United Nations Scientific Committee on the Effects of Atomic Radiation

ATTACHMENT A-3

THE ESTIMATION OF WHOLE-BODY DOSES FROM
THE INTAKE OF RADIOCAESIUM FOLLOWING THE
ACCIDENT AT THE FUKUSHIMA DAIICHI NUCLEAR
POWER STATIONUNSCEAR 2020/2021 Report, annex B, Levels and effects of radiation exposuredue to the accident at the Fukushima Daiichi Nuclear Power Station: implicationsof information published since the UNSCEAR 2013 Report
Content
This attachment describes the approaches the Committee has used to estimate the intakes ofradiocaesium and resulting whole-body doses from internal exposure following the accident at
the Fukushima Daiichi Nuclear Power Station (FDNPS). Four different approaches have beenused to estimate intakes and doses in the first year after the accident based, respectively, on:(a) Whole-body measurements of radiocaesium in several thousand people in municipalities
mainly within Fukushima Prefecture;(b) Measurements of concentrations of radiocaesium in food and drinking water, including
market-basket and duplicate-diet surveys;(c) Measurements of radiocaesium concentrations in air; and(d) Predictions of radiocaesium concentrations in air based on a source term and atmospherictransport, dispersion and deposition model (ATDM).
The estimated intakes and resulting doses in the first year using these four approaches arecompared and the approach adopted by the Committee to update its estimates of doses in the
UNSCEAR 2013 Report is described. Intakes and doses beyond the first year have been
estimated using an empirical model based on measurements over decades of the transfer ofradiocaesium deposited from weapons’ fallout to food in Japan.
Notes
The designations employed and the presentation of material in this publication do not imply theexpression of any opinion whatsoever on the part of the Secretariat of the United Nations
concerning the legal status of any country, territory, city or area, or of its authorities, orconcerning the delimitation of its frontiers or boundaries.
Information on Uniform Resource Locators (URLs) and links to Internet sites contained in thepresent publication are provided for the convenience of the reader and are correct at the time ofissue. The United Nations takes no responsibility for the continued accuracy of that informationor for the content of any external website.
© United Nations, April 2022. All rights reserved, worldwide.
This attachment has not been formally edited

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

CONTENTS
I. INTRODUCTION .................................................................................................. 5
II. DOSE ASSESSMENT IN THE UNSCEAR 2013 REPORT ................................ 5
III. ESTIMATING DOSES FROM INTERNAL EXPOSURE DUE TO
INTAKES OF RADIOCAESIUM IN THE FIRST YEAR ................................... 7
A. Estimates of intakes of radiocaesium and doses from whole-bodymonitoring data ................................................................................................ 7
B. Estimates of intakes by ingestion and doses from measurements ofradiocaesium in food and drinking water ....................................................... 16
C. Intakes from inhalation based on measurements of radiocaesium
concentrations in air ....................................................................................... 20
D. Intakes from inhalation based on predicted radiocaesium concentrations in air.....22
E. Comparison of doses estimated from whole-body measurements withestimates made using a combination of the other approaches........................ 23
F. Approach adopted by the Committee in updating its estimates in the UNSCEAR
2013 Report of doses from the intake of radionuclides in the first year ............. 28
IV. ESTIMATING DOSES FROM INTERNAL EXPOSURE DUE TO INTAKESOF RADIOCAESIUM BY INGESTION AFTER THE FIRST YEAR .............. 29
V. UPDATED ESTIMATES OF COMMITTED EFFECTIVE DOSES FROMINTAKE OF RADIOCAESIUM ......................................................................... 32
VI. MICROPARTICLES ........................................................................................... 34
REFERENCES ........................................................................................................... 353

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

I.

5

INTRODUCTION

1.
This attachment summarizes the approaches and models used by the Committee toestimate doses to the population of Japan resulting from intakes of radiocaesium following theaccident at FDNPS. Data and information that have been published, or made available to theCommittee, since the UNSCEAR 2013 Report [UNSCEAR, 2014] are summarized, in particularwhere these have the potential to improve the validity of the estimated doses in the UNSCEAR
2013 Report, and/or reduce their uncertainty. The Committee has used this new information toadapt the approaches and models it had used in the UNSCEAR 2013 Report to estimate doses,
and the more significant changes are described, in particular more realistic estimates arepresented of the amount of radiocaesium ingested in the first year and in subsequent years
following the accident.
2.
The Committee has used four different approaches to estimate doses from the intake ofradiocaesium in the first year following the accident. These were based, respectively, on:(a) whole-body measurements of radiocaesium in several thousand people in municipalities
mainly within Fukushima Prefecture; (b) measurements of concentrations of radiocaesium infood and drinking water, including market-basket and duplicate-diet surveys; (c) measurementsof radiocaesium concentrations in air; and (d) predictions of radiocaesium concentrations in air
based on a source term and atmospheric transport, dispersion and deposition modelling (ATDM).
The estimated intakes and resulting doses in the first year using these approaches are comparedand the approach adopted by the Committee to update its estimates of doses in the UNSCEAR
2013 Report [UNSCEAR, 2014] is described. Intakes and doses beyond the first year have been
estimated using an empirical model based on measurements over decades of the transfer ofradiocaesium deposited from weapons’ fallout to food in Japan.
3.
The Committee has focused on estimating doses for four groups of geographical areas ofJapan: Group 1 included municipalities in Fukushima Prefecture from which some or all of the
population was evacuated in the days to months after the accident; Group 2 included
municipalities and parts of municipalities of Fukushima Prefecture that were not evacuated;
Group 3 included selected prefectures in eastern Japan that were neighbouring Fukushima
Prefecture (Ibaraki, Miyagi, Tochigi and Yamagata prefectures); and Group 4 included all theremaining prefectures of Japan. Within these groups, the Committee has assessed doses for thethree age groups: 1-year-old infants, 10-year-old children and adults.

II.

DOSE ASSESSMENT IN THE UNSCEAR 2013 REPORT

4.
Assessment of doses from the intake of radiocaesium (and other radionuclides) into thebody in the UNSCEAR 2013 Report [UNSCEAR, 2014] took account of intakes via inhalationand ingestion of food and drinking water. The former was based on the source term assumed in
the UNSCEAR 2013 Report and an ATDM of released radiocaesium; and the latter was basedon numerous measurements of the concentrations of radionuclides in food products in a database
compiled by the Food and Agriculture Organization (FAO) and the International Atomic Energy
Agency (IAEA) in collaboration with the Ministry of Agriculture, Forestry and Fisheries(MAFF) and the Ministry of Health, Labour and Welfare (MHLW) of Japan [UNSCEAR, 2014]
in March–May 2011.
5.
Two methods were used to estimate doses from the intake of radiocaesium by inhalation.
The first was based on ATDM of the time-dependent concentrations in air of 134Cs, 136Cs and137
Cs on a 5 × 5 km uniform grid covering Japan. While these concentrations were derived usingANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

6

the then best available source term and ATDM, there were significant uncertainties in theirvalues at specific locations and times. This approach was used to estimate doses received bypeople from evacuated municipalities of Fukushima Prefecture.
6.
The second was based on the estimated time-integrated concentrations of radiocaesiumin air derived from measured ground deposition levels scaled by the ratio of time-integrated air
concentration to deposition density derived from ATDM. This approach was used to estimate
doses received by people living in non-evacuated municipalities of Fukushima Prefecture andthe rest of Japan.
7.
The Committee used standard values of the age-dependent breathing rates and dosecoefficients for organ doses and for effective dose [ICRP, 1995] for the purposes of estimating
doses from the time-integrated air concentrations. These dose coefficients were based on a
default particle size of 1 µm. No allowance was made for any possible reduction inconcentrations of radiocaesium in air indoors compared with those outdoors.
8.
Doses from ingestion in the first year were based on measurements of concentrations ofradiocaesium in food compiled under the guidance of FAO and IAEA in collaboration with
MAFF and MHLW. The measured concentrations were combined with information on thequantity and types of foods people ate to obtain estimated doses.
9.
Within Japan, extensive measurements were made of the concentrations of radionuclides
in different foods (terrestrial and aquatic) starting in parts of Fukushima Prefecture a few days
after the accident. These measurements were mainly intended to identify where restrictions onfood supplies were required rather than to assess the doses to different population groups. The
measurement data were for foods as marketed, not as consumed (e.g., after culinary preparation,etc.). Many of the measurements were at or below the minimum detection level (MDL) of
10 Bq/kg and, in these cases, in estimating doses, it was assumed that the concentrations of 134Cs
and 137Cs were each at MDL in each type of food.
10.
There were insufficient data in the first months after the accident to adopt a fine spatial
resolution for the assessment of the doses from ingestion of radionuclides. It was assumed thatthe majority of people in Japan obtained their food from supermarkets where food is sourced
from the whole of the country, and the average concentrations of radionuclides in foodstuffs overwide areas were used to estimate the average exposures of groups within the population. Mean
concentrations measured in groups of foodstuffs in Fukushima Prefecture, five surrounding
prefectures (Chiba, Gunma, Ibaraki, Miyagi and Tochigi) and the rest of Japan formed the basis
for the main assessment of doses from ingestion.
11.
Information on the quantities and types of foodstuffs consumed per capita of the
population, based on surveys carried out in Japan, was provided by the Government of Japan foruse in the assessment.
12.
After the first year, the Committee estimated intakes and doses from ingestion of foods
using the FARMLAND model [Brown and Simmonds, 1995] to predict the transfer ofradionuclides through terrestrial food chains. Information about the agricultural practices inJapan and Japanese-specific data on the transfer of radionuclides to specific foodstuffs wereused. Account was taken of the restrictions in place on food supplies.
13.
The Committee compared its dose estimates with results emerging from whole-bodymonitoring campaigns that had been and were being carried out, in particular, the studies ofMomose et al. [Momose et al., 2012] and Hayano et al. [Hayano et al., 2013]. The Committee

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

7

judged that the available measurements (i.e., those of which it was aware and/or had access to)of radiocaesium in people from these whole-body monitoring campaigns were insufficient toestimate directly the internal exposure of the population of Fukushima Prefecture or the rest ofJapan. It noted, however, that dose estimates based on whole-body monitoring were substantiallylower than those estimated on the basis of the data base compiled by FAO and IAEA on
radionuclide concentrations in food.

III. ESTIMATING DOSES FROM INTERNAL EXPOSURE DUE TO
INTAKES OF RADIOCAESIUM IN THE FIRST YEAR
14.
Four approaches have been used by the Committee to estimate updated doses fromintakes of radiocaesium in the first year. These were based on: (a) whole-body measurements ofradiocaesium in several thousand people in municipalities mainly within Fukushima Prefecture;(b) measurements of concentrations of radiocaesium in food and drinking water, including
market-basket and duplicate-diet surveys; (c) measurements of radiocaesium concentrations inair; and (d) predictions of radiocaesium concentrations in air based on a source term and ATDM.
Each is considered in the following subsections.
A.

Estimates of intakes of radiocaesium and doses from whole-bodymonitoring data

15.
The Committee has revisited the information available from whole-body monitoring
campaigns and evaluated the extent to which plausible estimates of internal doses can be made fromthem, not least as there has been a modest increase in the amount of monitoring data now available.
16.
Whole-body monitoring was carried out after the accident at FDNPS by national
institutes, such as the Japan Atomic Energy Agency (JAEA) and the National Institute ofRadiological Sciences (NIRS), and by universities, hospitals and local authorities. The
measurements provide direct information, subject to measurement uncertainties, about theamount of radiocaesium in the body at the time the measurements were made. If there is further
information available about how and when the intake or intakes of radiocaesium occurred, themeasurements can be used with a model of radiocaesium metabolism in the body to estimate thedose from internal exposure.
17.
Monitoring was generally carried out using large NaI(Tl) detectors scanning the body fora few minutes, with the recorded spectrum enabled, either to measure the radiocaesium bodycontent through proper calibration, or to put an upper limit on the content in the case ofmeasurements below MDL. The focus of many of these studies was on estimating maximum
doses to provide reassurance to those monitored rather than on making realistic assessment of
the distributions of doses among the exposed population. The published results of thesecampaigns are summarized in table A-3.1.
18.
The study of Sugimoto et al. [Sugimoto et al., 2014] provided further analysis ofessentially the same measurement data included in the earlier study of Tsubokura et al.
[Tsubokura et al., 2012]. The second study by Tsubokura et al. [Tsubokura et al., 2014] covered
later measurements made at Minamisoma Municipal General Hospital and Hirata Central
Hospital, with lower proportions of measurements above MDL, and less useful results for theCommittee’s purposes, than the earlier studies. Neither the Sugimoto et al. [Sugimoto et al.,2014] or the Tsubokura et al. [Tsubokura et al., 2014] studies have therefore been consideredfurther in this attachment.

Age group

Number ofpeoplemonitored

Adult evacuees and first
responders

Whole-body counter

Adults173

39% of measurements of 134Cs above MDL (33 Bq)
32% of measurements of 137Cs above MDL (33 Bq)
Acute intake by inhalation assumed

Evacuees from various
municipalities ofFukushima Prefecture

NIRS fixedinstallation

Adults125Children(<15 years)

49

47% of measurements of 134Cs above MDL
26% of measurements of 137Cs above MDL
137Cs/134Cs = 1.1
Acute intake by inhalation assumed on 12 March
2011
Data compare well with JAEA estimates [Momose etal., 2012]
134Cs body burden adult: ~550 Bq/body (mean),
300 Bq/body (median), 7 kBq/body (max)No significant difference in doses estimated for adults
and children

Measurement dates

Target population[Matsuda et al.,2013; Morita et al.,2013]

March–April 2011

[Kim et al., 2016]

27 June–28 July2011

Summary of results[Hayano et al.,2014]

11 July–29 July2011

Evacuees from
Minamisoma City who
had subsequently
returnedAnzai chair-typewhole-body counter

Adults (≥16 years)

566

Complex and indirect corrections had to be applied tothe measurements for shielding by the body
Average body burden of 134Cs in July 2011 was
825 ± 360 ± 110 Bq (see text below)
Acute intake by inhalation assumed[Momose et al.,2012]

11 July 2011–31 January 2012

Evacuees from
11 municipalities ofFukushima Prefecture

JAEA fixed wholebody counter inTokai Village
JAEA mobile units
in Fukushima
Prefecture

Adults3 128Children(<17 years)

6 799

20% of measurements above MDL of 300 to 370 Bq
137Cs/134Cs ratio is between 1.12 and 1.26
No correlation between committed effective dose ofchildren and parents
Maximum body burden: 2.7 kBq (<8 years old),
14 kBq (adults)
Acute intake by inhalation assumed
Measurement results up to end of December 2011
may have been affected by contamination on clothes

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM

Measurement
programme

Reference

8

Table A-3.1. Summary of whole-body monitoring campaigns carried out following the Fukushima Daiichi Nuclear Power Station accident(ordered by the date measurements began)Reference

Measurement dates

Target population

Measurement
programme

Number ofpeoplemonitored

Adults

4 716

Children(<15 years)

6 310

Adults

8 066

Children(<15 years)

1 432

Summary of results[Hayano et al.,2013]

October 2011–
February 2012

Residents of Fukushima
Prefecture (73%),
Ibaraki Prefecture(23%)

Hirata Central
Hospital

Some measurements up to end of February 2012
might have been affected by external contamination
on clothes
Maximum of 15% of measurements of 137Cs above
MDL (in November–December 2011); less than 5%of measurements above MDL after February 2012
(but see above)
137Cs body burden, whole population: ~12 Bq/kg(mean), ~9.5 Bq/kg (median), 77 kBq/kg (max)[Tsubokura et al.,2012]

October 2011–
March 2012

Residents of
Minamisoma City

Minamisoma
Municipal General
Hospital[Sugimoto et al.,2014]

October 2011–
March 2012

Residents of
Minamisoma City

Minamisoma
Municipal General
Hospital

AdultsChildren(<15 years)

7 214
1 067

40% of measurements on adults and 9% of
measurements on children above MDL
For positive measurements, median body burden was
11 Bq/kg for adults and 8.5 Bq/kg for children
Contains an analysis of risk factors (foodconsumption and habits) related to radiocaesium
detection, not detailed here

[Tsubokura et al.,2014]

April 2012–
March 2013

Residents of
Minamisoma City

Minamisoma
Municipal General
Hospital and Hirata
Central HospitalMedian age
14 years
Age range
2–97 years

30 622

Measurements of 137Cs above MDL: 612 participants(6.1%) from Minamisoma Hospital and
144 participants (0.7%) from Hirata Hospital>50 Bq/kg 137Cs measured in 9 participants
Median 137Cs content in body of these 9 participants:
4 830 Bq (69.6 Bq/kg); range 2 130–15 918 Bq(50.7–216.3 Bq/kg)
All 9 participants consumed homegrown produce andwild mushrooms

16.4% of measurements on children above MDL;
median body content = 590 Bq (for positive
measurements)
38% of measurements on adults above MDL; medianbody content = 744 Bq (for positive measurements)
Difference in exposure between adults and children is
statistically significant

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM

Age group

9

10

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

19.
As well as the published studies, Minamisoma City municipal administration has madethe results of whole-body monitoring carried out at Minamisoma Municipal General Hospital
available on its web portal [Minamisoma, WEB]. Monitoring started on 11 July 2011 and morethan 10,000 measurements had been carried out by the end of January 2012. The percentages of
those measured with levels of radiocaesium in the body above the MDL was about 40% among
adults in the first three months but declined rapidly (see figure A-3.I). Among the results
available are those of repeated measurements made on the same subjects that generally show a
gradual decrease in the levels of radiocaesium in the body.
Figure A-3.I. Reduction over time of the percentage of whole-body measurements made on
adults and children at hospitals and schools in Minamisoma City that were above the minimum
detection level (4 Bq/kg body mass of 137Cs or 134Cs) [Minamisoma, WEB]

20.
In addition, Fukushima Prefecture has carried out screenings of more than
100,000 residents with whole-body counters. Hayano et al. [Hayano et al., 2013] reported that,in this monitoring campaign, different assumptions were made to assess doses: (a) for
measurements made before February 2012, an acute intake by inhalation in March 2011 wasassumed; and (b) for measurements made from February 2012 onwards a constant daily intakeof radiocaesium was assumed. Hayano et al. [Hayano et al., 2013] reported that only
52 individuals in the study were assessed as receiving doses of more than 1 mSv. A detailed
breakdown of the results has not been made available to the Committee.
1.

Summary of results of whole-body measurements studies

21.
Most of the whole-body monitoring campaigns began in June and July 2011, three tofour months after the accident. One earlier study, published since the UNSCEAR 2013 Report,
is worthy of note [Matsuda et al., 2013], as the measurements enable a reasonable assessment of
the dose due to intake in the short-term [UNSCEAR, 2015]. Matsuda et al. [Matsuda et al., 2013],
reported on measurements made at Nagasaki University in March and April 2011 on 173 adultevacuees and first responders who were in Fukushima Prefecture at the time of the accident. The
overall detection rates (per cent of subjects above MDL) of 134Cs and 137Cs were, respectively,
39% and 32%, although subjects measured in the first week after the accident had detection rates
of about 50%. The mean measured amounts of 134Cs and 137Cs in the body were 450 and 540 Bq,
respectively, and ranged from 160 to 16,000 Bq of each radionuclide, for subjects measured in
the first week, to 130–1,900 Bq for 134Cs and 130–1,100 Bq for 137Cs, for those measured later.

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

11

Committed effective doses 1 from internal exposure due to the radionuclides in the body were
estimated assuming an acute intake via inhalation of particulate aerosol (activity medianaerodynamic diameter (AMAD) = 1 µm) with absorption Type F on either the first day or thelast day of the stay of the subject in Fukushima Prefecture, to give a range spanning the true
dose. Committed effective doses from radiocaesium intakes were estimated to be between about
2 and 300 µSv for those measured in the first week and between about 2 and 20 µSv for thosemeasured later.
22.
Kim et al. [Kim et al., 2016] reported on measurements made on 174 residents ofFukushima Prefecture between 27 June and 28 July 2011: 12 from Futaba Town, 6 from Okuma
Town, 5 from Tomioka Town, 6 from Naraha Town, 5 from Hirono Town, 90 from Namie Town,
8 from Kawauchi Village, 5 from Katsurao Village, 5 from Tamura Town, 20 from Iitate Village
and 12 from Kawamata Town. Although this study was published some years after the
UNSCEAR 2013 Report, the measurements were carried out as a pilot study for the larger
measurement campaign reported by Momose et al. [Momose et al., 2012], which was available
before publication of the UNSCEAR 2013 Report [UNSCEAR, 2014]. The focus of thecampaign was initially on the residents (before the accident) of Iitate Village, Namie Town andof Yamakiya municipality in Kawamata Town, who were chosen by the Fukushima prefectural
government. The other subjects were chosen by each municipality and were added to the study
at the request of the municipalities. The percentage of measurements with a positive detection(above MDL of 320 Bq for 134Cs and 570 Bq for 137Cs, before correction for body size) was:
26% (43 adults and 2 children) for 137Cs; 47% (66 adults and 15 children) for 134Cs; and 22%(36 adults and 2 children) for both radionuclides. Detection rates were highest in the residents
from Futaba Town and from Iitate Village and were about 50% in the residents from Namie
Town (where the majority of those measured were from).
23.
The whole-body contents of 134Cs ranged from MDL up to 2,600 Bq for adults and from
MDL up to 1,400 Bq in children. Doses were estimated assuming an acute intake of radiocaesiumby inhalation on 12 March 2011, as this scenario was considered reasonable for conservativeinternal dose estimations. The measurements of 134Cs were used because the detection rate of137
Cs was much lower. The maximum committed dose was 0.63 mSv (630 µSv) in an elderly
male subject; the highest dose in children was 0.20 mSv (200 µSv). Median doses were only
estimated for adult residents of Namie Town (26 µSv), Iitate Village (27 µSv) and Futaba Town
(68 µSv), where there were sufficient measurements above MDL. The 95th percentiles of doses
ranged from 85 to 370 µSv for adults and from 110 to 130 µSv for children. The authors
considered the influence of different scenarios on the total intakes corresponding to a given
measured body content of 137Cs on the 120th day of exposure. Compared with an acute intake
on the first day, assuming a chronic intake over 100 days reduced the total intake by around 30%
in adults and by about a factor of four for children.
24.
The study by Hayano et al. [Hayano et al., 2014] was reviewed by the Committee in its
2015 White Paper [UNSCEAR, 2015] and was considered to provide one of the most reliable
retrospective assessments of dose from internal exposure due to intakes of radiocaesium. The
authors reported on whole-body counting measurements made at Minamisoma Municipal
General Hospital between 11 and 29 July 2011. The measurements were made using an Anzai
chair-type whole-body counter, where interpretation of the measurements was complicatedbecause of shielding of the environmental background by the human body. The authors
developed a method to correct for this shielding which they tested and validated, but the resulting
estimates of body burdens and doses were associated with considerable uncertainty.
Measurements were made on 566 adults (≥16 years) from Minamisoma City, about 85% of1Committed effective dose from intake up to the time of measurement.

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

12

whom were evacuated during March 2011 but had subsequently returned. Of the subjects,
256 were males and 310 were females; 240 subjects lived in Kashima Ward (outside the 30-kmzone) before the accident, 322 in Haramachi Area (inside the 30-km zone) and 4 in Iitate Village.
The average body burden of these subjects was estimated at 825 Bq of 134Cs, with statisticaluncertainty of ±360 Bq, derived by measuring 287 subjects twice on the same day, andsystematic uncertainty of ±110 Bq, derived by comparing measurements made with the chairtype counter and by a better shielded whole-body counter a short time later. The initial bodyburden of 134Cs was estimated assuming acute inhalation of radiocaesium in March 2011 and nofurther radiocaesium intake before the day of measurement. Using a ratio of 1:1 for 134Cs:137Cs
in the early phase of the accident, committed effective doses from radiocaesium intakes were
estimated. The distribution of committed effective doses for males and females was reproducedin the Committee’s 2015 White Paper [UNSCEAR, 2015]. The average committed effective
doses for males and for females were both around 80 µSv.
25.
Momose et al. [Momose et al., 2012] examined 9,927 evacuees from Futaba Town,
Hirono Town, Iitate Village, Katsurao Village, Kawamata Town, Kawauchi Village,
Minamisoma City, Namie Town, Naraha Town, Okuma Town and Tomioka Town.
Measurements were made on evacuees from Iitate Village, Kawamata Town and Namie Town
(all in the deliberate evacuation area, where evacuation took place between April and June 2011)
from 11 July 2011 to the end of August 2011. For evacuees from the other municipalities (someof whom were evacuated in March 2011), measurements started on 1 September 2011. The
subjects were selected by the relevant municipality, and priority was given to pregnant women,
followed, in order, by mothers of children less than 4 years old, children aged 4–12 years of age,children aged 13–17 years of age and adults.
26.
Approximately 20% of those monitored had levels of radiocaesium in the body above
MDL, which varied with the equipment used from 160 to 340 Bq of 134Cs and from 210 to 370 Bq
of 137Cs. Whole-body contents ranged from MDL up to 2,700 Bq, of 134Cs and 137Cs in total, forchildren up to 8 years of age, and up to 14,000 Bq for adults. Doses were conservatively
estimated based on the assumption of a single intake via inhalation on 12 March 2011. Dose
distributions suggested that committed effective doses corresponding to whole-body content
close to MDL were overestimated. The results showed that 99.8% of those monitored hadcommitted effective doses less than 1 mSv. Twenty-two individuals received doses that exceeded
1 mSv, all but one being children, and the maximum dose was 3 mSv. By fitting a log-normal
distribution to the measurements (and resulting estimated doses) and extrapolating below MDL,
median doses of 25 µSv for adults and 20 µSv for 13 to 17-year-old children were estimated.
Doses estimated for different municipalities varied within a range of about a factor of four, withthe highest doses generally in Iitate Village and lowest in Naraha Town.
27.
The authors acknowledged that the higher doses estimated for children than adults were
not consistent with the assumption of a single acute intake via inhalation. There was also nocorrelation between the effective doses of children with a significant body content greater than
MDL and the effective doses of their parents.
28.
Changing into contamination-free gowns before measurement decreased the number ofmeasurements above MDL significantly, and the authors concluded that a small amount ofcontamination on clothes may have affected the measurement results up to the end of December
2011. The authors also concluded that the dose estimates were associated with a large uncertainty
because of the lack of information on how and when radionuclides were taken into the bodies of
those measured.

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

13

29.
Tsubokura et al. [Tsubokura et al., 2012] reported on voluntary screening carried out on
residents of Minamisoma City, aged 6 years and older, between 26 September 2011 and
31 March 2012. The authors noted that many residents had been evacuated but approximately
half had returned by August 2011. A total of 9,498 residents enrolled in the study (24% of theregistered population on 15 August 2011). A total of 3,286 individuals (35% of those measured)
had detectable levels of radiocaesium, 235 children and 3,051 adults. In adults, the detectedradiocaesium levels ranged from 210 to 12,771 Bq with a median of 744 Bq; in children, thelevels ranged from 210 to 2,953 Bq with a median of 590 Bq. The measured levels were reported
to have been converted to committed effective dose based on the assumption of acute inhalation
immediately after the accident in adults, and of chronic ingestion after the accident in children.
However, the authors only reported that committed effective doses were less than 1 mSv in all
but one resident. The authors commented that it was uncertain whether the measured bodycontents were due to continuing chronic intakes or from acute intakes still present in the body,since there was no information available about individual intake scenarios.
30.
Hayano et al. [Hayano et al., 2013] reported on measurements made on residents ofFukushima Prefecture and surrounding prefectures at Hirata Central Hospital. A total of
32,811 subjects were measured, 73% from Fukushima Prefecture, 23% from Ibaraki Prefectureand smaller numbers from Tochigi and Miyagi prefectures. Measurements were made between
17 October 2011 and 30 November 2012. Of those measured, 1,340 out of 11,026 adults (12%)
and 487 out of 6,310 children (8%) measured between October 2011 and the end of February
2012 exceeded the detection limit of 300 Bq for both 134Cs and 137Cs. These detection rates fellsignificantly in the period March to November 2012, to less than 1% (212 out of 21,785) for
adults and less than 0.1% (12 out of 13,220) for children, following the introduction of a policyof having every subject change into a hospital gown before measurement. The authors noted that
surface (clothes) contamination may have affected the measurements made in the first
five months. The authors, therefore, restricted their analysis to measurements made after
March 2012 and made no estimates of the distribution of committed effective doses in the
population studied. For children, based on MDL and assuming a constant daily intake, theauthors indicated that committed effective doses would have been less than 21 µSv (for children
around the age of 10 years) and less than 13 µSv (for children around the age of 15 years). The
authors also acknowledged that the results were not conclusive for Fukushima Prefecture as awhole but were consistent with results obtained from other municipalities and with prefecturaldata. The highest radiocaesium concentrations (maximum concentrations of 184 Bq/kg of 137Cs
and 108 Bq/kg of 134Cs, corresponding to a committed dose of about 1 mSv) were found in asmall number of senior residents that were linked with their regular consumption of foods, suchas wild mushrooms, wild boar, fresh-water fish, for which contamination advisories had been
issued. The individuals’ body burdens decreased at rates consistent with the biological half-lifeof radiocaesium after the subjects were advised to avoid such foodstuffs.
2.

Inferring intakes and doses from whole-body measurements

31.
These whole-body monitoring campaigns provide direct measurements made on peopleof the contents of radiocaesium in their bodies, from which intakes of radiocaesium andcommitted effective doses can be estimated, subject to knowledge or assumptions of when andhow the intakes occurred. The total intake, Ia in Bq, can be deduced from a whole-bodymeasurement, Ma(t) in Bq of particular radionuclide, a, at a particular time, t, by taking into
account the whole-body retention function of the radionuclide, Ra(t) in relative units, that

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

14

corresponds to the fraction of the intake that is retained in the body at a given time after an intake
at time t = 0 (see equation A-3.1):
𝐼𝐼𝑎𝑎 =

𝑀𝑀𝑎𝑎 (𝑡𝑡)
𝑅𝑅𝑎𝑎 (𝑡𝑡), Bq(A-3.1)

32.
The retention function Ra(t) depends on the intake pathway, the chemical form of theradionuclide, and the age and sex of the subject [ICRP, 1993; ICRP, 1995]. Estimating an intake,and the resulting committed effective dose, from a whole-body measurement thus requires
information about the age and sex of the person measured and modelling to describe the temporal
pattern of intake.
33.
In all of the studies reviewed, there was a general lack of information about when andhow the intakes of radiocaesium occurred and estimates of intakes and doses have been madeusing assumptions about the timing and mode of intake. In the study of Matsuda et al. [Matsuda
et al., 2013], although the period during which the intakes of radionuclides could have occurred
was short (the average length of stay in Fukushima Prefecture was 4.8 days), there was no
information available as to where the subjects were before they were evacuated, and the rangesof estimated intakes and doses varied widely (by up to two orders of magnitude or more)according to whether it was assumed that the intake occurred on the first or the last day of theindividual’s stay in Fukushima Prefecture. No dose distributions were presented, only the rangesof doses for different groups.
34.
Kim et al. [Kim et al., 2016] and Momose et al. [Momose et al., 2012] made estimates ofthe median and various percentiles of the distributions of committed effective doses from thewhole-body measurements assuming an acute intake of radiocaesium by inhalation on 12 March
2011. In both cases, this acknowledged assumption was made because it would result inconservative estimates of the doses. Hayano et al. [Hayano et al., 2014] presented the distributionof committed effective doses subject to the same assumption of an acute intake of radiocaesiumby inhalation. In the absence of estimates of the dose distributions by the authors of two of thestudies [Hayano et al., 2013; Tsubokura et al., 2012], the Committee has made its own
assessments assuming that the intakes were short-term from either inhalation or ingestion ofradiocaesium. The Committee has further assumed that measurements that were below MDL ineach study could be assigned a whole-body content equal to half of MDL.
35.
The results for the five studies from which meaningful distributions of doses (including
estimates of means and/or medians and percentiles of the distribution) can be derived aresummarized in table A-3.2. The Committee considers these to be the best estimates of committed
effective doses from radiocaesium intakes that can be made from the whole-body measurement
information that was available to it. For most of the studies, the number of measurements above
MDL in children was much lower than in adults, and dose estimates could generally only bemade for adults.

Table A-3.2. Characteristics of distributions of committed effective doses from intakes of radiocaesium estimated from whole-bodymonitoring studies[Kim et al., 2016]a

Number ofpeoplemeasured

Numberabove MDL

174

81 (134Cs)

Time of measurements

Estimated committed effective dose from intakes up to the time of measurement
(µSv)
Mean

June–July 2011

(Evacuees from various
municipalities)

Median95th percentile

26 (adults from Namie Town)
27 (adults from Iitate Village)
68 (adults from Futaba Town)

Adults180 (Namie Town)
140 (Iitate Village)
370 (Futaba Town)
85 (remaining municipalities)
Children
130 (Namie Town)
110 (remaining municipalities)a[Hayano et al., 2014]b(Minamisoma City – mainly
evacuees)

566[Momose et al., 2012]c(Evacuees from various
municipalities)

9 927

1 900

July 2011–January 2012

[Tsubokura et al., 2012]d(Minamisoma City – including
evacuees)

9 498

3 286

September 2011–March 201250

180 (adults)[Hayano et al., 2013]e
Measured at Hirata Central Hospital

32 811

1 552

October 2011–November 201250

150 (adults and children)

July 201180

170

25 (adults: >17 years)
20 (children: 13–17 years)

150 (adults)
100 (children)

Median and 95th percentile committed effective doses estimated by the authors for subjects from the named municipalities assuming intake was by inhalation on 12 March 2011; there were too few subjects
and too few children with detectable amounts of radiocaesium to make estimates of median values for other municipalities.
Mean value and standard deviation estimated by the authors assuming intake was by acute inhalation in March 2011; 95th percentile derived by the Committee distribution of doses.
cMedian and 95th percentile committed effective doses estimated by the authors assuming intake was by inhalation on 12 March 2011; median committed effective doses for adults and children were estimatedby extrapolation below MDL assuming a log-normal distribution.
dMean and 95th percentile committed effective doses estimated by the Committee from the distributions of measured radiocaesium concentrations in the body by setting all measurements below MDL to half of
MDL (125 Bq for 137Cs and 105 Bq for 134Cs) and assuming a short-term intake of radiocaesium.
e
Mean and 95th percentile committed effective doses estimated by the Committee from the distributions of measured radiocaesium concentrations in the body by setting all measurements below MDL to half of
MDL (150 Bq for both 137Cs and 134Cs) and assuming a short-term intake of radiocaesium. The Committee used all of the measurement data from October 2011 for its estimates; the authors restricted their analysis
to measurement data taken after March 2012 because of possible surface contamination on clothing before that date; the doses may, therefore, be overestimates. Of those measured, 73% were from Fukushima
Prefecture, 23% from Ibaraki Prefecture and smaller numbers from Tochigi and Miyagi prefectures.
b

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM

Study

15

16

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

36.
Subject to the uncertainties associated with the assumptions made in estimating the doses,
the dose estimates summarized in table A-3.2 are representative of the people who weremonitored. It is less clear how representative those monitored were, either of the populations
from which they were selected, or of wider population groups affected by the FDNPS accident.
In the study of Kim et al. [Kim et al., 2016], the subjects were chosen either by the prefectural
government or by the relevant municipality, but the basis of the selection of the subjects is notstated; more than half of the subjects were from Namie Town, with 11% from Iitate Village and7% from Kawamata Town. Hayano et al. [Hayano et al., 2014] provided information on thesubjects measured in their study: about 85% were evacuated at different times in March 2011;
and 42% were from Kashima Area of Minamisoma City and 57% from Haramachi Area. The
results of this study could therefore be considered representative of evacuees from theselocations, but their wider applicability to other evacuees is less clear. No detailed information
was provided about the selection of subjects in the study of Momose et al. [Momose et al., 2012],
only the municipalities covered and the priority order in which the measurements wereconducted. The only information provided in the study of Hayano et al. [Hayano et al., 2013]
was that 73% of subjects were residents of Fukushima Prefecture, 23% of Ibaraki Prefecture,and small numbers were from Tochigi and Miyagi prefectures. The study of Tsubokura et al.
[Tsubokura et al., 2012], on the other hand, could be considered representative of the populationof Minamisoma City as this campaign was reported to have comprised voluntary screening of
all residents aged six years and over, and covered 24% of the registered population.
37.
Irrespective of how representative those measured were of the population studied in eachcase, there is also the question of the extent to which the doses estimated from the whole-bodymeasurements made in each of these studies can be used to infer or estimate the doses fromintakes of radiocaesium in other groups of the population. In the studies of Kim et al. andMomose et al. those measured were all described as evacuees, although the measurements by
Kim et al. and Momose et al. were initially focused on those from the deliberate evacuation area
who were not evacuated until April to June 2011 [Kim et al., 2016; Momose et al., 2012], with
evacuees from the 20-km precautionary evacuation zone monitored either in smaller numbers orlater. Those measured by Tsubokura et al. and Hayano et al. were all residents of Minamisoma
City, many of whom were reported to have been evacuated, but approximately half of whomwere reported to have returned [Hayano et al., 2014; Tsubokura et al., 2012]. Furthermore, thosemeasured by Hayano et al. [Hayano et al., 2013] were described only as residents of Fukushima
and surrounding prefectures. The application of the results of these whole-body monitoringstudies to the estimation of doses to groups of the population other than those measured is,therefore, not straightforward and will bring added uncertainty. Most of the estimated doses werealso for adults, with only sparse information from which to estimate doses to children. In general,
therefore, doses to children need to be estimated from the adult doses.
B.

Estimates of intakes by ingestion and doses from measurements ofradiocaesium in food and drinking water38.
The second approach to the estimation of intakes of radiocaesium and doses from internal
exposure is based on measurements of the radiocaesium content of food and drinking water as
consumed. This approach is less direct than measurements of the radiocaesium in the body, but
enables intakes from one of the pathways (ingestion) to be estimated from measurements withthe minimum of further assumptions. Intakes from ingestion can be derived from measurementsof the radiocaesium content in the whole daily diet (or ration) sampled by the market-basket or
duplicate-diet surveys. Alternatively, and less directly again, intakes from ingestion can bederived from measurements of radiocaesium concentrations in food and drinking water, with

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

17

additional assumptions about how much of each type of food is consumed and how each foodtype is sourced and distributed to consumers.
1.

Intakes from ingestion based on market-basket and/or duplicate-dietstudies

39.
The dose from intake of radiocaesium by ingestion can be derived from measurementsof the radiocaesium content in the whole daily diet (or ration) sampled by the market-basket or
duplicate-diet methods. In the available literature, six publications were found with data of thistype collected in the period 2011–2013 in Fukushima Prefecture, four neighbouring prefectures(Ibaraki, Iwate, Miyagi and Tochigi) and eight distant prefectures (Hokkaido, Kanagawa, Kochi,
Nagasaki, Niigata, Osaka, Saitama and Tokyo) of Japan.
40.
Koizumi et al. [Koizumi et al., 2012] collected 10–25 pre-packed daily food setspurchased in grocery stores in each of the Fukushima, Iwaki, Nihonmatsu and Soma cities at the
beginning of July 2011. The average daily intake of both 134Cs and 137Cs varied from 0.4 Bq/din Fukushima City to 3 Bq/d in Soma City, and, for the 55 samples from Fukushima Prefecture,
the average was estimated as 1.1 ± 1.5 Bq/d. Tsutsumi et al. [Tsutsumi et al., 2013] purchased
total diet samples in 14 food categories in September 2011 at local food markets in Fukushima
Prefecture, Miyagi Prefecture and Tokyo. Following regular culinary processing, food samples
were measured with a gamma spectrometer. The daily intake rate for adults was assessed to beequal to 0.4, 3 and 3.3 Bq/d in Tokyo, Miyagi Prefecture and Fukushima Prefecture, respectively.
Co-op Fukushima (a regional retail consumer cooperative) conducted a broad survey of 134Cs
and 137Cs content in daily meals in Fukushima Prefecture [Sato et al., 2013] from November
2011 to March 2012 and from June 2012 to September 2012, each covering 100 families
throughout the prefecture. Mean concentration of 134Cs in food was 0.27 ± 0.45 Bq/kg (range
0.05–5.0 Bq/kg) and that of 137Cs was 0.37 ± 0.61 Bq/kg (range 0.07–6.7 Bq/kg).
41.
Harada et al. [Harada et al., 2013] collected 53 sets of 24-hour food-duplicate samples
on 4 December 2011 from families in Fukushima Prefecture and neighbouring areas andanalysed them for their content of 134Cs and 137Cs. In Fukushima Prefecture, the mean dietaryintake rate of 134Cs and 137Cs was 4.5 ± 2.6 Bq/d (range <0.26−17 Bq/d). The estimated intake
was significantly lower in the Tokyo region and especially in western Japan. In a comprehensive
paper, Harada et al. [Harada et al., 2014] evaluated the main routes of exposure to Fukushima
Prefecture residents. In August 2012, duplicate-diet samples were collected from 125 residentsof three municipalities. The average intake of 134Cs and 137Cs with diet was from 1.1 Bq/d in
Kawauchi Village to 3.5 Bq/d in the Tamano Area of Soma City. In the same municipalities,
aerosol samples were taken and the annual inhalation of 134Cs and 137Cs (from resuspension ofdeposited material) was estimated to be 1–2 orders of magnitude lower than the annual intake
from foods.
42.
Uekusa et al. [Uekusa et al., 2014] conducted a comprehensive study of radionuclide foodintake with both market-basket and duplicate-diet sampling in Fukushima Prefecture(three municipalities), four neighbouring prefectures (Ibaraki, Iwate, Miyagi and Tochigi) andeight distant prefectures (Hokkaido, Kanagawa, Kochi, Nagasaki, Niigata, Osaka, Saitama andTokyo). The total number of samples was 939. The intake rate of radiocaesium (134Cs and 137Cs)
was estimated with the market-basket method to be 0.17–1.7 Bq/d, 0.15–0.68 Bq/d and 0.15–1.3
Bq/d in March 2012, September 2012 and March 2013, respectively. The intake was higher inFukushima Prefecture and its neighbouring prefectures than in distant areas in all the considered
periods. The intake rate was observed to decrease over time in most areas.

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

18

43.
These market-basket and duplicate-diet studies provide direct information about intakesof radiocaesium in food. The results are summarized in table A-3.3. The estimated intakes ofradiocaesium from ingestion are generally low (a few Bq/d). Estimated intakes in Fukushima
Prefecture were generally higher than those in neighbouring prefectures, which were in turngenerally higher than those in more distant prefectures. The range of estimated intakes ofradiocaesium from ingestion for locations within Fukushima Prefecture was generally less thanan order of magnitude. Estimated annual committed effective doses from these intakes ofradiocaesium, assuming the daily intakes remained the same over a year, ranged from about
1 µSv to some tens of microsievert. However, these studies provide an estimate based on
measured intakes at particular points in time, so estimates of annual doses from the intakes must
be considered uncertain. In addition, the studies did not start until July 2011 and can provide no
information about intakes at earlier times, without the use of further assumptions and models.
Table A-3.3. Summary of results of market-basket and duplicate-diet studiesaTime ofmeasurements

Estimated intake rate of
137Cs and 134Cs (Bq/d)

Estimated annual
committed effective
dose (µSv)aJuly 2011

1.1 ± 1.5 (mean)
0.4 (Fukushima City) –3 (Soma City)

6.4 ± 13 (mean)
2.6 (Fukushima City) –17 (Soma City)

September 2011

0.4 (Tokyo) –3.3 (Fukushima
Prefecture)

2 (Tokyo) –19 (Fukushima
Prefecture)

200 samples in total overtwo seasons prepared byfamilies from across
Fukushima Prefecture

November 2011–
March 2012
(winter 2011–2012), June 2012–
September 2012
(summer 2012)

3.0–24 (winter 2011–2012; 10 samples>1 Bq/kg)
6.5–7.0 (summer 2012;
2 samples>1 Bq/kg)

17–130 (winter 2011–2012; 10 samples>1 Bq/kg; assuming
intake over whole year)
37–40 (summer 2012;
2 samples >1 Bq/kg;
assuming intake overwhole year)[Haradaet al., 2013]

53 samples from families inFukushima Prefecture,
Tokyo region and westernJapan

4 December 2011

4.5 ± 2.6 (mean)

27 ± 16[Haradaet al., 2014]

125 samples from families in
Kawauchi Village, Tamano
Area of Soma City andHaramachi Area of
Minamisoma City

August 2012

1.0 ± 0.99 (Kawauchi
Village)
3.5 ± 3.9 (Tamano
Area)
1.6 ± 1.4
(Haramachi Area)

5.8 ± 7.4
(Kawauchi Village)
19 ± 30 (Tamano Area)
8.8 ± 10.7
(Haramachi Area)[Uekusa
et al., 2014]939 samples overthree periods from
Fukushima Prefecture, fourneighbouring prefectures andeight more distantprefectures

March 2012,
September 2012,
March 2013

<MDL–1.7(March 2012)
0.15–0.68 (September
2012)
0.15–1.3 (March 2013)

0–9.4 (March 2012)
0.88–3.8(September 2012)
0.85–7.1 (March 2013)

Study

Number of samples[Koizumi
et al., 2012]

10–25 food sets from each of
the Fukushima, Iwaki,
Nihonmatsu and Soma cities[Tsutsumi
et al., 2013]14 sample groups inFukushima Prefecture,
Miyagi Prefecture andTokyo[Sato et al.,2013]

Estimated by those who conducted the studies, assuming the same daily intake from food for the whole year.

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

2.

19

Intakes from ingestion based on food monitoring data

44.
Making realistic estimates of radionuclide intake from measured levels of radionuclides
in food and drinking water (and the resulting doses) requires the collection of data in a systematicand random manner and use of a model or models to account properly for the daily food ration,
the food delivery and distribution system, culinary losses, etc. Following the natural catastropheof an earthquake and tsunami and the subsequent accident at FDNPS, the acquisition of suchdata will have been challenging and, potentially, associated with much uncertainty. The databaseof concentrations of radionuclides in foodstuffs used in the UNSCEAR 2013 Report to estimate
doses in the first year from ingestion provides an example of the potential pitfalls. While thisdatabase was extensive and the only one available at the time of the UNSCEAR 2013 Report, it
was not suitable for making realistic estimates of doses from intakes by ingestion. In particular,
the focus was on identifying food with radionuclide concentrations above the standard limits at
which food restrictions were applied. In addition, the Committee assumed that food with ameasured concentration less than MDL had a concentration equal to MDL. Taken together, these
two factors resulted in the doses from ingestion estimated in the UNSCEAR 2013 Report for the
first year after the accident being about an order of magnitude too high; this was confirmed by
the results of whole-body monitoring campaigns reported just prior to the publication of the
UNSCEAR 2013 Report [UNSCEAR, 2014]. Doses estimated on the basis of measured levels
in food and drinking water require validation either by means of estimates from market-basket
or duplicate-diet studies or from whole-body monitoring of people.
45.
Murakami and Oki [Murakami and Oki, 2014] estimated doses from ingestion in the firstyear after the accident based on measured concentrations of radionuclides in food and drinking
water. But they used data from a wider range of sources than was available to the Committee when
preparing the UNSCEAR 2013 Report, and also took account of the regional trade in foods(specifically, of the relative contribution of foods from different parts of Japan arriving at foodmarkets, where most Japanese people purchase food). The authors carefully studied and took into
account the stochastic nature of food contamination, countermeasures, culinary losses, etc. They
have provided estimates, with uncertainties, by age and sex, of equivalent dose to the thyroid andeffective dose from 131I intakes and of effective dose from 134Cs and 137Cs intakes for residents ofFukushima City, Osaka and Tokyo. They estimated average doses in these three locations, as wellas doses to agricultural workers (about 4% of the population) in Fukushima City, who may havepreferentially consumed locally produced vegetables, and evaluated the effect of countermeasures(e.g., restricting the distribution of food, voluntarily withholding rice, and providing bottled waterinstead of tap water for infants). They compared their estimates of the effective dose from ingestionof 134Cs and 137Cs in food and drinking water with the estimates of Koizumi et al. [Koizumi et al.,2012] and Harada et al. [Harada et al., 2013], that were based on market-basket and food-duplicate
surveys in five periods from July 2011 to March 2012. A similar comparison including some ofthe other studies in table A-3.3 is presented in figure A-3.II.

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

20

Figure A-3.II. Comparison of estimates of effective dose to adults from intakes of radiocaesiumby ingestion within Fukushima Prefectureaa

The ranges of uncertainty shown correspond to plus or minus one standard deviation.

46.
Given the large uncertainties in the estimated dose rates, there is broad agreement (within
one or two standard deviations) between the estimates based on the market-basket and duplicatediet studies and those based on the modelling approach of Murakami and Oki [Murakami andOki, 2014]. The Committee has assumed that Murakami and Oki’s estimate for Fukushima Cityis applicable to the whole of Fukushima Prefecture while recognizing that there will be somevariation with location. The results of the market-basket and duplicate-diet studies in Fukushima
Prefecture and other prefectures indicate that the spatial variation in ingestion doses is not large
and the Committee has judged that the variation between municipalities within Fukushima
Prefecture is unlikely to be more than a factor of a few.
47.
Murakami and Oki estimated the average committed effective dose from ingestion ofradiocaesium for residents of Fukushima City to be 19 µSv in the first year after the accident(with a median of 8.2 µSv and 95th percentile of 43 µSv) [Murakami and Oki, 2014].
C.

Intakes from inhalation based on measurements of radiocaesium
concentrations in air

48.
The third approach makes use of measurements of concentrations of radiocaesium in the
air at various locations in Fukushima Prefecture and elsewhere, derived from re-analysis of filter
tapes for measuring suspended particulate matter at air pollution monitoring stations [Ebihara etal., 2019; Oura et al., 2015; Tsuruta et al., 2014; Tsuruta et al., 2018]. Attachment A-9 provides
further details of these measurements. Twenty-two such monitoring stations are located in, or
close to, Fukushima Prefecture (see figure A-9.II of the annex and figure A-9.XI of attachment A-9).
The time-integrated concentrations of 137Cs in air as measured at these monitoring stations, as well

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

21

as the average for 11 monitoring stations in Tokyo Metropolitan Area, are given in table A-3.4;
in addition, estimated intakes of 137Cs by inhalation (during the period when the plumes
containing the measured concentrations of 137Cs passed by each monitoring station) are given
together with the estimated committed effective doses for an adult from the intake by inhalationof both 134Cs and 137Cs. The uncertainties associated with these measured air concentrations are
relatively small (standard deviation typically less than 10%) and they provide, therefore, a morereliable basis for estimating the contribution of inhalation to the total intake of radiocaesium thanthose based on air concentrations derived from ATDM (see section III.E and table A-3.7).
Table A-3.4. Measured time-integrated concentrations of 137Cs in air and estimates of its intake
by inhalation and resulting committed effective doses
Site of monitoring station

Measured time-integrated
concentration of 137Cs in air
outdoors (Bq s/m3)

Intake of 137Cs by inhalation
for adults (Bq)aCommitted effective dose toadults from intake of 134Cs
and 137Cs (µSv)b

Fukushima Prefecture
Aizuwakamatsu

1 × 105

14

0.16

Asahi

2 × 106280

3.2

Daishin2 × 106

280

3.2

Furukawa

1.5 × 106

220

2.4

Futaba c

2 × 108

28 000320

Haramachi c

1.8 × 107

2 600

29

Kitakata

1 × 10514

0.16

Minami-aizu

4 × 10557

0.63

Minamimachi

2.0 × 106

280

3.1

Moriai

1.9 × 106

260

2.9

Naraha c

7 × 107

9 900

110

Nihonmatsu

3 × 106

420

4.7

Shibata

3 × 10542

0.47

Shinchi

3 × 106420

4.7

Shirakawa2 × 106280

3.2

Shiroishi

1 × 106

140

1.6

Soma

1 × 107

1 400

16

Sugitsumacho

1.8 × 106

250

2.8

Sukagawa

3 × 106

420

4.7

Tanakura

1 × 106

140

1.6

Yabuki2 × 106280

3.2

Yonezawa-kanaike

5 × 105

71

0.79

110

1.2

Tokyo Metropolitan Area
Average of 11 monitoring
stations

7.4 × 105a
Intake assuming 90% occupancy indoors and the ratio of indoor to outdoor concentration of radiocaesium in air of 0.5. Intake of 134Cs assumed
to be the same as that of 137Cs.
b
Committed effective dose assuming 90% occupancy indoors and the ratio of indoor to outdoor concentration of radiocaesium in air of 0.5.
c
Monitoring station located within the 20-km precautionary evacuation zone; people living in the vicinity of the station were evacuated on
12 March 2011 and would not have been exposed to the measured air concentrations.

49.
The parameters used to derive the intakes and committed effective doses are given in table
A-3.5 and it has been assumed that the concentration of 134Cs in air was the same as that of 137Cs.

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

22

Table A-3.5. Ingestion and inhalation effective dose coefficients and daily breathing rates[ICRP, 1993; ICRP, 1995]

Ingestion dose coefficient e50(mSv/Bq)

Inhalation dose coefficient e50(mSv/Bq)a

Daily breathing rate, V (m3/d)aRadionuclide

1-year-old

10-year-old

Adult

134Cs

1.6 × 10−5

1.4 × 10−5

1.9 × 10−5

137Cs

1.2 × 10−5

1.0 × 10−5

1.3 × 10−5

134Cs

7.3 × 10−6

5.3 × 10−6

6.6 × 10−6

137Cs

5.4 × 10−6

3.7 × 10−6

4.6 × 10−6

5.2

15.3

22.2

For aerosols, Type F, AMAD = 1 µm.

50.
It should be noted that the monitoring stations with the highest measured concentrations
137
of Cs in air (Futaba, Naraha, and Haramachi) are within the 20-km precautionary evacuation
zone and that people living in these municipalities (Futaba Town, Naraha Town, and theHaramachi Area of Minamisoma City) were evacuated on 12 March 2011 and would not havebeen exposed to the measured air concentrations. Committed effective doses from intakes byinhalation have been estimated using the assumptions set out in detail in attachment A-10 (i.e.,
people assumed to spend 90% of their time indoors with the time integral of the radiocaesium
concentration indoors being about one half of that outdoors). Subject to these assumptions andexcluding the locations from which people were evacuated, intakes of 137Cs from inhalation
range from about 14 Bq in Aizuwakamatsu City in the west of Fukushima Prefecture to about
1,400 Bq in Soma City to the north of FDNPS. The corresponding committed effective doses
from intakes of radiocaesium by inhalation range from about 0.16 to about 16 µSv.
51.
While these measurements provide a fairly direct and reliable estimate of intakes byinhalation and resulting doses from internal exposure at the monitoring stations where themeasurements were made, they provide no information about the intakes and doses at otherlocations in Fukushima Prefecture or elsewhere in Japan. In order to estimate doses from intakes
by inhalation to the wider population, some interpolation between the measurements or a moregeneral modelling approach would be needed.
D.

Intakes from inhalation based on predicted radiocaesium
concentrations in air

52.
The fourth approach makes use of estimates of concentrations of radiocaesium in the air
derived using an assumed source term and ATDM. This approach is the least direct but still has
its origins in measurements (i.e., the totality of measurements in the environment, in particular,of dose rates and radionuclide concentrations in air and on the ground).
53.
Doses from inhalation of radiocaesium (and other radionuclides) have been estimatedbased on an assumed source term for releases to the atmosphere and models to describe how
released material is dispersed in, and deposited from, the atmosphere. Further details are set out
in attachment A-10. Time-integrated concentrations of radiocaesium in the air, either over thecomplete period of the release for residents, or over the relevant shorter periods for thoseevacuated, can be used with the breathing rates and dose coefficients set out in table A-3.5 toestimate intakes of radiocaesium by inhalation and the corresponding committed effective doses.
54.
The committed effective dose from inhalation of radiocaesium in each municipality ofFukushima Prefecture has been estimated using the methods described in attachment A-10. For
adults who were not evacuated, the committed effective dose from inhalation of radiocaesium inANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

23

each municipality varied over several orders of magnitude from less than 0.001 µSv to more than
100 µSv depending on the temporal pattern of the releases from FDNPS and their dispersion in
the atmosphere. The population-weighted average committed effective dose from inhalation ofradiocaesium to those who were not evacuated in Fukushima Prefecture was about 4 µSv. The
intakes that resulted in these doses would have occurred within the first few days of the accident
during the passage of the plumes of released material. The committed effective dose frominhalation of radiocaesium to adults who were evacuated also varied, from about 0.2 µSv to morethan 100 µSv, depending on the evacuation scenario (i.e., the start, duration, route and finaldestination of the evacuation). The population-weighted average over all of the scenarios was
about 12 µSv.
55.
A comparison has been made in attachment A-9 of the time-integrated concentrations of
Cs in air predicted using the source term and ATDM and the time-integrated concentrations
measured at the monitoring stations (see figure A-9.XII and table A-9.4). At higher
concentrations, the predictions are in good agreement with the measurements (within a factor of
two to three); and at lower concentrations the agreement is less good, with the predictions being
lower than the measurements by up to an order of magnitude or more.
137

E.

Comparison of doses estimated from whole-body measurements withestimates made using a combination of the other approaches

56.
A comparison is made in table A-3.6 between the committed effective doses to adults fromradiocaesium intakes by inhalation and ingestion, as measured in the whole-body monitoringstudies, with the committed effective doses estimated using a combination of the other approaches(specifically, intakes by inhalation based on measured air concentrations and/or estimated using asource term and ATDM and those by ingestion based on Murakami and Oki’s analysis of measured
concentrations of radiocaesium in food and drinking water). Uncertainties, in terms of the 5th and95th percentiles about the estimated doses, are also presented in table A-3.6 and have been derived
as follows: (a) uncertainties were estimated by the respective authors for doses estimated fromwhole-body counting measurements made by Momose et al. [Momose et al., 2012], Hayano et al.
[Hayano et al., 2014] and Kim et al. [Kim et al., 2016], and by the Committee for measurements
made by Tsubokura et al. [Tsubokura et al., 2012] and Hayano et al. [Hayano et al., 2013];(b) uncertainties in doses from intakes by ingestion were those estimated by Murakami and Oki[Murakami and Oki, 2014] for Fukushima City and have been assumed to be equally applicable toother locations throughout Fukushima Prefecture, albeit recognizing that this will introduce
additional uncertainty; 2 and (c) uncertainties in doses from intakes by inhalation, and in doses frominhalation and ingestion combined, were estimated by the Committee using the methods describedin attachment A-12.
57.
Making direct and meaningful comparisons of doses estimated using the different
approaches is not straightforward for two main reasons:(a) Firstly, the dose quantities estimated are often not the same: some estimates are averages
while others are median values; and doses estimated from whole-body measurements
generally represent committed doses from intakes up to the time of the measurement,
whereas doses estimated on the basis of measured levels of radiocaesium in food or air
represent committed doses from annual intakes;

2

The results of the market-basket and duplicate-diet studies for Fukushima Prefecture and other prefectures indicatethat the spatial variation in ingestion doses is not large and the Committee has judged that the variation between
municipalities within Fukushima Prefecture is unlikely to be more than a factor of a few.

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

24(b) Secondly, there is generally insufficient information available (in published material)
about where those measured by whole-body monitoring were at the time of the accident andsubsequently, how they were selected for measurement, to determine how representative
their estimated doses are of the exposures of the wider population groups from which they
were drawn (e.g., of a municipality, a prefecture, an evacuated area, etc.); this hinders
meaningful comparisons with doses estimated using other approaches which are generally
for well-defined populations. Caution therefore needs to be exercised in comparing the doses
in table A-3.6, in particular careful note should be taken of the relevant footnotes that include
qualifications to the entries in the table, in particular their comparability.
58.
Some comments are also warranted about the representativeness of the results of wholebody monitoring included in the table:− Minamisoma City: Hayano et al. [Hayano et al., 2014] and Tsubokura et al. [Tsubokura
et al., 2012] both present results for Minamisoma City. Hayano et al. reported on
measurements made on people who lived in the “most contaminated zone”, about 85%
of whom had been evacuated at various times during March but had since returned. These
measurements cannot therefore be considered representative of residents of Minamisoma
City as a whole. Tsubokura et al. reported on measurements made on 24% of the
population of Minamisoma City many of whom had been evacuated but approximately
half had returned by the time the measurement campaign began. They also stated that theresults may not be representative of the entire population of Minamisoma City because
those measured were volunteers. Disaggregation of the measurements made by bothHayano et al. and Tsubokura et al. (i.e., distinguishing between those who were, and those
who were not, evacuated) would, in principle, enable more reliable estimates to be madeof doses to evacuees and non-evacuees in Minamisoma City; in addition, it would better
inform judgments on how the measurements could be used to infer doses in otherpopulation groups;− Evacuated municipalities: Both Kim et al. [Kim et al., 2016] and Momose et al.
[Momose et al., 2012] reported on measurements made on people from several of themunicipalities that were evacuated, either in March or later. Momose et al. [Momose etal., 2012] presented distributions of dose for six of the municipalities and for all of the
11 municipalities taken together. Subject to any potential bias in the selection of people
measured (with priority given to younger adult females), the estimated doses can beconsidered broadly representative of the evacuated municipalities. The number of people
measured from each of the municipalities included in the study of Kim et al. was notproportional to the population of each municipality (ranging from 1/200 to 1/3,000), andin most of the municipalities was too small (generally less than 10 people) to provide
dose estimates that were either statistically meaningful or that could be considered
representative of a municipality. Even for Namie Town, where the largest number ofpeople measured (90) were from, there is no information about whether those measured
were evacuated before or after the passage of the plumes of released radioactive material;in these circumstances, the estimated doses cannot be considered representative of all of
those evacuated;− Hirata Central Hospital: Hayano et al. [Hayano et al., 2013] reported on measurements
made on residents of a number of prefectures (73% from Fukushima Prefecture, 23% from
Ibaraki Prefecture and the remainder from Miyagi and Tochigi Prefectures). No further
information was provided about where, within these prefectures, those measured were at
the time of the accident or subsequently. The authors acknowledge that their results are notconclusive for the prefecture as a whole and, therefore, the distributions of doses derived
from these measurements cannot be considered representative of Fukushima Prefecture as

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

25

a whole or of any other subset of the population measured. Disaggregation of the measured
intakes and related doses by municipality would be helpful in judging therepresentativeness of the measurements for particular population groups.
59.
Within the uncertainty bounds, and given the inherent differences in the quantities being
compared, the sums of the doses from inhalation and ingestion intakes estimated using the otherapproaches are broadly in agreement with the committed effective doses estimated from the wholebody counting measurements (see table A-3.6). This indicates that the other approaches are able toprovide estimates of doses comparable with the measurements made in people and therefore are
more realistic than the doses presented in the UNSCEAR 2013 Report [UNSCEAR, 2014].
60.
Irrespective of the approach used, the average effective doses from intakes ofradiocaesium are low (both in absolute terms and relative to the total doses from all radionuclides
and all exposure pathways), ranging from a few tens of µSv to about 100 µSv for those
population groups for which whole-body measurements were made.
Table A-3.6. Comparison of effective doses from intakes of radiocaesium estimated from wholebody measurements with those estimated using a combination of other approaches

Population measured
using whole-bodycounting

Minamisoma City aaWhole-body counting(all intakes)

Other approaches(based on measured and predicted concentrationsof radiocaesium in air, food and drinking water)

Committed effective dose
up to time of measurement (μSv)(5th to 95th percentile)

Average committed effective dose from intakes
within first year (μSv)(5th to 95th percentile)

Average

Inhalation

Median~50b~42c/29d[Tsubokura et al., 2012](18–180)(2.6–160e/
18–39f)Minamisoma City i[Hayano et al., 2014]~80j(7–160)

Hirata Central
Hospital m[Hayano et al., 2013]~50n(15–150)

Ingestiong

All intakes~19(8–43h)~61/4813k(4.1–30l)~19g(8–43h)~32~5.1o(0.0040–20p)~19g(8–43h)~24

Evacuated
municipalities q[Momose et al., 2012]~25r(4–150)~7.8s(3.8–14t)~19g(8–43h)~27

Evacuated
municipalities u[Kim et al., 2016]~30–70v(large)w~4.8x(2.4–8.4y)~19g(8–43h)~24

Adult residents of Minamisoma City. According to Tsubokura et al. [Tsubokura et al., 2012], those measured were volunteers and may not be
representative of the whole population; many had been evacuated and approximately half of them had returned by August 2011.
b
Estimated by the Committee assuming short-term intake with all measurements less than MDL assumed to be equal to half MDL. Committed
dose for intakes up to September 2011 to March 2012 (i.e., 6 to 12 months after the accident) and are not directly comparable with those estimatedby other approaches for intakes within the first year. The assumption of a short-term intake may have resulted in a small overestimate (up to a
few tens of per cent) of the dose up to the time of measurement, and including intakes after the time of measurement to derive a dose in the firstyear may add a few tens of per cent to the dose estimated from the whole-body measurement (i.e., the two factors will have partially compensatedeach other). Alternative, plausible, assumptions about how to treat measurements less MDL would be unlikely to alter the estimated dose by
more than several tens of per cent.
cEstimated by the Committee as the average dose for residents of Minamisoma City from air concentrations predicted by scaling measured
deposition densities by ratios derived from ATDM. Not directly comparable with the dose estimated on the basis of whole-body counting as it
is not known what proportion of those measured were evacuees or residents.
d
Estimated by the Committee from the measured time-integrated air concentration in the Haramachi Area of Minamisoma City. May not bedirectly comparable with doses estimated on the basis of whole-body counting as it is not known what proportion of those measured had been
evacuated before the arrival of the plumes nor how representative the measured concentration was for Minamisoma City as a whole.
eEstimated by the Committee taking account of all significant contributors to uncertainty and variability in the predicted doses of residents of
Minamisoma City.
f
Estimated by the Committee taking account of the uncertainty in the measured air concentrations and in the extent to which air concentrations
are reduced inside buildings.

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …
g

26

Estimated by Murakami and Oki [Murakami and Oki, 2014] from measured concentrations in food and drinking water in Fukushima City. The
Committee has assumed this estimate to be applicable to the whole of Fukushima Prefecture while recognizing that there will be some variation
with location. The results of the market-basket and duplicate-diet studies for Fukushima Prefecture and other prefectures indicate that the spatial
variation in ingestion doses is not large and the Committee has judged that the variation between municipalities within Fukushima Prefecture isunlikely to be more than a factor of a few.
h
The quoted percentiles are those estimated by Murakami and Oki for their estimates of doses from ingestion in Fukushima City. The Committee’s
assumption that the estimates for Fukushima City are applicable to Fukushima Prefecture as a whole will increase the quoted uncertainties.
i
Hayano et al. [Hayano et al., 2014] reported only on measurements made of those who lived in “the most contaminated zone”, about 85% ofwhom had been evacuated at different times during March 2011, but had returned in July 2011.
j
Estimated by the authors assuming acute inhalation of radiocaesium in March 2011 and no further intake of radiocaesium up to the time of
measurement (July 2011) and are not directly comparable with those estimated by other approaches for intakes within the first year. The
assumption of an acute intake by inhalation on 12 March may have resulted in a small overestimate (up to a few tens of per cent) of the committed
dose from intakes up to the time of measurement. The estimated doses are not representative for Minamisoma City as a whole as the authors
only reported the results of measurements for those living in the “most contaminated zone”, about 85% of whom were evacuated at various times
in March 2011.
k
Estimated by the Committee as the average dose for evacuees from Haramachi and Kashima Areas of Minamisoma City (who comprised 82%of those measured).
l
Estimated by the Committee taking account of all significant contributors to uncertainty and variability in the predicted doses of evacuees fromHaramachi and Kashima Areas of Minamisoma City.
m
Seventy-three per cent from Fukushima Prefecture, 23% from Ibaraki Prefecture with the remainder from Miyagi and Tochigi prefectures. No
information available on where, within the prefectures, those measured were at the time of the accident or where they lived subsequently within
the respective prefectures.
n
Estimated by the Committee assuming short-term intake with all measurements less than MDL assumed to be equal to half MDL. Committed
dose for intakes up to October 2011 to March 2012 (i.e., 7 to 12 months after the accident) and are not directly comparable with those estimatedby other approaches for intakes within the first year. The Committee has used the measurement data in the first year after the accident at FDNPS,
although the authors restricted their analyses to measurements made after March 2012 because of possible surface contamination of clothes
before this date. The assumption of a short-term intake may have resulted in a small overestimate (up to a few tens of per cent) of the dose up to
the time of measurement. Alternative, plausible, assumptions about how to treat measurements less MDL would be unlikely to alter the estimateddose by more than several tens of per cent. The quoted dose is the average of those measured but, without knowing where the people were,
within the respective prefectures, at the time of the accident and subsequently, it is difficult to attribute this dose to one or other specific populationgroup. The authors acknowledge that their results are not conclusive for Fukushima Prefecture as a whole.
oEstimated by the Committee as the average dose to residents in Fukushima Prefecture based on predicted air concentrations derived by scalingmeasured deposition densities by ratios derived using source term and ATDM. It may not be directly comparable with the dose estimated fromwhole-body counting as it is not known whether those measured were representative of the population of Fukushima Prefecture as a whole.
p
Estimated by the Committee taking account of all significant contributors to uncertainty and variability in the predicted doses of residents ofFukushima Prefecture.
q
Adult evacuees from Futaba Town, Hirono Town, Iitate Village, Katsurao Village, Kawamata Town, Kawauchi Village, Minamisoma City,
Namie Town, Naraha Town, Okuma Town and Tomioka Town. Measurements initially made (from 11 July 2011) on evacuees from Iitate
Village, Kawamata Town and Namie Town, and from 1 September 2011 on those from elsewhere. No information is available on the numbersof those measured in each municipality.
r
Estimated by the authors by extrapolating to the 50th percentile assuming a log-normal distribution. Committed dose for intakes up to July
2011 to January 2012 (i.e., 3 to 10 months after the accident) and are not directly comparable with those estimated by other approaches forintakes within the first year. The assumption of an acute intake by inhalation on 12 March may have resulted in a small overestimate (up to a
few tens of per cent) of the committed dose from intakes up to the time of measurement. The median dose and percentiles take no account ofpotential bias consequent upon a fraction of the measurements being affected by contamination on clothes (see section III.A.1). The quoted value
is the median dose of those measured which is not necessarily the median dose of the population of the evacuated municipalities and, therefore,
not directly comparable with the doses estimated using other approaches which are the averages for the population of all of the evacuatedmunicipalities. The authors also presented dose distributions for each of the six evacuated municipalities, with the doses varying from about afactor of two lower, to a few tens of per cent higher, than those for all municipalities.
s
Estimated by the Committee as the average dose for all evacuees from Fukushima Prefecture based on predicted air concentrations using source
term and ATDM. It may not be directly comparable with the dose estimated from whole-body counting as it is not known whether those measured
were representative of evacuees as a whole.
t
Estimated by the Committee taking account of all significant contributors to uncertainty and variability in the predicted doses of evacuees as a whole.
u
Adult evacuees from the same municipalities as in footnote q apart from Minamisoma City and inclusion of Tamura Town. More than half of
those measured were from Namie Town, about 11% from Iitate Village and about 7% from each of Kawamata Town and Futaba Town. Mediandoses only estimated for Namie Town, Iitate Village and Futaba Town.
v
Estimated by the authors assuming a log-normal distribution. Committed dose for intakes up to June 2011 to July 2011 (i.e., 3 to 4 months after
the accident) and are not directly comparable with those estimated by other approaches for intakes within the first year. The assumption of anacute intake by inhalation on 12 March may have resulted in a small overestimate (up to a few tens of per cent) of the committed dose fromintakes up to the time of measurement. The quoted values are the range of median doses of those measured in Futaba Town (68 μSv), Iitate
Village (27 μSv) and Namie Town (26 μSv), which are not necessarily the median dose in the whole population of the evacuated municipalities
and, therefore, not directly comparable with the average doses for the whole population of the 11 evacuated municipalities estimated using theother approaches.
w
Uncertainties are large because of the small numbers of people measured (90, 20 and 12 in Namie Town, Iitate Village and Futaba Town,
respectively). 5th percentiles not determined (less than MDL) and the 95th percentiles are a factor of about 5 to 6 times greater than the median values.
x
Estimated by the Committee as the average dose for evacuees, with account taken of where those measured were evacuated from, based on
predicted air concentrations using source term and ATDM; the estimated dose is directly comparable with that estimated based on whole-bodycounting but is not representative of the dose for all evacuees, rather just those measured.
yEstimated by the Committee taking account of all significant contributors to uncertainty and variability in the predicted doses of evacuees taking
account of where those measured were evacuated from.

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

27

61.
The comparison between doses estimated from whole-body counting and the otherapproaches can also provide some insights into the relative contribution of inhalation andingestion to the intake of radiocaesium; caution should however be exercised in drawing too
definitive conclusions given the various qualifications on the estimated doses and theircomparability (see footnotes to table A-3.6). For Minamisoma City, where those measured werecombinations of evacuees and residents, the contribution of inhalation is of the order of 60 to80%, based on measured and predicted air concentrations, respectively. In evacuatedmunicipalities, the contribution of inhalation is about 20–40%, albeit associated with large
uncertainty owing to significant uncertainties in the intakes, in particular, the predicted air
concentrations. For those measured by Hayano et al. [Hayano et al., 2013] at Hirata Central
Hospital (about three-quarters and one-quarter, respectively, from Fukushima and Ibaraki
prefectures), the contribution of inhalation is about 15–20%, albeit associated with significant
uncertainty owing to lack of information on where those measured were within the respective
prefectures (i.e., whether they were distributed pro rata with the prevailing population density)
at the time of the accident and subsequently.
62.
More meaningful estimates of the contribution of inhalation can be obtained frommeasured air concentrations [Oura et al., 2015] of radiocaesium at numerous locations inFukushima Prefecture and elsewhere in Japan, in particular as they are associated with muchsmaller uncertainties than those predicted on the basis of an assumed source term and ATDM. The
relative contributions of inhalation and ingestion to the average committed effective dose in thefirst year for Fukushima City and the Tokyo Metropolitan Area are given in table A-3.7. The doses
from inhalation are based on the average measured air concentrations at four monitoring stations
in Fukushima City and 11 stations in the Tokyo Metropolitan Area; the doses from ingestion arethose estimated by Murakami and Oki [Murakami and Oki, 2014]. The contribution of inhalation
to the total dose is about 13% at Fukushima City and about 16% for the Tokyo Metropolitan Area.
These may be more indicative of the contribution from inhalation across larger (non-evacuated)areas of Fukushima Prefecture than those that can be derived from table A-3.6.
Table A-3.7. Relative contributions of inhalation and ingestion to committed effective dose fromthe intake of radiocaesium
Average committed effective dosefrom intakes of radiocaesium within the first year (μSv)(5th to 95th percentile)

Location

Fukushima City
Tokyo Metropolitan Areaa

Inhalation

Ingestion

All intakes

~2.8a

~19b

(1.7–4.0)(8–43)~22(4–39)~1.2c(0.11–2.4)~6.1b(3.0–12)~7.3(2.7–12)

Average of measured time-integrated air concentrations of 137Cs at four monitoring stations in Fukushima City (Furukawa, Minamimachi,
Moriai and Sugitsumacho) [Oura et al., 2015]; average time-integrated air concentration 1.8 106 Bq s/m3.
b
Average ingestion doses estimated by Murakami and Oki [Murakami and Oki, 2014].
c
Average of measured time-integrated air concentrations of 137Cs at 11 monitoring stations in Tokyo Metropolitan Area (Edogawakuminamikasai, Hachiojishi-Kawaguchimachi, Hachiojishi-tatemachi, Himonya, Kannanadori-kakinokizaka, Kannanadori-matsubarabashi,
Katsushikaku-mizumotokoen, Machidashi-nogaya, Nakaharakaido-minamisenzoku, Omeshi-higashiome and Setagayaku-seijyo) [Oura et al.,2015]; average time-integrated air concentration 7.4 105 Bq s/m3.

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

F.

28Approach adopted by the Committee in updating its estimates in the
UNSCEAR 2013 Report of doses from the intake of radionuclides in
the first year63.
As in its UNSCEAR 2013 Report [UNSCEAR, 2014], the Committee has chosen to use
a less direct modelling approach in updating its estimates of doses from the intakes of allradionuclides (including those of radiocaesium) by inhalation and ingestion. Doses from intakes
by inhalation have been estimated using an assumed source term and ATDM as described inattachment A-10. Doses from intakes by ingestion in the first year have been based on theestimates of Murakami and Oki [Murakami and Oki, 2014]. This approach was adopted taking
account of the following:(a) While the whole-body counting measurements are informative of intakes of, and doses
from, radiocaesium at particular locations or for particular population groups (e.g.,
Minamisoma City, the evacuated municipalities), they are limited in the extent to which
they can provide a basis for estimating doses from intakes of radiocaesium elsewhere(i.e., for the whole of Japan) and/or for the wide spectrum of radionuclides released in a
nuclear accident;(b) In these circumstances, the use of an assumed source term and ATDM was the only way
in which the Committee could estimate the spatial variation in doses from intakes of allradionuclides by inhalation across the whole of Fukushima Prefecture and elsewhere in
Japan;(c) The analysis carried out by Murakami and Oki of intakes of, and related doses from,ingestion of radionuclides provides the only method currently available for consistently
estimating doses from all relevant radionuclides from ingestion of food and drinking
water from the early period after the accident onwards;(d) Whole-body monitoring measurements are only informative about total intakes ofradiocaesium (and not of other radionuclides, or about the relative contribution frominhalation or ingestion) up to the time of measurement; market-basket and duplicate-dietstudies are only informative about intakes by ingestion at the time the studies were carriedout.
64.
For doses from ingestion, the estimates of Murakami and Oki have been used. The
authors made estimates of doses (and their associated uncertainties) to males and females andfor several age groups: (a) the average dose estimates for males and females have been used,(b) the doses for those aged 1–6 years have been used for the 1-year-old infant, (c) the doses for
those aged 7–12 years have been used for the 10-year-old child, and (d) the doses for those aged
19 years or more have been used for adults. For the 1-year-old infant, this may have resulted inan overestimate in the dose by a few tens of per cent because of the age dependence of the dosefrom internal exposure from ingestion of radiocaesium. This approach is consistent with theapproach adopted for intakes of radioiodine (see attachment A-2) and results in estimates ofdoses from ingestion that are broadly comparable with those from the market-basket andduplicate-diet studies and with the whole-body monitoring studies. The Committee has assumed
that Murakami and Oki’s dose estimates for Fukushima City are applicable to the whole of
Fukushima Prefecture while recognizing that there will be some variation with location. The
results of the market-basket and duplicate-diet studies for Fukushima Prefecture and otherprefectures indicate that the spatial variation in ingestion doses is not large and the Committee
has judged that the variation between municipalities within Fukushima Prefecture is unlikely to
be more than a factor of a few.

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

29

65.
For neighbouring (Group 3) and distant (Group 4) prefectures, doses from ingestion ofradiocaesium have been estimated from the doses for Fukushima Prefecture according to the ratiosof the average doses from ingestion for these groups of prefectures to the average dose fromingestion for Fukushima Prefecture estimated in the UNSCEAR 2013 Report [UNSCEAR, 2014].
These average doses in the UNSCEAR 2013 Report had been estimated from a large database ofmeasurements of food sampled in 2011 from markets all over the country (see attachment C-8 of
the UNSCEAR 2013 Report), and have been used as a surrogate for the averages of the measured
concentrations. The resulting ratios for radiocaesium are: Group 3/Group 2 = 0.23 and Group
4/Group 2 = 0.143 (see appendix C and attachment C-15 of the UNSCEAR 2013 Report). The
resulting doses for the Group 3 and Group 4 prefectures are broadly consistent with the estimatesfrom Murakami and Oki [Murakami and Oki, 2014] for the Osaka and Tokyo Metropolitan Areas.
66.
Since food rations were sampled either from local families or from food markets withsubsequent culinary processing, the data on the radiocaesium content of the food and drinks takes
into account the effects of remediation and of the monitoring and inspection measures applied inagriculture and forested areas (see chapter IV of the annex B). In the long term, if these measures
were to be relaxed there may be some minor increase in corresponding ingestion doses, and thenthe long-term dose projections may become somewhat underestimated.
67.
Absorbed doses to red bone marrow, breast and colon from the ingestion of radiocaesium
have been assessed from the effective dose estimates using the respective ratios of the dosecoefficients for the absorbed dose in each organ from ingestion of radiocaesium to the effective
dose coefficients in each age group [ICRP, 1993; ICRP, 1995].

IV. ESTIMATING DOSES FROM INTERNAL EXPOSURE DUE TO
INTAKES OF RADIOCAESIUM BY INGESTION AFTER THE
FIRST YEAR
68.
To assess doses from ingestion after the first year, the information from the market-basket
and duplicate-diet studies has been used. These studies provide a direct estimate of intakes ofradiocaesium from ingestion from about July 2011 onwards and an indication of intakes in 2012
and 2013 [Harada et al., 2013; Harada et al., 2014; Koizumi et al., 2012; Sato et al., 2013;
Tsutsumi et al., 2013; Uekusa et al., 2014]. The data were collected between July 2011 andMarch 2013. In order to use the combined results of these studies, the Committee has adjusted
the resulting estimates of intakes to the same date, 15 March 2012, taking account of both
radioactive decay and the decline in the radiocaesium concentrations in foods predicted by themodel of Smith et al. [Smith et al., 2017] following the deposition of the radiocaesium on to theground (see below).
69.
The results are summarized in table A-3.8, which gives the mean, median and otherstatistical parameters of the distributions of the estimates of the daily intake by ingestion of 134Cs
and 137Cs for adult residents of Fukushima Prefecture, four neighbouring prefectures and eight
distant prefectures of Japan.
70.
The intakes were highest in Fukushima Prefecture, lower by a factor of 1.3 in theneighbouring prefectures, and lower by a factor of three in distant prefectures of Japan. The ratios
do not directly reflect the ratios of 137Cs soil deposition densities in corresponding areas becauseof the system of food supply and distribution in Japan.
71.
For comparison, Murakami and Oki [Murakami and Oki, 2014] estimated an effective
dose rate for adults from ingestion of 134Cs and 137Cs in Fukushima City in March 2012 of

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

30

0.44 µSv per month. Assuming that the ratio of 134Cs to 137Cs at the time of the accidental releaseof these radionuclides was 1:1, this dose rate would correspond to intake rates of about 0.4 Bq/dof 134Cs and of about 0.5 Bq/d of 137Cs. These intakes are within a factor of two of the mean
daily intakes in Fukushima Prefecture estimated for March 2012 from the market-basket andduplicate-diet studies, as presented in table A-3.8.
72.
Uekusa et al. [Uekusa et al., 2014] provides information to enable comparisons between
the estimated intakes of children of various age groups with the intakes of adults. The authors
collected duplicate diets from six children in each of three age groups and from 21 adults (definedas 13 years old and above) in each of the nine prefectures, and analysed the samples for theirradiocaesium content. The Committee derived the ratios of the median intakes for children to themedian intakes for adults in each prefecture in 2011–2012. The average value of these ratios was
0.57 for both of the age groups 1–6 years and 6–12 years. Although the number of participantsin each prefecture was quite limited, the ratios were similar in all the nine studied prefectures.
Table A-3.8. Estimates of the daily intake for adults from ingestion of radiocaesium, derived
from the market-basket and duplicate-diet studies, adjusted to 15 March 2012 [Harada et al.,2013; Harada et al., 2014; Koizumi et al., 2012; Sato et al., 2013; Tsutsumi et al., 2013;
Uekusa et al., 2014]
Location
Fukushima Prefecture

Neighbouring prefectures

Distant prefecturesab

Daily intake (Bq/d)

No. ofstudies aRadionuclide

18

11

33

Mean

Median

SD b

Min.

Max.

134Cs

0.72

0.44

0.53

0.19

2.1

137Cs

1.0

0.78

0.75

0.27

3.1

134Cs

0.43

0.37

0.16

0.28

0.79

137Cs

0.60

0.49

0.21

0.36

1.1

134Cs

0.26

0.24

0.16

0.075

0.68

137Cs

0.32

0.25

0.22

0.090

0.99

The six papers cited included 62 studies in total in different prefectures/municipalities.
Standard deviation.

73.
To estimate doses over the longer term from ingestion of food containing radiocaesium,
Smith et al. [Smith et al., 2017] have developed a model to predict the time-dependent changes
in the concentration of radiocaesium in foods following its deposition. The authors focused on
137
Cs as being the radionuclide of most concern over the longer term, given the 2-year half-lifeof 134Cs. They made use of over 4,000 measurements of the concentration of 137Cs in foods andin the whole diet in Japan carried out over 50 years prior to the FDNPS accident, where thesources of the 137Cs were atmospheric nuclear weapons’ testing and the Chernobyl accident. The
model included: (a) a fast decline in concentrations in foods or the whole diet following
deposition, to represent rapid wash-off from plant surfaces and initial sorption to soil; (b) a slow
decline, to represent soil fixation processes; and (c) a very long-term component, to represent
declines due to vertical migration, erosion and further slow reductions in bioavailability.
Different combinations of the model parameters were used to find the best fit to the long-term
measurement data. Measurement data from five regions not used in model development werethen used to test the model predictions and good agreement was found. In addition, whole dietmeasurements made following the FDNPS accident provided a further test of the model andshowed consistency with the rapid decline component.

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

31

74.
The doses from ingestion of radiocaesium after the first year were assessed using themodel of Smith et al. [Smith et al., 2017], which used the following generic equation A-3.2:𝑡𝑡

𝐶𝐶(𝑡𝑡) = ∫−∞ 𝐷𝐷(𝜏𝜏) ∙ (𝐴𝐴 ∙ 𝑒𝑒 − (λ+k1)(t-τ)+B ∙ 𝑒𝑒 −( λ+k2)(t-τ)+C ∙ 𝑒𝑒 − (λ+k3)(t-τ))d𝜏𝜏(A-3.2)where C(t) is the activity concentration of the radionuclide in the environmental compartment ofinterest (wheat, rice, vegetables, in Bq/kg and whole diet, in Bq/d) at time t (y), and D(τ) in(Bq/(m2 y)) is the time-dependent radionuclide ground deposition rate at time, τ (y) precedingtime t. A, B, and C (m2/kg for foodstuffs; m2/d for diet) are coefficients representing, respectively,a fast decline in activity concentrations after fallout (at rate k1, y−1), a slow decline (at rate k2, y−1)
as a result of soil fixation processes, and the very long-term component (at rate k3, y−1), which
declines due to vertical migration, erosion and further slow reductions in bioavailability; λ is thephysical decay constant of 137Cs.
75.
Equation A-3.2 was fitted to the monitoring data from 1963–2008 collected innine prefectures of Japan to derive the following parameter values for the whole diet (with 98%
coverage limits in brackets):− B (m2/d) = 9.6 × 10−4 (6.1×10−4 – 1.3×10−3)− k2 (y−1) = 0.89 (0.52 – 1.3)
− C (m2/d) = 6.4 × 10−5 (4.7×10−5 – 8.1×10−5)− k3 (y−1) = 0.051 (0.042 – 0.060).
76.
data.

The short-term parameters A and k1 are not necessary for fitting long-term monitoring77.
For a single deposition on the ground D (Bq/m2) at t = 0, and for times, t, greater than ayear after this deposition (when the short-term decline has had effect and can be ignored), thismodel can be used to predict the intake, ia, of caesium radionuclide, a, in the whole daily diet asa result of this short-term deposition according to the following equation A-3.3:
Ia(t) = D·exp-(λa.t).(B·exp-(k2.t) + C·exp-(k3.t)), Bq/d,(A-3.3)where the parameter values and their uncertainty are presented above.
78.
The declines over time given by this equation have been used with the estimated intakes
adjusted to 15 March 2012 (t = θ) from the market-basket and duplicate-diet studies describedabove, and set out in table A-3.8, according to the following equation A-3.4:
Ia(t) = Ia(θ).exp-(λa.(t-θ)).(2.1 exp (−0.89·t) + 0.14 exp (−0.051·t)), Bq d−1(A-3.4)

where λ137 = 0.023 y−1 and λ134 = 0.336 y−1 are the physical (radioactive) decay constants for137
Cs and 134Cs, respectively, and the factors of 2.1 and 0.14 (unitless) have been derived fromequation A-3.3 for time θ = 1 y, as follows:
D = Ia(θ)/(exp-(λa.θ).(B·exp-(k2.θ) + C·exp-(k3.θ)))Therefore,
Ia(t) = Ia(θ).exp-( λa.(t-θ)).(B* exp (-k2·t) +C* exp (-k3·t))
where (for θ = 1 y):B* = B/(B·exp-k2 + C·exp-k3) = 2.1
C* = C/(B·exp-k2 + C·exp-k3) = 0.14

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

32

79.
The committed effective dose, Ea, in mSv can then be calculated from the intake in Bq
using the dose coefficients for ingestion for each radionuclide given in table A-3.5. Doses
projected for the long-term periods of 1–10 years and 11–60 years (i.e., up to age 80 for adults)
after deposition have been calculated using the formulae A-3.5a and 5b:
10

Ea(1–10) = ∫1 𝐸𝐸𝑎𝑎 (𝑡𝑡) ∙ 𝑑𝑑𝑑𝑑, mSv(A-3.5a) or60

Ea(11–60) = ∫11 𝐸𝐸𝑎𝑎 (𝑡𝑡) ∙ 𝑑𝑑𝑑𝑑, mSv(A-3.5b)

V. UPDATED ESTIMATES OF COMMITTED EFFECTIVE DOSESFROM INTAKE OF RADIOCAESIUM
80.
Updated estimates of committed effective doses from inhalation of radiocaesium (alongwith all other radionuclides), using a source term and ATDM, are presented in attachment A-10
and are not addressed further here.
81.
The updated estimate of the committed effective doses from ingestion of radiocaesium
for adults in Fukushima Prefecture is 19 μSv in the first year. This value was estimated by
Murakami and Oki [Murakami and Oki, 2014] for Fukushima City and has been assumed toapply to the whole of Fukushima Prefecture. The corresponding committed effective doses for
10-year-old children and 1-year-old infants are given in table A-3.9, as are the committed
effective doses in neighbouring prefectures and other prefectures in Japan estimated as describedin section III.F above.
Table A-3.9. Updated estimates of the prefecture average committed effective doses to adults,
children and infants, in different population groups, from the ingestion of 134Cs and 137Cs fromfood and drinking water in the first year
Population
group

Location

Prefecture average committed effective dose from ingestion of
134Cs and 137Cs (μSv)
1-year-old

10-year-old

Adult

2

Fukushima Prefecture

8.0

12

19

3

Neighbouring prefectures

1.8

2.8

4.4

4

Distant prefectures

1.1

1.7

2.7

82.
The 5th and 95th percentiles on these estimates are about a factor of two below and afactor of five above the average committed effective dose for Fukushima Prefecture [Murakami
and Oki, 2014]; for other prefectures, expert judgment has been used by the Committee to derive
5th and 95th percentiles of factors of 0.3 to 3 times the average dose.
83.
For those evacuated, surveys have indicated that intakes of radionuclides in food would
have been very low in the period before and during evacuation, because most of the food that
evacuees consumed immediately after the accident was sourced from either stockpiles prepared
before the accident or relief supplies from outside the affected areas [Hirakawa et al., 2017]. So,
only committed effective doses from ingestion of food once the evacuees reached theirdestination have been included in their estimated first year doses.
84.
Intakes of radiocaesium from ingestion in the first year would have continued over thewhole of the year at a generally declining rate, albeit with shorter term deviations from this trend
depending on the foods consumed (e.g., consumption of wild produce with enhanced levels ofradiocaesium).

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

33

85.
Committed effective doses from intakes of radiocaesium by ingestion after the first year
have been estimated using intakes of radiocaesium from ingestion derived from the market-basket
and duplicate-diet studies and the model of Smith et al. [Smith et al., 2017] (see section IV). The
average doses up to 10 years after the accident and for lifetimes are shown in table A-3.10 for
adults for Fukushima Prefecture, four neighbouring prefectures and for the rest of Japan. The
5–95% range of doses was estimated by the Committee using the Monte-Carlo simulation.
86.
The data in table A-3.10 show that projected doses to adults from ingestion ofradiocaesium are very low, ranging from 5 to 14 µSv over 1–10 years and from 1 to 4 µSv over
11–60 years over all prefectures. The new ingestion dose estimates for doses after the first year
based on whole ration measurements in 2011–2013 and the model of Smith et al. [Smith et al.,2017] are about a factor of five to six times lower than similar internal doses presented in the
UNSCEAR 2013 Report [UNSCEAR, 2014].
Table A-3.10. Updated estimates of prefecture average and percentiles of committed effective
doses to adults from ingestion of radiocaesium in food and drinking water after the first year
Committed effective dose to adults (μSv)
Time period(years)QuantityGroup 2
Fukushima PrefectureGroup 3Neighbouring
prefectures

Group 4
Distant prefectures

1–10

Average

14

8.3

4.6

5–95%

6–31

4–18

2.1–10

Average

3.8

2.3

1.2

5–95%

1.0–15

0.4–15

0.3–5

11–60

87.
Mean committed effective doses to other age groups from ingestion of 134Cs and 137Cs
were estimated taking account of the age dependence of the intakes by ingestion derived from
[Uekusa et al., 2014]. Resulting average committed effective doses in the first year, in the first
10 years and up to age 80 years for all three age groups are given in table A-3.11.
Table A-3.11. Updated estimates of prefecture average committed effective doses (µSv) to
1-year-old infants, 10-year-old children and adults from ingestion of radiocaesium in food anddrinking water over different time periods
Age(in 2011)
1-year-old infants

10-year-old children

AdultsExposure duration(years)Group 2
Fukushima PrefectureGroup 3Neighbouring
prefectures

Group 4
Distant prefectures

1

8.0

1.8

1.1

10

16

6.5

3.7

Up to age 80

20

8.8

4.9

1

12

2.8

1.7

10

23

8.3

5.3

Up to age 80

27

11

6.5

1

19

4.4

2.7

10

33

13

7.3

Up to age 80

37

15

8.5

88.
Based on Murakami and Oki [Murakami and Oki, 2014], a Monte-Carlo simulation of
long-term processes (see table A-3.10) and expert judgment, the Committee has assessed thecoverage interval (5–95%) for the prefecture-averaged doses in table A-3.11 as being between
0.3 and 3.0 times the respective doses.

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

34

VI. MICROPARTICLES
89.
Several studies have identified radiocaesium in the environment associated with waterinsoluble “glassy spherules”. The fraction of the radiocaesium deposited on to the ground in the formof such microparticles varies from a few per cent at distances of up to 30 km from FDNPS to up to
about 80% at large distances (more than 200 km) [Ikehara et al., 2020; Utsunomiya et al., 2019].
90.
The solubility of these microparticles in water, sea water and a pulmonary fluid simulator
has been studied in several experiments [Okumura et al., 2019; Suetake et al., 2019; Utsunomiya
et al., 2019]. Dissolution of microparticles was found to occur much faster in seawater (Т1/2 =1.7 years) than in pure water (Т1/2 = 17 years excluding decay) [Okumura et al., 2019]. In anotherseries of experiments with larger particles, Suetake et al. [Suetake et al., 2019] showed that the
dissolution of microparticles in a pulmonary fluid simulator occurs more rapidly than in purewater or seawater, however, the dissolution time in this case was of the order of a few decades.
91.
Due to the low solubility of radiocaesium associated with microparticles, one can assume
their slower migration deep into the soil and, accordingly, a slower decrease in dose rate fromexposure to deposited material. On the other hand, these particles are not fixed in clay, likecaesium cations, and can be transported faster from the soil by precipitation, including into water
bodies. The overall effect of these processes on the external exposure of a person has not yet
been studied. However, the updated model used in this report to assess external exposures todeposited material has taken account of the observed slower decrease in the dose rate over soils
in Japan than observed after the Chernobyl accident in Ukraine [Likhtarev et al., 2002] and theRussian Federation [Golikov et al., 2002] (see attachment A-1); however, it is not apparent what
influence microparticles play in this process.
92.
With regard to inhalation of radiocaesium from the plume of released radionuclides, theslow dissolution of the microparticles would class them according to type S (slow) biokinetics
in the respiratory tract. For this category, dose coefficients [ICRP, 1995] are an order ofmagnitude higher than for more highly soluble forms (type F). The respiratory tract, in particular
the lungs, would be predominantly exposed. It would follow that, in the presence of a significant
fraction of microparticles (10% or more) in the mixture of caesium radionuclides inhaled fromthe plume, these particles could increase the estimated dose from inhalation.
93.
In the case of surface contamination of vegetables with caesium-bearing microparticles,
the ingestion dose would be lower compared with soluble forms of radiocaesium because of theirmuch lower solubility in the gastro-intestinal tract (i.e., by about an order of magnitude). In
addition, the reduced solubility of the microparticles would reduce the uptake of radiocaesium
from soil into the food chain.
94.
The effect of such microparticles on estimated doses is therefore complex, resulting inhigher doses from one exposure pathway and lower doses from another, than as assumed in themodels used in this report. While the presence and behaviour of radiocaesium in the environment
in the form of microparticles is worthy of further scientific investigation, the Committee judgesthat it will have no material impact on the overall levels of dose to the public estimated in its
update of its UNSCEAR 2013 Report [UNSCEAR, 2014].

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

35

REFERENCES
Brown, J. and J.R. Simmonds. FARMLAND a dynamic model for the transfer of radionuclides
through terrestrial foodchains. NRPB-R273. National Radiological Protection Board,
Chilton, 1995.
Ebihara, M., Y. Oura, N. Shirai et al. A new approach for reconstructing the (131)I-spreading
due to the 2011 Fukushima nuclear accident by means of measuring (129)I in airborne
particulate matter. J Environ Radioact 208-209: 106000 (2019).
Golikov, V.Y., M.I. Balonov and P. Jacob. External exposure of the population living in areasof Russia contaminated due to the Chernobyl accident. Radiat Environ Biophys 41(3):185-193 (2002).
Harada, K.H., Y. Fujii, A. Adachi et al. Dietary intake of radiocesium in adult residents inFukushima prefecture and neighboring regions after the Fukushima nuclear power plant
accident: 24-h food-duplicate survey in December 2011. Environ Sci Technol 47(6):2520-2526 (2013).
Harada, K.H., T. Niisoe, M. Imanaka et al. Radiation dose rates now and in the future forresidents neighboring restricted areas of the Fukushima Daiichi Nuclear Power Plant.
Proc Natl Acad Sci U S A 111(10): E914-923 (2014).
Hayano, R.S., M. Tsubokura, M. Miyazaki et al. Internal radiocesium contamination of adults
and children in Fukushima 7 to 20 months after the Fukushima NPP accident as measured
by extensive whole-body-counter surveys. Proc Jpn Acad Ser B Phys Biol Sci 89(4): 157163 (2013).
Hayano, R.S., Y.N. Watanabe, S. Nomura et al. Whole-body counter survey results 4 months
after the Fukushima Dai-ichi NPP accident in Minamisoma City, Fukushima. J Radiol
Prot 34(4): 787-799 (2014).
Hirakawa, S., N. Yoshizawa, K. Murakami et al. Surveys of food intake just after the nuclear
accident at the Fukushima Daiichi Nuclear Power Station. Shokuhin Eiseigaku Zasshi
58(1): 36-42 (2017).
ICRP. Age-dependent doses to members of the public from intake of radionuclides: Part 2.
Ingestion dose coefficients. ICRP Publication 67. Annals of the ICRP 23. International
Commission on Radiological Protection, Pergamon Press, Oxford, 1993.
ICRP. Age-dependent doses to members of the public from intake of radionuclides: Part 4.
Inhalation dose coefficients. ICRP Publication 71. Annals of the ICRP 25. International
Commission on Radiological Protection, Pergamon Press, Oxford, 1995.
Ikehara, R., K. Morooka, M. Suetake et al. Abundance and distribution of radioactive cesiumrich microparticles released from the Fukushima Daiichi Nuclear Power Plant into theenvironment. Chemosphere 241: 125019 (2020).
Kim, E., O. Kurihara, N. Kunishima et al. Early intake of radiocesium by residents living near
the TEPCO Fukushima Dai-Ichi Nuclear Power Plant after the accident. Part 1: Internal
doses based on whole-body measurements by NIRS. Health Phys 111(5): 451-464(2016).
Koizumi, A., K.H. Harada, T. Niisoe et al. Preliminary assessment of ecological exposure ofadult residents in Fukushima Prefecture to radioactive cesium through ingestion andinhalation. Environ Health Prev Med 17(4): 292-298 (2012).

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

36

Likhtarev, I.A., L.N. Kovgan, P. Jacob et al. Chernobyl accident: retrospective and prospective
estimates of external dose of the population of Ukraine. Health Phys 82(3): 290-303(2002).
Matsuda, N., A. Kumagai, A. Ohtsuru et al. Assessment of internal exposure doses in Fukushima
by a whole body counter within one month after the nuclear power plant accident. Radiat
Res 179(6): 663-668 (2013).
Minamisoma. Results of internal exposure examination. [Internet] Available from(https://www.city.minamisoma.lg.jp/portal/health/hoshasen_hibaku/3/4/index.html) on
01 October 2020. (Japanese).
Momose, T., C. Takada, T. Nakagawa et al. Whole-body counting of Fukushima residents after
the TEPCO Fukushima Daiichi nuclear power station accident. pp.67-82 in: The 1st
NIRS Symposium on Reconstruction of Early Internal Dose in the TEPCO Fukushima
Daiichi Nuclear Power Station Accident (O. Kurihara et al., eds.). National Institute ofRadiological Sciences, Chiba, 2012.
Morita, N., M. Miura, M. Yoshida et al. Spatiotemporal characteristics of internal radiation
exposure in evacuees and first responders after the radiological accident in Fukushima.
Radiat Res 180(3): 299-306 (2013).
Murakami, M. and T. Oki. Estimated dietary intake of radionuclides and health risks for the
citizens of Fukushima City, Tokyo, and Osaka after the 2011 nuclear accident. PLoS One
9(11): e112791 (2014).
Okumura, T., N. Yamaguchi, T. Dohi et al. Dissolution behaviour of radiocaesium-bearing
microparticles released from the Fukushima nuclear plant. Sci Rep 9(1): 3520 (2019).
Oura, Y., M. Ebihara, H. Tsuruta et al. A database of hourly atmospheric concentrations ofradiocesium (134Cs and 137Cs) in suspended particulate matter collected in March 2011at 99 air pollution monitoring stations in eastern Japan. J Nucl Radiochem Sci 15(2):1-12 (2015).
Sato, O., S. Nonaka and J.I. Tada. Intake of radioactive materials as assessed by the duplicate
diet method in Fukushima. J Radiol Prot 33(4): 823-838 (2013).
Smith, J.T., K. Tagami and S. Uchida. Time trends in radiocaesium in the Japanese diet following
nuclear weapons testing and Chernobyl: Implications for long term contamination postFukushima. Sci Total Environ 601-602: 1466-1475 (2017).
Suetake, M., Y. Nakano, G. Furuki et al. Dissolution of radioactive, cesium-rich microparticles
released from the Fukushima Daiichi Nuclear Power Plant in simulated lung fluid, purewater, and seawater. Chemosphere 233: 633-644 (2019).
Sugimoto, A., S. Gilmour, M. Tsubokura et al. Assessment of the risk of medium-term internal
contamination in Minamisoma City, Fukushima, Japan, after the Fukushima Dai-ichi
nuclear accident. Environ Health Perspect 122(6): 587-593 (2014).
Tsubokura, M., S. Gilmour, K. Takahashi et al. Internal radiation exposure after the Fukushima
nuclear power plant disaster. JAMA 308(7): 669-670 (2012).
Tsubokura, M., S. Kato, S. Nomura et al. Reduction of high levels of internal radiocontamination by dietary intervention in residents of areas affected by the Fukushima
Daiichi Nuclear Plant Disaster: a case series. PLOS ONE 9(6): e100302 (2014).
Tsuruta, H., Y. Oura, M. Ebihara et al. First retrieval of hourly atmospheric radionuclides justafter the Fukushima accident by analyzing filter-tapes of operational air pollution
monitoring stations. Sci Rep 4: 6717 (2014).

ANNEX B, ATTACHMENT A-3: THE ESTIMATION OF WHOLE-BODY DOSES FROM THE INTAKE OF RADIOCAESIUM …

37

Tsuruta, H., Y. Oura, M. Ebihara et al. Time-series analysis of atmospheric radiocesium at two
SPM monitoring sites near the Fukushima Daiichi Nuclear Power Plant just after the
Fukushima accident on March 11, 2011. Geochem J 52(2): 103-121 (2018).
Tsutsumi, T., H. Nabeshi, A. Ikarashi et al. [Estimation of the committed effective dose ofradioactive cesium and potassium by the market basket method]. Shokuhin Eiseigaku
Zasshi 54(1): 7-13 (2013). (Japanese).
Uekusa, Y., H. Nabeshi, T. Tsutsumi et al. [Estimation of dietary intake of radioactive materials
by total diet methods]. Shokuhin Eiseigaku Zasshi 55(4): 177-182 (2014). (Japanese).
UNSCEAR. Sources, Effects and Risks of Ionizing Radiation. Volume I: Report to the General
Assembly and Scientific Annex A. UNSCEAR 2013 Report. United Nations ScientificCommittee on the Effects of Atomic Radiation. United Nations sales publication
E.14.IX.1. United Nations, New York, 2014.
UNSCEAR. Developments since the 2013 UNSCEAR Report on the Levels and Effects ofRadiation Exposure due to the Nuclear Accident following the Great East-Japan
Earthquake and Tsunami. A 2015 white paper to guide the Scientific Committee's future
programme of work. United Nations Scientific Committee on the Effects of Atomic
Radiation. United Nations, New York, 2015.
Utsunomiya, S., G. Furuki, A. Ochiai et al. Caesium fallout in Tokyo on 15th March, 2011 isdominated by highly radioactive, caesium-rich microparticles. arXiv: 1906.00212(2019).