SOURCES AND EFFECTS OFIONIZING RADIATION
United Nations Scientific Committee on the
Effects of Atomic Radiation
UNSCEAR 2008
Report to the General Assemblywith Scientific Annexes

VOLUME II
Scientific Annexes C, D and E

UNITED NATIONSNew York, 2011

NOTE
The report of the Committee without its annexes appears as Official Records of the General
Assembly, Sixty-third Session, Supplement No. 46.
The designations employed and the presentation of material in this publication do not imply
the expression 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, or ­concerning
the delimitation of its frontiers or boundaries.
The country names used in this document are, in most cases, those that were in use at the time thedata were collected or the text prepared. In other cases, however, the names have been updated,
where this was possible and appropriate, to reflect political changes.

UNITED NATIONS PUBLICATION
Sales No. E.11.IX.3
ISBN-13: 978-92-1-142280-1
e-ISBN-13: 978-92-1-054482-5© United Nations, April 2011. All rights reserved.
Publishing production: English, Publishing and Library Section, United Nations Officeat Vienna.

CONTENTS
Page

VOLUME I: SOURCES
Report of the United Nations Scientific Committee on the Effects of Atomic Radiation
to the General Assembly
Scientific Annexes
Annex A. Medical radiation exposures
Annex B. Exposures of the public and workers from various sources of radiation
VOLUME II: EFFECTS
Annex C. Radiation exposures in accidents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1Annex D. Health effects due to radiation from the Chernobyl accident. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Annex E. Effects of ionizing radiation on non-human biota . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221

iii

ANNEX dhealth effects due to radiationfrom the chernobyl accident
Contents
Page

I. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 A.	Past assessments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 B. Structure of the present scientific annex. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

47
47
49

II.	Physical and environmental context . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 A. Radionuclide release and deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 B. Environmental transfer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 C. Environmental countermeasures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

49
49
51
53

III. Radiation doses to exposed population groups. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 A. Doses to workers involved in response and recovery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 B. Doses to general population. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

53
54
54

IV.
		
		
		
		

Attribution of health effects to radiation exposure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A. General discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B. Deterministic effects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C. Stochastic effects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
D.	Psychological trauma and other related effects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

56
56
56
56
57

V. Early health effects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 A. Acute radiation syndrome in emergency workers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 B. General public. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

58
58
59

VI. Late health effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 A. Actual observations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			 1. Late health effects in ARS survivors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			 2. Thyroid cancer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			 3. Leukaemia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			 4. Other solid cancers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			 5. Non-cancer effects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 B. Theoretical projections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			 1. Review of published projections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			 2. Scientific limitations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			 3. UNSCEAR statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

59
59
59
60
61
62
62
63
63
64
64

VII.
		
		
		
		

64
64
65
65
66

General conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A. Health risks attributable to radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B. Comparison of present annex with previous reports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C. Comparison of observed late health effects with projections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
D. New knowledge from studies of the accident. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
45

Page

ACKNOWLEDGEMENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

66

APPENDIX A. PHYSICAL AND ENVIRONMENTAL CONTEXT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

67

APPENDIX B.

RADIATION DOSES TO EXPOSED POPULATION GROUPS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

APPENDIX C.

EARLY HEALTH EFFECTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

APPENDIX D.

LATE HEALTH EFFECTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205

46

I. introduction
1. The 1986 accident at the Soviet Union’s Chernobyl
nuclear power plant (ChNPP) was the most severe ever tohave occurred in the civilian nuclear power industry.1 It triggered an unprecedented international effort to improveunderstanding of the health effects due to radiation from theaccident and has become the most extensively studied­accident involving radiation exposure.

populations in Belarus, the Russian Federation and Ukraine5(the three republics). Two radionuclides, the short‑lived
iodine-131 (131I with a half‑life of 8 days) and the long‑lived
caesium‑137 (137Cs with a half‑life of 30 years), were particularly significant for the radiation dose they delivered tomembers of the public.
4. In the former Soviet Union, the contamination of freshmilk with 131I and the lack of prompt countermeasures led tohigh thyroid doses, particularly among children. In the longer
term, mainly due to radiocaesium, the general population was
also exposed to radiation externally from radio­active deposition and internally from consuming contaminated foodstuffs.
However, in part because of the countermeasures taken, theresulting radiation doses were relatively low (the average
additional dose in 1986–2005 in “contaminated areas”6 of thethree republics was about equivalent to that from a computed
tomography (CT) scan in medicine), and should not lead to
substantial health effects in the general population that could
be attributed to radiation exposure from the accident. Evenso, the severe disruption caused by the accident, confoundedwith the remarkable political changes that took place in theSoviet Union and the new republics, resulted in major socialand economic impact, and great distress for the affected
populations.

2. Two workers died in the immediate aftermath; andhigh doses of radiation2 to 134 plant staff and emergency
personnel3 resulted in acute radiation syndrome (ARS),
which proved fatal for 28 of them. Other than this groupof emergency workers, several hundred thousand wereinvolved in recovery operations;4 they were exposed
externally and, to a lesser degree, internally to radiationfrom the damaged ­reactor and from radionuclides released
to the environment.
3. The accident caused the largest uncontrolled radioactive
release into the environment ever recorded for any civilian
operation; large quantities of radioactive substances werereleased into the air for about 10 days. The radioactive cloud
dispersed over the entire northern hemisphere, and deposited
substantial amounts of radioactive material over large areasof the former Soviet Union and some other countries in
Europe, contaminating land, water and biota, and causing
particularly serious social and economic disruption for large

A. Past assessments
5. There has been an unprecedented effort by the inter­national community to assess the magnitude and characteristics of the health effects due to the radiation exposure
resulting from the accident. As early as August 1986, a
widely attended international gathering, the “Post-­Accident
Review Meeting”, was convened in Vienna. The resulting
report of the International Nuclear Safety Advisory Group(INSAG) contained a limited but essentially correct earlyaccount of the accident and its expected radiological consequences [I31]. In May 1988, the International Scientific
Conference on the Medical Aspects of the Accident at the
Chernobyl Nuclear Power Plant [I32] held in Kiev summarized the available information at the time and confirmedthat some children had received high doses to the thyroid.
In May 1989, scientists obtained a more comprehensive
insight into the scale of the consequences of the accident at
an ad hoc meeting convened at the time of the 38th session

The accident site is located in present‑day northern Ukraine, some 20 km
south of the border with Belarus and 140 km west of the border with theRussian Federation. The accident occurred on the 26 April 1986 during alow‑power engineering test of the Unit 4 reactor. Improper, unstable operation of the reactor, which had design flaws, allowed an uncontrollable power
surge to occur, resulting in successive steam explosions, which severely
damaged the reactor building and completely destroyed the reactor [I7, I31].
2
The term dose is used in this scientific annex in a number of ways: in a
general sense, to indicate an amount of radiation absorbed from a given
exposure, and in two specific senses, to indicate either the physical quantity,
absorbed dose, or the protection quantity, effective dose. Absorbed dose isgiven in the unit, gray (Gy) (or appropriate submultiples) and effective dose
is given in the unit, sievert (Sv) (or appropriate submultiples). In general,
absolute values of dose relate to absorbed dose, unless otherwise indicated.
The concepts of collective absorbed dose and collective effective dose arealso used.
3
Approximately 600 workers responded on site within the first day to theimmediate emergency, including staff of the plant, firemen, security guards
and staff of the local medical facility.
4
In 1986 and 1987 some 440,000 recovery operation workers worked at the
Chernobyl site, and more such recovery workers were involved in various
activities between 1988 and 1990. The work included, among other things,
construction of the sarcophagus over the damaged reactor and decontamination of the site and roads. Special health registers currently hold records on
more than 500,000 recovery operation workers in total.
1

5
At the time of the accident, these were three constituent Soviet Socialist
Republics of the Soviet Union.
6
The “contaminated areas” were defined arbitrarily in the former Soviet
Union as areas where the 137Cs levels on soil were greater than 37 kBq/m2.

47

48

UNSCEAR 2008 REPORT: VOLUME II

of UNSCEAR [G15, K25]. In October 1989, the former
Soviet Union formally requested “an international experts’assessment” and, as a result, the International Chernobyl
Project (ICP) [I5] was launched in early 1990; its conclusions and recommendations were presented at an International Conference held in Vienna, 21–24 May 1991 [I5].
Many national and international initiatives7 followed aimed
at developing a better understanding of the accident consequences and in assisting in their mitigation. The results ofthese initiatives were presented at the 1996 International
Conference on One Decade After Chernobyl8 [I29]. There
was a broad ­agreement on the extent and character of theconsequences.
6. The Committee considered the initial radiological consequences of the accident in its UNSCEAR 1988 Report[U7]. The short‑term effects of radiation exposure and thetreatment of the radiation injuries to workers and firefighters
who were on the site at the time of the accident were reviewed
in the appendix to annex G, “Early effects in man of highdoses of radiation”, of the UNSCEAR 1988 Report. The
estimated average individual and collective doses to the
popu­lation of the northern hemisphere were given in annex
D, “Exposures from the Chernobyl accident”.
7. Annex J, “Exposures and effects of the Chernobyl accident”, of the UNSCEAR 2000 Report [U3] provided a
detailed account of the known radiological consequences of
the accident up to 2000. It reviewed the information on thephysical consequences of the accident, the radiation doses tothe exposed population groups, the early health effects in theemergency workers, the registration and health monitoring
programmes, and the late health effects of the accident.
8. In spite of the general consensus of the international scientific community on the extent and nature of the radiation
health effects that is reflected in the UNSCEAR 2000 Report[U3], there was still considerable public controversy within
the three republics. Thus, in 2003, eight bodies of theSome of the more significant multinational initiatives were the following:
the WHO launched an International Programme on the Health Effects of theChernobyl Accident (IPHECA), the results of which were discussed at the
WHO International Conference on the Health Consequences of the Chernobyl and other Radiological Accidents, held in Geneva, 20–23 November 1995 [W6]; the EC supported many scientific research projects on theaccident consequences and their results were summarized at the First International Conference of the European Union, Belarus, the Russian Federation and Ukraine on the Consequences of the Chernobyl Accident, held in
Minsk, 18–22 March 1996 [E4]; and UNESCO supported several studies,mainly on psychological impact [U20].
8
The International Conference on One Decade After Chernobyl: Summingup the Accident's Consequences, which took place in Vienna in April 1996,
was cosponsored by IAEA, WHO and EC in cooperation with the UN,
UNESCO, UNSCEAR, FAO and the Nuclear Energy Agency of OECD.
The Conference was presided over by A. Merkel, Germany’s Federal Minister for the Environment, Nature Conservation and Nuclear Safety. It was
attended by high‑level officials of the three most affected States (including
the President of Belarus, the Prime Minister of Ukraine, and the RussianFederation's Minister for Civil Defence, Emergencies and Elimination ofConsequences of Natural Disasters) and by 845 scientists from 71 countries
and 20 organizations.
7

United Nations family9 (including the Committee) and thethree republics launched the “Chernobyl Forum” to generate“authoritative consensual statements” on the environmental
and health consequences attributable to radiation exposureand to provide advice on issues such as environmental remediation, special health‑care programmes, and research activities. Drawing heavily on the UNSCEAR 2000 Report [U3],the IAEA led the environmental assessment and the WHO
led the health assessment. The Forum’s work was reviewed
at the International Conference: Chernobyl—Looking Back
to Go Forwards: Towards a United Nations Consensus on the
Effects of the Accident and the Future, held in Vienna,
6–7 September, 2005. Three detailed reports were issued[C22, I21, W5] in early 2006. The Chernobyl Forum essentially reconfirmed all previous assessments of the scale andcharacter of the radiation health consequences. The Forum
reports have been used as appropriate in the preparation ofthis annex.
9. The objective of the present annex is to provide anauthoritative and definitive review of the health effects
observed to date that are attributable to radiation exposure due to the accident and to clarify the potential risk
projections, taking into account the levels, trends andpatterns of radiation dose to the exposed populations.
The Committee has evaluated the relevant new information that has become available since the 2000 Report, inorder to determine whether the assumptions used previously to assess the radiological consequences are stillvalid. In addition, it recognized that some issues merited
further scrutiny and that its work to provide the scientificbasis for a better understanding of the radiation‑related
health and environmental effects of the Chernobyl accident needed to continue. The information considered
included the behaviour and trends of the long‑lived radio­
nuclides in foodstuff and the environment in order toimprove the estimates of exposure of relevant populationgroups, and the results of the latest follow‑up studies of
the health of the exposed groups. The effects of radiation
on plants and animals following the Chernobyl accident
are discussed separately in annex E, “Effects of ionizing
radiation on non‑human biota”. Other effects of the­accident, in particular, distress and anxiety, and socio‑­
economic effects, were considered by the Chernobyl
Forum [W5] but are ­outside the ­Committee’s remit.
10. The Committee, in general, bases its assessments onreports appearing in peer‑reviewed scientific literature andon information submitted officially by Governments in
response to its requests. However, the results of many of
the studies related to the Chernobyl accident have beenpresented at scientific meetings without formal scientificpeer review. The Committee decided that it would only
make use of such information when it could judge that theresults and the underlying work were scientifically andtechnically sound.

9

FAO, IAEA, OCHA, UNDP, UNEP, UNSCEAR, WHO and the World Bank.

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

B.

Structure of the present scientific annex

11. The annex comprises a main text with four supporting
appendices. The main text summarizes the physical andenvironmental context of the accident and updates the estimates of radiation dose to the various exposed populationgroups (appendices A and B, respectively, provide additional details). Before considering the results of the health49

studies, the annex discusses some of the difficulties involvedin attributing health effects to radiation exposure. It thenbriefly recapitulates the early health effects that had been
seen among the emergency workers (appendix C provides
details). Section VI (with details in appendix D) discusses
the theoretical projections of the late health effects and theactual observations of effects to date that can be attributed
to ­radiation exposure from the accident.

II. Physical and environmental context
12. This section briefly reviews the physical and environmental context of the accident with a particular focus on
those aspects for which knowledge has improved and thathave implications for refining the radiological assessment.
Appendix A provides more details.
A.

Radionuclide release and deposition

13. The accident released a mixture of radionuclides into the
air over a period of about 10 days. Most of the radionuclides

that were released in large amounts (in terms of activity)
were of short half‑life; radionuclides of long half‑lifewere generally released only in small amounts. The mostup‑to‑date estimates of the amounts released (table 1) aresimilar to those of the UNSCEAR 2000 Report [U3],except for the refractory elements, which are now about
50% lower [K13]. However, these changes are academic
and have no influence on the assessment of radiation doses,
which are rather based on direct human and environmental
measurements.

Table 1. Principal radionuclides released in the accident
Refined estimates of the activities released
Radionuclide

Half-life

Activity released(PBq)

Radionuclide

Inert gasesa
10.72 a

33

89

Xe

5.25 d

6 500

90

133

Activity released(PBq)

Elements with intermediate volatilitya

Kr

85

Half-life

Volatile elementsa

Sr

50.5 d~115

Sr

29.12 a~10

Ru39.3 d

>168

Ru

368 d

>73

Ba

12.7 d

240

103

Te

33.6 d

240

106

Te

3.26 d

~1 150

140

131

I

8.04 d~1 760dI

20.8 h

910

95

Zr

64.0 d84

Cs

2.06 a

~47b

99

Mo

2.75 d>72

Cs

13.1 d

36

141

Ce

32.5 d84

Cs

30.0 a

~85e

144

Ce

284 d

~50

Np

2.35 d400

Pu87.74 a0.015

Pu

24 065 a

0.013

Pu

6 537 a0.018

Pu

14.4 a~2.6

Pu

376 000 a

0.00004Cm

18.1 a

~0.4

129m

132

133

134

136

137

a From references [D11, U3].
b Based on 134Cs/137Cs ratio 0.55 as of 26 April 1986 [M8].
c Based on fuel particle release of 1.5% [K13].
d For comparison, the global release of 131I from atmospheric nuclear weapon
testing was 675,000 PBq [U3].
e For comparison, the global release of 137Cs from atmospheric nuclear weapon
testing was 948 PBq [U3].

Refractory elements (including fuel particles)c

239

238

239

240

241

242

242

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UNSCEAR 2008 REPORT: VOLUME II

14. The radioactive gases and particles released were initially carried by the wind in westerly and northerly directions, but subsequently, the winds came from all directions(figure I) [B24, I21, U3]. There are essentially no new data,but research to improve understanding of the atmosphericdispersion patterns continues [T5, T6].

using measurements of the long‑lived 129I as an analogue.
Three main areas of the former Soviet Union (in total,
150,000 km2 with more than 5 million inhabitants) wereclassified as contaminated areas (figure II). Outside of theformer Soviet Union, other large areas of Europe were also
subjected to deposition of radioactive material (45,000 km2
had 137Cs deposition levels ranging from 37 kBq/m2 to
200 kBq/m2). It was possible to measure trace concentrations of the radionuclides in essentially all countries of thenorthern hemisphere. The area classified as contaminatedis gradually shrinking as the 137Cs decays, e.g. it is expected
to fall from 23% of the Belarusian territory in 1986 to 16%
in 2016 and 10% in 2046 [S23].

15. Material was deposited, mainly because of rainfall, in
a complex pattern over large areas of the three republics
and beyond. Owing to the emergency situation and theshort half‑life of 131I, few reliable measurements of the pattern of radioiodine deposition were made. There areon­going efforts to reconstruct the deposition pattern of 131I,

Figure I. Formation of plumes by meteorological conditions for instantaneous releases on the dates and at the times (UTC)indicated [B24]

LATVIA
LITHUANIARUSSIANFED.
VILNIUSPOLAND1

26 April, 0.00 hrs

4

29 April, 0.00 hrs

2

27 April, 0.00 hrs

5

2 May, 0.00 hrs

3

27 April, 12.00 hrs

6

4 May, 12.00 hrs

Smolensk
KalugaMINSK

1MogilevTula

B E L A R U S

BryanskWARSAW
Brest

3

Gomel

2
LublinRovno

Sumy
Zhitomir

Lvov

RY

HU

A
NG

ROMANIA

4

KIEV

IA

Vinnitsa
Chernovtsy

R U S S I A N
F E D E R AT I O N

Chernigov

Chernobyl

K
VA
SLO

Orel

6
REP. OFMOLDAVIA

5

Cherkassy

Kharkov

U K R A I N E
Kirovograd

0

50

100

150

200

250

300 kmANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

51

Figure II. Map of 137Cs deposition levels in Belarus, the Russian Federation and Ukraine as of December 1989 [I28]L

A

Baranovichi

R

S
E

I
R

U

S

I

O

PlavskBolkhov

MtsenskEfremov

OREL

Desna

Soligorsk

YeletsNovozybkov

Sosna

Pinsk
Mozyr

Pr i p y at

Khoyniki
Braginod

Narovlya

Shostkakh

OvruchPripyatPolesskoje
Chernobyl
Narodichi

G o r y n’

Sto

Seym

Slavutich

SUMY

Des

na

Korosten

BELGORODre

Ps e lv
Tete

Novograd Volynskiy

KIEV

ZHITOMIR
Berdichev

TernopolU
Dn

Belaya Tserkov
R o sk a

Khmelnitskiy

B.

VINNITSA

ep

K

R

A

I

POLTAVAr

CHERKASSY

Environmental transfer

16. The main transfer pathways of radionuclides in the terrestrial environment are illustrated in figure III. For the
short‑lived 131I, the main pathway of human exposure wasvia the transfer of deposited material on pasture grass tocow’s milk. Within a few weeks, the very high initial concentrations became negligible because of ­radioactive decay
and other physical and biological processes.
17. For the long‑lived radionuclides such as 137Cs, thelong‑term transfer processes through the environment
needed to be considered. From mid‑1986 onwards, internal exposure due to 134Cs and 137Cs in milk and meat werethe most significant sources of exposure. The levels infood depended not only on the deposition pattern, but also
on factors such as the soil type and agricultural practice.
During the first few years, there was a substantial reduction in the levels of radiocaesium in most foodstuffs, withthe levels in most of the contaminated areas falling below
those recommended by the Codex Alimentarius Commission [C12]. However, since the mid‑1990s, the levels havefallen more slowly. Further reductions in the levels infoodstuffs over the next decades are expected to be mainly
due to radio­active decay. In parts of the contaminatedareas, there are continuing difficulties for subsistence
farmers with ­privately‑owned dairy cows. The uptake andretention of 137Cs has generally been much higher inN

E

KHARKOV-2

1 480–3 700 kBq m

555–1 480 kBq m-2

185–555 kBq m-2

37–185 kBq m-2<37 kBq m-2

semi-natural ecosystems than in agricultural ecosystems[H9], and the clearance rate from forest ecosystems isextremely slow. The highest levels in foodstuffs continue
to be in ­mushrooms, ­berries, game and reindeer.
Figure III. The main transfer pathways of radionuclides inthe terrestrial environment [S13]Initial radionuclide fallout:- condensation component- fuel particles

Surface washout
Soil–vegetation litter
Dissolution offuel particles

Organic–mineral soil component

Soil solution
Sorption–desorption

Migration

ROVNO

Vo r s k l a

r
Sty

KURSK

CHERNIGOV

Oskol

g ki
Dn e pr-Bu s C anal

Pr i p y at

Sarny

Novomoskovsk
Kimovsk

Lyudinovo

BRYANSK

GOMEL

TULA

N

Dyatlovo

Krichev

Bobruysk

SlutskAleksin

KALUGAN
T

Kirov

Roslavl

Cherikov

Bykhov

A
A

ka

S
D

MOGILEV

Berezina

Novogrudok

E

U
E

So

MINSK

R
F

a

Lida

Gorki

SMOLENSKr

O

Borisov

ep

Ok

Molodechno

B

Dn

ORSHA

zh

VILNIUSRoot
uptakeSorbed radionuclides
Groundwater and rocks of geological environment

52

UNSCEAR 2008 REPORT: VOLUME II

18. Levels of radionuclides in rivers and lakes directly after
the accident fell rapidly and are now generally very low inwater used for drinking and irrigation, although the radiocaesium levels in the water and fish of some closed lakes
have fallen only slowly. Levels in seawater and marine fish
were much lower than in freshwater systems.
19. Deposition of radioactive material in human settlements
has also contributed to external exposure of inhabitants. The
behaviour of the deposited material depended initially on thetype of deposition (i.e. dry or wet) and on the characteristicsof the settlement. The external dose rates have fallen withtime, because of radioactive decay and weathering (e.g.
radio­caesium levels on asphalt have fallen by over 90%). In
most settlements, the dose rates have returned to pre‑accident

levels, although levels slightly above background can still bemeasured over undisturbed soil.
20. By 2008, most of the radionuclides released had longsince decayed to negligible levels. Over the next few ­decades,137
Cs will continue to be the most relevant radionuclide as far
as exposure to radiation is concerned. Within about 20 km of
the ChNPP, particles of the nuclear fuel (so‑called “hot­particles”) had been deposited with high concentrations ofradio­nuclides including isotopes of strontium and plutonium. The particles are slowly dissolving with time and will
release 90Sr over the next 10-20 years [F4, K14]. Over thevery long term, the only residual radioactivity from theseparticles will be trace levels of long‑lived radionuclides suchas isotopes of plutonium and 241Am (figure IV).

Figure IV. Total amounts in the environment of various long‑lived radionuclides as a function of time after the accident
Americium-241 is the only radionuclide whose levels are presently increasing with time owing to its ingrowth from the decay of 241Pu. The
total activity of 241Am in the environment will reach a maximum in the year 2058, after which levels will slowly decline. This peak value is small
compared to the initial levels of 241Pu. Eventually 241Am will be the most significant remaining radionuclide, albeit at trace levels

TOTAL ACTIVITY OF RADIONUCLIDE (PBq)

100

10
Caesium-137
1

Plutonium-241
Americium-241

0.1

Plutonium-239+240

0.01
Caesium-134
0.001

0

50

100

150

200

250

TIME AFTER ACCIDENT (a)

300

350

400

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

C.

Environmental countermeasures

21. Owing to uncertainty about future releases and weather
conditions, as well as to relatively high radiation dose rates,
the authorities evacuated the nearest town of Pripyat within
the first few days of the start of the accident and the surrounding settlements soon after (a total of 115,000 local people were evacuated in 1986). Subsequently, they resettled afurther 220,000 people. They also decontaminated settlements in many regions of the former Soviet Union in orderto reduce the long‑term exposure of the public.
22. In the first few weeks, management of animal fodder
and milk production (including prohibiting the consumption of fresh milk) would have helped significantly to reducethe doses to the thyroid due to radioiodine, particularly inthe former Soviet Union where the levels were high. However, implementation of countermeasures in the former
Soviet Union was flawed, because timely advice was lacking, particularly for private farmers. Many European countries changed their agricultural practices and/or withdrew
food, especially fresh milk, from the supply chain, and, in
Poland, iodine prophylaxis was promptly organized; theseactions generally reduced thyroid doses in those countries
to ­negligible levels.

III.

53

23. Over the months and years after the accident, theauthorities of the former Soviet Union introduced an extensive set of countermeasures, involving major human, economic and scientific resources. These helped to reduce thelong‑term exposures from the long‑lived radionuclides,
notably radiocaesium. During the first few years, substantial
amounts of food were removed from human consumption
because of concerns about the radiocaesium levels, especially in milk and meat. In addition, pasture was treated, andclean fodder and caesium binders were provided to ­livestock,
resulting in considerable reductions in dose.
24. In addition, countermeasures were instigated to reduce
exposures from living and working in forests and using forest products. They included: restrictions on access; restrictions on harvesting of forest foods, such as game, berries andmushrooms; restrictions on the gathering of firewood; andalteration of hunting practices.
25. Early restrictions on drinking water and changing to alternative supplies reduced internal doses from aquatic pathways in
the initial period. Restrictions on the consumption of freshwater
fish from some lakes also proved effective in Scandinavia andGermany. Other countermeasures to reduce the transfer of radionuclides from soil to water ­systems were ­generally ineffective.

Radiation doses to exposed population groups

26. The early assessments of dose to exposed populations
based on the measurements available at the time tended touse cautious assumptions about the countermeasuresapplied and the environmental and dosimetric parameters
involved. As a consequence, the doses were generally overestimated. Experience with the widespread application ofcountermeasures, and the extensive sets of measurements
and records that were subsequently obtained have since
been used to improve the models and dose assessments.
Appendix B provides details of the latest dose assessments
and the results, based on more than 20 years of experienceand measurements.
27. Compared to the UNSCEAR 2000 Report [U3]:(a) dose estimates have been updated for a larger number ofthe Belarusian, Russian, and Ukrainian recovery operation
workers (510,000 instead of 380,000), and new information
is presented on the Estonian, Latvian, and Lithuanian recovery operation workers; (b) thyroid dose estimates have been
updated for the Belarusian and Ukrainian evacuees, and new
information is presented for the Russian evacuees; (c) the
estimation of thyroid and effective doses has been expandedfrom 5 million to 100 million inhabitants of the three republics; and (d) thyroid and effective dose estimates have been
updated for the inhabitants of other European countries.

28. Doses to the thyroid are expressed in terms of thequantity, absorbed dose, in units of gray (Gy); while doses
to the whole body from external and internal irradiation
combined are expressed in terms of the weighted quantity
used in radiation protection, effective dose, in units of sievert (Sv). For comparison, the annual average effective dosefrom natural background radiation is 2.4 mSv, while thetypical effective dose from a medical CT scan is of the orderof 10 mSv.
29. The updated estimates of the average individual andcollective doses received by the population groups exposed
as a result of the Chernobyl accident are summarized intable 2. Because iodine concentrates in the thyroid gland,absorbed doses to the thyroid over the first few weeks after
the accident for those members of the population drinking
fresh milk containing 131I were much higher than the dose to
the thyroid due to natural sources of radiation; this was
especially true for infants and children who consumed­proportionally more milk than adults. In contrast, because­caesium behaves chemically like its analogue potassium,
and is therefore relatively evenly dispersed throughout thebody, the effective dose due to the accident is comparable toor even much lower than the effective dose due to natural­background radiation.

54

UNSCEAR 2008 REPORT: VOLUME IITable 2. Summary of updated dose estimates for the main population groups exposed
Population groupSize(thousands)

Average thyroid dosein 1986(mGy)

Average effective dosein 1986-2005(mSv)

Collective thyroid dosein 1986(man Gy)

Collective effective
dose in 1986-2005(man Sv)

Recovery operation workers

530

—a

117b

—

61 200Evacuees

115

490

31c

57 000

3 600

Inhabitants of contaminated areasd of
Belarus, Russia and Ukraine

6 400

102

9c,e

650 000

58 900Inhabitants of Belarus, the RussianF­ ederation and Ukraine

98 00016

1.3c,e1 600 000

125 000e

Inhabitants of distant countriesf

500 000

1.3

0.3c,e660 000

130 000ea Thyroid doses only exist for a very small number of workers; it is not possible to give a valid average value for the whole group.
b Effective dose estimates for the workers include only the doses from external irradiation, delivered essentially from 1986 to the end of 1990. It is assumed that the recorded
dose in mGy is numerically equal to the effective dose in mSv.
c Effective dose estimates are the sum of the contributions from external and internal irradiation, excluding the thyroid dose.
d The contaminated areas were defined arbitrarily in the former Soviet Union as areas where the 137Cs levels on soil were greater than 37 kBq/m2.
e The total dose will continue to accumulate to be perhaps 25% higher for the whole lifetime.
f All the European countries except the three republics, Turkey, countries of the Caucasus, Andorra and San Marino.

A. Doses to workers involved in response and recovery
30. The average effective dose received by the recovery
operation workers between 1986 and 1990, mainly due toexternal irradiation, is now estimated to have been about
120 mSv. The recorded worker doses varied from less than
10 mSv to more than 1,000 mSv, although about 85% of therecorded doses were in the range 20–500 mSv. Uncertainties
in the individual dose estimates vary from less than 50% to up
to a factor of 5, and the estimates for the military personnel aresuspected to be biased towards high values.
31. The collective effective dose to the 530,000 recovery operation workers is estimated to have been about
60,000 man Sv. This may, however, be an overestimate, as
conservative assumptions appear to have been used in­calculating some of the recorded doses.
32. There is not enough information to estimate reliably
the average thyroid dose to the recovery operation workers.
B.

Doses to general population

33. The high thyroid doses among the general population
were due almost entirely to drinking fresh milk containing
131
I in the first few weeks following the accident. Figure V
presents the estimated average thyroid dose to children andadolescents in 1986. The average thyroid dose to the evacuees is estimated to have been about 500 mGy (with individual values ranging from less than 50 mGy to more than
5,000 mGy). For the more than six million residents of thecontaminated areas of the former Soviet Union (i.e. thosewith 137Cs levels greater than 37 kBq/m2) who were not evacuated, the average thyroid dose was about 100 mGy, while

for about 0.7% of them, the thyroid doses were more than
1,000 mGy. The average thyroid dose to pre‑school children
was some 2 to 4 times greater than the population average.
For the 98 million residents of the whole of Belarus andUkraine and 19 oblasts of the Russian Federation, including
the contaminated areas, the average thyroid dose was much
lower, about 20 mGy; most (about 93%) received thyroid
doses of less than 50 mGy. The average thyroid dose to­residents of the other European countries was about 1.3 mGy.
34. The collective thyroid dose to the 98 million residentsof the former Soviet Union was some 1,600,000 man Gy. At
the country level, the collective thyroid dose was highest in
Ukraine, with 960,000 man Gy distributed over a populationof 51 million people, even though the average thyroid dosein Ukraine was about 3 times lower than in Belarus. At theregional level, the highest collective thyroid dose was to the
population of the Gomel oblast, where a collective thyroid
dose of about 320,000 man Gy was distributed over a population of 1.6 million people, corresponding to an average
thyroid dose of about 200 mGy.
35. As far as whole body doses are concerned, the six million residents of the areas of the former Soviet Union deemed
contaminated received average effective doses for the period
1986–2005 of about 9 mSv, whereas for the 98 million people considered in the three republics, the average effective
dose was 1.3 mSv, a third of which was received in 1986.
This represents an insignificant increase over the dose due tobackground radiation over the same period (~50 mSv). About
three‑quarters of the dose was due to external exposure, therest being due to internal exposure.
36. About 80% of the lifetime effective doses had been delivered by 2005. Over this 20‑year period, about 70% of theBrestOblast centre

Oblast borderState border>0.65

0.15–0.65

0.03–0.15

0.01–0.03<0.01

District average
thyroid doses (Gy)Rovno
Zhytomyr

Gomel

Mogilev

Kiyev

Chernobyl NPP

UkraineBelarus

Minsk

Chernigov

Tula

Bryansk

Orel

Russian Federation

KalugaFigure V. The estimated average thyroid doses to children and adolescents living at the time of the accident in the most affected regions of Belarus, the Russian Federation andUkraine [I14, K22, K25, L4, Z4]

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT
55

56

UNSCEAR 2008 REPORT: VOLUME II

population received effective doses below 1 mSv and about 20%
received effective doses between 1 and 2 mSv. However, about
150,000 people living in the contaminated areas received aneffective dose of more than 50 mSv over the 20‑year period. For
the population of about 500 million in other countries of Europe,

IV.

Attribution of health effects to radiation exposure

A. General discussion
37. There has been widespread misunderstanding among
the general public, media, authorities and even scientists
regarding the scale and nature of the health impact of theChernobyl accident. This is, in part, due to confusion regarding three aspects: (a) the nature of deterministic versus stochastic effects of radiation exposure; (b) the attribution ofeffects to radiation exposure for individuals and populations;and (c) theoretical projections of effects versus actual observations. This section aims to clarify the first two of theseissues. Section VI.B discusses the third.
38. The effects of radiation exposure fall into two mainclasses: deterministic effects, where the effect is certain tooccur under given conditions (e.g. individuals exposed toseveral grays over a short period of time will definitely suffer
ARS); and stochastic effects, where the effect may or may
not occur (e.g. an increase in radiation exposure may or may
not induce a cancer in a particular individual but if a sufficiently large population receive a radiation exposure above acertain level, an increase in the incidence10 of cancer may
become detectable in that population).
39. Attribution is the process of ascribing an effect to a particular cause. If radiation exposure is not the only known
cause of a particular effect, then it is only possible to ascribe
a probability that that effect was caused by radiation exposure. In practice, attributing, either wholly or partly, a specific effect to radiation exposure involves considering
whether the effect could have occurred by other means, andanalysing factors such as the nature of the exposure, the surrounding circumstances, and the clinical evolution of theobserved effect. Even though a vast scientific literature canbe used to support attribution, each effect must be examinedon its own merits; and varying degrees of confidence will be
associated with any judgement.
B. Deterministic effects
40. Attribution of observed deterministic effects to radiation exposure requires at least a suspicion of an exposure
The term incidence has two uses in this annex: in a general sense, often
to contrast cancer incidence with cancer mortality, and in a specific sense,
where the incidence of a disease is the number of cases of the disease that
occur during a specified period of time (usually a year). The incidence rateis this number divided by a specified unit of population (see paragraph 4 ofannex A of reference [U1]).
10

the average effective dose is estimated to have been 0.3 mSv
over this period. The collective effective dose is estimated atabout 125,000 man Sv to the combined populations of Belarus,
Ukraine and the relevant parts of the Russian Federation, andabout 130,000 man Sv to the population in the rest of Europe.

above a threshold level, usually of a gray or more. It also
requires observation of a specific set of clinical or laboratory
findings in a particular time sequence. Acute radiation syndrome is a good example of a deterministic effect that is relatively easy to attribute to radiation exposure, because theobserved signs and symptoms (e.g. depressed production ofblood in the bone marrow with concurrent infection andhaemorrhage, and high incidence of chromosome aberrations in the peripheral blood) are not easily produced byother causes. Although there are essential difficulties indetermining the diagnosis, an experienced pathologist ought
to be able to attribute the observed signs and symptoms toradiation exposure [I6].
41. There are deterministic effects, such as cataracts, forwhich radiation exposure is not the only known cause. If
these effects occur, usually some time after high levels of
exposure, and there is no specific marker for radiation
exposure having caused them, it is not possible to attributethe effect with certainty to radiation exposure, but only to
express a probability that radiation was wholly or partly
the cause.

C. Stochastic effects
42. Cancer is the major stochastic effect of radiation
exposure that has been demonstrated in human populations (inherited effects have only been observed in animal
populations exposed to relatively high doses of radiation,although they are also presumed to occur in humans).
Because there is currently no means of distinguishingtumours that are radiation‑induced from those that are not,it is essentially impossible to attribute definitely a specificcase of cancer to radiation exposure. On the other hand, if
there is an increased incidence of cancer observed in an
exposed population compared to that in an unexposed population that is matched for age, sex, genetic predisposition,
lifestyle and other relevant factors, and if the observed
increase is not inconsistent with the existing knowledge
base derived from other exposed populations, then it ispossible to attribute the increase to the radiation exposure,especially if there is an observed dependence of the incidence on the level of dose. Epidemiological studies needto have sufficient statistical power to attest to the occurrence of such stochastic effects and hence to their attributability to radiation exposure; the level of dose below which
it is intrinsically impossible to detect such effects depends
on the size of the population that is being studied.

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

43. The factors that need to be considered for the purposes of consistency with the existing knowledge base on­radiation‑induced cancer include tumour type, time of onset,
age of patient at exposure and radiation dose. Tumour type isimportant because some specific tumours are normally veryrare in particular populations (e.g. thyroid cancer is normallyvery rare among children). Where this is the case, increases
in the incidence of the tumour following radiation exposure
may be much more apparent than when it is relatively common. Moreover, some tissues are more radiosensitive thanothers (again, for children who have particularly active thyroids, the thyroid is highly sensitive to radiation exposure).

57

cancer several months after the accident, the probability
that radiation was the cause would be very low, because
the adult thyroid appears to be very resistant to tumour
induction by radiation, and the tumour occurred too soon
relative to the known minimum latent period between
exposure and ­cancer appearance.
D. Psychological trauma and other related effects
45. Deterministic and stochastic effects both have a biological basis traceable to radiation dose, i.e. to ionizing radiation depositing energy in tissue. However, the Chernobyl
accident is known to have had major effects that are notrelated to the radiation dose. They include effects brought onby anxiety about the future and distress, and any resulting
changes in diet, smoking habits, alcohol consumption andother lifestyle factors, and are essentially unrelated to any
actual radiation exposure [U3]. Figure VI illustrates schematically some of the factors that might possibly influence
the observation of health effects after the accident.

44. Even for thyroid cancers occurring after the Chernobyl accident, the probability that radiation exposure caused
the cancer may vary markedly from one individual toanother. For a child who developed thyroid cancer several
years after the accident and probably received a relatively
high dose to the thyroid at the time, the probability thatradiation exposure caused the cancer may also be relatively high. However, for an adult who developed thyroid

Figure VI. Schematic illustration of some of the factors possibly influencing the observed health effects

Chernobyl
accident

Response to theaccident andremediation
measures

Anxiety about
the futureand distress

DOSE
DUE TOACCIDENT

Socio-economicchanges

Political
decisions

Healthmonitoring andcare system

Diet, smoking,drinking, otherlifestyle factors

Probabilistic
factors

Health effect progression

OBSERVED
EFFECTS

Dose due tonaturalsources

Dose due toother sources(e.g. medical)

Radiation exposure

Other known
physical, chemical,
biological agents

Unknown
factors

Genetic
predisposition

Sex and age

58

UNSCEAR 2008 REPORT: VOLUME II

46. The Chernobyl Forum [W5] concluded that stresssymptoms, increased levels of depression, anxiety (including
post‑traumatic stress symptoms), and medically unexplained
physical symptoms, have been found in the exposed populations compared to control groups. Mostly, these conditions
were subclinical and did not meet the criteria for classification as psychiatric disorders. Nevertheless, these subclinicalsymptoms had important consequences for behaviour, suchas diet, smoking habits, drinking and other lifestyle factors.
The Chernobyl Forum Expert Group “Health” concluded thatthey were unable to partition the attribution of these effects
among radiation fears, issues with distrust of government,V.

inadequate communications, the break‑up of the Soviet
Union, economic issues and other factors. Nevertheless, it isclear that a significant fraction of the effects is attributable to
the Chernobyl accident, if not directly to radiation exposure.
47. In summary, the effects of the Chernobyl accident are
many and varied. Early deterministic effects can be attributed
to radiation with a high degree of certainty, while for othermedical conditions, radiation almost certainly was not thecause. In between, there was a wide spectrum of conditions.
It is necessary to evaluate carefully each specific condition
and the surrounding circumstances before attributing a cause.

Early health effects

A. Acute radiation syndrome in emergency workers

so only a short recapitulation is provided here (more detailed
information is provided in appendix C).

48. The first information on the early severe health effects
due to high acute levels of radiation exposure was presented
to the international community in August 1986 [I31]. Analyses of clinical data were presented in the appendix toannex G, “Early effects in man of high doses of radiation”,
of the UNSCEAR 1988 Report [U7]. Updated informationon the early health effects among emergency workers wasprovided in annex J, “Exposures and effects of the Chernobyl accident”, of the UNSCEAR 2000 Report [U3]. There
are no substantive new data regarding the early health effects,

49. A total of 237 emergency workers were initially examined for signs of ARS. Within several days, ARS was verified in 104 of these individuals, and in a further 30 at a later
date. Of these 134 patients, 28 died within the first fourmonths, their deaths being directly attributable to the highradiation doses (two other workers had died from injuries
unrelated to radiation exposure in the immediate aftermathof the accident). Figure VII presents the outcome for the
ARS patients.

Figure VII. Outcome for patients with ARS
While the figure indicates the numbers of later deaths for each category of ARS, most of the cases are not attributable to radiation exposure
60

NUMBER

50
40

Survivors

30

Later deaths

20

Deaths in
the short term

100

0.8–2.1

2.2–4.1

4.2–6.4

6.5–16

Mild (I)

Moderate (II)Severe (III)Very severe (IV)GRADE OF ARS AND DOSE RANGE (Gy)

50. The dominant exposures were external irradiation of thewhole body at high dose rates and beta irradiation of the skin.
Internal contamination was of relatively minor ­importance,
while neutron exposure was insignificant.

51. Underlying bone marrow failure from the external
whole body irradiation was the major contributor to all thedeaths during the first two months. Bone‑marrow transplantation was conducted on 13 patients, 12 of whom died, and 3

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

of whom were felt to have died partly because of inappropriate bone‑marrow transplantation. Each patient with bonemarrow syndrome of grade III–IV usually also had serious
radiation damage to the skin and required continuous­intensive nursing by highly qualified personnel.
52. Skin doses exceeded bone marrow doses by a factor of
10–30, and many ARS patients received skin doses in therange of 400–500 Gy. Radiation damage to the skin aggravated other conditions. Radiation burns to the skin were felt
to be a major contributor to at least 19 of the deaths and significantly increased the severity of the ARS, especially whenskin burns exceeded 50% of the body surface area and led tomajor infections. After 50–60 days, if the skin was not healing, a number of patients received skin graft surgery. In addition, the leg of one patient was amputated more than 200 days

VI.
A.

59

after the accident, gastrointestinal syndrome was seen in
15 patients and radiation pneumonitis in 8 patients.
53. There is essentially no doubt that the initial 28 deaths
and the clinical findings on the other 106 ARS patients were
attributable to radiation exposure from the accident.
B. General public
54. There were no cases of ARS among the general public,
either among those evacuated or those not evacuated. This isconsistent with the assessment of the radiation exposures,
which showed that the whole body radiation doses to­members of the general public were much lower than thewell‑known dose thresholds for ARS.

Late health effects

Actual observations

55. The Committee decided in this annex to focus on theincidence of thyroid cancer, leukaemia, all solid cancers as awhole, cardiovascular mortality, cataract development andautoimmune thyroiditis. This decision was based on thepotential sensitivity of these outcomes to radiation andbecause the Committee considered there were insufficient
new data in other areas to potentially modify the conclusionsof the UNSCEAR 2000 Report [U3]. A more detailed reviewof the various studies is provided in appendix D.
56. Even if an empirical epidemiological study provides
evidence of an increased incidence of a potentially radiogenic disease, it still remains necessary to consider the issue
of attributability of that effect to radiation. It is necessary totake detailed account of such possible confounding and bias
factors as industrial pollution, environmental features (e.g.
stable iodine levels in soil), lifestyle (e.g. smoking habits or
alcohol consumption), reproductive history, improvement of
diagnostic tools, and increased medical attention for affected
populations.
57. Bias due both to screening and to diagnostic suspicion
may operate in studies of the emergency and recovery operation workers, who are examined every year for various diseases and for whom there is consequently a greater likelihoodof detection of small tumours. Trends of disease rates ingroups of emergency and recovery operation workers are
only scientifically informative if the same methods of detection in diagnosis are applied over the whole period of interest and are independent of the individual exposure level.
Overall, interpretation of the results from studies on the populations exposed after the Chernobyl accident has to take
into account the variation of detection methods with time,
and the likelihood of different screening frequencies for­different populations.

1.

Late health effects in ARS survivors

58. The Committee in its 2000 Report [U3] summarized
the observations made in the treatment of the workers who
had developed ARS. Among those patients surviving ARS
grades III and IV, haematopoietic recovery occurred withina matter of months. However, recovery of the immune system took at least half a year, and complete normalization
several years. Cataracts, scarring and ulceration are important ongoing problems in the ARS survivors. Between 1990
and 1996, 15 ARS survivors with extensive skin injuries
underwent surgery. Most ARS survivors had suffered functional sexual disorders up to 1996; however, 14 normalchild­ren were born to survivor families within the first five
years of the accident.
59. Currently, only 10 patients are under clinical surveillance at the clinic of the Burnazyan Federal Medical Biophysical Center (former Russian State Research Center of
the Institute of Biophysics) in Moscow, and 59 patients arebeing followed up by the Ukrainian Research Center ofRadiation Medicine (URCRM) in Kiev. Unfortunately, it isvery difficult to analyse and use the two sets of data fromthese clinics because they are presented in different formats,using different diagnostic criteria and time periods; furthermore, there are significant differences in the prevalence ofdiseases reported by the two clinics. For these reasons andalso because of the small numbers of cases and the lack ofanalyses using formal epidemiological methods, it is generally not possible to infer trends in disease and mortality rates
from these data.
60. The major health consequences from the radiation
exposure of the ARS survivors remain the skin injuries andradiation‑induced cataracts. The current nature and severityof the skin injuries depend on their severity during the early
period. Patients who had suffered first‑degree skin injuries

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UNSCEAR 2008 REPORT: VOLUME II

displayed various levels of skin degeneration, ranging fromslight smoothing of the skin surface to more pronounced
changes. However, over longer periods, the slight changes
disappeared almost completely. With the second‑degree skin
injuries, degeneration was pronounced. With third‑ andfourth‑degree injuries, there were areas of scarring, contractures, and radiation‑induced ulcers. However, since the early
1990s, microsurgery techniques have significantly reduced
the problems of radiation‑induced ulcers.
61. Many of the patients who suffered moderate or severe
ARS, developed radiation‑induced cataracts in the first few
years after the accident, with a strong correlation between
the grade of ARS and cataract prevalence.
62. A high prevalence of nervous system diseases among thesurvivors had been registered during the first decade. Similarly,
there have been reports of a high percentage of cardiovascularand gastrointestinal diseases. However, studies have shown nocorrelation with the grade of ARS, probably ­indicating a cause
other than radiation exposure [B9, B39, B42].
63. Over the period 1987–2006, 19 ARS survivors died forvarious reasons [B9, B39, B41, B44, G9, U3], including
seven deaths from non‑cancer disease of internal organs(including two from pulmonary tuberculosis and two fromcirrhosis of the liver), six from sudden cardiac arrest and fivefrom malignancy; and, in one case, the cause of death was
due to trauma (figure VII). As time progressed, the assignment of radiation as the cause of death has become less clear.
64. Among the ARS survivors under observation at the
URCRM, there have been four confirmed cases of solid cancer, three cases of myelodysplastic syndrome, one case of
acute myelomonoblastic leukaemia and one case of chronic
myeloid leukaemia.

65. The follow‑up of the ARS survivors indicates that:the initial haematological depression has recovered substantially in many patients; there remain significant local
injuries; there has been an increase in haematologicalmalignancies; and the increase in other diseases is probably largely due to ageing and other factors not related toradiation exposure.
2.

Thyroid cancer

66. A substantial increase in thyroid cancer incidence has
occurred in the three republics (the whole of Belarus andUkraine, and the four most affected regions of the RussianFederation) since the Chernobyl accident among those
exposed as children or adolescents. Amongst those underage 14 years in 1986, 5,127 cases (under age 18 years in
1986, 6,848 cases) of thyroid cancer were reported between
1991 and 2005 [I8].
67. Figure VIII demonstrates that in Belarus, after the
Chernobyl accident in 1986, thyroid cancer incidence rates
among children under age 10 years increased dramaticallyand subsequently declined, specifically for those born after
1986 (see 1996–2005). This pattern suggests that the dramatic increase in incidence in 1991–1995 was associatedwith the accident. The increase was primarily among thechildren under age 10 years at the time of the accident [J4].
For those born after 1986, there was no evidence for an
increase in the incidence of thyroid cancer. The increase in
the incidence of thyroid cancer among children and adolescents began to appear about 5 years after the accident andpersisted up until 2005 (see figure IX). The background rateof thyroid cancer among children under age 10 years isapproximately 2 to 4 cases per million per year.

Figure VIII. Thyroid cancer incidence rate in Belarus for children under 10 years old at diagnosis

CRUDE ANNUAL INCIDENCE RATE
(per million)

35
30
25
Age at diagnosis(years)200-10 Females

15

0-10 Males

10
50

1986–1990

1991–1995

1996–2000

Exposed at less than 10 years
CALENDAR PERIOD

2001–2005

Born after 1986

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

68. Figure IX shows the increase in thyroid cancer incidence rates with time among those exposed as children andadolescents in Belarus. There is no evidence for a decreasein the excess incidence of thyroid cancer up to 2005. Part of61

the increase is related to the normal age pattern of disease
occurrence but the majority of the increase is attributed tothe prior radiation exposure.

Figure IX. Thyroid cancer incidence rate among those exposed as children and adolescents (age under 18 years in 1986)
in Belarus

CRUDE ANNUAL INCIDENCE RATE
(per million)

140
120
100
80

Females

60

Males

40
20
0

1986–1990

1991–1995

1996–2000

2001–2005

CALENDAR PERIOD

69. This increase has been confirmed in several case‑­
control and cohort studies that have related the excess incidence of thyroid cancer to the estimated individual doses due
primarily to the radioiodine released during the accident.
The estimates of radiation risk from these studies remain
somewhat uncertain, however, and may have been influenced by variations in the use of ultrasonography and mass
screening after the accident.

73. Evidence has also emerged since the UNSCEAR 2000
Report [U3] indicating that iodine deficiency might haveinfluenced the risk of thyroid cancer resulting from exposure
to the radioactive isotopes of iodine released during the­accident [C8, S6].

70. There is little suggestion of increased thyroid cancer
incidence among those exposed as adults in the general
population.

74. The interest in leukaemia arises because of its known
sensitivity to induction by ionizing radiation and also
because of the short latent period expected between exposure and appearance of the condition. Amongst adults, themost promising studies are of the recovery operations workers. Although not conclusive, recent reports suggest an
increase in the incidence of leukaemia among the recovery
operation workers from Belarus, the Russian Federation,
Ukraine and the Baltic Countries. The limitations of thesestudies include low statistical power, uncertainties in dosereconstruction, and internal inconsistencies that suggest
potential biases or confounding factors that are difficult toaddress. Future studies may resolve these issues, although
after about 5–15 years post exposure, the risk of radiation‑­
induced leukaemia declines over time and most newly diagnosed leukaemia cases will be unlikely to have been due toradiation.

71. Among the recovery operation workers, elevated ratesof thyroid cancer compared to the general population havebeen reported, but no clear association with external dose
has been found. In addition, there are no current estimates ofthyroid doses from inhaled radioiodine to those who workedon the Chernobyl site in April–June 1986. The influence ofannual screenings and active follow‑up of these cohorts
make comparisons with the general population problematic.
72. Among the various radioactive isotopes of iodine
released during the accident, 131I is considered to be the mostsignificant contributor to dose to the thyroid gland. The
shorter‑lived radioactive isotopes of iodine may also havecontributed to the increased incidence of thyroid cancer.
However, epidemiological studies to date have not been able
to evaluate this possibility meaningfully.

3.

Leukaemia

75. Among those exposed in utero and as children, no persuasive evidence has been found of a measurable increase in

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UNSCEAR 2008 REPORT: VOLUME II

the incidence of leukaemia attributable to radiation exposure. This is not unreasonable given that the doses involved
were generally small, comparable with natural background
doses, and therefore epidemiological studies lack the statistical power to confirm any radiation‑related increases had theyoccurred.
76. Amongst adults, the most meaningful evidence comesfrom studies of the recovery operations workers. Although
at this time, some evidence exists of an increase in the incidence of leukaemia among a group of recovery operation
workers from the Russian Federation, this is far from conclusive. As yet, it would be premature to elevate the findingsof these studies to the status of those, for example, fromthe survivors of the atomic bombings. Nevertheless, future
results from such studies ought to provide important­scientific information.

the atomic bombings, would suggest that the doses are too
low—they are comparable with natural background radiation levels—to yield sufficient statistical power to detect any
measurable increase in the incidence or mortality of all solidcancers combined in the populations exposed to radioactive
material that was deposited after the ­Chernobyl accident.
5.
(a)Non-cancer effects

Cataracts

81. Clinically significant cataracts developed in some of
the ARS survivors exposed to high radiation doses. Several
new studies have suggested that lens opacity may form after
doses of less than 1 Gy. Although most of these refer topre‑clinical lesions, a recent study of the survivors of theatomic bombings suggests that there may be an increased
incidence of clinical cataracts at these dose levels [N17].

4. Other solid cancers
77. There appears, at present, to be no hard evidence of any
measurable increased incidence of all solid cancers taken
together among the populations of the Russian Federationand Ukraine. That conclusion takes account of the resultsfrom a few studies of breast cancer in women exposed as aresult of the Chernobyl accident. The weaknesses of the studies of the incidence of breast cancer are numerous; in particular, they do not take into account some major confounding
factors, such as the age at first pregnancy, other hormonal factors and nutrition. There appears to be no pattern of increased
incidence of breast cancer among the inhabitants of the contaminated areas compared to that among those of the uncontaminated areas, and no difference in time trends in areas
with different levels of radioactive deposition.
78. The evidence with respect to solid cancer incidence
among the recovery operation workers is mixed. Althoughsome groups show elevated incidence, significant relationships with increasing dose have not been quantified. In contrast, two Russian studies reported correlations between thesolid cancer mortality rate and dose.
79. Some caution needs to be exercised in interpreting theresults from these studies. First, for many cancers, a latent
period of 10 years or more is expected, so if this applies tothe incidence of all cancers taken together, one would not
expect to see any effect manifest itself until the mid to late
1990s. Second, interpretation of comparisons of the results
for the recovery operation workers with those for the general
population is difficult owing to the regular annual medical
examination offered to all recovery operation workers.
Third, the risk values derived from some of the studies aresubstantially higher than those determined from other epidemiological studies that are reviewed in annex A [U1] and,
therefore, need further analysis.
80. Assessments of statistical power, based on the ­follow‑up
to date and using findings from the study of the survivors of

82. The Ukrainian-American Chernobyl Ocular Study [C17,W7] indicates that lens opacity arising in the recovery operation workers, corrected for the most important confounding
factors, is related to the dose received. For the most part, thedoses were less than 0.5 Gy of low‑LET radiation acquired
in a somewhat protracted/fractionated manner. A key finding
was that the data were not compatible with a dose–effectthreshold of more than 0.7 Gy, and that the lower boundaryof the estimated dose threshold was close to the current dose
limit for the lens of the eye, i.e. 150 mSv, although this needs
to be tempered by consideration of the uncertainties in thedosimetry.
83. While a specific type of cataract (i.e. posterior subcapsular cataract, PSC) is characteristic of radiation exposure,several sets of data suggest that broader categories (i.e. posterior cortical cataracts) may also be regarded as radiation‑­associated. PSC can also be caused by: drugs, systemic
disorders, certain inflammatory or degenerative eye diseases
and eye trauma. However, the studies of those exposed asa result of the Chernobyl accident [D3, W7] have largely
addressed this issue of alternate causes by statistically­eval­uating and adjusting for various other risk factors.
84. A critical analysis of all existing information onradiation‑­induced cataracts, which, in particular, compares
the new data with existing knowledge, is necessary in orderto obtain a better understanding of any inconsistencies.
Follow­‑up of the major cohorts is necessary in order to better
evaluate latency and cataract progression, and to better characterize the risk to the lens of the eye from exposure to
low‑to‑­moderate radiation doses.
(b)Cardiovascular and cerebrovascular diseases

85. It has long been known that irradiation of the heart at
the very high doses used in radiotherapy leads to increased
risks of circulatory disease. However, little solid evidenceANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

exists of any demonstrable effect of the lower radiation
exposures due to the Chernobyl accident on cardiovascularand cerebrovascular disease incidence and mortality. One
study of the recovery operation workers in the Russian Federation has provided evidence of a statistically significant
association between radiation dose and both cardiovasculardisease mortality rates and cerebrovascular disease incidence. The observed excess of cerebrovascular disease islinked to those having worked during less than six weeks
and having cumulated doses of more than 150 mSv. However, the study was not adjusted for other factors, such as
obesity, smoking habits and alcohol consumption. Moreevidence is needed to conclude whether or not radiation
exposure due to the Chernobyl accident has increased theincidence of cardiovascular and cerebrovascular disease andassociated mortality.

applying those data to the populations exposed as a result of
the Chernobyl accident requires various assumptions to be
made. These include how to transfer the risk profile between
populations with different demography, ethnic origins andbackground disease rates, and how to transfer the resultsfrom a population acutely exposed to high doses and dose
rates to one that essentially received increased protracted
radiation doses at levels comparable to natural backgroundover several years and for which no increased incidence has
actually been observed. Analysts have to make otherassumptions regarding the future level of contributing factors (such as smoking), future levels of medical care andefficacy of treatment, and the average lifespan in future­decades, among others.

1.
(c)Autoimmune thyroiditis

86. Autoimmune thyroiditis is a progressive disease of the
thyroid gland characterized by the presence of antibodies
directed against the thyroid. It almost certainly involves aninteraction between genetic predisposition and environmental factors, such as the level of dietary iodine intake [D7].
However, its association with radiation exposure is controversial [E3]. In addition, the underlying incidence of auto­
immune thyroiditis increases with age [D8]. Therefore,
dissecting out the effect of radiation exposure due to theChernobyl accident from the other elements that may or may
not have a bearing on the incidence of autoimmune thyroid
disease in the population requires extremely careful study.
87. There have been few studies of significant size thathave addressed the relationship between autoimmune thyroiditis and exposure to radiation from the Chernobyl accident. The largest study [T7] could not demonstrate any
conclusive evidence of a relationship between thyroid doseand autoimmune thyroid disease. This is consistent with thefindings from studies on other exposed populations [D9,I27, N11].
B. Theoretical projections
88. In order to guide decision‑making on public healthresource management, and given that there is a latent period
between exposure and the appearance of any increased incidence in stochastic effects, various groups have attempted to
predict the health impact on populations exposed to radiation
by applying radiation risk models to the estimates of population dose. These models are based partially on epidemiolo­
gical data and partially on an understanding of biologicalprocesses [U3, U7, U17].
89. The major source of data for modelling increased incidence of stochastic effects due to radiation exposure remains
the detailed study of long‑term health effects among the survivors of the atomic bombings in Japan [P3]. However,63

Review of published projections

90. The first prognoses of the health consequences of theChernobyl accident conducted in 1987 yielded four important conclusions for policymakers on the scale and nature of
the effects [B47, I43, R4]:
- There would be no deterministic radiation effects
among the general public;- The increased incidence of cancers due to radiation
exposure would not be significant from the pointof view of organizing health care, although someeffects on some population groups at specific periods of time might be detected using epidemiologicalmethods;- A considerable increase in the incidence of thyroid cancer due to radiation exposure should be
expected, particularly among those exposed as
children; and- Psychological trauma caused by the accident would
affect millions of people.
91. Subsequently, a large number of radiation risk projections have been made by various groups regarding the healthconsequences of the Chernobyl accident [A11, C1, C11, I43,
T4, W5]; see appendix D for details. They predicted a potential increase in cancer mortality due to radiation‑induced
cancer in the range from 3% for the most affected parts ofthe former Soviet Union to 0.01% for the rest of Europe. All
the projections were based on estimates of population doses
made at the time; they usually assumed the linear non‑­threshold (LNT) model for the dependence of increased cancer incidence or mortality following an increase in dose, andused nominal parameters derived from reports of UNSCEAR[U9] and of the ICRP [I44, I45] and/or from some national
publications, e.g. [N4]. As new dosimetric and epidemiological data became available, some groups updated theirdose estimates, risk models and associated projections.
92. Although there is reasonable agreement between the
projections subsequently made, it is very unlikely that monitoring national cancer statistics would be able to identify any

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UNSCEAR 2008 REPORT: VOLUME II

increase in cancer incidence due to radiation exposure. However, for particular population groups at specific periods oftime after the accident, it was felt that some effects due toradiation exposure could be detected using scientific methods (e.g. an increased incidence of leukaemia among therecovery operation workers and of thyroid cancer in people
who were children in 1986).
2.

Scientific limitations

93. The interpretation and communication of radiation risk
projections is fraught with difficulties, because it is not easy
to communicate their intrinsic limitations adequately.
94. As discussed previously in the section on the attribution of effects to radiation exposure, because presently there
are no biomarkers specific to radiation, it is not possible tostate scientifically that radiation caused a particular cancer in
an individual. This means that in terms of specific individuals, it is impossible to determine whether their cancers are
due to the effects of radiation or to other causes or, moreover,whether they are due to the accident or background radiation. The situation with the ARS survivors of the accident isfundamentally different since each of them is known byname and ARS was diagnosed and attribution to radiation
exposure was based on conclusive medical findings. However, projected numbers of stochastic effects in anonymous
individuals could be misunderstood to be of a similar nature
to actual identified cases.

96. Because of the absence of proper experimental evidence, the dependence of the frequency of adverse radiation
effects on dose can be assessed only by means of biophysical models, among which, the LNT model has been usedwidely for radiation protection purposes [B48, U3]. However, others have been suggested, including superlinear andthreshold ones, and even models assuming hormesis. It is
important to understand the considerable statistical uncertainty associated with any projection based on modelling,which lends itself rather to estimations that are within anorder of ­magnitude or even more.
97. The currently available epidemiological data do notprovide any basis for assuming radiogenic morbidity andmortality with reasonable certainty in cohorts of the residents of the areas of the three republics and other countries
in Europe who received total average doses of below 30 mSv
over 20 years [A11, C1, C11, R4, T4]. Any increases would
be below the limit of detection. At the same time, it cannot
be ruled out that adequate data on the effects of low‑dosehuman exposure will be obtained as further progress ismade in understanding the radiobiology of man and othermammals, and using this knowledge to analyse the epidemiological data. This may provide in the future the scientific basis for evaluating the radiation health consequencesof the Chernobyl accident among residents of areas withlow radiation levels.

3.
95. An additional misunderstanding occurs regarding thenature of the evidence for stochastic effects from studies of
exposed populations. For example, there is reasonable evidence that acute radiation exposure of a large population withdoses above 0.1 Sv increases cancer incidence and mortality.
So far, neither the most informative study of the survivors of
the atomic bombings nor any other studies of adults have provided conclusive evidence for increased incidence of carcinogenic effects at much smaller doses [U3, annex A of U1].

UNSCEAR statement

98. The Committee has decided not to use models to
project absolute numbers of effects in populations exposed
to low radiation doses from the Chernobyl accident, becauseof unacceptable uncertainties in the predictions. It should be
stressed that the approach outlined in no way contradicts theapplication of the LNT model for the purposes of radiation
protection, where a cautious approach is conventionally andconsciously applied [F11, I37].

VII. General conclusions
A.

health risks attributable to radiation

99. The observed health effects currently attributable toradiation exposure are as follows:- 134 plant staff and emergency workers received
high doses of radiation that resulted in acute radiation syndrome (ARS), many of whom also incurred
skin injuries due to beta irradiation;- The high radiation doses proved fatal for 28 ofthese people;- While 19 ARS survivors have died up to 2006, their
deaths have been for various reasons, and usually
not associated with radiation exposure;- Skin injuries and radiation‑induced cataracts aremajor impacts for the ARS survivors;- Other than this group of emergency workers, several
hundred thousand people were involved in recovery
operations, but to date, apart from indications of anincrease in the incidence of leukaemia and cataracts
among those who received higher doses, there is noevidence of health effects that can be attributed toradiation exposure;- The contamination of milk with 131I, for which
prompt countermeasures were lacking, resulted inlarge doses to the thyroids of members of the generalpublic; this led to a substantial fraction of the more

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

than 6,000 thyroid cancers observed to date amongpeople who were children or adolescents at the timeof the accident (by 2005, 15 cases had proved fatal);- To date, there has been no persuasive evidence of
any other health effect in the general populationthat can be attributed to radiation exposure.
100. From this annex based on 20 years of studies and fromthe previous UNSCEAR reports [U3, U7], it can be concluded that although those exposed to radioiodine as child­ren or adolescents and the emergency and recovery operation
workers who received high doses are at increased risk ofradiation‑induced effects, the vast majority of the populationneed not live in fear of serious health consequences from the
Chernobyl accident. (This conclusion is consistent with thatof the UNSCEAR 2000 Report [U3]). Most of the workers
and members of the public were exposed to low level radiation comparable to or, at most, a few times higher than theannual natural background levels, and exposures will continue to decrease as the deposited radionuclides decay or are
further dispersed in the environment. This is true for populations of the three countries most affected by the Chernobyl
accident, Belarus, the Russian Federation and Ukraine, andall the more so, for populations of other European countries.
Lives have been disrupted by the Chernobyl accident, butfrom the radiological point of view, generally positive prospects for the future health of most individuals involved
should prevail.
B.

Comparison of present annex with previous reports

101. This annex reviews the scientific information obtainedsince the UNSCEAR 2000 Report [U3] on the exposures andeffects due to radiation from the Chernobyl accident.
Although many more research data are now available, themajor conclusions regarding the scale and nature of the healthconsequences are essentially consistent with the ­previous
UNSCEAR reports [U3, U7].
102. The radioactive release has been re‑evaluated, but
the changes are academic and not relevant to the assessment of radiation dose, which is based on direct human andenvironmental measurements.

65

11 ARS survivors had died [U3]; since then another 8 havedied up to 2006. The annex discusses the causes of death in
the context of their radiation exposure.
105. For the larger number of emergency and recovery
operation workers, there are indications of an increased incidence of leukaemia and cataracts among those who received
higher doses, although further clarification of the epidemiological information is still needed. The information on cataracts indicates that the threshold for induction may be lower
than previously thought. While there have been indicationsof an increase in the incidence of cardiovascular and cerebrovascular diseases among the recovery operation workers
that correlate with the estimated doses, major concerns overthe possible influence of confounding factors and potential
study biases remain.
106. In the UNSCEAR 2000 Report [U3], fewer than
1,800 thyroid cancers had become evident among those
aged under 18 at the time of the accident; this had increased
to more than 6,000 by the year 2006. Several studies havenow been conducted that provide rather consistent estimatesof the radiation risk factors for thyroid cancer.
C. Comparison of observed latehealth effects with projections
107. Early assessments [B47, I43, R4] conducted in 1987
projected a considerable increase in thyroid cancer incidence
due to radiation exposure in the three republics, particularly
among children. To date, some 6,000 thyroid cancers havebeen seen among those in the three republics who were
under 18 at the time of the accident, of which a substantial
fraction is likely to have been due to radiation exposure.
108. Projections [C1] made in 1996 using dosimetric information on the emergency and recovery operation workers
had indicated that there might be a detectable increase in theincidence of leukaemia among those who had received relatively high doses of radiation. There has been some evidenceof a detectable increase among a group of Russian workers,
although at present, it is far from conclusive.

103. Dose estimates have been extended for an additional
number of about 150,000 emergency and recovery operation
workers. Based on direct human and environmental measurements made since 1988 and models that take into accountthe actual countermeasures, the estimates of the thyroid doseto the evacuees have been updated. The estimated thyroid
and effective doses to the inhabitants of Belarus, the RussianFederation and Ukraine have been expanded from five million to about one hundred million people and the estimatedthyroid and effective doses to about 500 million inhabitantsof most other European countries have been updated.

109. Several groups [A11, B47, C1, C11, F10, I43, R4]
have projected possible increases in solid cancer incidence
for the general population. These assessments differ in theexact populations considered and the dosimetry and projection models used. However, for all the populations considered, the doses are relatively small, comparable with thosefrom natural background radiation, and any increase wasunlikely to be detected by epidemiological studies. Although
it is now one decade after the minimum latent period forsolid cancers, no increases in cancer incidence (other thanof thyroid cancer) have been observed to date that can be
attributed to irradiation from the accident.

104. With regard to the follow‑up of the ARS survivors,
there is significant new information in this annex. By 1998,

110. The use of theoretical projections is fraught with­difficulty. It is extremely difficult to communicate such

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UNSCEAR 2008 REPORT: VOLUME II

projections accurately and honestly to officials and the generalpublic. Moreover, there is a limit to the epidemiologicalknowledge that can be used to attribute conclusively an
increased incidence to radiation exposure. Therefore, any
radiation risk projections in the low dose area should be considered as extremely uncertain, especially when the projection of numbers of cancer deaths is based on trivial individual
exposures to large ­populations experienced over many years.
D. New knowledge from studies of the accident
111. Although there is general consensus on the scale andcharacter of the health consequences due to radiation fromthe accident, studies of the world’s worst nuclear accident
have clearly produced a vast amount of useful scientificinformation. Most of this can be used to validate predictive
capabilities and knowledge developed from research andexperience before the accident. Other information is completely new and is helping to fill gaps in the current scientificknowledge base.
112. The accident has provided clear evidence that confirms pre‑existing knowledge of the importance of 131I in the
pasture–cow–milk pathway, of the need to take prompt
countermeasures, of the potential high doses to the thyroids,
and of the anticipated increase in thyroid cancer incidence,

particularly among those exposed during childhood or adolescence. Ongoing research is helping to refine this know­
ledge, particularly with respect to the patterns of thyroid
cancer incidence for different doses, pathways, age groups,
and levels of dietary iodine.
113. Similarly, for protracted irradiation due to thelonger‑lived radionuclides, the pre‑existing understanding of
the important pathways of exposure to humans has beenvalidated by the experience obtained from the accident.
Moreover, there has been a greater recognition of the importance of soil type in determining the transfer of radiocaesium
to foodstuffs, a greater understanding of the radioecology inurban, semi‑natural and forest environments, and considerable experience in the implementation of a whole range ofcountermeasures.
114. With regard to health effects, there have been dramatic improvements in the understanding of acute radiation
effects and their treatment, and of the long‑term sequelae of
local radiation injuries due to irradiation of the skin and lensof the eye. With respect to the incidence of stochastic effects
other than thyroid cancer, so far there have been few observations that have challenged pre‑existing understanding
derived from the studies of other exposed groups, such as thesurvivors of the atomic bombings in Japan and other studiesof radiation exposed populations.

ACKNOWLEDGEMENTS
115. The Committee wishes to express its deep gratitude
for the contributions made by the following individuals insupporting the lead author, M. Balonov, in preparing thisannex: the late G.R. Howe, L. Anspaugh, A. Bouville, A.
Guskova, V. Ivanov, J. Kenigsberg, I. Likhtarev, F. Mettler,
R. Shore, G. Thomas, M. Tirmarche and L. Zablotska.

In addition, the Committee would like to recognize the valuable contributions of V. Bebeshko, D. Belyi, M.O. Bernier,
G. Bruk, V. Chumak, S. Davis, V. ­Drozdovitch, I. Galstyan,
N. Gentner, V. Golikov, L. ­Kovgan, Yu. Kruk, J. Kurtinaitis,
V. Minenko, K. Rahu, S. Shinkarev, A. Stengrevics, andI. Zvonova.

Appendix A.
Physical and environmental context
I.

Summary from the UNSCEAR 2000 Report [U3]A1. The accident on 26 April 1986 at the Chernobyl
Nuclear Power Plant (ChNPP) occurred during a low‑powerengineering test of the Unit 4 reactor. Safety systems had
been switched off and improper, unstable operation of thereactor allowed an uncontrollable power surge to occur that
resulted in successive steam explosions; these steam explosions severely damaged the reactor building and completely
destroyed the reactor.

and 137Cs were estimated to have been ~1,760 and ~85 PBq,
respectively (1 PBq = 1015 Bq). It is worth noting, however,that doses in the following sections of this appendix are estimated on the basis of measurements of radionuclides inhumans, foodstuffs and other environmental media, and of
external gamma exposure rates. Thus, knowledge of thequantities of radionuclides released was not needed for the
purpose of assessing doses.

A2. The radionuclide releases from the destroyed reactor
occurred mainly over a 10‑day period, but with varying
release rates. An initial high release rate on the first day wascaused by mechanical discharge as a result of the explosions
in the reactor. There followed a 5‑day period of declining
releases associated with the hot air and fumes from thered‑hot core material. During the next few days, the release
rate of radionuclides increased until day 10, when the releases
dropped abruptly, thus ending the period of intense release.
The radionuclides released in the accident were deposited
with greater density in the regions surrounding the reactor in
the European part of the former Soviet Union.

A5. The deposited material consisted of hot particles in
addition to more homogeneously distributed radioactive
material. These hot particles have been classified into two
broad categories: (a) fuel fragments with a mixture of fission
products bound to a matrix of uranium oxide, similar incomposition to that of the fuel in the core, but sometimes
very much depleted in caesium, iodine and ruthenium, and(b) particles consisting of one dominant element (ruthenium
or barium) but sometimes having traces of other elements.
These monoelemental particles might have originated fromembedments of these elements produced in the fuel during
reactor operation and released during the fragmentation of
the fuel. Typical activities were 0.1–1 kBq for a fuel fragment hot particle and 0.5–10 kBq for a ruthenium hot particle; a typical effective diameter was about 10 μm, to becompared with 0.4–0.7 μm for particles associated with 131I
and 137Cs. Hot particles deposited in the pulmonary region
have a long retention time and this can lead to considerable
localized doses. Although it had been demonstrated in the
1970s that alpha‑emitting hot particles are no more radiotoxic than the same activity uniformly distributed in thewhole lung, it was not clear whether the same conclusion
could be reached for beta‑emitting hot particles.

A3. Two basic methods were used to estimate the releaseof radionuclides in the accident. The first method consisted
in evaluating separately the inventory of radionuclides in thereactor core at the time of the accident and the fraction of theinventory of each radionuclide that was released into theatmosphere; the products of those two quantities are theamounts released. The second method consisted in measuring the density of radionuclide deposition on the ground all
around the reactor; if it is assumed that all of the released
amounts were deposited within the area where the measurements were made, the amounts deposited would be equal tothe amounts released. In both methods, air samples taken
above the reactor or at various distances from the reactor
were analysed for radionuclide content to determine or
to confirm the radionuclide distribution in the materials
released. The analysis of air samples and of deposited material also led to information on the physical and chemical
properties of the radioactive material that was released into
the atmosphere.

A6. Radioactive deposition on the ground was found tosome extent in practically every country of the northernhemisphere [U9]. In annex J, “Exposures and effects of theChernobyl accident”, of the UNSCEAR 2000 Report [U3],“contaminated areas” were defined as areas where theaverage deposition density of 137Cs exceeded 37 kBq/m2(1 Ci/km2). Caesium‑137 was chosen as a reference radionuclide for the ground contamination resulting from the
Chernobyl accident for several reasons: its substantial
contribution to the lifetime effective dose; its long radioactive half-life; and its ease of measurement. The areas
deemed contaminated were found mainly in Belarus, theRussian Federation and Ukraine.

A4. From the radiological point of view, 131I and 137Cs werethe more important radionuclides released because they
were responsible for most of the radiation dose incurred by
the members of the general population. The releases of 131I
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UNSCEAR 2008 REPORT: VOLUME II

A7. The main radionuclide releases lasted 10 days, during
which time, the wind often changed direction with the resultthat material was deposited in all areas surrounding the reactor site at one time or another. Details of the developmentof the plume over time had been given by Borzilov and­Klepikova [B24] and are reproduced in figure A‑I. The initial plumes of material moved towards the west. On 27 April,
the winds shifted towards the northwest, then on 28 April,
towards the east. Two extensive areas, Gomel–Mogilev–
Bryansk and Orel–Tula–Kaluga, became contaminated as aresult of the deposition of radioactive material from theplume that passed over at that time (figure A‑I, trace 3). The
deposition onto Ukrainian territory south of Chernobyl
occurred after 28 April (figure A‑I, traces 4, 5 and 6). Rainfall occurred in an inhomogeneous pattern, and this caused
uneven areas of radionuclide deposition. The general patternof 137Cs deposition calculated based on simulations of themeteorological conditions had been shown to match themeasured deposition pattern rather well.
A8. The principal physicochemical forms of the deposited radionuclides were: (a) dispersed fuel particles;(b) condensation‑­generated particles; and (c) mixed-typeparticles, including ones generated by adsorption. The radionuclide distribution in the nearby contaminated zone (lessthan 100 km from the damaged reactor), also called the“near zone”, differed from that in the “far zone” (from100 km to approximately 2,000 km). Deposition in the nearzone reflected the radionuclide composition of the fuel.
Larger particles, which were primarily fuel particles, andthe refractory elements (zirconium, molybdenum, ceriumand neptunium) were to a large extent deposited in the nearzone. Elements with intermediate volatility (ruthenium,
barium and strontium) and fuel elements (plutonium anduranium) were also deposited largely in the near zone. The
volatile elements (iodine, tellurium and caesium), in theform of condensation‑generated particles, were more widelydispersed into the far zone.
A9. The three main areas of radionuclide deposition were
designated the Central, Gomel–Mogilev–Bryansk and
Kaluga–Tula–Orel areas. The Central area is in the nearzone, predominantly to the west and northwest of the reactor. Caesium‑137 was deposited during the active period of
release, and the deposition density of 137Cs was greater than
37 kBq/m2 (1 Ci/km2) in large areas of Ukraine and in thesouthern parts of the Gomel and Brest oblasts of Belarus.
The 137Cs deposition was highest within the 30‑km-radius
area surrounding the reactor, known as the “30‑km zone”.
Deposition densities exceeded 1,500 kBq/m2 (40 Ci/km2)
in this zone and also in some areas of the near zone to thewest and northwest of the reactor, in the Gomel, Kiev andZhitomir oblasts.
A10. The Gomel–Mogilev–Bryansk area is centred 200 km
to the north‑northeast of the reactor at the boundary of theGomel and Mogilev oblasts of Belarus and of the Bryansk
oblast of the Russian Federation. In some areas, deposition
was comparable to that in the Central area; deposition

densities even reached 5 MBq/m2 in some villages of the
Mogilev and Bryansk oblasts.
A11. The Kaluga–Tula–Orel area is located 500 km to thenortheast of the reactor. Radionuclide deposition here was a
result of rainfall on 28–29 April during the passage of thesame radioactive cloud that had deposited radionuclides in
the Gomel–Mogilev–Bryansk area. The 137Cs‑deposition
density was, however, lower in this area, generally less than
500 kBq/m2.
A12. Outside these three main affected areas, there weremany areas where the 137Cs‑deposition density was in therange of 37–200 kBq/m2. Rather detailed surveys of theradio­nuclide deposition on the entire European part of theformer Soviet Union had been completed. A map of measured 137Cs deposition is presented in figure A‑II. The total
quantity of 137Cs deposited in the former Soviet Union as aresult of the accident, including in areas of lesser deposition,
was estimated to be approximately 40 PBq. The total wasapportioned as follows: 40% in Belarus; 35% in the RussianFederation; 24% in Ukraine; and less than 1% in otherrepublics of the former Soviet Union. The amount of 137Cs
deposited in the contaminated areas (>37 kBq/m2) of theformer Soviet Union was estimated to be 29 PBq (for comparison, the residual activity resulting from atmosphericnuclear weapons testing was about 0.5 PBq with averagesoil‑deposition density of about 2 kBq/m2).
A13. The environmental behaviour of the deposited radionuclides depended on the physical and chemical characteristics of the radionuclide considered, on the type of deposition(i.e. dry or wet), and on the characteristics of the environment. Special attention was devoted to 131I, 137Cs and 90Sr andtheir pathways of exposure of humans. Deposition occurredon the ground and on water surfaces.
A14. For most short‑lived radionuclides such as 131I, themain pathway of exposure of humans was the ingestion ofmilk, which was contaminated as a consequence of 131I
deposited on pasture grass grazed by cows or goats, or ofcontaminated leafy vegetables that were consumed within a
few days. The amounts deposited on vegetation wereretained with an ecological half‑time of about two weeks
before removal to the ground surface and to the soil.
A15. Radionuclides deposited on soil migrate downward
into the soil column and are partially absorbed by plant roots,
leading in turn to upward migration into vegetation. These
processes did not need to be considered for short‑lived radionuclides, such as 131I (which has a physical half‑life of only
eight days); however, they needed to be considered forlong‑lived radionuclides, such as 137Cs and 90Sr. The rate anddirection of radionuclide migration through the soil–plant
pathway were determined by a number of natural phenomena, including relief features, the type of plant, the structure
and composition of soil, and hydrological conditions andweather patterns, particularly at the time that deposition
occurred. The vertical migration of 137Cs and 90Sr in soil ofANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

different types of natural meadows was rather slow, and thegreater fraction of radionuclides was still contained in its
upper layer (0–10 cm). On average, in the case of mineralsoils, up to 90% of 137Cs and 90Sr was found in the 0–5 cm
layer; in the case of peaty soils, in which radionuclide migration is faster, only 40–70% of 137Cs and 90Sr was found in thatlayer. The effective half‑time of clearance from the root layer(0–10 cm) in meadows with mineral soils was estimated torange from 10 to 25 years for 137Cs and to be 1.2–3 times
faster for 90Sr than for 137Cs; therefore, the effective clearance
half‑time for 90Sr was estimated to be 7–12 years.
A16. For a given initial deposition on soil, the transferfrom soil to plant varies with time as the radionuclide isremoved from the root layer and as its availability inexchangeable form decreases. The 137Cs content in plants
was at its maximum level in 1986, when the amount wasdue to direct deposition on aerial surfaces. In 1987, 137Cs
activities in plants were much lower than in 1986, as theamounts in plants were then mainly due to root uptake.
Since 1987, the transfer coefficients from deposition toplants continued to decrease, although the rate of decrease
slowed: from 1987 to 1995, the transfer coefficients of137
Cs decreased by 1.5–7 times, on average. Compared withthe 137Cs deposited as fallout from nuclear weapons tests,137
Cs resulting from the Chernobyl accident in the far zone
was found to be more mobile during the first four years
after the accident, as the water‑soluble fractions of 137Cs
resulting from the Chernobyl accident and from weapons
testing fallout were about 70% and 8%, respectively. Lateron, ageing processes led to similar mobility values for 137Cs
resulting from the Chernobyl accident and from fallout
from the testing of nuclear weapons.
A17. In contrast to 137Cs, it seemed that the exchangeabilityof 90Sr did not keep decreasing with time after the accident but
might in fact have been increasing. In the Russian ­Federation,
no statistically significant change had been found in the 90Sr
transfer coefficient from deposition to grass during the first
4–5 years following the accident. This was attributed to twocompeting processes: (a) conversion of 90Sr from a poorly
soluble form, which characterized the fuel particles, to a soluble form easily assimilated by plant roots; and (b) the verticalmigration of 90Sr into deeper layers of soil, which hindered its
assimilation by vegetation.
A18. Milk, meat and potatoes usually accounted for thebulk of the dietary intake of 137Cs. However, for residents of69

rural regions, mushrooms and berries from forests represented an important dietary component. The decrease withtime of the 137Cs concentrations in those foodstuffs was
extremely slow, with variations from one year to anotherdepending on weather conditions.
A19. Radioactive material had also been deposited onto
water surfaces. Deposition on the surfaces of seas and oceans
resulted in low doses because the radioactive material had
been rapidly diluted in extremely large volumes of water.
A20. In rivers and small lakes, the levels of radionuclides
resulted mainly from erosion of the surface layers of soil inthe watershed, followed by run‑off into the water bodies. In
the 30‑km zone, where relatively high levels of 90Sr and 137Cs
had been deposited, the most important contaminant of surface water was found to be 90Sr, as 137Cs was strongly
adsorbed by clay minerals in the soil. Much of the 90Sr inwater had been found to be in a soluble form; low levels of
plutonium isotopes and of 241Am had also been measured in
the rivers of the 30‑km zone.
A21. The contribution of aquatic pathways to the dietaryintake of 137Cs and 90Sr was usually quite small. However,the 137Cs concentration in the muscle of predator fish, such asperch or pike, might have been quite high in lakes with longwater-retention times, as had been found in Scandinavia andin Russia. For example, the concentration of 137Cs in thewater of Lakes Kozhany and Svyatoe (located in the area of
the Bryansk oblast of the Russian Federation deemed contaminated) was still high in 1996 because of special hydrological conditions: 10–20 Bq/L of 137Cs and 0.6–1.5 Bq/L of90
Sr. The concentration of 137Cs in the muscles of the silver
crucian (Carassius auratus gibelio) sampled in Lake ­Kozhany
was in the range of 5–15 kBq/kg and of pike (Esox lucius) in
the range 20–90 kBq/kg. In the summer of 1986, wholebody counters were used to measure the activity of 137Cs ininhabitants of the village of Kozhany located along the coastof Lake Kozhany. The mean body content was 7.4 ± 1.2 kBq
for 38 adults who did not consume lake fish (according tointerviews performed before the measurements), but was
49 ± 8 kBq for 30 people who often consumed lake fish.
The average annual internal doses were estimated to be
0.3 mSv and 1.8 mSv to persons in these two groups,
respectively. In addition, the relative importance of theaquatic pathways, in comparison to terrestrial pathways,
might have been high in areas downstream of the reactorsite where ground ­deposition had been small.

II. Update
A22. The Chernobyl Forum issued a report in 2006 [I21]on the environmental consequences of the accident,­including the assessment of individual and collective doses
to members of the general public. The report was preparedby a group of 35 scientists, collectively referred to as the“Expert Group Environment”. These experts were from thethree most affected countries—Belarus, the Russian Federation and Ukraine—and also from the international community of scientists who had worked either with colleagues
from these three countries or who had performed scientificwork related to the environment and to deposition of radionuclides resulting from the Chernobyl accident in their

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own countries. The work of this expert group was managed
by the International Atomic Energy Agency. Unless specified otherwise, the materials in section (A.II) are takenfrom [I21].
A.

A24. By 2005, most of the radionuclides released had longsince decayed to negligible levels. Over the next few decades, 137Cs will continue to be the most important radio­
nuclide; 90Sr will be of interest, but to a lesser extent, in thenear zone. Over the very long term (hundreds to thousands ofyears), the only radionuclides of interest will be the plutonium isotopes and 241Am. The initial amounts of 241Am
released were so small that they have not been estimated.
However, 241Am results from the radioactive decay of 241Pu.
With an initial amount of 241Pu released into the environmentof 2.6 PBq (see table A1) the decay of 241Pu and the resulting
ingrowth and subsequent decay of 241Am are shown in figure A‑III. The maximum total activity of 241Am in the environment will be 0.077 PBq in the year 2058. This is a small
amount compared to the initial 2.6 PBq of 241Pu, but it is morethan two times larger than the combined amounts of 239Pu and240
Pu that will be present at that time. Americium‑241 is the
only radionuclide whose amount is presently increasing withtime; the amounts of the other radionuclides will continue todecrease with time.

Radionuclide release and deposition
1. Radionuclide source term

A23. Over the years, the understanding of the amountof material released during the course of the accident has
improved considerably; the current best estimates are
given in table A1. Most of the radionuclides released inlarge quantities have short physical half‑lives; the radionuclides with long half‑lives had generally been released
in small quantities. These release estimates are similar
to those given in reference [U3], but the amounts ofrefractory elements released are now estimated to havebeen smaller.

Table A1. Revised estimates of the total release of principal radionuclides to the atmosphere during the course of theChernobyl accidenta
Radionuclide

Half-life

Activity released(PBq)

Inert gases
Kr

10.72 a33

Xe

5.25 d

6 500

85

133

Volatile elements
Te33.6 d240Te3.26 d

~1 150131

I8.04 d~1 760I

20.8 h910

Cs

2.06 a~47b

Cs

13.1 d36

Cs

30.0 a

~85

129m
132

133
134
136
137

Elements with intermediate volatility
Sr

50.5 dSr

29.12 a~10

Ru39.3 d

>168

Ru

368 d

>73

Ba

12.7 d

240

89
90

103
106

140

~115

Refractory elements (including fuel particles)c
Zr

64.0 d84

Mo2.75 d>72

Ce32.5 d

84

95
99

141

Ce

284 d

~50

Np

2.35 d400

Pu87.74 a

0.015

144
239

238

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

Radionuclide

Half-life

Activity released
(PBq)

Pu

24 065 a

0.013

Pu

6 537 a

0.018

239
240

Pu

14.4 a~2.6

Pu

376 000 a

0.00004Cm

18.1 a

~0.4

241
242
242

71

a Most of the data are from references [D11, U3].
b Based on 134Cs/137Cs ratio 0.55 as of 26 April 1986 [M8].
c Based on fuel particle release of 1.5% [K13].

2. Physical and chemical form of
released material; hot particles
A25. Radionuclides in the released material were in theform of gases, condensed particles and fuel particles. The
presence of fuel particles was an important characteristic of
the accident. During oxidation and dispersal of the nuclear
fuel, volatilization of some radionuclides took place. Afterthe initial cloud cooled, some of the more volatile radio­
nuclides remained in the gaseous phase, while other volatile
radionuclides, such as 137Cs, condensed onto particles of
construction materials, soot and dust. Thus, the chemicaland physical forms of the radionuclides in the release were
determined by the volatility of their compounds and the conditions inside the reactor. Radioactive material with relatively high vapour pressures (primarily isotopes of inert
gases and of iodine in different chemical forms) were transported in the atmosphere in the gaseous phase. Isotopes ofrefractory elements (e.g. cerium, zirconium, niobium, andplutonium) were released into the atmosphere primarily inthe form of fuel particles. Other radionuclides (isotopes of
caesium, tellurium, antimony, etc.) were found in both fueland condensed particles. The relative contributions of condensed and fuel components to the deposition at a given site
can be estimated from the activity ratios of the radionuclides
of different volatility classes.
A26. Fuel particles made up the most important part of thedeposited material in the vicinity of the damaged reactor.
Radionuclides such as 95Zr, 95Nb, 99Mo, 141,144Ce, 154,155Eu,
237,239
Np, 238-242Pu, 241,243Am and 242,244Cm were released in amatrix of fuel particles only. More than 90% of the 89,90Sr and
103,106
Ru activities that were released were also in fuel­particles. The released fraction of 90Sr, 154Eu, 238Pu, 239+240Pu
and 241Am (and, therefore, of the nuclear fuel itself) deposited
outside the ChNPP industrial site has been recently estimatedto be only 1.5±0.5% [K13], which is half that of earlier
estimates.
A27. The chemical and radionuclide composition of fuelparticles was close to that of irradiated nuclear fuel, but witha lower fraction of volatile radionuclides, a higher oxidation
state of uranium, and the presence of various admixtures,
especially in the surface layer. In contrast, the chemical
and radionuclide composition of condensed particles varied

widely. The specific activity of radionuclides in thesep­ articles was governed by the duration of the condensation
pro­cess and the process temperature, as well as the particle
characteristics. The radionuclide content of some of the particles was dominated by just one or two radionuclides, e.g.
103,106
Ru or 140Ba/140La.
A28. The form of a radionuclide in the release influenced
the distance of its atmospheric transport. Even the smallest
fuel particles consisting of a single grain of nuclear fuelcrystallite had a relatively large size (up to 10 mm) and highdensity (8–10 g/cm3). Because of their size, they were transported only a few tens of kilometres. Larger aggregates ofparticles were found only within distances of several kilometres from the power plant. For this reason, the depositionof refractory radionuclides strongly decreased with distancefrom the damaged reactor and only traces of refractory elements could be found outside the industrial site of the power
plant. In contrast, significant deposition of gaseous radio­
nuclides and sub‑micron condensed particles took place at
distances of thousands of kilometres from the site. Ruthenium particles, for example, were found throughout Europe.
A29. Another important characteristic of the depositedmaterial is its solubility in aqueous solution. This determined
the mobility and bioavailability of deposited radionuclides insoils and surface waters during the initial period after deposition. The contribution of the water‑soluble and exchangeable(extractable with 1M ammonium acetate solution) forms of137
Cs varied from 5% to more than 30% in deposited material
sampled daily at the Chernobyl meteorological station from26 April to 5 May 1986. The water‑soluble and exchangeable
forms accounted for only about 1% of the 90Sr in material
deposited on 26 April, and this value increased to 5–10% inmaterial deposited on subsequent days.
A30. The low solubility of deposited 137Cs and 90Sr near the
power plant indicates that fuel particles were the major partof the deposited material, even 20 km from the source. At
shorter distances, the proportion of water‑soluble and exchangeable forms of 137Cs and 90Sr was lower owing to thepresence of larger particles; at further distances, the fractionof soluble condensed particles increased. As one example,
almost all 137Cs deposited in 1986 in the United Kingdom
was water‑soluble and exchangeable.

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3. Meteorological conditions during
the course of the accident
A31. The meteorological conditions during the accident
have been described in references [I21, U3]. There are no
new data, but efforts to understand better the meteorologicalconditions during the accident are the subject of continuingresearch [T5, T6]. In this case, the primary goal is to be able
to reconstruct the pattern of 131I deposition after the accident.
This is because the reconstruction of doses to the thyroid due
to radioiodine continues to be a major research effort, andreliable measurements of the deposition densities of 131I arelacking, especially in Ukraine.
4.

Concentration of radionuclides in air

A32. The activity concentration of radioactive material in
air was measured at many locations in the former Soviet
Union and throughout the world. Examples of the results ofthe measurements made are shown in figure A‑IV for two
locations: Chernobyl and Baryshevka, Ukraine. The locationof the sampler at Chernobyl was the meteorological stationin the City of Chernobyl, which is about 15 km southeast of
the ChNPP. The initial concentrations of airborne materials
were very high, but dropped in two phases. There was a
rapid fall over a few months, and then a more gradualdecrease over several years. Over the long term, the sampler
at Chernobyl recorded consistently higher activity concentrations than the sampler at Baryshevka (about 150 km
southeast of the ChNPP), presumably owing to higher levelsof resuspended material [H5].
A33. Even with the data smoothed by a rolling average,
there are some notable features in the data collected over thelong term. The clearly discernible peak that occurred during
the summer of 1992 (month 78) was due to widespread­forest fires in Belarus and Ukraine.
5. Deposition of radionuclides on soil surfaces
A34. Mapping the deposition density of 137Cs throughout
the northern hemisphere was intensively pursued through2000. Efforts continue to map the deposition density of 131I,
particularly in areas where an increase in the incidence of
thyroid cancer in children has been noted. Because thehalf‑life of 131I is short, direct measurements of deposition
densities are limited. In the absence of such data, three
approaches are being used to reconstruct the pattern of 131I
deposition: (a) use of 137Cs as a surrogate; (b) use of 129I as asurrogate; and (c) use of advanced models of atmospherictransport and deposition.
A35. The use of 137Cs as a surrogate for 131I has been
described in several publications but there is not a consistent relationship between the depositions of the two
radionuclides. This is because the two elements have differing volatilities and rates of deposition on soil via dry

and wet processes. Iodine‑129 (half‑life of 16 million
years) is generally regarded as a more natural surrogate,
but analysis is costly and time consuming. Nevertheless,such work is proceeding, and four major papers [M6, M7,
P4, S17] have been published since 2000. If soil samples
are taken to sufficient depths to capture the deposited 129I,
then the deposition density of 129I can be calculated. Then,
if the isotopic ratio of 129I to 131I at the time of deposition
is known or can be inferred, the deposition density of 131I
can be calculated. There is substantial variability in themeasured or derived values of this ratio. Pietrzak‑Flis etal. [P4] used a value of 32.8 for deposition in Warsaw,
Poland, whereas Straume et al. [S17] used a value of 12±3
for deposition in Belarus. Schmidt et al. [S11] have­recommended that “…the smallest measured 129I to 131I
atomic ratio should come closest to the real emission
value”. This is because it is much more likely that ­samples
would have been contaminated with extraneous sourcesof 129I than of 131I.
A36. The effort by Talerko [T5, T6] to reconstruct thedeposition densities of 131I using an atmospheric transportmodel has been mentioned above. This type of calculation
is dependent on a great many assumptions, which are basedon very limited data; thus, the method is subject to large
uncertainties.
B.

Urban environment

A37. Deposited radioactive material resulted in both short‑and long‑term increases in the radiation levels over the natural background levels in thousands of settlements, which inturn resulted in additional external exposures of the inhabitants and internal exposures due to the consumption of foodcontaining radionuclides. Near the ChNPP, the towns of
Pripyat and Chernobyl and some other smaller settlements
were subjected to substantial deposition from the “undiluted” radioactive cloud under dry meteorological conditions, whereas many more distant settlements incurredsignificant deposition owing to precipitation at the time ofthe passage of the cloud.
A38. The radioactive material deposited on exposed surfaces such as lawns, parks, streets, building roofs and walls.
The level and composition of the deposited material was significantly influenced by whether the deposition was via dryor wet processes. Under dry conditions, trees, bushes, lawns
and roofs became more contaminated than when there was
precipitation. Under wet conditions, horizontal surfaces—
including soil plots and lawns—received the highest deposition. These differences, including some marked changes
with time, are illustrated in figure A‑V.
1.

Migration of radionuclides in the urban environment

A39. Radionuclides became detached from surfaces inurban environments owing to natural weathering processes

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

(such as rain and snow melting) and human activities(including traffic, street washing and other clean‑up activities). The major processes of removal of radionuclides were
through run‑off into storm and/or sanitary sewer systems
and through seasonal abscission of vegetation. These naturalprocesses and human activities significantly reduced thedose rates in inhabited and recreational areas during 1986
and thereafter.
A40. In general, vertical surfaces of houses do not exhibit
the same degree of deposition or of weathering of depositedradioactive material as horizontal surfaces. After 14 years,
the loss of radionuclides deposited on walls was typically
50–70% of the initial amount deposited. Levels of radio­
nuclides on roofs in Denmark naturally decreased by
60–95% of those originally present over the same period, as­illustrated in figure A‑VI [A6].
A41. The level of radiocaesium on asphalt surfaces has
decreased so much that generally less than 10% of the initialamount of deposited material is now left. Only a small fraction is associated with the bitumen of asphalt; most is associated with a thin layer of street dust, which is expected to be
removed eventually by weathering.
A42. One of the consequences of these processes has been
secondary contamination of sewerage systems and sludge
storage, which necessitated special clean‑up measures. Generally, radionuclides were not transferred from soil to otherurban areas within cities, but migrated down into the soil
through natural processes or mixing as a consequence ofdigging of gardens and parks.

2.

Dynamics of exposure rate in urban environments

A43. Gamma radiation from radionuclides deposited in
the urban environment has been a major contributor to
the additional external exposure of humans due to theaccident. Compared to the dose rate in open fields, thedose rate within a settlement has always been significantly lower, because of photon absorption by building
structures, especially those made of brick and concrete.
Lower dose rates have been observed inside buildings,
especially on the upper floors of multi‑storey buildings.
Owing to radioactive decay of the initial radionuclide
mixture, wash‑off from solid surfaces and migration into
soil, dose rates in air have been gradually decreasing
with time.
A44. A relevant aspect is the time dependence of theratio of the dose rate in air at an urban location comparedto that in an open field (this ratio is often called the “location factor”). The dependence of location factors on timeafter the Chernobyl accident is shown in figure A‑VII for
measurements performed in Novozybkov in the RussianFederation [G4].

73

C. Agricultural environment
1.

Radionuclide transfer in the terrestrial environment

A45. Radionuclides may behave differently in the environment. Some radionuclides, such as radiocaesium, radio­
iodine and radiostrontium, are environmentally mobile andtransfer readily to foodstuffs. In contrast, radionuclides
with low solubility, such as the actinides, are relatively
immobile and largely remain in the soil. The main pathways
leading to exposure of humans are shown in figure A‑VIII[S13].
A46. Many factors influence the extent to which radio­
nuclides are transferred through ecological pathways. If thetransfer is high in a particular environment then that environment is referred to here as “radioecologically sensitive”,
because such transfer can lead to relatively high radiation
exposure [H7].
A47. During the short early phase after the Chernobyl accident (0–2 months), 131I was the most important radionuclide
for human exposure via agricultural food chains; in thelonger term, 137Cs was the most important.
A48. Radioecological sensitivity to radiocaesium insemi‑natural ecosystems is generally higher than in agricultural ecosystems, sometimes by a few orders of magnitude [H9]. This difference is caused by a number of factors,
the more important being the differing physicochemical
behaviour in soils, the lack of competition between Cs andK which results in higher transfer rates for radiocaesium innutrient‑poor ecosystems, and the presence of specificfood‑chain pathways that lead to high activity concentrations in produce from semi‑natural ecosystems. Also,­forest soils are fundamentally different from agriculturalsoils; the former have a clear multilayered vertical structure characterized mainly by a clay‑poor mineral layer,
which supports a layer rich in organic matter. In contrast,
agricultural soils generally contain less organic matter andhigher amounts of clay.
2.

Food-production systems affected by the accident

A49. The material deposited as a result of the Chernobyl
accident had a major impact on the management of both
agricultural and natural ecosystems. This was true not only
within the former Soviet Union but also in many other­countries in Europe.
A50. In the countries of the former Soviet Union, the prevailing food production system at the time of the accident
consisted of two types: large collective farms and small private farms. Collective farms routinely used land rotation
combined with ploughing and fertilization to improve productivity. In contrast, traditional small private farms seldom
applied artificial fertilizers and often used manure for

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UNSCEAR 2008 REPORT: VOLUME II

improving yield. Private farms had one or a few cows, andmilk was produced mainly for family consumption. The
grazing regime of private farms was initially limited to utilizing marginal land that was not used by the collective
farms. Nowadays, private farms also use better quality
pasture.

effective half‑life of about two weeks because of weathering, biomass growth and other natural processes. However,the concentration of 137Cs increased again during the winterof 1986/87 owing to cows being fed contaminated hay that
had been harvested in the spring/summer of 1986. This­phenomenon was observed in many countries.

A51. In western Europe, poor soils are used for extensive
agriculture, mainly for grazing of ruminants (e.g. sheep,goats, reindeer and cattle). Areas with poor soils include
alpine meadows and upland regions in western and northern
Europe with organic soils.

A56. The transfer to milk of many of the other radio­
nuclides present in the terrestrial environment during theearly phase was low. This was because of the low inherent
absorption of the elements in the ruminant gut, compoundedby their low bioavailability owing to their association within
the matrix of fuel particles.

(a)Effects on agricultural systems soon after the accident(b)A52. At the time of the accident, vegetation was at different growth stages that depended on latitude and elevation.
Initially, interception by plant leaves was the main pathway of contamination. In the medium and long‑term, root
uptake dominated. The highest activity concentrations ofradio­nuclides in most foodstuffs occurred in 1986.
A53. In the early phase, 131I was the main contributor tointernal dose through the pasture–cow–milk pathway.
Radio­iodine ingested by cows was completely absorbed in
the gut and then rapidly transferred to the animal’s thyroid
and milk (within about 1 day). Thus, peak concentrations
occurred rapidly after deposition (in late April or early May
1986, depending on when deposition occurred in different
countries). In several countries of the former Soviet Unionand elsewhere in Europe, concentrations of 131I in milk
exceeded national and regional (European Union) actionlevels, which ranged from a few hundred to a few thousand
becquerels per litre.
A54. In late April/early May 1986 in northern Europe,
dairy cows and goats were not yet on pasture; therefore,
there were very low activity concentrations of 131I in milk.
In contrast, in southern regions of the former Soviet Union,
as well as in Germany, France and southern Europe, dairy
animals were already grazing outdoors and there were significant levels of activity concentration in cow, goat andsheep milk. The activity concentration of 131I in milk
decreased with an effective half‑life of 4–5 days owing to
its short physical half‑life and the processes that removed itfrom leaves. The mean “weathering” half‑life for radio­
iodine on grass was 9 days; that for radiocaesium was
11 days [K15]. Consumption of leafy vegetables onto whichradionuclides had been deposited also contributed to theintake of radionuclides by humans.
A55. Plants and animals also had elevated levels of radiocaesium in comparison with those caused by the fallout fromatmospheric nuclear weapons testing. From June 1986
onwards, radiocaesium was the dominant radionuclide in
most environmental samples (except within the 30‑km zone)
and in food products. As shown in figure A‑IX, the levels of
137
Cs in milk decreased during the spring of 1986 with an

Effects on agricultural systems during the longer term

A57. Since the autumn of 1986, the radionuclide levels inboth plants and animals have been largely determined byinteractions between the radionuclides and different soil components, because soil is the main reservoir of the long‑lived
radionuclides that were deposited on terrestrial ecosystems.
These interactions control radionuclide bioavailability for
uptake into plants and animals and also ­influence radionuclide
migration down the soil column.
3.

Physicochemistry of radionuclides in the soil‑plant system

A58. Many measurements taken following the accident
demonstrate that the amount and nature of clay minerals
present in soils are key factors in determining radioecological sensitivity with regard to radiocaesium. These features
are crucially important for understanding the behaviour ofradiocaesium, especially in areas distant from the ChNPP
where 137Cs was initially deposited mainly in condensed,
water‑soluble, forms.
A59. Close to the ChNPP, radionuclides were deposited ina matrix of fuel particles, which have been slowly dissolving
with time. The more significant factors influencing the dissolution rate of fuel particles in soil are the acidity of the soil
solution and the physicochemical properties of the particles(notably the degree of oxidization). At low pH of 4, the time
taken for 50% dissolution of particles was about 1 year,
whereas at a higher pH of 7, as many as 14 years were needed[F4, K14]. Thus, in acid soils most of the fuel particles have
now already dissolved. In neutral soils, the amount of mobile90
Sr released from the fuel particles is still increasing, andthis will continue for the next 10–20 years.
A60. In addition to soil minerals, microorganisms cansignificantly influence the fate of radionuclides in soils[K12, S21]. Microorganisms can interact with minerals
and organic matter and consequently affect the bioavailability of radionuclides. In the specific case of mycorrhizal fungi, soil microorganisms may even act as a carriertransporting radionuclides from the soil solution to theassociated plant.

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

A61. With use of sequential extraction techniques, thefraction of exchangeable 137Cs was found to decrease by afactor of 3–5 within the decade after 1986. This time trend
may be because of progressive fixation of radiocaesium ininterlayer positions of clay minerals and to its slow diffusion
and binding to frayed‑edge sites of clay minerals. These
processes reduce the exchangeability of radiocaesium so thatis not then available to enter the soil solution from whichplants take up radiocaesium via their roots. For 90Sr, an
increase with time of the exchangeable fraction has been
observed, which is attributed to the leaching of the fuel­particles [K14].
(a)Migration of radionuclides in soil

A62. Vertical migration of radionuclides down the soilcolumn could arise from various transport mechanisms that
include convection, dispersion, diffusion and biologicalmixing. High degrees of root uptake of radionuclides byplants are correlated with high degrees of vertical migration, because in both processes the radionuclides are­relatively mobile. Typically, the rate of movement of radionuclides thus varies with soil type and physicochemical
form. As an example, figure A‑X shows the change withtime in the depth profiles of the activity concentrations of90
Sr and 137Cs in soil measured in the Gomel oblast of­Belarus. Although there has been a significant downward
migration of both radionuclides, much of the radionuclide
activity has remained within the rooting zone of plants(0–10 cm). At such sites where deposition occurred directlyfrom the atmosphere, there is a low risk of radionuclide
migration to groundwater.
A63. The rate of migration down the column of different types of soils varies for both radiocaesium and radio­
strontium. Low rates of 90Sr vertical migration wereobserved in peat soils, whereas 137Cs migrated at thehighest rate in these highly organic soils, but moved
much more slowly in soddy–podzolic sandy soils. In dry
meadows, migration of 137Cs below the rooting zone
(0–10 cm) was hardly detectable 10 years after the accident. Thus, the contribution of vertical migration to thedecrease in activity concentration of 137Cs in the rooting
zone of mineral soils is negligible. On the contrary, in
wet meadows and in peatland, downward migration canbe an important factor that reduces the 137Cs‑activity
concentration in the root zone.
A64. Higher rates of 90Sr vertical migration wereobserved in low‑humified sandy soil, soddy–podzolic
sandy soil, and sandy‑loam soil with low organic content(<1%) [S13]. Generally, the highest rate of 90Sr verticalmigration is characteristic of non‑equilibrium soil conditions. This occurs in flood plains of rivers where soil is not
fully structurally formed (light humified sands), arable
lands in a non‑equilibrium state, and in soils where theorganic layers have been removed, for instance, as a consequence of forest fires and sites with sedimentary sand75

with a low content of organic matter (<1%). In such conditions, there is a high rate of vertical migration of radio­
strontium to groundwater with convective moisture flow,
and high activity in localized soil zones can occur. Thus,
the spatial distribution of 90Sr can be particularly heterogeneous in soils where there have been changes in sorption
properties.
A65. Agricultural practices have a major impact on radionuclide behaviour. Depending on the type of soil tillage andon the tools used, a mechanical redistribution of radio­
nuclides in the soil may occur. In arable soils, radionuclides
are distributed fairly uniformly along the whole depth of thetilled layer.
A66. Lateral redistribution of radionuclides in catchments,
which can be caused by both water and wind erosion, is significantly less than their vertical migration into the soil layer
and the deep geological environment [S13]. The type anddensity of plant cover may significantly affect erosion rates.
Depending on the intensity of erosive processes, the content
of radionuclides in the arable layer on flat land with small
slopes may vary by up to 75% [B16].
(b)Transfer of radionuclides from soil to crops

A67. The uptake of radionuclides by plant roots is acompetitive process associated with plant physiology[E2]. For radiocaesium and radiostrontium, the maincompeting chemical elements are potassium and calcium,
respectively. The major processes influencing radio­nu­
clide transport within the rooting zone are schematically
represented in figure A‑XI, although the relative importance of each component varies with the radio­nuclide andsoil type.­
A68. The main process controlling root uptake of radiocaesium is the interaction between the soil matrix andsolution, which depends primarily on the cation‑exchange
capacity of the soil. For mineral soils, this is influenced by
the concentrations and types of clay minerals and the concentrations of the major competitive cations, especiallypotassium and ammonium. Examples of these relationships are presented in figure A‑XII for both radiocaesium
and radiostrontium. Modelling of soil–solution physicochemistry, which takes into account these major factors,
enables the uptake of both radionuclides by plant roots to
be calculated [K16, Z5].
A69. The fraction of a deposited radionuclide taken up by
plant roots differs by orders of magnitude depending primarily on the soil type. For radiocaesium and radiostrontium,
the radioecological sensitivity of soils can be broadly divided
into the categories listed in table A2. For all soils and allplant species, root uptake of plutonium is negligible compared to the direct contamination of leaves via rain splash or
resuspension.

76

UNSCEAR 2008 REPORT: VOLUME IITable A2.
Sensitivity

Classification of radioecological sensitivity for soil–plant transfer of radiocaesium and radiostrontium [I21]
Characteristics

Mechanism

ExampleFor radiocaesiumHigh

Low nutrient content
Absence of clay minerals
High organic content

Little competition with potassium and ammonium
in root uptake

Peat soils

MediumPoor nutrient status, consisting of minerals
including some clays

Limited competition with potassium and ammonium
in root uptake

Podzol, other sandy soils

LowHigh nutrient status
Considerable fraction of clay minerals

Radiocaesium strongly held to soil matrix (clayminerals)
Strong competition with potassium and ammonium
in root uptake

Chernozem, clay and loam soils (used forintensive agriculture)

For radiostrontiumHigh

Low nutrient status
Low organic matter content

Limited competition with calcium in root uptake

Podzol sandy soils

LowHigh nutrient status
Medium to high organic matter content

Strong competition with calcium in root uptake

Umbric gley soils, peaty soils

A70. Transfer from soil to plants is commonly quantified using either the transfer factor (TF, a dimensionlessquantity defined as the activity concentration in the plant,
Bq/kg, divided by activity concentration in soil, Bq/kg) or
the aggregated transfer coefficient (Tag, m2/kg, defined as
the activity concentration in the plant, Bq/kg, divided by
the deposition density on soil, Bq/m2). It is common touse dry weights for soil and vegetation when computing
such values.

A73. Thus, differences in the radioecological sensitivities
of soils explain why in some areas of relatively low deposition, there are high concentrations of radiocaesium in plants
and mushrooms harvested from semi‑natural ecosystems
and, conversely, why areas of relatively high deposition may
show only low to moderate concentrations of radiocaesiumin plants.
(c)

A71. The highest 137Cs uptake from soil to plants throughthe roots occurs for peaty, boggy soils, and is one to twoorders of magnitude higher than that for sandy soils; thisuptake often exceeds that of plants grown on fertile agricultural soils by more than three orders of magnitude. The
high radiocaesium uptake from peaty soil became important after the Chernobyl accident, because in many European countries such soils are vegetated by natural
unmanaged grassland used for the grazing of ruminants
and the production of hay. Agricultural activity often
reduces the transfer of radionuclides from soils to plants byphysical dilution (e.g. ploughing) or by the addition ofcompetitive elements (e.g. in fertilizers).
A72. There are also differences in radionuclide uptake
among plant species. Although variations in transfer fromsoil to plant among species may exceed one or moreorders of magnitude for radiocaesium, the impact of differing radioecological sensitivities of soils is often more
important in explaining the spatial variation in transfer
within agricultural systems. Accumulation of radiocaesium in crops and pastures is related to soil texture. In
sandy soils, uptake of radiocaesium by plants is approximately twice as high as in loam, but this effect is mainly
because of the lower concentration of its main competing
element, potassium, in sand.

Dynamics of radionuclide transfer to crops

A74. In 1986, the 137Cs content in plants was primarily
determined by aerial deposition and reached its maximum
value. During the first post‑accident year (through 1987),
the 137Cs content in plants dropped by a factor of 3–100 as
only the root uptake from different soil types remained
important.
A75. For meadow plants in the first years after deposition,
the behaviour of 137Cs was considerably influenced by theradionuclide distribution between soil and mat. In thisperiod, 137Cs uptake from the mat exceeded significantly (upto 8 times) that from soil. Further, as a result of mat decomposition and subsequent radionuclide transfer to soil, thecontribution of the mat decreased rapidly, and in the fifth
year after the initial deposition, it did not exceed 6% forautomorphous soils and 11% for hydromorphous ones [F4].
A76. For most soils, the transfer rate of 137Cs to plants has
continued to decrease since 1987, although the rate ofdecrease has slowed, as can be seen from figure A‑XIII [F7].
A similar decrease with time has been observed in manystudies of plant–root uptake with different crops.
A77. For the soil–plant transfer of radiocaesium, a decrease
with time is likely to reflect: (a) physical radioactive decay;

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT(b) the downward migration of the radionuclide out of therooting zone; and (c) physicochemical interactions with thesoil matrix that result in decreasing bioavailability. In manysoils, ecological half‑lives of plant‑root uptake of radiocaesium can be characterized by two components: (a) a relatively fast decrease with a half‑life of between 0.7 and
1.8 years (this dominated for the first 4–6 years after theaccident, and led to a reduction of concentrations in plants
by about an order of magnitude compared with 1987); and(b) a slower decrease with a half-life of between 7 and60 years [B20, F5, F7, P8].
A78. Caution should be used in generalizing these observations, because some data show almost no decrease ofroot uptake of radiocaesium with time beyond the first
4–6 years, which suggests no reduction in bioavailability
in soil within the time period of observation. Furthermore,quantifying ecological half‑lives that exceed the period of
observation is highly uncertain. The successful application of any countermeasures aimed at reducing the concentrations of radio­caesium in plants will also modify theecological half‑life.
A79. Compared to radiocaesium, the uptake of 90Sr byplants has often not shown such a marked decrease withtime. In the areas close to the ChNPP, gradual dissolution offuel particles has enhanced the bioavailability of 90Sr and,
therefore, there was an increase with time in the uptake of90
Sr by plants [K14].
A80. In remote areas, where radiostrontium was predominantly deposited in condensed form, and in lesser amounts
as fine dispersed fuel particles, the dynamics of long‑term
transfer of 90Sr to plants were similar to those for radio­
caesium, but with different ecological half‑lives of plant‑root
uptake and with differing fractional amounts accorded to thetwo components. These differences reflected various mechanisms of transfer of these two elements in soil. The fixationof radiostrontium by soil components depends less on theclay content of soil than is the case for radiocaesium (seetable A2). More generally, the values of parameters for thetransfer of 90Sr from soil to plants depend less on the soil
properties than they do for radiocaesium [A3].
4. Transfer of radionuclides to animals
A81. Animals take up radionuclides in forage and throughdirect ingestion of soil. Milk and meat were major sources ofinternal radiation doses to humans after the Chernobyl accident, both in the short term (owing to 131I) and in the longterm (owing to radiocaesium).
A82. Levels of radiocaesium in animal products fromextensively farmed ecosystems can be high and persist for along time, even though the original deposition may have been
relatively low. This is because: (a) the soils often allow significant uptake of radiocaesium; (b) some species accumulate
relatively high levels of radiocaesium, e.g. ericaceous species

77

and fungi; and (c) these areas are often grazed by small ruminants that accumulate higher concentrations of radiocaesium
than larger ruminants [H8].
A83. Levels of radionuclides in animal products dependon the behaviour of the radionuclide in the plant–soil system, rate of absorption in the gut, metabolic fate in the animal and the rate of loss from the animal (principally inurine, faeces and milk). Ingestion of radionuclides in feed,and subsequent absorption through the gut, is the majorroute of entry of most radionuclides. Absorption of mostelements from feed takes place in the rumen or the small
intestine at rates that vary from almost negligible, in thecase of actinides, to 100% for radioiodine, and varying
between 60% and 100% for radiocaesium depending on its
form [B15].
A84. After absorption, radionuclides circulate in the blood.
Some concentrate in specific organs; for instance, radio­
iodine concentrates in the thyroid and many metal ions,
including 144Ce, 106Ru, and 110mAg, in the liver. Actinides andradiostrontium tend to be deposited in the bone, whereas
radiocaesium is distributed throughout the soft tissues.
A85. The long‑term time trend of radiocaesium levels inmeat and milk (e.g. see figure A‑XIV) mimics that for vegetation, and can be divided into two time periods. For the
first 4–6 years after the initial deposition of radiocaesium,
there was an initial fast decrease with an ecological half‑lifeof between 0.8 and 1.2 years. For later times, only a small
decrease has been observed [F7].
A86. A significant amount of production in the former
Soviet Union was confined to the grazing of privately
owned cows on poor, unimproved meadows. Because of
the poor productivity of these areas, radiocaesium uptake
was relatively high compared to that for land used by collective farms. As an example of the differences for the two
farming systems, changes in activity concentrations of137
Cs in milk from private and from collective farms in the
Rovno oblast, Ukraine, are shown in figure A‑XV [P6].
The activity concentrations in milk from private farms
exceeded the national action level (referred to in the countries of the former Soviet Union as temporary permissiblelevels, TPLs), until 1991, when countermeasures for­private farms were implemented.
5. Current levels of radionuclides in foodstuffs
and expected future trends
A87. Table A3 presents a summary of activity concentrations of radiocaesium measured between 2000 and 2003 in
grain, potatoes, milk and meat produced in the contaminatedareas of Belarus, the Russian Federation and Ukraine; theresults cover many different types of soil with widely differing radioecological sensitivities. The activity concentrationsof 137Cs were consistently higher in animal products than inplant products.

78

UNSCEAR 2008 REPORT: VOLUME IITable A3. Mean and range of current activity concentrations of 137Cs in agricultural products across the contaminated areasof Belarus [B16], the Russian Federation [F7] and Ukraine [B14](Data are in Bq/kg fresh weight for grain, potato and meat and in Bq/L for milk)
Cs deposition density on soil

137

Grain

Potatoes

Milk

Meat

Belarus>185 kBq/m2 (contaminated districts of the Gomel oblast)

30 (8–80)

10 (6–20)

80 (40–220)

220 (80–550)

37–185 kBq/m2 (contaminated districts of the Mogilev oblast)

10 (4–30)

6 (3–12)30 (10–110)

100 (40–300)

Russian Federation>185 kBq/m2 (contaminated districts of the Bryansk oblast)

26 (11–45)

13 (9–19)

110 (70–150)

240 (110–300)

37–185 kBq/m2 (contaminated districts of the Kaluga, Tulaand Orel oblasts)

12 (8–19)

9 (5–14)20 (4–40)

42 (12–78)

Ukraine>185 kBq/m2 (contaminated districts of the Zhitomir andRovno oblasts)

32 (12–75)

14 (10–28)

160 (45–350)

400 (100–700)

37–185 kBq/m2 (contaminated districts of the Zhitomir andRovno oblasts)

14 (9–24)

8 (4–18)90 (15–240)

200 (40–500)

A88. In 2008, owing to both natural processes and agricultural countermeasures, the activity concentrations of 137Cs inagricultural food products were generally below national,
regional (EU) and international1 action levels. However, insome limited areas with high radionuclide deposition (partsof Gomel and Mogilev oblasts in Belarus and of Bryansk
oblast in the Russian Federation) or with poor organic soils(Zhitomir and Rovno oblasts in Ukraine) the activity concentrations of 137Cs in food products, especially milk, still
exceed the national TPLs of about 100 Bq/kg.
A89. Milk from privately-owned cows with activity concentrations of 137Cs exceeding 100 Bq/L (the current TPL formilk) was being produced in more than 400, 200 and 100
Ukrainian, Belarusian and Russian settlements, respectively,
15 years after the accident. Concentrations of 137Cs in milk
higher than 500 Bq/L were occurring in six Ukrainian, five
Belarusian and five Russian settlements in 2001.
A90. Scrutiny of the activity concentrations and associatedtransfer coefficients shows that there has been only a slow
decrease in activity concentrations of 137Cs in most plant andanimal foodstuffs during 1998–2008. This indicates that radionuclides must be close to equilibrium within the agricultural
ecosystems. However, continued reductions with time would
be expected owing to continuing migration down the soil profile and to radioactive decay, even if there was an equilibrium
established between 137Cs in the labile and non‑labile fractionsof soil. Given the present slow declines and the large uncertainties in quantifying long‑term effective half‑lives based on
1
Current Codex Alimentarius Guideline Levels for 137Cs in foods for use ininternational trade are equal to 1,000 Bq/kg [C12].

data currently available, it is not possible to conclude that there
will be any further substantial decrease over the next decades,
except as a consequence of further radioactive decay of both137
Cs and 90Sr, each with half‑lives of about thirty years.
A91. Activity concentrations of radionuclides in foodstuffs
can increase in some limited geographic areas located close
to the Chernobyl NPP through the dissolution of fuel particles, changes to the water table resulting from changes in the
management of the currently abandoned land or the ­cessationof countermeasures.
D. Forest environment
1.

Radionuclides in European forests

A92. Forest ecosystems were one of the semi‑natural ecosystems significantly affected as a result of deposited material from the radioactive plumes. The primary concerns froma radiological perspective are the long‑term levels of 137Cs(owing to its 30‑year half‑life and bioavailability) in the forest environment and forest products. In the years immediately following the accident the shorter‑lived 134Cs isotope
was also significant. In forests, other radionuclides (such as
90
Sr and the plutonium isotopes) are of limited significancefor human exposure, except in relatively small areas in andaround the 30‑km zone. As a result, most of the available
environmental data collected have been focused on theassessment of the behaviour of 137Cs and the associated radiation doses. The emphasis of this subsection is on the distribution of 137Cs in the forest environment and the relevant
pathways of human exposure to radiation.

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

A93. Following the accident, substantial amounts of radioactive material were deposited on forests in Belarus, theRussian Federation and Ukraine and also in countries beyond
the borders of the former Soviet Union, notably Finland,
Sweden and Austria. The levels of 137Cs deposition on theforests of these countries ranged from more than 10 MBq/m2
in some locations down to between 10 and 50 kBq/m2 inseveral countries of western Europe. In each of these countries, not only do forests represent an economic resource ofmajor importance, but they also play a central role in manysocial and cultural activities. In some cases, these activities
have been curtailed on account of concerns and restrictions
relating to the 137Cs levels.
A94. Previous studies related to the global fallout from theatmospheric testing of nuclear weapons had shown that theclearance rate of radionuclides from the forest ecosystems
by natural processes is extremely slow. The net clearance
rate for 137Cs in forests contaminated by the radionuclides
deposited following the Chernobyl accident has been lessthan 1% per year, so it is likely that, without artificial intervention, the physical radioactive decay rate will largely
influence the long‑term levels. recycling of radiocaesium
within the forest ecosystem is a dynamic process, in which
two‑way transfers between biotic and abiotic components ofthe ecosystem occur on a seasonal, or longer‑term, basis.
Much information on such processes has been obtained fromexperiments and field measurements, and many of these data
have been used to develop predictive mathematical models[I18].
2. The dynamics of radionuclide levels during the early phase
A95. The levels of radioactivity in forests of the former
Soviet Union located along the trajectory of the first radio­
active plume were primarily the result of dry deposition,
while farther afield, in countries such as Sweden and ­Austria,
wet deposition also occurred and resulted in significant “hotspots” of activity. Radionuclides were also deposited withrain on other areas in the former Soviet Union, such as the
Mogilev oblast in Belarus and the Bryansk oblast and otheroblasts in the Russian Federation.
A96. The primary mechanism by which trees became contaminated after the accident was direct interception by thetree canopy (between 60% and 90% of the initial depositionof radiocaesium). Within a 7‑km radius of the reactor, this led
to very high levels of deposition on the canopies of pine trees,
which consequently received lethal doses of radiation fromthe complex mixture of short‑ and long‑lived radionuclides
released by the damaged reactor. Gamma dose rates in thedays and weeks immediately following the accident were inexcess of 5 mGy/h in the area close to the reactor. The calculated absorbed gamma dose amounted to some 100 Gy to theneedles of pine trees. This small area of forest became
known as the “Red Forest”, as the trees died and became a­reddish‑brown colour; this was the most readily observableeffect of radiation damage on organisms in the area.

79

A97. The levels of radionuclides in the tree canopies
reduced rapidly over a period of weeks to months owing to
the natural processes of wash‑off by rainwater and of leaf/
needle fall. Absorption of radiocaesium by leaf surfaces also
occurred, although this was difficult to measure directly. By
the end of the summer of 1986, approximately 15% of theinitial radiocaesium burden in tree canopies remained and,by the summer of 1987, the amount remaining had been further reduced to approximately 5%. Within this roughly
one‑year period, therefore, most of the radiocaesium had
been transferred from the tree canopy to the underlying soil.
A98. During the summer of 1986, radiocaesium levels innatural products, such as mushrooms and berries, increased
and this led to increasing body burdens of forest animals,
such as deer and moose. In Sweden, activity concentrationsof 137Cs in moose exceeded 2 kBq/kg fresh weight and thosein roe deer were even higher.
3. The long-term dynamics of radiocaesium levels in forests
A99. By approximately one year after the initial deposition,
the major fraction of radiocaesium in the forest was that contained in the soil. As radiocaesium migrated deeper into thesoil, root uptake by trees and understorey plants became predominant over the longer term. Just as in the case of its chemical analogue, the nutrient potassium, the rate of radiocaesium
cycling within forests is rapid and a quasi‑­equilibrium of its
distribution is reached within a few years after the initial
depo­sition [S12]. The upper, organic‑rich soil layers act as along‑term store, but also as a general source of radiocaesium
for forest vegetation, although individual plant species differ
greatly in their ability to accumulate radiocaesium from thisorganic soil (figure A‑XVI).
A100. Loss of radiocaesium from the ecosystem via drainage water is generally limited because the element fixes
onto micaceous clay minerals. An important role of forest
vegetation in the recycling of radiocaesium is partial andtransient storage of radiocaesium, particularly in perennial
woody components. Although the concentration in tree
trunks and branches is low, their biomass can be large andthe total storage of 137Cs can be significant. A portion ofradiocaesium taken up by vegetation from the soil, however, is recycled annually through leaching and needle/leaf
fall, which results in long‑lasting biological availability ofradiocaesium in surface soil. The store of radiocaesium inthe standing biomass of the forest amounts to approximately
10% of the total activity in the temperate forest ecosystem;
most of this ­activity resides in trees.
A101. Because of biological recycling and storing ofradio­caesium, migration within forest soils is limited and, inthe long term, most of the radiocaesium resides in the upperorganic horizons. Slow downward migration of radio­
caesium continues to take place, however, although the rateof migration varies considerably depending on the soil typeand climate.

80

UNSCEAR 2008 REPORT: VOLUME II

A102. The hydrological regime of forest soils is an important factor governing radionuclide transfer in forest ecosystems. Depending on the hydrological regime, the radiocaesium
Tag for trees, mushrooms, berries and shrubs can vary over arange of more than three orders of magnitude. Minimal Tag
values were found for automorphic (dry) forests and soils
developed on relatively flat surfaces with low run‑off. Maximal Tag values are related to hydromorphic forests developed
under prolonged stagnation of surface waters. Among otherfactors influencing radionuclide transfer in forests, the distribution of root systems (mycelia) in the soil profile and thecapacity of different plants to accumulate radiocaesium areof importance [F6].
A103. The vertical distribution of radiocaesium within soil
has an important influence on the dynamics of uptake by herbaceous plants, trees and mushrooms. Another major consequence is a reduction in the external gamma dose rate withtime, because the upper soil layers provide shielding against
the radiation emitted as the radionuclide migrates deeper into
the subsurface. The most rapid downward vertical transfer
was observed for hydromorphic forests.
A104. After the initial deposition onto forests, large‑scale
geographical redistribution of radiocaesium is limited.
­Pro­cesses of small‑scale redistribution include resuspension
because of wind and fire, and erosion/runoff; however, noneof these processes is likely to result in any significant further transport of radiocaesium beyond the area of initialdeposition.
4. Uptake into edible products
A105. Edible products obtained from the forest include
mushrooms, fruits and game animals; where radioactive
material was deposited on the forest, radionuclides havebeen found in each of these products. The highest levels ofradiocaesium have been observed in mushrooms, due totheir great capacity to accumulate some mineral nutrients,
including radiocaesium. Mushrooms provide a commonand significant food source in many of the more affected
countries, particularly those within the former Soviet
Union. Changes with time in the activity concentrations inmushrooms reflect the bioavailability of 137Cs in the­various relevant nutrient sources utilized by ­different­mushroom species.
A106. The high levels of radiocaesium in species of mushroom are due to generally high soil–mushroom transfer coefficients. However, these aggregated transfer coefficients(Tag) are also subject to considerable variability and canrange from 0.003 to 7 m2/kg, i.e. by a factor of more than
2,000 [I15]. Significant differences in accumulation of radio­
caesium occur among species of mushrooms; the rate ofaccumulation generally reflects the ecological niche that theindividual species occupies. Like in plants, the agrochemical
properties of forest soils and growth conditions strongly
influence the aggregated transfer factors for 137Cs from soil

to different species of forest mushrooms [K12]. The degreeof variability of radiocaesium levels in mushrooms is illustrated by figure A‑XVII [I18], which also indicates a slowly
decreasing trend during the 1990s.
A107. The level of radiocaesium in mushrooms in forests
is often much higher than that in forest fruits such as bilberries. This is reflected in the aggregated transfer coefficientsfor forest berries, which range from 0.02 to 0.2 m2/kg [I15].
Owing to the generally lower levels of radiocaesium and to
the lower masses eaten, exposure due to consumption of forest berries is smaller than that due to consumption of mushrooms. However, both products contribute significantly tothe diet of grazing animals and, therefore, provide a secondroute of exposure to humans via game consumption. Animals grazing in forests and other semi‑natural ecosystems
often produce meat with high activity concentrations ofradio­caesium. Such animals include wild boar, roe deer,moose and reindeer, but also domestic animals such as cows
and sheep, which may graze marginal areas of forests.
A108. Most data on levels of radionuclides in game animals such as deer and moose have been obtained from thosewestern‑European countries where the hunting and eating ofgame is commonplace. Significant seasonal variations occur
in the body burden of radiocaesium in these animals owing
to the seasonal availability of foods such as mushrooms andlichens; the latter are a particularly important component of
the reindeer’s diet. Particularly good time‑series measurements have been made in the Nordic countries and in­Germany. Figure A‑XVIII shows a complete time series ofannual average activity concentrations of radiocaesium inmoose from one hunting area in Sweden between 1986 and2003. A major factor for the radionuclide intake by game—roe deer, in particular—is the high activity concentration ofradiocaesium in mushrooms. Aggregated transfer coefficients for moose range from 0.006 to 0.03 m2/kg [I15]. The
mean Tag for moose in Sweden has been falling since theperiod of high initial levels, which indicates that the ecological half‑life for radiocaesium in moose is measurably lessthan 30 years, the physical half‑life of 137Cs.
5.

Radionuclides in wood

A109. The accident deposited radionuclides in many forests in Europe and countries of the former Soviet Union;
most of these forests are planted and managed for the production of timber. Potentially, one of the significant exposure pathways to humans is through timber production. The
export and subsequent processing and use of timber containing radionuclides are pathways that can lead to the exposureof people who would not normally be exposed in the forest
itself. Uptake of radiocaesium from forest soils into wood israther low; aggregated transfer factors range from 0.0003 to
0.003 m2/kg. Hence, wood used for making furniture or thewalls and floors of houses is unlikely to give rise to significant radiation exposure of people using these products [I19].
However, the manufacture of consumer goods such as paper

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

involves the production of both liquid and solid wastes inwhich radiocaesium concentrates. Handling of these wastes
by workers in paper‑pulp factories can give rise to occupational exposure to radiation.
A110. Combustion of other parts of trees (such as needles,
bark and branches) may give rise to the problem of disposalof radioactive wood ash. This practice has increased inrecent years due to the upsurge in biofuel technology in theNordic countries. The problem of radiocaesium in wood ash
is particularly notable because the activity concentration ofradiocaesium in ash is a factor of 50–100 times greater thanin the original wood. Domestic users of firewood from these
forests may be exposed externally to gamma radiation andinternally through inhalation as a consequence of thebuild‑up of ash in the home and/or garden [I19]. Such
­exposures however are generally insignificant.
E.

Radionuclides in aquatic systems
1.

Introduction

A111. Surface‑water systems in many parts of Europe
had elevated levels of radioactive material due to the­Chernobyl accident. Most of the radioactive material, however, was deposited in the catchment area of the Pripyat
River, which forms an important component of the Dnieper
River–­Reservoir system, one of the larger surface‑water
systems in Europe. After the accident, therefore, there wasparticular concern about possible radioactive contamination of the water supply for the area along the Dnieper cascade of reservoirs, which covers a distance of approximately
1,000 km to the Black Sea. Levels of radioactive material
increased in other large river systems in Europe, such as
the Rhine and the Danube, although the levels in the rivers
were not significant [U3].
A112. Initial activity concentrations in river water in partsof Belarus, the Russian Federation and Ukraine were relatively high, compared both to those in other European rivers
and to the standards for radionuclides in drinking water,owing to direct deposition onto river surfaces and to transport of radionuclides in run‑off water from the catchment
area. During the first few weeks after the accident, the activity concentrations in river waters rapidly declined, becauseof the physical decay of the short‑lived radionuclides and ascatchment soils and bottom sediments absorbed the radionuclides. In the longer term, the long‑lived 137Cs and 90Sr
became the dominant radionuclides in aquatic ecosystems.
Although the levels of these radionuclides in rivers in thelong term were low, temporary increases in the activity concentrations during flooding of the Pripyat caused serious
concern in areas using water from the Dnieper cascade.
A113. Lakes and reservoirs had increased levels of radioactivity due to direct deposition of radionuclides onto thewater surface and transfers of radionuclides in run‑off waterfrom the deposited material on the surrounding catchment

81

area. The radionuclide concentrations in water declined­rapidly in reservoirs and in those lakes with significant
inflow and outflow of water (“open” lake systems). In somecases, however, the activity concentrations of radiocaesiumin lakes remained relatively high because of run‑off fromorganic soils in the catchment. In addition, internal cyclingof radiocaesium in “closed” lake systems (i.e. lakes with little inflow and outflow of water) led to much higher activity
concentrations in their water and aquatic biota than weretypically seen in open lakes and rivers.
A114. Bioaccumulation of radionuclides (particularly radio­
caesium) in fish resulted in activity concentrations (both in themost affected regions and in western Europe) that were insome cases significantly above national action levels for consumption, i.e. of the order of some hundreds to some thousandsand even tens of thousands of becquerels per kilogram. In
some lakes in Belarus, the Russian Federation and Ukraine,
these problems have continued to the present day and may continue for the foreseeable future. Freshwater fish provide animportant food source for many inhabitants of the affected
regions. In the Dnieper cascade in Ukraine, commercial fisheries catch more than 20,000 tonnes of fish per year. In someother parts of Europe, particularly parts of Scandinavia, activity concentrations of radiocaesium in fish are still higher thanaction levels.
A115. The closest marine systems to the ChNPP are theBlack Sea and the Baltic Sea, both several hundred kilometres from the site. The activity concentrations of radio­
nuclides in water and fish of these seas have been intensively
studied since the accident. Because the average direct deposition onto these seas was relatively low, and owing to thelarge dilution in marine systems, activity concentrations
were much lower in these seas than in freshwater systems[I20].
2. Uptake of radionuclides to freshwater fish
A116. Consumption of freshwater fish is an important partof the aquatic pathway for transfer of radionuclides tohumans. Although transfer of radionuclides to fish has beenstudied in many countries, most attention here will befocused on Belarus, the Russian Federation and Ukraine
because of the relatively high activity concentrations inwater bodies of these countries.
(a)

131

I in freshwater fish

A117. There are limited data on 131I levels in fish.
Iodine-131 was rapidly absorbed by fish in the Kiev Reservoir; maximum concentrations in fish were observed in earlyMay 1986. Activity concentrations in fish muscle declined
from around 6,000 Bq/kg fresh weight on 1 May 1986 toaround 50 Bq/kg fresh weight by 20 June 1986. This represents a rate of decline similar to that of the physical decay of131
I. Because of the rapid physical decay, activity

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UNSCEAR 2008 REPORT: VOLUME II

concentrations of 131I in fish became insignificant within a
few months after the accident.
(b)

137

Cs in freshwater fish and other aquatic biota

A118. During the years following the Chernobyl accident,
there have been many studies of the levels of radiocaesiumin freshwater fish. As a result of high bioaccumulation factors for radiocaesium, fish have retained high radiocaesium
levels in some areas, despite low levels in water. Uptake ofradiocaesium in small fish was relatively rapid, the maximum concentration was observed during the first weeks after
the accident. Because of the slow uptake rates of radiocaesium in large predatory fish (pike and eel) maximum activity
concentrations were not observed until 6–12 months after
the initial deposition, as shown in figure A‑XIX [U19].
A119. In the Kiev Reservoir, activity concentrations of
Cs in fish were 0.6–1.6 kBq/kg fresh weight (in 1987) and
0.2–0.8 kBq/kg fresh weight (for 1990–1995) and declined
to 0.2 kBq/kg or less for adult non‑predatory fish in 2002.
Values for predatory fish species were 1–7 kBq/kg during
1987 and 0.2–1.2 kBq/kg between 1990 and 1995.

137

A120. In the lakes of the Bryansk oblast of Russia, approximately 200 km from Chernobyl, activity concentrations of137
Cs in a number of fish species varied within the range
0.2–19 kBq/kg fresh weight during the period 1990–1992. Inshallow closed lakes such as Kozhanovskoe (Bryansk oblast,
the Russian Federation) and Svyatoe (Kostiukovichy Raion,
Belarus), activity concentrations of 137Cs in fish havedeclined slowly in comparison with fish in rivers andopen‑lake systems, because of the slow decline in activity
concentrations of 137Cs in the water of the lakes [B22].
A121. The differences in bioaccumulation of radiocaesiumin different fish species can be significant. For example, in
Lake Svyatoe, Belarus, the activity levels in large pike andperch (predatory fish) were 5–10 times higher than in
non‑predatory fish such as roach. Similarly, bioaccumulation factors in lakes of low potassium concentration can beone order of magnitude higher than in lakes of high potassium concentration. Thus, it was observed [S15] that fishfrom lakes in agricultural areas of Belarus (where run‑off ofpotassium fertilizer was significant) had lower bioaccumulation factors than fish from lakes in semi‑natural areas.
(c)90

the maximum level of 90Sr concentration in the muscles of
predatory and non‑predatory fish varied between 2 and15 Bq/kg fresh weight. In 2002–2003, the activity concentrations of 90Sr in fish in reservoirs of the Dnieper cascade were
only 1–2 Bq/kg, which is close to the pre‑accident levels.
Freshwater molluscs showed significantly stronger bioaccumulation of 90Sr than fish. In the Dnieper River, molluscs
had approximately ten times more 90Sr per kilogram in theirtissues than fish muscle. Similarly, bioaccumulation of 90Srin the bones and skin of fish is approximately a factor of 10
higher than in muscle.
3. Radioactivity levels in marine ecosystems
A123. Marine ecosystems were not seriously affected bydeposited material from the accident; the nearest seas to thereactor are the Black Sea (around 520 km) and the Baltic Sea(about 750 km). Activity levels increased in these seas primarily because of direct deposition from the radioactive
cloud, with smaller inputs from riverine transport occurring
over the years following the accident. The total surface deposition of 137Cs was approximately 2.8 PBq on the Black Sea
and 3.0 PBq on the Baltic Sea.
F.

Countermeasures and remediation

A124. Since the very first days after the Chernobyl accident, countermeasures were instituted with the purpose of
reducing doses to humans. The range of countermeasuresapplied was notably wide, i.e. from urgent evacuation in1986 of inhabitants from the nearby areas of highest radionuclide deposition, to bans on the use of contaminated foodstuffs in many European countries [S16]. The whole
spectrum of the applied countermeasures and their effectiveness has been considered in a number of international reports(e.g. [I17, U3]).
A125. This section does not consider specifically the past
emergency mitigation actions at the ChNPP that were aimed
at reducing and halting the radioactive releases to the environment. It considers neither the protection criteria and practices for workers involved in the emergency and mitigation
actions, nor the practice and policy of evacuating 116,000
residents of the most contaminated areas of the former
Soviet Union in 1986, and of subsequently relocating
220,000 additional residents in 1989–1992 [U3] from thecontaminated areas to “clean” areas.

Sr in freshwater fish

A122. Strontium behaves, chemically and biologically, ina similar way to calcium. Bioaccumulation of strontium
occurs most strongly in low calcium (“soft”) waters. Relatively low bioaccumulation factors for 90Sr in freshwater (ofthe order of 100 L/kg) and the lower deposition density ofthis radionuclide meant that the activity concentrations of
90
Sr in fish were typically much lower than those of 137Cs. In
2000, for the lakes with higher activity levels around ChNPP,

A126. Some countermeasures were applied directly tomembers of the general public, such as evacuation and relocation mentioned above. In addition, there was a variety oforganized and self‑selected temporary relocation of children
from areas thought to be contaminated. In some cases, potassium iodide (KI) pills were distributed to residents with
instructions on their use. Unfortunately, this distribution was
not well organized and was of limited effectiveness in the
more contaminated territories of Belarus, the Russian

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

Federation and Ukraine. The more successful experience of
KI distribution in Poland is presented in appendix B in thecontext of the thyroid dose assessment.
A127. Countermeasures have been applied since 1986 in
urban, agricultural, forest and aquatic environments. Manyof these countermeasures were driven by the need to comply
with relevant international or national radiological criteria;
all countermeasures were driven by the goal of reducing
doses to humans.
1.

83

A132. Depending on the decontamination technologies
used, the dose rate over various measured plots was reduced
by a factor of 1.5–15. But the high cost of these activities
hindered their complete application to the areas deemed
affected. Because of these limitations, the reduction in
annual external dose was 10–20% for the average population, and ranged from about 30% for children attending kindergarten and schools to less than 10% for outdoor workers(herders, foresters, etc.). These data were confirmed by individual external dose measurements conducted before andafter large‑scale decontamination campaigns in 1989 in the
Bryansk oblast of the Russian Federation [B12].

Decontamination of populated areas

A128. Decontamination of settlements was one of themain countermeasures applied to reduce external exposureof the public during the initial stage of the response to theaccident. Analysis of the contributors to external dose fordifferent population groups living in such areas revealed thata significant fraction of dose was received by people fromradionuclides in soil, on coated surfaces like asphalt andconcrete and, to a small extent, on building walls and roofs.
This is why one of the more effective decontamination­technologies involved removal of the upper soil layer.
A129. Following dry deposition, street cleaning, removalof trees and shrubs and ploughing gardens were efficient andinexpensive means of achieving substantial reductions indose. Contaminated roofs were important contributors todose, while contaminated walls were less important.
A130. Large‑scale decontamination was performed in
1986–1989 in the cities and villages of the former Soviet
Union with higher levels of activity. This was performed
usually by military personnel and included washing ofbuildings with water or special solutions, cleaning of residential areas, removal of contaminated soil, cleaning andwashing of roads, and decontamination of open water supplies. Special attention was paid to kindergartens, schools,
hospitals and other buildings frequently visited by large
numbers of persons. In total, about one thousand settlements were treated; this included cleaning tens of thousandsof residences and social buildings and more than a thousand­agricultural farms (e.g. [A7]).
A131. In the early period following the accident, there wasconcern that inhalation of resuspended radioactive particles
of soil and nuclear fuel could significantly contribute tointernal dose. To suppress dust formation, organic solutions
were dispersed over contaminated plots, which after drying
created an invisible polymer film. Streets in cities were
sprayed with water to prevent dust formation and to wash theradionuclides into the sewerage system.2
2
The effectiveness of the early decontamination efforts in 1986 still remains
to be quantified. However, according to Los and Likhtarev [L7] daily washing of streets in Kiev decreased the collective external dose to its 3 million
inhabitants by 3,000 man Sv, and decontamination of schools and school
areas saved an additional 600 man Sv.

A133. Regular monitoring of decontaminated plots insettle­ments over a five‑year period showed that after 1986
there was no significant recontamination and the exposure
rate was decreasing over the long term. The averted collective dose from external exposure of 90,000 inhabitants of
the 93 more affected settlements of the Bryansk oblast was­estimated to be about 1,000 man Sv [B12].
A134. Since 1990, large‑scale decontamination in the
countries of the former Soviet Union has been abandoned,
but particular plots and buildings with high measured­radiation levels have been cleaned.
A135. Another continuing activity is the clean‑up ofindustrial equipment and premises that were contaminatedas a result of ventilation systems being operated during
the release/deposition period in 1986 and immediately
afterwards.
2.

Agricultural countermeasures

A136. The implementation of agricultural countermeasures
after the Chernobyl accident has been extensive, both in themost affected countries of the former Soviet Union and inwestern Europe. The main aim of agricultural countermeasures
was the production of food products with activity concentrations of radionuclides below action levels. Many counter­measures were used extensively in the first few years after theaccident and their application continues today. Generally, theearlier agricultural countermeasures were applied, the morecost‑effective they were [P7]. Agricultural countermeasures
have been reviewed by Fesenko et al. [F9].
(a)Early phaseA137. From 2–5 May 1986, about 50,000 cattle, 13,000 pigs,
3,300 sheep and 700 horses were evacuated from the 30‑km
zone together with the people [N8]. In the 30‑km zone, morethan 20,000 remaining agricultural and domestic animals were
killed and buried. Owing to a lack of forage for the animals
evacuated and difficulties in managing the large number of animals in the territories to which they were moved, many were
subsequently slaughtered. In the acute period after the accident,
it was not possible to differentiate the different levels of

84

UNSCEAR 2008 REPORT: VOLUME II

contamination in animals and in the period of May–July 1986,
the total number of slaughtered animals reached 95,500 cattle
and 23,000 pigs.

effective method was to delay harvesting of forage and foodcrops. Radiation control of products was introduced at eachstage of food production, storage and processing.

A138. Many carcasses were buried and some were stored
in refrigerators, but this presented great hygienic, practicaland economic difficulties. Condemnation of meat was an
immediately available and effective countermeasure to
reduce potential doses from ingesting animal products andwas widely used both in the former Soviet Union and elsewhere. However, this was very expensive and resulted inlarge quantities of contaminated waste.

A144. Based on a radiological survey performed from
May to July 1986, approximately 130,000 ha, 17,300 ha and57,000 ha of agricultural land were initially excluded from
economic use in Belarus, the Russian Federation andUkraine, respectively.

A139. In the first weeks after the accident, the main aim of
the countermeasures in the former Soviet Union was tolower the activity concentrations of 131I in milk or to prevent
milk with elevated radionuclide levels entering the humanfood chain. Recommendations were made to exclude contaminated pasture from animals’ diets by changing to indoor
feeding with “clean” feed; to conduct radiation monitoringand subsequently to reject milk at processing plants in which
activity concentration of 131I was above the national TPL(3,700 Bq/L at that time); and to process rejected milk
(mainly by converting milk to storable products, such ascondensed or dried milk, cheese or butter).
A140. In the first few days after the accident, the countermeasures were largely directed towards milk from collective
farms and few private farmers were involved. Informationon countermeasures for milk was confined to managers andlocal authorities and was not distributed to the private farming system of the rural population. This resulted in limited ordelayed application of the countermeasures, especially inrural settlements where milk was privately produced; thisresulted in low effectiveness of the countermeasures in someareas.
A141. Within a few weeks of the accident, feeding of animals with “clean” fodder began, because this had the potential to reduce 137Cs levels in cattle to acceptable levels within
1–2 months. However, this countermeasure was not in widespread use at this stage, partly owing to a lack of “clean”
feed early in the growing season.
A142. As early as the beginning of June 1986, maps wereconstructed of the density of radioactive deposition in theaffected regions. This allowed estimates to be made of theextent of deposition on pasture and identification of where
milk was likely to be contaminated.
A143. During the growing period of 1986, when there wasstill substantial surface contamination of plants, the majorcountermeasures in agriculture were of a restrictive nature.
In the first few months, land severely contaminated was
taken out of use, and recommendations were developed onsuitable countermeasures that would allow continued production on less heavily contaminated land. In the more heavily contaminated regions, a ban was imposed on keeping
dairy cattle. To reduce radionuclide levels in crops, an

A145. From June 1986, other countermeasures aimed at
reducing 137Cs uptake into farm products were implemented
as follows: banning cattle slaughter in regions where the­levels of deposition of 137Cs exceeded 555 kBq/m2 (animals
had to be fed clean food for 1.5 months before slaughter);minimizing external exposure and formation of contaminated dust by omitting some procedures normally used incrop production; limiting the use of contaminated manure
for fertilization; preparing silage from maize instead of hay;
restricting the consumption of milk produced in the private
sector; obligatory radiological monitoring of agricultural
products; and obligatory milk processing.
A146. Decontamination by removal of the top soil layer
was found to be inappropriate for agricultural lands becauseof its high cost, destruction of soil fertility and severe ecological problems related to the burial of the contaminatedsoil.
A147. As early as August–September 1986, each collective farm received maps of 137Cs deposition on theiragricultural land and guidance on potential radionuclide
levels in products, including instructions on farming ofprivate plots.
A148. Sweden received some of the higher levels of deposition outside of the countries of the former Soviet Union.
Initially, Sweden imposed controls on the 131I and 137Cs
activities in imported and domestic foods. A range of otheractions were taken: (a) cattle were not put onto pasture if theground deposition exceeded 10 kBq/m2 of 131I or 3 kBq/m2 ofradiocaesium; (b) advice was given not to consume fresh
leafy vegetables and to wash other fresh vegetables;(c) restrictions were placed on the use of sewage sludge as
fertilizer for soil; (d) deep ploughing was recommended; and(e) a higher cutting level for harvesting grass was advised.
A149. In Norway, crops in fields were monitored after harvesting, and those with radiocaesium levels above 600 Bq/kg
fresh weight were discarded and ploughed in. In addition,
hay and silage harvested in June were monitored, and thosewith activity concentrations exceeding the guidelines were
not used as forage.
A150. In Germany, some milk in Bavaria was diverted
into food‑processing plants to be converted into milk
­powder. It was intended to use the milk powder as feed for
pigs, but this was not done owing to the high radiocaesium
content.

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

A151. In the UK, advice was issued to regulate the consumption of some game in upland regions, and restrictions
were imposed on the movement and slaughter of uplandsheep from a number of the more affected areas.
A152. In Austria, there was advice not to feed fresh grass
to cows for a short period in May 1986.
(b)

Late phase

A153. Radiological surveys of agricultural products
showed that by the end of 1986, four oblasts of the RussianFederation (Bryansk, Tula, Kaluga, and Orel), five oblasts of
Ukraine (Kiev, Zhitomir, Rovno, Volyn and Chernigov) andthree oblasts of Belarus (Gomel, Mogilev and Brest) had
food products with activity concentrations of radiocaesiumthat exceeded the national TPLs. In the more affected areasof Gomel, Mogilev, Bryansk, Kiev and Zhitomir oblasts inthe first year after the accident, the proportion of grain andmilk exceeding the TPLs was about 80% [I17, N8].
A154. From 1987, high activity concentrations of radiocaesium in agricultural products were only observed in animal products; application of countermeasures aimed atlowering the activity concentrations of 137Cs in milk andmeat was the key focus of the remediation strategy for intensive agriculture. Potatoes and root vegetables were being
produced in which the radiocaesium levels were acceptably
low. In the second year, the activity concentrations of radiocaesium in grain were much lower than in the first year, andtherefore countermeasure application ensured that mostgrain was below the TPLs. By 1991, less than 0.1% of thegrain in all three countries had radiocaesium levels above
370 Bq/kg.
A155. The most difficult issue remaining was the production of milk in compliance with the adopted standards. However, large‑scale application of a range of countermeasures(described below) made it possible to achieve a sharp
decrease in the amount of animal products with activity concentrations of radiocaesium above the TPL in all three countries. The changes with time in the quantity of milk exceeding
the TPLs can be seen in figure A‑XX [N8]; however, it isimportant to note that the values of the TPLs have been
reduced with time in each of the three countries, so the data
are not directly comparable. Changes in the action levels ineach country are shown in figure A‑XXI [S14].
A156. Differences in the time trend in figure A‑XX among
the countries largely relate to changes in the national TPLs,
but also to the scale of countermeasure application. This isparticularly clear for Russian milk, where the activity concentrations of radiocaesium rose after 1997 owing to a reduction in the use of the countermeasure. The recent reduction in
the quantity of meat above the national TPLs in ­Belarus andUkraine is because animals are monitored before slaughter toensure that the meat is below the required level. In the­Russian Federation, where animals are also monitored before

85

slaughter, the concentration values are higher, because theyrefer to meat from both private and collective farms. The
small quantity of meat in each country now above the national
TPL is largely due to the slaughter of animals that have been
injured and have not been fed clean feed.
A157. The maximum dose‑reduction effect due to countermeasure application was achieved in the period 1986–1992.
Thereafter, because of financial constraints in the mid‑1990s,
the use of agricultural countermeasures was drasticallyreduced. However, by optimizing available resources theeffectiveness of countermeasures remained at a level sufficient to maintain an acceptable 137Cs content in most animal
products.
(c) Countermeasures applied to intensive agricultural production
A158. The main countermeasures used in the former
Soviet Union and later in the independent three countries arebriefly described below. The focus was on chemical amendments to improve soil fertility and to reduce the uptake ofradiocaesium by crops and plants used for fodder. The extent
to which each measure was used varied among the three
countries. The recommendations on which countermeasures
to use were repeatedly revised and updated [A4, B19, P5].
(i)

Soil treatment

A159. Soil treatment reduces the uptake of radiocaesium(and radiostrontium). The procedure can involve ploughing,reseeding and/or the application of nitrogen, phosphorus,
potassium (NPK) fertilizers and lime. Ploughing dilutes theradioactive content originally in the upper soil layers wheremost plant roots absorb their nutrients. Both deep and­shallow ploughing were used extensively; skim and burial
ploughing was also used. The use of fertilizers increases
plant production, thereby diluting the activity concentrationin the plant. In addition, the use of fertilizers reduces plant–
root uptake by decreasing the Cs:K ratio in the soil solution[A5].
A160. In the first few years after the accident, the focus
was on radical improvement, which included greatly
increased use of fertilizers. Commonly, high value legume
and cereal grasses were grown on the treated land. The
nature of the action and the efficiency of the radical improvement of hay fields and pastures strongly depended on thetype of meadow and the soil properties. Traditional surface
improvement, involving soil discing, fertilization and surface liming was less effective. Acid soil was limed. Somemarshy plots were drained, deep ploughed, improved andused as grassland. In the 1990s, there was a greater focus onsite‑specific characteristics to ensure that the soil treatment
used was the most appropriate and effective for the prevailing conditions. With time, repeated fertilization of alreadytreated soils was necessary, but the appropriate application
rates were carefully assessed. However, actual rates of86

UNSCEAR 2008 REPORT: VOLUME II

application were sometimes constrained by availability offunds [A5, V1].
A161. The effectiveness of soil treatment is influenced bysoil type, nutrient status and pH, and also the plant species
selected for reseeding. In addition, the application rates of
NPK fertilizers and lime affect the reduction achieved.
Several studies have shown that the reduction factors
achieved for soil–plant transfer of radiocaesium following
radical improvement, liming and fertilization were in therange of 2–4 for poor, sandy soils and 3–6 for more organicsoils. An added benefit was the reduction in external dose
rate by a factor of 2–3 due to the dilution of the surface
layer of radiocaesium after ploughing.
A162. Even though problems associated with 90Sr wereless acute than those with 137Cs, some countermeasures weredeveloped and a reduction of 2–4 in soil–plant transfer ofradiostrontium following discing, ploughing and reseeding
was achieved.
A163. Despite these countermeasures, in the more highly
affected districts (raions) of the Bryansk oblast, levels ofradiocaesium in 20% of pasture and hay on farms in thesouth‑western zone still exceeded the national TPL in 1997–
2000. Concentrations of 137Cs in hay varied between 650 and
66,000 Bq/kg dry weight.
(ii)

Change in fodder crops grown on affected land

A164. Some plant species take up less radiocaesium thanothers, as can be seen in figure A‑XXII for experimental
data collected in Belarus over the period 1997–2002 [B18].
The extent of the difference is considerable and fodder
crops, such as lupin, peas, buckwheat and clover, whichaccumulate relatively high amounts of radiocaesium, werecompletely or partly excluded from cultivation.
A165. In Belarus, rapeseed is grown on affected areas withthe aim of producing two products: edible oil and proteincake as animal fodder. Varieties of rapeseed are grown thatare known to have a 2–3‑fold lower uptake rate of 137Cs and90
Sr than many other varieties. When the rapeseed is grown,
additional fertilizers (liming 6 t/ha and fertilization with
N90P90K180) are used to reduce the uptake of radiocaesium
and radiostrontium into the plant by a factor of about two.
This reduces the levels of radiocaesium in the seed used forthe protein cake. During processing of the rapeseed, both
radiocaesium and radiostrontium are effectively removed.
During the last decade, the area under rapeseed cultivation
has increased fourfold to 22,000 ha [B17].
(iii) Clean feeding
A166. The provision of uncontaminated feed or pasture toanimals for an appropriate period before slaughter (so called“clean feeding”) effectively reduces the radionuclide content

in meat and milk at a rate depending on the biological half‑lifefor each radionuclide in the animal. The activity concentration of radiocaesium in milk responds rapidly to changes inthe diet, as the biological half‑life is a few days. For meat, theresponse time is longer owing to the longer biologicalhalf‑time in muscle [P5].
A167. Clean feeding has been one of the more importantand frequently used countermeasures for meat from agricultural animals in both the countries of the former Soviet
Union and those of western Europe after the Chernobyl accident. Official estimates of the number of cattle treated were
between 5,000 and 20,000 annually in the Russian ­Federationand 20,000 in Ukraine (supported by the government up to
the year 1996). Clean feeding is routinely used in all three
countries of the former Soviet Union for meat production
and is combined with live monitoring of animals so that if
the radionuclide concentrations in the animals’ muscles areabove the national TPL, they can be returned to the farm forfurther clean feeding.
(iv)

Administration of caesium binders

A168. Hexacyanoferrate compounds (commonly referred
to as “Prussian Blue”) are highly effective radiocaesium
binders; such compounds may be added to the diet of dairy
animals and to meat‑producing animals to reduce radiocaesium transfer to milk and meat by reducing absorption in
the gut. These binders have a low toxicity and are safe touse. Many different formulations of hexacyanoferrates
have been developed in different countries, partly to identify the most effective compound and partly to produce acheaper, locally available product. Hexacyanoferrate compounds can achieve reduction factors in animal products of
up to 10 [I16].
A169. Prussian Blue has been added to the diet of animals
as a powder, incorporated into pelleted feed during manufacturing, or mixed with sawdust. In the Russian Federation, a
locally manufactured hexacyanoferrate called ferrocyn (amixture of 5% KFe[Fe(CN)6] and 95% Fe4[Fe(CN)6]) was
developed. It has been administered as 98% pure powder,
salt licks (10% ferrocyn) and in sawdust with 10% adsorbed
ferrocyn (called bifege) [R5].
A170. Slow release boli containing hexacyanoferrate havealso been developed, which are introduced into the animals
rumen and gradually release the caesium binder over a few
months. The boli, originally developed in Norway, consistof a compressed mixture of 15% hexacyanoferrate, 10%
beeswax and 75% baryte [H6].
A171. Prussian Blue has been used to reduce the 137Cs
levels in animal products since the beginning of the
1990s. Prussian Blue application has been especially useful and effective in settlements where there is a lack of
meadows suitable for radical improvement. In initial trials, Prussian Blue reduced the 137Cs transfer from fodder

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

87

to milk and meat by a factor of 1.5–6.0. In Belarus, aspecial concentrate with Prussian Blue is produced and distributed at a rate of 0.5 kg of concentrate per cow daily andan average reduction factor of 3 for milk has been achieved.
Boli are given to dairy cows in intensive systems in both
Belarus and the Russian Federation.

increased at the time when the animals are collected forslaughter. Brynildsen et al. [B21] estimated that the use ofboli as a countermeasure for sheep was 2.5 times ascost‑effective as feeding with uncontaminated feed. Salt
licks containing AFCF have also been used, but are lesseffective.

A172. In Ukraine, locally available clay‑mineral binders
have been used on a small scale. These local products are
somewhat less effective than Prussian Blue, but cheaper.

A177. Management regimes have been modified forsome animals in affected areas. For instance, slaughter
times are modified to ensure that the activity concentrations of 137Cs are relatively low. In the United Kingdom,
the movement and slaughter of upland sheep in some areas
are restricted and the animals are monitored to ensure thatthe activity concentration of 137Cs is below the national
action level before they are slaughtered. The use of monitoring is also important in maintaining public confidence
in the products from affected areas. Such management
regimes in some areas have proven to be more useful andpractical countermeasures than the use of Prussian Blue.

A173. However, the use of Prussian Blue and similar compounds has not been universally successful. Boli can be difficult to administer, and adequate intake via salt licks has notalways been achieved.
(d) Countermeasures applied to extensive agricultural production
A174. Extensive production in the three countries of theformer Soviet Union is largely confined to the grazing ofprivately owned cows on poor, unimproved meadows.
Because of the poor productivity of these areas, radiocaesium uptake is relatively high compared to that on land
used by collective farms. Radical improvement of themeadows used by privately owned cows has been appliedin all three countries since the early 1990s. Clean feeding
is not generally used by private farmers, although on
occasion, collective farms may supply private farmers
with uncontaminated feed or pastures. Prussian Blue isused by private farmers in both Belarus and the RussianFederation. In the Russian Federation, all three PrussianBlue delivery systems are used, according to availability
and preference.
A175. In extensive systems, such as the upland grazed
areas in western Europe, the most commonly used countermeasures for free‑ranging animals have been clean feeding,administration of caesium binders, monitoring of live animals, management restrictions, and changes in slaughter
times. Many of these countermeasures were still in use in
2004. The application of long‑term countermeasures has
been most extensive in Norway and Sweden, but has also
been applied in the United Kingdom and Ireland.
A176. AFCF, also called Prussian Blue, is a highly effective hexacyanoferrate compound achieving up to a 5‑foldreduction in 137Cs in lamb and reindeer meat and up to a
3‑fold reduction in cow’s milk and 5‑fold reduction ingoat’s milk. The use of AFCF has been temporarily authorized in the EU and some other countries. AFCF as a caesium binder is effective in extensive production systems,
in contrast to many other countermeasures where theapplicability is limited. Boli are particularly favourable
for infrequently handled free‑grazing animals, as the boli
can be administered when the animals are gathered forroutine handling operations. For use in extensive systems,
the boli can be given a protective surface coating of wax todelay the onset of AFCF release, so that its effectiveness is

3.

Forest countermeasures

A178. Prior to the Chernobyl accident, countermeasures
to offset doses due to large‑scale radioactive contaminationof forests had not been given significant international attention. However, in the three countries of the former Soviet
Union, actions were taken to restrict activities in the more
affected zones, which included significant areas of forestry[F3]. These actions were, in general, rather simple andinvolved restrictions on basic activities, such as access toforests and gathering wild foods and firewood. A major
question remains as to whether any more complex or
techno­logically based countermeasures can be applied inforests on a realistic scale.

4. Aquatic countermeasures
A179. In the context of an atmospheric deposition ofradio­nuclides on both terrestrial and aquatic systems, it has
been shown that doses to humans from terrestrial foodstuffs
are, in general, much more significant than doses fromdrinking water and aquatic foodstuffs. However, for the
Dnieper system, the river water transported radionuclides toareas that were not significantly affected by atmosphericdeposition. This created significant anxiety in the population and a demand on decision makers to reduce radio­
nuclide fluxes from the zone via the aquatic system. Many
remediation measures were put in place, but because actions
were not taken on an objective basis of dose reduction, mostof these measures were ineffective. Moreover, radiation
exposures to workers implementing these countermeasures
were relatively high.
A180. To the Committee’s knowledge, no countermeasures were required, or applied, in marine systems after the
Chernobyl accident.

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UNSCEAR 2008 REPORT: VOLUME II

III.

SummaryA181. The largest nuclear reactor accident occurred at the
Chernobyl nuclear power plant on 26 April 1986. It occurred
during a low‑power engineering test of the Unit 4 reactor.
Improper, unstable operation of the reactor allowed an
uncontrollable power surge to occur, resulting in successive
steam explosions that severely damaged the reactor building
and completely destroyed the reactor.
A182. The radionuclide releases from the damaged reactor
occurred mainly over a 10‑day period, but with varying
release rates. Iodine‑131, 134Cs and 137Cs were the more
important radionuclides, because they were responsible formost of the radiation exposure of the general population.
The releases of 131I, 134Cs and 137Cs are estimated to havebeen 1,760 PBq, 47 PBq and 85 PBq, respectively. However, doses resulting from the accident have been estimatedon the basis of environmental and thyroid or body measurements; thus, knowledge of the quantities released was notneeded for that purpose.
A183. The three main areas of contamination, defined as
those with a deposition density of 137Cs greater than 37 kBq/m2(1 Ci/km2), are in Belarus, the Russian Federation andUkraine; they have been designated the Central, Gomel–
Mogilev–Bryansk and Kaluga–Tula–Orel areas. Altogether,territories with an area of approximately 150,000 km2 were
designated as “contaminated” in the former Soviet Union.
More than six million people lived in these areas.

disappeared by radioactive decay and 137Cs is currently of
most concern. For the future (more than 100 years) only plutonium isotopes and 241Am will remain. However, the contribution of these very long‑lived radionuclides to human
exposure will be minimal.
A187. The deposition in urban areas in the nearest city of
Pripyat and the surrounding settlements could have initially given rise to substantial external doses, which were
averted by the evacuation of the public. The deposition ofradioactive material in other urban areas has provided substantial contributions to dose during subsequent years after
the accident up to the present.
A188. During the first weeks to months after the accident,
the transfer of short‑lived radioisotopes of iodine to milk
was rapid and high, leading to substantial radiological problems in the former Soviet Union. Owing to the emergency
situation and the short half‑life of 131I, there are few reliabledata on the spatial distribution of the deposited radioiodine.
Current measurements of 129I may assist in estimating the 131I
deposition better, thereby improving the reconstruction ofdoses to the thyroid.
A189. The high concentrations of radioactive substancesin surface water directly after the accident fell rapidly, anddrinking water as well as water used for irrigation have very
low concentrations of radionuclides today.

A184. Outside the former Soviet Union, there were many
areas in western Europe with a deposition density of 137Cs in
the range of 37–200 kBq/m2. These regions represent an areaof 45,000 km2, or about one third of the contaminated areas
found in the former Soviet Union.

A190. At present, in most of the settlements subjected toradioactive deposition, the dose rates in air above solid surfaces have returned to the pre‑accident background levels.
Elevated dose rates in air remain mainly over undisturbed
soil.

A185. The environmental behaviour of deposited radio­
nuclides depends on the physical and chemical characteristicsof the radionuclide considered, on the type of deposition (i.e.
whether dry or wet), and on the characteristics of the environment. For short‑lived radionuclides, such as 131I, the main
pathway of exposure to humans was the transfer of radio­
nuclides deposited on pasture grazed by cows or goats to milk.
The consumption by humans of contaminated leafy vegetables was also an important pathway for some humans within a
few weeks of the accident. Radionuclides deposited on vegetation are retained with an ecological half‑time of about two
weeks before removal to the ground surface and to the soil.
For long‑lived radionuclides such as 137Cs, the long‑term
transfer processes from soil to foods consumed several weeks
or more after deposition needed to be considered.

A191. From the summer of 1986 onwards, 137Cs and 134Cs
in milk and meat were the dominant radionuclides of concern in agricultural products. During the first few years, substantial amounts of food were removed from humanconsumption. The highest activity concentrations of radiocaesium have been found in food products from forested
areas, especially mushrooms, berries, game and reindeer.
High activity concentrations of radiocaesium in fish occurredin lakes with slow or no turnover of water, particularly if thelake was also shallow and poor in mineral nutrients.

A186. Strontium and plutonium radioisotopes were also
released, but were mostly deposited close to the reactor andwere associated with fuel particles. The environmental
mobility of these radionuclides contained in fuel particles
has been low, but is increasing with time as the fuel particles
dissolve. Most of the originally released radionuclides haveA192. There has been a particularly slow decrease since
the initial deposition in activity concentrations of 137Cs insome products from the forest, and some species of mushrooms are expected to have high activity concentrations of137
Cs for decades to come. Under certain weather conditions, the biomass of mushrooms in autumn can be muchhigher than normal leading to relatively high seasonalincreases in the activity concentrations of 137Cs in game.
Thus, it must not always be assumed that the activity concentrations of 137Cs in animals will remain as they are now
or decline each year.

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

A193. There have been large long‑term variations in theactivity concentrations of 137Cs in food products owing
not only to differences in deposition levels, but also todifferences in soil types and management practices. In
many areas, there are still food products, particularly
from extensive agricultural production systems and forests, with activity concentrations of 137Cs exceeding theaction levels.
A194. The major and persistent problems in the affectedareas occur in extensive agricultural systems with soils having
a high organic content and animals grazing on unimproved
pastures. This particularly affects rural residents in the former
Soviet Union, who are commonly subsistence farmers withprivately owned dairy cows.
A195. In general, there has been an initial substantial
reduction in the transfer of 137Cs to vegetation and animals,
as would be expected because of weathering, physicaldecay, migration of radionuclides down the soil column andreductions in bioavailability. However, in the last decade,there has been little further obvious decline and long‑term
effective half‑lives have been difficult to quantify.
A196. Because of dilution, there was never a high concentration of 137Cs in marine fish in the Black Sea or theBaltic Sea.
A197. The Chernobyl accident led to an extensive set ofactions by the authorities of the former Soviet Union who
introduced a range of short‑ and long‑term environmental
countermeasures aimed at reducing the negative consequences. The countermeasures involved a great amount of
human, economic and scientific resources.
A198. Some of the more important comments on countermeasures are as follows:- Countermeasures applied in the early phase of theChernobyl accident were only partially effective in
reducing radioiodine intake via milk, because of
the lack of timely information about the accident
and advice on appropriate actions, particularly for
private farmers.

89- The most effective countermeasures in the earlyphase were exclusion of affected pasture from animal diet and rejection of milk (with further processing) based on radiation monitoring data. Feeding animals with “clean” fodder was effectively ­performed
in some countries.
- The greatest long‑term problem has been the radiocaesium content of milk and meat. In the former
Soviet Union and later in the three independent
countries, this has been addressed by the treatmentof land used for fodder crops (including enhanced
fertilization and cultivation changes), clean feeding
and the application of caesium binders to animals
that enabled most farming practices to continue inthe affected areas and resulted in a large reduction
in dose.
- Decontamination of settlements was widely appliedin regions of the former Soviet Union during thefirst few years after the accident as a means of
reducing external exposure of the public.
- The following forest‑related restrictions widely
applied in the former Soviet Union and later inthe three independent countries and partially in
Scandinavia, have reduced human exposure thatwould have resulted from residence in forests anduse of forest products: restrictions on public andforest‑worker access as a countermeasure against
external exposure; restricted harvesting by the
public of food products, such as game, berries andmushrooms (in the affected countries, mushrooms
are readily consumed and, therefore, this restriction
has been particularly important); and alteration of
hunting practices aimed at avoiding consumptionof meat with high seasonal levels of radiocaesium.
- The early restriction of drinking water and changing to alternative supplies reduced internal doses
from aquatic pathways in the initial period. Restrictions on the consumption of freshwater fish havealso proved effective in Scandinavia and Germany.
It is expected that restrictions on the consumptionof fish will remain, in a few cases (for so‑called“closed lakes”) for several more decades.

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UNSCEAR 2008 REPORT: VOLUME II

Figure A-I. Estimated plumes for instantaneous releases on the dates and at the times (UTC) indicated taking into account theprevailing meteorological conditions [B24]
LATVIA
LITHUANIARUSSIANFED.
VILNIUSPOLAND1

26 April, 0.00 hrs

4

29 April, 0.00 hrs

2

27 April, 0.00 hrs

5

2 May, 0.00 hrs

3

27 April, 12.00 hrs

6

4 May, 12.00 hrs

Smolensk
KalugaMINSK

1MogilevTula

B E L A R U S

BryanskWARSAW
Brest

3

Gomel

2
LublinSumy
Zhitomir

Lvov

ARY
NG
U
H
ROMANIA

4

KIEV

IA

Vinnitsa
Chernovtsy

R U S S I A N
F E D E R AT I O N

Chernigov

Chernobyl
Rovno

K
VA
SLO

Orel

6
REP. OFMOLDAVIA

5

Cherkassy

Kharkov

U K R A I N E
Kirovograd

0

50

100

150

200

250

300 kmE

Pinsk

Baranovichi

B

Novogrudok

Lida

Ternopol

ROVNO

r

Sto

kh

od

Pr i p y atg ki
Dn e pr-Bu s C anal

Sty

’

Goryn

L

Khmelnitskiy

Narovlya

Mozyr

Pripyat

VINNITSA

Berdichev

KIEV

Cherikov

e
Dn

R
F

pr

zh

Dn

ep

r

U

S
D

K

Novozybkov

CHERKASSY

Slavutich

U
E

S
E

R

A

Shostka

POLTAVA

N

SUMY

I

N
T
O

E

KURSK

BolkhovI

KALUGAN

185–555 kBq m-2

Plavsk-2

37–185 kBq m-2

555–1 480 kBq m-2

KHARKOV

Yelets<37 kBq m-2

BELGOROD

Seym

Kimovsk

Novomoskovsk

Efremov

Sosna

TULA

Aleksin

MtsenskOREL

1 480–3 700 kBq m

Lyudinovo

Kirov

A
A

Dyatlovo

I
R

BRYANSK

Roslavl

SMOLENSK

KrichevSo

CHERNIGOVGOMELBelaya Tserkov
Rosk aZHITOMIR

Korosten

Gorki

MOGILEV

Khoyniki
BraginBobruysk

Bykhov

ORSHA

Polesskoje
Chernobyl
Narodichi

S

Borisov

Berezina

OvruchPr i p y atU

Novograd Volynskiy

SarnySlutskR

MINSKSoligorsk

A

Molodechno

v
re
te
Te

na
Des

Desna

VILNIUSPs e laOkkaO

Map of levels of 137Cs deposition in 1989 in Belarus, the Russian Federation and Ukraine [I28]

Vo r s k l a

Oskol

Figure A-II.

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT
91

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UNSCEAR 2008 REPORT: VOLUME II

Figure A-III. The total amounts in the environment of various released radionuclides and their progeny as a function of timeafter the accident
While the amount of 241Am originally released was very small, the total activity of 241Am will increase with time due to the decay of 241Pu. It
will reach a peak after 72 years, after which it will slowly decline. After 320 years, the total activity of 241Am will be the highest of all theremaining radionuclides

TOTAL ACTIVITY OF RADIONUCLIDE (PBq)

100

10
Caesium-137
1

Plutonium-241
Americium-241

0.1

Plutonium-239+240

0.01
Caesium-134
0.001

0

50

100

150

200

250

300

350

400

TIME AFTER ACCIDENT (a)Rolling seven month mean concentration of 137Cs in air at Baryshevka and Chernobyl (June 1986 to August 1994)

106
CONCENTRATION (µBq/m3)

Figure A-IV.
[H5]

Baryshevka
Chernobyl

104

102

100

0

30

60

90

TIME AFTER JUNE 1986 (months)

120

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

93

Figure A-V. Typical relative distribution of 137Cs on different surfaces within settlements in 1986 and 14 years later (undisturbed
soil deposition in 1986 or 2000 is taken equal to 1) [R10](a) Dry deposition
1986

2000

DISTRIBUTION OF CAESIUM-137(relative to undisturbed soil)

4

3

2

1

0

UNDISTURBEDSOIL

TREES,
BUSHES

ROOFS

WALLS

STREETS,PAVEMENTS

WALLS

STREETS,PAVEMENTS(b) Wet deposition
1986

2000

DISTRIBUTION OF CAESIUM-137(relative to undisturbed soil)

1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0

UNDISTURBEDSOIL

TREES,
BUSHES

ROOFS

94

Figure A-VI.
[A6]

UNSCEAR 2008 REPORT: VOLUME II

Measured 137Cs activity levels (relative to the initial deposition on soil) on three types of roof at Risø, Denmark

1.0
Corrugated Eternit – 45°
ACTIVITY LEVEL AFTER TIME, t,
RELATIVE TO INITIAL LEVEL

0.8

0.6

Red clay tile – 45°

0.4

0.2

0.0

Silicon treated Eternit – 30°

0

2

4

6

8

10

12

14

TIME AFTER DEPOSITION, t (a)Figure A-VII. Ratio of the dose rate above different surfaces to that in open fields for the town of Novozybkov, the RussianFederation [G4]1.00.9

LOCATION FACTOR

0.8

Virgin land (inside town)

0.7
0.6
0.5
Dirt surfaces

0.4
0.3

Asphalt

0.2
0.1
0.0

0

1

2

3

4

5

6

TIME AFTER THE ACCIDENT (a)

7

8

9

10

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

95

Figure A-VIII. The main transfer pathways of radionuclides in the terrestrial environment [S13]Initial radionuclide fallout:- condensation component- fuel particles

Surface washout
Soil–vegetation litter

Migration

Dissolution offuel particles

Organic–mineral soil component

Soil solution
Sorption–desorption

RootuptakeSorbed radionuclides
Groundwater and rocks of geological environment

Figure A-IX. The activity concentrations of 137Cs in cow milk near Munich following the Chernobyl accident as observed andas simulated by the ECOSYS-87 model [M9]CAESIUM-137 CONCENTRATION IN MILK
(Bq/L)

103

102
Measurement
Model: 95-percentile
Model: 50-percentile
Model: 5-percentile

10

1

100

10-1

0

200

400

600

TIME AFTER DEPOSITION (days)

800

1 000

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UNSCEAR 2008 REPORT: VOLUME II

Figure A-X. Depth profiles for 137Cs and 90Sr measured in 1987 and 2000 in a soddy–gley–sandy soil (in % of total activity)[S14]
Sr ACTIVITY (%)

Cs ACTIVITY (%)

90

137

20

40

60

80

100

0

0–5

0–5

6–10

6–10

11–15

11–15

DEPTH (cm)

DEPTH (cm)

0

16–20
21–25

40

60

80

100

16–20
21–25

26–30

26–30

31–35

31–35
1987

20

2000

1987

2000

Figure A-XI. Pathways of radionuclide transfer from soil to plants, taking into account both biotic and abiotic processes [T8]

PlantsFertilizers

Roots, mycorrhiza
Soil solution
Soil mineral matrix

Soil microorganisms

Soil organic matrix

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

97

Figure A-XII. (a) Transfer of 137Cs into oat grain in soddy–podzolic soils of various textures with varying potassium contents[B25] and (b) transfer of 90Sr into seeds of winter rye with varying concentrations of exchangeable calcium in different soils
[K20]
(a)
0.35

Tag (137Cs) (10–3 m2/kg)

0.3
0.25
0.2

Sands

0.15

Sandy loam
Clay loam

0.1
0.05
0

<80

81–140

141–200

201–300>300

POTASSIUM CONTENT (mg/kg)(b)

Tag (90Sr) (10–3 m2/kg)

8
6
Tag = 3.9 Ca–1

4
2
0
0

2

4

6

8

CALCIUM CONTENT (mg-equ/100 g)

10

12

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UNSCEAR 2008 REPORT: VOLUME II

Figure A-XIII. Concentrations of 137Cs in grain and potato produced in contaminated districts of the Bryansk oblast, theRussian Federation [F7]ACTIVITY CONCENTRATION(Bq/kg)

1 000

100
Grain
Potato101986 1988 1990 1992 1994 1996 1998 2000 2002 2004
YEAR

Figure A-XIV. Mean activity concentration of 137Cs in meat and milk produced in contaminated districts of the Bryansk oblast,
the Russian Federation [F7]ACTIVITY CONCENTRATION(Bq/kg)

10 000

1 000
Meat
Milk
100

10
1986 1988 1990 1992 1994 1996 1998 2000 2002 2004
YEAR

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

99

Figure A-XV. Typical dynamics of activity concentrations of 137Cs in milk produced on private and collective farms in the
Rovno oblast, Ukraine with a comparison to the national temporary permissible level (TPL) [P6]aACTIVITY CONCENTRATION(Bq/L)

2 000

1 500
Private farms
Collective farms
TPL

1 000

500

0
1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000
YEAR
a The current Codex Alimentarius Guideline Level for 137Cs in food for use in international trade is 1,000 Bq/kg [C12].

Estimated percentage distributions of radiocaesium among various components of coniferous forest ecosystems

102
101
100
90th percentile
10-1

Median10th percentile

10-2
10-3

E
M
GA

I
NG

RS
TO
R
DE
UN

FU

EY

EE
TR

IL

10-4

SO

PERCENTAGE

Figure A-XVI.
[S22]

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UNSCEAR 2008 REPORT: VOLUME II

Figure A-XVII. Activity concentrations of 137Cs in selected mushroom species
The mushrooms were harvested from a pine forest in the Zhytomir oblast of Ukraine, approximately 130 km southwest of Chernobyl (Bq/kg dryweight). The deposition density of 137Cs in soil at this site in 1986 was 555 kBq/m2 [I18]4 500 000

ACTIVITY CONCENTRATION(Bq/kg)4 000 000
Xerocomus
badius3 500 000

Suillusluteus3 000 000
2 500 000

Russulapaludosa

2 000 000Cantharellus
cibarius

1 500 000
1 000 000

Boletusedulis500 000
01990 1991 1992 1993 1994 1995 1996 1997 1998 1999
YEAR

Figure A-XVIII. The average concentration of 137Cs in moose in one hunting area in Sweden
The data are based on measurements of approximately 100 animals each year [J5]
900

700
600
500
400
300
200
100

03

02

20

01

20

00

20

99

20

98

19

97

19

96

19

95

YEAR

19

94

19

93

19

92

19

91

19

90

19

89

19

88

19

87

19

19

86

0

19

CONCENTRATION OF 137Cs(Bq/kg)800

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

Figure A-XIX.

101

Averaged activity concentrations of 137Cs in fish from the Kiev reservoirs [U19]
Bream (non-predatory)

1 000
900
CONCENTRATION OF 137Cs(Bq/kg, fresh weight)

800
700
600
500
400
300
200
100
0

1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000
YEAR

Pike (predatory)

1 800

CONCENTRATION OF 137Cs(Bq/kg, fresh weight)

1 600
1 400
1 200
1 000
800
600
400
200
0

1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000
YEAR

Figure A-XX. Amounts of milk and meat exceeding the temporary permissible levels in the Russian Federation (from collective
and private farms), Ukraine and Belarus [N8]These figures relate to milk and meat entering processing plants

Milk

1 000

100 000

Meat

AMOUNT(TONNES)

100
1 000

100

10
10

YEAR

YEAR
Russian Federation

UkraineBelarus

04

02

20

20

00
20

98
19

96
19

94
19

92
19

90
19

88
19

19

86

04

02

20

00

20

20

98
19

96
19

94
19

92
19

90
19

88

1
19

86

1
19

AMOUNT(THOUSAND TONNES)

10 000

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UNSCEAR 2008 REPORT: VOLUME II

400

4 000

350

3 500
TPL FOR MEAT (Bq/kg)

TPL FOR MILK (Bq/L)

Figure A-XXI. Changes with time in temporary permissible levels (TPLs) in the former Soviet Union (until 1991) and later inthe three independent countries [S14]a

300
250
200
150
100
50

3 000
2 500
2 000
1 500
1 000
500

0
1985

1990

1995

2000

2005

2010

0
1985

1990

1995

YEAR

2000

2005

YEAR

Russian Federation

UkraineBelarusa The current Codex Alimentarius Guideline Level for 137Cs in food for use in international trade is 1,000 Bq/kg [C12].

Figure A-XXII.

Comparison of 137Cs uptake in different crops normalized to that for peas [B18]100

PERCENTAGE UPTAKE COMPARED WITH PEAS

90
80
70
60
50
40
30
20
10
0

CarrotCabbageTomatoPotatoHaricot

CROPS

Beetroot

CucumberRadishPea

2010

APPENDIX B.
RADIATION DOSES TO EXPOSED POPULATION GROUPS
I.

Summary from previous UNSCEAR Reports

B1. Average doses from the radioactive fallout from the
Chernobyl accident to populations of countries and somesubregions within countries of the northern hemisphere
were assessed in the annex D, “Exposures from the Chernobyl accident”, of the UNSCEAR 1988 Report [U7]. In its
assessment, the Committee relied on the numerous environmental measurements performed during the first year following the accident and on general modelling. Occupational
exposures were not included as information on the doses toworkers participating in the accident mitigation and restoration work in the former Soviet Union was not then available.
Furthermore, relatively little information was available on
the radiation exposures of members of the public in theformer Soviet Union.

estimated for: (a) the workers who had been involved in the
mitigation of the accident during the accident itself (“emergency workers”), and those who had been involved after theaccident (“recovery operation workers”); and (b) membersof the public who had been evacuated to avert excessive
radiation exposures, and those who were still resident in thecontaminated areas (defined as those areas in Belarus, theRussian Federation and Ukraine with a 137Cs deposition
density greater than 37 kBq/m2). A large number of radiation measurements (with film badges, TLDs, whole‑bodycounters, thyroid counters, and so on) had been made toevaluate the radiation exposures of the population groups
that were considered.
B6. The highest doses were received by the emergency
workers—of which there were approximately 600—who
had been on the site of the Chernobyl nuclear power plant
during the night of the accident. The most important exposures were due to external irradiation, because the intake ofradionuclides via inhalation was relatively small in mostcases. Acute radiation sickness was confirmed in 134 of theemergency workers. Forty one of these had received whole‑­
body doses due to external irradiation of less than 2.1 Gy.
Ninety three had received higher doses and had more severe
acute radiation sickness: 50 persons had doses between 2.2
and 4.1 Gy; 22 between 4.2 and 6.4 Gy; and 21 between 6.5
and 16 Gy. The skin doses due to beta‑radiation exposure,which were evaluated for eight of those with acute radiation
sickness, ranged from 10 to 30 times the whole‑body doses
due to external irradiation.

B2. The general conclusion from the assessment of doses tomembers of the public was that “although populations were
exposed in the countries of Europe and, to a lesser extent, incountries throughout the northern hemisphere, the radiation
exposures were, in perspective, not of great magnitude” [U7].
B3. In Europe, the highest national average effective dosesin the first year were 760 μSv in Bulgaria, 670 μSv in ­Austria,
590 μSv in Greece and 570 μSv in Romania. These were followed by other countries in northern, eastern and south‑­eastern Europe. The doses in countries further to the west in
Europe and in the countries of Asia, Africa, and North andSouth America were much less, which is in accord with theradionuclide deposition patterns.
B4. The Committee predicted [U7] that “exposures, mainly
from released 137Cs, will continue for a few tens of years
from the external irradiation and ingestion pathways”. Estimates of dose commitments were made for larger geo­
graphical regions, based on projection models that had beendeveloped from measurements of the global fallout from theatmospheric testing of nuclear weapons. Doses to the entire
population of the northern hemisphere were estimated frominformation on the relationship between the levels of 137Cs
deposition and distance from Chernobyl. The collective
effective dose commitment to members of the public wasestimated to be of the order of 600,000 man Sv.

B7. About 600,000 persons (civilian and military) received
special certificates confirming their status as recovery operation workers (also known as “liquidators”), according tolaws promulgated in Belarus, the Russian Federation andUkraine. Of those, about 240,000 were military servicemen.
The principal tasks carried out by the recovery operation
workers included decontamination of the reactor block,
reactor site and roads, as well as construction of the “sarcophagus” to cover the damaged reactor, a town for reactor
personnel and waste repositories. These tasks had been­completed by 1990.

B5. Updated information on radiation doses was provided
in annex J, “Exposures and effects of the Chernobyl accident”, of the UNSCEAR 2000 Report [U3]. Doses were

B8. An official registry of recovery operation workers had
been established in 1986. This registry included estimates ofdoses due to external irradiation, which was the predominant
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pathway of exposure for these workers. The registry data
showed that the average recorded doses decreased from year
to year, being about 0.17 Sv in 1986, 0.13 Sv in 1987, 0.03 Sv
in 1988, and 0.015 Sv in 1989. It was generally difficult, however, to assess the validity of the results that had been reported
for a variety of reasons, including: (a) the fact that different
dosimeters had been used by different organizations, without
any intercalibration; (b) the large number of recorded dosesthat were very close to the dose limit; and (c) the large numberof rounded values, such as 0.1 Sv, 0.2 Sv or 0.5 Sv. Nevertheless, it seemed reasonable to assume that the average effective
dose due to external gamma irradiation to recovery operation
workers in the years 1986–1987 was about 0.1 Sv.
B9. The radionuclide releases from the damaged reactor
had led to deposition of radioactive material over large areas,
which resulted in radiation doses to members of the public.
The radionuclide releases occurred mainly over a 10‑day
period, with varying release rates. The most important radionuclides to consider were 131I and 137Cs. Iodine‑131 was themain contributor to the thyroid doses, received mainly via
internal irradiation within a few weeks after the accident. In
contrast, 137Cs was (and remained) the main contributor to
the doses to organs and tissues other than the thyroid, due toeither internal or external irradiation; these doses would­continue to be received at low rates over several decades.
B10. Within a few weeks of the accident, approximately
116,000 persons had been evacuated from the areas of Belarus and Ukraine with the highest deposition levels of radionuclides. The thyroid doses received by the evacuees varied
according to their age, place of residence and date of evacuation. For example, for the residents of Pripyat, who had
been evacuated essentially within 48 hours after the accident, the population‑weighted average thyroid dose was estimated to be 0.17 Gy, and to range from 0.07 Gy for adults to

2 Gy for infants. For the entire population of evacuees, thepopulation‑weighted average thyroid dose was estimated tobe 0.47 Gy. Doses to organs and tissues other than the ­thyroid
had been, on average, much smaller.
B11. Thyroid doses were also estimated for residents ofthe contaminated areas who had not been evacuated. In eachof the three republics, thyroid doses exceeding 1 Gy were
estimated for the most exposed infants. For residents of agiven locality, thyroid doses to adults were smaller thanthose to infants by a factor of about 10. The average thyroid
dose received by the population of the three republics was­estimated to be 7 mGy.
B12. Following the first few weeks after the accident when131
I had been the main contributor to the radiation exposures,
doses were delivered at much lower dose rates by radio­
nuclides with much longer half‑lives. Since 1987, the doses
received by the populations of the contaminated areas
resulted essentially from external exposure due to 134Cs and137
Cs deposited on the ground and from internal exposuredue to incorporation of 134Cs and 137Cs into foodstuffs. Other,usually minor, contributions to the long‑term radiation exposures included that due to the consumption of foodstuffs
containing 90Sr and to the inhalation of aerosols containing
isotopes of plutonium. Both external irradiation and internal
irradiation due to 134Cs and 137Cs resulted in relatively uniform doses to all organs and tissues of the body. The average
effective doses due to 134Cs and 137Cs that had been received
during the first 10 years after the accident by the residents ofcontaminated areas were estimated to be about 10 mSv. The
median effective dose was about 4 mSv and only about
10,000 people were estimated to have received effective
doses greater than 100 mSv. The lifetime effective doses
were expected to be about 40% greater than the doses
received during the first 10 years following the accident.

II. Update
B13. The Committee has updated the dose estimates forthe same population groups as in annex J, “Exposures andeffects of the Chernobyl accident”, of the UNSCEAR
2000 Report [U3]. In addition, dose estimates have been
updated for the populations residing in all areas of Belarus and Ukraine, as well as for those residing in specificareas of the Russian Federation. Some information is also
provided for the populations exposed in more distant
European countries.
B14. A thorough analysis of the possible radiation‑induced
health effects in emergency and recovery operation workers
and in members of the public requires an adequate dosimetric basis so as to determine such matters as the radiation risk
coefficients and the dose–effect relationship. It is generally
recognized that the most suitable dosimetric parameters for
epidemiological studies are absorbed doses in organs or tissues, complemented by information on the linear energy

transfer (LET) of the radiation and the dose rate. Following
the Chernobyl accident, both workers and members of the
public were exposed, externally and internally, to low‑LET
beta and gamma radiation.
B15. In the studies that focused on the acute radiation
effects in emergency workers [U7], the absorbed dose in thewhole body (red bone marrow) and to the skin were used.
These doses were reconstructed from biological indicators,
such as blood cell concentration and cytogenetic parameters.
However, in many studies of the long‑term radiation‑induced
health effects in various cohorts exposed as a consequence of
the accident, also including those undertaken for this report,
some other dosimetric quantities were used that were notoriginally intended for use in an analysis of the dose–effectrelationship. For example, the exposures of the recovery
operation workers to external gamma radiation were usually
recorded in terms of the physical quantity “exposure in air”

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

(expressed in units of roentgen) and later, for storing in electronic databases, converted to absorbed doses (expressed inmilligray) by simple multiplication by a factor of ten.
Although exposure in air is generally not sufficient for determining the dose in the human body, nevertheless, for the
typical conditions of post‑accident exposure (360º rotational
geometry and mean gamma radiation energy of 0.6‑0.8 MeV),
the absorbed dose calculated in this way is close to theabsorbed dose in surface body tissues. However, the absorbed
dose in organs and tissues located deeper is a factor of
1.2‑1.8 lower for the same exposure conditions [G11, I33].
The lengths of time that the recovery operation workers were
exposed to radiation were estimated using information on
the duration of work on‑site or in other radioactively contaminated areas; these usually ranged from a few days tosome months.
B16. The dosimetric assessments for the studies of theradiation effects on the thyroid were, from the very beginning, based on the mean absorbed dose in the thyroid(expressed in gray or milligray), which was considered to
be an adequate quantity for this purpose. The duration of
thyroid exposure was estimated from the physical half‑life,
the half‑time of reduction of the activity concentrations infood, and the retention in the thyroid of 131I, which was the
major contributor to the thyroid dose. The effective half‑lifeof 131I in the thyroid was five to seven days, depending onage, which corresponds to a duration of exposure of about
one month.
B17. The external and internal exposure of members of thegeneral public due to the mixture of radionuclides in theenvironment (dominated by 137Cs and 134Cs) were usuallypresented in terms of effective dose (expressed in millisieverts). However, as stated elsewhere, effective dose is a quantity developed for radiation protection purposes and is notdirectly applicable to the interpretation of data on healtheffects. The quantity, effective dose, incorporates judgements on radiation quality and on the relative radiosensitivity of organs and tissues with regard to stochastic healtheffects, and its use, therefore, is not applicable to dose–effectanalysis. The fact that it was widely used is due to its importance in modern radiation protection [I30, I33] and the availability of nominal dose coefficients for both external andinternal exposures that have been developed by the ICRP.
However, for relatively isotropic external exposure of ahuman body to gamma radiation from radionuclides distributed in the environment and for relatively uniform internal
exposure due to incorporated 137Cs and 134Cs, the numericalvalues of absorbed dose (in milligray) in many organs andtissues are within about 30% of the numerical values ofeffective dose (in millisieverts). The estimates of effective
dose due to internal irradiation that are presented in thisappendix do not include any contribution from the intakes ofradioiodine and radiotellurium, whereas the contribution
from these radionuclides was taken into consideration in theestimation of doses due to external irradiation. Public exposure due to radionuclides deposited in the environment following the accident has extended over several decades, with105

the contribution of the first year’s dose being 30‑40% of the
lifetime dose. The estimates of effective dose due to external
irradiation represent the dose received during the period
under consideration, whereas doses due to internal irradiation (i.e. committed doses) reflect the doses over the entire
period that the radionuclide is present in the body until its
decay and clearance.
B18. A very large number of scientific papers, books,
reports and conference proceedings have been published in
Russian, English and other languages on various dosimetricaspects of the Chernobyl accident. Key references in the English literature include the two main reports of the Chernobyl
Forum [I21, W5], the two previous reports of the Committee[U3, U7] and many books and conference proceedings [A8,E4, I25, I29, I34, K21, K29, M12, M17, N13, N15, N16, V2,
V3, Y2, Y3]. Most of the material presented here is based on
the four main reports prepared by the United Nations or its
agencies [I21, U3, U7, W5], with complementary information taken from recent publications and submitted by focal
points in Belarus, the Russian Federation and Ukraine.
A. Workers involved in response and recovery
B19. The emergency workers were those involved in
responding to the accident, such as fire-fighting, during thefirst day (26 April 1986). The recovery operation workers
were those involved during 1986–1990 at the power station
or in the zone surrounding it in decontamination work, sarcophagus construction and other recovery operation activities. Those workers who operated the other units of thenuclear power plant were also included in this group.
1. Emergency workers
B20. Information on the emergency workers who received
very high doses was reviewed in detail in annex J, “Exposures and effects of the Chernobyl accident”, of the
UNSCEAR 2000 Report [U3]. The 134 emergency workers
who had been diagnosed with acute radiation sickness
received whole-body (or bone‑marrow) doses due to external gamma radiation ranging from 0.8 to 16 Gy. The skindoses to some individuals exceeded the bone‑marrow doses
by a factor of 10–30; some received skin doses that were
estimated to be in the range of 400 to 500 Gy [M13]. Doses
had been estimated mainly using clinical dosimetry ­methods,i.e. analysis of blood counts and/or cytogenetic parametersof blood lymphocytes [U3]; these methods are appropriate
for small numbers of human subjects but not for large‑scale
epidemiological studies.
2.

Recovery operation workers

B21. The main pathway of exposure of the recovery operation workers was external gamma irradiation from the radioactive material deposited on the ground and building surfaces.

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These external doses were recorded in national registries forabout half of the workers. Effective doses and absorbed doses
to the skin and the lens of the eye from external beta irradiation, and to the thyroid from internal ­irradiation were only
estimated for a limited number of workers.
(a)

Doses due to external irradiation by gamma-ray emitters

B22. Estimates of doses to the recovery operation workers
resulting from external gamma irradiation could be obtained
from assessments conducted either at the time of exposure orsubsequently. At the time of exposure, three methods wereused: (a) individual dosimetric measurements for atomic
energy workers and a small fraction of the military personnel
after June 1986; (b) group dosimetric measurements (i.e.
through the use of an individual dosimeter worn by one
member of a group of recovery operation workers assigned
to perform a particular task; all members of the group wereassumed to receive the same dose); and (c) prior assessmentof dose to a group of recovery operation workers based on
the dose rate at the work location and the planned duration ofwork. Methods (b) and (c), either separately or combined,
were used to assess the doses to the majority of the military
personnel at all times. Subsequently, retrospective assessments of dose were undertaken. The methods included:(d) time‑and‑motion studies (i.e. measurements of gamma‑­
radiation levels were made at various points of the reactor
site, and an individual’s dose was estimated as a function of
the points where he or she worked and the time spent in theseplaces); and (e) biodosimetry (i.e. electron paramagnetic
resonance (EPR) measurements on teeth, or fluorescencein‑situ hybridization (FISH) measurements on blood lymphocytes). So far, method (e) has only been used for validation purposes on a limited number of workers [W5]. At thetime of the clean‑up work in 1986–1990, all radiometric anddosimetric devices were calibrated in terms of the physicalquantity, exposure rate (expressed in units with symbols,
mR/h or R/h), but the results that are reported in the scientific literature are usually in terms of absorbed dose
(expressed in milligray) or of effective dose (expressed inmillisieverts), using the approximation that 1 R = 10 mGy =10 mSv. In this appendix the results are given in terms ofabsorbed dose.
B23. The main sources of uncertainty associated with thedifferent methods of dose estimation are as follows: for (a)individual dosimetry: incorrect use of dosimeters (inadvertent or deliberate actions leading to either an overexposure oran underexposure of the dosimeters); for (b) and (c) groupdosimetry: very high gradient of exposure rate at the working places at the reactor site; for (d) time-and-motion studies: deficiencies in data on itineraries and time spent at thevarious working places, combined with uncertainties in the
exposure rates; and for (e) biodosimetry: a relatively highsignal from background radiation, which prevents additional
low doses from being measured precisely, and a lack ofknowledge of the doses from other natural and artificial
sources of radiation exposure [W5]. A high degree ofconservatism was used in the early applications of method(e). Uncertainties associated with the different methods ofdose estimation have been assessed to be: up to 50% formethod (a) (if the dosimeter was correctly used); up to a­factor of 3 for method (b); and up to a factor of 5 for methods(c) and (d) [P1]. The uncertainty of the EPR dosimetry usedin method (e) has been assessed to have an absolute value of
25 mGy (one standard deviation) at doses below about
250 mGy, and a relative value of about 10% at doses above
250 mGy [C15].
B24. Altogether, the national registries of Belarus, the­Russian Federation, Ukraine, Estonia, Latvia and Lithuania
include, as of 2006, information on about 500,000 recovery
operation workers and the recorded doses due to external
gamma irradiation for about 250,000 of them (table B1).
These numbers are different from those of the previous
UNSCEAR report [U3] and from those of the more recent
Chernobyl Forum report [W5] because: (a) updating of thenational registries has continued since 2000; and (b) data on
workers from the three Baltic countries are now included. As
a result, the information includes data on 38% more recovery
operation workers than in 2000 [U3]. The number of workers
who were designated as recovery operation workers decreased
from year to year. The average of the recorded doses also
decreased; the mean dose was about 150 mGy in 1986,
100 mGy in 1987, and 40–50 mGy in 1988–1990. The
decrease in recorded doses with time after the accident reflects
the decreases in both the dose rates and the dose limit (formost workers, the dose limit was 250 mGy in 1986, 100 mGy
in 1987, and 50 mGy in a year since 1988). The percentage ofrecovery operation workers with a recorded dose was lowest(35%) in 1986, because it took time for the dosimetric monitoring system to become fully operational [C13]; it increased
to 64% in 1987; and then remained fairly constant until 1990.
Although the dose values presented in table B1 provide anindication of the radiation exposures, they cannot be relied
upon for epidemiological studies without further analysis
because of biases introduced by some of the methods of dose
estimation and because the data for a small percentage ofworkers may have been falsified [B11, C13].
B25. The mean external dose to all recovery operation
workers was about 120 mGy (table B1). Among the countries supplying emergency recovery workers, the highest
mean dose (about 150 mGy) was received by the Ukrainian
workers, who were involved in the most difficult early operations at the Chernobyl site and within the 30‑km zone. The
lowest mean dose (about 50 mGy) was received by the Belarusian workers, because they were not assigned to work in
the industrial zone. A study of the Russian recovery operation workers [I14, I25] seems to indicate that the average
dose to them was relatively independent of the time that theyspent on site during their first mission (table B2). This tablealso shows that most recovery operation workers spent lessthan six months on site during their first mission. However,some of the recovery operation workers were subsequently
involved in multiple missions, representing several years intotal spent on site [C16].

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

B26. The distribution, with respect to external dose, of theapproximately 250,000 recovery operation workers who had
doses recorded is given in table B3 for Belarus, the RussianFederation, Ukraine, Estonia, Latvia and Lithuania, as well
as for all those countries together. For most countries, thelargest number of workers was in the dose interval,
50–500 mGy. The doses vary from less than 10 mGy to morethan 1,000 mGy, but about 85% of these workers received
doses within the range of 20 to 500 mGy. Doses greater than
1 Gy were recorded for 219 workers; the reliability of thedoses to these workers was established. The average dose to
all workers with a recorded dose was 110 mGy; the averagefor each country ranges from 43 mGy for the workers from
Belarus to 180 mGy for the workers from Latvia.
B27. The dosimetric information needed for analytical epidemiological studies is the absorbed dose in the organ ofinterest (bone marrow for blood diseases, breast for breast
cancer, and so on) for all individuals enrolled in the particular study, as well as an assessment of the uncertainty associated with the dose estimates. In order to carry out such a
study, the registry data was supplemented or substituted withother information, including some obtained during personal
interviews. Studies performed in Ukraine to evaluate thevalidity of the dose records of military recovery operation
workers (about half of the total number of workers) revealed
that the majority (90–95%) of these dose records wereunlikely to have been falsified [C14], but that the doses had
been overestimated by a factor of about 2 [C13, C17].
On­going epidemiological studies are using a time‑and‑motion
study method, called RADRUE [C16, K5, K30]. Thismethod relies on knowledge of the locations occupied by theworker (which were obtained by means of personal interviews) and the radiation field at these locations. Biodosimetric methods can also be used to calibrate the dosimetry
results recorded in the registries or obtained with RADRUE,
although, at the present time, the accuracy and precision ofthese methods are insufficient for epidemiological studies at
low doses [B11].
(b) Doses to the skin and to the eye lens due to external beta
irradiation
B28. The dose to unprotected skin resulting from exposures to beta radiation is estimated to have been several times
greater than the gamma dose. The ratios of the total dose
rates from beta plus gamma exposures to those from the
gamma exposures alone, measured at the height of the face,ranged from 2.5 to 11 (average of about 5) for general decontamination work, and from 7 to 50 (average of about 28) for
decontamination of the central hall of the Unit 3 reactor[O1]. The clothes shielded most of the skin and therefore thebeta dose to protected skin was much smaller than that tounprotected skin. The assessment of the beta dose to the lensof the eye was addressed in the framework of the ­Ukrainian–American Chernobyl Ocular Study, which is a cohort studyof cataracts among 8,607 Ukrainian recovery operation
workers. Beta doses were derived from the gamma exposure

107of the subjects. Gamma–beta dose conversion coefficientswere calculated using Monte‑Carlo methods for a variety ofbeta‑energy spectra and conditions of exposure. It was foundthat the distribution of individual beta/gamma ratios wasquite broad, ranging from essentially 0 to 3.5, with 56% of
the ratios being less than 0.5 and 32% greater than or equal
to 1 [C17].
(c)

Doses due to internal irradiation

B29. Because of the abundance of 131I and shorter‑lived
isotopes of iodine in the vicinity of the reactor during theevolution of the accident, those recovery operation workers
who were on site during the first few weeks after the accident may have received substantial thyroid doses due tointernal irradiation [U3]. On the basis of a limited numberof measurements made from 30 April to 7 May 1986, thyroid doses to more than 600 workers were estimated to average 0.21 Gy [K6, U3], assuming a single intake on the dateof the accident and no stable iodine prophylaxis. The medianvalue of the ratio of the thyroid dose to the effective dose
was estimated to be 0.3 [K6]. In comparison to the external
doses that were incurred after May 1986, the internal doses
due to intakes of 131I were negligible. More detailed information is provided in annex J of the UNSCEAR 2000
Report [U3].
B30. Limited information on the internal doses resulting
from intakes of 90Sr, 137Cs, 239Pu and other radionuclides was
also provided in annex J of the UNSCEAR 2000 Report[U3]. The average value of the committed effective dosefrom the intake of those radionuclides was estimated to be
85 mSv for about 300 recovery operation workers who had
been selected for study on the basis of their high levels of
external exposure.
3.

Collective doses

B31. The collective dose due to external exposure received
in 1986–1990 by about half a million registered emergency
and recovery operation workers at the Chernobyl site and inother areas contaminated with radionuclides is estimated to
be about 60,000 man Gy. Of that dose, 73% was incurred in
1986, 22% in 1987 and the remaining 5% in the subsequent
three years. More than half of the collective dose (56%) was
incurred by Ukrainian workers, 33% by Russian workers,
and the remaining 11% by workers from Belarus, Estonia,
Latvia and Lithuania. Doses received by workers from othercountries within the former Soviet Union have not beenassessed.
B32. The distribution of the collective dose according toindividual dose level is also presented in table B3 for Belarus, the Russian Federation, Ukraine, Estonia, Latvia and
Lithuania, as well as for all those countries together. About
85% of the collective dose to all the workers with recorded
doses was delivered to those in the interval 50–500 mGy.

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B. Doses to general population
B33. Regarding doses incurred by the members of the general public resulting from the deposition of radioactive material, it is essential to deal separately with the dose to thethyroid and that to the whole body. Iodine-131 was the main
contributor to the thyroid doses, received mainly via internal
irradiation within a few weeks after the accident. However,137
Cs was and still is the main contributor to the doses toother organs and tissues, from both internal and external irradiation; these doses will continue to accumulate at low rates
for several decades more.
B34. There were four components to the thyroid doses
resulting from the Chernobyl accident: (a) the dose due tointernal irradiation resulting from intakes of 131I; (b) the
dose due to internal irradiation resulting from intakes ofother short‑lived isotopes of iodine (132I, 133I and 135I) and of
short‑lived isotopes of tellurium (131mTe and 132Te); (c) the
dose due to internal irradiation resulting from intakes oflong‑lived radionuclides such as 134Cs and 137Cs; and (d) the
dose due to external irradiation resulting from the deposition of radionuclides on the ground and other materials. For
most individuals, the dose due to internal irradiation resulting from intakes of 131I was by far the most important andhas received almost all of the attention by the scientificcommunity.

either as whole‑body doses (in milligrays) or as effective
doses (in millisieverts) and, by convention, do not include
the thyroid doses due to the 131I intakes that were received
during the first few weeks after the accident.
B37. The Committee has considered three populationgroups: (a) the evacuees; (b) the populations of Belarus, theRussian Federation and Ukraine who lived on territories
deemed contaminated; and (c) the populations of most of theother European countries. For the first two populationgroups, thyroid doses were estimated for four age groups:
pre‑school children (aged 0–6), school children (aged 7–14),
adolescents (aged 15–17) and adults. For each age group, thedistributions of the numbers of people and of the collective
dose according to dose level have been assessed. The effective doses due to both external and internal irradiation havealso been calculated for the first two population groups. For
the populations of Belarus, the Russian Federation andUkraine, the distributions of the numbers of people and of
the collective dose according to the level of 137Cs deposition
density have been assessed. For the populations of most of
the other European countries, only national average thyroid
and effective doses have been estimated for the purpose ofcomparison with the doses received in Belarus, the RussianFederation and Ukraine.
1.

B35. The assessment of the thyroid doses that resulted
from the intakes of 131I was based on the results of measurements of gamma radiation performed by means of radiation
detectors placed against the neck. Within a few weeks after
the accident, approximately 350,000 of these measurements(called “direct thyroid measurements”) were made in Belarus, the Russian Federation and Ukraine [G1, L1, S31, U6,
Z1]. Usually, individuals were only measured once, so thatjust the thyroid dose rate at the time of the measurement
could be readily obtained. To calculate the thyroid dose, thevariation of the thyroid dose rate with time was assessed,
taking into account the relative rate of intake of 131I, both
before and after the direct thyroid measurement, and themetabolism of 131I in the body, which may have been affectedby the intake of stable iodine for prophylactic purposes.
B36. Following the first few weeks after the accident, during which 131I was the main contributor to the radiation exposures, doses were also delivered at much lower dose rates byradionuclides with much longer half‑lives. There was a transition period of a few months, during which radionuclides
with intermediate half‑lives, such as 95Zr, 95Nb, 103Ru, 106Ru,
141
Ce and 144Ce, variously contributed to the doses due toexternal irradiation. Since 1987, the doses received by the
populations in the contaminated areas have resulted essentially from external exposure due to 134Cs and 137Cs depositedon the ground, and from internal exposure due to 134Cs and137
Cs in foodstuffs. Both external irradiation and internal
irradiation due to these radionuclides result in relatively uniform doses to all organs and tissues of the body. These doses
resulting from the Chernobyl accident have been reported

Evacuees

B38. In its 2000 report, the Committee estimated that about
116,000 people had been evacuated in 1986 from the mostcontaminated areas of Belarus, the Russian Federation andUkraine mainly during the months of April–June, but also inAugust and September of that year. The number of evacuees
has been re‑evaluated and is now estimated to be about
115,000, consisting of about 25,000 persons from Belarus,
200 from the Russian Federation and 90,000 from Ukraine.
The areas from which people were evacuated form what iscalled the “exclusion zone”, which includes not only the
30‑km zone, which is the area within a 30‑km radius centredon the location of the Chernobyl reactor, but also highly‑­contaminated areas adjacent to the 30‑km zone and moredistant areas where high levels of 137Cs deposition density
were measured.
(a)Thyroid doses

B39. The thyroid doses received by the evacuees varied
according to their age, place of residence, consumption ­habitsand date of evacuation. For example, for the residents of­Pripyat, who were evacuated essentially within 40 h after theaccident, the population‑weighted average thyroid dose isestimated to be 370 mGy and to range from 275 mGy for
adults to about 1,000 mGy for pre‑school children [B35].
Much higher doses are estimated for the population of Belarus that was evacuated in May 1986; the values are about
1,400, 920 and 4,600 mGy for the population‑weighted average, adults and pre‑school children, respectively (table B4).

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENTFor the entire population of evacuees, the population‑weighted
average thyroid dose is estimated to be 490 mGy, while thecorresponding rounded values for the evacuees from Belarus,
the Russian Federation and Ukraine are 1,100, 440 and
330 mGy, respectively (table B4).
B40. The distribution of the Belarusian and Ukrainianevacuees according to thyroid dose interval is presented intable B5. Thyroid doses of evacuees varied from less than
0.05 Gy to more than 5 Gy; nearly 5% of the evacuatedpre‑school children received thyroid doses of more than
5 Gy. Two groups of Belarusian evacuees were considered;those evacuated in May, and those evacuated in June–­
September 1986. For those Belarusians who had been evacuated in May, the category with the largest number ofpre‑school children was that with thyroid doses greater than
5 Gy; the category with the largest number of school child­
ren was that with thyroid doses from 2 to 5 Gy; and the category with the largest numbers of adolescents and adults wasthat with thyroid doses from 0.2 to 0.5 Gy. In general, thyroid doses were lower for the Ukrainian evacuees and for the
Belarusians who were evacuated in June–September 1986.
However, the category with the largest numbers of adolescents and adults was consistently that with thyroid doses
ranging from 0.2 to 0.5 Gy.
B41. For most of the evacuees, except for those evacuatedfrom Pripyat, the dominant contributor to thyroid dose wasthe consumption of milk containing 131I, with only minor
contributions from other radionuclides and pathways. The
largest contribution made by the intake of the short‑lived
radionuclides (132I and 133I) to the thyroid dose was for thosepeople who inhaled radioiodine soon after the accident andwere then evacuated from the areas deemed contaminated;
for these people, the dominant pathway for thyroid exposure was inhalation. The analysis of the early in‑vivo counting data of Pripyat residents, who had inhaled radioiodine
over about 1.5 days before they were evacuated, showedthat the contribution of the short‑lived isotopes of iodine totheir thyroid doses was very substantial [B4]. Thus, forpeople in this group who could not or did not employ stableiodine prophylaxis (specifically, oral intake of KI tablets),the mean contribution of 132I to the thyroid dose is estimated to be about 9% and that of 133I, about 21%. In total,
about 30% of the thyroid dose due to internal exposure ofpeople who did not take stable iodine derived from theshort‑lived radioiodine. However, for persons who took KI
tablets on 26–27 April, the contribution was significantly
higher, i.e. about 40% from 132I and about 14% from 133I.
Thus, in this group, more than half of the thyroid dose due
to internal exposure originated from the short‑lived isotopes of iodine. Furthermore, in this group stable iodine
prophylaxis reduced the committed thyroid dose due to 131I
by an order of magnitude and the total thyroid dose due toradioiodine by a factor of about five. Those people who
spent most of the time indoors before being evacuated,
received, on average, a thyroid dose due to 131I that was
about half that received by people who spent most of theirtime outdoors [B4].

(b)

109

Effective doses

B42. The (arithmetic) mean effective doses due to external irradiation were estimated to have been about 30 mSv
for the Belarusian evacuees, about 25 mSv for the Russianevacuees, and about 20 mSv for the Ukrainian evacuees[U3]. These values are at least 10 times smaller than thecorresponding numerical values of thyroid doses resulting
from internal irradiation [B31]. The (arithmetic) meaneffective doses due to internal irradiation were estimated tohave been about 6 mSv for the Belarusian evacuees andabout 10 mSv for the Ukrainian evacuees [U3], and about
10 mSv for the Russian evacuees [B28]. These values are atleast half of the corresponding effective doses due to external irradiation. Estimates of the average effective doses tothe evacuees from Belarus, the Russian Federation andUkraine are summarized in table B6.
(c)Collective doses

B43. The distribution of the collective dose to the thyroidwith respect to ranges of individual dose is presented intable B7. The largest contributions to the collective doses tothe thyroid were from the category of doses greater than
5 Gy for the Belarusian evacuees and in the dose intervalfrom 0.2 to 0.5 Gy for the Ukrainian evacuees. For the entire
population of evacuees, the greatest contribution to the collective dose to the thyroid was from those who received
doses in the interval from 0.2 to 0.5 Gy. The total collective
dose to the thyroid for the evacuees from the two countries is
estimated to have been about 60,000 man Gy.
B44. A summary of the estimated collective effective doses
to populations of areas evacuated in 1986 is presented intable B6. The total collective effective dose is estimated to
be about 3,600 man Sv. Ukraine represented the largest component of the collective effective dose, mainly because it had
the largest number of evacuees.
2. Inhabitants of Belarus, the Russian Federation and Ukraine
B45. In its 2000 report [U3], the Committee focused its
attention on the approximately five million residents of thecontaminated areas, defined as those areas with a 137Cs deposition density greater than 37 kBq/m2. In this appendix, thyroid and effective doses have been estimated for the entire
populations of Belarus and Ukraine, as well as for the population of the regions of the Russian Federation deemed
affected;1 altogether, this represents a population of about
one hundred million persons. In addition, special attention
has been paid to the estimation of the thyroid doses received
by the subjects of ongoing epidemiological studies.

1
These are the 19 regions of the Russian Federation in which there are someareas deemed “contaminated” (i.e. with deposition densities greater than
37 kBq/m2).

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UNSCEAR 2008 REPORT: VOLUME II

Thyroid doses

B48. There are, therefore, different types of thyroid dose
estimates, each having different quality and associated levelsof uncertainty:

B46. As was the case for the evacuees, the dominant contributor to the thyroid doses received by the inhabitants ofBelarus, the Russian Federation and Ukraine was the consumption of fresh milk containing 131I. As previously indicated, the assessment of thyroid doses resulting from theintake of 131I was based on the results of direct thyroid measurements performed within a few weeks of the accident
using radiation detectors placed against the neck. The developments in thyroid dosimetry since the UNSCEAR 2000
Report [U3] have focused on the reconstruction of doses foruse in various epidemiological studies that have either been
extended or initiated since that report.

(a) Dose estimates for specific individuals (called “individual doses”) are needed for analytical epidemiological studies. The most reliable individual thyroid doses are those thatderived from direct thyroid measurements on individuals andthat make use of personal information on residence history anddietary habits obtained during interviews. Environmental andmetabolic models, simulating the behaviour of 131I in the environment and in man, are also necessary to estimate the relative
variation with time of the content of 131I in the thyroid, both
before and after the direct thyroid measurement. The thyroid
dose estimates obtained in this manner for the approximately
25,000 cohort members of two epidemiological studies conducted in Belarus and Ukraine are presented in table B8; thedistributions of the thyroid doses are similar in the two countries, with median thyroid doses of about 0.5 Gy and 0.3 Gy,
respectively (table B9). A substantial proportion of the studied
populations received doses in excess of 1 Gy (table B8).

B47. Thyroid doses were estimated for those individuals
who were not directly monitored but who lived in areas where
many persons had been monitored. These were estimated on
the basis of the statistical distribution of the thyroid doses
reconstructed for those people with direct measurements,
together with knowledge of the dietary habits of the individuals under consideration. In addition, thyroid doses werereconstructed for people who lived in areas where very few or
no direct thyroid measurements were made within a few
weeks of the accident. This was conducted using relationships established between the available data on 131I or 137Cs
deposition, exposure rates or concentrations of 131I in milk
and the thyroid doses [U3].

(b) Less reliable individual thyroid dose estimates wereobtained for the case‑control studies conducted, in which no
direct thyroid measurements had been made on a large
number of individuals. The thyroid doses to these individuals were assessed by means of models. Personal informationon the residential history and dietary habits of the subjects
was obtained during interviews [G2, S32].

Figure B-I. Spatial distribution of the estimated thyroid doses to children and adolescents living at the time of the accident in
the most affected regions of Belarus, the Russian Federation and Ukraine [K8, L4, R6, Z4]
District average
thyroid doses (Gy)<0.01
0.01–0.03
0.03–0.15

Kaluga

0.15–0.65
>0.65

Minsk

Tula

State border
Oblast borderRussian Federation

Mogilev

Oblast centre

Belarus

Bryansk

Brest

Gomel

Chernigov
Chernobyl NPP
Rovno

UkraineKiyev
Zhytomyr

OrelANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT(c) In geographical correlation (often termed “ecological”) studies, it is sufficient to have doses to unspecified individuals (called “group doses”), who are representative of theaverage dose received by the members of the group of a given
age living in a specified area (settlement, district, or part of anoblast). Average thyroid doses to individuals in particular age
groups in settlements, which have been obtained from a sufficient number of measurements of the 131I content in thehuman thyroid have, in general, the lowest uncertainty. This isbecause the individual dose uncertainties due to the unknown
thyroid mass of the individual contribute less to the average
dose uncertainty [J4, L8]. For example, in the Russian Federation, an official method for reconstructing the average thyroid
dose for a settlement has been adopted [B3]. Using thismethod, average thyroid doses were calculated for six age
groups in more than 3,500 settlements of the four most contaminated regions of the Russian Federation: Bryansk, Tula,
Orel and Kaluga. They were published in a reference book of
average thyroid doses [B31] and are used now for geographical correlation (ecological) epidemiological studies in the
Russian Federation. A similar catalogue of thyroid dose estimates is also available for the exposed populations of Ukraine.

111

Estimated average and collective doses to the thyroid for different population groups in Belarus, the Russian Federationand Ukraine (for the entire countries and for the contaminatedareas) are presented in tables B10, B11 and B12, as well as in
the form of a map, see figure B‑I.
B49. There are differences in the methods used to estimate
the thyroid doses in the three countries, but the concepts used
are similar. The methods are basically of two types:
semi‑empirical; and environmental‑transfer based. It would
be very difficult to merge them in order to develop a common
method. However, the results of limited intercomparison studies conducted by the International Agency for Research on
Cancer (IARC) show that the methods used give results thatare in reasonably good agreement, except for areas with low
deposition density [B35]. A comparison of the estimates ofmean doses in settlements, in which large numbers of direct
measurements of the 131I activity in the human thyroid were
performed in May/June 1986, showed a high consistency of
dosimetric results in Belarus and Ukraine. Dose estimates for
the Belarusian and Ukrainian settlements close to the borderof the two countries were also very similar (figure B‑II) [J4].

Figure B-II. Average thyroid dose (Gy) of the birth cohort 1968-85 in 608 Ukrainian and 426 Belarusian settlements for whichmore than 10 measurements of the 131I activity in human thyroids were performed in May–June 1986 [J4]Minsk

DISTANCE NORTH OF SITE
(km)

200

RussianFederation
3-10
1-3
0.3-1
0.1-0.3
0.03-0.1
0.01-0.03

Gomel

100

Belarus0
Chernihiv

Ukraine−100

Kyiv
Zhytomyr
−150

−100

−50

0

DISTANCE EAST OF SITE
(km)

50

100

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UNSCEAR 2008 REPORT: VOLUME II

B50. Uncertainties associated with the 131I thyroid dose
estimates. Extensive efforts have been made to evaluate theuncertainties associated with the estimates of individual andgroup thyroid doses used in epidemiological studies. As an
example, thyroid dose estimates were made in the framework of cohort studies conducted in Belarus and Ukraine
jointly with the US National Cancer Institute. The distributions of the uncertainties in dose estimates, expressed asgeometric standard deviations, vary from one individual toanother, and range from 1.6 to more than 5.0 [L3] for all
those dose estimates based on direct thyroid measurements.
The medians of the distribution of the geometric standard
deviations were 1.7 for the Ukrainian subjects and 2.1 for the
Belarusian subjects. In another study [J4], the uncertainty
distribution of average age‑specific thyroid dose estimatesfor Belarusian settlements with more than 10 measurementsof the 131I activity in the human thyroid was estimated to­correspond to a geometric standard deviation of 1.6.
B51. A sensitivity analysis has been conducted of the contributions that various parameter uncertainties make to theuncertainty in the dose estimates. The results show that theuncertainties in the thyroid mass and those related to thedetermination of the content of 131I in the thyroid at the timeof the direct thyroid measurement are most significant.
Because the uncertainties in the direct thyroid measurements
were greater for Belarus than for Ukraine, the uncertainties
in the thyroid dose estimates are, on average, greater for the
Belarusian subjects than for the Ukrainian subjects. Larger
uncertainties would be expected to occur for subjects ofcase‑control studies, for which doses were reconstructed bymeans of models.
B52. Reasonably accurate assessments of the uncertainties
in the thyroid dose estimates are important as they can beused to identify those parameters that give rise to the largest
uncertainties, and thence prompt research aimed at reducing
them. In addition, the values of any risk coefficients that arederived from the epidemiological studies may be strongly
influenced by the magnitude of the dosimetric uncertainties
and by the structure of the measurement errors.
B53. Influence of dietary iodine deficiency. Publishedresults [Z2] indicate that the thyroid dose estimates based on
assessing radioiodine intake are roughly independent of thelevel of stable iodine intake in the diet, because the variationin radioiodine uptake into the thyroid among individuals iscompensated to some degree by the variation in the thyroid
mass. For that reason, the models for estimating thyroid dosethat have been applied so far use the reference values recommended by the ICRP. However, there are regions of Belarus,
the Russian Federation and Ukraine with endemic iodine
deficiency, for which it is expected that the uptake of radioiodine into the thyroid would have been exacerbated. Unpublished recent results [L4] seem to show that the thyroid dose
per unit intake of radioiodine may indeed have been higher
for people with lower levels of stable iodine intake. If this isconfirmed, it will be necessary to re‑evaluate the thyroid
dose estimates taking into account the dietary level of stableiodine intake. In any case, as indicated above, it is importantto adjust the thyroid mass according to the level of stableiodine intake in the diet when estimating thyroid doses fromdirect thyroid measurements.
B54. Role of iodine prophylaxis. In order to protect efficiently against doses due to 131I intake, iodine prophylaxis
needs to be conducted before or immediately after exposure
to 131I [I2]. Unfortunately, this does not seem to have been
the case for large segments of the affected population. Iodine
prophylaxis was only applied in a satisfactory manner for(a) the residents of Pripyat city by local medical experts who
were aware of the risks resulting from exposure to 131I, and(b) the recovery operation workers, who were offered stableiodine tablets on their arrival at the Chernobyl site during thefirst few weeks after the accident [U3]. Sixty to seventy­percent of Pripyat residents took KI pills within 1.5 days
­following the accident [B4, G8].
B55. Estimation of doses received in utero. The thyroid
doses received in utero vary substantially with the stage ofpregnancy, but are in any case smaller than the doses received
by infants. The in‑utero doses have so far been estimatedusing a model published by Johnson in 1982 [J3], which was
based on sparse human data. Recently, Berkovski [B6] published a model that makes use of animal as well as humandata. This model has been adopted by ICRP [I4] and leads tothyroid dose estimates that are larger than those obtainedusing Johnson’s model for foetuses exposed during the last
two months of pregnancy.
B56. Thyroid doses due to other radionuclides and pathways. As previously indicated, usually minor contributions to
the thyroid dose include: (a) the dose due to intakes ofshort‑lived radioiodine (132I, 133I and 135I) and of short‑lived
radiotellurium (131mTe and 132Te); (b) the dose due to external
irradiation resulting from the deposition of radionuclides on
the ground and other materials; and (c) the dose due to internal
irradiation resulting from intakes of long‑lived radionuclides,
such as 134Cs and 137Cs.
B57. The contributions of these radionuclides and exposure pathways to the thyroid doses received by the subjectsof an epidemiological study of children from Belarus [A1]have been evaluated and presented in two publications [G2,
M16]. Short‑lived radionuclides, in general, played a minor
role for the populations that were not evacuated within a few
days after the accident. For those populations, the contribution of the short‑lived radionuclides was estimated to havebeen up to 20% of the 131I thyroid dose, if the radionuclide
intake occurred only via inhalation and, of the order of a few
percent, if contaminated foodstuffs were consumed [G2].
B58. External exposure of the population after the Chernobyl
accident was mainly due to deposition of the gamma‑­emitting
radionuclides 132Te, 131/132I, 140Ba, 140La, 95Zr, 95Nb, 99Mo,
103/106
Ru, 141/144Ce and 134/136/137Cs. Because 137Cs was the radionuclide most commonly measured throughout the contaminated areas, deposition densities of the other radionuclides

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

have generally been related to that for 137Cs. The external doses
due to 137Cs and the other relatively long‑lived radionuclides
are delivered at low dose rate and accumulate only slowly withtime because of the long radioactive half‑lives (about 30 years
for 137Cs). The contribution of external exposure to the thyroid
dose of the study subjects was generally larger and more variable than that of short‑lived radioiodine, with median andmean contributions of 1.2% and 1.8% of the total thyroid
doses, respectively [M16].
B59. After the decay of 131I within a few weeks after theaccident, ingestion of radiocaesium contained in locally produced foodstuffs became the main pathway of internal exposure. Thyroid doses due to ingestion of radiocaesium (134Cs
and 137Cs) depended in the first year after the accident on theexternal contamination of the plants and later on the level ofroot uptake and consequently on the type of soil on which thedeposition occurred. Analysis showed that ingestion of thelong‑lived radionuclides, primarily radiocaesium, typicallycontributed less than 3% of the thyroid dose received by thestudy subjects. The median and mean fractional contributions
were 0.76% and 0.95%, respectively [M16].
(b)

Other organ doses and effective doses

B60. The principal contributors to the doses to organs otherthan the thyroid, and to effective doses were 137Cs and, to aminor degree, 134Cs in the environment. Both external andinternal irradiation due to 134Cs and 137Cs result in relatively
uniform doses to all organs and tissues of the body. By convention, the effective doses due to internal irradiation thatwere calculated in the framework of studies concerning theChernobyl accident do not include the contribution from thethyroid doses. Consequently, the estimated effective doses,
expressed in millisieverts (mSv), are to a first approximation
numerically equal to the doses to any organ (other than the
thyroid) of the body, expressed in milligray (mGy).
B61. Methodologies for the estimation of dose havebeen prepared in Belarus, the Russian Federation andUkraine, and applied for the populations of the contaminated areas (e.g. for the Russian Federation, see references [B2, B30]). The doses due to external irradiation
were based on (a) the large number of measurements of
exposure rates and of radionuclide (especially 137Cs) concentrations in soil that were made in the three countries,and (b) population surveys of indoor and outdoor occupancy as a function of age, season, occupation and type ofbuilding [I21, U3]. The models used for radiation transport took into account the environmental behaviour of thedeposited activity in urban and in rural areas [E6, G3, G4,
L2, U3, U7]. The estimates of doses due to internal irradiation, which mainly resulted from ingestion, were basedon whole‑body measurements of 134Cs and 137Cs, whenavailable (see, for example, references [H14, H15]), butmore often on the estimation of dietary intake from measured concentrations of 134Cs and 137Cs in foodstuffs andstandard assumptions about ­consumption [I21, U3].

113

B62. Catalogues of estimated average doses to those in all
settlements located in the contaminated areas of the RussianFederation and Ukraine are available [B28, B36, M5]. Effective doses due to internal and external irradiation have been
estimated for the approximately one hundred million residents of Belarus, the Russian Federation and Ukraine (tables
B13, B14 and B15). The average effective doses due to 134Cs
and 137Cs that were received during the first twenty years
after the accident by the residents of contaminated areas are
estimated to be about 0.9 mSv due to external irradiation and
0.4 mSv due to internal irradiation. Because doses have beendelivered at a varying rate since 1986, and will continue tobe delivered over the next several decades, it is of interest tocompare the doses in relative terms over different time periods. For the populations of the contaminated areas, it wasestimated [I21] that, with regard to external irradiation, typically 25% of the lifetime (taken to correspond to the period
1986–2056) effective dose will have been due to the radiation exposure during 1986; corresponding values for 1987–
1995, 1996–2005, and 2006–2056 are 40%, 15% and 20%,
respectively. In comparison to external irradiation, more of
the dose due to internal irradiation was delivered in 1986 andless remains to be delivered in the future. Consequently,
more than 80% of the internal lifetime dose was delivered by
2005, and less than 20% remains to be delivered, at a low
rate, over the next 50 years.
B63. The dosimetric information needed for analytical epidemiological studies consists of individual absorbed dosesin the tissue of interest for all subjects, as well as estimatesof the associated uncertainty. The method currently used toderive the individual dose estimates consists in modifying
the average dose estimates provided in the catalogues, using
information obtained by means of personal interviews. For
external irradiation, the information required is the residence
history, together with the type of buildings where the subject
worked and resided. For internal irradiation, information on
foodstuffs (type, origin and consumption rates) is needed. Inorder to assess or reduce the uncertainties in the individual
dose estimates, validation studies have been conducted [G3]using personal dosimeters for external irradiation and dataon whole‑body content or radionuclide concentrations infoodstuffs (usually milk) for internal irradiation [B12, B32].
Routine personal thermoluminescent dosimeters are able toprovide only the value of the dose that was accumulated during the relatively short time when the dosimeter was worn.
Validation of the cumulated dose for the whole period—
starting from the time of the accident until the time of interest for the epidemiological study—can be performed
directly, using Electron paramagnetic Resonance (EPR) on
samples of human tooth enamel [I36, S28] or indirectly,
using Luminescence Retrospective Dosimetry (LRD) on
samples of quartz inclusions in bricks [B26, B27]. It should
be noted, however, that the uncertainty of EPR estimates ofabsorbed doses below 100 mGy is too large to allow a validation of the other estimates of individual doses. Further,since LRD may only be used to validate absorbed doses inenvironmental media, it is of limited value in the validationof internal dose estimates.

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UNSCEAR 2008 REPORT: VOLUME II

Collective doses

B64. Estimates for the collective dose to the thyroid arepresented for four age categories and the total population intable B10 according to the region/oblast or city of residence
and for contaminated areas of the three countries (all of
Belarus and Ukraine and 19 regions of the Russian Federation). In table B12, the estimates of the collective dose to thethyroid are presented according to 8 individual dose intervals, ranging from less than 0.05 Gy to more than 5 Gy; thenumber of people in each age category and dose interval isgiven in table B11. Similarly disaggregated information on
the estimated collective effective doses is provided in tables
B13, B14 and B15. In table B13, the estimated collective
effective doses for 1986–2005 is given for each region andlarge city and for five intervals of 137Cs deposition density,
ranging from less than 37 to more than 1,480 kBq/m2. In
table B15, the estimated collective effective doses are presented separately for the dose committed in 1986 and for thedose committed during 1986–2005 for each of the 8 doseintervals. The numbers of people in each dose category areprovided in table B14.
B65. At the regional level, the highest estimated collective
dose to the thyroid was in the Gomel oblast, where about
320,000 man Gy were distributed over a population of
1.6 million, corresponding to an average thyroid dose ofabout 200 mGy. However, at the country level, the collective
dose to the thyroid is estimated to have been highest for
Ukraine, with 960,000 man Gy distributed over a populationof 51 million, even though the average thyroid dose estimate
for Ukraine was about three times lower than for Belarus.
Altogether, the collective dose to the thyroid received by the
98 million people considered in the three countries is estimated to have been 1,630,000 man Gy; most of the people
received less than 0.05 Gy, and only 1% received doses
greater than 0.2 Gy. Only 40% of the collective thyroid dose
was received by residents of contaminated areas; the remaining 60% was received by inhabitants of the areas in the three
countries where 137Cs deposition density was less than
37 kBq/m2. As expected, the average thyroid dose generally
decreased with age: the dose to pre‑school children is estimated to have been 2 to 4 times greater than the average doseto the population; and 4% of the pre‑school children are estimated to have received thyroid doses greater than 0.2 Gy and0.005% received doses greater than 5 Gy (table B11).
B66. In the UNSCEAR 1988 Report [U7], the Committee
estimated a dose to the thyroid, averaged over a population of
the former Soviet Union of 279.1 million, of 5 mGy for
infants and 1.4 mGy for adults. These 1988 estimates correspond to a collective dose to the thyroid of about
500,000 man Gy. Because the 1988 data were provided to theCommittee with little explanation, it is not feasible to investigate the reasons why the two estimates differ by a factor of
about 3. However, it can be reasonably assumed that the populations considered to be “affected” are the same in both the
UNSCEAR 1988 Report and in this appendix. Given the factthat comprehensive efforts to reconstruct the thyroid doses inBelarus, the Russian Federation and Ukraine had not been
undertaken at the time of preparation of the UNSCEAR 1988
Report, the two estimates of collective doses to the thyroid
can nevertheless be considered to be reasonably close.
B67. The collective effective dose received over the period
1986–2005 by the 98 million people considered in thethree countries is estimated to have amounted to125,000 man Sv; about half of this collective dose was topeople who lived in areas with 137Cs deposition densities ofless than 37 kBq/m2. The corresponding average effective
dose for 1986–2005 is estimated to have been 1.25 mSv,
which is about 3 times greater than the estimate of the average effective dose in 1986. A factor of about 3 is also
observed for both the external and internal dose componentsof the total dose. Regarding the estimate for the effective
dose received over the period 1986–2005, about 70% of the
population received doses in the <1 mSv dose interval, and
20% received doses in the 1–2 mSv dose interval. The collective effective dose to those who received doses in the<1 mSv, 1–2 mSv and 2–5 mSv dose intervals is estimated to
be about 20% of the total. As was the case for the thyroid
doses, the estimates of the average effective dose are greaterfor Belarus than for Ukraine or the Russian Federation, but
the collective effective dose estimate is greater for Ukraine
than for the Russian Federation (19 regions deemed affected)
and Belarus, principally because of the larger Ukrainian
population.
B68. The collective effective dose of 125,000 man Sv tothe inhabitants of Belarus, Ukraine and the Russian Federation (19 regions deemed affected) for the period 1986–2005
can be compared with the estimate previously published by
the Committee in the UNSCEAR 1988 Report [U7]. The
Committee had estimated a value of 0.82 mSv for the effective dose equivalent commitment averaged over a populationof the former Soviet Union of 279.1 million, which would
correspond to a collective effective dose equivalent commitment of about 230,000 man Sv. Assuming that (1) the populations deemed affected are the same, and (2) the effective
dose during 1986–2005 represents 80% of the effective dose
commitment [I21], the two estimates of collective effective
dose differ only by 50%. This is a remarkably close agreement, as most of the effective dose commitment in the
UNSCEAR 1988 Report had to be predicted using environmental transfer models. Furthermore, while the original estimate took account of countermeasures that had been imposed
immediately, there was no attempt to consider the effects ofpossible long‑term countermeasures.
3.

Inhabitants of distant countries

B69. In the UNSCEAR 1988 Report [U7], the Committee
estimated thyroid and effective doses for most countries of
the northern hemisphere in part based on the predictions ofmodels of future environmental transfer. Since that time,
however, numerous measurements have been made of radionuclide levels in the environment, in foodstuffs and inANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

humans, including a comprehensive monitoring programme
undertaken in order to prepare an Atlas of 137Cs deposition in
Europe after the Chernobyl accident [E5]. Drozdovitch et al.
[D13] have recently re‑evaluated the deposition density­values for the most important radionuclides as well as thedose estimates for the populations of all European countries(excluding Turkey, Andorra, San Marino and the Republics
in the Caucasus).
B70. The estimates of average 137Cs deposition densities inthe various countries resulting from the Chernobyl accident
are presented in table B16. Subsequent to the information
presented in the UNSCEAR 1988 Report [U7] or reported in
the Atlas prepared for the European Commission [E5],updated data on the deposition densities of 137Cs have beenobtained for Belarus [S29], Bulgaria [A9], Estonia [R14],
the Russian Federation [R13], Serbia and Montenegro [K27]and Ukraine [N12]. The data for Belarus, the Russian Federation and Ukraine are included for the purpose of consistency with the corresponding values for other European
countries. Average levels of 137Cs deposition density greaterthan 50 kBq/m2 are estimated only for some regions of Belarus, the Russian Federation and Ukraine; average levels in
the range from 10 to 20 kBq/m2 are estimated for Austria,
Finland, Liechtenstein, Moldova and Slovenia. Estimates forthe average 137Cs deposition densities are lower than 5 kBq/m2
for most other countries. The 137Cs deposition densities presented in table B16 do not include pre‑existing levels of 137Cs
deposition from the fallout from the atmospheric testing of
nuclear weapons, levels of which are currently in the rangeof 1 to 3 kBq/m2 in various parts of Europe [E5].
B71. Information on the deposition densities of otherradio­nuclides (95Zr, 103Ru, 106Ru, 131I, 132Te, 134Cs and 140Ba) ispresented in table B16 in terms of the ratios of deposition
density of the radionuclide to that of 137Cs at the time ofdepo­sition. Most of the 132Te values were derived from themeasured concentrations of 132Te and 137Cs in air at groundlevel, based broadly on the assumption that the activity ratio
in the deposited material was equal to the activity ratio in air.
In comparison to the information presented in the UNSCEAR
1988 Report [U7], additional or revised data were obtainedfor Austria [B34], Belarus [M16], Bulgaria [A9], Croatia[I35], Czechoslovakia [B37], Finland [A10], Greece [K26],
Lithuania [N19], the Russian Federation [B30] and Ukraine[L2]. The activity ratios, which were averaged over large
regions or countries, are, as expected, constant for 134Cs, vary
within a small range for 103Ru and 106Ru, but show a large
degree of variability for 95Zr, 131I, 132Te and 140Ba (table B16).
(a)Thyroid doses

B72. Drozdovitch et al. [D13] estimated the average
age‑dependent thyroid doses for the European countries
considered,2 using, whenever available, information from2
The values quoted in reference [D13] have not necessarily been endorsedby the individual countries concerned.

115

the direct thyroid measurements or on 131I concentrations inmilk [A9, A10, B37, H16, N19, U7]. Estimates of the thyroid doses incurred by pre‑school children, school children,
adolescents and adults are presented in table B17, while­figure B‑III illustrates in the form of a map the thyroid dose
estimates for pre‑school children, aged 0–6 years. In figure
B‑III, the estimates for Belarus, the Russian Federation andUkraine are those presented earlier in this appendix, whereas
the estimates for all other countries were derived from­Drozdovitch et al. [D13]. The thyroid dose estimates reflect,
to a first approximation, the 137Cs deposition densities, butwere also influenced by a number of factors, including the131
I to 137Cs ratio in the deposited activities, the start of thegrazing season, the human consumption rate of fresh cow’s
milk, and the application of countermeasures. In general, thedominant component of the thyroid dose was due to theingestion of 131I in milk and fresh vegetables. However, theinhalation pathway played a substantial role for those countries where countermeasures had been applied shortly after
the accident to reduce the ingestion of radionuclides inlocally produced foodstuffs, as well as for the countries ofnorthern Europe [D13].
B73. The methodology for reconstructing the thyroid doses
to inhabitants of distant European countries was based on theassessment of radioiodine intakes via inhalation and ingestion. This is fundamentally different from the methodology
for thyroid dose reconstruction applied in Belarus, the­Russian Federation and Ukraine, which was rather based on
the direct measurements of 131I in human thyroids performed
in May–June 1986 and radioecological patterns. The comparison of the estimates of internal dose based on intake
assessment methodology with the methodology based on
measurements on human shows that the former are usuallysystematically higher and more uncertain than the latter [I46,
U7]. Furthermore, dose assessments based on intake via
ingestion [D13, U7] do not usually account for the contribution from foods imported from regions of the world thatwere not affected by the Chernobyl accident, e.g. from othercontinents. The likely overestimation of the thyroid doses toinhabitants of distant European countries associated withthose factors needs to be taken into account in any risk
assessment process.
B74. Poland was the only country that implemented iodine
prophylaxis for almost all its children at the time of the accident [K7, N7]. The presence of radionuclides in air and theincrease in the background gamma dose rate were registeredduring the night of 27 April, and 131I concentrations in milkreached 500 Bq/L on 29–30 April [K7]. A governmental
commission decided to undertake compulsory stable iodine
prophylaxis for the population group most at risk—11 ­million
children and adolescents up to 16 years old—and to allow
voluntary prophylaxis for other people. Altogether, about
18 million Poles were given single doses of KI starting on
29 April. According to assessments made by Polish authors, asingle dose of KI taken on 29 April would have reduced thethyroid dose by 40%, whereas the same dose of KI taken
on 30 April would have reduced it by about 25% [N7].

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UNSCEAR 2008 REPORT: VOLUME II

Figure B-III. Spatial distribution of the average thyroid doses to the populations of pre‑school children in Europe at the timeof the accident [based on D13]
The radiation trefoil symbol denotes the location of the Chernobyl nuclear power plant. Names of countries are abbreviated according to ISO.
For Belarus, the Russian Federation and Ukraine, the spatial distribution of doses is also given by oblast. The oblasts are abbreviated as follows:
Belarus: Brest, BY-br; Gomel, BY-go; Grodno, BY-gr; Minsk, BY-mi; Mogilev, BY-mo; Vitebsk, BY-vt;
The Russian Federation: Bryansk, RU-br; Kaluga, RU-ka; Orel, RU-or; Tula, RU-tu;
Ukraine: Chernihiv, UA-ch; Kyiv, UA-ky; Rivno, UA-ri; Zhytomir, UA-zh.

However, in another study involving direct 131I measurements on the thyroids of 578 Warsaw citizens [K7], no statistically confirmed effect of stable iodine prophylaxis wasobserved. The explanation given was that in spite of local
food bans, people still continued to consume contaminatedfoods. The overall reduction in dose to the thyroid when KI
was taken on 28 April, 30 April and 1 May was estimatedby the author as 28%, 25% and 10%, respectively [K7].
Because of the uncertainties involved, the effect of stableiodine prophylaxis was not taken into account in the current
European dose estimates.
B75. As shown in figure B‑III, the average thyroid doses topre‑school children are estimated to be greater than 100 mGy

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

for at least one oblast in each of Belarus, the Russian Federation and Ukraine. In the other European countries, the average thyroid doses to pre‑school children are estimated to beless than 20 mGy. Thyroid doses from 10 to 20 mGy were
mostly observed in the southern part of Europe, where thegrazing season started earlier than in the northern part.
(b)

Effective doses

B76. Effective doses due to external and internal irradiation for 1986–2005 have been estimated for the populationsof European countries using standard procedures [D13].
Doses due to external irradiation were based on the numerous measurements of deposition density of 137Cs and othergamma emitters, using a model of radiation transport thattook into account the decreasing dose rate in outdoor air
with time due to radioactive decay and the migration of thedeposited activity to deeper layers of soil [G4]. The effective doses delivered in 1986 were then derived from the outdoor dose rates in air using “behavioural” factors of 0.36
and 0.18 for the rural and urban populations, respectively.
For the estimation of doses delivered in the following years,
the values of the behavioural factors were taken to be 0.31
and 0.16 for the rural and urban populations, respectively[G3, U3, U7].
B77. The effective doses due to internal irradiation were
estimated separately for the inhalation and the ingestion
pathways. Consumption of milk and milk products, leafy
vegetables, grain products, other fruits and vegetables, andmeat was considered for the ingestion pathway. For mostcountries, the values of the time‑integrated 137Cs concentrations in foodstuffs for 1986 and of the consumption rates

were taken from the UNSCEAR 1988 Report [U7]. The variation with time of the dietary intake of 137Cs, normalized to
the 1986 values, was found to be similar in a number ofcountries (figure B‑IV). It was assessed using reduction factors of 0.65 and 0.25 for 1987 and 1988, respectively; forlater years, exponential decreases with half‑times of 1.7 years
for 1989–1993 and 7.3 years for 1993–2005 were used
[D13]. In addition, local experts from Bulgaria, the Czech
Republic, Finland, Lithuania and Switzerland provided dose
estimates for their respective countries [D13].
B78. As was the case for the estimates of the thyroid doses,internal effective doses for most of the distant European
countries were estimated using models of the intake radio­
nuclides in foodstuffs. However, internal doses could be substantially overestimated by this approach as shown bywhole‑body counting, which enables a direct assessment of
the internal doses from incorporated radiocaesium to bemade [I46, U7]. A detailed comparison of the two methodsof dose assessment was performed in a contaminated area in
the Russian Federation, revealing that internal doses assessedusing intake modelling overestimated actual intakes by afactor of two to three [B2, I46]. As indicated in the
UNSCEAR 1988 Report [U7] (paragraphs 88 and 142 ofannex D), a possible explanation was that the results of thefood sampling used in the models might have been biased
towards areas of high deposition. In addition, such models
often do not take account of the contribution to diet of foodstuffs imported from regions of the world that were notaffected by the Chernobyl accident, or of culinary losses ofradionuclides during the preparation of meals [D13, U7].
Nevertheless, this overestimation of effective internal doses
to inhabitants of distant European countries should be taken
into account in any risk assessment.

Figure B-IV. Time-dependence of dietary intake of 137Cs activity
Based on measurements in Austria [M19, S25], Belarus [M16], the Czech Republic [M10], Finland [M18], and Norway [T10]1
RELATIVE INTAKE OF 137Cs WITH DIET

0.9
0.8
0.7
Austria
Belarus
Czech Republic
Finland
Norway

0.6
0.5
0.4
0.3
0.2
0.1
0
1987

1989

1991

1993

1995

YEAR

117

1997

1999

2001

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UNSCEAR 2008 REPORT: VOLUME II

B79. The total effective doses estimated for the period
1986–2005 for most European countries are presented in figure B‑V and in table B17. The estimates for Belarus, the Russian Federation and Ukraine are those previously presented inthis appendix, whereas the estimates for all other countries
were derived from Drozdovitch et al. [D13]. The effective
doses (expressed in millisieverts, mSv) were generally muchsmaller numerically than the estimated absorbed doses to thethyroid of pre‑school children (expressed in milligray, mGy).

The ratios of the thyroid doses to the effective doses topre‑school children during 1986–2005 were about 50 inBelarus, the Russian Federation and Ukraine, about 10 for
those in central and western Europe, and about 2 or less for
those in Scandinavia. This variation was due in part to thecountermeasures applied in Belarus, the Russian Federationand Ukraine to reduce the effective doses and, in the case of
the Scandinavian countries, to the low thyroid doses owing to
the late start of the grazing season.

Figure B-V. Spatial distribution of the effective doses to European populations for 1986–2005 [based on reference D13]
Abbreviations are the same as in figure B-III.

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

(c)Collective doses

B80. On the basis of the estimated thyroid and effective
doses provided by Drozdovitch et al. [D13] and using the
popu­lation data for 1986 (some 500 million people), the collective thyroid and effective doses, for 1986–2005, are estimated to be 660,000 man Gy and 130,000 man Sv, respectively,
for the population of Europe (excluding Belarus, the RussianFederation, Ukraine, the countries of the Caucasus, Turkey,
Andorra and San Marino) (table B18). The per caput doses forthat same population were 1.3 mGy for the thyroid dose and
0.3 mSv for the effective dose (excluding the contribution
from the thyroid dose) during 1986–2005.
B81. The collective thyroid and effective doses of 660,000
man Gy and 130,000 man Sv, respectively, for the populations of the distant countries, which are presented intable B19 can be compared with corresponding estimates of
760,000 man Gy and 260,000 man Sv that can be derived
from information provided in the UNSCEAR 1988 Report[U7]. The two estimates of collective thyroid dose are very

119

close because the information presented in the 1988 report
was only updated for a few countries, because the thyroid
doses had already been delivered by 1988, and it was felt thatfor most countries there was no need to re-evaluate them. In
contrast, the present estimate for collective effective dose isapproximately half that of the 1988 estimate, which is similar to the factor of 1.5 lower obtained for the populations ofBelarus, Ukraine, and for the 19 regions of the Russian­Federation deemed affected. As previously indicated, the1988 assessment was actually completed in 1987, when theamount of data available varied greatly from country tocountry and most of the effective dose commitment had to bepredicted using models for future environmental transfers.
Also, because much of the then available data had been collected for radiation protection purposes, it is recognized thata bias existed in those data, which would have led to an overestimate of the actual exposures. Furthermore, while theoriginal estimate of the UNSCEAR 1988 Report tookaccount of countermeasures that had been imposed immediately, there was no attempt to consider the effects of possible
long-term countermeasures.

III. Summary
B82. In this appendix, in comparison with the UNSCEAR
2000 Report [U3]: (a) updated dose estimates are provided
for the now larger number of recovery operation workers in
Belarus, the Russian Federation, and Ukraine (510,000
instead of 380,000 in reference [U3]), and new information
is presented giving the dose estimates for recovery operation workers in Estonia, Latvia and Lithuania; (b) updated
thyroid dose estimates are provided for the Belarusian andUkrainian evacuees, and new information is presented for
the Russian evacuees; (c) the estimation of thyroid andeffective doses for the inhabitants of Belarus, the RussianFederation and Ukraine has been expanded from five ­million
to one hundred million people; and (d) thyroid and effective
doses have been re‑evaluated for the inhabitants of mostother European countries.
B83. The updated average individual and collective doses
estimated to have been received by the population groups inEurope exposed as a result of the Chernobyl accident aresummarized in table B19. As far as possible, the dosimetric
information is presented in a uniform manner for the evacuees, for the inhabitants of Belarus, the Russian Federationand Ukraine, and for the inhabitants of all other European
countries (excluding those in Caucasus, Turkey, Andorra andSan Marino). In addition, special attention has been given to
the methods used to estimate individual doses for the ­purposeof epidemiological studies.
B84. The average effective dose received by the recovery
operation workers, mainly due to external irradiation,
between 1986 and 1990, was about 120 mSv. This is muchhigher than the average effective doses, due to both external
and internal exposures, received by members of the generalpublic during 1986–2005, that is, about 30 mSv for the­evacuees, 1 mSv for the residents of the former Soviet Union,
and 0.3 mSv for the populations of the rest of Europe. The
recorded worker doses varied from less than 10 mGy to morethan 1,000 mGy, but about 85% of the workers with recorded
doses received doses in the interval from 20 mGy to
500 mGy.
B85. The average thyroid dose, due mainly to intakes ofmilk containing 131I over the first few weeks following theaccident, were highest for the evacuees—estimated to beabout 500 mGy. It was much greater than the average thyroid
doses received by the residents of the former Soviet Union
who were not evacuated (about 20 mGy), those residing in
the contaminated areas (about 100 mGy), and the residents
of most other European countries (about 1 mGy). There was
not enough information to make a reliable estimate of theaverage thyroid dose to the recovery operation workers.
B86. The distributions of the numbers of individuals inparticular intervals of dose to the thyroid show a very large
variability of individual doses for all population groups. For
example, the thyroid doses to evacuees range from less than
50 mGy to more than 5,000 mGy; the dose interval with thelargest number of pre‑school children was 1,000–2,000 mGy,
but, for all other age categories, the largest number was in
the 200–500 mGy dose intervals. With respect to thenon‑evacuated population of 98 million people under consideration in Belarus, the Russian Federation and Ukraine,most of the people (93%) received thyroid doses of less than
50 mGy; only 1% received thyroid doses greater than
200 mGy. As expected, the average thyroid dose generally
decreased with age at exposure; the dose to pre‑school

120

UNSCEAR 2008 REPORT: VOLUME II

children was 2–4 times greater than the population average,
with more than 4% of the pre‑school children receiving thy‑roid doses greater than 200 mGy and 0.3% receiving doses
greater than 1,000 mGy.
B87. The effective dose to members of the public, which by
convention do not include the contributions of the thyroid
doses, were much lower than the thyroid doses. For the 98 mil‑lion people considered in the 3 countries, the average effective
dose for 1986–2005 was 1.25 mSv, whereas the six million
residents of the “contaminated areas” received average effec‑
tive doses for the same period of about 9 mSv. Both values
were about 3 times greater than the corresponding effective
doses for 1986 alone; the same ratio of about 3 was observed
for both the external and the internal doses. About 80% of the
lifetime effective doses are estimated to have been deliveredby 2005. Most of these people were residing in areas with137
Cs deposition densities of less than 37 kBq/m2, and there‑
fore, about 70% of the population received doses of lessthan 1 mSv and 20% received doses in the range 1–2 mSv.
However, about 150,000 people (0.1%) accumulated a doseof more than 50 mSv.
B88. The assessment of the uncertainties attached to theindividual dose estimates is a topic of increasing interest,
especially in the framework of epidemiological studies.
When estimated from direct thyroid measurements, theuncertainties in the individual thyroid dose estimates havebeen found to vary among individuals and to range from 1.6
to more than 5.0 (in terms of geometric standard deviations).
Uncertainties in the dose estimates for the recovery opera‑tion workers vary, according to the method of dose assess‑ment, from less than 50% to up to a factor of 5. The bias isthought to be on the higher side for the military recovery
operation workers.
B89. The collective effective dose to the recovery opera‑tion workers is estimated to be about 60,000 man Sv; thismay, however, be an overestimate, as there is evidence thatconservative assumptions were used in the calculation ofsome of the recorded doses. About 85% of the collective
dose to the workers with recorded doses was in the ­individual
dose interval 50–500 mGy.
B90. The highest collective dose to the thyroid is estimatedto have been to the residents of the former Soviet Union andamounted to 1,600,000 man Gy. In the individual countries,
the collective thyroid dose was highest in Ukraine, with
960,000 man Gy distributed over a population of 51 million
people, even though the average thyroid dose in Ukraine wasabout 3 times lower than in Belarus. The highest collective
thyroid dose in a region was in the Gomel oblast, where
about 320,000 man Gy were distributed over a population of
1.6 million people, corresponding to an average thyroid doseof about 200 mGy.
B91. In terms of the collective effective dose to the popula‑tions of Belarus, the Russian Federation and Ukraine, 20%
was contributed by individuals exposed to a dose of less than
5 mSv. The contribution of those exposed to more than
50 mSv was about 10%. As is the case for the thyroid doses,
the average effective dose was greater in Belarus than in
Ukraine, but the collective effective dose was greater in
Ukraine than in the Russian Federation (19 regions deemed
affected) and Belarus, principally because of the larger
Ukrainian population.
B92. Finally, for the population of about 500 millionp­ eople in the rest of Europe (excluding the countries of the
Caucasus, Turkey, Andorra and San Marino), the per caput
doses for 1986–2005 are estimated to have been 1.3 mGy forthe absorbed dose to the thyroid and 0.3 mSv for the effec‑
tive dose, while the collective effective dose is estimated tohave been about the same value (130,000 man Sv) as that forthe populations of Belarus, Ukraine and relevant parts of theRussian Federation.

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

121

Table B1. External dosesa to recovery operation workers as officially recorded in national registries [K8, K23, K24, K31, N14,
R7, R12, S10, S30, T9]
PeriodNo. of recovery operation workers

Absolute
number

Percentage ofworkers withrecorded doses

External doseb (mGy)
MeanMedian75th percentile

95th percentile

Collective doseb(man Gy)%
Belarus (as of 1996) [K8, K23]

1986

68 000

74.7

8

60

53

93

138

4 080

1987

17 000

18.7

12

28

19

29

54

476

1988

4 000

4.4

20

20

11

31

93

80

1989

2 000

2.2

16

20

15

30

42

40

1990

0

0

—

—

—

—

—

0

1986–1990

91 000

100.0

9

51

—

—

—

4 676

Russian Federation (as of 2006) [R12]1986

87 772

46.6

62.0

149

175

220

250

13 0781987

65 811

35.0

78.6

89

91

100

210

5 857

1988

24 160

12.8

83.4

35

27

46

96

845

1989

8 626

4.6

77.0

34

33

49

72

293

1990

1 805

1.0

72.2

39

43

49

66

70

1986–1990

188 174

100.0

71.3

107

94

188

244

20 143

Ukraine (as of 2005) [S30]1986

141 340

61.7

28.9

186

200

239

250

26 2191987

49 3651988

20 819

21.5

60.1

127

93

100

230

6 259

9.1

65.4

57

45

50

95

1 191

1989

12 979

5.7

70.8

49

48

49

50

635

1990

3 938

1.7

63.4

51

47

49

50

200

Unknown

778

0.3

—

—

—

—

—

1986–1990

229 219

100

42.5

151

140

218

250

34 504

Estonia [N14, T9]
1986

2 936

60.8

87.8

109

101

154

212

321

1987

1 089

22.6

84.7

111

89

162

207

121

1988

561

11.6

80.0

32

35

44

65

18

1989

108

2.2

91.7

45

44

45

94

5

1990

1

0.0

0.0

—

—

—

—

0

1991

1

0.0

0.0

—

—

—

—

0

Unknown

136

2.8

2.9

44

45

45

45

6

1986–1991

4 832

100.0

83.9

99

88

146

208

471

Latvia (as of 1998) [R7, S10]
1986

3 338

55.0

78

146

487

1987

1 757

29.0

80

106

186

1988

732

12.1

71

31

23

1989

169

2.8

78

45

7

1990

19

0.3

68

55

1

1991

4

0.07

—

—

0

Unknown

46

0.8

—

—

0

1986–1991

6 065

100.0

77

117

704

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UNSCEAR 2008 REPORT: VOLUME II

PeriodNo. of recovery operation workers

Absolute
number

Percentage ofworkers withrecorded doses

External doseb (mGy)
MeanMedian75th percentile

95th percentile

Collective doseb(man Gy)%
Lithuania [K24, K31]

1986

2 440

35.1

69

144

140

201

250

351

1987

3151

45.3

80

108

98

107

220

340

1988

1 006

14.5

64

43

42

50

100

43

1989

246

3.5

79

50

49

50

120

12

1990

3

0.04

67

28

28

40

40

0.08

Unknown

114

1.6

21

107

75

135

260

12

1986–1990

6 960

100.0

73

109

98

159

240

758

All countries1986

305 826

58.1

35

146

44 5351987

138 173

26.3

64

96

13 2401988

51 278

9.7

71

43

2 200

1989

24 128

4.6

69

41

993

1990

5 766

1.1

66

47

271

1991

5

<0.001——0

Unknown

1 074

0.2

—

—

18

1986–1991

526 250

100

48

117

61 256a The external dose is expressed in milligray (mGy) for reasons of convenience. In fact, the quantity measured was, in many cases, exposure.
b The statistical parameters of dose distributions for particular years are given for workers with recorded doses (see percentiles in the 4th column). For 1986–1990, the statistical parameters and collective effective dose values are given assuming that dose distributions obtained for the workers with recorded doses apply to the entire population ofworkers. For some populations, this assumption might be rather questionable.

Table B2. Distribution of the number of Russian recovery operation workers and corresponding average doses according to
the duration of their first mission to Chernobyl [I14, I25]
Duration of the first mission (months)

<1

1–2

2–3

3–6

6–12

>12

Total or average

Percentage of recovery operation workers

11.3

26.8

28.4

30.5

1.9

1.1

100

Average dose (mGy)

122

129

117

85

90

97

110

Table B3. Distribution of the number of recovery operation workers having recorded doses according to external dose [K8,K23, K24, K31, N14, R7, R12, S10, S30, T9]
Dose range(mGya)

Recovery operation workers having recorded doses
NumberRounded %Percentage of collective dose

Average dose (mGy)

Belarus [K8, K23]
<10

2 196

25

4.7

2.7

10–20

1 791

20

16

7.7

20–50

1 858

21

33

15.9

50–100

1 865

21

75

36.8

100–200

1 032

12

120

33.1

200–500

48

1

260

3.3

500–1 000

3

0.03

630

0.5

>1 00000—0Rounded totals

8 793

100

43

100

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

Dose range(mGya)

Recovery operation workers having recorded doses
NumberRounded %123

Percentage of collective dose

Average dose (mGy)

Russian Federation [R12]<10

17 297

13

4.5

0.5

10–20

8 300

6

14

0.8

20–50

21 347

16

36

5.4

50–10033 656

25

81

19.0

100–200

27 185

20

150

27.6

200–500

25 945

19

230

41.7

500–1 000

401

0.3

610

1.7

>1 000b

51

0.04

9 400

3.3

Rounded totals

134 182

100

107

100

Ukraine [S30]
<10

3 426

3.6

5.0

0.1

10–20

2 164

2.4

16

0.3

20–50

23 796

26

43

8.5

50–10023 592

26

86

17.0

100–200

16 357

18

160

22.4

200–500

20 755

23

240

41.1

500–1 000

129

0.1

710

0.8

>1 000b

168

0.2

6 900

9.7

Rounded totals

90 387

100

132

100

Estonia [N14, T9]
<10

174

4.3

5.2

0.2

10–20

119

2.9

14

0.4

20–50

810

20

38

7.6

50–100

1 275

31

78

24.6

100–200

1 377

34

150

50.5

200–500

295

7.3

220

16.2

500–1 000

3

0.1

570

0.4

>1 00000—0Rounded totals

4 053

100

99

100

Latvia [R7, S10]
<10

323

7.4

5

0.2

10–20

411

9.4

15

0.8

20–50

110

2.5

35

0.5

50–100

1 311

30

75

12.5

100–200

530

12

150

10.1

200–500

1 701

39

350

75.6

500–1 000

4

0.1

750

0.4

>1 00000—0Rounded totals

4 390

100

180

100

124

UNSCEAR 2008 REPORT: VOLUME II

Dose range(mGya)

Recovery operation workers having recorded doses
NumberRounded %Percentage of collective dose

Average dose (mGy)

Lithuania [K24, K31]
<10

144

2.8

4.9

0.1

10–20

178

3.5

12

0.4

20–50

634

13

35

4.0

50–100

1 699

34

76

23.4

100–200

1 525

30

130

35.6

200–500

886

17

230

36.2

500–1 000

3

0.06

600

0.3

>1 00000—0Rounded totals

5 069

100

109

100

All countries<10

23 560

9.5

4.6

0.4

10–20

12 963

5.3

14

0.7

20–50

48 555

20

39

6.7

50–10063 398

26

82

18.4

100–200

48 006

19

150

25.5

200–500

49 630

20

240

41.4

500–1 000

543

0.2

630

1.2

>1 000b

219

0.1

7 500

5.7

Rounded totals

246 874

100

110

100

a The external dose is expressed in milligray (mGy) for convenience. In fact, the quantity measured was, in many cases, exposure.
b Doses above 1,000 mGy have been included in this table for the sake of completeness. It is believed that emergency workers or witnesses of the accident received such doses.
The occurrence of clerical errors in these data cannot be completely excluded.

Table B4. Information on the population groups that were evacuated from the exclusion zone in 1986: numbers of persons,average thyroid doses and collective thyroid doses [B31, L4, S26]
QuantityAge groupPre-school children(0–6 y)School children(7–14 y)Adolescents(15–17 y)

Adults(>17 y)All ages

Belarus (population evacuated in May 1986)
Population, persons

1 126

1 049

478

8 705

11 358Average thyroid dose (mGy)

4 616

1 967

1 518

918

1 407

Collective thyroid dose (man Gy)

5 198

2 064

725

7 991

15 978Belarus (population evacuated in June–September 1986)
Population, persons

1 199

1 328

645

10 19513 367

Average thyroid dose (mGy)

3 024

1 192

735

487

797

Collective thyroid dose (man Gy)

3 626

1 583

474

4 965

10 648Belarus (total population evacuated in 1986)
Population (persons)

2 325

2 377

1 123

18 90024 725

Average thyroid dose (mGy)

3 796

1 534

1 068

686

1 077

Collective thyroid dose (man Gy)

8 824

3 647

1 200

12 95626 627

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

Quantity125

Age groupPre-school children(0–6 y)School children(7–14 y)Adolescents(15–17 y)

Adults(>17 y)All ages

Russian Federation
Population (persons)

19

22

10

135

186

Average thyroid dose (mGy)

1 280

500

450

310

440

Collective thyroid dose (man Gy)

24

11

4.5

42

82

UkrainePopulation (persons)

9 587

10 721

4 692

64 61089 600

Average thyroid dose (mGy)

1 004

278

230

250

333

Collective thyroid dose (man Gy)

9 622

2 985

1 077

16 17529 859Entire population evacuated in 1986
Population (persons)

11 93113 1205 815

83 645

114 511

Average thyroid dose (mGy)

1 548

506

392

349

494

Collective thyroid dose (man Gy)

18 471

6 643

2 280

29 17256 567

Table B5. Distribution of the thyroid doses to the Belarusian and Ukrainian evacuees [L4, S26]
Dose
interval(Gy)

Pre-school children
Number(persons)%

School children
Number(persons)%

Adolescents
Number(persons)

Adults%All ages

Number(persons)%

Number(persons)%

Belarus (population evacuated in May 1986)
<0.05

8

0.7

5

0.5

11

2.3

333

3.8

357

3.1

0.05–0.1

31

2.8

36

3.4

15

3.1

637

7.3

719

6.3

0.1–0.2

34

3.0

61

5.8

40

8.4

998

11.5

1 133

10.0

0.2–0.5

126

11.2

142

13.5

102

21.3

2 159

24.8

2 529

22.3

0.5–1.0

146

13.0

200

19.1

93

19.5

2 135

24.5

2 574

22.7

1.0–2.0

213

18.9

242

23.1

95

19.9

1 537

17.7

2 087

18.4

2.0–5.0

275

24.4

277

26.4

98

20.5

782

9.0

1 432

12.6

>5.0

293

26.0

86

8.2

24

5.0

124

1.4

527

4.6

Total

1 126

100

1 049

100

478

100

8 705

100

11 358100

Belarus (population evacuated in June–September 1986)
<0.05

19

1.6

19

1.4

35

5.4

1 254

12.3

1 327

9.9

0.05–0.1

17

1.4

37

2.8

44

6.8

1 026

10.1

1 124

8.4

0.1–0.2

44

3.7

98

7.4

82

12.7

1 942

19.1

2 166

16.2

0.2–0.5

158

13.2

344

25.9

210

32.6

2 985

29.3

3 697

27.7

0.5–1.0

191

15.9

335

25.2

132

20.5

1 691

16.6

2 349

17.6

1.0–2.0

277

23.1

278

20.9

92

14.3

962

9.4

1 609

12.0

2.0–5.0

300

25.0

185

13.9

46

7.1

288

2.8

819

6.1

>5.0

193

16.1

32

2.4

4

0.6

47

0.5

276

2.1

Total

1 199

100

1 328

100

645

100

10 195100

13 367

100

126

UNSCEAR 2008 REPORT: VOLUME II

Doseinterval(Gy)

Pre-school children
Number(persons)%

School children
Number(persons)

Adolescents%

Number(persons)

Adults%All ages

Number(persons)%

Number(persons)

%

1 587

8.4

1 684

6.8

Belarus (entire population evacuated in 1986)
<0.05

27

1.2

24

1.0

0.05–0.1

48

0.1–0.2

78

46

4.1

2.1

73

3.1

59

5.3

1 663

8.8

1 843

7.5

3.4

159

6.7

122

10.9

2 940

15.6

3 299

13.3

0.2–0.5

284

12.2

486

20.5

312

27.8

5 144

27.2

6 226

25.2

0.5–1.0

337

14.5

535

22.5

225

20.0

3 826

20.2

4 923

19.9

1.0–2.0

490

21.1

520

21.9

187

16.7

2 499

13.2

3 696

15.0

2.0–5.0

575

24.7

462

19.4

144

12.8

1 070

5.7

2 251

9.1

>5.0

486

20.9

118

5.0

28

2.5

171

0.90

803

3.3

Total

2 325

100

2 377

100

1 123

100

18 900100

24 725

100

2.1

2 617

4.1

2 857

3.2

Ukraine
<0.05

—

—

143

1.3

97

0.05–0.1

4

0.04

1 504

14.0

985

21.0

10 306

16.0

12 79914.3

0.1–0.2

458

4.8

1 234

11.5

1 384

29.6

7 090

11.0

10 16611.4

0.2–0.5

1 813

18.9

7 011

65.4

2 071

44.2

42 46965.7

53 36459.6

0.5–1.0

3 400

35.5

631

5.9

74

1.6

674

1.0

4 779

5.3

1.0–2.0

3 525

36.8

133

1.2

51

1.1

1 067

1.7

4 776

5.3

2.0–5.0

306

3.2

65

0.6

20

0.4

387

0.6

778

0.9

>5.0

81

0.8

—

—

—

—

—

—

81

0.1

Total

9 587

100

10 721

100

4 682

100

64 610100

89 600100

Belarus and Ukraine combined
<0.05

27

0.2

167

1.3

143

2.5

4 204

5.0

4 541

4.0

0.05–0.1

52

0.4

1 577

12.0

1 044

18.0

11 96914.3

14 64212.8

0.1–0.2

536

4.5

1 393

10.6

1 506

25.9

10 030

12.0

13 46511.8

0.2–0.5

2 097

17.6

7 497

57.2

2 383

41.1

47 613

57.0

59 59052.1

0.5–1.0

3 737

31.4

1 166

8.9

299

5.2

4 500

5.4

9 702

8.5

1.0–2.0

4 015

33.7

653

5.0

238

4.1

3 566

4.3

8 472

7.4

2.0–5.0

881

7.4

527

4.0

164

2.8

1 457

1.7

3 029

2.7

>5.0

567

4.8

118

0.9

28

0.5

171

0.2

884

0.8

Total

11 912100

13 098

100

5 805

100

83 510100

114 325

100

Table B6. Summary of estimated average and collective effective doses to the populations of areas evacuated in 1986 [B28,
L4, S26, U3]
Country

Population(persons)

Estimated meana effective dose (mSv)

Collective effective dose (man Sv)

External

Internal (excluding thyroid)

Total

Belarus24 725

30

6

36

890

Russian Federation

186

25

10

35

7

Ukraine89 600

20

10

30

2 688

Total

114 511

22

9

31

3 585

a Arithmetic mean.

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

127

Table B7. Distribution of the collective dose to the thyroid of the Belarusian and Ukrainian evacuated populations according
to thyroid dose interval [L4, S26]
Dose interval(Gy)Pre-school children
man Gy%School children
man Gy%Adolescentsman GyAdults%All agesman Gy%man Gy%Belarus (population evacuated in May 1986)
<0.05

0.3

0.01

0.2

0.01

0.4

0.05

11

0.1

12

0.1

0.05–0.1

2.3

0.04

3.0

0.2

1.2

0.2

47

0.6

54

0.3

0.1–0.2

5.4

0.1

8.9

0.4

5.9

0.8

155

1.9

175

1.1

0.2–0.5

41

0.8

50

2.4

32

4.4

728

9.1

851

5.3

0.5–1.0

108

2.1

145

7.0

68

9.4

1 539

19.3

1 860

11.6

1.0–2.0

306

5.9

346

16.8

127

17.5

2 188

27.4

2 967

18.6

2.0–5.0

906

17.4

848

41.1

280

38.6

2 347

29.4

4 381

27.4

>5.0

3 829

73.7

663

32.1

211

29.1

976

12.2

5 679

35.5

Total

5 198

100

2 064

100

726

100

7 991

100

15 979

100

33

0.7

35

0.3

Belarus (population evacuated in June–September 1986)
<0.05

0.6

0.02

0.6

0.04

1.1

0.2

0.05–0.1

1.3

0.04

2.7

0.2

2.9

0.6

78

1.6

85

0.8

0.1–0.2

7.3

0.2

15

0.9

12

2.5

283

5.7

317

3.0

0.2–0.5

56

1.5

121

7.6

69

14.6

970

19.5

1 216

11.4

0.5–1.0

145

4.0

246

15.5

94

19.8

1 173

23.6

1 658

15.6

1.0–2.0

407

11.2

395

25.0

131

27.6

1 282

25.8

2 215

20.8

2.0–5.0

948

26.1

579

36.6

142

30.0

853

17.2

2 522

23.7

>5.0

2 061

56.8

224

14.2

22

4.6

293

5.9

2 600

24.4

Total

3 626

100

1 583

100

474

100

4 965

100

10 648100

Belarus (entire population evacuated in 1986)
<0.05

1.0

0.01

0.8

0.02

1.5

0.1

44

0.3

47

0.2

0.05–0.1

3.6

0.04

5.7

0.2

4.1

0.3

125

1.0

138

0.5

0.1–0.2

12.7

0.1

23.9

0.7

17.9

1.5

438

3.4

493

1.9

0.2–0.5

97

1.1

171

4.7

101

8.4

1 698

13.1

2 067

7.8

0.5–1.0

253

2.9

391

10.7

162

13.5

2 712

20.9

3 518

13.2

1.0–2.0

713

8.1

741

20.3

258

21.5

3 470

26.8

5 182

19.5

2.0–5.0

1 854

21.0

1 427

39.1

422

35.2

3 200

24.7

6 903

25.9

>5.0

5 890

66.8

887

24.3

233

19.4

1 269

9.8

8 279

31.1

Total

8 824

100

3 647

100

1 199

100

12 956100

26 627

100

Ukraine
<0.05

—

—

6.7

0.2

3.4

0.3

119

0.7

129

0.4

0.05–0.1

0.4

0.0

106

3.6

70

6.5

834

5.2

1 010

3.4

0.1–0.2

76

0.8

173

5.8

253

23.5

1 065

6.6

1 567

5.2

0.2–0.5

629

6.5

1 976

66.2

573

53.3

11 62371.9

14 801

49.6

0.5–1.0

2 540

26.4

358

12.0

47

4.4

349

2.2

3 294

11.0

1.0–2.0

4 720

49.1

180

6.0

71

6.6

1 347

8.3

6 318

21.2

2.0–5.0

887

9.2

185

6.2

59

5.5

837

5.2

1 968

6.6

>5.0

770

8.0

—

—

—

—

—

—

770

2.6

Total

9 622

100

2 985

100

1 076

100

16 174100

29 857

100

128

UNSCEAR 2008 REPORT: VOLUME II

Dose interval(Gy)Pre-school children
man Gy%School children
man GyAdolescents%man GyAdultsAll ages%man Gy%man Gy%Belarus and Ukraine combined
<0.05

1.0

0.01

7.5

0.1

4.9

0.2

163

0.6

176

0.3

0.05–0.1

4.0

0.02

112

1.7

74.1

3.3

959

3.3

1 149

2.0

0.1–0.2

88.7

0.5

197

3.0

271

11.9

1 503

5.2

2 060

3.6

0.2–0.5

726

3.9

2 147

32.4

674

29.6

13 32145.7

16 86829.9

0.5–1.0

2 793

15.1

749

11.3

209

9.2

3 061

10.5

6 812

12.1

1.0–2.0

5 433

29.5

921

13.9

329

14.5

4 817

16.5

11 50020.4

2.0–5.0

2 741

14.9

1 612

24.3

481

21.1

4 037

13.9

8 871

15.7

>5.0

6 660

36.1

887

13.4

233

10.2

1 269

4.4

9 049

16.0

Total

18 447

100

6 632

100

2 276

100

29 130100

56 485100

Table B8. Distribution of the Ukrainian and Belarusian cohort subjects according to the geometric mean of their thyroid doses [L3]
Thyroid dose group(Gy)

Table B9.

Number of persons
UkraineBelarus

Total

<0.3

6 990

3 934

10 924

0.3–1.0

3 597

3 337

6 934

≥1.0

2 540

3 749

6 289

Total

13 127

11 02024 147

Characteristics of the thyroid dose distributions for the Ukrainian and Belarusian cohort subjects [M14, T3]
Thyroid dose (Gy)

UkraineBelarusArithmetic mean

0.78

1.38

Standard deviation

1.85

2.97

Median0.26

0.54

Table B10. Average and collective doses to the thyroid for the populations of Belarus, the Russian Federation and Ukraine[K8, L4, Z4]
City or oblast

Average thyroid dose (mGy)Pre-school
children

Schoolchildren

Adolescents

Adults

Total

Population(persons)

Collective dose(man Gy)

Belarus
Minsk city

52.0

26.2

17.3

17.8

22.6

1 518 790

34 310

Brest

77.8

39.6

23.9

24.7

32.7

1 382 710

45 170Vitebsk

5.5

2.6

1.6

1.7

2.1

1 269 530

2 720

Gomel

475.8

250.3

145.0

148.1

197.3

1 631 040

321 750

Grodno

16.7

8.7

5.2

5.4

6.9

1 126 230

7 780

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

City or oblast

Average thyroid dose (mGy)129

Population(persons)

Collective dose(man Gy)

Pre-school
children

Schoolchildren

Adolescents

Adults

Total

Minsk

22.9

11.8

7.1

7.4

9.6

1 509 060

14 530

Mogilev

97.6

51.0

29.4

30.7

40.1

1 248 560

50 020Rounded total or average for entire
country

122

63

37

37

49

9 686 000

476 000

Rounded total or average for­“contaminated areas”a

449

210

135

138

182

1 770 000

322 000

Russian Federation (19 affected regionsb)
Bryansk

155

52

31

26

42

1 429 000

60 500

Tula

44

14

8

6

10

1 796 000

18 700

Orel

58

19

12

9

15

860 000

13 000Kaluga

13

4

3

2

3

1 006 000

3 500

Other 15 “affected” regionsa

10

3

2

2

3

32 134 000

94 000Rounded total or average for entire
19 regions

18

6

4

3

5

37 225 000

190 000

Rounded total or average for­“contaminated areas”a

107

35

20

17

27

2 474 000

68 000

UkraineVinnytsia

37

13

9.8

9.2

12

1 953 000

23 900Volyn’

87

33

25

21

31

1 047 000

32 000Luhans’k

12

4.0

3.1

3.1

4.1

2 832 000

11 600Dnipropetrovs’k

13

4.4

3.4

3.4

4.5

3 810 000

17 200Donets’k

24

8.0

6.0

6.1

8.1

5 328 000

42 900Zhytomyr

231

87

67

60

81

1 549 000

126 200

Zakarpattia

7.6

2.8

2.1

1.8

2.7

1 203 000

3 200

Zaporizhzhia

26

8.8

6.2

6.5

8.8

2 045 000

17 900Ivano-Frankivs’k

19

7.1

5.3

4.6

6.7

1 375 000

9 200

Kyiv

202

75

58

53

71

1 882 000

133 600

Kirovohrad

89

31

23

23

30

1 233 000

37 300

Crimea

34

12

8.8

8.4

12

2 005 000

23 200

L’viv

14

4.9

3.8

3.5

4.8

2 671 000

12 900

Mykolaiv

20

7.1

5.4

5.0

7.0

1 301 000

9 100

Odesa

15

5.2

3.8

3.7

5.1

2 656 000

13 600

Poltava

54

19

15

13

18

1 732 000

30 500

Rivne

177

64

49

42

62

1 162 000

71 700

Sumy

71

25

19

19

24

1 425 000

34 800Ternopil’

18

6.4

4.8

4.5

6.2

1 150 000

7 100

Kharkiv

26

8.7

6.5

6.6

8.6

3 163 000

27 300Kherson

30

11

7.8

7.3

10

1 222 000

12 500Khmel’nyts’k

39

15

11

10

14

1 528 000

20 900Cherkasy

142

52

39

37

49

1 522 000

74 300Chernivtsi

40

14

10

9.3

13

914 000

12 200Chernihiv

151

55

43

37

50

1 427 000

70 900130

UNSCEAR 2008 REPORT: VOLUME II

City or oblast

Average thyroid dose (mGy)

Population(persons)

Collective dose(man Gy)

Pre-school
children

Schoolchildren

Adolescents

Adults

Total

Kyiv city

94

30

23

24

32

2 469 000

80 000Sevastopol’ city

56

18

14

14

19

381 000

7 300

Rounded total or average for entire
country

55

20

15

14

19

50 986 000

963 300

Rounded total or average for“­ contaminated areas”a

367

115

115

91

123

2 151 000

265 000

Belarus, Russian Federation and Ukraine combined
Rounded total or average for three
countries

48

19

13

12

16

97 900 000

1 630 000Rounded total or average for“­ contaminated areas”a

289

110

84

75

102

6 395 000

655 000

a The “contaminated” areas were defined arbitrarily in the former Soviet Union as areas where the 137Cs levels on soil were greater than 37 kBq/m2.
b Belgorod, Kursk, Leningrad, Lipetsk, Nizhny Novgorod, Penza, Ryazan, Saratov, Smolensk, Tambov, Ulyanovsk and Voronezh oblasts, Chuvash, Mordoviya and Tatar autonomous
republics.

Table B11. Distribution of the affected populations of Belarus, the Russian Federation and Ukraine according to age andthyroid dose interval [K8, L4, Z4]
Dose interval(Gy)Pre-school children
Number(persons)%

School children
Number(persons)

Adolescents%

Number(persons)

AdultsTotal population%

Number(persons)%

Number(persons)%

Belarusa<0.05

574 300

54.3

836 300

74.9

433 900

81.2

5 680 100

81.4

7 524 600

77.7

0.05–0.1

223 300

21.1

99 8008.9

41 3007.7

463 100

6.6

827 500

8.5

0.1–0.2

88 0008.3

82 7007.4

43 1008.1

617 800

8.9

831 600

8.6

0.2–0.5

113 800

10.8

78 800

7.1

14 4002.7

182 800

2.6

389 800

4.0

0.5–1.040 3003.8

16 400

1.5

1 900

0.4

31 8000.5

90 4000.9

1.0–2.0

17 800

1.7

2 500

0.2

20

0.004

300

0.004

20 6200.2

2.0–5.0

1 000

0.1

100

0.01

—

—

—

—

1 100

0.01

≥ 5.0

50

0.01

5

4 × 10

—

—

—

—

55

6 × 10-4

Rounded total or
average

1 058 550100

1 116 605

100

534 620100

6 975 900

100

9 686 000

100

-4Russian Federation (19 affected regionsb)< 0.05

3 483 000

92.0

3 921 000

98.7

1 860 000

99.5

27 515 000

99.7

36 779 000

98.8

0.05–0.1

206 000

5.4

36 000

0.9

5 800

0.3

50 0000.2

297 800

0.8

0.1–0.2

68 0001.8

10 000

0.3

2 300

0.1

28 0000.1

108 300

0.3

0.2–0.5

23 000

0.6

4 000

0.1

500

0.03

5 500

0.02

33 0000.1

0.5–1.0

4 000

0.1

400

0.01

100

0.005

1 100

0.004

5 600

0.02

1.0–2.0

1 200

0.03

20

0.001

—

—

—

—

1 220

0.003

2.0–5.0

100

0.003

—

—

—

—

—

—

100

3 × 10-4>5.0

20

5 × 10-4

—

—

—

—

—

—

20

5 × 10-5

Rounded total or
average

3 785 320100

3 971 420100

1 868 700

100

27 599 600

100

37 225 040

100

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

Dose interval(Gy)Pre-school children
Number(persons)%

School children
Number(persons)%

Adolescents

AdultsNumber(persons)

131

Total population%

Number(persons)%

Number(persons)%

Ukrainea< 0.05

3 768 000

71.9

5 495 000

92.5

2 660 000

94.7

35 124 000

94.9

47 048 000

92.3

0.05–0.1

794 000

15.1

263 000

4.4

98 0003.5

1 372 000

3.7

2 527 000

5.0

0.1–0.2

429 000

8.2

129 000

2.2

37 0001.3

407 000

1.1

1 002 0002.0

0.2–0.5

196 000

3.7

45 0000.8

11 0000.4

78 0000.2

330 000

0.6

0.5–1.0

40 000

0.8

4 600

0.08

1 300

0.05

15 0000.04

60 9000.1

1.0–2.0

8 000

0.2

1 600

0.03

510

0.02

3 500

0.01

13 6100.03

2.0–5.0

2 100

0.04

420

0.007

150

0.005

1 300

0.004

3 990

0.008

>5.0

470

0.01

30

5 × 10-4

—

—

—

—

500

0.001

Rounded total or
average

5 237 570

100

5 938 650

100

2 807 960

100

37 000 800

100

50 986 000

100

Belarus, Russian Federation and Ukraine combined< 0.05

7 825 300

77.6

10 252 300

93.0

4 953 900

95.1

68 319 100

95.4

91 350 600

93.3

0.05–0.1

1 223 300

12.1

398 800

3.6

145 100

2.8

1 885 100

2.6

3 652 300

3.7

0.1–0.2

585 000

5.8

221 700

2.0

82 4001.6

1 052 800

1.5

1 941 900

2.0

0.2–0.5

332 800

3.3

127 800

1.2

25 9000.5

266 300

0.4

752 800

0.8

0.5–1.084 3000.8

21 400

0.2

3 300

0.06

47 9000.07

156 9000.2

1.0–2.0

27 000

0.3

4 120

0.04

530

0.01

3 800

0.005

35 4500.04

2.0–5.0

3 200

0.03

520

0.005

150

0.003

1 300

0.002

5 170

0.005

>5.0

540

0.005

35

3 × 10-4

0

0

0

0

575

6 × 10-4

Rounded total or
average

10 081 440

100

11 026 675

100

5 211 280

100

71 576 300

100

97 895 695

100

a Evacuees not included.
b Belgorod, Bryansk, Kaluga, Kursk, Leningrad, Lipetsk, Nizhny Novgorod, Orel, Penza, Ryazan, Saratov, Smolensk, Tambov, Tula, Ulyanovsk and Voronezh oblasts, Chuvash,
Mordoviya and Tatar autonomous republics.

Table B12. Distribution of the collective dose to the thyroid of the affected populations of Belarus, the Russian Federation andUkraine according to age and thyroid dose interval [K8, L4, Z4]
Dose interval(Gy)Pre-school children
man Gy%School children
man Gy%Adolescentsman GyAdultsTotal population%

man Gy%man Gy%Belarusa<0.05

10 692

8.3

13 523

19.2

5 188

26.3

67 35526.2

96 75820.3

0.05–0.1

14 992

11.6

7 087

10.1

3 067

15.5

32 835

12.8

57 981

12.2

0.1–0.2

12 322

9.6

12 379

17.6

5 664

28.7

78 571

30.6

108 936

22.9

0.2–0.5

37 62829.2

23 065

32.8

4 778

24.2

60 822

23.7

126 293

26.6

0.5–1.0

26 61920.6

11 041

15.7

1 023

5.2

17 094

6.7

55 777

11.7

1.0–2.0

24 285

18.8

2 833

4.0

31

0.2

375

0.1

27 524

5.8

132

UNSCEAR 2008 REPORT: VOLUME II

Dose interval(Gy)Pre-school children

School children

Adolescents

AdultsTotal population

man Gy%man Gy%man Gy%man Gy%man Gy%2.0–5.0

2 254

1.7

420

0.6

—

—

—

—

2 674

0.6

>5.0

302

0.2

38

0.05

—

—

—

—

340

0.07

Rounded total or
average

129 094

100

70 386100

19 751100

257 052100

476 283

100

Russian Federation (19 affected regionsb)<0.05

34 30050.1

18 500

76.7

6 600

87.5

80 10089.1

139 500

73.4

0.05–0.1

13 500

19.7

2 500

10.4

400

5.3

3 400

3.8

19 80010.4

0.1–0.2

9 200

13.4

1 500

6.2

300

4.0

4 000

4.4

15 0007.9

0.2–0.5

6 400

9.3

1 300

5.4

150

2.0

1 700

1.9

9 550

5.0

0.5–1.0

2 900

4.2

300

1.2

90

1.2

700

0.8

3 990

2.1

1.0–2.0

1 700

2.5

35

0.1

—

—

—

—

1 735

0.9

2.0–5.0

400

0.6

—

—

—

—

—

—

400

0.2

>5.0

120

0.2

—

—

—

—

—

—

120

0.1

Rounded total or
average

68 520100

24 135

100

7 540

100

89 900100

190 095

100

Ukrainea<0.05

67 28023.4

60 89052.3

23 78058.4

328 39063.3

480 34049.9

0.05–0.1

55 25019.2

18 730

16.1

6 800

16.7

93 60018.0

174 380

18.1

0.1–0.2

57 60020.1

17 600

15.1

5 000

12.3

55 54010.7

135 740

14.1

0.2–0.5

59 63020.8

12 580

10.8

3 120

7.7

22 5304.3

97 86010.1

0.5–1.0

26 630

9.3

3 030

2.6

900

2.2

11 4602.2

42 0204.4

1.0–2.0

10 520

3.7

2 260

1.9

680

1.7

4 150

0.8

17 6101.8

2.0–5.0

6 550

2.3

1 200

1.0

440

1.1

3 400

0.7

11 590

1.2

>5.0

3 570

1.2

170

0.1

5

0.01

—

—

3 745

0.4

Rounded total or
average

287 030100

116 460

100

40 725100

519 070100

963 285

100

Belarus, Russian Federation and Ukraine combined<0.05

112 272

23.2

92 91344.0

35 56852.3

475 84555.9

716 598

44.0

0.05–0.1

83 74217.3

28 317

13.4

10 26715.1

129 835

15.0

252 161

15.5

0.1–0.2

79 12216.3

31 47914.9

10 964

16.3

138 111

16.0

259 676

15.9

0.2–0.5

103 658

21.4

36 945

17.5

8 048

11.8

85 0529.8

233 703

14.3

0.5–1.0

56 14911.6

14 371

6.8

2 013

3.0

29 254

3.4

101 787

6.2

1.0–2.0

36 505

7.5

5 128

2.4

711

1.0

4 525

0.5

46 8692.9

2.0–5.0

9 204

1.9

1 620

0.8

440

0.6

3 400

0.4

14 664

0.9

>5.0

3 992

0.8

208

0.1

5

0.007

0

0

4 205

0.3

Rounded total or
average484 644100

210 981100

68 016100

866 022100

1 629 663

100

a Evacuees not included.
b Belgorod, Bryansk, Kaluga, Kursk, Leningrad, Lipetsk, Nizhny Novgorod, Orel, Penza, Ryazan, Saratov, Smolensk, Tambov, Tula, Ulyanovsk and Voronezh oblasts, Chuvash,
Mordoviya and Tatar autonomous republics.

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

133

Table B13. Estimates of average effective dosesa for oblasts and cities and corresponding collective doses due to external
and internal exposure [B29, L4, M14]
Oblast137
Cs soil
deposition(kBq/m2)

External dose (mSv)

Internal dose (mSv)

1986

1986

1986–2005

1986–2005

Total dose (mSv)
1986

1986–2005

Population(persons)

Collective
dose in1986–2005(man Sv)

Belarus [M14]Gomel

Vitebsk

Minsk

Minsk city

GrodnoBrest

Mogilev

Roundedtotal/
weighted
mean

<37

0.72

1.56

0.15

0.51

0.87

2.07

251 000520

37–185

1.90

4.13

0.32

1.04

2.22

5.17

1 202 000

6 220

185–555

8.68

21.62

2.48

8.50

11.16

30.12

139 000

4 200

555–1 480

14.87

40.75

5.20

17.82

20.08

58.57

66 400

3 890>1 480

31.54

49.00

3.66

12.54

35.20

61.53

8 730

540

<37

0.02

0.09

0.01

0.05

0.04

0.14

1 410 000

200

37–185

0.56

2.10

0.33

1.12

0.88

3.22

93

0.3

<37

0.09

0.26

0.03

0.10

0.12

0.36

1 540 000

550

37–185

1.45

4.23

0.57

1.96

2.02

6.18

35 900220

185–555

4.75

13.85

1.88

6.42

6.63

20.27

2 150

40

<37

0.03

0.12

0.01

0.04

0.04

0.15

1 610 000

250

<37

0.09

0.27

0.03

0.10

0.12

0.37

1 110 000410

37–185

1.17

3.41

0.46

1.58

1.63

4.99

52 200260

185–555

5.35

15.58

2.11

7.22

7.46

22.81

295

7

<37

0.11

0.33

0.04

0.13

0.15

0.46

1 290 000

590

37–185

1.47

4.24

0.55

1.86

2.02

6.10

154 000940

185–555

5.01

14.38

1.94

6.63

6.94

21.01

7 600

160

<37

0.15

0.54

0.06

0.21

0.21

0.75

1 070 000

800

37–185

1.36

4.99

0.77

2.62

2.13

7.61

97 700740

185–555

3.53

12.93

1.90

6.43

5.42

19.36

84 700

1 640

555–1 480

12.84

47.00

7.20

24.65

20.04

71.65

18 600

1 330>1 480

29.09

80.21

16.32

46.08

45.41

126.29

5 200

660

<37

0.10

0.29

0.03

0.11

0.13

0.40

8 280 000

3 330

37–185

1.79

4.18

0.38

1.26

2.17

5.44

1 540 000

8 380

185–555

6.65

18.16

2.25

7.67

8.90

25.83

230 000

6 050

555–1 480

14.43

42.12

5.64

19.31

20.07

61.43

85 0005 220>1 480

30.62

60.65

8.39

25.06

39.01

85.71

13 900

1 190<37–>1 480

0.67

1.73

0.20

0.65

0.87

2.38

10 150 000

24 180Russian Federation (19 affected regionsb) [B29]

Bryansk

<37

0.2

0.5

0.6

1.1

0.8

1.6

1 006 000

1 600

37–185

1.0

3.0

2.5

5.0

3.5

8.0

183 000

1 500

185–555

4.1

11.6

3.3

8.4

7.4

20.0

148 000

3 000

555–1 480

10.0

28.2

3.0

11.4

13.0

39.6

85 000

3 400>1 480

40.1

120.0

6.7

24.6

46.8

144.6

7 000

1 000

134

UNSCEAR 2008 REPORT: VOLUME II

OblastKalugaOrel

Tula

Other 15
“affected”
regionsb

Total(19 regions)Cs soil
deposition(kBq/m2)

External dose (mSv)

Internal dose (mSv)

Population(persons)

Collective
dose in1986–2005(man Sv)

1986

1986–2005

1986

1986–2005

1986

1986–2005

<37

0.1

0.2

0.1

0.2

0.2

0.4

893 000400

37–185

0.9

2.7

0.4

0.9

1.3

3.6

103 000

400

185–555

3.5

10.2

1.5

3.8

5.0

14.0

11 000

200

<37

0.3

0.9

0.2

0.3

0.5

1.2

678 000800

37–185

0.9

2.8

0.7

1.2

1.6

4.0

168 000700

185–555

2.2

6.1

1.1

2.6

3.3

8.7

14 000

100

<37

0.2

0.6

0.2

0.3

0.4

0.9

1 017 000

900

37–185

1.2

3.4

0.7

1.1

1.9

4.5

710 000

3 200

185–555

3.4

9.7

1.1

2.1

4.5

11.8

69 000

800

<37

0.1

0.4

0.1

0.2

0.2

0.6

31 167 000

19 500

37–185

0.7

2.1

0.2

0.6

0.9

2.7

967 000

2 600

<37

0.1

0.4

0.1

0.2

0.2

0.6

34 760 000

23 200

37–185

0.9

2.7

0.7

1.3

1.6

4.0

2 131 000

8 400

185–555

3.7

10.6

2.5

6.0

6.2

16.6

243 000

4 100

555–1 480

10.0

28.2

3.0

11.4

13.0

39.6

85 000

3 400>1 480

40.1

120.0

6.7

24.6

46.8

144.6

7 000

1 000

<37–>1 480

0.2

0.7

0.2

0.4

0.4

1.1

37 226 000

40 100137

Total dose (mSv)

Ukraine [L4]
<37

0.24

0.65

0.12

0.24

0.36

0.89

1 831 000

1 600

37–185

1.7

4.6

1.1

1.4

2.8

6.0

123 000

730

<37

0.19

0.52

0.12

2.0

0.31

2.5

1 019 000

2 500

37–185

1.4

3.9

0.9

11

2.4

15

28 000

410

<37

0.34

0.93

0.10

0.22

0.44

1.2

2 812 000

3 200

37–185

1.0

2.9

0.6

0.8

1.6

3.7

20 000

70

<37

0.10

0.26

0.05

0.15

0.15

0.41

3 810 000

1 600

37–185

1.3

3.5

0.9

1.2

2.2

4.7

580

3

<37

0.20

0.54

0.07

0.18

0.27

0.72

5 028 000

3 600

37–185

1.1

3.0

0.2

0.4

1.3

3.4

301 000

1 000

<37

0.20

0.54

0.09

0.46

0.29

1.0

1 165 000

1 200

37–185

2.6

6.9

0.5

5.1

3.0

12

262 000

3 100

185–555

6.8

19

0.7

3.5

7.6

22

111 000

2 500

555–1 480

20

54

3

12

22

66

11 000700>1 480

52

140

7

32

58

172

870

150

Zakarpattia

<37

0.12

0.33

0.08

0.21

0.20

0.55

1 203 000

660

Zaporizhzhia

<37

0.07

0.20

0.05

0.13

0.12

0.33

2 045 000

670

<37

0.26

0.71

0.15

0.38

0.41

1.1

1 311 000

1 400

37–185

1.7

4.6

1.1

1.5

2.8

6.1

64 000390

Vinnytsia

VolynsLuhans’k

Dnipropetrovs’k

Donets’kZhytomyrIvanoFrankivs’k

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

Oblast

Kyiv

Kirovoh-rad
CrimeaL’viv

Mykolaiv

Odesa
Poltava

Rivne

Sumy

Ternopil’

Kharkiv
KhersonSumy
Ternopil’

Cherkasy

Chernivtsi

Chernihiv

Cs soil
deposition(kBq/m2)

External dose (mSv)

Internal dose (mSv)

Population(persons)

Collective
dose in1986–2005(man Sv)

1986

1986–2005

1986

1986–2005

1986

1986–2005

<37

0.45

1.2

0.14

0.45

0.59

1.7

1 411 000

2 300

37–185

1.9

5.1

0.5

1.4

2.4

6.5

405 000

2 600

185–555

8.2

22

2.1

4.2

10

26

21 000540

555–1 480

26

71

3

4

29

75

12 000910>1 480

92

252

13

58

106

309

1 500

450

<37

0.20

0.55

0.10

0.19

0.30

0.74

1 224 000

910

37–185

1.6

4.4

1.1

1.4

2.7

5.8

8 300

50

<37

0.12

0.32

0.06

0.16

0.17

0.47

2 005 000

950

<37

0.09

0.24

0.05

0.14

0.13

0.37

2 670 000

1 000

37–185

1.2

3.3

0.8

2.1

2.0

5.4

220

1

<37

0.12

0.33

0.06

0.14

0.18

0.47

1 300 000

610

37–185

2.4

6.6

1.7

2.1

4.1

8.7

740

10

<37

0.19

0.52

0.06

0.15

0.25

0.66

2 651 000

1 800

37–185

1.3

3.7

0.9

2.2

2.3

5.9

5 100

30

<37

0.17

0.45

0.09

0.24

0.26

0.70

1 732 000

1 200

<37

0.28

0.76

0.11

0.85

0.39

1.6

910 000

1 500

37–185

2.2

5.9

0.6

11

2.8

17

247 000

4 300

185–555

7.2

20

1.9

13

9.1

33

4 500

150

<37

0.21

0.57

0.10

0.26

0.31

0.83

1 411 000

1 200

37–185

1.9

5.2

1.3

2.3

3.2

7.4

14 000

100

<37

0.15

0.42

0.10

032

0.25

0.74

1 116 000

820

37–185

1.6

4.2

1.0

1.7

2.6

5.9

35 000

210

<37

0.18

0.49

0.08

0.19

0.26

0.67

3 162 000

2 100

37–185

1.1

3.0

0.8

1.2

1.9

4.3

160

1

<37

0.07

0.19

0.05

0.12

0.12

0.32

1 222 000

390

<37

0.16

0.44

0.09

0.23

0.26

0.67

1 502 000

1 010

37–185

1.6

4.5

1.1

1.4

2.8

5.8

26 000150

185–555

6.7

18

4.6

4.7

11

23

50

1

<37

0.30

0.81

0.14

0.27

0.44

1.1

1 281 000

1 400

37–185

1.9

5.1

1.0

1.5

2.8

6.6

236 000

1 600

185–555

7.3

20

5.0

5.1

12

25

5 700

140

<37

0.36

0.98

0.15

0.32

0.51

1.3

842 000

1 100

37–185

1.7

4.6

1.0

1.4

2.7

6.0

70 000420

185–555

5.9

16

4.1

4.3

10

20

2 800

60

<37

0.23

0.62

0.09

0.40

0.31

1.02

1 380 000

1 400

37–185

1.8

4.9

0.8

2.5

2.5

7.4

46 000340

185–555

7.4

20

2.6

5.7

10.0

26

1 200

30

555–1 480

18

48

11

21

29

68

140

10

137

Total dose (mSv)

135

136

UNSCEAR 2008 REPORT: VOLUME II

OblastCs soil
deposition(kBq/m2)

External dose (mSv)

Internal dose (mSv)

1986

1986–2005

1986

1986–2005

1986

1986–2005

Kyiv city

<37

0.48

1.3

0.03

0.08

0.51

Sevasto-pol’
city

<37

0.20

0,54

0.03

0.09

<37

0.21

0.56

0.08

37–1851.9

5.0

185–5557.0

555–1 480

Roundedtotal oraverage

Population(persons)

Collective
dose in1986–2005(man Sv)

1.4

2 469 000

3 400

0.23

0.63

381 000

240

0.26

0.29

0.82

48 893 000

39 800

0.6

3.2

2.5

8.2

1 876 100

15 600

19.3

0.9

3.6

8.0

22.9

132 000

3 100

23.1

62.8

2.6

7.7

25.7

70.3

23 000

1 600>1 480

77.3

210.9

10.8

48.5

88.1

259.4

2 370

600

<37–>1 480

0.30

0.81

0.11

0.39

0.41

1.2

51 000 000

61 000137

Total dose (mSv)

Belarus, Russian Federation (19 regions) and Ukraine combined

Roundedtotal oraverage

<37

0.16

0.48

0.08

0.22

0.24

0.70

91 930 000

66 600

37–185

1.5

3.9

0.59

1.9

2.1

5.8

5 565 000

32 300

185–555

5.6

15.4

2.1

6.2

7.7

21.6

624 000

13 500555–1 480

13.5

38.5

4.1

14.5

17.6

53.0

193 000

10 300>1 480

38.2

93.7

8.2

27.3

46.4

121.0

23 000

2 800<37–>1 480

0.30

0.86

0.13

0.39

0.43

1.25

98 000 000

125 000a	Population-weighted average doses assessed as doses of adults (≥18 years old).
b Belgorod, Kursk, Leningrad, Lipetsk, Nizhny Novgorod, Penza, Ryazan, Saratov, Smolensk, Tambov, Ulyanovsk and Voronezh oblasts, Chuvash, Mordoviya and Tatar autonomous
republics.

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

137

Table B14. Distribution of the affected populations of Belarus, the Russian Federation and Ukraine according to time period
and effective dosea interval [B29, L4, M14]
Dose interval
(mSv)

1986
Number of persons

1986–2005%

Number of persons%

Belarus [M14]<1

8 268 000

81.4

7 679 000

75.6

1–2

631 000

6.2

410 000

4.0

2–5

919 000

9.0

1 261 000

12.4

5–10

179 000

1.8

345 000

3.4

10–20

91 0000.9

219 000

2.2

20–50

61 0000.6

147 000

1.4

50–100

3 400

0.03

77 000

0.7

>100

500

0.005

16 0000.2

Rounded total or average

10 150 000100

10 150 000

100

Russian Federation (19 affected regionsb) [B29]<135 282 000

94.8

25 842 000

69.4

1–2

993 000

2.8

8 028 000

21.6

2–5

557 000

1.5

2 518 000

6.8

5–10

262 000

0.70

390 000

1.0

10–20

110 000

0.30

276 000

0.74

20–50

18 0000.05

140 000

0.38

50–100

3 000

0.008

27 000

0.07

>100

0

0

5 000

0.01

Rounded total or average

37 000 000

100

37 000 000

100

Ukraine [L4]<1

48 072 000

94.3

36 096 000

70.8

1–2

1 694 000

3.3

10 322 000

20.3

2–5

912 000

1.8

2 948 000

5.8

5–10

213 0000.42

850 000

1.7

10–20

43 0000.08

532 000

1.0

20–50

17 0000.03

182 000

0.36

50–100

1 400

0.003

18 000

0.04

>100

980

0.002

5 200

0.01

51 000 000

100

51 000 000

100

Rounded total or average

Belarus, Russian Federation (19 regions) and Ukraine combined<1

91 622 000

93.2

69 617 000

70.8

1–2

3 318 000

3.4

18 760 000

19.1

2–5

2 388 000

2.4

6 727 000

6.8

5–10

654 000

0.7

1 585 000

1.6

10–20

243 000

0.2

1 027 000

1.0

20–50

96 0000.1

469 000

0.5

50–100

7 800

0.008

121 000

0.1

>100

1 500

0.002

26 000

0.03

Rounded total or average

98 000 000

100

98 000 000100

a Effective doses assessed as doses of adults (≥18 years old).
b Belgorod, Bryansk, Kaluga, Kursk, Leningrad, Lipetsk, Nizhny Novgorod, Orel, Penza, Ryazan, Saratov, Smolensk, Tambov, Tula Ulyanovsk and Voronezh oblasts, Chuvash,­Mordoviya and Tatar autonomous republics.

138

UNSCEAR 2008 REPORT: VOLUME IITable B15. Distribution of the collective effective dose to the relevant populations of Belarus, the Russian Federation andUkraine according to time period and effective dosea interval [B29, L4, M14]
Dose interval
(mSv)

1986
Collective effective dose(man Sv)

1986–2005%

Collective effective dose(man Sv)%

Belarus [M14]
<1

1 040

11.9

2 180

9.0

1–2

860

9.8

630

2.6

2–5

2 360

26.9

4 570

18.9

5–10

1 240

14.1

2 490

10.3

10–20

1 280

14.6

3 110

12.9

20–50

1 720

19.6

4 320

17.9

50–100

210

2.4

5 000

20.7

>100

60

0.7

1 870

7.7

Rounded total or average

8 800

100

24 000100

Russian Federation (19 affected regionsb) [B29]
<1

9 000

57.7

9 800

24.4

1–2

1 200

7.7

10 400

25.9

2–5

1 500

9.6

7 100

17.7

5–10

1 700

10.9

2 300

5.7

10–20

1 500

9.6

3 800

9.5

20–50

500

3.2

4 100

10.2

50–100

200

1.3

1 800

4.5

>100

0

0

800

2.0

Rounded total or average

15 600100

40 000100

Ukraine [L4]<1

12 85062.4

17 230

28.3

1–2

2 390

11.6

14 260

23.4

2–5

2 730

13.3

8 380

13.7

5–10

1 390

6.7

5 960

9.8

10–20

530

2.6

7 710

12.6

20–50

500

2.4

5 180

8.5

50–100

90

0.4

1 320

2.2

>100

120

0.6

930

1.5

20 600100

61 000100

50.9

29 21023.3

Rounded total or average

Belarus, Russian Federation (19 regions) and Ukraine combined<1

22 890

1–2

4 450

9.9

25 290

20.2

2–5

6 590

14.7

20 050

16.0

5–10

4 330

9.6

10 750

8.6

10–20

3 310

7.4

14 620

11.7

20–50

2 720

6.0

13 60010.9

50–100

500

1.1

8 120

6.5

>100

180

0.4

3 600

2.9

Rounded total or average

45 000100

125 000

100

a Effective doses assessed as doses of adults (≥18 years old).
b Belgorod, Bryansk, Kaluga, Kursk, Leningrad, Lipetsk, Nizhny Novgorod, Orel, Penza, Ryazan, Saratov, Smolensk, Tambov, Tula Ulyanovsk and Voronezh oblasts, Chuvash,­Mordoviya and Tatar autonomous republics.

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

139

Table B16. Estimated average deposition densities of 137Cs resulting from the Chernobyl accident and ratios of deposition
densities of selected radionuclides to 137Cs in European countries [D13, E5, U7]
Country or region

Estimate of average 137Cs
deposition density(kBq/m2)

Estimate for the ratio of deposition density of various radionuclides
to that of 137Cs at the time of deposition
95

Zr

103

Ru

106

Ru

131

I

132

Te

134

Cs

140

Ba

Albania

7.2

0.1

2.5

0.6

3.8

7

0.5

1.5

Austria

18.7

—

1.3

0.46

5

4.8

0.57

—

Belarus, Brest Oblast

18.2

0.5–0.8

2.2–2.8

0.7–0.919–23

7.6–120.5

1.5–2.1

Belarus, Vitebsk Oblast

1.1

0.2

1.8

0.4

24

4.8

0.5

0.8

Belarus, Gomel Oblast

154

0.17–4

1.6–3.7

0.42–1

8.3–21

4.2–11

0.5

0.76–7.6

Belarus, Grodno Oblast

8

0.5

2.8

0.7

23

12

0.5

1.5

Belarus, Minsk Oblast

5.8

0.5

2.8

0.7

23

12

0.5

1.5

Belarus, Minsk City

6.2

0.3

1.5

0.45

14

2.8

0.5

1

Belarus, Mogilev Oblast

61

0.17–4

1.6–2.4

0.3–0.9

8.3–21

4.2–11

0.5

0.76–7.6

Belgium

0.3

—

1.7

0.5

6.2

4

0.55

1.6

Bosnia and Herzegovina

6.4

—

1.4

0.3

5.9

7.2

0.4

0.7

Bulgaria

7

0.14

1.4

0.36

1.7

4

0.5

1.6

Croatia

3.7

0.14

2.6

1

3.3

6.1

0.4

0.7

Cyprus

0.6

—

—

—

3.3

—

0.55

—

Czech Republic

4.7

—

1.9

0.3

13.8

5.1

0.5

1.0

Denmark

0.36

—

1.5

0.5

4.7

4.3

0.55

—

Estonia

2

1.1

2.2

0.5

4.2

5.9

0.6

0.7

Finland

12.2

1.7

2.2

0.5

4.2

5.9

0.6

0.7

France

0.7

—

1.4

0.3

7.3

4.8

0.55

—

Germany

2.8

—

1.5

0.3

5.8

6.8

0.55

—

Greece

5.2

0.1

2.5

0.6

3.8

7

0.5

1.5

Hungary

1.9

—

2.5

0.6

6.2

6.7

0.55

—

Iceland

0.3

—

—

—

—

—

0.55

—

Ireland

3.1

—

1.5

0.4

3.1

3.4

0.55

0.8

Italy

2.1

—

2

0.55

4

7.8

0.55

—

Latvia

0.85

0.2

1.8

0.4

24

4.8

0.5

1.5

Liechtenstein

11.8

—

1.3

0.46

5

4.8

0.57

—

Lithuania

3.7

0.4

1.5

—

23

12

0.55

0.72

Luxembourg

1.2

—

1.7

0.5

7

4

0.55

—

Macedonia (Former Yugoslav Rep. of)

8.5

—

1.5

0.3

6

7.6

0.4

—

Malta

1.9

—

1.8

0.5

3.8

8.5

0.55

—

Netherlands

0.3

—

1.9

0.5

6.3

3.3

0.55

—

Norway

4.7

—

2

0.5

16

2.6

0.55

—

Poland

1.3

—

2.5

0.3

7.3

8.4

0.55

—

Portugal

0.02

—

2

0.6

3.5

0.2

0.55

—

140

UNSCEAR 2008 REPORT: VOLUME IICountry or region

Estimate of average 137Cs
deposition density(kBq/m2)

Estimate for the ratio of deposition density of various radionuclides
to that of 137Cs at the time of deposition
95

Zr

103

Ru

106

Ru

131

I

132

Te

134

Cs

140

Ba

Republic of Moldova

10.1

—

2.9

0.7

5.2

6.4

0.55

—

Romania

6.5

—

2.9

0.7

5.2

6.4

0.55

—

Russia, Bryansk Oblast

110

0.07–0.14

1.6

0.45

7.6–11

6.7–100.54

0.41–0.63

Russia, Kaluga Oblast

14.2

0.07

1.5

0.42

7.7

6.3

0.5

0.48

Russia, Orel Oblast

41

0.07

1.6

0.43

8.1

7.1

0.5

0.49

Russia, Tula Oblast

67

0.07

1.6

0.46

7.9

6.5

0.5

0.5

Serbia and Montenegro

9

—

1.5

0.3

6

7.6

0.55

—

Slovakia

3.6

—

1.8

0.3

11

7.3

0.50

—

Slovenia

16.3

—

1.4

0.3

5.9

7.2

0.4

—

Spain

0.06

—

1.5

0.3

3.9

-

0.55

—

Sweden

4.6

—

2

0.78

15.9

1.1

0.55

—

Switzerland

5.6

—

1.9

0.6

7

8.6

0.55

—

Ukraine, Chernihiv Oblast

~15

2

8

2

13

20

0.5

2

Ukraine, Kyiv Oblast

~30

2

8

2

13

20

0.5

2

Ukraine, Kyiv-City

~15

2

8

2

13

20

0.5

2

Ukraine, Rivno Oblast

~40

2

8

2

13

20

0.5

2

Ukraine, Zhytomir Oblast

~50

2

8

2

13

20

0.5

2

Ukraine, remainder

~20

2

8

2

13

20

0.5

2

United Kingdom

0.9

—

1.8

0.6

7.1

12.9

0.55

—

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

141

Table B17. Average thyroid and effective doses to the populations of European countriesa [based on D13]Country or region

Thyroid dose (mGy)Pre-school
children(0–6 y)School children(7–14 y)Adolescents(15–17 y)

Adults(>17 y)All ages

Effective dose (mSv)
accrued in the period
1986–2005

Albania

7.9

4.7

3.3

2.8

3.5

0.52

Austria

6.0

2.3

1.1

0.9

1.5

0.98

Belgium

1.6

0.7

0.4

0.4

0.5

0.03

Bosnia and Herzegovina

15.6

9.5

6.7

5.7

7.0

0.41

Bulgaria

13.6

6.7

3.8

3.1

4.5

0.64

Croatia

17.3

10.2

6.3

5.0

6.8

0.47

Cyprus

3.7

2.0

1.3

1.1

1.4

0.08

Czech Republic

8.5

3.8

2.2

1.7

2.6

0.37

Denmark

0.09

0.05

0.03

0.02

0.03

0.03

Estonia

1.9

1.3

0.8

0.7

0.9

0.14

Finland

0.9

0.7

0.4

0.3

0.4

1.36

France

1.5

0.6

0.3

0.3

0.4

0.07

Germany

1.6

0.7

0.4

0.3

0.5

0.17

Greece

12.5

4.9

2.6

2.0

3.3

0.72

Hungary

4.1

1.7

1.0

0.7

1.2

0.3

Iceland

—

—

—

—

—

0.01

Ireland

1.8

0.8

0.5

0.4

0.6

0.21

Italy

6

2.6

1.5

1.2

1.8

0.33

Latvia

4.2

2.4

1.7

1.5

1.8

0.1

Liechtenstein

6.2

2.3

1.2

0.9

1.6

0.91

Lithuania

18.4

8.8

5.3

4.3

6.2

0.33

Luxembourg

1.8

0.9

0.5

0.4

0.6

0.11

Macedonia (Former Yugoslav Rep. of)

7.9

4.8

3.4

2.8

3.5

0.47

Malta

5.3

1.9

0.9

0.7

1.2

0.29

Netherlands

0.8

0.5

0.4

0.3

0.4

0.05

Norway

0.7

0.4

0.3

0.2

0.3

0.38

Poland

5.5

2.1

1.1

0.8

1.4

0.25

Portugal

0.007

0.004

0.003

0.002

0.003

0.003

Republic of Moldova

15.9

7.0

4.5

3.9

5.4

0.97

Romania

12.3

4.9

2.6

2.0

3.3

0.61

Serbia and Montenegro

7.8

4.7

3.3

2.8

3.5

0.55

Slovakia

12.3

5.0

2.7

2.1

3.4

0.41

Slovenia

17.3

10.6

7.5

6.3

7.8

0.98

Spain

0.08

0.04

0.02

0.02

0.03

0.009

Sweden

0.6

0.3

0.2

0.2

0.2

0.31

Switzerland

3.9

4.0

2.6

2.0

2.4

0.46

United Kingdom

0.5

0.2

0.1

0.08

0.1

0.05

a The values quoted in [D13] have not necessarily been endorsed by the individual countries concerned.

142

Table B18.

UNSCEAR 2008 REPORT: VOLUME II

Collective thyroid and effective doses to the populations of European countriesa [based on D13]Country

Population in 1986
(millions)Collective thyroid dose(man Gy)

Collective effective dose accrued in
1986–2005 (man Sv)

Albania

3.02

11 0001 600

Austria

7.56

11 000

7 400

Belgium

9.86

5 100

300

Bosnia and Herzegovina

4.4

31 0001 800

Bulgaria

8.89

40 0005 700

Croatia

4.72

32 000

2 200

Cyprus

0.64

900

50

Czech Republic

10.34

2 700

3 800

Denmark

5.12

200

150

Estonia

1.53

1 300

200

Finland

4.92

1 900

6 700

France53.6

23 000

3 800

Germany

77.66

37 000

13 000

Greece9.83

33 000

7 100

Hungary

10.62

12 000

3 200

Iceland

0.24

—

2

Ireland

3.54

2 100

700

Italy

56.91

100 000

19 000Latvia

2.6

4 800

300

Liechtenstein

0.03

50

30

Lithuania

3.58

22 0001 200

Luxembourg

0.37

200

40

Macedonia (Former Yugoslav Rep. of)

1.92

6 800

900

Malta

0.34

200

100

Netherlands

14.49

5 300

700

Norway

4.17

1 200

1 600

Poland37.46

54 0009 400

Portugal

10.01

30

30

Republic of Moldova

4.25

23 000

4 100

Romania22.73

75 000

14 000

Serbia and Montenegro

10.5

37 0006 000

Slovakia

5.19

18 000

2 000

Slovenia

1.99

16 000

2 000

Spain

37.3

1 000

300

Sweden

8.35

1 800

2 600

Switzerland

6.49

15 000

3 000

United Kingdom

55.87

7 400

2 800

Total (rounded)~500

660 000

130 000

a The values quoted in [D13] have not necessarily been endorsed by the individual countries concerned.

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

143

Table B19. Summary of doses (rounded) to the main population groups exposed to radiation as a result of the Chernobyl accident
Country

Population size
(thousands)

Average thyroid dose(mGy)

Average effective dosein 1986-2005 a,b(mSv)

Collective thyroid
dose(man Gy)

Collective effective
dose in 1986–2005(man Sv)

Recovery operation workersc,d [K8, K23, K24, K31, N14, R7, R12, S10, S30, T9]
Belarus

91

—

51

—

4 700

Russian Federation

190

—

107

—

20 100

Ukraine

230

—

151

—

34 500Estonia

4.8

—

99

—

460

Latvia

6.1

—

117

—

700

Lithuania

7.0

—

109

—

750

All

530

—

117

—

61 200Evacuees [B28, B31, L4, S26, U3]
Belarus

25

1 100

36

27 000900

Russian Federation

0.19

440

35

82

7

Ukraine

90

330

30

30 000

2 700

All

115

490

31

57 000

3 600

Inhabitants of contaminated areas of Belarus, Russian Federation and Ukrainee [B29, K8, L4, M14, Z4]
Belarus

1 800

182

12

320 000

20 800Russian Federation

2 500

27

7

70 00016 900

Ukraine

2 100

123

10

260 000

21 200

All

6 400

102

9

650 000

58 900Inhabitants of Belarus, Russian Federation and Ukraine [B29, K8, L4, M14, Z4]
Belarus

10 00049

2.4

480 000

24 000Russian Federation(19 “affected” regions)

37 0005

1.1

190 000

40 000

Ukraine51 00019

1.2

960 000

61 000All

98 00016

1.3

1 600 000

125 000

660 000

130 000

Inhabitants of distant countriesf [D13]All

500 000

1.3

0.3

a The effective dose to workers includes only the dose due to external irradiation, which was delivered essentially from the accident in 1986 to the end of 1990. The effective
dose was assumed to be numerically equivalent to the dose recorded in the national registry.
b The effective dose to the general population is the sum of the effective doses due to external and internal irradiation, excluding the contributions from the thyroid dose. The
external dose was calculated for 1986–2005. The internal dose is the committed dose from intakes during 1986–2005.
c The average and collective effective dose have been calculated using the assumption that the dose distribution obtained for the workers with recorded doses applies to theentire population of workers.
d The thyroid doses are not summarized in this table, as they are only available for a very small number of workers.
e The contaminated areas were defined arbitrarily in the former Soviet Union as areas where the 137Cs levels on soil were greater than 37 kBq/m2.
f The distant countries that have been considered are all the European countries, with the exception of Belarus, Russian Federation, Ukraine, Turkey, countries of the Caucasus,
Andorra, and San Marino.

APPENDIX C.
early HEALTH EFFECTS
I. Summary from PRevious UNSCEAR Reports­cornea (keratitis) and the lungs (pneumonitis), and withintestinal and oropharyngeal injuries.

C1. The first information on the early manifestations andoutcomes of acute radiation syndrome (ARS) in persons
who were exposed to ionizing radiation in the early phaseof the Chernobyl accident was provided to the international community in Vienna in August 1986 [I31]. The
analytical data derived from clinical observations of thevictims of the accident at the Chernobyl nuclear power
plant (ChNPP) were presented in the appendix, “Acuteradiation effects in victims of the Chernobyl nuclear power
plant accident”, and annex G, “Early effects in man ofhigh doses of radiation”, of the UNSCEAR 1988 Report[U7]. Updated information on the early health effects,
some longer term effects and the causes of death among
emergency workers was provided in section III of annex J,“Exposures and effects of the Chernobyl accident”, of the
UNSCEAR 2000 Report [U3].

C3. The average bone‑marrow doses and the prognoses
regarding the further course of the ARS were determined using
biological criteria. During the early period, most of the information was obtained from chromosome analysis, lymphocyte
counts and the primary reaction periods; later, most of theinformation was obtained from the granulocyte counts. Other
indications were of a supplementary nature. For three cases,
the estimated dose agreed closely with that obtained from anelectron spin resonance study of dental enamel after death.
C4. There was a need for further analysis of the evolutionof the early effects, for a more accurate understanding of thenature of the lung and neurological injuries, and for moredetailed data on the relevance of biological dose indicatorsand the reasons for disparities between them.

C2. The simultaneous treatment of a large group of patients(134) for ARS with varying degrees of severity clarified
many aspects of the early effects in man of acute irradiation,
especially of the bone‑marrow syndrome, which was theprincipal clinical syndrome. For many patients, the bone‑­marrow syndrome was combined with radiation damage tothe skin; for some, it was combined with damage to theC5. Both the UNSCEAR 1988 and 2000 Reports contained
detailed information on the acute health effects from the Chernobyl accident. There are no substantive new data regarding
the acute effects and therefore the material presented in thefollowing section is a summary of that presented previously.

II. Update
A.

Acute radiation syndromeof the Institute of Biophysics (currently Burnasyan Federal
Medical Biophysical Center) in Moscow.

C6. There are several publications that have described theacute health effects of the Chernobyl accident in detail [A8,B1, G12, G13, G14, I34, M13, R11, V3]. During the first
few hours after the accident, a number of ChNPP personnel
and firemen were admitted to the local hospital with symptoms of possible radiation injury. Emergency dosimetry was
virtually non‑existent. Based on the expected radiation
effects, there appeared to be about 150 victims identified
within 4.5 hours of the explosion who would probably needadvanced treatment at the Radiation Medicine Department

C7. The possible diagnosis of acute radiation syndrome
was initially considered for 237 persons. From this group,
115 were transported to the Radiation Medicine Department of the Institute of Biophysics, Moscow. Within ­several
days, ARS was verified in 104 of these persons. Later,
30 additional patients were also verified retrospectively tohave ARS, making a total of 134. The estimated doses tothese patients and the clinical outcomes are shown intable C1 [A8].

145

146

UNSCEAR 2008 REPORT: VOLUME IITable C1. Data for the 134 patients with acute radiation syndrome [U3]
Absored dose range (Gy)

Number of patientsa

Number of early deathsb

Number of survivors

Mild (I)

0.8–2.1

41

0 (0%)

41

Moderate (II)

2.2–4.150

1 (2%)

49

Severe (III)

4.2–6.422

7 (32%)

15

Very severe (IV)

6.5–1621

20 (95%)1

Total

0.8–16

134

28

106

Degree of ARS

a Acute radiation syndrome was not confirmed in a further 103 treated workers.
b	Percentage of treated patients in parentheses.

C8. During the first two days, analyses were conducted
to ascertain the degree of radioactive contamination of theskin and the activity of the radionuclides (including radioiodine and radiocaesium) taken into the body. These
analy­ses were carried out on 75% of the total number ofpatients. The majority of patients did not show radio­
nuclide body burdens above 1.5–2.0 MBq (40–50 μCi).

Some 6% of the patients had internal burdens approximately 2–4 times higher than this. The patients were also
analysed for the presence of 24Na, to ascertain the neutron
exposure. Neutron exposure, however, was found to contribute only a very small part of the total exposure of thepatients. Data on internal and external exposures are­presented in table C2.

Table C2. Doses of external and internal exposure of the lungs and thyroid to 23 patients who died shortly after the Chernobyl
accidenta [U3]Personal code

Internal absorbed dosea (mGy)

External absorbed dose (Gy)Thyroid

Lungs

25

21

0.26

8.2

18

24

2.8

6.4

22

54

0.47

4.3

5

62

0.57

6.2

9

71

0.77

5.6

21

77

0.68

6.4

8

130

1.5

3.8

2

130

2.2

2.9

19

210

3.5

4.5

23

310

2.3

7.5

1

340

8.7

11.1

15

320

27

6.4

16

470

4.1

4.2

3

540

6.8

7.2

17

600

120

5.5

4

640

34

6.5

7

780

4.7

10.2

10

890

9.4

8.6

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

Personal code

Internal absorbed dosea (mGy)147

External absorbed dose (Gy)Thyroid

Lungs

11

740

29

9.1

14

950

20

7.2

20

1 900

19

5.6

24

2 200

21

3.5

13

4 100

40

4.2

a Internal doses were accumulated to the moment of death and doses of external exposure evaluated using chromosomal analysis of peripheral blood lymphocytes. The relative
errors in the internal organ doses are estimated to be less than 30%.

C9. Serial blood samples were obtained during the first
three days for analysis of a number of factors, particularly thepresence and severity of lymphopenia. This, combined withinformation on the time when symptoms such as nausea, vomiting and diarrhoea occurred, was of the greatest value for
medical prognosis [B33, K18]. Cytogenetic dosimetry was
also conducted using blood samples [P17, S24]. During thefirst 7–10 days, the depth and persistence of bone‑marrowdepression became more evident, as well as the presence orabsence of gastrointestinal symptoms. Less informative andmore difficult to evaluate for the purposes of prognosis wereradiation dermatitis due to beta irradiation, and epithelial radiation damage of the upper digestive and pulmonary tracts.
Based on the clinical and laboratory data, bone‑marrow allogenic transplantation was considered and criteria for patient
selection were developed. These criteria were later found to be
too lax. Allogenic bone‑marrow transplantation was subsequently performed on 13 patients, and implantation of humanfoetal liver cells was performed on only 6 other patients owing
to the absence of appropriate donors [G13, I31].

Table C3.

C10. All of the expected major clinical symptoms of
ARS, either singly or in combination, were observed inpatients with whole‑body gamma exposures of more than
1 Gy. As mentioned earlier, bone‑marrow depression wasseen in all 134 ARS patients. Gastrointestinal syndrome
was observed in 15 patients and radiation pneumonitis in
8 patients. Combinations of these syndromes with severe
widespread radiation dermatitis occurred in 19 patients(table C3) [B38]. Skin doses exceeded bone‑marrow doses
by a factor of 10–30 in some patients and a number of thesepatients had estimated skin doses in the range of 400–
500 Gy. This local radiation damage to the skin resulted insignificant aggravation of existing pulmonary and hepaticor renal abnormalities. Burns due to beta irradiation were
the primary cause of death in a number of patients and significantly increased the severity of the ARS. In particular,when skin burns extended over more than 50% of the­surface area of the body, this was a major contributing
cause of morbidity and mortality.

Relationship of ARS severity grade and percentage of skin burns and skin dose in Chernobyl patients [A8, B38]

Number of patients

ARS severity grade

Percentage of skin burn
1–10%

10–50%

50–100%Approximate absorbedskin dose (Gy)

31

I

2

1

0

8–12

43

II

2

9

1

12–20

21

III

3

15

3

20–25

20

IV

1

10

9

>20

C11. In the early period (14–23 days post exposure),
15 patients died of skin or intestinal complications and2 patients died of pneumonitis. In the period 24–48 days
after exposure, there were six deaths from skin or lung injury
and two from secondary infections following bone‑marrowtransplantation. A patient who had severe ARS developed
acute diffuse interstitial pneumonia with rapid developmentof hypoxemia, which proved fatal. Bacterial and fungal

pneumonia was not confirmed at autopsy, and it appeared that
there was acute radiation pneumonitis with possible cytomegalovirus being present. There were two deaths at relatively
late periods (86–96 days) related to infection complications
due to local radiation injury of the skin and insufficient renal
function. One female patient died at 112 days from a brain
haemorrhage. Underlying bone‑marrow failure was the major
contributor to all of the deaths during the first two months.

148

UNSCEAR 2008 REPORT: VOLUME II

C12. In addition to using blood counts for dose assessment, lymphocytes were also cultured for counting. The
exact dose that patients had received was difficult to assess
since estimates were based on a set of clinical symptoms;
assessments based on marrow depression and on cytogene­tics often yielded somewhat different results. Biochemicaland haematological indices were determined twice daily forpatients with ARS grades I-II; daily evaluations were carriedout for the more severe patients. These serial counts werevery important for the selection of supportive therapy and inorder to assess its effectiveness. Bacteriological tests werealso important for the effective management of antibiotic or
antifungal therapy. In the absence of signs of active healingof the skin after 50–60 days, a number of patients received
surgical grafts. The leg of one patient was amputated morethan 200 days after the accident [B40].
B.

Therapy and outcomes of patients with ARS

C13. The basic components of ARS therapy employedincluded:– Prophylaxis and therapy for infectious complications;– Detoxification;– Parenteral nutrition;– Transfusion therapy (allogenic transplantation of bonemarrow and human hepatic foetal‑cell infusion);– Topical therapy of damaged skin areas; and– Correction of secondary toxic metabolic disturbances.
C14. All patients who had grade II or more ARS wereplaced in single rooms, managed for delivering an aseptic
regimen. Ultraviolet lamps were used for sterilization andmedical staff were required to wash their hands thoroughly,
wear laboratory coats and masks and wash their shoes withan aseptic solution. Patients’ clothes were changed daily.
Microbial contamination indices were periodically monitored. Concentrations of micro‑organisms in air were kept
below 500 colonies per cubic metre.
C15. These same patients received prophylaxis against
endogenous infections, using Biseptol and Nystatin in theevent of fever. The patients were administered intravenouslywith a broad spectrum of antibiotics including aminoglycosides, cephalosporins and semi-synthetic penicillins. In morethan half of the cases, this usually terminated any fever.
However, if the fever had not gone within 24 to 48 hours, thepatients were each given 4–5 intravenous injections of 6 g
gamma globulin every 12 hours. Acyclovir was, for the firsttime, widely and successfully applied to acute ARS patientswith herpes infections. About one third of the patients­manifested herpes on the face, lips and oral mucosa.
C16. Many of the patients received multiple transfusions
with fresh donor thrombocytes. The efficacy of thesetransfusions was confirmed, not only by the absence oflife‑threatening bleeding in the patients with prolonged(more than 2–4 weeks) thrombocytopenia (below 5,000–
10,000 per microlitre), but also by the absence of any visible signs of increased bleeding in the majority of thepatients. On average, 3–5 thrombocyte transfusions werenecessary for the successful therapy of each patient withgrade III ARS.
C17. Red cell transfusions were not necessary for the therapy of agranulocytic infectious complications. Red celltransfusions were however needed for a number of patientswith grade II–III ARS who also had significant injury. All
patients who had severe multiple organ damage were treatedby modern detoxification techniques and anti‑infectious andsymptomatic therapies. Haemoabsorption, plasma absorption and plasmapheresis were applied. Direct anticoagulation was also used as a means to improve microcirculation.
The major feature of intestinal syndrome therapy was total
parenteral nutrition with correction of volume deficiency bymeans of nutritive liquids and electrolytes. This therapy was
highly effective.
C18. Myelodepression and the potential need for additional measures were evaluated according to the scheme
previously elaborated by Konchalovsky et al. [K18] andothers [G14]. Additional data from blood lymphocyte
counts indicating a dose over 6 Gy were also used. Bonemarrow was sampled from relatives of patients who wereidentical (six cases), haploidentical (four cases), or haplo­
identical plus one common antigen in second haplotype(three cases). Typing was only conducted for A, B, and C
loci because of the urgency of the situation. The cases of
haploidentical bone‑marrow transplantation were conducted with elimination of T‑lymphocytes. Three deaths
were considered to have occurred unnecessarily as a resultof inappropriate bone‑­marrow transplantation. Bone‑­marrow transplantation for patients with doses below
9 Gy only worsened the ARS therapy results owing to thedevelopment of side effects [B40].
C19. Application of allogenic bone‑marrow transplantation to these patients has demonstrated that:– In radiation accidents, the percentage of victims
for whom allogenic bone‑marrow transplantation
is absolutely indicated and who can obtain a clear
benefit from such transplantation is very small;– In the case of bone‑marrow damage resulting fromwhole‑body gamma exposure of 6–8 Gy, transplantsurvival is possible; however, the transplantation
may be life threatening owing to the developmentof secondary disease and disease due to graft versus
host; and– Recovery of myelopoiesis and survival is possible
following whole‑body exposures of 6–8 Gy, andthis was found after rejection of haploidenticaltransplants (three cases) as well as in patients who
were not given transplants owing to the absence ofan appropriate donor (four cases).

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

C20. Each patient who had grade III–IV bone‑marrowsyndrome usually also had radiation skin damage andrequired continuous nursing by highly qualified personnel.
The effectiveness of therapy was judged as satisfactory
since there were no fatalities with patients with ARS
grade II (2–4 Gy doses), excluding the one female patient

III.

149

who later died from a brain haemorrhage. There were
27 patients in the clinic with ARS grade III–IV. The fatal
outcomes in this group basically resulted from acute severe
cutaneous injuries, from lung damage and from a combination of skin and intestinal damage combined withbone‑marrow depression.

SUMMARy

C21. The Chernobyl accident resulted in many of thecases of acute radiation syndrome that have been reported
worldwide. Cases occurred among the plant employees andfirst responders but not among the evacuated populations or
the general population. The diagnosis of acute radiation
syndrome was initially considered for 237 persons basedon symptoms of nausea, vomiting and diarrhoea. Subsequently, the diagnosis of ARS was confirmed in 134 ­persons.
There were 28 early deaths of which 95% occurred withpeople with whole‑body doses in excess of 6.5 Gy. Underlying bone‑marrow failure was the main contributor to all
deaths during the first two months.

C22. Allogenic bone‑marrow transplantation was performed on 13 patients and an additional 6 received
human foetal liver cells. All of these died except one
individual who later was discovered to have recovered
his own marrow and rejected the transplant. Two or threepatients were considered to have died as a result of transplant complications. Skin doses exceeded bone‑marrowdoses by a factor of between 10 and 30 and at least 19 of
the deaths were considered to be primarily due to infection resulting from large area burns caused by beta
­i rradiation. Internal contamination was of relatively
minor importance.

APPENDIX D.
LATE HEALTH EFFECTS
I.

A.

LATE HEALTH EFFECTS IN WORKERS WHO SURVIVED
ACUTE RADIATION Syndrome

Summary from the UNSCEAR 2000 Reportleast half a year, and normalization may not have occurred
for several years after exposure. This does not necessarilymean that after the acute phase (i.e. the first three months),
recovering patients displayed major immunodeficiency,
and it was not surprising that studies of immune status
revealed a pattern of changes in blood cell concentrations
without clinical manifestations of immuno­deficiency. For
higher doses of radiation, T‑cell immunity may have shown
protracted abnormalities; however, these abnormalities
were not necessarily associated with ­clinically ­manifested
immunodeficiency.

D1. The early adverse health effects in emergency workers
subjected to high levels of radiation mostly during the firstnight following the accident at the Chernobyl nuclear power
plant (ChNPP) were presented in detail in the appendix,“Acute radiation effects in victims of the Chernobyl nuclear
power plant accident”, of the UNSCEAR 1988 Report [U7].
Updated information on the early health effects in emergency workers, some long‑term effects and the causes ofdeath was provided in annex J, “Exposures and effects of theChernobyl accident” of the UNSCEAR 2000 Report [U3].
A summary of that information and the experience in treating workers who developed acute radiation syndrome (ARS)
is presented in appendix C, “Acute radiation health effects”,
of this annex. The material presented in the following­section is focused on the late health effects in emergency­workers who survived ARS.

B.

UpdateD5. According to the data from retrospective analysis ofcase histories, the total number of verified cases of ARS was
134 out of the 237 cases that were initially registered [B41,
U3]. During the acute phase, 28 fatalities were recorded;
information on this phase was provided in the UNSCEAR
1988 Report [U7].

D2. Cataracts, scarring and ulceration were the mostimportant causes of persistent disability in the ARS survivors. The consequence of severe skin ulceration was cutaneous fibrosis, which had been successfully treated with
low‑dose interferon. Surgical treatment was provided to
15 ARS survivors with extensive cutaneous radiation injuries, including ulcerations and fibrosis, between 1990 and
1996. Follow‑up of these survivors had not shown a single
case of skin cancer. The recovery of physical ability was
related to the severity of the initial symptoms of ARS. To
limit further occupational radiation exposure of the ARS
survivors, legal measures were adopted in the Russian­Federation and other countries of the former Soviet Union
which restricted their activities or caused them to change
their occupations.

D6. From 1986 to 1990, 83 emergency workers diagnosed
with ARS of different levels of severity were under clinicalsurveillance at the clinic of the Burnasyan Federal Medical
Biophysical Center (FMBC)—formerly the Radiation Medi­cine Department at the Institute of Biophysics, Moscow. By
1996, the number of patients being followed up at the FMBC
clinic had fallen to ten. The distribution of patients seen at
FMBC according to the grade of ARS that they survived andto local radiation injuries that they incurred is presented intable D1.
D7. Since 1990, a large group of ARS survivors as well asa group of people initially suspected of having ARS, butlater confirmed as not having ARS (hereafter expressed as
people with “unconfirmed ARS” or “ARS grade 0”) were
under surveillance at the Ukrainian Research Center ofRadiation Medicine (URCRM), Kiev [B9, B39, B42]. The
distribution of patients seen at the URCRM according to thegrade of ARS is shown in table D2. The number of patients
reported in different publications vary; this is because ofdifferent time periods of observation and because about
20% of the patients have been lost from the follow‑up system. Early in 2008, there were 59 patients with ARS being

D3. Sexual function and fertility among the ARS survivors
were investigated up to 1996. In the majority of cases, functional sexual disturbances predominated, while 14 normalchildren were born to the ARS survivors within the first five
years after the accident.
D4. Patients with ARS grades III and IV were severely
immunosuppressed. Whereas haematopoietic recovery had
occurred within a matter of weeks or, at most, months, fullreconstitution of functional immunity may have taken at
151

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UNSCEAR 2008 REPORT: VOLUME II

followed up in Ukraine. The ARS grade 0 patients are sometimes used as a comparison group; however, they clearly do
not represent a true unexposed control group and appear tohave been exposed to absorbed doses in the range of about
0.1 Gy to about 1.0 Gy.

of ARS or on dose is ambiguous. The cytopenia frequency
among the ARS survivors was higher than among persons
with unconfirmed ARS (see figure D‑I). The frequency ofcytopenia in both groups decreased with time after exposure[B9, B39, B42] and was essentially equal by 2006.

D8. In both clinics, the patients undergo annual examinations of the main systems of the body. As will be evident
from the following sections, the follow‑up data are difficult
to analyse, compare and use because the data from the two
clinics have been presented in different formats, have useddifferent diagnostic criteria and only overlap for part of thetime (partially in 1986–1990 and, to a lesser extent, in 1991–
1995). For these reasons and also because of the small numbers of cases and the lack of analyses using formal
epidemiological methods, it is generally not possible to infer
trends in disease and mortality rates from these data.

D13. The URCRM has reported on the frequency of deviations of various peripheral blood values but these data are
difficult to interpret without knowing the exact time period,
criteria and values used to define the term “deviation”. For
example, deviations in erythrocytes were reported to occur
in 67–91% of the ARS patients [B39], while the Moscow
group reported abnormal values in erythrocytes in less than
17% of the ARS patients for the entire 20‑year period after
the accident.
2.

D9. The data primarily refer to the following specific healthoutcomes: transient peripheral cytopenia, cataracts, thyroid
disorders, local skin injuries, neuropsychological disorders,
oncological diseases and deaths, and non‑­oncological diseases and death. Most of these topics are also discussed more
extensively later in this appendix for the ARS survivors,other emergency workers, the recovery operation workers,
and the general population.
1.

Transient peripheral cytopenia

D10. Studies of peripheral blood indicators on patients at
1.5–2 years, 2–5 years, 5–10 and 10–20 years at FMBC,
and 10–15 years at URCRM, after the accident produced
generally similar results. During the first five years after theaccident, the patients’ peripheral blood indicators returned
practically to normal although transient moderate cyto­
penia was observed in many patients. Granulocytopenia,
thrombocytopenia, erythrocytopenia and lymphocytopenia
were most frequently observed during the first 5 years after
the accident, but from 5–15 years after the accident, theprevalence of cytopenia cases gradually declined.
D11. The frequency of haematological abnormalities inperipheral blood for the ARS survivors seen at FMBC overa 20‑year period is shown in table D3. Reduction was seen
mainly in thrombocytes and, to a lesser extent, in neutrophils
and lymphocytes. There was little, if any, reduction in either
haemoglobin or erythrocytes.
D12. For both the group of ARS survivors and the group of
persons with unconfirmed ARS seen at URCRM, haematosis has generally recovered [B9, B39, B42]. Furthermore,recovery of the values of the blood parameters to minimum
normal levels basically occurred during the first two months
after exposure. The average levels of granulocytes, thrombocytes and lymphocytes in peripheral blood were within
the normal range, although in some patients transient cytopenic conditions were noticed. Any dependence of haematological indices beyond two years post accident on the grade

Radiation‑induced cataracts

D14. There are major differences in the data and conclusions of the FMBC and URCRM physicians and researchers regarding radiation‑induced cataracts. According to
the FMBC findings, the threshold for the development ofradiation‑induced cataracts due to beta and gamma irradiation was 3.2 Gy, while the researchers at URCRM indicated that radiation‑induced cataracts have been found atabsorbed doses of less than 1 Gy. This may be because ofdifferences between the criteria used at URCRM andthose used in previous studies [B39, K1, N2, N5].
D15. For the ARS survivors seen at the FMBC, the prevalence of eye disease was 15% versus 6% in the group withunconfirmed ARS, owing to a rise in the number of radiation‑induced cataracts. Most of the radiation‑induced cataracts in the patients who suffered moderate or severe ARS
developed in the first few years after the accident. The latent
period for cataract development was shorter for the patients
who had received higher radiation doses [G9, N5, N6]. The
relationship between the estimated dose and the latent period
is shown in figure D-II. There was no relationship between
the latent period and the age of the patient at the time of
exposure. The cataractogenic effect appeared to have ceased
after 200 months post exposure, and no new cases werediagnosed after 1999. The estimated doses due to beta andgamma irradiation of various parts of the eye, and the significant difference in depth–dose distribution, are shown intable D4 [G9] and in reference [G10].
D16. For the group of patients followed up at URCRM,
numerous cases of radiation‑induced (subcapsular posterior)cataract were reported, i.e. 23 cases among the ARS survivors and 3 cases among the persons with unconfirmed ARS[B44, G9]. A strong dependence of cataract prevalence inthe long term on the grade of the ARS, and therefore thedose, is shown in figure D-III [B9, B44]. The majority ofcataract cases developed during the first five years after
exposure, and the dependence of the latent period on dose oron the ARS grade was not statistically significant. Furthermore, in contrast to the FMBC findings, a monograph by

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

153

Bebeshko et al. [B39] of URCRM does not account for thecontribution of beta radiation to the dose to the lens of theeye, which may result in an underestimation of the total(beta + gamma) dose, and therefore of the value of thethreshold dose.

problems of treating recurring radiation‑induced ulcers—atleast in the case of five patients suffering from the consequences of local radiation injuries sustained at the ChNPP
who were under observation at the FMBC. Repeat operations necessitated by the recurrence of late radiation‑induced
ulcers at the same site, have not been reported [G9].

3. Thyroid abnormalities

D22. Up to 2005, 38 patients suffering from the consequences of local radiation injuries were under observation(5 at FMBC and 33 at the URCRM). These included
18 persons with skin injuries of grades 2 and 3. Amputations (a lower leg, a finger and part of a finger) were performed on 3 patients [G9]. In the long term, telangiectasia
was observed in 20 patients and repeated skin ulcerationand fibrosis were observed in 6 patients. The remainder
had moderate local skin atrophy and hyperkeratosis. There
was a strong dependence of the frequency and intensity of
the long‑term effects on the grade of local skin injury
incurred during the acute phase.

D17. Hypothyroidism among the ARS survivors is ofinterest owing to the high ambient levels of radioiodine­during the accident. According to the results of the thyroid
radio­metry carried out on 81 patients during the acute periodof ARS, the absorbed dose to the thyroid in only one patientreached 11 Gy.
D18. Among the patients monitored at the FMBC laboratory, signs of thyroid‑function abnormalities were observed
mainly during the first five years, with hypothyroidism
found in 4 out of 83 patients (4.8%) and hyperthyroidism in
one patient (1.2%). During the period 2001–2007, only 1 in
10 patients was hypothyroid. The number of cases of nodular goitre has increased from one during the first five years
post accident and is now present in 4 out of 10 patients [G9].
D19. The URCRM researchers reported that 15 ARS
patients suffered hypothyroidism in 1986 with 12 of them
returning to normal in 1987. Three cases of moderately
pronounced hypothyroidism were observed in subsequent
years [B39].
4. Local radiation‑induced skin injuries
D20. The major health consequences observed among the
ARS survivors were related to local radiation‑induced injuries (skin burns and radiation‑induced cataracts) that often
required surgery, sometimes repeated [N5]. In contrast to
ARS, the local radiation injuries were a function of the dose
due to beta and, to a lesser extent, gamma irradiation. The
nature and severity of the skin injuries incurred during thelate stage were a consequence of the severity of the injuries
incurred during the acute phase. At the late-sequelae stage,
the patients who suffered first‑degree local radiation injuries
displayed various levels of skin atrophy, ranging from slightsmoothing of the skin surface to more pronounced changes.
Over longer periods, the slight atrophic changes of the skindisappeared almost completely. With second‑degree local
radiation injuries, there was pronounced atrophy of theskin—areas of hypo‑ and hyperpigmentation, hyperkeratosis and telangiectasia, scarring, radiation‑induced fibrosis,
and late radiation‑induced ulcers [G9].
D21. With third‑ and fourth‑degree local radiation injuries, there were areas of fibrous scarring, contractures,
non‑healing primary radiation‑induced ulcers and persistently recurring late radiation‑induced ulcers. With the introduction in the 1990s of skin autoplasty using microsurgery
techniques, it became possible to significantly reduce theD23. Seven patients out of ten who were followed up in
recent years at the FMBC clinic had local radiation injuriesof the skin, i.e. radiation‑induced fibrosis, relapsed ulcers
and contraction. For the ARS survivors seen at the FMBC,
the prevalence of dermatological diseases due to local radiation injury in 1986 was 7%. The data are shown infigure D‑IV.
D24. The late effects of local radiation injuries to the skinwere studied at the URCRM in 39 persons from both groups(the ARS survivors and persons with unconfirmed ARS). In
15 (39%) out of the 39 persons, no changes were found in theskin at the places of the former radiation injury. For the restof the patients, local skin atrophy, skin hyper‑ and hypopigmentation, peeling and telangiectasia were observed. There
was a strong dependence of the frequency and intensity oflong‑term effects on the grade of ARS and on the grade ofthe local skin injury in the acute phase [B39]. The data areshown in figure D‑V.
5.

Neuropsychological disorders

D25. Much attention was paid in the URCRM studies to agroup of persons for whom a high prevalence (up to 100%)of nervous‑system diseases (including functional abnormalities, such as vegetative and vascular dystonia) was registeredduring the first decade. The diagnostic criteria used were notalways clear and the diagnoses were often based on subjective judgement. The URCRM also reported that during thesecond decade after the accident, there was a large contribution from organic diseases (cerebral atherosclerosis, and soon). There was no dependence of the frequency of diseaseon the grade of ARS and therefore, the dose. This indicatesan aetiology other than radiation [B9, B39, B42].
D26. The majority of the ARS patients followed up were
officially recognized as invalids with limited work ability.
The small number of cases of people returning to work did

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not correlate with the severity of ARS that they survived orwith their local radiation injury; their return was mostly
determined by their personal motivation and the ­competenceof the medical doctor [G9].
6.

Oncological disease incidence and mortality

D27. According to Galstyan et al. [G9] the percentage of
the ARS patients with cancer was 4.6% and included
four cases of solid cancer (a kidney cancer, a colon cancer
and two cases of thyroid cancer) with an average age of
45 years at diagnosis and an average latent period of about
11.5 years. There were also three cases of myelodysplastic
syndrome, one case of acute myelomonoplastic leukaemia
and one case of chronic myeloid leukaemia. The average
age at diagnosis was 53 years with an average latent periodof 11.8 years. No malignant thyroid neoplasms weredetected in the 10 patients under observation in recent
years at the FMBC, although multiple basal cell carcinomas have been detected in 2 patients who had sufferedfrom grade III-IV ARS.
D28. Among 13 solid cancers diagnosed in the patients followed at the URCRM, 4 were in the ARS survivors and 9 in
the persons with unconfirmed ARS (used as the control
group) (table D5) [B44]. The mean latent period after exposure was 14 years for both groups. No statistically significant
dependence of the disease frequency or severity on the gradeof ARS and therefore the dose, has been observed. In fact, thecrude incidence rate for solid cancers was higher for the groupof unconfirmed ARS patients (9 out of 96), who had lower
doses, compared to that for the ARS patients (4 out of 72).
D29. During 20 years (1987–2006), 19 ARS survivors and
14 persons with unconfirmed ARS died for various reasons[B10, B39, B41, B42, B44, G9, U3]. Among the ARS survivors, the most frequent cause of death (4 cases out of 19) was
haematological malignancy with a mean latent period of
9 years [G9].
7. Non‑oncological disease incidence and mortality
D30. Data on non‑oncological diseases among the ARS
survivors are complicated by the fact that often what isreported are either the number of patients suffering from acategory of disease or the number of new diagnoses for acategory of disease. Without specific diagnoses, meaningfulconclusions regarding potential radiation effects are difficult
to draw. For example, the category of respiratory disease
would include infectious and neoplastic aetiologies as well
as diseases resulting from smoking.
D31. The increasing age of the population with time is also
an important factor influencing the increases in the numbersof disease cases and deaths. The long‑term morbidity andmortality of the ARS survivors was analysed by the FMBC
and by the URCRM. During the follow‑up period 1986–2006,

the mean age of the patients increased from 35.5 to 54 years,
which, in itself, would imply an increased number of somatic
diseases unrelated to radiation exposure.
D32. As for the other areas of medical follow‑up of the
ARS survivors, there appear to be significant differences
between the prevalence of diseases reported by the FMBC
and URCRM. Both groups however have generally been
unable to link the prevalence of non‑neoplastic diseases to
the grade of ARS.
D33. The number of patients with diseases in four selected
systems of the body followed up at the FMBC clinic is presented in table D6. It is reported that the general health condition of the ARS survivors is similar to that of the malepopulation of the Russian Federation of corresponding age.
An important exception is the increase in the percentage ofpatients with cardiovascular disease from 53% in 1986–1990
to 100% in 2001–2007; the increase correlates with theirincrease in age. The increase in the observed number of disease cases is largely attributable to the targeted diagnosticsof the FMBC clinic. A comparison was made of the morbidity of the ARS survivors with that of the unconfirmed ARS
group followed up at the FMBC clinic over the 15 years
since the Chernobyl accident; it was concluded that, apartfrom dermatological and eye disease, the total disease prevalence and component disease prevalences are similar forboth groups [G9].
D34. The percentage of the ARS survivors with cardiovascular diseases reported among the patients seen at the
URCRM, in particular of essential hypertension and ischaemic heart disease, progressed with time and approached 90%
in 2006. The prevalence of gastrointestinal disease was also
reported to be high; it had grown from 80% in 1991 to almost
100% in 2006. The prevalence of hepatobiliary disease issimilar to that of gastrointestinal tract disease [B9, B39,
B42]. There was no dependence of the disease frequency on
the grade of ARS and therefore the dose; this indicates that
other risk factors than radiation are significant.
D35. The follow‑up of the ARS survivors at the URCRM
to the end of 2006, more than 20 years after exposure [B42],
indicated a high prevalence of various groups of disease.
Yet, no substantial difference between the ARS survivors
and the persons with unconfirmed ARS (control group)
regarding both the prevalence and morbidity structure was
identified (e.g. see figure D‑VI). The prevalence of reported
respiratory and endocrine diseases seen in patients at the
URCRM, has increased significantly with time, i.e. from
10–30% in 1991 to 70–80% in 2006, and from 5–15% in1991 to 60–70% in 2006, respectively.
D36. An increase in the number of cases of cardiovasculardisease was recorded later and correlated with the increasing age of the patients. The prevalence of this disease among
the ARS patients was lower during the second and third fiveyear periods but increased during the fourth five-year period.
Although there were considerable changes in the values ofANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

the biological parameters studied at the laboratory level, themajority of actual clinical manifestations took uncomplicated, compensated courses. Dependence of the disease frequency on the grade of ARS, and therefore the dose, has notbeen confirmed statistically [B39]. The use of the groupwith unconfirmed ARS as the internal control group is amethodological deficiency of the URCRM studies.
D37. By the beginning of 2007 (more than 20 years after
the accident), 19 ARS survivors (6 with ARS grade I;
8 with ARS grade II; and 5 with ARS grade III) and14 persons with unconfirmed ARS had died from various
causes [B10, B39, B41, B42, B44, G8, U3]. The mean age
of death, its standard error and range was: 45.5 ± 4.3 (26–53) years for persons with ARS grade I; 61.9 ± 4.9 (45–81)
years for those with ARS grade II; 62.2 ± 7.7 (41–87) years
for those with ARS grade III; and 57.0 ± 3.3 (32–73) years
for those with unconfirmed ARS (ARS grade 0). The
causes of death for the ARS survivors are presented intable D7. Among the causes of death were non‑oncologicaldiseases of internal organs (7, including 2 from pulmonary
tuberculosis and 2 from cirrhosis of the liver), sudden­cardiac death (6), oncological and onco‑haematological­d iseases (5) and trauma (1).
D38. The numbers of deaths due to various somatic diseases during the 20 years since the accident along with thegrade of ARS of the survivors are shown in table D8. deaths
from trauma and accidents are not included. In particular,
the proportion of survivors who died from somatic diseases
is substantially higher for those who survived ARS grade III
than for those who suvived ARS grades 0 or I; however, themortality coefficient is not age‑standardized, the number ofpatients is small, and 4 cases of haematological death playeda predominant role.

II.
A.

155

C. Summary
D39. The follow‑up of the ARS survivors indicates that:the initial haemotological depression has decreased substantially in many patients; there remain significant local
skin injury sequelae; there has been an increase in thenumber of cases of haematological malignancies; and anincrease in the number of cases of non‑haematological diseases is likely to have been a result of ageing and other factors unrelated to radiation exposure. However, the small
numbers of cases and deaths, the lack of formal epidemiological analyses and the impact of some loss of patientsfrom the follow‑up, make inferences about disease or mortality rates problematic. While an increased number ofcata­racts has been documented, debate remains about thethreshold dose for their induction and the criteria to be usedin their diagnosis as well as their clinical importance andprogression with time.
D40. The follow‑up of the subjects who had ARS should
be continued, especially because more than twenty years
have passed since the accident and late carcinogenic effects
may now be manifested. It would be very useful if thegroups following these patients would use the same metho­
dology and criteria for diagnosis and if these were carefully
explained in any publication. Special attention should begiven to the haematological proliferative diseases, tumoursof the endocrine system and skin cancers. The control group
could be composed of recovery operation workers exposed
in 1986 to doses below the threshold for deterministic
effects [N6]. Formal epidemiological methods should be
used in analysing these data. Furthermore, the data on the
ARS survivors of the Chernobyl accident should be analysed with reference to the ARS consequences in other­accidental situations [N5, O2].

REGISTRATION AND HEALTH MONITORING PROGRAMMESSummary from the UNSCEAR 2000 Report

D41. Following the Chernobyl accident, compulsory registration and continuous health monitoring of the recovery
operation workers and residents of the most contaminatedareas, including their offspring, had been initiated throughout the Soviet Union. Until the end of 1991, the All‑Union
Distributed Clinico‑Dosimetric Registry had recorded
information on 659,292 persons. After the dissolution of theSoviet Union into independent states, national Chernobyl
registries had continued to operate, but independently ofeach other. Changes in national registration criteria, compensation laws, dose‑reconstruction methods and follow‑up
mechanisms had increasingly limited the comparability ofdata from those different national sources. More detailed
registries of exposed populations had existed in the RussianFederation (Registry of Professional Radiation Workers,
Registry of Military Workers and the cohort of Helicopter

Pilots and Crew). However, the quality and completeness of
those registries remained largely unknown.
D42. The number of people registered in the national
Chernobyl registries continued to increase, even in recent
years, which raised questions about the completeness andaccuracy of registration. Information on mortality andcancer incidence had been collected from many different
sources and coded independently of international guidelines. Evidence from recent cohort studies suggested that
the Chernobyl health outcome data could not be successfully compared with health data obtained from official
statistical sources.
D43. Systematic linkage of the data from the Chernobyl
registries with existing mortality and/or cancer incidence registries, and the subsequent comparison of the health outcome
experience in the exposed cohorts with the corresponding

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national reference statistics were thought to be potentiallyvaluable tools for epidemiological research. Internal comparisons, e.g. using a low‑dose comparison group, were thought
likely to provide information on the risks associated with ionizing radiation in subsequent years. However, complete information (e.g. on previous exposure to ionizing radiation in an
occupational setting) would most probably only be available
for small subcohorts.
D44. Health outcome registries were considered to be an
important source of information for assessing the consequences of the Chernobyl accident. Their primary advantages were thought to be that the information had beencollected in a systematic way before and after the accident
and the criteria for data collection were the same in all countries of the former Soviet Union. However, most of these registries, whether related to mortality, cancer incidence or
special diseases, continued to be operated largely manually,
which seriously limited their use for epidemiologicalresearch purposes. The Chernobyl accident led to majorinternational efforts to computerize the cancer incidence
and special disease registries and to improve their registration methods so as to comply with international standards.
However, mortality registration systems had received little
attention. Information on the quality and completeness ofthese systems remained scarce.
D45. Compulsory cancer registration had been introduced
throughout the former Soviet Union in 1953. The systemrelied on passive reporting of information on all newly diagnosed cancer cases to the regional cancer registry for thepatient’s place of residence. Since the early 1990s, efforts
had been made to computerize the existing systems and to
gradually improve their quality in order to meet international standards. Belarus had been covered by a network ofcomputerized cancer registries since 1991. Computerization
had been well advanced in Ukraine, and full population coverage was expected soon. In the Russian Federation, efforts
to develop computerized cancer registration had started onlyin the late 1990s and were to be focused on the areas deemed
contaminated and control areas.
D46. Specialized population‑based registries for haematological malignancies and thyroid cancer had been set up in
the wake of the Chernobyl accident and in response to theunknown quality and lack of detail for these cancers in thegeneral registries. Childhood cancer registries had also beendeveloped for the same reasons. Assessments of the qualityof these registries were underway. Other registries for hereditary disorders and malformations exist, but their quality
and completeness had not been independently assessed.
D47. Shortly after the Chernobyl accident, efforts had been
devoted mainly to developing adequate registration systems
for future follow‑up of those population groups most affectedby radionuclide deposition. Later, international collaborations had helped to modernize the existing disease registration infrastructure. However, information on the quality andcompleteness of all these registries was still very scarce. The

usefulness of the vast amount of data collected was expected
to become clearer in the following decades as the long‑term
consequences of the accident were studied. In particular,
matching the health outcomes with the dosimetric data wasconsidered to be of great importance.
B. Update1.
(a)Registration and monitoring of exposed populations

The Chernobyl registries

D48. Since the dissolution of the former Soviet Union, registration practices in Belarus, the Russian Federation andUkraine diverged. As a result, in many instances the data are
no longer comparable for the four main groups of registrants,
i.e. the recovery operation workers, the evacuees from theexclusion zone, the residents of the contaminated regions,and the children born to parents from the above three groups.
For example, the Russian National Medical and Dosimetric
Registry (RNMDR) only contains data on children born torecovery operation workers. Table D9 shows the most recent
data on the nearly five million registrants in the three
countries.
D49. Because registration is tied to social and economic
benefits, concerns have been raised that this might have led
to large numbers of people inappropriately being included in
the registries in all three countries. These concerns are supported by the evidence of a continued rise in the number ofpeople registered, even in recent years.
D50. Systematic medical follow‑up of those registeredvaries by country. These differences stem from recentchanges in the health systems in the three countries. The
Russian Federation, in particular, has undergone a majorchange connected with a shift to private medical insurance.
While Ukraine maintains the system of universal medical
coverage, very limited funds are available for medical care,and, in particular, for the specialized care for those exposed
to radiation resulting from the Chernobyl accident. Of thethree countries, Belarus is the only one that maintains theregime of systematic examinations for the four main categories of registrants. Table D10 summarizes the information on the medical follow‑up of those included in the
Chernobyl registries for 2001–2005.
D51. Accurate and precise information on the state of theregistries in the three countries is not readily available. Only
one country (the Russian Federation) has a publicly accessible website for its registry [N1] that contains regulatory
documents for and general information on the operation andstructure of the registry, the number for those registered,their categorization and places of residence as well as basic
results of radiation epidemiology studies. In recent years,
many papers have appeared analysing subcohorts of registrants. These provide more detailed information on the rising number of people registered in the RNMDR [I41, M11].

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

D52. Since 1998, efforts have been underway to establish
a “United Registry” for those exposed to radiation resulting from the Chernobyl accident in Belarus and the ­RussianFederation in order to facilitate joint epidemiological studies and thereby increase their statistical power. During
1998–2006, information on 256,000 emergency and recovery operation workers and 43,000 of their children was
included in the United Registry. The registry also contains
information on 23,000 cases of thyroid cancer, more than
5,000 cases of leukaemia and 18,000 cases of breast cancer
diagnosed in the populations of the most radioactively­contaminated areas of both countries [J8].
(b)Specialized registries

D53. In recent years, several initiatives to register andf­ ollow‑up particular groups of those exposed to radiation
resulting from the accident were started. In Belarus, a register of those exposed to radiation from nuclear accidents
other than at Chernobyl was recently established. It mainly
includes former professional nuclear workers who were
exposed to high doses of radiation at various civilian andmilitary nuclear facilities of the former Soviet Union. The
number of registrants, however, is relatively small (772) and
it is not clear what information and dosimetric records areavailable on these subjects [S14].
D54. The RNMDR continues to register and follow‑up a
number of special groups, including current and former
professional nuclear workers, military clean‑up workers
and helicopter pilots who participated in the clean‑up workat Chernobyl. In addition, it maintains ties with the fiverecently established professional registries of the Ministries of Defence, Interior, Atomic Power and Industry,­Federal Security Service and Transportation, where themajority of clean‑up workers were or are still employed
and receive medical care [N1]. Currently, no information isavailable on the completeness and utility of these registries
for epidemiological research. However, some of them (e.g.
the Russian specialized registry of nuclear workers maintained at the Institute of Biophysics, Moscow) are used for
epidemiological studies [I47].
2.
(a)Registration of mortality and diseasein the general population

Mortality

D55. Several major changes in the registration of vitalstatistics occurred in the three republics in recent years.
In particular, the Russian Federation and then Ukraine
began to introduce a universal taxation identification
number for all citizens and legal residents after 2000.
This could prove instrumental in tracing those registeredin the ­Chernobyl registries through local birth/marriage
and death registration offices. However, until computerized national death indexes are created, epidemiological157

research using passive follow‑up methods would be very
cumbersome and impractical.
(b)

Cancer incidence

D56. The Belarusian Cancer Registry has been in existence
in computerized form since 1973. Individual patient records,
however, have only been available since 1985. The registryroutinely contributes data to Cancer Incidence on Five Continents (volumes VI, VII and VIII) and is considered to be ofvery good quality [P13, P14, P15]. Very high proportions of
all cancer cases have verified pathology and morphology. For
example, while in 1980–1986, only 71% of all thyroid cancer
cases had confirmed pathology, in 1997–2001, 95% were
pathologically verified. Very low rates (less than 0.4%) ofregistrations by death certificate alone also attest to the highquality of the registry [M15]. The high quality of the datameans that they are often used for comparison of cancer incidence from before and after the accident not just in Belarus,
but also for the geographically close populations of the­Russian Federation and Ukraine. However, caution in interpretation of time trends is recommended because, since 1990,
there have been improvements in the completeness and accuracy of cancer registration related in part to early detection
and treatment of various cancers in the most contaminatedareas [C11].
D57. The Ukrainian Cancer Registry (UCR) was established in 1996 and now effectively covers 93% of the population (up to 97% in the six oblasts surrounding the site of
the Chernobyl accident). The UCR is a population‑based
registry containing information about all malignant diseases
diagnosed in Ukraine. Data are collected from hospital databases and combined at the oblast level, and then transferredin electronic format to the central office. Individual patient
records include information on patient demographics, primary tumour site, tumour morphology and stage at diagnosis, treatments and follow‑up for vital status, as well as theplace and date of diagnosis and death. The majority of diagnoses come from specialized oncology hospitals and are
generally of high quality. In 2004, for example, 98.5% and50.6% of all leukaemia diagnoses had confirmed morphology and histology, respectively. Only 2.0% of all cases werebased on death certificates alone, again suggesting highquality of the data. The majority of cancers are registered
within the same year they were diagnosed, with complete
coverage achieved by two years after diagnosis. Detailed
reports are issued annually and the UCR data are accessible
to researchers.
D58. The National Cancer Registry in the Russian Federation is only beginning to emerge after its founding in 1999.
While some regions, such as St. Petersburg, could be considered to have complete population‑based registries, coveragein other areas is patchy and frequently not in a computerized
form [S27]. Reliability of information from other regional
cancer registries varies widely. Thus, currently, these datacannot be used for epidemiological research.

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(c)

UNSCEAR 2008 REPORT: VOLUME IISpecialized cancer registries

D59. Several specialized cancer registries were establishedin the 1990s and are currently in use. All three countries
have registries of leukaemia, but while in Belarus, it is population‑based, in the Russian Federation and Ukraine, they
are attached to the Chernobyl registries and only seek information on those exposed to radiation resulting from the accident. The quality of these registries has not been evaluateddespite the fact that their data have been used in several publications. In particular, the leukaemia registry operating
under the RNMDR was a source for several quantitative
studies of leukaemia among the recovery operation workers[I11, I12, I13, K11]. These multiple analyses from the sameregistry provide some evidence of increased risks of leukaemia from the exposures received during the clean‑up work.
The utility of the registry for epidemiological research hassignificantly improved due to the established system of caseidentification and verification procedures. Thus, in one of
the studies, 92% of the leukaemia cases were said to be­morphologically verified [I12].
D60. Other specialized registries include the Belarusian
Thyroid Surgery Registry and Childhood Cancer Subregistry of Belarus, the Registry of Non‑Cancer Diseases
within the RNMDR, the Clinical and Morphological Registry of Thyroid Cancer of Ukraine. At present their computerization, standardization and, ultimately, aptness for
epidemiological research need further attention.

D62. The following special issues that are substantial for the
successful use of the Chernobyl registries in epidemiologicalstudies require further attention:
For the Chernobyl registries:– Clarification of the eligibility criteria for registration;– Collection and verification of retrospective data;– Assessment of doses received after the accident;– Standardization of government policies acrosscountries governing the medical follow‑up of thosedeemed affected by the accident;– Flow of information from the local medical facilities
conducting medical follow‑up of those exposed, tothe central offices of the Chernobyl registries; and– Computerization of the data and their accessibility
to researchers;
For specialized registries:– Sharing of information with the Chernobyl Registries;
and– Utilization of collected data;
For cancer registries:– Complete coverage at the national level;– Verification of diagnoses; and– Inclusion of follow‑up information in individual
patient records;

C.

Summary

D61. Chernobyl registries have a good possibility of
becoming reliable sources of information on the long‑term
health effects of radiation exposure after the accident.
Standardization of procedures across the three registries
would greatly improve their utility for epidemiologicalresearch.

III.

For death indexes:– Complete coverage at the national level;– Computerization of the data and their accessibility
to researchers; and– Utilization of the international classification of­diseases on all death certificates.

LATE HEALTH EFFECTS OF THE CHERNOBYL ACCIDENT
in workers and THE general public

D63. Apart from the economic, social and psychologicaleffects of the Chernobyl accident, a major concern is thepotential long‑term health effects due to radiation exposure.
The Committee decided in this annex to focus on the incidence of thyroid cancer, leukaemia, all solid cancers as awhole, cardiovascular mortality, cataract development andautoimmune thyroiditis. This decision was based on thepotential sensitivity of these outcomes to radiation andbecause the Committee considered that there were insufficient new data in other areas to modify the conclusions of
the UNSCEAR 2000 Report.

A.

Summary from the UNSCEAR 2000 Report

D64. The majority of the studies completed before the
UNSCEAR 2000 Report on the health effects of the Chernobyl accident were of the geographical correlation type(often called “ecological studies”). These studies compared average population exposure with the average rate ofhealth effects or cancer incidence in time periods before
and after the accident, or between different periods after
the accident. As long as individual dosimetry was not performed, no reliable quantitative estimates could be made.

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENTThe reconstruction of valid individual doses would be a
key element in future research on the health effects related
to the Chernobyl accident.
D65. The number of thyroid cancers in groups of individuals who had been exposed in childhood, particularly in thecontaminated areas of Belarus, the Russian Federation andUkraine, increased dramatically during the previous
15 years. The high incidence and the short induction period
had not been experienced in other exposed populations, andfactors other than ionizing radiation were thought almost
certainly to have influenced the risk. Some such factors thatwere considered included age at exposure, iodine intake andmetabolic status, endemic goitre, screening, short‑lived isotopes other than 131I, higher doses having been received than
had been estimated, and, possibly, genetic predisposition.
Approximately 1,800 thyroid cancer cases had been reported
in Belarus, the Russian Federation and Ukraine in children
and adolescents for the period 1990–1998. Age at exposure
seemed to be an important modifier of risk. The influence ofscreening was difficult to estimate. Approximately 40–70%
of the cases had been found through screening programmes,
and it was unclear how many of these cancers would otherwise have gone undetected. Taking the advanced stage of thetumours at the time of diagnosis into consideration, it wasthought likely that most of the tumours would have been
detected eventually.
D66. Results from some studies had indicated that the
majority of the post‑accident thyroid carcinomas in children showed the intrachromosomal rearrangements characterized as RET/PTC1 and RET/PTC3. There were,
however, several questions left unanswered, e.g. the influence of age at exposure and time since exposure on the rateof chromosome rearrangements.
D67. The risk of leukaemia had been shown clearly to be
increased by radiation exposure in epidemiological studies onother exposed populations. Up till the time of the UNSCEAR
2000 Report, no increased risk of leukaemia linked to ionizing
radiation had been confirmed in children, in the recovery operation workers, or in the general population of the former Soviet
Union or other areas with measurable levels of ­radioactivity
due to the Chernobyl accident.
D68. Increases had been reported in a number of non‑­
specific detrimental health effects other than cancer among
the recovery operation workers and among the residents ofcontaminated areas. It was difficult to interpret these findings
without referring to a known baseline or background incidence. Because health data obtained from official statisticalsources, such as mortality or cancer incidence statistics, were
often passively recorded and were not always complete, it
was not appropriate to compare them with data on the
exposed populations, which underwent much more intensive
and active health follow‑up than the general population.
D69. Some investigators had interpreted a temporary lossof ability to work among individuals living in contaminated159

areas as an increase in general morbidity. High levels ofchronic diseases of the digestive, neurological, skeletal,
muscular and circulatory systems had been reported. However, most investigators related these observations to changes
in the age structure, the worsening quality of life and thepost‑accident countermeasures such as relocation.
D70. Many papers had been published on the immunological effects of exposure to radiation due to the Chernobyl
accident. Since it was unclear, however, whether possible
confounding factors had been taken into account (including,in particular, infections and diet), it was difficult to interpretthese results.
B. Methodological approaches
1.

Types of studies

D71. Two approaches are commonly used to assess thelong‑term health effects of the accident. The first approach is
to use risk models derived from other populations exposed
to radiation exposure, for example, the survivors of theatomic bombings of Hiroshima and Nagasaki, and thenapply these models to the estimated doses received by therelevant population after the accident and thus project thesubsequent risks to that population. The second approach is
to conduct empirical studies of the populations exposed as aresult of the accident in order to assess the health effects
directly in these populations.
D72. The approaches have different advantages and­d isadvantages. The first approach, often called the risk‑­
projection approach, is based on studies of populations
with higher doses than those experienced by populations
after the Chernobyl accident. But, the main disadvantage
is that it involves extrapolation of the risk observed in one
exposed population, with its own specific characteristics,
to another one, for which the levels of dose and dose rateor the mixture of types of radiation are different. In the
populations exposed as a consequence of the accident,
internal exposure to radioiodine played a major role in the
induction of thyroid cancer; this specific type of exposure
could not be studied through follow‑up of the survivors of
the atomic bombings.
D73. On the other hand, the empirical approach suffersfrom low statistical power because of the relatively low
doses, and the need for a long‑term follow‑up; however it has
the advantage of considering the directly affected populations. This appendix focuses mainly on the empirical studies, i.e. those carried out directly on the relevant populations,and considers preferentially those populations for which
there are precise estimates of individual dose. These studies,called “analytical studies”, provide the most direct and convincing evidence of the long‑term health effects in humans[I1]. Disciplines such as dosimetry, clinical medicine andanatomopathology are part of these analytical studies andcontribute to a valid interpretation of the observations.

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D74. When an empirical epidemiological study provides
evidence of an increase in incidence of or mortality due to apotentially radiogenic disease, it is still necessary to consider the issue of the attributability of that effect to radiation.
Epidemiological studies are observational in nature and, assuch, any observed associations may not necessarily indicate causality. It is necessary to take detailed account of factors that may confound or bias the results, such as industrial
pollution, environmental features (e.g. stable iodine levels insoil), lifestyle (e.g. smoking habits, alcohol consumption or
reproductive history), improvement of diagnostic tools, andincreased medical attention to affected populations (e.g.
special screening). In combination, confounding factors cansimulate an apparent radiation effect or mask a true effect,
and lead to incorrect conclusions, if they are not properly
taken into account.
D75. Currently published studies may be divided into theso‑called geographical correlation studies (“ecological studies”) and analytical studies. In most ecological studies,
exposure is reconstructed at the group level, whereas in analytical studies, exposure is assessed at the individual level. It
should be noted, however, that ecological studies have been
published that are based on a large number of individual
dose measurements, and case‑control studies have been published that are based on radioecological models. Examples
of geographical correlation studies include those that monitor cancer incidence as a function of time and/or geography,
e.g. rates before and after the Chernobyl accident, or rates inoblasts with varying levels of radionuclide deposition. Geographical correlation studies have the disadvantage that
potential confounding or biasing factors, such as screening(see below), can only be studied at the group level and may
thus be subject to residual individual confounding. This concern regarding the attributability of geographical correlation
study results to radiation has already been discussed in the
UNSCEAR 2000 Report [U3] and annex A, “Epidemiological studies of radiation and cancer”, of the UNSCEAR 2006
Report [U1].
D76. Analytical epidemiological studies are typified bycase‑control and cohort studies. In this case, adjustments
for confounding factors (if known and available) can bemade at the individual level. Biases, such as in selection ofsubjects or in information acquisition, however, are inherent flaws in study design and cannot be readily accounted
for in analyses. Generally, analytical studies are regarded
as providing stronger evidence of possible attribution toradiation exposure than geographical correlation studies.
D77. In addition to the fundamental consideration of thestudy design, the criteria that should be used to determine
the potential quality of the study include:– Availability of accurate and precise dose estimates,
at either the individual or group level (appendix B);– Well‑defined study population;– Confirmation of disease diagnoses, preferably
made independently;– Complete ascertainment of disease cases, with anascertainment mechanism that is independent ofdose. The existence of high quality and independent cancer registers on a regional or national basis
are important;– Reporting of appropriate dose–response analyses,
taking into account appropriate time factors suchas minimal latent period, age at exposure and age
attained;– Sources of data and methods being clearly reported.
D78. Studies vary in their concordance with these criteria,
and may provide useful information even if one or more ofthem is not satisfied. Nevertheless, each study should beconsidered in terms of its concordance with these criteria for
an appropriate evaluation to be made.
D79. A number of epidemiological studies have beenreported that have been conducted in the three republics.
In general, these studies have considered one or more of
the following groups: the evacuees; the residents of contaminated territories; and the recovery operation workers. The third group is of particular interest because, on
average, their doses were generally higher than those to
the people in the other two groups. However, caution must
be exercised in considering the studies of the recovery
operation workers based only on “official” doses and/or
diagnoses recorded in the state registries. The official
doses are known to be incomplete and possibly biased insome cases (appendix B). Diagnoses made without independent confirmation may also be of inadequate quality.
In addition, more intensive and frequent medical examinations were carried out on the recovery operation workers, which may have led to the earlier detection of disease
and provided more specific diagnosis than would havebeen the case for the general population covered by thenormal health care system. Comparison of the data for therecovery operation workers with different exposure levels
but the same level of medical attention may avoid these
problems.
D80. Generally then, two types of study are consideredwhen evaluating the incidence of cancer and non‑cancer­diseases in populations exposed as a result of the accident:i.	Geographical correlation studies (often termed “ecological studies”) describe incidence rates of diseasecharacterized by age attained or place of residence atdiagnosis. A description in relation to the place at
exposure should be considered carefully, as it presupposes either that this information (the place of residence in April 1986) has been registered systematicallyin the cancer register or that the place of diagnosis isequivalent to the place of residence. The latter has tobe verified as it presupposes no migration of this population. This may be true if the follow‑up is limited intime, but after more than 15 years, it may no longer betrue if people, exposed in one oblast, are now livingin the city of another oblast. In some geographicalANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

correlation studies, the average doses have beenreconstructed at group level (village, settlement oroblast). Quantitative estimates of measures of risk
derived from these data have to be considered withcaution, because uncertainties linked to individual
behaviour could not be taken into account in thistype of dose reconstruction. A special type of geographical correlation study resulting in more reliable risk estimates has been introduced to analyse
thyroid cancer risk after the Chernobyl accident.
The cases were related to the place of residence atthe time of exposure (and not at the time of diagnosis) and based on dose estimates in settlements, forwhich more than 10 individual dose measurements
had been performed.
ii.	Analytical studies (with two subtypes: case‑control
or cohort) use individual‑specific information, andare considered to be more reliable and valid for
examining the dose–response relationship. Any
resulting dose–response relationship has at least
two interpretations:–

If the risk of a specific disease like thyroid cancer
increases with increasing exposure, and other confounding factors are accounted for, then the radiation exposure should be considered as playing arole in the development of this cancer;–

The possibility to legitimately compare the risk
for this population with the risk observed in othersituations of human exposure, even when the
exposure in those situations was at higher ­levels(radio­therapy patients) or of different nature­(survivors of the atomic bombings).

2. Diagnostic and screening issues
D81. In epidemiological studies, it is necessary that thefrequency of detection of a disease and the quality of diagnosis are independent of the degree of exposure. In the caseof studies related to the Chernobyl accident, three issues areof particular concern.
D82. The first is improvement in diagnostic techniques.
Specifically in relation to the Chernobyl situation, this refers
to the introduction of ultrasonography for the detection of
thyroid cancer. Since the accident, there has been a substantial increase in the number of ultrasound examinations used
to detect thyroid cancer. Figure D‑VII shows, for example,
the number of ultrasound examinations performed per 105
inhabitants in the three most contaminated oblasts in
Ukraine in 1990, 1995 and 2002 [L5]. During the same
period, an increasing incidence of thyroid cancer was
reported in these oblasts [L5]. Thus, part of the increase in
the observed thyroid cancer incidence may be attributable tothe improved detection of cancers because of the greater use
of ultrasonography.

161

D83. The second issue is that these screening programmes
make it possible to detect smaller tumours that may havebeen latent for many years. Screening refers to examining
individuals who do not have clinically manifest disease in an
attempt to diagnose any disease earlier in its natural history
and, hopefully, to improve the prognosis and treatment forthat disease. A number of formal screening programmes
have been introduced in the three republics since the Chernobyl accident, again with thyroid cancer being the target
disease, particularly in those exposed as children, e.g. theSasakawa project [S8, S9]. This type of surveillance inevitably increases the apparent incidence of thyroid cancer either
by detecting thyroid cancers at an earlier stage than would
otherwise have been the case or possibly by detecting thyroid cancers that otherwise would never have come to clinical attention (the so‑called “occult cancers”). However, only
174 of about 4,000 thyroid cancer cases were detected bysuch formal screening programmes [J7].
D84. Apart from these formal ultrasound screening programmes, the response to the Chernobyl accident led to
informal screening, i.e. examination of individuals who
were under medical care for other reasons, to determine
whether or not there is evidence of thyroid disease. Thus, if
a physician knew that a person had been exposed to radiation as a result of the Chernobyl accident and considered thatthyroid disease was a possible consequence, he or she may
have been inclined to look for it more thoroughly than would
otherwise be the case. This is termed here “diagnostic suspicion bias” and is the third issue of particular concern. The
baseline thyroid cancer incidence did in fact increase due tothe intensified surveillance of the thyroid during regular
medical examinations and an improved reporting system,from 1988 to 1999, by a factor of 3 in Belarus and the morecontaminated regions of Ukraine, and by a factor of 2 in theless contaminated regions of Ukraine [J7].
D85. The above issues are closely related. Thus, if the cancer incidence in the residents of areas with high levels ofradioactive contamination is compared to that in the residents of areas with low levels, part of the observed excessprobably relates to better detection methods. Similarly, comparisons of thyroid cancer rates before and after the Chernobyl accident, which do not take into account the use ofultrasonography, cannot sensibly be used to quantify the
thyroid cancer risks due to radiation exposure.
D86. Both screening and diagnostic suspicion bias may
operate in the studies of the recovery operation workers,
who are examined every year for various diseases and consequently for whom there is a higher likelihood of detection of small tumours. Comparison of disease rates between
groups of recovery operation workers is only informative if
the same detection methods used in diagnosis were applied
over the whole period and regardless of the individual
exposure level.
D87. Overall, interpretation of the results from studies ofthe populations exposed as a consequence of the Chernobyl

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accident must take into account the variation in detection
methods with time, and the likelihood of detection for thedifferent frequencies of screening between the populations
exposed to high levels of radiation and those exposed to
low levels.
C.

Empirical studies on specific diseases
1. Thyroid cancer in groups exposed
as children and adolescents(a)Introduction

D88. The thyroid gland of children is one of the organs
most susceptible to the carcinogenic effect of ionizing radiation [U1]. There have been a number of studies of children
whose thyroids had been exposed to external low‑LET radiation (i.e. gamma and X‑rays). These include studies ofchild­ren exposed as a result of the atomic bombings of Hiroshima and Nagasaki and those exposed for therapeutic reasons, like in the treatment of tinea capitis or enlarged tonsils
and adenoids. A combined analysis of the data from thesestudies was reported by Ron et al. [R1]; this demonstrated an
excess relative risk (ERR) of 7.7 (95% CI: 2.1, 28.7) Gy–1 andan excess absolute risk (EAR) of 4.4 (95% CI: 1.9, 10.1)(104 PY Gy) ‑1 in children under age 15 at exposure. This
analysis also showed a marked effect of the age at exposure,with the highest risks being seen in the youngest ages. The
analysis also showed an effect of the time since exposure,with the risk dropping substantially 30 years after the first
exposure. The ERR estimates were also dependent on thesex (p = 0.07), but the findings from individual studies were
not consistent.
D89. There have been fewer studies specifically of child­ren exposed to 131I and other shorter‑lived iodine isotopes.
There have been studies of those who had received 131I for
diagnostic purposes [D12, H1, H2], those who were exposed
to weapons testing fallout in the Marshall Islands [C4, H3,
R2], those who were exposed to fallout from the atomic
bomb tests conducted in Nevada, USA [K2] and those who
were exposed to 131I from the Hanford Nuclear Site in thestate of Washington, USA [C2, D9].
D90. Except for the studies of the Marshall Islanders, thesestudies of exposure to iodine isotopes have not provided convincing evidence of any measurable increase in the risk ofthyroid cancer. However, all these studies have considerable
limitations in terms of their statistical power, and the results
are generally consistent with both a null effect and anincreased risk. An analysis by Shore [S1] suggested that any
effect of 131I exposure would be lower than that predicted byapplying the risks observed with exposure to external
low‑LET radiation, primarily due to the differences in dose
rate. Some animal data, however, are consistent with aneffect that is equal for both 131I exposure and exposure toexternal low‑LET radiation. It has also been shown that theradiation risk coefficients observed after the Chernobyl

accident are consistent with observations made in the studies
involving external exposure [J2]. Thus, this remains animportant and unresolved issue.
D91. Releases of 131I and other shorter‑lived isotopes ofiodine from the Chernobyl accident led to the exposure of the
thyroid gland to substantial doses of radiation in many areasof Belarus, the Russian Federation and Ukraine mainly
through drinking contaminated milk. Therefore, the potential risk of thyroid cancer, particularly among those exposedat very young ages, is one of the major concerns and needs tobe discussed carefully in regard to all available approaches(registers, geographical correlation studies and analyticalstudies). The observed large excess of thyroid cancer inchild­ren is clearly the major public health problem associatedwith radiation exposure encountered in the three republics.
D92. In view of the higher radiosensitivity of children andadolescents than of adults, the former group is discussed in
the present section and the latter in the following section.
(b)

Assessment of current evidence

D93. Since the Chernobyl accident, there has been a striking increase in the reported incidence of thyroid cancer inchildren and adolescents residing in Belarus, Bryansk andOrel oblasts of the Russian Federation and Ukraine. The
increase started some four to five years after the accident
and has continued to manifest itself. As the underlying incidence rate of thyroid cancer in young children is very low(few cases per million children per year) [D10, I38], manyof the cases diagnosed before age 15 years have been attributed to the releases from the Chernobyl accident. For thyroid cancers diagnosed at ages 20–30 years, the underlying
incidence rate is close to some tens of cases per million
persons per year, and hence any apparent excess has to beinterpreted more cautiously; screening techniques may havebeen responsible for a substantial part of the apparent excess(this also suggests that screening may have played a role in
the excess incidence rate reported among children underage 15 years). For these age groups, analytical studies using
accurate individual dose estimates need to be used.
D94. The thyroid cancer incidence rates for both sexes andvarious ages at exposure for children and adolescents areshown for the whole of Belarus, the four most affectedoblasts of the Russian Federation and the whole of Ukraine
in table D11. These data are for periods between 1982 and2005 and were obtained from the corresponding national
cancer registries and the specific Chernobyl registries for theparticular areas, see section II of this appendix. Amongst
those under age 14 years in 1986, 5,127 cases (under age
18 years in 1986, 6,848 cases) of thyroid cancer werereported between 1991 and 2005 [I8]. There is no evidenceof a decrease in the excess incidence of thyroid cancer up to
2005. Part of the increase is related to the normal age patternof disease occurrence but the majority of the increase isattributed to the radiation exposure.

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

D95. It has been estimated that 60% of the Belarusian
thyroid cancer cases and 30% of the Ukrainian cases
among those who were children or adolescents at the timeof the accident may be related to the radiation exposure[J7]. The remaining increase in the incidence rate of thyroid cancer is related to enhanced surveillance, improved
diagnostic technology and other non‑radiation factors.
Risk estimates that are relatively independent of such factors need to be developed from studies with identicalscreening of all cohort members.
D96. The thyroid cancer incidence rates for both sexes andvarious ages at diagnosis in the three countries are shown intables D12 to D14. These data were also obtained from thenational cancer registries and the specific Chernobyl registries for the particular areas. To provide a better appreciationof the information, figures D-VIII to D-XIII were constructed using the incidence rates for various ages at diagnosis separately for males and females. For all age groups, therates are higher for females than for males.
D97. Annual incidence rates of thyroid cancer are presented in figures D-VIII to D-XIII for the period from 1990
to 2005. Data from before 1990 are omitted from the figures,
because the data in several registries for some age groups
seem to be incomplete. Indeed for Belarus and Ukraine, forthe period before 1990, the average incidence rate for the agegroup 20–29 years old at diagnosis was very low in comparison to the expected average rates (derived from European
and/or Russian sources). The major reason is that because
thyroid cancer is a rare disease (and especially so for young
age groups), at the period before or close to 1986, thyroid
cancers were included in a common group of “other solid
tumours”; they were not recorded separately in the national
registries. Following the Chernobyl accident, major efforts
were made to collect this information and, since 1990–1992,
the data can be considered as largely complete. Moreover, if
a minimum of 4–5 years were necessary before an excess
risk linked to the Chernobyl accident might be expressed,then data for the period before 1990 would in any case beless informative.
D98. For each country, the incidence rates in the three
diagnosis age groups follow parallel trend lines, but withsome discrepancies. These discrepancies reflect fluctuationsin the annual incidence rates between countries, as thyroid
cancer is a rare disease and the number of cases is low. However, they may also reflect different practices for the detection of the disease (see the discussion in section III.B.2
above on the screening effect) that may affect the results fordifferent age groups at different times; and they also reflect
the fact that the average thyroid doses to the populations of
the three countries were not the same. At the national level,
the Belarusian population experienced higher exposure levels than the population of Ukraine. For the Russian data,
because they are limited to the oblasts with high radioiodine
levels, the incidence rate is also relatively high, but withlarge annual fluctuations.

163

D99. The observations may be considered as expressing
different time trends for the different age groups, and may
suggest that for the near future, any increased incidence rate
will continue in groups exposed at young ages. Thosegroups exposed as very young children expressed their risk
at the beginning of 1990s in the age group 0–9 years. They
then entered the age group 10–19 years. During recent
years, their thyroid cancer risk will be expressed in the agegroup 20–29 years. The different “waves” of increase in theincidence rate for each age group, followed by a decrease,reflect the movement of people from the young exposedcohort through the other two age groups over the last
20 years. These waves are illustrated clearly by the Belarusian data for females, but can be observed also in the data
for the other countries.
D100. An increased incidence rate of thyroid cancer isevident in the age group 0–9 years at diagnosis for both
sexes and each country during the first part of the 1990s
compared with that in the second part of that decade. The
children in this group were under 5 years old at the time of
the Chernobyl accident; since 1996, all of those exposed
before the age of 10 years became members of the age group
10–19 years. These data indicate that the risk to those child­ren born since 1986 is close to that observed before the accident, even though they could have been subject to increased
medical surveillance (i.e. possible post‑accident screening
effects).
D101. For the category of people aged 10–19 years at
diagnosis of thyroid cancer, an increased incidence rate isevident in each country from about 1991–1992 until about
2000. For some countries, a decrease in incidence rate since
2002 also can be seen. The beginning of the increase relates
to those children who were 5–10 years old at the time of theaccident.
D102. For the category of people 20–29 years old atdiagnosis of thyroid cancer, an increased incidence rate isevident in each country from 1991, which persists up to
the years 2000–2005. The underlying incidence rate in1990 (i.e. in the absence of a radiation effect), would be
expected to lie between 10 and 50 per million persons (seee.g. [J7]); however it seems to be lower for some countries.
For the age group 20–29 years, the increase in incidence
rate reflects better screening, but also the fact that 15 years
after the accident, the risk continues to increase for those
exposed at ages less than 10 years.
D103. Since the Committee’s evaluation in the UNSCEAR
2000 Report [U3], several “ecological studies” have been
published in the literature.
D104. Shibata et al. [S4], in a screening‑based study ofschool children in the Gomel oblast of Belarus, reported asignificant relationship between exposure to radioactive deposition and the frequency of thyroid cancer, comparing thoseborn after the accident to those born before the accident, after
adjustment for sex and age (p = 0.006).

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D105. Tronko et al. [T2] reported a total of 1,876 cases ofthyroid cancer occurring in Ukraine between 1986 and 2000
among those aged 0–18 years at the time of the accident.
There was a statistically significant increase in thyroid­cancer incidence with time since the accident.
D106. In a study conducted in the Bryansk oblast of theRussian Federation, Shakhtarin et al. [S6] focused on therelationship between iodine deficiency and the risk ofradiation‑­induced thyroid cancer. A sample of 3,070 individuals resident in 1996 in the 75 most heavily contaminatedsettlements of the oblast was used to estimate the mean urinary excretion of iodine and the level of iodine deficiency inthose settlements. The sample was heavily weighted towards
children and adolescents. Based on these data and 34 histologically confirmed cases of thyroid cancer that occurred inthose aged 0–18 years in 1986 in the oblast, excess risks
were calculated using estimates of the average radiationdose in the various areas. A statistically significant relationship of excess relative risk with radiation dose was observed.
The risk values were twice as great in the areas where there
was iodine deficiency compared to those areas where there
was adequate iodine nutrition; this seemed to suggest thatiodine deficiency may enhance the risk of thyroid cancer following radiation exposure. However, several limitations of
this study have to be mentioned. There were no individual
measurements (e.g. of radiation doses and of iodine deficiency) but rather approximations based on aggregated data
(e.g. mean urinary excretion of iodine based on averaging
measurements on a limited number of persons). Any migration of the population since 1986 could not be taken into
account and the expected number of thyroid cancer cases
calculated from the Russian national incidence rates was
possibly underestimated, when considering the effect ofscreening for thyroid cancer in these contaminated areas.
D107. Another study by Ivanov et al. investigated the thyroid cancer incidence between 1991 and 2001 in persons
from the Bryansk oblast who were exposed at ages between
0 and 17 years [I22]. Dosimetric information was evaluatedusing data on their place of residence and age at exposure.
The analysis revealed statistically significant radiation risk
only for those exposed as children at an age of 0–9 years. In
this group, the standardized incidence ratio (the national
incidence rate was used as a reference) in the consideredtime period is estimated to be 6.7 (95% CI: 5.1, 8.6) and 14.6
(95% CI: 10.3, 20.2) for girls and boys, respectively. The
same limitations as mentioned above apply to this study.
D108. An ecological study of the thyroid cancer incidence
in the whole population of Belarus was undertaken. The
results were presented separately for those who were exposed
as children and adolescents (0–18 years old in 1986 [K10,K22]) and adults (older than 18 years in 1986 [K22]). The
sources of information on thyroid cancer were the medical
records of the patients treated in the national Scientific andPractical Center and the Belarusian cancer registry. The
incidence rate attributable to radiation was estimated by subtraction from the total incidence rate of the relatively small

baseline rate estimated from the data for 1986–1990(assumed to be minimum latent period for thyroid cancer
induction), with account being taken of the time trend inincidence rate during that period. Average thyroid doses toresidents of the administrative districts and dose uncertainties were estimated by means of a radioecological model[K10, K22, K28] and were verified using available radiation
measurements on the thyroids of the residents of a number ofBelarusian settlements. The relationship between thyroid
cancer incidence rate in five selected dose groups and theaverage thyroid dose, which was in the range of 0.1–2.7 Gy,
was found to be close to linear. The calculated value of theexcess absolute risk (EAR) in 1990–1998 for children andadolescents (table D16) was about half of that obtained fromthe studies involving external exposure of the thyroid ofchildren [R1], but the ERR was a factor of five higher thanthat obtained in reference [R1]. The EAR for girls was twice
as high as that for boys. The EAR values for children aged
0–6 years and 7–14 years were close to each other, but foradolescents, no significant dose–response relationship was
found.
D109. Heidenreich et al. [H4], using the 1986–1998 datafrom the Ukrainian thyroid cancer register for patients bornafter 1968, reported that the EAR coefficient increased withtime after exposure and demonstrated no statistically significant dependence on age at exposure, up to age 15 years. This
was a relatively small study where thyroid doses were averaged over large areas; it was later replaced by the study
reported in reference [J4].
D110. A more recently published formal dose–response
analysis by Jacob et al. [J4] covered a larger population(Belarus and Ukraine) but was partly overlapping with the
Ukrainian population studied in reference [H4]. This study
focused on the more detailed dose estimates for the
1,034 settlements in Ukraine and Belarus in which morethan 10  measurements of the 131I activity in the human thyroid had been performed. Thyroid doses were assessed forthe birth years 1968–1985 and related to the incidence of
thyroid cancers that were surgically removed during theperiod 1990–2001 (data obtained from registries). The central estimate for the linear coefficient of the dose response
was estimated as an ERR of 18.9 (95% CI: 11.1, 26.7) per
Gy. The ERR was found to be smaller for females than formales and decreased strongly with age at exposure. In contrast, the EAR increased with time after exposure; this was
explained by a faster increase over age and over the period of
observation in the underlying thyroid cancer incidence thanin the radiation‑induced excess incidence. The best estimateof the ERR per unit dose is higher than that expected fromthe studies involving exposure to external radiation. However, the difference is not significant and the authors notedthat uncertainties in underlying rates may have made theestimate for the ERR less stable than the EAR per unit dose,
which was estimated to be 2.66 (96% CI: 2.19; 3.13) per 104
PY Gy. It should be noted that the present follow‑up period
is shorter than that for the pooled study of populations
exposed to external radiation.

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

D111. The incidence of thyroid cancer for children (up to
age 18 years in 1986) in the settlements within the threenorthernmost oblasts of Ukraine, which received the highest
concentrations of radioactive deposition, has been comparedby Likhtarov et al. [L5] to the corresponding estimated average doses to the populations of these settlements. The individual doses were estimated using direct thyroid
measurements on about 25% of the study population. For thepeople without direct measurements, group average doses
were reconstructed. The corresponding thyroid cancer rates
were modelled as a function of age at exposure, sex andoblast. The degree of screening operating in an oblast in aparticular calendar year was taken into account and wasfound to be significantly associated with an increased thyroid cancer incidence (p < 0.0001). A strong dose–response
relationship was observed, with an overall estimated ERR of
8 (95% CI: 4.6, 15) per Gy and an estimated EAR of 1.5(95% CI: 1.2, 1.9) per 104 PY Gy. The risk estimates weremodified both by sex (males had a higher estimated risk thanfemales), age at exposure (those older at exposure had lower
corresponding radiation risk estimates) and calendar year(the risk increased in recent years). The estimates for the
ERR and EAR differed significantly for those people withdoses derived from direct thyroid measurements and thosepeople with reconstructed doses, the risk being lower in theformer group.

165

on fitting a log‑linear model to the data, there was a statistically significant increase in risk with increasing dose
(p = 0.009), with an estimated ERR of 1.65 (95% CI: 0.10,
3.20) per Gy. This study is however based on a small
number of cases.
D115. A later study, which extended the Bryansk study toinclude all of the Bryansk oblast and an additional year of
thyroid cancer diagnoses [K17], included 66 confirmed
cases of primary thyroid cancer diagnosed between 1986
and 1998 in people who were age 0–19 years at the time of
the accident. Two controls were identified for each case.
Individual doses were estimated as outlined above. According to a log‑linear model, the estimated ERR was 1.54 (95%
CI: 0.50, 4.50) per Gy, increasing to 3.84 (95% CI: 1.19,
13.9) per Gy after adjusting for uncertainty in the dose estimation. The various linear models gave extremely broad
ranges of risk which are essentially not interpretable. Estimates of the ERR reported here must be viewed with caution
because of the extremely wide confidence intervals related
in part to the relatively small number of cases in the study
and to the models used.

D113. A case‑control study of 107 children diagnosed withthyroid cancer in 1987–1992 has been conducted in Belarus[A1]. The primary objective was to assess the relationshipbetween the dose to the thyroid and the incidence of thyroid
cancer. Individual doses were estimated based on grounddeposition of 137Cs, ground deposition of 131I, a data bank ofmeasurements made in 1986 of radiation exposure of the
thyroid, questionnaires and interviews. Although no formal
dose–response analysis was presented (because the dose
estimates were considered to be too imprecise for such ananalysis), the risk nevertheless increased monotonicallywith the estimated group dose, with the odds ratio (OR) forthe highest (>1.0 Gy) versus the lowest (<0.3 Gy) dose group
being generally of the order of 5, (OR) = 5.04 (95% CI: 1.5,
16.7).

D116. The results of a population‑based case‑control
study conducted in the most heavily contaminated areas ofBelarus and the Russian Federation have recently beenreported by Cardis et al. [C8]. The number of cases waslarge: n = 276; they represent all those thyroid cancer
patients identified between 1992 and 1998 among those
whose thyroids had been exposed to radiation resulting
from the accident at age 0–14 years in Belarus or 0–18 years
in the Russian Federation. The study period did not overlap
with a previous case‑control study in Belarus [A1]. A totalof 1,300 controls were used. The aim of the study was toestimate the radiation‑related thyroid cancer risk, and possible interactions of other factors, such as iodine status at
the time close to exposure. Individual doses for all study
subjects were estimated based on their whereabouts anddietary habits at the time of the accident. Their stable iodine
intake was also evaluated and their iodine deficiency
approximated from the area‑specific mean iodine content in
the soil since 1986. A strong dose–response relationshipwas observed between the radiation dose received by the
thyroid during childhood and the thyroid cancer risk
(p < 0.01). The OR at the dose of 1 Gy varied from 5.5(95% CI: 3.1, 9.5) to 8.4 (95% CI: 4.1, 17.3), depending on
the risk model used (table D15).

D114. The second reported analytical study is that conducted by Davis et al. [D1] in the contaminated areas of
the Bryansk oblast (Russian Federation) with high levelsof radioactive deposition. Cases were those identified
before October 1997 (n = 26) and who were aged 0–19
years at the time of the accident; two controls were selected
for each case and matched by sex, birth year, district(raion) of residence and type of settlement (rural or urban).
A semi‑empirical dose model was used to estimate individual thyroid doses for all cases and controls, with data
provided by interview of the participants’ mothers. Based

D117. In this study, the excess risk was three times higher
in iodine‑deficient areas than elsewhere. If potassium iodide
had been administered, the risk of radiated‑related cancer
was lower by a factor of 3, even if the administration had
been delayed after the accident. This observation is important and could be explained not only because stable iodine
given shortly after exposure reduces the uptake of radioiodine by the thyroid, but also because long‑term use of iodine
as a dietary supplement reduces the size and growth of the
thyroid in iodine‑deficient areas and could be expected to be
associated with a reduced incidence of cancer.

D112. To date, few analytical studies of thyroid cancer
occurring in those exposed as children or adolescents havebeen reported. Most of them are case‑control studies, andone is a cohort study.

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D118. A cohort study of the relationship between the exposure to radiation resulting from the accident and theincreased risk of thyroid cancer in those exposed as children
or adolescents has been designed and is being conducted inparallel in Belarus and Ukraine [S7]. Results of the follow‑up of the Ukrainian part of the cohort have beenreported by Tronko et al. [T3]. In total, a cohort of approximately 32,000 individuals younger than 18 years of age andresident in the most heavily contaminated areas in Ukraine
at the time of the accident was followed by biennial screening examinations using ultrasonography, palpation andblood assays. An important feature of this study was theavailability, for all study subjects, of thyroid activity measurements made in 1986, shortly after the accident. These
activity measurements, in combination with personal dataobtained from questionnaires and radioecological models,
have been used to estimate the individual thyroid doses foreach study subject (see appendix B). The thyroid cancer risk
based on the first round of screening, from 1998 to 2000,
showed a strong approximately linear relationship with theindividual thyroid dose estimate (p < 0.01); the ERR was
estimated to be 5.25 (95% CI: 1.70, 27.5) per Gy. This study
provides quantitative risk estimates that appear to be minimally confounded by any screening effects. However, only
44% of the cohort had actually been screened.

D121. Nonetheless, the effect of iodine deficiency inenhancing the risk of radioiodine‑induced thyroid cancer
and the protective effect of stable iodine supplements months
or even years after exposure would caution against generalizing the Chernobyl findings to other exposed populations ofchildren whose diets are not deficient in iodine.

D122. The substantial increase in thyroid cancer incidence seen among those exposed as children or adolescentsin Belarus, the Russian Federation and Ukraine since theChernobyl accident shows no signs of diminishing up to
20 years after exposure. On the contrary, the EAR has been
observed to increase with time after exposure [J4], indicating that the number of annual excess cases may also continue to increase. The data from the national and regional
registers show clearly that the main increased incidence for
future years will be in those who were children or adolescents in 1986. Systematic follow‑up of these populations
would need to be continued in order to detect any benign ormalignant tumour as soon as possible and consequently
provide adequate medical treatment.

D119. The results of geographical correlation and analyticalstudies that have led to quantitative estimates of risk are summarized in table D16. It is notable that the geographical correlation studies give EARs very similar to each other, i.e.
EAR ~2 per 104 PY Sv. These EARs are about a half of thecorresponding value reported for populations followed after
external X‑ or gamma‑ray exposure [R1]. It should be mentioned that the EAR is increasing with time after exposure[J4], and consequently, as the time after exposure is shorter inthe currently published Chernobyl studies than in the analysisof populations exposed exclusively to external radiation [R1],
the EAR shown in table D16 may continue to increase in the
future. Consequently, these EAR values may differ if notbased on the same age groups and durations of follow‑up.

D123. There is no doubt that there is a substantial contribution to this excess incidence from exposure to radioiodine
due to the Chernobyl accident. The magnitude of the dose
response remains uncertain but the recent results from published analytical studies show some agreement in estimatesof the ERR at 1 Gy. The results from the geographical correlation studies, which are summarized in table D16, showthat the EAR associated with exposure of the thyroid toradio­iodine is somewhat smaller than the corresponding risk
associated with external exposure by a factor of about
one‑half or two‑thirds, but nevertheless, still indicate a significant health hazard to those exposed [R1]. This difference
can be partially explained by the shorter follow‑up period in
the Chernobyl studies.

D120. The ERR shows large variation, both in thecase‑control and in geographical correlation studies.
Whereas in the former, this variation probably reflects thelarge dose uncertainties, in the latter, it probably reflects theinfluence of the underlying disease rates, which may change
as a function of the quality of the follow‑up, completenessof registration, and the degree to which account has beentaken of any screening programmes and migration of the
population. The ERR is strongly influenced by the age
attained in the population considered, which may differ
from one study to another. In view of the uncertainties
involved, the values of ERR that are estimated here fromanalytical studies can be considered as close to that expectedfrom studies of other populations exposed to external radiation. The studies reported in references [C8, T3] are themost informative; they have a larger statistical power andan individual approach to dosimetry; they indicate quite
comparable results for the ERR.

D124. Evidence has also emerged since the UNSCEAR
2000 Report [U3] that iodine deficiency may well increase
the risk of thyroid cancer due to radioiodine released in theaccident. Two studies so far have provided support for this[C8, S6]; both suggest that iodine deficiency sometime
between exposure and diagnosis may double the radiation
risk. Nevertheless, individual measurements of iodine status at the time of the accident are not available and approximations derived in these studies from iodine concentrations
in soil or urine 10 years after the accident, have to be considered with caution. In another analytical study [T3], it
was noted that neither stable iodine excretion in 1998–2000
nor the presence of diffuse goitre was associated with therisk of radiation‑induced thyroid cancer. Future study ofthis effect will be important in terms of extrapolating theresults from the experience of the Chernobyl accident toother scenarios where iodine deficiency may be different
from that in the study area.

(c)Conclusions

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

D125. Strengths and limitations of epidemiological studies have to be taken into consideration in interpreting theresults regarding the risk of thyroid cancer. Uncertainty inthe estimated average dose is a main concern in geographical correlation studies. Some studies have made more reliable estimates of the average dose by considering thosesettlements in which a large number of individual 131I thyroid measurements were made in 1986. Analytical studies
provide more informative quantitative estimates of the riskof thyroid cancer associated with radiation exposure, but
are also not free of bias. For example, the reliability of
information from retrospective interviews on dietary habitsat the time of the accident and some of the estimates of past
exposure conditions depend on the quality of the memory of
the interviewed cases and controls. Studies that are notbased on measurements of thyroid doses suffer particularly
from very large uncertainties in the estimates of individual
thyroid doses. Nevertheless, these studies have contributed
significantly to a better understanding of how iodine status
and radioiodine may play a role in the development of­thyroid cancer.
D126. Estimates of increased incidence of thyroid cancer
cannot be considered reliable unless account has been takenof the increasing use of ultrasonography, and the introduction of mass screening programmes after the accident. However, the similarity of risk estimates between the cohort
study where screening apparently was “matched out” andthose of other studies suggests that the potential confounding effects of screening may not have seriously affected
those relative risk estimates.
D127. The other issue in extrapolation is the mixture ofradioactive isotopes of iodine released in the accident. The
most significant of these as far as irradiation of the thyroid
is concerned was 131I (contributing more than 90% of the
thyroid dose). The possibility has been suggested that the
shorter‑lived isotopes are more effective in inducing thyroid cancer than 131I. However, so far, little empirical evidence has emerged to permit an evaluation to be made to
determine whether the carcinogenic effect of the various
isotopes differ. The contributions of other radioactive isotopes of iodine than 131I to the thyroid dose were relatively
small and therefore their influence cannot be evaluated inepidemiological studies of groups exposed to radiationfrom the accident.
2. Thyroid cancer in those exposed as adults(a)Introduction

D128. As far as induction of thyroid cancer in those who
were exposed as adults is concerned, there are two groups ofinterest. The first group is the general population (the evacuees and residents of the contaminated areas), for whom themain source of radiation exposure of the thyroid was radioiodine shortly after the accident. However, it should be notedthat this group also was subjected to long‑term exposure

167(both external and internal) from long‑lived radionuclides
such as 137Cs (see appendix B).
D129. The second group of interest is that of the recovery
operation workers. Apart from those who worked during
the early days after the accident, for whom internal doses
due to radioiodine may have been important, the recovery
operation workers received doses to the thyroid essentially
due to external radiation exposure that were much higher on
average than the external doses received by the population.
D130. These two groups of individuals are now consideredseparately.
(b)Assessment of current evidence of risk for the general
population

D131. In the Russian Federation, standardized incidence
ratios (SIRs) have been reported for residents of the Bryansk
oblast, the one most heavily contaminated with radio­
nuclides [I3]. The data are shown in table D17. There is astatistically significant excess of thyroid cancers in the­Bryansk oblast compared to the general population for theperiod 1991–1998.
D132. These data have been subject to a dose–response
analysis. This yielded estimates for ERR of ‑1.3 (95% CI:‑2.8, 0.1) Gy–1 for females and ‑0.4 (95% CI: ‑3.5, 2.7) Gy–1
for males. These negative dose–response trends, i.e. thehigher the dose the lower the risk of thyroid cancer, suggestthat the increased SIRs for adult thyroid cancers may be aneffect of screening rather than of radiation exposure [I3]. Ina more recent paper, the authors have expanded the study
population to include the inhabitants of the Bryansk, Tula,
Kaluga and Orel oblasts [I23].
D133. From an ecological study of post‑accident thyroid
cancer incidence in the total Belarusian population, a substantial increase in incidence among adults (older than
18 years in 1986) in 1992–2000 was reported, but the SIR
values were not presented [K22]. The incidence rate attributable to radiation was separated from the total incidence
rate by subtraction of the expected baseline rate estimatedfor the study period from the data for 1986–1990 (minimum
latent period), accounting for the time trend in incidence
during that period. Details of exactly how this was done
were not provided. This methodological approach may haveproduced misleading results because medical attention to
detecting thyroid cancer in the contaminated areas may
have resulted in a substantial screening bias, particularly inthe 1990s following the discovery of the excess thyroid cancer incidence in children related to radiation exposure[K32]. Average thyroid doses to the residents of administrative districts and the uncertainties in the dose estimates
were analysed by means of a radioecological model [K10,K22, K28] and verified with the available radiation measurements on the thyroids of the residents. The relationshipbetween the excess thyroid cancer incidence in three

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selected dose groups and average thyroid dose in the range
from 0.01 to 0.3 Gy is apparently non‑linear; although values for the uncertainties were not provided. For this period,
the calculated EAR was 1.7 (0.3–3.2) per 104 PY Gy and
ERR 3.8 (0.1–9.8) Gy–1. The influence of screening practiceand adjustment for age groups were not mentioned; thesefactors may have influenced the observed results.
D134. In Ukraine, the overall incidence of thyroid cancer
approximately doubled during the post‑accident period[S18]. Three major groups were considered in a recent­follow‑up study to 2004. The highest incidence was observed
among the recovery operation workers. Among the general
population, the most significant increase occurred with theevacuees (table D17). For residents of the contaminatedareas, a statistically significant increase was also observed.
D135. However, no quantitative risk estimates from ananalysis of the dose–response data have been reported
for Ukraine. Therefore, distinguishing between a screening effect and a radiation effect in the data for Ukraine,
which are shown in table D17, is not possible, and effects
due to migration out of the contaminated areas cannot be
excluded.
(c) A ssessment of current evidence of risk for the emergency
and recovery operation workers
D136. Two cohorts of Chernobyl recovery operation workers from Estonia (4,786 men) and Latvia (5,546 men) were
followed from 1986 to 1998 [R7]. Cancers were ascertainedby linkage with nationwide cancer registries. Overall, two
thyroid cancer cases were identified in the Estonian cohortand five in the Latvian cohort. Statistically significant excess
cases of thyroid cancer were observed: SIR = 7.08 (95% CI:
2.84, 14.55). However, there was no evidence of a dose–
response relationship. Screening bias was likely because all
thyroid cancers reported from Estonia had been detectedduring a special screening study so that comparison with thegeneral population not undergoing such screening would be
misleading. Further, the number of cases was small.
D137. Another cohort study conducted among 99,000 Russian recovery operation workers showed a significant excessof thyroid cancer (SIR = 4.33 (95% CI: 3.29, 5.6)) but noassociation with radiation dose [I9]. Data on thyroid cancer
incidence are shown in table D18, which provides the SIRs
for thyroid cancer in the different groups, analysed according
to the period that they worked within the 30‑km zone andwhether the cancer appeared in the latent (1986–1991) or the
post‑latent (1992–1998) period. The values of SIR are withrespect to the comparable age‑, sex‑ and period‑specific rates
for the Russian Federation as a whole.
D138. Significantly elevated thyroid cancer SIRs wereobserved during both the latent period and the post‑latent
periods; the values were higher in the post‑latent period.
Within the post‑latent period, the thyroid cancer SIRs werelargest for the recovery operation workers who worked either
from April–July or from August–December in 1986. The
ratios also remained significantly elevated (SIR was ~4) for
workers who started work in 1987 or in the period 1988–
1990 when there was no radioiodine in the environment [I9].
D139. To address whether the elevated SIRs in table D18
might represent an association between excess thyroid cancer incidence and external radiation exposure received during the course of their work, values of the ERR per unit
dose were calculated. The authors observed no significant
ERR during any work period related to external radiation
dose. Most of the point estimates indicated, in fact, a negative correlation with dose for the entire 1986–1990 work
period. These results, taken together with those in table D18,
argue strongly that the external radiation dose received by
the recovery operation workers is, so far, not a significant
factor for increased risk of thyroid cancer in this cohort, andthat screening bias contributed to, at least, part of the excess
incidence of thyroid cancer.
D140. In earlier studies of the Russian recovery operation
workers, Ivanov et al. [I10, I11] did find a suggestion of anincreased risk of thyroid cancer in the “early” workers, i.e.
those exposed within several weeks of the accident to radioiodine in addition to the external radiation to which the“later” workers had been exposed. However, estimates ofinternal dose caused by inhalation of radioiodine for those
who worked on site in April–June 1986 were not available.
D141. In Ukraine, the overall incidence of thyroid cancer up
to 2004 was approximately eight times higher in the group of
recovery operation workers than the reference rate [S18]. However, no quantitative risk estimates from an analysis of dose–
response data have been reported for Ukraine, so the relatively
high SIR reported for the recovery operation workers may
partly reflect better screening of this population.
(d)Conclusions

D142. The evidence from studies of adults in Belarus, theRussian Federation and Ukraine is somewhat mixed, withsome groups showing elevated SIRs and others showing
substantially smaller effects. The Russian study [I3] showsthat using internal comparisons instead of external comparisons (i.e. with the general population rates) produces
no evidence of any association between the incidence of
thyroid cancer in adults and the estimated thyroid dose. It
remains unresolved whether the increase in thyroid cancer
over the baseline rate in the Belarusian study is simply aresult of changes in diagnosis and detection activities. Thisstrongly suggests that increased screening of the exposedgroups, as well as increased awareness of the general population, substantially complicates the detection of radiogenic thyroid cancers in adults. Thus, there is little
suggestion in the various exposed population groups ofincreased thyroid cancer incidence among those exposed
as adults in the general population.

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

D143. Elevated rates of thyroid cancer among the recovery operation workers compared to the general population
were observed, but no clear association with external dose(among the Russian recovery operation workers) has beenfound. Estimates of the internal doses received by those
who worked on site in April–June 1986 are not available.
The complex follow‑up of the recovery operation workers
after the Chernobyl accident is discussed further in the later
section on solid cancers.
3. Biological aspects of thyroid cancer
following the Chernobyl accident(a)

The Chernobyl Tissue Bank

D144. Many research studies depend on the availability ofhigh quality, pathologically verified, biological material.
The Chernobyl Tissue Bank was established to provide
material for molecular biological research into post‑accident
thyroid tumours. The Chernobyl Tissue Bank comprises two
separate banks (one for Russian citizens and the other for
Ukrainian citizens) of biological material and informationconsisting of: (a) samples from tumour and normal tissue,
and where possible metastatic tissue from post‑operative
specimens; (b) nucleic acid extracted from these specimens;(c) vials of serum from patients whose thyroid tissue is heldin the bank; (d) samples of blood; (e) DNA extracted fromblood; and (f) a computerized database in which relevant
information on the patient (date of birth, date of operation,
sex, oblast of residence at the time of the accident and of theoperation) is held, together with location coordinates foreach sample of tissue, DNA or RNA extracted from tissue,
and blood serum and DNA extracted from blood.
D145. It was a political imperative that biological specimens collected for the Chernobyl Tissue Bank be stored in
the institutes in which the patients were operated on andwhere they continue to be treated. One bank of biologicalmaterial is therefore situated in the Institute of Endocrino­
logy and Metabolism in Kiev, Ukraine and a second in the
Medical Radiological Research Centre of the Russian Academy of Medical Sciences in Obninsk, Russia. Each bankhouses only material and information from its own national
population. A back‑up copy of all data is kept at the Coordinating Centre, Imperial College, London and a web‑based
database is currently being developed. The two banks of biological samples plus the databases in Ukraine and the Russian Federation together with the integrated database arecollectively referred to as the Chernobyl Tissue Bank. The
project builds on relationships that have been establishedbetween scientists in Ukraine and the Russian Federationand those based in Europe, Japan and the United States overa period of nearly 10 years.
D146. The Chernobyl Tissue Bank integrates a number of
research projects in different countries and provides a pooleddata set on the results of the various studies. The material
held in the bank has been reviewed by an international panel

169

of expert thyroid pathologists, and all extracted nucleic acidsamples are subject to extensive quality control. Researchers
are provided with a minimum data set (date of birth, date ofoperation, place of residence at the time of accident, sex andthe consensus diagnosis from the pathology panel) together
with samples of DNA extracted from blood, DNA/RNA
from tissue, and/or serum or sections from formalin‑fixed,
paraffin‑embedded material. Currently there are more than
2,137 reviewed cases of thyroid cancer and adenoma in the
Chernobyl Tissue Bank, the majority of which will have
DNA and RNA from frozen samples available. Most cases
have paired samples of tumour and normal tissue. These
2,137 sets include a small number of cases of cancer andadenoma that occurred in children aged less than three months
who were in utero at the time of the accident and can therefore be considered as unexposed to radioiodine resulting
from the accident. Paraffin sections from tissue microarrays
are also available. More detailed pathological and clinicalinformation is held in the Ukrainian and Russian institutes
that participate in this project. The studies supported so far
encompass research groups from Japan, the United Statesand six European countries, and include single and multigene
cDNA array and comparative genomic hybridization (CGH)
studies. The results from each research project using theresource are returned on a case‑by‑case basis and enteredinto a database for later correlation. Many of the studies
quoted below have utilized material from the resource.
(b)

Pathology

D147. Thyroid cancers derived from the follicular cell canbe divided into two main types: papillary and follicular cancers. Papillary cancer arises de novo from the follicular epithelial cell. Follicular cancers are morphologically similar tofollicular adenomas, which are benign lesions. Evidence ofinvasion through the capsule into veins or extra‑thyroid tissues distinguishes carcinoma from adenoma. Papillary andfollicular cancers show different clinical and molecular biological features as well as characteristic morphological features. Diagnosis is made on using a number of featurescharacteristic of papillary cancers (e.g. characteristic featuresof the cell nucleus include grooved pale nuclei that frequently
show intranuclear cytoplasmic inclusions, and the tumours
contain calcified structures called psammoma bodies) that arelacking in follicular tumours. The diagnosis of papillary cancer depends on the presence of a number of these features,
although not all have to be present for a diagnosis of papillarycancer to be made.
D148. In addition to the two main types of cancer derived
from the follicular cells, there are a number of subtypes ofpapillary cancer. These are named on the dominant structural component. The classic papillary cancer, most commonly found in adults, is composed of papillary structures.
The follicular variant of papillary cancer is composed offollicular structures but has the nuclear features and­psammoma bodies that are indicative of papillary cancer.
The solid or solid follicular variant is composed of solid

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UNSCEAR 2008 REPORT: VOLUME II

sheets of cells with or without a follicular component. The
latter variant shows variable nuclear features but does
contain psammoma bodies.
D149. The majority of thyroid cancers diagnosed in those
who were children or adolescents at the time of the accident
in Belarus and Ukraine are papillary thyroid cancers (90%).
This is the most common of the two main types of thyroid
cancer in unexposed populations. Early reports of the pathology of post‑accident thyroid cancer suggested that there wasa particularly high frequency of the solid and solid follicularvariants of papillary cancer. This subtype of papillary cancer is also seen in young children who were not exposed toradiation. An international panel of expert thyroid pathologists has reviewed all cases of thyroid cancer in people (agedunder 19 years at the time of the accident) living in the contaminated areas of the Russian Federation and Ukraine from
October 1998 to the present that are included in the Chernobyl Tissue Bank and all those that had occurred in Belarus
from October 1998 to February 2001. Whilst in the majorityof cases it has been easy to distinguish papillary cancers
from follicular cancers, there are a few cases where a definitive diagnosis has not been possible. This type of intermediate lesion is also seen in unexposed populations and has led
to a suggested reclassification of thyroid tumours [W2].
Only 2% of the cancers diagnosed in this population are
medullary carcinomas, and 0.3% are poorly differentiatedcarcinomas. The remainder are split evenly between follicular cancers and an entity termed well‑differentiated carcinoma not otherwise specified by the Pathology Panel of theChernobyl Tissue Bank.
D150. Annex J of the UNSCEAR 2000 Report [U3] suggested on the evidence then available that there might be alink between the morphological subtype (i.e. solid/follicularvariant) of papillary cancer observed in children and exposure to radiation. More recent evidence raises questions as towhether there is a causal relationship between radiation
exposure and the solid/follicular morphology of papillarycancer. The morphology and aggressiveness of papillarycancer groups were shown to be a function of the latency ingroups of children exposed at different ages, and it was suggested that they were independent of age at exposure [W4].
The proportion of papillary cancers that are composed
mainly of papillae increases with time after the accident,
whilst the solid/follicular variant appears to be decreasing
with time after the accident [B23]. This is illustrated in­figure D-XIV with data from Ukraine. In addition, the percentage of small (≤1 cm) papillary cancers appears to be
increasing with time [B23]. This could be a function of moresensitive screening or of a decrease in growth rate or
aggressiveness.
(c)

Molecular biology

D151. Earlier studies reported that there was a higher than
expected frequency of RET rearrangement in post‑accident
thyroid cancer, suggesting some RET rearrangements might

be regarded as a marker for radiation exposure [F2, K4].
More recent papers have suggested that there is no link
between radiation exposure and RET rearrangements. The
high prevalence of PTC3 versus PTC1 in post‑accident PTC
may reflect the association between the solid morphologicalsubtype with PTC3 rearrangement and the age of the patient
at diagnosis, rather than the aetiology of the tumour [N3,T1]. There have been few statistically valid studies of RET
rearrangement in paediatric thyroid cancers not associatedwith the accident [F1, W3], making substantiation of theassociation of RET rearrangements with age at diagnosis
difficult. It is important to remember that the correlation
between molecular biology and pathology is not absolute: inall of the series published so far, a substantial proportion(30–50%) of the papillary cancers do not harbour a RET
rearrangement. A variety of different techniques have beenused to assess the frequency of RET rearrangements and,
although this may explain the variation in frequency of RET
rearrangements among studies [Z3], there still remains alarge proportion of papillary carcinomas for which alternative molecular pathways need to be identified. Moreover, a
few studies have demonstrated RET rearrangements inbenign tumours associated with radiation exposure [B8, E1,
S19]; however, other studies have failed to substantiatethese findings [T1], adding further uncertainty to the specific association of RET rearrangement with papillary­thyroid cancer. A recent paper by Port el al. [P18], has suggested that radiation signatures do exist—however, caution
is urged in the interpretation of this paper because the­radiation‑associated group was substantially younger thanthe control group and of a different ethnic origin, anddetailed pathological information is lacking.
D152. Despite the evidence that RET is able to transformthe follicular cell in vitro, the evidence from transgenic
mice suggests that other oncogenic mutations must be
required for the development of the tumour. The clinicalrelevance of RET rearrangements in post‑accident papillarycarcinoma still remains unclear. Some studies in adults
have suggested that the presence of RET rearrangements
may confer a better prognosis, but other studies suggest the
opposite [B5, B7, M2, S3]. In addition, it has also been suggested that RET rearrangements are not found in all cells inpost‑accident papillary carcinomas, and that cells harbouring the rearrangement may be clustered [U17]. The degreeof clustering appears to be related to the latency of thetumours, with shorter latency giving a more homogenous
profile than longer latency [U18]. This suggests either apolyclonal origin for these tumours or that RET rearrangement is a later event in thyroid papillary carcinogenesis
than had previously been thought [U17].
D153. In addition, the B‑raf oncogene has recently emerged
as the most commonly mutated oncogene in papillary carcinoma in adults. The frequency varies in a number of studies
from 36% to 69% in adult PTC [C5, K3], including one
study on Ukrainian tumours [P2]. The frequency of B‑raf
mutation in post‑accident cases (aged under 18 years at operation) is much lower: less than 10% [N3]; and does not

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

appear to be significantly different from that observed insporadic cases of childhood thyroid papillary carcinoma[L6]. This finding is perhaps not surprising as B‑raf and
RET oncogenic alterations appear to be virtually mutually
exclusive in the series published thus far. However, it is clearthat all cases that are negative for B‑raf in young onset papillary cancer are not necessarily positive for RET rearrangement, and that there are as yet unidentified oncogenic
changes in these tumours. A novel rearrangement involving
inversion of chromosome 7, resulting in fusion of part of the
BRAF gene with the AKAP9 gene has also been describedin three papillary carcinomas from young children in ­Belarus[C6]. However, further studies in age‑matched cases will beneeded to establish whether this is a radiation‑specific event.
BRAF gene reduplication has also been shown to be present
in follicular tumours [C9], suggesting that activation of thispathway is critical in thyroid follicular cell tumourigenesis. To
date, there have been no studies specifically related to themolecular biology of follicular rather than ­papillary tumoursof the thyroid following radiation exposure.
D154. To further complicate matters, there is now evidence that the morphology of post‑accident papillary cancer is changing with time [T7, W4]. This suggests that themolecular profile observed in the early cases may owe moreto the age of the patient at diagnosis than to the aetiologicalagent. Although the rate of increase of papillary carcinomas
appears to be slowing in those aged under 19 years at operation, it may be that, as with other types of radiation‑induced
cancers such as leukaemia, there are a number of different
subtypes of the disease, which show different latencies.
This may be further complicated by differential effects ofradiation exposure, depending on the age of the patient at
exposure.
D155. One recent publication highlights the change inproliferative activity of the thyroid during maturation.
However, the authors were unable to relate the increased
sensitivity of the young thyroid gland simply to proliferative
rate, suggesting that a number of factors may also influence
this sensitivity [S20].
D156. The evidence so far suggests that the molecular biology of post‑accident childhood thyroid cancer is similar tothat seen in age‑matched series from non‑irradiated populations. Post‑accident papillary thyroid carcinomas, in common with childhood papillary carcinomas not associatedwith radiation exposure, do not harbour RAS [S2] or p53
mutations [S2, S5], or show specific microsatellite instability [S2]. However, two publications have indicated thatpost‑accident thyroid cancers may show gains and losses ofchromosomal material when DNA is analysed on a global
scale [K19, R8].
D157. A number of studies have recently been publishedgiving transcriptomic analyses demonstrating different
expression profiles between normal follicular thyroid epithelium or follicular tumours and papillary carcinomas[B45, C21, H13, J6, M3]. Similar methods have not yet been

171

shown to be able to differentiate between different types ofpapillary carcinomas; and in one recent paper analysed, it
has been shown that the overall profile of post‑accident papillary cancers was found to be similar to papillary carcinomas from Belgium and France [D2]. Taken together, theseresults suggest that DNA aberrations may not necessarily
lead to differences in gene expression. However, similar
studies need to be carried out on DNA and RNA from thesame series of tumours before adequate conclusions can be
drawn. The consensus opinion appears now to be that RET
rearrangements are more frequent in childhood papillarycarcinomas regardless of their aetiology.
D158. There has been little work carried out on the effect of
single nucleotide polymorphisms in DNA and post‑­accident
thyroid carcinoma. A number of studies are underway, but
their results are too preliminary to be included in this annex.
One published observation suggested that polymorphisms in
the p53 gene may contribute to the risk of developing papillary thyroid cancer after radiation exposure [R9]. Further
studies are clearly needed in this important area.
D159. There are a number of large studies of the molecularbiology of post‑accident thyroid cancer currently underway,
with pathologically verified material supplied by the Chernobyl
Tissue Bank. There is no doubt that these studies will ­enable
the separation of those elements that are due to the effects ofage from those that are truly due to radiation exposure.
4.
(a)Leukaemia

Introduction

D160. Studies such as those of the survivors of the atomic
bombings have demonstrated that leukaemia can be inducedby ionizing radiation delivered at high doses and dose rates[U1]. Further, leukaemia is one of the cancers most sensitive to induction by ionizing radiation and has the shortest
minimum induction period of any such cancer, of the orderof two years. Detailed analysis of the latest data on the survivors of the atomic bombings, shows that in terms of relative risk, the risks are highest for those exposed at an earlyage, and follow a wave pattern with time after exposure.
The fall in risk with time since exposure occurs more rapidly among those exposed at an early age than among those
exposed at a later age. Therefore, studies relevant to theChernobyl accident have to be reviewed according to age at
the time of exposure.
D161. Analysis of pooled data from several studies ofnuclear workers [C3, C10] have yielded estimates of leukaemia risk that are consistent with those from studies of thesurvivors of the atomic bombings. In this pooled analysis,
the selected nuclear workers were monitored for exposure
to external radiation on a monthly or yearly basis and, consequently, might be expected to provide a better estimate ofany effect due to dose rate. However, despite the huge
number of workers involved in this pooled analysis, the172

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confidence intervals in relation to the estimated leukaemia
risk remain very large; the ERR was 1.93 (95% CI: <0,8.47) Sv–1 and was not statistically significant. So, the effectof protracted radiation exposure on leukaemia risk and, inparticular, the magnitude of any dose and dose‑rate effectiveness factor (DDREF) [U1, U3] are matters that stillneed to be resolved. The non‑linear dose–response relationship for leukaemia, particularly that seen in the survivors of
the atomic bombings, should be taken into account when­discussing values for the DDREF.
D162. The population exposed as a result of the Chernobyl accident includes the recovery operation workers, someof whom were exposed at high or moderate dose rates(depending on when they worked on the industrial site), andmembers of the general population, who have been subject
to exposures at low dose rates (primarily from 137Cs) for anumber of years and will continue to be exposed in thismanner in the future. Thus, the risk of leukaemia in the
exposed population is a matter both of public health concern and scientific interest. A number of studies have beenreported in which the incidence of leukaemia in various
subgroups of the population have been examined.
D163. Studies of leukaemia incidence in those exposed inutero or at an early age as a consequence of the accident havebeen reported specifically, in view of the increased susceptibility of such individuals to radiation‑induced leukaemia.
These studies are discussed first, followed by more general
studies of those exposed as adults. Some of the more general
studies presumably include those exposed as children oradolescents, since results with respect to age at exposure are
not always presented separately in these studies.
(b)

Assessment of current evidence for those exposed in utero

D164. Several geographical correlation studies were available in the UNSCEAR 2000 Report [U3] which comparedleukaemia rates in those exposed in utero with those not so
exposed. These studies did not provide any convincing evidence of a measurable association, with the possible exception of the study in Greece [P9]. Rates of leukaemia in those
exposed in utero and those born either before the accident ora year after, differed by a factor of 3. However, the numbersof cases in each exposure category were small. Furthermore,a similar study design was applied to the inhabitants of othercountries exposed to radioactive deposition, but the findings
were negative [S8].
D165. Since then, a further study has been published by
Noshchenko et al. [N9] comparing the cumulative incidence ofleukaemia amongst those exposed in utero in a highly contaminated area of Ukraine with that in one with lower levels ofradioactive deposition. This yielded a relative risk of 2.7 (95%
CI: 1.9, 3.8) for all leukaemias. The number of cases available
for analysis was not large (21 in the exposed area and 8 in thecontrol area), and the descriptive nature of the study limits theinterpretation that can be placed on this estimate.

D166. Information on infant leukaemia rates following
the accident has been evaluated by the UK Committee
Examining Radiation Risks of Internal Emitters (CERRIE)[C24]. Whilst the data from Great Britain were too sparsefor firm conclusions to be drawn, CERRIE concluded thatthe findings on infant leukaemia in various countries after
the Chernobyl accident do not provide sufficient persuasive
evidence that the risk of internal exposure to radionuclides
is seriously underestimated by using risk estimates obtained
from studies of exposure in utero to sources of externalradiation [C24].
(c) Assessment of current evidence for those exposed as children
D167. In the UNSCEAR 2000 Report [U3], a number ofgeographical correlation studies of leukaemia incidence
occurring in populations exposed as children to radiation
resulting from the Chernobyl accident were reviewed.
These studies provided little or no evidence of any increasein leukaemia risk due to the radiation exposure.
D168. Since the UNSCEAR 2000 Report, similar geographical correlation studies, which compared rates of leukaemia before and after the accident among those exposed
as children, have again provided no support for the hypothesis of a measurable increase in leukaemia risk in Belarus[G5], the Russian Federation [I24] or Hungary [T4].
D169. In addition to the geographical correlation studies,
the results of two analytical studies of leukaemia occurring amongst those exposed in childhood have appeared[D5, N10]. In the first case‑control study [N10], carriedout in Ukraine, all cases of leukaemia among those aged
0–20 years at the time of the accident were diagnosed in
the Rivne and Zhytomyr oblasts between 1987 and 1997.
Controls were selected from the same two oblasts, butfrom districts other than those that provided the cases, andthey were matched by age at exposure, sex and type of settlement. The mean cumulative bone marrow dose to all
study subjects was very small (4.5 mSv). A total of 98 outof 272 potentially eligible cases were independently confirmed and interviewed; no explanation was given for the
method of their selection. Statistically significant associations were found for acute leukaemia between 1993 and1997 among males with doses of 10 mSv or more, and for
acute myeloid leukaemia among those diagnosed between
1987 and 1992. Possible biases in the selection of casesand controls cast doubts about the findings of this study[D5, U1, W5].
D170. The larger case‑control study reported in reference[D5] was conducted in the three republics, and included
cases from the earlier study [N10] as a subset. This study
showed mixed results: those from the Ukraine data showeda significant association of leukaemia risk with the radiation exposure; those from the Belarus data showed anon‑significant association; and those from the RussianFederation data showed no association. The ERRs in the

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173

three countries were 78.8, 4.09 and ‑4.94 Gy–1, respectively.
Because radiation doses were very low (median dose wasless than 10 mGy), the statistical power of the analyses wasdiminished [U1]. The authors concluded that “this study
provides no convincing evidence of an increased risk ofchildhood leukaemia as a result of exposure to Chernobyl
radiation” [D5].

confirmed leukaemia between 1986 and 1998. Afterexcluding CLL (n = 16), the type of leukaemia thought not
to be induced by radiation, they obtained an SIR of 2.5(90% CI: 1.3, 3.7) comparing those who incurred doses of
150–300 mGy with those who incurred doses below
150 mGy; they estimated an ERR of 6.7 (90% CI: 0.8,23.5) Gy–1.

D171. Thus, overall, so far there are few studies available
and little convincing evidence to suggest a measurable
increase in the risk of leukaemia among those exposed as
children to the radiation resulting from the accident at
Chernobyl. This conclusion is consistent with the earlier
cancer registry studies of childhood cancer risk in Europe
following the Chernobyl accident [P12].

D175. An earlier case‑control analysis from the same registry initially showed no significant trend with dose for all
leukaemias, or for leukaemia excluding CLL, among therecovery operation workers who worked in the 30‑km zone
in 1986–1987 [I10]; however a later analysis estimated significant ERRs ranging from 0.28 Gy–1 to 15.59 Gy–1 foressentially the same groups [K11]. In the latter study, a totalof 36 non‑CLL cases diagnosed between 1986 and 1993
were compared with controls (case : control ratio = 1:3). The
mean doses for cases were lower than those for the corresponding controls, but nevertheless an elevated (but not statistically significant) relative risk was observed in the highest
dose group.

(d) Assessment of current evidence for those exposed as adults
D172. General population groups. A few studies of leukaemia incidence in groups of people exposed as adults toradiation resulting from the Chernobyl accident were available in the preparation of the UNSCEAR 2000 Report [U3].
Again, none of these studies provided persuasive evidenceof any measurable effect. The majority of the geographicalcorrelation studies conducted in various countries relied on
the data available from national registries and showed noconvincing evidence of any trends of increasing incidence ofleukaemia.
D173. Emergency and recovery operation workers. In
1996, a large cohort study of the Russian recovery operation
workers (>142,000) was reported by Ivanov et al. [I11]. A
total of 48 cases of leukaemia, including chronic lymphatic
leukaemia (CLL), were diagnosed in the period 1986–1993
in the cohort. A statistically significant SIR of 1.77 (95% CI:
1.22, 2.47) was estimated comparing the rates of leukaemia
in this cohort to the rates in the Russian population for
1990–1993. The value of the SIR estimated using population
rates from before 1990 as a comparison was much lower andnot statistically significant. A statistically significant ERR of
4.3 (95% CI: 0.83, 7.75) Gy–1 was estimated from the data.
Risk estimation was based on a comparison of the observed
incidence with the national incidence of leukaemia for malesof the same age groups. This estimate appeared comparable
in magnitude with the leukaemia risk estimate derived fromdata on the survivors of the atomic bombings who wereolder than 20 years of age at the time of the bombings (ERR
= 3.70 Sv‑1, averaged over sexes) [U3]. However, it should be
noted that the estimate in the Ivanov et al. study [I11]
included cases of CLL (n = 10).
D174. In a further study of the Russian recovery operation workers, Ivanov et al. [I13] studied the occurrence ofleukaemia in a cohort of 71,870 workers engaged in recovery operations within the 30‑km zone between 1986 and1990, and for whom estimates of individual external radiation doses were available from the Russian national dosimetric registry. They observed 58 cases of pathologicallyD176. The results from these studies have been questioned,
see reference [U3]. In discussing the discrepancy between
the findings of the case‑control and cohort studies, Boiceand Holm [B46] suggested that the increased incidence
observed in the cohort analyses reflected a difference in caseascertainment between the recovery operation workers andthe general population and not an effect of radiation exposure. The magnitude of the risk is also questionable becauseof the large uncertainties in the “official” doses from theRussian State Chernobyl Registry and the procedures used
to verify leukaemia cases were unknown.
D177. Buzunov et al. [B13] studied the incidence of leukaemia in 1987–1993 in a group of approximately 175,000 recovery operation workers in Ukraine. They compared the rates
of leukaemia in those first employed in 1986 and those
employed in 1987, when doses were lower. They found thatthe rate of leukaemia was approximately double in the firstgroup, but dose dependence within the groups was notstudied.
D178. Two other albeit smaller cohorts of recovery operation workers were followed. In the initial study, Rahu et al.
reported no cases of leukaemia in the cohort of Estonian
recovery operation workers who worked during 1986–1993[R3]. In the second study, which involved follow‑up of theEstonian and Latvian recovery operation workers until 1998
[R7], the incidence of leukaemia in the Estonian workers
remained unchanged, but that in the Latvian workers was
significantly higher compared to the age‑matched general
population (SIR = 2.59; 95% CI: 1.04, 5.34; n = 7 cases).
The overall leukaemia excess, however, was not significantly
increased (SIR = 1.53; 95% CI: 0.62, 3.17); and the authors
were concerned that “ascertainment bias stemming fromincreased awareness and medical attention may increase
false‑positive diagnoses of leukaemia, and hence explain theexcess number of cases in the Latvian cohort.”

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D179. Two case‑control studies of recovery operation
workers—one using data from Belarus, the Russian Federation and the Baltic countries, and the other data from
Ukraine—were conducted [H11]. Both utilized the samequestionnaire and had the same nested case‑control
design, with both cases and controls having been drawn
from the cohorts of recovery operation workers in eachcountry. The cohorts were assembled on the basis of thenational Chernobyl State Registries. Both studies used thesame method of dose reconstruction (RADRUE) based oninterviews and various measurements of dose fields in the
30‑km zone around Chernobyl [B11]. The Committee wasinformed that the unpublished results of both studies indicate similar non‑significant increases in both non‑CLL
and CLL leukaemia. This is somewhat surprising in viewof the lack of any significantly increased radiation risk for
CLL observed in most other studies. The Committee has
recently concluded that CLL is not established as beingcaused by ionizing radiation [U1].
(e) Conclusions
D180. The interest in leukaemia arises because of its
known sensitivity to induction by ionizing radiation and also
because of its short latent period. So far, no persuasive evidence has been found to suggest that there is a measurable
increase in the risk of leukaemia among those exposed inutero and as children. This is not unreasonable given that thedoses involved were generally very small, and therefore epidemiological studies would lack sufficient statistical power
for an effect to be observed.
D181. Amongst adults, the most meaningful evidence
comes from the studies of recovery operation workers. At
present, there is some evidence of a detectable effect amonga group of recovery operation workers from the RussianFederation, but this is far from conclusive. It would therefore
be premature to make a direct comparison between the dataobtained from these studies directly with the risk estimatesobtained from studies involving high doses and dose‑rate(such as of the survivors of the atomic bombings). The limitations discussed earlier of the studies of the recovery operation workers must be borne in mind. Nevertheless, future
results from studies of the recovery operation workers will,
hopefully, provide meaningful data that can be comparedwith those from other studies.
5. Other solid cancers(a)Introduction

D182. A few studies have been reported on specific solid
tumours following the Chernobyl accident, but evidence so
far is extremely limited. Other studies have examined therisk of all solid cancers combined (i.e. excluding leukaemia
and sometimes thyroid cancer). Although using such an
aggregated endpoint could obviously mask an effect for any

individual cancer, statistical power is increased as it provides greater numbers for analysis, even though any derived
risk estimate would actually be lower than the risks of any
individual cancers that are induced by radiation exposure.
(b) ssessment of current evidence in groups of the generalA
population

D183. Table D19 shows the SIRs for all solid cancers
combined occurring among various exposed groups in the
Russian Federation and Ukraine. The data are shown forseparate time periods, where available.
D184. For the Russian Federation, the SIRs in table D19
are for the seven contaminated districts of the Bryansk
oblast with a total population of 316,000 persons in 1991 andof 291,000 in 2005. The incidence of solid cancer for thewhole of the Russian Federation was used as a reference
value. There is no evidence of any significant increase in theincidence of all solid cancers in the seven contaminated districts for any time period of observation within the period
1991–2005 [I25, I26]. The observed incidence of cancer
among the residents of the worst affected areas of the ­Bryansk
region did not differ significantly from the expected value.
Although comparison with the national cancer registration
rate creates a potential for bias, the SIR for the whole period
is essentially equal to unity.
D185. The data for Ukraine in table D19 show that generally the rates of all solid cancers are lower both among evacuees and among permanent residents of the contaminatedareas of the country compared to the rest of the country
despite any potential bias caused by using national cancer
registration rates as the basis for the comparison [P16, S18].
D186. A geographical correlation study conducted by
Pukkala et al. [P10] investigated the potential relationshipbetween radiation exposure and breast cancer incidence inBelarus and Ukraine. Cumulative dose estimates were basedon average district‑specific whole body doses accumulated
since the accident due to external exposure and to ingestionof long‑lived radionuclides. Values of breast cancer incidence were derived from information in the national registries. Analysis of the pooled Belarusian and Ukrainian data
showed a significantly increased relative risk (RR) between
1999 and 2001 in districts with average cumulative dose of
40 mSv or more. This increase was seen in particular among
women who were younger than 45 years old at the time of
the accident. For Belarus, the RR in the group with an average dose of 40 mSv or more was 2.24 (95% CI: 1.51, 3.32).
No significant excess was seen for earlier periods. The RR
was higher for metastatic breast cancer (RR = 3; 95% CI:
1.70, 5.29) than for localized cancer (RR = 2.01; 95% CI:
1.16, 3.51). For Ukraine, the RR in the group with an average
cumulative dose of 40 mSv or more was 1.78 (95% CI: 1.08,
2.93) in the period 1997–2001. A significant increase in the
RR was also observed in the period 1992–1996 in areas withan average cumulative dose of 20–39.9 mSv. Risk values

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

derived from this study are substantially higher than thosedetermined from the other epidemiological studies that werereviewed in annex A of the UNSCEAR 2006 Report [U1]and need, therefore, to be interpreted cautiously.
D187. A publication by Dardynskaia et al. [D6] in contrast
shows no clear increase in the incidence of breast cancer in
Belarus, but it does not present breast cancer incidence withrespect to dose, except in order to contrast the data for the
Vitebsk oblast (with minimal deposition due to the accident)with those for the Gomel oblast (with much higher levels). It
is a descriptive study comparing trends for all women from1978 to 2003 and for those of age 30–49 years. In a separate
analysis, the rates in the Gomel and Vitebsk oblasts werecompared: there is a tendency for an increased incidence ofbreast cancer since 1976 in both oblasts and the authors concluded that “these data provide no convincing evidence for
Chemobyl‑induced breast cancer in Belarus”.
D188. Other epidemiological studies have demonstrated aclear association between external radiation exposure andthe risk of breast cancer, with the ERR per unit dose being
greatest for exposure at young ages [U1]. Only very few
studies on women exposed as a result of the Chernobyl accident have considered breast cancer. There are numerous
weaknesses in these studies—they are unable to take into
account some major cofactors that have to be considered,such as the age at first pregnancy, other hormonal factors,
and nutrition. These factors could be studied through afuture case‑control study, but reconstruction of individualorgan doses needs unbiased information on past exposures.
D189. Analyses were conducted of the trends in the data on
cancer registry and cancer mortality in Europe [C11]. The
incidence of most cancer groupings of interest increased inEurope after 1981. However, after 1991, the time slope of that
increase for all cancers combined, breast cancer and leukaemia decreased. Only for thyroid cancer was there a statistically significant increase in the slope of the trend noted after
1991. The authors concluded that the “results of analyses oftrends in cancer incidence and mortality do not appear toindicate (except for thyroid cancer) a measurable increase incancer incidence in Europe to date, related to radiation fromthe Chernobyl accident”. Furthermore, in discussing the concerns over surveillance and better diagnostic capabilities inareas with elevated deposition due to the Chernobyl accident,
they stated, “The interpretation of trends in cancer incidence
should be made with caution, as cancer registration data aresubject to a number of potential biases”.
(c) ssessment of current evidence among emergency andA
recovery operation workers

D190. Various studies of all solid cancers combined for
Russian and Ukrainian emergency and recovery operation
workers have been reported. Table D20 shows the SIRs forall solid cancers combined in various groups of workers,
over various time periods following the accident.

175

D191. In two studies, Ivanov et al. [I47, I48] examined thedata for the Russian emergency and recovery operation
workers regarding the incidence of solid cancers. In thelarger of them [I48], they studied a cohort of 55,718 workers
who worked within the 30‑km zone during 1986–1987, andfor whom the documented estimates of external dose ranged
from 0.001 Gy to 0.3 Gy (mean 0.13 Gy). A total of
1,370 solid cancer cases were diagnosed during 1991–2001.
In the smaller study [I47], they examined 8,654 nuclear
workers who participated in the recovery operations at Chernobyl and who had their external doses documented. In thissmaller cohort, which had an average external dose of
0.05 Gy, 179 solid cancers had occurred during 1996–2001.
In both cohorts, solid cancer incidence was lower than in therelevant age/gender groups of the Russian general population and although the value of the ERR per unit dose waspositive, it was not significantly different from zero.
D192. Ivanov recently transmitted to the Committee
updated information from the RNMDR system; it addressed
the cohort of male recovery operation workers residing insix regions of the European part of the Russian Federation(39 jurisdictions). The information related to 104,466 persons as of 2005 (55.5% of the total number of recovery operation workers registered in the RNMDR). Figure D-XV
summarizes the number of workers by year of entry into the
30‑km zone. This cohort was established in 1991 when thenumber of its members was 76,229. Complete personalized
medical information is available for this cohort: 4,220 solidcancer cases were registered from 1991 to 2005 [I26]. Official external dose records are available for 74% of the cohort
members; the average dose was 107 mGy.
D193. The SIRs for the recovery operation workers were
calculated using the age‑specific incidence of all solid cancers combined in the male population of the Russian Federation as the external control (table D20). These updated data
indicate an apparent excess of solid cancers among the
emergency workers (16%), and a tendency for a decrease
with time since exposure. However, the apparent excess
observed may be explained by the more sophisticated medical screening of the population than for the Russian population in general [I25, I26]. Caution therefore needs to be
exercised in interpreting these data.
D194. Ivanov et al. also studied mortality from solid cancer
in a cohort of 61,000 Russian emergency and recovery operation workers with documented estimates of external dose(average dose 107 mGy) [I25, I40, I49]. In the first study covering 1991–1998, out of 4,995 recorded deaths, 515 were due
to solid cancers [I25, I40]. Although neither the mortality rate
due to all causes nor the mortality rate due to solid cancer
exceeded the corresponding mortality rates for the relevant
age/gender groups of the Russian population in general, thedependence of SMR on dose was statistically significant:
ERR = 2.11 (95% CI: 1.31, 2.92) Gy–1. In the second study[I49], the authors focused on the most exposed fraction of thecohort, i.e. on the 29,000 workers who entered the 30‑km
zone in the period April 1986 to April 1987. The average dose

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to this subcohort was 156 mGy. From the time of the accident
to the end of 2002, some 4,719 deaths were registered in thissubcohort and 651 of them were caused by solid cancers.
Moreover the mortality rate for this subcohort from all causes
did not exceed the corresponding mortality rates of the relevant age/gender groups of the Russian population in general.
The only group of diseases for which the dependence of SMR
on dose was statistically significant were solid cancers (ERR
= 1.52 (95% CI: 0.20, 2.85) Gy–1). The weakness of thesestudies is that most of the deaths from solid cancer would havebeen registered during the latent period for most solid cancers
if they had been initiated by radiation exposure from the
Chernobyl accident, i.e. many years before radiation‑related
fatal cancers would have occurred.
D195. The Ukrainian recovery operation workers showeda similar, statistically significant increase in the SIR for all
cancers combined for the period 1991–2004 (table D20)
[P16, S18]. This result suffers from the same weakness asthat of the Russian studies.
(d)Conclusions

D196. There appears at present to be no persuasive evidence of any measurable increased incidence of all cancers
combined or breast cancer alone among the general populations of the Russian Federation and Ukraine. There also
appears to be no pattern of increased incidence of solid cancers among the inhabitants of the areas deemed contaminated compared to the inhabitants of the areas deemeduncontaminated, and no difference in the trends with time
for areas with different levels of radioactive deposition.
D197. The evidence regarding any increased incidence ofsolid cancers among recovery operation workers is mixed.
Although some groups showed elevated SIRs, statisticallysignificant quantitative risks of increased cancer incidence
per unit of additional dose have not been reported. In contrast, two Russian studies reported a dose dependence of thesolid cancer mortality rate with a corresponding statisticallysignificant ERR per unit dose.
D198. Several limitations need consideration when interpreting these results. First, for many cancers, a latent periodof 10 years or more is to be expected between the time of
exposure and the observation of an effect. If this applies tothe incidence of all solid cancers combined, one would not
expect to see any effect manifest itself until the mid‑ to late
1990s. Second, interpretion of the results of comparisons of
the data on the recovery operation workers with those for thegeneral population should take into account the fact that allof the workers are offered a regular annual medical examination. This has the possible effect of introducing a screening bias, as discussed earlier. Furthermore, the risk values
derived from the various studies are substantially higher
than those determined from other epidemiological studies
reviewed in annex A of the UNSCEAR 2006 Report [U1]and need, therefore, to be interpreted cautiously.

D199. Assessments of statistical power, based on thef­ ollow‑up to date and using findings from the study of the survivors of the atomic bombings and other studies summarizedin annex A of [U1], would suggest that doses in the general
population are too low to yield sufficient statistical power todetect any measurable increase in the risk of all solid cancers
combined among such individuals exposed to radioactive
deposition after the Chernobyl accident. Certainly, empiricalstudies to date do not suggest that risks are substantiallygreater than those predicted by risk projection models.
6. Autoimmune thyroiditis
D200. Autoimmune thyroiditis is a complicated phenomenon and almost certainly involves interaction between genetic
predisposition and environmental factors, such as the level of
dietary iodine intake [D7]. However, its association with radiation exposure is controversial [E3]. In addition, the underlying incidence of autoimmune thyroiditis increases with age[D8]. Therefore, dissecting out the effect of radiation exposure from the other elements that may or may not have a bearing on the incidence of autoimmune thyroid disease in the
population requires extremely careful study.
D201. There have been few studies of significant size thathave addressed the relationship between autoimmune­thyroiditis and exposure to radiation resulting from the­Chernobyl accident. The largest study to date involved
12,240 subjects who resided in an area of mild to moderate
iodine deficiency in Ukraine [T7]. All subjects had estimatesof thyroid dose due to the intake of 131I based on individual
radiation measurements on the thyroid performed in May–
June 1986. Measurements of circulating antibodies and TSHlevels together with ultrasonography of the thyroid gland weretaken to determine whether the autoantibodies produced weresignificantly affecting thyroid function. The presence of thyroid autoantibodies is not considered on its own to be an indicator of clinically significant destruction of the thyroid by the
immune response (i.e. true autoimmune thyroiditis), but torepresent evidence of thyroid autoimmunity.
D202. This study, despite its size, did not provide any conclusive evidence of a relationship between thyroid dose andautoimmune thyroid disease, defined by both the presence of
circulating autoantibodies and evidence of thyroid dysfunction by ultrasonography, and/or TSH elevation. This study
therefore agrees with the findings of studies of exposed individuals from the Hanford nuclear site [D9] and from theHiroshima and Nagasaki bombings [I27, N11].
D203. The clinical significance of elevated levels of thyroid autoantibodies in the absence of signs of destruction of
thyroid cells by an autoimmune response remains unclear.
Furthermore, caution is necessary when extrapolating fromone study that comprises individuals studied at a single point
in time (12–14 years) after the accident. However the findings are in general consistent with earlier, less robust studies[P11, V4].

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

7. Cardiovascular and cerebrovascular diseases(a)Introduction

D204. High doses of radiation to the heart and blood vessels can cause a spectrum of cardiovascular diseases, including coronary heart disease. Recent reports have clearly
demonstrated the direct association between high levels ofradiation exposure (such as in radiation therapy for Hodgkin
lymphoma [A2] or breast cancer [D4]) and cardiovasculardisease during long‑term follow‑up. The risk of radiation‑­
related cardiac disease is strongly related to age at irradiation and is especially high when exposure occurred duringchildhood or adolescence. Little information is available
regarding the possible effects of smoking and other cardiovascular risk factors on the radiation‑related risk of ischaemic heart disease. The biological mechanisms by which
low‑dose radiation exposure induces risks of cardiovasculardisease are currently unclear. Although several plausible
biological models have been suggested, more research isneeded to explore possible models [U1].
D205. Studies of the survivors of the atomic bombings inJapan, who received single doses ranging from 0 to 4 Gy to
the whole body, showed that the risk of death caused by
non‑cancer diseases, including cardiovascular and cerebro­
vascular diseases, is dose‑related with an ERR of 0.14 Gy–1
[P3]. This evidence has been recently confirmed by thelonger observation times in the Adult Health Study from1958 to 1998 [Y1]. According to this study, a significant
positive dose–response relationship has been confirmed for
myocardial infarction among survivors exposed at ages
younger than 40 years (p = 0.049). Analysis of the cause ofdeath between 1968 and 1997 among the survivors of theatomic bombings led to an estimate of the ERR for heartdisease of 0.17 (90% CI: 0.08, 0.26) Sv–1 and to that forstroke of 0.12 (95% CI: 0.02, 0.22) Sv–1 [P3, U1].
D206. In annex B of the UNSCEAR 2006 Report [U1], theCommittee concluded that “to date, the evidence for an association between fatal cardiovascular disease and radiation
exposure at doses in the range of less than about 1–2 gray (Gy)comes only from the analysis of the data on the survivors of
the atomic bombings in Japan. Other studies have provided noclear or consistent evidence of a fatal cardiovascular diseaserisk at radiation doses of less than 1–2 Gy … the present­scientific data are not sufficient to establish a causal relationship between ionizing radiation and cardiovascular disease atdoses of less than about 1‑2 Gy”.
(b)

Assessment of current evidence

D207. Two studies conducted by Ivanov et al. [I12, I39]
focused on cardiovascular and cerebrovascular incidence
among the cohort of Russian recovery operation workers.
About 60,000 men with an average dose of 109 mGy were
followed from 1986 to 2000. The authors observed a statistically significant excess relative risk of ischaemic heart177

disease: ERR = 0.41 (95% CI: 0.05, 0.78) Gy–1; of essential
hypertension: ERR= 0.36 (95% CI: 0.005, 0.71) Gy–1; andof cerebrovascular diseases: ERR= 0.45 (95% CI: 0.11,0.80) Gy–1. The authors focused on the 29,003 workers withan average dose of 162 mGy who worked in and around theChernobyl site during the first year after the accident. The
authors considered that the group at risk with respect tocerebrovascular diseases are those who received externalradiation doses greater than 150 mGy over a short period(less than six weeks), with a relative risk equal to 1.18
(95% CI: 1, 1.4). Nevertheless, several weaknesses of thestudy have to be considered: the absence of information on
the percentage of people lost from the follow‑up process,the use of death certificates for assessing part of the disease
incidence, and the absence of adjustment for the wellknown risk factors of cerebrovascular diseases (i.e.
­smoking, obesity, hypercholesterolaemia and others).
D208. In a cohort of 60,910 emergency workers in the Russian Federation (basically the same cohort as in references[I12, I39]) followed for overall mortality, 4,995 deaths werereported in 1991–1998. Of these, 1,728 died of cardiovascular disease, which was indicative of a much higher rate thanfor the normal population [I40]. The estimate of the ERR for
deaths from cardiovascular disease was 0.54 (95% CI: 0.18,
0.91) Sv–1. The ERR for the incidence of cardiovascular disease was less, at 0.23 (95% CI: ‑0.03, 0.50) Sv‑1 [I25]. Thislatter value was driven primarily by hypertensive diagnoses
and it appears paradoxical that the incidences of ischaemic
heart disease and acute myocardial infarction (which might
be expected to correlate with mortality) did not increase
with dose.
D209. Another study conducted by Rahu et al. [R3] on acohort of 4,742 emergency workers from Estonia followedfrom 1986 to 1993, found no association between the dose
and the incidence of cardiovascular disease, based on an
estimation of SMR by categories of dose.
D210. Recently, an analysis of non‑cancer incidence andmortality rates in various groups registered in the Ukrainian
State Chernobyl Registry (USCR)—including workers,
evacuees and residents of contaminated areas—was published by Buzunov et al. [B43]. The authors attempted toevaluate total and disease‑specific incidence and mortality
rates from 1988 to 2004. The most surprising finding was adecrease in the incidence of non‑cancer diseases among therecovery operation workers since 2000. However, since thepaper lacks any presentation of the methodology used inestimating the rates, it is not possible to determine if therates were age‑adjusted or if the denominators of the rates
were adjusted for the numbers of deaths that occurred,
which, according to some sources, were more than 15% of
this cohort. Another limitation is the absence of the underlying numbers of cases in the tables. Since only roughly 40%of those registered in the USCR have official doses, and in
most instances these subjects had higher doses, any calculations based only on those with doses would be biased. In
summary, this paper does not provide any new reliable

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information on non‑cancer morbidity and mortality due toradiation exposure resulting from the Chernobyl accident.
D211. In Belarus, there have been studies of the incidenceof coronary heart disease and mortality due to that disease
in contaminated and uncontaminated districts [G6, G7].
The age‑standardized incidence of coronary heart disease
among 617 male agricultural workers residing in the Narovlyansky district of the Gomel oblast (one of the most contaminated districts of Belarus) was 5.0%, whereas thatamong 213 workers in an uncontaminated district of Minsk
was 9.1% [G7]. Reference [G6] considered mortality caused
by cardiovascular diseases among agricultural workers who
lived in the same two districts. Correlations were foundbetween cardiovascular mortality and the various non-­radiation risk factors (arterial hypertension, smoking, etc.)
known to cause heart disease. However, the cohorts described
were very small and unlikely to be informative, and, as yet,there are no studies specifically devoted to analy­sing the possible associations between disease ­prevalence and mortality
and radiation dose.
(c)D214. It is common practice to grade radiation‑induced
cataracts. grade I cataracts or opacities are subclinicaleffects that have little or no impact on daily life, while thehigher grades may result in visual impairment. Cataracts are
believed to be a deterministic effect of radiation exposure,i.e. one in which the severity of the effect varies with doseand for which a threshold may therefore occur. The vast
majority of radiation‑induced opacities identified after radiation exposure do not impair vision. However, especiallyhigh doses, e.g. 7 Gy, may lead to severe visual impairmentthat requires replacement of the lens.
D215. While not pathognomonic, typically radiation‑induced
cataracts initially manifest themselves as defects in the transparency of the posterior superficial cortex of the tissue and arereferred to as posterior subcapsular cataracts (PSC).

Conclusions

D212. Little solid evidence exists of any demonstrable
effect of radiation exposure due to the Chernobyl accident on
cardiovascular and cerebrovascular disease incidence andmortality. One study of the recovery operation workers in the
Russian Federation has provided evidence of a statisticallysignificant association between radiation dose and both mortality rates due to cardiovascular disease and cerebrovasculardisease incidence. The observed excess of cerebrovasculardisease was linked to those having worked for less than six
weeks and having received a dose of more than 150 mSv.
However, the revealed excess per unit dose was not adjusted
for other factors such as excessive weight and smoking habits, and therefore, the authors qualified their results as preliminary. Furthermore, the latency interval for cardiovasculardisease mortality was too short to be consistent with what isalready known about radiation‑related heart disease fromhigher dose studies. Further study is required before it can beconcluded whether or not radiation exposure due to the Chernobyl accident has increased the risk of cardiovascular andcerebrovascular disease and associated mortality.
8. The eye and cataractogenesis(a)cumulative doses if the exposure is protracted or fractionated.
If the exposure is fractionated, vision‑impairing damage tothe retina and the optic nerve may require a cumulative doseof the order of 50–60 Gy. Recent studies have suggested thatthe lens of the eye may be more radiosensitive than previously
considered [C17, M4, N18, W1, W7].

D216. Cataracts appear after a latent period, the length ofwhich is inversely related to dose. The latent period isdependent on the rate at which damaged epithelial cells
undergo aberrant differentiation and accumulate in the PSC
region [I37, K1, M1, U9].
(b)

Studies of Chernobyl ARS survivors

D217. Among the ARS patients surviving the Chernobyl
accident, the time of appearance and dose dependence of
PSCs did not reveal any new features. With more than
15 years of clinical observation of 77 workers, 11 cases ofclinically significant radiation‑induced cataract were foundamong persons who survived doses from 2.6 to 8.7 Gy. The
latent period varied from 1.5 years (for the most exposed
person) to 12 years (for the least exposed person) [K1, N2,
N5]. Table D21 and figure D-II present these data.
D218. The Committee is aware that a number of otherUkrainian studies of cataracts among the ARS survivors
and the recovery operation workers are currently underway. Unfortunately, the Committee has not yet seen andevaluated this material.

Introduction(c)D213. Although all tissues of the eye and adnexa may sufferradiation injury, lesions are far more common in the lens, eyelid and retina than in the sclera. The eye is considered a relatively radiosensitive organ compared with other organs andtissues mainly because of the frequent development of posterior subcapsular cataracts. It is usually thought that cataract
development due to radiation exposure requires single acutedoses of low‑LET radiation of 2 Gy or more, or higher

Studies of emergency and recovery operation workers

D219. The Ukrainian–American Chernobyl Ocular Study(UACOS) [C17, W1, W7]. Two ophthalmological examinations have been conducted among the Ukrainian recovery
operation workers 12 and 14 years after the accident. Reconstruction of the individual doses received by these workers
has also been undertaken. Ophthalmic examinations of
8,607 workers were conducted in six cities located in five

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

Ukrainian oblasts. A variation of the Merriam/Focht radiation‑induced cataract scoring method was used on all workers [W7]. The ophthalmologists were kept “blinded” as to thedoses to the lens of the eye, and those undertaking the dosereconstruction were not informed as to ophthalmological status. The recovery operation workers in the study were
32.7 years of age on average at the time of exposure (standard
deviation: 7.3 years), 44.9 years at the first examination and
47.0 years at the second examination. The dose reconstruction involved a comparison of the gamma doses obtained
from the official records of occupational exposure with theestimates of dose and their uncertainties obtained by ESR
analyses of teeth from a sample of workers [C17]. Beta doses
to the lens of the eye were modelled using information aboutbeta exposure levels at various work locations within the
Chernobyl complex during particular time periods. The
doses to the recovery operation workers were moderately
fractionated/protracted and the cumulative doses to the lensof the eye were low to moderate. The median estimated lensdose was 0.12 Gy, and 95% of the doses were less than 0.5 Gy.
D220. Although the UACOS workers examined were still
relatively young (76% were under age 50 at the first examination), there was a high frequency of lens opacity: a total of
26% (2,251) had grade I opacities, including 20% (1,716) withposterior subcapsular opacities found during one or other ofthe examinations [W7]. Only 1.5% (131) had grade II–V cataracts, but these are of importance because higher grade opacities are more likely to cause visual disability than the grade I
opacities. Since the radiation exposures occurred at youngages, the opacities observed largely represent the cumulative
incidence of opacities that had developed subsequent to the
exposures due to the accident.
D221. The analyses of the UACOS data were controlled fora number of potential risk factors for cataract development,
including age at exposure, age and clinic at first examination,sex (96% males), current and past smoking habits, diabetes
mellitus, history of corticosteroid or phenothiazine use, andoccupational exposures to hazardous chemicals, ionizing radiation exposure (other than that due to the recovery operations),
and exposure to infrared or ultraviolet radiation.
D222. In order for selection factors to bias the results of theChernobyl worker cataract study, they would have to berelated to both dose and cataract risk. Consideration of theselection process suggests that most factors would not haveproduced such bias. The Chernobyl worker cataract cohort
was based almost wholly on the Ukrainian SCRM dose registry, which consisted of 32,826 individuals. Many of theindividuals had no addresses, had addresses outside theregions of the ophthalmologic clinics, or had died. It seems
unlikely that these factors would have been substantiallyrelated to both dose and cataract risk. A total of 12,051 wereconsidered eligible and contacted. Of those, 507 either had
only one examination or had another ocular condition thatdisqualified them; it also seems unlikely that either of thosefactors was related to radiation dose. For another 1,346,
there was insufficient information in the USCRM registry to179enable estimates to be made of their dose; there is no reason
why this would be related to cataract risk. Finally, 1,337 did
not complete the epidemiologic/health questionnaire, primarily because personnel were unavailable to administer it;
this also is probably not related to dose, since clinic personnel were “blinded” as to the doses. This left a total of 8,607
in the study. Perhaps the greatest uncertainty regarding
selection bias relates to self‑chosen participation. Although
the participation rate of 71% was reasonably good for a clinical study of basically healthy individuals, the possibility
exists of a higher participation rate among individuals who
knew that they had received substantial doses and who
thought that they might have some loss of visual acuity;
there was no direct way to check this. However, since themain findings pertain to subclinical cataracts that, at thatstage of development, caused little loss of visual acuity, thispossibility seems rather unlikely as well.
D223. For grade I opacities, the OR was 1.49 (95% CI:
1.08, 2.06) at 1 Gy, with adjustment for the other cataract
risk factors mentioned above. Similarly, for grades II–V cataracts, the OR was 1.57 (95% CI: 0.79, 3.11) at 1 Gy, but was
not statistically significant, possibly owing to the smaller
numbers (n = 131 cataract cases). When grade I opacities
were examined by location, posterior subcapsular opacities(OR = 1.42 (95% CI: 1.01, 2.00) at 1 Gy) and the somewhat
more inclusive category of cortical opacities (OR = 1.51
(95% CI: 1.09, 2.10) at 1 Gy), both of which may be­radiation‑related, showed statistically significant increases
with dose, whereas nuclear opacities/cataracts (of any stage),which are not thought to be associated with radiation exposure, showed no elevation (OR = 1.07 (95% CI: 0.56, 2.04) at
1 Gy). When the data were examined by dose group, bothposterior subcapsular and cortical lens opacities showedsuggestive or significant elevations in risk at about 0.5 Gy or
more (table D22) [W7].
D224. Because cataract formation is thought to be a deterministic effect, a statistical analysis was made for a dose–
effect threshold. Maximum likelihood estimates of thedose–effect threshold for various classes of cataracts areshown in table D23. The results from the UACOS study[W7] suggest that the data are incompatible (at the 95% confidence level) with a dose–effect threshold of more than
0.7 Gy for grades I–V cataract in total, with a strong prevalence of grade I opacity, although this statement needs to bequalified because of the uncertainties in the individual dose
estimates [C17].
D225. In summary, the UACOS study indicates that cataracts arising in the population of recovery operation workers, corrected for the most important confounding factors,
are related to the dose received. For the most part, thedoses were less than 0.5 Gy of low‑LET radiation acquired
in a somewhat protracted/fractionated manner. A key
finding was that the data were not compatible with a dose–
effect threshold of more than 0.7 Gy, although this needs
to be tempered by consideration of the uncertainties in thedosimetry.

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Studies of general population

D226. An extensive study [D3] was conducted to deter‑mine the prevalence and characteristics of lens changes in apaediatric population (5–17 years of age) that had lived in anarea close to Chernobyl. Representative groups of
996 exposed and 791 unexposed children were given oph‑
thalmological examinations, and opacities were gradedaccording to a standard scoring system (LOCSIII; [C18]).
Many (38%) of the PSC opacities were examined a second
time to confirm the original findings. A small (3.6%) but
significant (p = 0.0005) group of exposed children mani‑
fested PSC lens changes [D3]. This included 2.8% scored ashaving grade I or greater PSC opacities, as compared to
1.0% in the unexposed group (p = 0.007). The study hadsome weaknesses in that it was not possible to reconstructindividual doses, and the examiners were not “blinded” as tothe examinee’s exposure status (which was defined by thegeographical location of the examination). Nevertheless, thestudy was carefully conducted, with standardized examina‑tion and cataract scoring procedures, and with examiner
training and other quality‑control measures in place.
(e) O ther recent studies of low‑dose radiation exposure andcataracts
D227. A number of studies have been published that are
relevant to exposures at low doses and can be used for com‑
parison purposes. Two cross‑sectional studies have exam‑
ined cataract prevalence in relation to individuals’ ownreporting of their history of computed tomography (CT)scans of the head. One reported a positive association [K9],but the other did not [H10]. A study of US astronauts
reported that those with higher lens doses from space flights(mean of 45 mSv) showed a significant elevation in cataract
risk compared to those with lower doses (mean of 4 mSv)
[C7]. The astronaut exposures were primarily due tohigh‑LET heavy ions and secondary neutrons in space.
D228. A Swedish study examined 484 individuals with amean age of 46 years (range 36–54 years) who were treatedwith radium plaques in infancy (at ages 0–18 months) for
haemangiomas, and 89 unexposed individuals, who had
been treated by other means [H12]. The median dose rate to
the lens was 0.05 Gy/h (mean 0.13 Gy/h). Individual doses
to the lens were estimated and examinations were con‑ducted using a standardized protocol and cataract scoring
system (LOCSII; [C19]). A dose gradation was seen withregard to the prevalence of cortical and PSC cataracts ofgrade I or greater. The prevalences and, in parentheses, thenumber of cataracts compared with the number of lenses
examined were: unexposed, 5% (9/178); <0.5 Gy, 12%(89/748); 0.5–1.0 Gy, 18% (20/115); and >1 Gy, 22%(20/89). Because of concerns about the possible dissimilar‑
ity of the unexposed and exposed groups, the investigators
limited their analyses of dose response to the exposedgroup. After adjusting for age at examination, dose rate andsteroid treatment, the OR at 1 Gy for cataracts of grade I or

greater was 1.49 (95% CI: 1.07, 2.08) for PSC and 1.50
(95% CI: 1.15, 1.95) for cortical cataracts.
D229. An ophthalmological examination was conductedbased on the Japanese survivors of the atomic bombings, pri‑marily on those who were younger than 13 years at the time of
the bombings [M4]. The examiners were “blinded” as to thedose due to the atomic bombings, and the examination was
standardized through examiner training and use of the LOC‑SII scoring system [C19]. The data were analysed on the LOC‑
SII graded scale, so the analysis estimated the incremental riskof more severe grades of cataract using a proportional OR. The
models included adjustment for city, sex, age at examinationand smoking. They found no association for nuclear cataracts(OR = 1.1 (95% CI: 0.9, 1.3) at 1 Gy), but found statisticallysignificant dose–response relationships for cortical cataracts(OR = 1.3 (90% CI: 1.1, 1.5) at 1 Gy) and posterior subcapsularcataracts (OR = 1.4 (90% CI: 1.2, 1.6) at 1 Gy).
D230. A further analysis of the data from the ophthalmo‑
logical examinations on the survivors of the atomic bombings
provided estimates of the dose–effect threshold. For cortical
cataracts, the maximum likelihood estimate of the dose–effectthreshold was 0.6 (90% CI: <0, 1.2) Gy and for posterior sub‑capsular cataracts, it was 0.7 (90% CI: <0, 2.8) Gy [N18](table D23). The most recent analysis considered the preva‑
lence of surgically removed cataracts in the cohort of survi‑
vors of the atomic bombings late in life, by 2000–2002. These
data are important because they refer primarily to cataracts ofsufficient severity to cause visual limitation. Again, a statisti‑cally significant dose–response association was found (OR =1.4 (95% CI: 1.2, 1.6) at 1 Gy). A dose–effect threshold analy‑
sis yielded a maximum likelihood ­estimate of 0.1 (95% CI:<0, 0.8) Gy [N17].
D231. The UNSCEAR 1993 Report [U6] which dealt withlate deterministic effects in children contained very limited
evidence of cataractogenic sensitivity in young persons.
The only substantial study available was based on the survi‑
vors of the atomic bombings in Japan, which suggested thatthe risk of cataract formation was higher in persons younger
than 15 years of age at the time of the bombings, comparedto persons who were 15 or more years of age [C20]. The
newer ocular examination data on the survivors of theatomic bombings have confirmed that the radiation effectdiminishes among those exposed at older ages [N18].
D232. Both the study of children exposed to radioactive
deposition arising from the Chernobyl accident [D3] andthose given radium treatments for haemangiomas [H12]confirm that children are sensitive to cataract induction byionizing radiation, although it is not possible to determine a
specific age effect from these studies.
(f)Conclusions

D233. While posterior subcapsular cataracts are charac‑
teristic of radiation exposure, several sets of data suggest

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

that the broader category of posterior cortical cataracts may
also be regarded as radiation‑associated. PSC are notpathognomonic for radiation but can be caused by: drugs(steroids, allopurinol, dilantin, chlorpromazine and others);
systemic disorders (diabetes, hypocalcaemia, riboflavindeficiency); certain inflammatory or degenerative eye diseases; and eye trauma. The Chernobyl childhood exposure
study [D3], the childhood haemangiomas study [H6], theUACOS Chernobyl worker study [W7] and the study of thesurvivors of the atomic bombings [M4] have largely
addressed the issue of other causes of cataracts by statistically evaluating and adjusting for these other risk factors.
Continuing the above studies would be useful in order togenerate a clearer picture of the risk of radiation‑induced
cataracts at low doses.
D234. In summary, several new sets of data suggest thatcataract formation occurs after relatively low doses of ionizing radiation and that the dose–effect threshold is probably
under 1 Gy. Although most of these data relate to the lower
grade cataracts, a recent finding from the study of the Japan­
ese survivors of the atomic bombings suggests that higher
grade cataracts are also in excess following exposure to relatively low doses after a sufficient latent period [N17].
Whether or not some fraction of the radiation‑associatedgrade I opacities eventually progress to become more severe
vision‑disabling cataracts remains to be resolved.
D235. A critical analysis of all existing information on
the subject, especially in order to better understand the reasons for the differences between the new and older data, isnecessary. Follow‑up of the major cohorts is also needed inorder to better evaluate latency of cataract induction and its
subsequent progression, and to better characterize the risk
at low‑to‑moderate doses to the lens of the eye. A numberof study designs and methodological issues need to be considered for all the studies, such as developing accurate dosereconstructions, having an adequate control group, assessing subjects in a “blinded” and standardized manner toguard against bias, using a sufficiently sensitive observational method (e.g. slit‑lamp examination with adequate
pupil dilation), documenting the presence of other cataract
risk factors, and conducting analyses of the dose–response
relationship, cataract severity and cataract latency.
D.

Risk projection

D236. The possible health risk to large populations
exposed to radiation can be projected by means of radiation
risk models that are based partially on epidemiological dataand partially on biophysical modelling [U3, U7, U17]. The
practical aim of risk projection may be for the provision of
information for decision-making on specialized health careof relevant populations, for the provision of public information or both. It can also be used for the purposes of assessing the statistical power and hence the feasibility of a
proposed epidemiological project. It should be stressed thatradiation risk projections are not directly applied for the181

purposes of radiation protection, since decision-making forsuch purposes is usually based on practical dose criteria[B49, F11, I37].
D237. The major source of data for modelling stochastic
risks due to radiation exposure remains the “Life Span
Study” (LSS) of the survivors of the atomic bombings,
which has involved more than half a century of detailed
study of the long‑term health effects in a large population
exposed to a wide range of radiation doses [P3]. However,application of LSS results to those exposed as a consequenceof the Chernobyl accident requires a number of assumptions
relating to such matters as the magnitude of the dose anddose‑rate and the nature of the population. Such assumptions increase the uncertainty of any projections that are
made using the LSS results [J7]. Additional data from otherhuman and experimental radiobiological studies, for example, on the value of the dose and dose‑rate effectiveness­factor (DDREF) are therefore necessary.
D238. Projections of potential radiation risks have been
made by many research groups in the high dose range relevant to hypothetical nuclear war scenarios [I42], in the intermediate dose range relevant to nuclear and radiologicalaccidents and in the low dose range relevant to the routine
operation of nuclear facilities. Various risk models wereused for different types of radiation and dose ranges, taking
into account age at exposure, sex and other factors. A large
number of radiation risk projections have been conductedwith regard to the health consequences of the Chernobyl
accident [A11, C1, C11, I43, T4, W5].
D239. All of the risk projections were based on information
known at the time on the doses to the public; they usuallyassumed the linear non‑threshold (LNT) model for the
dependence of the probability of radiogenic cancers on dose,and used parameters from UNSCEAR and ICRP reports[I44, I45, U9] and from some national publications, for example, reference [N4]. As new epidemiological data became
available, the risk models and projections were updated.
D240. The first projections of the potential health consequences of the accident were prepared by a group of Soviet
specialists at the request of the authorities in the autumn of1986 and published in the collected proceedings of a symposium held in Moscow in June 1987 [I43], which were classified until 1989. The morbidity prognosis for the recovery
operation workers was not examined in these articles.
D241. One article was concerned with the possible healthconsequences for inhabitants of the areas in Belarus, theRussian Federation and Ukraine with the highest levels ofradioactive deposition [B47]. Among the 1.1 million inhabitants of these areas, it was predicted that the death rate due
to cancer in the 70 years following the accident, might
increase, on average, by 3.3%, and that there would beapproximately 7,500 cases of thyroid cancer, including
around 1,000 cases in children who were below the age ofseven at the time of the accident.

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D242. A second article examined separately the possible
health consequences for the Russian population [R4]. For
the 600,000 inhabitants of the most contaminated areas infour oblasts (Bryansk, Tula, Kaluga and Orel), the potential
increase in the death rate due to cancer was predicted to be
3.5%, while for the 60 million inhabitants of the European
part of the Russian Federation, it was predicted to be 0.2%.
In addition, 1,400 cases of thyroid cancer were predicted tooccur in the four oblasts, including more than 300 cases inchildren below the age of seven, and up to 9,000 cases (3,000of them in children) in the European part of the RussianFederation. Overall, these studies yielded four important
conclusions:– There would be no deterministic radiation effects in
the general population;– The potential increase in radiogenic cancers would
not be significant from the point of view of organizing health care, although those effects on some
population groups at specific periods of time could
be detected using epidemiological methods;– A considerable increase in the incidence of radiogenic thyroid cancer should be expected, particularly
among children;– Psychological trauma caused by the accident could
affect millions of people.
D243. In 1988, US scientists published the first assessmentof the global impact of the Chernobyl accident [A11]. Basedon monitoring data and on available environmental models,
they estimated the lifetime collective whole-body dose commitment to the population of the Northern Hemisphere to beabout 900,000 man Gy and its distribution among countriesof Europe (97%), Asia and North America. They projected
2–17 thousand possible cancer deaths due to radiation exposure from the accident—40% in the former Soviet Union
and 60% in the rest of Europe. However, the corresponding
average increase in the population cancer mortality would
be negligible, i.e. 0.02% in the former Soviet Union and
0.01% in Europe. The authors also noted the huge economic
and social effect of the accident.
D244. Ten years after the accident, an international groupof specialists, who had participated actively in the post‑­
accident epidemiological studies, gave a more detailed projection of the potential consequences in terms of cancer
incidence, based on more accurate estimates of the effective
doses, the relevant radiation risk factors and the LNT model(table D24) [C1]. Populations were divided into the 600,000
more exposed groups of people—the recovery operation
workers who worked in 1986–1987, the evacuees and theresidents of the strict control zone1—and around 7 million
residents of other contaminated territories with radioactive
deposition.

1
The strict control zones are the areas which had levels of 137Cs deposition
density above 555 kBq/km 2 in 1986.

D245. According to the 1996 assessment, approximately
4,000 additional premature deaths from cancer (solid cancer
and leukaemia) due to the increased radiation exposure were
estimated to occur over the lifetime of the more exposedgroups of people (600,000) and a further 5,000 cases among
the other 7 million residents. The predicted average increasein the frequency of radiation‑induced solid cancers over a
lifetime was 3.3% among the more exposed population and
0.6% among the other residents. The predicted averageincreases in the frequency of radiation‑induced leukaemia
were 12% and 1.5%, respectively.
D246. There is reasonable agreement between the projections of 1986, 1988 and 1996. From table D24, it is also evident that for large cohorts, any increase in cancer incidence
due to radiation exposure would be scarcely noticeable.
However, an increase in cancer incidence should be detectable using scientific methods in particular population groups
at specific periods of time after the Chernobyl accident. In
particular, an increased frequency of leukaemia among therecovery operation workers ought to have been detected during the first decade. However, no increase in cancer incidence was apparent in 1996 in the more exposed populationgroups [C1].
D247. Thyroid cancer resulting from internal exposure toradioiodine was not examined in reference [C1] or in reference [A11]. The reason for this was because the increased
incidence of thyroid cancer among children and adolescents
who were living in the spring of 1986 in the more contaminated areas was already widely recognized [K32, L9] andefforts were focused on analysing the surveillance data.
D248. The issues arising from a comparison of the projections of the possible increased incidence of cancer due
to the accident and data from 20 years of surveillance ofthe various population groups were examined by the Chernobyl Forum in 2003–2005 [C22, W5]. Based on the available epidemiological data, the Forum did not consider it
necessary to change the projections of Cardis et al. [C1],despite there being some differences in the demographicand dosimetric data.
D249. In 2006, a UK committee published an independent assessment of the environmental and potential healthconsequences of the Chernobyl accident for the European
population [F10]. In essence, they considered many published assessments of the collective dose and the predicted
health effects and apparently selected the maximum values.
They selected 30–60 thousand as the most credible range forthe number of additional deaths due to radiation exposureand estimated that most of these would occur in Europe
beyond Belarus, the Russian Federation and Ukraine. In
undertaking this assessment, the UK Committee erroneously estimated that “more than half of Chernobyl’s fallout
was deposited outside these countries” (i.e. outside Belarus,
the Russian Federation and Ukraine). In fact, only 23% of
the radiocaesium from Chernobyl was deposited in the restof Europe [E5].

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

D250. In 2006, Cardis et al. made another attempt toproject the possible incremental increase in cancer incidence in European populations due to the additional radiation exposure arising from the Chernobyl accident. They
used updated estimates of the collective dose andstate‑of‑the‑art risk models developed recently by the
BEIR (Biological Effects of Ionizing Radiation) VII Committee [C11, C23]. The risk projections suggested that bythen the Chernobyl accident may have caused about anadditional 1,000 cases of thyroid cancer and an additional
4,000 cases of other cancers in Europe, representing about
0.01% of all cancers since the accident. The models predicted that by 2065, about 16,000 (95% CI: 3,400, 72,000)
cases of thyroid cancer and 25,000 (95% CI: 11,000,
59,000) cases of other cancers could occur owing to radiation exposure resulting from the accident, whereas several
hundred million cancer cases would be expected fromother causes. It is very unlikely that this additional cancer
burden due to the largest nuclear accident to date could be
detected by monitoring national cancer statistics.
D251. In order to adequately interpret and communicate
radiation risk projections, it is necessary to understand theirscientific limitations. At today’s level of knowledge, there
are reliable epidemiological data on risks of cancer morbidity and mortality due to radiation exposure of cohorts ofindividuals with an acute average dose of the order of
100 mSv and above. So far, neither the most informative
LSS study nor any other studies have provided conclusive
evidence of carcinogenic effects of radiation at smaller
doses. This is the position formulated by UNSCEAR inannex G, “Biological effects of low radiation doses”, of the
UNSCEAR 2000 Report [U3], which states “There is substantial and convincing scientific evidence for health risks athigh dose. Current summarized data, which represent international consensus, show that radiation-induced cancer
cases (excess above background cases) could be observed inhumans at effective doses in excess of 0.1 Sv delivered athigh dose rates”.
D252. Since predictions of possible health consequences
are not directly intended for substantiating necessary
radiation protection measures, they do not have to be
based on a cautious approach (such as the LNT model)
but rather they should be based on firmly established scientific facts. In the dose range below 0.1 Sv, because of
the absence of persuasive evidence related in part to thesubstantial statistical uncertainties, the dependence of thefrequency of adverse radiation effects on dose can beassessed only by means of biophysical models among
which the models based on the LNT approach are themost popular [B48, U3]. However, there are also others,
including superlinear and threshold ones, and even ­models
that account for a possible beneficial e­f fect of radiation,

183

termed hormesis. For these reasons, the Committee will
not use these models to project absolute numbers of possible health effects in populations exposed to low doses ofradiation, because of unacceptable levels of uncertainty
in the predictions.
D253. Two important features of radiation‑induced cancer projection should be noted. First, there are as yet no
known markers that are specific to radiogenic cancer. Thismeans that it is impossible to determine whether a particular cancer is due to the effects of radiation exposure or toother causes or, more specifically, whether it is due to radiation resulting from an accident or from natural sources. It
is possible only to estimate the risk to an individual basedon the dose to that individual. This is fundamentally different from the situation with the ARS victims in 1986, when
all of them were known by name and ARS was diagnosed
based on conclusive medical findings. Secondly, it isimportant to understand the considerable statistical uncertainty of any projection based on the LNT model. Thismodel only really lends itself to estimations that are within
an order of magnitude.
D254. For cohorts of the residents of the areas of Belarus,
the Russian Federation, Ukraine and other countries in
Europe [A11, C1, C11, R4, T4] with average effective dosesof below 30 mSv over 20 years, there are today no conclusive
data for predicting radiogenic morbidity and mortality withany reasonable certainty. At the same time, it cannot be
ruled out that adequate data on the health effects of low‑dosehuman exposure will be developed as further progress ismade in understanding the radiobiology of man and othermammals. This may provide in the future the scientific basis
for evaluating the health consequences of the Chernobyl
accident among residents of areas with low radiation levels.
D255. In view of the above, any projection of potential
health effects caused by low radiation doses to large population groups should be accompanied by a detailed explanation of the associated conceptual caveats and projection
uncertainties. In order to put such projections in an appropriate context, they should preferably be presented as relative increments over the underlying incidence or mortality
rates, with associated statements regarding their uncertainty. This will allow comparison of the health risk ofionizing radiation with other health risks and with theunderlying incidence or mortality rate.
D256. During the last decade, the Committee has avoided
making projections of the health effects that might be caused
by low‑level exposure of large population groups, mainly
because of the substantial uncertainties associated with any
such projection and potentially serious misinterpretation incommunication with the public.

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UNSCEAR 2008 REPORT: VOLUME II

IV. General conclusions
D257. The long‑term nature and severity of the radiation‑­
induced skin injuries to those persons who survived ARS in1986 was naturally related to the severity of injuries during
the acute period. In the long term, telangiectasia, repeatedulcers and fibrosis were observed in patients with higher
doses, and there were moderate atrophic changes and hyper­
keratosis in other patients. The prevalence of radiation‑induced
cataracts in the long term increased with the ARS grade andthe level of dose received. Most of the ­radiation‑induced cataracts developed during the first five years after exposure. The
latent period for cataract development was lower in persons
with high doses.
D258. A significant frequency of neurosomatic diseases in
the ARS survivors, who have been subjected to ongoingdetailed medical surveillance, was revealed during the first
five years after the accident, including those of the otolaryngological organs, the nervous system and the gastrointestinal tract. An increase in the frequency of cardiovasculardisease was detected later and it correlated with the ageingof patients. Out of 13 cases of solid cancer, four cases were
found among the ARS survivors and nine cases among persons with unconfirmed ARS. The mean latent period for thesolid cancers diagnosed by 2006 was 14 years.
D259. Over the 20 years since the accident (1987–2006),
19 out of 106 ARS survivors and 14 out of 99 persons
with unconfirmed ARS diagnosis have died for various
reasons. There is a tendency for increased mortality rates
due to somatic disease with the grade of ARS although
there has been no formal epidemiological analysis ofmortality rates among the ARS survivors. Among thecauses of death of those who survived ARS, there werefour cases of onco-haematological disease.
D260. The Chernobyl registries have the potential to
become important sources of information on the long‑term
health effects of radiation exposure. Standardization of theprocedures across the three registries would greatly improvetheir usefulness for epidemiological research.
D261. The possible long‑term health effects resulting fromradiation exposure due to the Chernobyl accident remain anissue. This annex focuses on studies of the incidence of thyroid cancer, leukaemia, all solid cancers as a whole, cardiovascular morbidity and mortality, cataract development andautoimmune thyroiditis. This selection was based on thepotential sensitivity of these outcomes to radiation, andbecause the Committee considered that there were insufficient new data in other areas that would justify modifying
the conclusions of the UNSCEAR 2000 Report.
D262. Two types of studies are considered when evaluating the cancer risk to populations exposed during theChernobyl accident: geographical correlation studies
relating aggregated rates of disease with average

exposures; and analytical studies (case‑control or cohort)
where individual information is used. The latter are considered to be more reliable and valid for examining thedose–response relationship.
D263. Bias due both to screening and to diagnostic suspicion may operate in studies of the emergency and recovery
operation workers, who are examined every year for various
diseases and for whom there is consequently a greater likelihood of detection of small tumours. Trends in disease rates
in groups of emergency and recovery operation workers are
only scientifically informative if the same methods of detection in diagnosis are applied over the whole period of interest and are independent of the individual exposure level.
Overall, interpretation of the results from studies on the
populations exposed as a consequence of the Chernobyl
accident have to take into account the variation of detection
methods with time, and the likelihood of different screening
frequencies for different populations.
D264. The substantial increase in thyroid cancer incidence seen amongst those exposed as children or adolescents in Belarus, the Russian Federation and Ukraine since
the Chernobyl accident shows no signs of diminishing up to
20 years after exposure. Amongst those under age 14 years
in 1986, 5,127 cases (for those under age 18 years in 1986,
6,848 cases) of thyroid cancer have been reported between
1991 and 2005 for the whole of Belarus and Ukraine andthe four more affected regions of the Russian Federation[I8]. Continuing the systematic follow‑up of these populations should help to ensure early detection and medical
treatment of any benign or malignant tumour.
D265. There is no doubt that a substantial contributor to theexcess incidence of thyroid cancer has been exposure to radioiodine released during the Chernobyl accident. From the geographical correlation studies, it would appear that the excess
absolute risk (EAR) due to exposure to radioiodine is somewhat
smaller than the corresponding risk due to external exposure.
However, this difference can be explained by the shorter timeafter exposure in the Chernobyl studies than those of studies ofthyroid cancer after exposure to external radiation.
D266. Evidence has also emerged that iodine deficiency
may well increase the risk of thyroid cancer resulting fromexposure to radioiodine released during the accident. Twostudies suggest that iodine deficiency sometime between
exposure and diagnosis may double the corresponding radiation risk. If confirmed by future studies, this will be important in terms of extrapolating the results from the studies of
the Chernobyl accident to other scenarios in which iodine
deficiency may play a role.
D267. The most significant radionuclide among the mixture of radioactive isotopes of iodine irradiating the thyroid
gland was 131I. The possibility has been suggested that

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

185

shorter‑lived isotopes of iodine are more effective in causing thyroid cancer than 131I. The contributions of otherradio­active isotopes of iodine than 131I to the thyroid dosewere relatively small and therefore their influence cannot be
evaluated in epidemiological studies of groups exposed toradiation from the accident.

and no difference in rates with time for areas with different
levels of radioactive disposition. With regard to solid cancer
incidence among the recovery operation workers, somegroups show elevations in SIRs; however, quantitative risk
estimates of cancer incidence per unit of dose have not yet
been reported.

D268. The evidence from studies of thyroid cancer among
adult residents of Belarus, the Russian Federation andUkraine and among the recovery operation workers is somewhat mixed, with some groups showing elevated SIRs andothers showing substantially smaller effects. Lack of persuasive evidence of any association with the estimated thyroid
doses strongly suggests that increased screening of the
exposed groups compared to the general population would
account for a large part of the observed excess.

D274. Assessments, based on the follow‑up to date andusing the findings from the study of the survivors of theatomic bombings and other studies, would suggest that thedoses received by the general population after the accident
were too low to yield sufficient statistical power for studies
to be able to detect any increase in the risk of all solid cancers combined, had there been an increase. Although thenumbers of cancers projected to be induced by radiation
exposure from the accident are very small relative to thebaseline cancer risk, they could potentially be substantial inabsolute terms. Certainly, the empirical studies to date do
not suggest that the risks are substantially greater than would
be predicted by the existing risk projection models.

D269. The UNSCEAR 2000 Report [U3] suggested, basedon the evidence then available, that there may be a link
between the morphological subtypes (i.e. solid/follicularvariant) of papillary cancer observed in children and exposure to radiation. More recent evidence raises questions
regarding this postulated causal relationship between solid/
follicular morphology of papillary cancer and radiation
exposure.
D270. The evidence so far suggests that the molecularbiology of post‑accident childhood thyroid cancer is similar
to that seen in age‑matched series from non‑irradiated populations. There are a number of large studies of the mole­cular biology of post‑accident thyroid cancer currently
underway using pathologically verified material suppliedby the Chernobyl Tissue Bank.
D271. Among those exposed in utero and as children, no
persuasive evidence has accrued to suggest that there is ameasurable increase in the risk of leukaemia due to radiation
exposure. This is not unreasonable since the doses involved
were generally very small, and therefore it is expected thatepidemiological studies would lack sufficient statisticalpower to observe any effect had there been one.
D272. Among the recovery operation workers, there issome evidence of a detectable increase in the risk of leukaemia, primarily based upon results from the Russian Federation. As yet, it would be premature to compare any risk
estimates based on this evidence directly with the estimatesobtained from studies of populations exposed at high doses
and dose-rates, such as the survivors of the atomic bombingsin Japan; the limitations of studies of the recovery operation
workers must be borne in mind. Future evidence from suchstudies will, hopefully, provide meaningful data.
D273. At present, there is no persuasive evidence of any
measurable increase in the risk of all solid cancers combined or breast cancer for the general populations of thethree most affected republics. There appears to be no pattern of increased risk in those areas with high levels ofradio­active deposition compared to those with low levels,

D275. There have been few studies of significant size andquality that have addressed the relationship between autoimmune thyroiditis and exposure to radiation following theChernobyl accident. The clinical significance of elevatedthyroid autoantibodies in the absence of any signs of destruction of thyroid cells by an autoimmune response remains
unclear. The evidence to date does not suggest an association between radiation exposure and clinically significant
autoimmune thyroiditis.
D276. Little solid evidence exists of any demonstrable
effect of radiation exposure due to the Chernobyl accident
on the incidence of cardiovascular and cerebrovascular disease and mortality rates. One study of the recovery operation workers in the Russian Federation has provided
indications of a statistically significant association between
radiation dose and both cardiovascular disease mortality
rates and the incidence of cerebrovascular disease. Although
the results of this study are statistically compatible withthose of the study of the survivors of the atomic bombings,
the increase in circulatory disease is not consistent withmost other studies involving doses below about 4 Gy. Furthermore, the increase seen among the recovery operation
workers is inconsistent with the expected latency interval
seen in other investigations. It will be necessary to havemore persuasive evidence to conclude whether or not radiation exposure due to the Chernobyl accident has increased
the risk of cardiovascular and cerebrovascular disease andassociated mortality.
D277. Cataracts developed among the ARS survivors
who were exposed to high radiation doses. However, several new sets of data suggest that cataract formation also
occurs after relatively low doses of ionizing radiation andthat the dose–effect threshold may be under 1 Gy. Althoughmost of these data are related to lower grade cataracts/lens
opacities, a recent finding from the study of the survivorsof the atomic bombings suggests that the incidence of186

UNSCEAR 2008 REPORT: VOLUME IIhigher grade cataracts is also in excess at relatively low
doses after a sufficient latent period. Whether some fraction of the radiation‑associated grade I opacities eventuallyprogress to become more severe, vision‑disabling cataracts
is still an unresolved issue.
D278. Even if an empirical epidemiological study provides
evidence of an increased incidence of a potentially radiogenic disease, it is still necessary to consider the issue of theattributability (i.e. the likely causal nature of the reported
association) of that effect to radiation exposure. It is necessary to take detailed account of possible confounding andbias factors, such as industrial pollution, environmental features (e.g. stable iodine levels in soil), lifestyle (e.g. smoking
habits or alcohol consumption), reproductive history,
improvement of diagnostic tools, and increased medical
attention of the affected populations (e.g. screening).
D279. Projections of the health risk for large populations
exposed to radiation are often made using radiation risk
models based on epidemiological studies obtained fromother exposure situations and on biophysical modelling.
The practical aims of such risk projection may be to provide information for decisions on health care for the population or for public information. Several projections of thehealth consequences of the Chernobyl accident based on
the linear non‑threshold model have been conducted byvarious groups. However, there is a limit to the use of thedata derived from epidemiological studies. Below doses ofabout 0.1 Sv, the experimental evidence for radiation‑­
induced health effects is ambiguous and risk coefficients
become more uncertain. Therefore, any radiation risk
­projections in the low‑dose area should be considered as
extremely uncertain, especially when the computation ofcancer deaths is based on collective effective doses involving very small additional exposures to very large populations over many years. It is inappropriate to use ­collective
effective dose for risk projections because the ­biologicaland statistical uncertainties are too great.
D280. Based on 20 years of study, the conclusions of the
UNSCEAR 2000 Report can now be confirmed. Essentially,
persons who were exposed as children to radioiodine from the
Chernobyl accident and the emergency and recovery operation workers who received high doses of radiation are at anincreased risk of radiation‑induced health effects. The vast
majority of the population were exposed to low levels of radiation comparable, at most, to or a few times the annual natural
background radiation levels and need not live in fear of ­serious
health consequences. This is true for the populations of thethree countries most affected by the Chernobyl accident,
Belarus, the Russian Federation and Ukraine, and even more
so for the populations of other European countries. Lives havebeen disrupted by the Chernobyl accident, but from the radiological point of view, generally positive prospects for the
future health of most individuals should prevail.

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT187

Table D1. Number of patients followed up at the hospital of the Burnasyan Federal Medical Biophysical Centre (FMBC),
Russian Federation according to severity grade of ARS and radiation injury [G9]ARS grade

Acute phase

1986–1990

1991–1995

1996–2000

2001–2006

I

23

26

8

1

2

II

43

42

16

5

4

III

14

14

5

3

3

IV

1

1

1

1

1

I-IV

81

83

30

10

10

35.0±2.5(range 17–72)

35.2

39.6±3.6

44.0±5.0

48.7±4.9

Local injury

54

40

18

5

5

Died

27

Mean age (years)

Table D2.

1

Number of patients followed up at the clinic of URCRM, Ukraine according to severity grade of ARS [G9]ARS grade

1986–1990

1991–1995

1996–2000

2001–2005

I

30

30

26

26

II

31

30

28

25

III

11

11

8

8

Died ARS

2

8

3

5

Unconfirmed ARSa

96

93

90

90

Died (unconfirmed ARS)

3

3

—

1

a These are people who were initially suspected of having ARS, but were later confirmed not to have the syndrome. They are known variously as “unconfirmed ARS” patients,
or “ARS grade 0”.

Table D3. Number of ARS survivors with blood values deviating from normal during the 20 years after the accident (FMBC,
Russian Federation) [G9]Blood values

Number of patientsa

Erythrocytes (×1012/L)
<4.0
>5.0

10 (8.7%)
11 (8.9%)

Haemoglobin (g/L)
<130
>160

10 (8.7%)
19 (16.6%)

Leukocytes (×109/L)
<4.0
>9.0

14 (12.2%)
10 (8.7%)

Neutrophils (×109/L)
<2.0
>5.5

15 (13.1%)
8 (7.0%)

188

UNSCEAR 2008 REPORT: VOLUME II

Blood values

Number of patientsa

Lymphocytes (×109/L)
<1.2
>3.0

12 (10.5%)
6 (5.2%)

Thrombocytes (×109/L)
<180
>320

26 (22.7%)
4 (3.5%)a	Percentages are expressed with respect to the total number under observation.

Table D4.

Estimated beta and gamma doses to various portions of the eyes of ARS survivors [G9]Gamma dose
(Gy)

Beta dose to the front surface of the eye(Gy)

Beta dose to the retina and posterior surface of the eye
(Gy)

1

3.0

0.8

2

6.0

1.5

3

9.0

2.3

4

12.0

3.0

5

15.0

3.8

6

18.0

4.5

7

21.0

5.3

8

24.0

6.0

9

27.0

7.0

10

30.0

7.5

Table D5.

Solid cancer morbidity among the 72 ARS survivors and 96 persons with unconfirmed ARS [B44]
Number

ARS grade

Diagnosis

First diagnosed

Outcome10

Sarcoma of hip soft tissues

1992

Died in 1993

20

Leiomyosarcoma of shin

1998

Operated in 1998

Cancer of colon

1999

Operated in 1999

30Cancer of colon

2001

Died in 2005

40

Cancer of kidney

2000

Operated in 2001

50Cancer of stomach

2004

Died in 2004

60Cancer of stomach

2004

Died in 2005

7

0Cancer of lung2001

Operated in 2003

80Cancer of prostate

2001

Died in 2003

90Cancer of throat

2000

Died in 2001

10

1

Cancer of colon

1997

Operated in 1997

11

2

Cancer of thyroid gland

2000

Operated in 2000

12

2

Cancer of thyroid gland

2000

Operated in 2001

13

2

Neurinoma of lower jaw

2003

Died in 2004

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

Table D6.

189

Number of patients followed up at the hospital of FMBC over time with diseases of four systems of the body [G9]Time periods

Diseases

1986–1990

1991–1995

1996–2000

2001–2006

Number of persons%

Number of persons%

Number of persons%

Number of persons%

Gastrointestinal

60

72.3

23

76.7

8

80.0

9

90.0

Cardiovascular

44

53.0

22

73.3

9

90.0

10

100.0

Endocrine

16

19.2

3

10.0

4

40.0

7

70.0

Respiratory

11

13.3

7

23.3

2

20.0

3

30.0

Table D7.

Causes of death among Chernobyl ARS survivors in the later period [B10, B39, B41, B42, B44, G9, U3]

NumberName

ARS gradeYear of deathAge (years)

Cause of death

1

P.V.A.

I

1993

41

Sudden cardiac death2

V.O.E.

I

1995

51

Lung TB

3

K.A.P.

I

1995

53

Post-traumatic fatty embolism

4

S.M.A.

I

1995

26

Sudden cardiac death

5

S.V.G.

I

2002

51

Myelodysplastic syndrome

6

R.G.I.

I

2002

51

Trauma7

V.M.P.

II

1987

81

Lung gangrene

8

K.Ya.F.

II

1990

68

Sudden cardiac death

9

B.V.I.

II

1995

46

Liver cirrhosis

10

G.M.Yu.

II

1998

45

Liver cirrhosis

11

Sh.V.K.

II

1998

61

Acute myelomonoblastic leukaemia

12

B.V.M.

II

1998

80

Sudden cardiac death

13

M.A.S.a

II

1999

61

Stroke14

T.L.P.

II

2004

53

Lower jaw neurinoma

15

V.M.P.

III

1992

67

Sudden cardiac death

16

B.G.V.

III

1993

52

Myelodysplastic syndrome

17

D.A.S.

III

1995

64

Myelodysplastic syndrome

18

B.I.Z.

III

2001

87

Sudden cardiac death

19

P.A.N.

III

2004

41

Lung TBa	Patient lived in Russia; other 18 patients lived in the Ukraine.

Table D8.

20 years mortality due to somatic diseases among patients surviving different grades of ARS in 1986 [B39, G9]

ARS grade

Number of survivors followed-up

Number of deaths from somatic diseasesa
in 1987–2006

Mortality from somatic diseasesa in 1987–2006(rel. units)

0

99

12

0.12

I

41

5

0.12

II

49

8

0.16

III

15

5

0.33

a Deaths caused by trauma and accidents have been excluded.

190

UNSCEAR 2008 REPORT: VOLUME IITable D9.

Number of people in the Chernobyl registries
Registration category

Group 1: Emergency and recovery operation workers

Belarus(2005)

Russian Federation(2006)

Ukraine(2006)

72 362a186 395

229 884
49 8875 951

9 944bGroup 3: Residents of the contaminated regions

1 513 826

367 850

1 554 269

Group 4: Children born to parents of above three groups

17 914c35 552d428 045

Total

1 610 053

599 741

2 262 085

Group 2: Evacuees from the exclusion zonea As of 2005 in contrast to table B1 where the data for Belarus are presented as of 1996.
b For Russia, the number of both evacuees from 1986 and some migrants from later years is presented.
c Children born to parents included in groups 1–3.
d Children born to recovery operation workers only.

Table D10. Summary of screening activities in the three countries
Belarus
Registration category

Frequency

Russian Federation
Completeness(%)

UkraineFrequency

Completeness(%)

Frequency

Group 1
– Emergency and recovery operation
workers, 1986–1987

Annually

Annually

75

Annually– Recovery operation workers after 1987

Annually

BienniallyaAnnually

Group 2

Annually

Annually

47

Annually

Group 3

Annually

Annually/bienniallyb

47

Annually

Group 4

Annually

Annually

81

Annuallya No data available.
b Depending on age and radionuclide levels in the environment.

97–99

Completeness
(%)

83–85

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

Table D11.

191

Thyroid cancer incidence rates in those exposed under the age of 18 years

Age at exposure(years)Sex

Parameter

Calendar year periods
1982–1985

1986–1990

1991–1995

1996–2000

2001–2005

11

155

258

209

0.57

8.02

13.35

10.82

Belarus [I8, K22]
F
0–4
M
F
5–9
M
F
10–14
M

F
15–18
M

F
Total (0–18)
M

Number of cases
Crude rate per 10 PY
5Number of cases

9

103

146

79

Crude rate per 105 PY

0.45

5.21

7.38

3.99

Number of cases

9

108

91

169

Crude rate per 105 PY

0.50

6.02

5.07

9.42

Number of cases

10

66

42

59

Crude rate per 105 PY

0.54

3.59

2.29

3.21

Number of cases

8

67

131

202

Crude rate per 105 PY

0.46

3.85

7.52

11.60

Number of cases

7

12

43

60

Crude rate per 105 PY

0.39

0.67

2.39

3.34

Number of cases

15

57

109

223

Crude rate per 105 PY

1.11

4.21

8.05

16.46

Number of cases

5

9

33

40

Crude rate per 105 PY

0.37

0.66

2.41

2.93

Number of cases

2

43

387

589

803

Crude rate per 105 PY

0.04

0.64

5.72

8.71

11.88

Number of cases

1

31

190

264

238

Crude rate per 105 PY

0.02

0.45

2.75

3.82

3.44

Russian Federation (Bryansk, Kaluga, Orel and Tula oblasts) [I8]
F
0–4
M

F
5–9
M

F
10–14
M

F
15–18
M

F
Total (0–18)
M

Number of cases
Crude rate per 10 PY
5

0

1

13

36

46

0.0

0.12

1.47

3.91

5.18

Number of cases

0

0

12

26

24

Crude rate per 105 PY

0.0

0.0

1.32

2.75

2.7

Number of cases

1

2

20

37

52

Crude rate per 105 PY

0.15

0.24

2.35

4.28

6.44

Number of cases

0

1

6

10

14

Crude rate per 10 PY

0.0

0.12

0.69

1.13

1.67

Number of cases

0

3

24

48

108

0.0

0.36

3.02

5.95

13.9

5

Crude rate per 10 PY
5Number of cases

0

1

9

9

10

Crude rate per 105 PY

0.0

0.12

1.07

1.05

1.23

Number of cases

1

8

43

61

87

Crude rate per 10 PY

0.18

1.24

7.21

9.97

13.87

Number of cases

0

1

8

14

17

Crude rate per 10 PY

0.0

0.15

1.26

2.14

2.64

Number of cases

2

14

100

182

293

Crude rate per 10 PY

0.09

0.44

3.2

5.68

9.46

Number of cases

0

3

35

59

65

0.0

0.09

1.07

1.77

2.04

5

5

5

Crude rate per 10 PY
5192

UNSCEAR 2008 REPORT: VOLUME II

Age at exposure(years)Sex

Parameter

Calendar year periods
1982–1985

1986–1990

1991–1995

1996–2000

2001–2005

Ukraine [L4, T2]
F
0–4
M

F
5–9
M

F
10–14
M

F
15–18
M

F
Total (0–18)
M

Number of cases

6

85

202

254

Crude rate per 105 PY

0.1

0.9

2.2

2.9

Number of cases

9

55

91

103

Crude rate per 105 PY

0.1

0.6

0.9

1.1

Number of cases

1

20

106

181

326

Crude rate per 105 PY

0.01

0.2

1.2

2.0

3.9

Number of cases

7

40

57

74

Crude rate per 105 PY

0.1

0.4

0.6

0.8

Number of cases

9

35

113

252

496

Crude rate per 105 PY

0.1

0.4

1.2

2.8

5.7

Number of cases

7

18

34

55

99

Crude rate per 105 PY

0.1

0.2

0.4

0.6

1.1

Number of cases

15

54

176

277

403

Crude rate per 105 PY

0.3

0.8

2.6

4.0

5.4

Number of cases

7

15

37

53

74

Crude rate per 105 PY

0.1

0.2

0.5

0.7

1.0

Number of cases

25

115

480

912

1 479

Crude rate per 105 PY

0.1

0.3

1.4

2.7

4.4

Number of cases

14

49

166

256

350

0.05

0.1

0.5

0.7

1.0

Crude rate per 10 PY
5Table D12. Thyroid cancer incidence rates in different age groups (age at diagnosis) of the Belarusian population between
1982 and 2005 [I8, K22]
Age at diagnosis(years)Sex

Parameter

Calendar year periods
1982–1985

F
0–9
M

F
10–19
M

F
20–29
M

F
Total
(0–29)
M

1986–1990

1991–1995

1996–2000

2001–2005

Number of cases

0

17

126

10

6

Crude rate per 106 PY

0.00

4.36

33.27

3.43

2.59

Number of cases

0

16

74

8

5

Crude rate per 106 PY

0.00

3.94

18.70

2.61

2.12

Number of cases

1

25

191

333

205

Crude rate per 106 PY

0.70

6.99

51.11

83.86

54.33

Number of cases

0

14

106

177

90

Crude rate per 106 PY

0.00

3.84

27.76

43.27

23.25

Number of cases

1

3

81

231

357

Crude rate per 106 PY

0.58

0.75

22.50

65.39

97.00

Number of cases

0

2

12

79

111

Crude rate per 106 PY

0.00

0.50

3.37

22.31

29.79

Number of cases

2

45

398

574

568

Crude rate per 106 PY

0.43

3.92

35.78

55.08

58.14

Number of cases

0

32

192

264

206

Crude rate per 106 PY

0.00

2.73

16.93

24.68

20.70

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

193

Table D13. Thyroid cancer incidence rates in different age groups (age at diagnosis) of the Russian population (Bryansk,
Kaluga, Orel and Tula oblasts) between 1982 and 2005 [I8]Age at diagnosis(years)

Sex

F
0–9
M

F
10–19
M

F
20–29
M

F
Total
(0–29)
M

Parameter

Calendar year periods
1982–1985

1986–1990

1991–1995

1996–2000

2001–2005

1

1

7

0

0

Crude rate per 10 PY

0.7

0.6

4.4

0.0

0.0

Number of cases

0

0

1

2

1

Crude rate per 10 PY

0.0

0.0

0.6

1.5

0.9

Number of cases

1

11

39

61

51

Crude rate per 10 PY

0.7

6.6

23.0

33.3

28.3

Number of cases

1

3

21

32

20

Crude rate per 10 PY

0.7

1.7

12.0

17.1

11.0

Number of cases

28

48

97

101

135

Crude rate per 10 PY

18.4

27.6

62.4

63.4

83.7

Number of cases

2

11

20

23

28

Crude rate per 10 PY

1.3

6.1

12.2

13.6

16.7

Number of cases

30

60

143

162

186

Crude rate per 10 PY

7.0

11.8

29.4

34.6

42.2

Number of cases

3

14

42

57

49

0.7

2.6

8.3

11.6

10.7

Number of cases
6

6

6

6

6

6

6

Crude rate per 10 PY
6Table D14. Thyroid cancer incidence rates in different age groups (age at diagnosis) of the Ukrainian population between
1982 and 2005 [L4, T2]
Age at diagnosis(years)Sex

Parameter

Calendar year periods
1982–1985

F
0–9
M

F
10–18
M

F
19–30
M

F
Total
(0–30)
M

1986–1990

1991–1995

1996–2000

2001-2005

Number of cases

3

14

38

7

7

Crude rate per 106 PY

0.2

0.8

2.2

0.5

0.8

Number of cases——

Crude rate per 106 PY

12

32

4

0.6

1.8

0.3

Number of cases

32

69

191

251

200

Crude rate per 106 PY

2.6

4.3

11.7

15.0

13.3

Number of cases

19

30

76

118

83

Crude rate per 106 PY

1.5

1.8

4.5

6.8

5.4

Number of cases—

Crude rate per 106 PY
Number of cases

—

33

252

627

863

1.7

12.6

30.0

41.0

7

58

136

193

0.4

2.8

6.3

9.0

35

116

481

885

1 070

Crude rate per 10 PY

0.8

2.2

9.0

17.4

22.1

Number of cases

19

49

166

258

276

0.4

0.9

3.0

4.9

5.5

Crude rate per 106 PY
Number of cases
6

Crude rate per 10 PY
6194

UNSCEAR 2008 REPORT: VOLUME IITable D15. Risk estimates for thyroid cancer resulting from exposure to 1 Gy using different models [C8]People exposed as children/adolescents in Belarus and the Russian Federation
Model

OR at 1 Gy (95% CI)

Logistic regression—excess relative risk modelLinear-quadratic model over the entire dose range
Linear model up to 2 Gy
Linear model up to 1.5 Gy
Linear model up to 1 Gy

4.9 (2.2, 7.5)
5.5 (2.2, 8.8)
5.8 (2.1, 9.4)
6.6 (2.0, 11.1)

Logistic regression—log-linear risk modelLinear-quadratic model up to 2 Gy
Linear quadratic model up to 1.5 Gy
Linear model up to 1 Gy

5.5 (3.1, 9.5)
5.9 (3.3, 10.5)
8.4 (4.1, 17.3)

OR = odds ratio at 1 Gy compared with no exposure.
CI = confidence interval.

Table D16. Summary of ERR and EAR estimates for thyroid cancer among those exposed as children or adolescents
Reference

ERR (95% CI)(Gy-1)EAR (95% CI)(104 PY Gy)-1

Geographical correlation studies
Jacob et al. [J1, J2, J4]

18.9 (11.1, 26.7)

2.66 (2.19, 3.13)

Kenigsberg et al. [K10, K22]

37.7 (35.1, 40.2)

1.93 (1.79, 2.06)   Girls

10.0 (4.2, 21.6) external control

1.8 (1.0, 2.9)   Boys

67.8 (17.1, 5 448) external control

2.0 (1.1, 3.0)

Ivanov et al. [I22]

Shakhtarin et al. [S6]4.4 (2.8, 6.6)

Likhtarov et al. [L5]8 (4.6, 15)

1.55 (1.2, 1.9)

Analytical studies
Astakhova et al. [A1]
Cardis et al. [C8]6.04 (2.5, 17.7)
4.5 (2.1, 8.5) to 7.4 (3.1, 16.3)

Tronko et al. [T3]

5.25 (1.70, 27.5)

Kopecky et al. [K17]48.7 (4.8, 1 151)

Davis et al. [D1]1.65 (0.10, 3.20)

Table D17. Thyroid cancer incidence among those exposed as adults
Standardized incidence ratios for exposed population, by country and calendar year period
Country/exposed group
Russian Federation, residents of Bryansk oblast [I3]

Calendar year periods
1986–1990

1991–1998

Males (95% CI)

1.27 (0.92, 1.73)

1.45 (1.20, 1.73)

Females (95% CI)

1.94 (1.70, 2.20)

1.96 (1.82, 2.10)

Ukraine [S18]1990–2004

Evacuees from 30-km zone

5.12 (n = 174) (4.36, 5.88)

Adult residents of contaminated areas

1.63 (n = 247) (1.43, 1.83)

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

195

Table D18. Thyroid cancer incidence among emergency and recovery operation workers
Standardized incidence ratios, by country and calendar year period
Emergency and recovery operation workers

Calendar year periods
Period working in 30-km zone

Russian Federation [I9]April–July 1986

Aug–Dec 1986

April–Dec 1986

1987

1988–1990

1986–1990

3.61 (n = 2)
(0.41, 13.04)

2.23 (n = 9)
(1.02, 4.22)

4.08 (n = 7)
(1.63, 8.40)

5.24 (n = 49)(3.88, 6.93)

1986–1991 (latent)   SIR   (95% CI)

4.20 (n = 4)
(1.13, 10.74)

0 (n = 0)(n.a., 3.22)

1.91 (n = 4)
(0.51, 4.89)

2.15 (n = 3)
(0.43, 6.28)

1992–1998 (post-latent)   SIR   (95% CI)

9.16 (n = 17)(5.33, 14.7)

5.14 (n = 12)(2.65, 8.97)

6.92 (n = 29)(4.63, 9.93)

3.78 (n = 13)(2.01, 6.47)

Ukraine [S18]1990–2004   SIR   (95% CI)

8 (n = 164)
(6.78, 9.23)

Table D19. Incidence of all solid cancers combined for exposed population groups in Russia and Ukraine (thyroid cancer
excluded)Standardized incidence ratios, by country and calendar year period
Country/exposed group
Russian Federation [I25, I26]
Population of seven contaminated districts(raions) of the Bryansk oblast(95% CI)

Calendar year periods
1991–1995

1996–2000

2001–2005

1991–2005

1.03 (n = 4 701)

0.99 (n = 4 751)

0.97 (n = 5 018)

1.00 (n = 14 470)

(1.00, 1.06)(0.96, 1.02)(0.95, 1.00)(0.98, 1.02)

Ukraine [P16, S18]

1990–2004

Evacuees from 30-km zone
(males and females)(95% CI)

0.84 (n = 2 182)

Adult residents of contaminated areas(males and females)(95% CI)

0.85 (n = 11 221)(0.80, 0.88)(0.83, 0.86)

Table D20. Incidence of all solid cancers combined among emergency and recovery operation workers (thyroid cancer
excluded)Standardized incidence ratios, by country and calendar year period
Country/exposed group
Russian Federation [I25, I26]
Emergency and recovery operation workers(males)(95% CI)
Ukraine [P16, S18]
Emergency and recovery operation workers(males)(95% CI)

Calendar year periods
1991–1995

1996–2000

2001–2005

1991–2005

1.25 (n = 1 018)

1.18 (n = 1 461)

1.10 (n = 1 741)

1.16 (n = 4 220)(1.17, 1.33)(1.12, 1.24)(1.05, 1.15)(1.12, 1.19)

1990–2004
1.17 (n = 5 396)
(1.14, 1.20)

196

UNSCEAR 2008 REPORT: VOLUME IITable D21. Latent period and grades of posterior subcapsular cataract (PSC) among Chernobyl ARS survivors (beta plus
gamma exposures)Parameter

Dose range (Gy) (degree of ARS)
2.7–4.0 (moderate ARS)

4.7–5.7 (severe ARS)

7.1–8.7 (very severe ARS)

4–12

2.8–4.0

1.5–2.5

Latent period (years)
Maximal grade of PSC
Time to development of maximal stage (years)

I–II

II

III

6.0–12

3.8–5.0

2.8–3.0

Table D22. Adjusted odds ratios and 95% confidence intervals by dose group among Chernobyl emergency and recovery
operation workers with various cataract grades
UACOS Chernobyl liquidator study [W7]Odds ratios (95% confidence intervals) by dose groupa

Dose range(mGy)

100–249

250–399

400–599

600–799

800+

Grade 1 PSC opacity

0.9 (0.8, 1.0)

0.9 (0.7, 1.2)

1.2 (0.9, 1.7)

1.2 (0.8, 1.8)

1.7 (1.1, 2.7)

Grade 1 cortical opacity

0.9 (0.8, 1.0)

1.0 (0.8, 1.2)

1.1 (0.8, 1.5)

1.4 (1.0, 2.1)

1.6 (1.0, 2.5)

Grade 2–5 cataract

1.0 (0.7, 1.7)

1.6 (0.9, 2.8)

2.4 (1.2, 4.6)

1.3 (0.5, 3.1)

1.3 (0.5, 3.4)

a Odds ratios are given relative to the baseline group of those who incurred doses in the range 0–99 mGy. Odds ratios were adjusted for factors including age at exposure, age
and clinic at first examination, sex (96% males), current and past smoking habits, diabetes mellitus, history of corticosteroid or phenothiazine use, and occupational exposuresto hazardous chemicals, ionizing radiation exposure (other than due to recovery operations), and exposure to infrared radiation or ultraviolet radiation, using logistic regression.

Table D23. Dose-effect thresholds: maximum likelihood estimates and likelihood-profile based on 95% confidence intervals
for various cataract classes
Ukrainian Chernobyl liquidator study (UACOS) [W7] and Japanese atomic bomb survivors study [N17, N18]
Study and cataract endpoint

Estimated value for dose threshold (95% CI) (Gy)UACOS, Grade I‑V cataract [W7]0.50 (0.17, 0.65)

UACOS, Grade I opacity [W7]0.34 (0.19, 0.68)

UACOS, Grade I cortical opacity [W7]0.34 (0.18, 0.51)

UACOS, Grade I posterior subcapsular opacity [W7]0.35 (0.19, 0.66)

Atomic bombings, cortical cataracts [N18]0.6 (<0, 1.2)aAtomic bombings, posterior subcapsular cataracts [N18]0.7 (<0, 2.8)

Atomic bombings, surgically removed cataracts [N17]0.1 (<0, 0.8)

a 90% confidence intervals were reported in the atomic bomb studies.

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT197

Table D24. Predictions of background and excess mortality from solid cancers and leukaemia in populations exposed as aresult of the Chernobyl accident (based on reference [C1])
Population

Population size andaverage dose

Cancer type

PeriodBackground cancer
mortality

Predicted excess
cancer mortality

AFa (%)

Emergency and recovery operation
workers (liquidators), 1986–1987

200 000
100 mSv

Solid cancers

Lifetime (95 years)

41 5002 000

5Lifetime (95 years)

800

200

20

First 10 years

40

150

79

Evacuees from 30‑km zone

135 000
10 mSvResidents of SCZsc

270 000
50 mSvResidents of other contaminatedareas

6 800 000
7 mSv

Leukaemia

Solid cancers

Lifetime (95 years)

21 500150

0.7b

Leukaemia

Lifetime (95 years)

500

10

2

First 10 years

65

5

7

Lifetime (95 years)

43 500

1 500

3Lifetime (95 years)

1 000

100

9

First 10 years

130

60

32

Solid cancers
Leukaemia

Solid cancers

Lifetime (95 years)

800 000

4 600

0.6

Leukaemia

Lifetime (95 years)

24 000370

1.5First 10 years

3 300

190

5.5

a AF: attributable fraction = (excess deaths/total death from the same cause) × 100.
b A misprint has been corrected which appeared in references [C1, W5].
c Strictly Controlled Zones, i.e. areas with 137Cs soil deposition above 555 kBq/m2 (15 Ci/km2) in 1986.

Figure D-I. Frequency of granulocytopenia (A) and trombocytopenia (B) among persons with unconfirmed ARS and among
ARS survivors [B9, B39, B42]
A

45
40

60

30

PERCENTAGEPERCENTAGE

35
25
20
15
10

50
40
30
20
10

5
0

B

70

1991

1996

2001

2006

0

1991

Unconfirmed ARS

1996

2001
YEAR

YEAR
ARS survivors

2006

198

UNSCEAR 2008 REPORT: VOLUME II

Figure D-II. Relationship between the dose due to beta and gamma irradiation and the length of the latency period for thedevelopment of radiation-induced cataracts
Data from FMBC, Russian Federation [G9]1614DOSE (Gy)1210y = –0.0343x + 7.9365;
R2 = 0.5805

8
6
4
2
0
0

50

100

150

200

LATENT PERIOD (months)

Figure D-III. Frequency of cataracts developed by 2006 among persons with unconfirmed ARS and among graded ARS
survivors: ARS-I, ARS-II and ARS-III
Data from URCRM [B9, B39, B42]
90

83.3

80

PERCENTAGE

70
60
50
40
30

22.9

20
10
0

4.1
Unconfirmed
ARS

8.8
I

II
GRADE OF ARS

III

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

Figure D-IV. The number of ARS survivors with local radiation injuries as a result of the Chernobyl accident
Data from FMBC, Russian Federation [G9]1412NUMBER

10
8
6
4
2
0
I

II

III

GRADE OF ARS
Epithelization

Atrophy

Late radiation ulcers

Figure D-V. The number of ARS survivors with local radiation injuries as a result of the Chernobyl accident
Data from URCRM [B39]65NUMBER

4

Telangiectasias
Keratosis

3

Late radiation ulcers
Fibrosis

2
1
0
I

II
GRADE OF ARS

III

199

200

UNSCEAR 2008 REPORT: VOLUME II

Figure D-VI. Prevalence of respiratory diseases among persons with unconfirmed ARS and among ARS survivors
Data from URCRM [B42]8070
PERCENTAGE

60
50
40
30
20
10
0

1991

1996

YEAR

Unconfirmed ARS

2001

2006
ARS survivors

Figure D-VII. Number of ultrasound examinations performed per 105 inhabitants in the three regions in Ukraine in 1990, 1995
and 2002 [L5]3 000

NUMBER OF EXAMINATIONS

2 500
2 000
Kyiv
1 500

Chernihiv
Zhytomyr

1 000
500
0

1990

1995
YEAR

2002

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

201

Figure D-VIII. Thyroid cancer incidence rates for different age groups (age at diagnosis) of the total Belarusian female
population
140120

20–29 years

INCIDENCE RATE
(per million)

100
80
60
10–19 years

40
20

0–9 years

0
1990

1992

1994

1996

1998

2000

2002

2004

YEAR OF DIAGNOSIS

Figure D-IX. Thyroid cancer incidence rates for different age groups (age at diagnosis) of the Russian female population of
the Bryansk, Kaluga, Orel and Tula oblasts
140
120

INCIDENCE RATE
(per million)

100
80

20–29 years

60
10–19 years

40
20
0

0–9 years
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
YEAR OF DIAGNOSIS202

UNSCEAR 2008 REPORT: VOLUME II

Figure D-X.

Thyroid cancer incidence rates for different age groups (age at diagnosis) of the total Ukrainian female population
140
120

INCIDENCE RATE
(per million)

100
80
60
40

19–30 years20

10–18 years
0–9 years

01990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
YEAR OF DIAGNOSIS

Figure D-XI.

Thyroid cancer incidence rates for different age groups (age at diagnosis) of the total Belarusian male population
60

INCIDENCE RATE
(per million)

50
40
20–29 years
30
20

10–19 years

10
0–9 years

01990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
YEAR OF DIAGNOSISANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

203

Figure D-XII. Thyroid cancer incidence rates for different age groups (age at diagnosis) of the Russian male population of the
Bryansk, Kaluga, Orel and Tula oblasts
60

INCIDENCE RATE
(per million)

50
40
20–29 years

30
20

10–19 years
10
0–9 years
01990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
YEAR OF DIAGNOSIS

Figure D-XIII.

Thyroid cancer incidence rates for different age groups (age at diagnosis) of the total Ukrainian male population

60

INCIDENCE RATE
(per million)

50
40
30
20
19–30 years

100

0–9 years
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
YEAR OF DIAGNOSIS

10–18 years

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UNSCEAR 2008 REPORT: VOLUME II

Figure D-XIV. Change in the proportion of papillary carcinoma subtypes with time after the accident
PTC SF = Solid/follicular subtype (Ukraine); PTC CP = Subtype composed mainly of papillae

PERCENTAGE OF ALL PTC

100
80
60
PTC SF40

PTC CP

20
01990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001
YEAR

Figure D-XV. Distribution of Russian emergency and recovery operation workers by year of entry into the 30-km zone
50 00046 78745 000NUMBER OF WORKERS

40 00037 44835 00030 00025 00020 231

20 000
15 000
10 000
5 000
0
1986

1987
YEAR OF ENTRY

1988–1990

ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

205

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