and missing observations (Yamagata, between March 29 and April 3; Fukushima, before March 27 and April 4), respectively. A soil-to-grass transfer factorof 0.13 (23) was used to convert grass to soil contamination. For Fukushima
prefecture, only the soil observations in Fukushima City were used, excluding
other observations close to the Fukushima NPP. The data source for the comparisons are summarized in Table S1.
PNAS Early Edition ∣3 of 5ENVIRONMENTALSCIENCES

Sum of observations
Case 0.1 estimate
Case 0.05 estimate
Case 0.01 estimate
Case 0.007 estimate
Case 0.005 estimate
Case 0.001 estimate

50,000Cs137 concentration-1
in soil [Bq kg ]Total Cs137 deposition-2[MBq km ]B 60,000ENVIRONMENTALSCIENCES0

to the limit under our upper bound estimate (Movie S4) and,
therefore, local-scale exceedance is likely given the strong spatial
variability of 137 Cs deposition. For those three prefectures,detailed soil sampling is recommended in the near future. Estimated and observed contaminations in the western parts of Japan
were not as serious, even though some prefectures were likely
effected to some extent (Fig. 3, Movie S4, and Table S4). Concentrations in these areas are below 25 Bq kg−1 , which is far
below the threshold for farming. However, we strongly recommend each prefecture to quickly carry out some supplementary
soil samplings at city levels to validate our estimates even if theconcentrations are low.
The relatively low contamination levels over western Japan canbe well explained by the Japanese topography. The eastern andnortheastern parts of Japan are surrounded by mountain ranges
such as the Kanto, Echigo, and Ohwu mountain ranges (Fig. S6)(25), which, to a large extent, sheltered the northwestern andwestern parts of Japan from the dispersion of radioactive material. It is worth noting, however, that relatively higher contamination levels can be seen over the Hida, Chugoku, and Shikoku
mountain ranges (Fig. 3, Fig. S6, and Movie S4), probably due toorographic enhancement of precipitation and, thus, wet deposition of 137 Cs. In Hokkaido, to the north of Japan’s main island,
both lower altitude and higher altitudes such as the Yubari and
Hidaka mountain ranges are effected by 137 Cs deposition, partially due to direct transport from the Fukushima NPP via the
Pacific Ocean as shown in Movies S1 and S2 and also as simulatedby another atmospheric transport model (12).
We estimate that a total of more than 5.6 and 1.0 PBq 137 Cs
were deposited over Japan and the surrounding ocean (130–150 °E and 30–46 °N), and the Japan Islands in this domain only,
respectively (Fig. 2A). Although the estimate for the larger domain is quite uncertain because it is constrained only by measurements in Japan, these numbers are consistent with a suspected
total release of about 12 PBq 137 Cs (2). Most of the deposition
occurred over the Pacific Ocean, yet soil concentrations of 137 Cs
are above 100 Bq kg−1 over large areas of eastern Japan (Fig. 3).
According to our results, food production in eastern Fukushima
prefecture is likely severely impaired by the 137 Cs loads of morethan 2;500 Bq kg−1 (upper limit of farming) and also partially impacted in neighboring provinces such as Iwate, Miyagi, Yamagata,
Niigata, Tochigi, Ibaraki, and Chiba, where values of more than
250 Bq kg−1 cannot be excluded (Fig. 3 and Movie S4). Noticealso that our estimates are based on a transport model driven withmeteorological analysis data from a global model. Such a modelcannot fully capture all complexities of the regional wind fieldover Japan and, in particular, does not resolve the high spatiotemporal variability of precipitation. Therefore, we expect the true soil
contamination across Japan to be considerably more variable thanin our estimate. Even in regions where we find relatively low soil
contamination levels, hot spots with high concentrations (e.g., due
to convective rain fall, orographic enhancement of rainfall, or
fine-grain soil flow by rainwater on the ground) may be possible.
In contrast, relatively clean patches may also be present in areas
with high overall contamination levels. Despite these shortcomings, we expect our results to be useful for regulatory measures andfor guiding monitoring activities toward areas with expected high137
Cs burdens. We hope this study will contribute to understanding
the contamination issue in Japan.
Materials and Methods
Observations of Cesium-137 Deposition and Concentration in Soil in each
Prefecture. From March 18, MEXT has been observing daily radioactivity levels
in deposition in most of the prefecture (17). The exact coordinates of thesampling locations were individually accessible through our contacts to MEXT
(Table S2). The deposition data between March 18 and 19 were not used inour estimate because of no depositions at observatories from the modeled
DR maps as mentioned in the main text. In some prefectures, data were missing or unavailable [Miyagi, March 18–April 19 (completely no observations);
4 of 5 ∣www.pnas.org/cgi/doi/10.1073/pnas.1112058108

Yamagata, March 29–April 3; Fukushima, March 18–March 26 and April 4;
Gifu, March 24, 25, 27, 28, and 30; Nara, March 18–21 and April 15–18; Oita,
March 22–26).
FLEXPART and Estimated 137 Cs Deposition. FLEXPART (9) is a Lagrangianparticle dispersion model simulating transport, diffusion, dry and wet deposition, and radioactive decay of radioactive materials such as 131 I, 137 Cs,
and 133 Xe (See http://transport.nilu.no for further details on FLEXPART). In
this study, continuous emission from the Fukushima Daiichi NPP was assumed
after 1800 hours coordinated universal time (UTC) on March 11, 2011. The
simulation ended at 0000 hours UTC on April 20. FLEXPART was forced with
the European Center for Medium-Range Weather Forecasts (ECMWF) operational analysis data with a global resolution of 1° × 1° and 0.18° × 0.18° for
120–168 °E and 25–50 °N. The output had a resolution of 0.2° × 0.2° and wasrecorded every 3 h (SI Text).
For each day, we first normalized the modeled daily accumulated
deposition in each grid cell with the maximum accumulated deposition value
for the model domain, hereafter called daily deposition ratio (DDR) maps:DDRðx;yÞ ¼

T1FPDðx;yÞi ;∑FPDmaxi[1]i¼1

where FPDðx;yÞi is the three-hourly modeled deposition in grid cell ðx;yÞ and
FPDmax is the maximum daily deposition value found in the entire model
domain. T is the number of model output timesteps per day (T ¼ 8). Daily
gridded deposition values of 137 Cs were estimated by scaling the DDR map
with available daily observed 137 Cs depositions in each prefecture by MEXT
(17) by the following equation:Depoðx;yÞ ¼

DDRðx;yÞ N DepoiðObs:Þ
;∑ DDRiðObs:LocÞ
N

[2]

i¼1

where Depoðx;yÞ is the estimated daily total 137 Cs deposition in grid cell ðx;yÞ,DepoiðObs:Þ is the observed 137 Cs deposition at location i (Table S2), N ≤ 47
is the number of available counts on a certain day in Japan’s 47 prefectures,DDRiðObs:Loc:Þ is the DDRðx;yÞ in the grid point where 137 Cs deposition wasobserved, and DDRðx;yÞ is the DDR in grid cell ðx;yÞ. Only the cases with boththe observed deposition and the DDRiðObs:Loc:Þ not equal to zero at each observatory location were used for counting N on each day. Because the
DepoiðObs:Þ to DDRiðObs:Loc:Þ scaling factor in Eq. 2 becomes infinite when
the simulated DDR value is close to zero but deposition is actually observed,
a minimum positive DDR value, DRT, needs to be used to derive the scaling.
Several DRTs of 0.001, 0.005, 0.007, 0.01, 0.05, and 0.1 for DDRiðObs:Loc:Þ within
the simulation domain on each day were used to avoid abnormally highDepoðx;yÞ values due to dividing by small values (SI Text). If DDRiðObs:Loc:Þ ata certain grid point was less than a DRT value, DDRiðObs:Loc:Þ was set to the
DRT value.
For computing total 137 Cs deposition between March 20 and April 19, we
corrected all values to April 19 using a half-life of 137 Cs of 30.1 y (4). The sumof all the daily observed or estimated 137 Cs depositions is the total 137 Cs deposition (Fig. 2 and Fig. S4A).
Observations on 137 Cs Concentrations in Soil and Grass. For comparison with
our estimates, measurements of 137 Cs concentrations in soil or grass wereused (SI Text and Table S1). Mean transfer factor of soil-to-grass of 0.13, which
was obtained from the observations in Japanese soil and grass, was used toconvert grass contamination to soil equivalent contamination (grass contamination divided by the transfer factor) (23). The times and locations of thosesamplings varied. To cover the time period of our study (March 20–April 19),
we also used some soil samples from later dates, but we did not use any data
after May 19. Notice also that the soil samples were also effected by 137 Cs
deposition before March 20 (SI Text). Some observatories measured total
cesium concentration including both 137 Cs and 134 Cs. In that case, we assumed
that half of the total Cs was 137 Cs.
To convert the 137 Cs deposition into soil concentration, soil depth anddensity information are needed. However, it is currently difficult to obtain
this information across all of Japan. There is an empirical relationship on
the ratio between 137 Cs concentration and deposition from 0 to 5 cm soil,
paddy soil, and field soil samples (22) (Fig. S5). We considered the mean valueof the ratio as CC of 53  15 kg m−2 reflecting the 5-cm depth soil information and its density. Our estimated CC value is close to the CC value of
65 kg m−2 assumed by MEXT (26) with 5-cm soil and a soil density of
1;300 kg m−3 .

Yasunari et al.

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http://www.mext.go.jp/english/incident/1304080.htm.
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and the US Department of Energy (DOE) (2011) Results of Airborne Monitoring by
the Ministry of Education, Culture, Sports, Science, and Technology and the US Department of Energy., Available at: http://www.mext.go.jp/english/incident/1304796.htm.
22. Japanese Ministry of Education, Culture, Sports, Science, and Technology (MEXT)(2011) Environmental radiation database., Available at: http://search.kankyohoshano.go.jp/servlet/search.top.
23. Tsukada H, Hisamatsu S, Inaba J (2003) Transfer of 137 Cs and stable Cs in soil-tograss-milk pathway in Aomori., Japan. J Radioanal Nucl Chem 255:455–458.
24. Ministry of Agriculture, Forestry, and Fisheries (MAFF) (2011) A point of view onplanting rice plant., Available at: http://www.maff.go.jp/j/kanbo/joho/saigai/pdf/
ine_sakutuke.pdf (in Japanese).
25. Holland DM (2000) Merged IBCAO/ETOPO5 global topographic data product.
National Geophysical Data Center (NGDC), Boulder Colorado, Available at: http://
efdl.cims.nyu.edu/project_aomip/forcing_data/topography/merged/overview.html.
26. Japanese Ministry of Education, Culture, Sports, Science, and Technology (MEXT)(2011) Calculation results and basis regarding internal exposure studied in summarizing the tentative approach., Available at: http://www.mext.go.jp/component/english/__icsFiles/afieldfile/2011/05/27/1306601_0512_1.pdf.

Yasunari et al.

PNAS Early Edition ∣5 of 5ENVIRONMENTALSCIENCESACKNOWLEDGMENTS. Useful comments were obtained from K.-M. Kim
Morgan State University (MSU)/Goddard Earth Sciences Technology andResearch (GESTAR) and Q. Tan Universities Space Research Association(USRA)/GESTAR. Daily deposition of radioactive materials, atmosphericradiations, and concentrations in soil used in this study were observed by
the Ministry of Education, Culture, Sports, Science, and Technology (MEXT),

each prefecture in Japan, the Ministry of Agriculture, Forestry and Fisheries(MAFF), and Prof. Yamazaki et al. at Kinki University. We also appreciate all
the people working on these measurements. The tropical rainfall measuring
mission (TRMM, 3B42 V6 product) data used in this study were acquired using
the Goddard Earth Sciences (GES)-Data and Information Services Center(DISC) as part of the National Aeronautics and Space Administration’s
GES-DISC. The Grid Analysis and Display System (GrADS) was use for plotting.
This paper was partially supported by Universities Space Research Association.

ENVIRONMENTALSCIENCES

Dividing our estimated deposition (MBq km−2 ¼ Bq m−2 ) by the CCs, we
empirically obtained the mean 137 Cs concentration in soil (Bq kg−1 ).

Supporting Information
Yasunari et al. 10.1073/pnas.1112058108
SI Text
Data of Japanese Prefecture Boundaries. The data of Japanese

prefecture boundaries for plotting Figs. 1–3, and Figs. S1, S4,
and S6 and Movies S1–S4 were obtained from the following web
site: http://www.geocities.jp/ne_o_t/GMT-USE/use-medium/ken.txt.
Details of Dispersion Model Setup. Cesium-137 was simulated using
FLEXPART (1) as an aerosol with lognormal size distribution(0.6 μm mean diameter and standard deviation of 0.3). Scavenging coefficients were set to A ¼ 10−4 s−1 for precipitation of
1 mm h−1 and a dependency on precipitation rate of B ¼ 0.80
(see ref. 1 for an explanation of these parameters). The source
strength was constant throughout the period of simulation. Preliminary comparisons with global radionuclide monitoring datasuggests that FLEXPART’s atmospheric 137 Cs concentrations
drop off too quickly with distance, likely because of an overestimation of wet deposition. Given that FLEXPART deposition
fields are not used in terms of absolute numbers here, not impacting our results strongly. However, proximal deposition values may
tend to be too high, whereas distal deposition values may tend to
be too low.
Deposition Ratio (DR). Although FLEXPART (1) can treat thetransport and deposition process of 137 Cs, constant emission fromthe Fukushima Daiichi NPP was assumed similar to some otherstudies of this event (2–8) because of missing emission source
information. Therefore, using direct deposition fields fromFLEXPART is not reliable and we computed relative 137 Cs deposition distributions by normalizing the FLEXPART output
by the maximum values within the output domain. The normalized output is DR and shows the potential areas of relatively high
137 Cs deposition. An example of three-hourly DR maps areshown in Movie S1. In the daily DR calculation, although the effect is negligible, we corrected negative deposition values to zerodeposition because of the decay process after a little depositionon the ground. The deposition outputs in each time interval are
the difference between two subsequent accumulated fields.

Note on DRT. Our estimates are an observation-based reconstruction of the 137 Cs deposition distribution for all of Japan. Although
our method is sensitive to the choice of DRT, we tested various
DRT values to determine realistic deposition ranges (Fig. S2and Table S3). The DRT values were determined covering
0.1–10% (0.001, 0.005, 0.007, 0.01, 0.05, and 0.1) of the daily
DR maximum (DR ¼ 1). To estimate 137 Cs deposition between
March 20 and April 19, we concluded that DRT values between
0.005 and 0.01 best explain the observed deposition in main prefectures because the estimates using DRT of 0.001 and 0.05–0.1
showed extremely high RMSEs in some prefectures (Fig. S2).
From the viewpoint of precautionary principle, overestimates
may be better than underestimates and, thus, we adopted DRT ¼
0.005 for our best guess estimates of the deposition distribution
between March 20 and April 19. In most prefectures of westernJapan, 137 Cs depositions were not detected at the locations of theobservatories during this period. Our estimates using
DRT ¼ 0.005 resulted in deposition of less than 50 MBq km−2
in many prefectures of western Japan (Table S3), which roughly
represents the uncertainty of our method. Therefore, it seems entirely possible that western Japan was not at all effected by noticeable amounts of 137 Cs deposition. Comparisons of future
observations with our estimates are essential for a more robust
assessment.
Note on Soil Contamination. It is worthwhile to note that the casein each prefecture and the estimated daily deposition were also
computed using the observations on available days between March
20 and April 19 (Fig. S2). When using DR threshold ðDRTÞ ¼
0.005 during the period, the RMSEs of estimated 137 Cs deposition
were less than 1;232.3 MBq km−2 (Fig. S2). Miyagi prefecture had
no observation on the deposition during the period and the RMSE
could have not estimated. Yamagata and Fukushima prefectures
had missing data and these two important observatories probably
do not show actual total depositions and underestimated realdeposition amounts between March 20 and April 19 (Fig. 2B).

for DRT ¼ 0.001 is closer to the direct soil observations thanresults for DRT ¼ 0.005 (Fig. 4), our best guess estimate for the
total 137 Cs deposition between March 20 and April 19 (Fig. 2A).
The estimates on the soil contamination from daily deposition
observations also showed lower concentrations than those of direct soil observations because the time period in our simulationand observation-based estimate in deposition did not include theperiod before March 20 and sometimes after April 19, whereas
soil samples include the information before March 20 including
the period just after the nuclear power plant accident and also
after April 19 in some samples as mentioned in the main text.
Hence, it is reasonable to say that 137 Cs concentration from direct
soil samples did show some higher concentrations of 137 Cs thanour deposition-based estimates for the period between March 20
and April 19. In Fukushima City where deposition observation
was carried out, the estimated 137 Cs concentration in soil using
DRT of 0.001 was closest to the observations but still was somewhat underestimated (Fig. 4A). Although our estimate is limited
to the period between March 20 and April 19, the estimated soil
contamination on 137 Cs using DRT of 0.001 are relatively well reconstructed compared to the sporadic soil observations beyond
the time period, probably considering the contributions to the total 137 Cs depositions before March 20 (Fig. 4). This discussion issimilar to the one for the deposition in the main text.

1. Stohl A, Forster C, Frank A, Seibert P, Wotawa G (2005) The Lagrangian particle
dispersion model FLEXPART, version 6.2. Atmos Chem Phys 5:2461–2474.
2. Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT)(2011) System for prediction of environment emergency dose information (SPEEDI).
Available at: http://www.nsc.go.jp/mext_speedi/index.html (in Japanese).
3. Japan Meteorological Agency (2011) Environmental emergency response. Available
at: http://www.jma.go.jp/jma/kokusai/eer_list.html.
4. Takemura T. et al. (2011) A numerical simulation of global transport of atmosphericparticles emitted from the Fukushima Daiichi Nuclear Power Plant. SOLA 7:101–104.
5. Visible Information Center Inc. (2011) Simulation on 137 Cs deposition due to theemission from Fukushima Daiichi Nuclear Plant. Available at: http://www.vic.jp/
fukushima/global/global-e.html.

6. Japan Atomic Energy Agency (2011) A trial calculation on total amount of radiation
exposure during 2 month after the accident of Fukushima Daiichi Nuclear Power
Plant in TEPCO. Available at: http://www.jaea.go.jp/jishin/kaisetsu03/kaisetsu03.htm(in Japanese).
7. The EURAD project (2011) Potential dispersion of the radioactive cloud over thenorthern hemisphere. Available at: http://www.eurad.uni-koeln.de/index_e.html.
8. Deutscher Wetterdienst (2011) Deutscher Wetterdienst zu den Folgen der FukushimaKatastrophe Wetter sorgt für starke Verdünnung der radioaktiven Konzentration. Available at: http://www.dwd.de/bvbw/generator/DWDWWW/Content/Presse/
Pressemitteilungen/2011/20110323__Japan,templateId=raw,property=publicationFile.pdf/20110323_Japan.pdf.

Note on the Root Mean Square Errors (RMSEs) of the Estimated 137 Cs
Depositions. The RMSEs between observed daily 137 Cs deposition

Yasunari et al. www.pnas.org/cgi/doi/10.1073/pnas.1112058108

1 of 8RMSE [MBq km-2]

Fig. S1. Daily DR over Japan (A) on March 18 and (B) on March 19. The DR data with 0.2° × 0.2° were interpolated into finer resolution using cubic
interpolation.
4,000

Case 0.1 - Obs.

3,500

Case 0.05 - Obs.
Case 0.01 - Obs.

3,000

Case 0.007 - Obs.

2,500

Case 0.005 - Obs.

2,000

Case 0.001 - Obs.

1,500
1,000
500
Niigata

Kanagawa

Tokyo

Chiba

SaitamaGunma

Tochigi

Ibaraki

Fukushima

Yamagata

Akita

Miyagi

Iwate

Aomori

Hokkaido0

Selected prefectures

Fig. S2. RMSEs for the selected prefectures between observation-based total deposition on 137 Cs and the estimates from this study between March 20 and
April 19. Orange, gray, and black boxes denote no observation and missing observations (Yamagata, between March 29 and April 3; Fukushima, before March
27 and April 4), respectively.
4.5

Ibaraki
Yamagata
Tochigi
Gunma
Saitama
Chiba
Tokyo
Kanagawa
Fukushima (Right scale)

Daily mean radiation [µSv h-1]

0.400
0.350
0.300
0.250
0.200

4.0
3.5
3.0
2.5
2.0

0.150

1.5

0.100

1.0

0.050

0.5

0.000

0.0

Daily mean radiation [µSv h-1]

0.450

6/25
6/20
6/15
6/10
6/5
5/31
5/26
5/21
5/16
5/11
5/6
5/1
4/26
4/21
4/16
4/11
4/6
4/1
3/27
3/22
3/17
3/12

Date

Fig. S3. Daily mean atmospheric radiation amount observed by Ministry of Education, Culture, Sports, Science, and Technology (MEXT) (1) in selected
prefectures around Fukushima. For the early period, Fukushima did not observe the atmospheric radiation and data were missing.
1 Japanese Ministry of Education, Culture, Sports, Science, and Technology (MEXT) (2011) Readings of environmental radioactivity level by prefecture. Available at: http://www.mext.go.jp/english/incident/1304080.htm.

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Fig. S4. Comparison between estimates of total 137 Cs deposition using different DRT. (A) Estimated total 137 Cs deposition using DRT of 0.001. (B) Increase of
estimated total 137 Cs deposition from using DRT of 0.005 to 0.001. Squares in black denote the locations of the observatories in each prefecture (Table S2).
Outputs with 0.2° × 0.2° in the daily estimates were interpolated into finer resolution using cubic interpolation.
Soil concentration [Bq kg-1]
Deposition onto surface [MBq km-2]
Conversion Coefficient (Right scale)

100

1,000

75

100

50

10

25

1

0

kg m-2

Bq kg-1 or MBq km-2

10,000

2008

2005

2002

2000

1997

1994

1991

1989

1986

1983

1980

1978

1975

1972

1970

Sampling Year

Fig. S5. Relationship between 137 Cs deposition and concentration in soil for determining conversion coefficient (CC). The historical observed data were obtained from the environmental radiation database (1) maintained by the Japan Chemical Analysis Center. The observed data at the same location and on thesame day in different units of Bq kg−1 (top 5 cm soil) and MBq km−2 (Bq m−2 ) are assumed to be the same sample and used the data for calculating the CC(kg m−2 ). Solid and dotted lines denote mean CC value and its standard deviations, respectively.
1 Japanese Ministry of Education, Culture, Sports, Science, and Technology (MEXT) (2011). Environmental radiation database. Available at: http://search.kankyo-hoshano.go.jp/servlet/
search.top.

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Fig. S6. Topography map over Japan. The Merged IBCAO/ETOPO5 Global Topographic Data Product (1) was used. The names on the mountain ranges are also
shown.
1 Holland, DM (2000) Merged IBCAO/ETOPO5 Global Topographic Data Product. National Geophysical Data Center (NGDC), Boulder Colorado. Available at: http://efdl.cims.nyu.edu/
project_aomip/forcing_data/topography/merged/overview.html.

Movie S1. Three-hourly DR over Japan, 0.2° × 0.2° outputs were interpolated into finer resolution using cubic interpolation.
Movie S1 (MOV)

Movie S2. Daily estimate of total 137 Cs deposition using DRT of 0.005. Outputs with 0.2° × 0.2° in the daily estimates were interpolated into finer resolution
using cubic interpolation. Squares in gray and black denote observatories (Table S2) that did not detect 137 Cs deposition (unavailable, missing, or below detection limit) or daily DR ¼ 0, and detected the depositions used for making the estimation map for the deposition, respectively.
Movie S2 (MOV)

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Movie S3. Daily accumulated precipitation by tropical rainfall measuring mission (TRMM, 3B42 V6 product) satellite data.
Movie S3 (MOV)

Movie S4. Estimated 137 Cs concentration range in soil using DRT of 0.001 and conversion coefficient (CC) of 38, 53, and 68 kg m−2 over Japan. CCs of 38, 53,
and 68 kg m−2 correspond to −1σ, mean value, and þ1σ in Fig. S5, respectively. Outputs 0.2° × 0.2° were interpolated into finer resolution using cubic interpolation. The Merged IBCAO/ETOPO5 Global Topographic Data Product (1) was used to mask out ocean area below 0 m above sea level (a.s.l.).
1 Holland, DM (2000) Merged IBCAO/ETOPO5 Global Topographic Data Product. National Geophysical Data Center (NGDC), Boulder Colorado. Available at: http://efdl.cims.nyu.edu/
project_aomip/forcing_data/topography/merged/overview.html.

Movie S4 (MOV)

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Table S1. Data sources for observed 137 Cs concentrations in soil or grass in selected prefectures
SampleSample type

Hokkaido
Aomori
Iwate
Miyagi
Akita
Yamagata

April 18, 19, 25
May 18May 11
May 11, 18, 19
May 14
April 2, 18, 22

Soil
Grass
Grass
Grass
Grass
Soil

Fukushima*

April 14
April 20†

School soil
Soil

IbarakiTochigi
Gunma
Saitama‡
Chiba
Tokyo¶

April 8
April 8
April 1, 2April 22
April 21§
March 31
April 10, 16

Soil
Soil
Soil
Grass
Grass
Soil
Soil

Kanagawa
NiigataMarch 25, 30 and May 16, 17 Soil
April 11
Soil

Sourcehttp://www.pref.hokkaido.lg.jp/ns/gjf/dojomonitoring230428.pdf
http://www.pref.aomori.lg.jp/soshiki/nourin/chikusan/files/grass-radi.pdf
http://www.pref.iwate.jp/download.rbz?cmd=50&cd=32320&tg=3
http://www.pref.miyagi.jp/tikusanka/0400-souchishiryou/110525pr2.pdf
http://www.pref.akita.lg.jp/www/contents/1305379159624/files/kekka.pdf
http://www.pref.yamagata.jp/ou/norinsuisan/140027/hosya-press_release/0506dojokekka.pdf
http://www.pref.yamagata.jp/ou/seikatsukankyo/050014/radiation/dojou.pdf
http://radioactivity.mext.go.jp/en/1380/2011/04/1305394_0419_1.pdf
http://radioactivity.mext.go.jp/en/monitoring_around_FukushimaNPP_soil_monitoring/2011/05/
1306622_053110.pdf
http://www.pref.ibaraki.jp/important/20110311eq/20110408_20/files/20110408_20a.pdf
http://www.pref.tochigi.lg.jp/kinkyu/houshanou_suiden.html
http://www.pref.gunma.jp/houdou/f1000020.html
http://www.maff.go.jp/j/kanbo/joho/saigai/syouhi/bokusou_kensa.html#saitama
http://www.maff.go.jp/j/kanbo/joho/saigai/syouhi/bokusou_kensa.html#tiba
http://www.pref.chiba.lg.jp/annou/h23touhoku/suidendojo.html
http://prayforjp.exblog.jp/13594347
http://savechild.net/wp-content/uploads/2011/05/300467512.jpg
http://www.pref.kanagawa.jp/cnt/f300508/
http://www.bousai.pref.niigata.jp/contents/dbps_data/_material_/localhost/704.pdf

Observed by prefecture, unless where indicated.
*Observed by Ministry of Education, Culture, Sports, Science, and Technology (MEXT).
Samples picked up before April 20. In the samples, we excluded the data with *3 of top 5-mm soil sample.
‡
Observed by Ministry of Agriculture, Forestry, and Fisheries (MAFF). Only April 22 samples were used.
§
Observed by MAFF. Only April 21 samples were used.
¶
Observed by Prof. Yamazaki et al. at Kinki University and published in the Asahi newspaper on May 15. These sources are an example of data available in the
Asahi newspaper.
†

Table S2. Observatory locations in each prefecture
Prefecture

Grid box X

Grid box Y

Hokkaido
Aomori
Iwate
Miyagi
Akita
Yamagata
Fukushima
IbarakiTochigi
Gunma
Saitama
Chiba
Tokyo
Kanagawa
NiigataToyamaIshikawa
Fukui
Yamanashi
NaganoGifu
Shizuoka
Aichi
Mie
Shiga
Kyoto
Osaka
Hyogo
Nara
Wakayama
Tottori
Shimane
Okayama
Hiroshima
Yamaguchi
Tokushima
Kagawa
Ehime
Kochi

107
104
106
105
101
102
103
103
100
96
99
101
99
97
95
86
84
82
93
91
85
91
85
83
80
79
78
76
80
76
70
66
70
63
58
73
71
63
68

91
80
74
67
74
67
64
57
59
58
55
53
54
52
65
59
58
56
54
59
53
49
52
50
50
50
49
49
49
47
53
53
48
48
46
46
47
43
43

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Prefecture

Grid box X

Grid box Y

Fukuoka
Saga
Nagasaki
Kumamoto
Oita
MiyazakiKagoshima
Okinawa

53
52
50
54
59
58
53
39

43
42
40
39
41
35
33
6

Grid numbers of X and Y correspond to the grid boxes of the observatories
ðX;YÞ within 0.2° × 0.2° horizontal resolution domain starting from 120 °E toeastward and from 25 °N to northward. Although Miyagi did not observe any
deposition during the time period in this paper, the location for atmosphericradiation measurement in Miyagi was temporarily put here for our
calculation process.

Table S3. Comparisons of 137 Cs depositions at each observatory location in each prefecture between March 20 and April 19(MBq km−2 )Sum of observations
Case 0.1 estimate
Case 0.05 estimate
Case 0.01 estimate
Case 0.007 estimate
Case 0.005 estimate
Case 0.001 estimate(MBq km−2 )Sum of observations
Case 0.1 estimate
Case 0.05 estimate
Case 0.01 estimate
Case 0.007 estimate
Case 0.005 estimate
Case 0.001 estimate(MBq km−2 )Sum of observations
Case 0.1 estimate
Case 0.05 estimate
Case 0.01 estimate
Case 0.007 estimate
Case 0.005 estimate
Case 0.001 estimate(MBq km−2 )Sum of observations
Case 0.1 estimate
Case 0.05 estimate
Case 0.01 estimate
Case 0.007 estimate
Case 0.005 estimate
Case 0.001 estimate(MBq km−2 )Sum of observations
Case 0.1 estimate
Case 0.05 estimate
Case 0.01 estimate
Case 0.007 estimate
Case 0.005 estimate
Case 0.001 estimate(MBq km−2 )Sum of observations
Case 0.1 estimate
Case 0.05 estimate
Case 0.01 estimate
Case 0.007 estimate
Case 0.005 estimate
Case 0.001 estimate

Hokkaido
2.3
13.0
13.1
14.0
14.3
16.0
74.4
Tochigi
2,669.1
4,583.0
5,311.3
9,274.4
10,423.8
11,519.0
21,525.7
Ishikawa
0.0
4.1
7.9
30.1
39.2
48.1
117.7
Shiga
0.0
3.6
6.7
24.5
31.1
37.1
91.0
Okayama
0.0
1.6
3.1
11.4
14.6
17.5
44.6
Saga
0.0
0.4
0.8
4.0
5.6
7.9
35.6

Aomori
0.0
23.8
47.5
213.6
297.7
401.7
1,252.4
Gunma
1,302.8
1,801.9
1,963.3
2,172.9
2,043.5
1,949.8
2,358.7
Fukui
3.9
7.8
14.2
54.0
70.1
88.3
251.1
Kyoto
0.0
4.1
7.8
30.0
39.1
48.4
135.7
Hiroshima
0.0
4.4
8.8
43.6
62.2
87.0
390.8
Nagasaki
0.0
0.4
0.7
3.4
4.9
6.8
30.4

Yasunari et al. www.pnas.org/cgi/doi/10.1073/pnas.1112058108

Iwate
795.8
2,301.3
2,101.6
3,285.7
3,533.8
3,800.6
5,939.0
Saitama
3,752.7
2,244.5
2,529.2
3,488.6
3,968.8
4,200.0
6,256.5
Yamanashi
114.6
46.5
61.7
127.3
137.3
141.1
158.2
Osaka
0.0
2.1
4.1
15.3
19.9
24.0
65.7
Yamaguchi
0.0
0.6
1.2
5.9
8.5
11.8
51.4
Kumamoto
0.0
0.3
0.5
2.5
3.6
5.1
22.7

MiyagiN/A
7,607.6
9,417.3
21,704.7
25,253.8
28,458.6
54,284.8
Chiba
4,844.1
1,584.6
1,754.3
2,103.1
2,219.3
2,460.1
4,847.8
Nagano
0.0
3.9
7.5
26.0
33.0
36.7
55.6
Hyogo
0.0
3.5
6.8
25.9
33.9
41.6
107.6
Tokushima
0.0
5.7
10.2
35.6
43.1
51.0
141.5
Oita
0.0
1.4
2.8
13.8
19.8
27.7
126.1

Akita
24.5
137.5
167.7
309.1
354.1
366.6
415.9
Tokyo
6,872.5
1,328.5
1,653.2
2,640.9
3,026.5
3,221.8
4,936.9
Gifu
4.7
7.4
12.9
45.9
59.5
73.8
185.1
Nara
0.0
3.1
5.7
20.2
25.0
29.2
70.8
Kagawa
0.0
1.8
3.3
12.3
15.4
18.9
58.0
Miyazaki
0.0
0.6
1.2
5.9
8.4
11.7
53.3

Yamagata
8,622.9
3,398.1
3,853.0
6,854.2
7,566.3
8,356.1
15,008.7
Kanagawa
550.2
343.4
565.4
1,502.5
1,830.2
2,091.0
5,189.2
Shizuoka
127.3
45.6
73.5
204.0
247.5
273.6
446.9
Wakayama
0.0
4.0
7.6
26.0
32.6
36.1
63.0
Ehime
0.0
2.4
4.6
20.8
28.8
38.4
154.7
Kagoshima
0.0
0.5
1.0
4.8
6.8
9.5
43.3

Fukushima
2,196.7
4,085.9
5,572.0
14,055.0
17,209.5
19,619.0
43,428.3
Niigata
15.0
8.4
14.3
48.6
63.5
77.2
232.6
Aichi
0.0
4.9
9.3
32.9
41.4
48.1
96.7
Tottori
0.0
8.6
16.6
61.0
79.3
93.1
224.0
Kochi
2.4
24.5
41.3
123.0
130.5
137.0
201.0
Okinawa
0.0
0.0
0.1
0.4
0.6
0.8
3.6

Ibaraki
28,429.7
6,482.1
7,158.5
14,923.2
16,786.8
18,036.1
27,248.9
Toyama
0.0
1.3
2.5
9.0
11.6
13.4
25.3
Mie
0.0
7.6
13.6
42.4
48.4
51.0
64.6
Shimane
0.0
1.8
3.6
18.0
25.6
35.7
154.0
Fukuoka
0.0
0.4
0.8
4.2
6.0
8.5
38.3

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Table S4. Comparisons of 137 Cs contamination in soil at each observatory location in each prefecture [conversion coefficientðCCÞ ¼ 53 kg m−2 ](Bq kg−1 )Sum of observations
Case 0.1 estimate
Case 0.05 estimate
Case 0.01 estimate
Case 0.007 estimate
Case 0.005 estimate
Case 0.001 estimate(Bq kg−1 )Sum of observations
Case 0.1 estimate
Case 0.05 estimate
Case 0.01 estimate
Case 0.007 estimate
Case 0.005 estimate
Case 0.001 estimate(Bq kg−1 )Sum of observations
Case 0.1 estimate
Case 0.05 estimate
Case 0.01 estimate
Case 0.007 estimate
Case 0.005 estimate
Case 0.001 estimate(Bq kg−1 )Sum of observations
Case 0.1 estimate
Case 0.05 estimate
Case 0.01 estimate
Case 0.007 estimate
Case 0.005 estimate
Case 0.001 estimate(Bq kg−1 )Sum of observations
Case 0.1 estimate
Case 0.05 estimate
Case 0.01 estimate
Case 0.007 estimate
Case 0.005 estimate
Case 0.001 estimate(Bq kg−1 )Sum of observations
Case 0.1 estimate
Case 0.05 estimate
Case 0.01 estimate
Case 0.007 estimate
Case 0.005 estimate
Case 0.001 estimate

Hokkaido
0.0
0.2
0.2
0.3
0.3
0.3
1.4
Tochigi
50.4
86.5
100.2
175.0
196.7
217.3
406.1
Ishikawa
0.0
0.1
0.1
0.6
0.7
0.9
2.2
Shiga
0.0
0.1
0.1
0.5
0.6
0.7
1.7
Okayama
0.0
0.0
0.1
0.2
0.3
0.3
0.8
Saga
0.0
0.0
0.0
0.1
0.1
0.1
0.7

Aomori
0.0
0.4
0.9
4.0
5.6
7.6
23.6
Gunma
24.6
34.0
37.0
41.0
38.6
36.8
44.5
Fukui
0.1
0.1
0.3
1.0
1.3
1.7
4.7
Kyoto
0.0
0.1
0.1
0.6
0.7
0.9
2.6
Hiroshima
0.0
0.1
0.2
0.8
1.2
1.6
7.4
Nagasaki
0.0
0.0
0.0
0.1
0.1
0.1
0.6

Yasunari et al. www.pnas.org/cgi/doi/10.1073/pnas.1112058108

Iwate
15.0
43.4
39.7
62.0
66.7
71.7
112.1
Saitama
70.8
42.3
47.7
65.8
74.9
79.2
118.0
Yamanashi
2.2
0.9
1.2
2.4
2.6
2.7
3.0
Osaka
0.0
0.0
0.1
0.3
0.4
0.5
1.2
Yamaguchi
0.0
0.0
0.0
0.1
0.2
0.2
1.0
Kumamoto
0.0
0.0
0.0
0.0
0.1
0.1
0.4

Miyagi
N/A
143.5
177.7
409.5
476.5
537.0
1,024.2
Chiba
91.4
29.9
33.1
39.7
41.9
46.4
91.5
Nagano
0.0
0.1
0.1
0.5
0.6
0.7
1.0
Hyogo
0.0
0.1
0.1
0.5
0.6
0.8
2.0
Tokushima
0.0
0.1
0.2
0.7
0.8
1.0
2.7
Oita
0.0
0.0
0.1
0.3
0.4
0.5
2.4

Akita
0.5
2.6
3.2
5.8
6.7
6.9
7.8
Tokyo
129.7
25.1
31.2
49.8
57.1
60.8
93.1
Gifu
0.1
0.1
0.2
0.9
1.1
1.4
3.5
Nara
0.0
0.1
0.1
0.4
0.5
0.6
1.3
Kagawa
0.0
0.0
0.1
0.2
0.3
0.4
1.1
Miyazaki
0.0
0.0
0.0
0.1
0.2
0.2
1.0

Yamagata
162.7
64.1
72.7
129.3
142.8
157.7
283.2
Kanagawa
10.4
6.5
10.7
28.3
34.5
39.5
97.9
Shizuoka
2.4
0.9
1.4
3.8
4.7
5.2
8.4
Wakayama
0.0
0.1
0.1
0.5
0.6
0.7
1.2
Ehime
0.0
0.0
0.1
0.4
0.5
0.7
2.9
Kagoshima
0.0
0.0
0.0
0.1
0.1
0.2
0.8

Fukushima
41.4
77.1
105.1
265.2
324.7
370.2
819.4
Niigata
0.3
0.2
0.3
0.9
1.2
1.5
4.4
Aichi
0.0
0.1
0.2
0.6
0.8
0.9
1.8
Tottori
0.0
0.2
0.3
1.2
1.5
1.8
4.2
Kochi
0.0
0.5
0.8
2.3
2.5
2.6
3.8
Okinawa
0.0
0.0
0.0
0.0
0.0
0.0
0.1

Ibaraki
536.4
122.3
135.1
281.6
316.7
340.3
514.1
Toyama
0.0
0.0
0.0
0.2
0.2
0.3
0.5
Mie
0.0
0.1
0.3
0.8
0.9
1.0
1.2
Shimane
0.0
0.0
0.1
0.3
0.5
0.7
2.9
Fukuoka
0.0
0.0
0.0
0.1
0.1
0.2
0.7

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