This publication contains:
Scientific Annexes
Annex C. Radiation exposures in accidents
Annex D. Health effects due to radiation from the Chernobyl accident
Annex E. Effects of ionizing radiation on non-human biota

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SOURCES AND EFFECTS OF IONIZING RADIATION — UNSCEAR 2008 REPORT — VOLUME II: EFFECTS

VOLUME II: EFFECTS

SOURCES AND EFFECTS
OF IONIZING RADIATION
United Nations Scientific Committee on the Effects of Atomic Radiation

UNSCEAR 2008 Report
Volume II: EFFECTS

Scientific Annexes C, D and E

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.

Corrigendum to Sales No. E.11.IX.3

18 May 2016

Sources and Effects of Ionizing Radiation: United Nations
Scientific Committee on the Effects of Atomic Radiation
2008 Report
Volume II
Annex C (Radiation exposures in accidents)
Corrigendum
1.

Page 24, table 3, section headed “Sealed radioactive sources”, column
headed “Industrial source/installation”, first row

For 137Co source read 60Co source

V.16-02681 (E)*1602681*

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 C
RADIATION exposures IN ACCIDENTS
Contents
Page

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1

I. ACCIDENTS AT NUCLEAR FACILITIES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 A. Accidents related to nuclear weapons programmes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			 1. Criticality accidents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			 2. Other accidents with only on-site consequences. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			 3. Accidents with releases to the environment and potentially significant population exposures. . . . . . .
		 B. Accidents not related to nuclear weapons programmes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			 1. Criticality accidents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			 2. Other accidents with only on-site consequences. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			 3. Accidents with releases to the environment and potentially significant population exposures. . . . . . .
		 C. Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2
2
2
5
5
5
5
6
6
7

II.
		
		
		

ACCIDENTS AT INDUSTRIAL FACILITIES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A. Sealed radioactive sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B. Accelerators and X-ray devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C. Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7
7
9
9

III. ACCIDENTS INVOLVING ORPHAN SOURCES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 A. Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9
13

IV.
		
		
		

ACCIDENTS AT ACADEMIC AND RESEARCH FACILITIES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A. Sealed radioactive sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B. Accelerators and X-ray devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C. Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

13
13
13
14

V.
		
		
		
		

ACCIDENTS ASSOCIATED WITH THE MEDICAL USE OF RADIATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A. Nuclear medicine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B. Sealed radioactive sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C. Accelerators and X-ray devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
D. Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

14
14
14
15
16

VI. OTHER ACCIDENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 A. Transport accidents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 B. Suspected malicious act. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

16
16
16

VII. SUMMARY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

17

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

18

TABLES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

19

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

39v

introduction
workers or members of the public in a fashion that results inacute (i.e. deterministic) health effects.” Selected accidents
of significant public interest and/or involving environmental contamination were also to be considered. Thus, forthe purpose of this annex, radiation accidents are definedas unintended events in which at least one person experienced early acute health effects that required some degreeof medical intervention, and unintended events that caused
significant population exposures due to environmental
contamination.

1. In the course of the research and development for andthe application of atomic energy and nuclear ­t echnologies,
a number of radiation accidents have occurred. Some ofthese accidents have resulted in significant health effectsand ­o ccasionally in fatal outcomes. The application of­t echnologies that make use of radiation is increasingly­w idespread around the world. Millions of people have­o ccupations related to the use of radiation, and hundredsof millions of individuals benefit from these uses. Facilities using intense radiation sources for energy production and for purposes such as radiotherapy, sterilizationof products, preservation of foodstuffs and gamma radiography require special care in the design and operationof equipment to avoid radiation injury to workers or to
the public. Experience has shown that such technology
is generally used safely, but on occasion controls havebeen circumvented and serious radiation accidents haveensued.

6. It should be noted that the Committee has not considered
accidents that may have been significant from a technicalpoint of view (e.g. failures in safety systems at nuclear power
plants) but that did not lead to radiation exposures. ­Moreover,
it is not the purpose of this annex, and indeed it is outside
the remit of the Committee, to investigate the root causesof the accidents, analyse accident ­progressions, conduct­probabilistic risk assessments and forecast trends. Never­theless, in order to provide a better qualitative ­appreciationof the range of characteristics and common features of theaccidents that have occurred, the Committee has provided
brief summaries of selected accidents, their circumstances
and their health consequences, and has described overall
trends when possible.

2. Reviews of radiation exposures from accidents havebeen presented in previous UNSCEAR reports. The lastreport containing an exclusive chapter on exposures from
accidents was the UNSCEAR 1993 Report [U6].
3. This annex is aimed at providing a sound basis for­conclusions regarding the number of significant radiation
accidents that have occurred, the corresponding levels ofradiation exposures and numbers of deaths and injuries,
and the general trends for various practices. Its conclusions are to be seen in the context of the Committee’s
overall evaluations of the levels and effects of exposure toionizing radiation.

7. Accidents were selected for inclusion in the text and/or tables if information about the accident was available
in published literature in medicine, radiation protection or
dosimetry, or other relevant scientific or government literature, or in publications of the International Atomic Energy
Agency (IAEA) or the World Health Organization (WHO).
Malicious acts (intentional as opposed to accidental), with
one exception of topical interest (see paragraph 124), are notincluded in this compilation, nor are accidents that occurred
during nuclear weapons testing. During the fifty-fifth session of the Scientific Committee, it was agreed that nodescriptions of accidents occurring after July 2007 would be
included in this annex.

4. The Committee’s evaluations of public, occupationaland medical diagnostic exposures are mostly concernedwith chronic exposures of various population groups at levels that are well below the thresholds for early acute (deterministic) health effects. In contrast, accidents can involve
relatively high exposures, above such thresholds, and it isnecessary to consider separately the early acute healtheffects, which essentially occur only in accidents and which
are clearly attributable to radiation exposure. In addition, a
few accidents have led to elevated exposures among larger
populations, usually by releasing radioactive material into
the environment; the Committee has attempted to assess thecontribution such accidents have made to overall population
radiation exposures.

8. The IAEA and WHO publish important documents
related to accidents for which they have provided assistance in response; these documents contain extensive
descriptions of the event, dose assessments, health consequences and medical treatment. Accident catalogues
are maintained by the Institute of Biophysics, Moscow,
Russian Federation; by SEARCH in Ulm, Germany; by
the Curie Institute, Paris, France; and by REAC/TS in
Oak Ridge, Tennessee, United States of America. Table 1

5. The scope of this annex was to include “a survey ofaccidents whereby exposure to radioactive material affected1

2

UNSCEAR 2008 REPORT: VOLUME IIprovides a summary of accidents recorded for the territoryof the former Soviet Union, some of which are described inthis report [M4].

11.

- Section I covers criticalities and other operational
accidents occurring at nuclear facilities, including
accidents resulting in releases to the environment.
- Section II describes accidents involving sources, accelerators and X-ray devices used in industrial facilities.

9. The Committee considers it likely that most of theserious accidents at nuclear facilities have been reported.
In contrast, it considers it probable that many smallerindustrial accidents, accidents with “orphan” sources,
accidents in academic or research work and very many
accidents in the medical uses of radiation have not beenreported. There may be various reasons for this, including cultural and professional attitudes, fear of prosecution and ineffective regulatory regimes. In any case, it isclear that this review of accidents cannot be considered
comprehensive.

- Section III provides examples of accidents associated with orphan sources and devices.
- Section IV describes accidents involving sources
and radiation-generating devices used in academic
and research environments.
- Section V provides examples of medical accidents
involving sources, radiation-generating devices andnuclear medicine.

10. Nevertheless the Committee considers that its assessment does provide a depiction of the number of significant
radiation accidents that have occurred, the corresponding
levels of radiation ­exposures and numbers of deaths andinjuries, and the general trends for various practices, as abasis for evaluating the ­contribution made by accidents tooverall radiation ­exposures and effects.

I.

The review of selected radiation accidents has six sections:- Section VI addresses other accidents, principallythose connected with the transport and movementof radioactive and nuclear materials in land, air,sea, undersea and space vehicles.
- Section VII summarizes information about accidents in various practices.

ACCIDENTS AT NUCLEAR FACILITIES- Accidents with releases to the environment andpotentially significant population exposures.
Tables 2a and 2b summarize key information onseven accidents (including one criticality accident)
at nuclear facilities that resulted in significant­exposures of the general public.

12. Accidents at nuclear facilities are considered in two
categories: those related to nuclear weapons programmes
and those not related to nuclear weapons programmes. Eachcategory is considered in three subsections:- Criticality accidents. These are generally considered significant owing to the potential loss of
special nuclear material, serious contamination of
the workplace, the possibility of off-site contamination and, in some cases, serious medical consequences. A large number of such accidents haveoccurred, although most of them took place in theearly research and development of nuclear ­weapons
technologies. This annex summarizes only thosecriticality accidents that led to serious medical
consequences, and tables 2a and 2b summarize
information on the 23 criticality accidents that havebeen reported.
- Other accidents with only on-site consequences.
These have occurred during operations at nuclear
facilities, and affected principally on-site workers.
Some also involved the release of radioactive material to the outside environment and possible exposureof off-site populations. Tables 2a and 2b summarize
key information on eight such accidents (other thancriticality accidents) that led to early health effects
among operators, plant staff or emergency response
personnel, but had no significant off-site exposuresof the general population or environment.

A.

Accidents related to nuclear weapons programmes
1. Criticality accidents

13. Of the 23 criticality accidents in total that have beenreported, 17 occurred at facilities related to nuclear weapons programmes, which are listed in table 2a and briefly
described below.
14. United States, Los Alamos National Laboratory, 1945.
Three serious accidents have occurred at Los ­Alamos National
Laboratory in Los Alamos, New Mexico. The first occurredin August 1945 when a critical assembly was being createdby stacking tungsten carbide bricks around a ­plutonium core.
The experimenter was moving the final block into place when
he noted the neutron count ­indicating that the addition of thelast brick would make the ­assembly supercritical. As he withdrew his hand, the final brick slipped and fell into the ­centre,
creating the criticality. His dose1 was ­estimated at 5.1 Gy from1

Dose, unless otherwise specified, refers to whole-body dose.

ANNEX C: RADIATION EXPOSURES IN ACCIDENTS

a yield of 1016 fissions. He died 28 days after the exposure. An
army guard assigned to the ­building but not directly involved
with the experiment received a dose ­estimated at 0.5 Gy [L1].
15. United States, Los Alamos National Laboratory, 1946.
In May 1946, the plutonium core described above was being
used in a demonstration of the techniques for creating a
metal critical assembly using beryllium as a reflector. The
individual conducting the demonstration was holding the top
cell with his left thumb and inadvertently allowed one edgeof the upper hemisphere to come into contact with the lower
hemisphere. He attempted to place a screwdriver under partof the upper hemisphere not in contact with the lower hemisphere. The screwdriver slipped, resulting in a criticality
excursion with an estimated yield of 3 × 1015 fissions. The
individual conducting the experiment died nine days after
the exposure, following a dose estimated at 21 Gy. Seven
other individuals in the room received doses ranging from
0.37 to 3.6 Gy [L1].
16. United States, Argonne National Laboratory, 1952.
In June 1952, an accident occurred at Argonne National
Labora­tory in Argonne, Illinois, in a light water moderated
core in which 6.8 kg of 235U oxide was embedded in strips ofpolystyrene plastic. The system became critical following anattempt to replace the control rod when the normal amountof water was in the core. Four individuals received radiation
doses of 1.36, 1.27, 0.6 and 0.09 Gy [L1].
17. Former Soviet Union, Mayak Complex, 1953. In March
1953, a criticality excursion occurred at the Mayak Complex
in Chelyabinsk involving seven 40 L tanks of unfavourable
geometry used for the mixing, dilution, sample storage andtransfer of plutonium nitrate derived from irradiated reactor fuel. No radiation monitoring equipment was available
to workers; therefore the seriousness of the event was notrecognized. The estimated yield was 2.5 × 1017 fissions. An
operator received about 10 Gy whole-body dose, but thiswas very non-uniform (more than 30 Gy to the legs). He
survived a moderate degree of acute radiation syndrome(ARS) but amputation of both legs was necessary. The doseto a second operator was about 1.5–2.0 Gy and she survived
a mild degree of ARS [G5, L1, V1].
18. Former Soviet Union, Mayak Complex, 1957. In April
1957, a second event occurred involving a tank used foroxalate purification and filtration of highly enriched uranium solutions. An unsafe geometry resulted in a criticality
with a fission yield estimated at 2 × 1017. The operator, who
remained in the area for approximately ten minutes, died
12 days later, having received a whole-body dose estimatedat about 10 Gy (based on an analysis of the 24Na levels in
his blood). Five other workers experienced ARS of different severities depending on the doses received, which ranged
from 2.0 to 6.0 Gy [G5, L1, V1].
19. Former Soviet Union, Mayak Complex, 1958. In ­January
1958, a third event occurred that was related to the use of atest tank built for determining critical parameters for solutions

3of uranium. After a test, a team of four persons decided to
speed the draining of a solution. The ­combination of the solution geometry in the tank and neutron reflection by the workers’ bodies resulted in a criticality involving approximately
2.3 × 1017 fissions. Three of the four persons died within
one week, with doses estimated to have been in the range
40–50 Gy. The fourth person, who had been 3 m away fromthe tank, received a dose estimated at 6 Gy and ­presented
symptoms of ARS and of visual impairment. She survived,
although ­long-term health problems related to organs on theleft side of her body were observed, including skin fibrosis,
kidney sclerosis and cataracts [B11, G5, K2, L1, V1].
20. United States, Y-12 plant, 1958. In June 1958, a­criticality ­accident occurred at the Y‑12 plant in Oak Ridge,­Tennessee, during recovery of enriched uranium from various solid wastes. Prior to the accident and unbeknown to anyone, uranyl nitrate had been collecting in a vessel because ofa leaking valve. When an operator opened the vessel to drainwater into a 55 gallon (208 L) drum, the water was precededby the enriched uranium solution. The unsafe geometry inthe drum resulted in a criticality excursion with an estimatedyield of 6 × 1016 fissions. A second excursion occurred 15
seconds later. Eight male workers (aged 25 to 56 years) were
exposed, with five of the men receiving whole-body dosesof between 2.36 and 3.65 Gy. Three others received dosesof below 0.7 Gy. Long-term follow-ups with annual medical
evaluations were conducted [A1].
21. United States, Los Alamos National Laboratory, 1958.
In December 1958, a third accident at Los Alamos National
Laboratory occurred during an annual physical inventory
when process streams were interrupted in a unit used topurify and concentrate plutonium from slag, crucible andother lean residues from recovery processes. Dilute aqueousand organic solutions from two vessels were washed into asingle large vessel. The addition of a nitric acid wash to thetank is believed to have separated the liquid phases, resulting
in an excursion when a stirrer was activated. The excursion
had a yield of 1.5 × 1017 fissions. The accident resulted in thedeath of the operator 36 hours after exposure, with a doseto the upper torso estimated at approximately 120 Gy. Twoother individuals suffered no ill effects after doses ­estimatedat 1.34 and 0.53 Gy [L1].
22. United States, National Reactor Testing Station, 1961.
In ­January 1961, a serious event occurred at the National
Reactor Testing Station in Idaho Falls, Idaho, involving a
direct-cycle boiling water reactor of 3 MW gross thermal
power. The reactor used enriched uranium fuel plates cladin aluminium, and was water moderated and cooled. Aftera routine shutdown for maintenance, a three-man crew was
assigned the task of reassembling the control rod drives andpreparing the reactor for start-up the following day. The
best available evidence suggests that the central control rod
was manually pulled out too fast, causing the power to rise.
A subsequent steam explosion destroyed the reactor andinstantly killed two men; the third man died two hours after
the accident as a result of a head injury [L1].

4

UNSCEAR 2008 REPORT: VOLUME II

23. Former Soviet Union, Siberian Chemical Complex,
1961. In August 1961, an accident occurred at the ­Siberian
Chemical Complex in Seversk at an experimental facility
used for purifying enriched (22.6%) uranium ­hexafluoride.
The main cylinder lacked sufficient cooling, and another­vessel was bypassed. The criticality alarm system was­activated, and personnel evacuated the facility. ­Radiation
surveys in the area using portable gamma monitoring­instruments did not indicate abnormal radiation levels, andwork resumed, resulting in a second criticality. The yieldof each pulse was estimated to be 1016 fissions. The process
operator received a dose estimated at 2 Gy and experienced
mild symptoms related to ARS [L1, V1].
24. United States, Hanford Facility, 1962. In April 1962,
an accident at a Recuplex System Process Plant in Richland,
Washington, occurred as a result of the following set of
conditions: cleaning the floor of a solvent extraction hood;a product receiver tank that could overflow into the hood;a temporary line running from the hood floor to a transfertank; and the apparent improper operation of valves. A criticality excursion occurred followed by supercriticality for37.5 hours as the power steadily decreased. The total excursion yield was 8 × 1017 fissions. Of the 22 individuals in thebuilding, only three received significant doses of radiation
ranging from 0.10 to 1.1 Gy [L1].
25. Former Soviet Union, Arzamas-16 Nuclear Centre,
1963. In March 1963, a criticality excursion occurred at theArzamas-16 Nuclear Centre in Sarov in a system using plutonium with a deuteride reflector. The accident was due tothe inadvertent closure of the assembly by the operator. Two
individuals received doses estimated at 3.7 and 5.5 Gy. Bothexperienced a mild form of ARS and survived more than 25
years after the exposure. Four other persons received dosesthat were medically insignificant [L1].
26. United States, Wood River Junction Chemical Process
Plant, 1964. In July 1964, an accident occurred at the Wood
River Junction Chemical Process Plant in Rhode Island. The
facility’s function was to recover highly enriched ­uranium
from scrap metal left over from the production of fuel­elements. A variety of chemical procedures were involved in
the overall process. On the day prior to the accident, a plantevaporator failed to operate properly, making it ­necessary todisassemble it for cleaning. During the cleaning process, aplug of uranium nitrate crystals was discovered in the connecting line. The crystals were dissolved with steam anddrained into polyethylene bottles that were identical to thosethat normally held a very low concentration of fissile material. The bottles were labelled as high-concentration solutions. On the day of the accident the operator mistakenly
poured the contents of a high-concentration bottle into the
make-up vessel, which already contained 41 L of sodium
carbonate solution that was being agitated by a stirrer. A
critical state was reached when nearly all the uranium had
been transferred. The excursion of 1.0 × 1017 to 1.1 × 1017
fissions created a flash of light and the loss of approximately
20% of the solution on to the ceiling, walls and operator.

The radiation dose to the operator was estimated to beapproximately 100 Gy. He died 49 hours after the exposure.
Two workers who entered the room received doses of 1 and
0.6 Gy [K1, L1].
27. Former Soviet Union, Russian Federal Nuclear ­Centre,
1968. In April 1968, two technicians failed to ­reposition thelower reflector of an assembly prior to ­initiating a new testat the Russian Federal Nuclear Centre in Chelyabinsk. There
was no criticality alarm system installed at the time, andhealth physics support was not present. The two ­techniciansreceived estimated neutron/gamma doses of 5–10 and
20–40 Gy. The technician who received the higher dose diedthree days later, and the other technician died after 54 days
[L1].
28. Former Soviet Union, Mayak Complex, 1968. In
December 1968, a fourth event occurred at the Mayak­plutonium extraction facility during a test of a new ­extraction
process when an unusually high plutonium concentrationand the presence of organic material were detected in thesolution. When the solution was poured into a vessel of
unsafe geometry, the operator saw a flash, the criticality
alarm was activated and all personnel evacuated the facility.
The shift supervisor later returned and attempted to poursome liquid into a drain, resulting in a second criticality. The
first excursion yielded 1016 fissions and the second 1015 fissions. The shift supervisor died on day 34 of very severe
ARS. The operator survived ARS of moderate severity, but
subsequently both legs and one arm were amputated [V1,V4].
29. Former Soviet Union, Siberian Chemical Complex,
1978. In December 1978, another event at the complex
occurred in a section of a glovebox line where plutonium
metal ingots were being packed into storage boxes. The box
design was deficient and it was possible to load more than
one ingot into a box. A criticality excursion occurred whenfour ingots were loaded into a single box. The yield was
3 × 1015 fissions. One ingot was physically ejected and theoperator removed the other ingots manually. The operator
received a dose estimated at 2.5 Gy to the whole body andabout 70 Gy to the hands; he experienced ARS of ­moderate
severity, but amputation to above the elbows was ­necessary.
Eyesight impairment occurred some time later. Seven otherworkers received doses estimated at between 0.05 and
0.6 Gy [B11, L1, V1].
30. Russian Federation, Arzamas-16 Nuclear Centre,
1997. In June 1997, a second criticality accident occurredat Arzamas-16 during experimental manipulation of a critical assembly. A technician was working alone in the assembly area when a component from the upper reflector slippedfrom his hand and fell on to the lower assembly containing the enriched uranium core. There was a flash of light,
and the technician realized that a criticality had occurred.
He left the experiment hall and reported the accident to his
supervisors and colleagues. Initial estimates suggested awhole-body dose of 45 Gy from neutrons and 3.5 Gy from

ANNEX C: RADIATION EXPOSURES IN ACCIDENTS

gamma rays. The technician was promptly hospitalized.
He died 66.5 hours after the exposure, despite prompt andintensive medical care [I5, L1].
2.

Other accidents with only on-site consequences

31. Of the eight accidents (other than criticality ­accidents)
in total that occurred during the operation of nuclear ­facilities
and that led to early health effects among ­operators, plantstaff or emergency response personnel, but had no ­off-site
consequences for health or the environment, five occurred at
facilities associated with nuclear weapons ­programmes andare listed in table 2a. A brief description of one of these isprovided here to illustrate the nature of such events.
32. United States, Hanford Facility, 1976. In August 1976,
a 64-year-old chemical operator was injured by a chemical
explosion of an ion exchange column used for recovery of241
Am at the Hanford Facility in Richland, Washington. The
operator sustained chemical burns of the face, eyes, neck andright shoulder, as well as lacerations and embedded foreign
bodies in these areas. He was heavily contaminated externally with 241Am and inhaled an estimated 40.7 MBq of theradionuclide. Aggressive medical therapy began immediately, including on-site decontamination and administrationof calcium- and zinc-DTPA. Chelation therapy continued formany months and was responsible for a significant reductionin the 241Am body burden. The estimated cumulative doses
three years after the accident to bone, lung and liver were
8.6, 2 and 1.6 Gy, respectively [H2].
3. Accidents with releases to the environment
and potentially significant population exposures
33. Of the seven accidents at nuclear facilities that resulted
in potentially significant exposures of the general public orthe environment, four were associated with nuclear weapons
programmes and are listed in table 2a. Three of these aredescribed briefly below.
34. Former Soviet Union, Mayak Complex, 1957. In
1957, at the Mayak Complex, overheating of a storagetank ­containing radioactive nitrate–acetate salts led toan ­explosion and the release of some 740 PBq of radio­
active products off-site to an area of some 20,000 km2 ofthe ­Chelyabinsk and ­Sverdlovsk regions. The contaminated zone had a population of 272,000. There were 1,154­individuals inhabiting areas with a 90Sr deposition density ofgreater than 40 MBq/m2 [U6].
35. United Kingdom, Windscale, 1957. In 1957, a fire in
the Windscale graphite reactor burned for three days, resulting in major releases of radioiodine and other nuclides into
the environment in and around Cumbria. The release of131
I was estimated at some 740 TBq. It was accompanied
by 22 TBq of 137Cs, 3 TBq of 106Ru, 16 PBq of 133Xe and
8.8 TBq of 210Po. The maximum doses to local individuals

5

were ­estimated to be 0.01 Gy to the thyroids of adults and
0.1 Gy to the ­thyroids of children. Measurements in Leeds
and London indicated thyroid doses of 0.001 and 0.0004 Gy[C2, G4, U6, U9].
36. Russian Federation, Siberian Chemical ­Enterprises,
1993. In April 1993, a serious accident occurred at the­Siberian Chemical Enterprises facility at Tomsk-7. The­accident caused damage to both the reprocessing line
and the building, resulting in the release of about 30 TBq
of beta- and gamma-emitting radionuclides and about
6 GBq of 239Pu. Radiological monitoring of plant ­personnel­demonstrated that only six individuals received doses ofabove the 0.2 mGy detection thresholds of the dosimetersused. Dosimetry on 14 of the 20 firefighters indicated­individual doses of 1–7 mGy [I19].

B.

Accidents not related to nuclear weapons programmes
1. Criticality accidents

37. Of the 23 criticality accidents in total that have beenreported, 6 occurred at facilities not related to nuclear­weapons programmes; they are listed in table 2b andbriefly described below. One of these, the 1999 accident
at ­Tokai-mura, is also listed under accidents with releases
to the environment and potentially significant population
exposures.
38. Former Yugoslavia, Boris Kidrich Institute, 1958.
In October 1958, a criticality accident occurred ­during
an ­experiment at a zero power reactor facility at the Boris­K idrich Institute in Vinca. The accident exposed six­individuals to relatively uniform doses of 4.36, 4.26, 4.19,
4.14, 3.23 and 2.07 Gy. One individual died as a result of theaccident [L1, M4].
39. Belgium, Venus Assembly, 1965. In December 1965,
an accident occurred at the Venus Assembly in Mol,
­involving a tank type water moderated (70% H 2O and
30% D2O) critical assembly operating with 7% enriched
UO2 rods. Although there was a written rule in the reactor
safety report that no ­manipulation of a manual rod shouldbe performed without first ­emptying the vessel, a written
order was given to a ­technician ­prescribing the loading ofa manual control rod followed by the unloading of anotherone. The ­technician inadvertently extracted the manual
rod instead of first ­inserting the other rod, and a criticality
resulted. The ­technician received approximately 3–4 Gy
to the head and approximately 3–10 Gy to the trunk. The
dose to his feet was estimated to be 40 Gy. Medical treatment was successful, but amputation of his left foot wasnecessary [J3, L1, P2].
40. Former Soviet Union, Kurchatov Institute, 1971. In
February 1971, an accident occurred at Kurchatov ­Institute in
Moscow during a series of experiments designed to evaluate

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UNSCEAR 2008 REPORT: VOLUME II

the relative effectiveness of iron and metallic beryllium as areflector on a power reactor core. The supervisor determinedthat the substitution of iron for beryllium would not result inany considerable increase in reactivity. He supervised the
addition of water prior to the arrival of the console operator and supervising physicist. The control rods had not been
actuated, and a criticality occurred, evidenced by a flash ofblue light. The supervisor and two visiting scientists were
exposed; each received a whole-body dose of about 3 Gy;
the supervisor and one of the visitors received doses to thelegs of between 15 and 20 Gy [L1, V4].
41. Former Soviet Union, Kurchatov Institute, 1971.
In May 1971, a second accident occurred at Kurchatov­Institute ­during an experimental programme to measure
critical masses formed by a certain type of highly enriched(about 90%) 235U fuel rod. Following the insertion of control
rods and removal of the neutron source from the core, the­supervisor ordered the water to be removed through a fast
dump valve. Because the gap size was smaller than the sizeof the fast dump outlet, an internal plate sagged and fuel rods
fell out of the lattice into an unsafe geometry, resulting in a
criticality excursion. The yield was estimated to be 5 × 1018
fissions. Four individuals were in the facility at the time of
the criticality. A technician received about 60 Gy and died
five days after the accident. The supervisor received about
20 Gy and died after 15 days. The other two individuals
survived doses estimated at 7–8 Gy, but suffered long-term
health effects [L1, S2].
42. Argentina, Constituyentes Atomic Centre, 1983. In
September 1983, at the Constituyentes Atomic Centre,a prompt criticality accident occurred at the RA-2 zero
power critical facility light water cooled test and training
reactor near Buenos Aires. RA-2 utilized 90% enricheduranium MTR-type fuel. Facility procedures requiredthat fuel and control rod alterations be performed without the moderator present. The operator attempted tomake changes to the core configuration without draining the moderator water. The core went prompt critical,
resulting in the moderator expanding rapidly and shutting down the reactor. It is estimated that the operator
received an initial average whole-body dose of 17 Gy due
to fast neutrons and about 20 Gy due to gamma photons.
He experienced symptoms of ARS, including neurological disorders, and died two days after the accident [B15,G6, L1, N1, P3, W4, W5].
43. Japan, Tokai-mura fuel conversion plant, 1999. In
September 1999, a criticality accident occurred in a fuel­conversion plant in Tokai-mura during the ­processing ofhighly enriched fuel for an experimental fast ­reactor. Using
unauthorized procedures, the workers poured 16.6 kg of
18.8% enriched uranium into a precipitation tank, ­resulting
in a criticality excursion. Two individuals ­working near
the precipitation tank received whole-body doses of
10–20 Gy Eq (individual A) and 6–10 Gy Eq (individual B)
from gamma rays and neutrons, using a value for the ­relative
biological effectiveness (RBE) of 1.7. A third individual,

several metres distant from the precipitation tank, received adose estimated to be 1.2–5.5 Gy Eq. Early administration of
granulocyte colony-stimulating factor (G-CSF) was used in
the medical management of these individuals. Individual A
died 83 days after exposure and individual B 211 days after
exposure. In the course of treatment, individual A received
peripheral blood stem cell transplantation from his HLAidentical sister, and individual B received a transplant ofumbilical cord blood.
44. The accident resulted in off-site doses from direct­neutron and gamma irradiation to nearby populations,although no significant long-term effects are expected.
Approximately 200 residents living within a 350 m radius
were evacuated. Ninety per cent of them received doses ofless than 5 mSv. Ten per cent received doses of between
5 mSv and 25 mSv. While there were measurable levelsof airborne fission products on local plant life, maximum­readings were less than 0.01 mGy/h, and the activity was
short-lived [A2, I6].

2.

Other accidents with only on-site consequences

45. Of the eight accidents (other than criticality ­accidents)
in total that occurred during the operation of nuclear ­facilities
and that led to early health effects among ­operators, plantstaff or emergency response personnel, but had no off-site
consequences for public health or the environment, threeoccurred at facilities not associated with nuclear weapons
programmes and are listed in table 2b.

3. Accidents with releases to the environment
and potentially significant population exposures
46. Of the seven accidents at nuclear facilities that
resulted in significant exposures of the general public or the environment, three were not associated with
nuclear ­weapons programmes; they are listed in table 2b.
Two of these are described briefly below. One other, the1999 ­accident at Tokai-mura, has been listed also under“­criticality accidents” and has been described briefly insubsection 1 above.
47. United States, Three Mile Island, 1979. In March
1979, an ­accident occurred at the Three Mile Island nuclear
power plant near Harrisburg, Pennsylvania. The sequenceof events leading to the accident began with the closureof a valve that fed water to the boiler. A series of events
thereafter led to core melt and the release of fission products through a relief valve in the primary water make-up
system. Most fission products were retained in the water,
but about 370 PBq of noble gases, mainly 133Xe, and some
550 GBq of 131I were released into the atmosphere. While
the accident released large amounts of activity from thefailed reactor core, the resulting exposures of the public
were negligible [U6, U9].

ANNEX C: RADIATION EXPOSURES IN ACCIDENTS

48. Former Soviet Union, Chernobyl nuclear power plant,
1986. The 1986 accident at the Chernobyl nuclear power
plant was the most severe accident ever to have occurredin the civilian nuclear power industry. Two workers died in
the immediate aftermath, and high doses of radiation to 134
plant staff and a number of emergency ­personnel resultedin ARS, which proved fatal for 28 of them. The accident
caused the largest uncontrolled radioactive release intothe ­environment ever recorded for any ­civilian ­operation,­including 1,760 PBq 131I and 86 PBq 137Cs. It depositedradioactive material over large areas of the former Soviet
Union and some other ­countries in Europe, ­contaminating
land, water and biota, and causing serious social and­economic disruption for large populations in Belarus,
the Russian ­Federation and Ukraine. The ­consumption of
fresh milk contaminated with 131I in the first weeks after
the accident led to thyroid doses that have been estimatedto range between 0.05 and 5 Gy to ­populations of ­Belarus,
the Russian Federation and Ukraine. More details are­provided in annex D, “Health effects due to radiation fromthe ­Chernobyl accident”.

II.

C. Summary
49. Tables 2a and 2b list 35 reported accidents at nuclear
facilities that resulted in acute health effects or caused­significant population exposures, of which 24 were at­facilities associated with nuclear weapons programmes.
In general, criticality accidents have occurred during­experiments or operations in research reactors, or ­during
work with fissile material in solution or slurries. One ­accident
occurred in the processing of metal ingots. Only one criticality resulted in the release of radioactive ­material off-site,
albeit a very small quantity. Of the 23 criticality accidents,
17 were at facilities associated with nuclear ­weapons programmes. Of the ­accidents at nuclear power plants, the 1986
Chernobyl accident was by far the most serious. Causes
identified in these accidents were: inadequate facility design,­process equipment that resulted in poor geometry, personnel
errors and violation of operational procedures. Because ofthe ­regulatory regimes in place, the Committee considers
it likely that most of the fatal radiation accidents at nuclear
facilities have been reported.

ACCIDENTS AT INDUSTRIAL FACILITIES

50. Table 3 summarizes information on 80 accidents thathave been reported at industrial facilities. Of these, 17 aredescribed briefly below to illustrate the characteristics ofthese events. Section A presents accidents with sealed radioactive sources and section B accidents involving machinegenerated radiation (i.e. from accelerators or X-ray devices).
A.

7

Sealed radioactive sources

51. Table 3 summarizes information on 59 accidents thathave been reported involving sealed radioactive sources
at industrial facilities; 13 of these accidents are describedbriefly here.
52. USSR, 1973. Disregarding rules, an operator entered
the main room of an industrial gamma–facility in the ­Moscow
area, where the 4.2 PBq 60Co source was unshielded. The
operator walked around the source and as soon as he sawthat it was in the “on” mode he immediately left the room.
The estimated distance from the source to the victim ranged
from 0.75 to 1 m. The whole-body dose appeared to be about
4 Gy and he survived a moderate ARS [B11].
53. United States, 1974. In June 1974, at a medical ­productsterilization facility in New Jersey, a 61-year-old man was
exposed for 5–10 seconds to gamma radiation from a 4.4 PBq
60
Co industrial source. The individual had failed to use asurvey meter upon entering the facility and received a non-­uniform exposure owing to partial shielding from Teflon-filled
fibre drums. Nausea and vomiting were evident one hour after

exposure, and the haematological nadir was reached about one
month after exposure. The estimated dose, using cytogenetic
dosimetry, was 4.1 Gy, and the patient was treated with standard antibiotic therapy and platelet/leucocyte trans­fusions. The
individual returned to work in October 1974 [B2].
54. United States, 1977. In September 1977. at a facility
in New ­Jersey, a 32-year-old man was exposed for about ten­seconds to gamma radiation from an 18.5 PBq 60Co source
used to sterilize medical and chemical products. The ­accident
was caused by construction work that had led to ­alterationsin the hot cell entry area, failure to see the interlock ­warningand interlock failure. The individual ­experienced nausea andvomiting two hours after ­exposure. The estimated dose, using
cytogenetic dosimetry, was 2.0 Gy. The patient reached thehaematological nadir about 30 days after exposure and wastreated with standard anti­biotic therapy. Peripheral bloodcounts returned to normal in August 1978 [B2].
55. United States, 1978. In June 1978, an industrial radio­
grapher working on a barge off the coast of Louisiana in
the Gulf of Mexico sustained a radiation injury to the handfrom a 3.7 TBq 192Ir source. A dosimeter malfunction was
thought to be the cause of the accident. About three weeks
after the ­suspected date of exposure, the individual experienced a burning sensation, swelling, erythema and drynessof the thumb, index finger and middle finger of the left hand.
The formation of bullae occurred one week later, and healing
was apparent within 5–8 weeks, although the palmar surfaces
demonstrated thin epithelium. Amputation of the digital two
thirds of the index finger was performed at six months [S1].

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UNSCEAR 2008 REPORT: VOLUME II

56. USSR, 1980. An accident occurred in a gamma­irradiation facility in Leningrad with a 22.2 PBq 60Co
source. The operator entered the irradiation room thinking
the source was “down”. Within less than a minute and assoon as he realized he was wrong, he left the room. However
the whole-body dose appeared to be more than 12 Gy, andhe died on day 10 [S2].
57. China, 1980. In 1980, a 25-year-old man was­accidentally exposed to a 60Co source in Shanghai. The­estimated source activity was 1.96 PBq, and the exposure
time was about 40 seconds. The individual experienced early
profuse vomiting and a rapid fall in lymphocytes and otherhaematological parameters. The estimated dose based on thesurvival of haemopoietic stem cells was 5.22 Gy. ­Following
treatment, the patient was discharged from the hospital fivemonths after exposure. Radiation-induced ­cataracts wereobserved three years after exposure [U3, Y1].
58. Norway, 1982. In 1982, an accident occurred ina gamma irradiation plant at the Institute of Energy­Technology at ­Kjeller near Oslo. The plant was used forsterilization of ­medical equipment. A 2.43 PBq 60Co source
could be raised to various positions above the shielded
position on the ­concrete floor. Owing to technical failure and human error, the operator entered the irradiation
room although the source was not in the shielded position.
He stayed in the ­irradiation room for several minutes andshortly afterwards was found sitting outside the plant andobviously ill. Shortly after the event he was admitted to a
local hospital ­suffering from nausea, vomiting and facial
erythema. ­During the next four days he had ­persistent nausea and increasing ­mucositis in the mouth. After a week
his haematological values were markedly reduced. On thebasis of dose ­reconstruction using electron spin ­resonance(ESR) spectroscopy of nitro­glycerine tablets in his pocket,
the mean whole-body dose was considered to have beenslightly above 20 Gy. The patient died 13 days after­exposure [R1, S3].

61. El Salvador, 1989. An accident occurred in February
1989 at an industrial irradiation facility near San ­Salvador.
The facility had 0.66 PBq of 60Co in a movable source
rack, badly degraded safety systems and poor maintenanceat the time of the accident. After the unshielded source
rack became stuck, three individuals entered the radiation
room and received non-uniform doses to the whole body.
­Subsequently they all developed ARS. Cytogenetic studies
indicated doses of 8 Gy to patient A, 3.6 Gy to patient B
and 3 Gy to patient C. Two of these individuals experienced
serious radiation-induced injuries of the lower extremities,
with doses estimated at 100 Gy. They were transferred toa specialized hospital in Mexico City. The leg of the most­seriously irradiated individual was amputated approximately
four months after exposure. Following transfer back to El
Salvador, this patient died as a result of a surgical procedureand complications due to radiation-induced lung damage.
Another individual required amputation of both legs. A third
individual experienced minor injuries to one foot. Before theaccident was fully understood, a fourth individual, a maintenance manager, entered the facility and received a wholebody dose that was medically insignificant [I1].
62. Israel, 1990. In June 1990, at a commercial ­irradiation
facility in Soreq, an operator bypassed safety systems toenter the irradiation room in order to free cartons stuck on
the conveyor system. He was not aware that the movable60
Co source rack was obstructed in the irradiation position.
At the time of the accident the total activity was 12.6 PBq.
He promptly developed symptoms and left the area. It wasdetermined that his whole-body dose was between 10 and
20 Gy. He was hospitalized with severe haematopoietic
and gastrointestinal syndromes, and skin injury was soon
­evident. Despite aggressive medical efforts, including useof haematopoietic growth factors and a bone marrow transplant, he died 36 days after exposure [I2].

59. China, 1986. In May 1986, in Kaifun, Honan ­Province,a young man and a young woman were accidentally exposed
to a 255 TBq 60Co source for about 1.5–2 minutes at a
local irradiation facility. The man received a whole-bodydose estimated at 3.5 Gy and the woman a dose estimatedat 2.6 Gy. Both individuals experienced radiation-induced
vomiting and haematological depression [W2, Y1].

63. China, 1990. In June 1990, seven workers were
exposed to radiation from a 60Co source at an industrial
facility in Shanghai. The accident was caused by improper­maintenance of safety features. None of the workers was
wearing a ­personal dosimeter at the time of the accident. One
individual, with a dose estimated at 12 Gy, died 25 days after
exposure. A second individual, whose dose was ­estimatedat 11 Gy, died 90 days after exposure. The other five workers received doses estimated to range from 2 to 5.2 Gy andrecovered after medical treatment [L2, P1].

60. China, 1987. In March 1987, in Zhengzhou, Honan
Province, a young man was exposed for 10–15 seconds tophotons from a 60Co source of 3.29 PBq. The ­estimated­exposure was 1.35–1.45 Gy. He experienced lassitude,
thirst and dryness of the eyes immediately after ­exposure.
Four hours later he experienced nausea and anorexia
but no ­vomiting. The nadir values of leucocytes and­platelets occurred on the 35th and 31st days, respectively.
­Restoration of his leucocyte count was rather slow, andthe count remained subnormal until the 120th day after­exposure [Y1].

64. Belarus, 1991. In October 1991, an accident occurred
at a 60Co irradiation facility used to sterilize agriculturaland medical products in the town of Nesvizh. The source
activity was 28.1 PBq at the time of the accident. Owing toa malfunction of the product transport system and humanerror, the operator entered the irradiation area and remained
inside for 1–2 minutes with the source array in the full “out”
position. He received prompt medical attention in Belarus
and then in Moscow. He experienced ARS and skin injuries
resulting from an estimated whole-body dose of 11–18 Gy.
His intensive medical treatment included administration of

ANNEX C: RADIATION EXPOSURES IN ACCIDENTS

granulocyte–macrophage colony-stimulating factor (GMCSF). He died 113 days after exposure of pulmonary andmultiorgan failure [I3].

9The amputation sites manifested lack of healing, and further necrosis led to 11 additional operative procedures overa 22 month period. The patient was eventually fitted withprostheses on all extremities. He required psychologicalsupport for many years [G2, G3].

B. Accelerators and X-ray devices
65. Table 3 summarizes 21 accidents involving machinegenerated radiation (i.e. from accelerators or X-ray devices),four of which are described briefly here.
66. United States, 1960. In March 1960 nine civilian­employees at a military installation in Lockport, New York,
were exposed to X-radiation from an unshielded klystrontube. Two of the individuals were seriously injured, fiveother ­individuals demonstrated less severe injuries and two­individuals remained asymptomatic. The highest dose received
was ­estimated to be 12–15 Gy (non-uniform). Seven exposed
individuals demonstrated varying degrees of nausea, ­vomiting,headache, erythema, fatigue, epilation and ­conjunctival­reddening. The individual with the highest ­estimated dosedemonstrated signs and symptoms of ARS [H5].
67. United States, 1967. In October 1967 three technicians in Pittsburgh, Pennsylvania, simultaneously incurred
accidental non-uniform whole-body exposures to radiationfrom a water-cooled Van de Graaff linear accelerator. The
water cooling system had failed, and the technicians wereattempting to repair the system. They followed all safety
procedures and entered the accelerator area unaware thatthe safety interlock system had failed. The workers experienced early signs and symptoms of radiation injury, anddosimetric tests indicated whole-body exposures of 1, 3 and6 Gy. The most seriously irradiated worker also had localized doses of 59 Gy to the hands and 27 Gy to the feet. He
had a more complicated clinical course, and demonstrated
pancytopenia and complete bone marrow depletion. His situation was unique because he had an identical twin brotherwho donated bone marrow for transplant on the eighth day
after exposure. The patient developed extensive local skin
injury to the hands and feet, and four months after exposure,amputation of portions of the hands and feet was performed.

III.

68. France, 1991. In July and August 1991, three ­individuals
working at an accelerator facility in Forbach received highdoses of radiation from a Van de Graaff device. The ­accident
was reportedly due to negligence and non-compliancewith regulatory requirements. The ­workers’ exposure was­associated with “dark current” after the ­accelerator had been
turned off, although the voltage was maintained to save time.
The residual dose rate was a few grays per second. The most
severely exposed individual suffered skin lesions ­following
a dose estimated at 40 Gy, while the other two were less­seriously affected [C1, U3, Z3].
69. United States, 1991. In 1991, an accelerator operator ata ­facility near Baltimore, Maryland, was exposed to electron
dark current during routine maintenance. The filament voltage was off, but the high voltage was on, resulting in dose
rates of 0.4–13 Gy/s. The operator placed his hands, head
and feet in the beam. Three months later, most of the digits
on both of the operator’s hands had to be amputated. Using
electron paramagnetic resonance (EPR) on bone samples
from the fingers, the dose was estimated to be 55 Gy [D3].
C. Summary
70. Table 3 lists 80 accidents at industrial facilities. Nine
deaths were reported in these accidents. They all occurred
at industrial irradiation facilities using high-activity sealed
sources, primarily because of improper entry into the hot
cell, and a lack or failure of safety mechanisms. At least 84
other people were excessively overexposed in these ­facilities.
In other industries, 36 workers were injured during the useof radiography sources, X-ray devices and ­accelerators, andduring manufacturing procedures. The Committee ­considers
it probable that some accidents at industrial ­facilities­involving deaths and injuries have not been reported.

Accidents involving orphan sources

71. Orphan sources are radioactive sources that were neverunder regulatory control or were under regulatory control
but then abandoned, lost, misplaced, stolen or otherwisetransferred without authorization [G1]. Orphan sources
have been the cause of serious accidents involving membersof the general public, who were entirely unaware that they
were being exposed to radiation. Table 4 summarizes key
information about 34 accidents involving orphan sources(sometimes multiple sources). Of these, 20 are describedbriefly below to illustrate some of the characteristics ofthese events.

72. Mexico, 1962. Between March and September 1962,an engineer left a 200 GBq 60Co source unprotected in theyard of a house in Mexico City. The source was found by a
10-year-old boy and subsequently taken to his home, where
it remained for approximately four months. The boy and his
sister died following estimated protracted whole-body dosesof 47 and 28.7 Gy, respectively. The children’s mother andgrandmother also died following doses estimated at 35 and30 Gy, respectively. The children’s father survived, although
he became permanently sterile, following an estimated­protracted dose of 120 Gy [M6].

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73. China, 1963. In 1963, a 60Co source with an ­estimatedactivity of 0.43 TBq was found in a lead cask by a farmer
fishing near the Anhui Agricultural Institute, locatedin Hefei City in Anhui Province. He took the source andreturned to his home. Nine days later, authorities located thesource. The six individuals living in the home were sent to a
hospital for medical assistance. Two individuals in the homereceived estimated whole-body doses of 80 Gy and 40 Gy,
and died within the following two weeks. The other fourindividuals received doses estimated at 8, 6, 4 and 2 Gy, andsurvived after medical treatment. No significant long-term
effects were noted 17 years after exposure [P1].
74. Mexico, 1973. On 24 May 1973, during the ­constructionof the refinery at Tula, in Hidalgo state, a truck was trans­
porting a container holding a 137Cs source. The container had
a “plug” made of a piece of wood. Owing to the motion of
the truck, the plug failed and allowed the source to emerge
from the container. The box that held the container had acrack, and the source fell out on to the road. A 38-year-old
bricklayer found it and took it home, carrying the source in
his trouser pocket for several hours. The dose to the thigh
was reported to be 1,386 Gy. He subsequently suffered radio­
dermatitis of the left thigh median third and the buttock. Hisleft leg was amputated from the hip down; the middle fingerof the right hand was also amputated. His family, who were
exposed to the source over three days, showed no symptomsof radiation injury [N5].
75. Algeria, 1978. In May 1978, a 925 GBq 192Ir source
used for industrial radiography fell from a truck travellingon the road from Algiers to Setif. Two young boys found thesource a few days later. Both boys handled the source, andit was eventually placed in their home. It remained there for
5–6 weeks, exposing the family to radiation under ­various
conditions depending on their location and time spent in
the kitchen. The two boys developed serious skin lesions;
their 47-year-old grandmother and four females aged 14,
17, 19 and 20 years, who spent most of their time in thehouse, were exposed to varying doses. The actual doses tothese five females were difficult to resolve, owing to many
­uncertainties, including those in the total time of exposure
per day, geometry, shielding and distance from the source
over a period of 38 days. Thus their treatment was based­primarily on haematological presentations. The ­grandmotherdied in late June 1978. The foetus of the ­pregnant 20-yearold woman also died during the haematological recovery
period of the mother, and both boys required ­surgery for
their skin injuries [J2].
76. United States, 1979. In June 1979 a worker at an industrial site in Los Angeles (Riverside), California, found alost 192Ir radio­graphy source with an estimated activity of
1.04–1.22 TBq. The worker placed the source in his right
hip pocket and left it there for approximately 45 minutes. He
subsequently developed a severe ulcerated radiation burn.
The estimated skin surface dose was 800–4,000 Gy, and the
1 cm tissue depth dose was 520 Gy to an area measuring
11 × 9 × 2 cm. At 36 days after exposure a full-thickness

myocutaneous flap, with vascular pedicle intact, was mobilized from the right thigh and sutured to the bed of theexcised ulcer. Additional surgeries were required since thelesion did not completely heal. Five other workers ­handled
the source before it was returned to the radiographer.
Four of these workers developed moderate injuries to the­fingertips. An additional five workers did not have medicallysignificant exposures [H8, R2].
77. Mexico, 1983. In early December 1983, a 60Co therapy
machine was dismantled and loaded into a pick-up truck. The
machine had been acquired in November 1977 by the Centro
Medico Hospital in Ciudad Juarez and had been in storage
since its acquisition. The source activity was about 16.6 TBq
contained in some 6,000 small pellets, each with an average
activity of 2.77 GBq. During the dismantling, the source container was punctured and a number of ­pellets (800–1,000), withan estimated activity of 1.85 TBq, were spilled into the truck’s
cargo area. The truck was later parked on a city street and was
not discovered for about seven weeks. The machine was soldat a local scrapyard and then to ­foundries in ­Chihuahua andDurango, Mexico, with subsequent ­contamination of metal.
During movement of the machine, some cobalt pellets werelost on the streets of Ciudad Juarez, in the scrapyard, along
highways and in the foundries.
78. The accident was not discovered until January 1984
when a truck loaded with contaminated rebar stopped at an
entrance to the Los Alamos National Laboratory in New
Mexico, United States, and tripped radiation alarms. An
investigation led to the discovery of the pick-up truck. No
acute effects were noted in the general population; doses
were protracted over a period of about 60 days. ­Cytogenetic
dosimetry was performed on two scrapyard employees
and eight individuals living near where the truck had beenparked. Owing to uncertainties regarding exposures of the­individuals, two mathematical models were used to ­estimate
doses. The mathematical model used to extrapolate dose
assuming acute exposure at a high dose rate resulted in­estimates of 0.09–1.91 Gy. The estimate assuming chronic
exposure at a low dose rate ranged from 0.13 to 15.16 Gy.
There were no fatalities reported following the accident [B3].
79. Morocco, 1984. In March 1984, a worker at a facility
in Casablanca took home an industrial radiography source(603 GBq of 192Ir) and placed it on a shelf near his bed. The
worker died 44 days after exposure. Over the next several
weeks, the worker’s pregnant wife and their four children also
died as a result of their exposures. After the father’s death,a cousin and his mother stayed in the house, using the room
where the source was located. These two individuals also diedas a result of their exposures. Three other persons living in
the house experienced bone marrow suppression but survived
their overexposures. Authorities recovered the source 80 days
after it was removed from the facility [M2, M5].
80. China, 1985. In April 1985, an accident occurred in
Mudanjiang when a lost source (370 GBq of 137Cs) was
brought into a dwelling where a 21-year-old man and his

ANNEX C: RADIATION EXPOSURES IN ACCIDENTS

p­ arents (the mother was 68 years old and the father 66 years
old) were exposed over a period of 150 days with ­estimated­cumulative whole-body doses of 8–10 Gy to each individual.
The father also experienced a radiation-induced burn on his
right thigh. The clinical findings upon ­hospital ­admission were­general malaise, bleeding and ­pancytopenia. The ­therapeutic­measures were bed rest, adequate ­nutrition and strict control
of infection. The father died from ­myelodysplastic syndrome
complicated by pulmonary ­fungal infection 22 months after
exposure. The other two individuals remained apparently well[Y1].
81. Brazil, 1987. In 1987, an abandoned 50.9 TBq 137Cs­teletherapy device located in Goiânia was stolen and­dismantled, and the source capsule ruptured. Over the next
two weeks, 137Cs chloride powder was spread throughout a scrapyard, surrounding homes and the vicinity. The­problem of radiation exposure was noted after numerous
individuals developed illness and skin lesions. Subsequentlya ­monitoring station was set up at a soccer stadium and
110,000 persons were monitored for contamination withradioactive material. Of these individuals, 249 were found tohave 137Cs deposits on their skin or clothing, and 129 of these
persons were found to be internally contaminated with 137Cs.
Outpatient care was provided to 79 ­individuals, while 50
required close medical surveillance. Of these ­latter patients,
14 required intensive medical care for ARS, ­internal contamination and local lesions. Four persons died, including
one child. There are 150 persons currently in a follow-up
cohort. A group of 755 professionals participated in extensive environmental decontamination. Eighty-five ­residences
required decontamination, and seven residences had to be
demolished. The total volume of waste generated for temporary storage amounted to 3,134.5 m3 and since 1987 has been
disposed in a repository [I11, I12, N8].
82. USSR, Ukraine, 1988–1991. This accident occurred
when a family consisting of a man, a woman and two­children moved to an apartment in a new complex built
200 km south-east of Kiev. After several months theolder son became ill and was found to have bone ­marrow­depression. The cause was not identified, and the boy­recovered and returned home. Over the next year the same
scenario was repeated several times, and the boy developed
osteosarcoma of the foot and died of metastatic disease. His
younger brother was then allowed to move into his bedroom,
and within several months developed severe bone marrowdepression. The younger boy also developed a necrotic lesion
on his foot. Thinking the problem was associated with theChernobyl accident, the boys’ mother requested ­authorities
to ­survey the apartment for radiation. Finally a 2.6 TBq137
Cs ­industrial source was found embedded in the wall of
the boys’ bedroom, located near the foot of the bed. How
the source came to be there was never clear. Several months
later the younger boy ­developed additional haematologicalproblems and ­subsequently died [M2, S2].
83. China, 1992. In November 1992, in Xinzhou, Shanxi
Province, a farmer was demolishing a closed irradiation

11

facility when he found a 100 GBq 60Co source contained ina ­cylindrical steel bar. The individual placed the bar in his
jacket. Later that afternoon he was sent to a local ­hospital
after ­complaining of nausea followed by vomiting. The
jacket containing the source remained with the individual
during his hospitalization. He died in early December. His
father and elder brother, who had taken care of him at the­hospital, died from exposure the following week. The­farmer’s wife also assisted in his care, and in mid-December
she requested ­medical assistance. The doctors suspected thatshe, too, was suffering from radiation exposure. Through dose­reconstruction, the farmer, his father and his brother were
estimated to have received doses of greater than 8 Gy, and thedose to his wife was estimated to be about 2.3 Gy [P1].
84. Turkey, 1993–1998. Unauthorized long-term storage(1993–1998) and subsequent transport and transfer to a newowner resulted in a loss of control over two 60Co therapy
sources in Istanbul. The packages containing the sourceswere sold as scrap. Later the shielding of one container was
opened at the scrapyard. In December 1998 ten persons fell
ill, and six experienced nausea and vomiting. The cause of
their illness was not diagnosed until four weeks later. Oncethe cause had been diagnosed, media reports caused alarm,and 404 persons applied for medical examinations. ­Eighteen
persons (including seven children) were admitted to ­hospital.
Ten of the hospitalized adults exhibited signs and symptomsof ARS. Five of these persons were hospitalized for 45 days.
One person had local injury to a finger [I7].
85. Estonia, 1994. In October 1994 in Tammiku, threebrothers entered a waste repository without authorization
and removed a metal container holding a 1.6 TBq 137Cs
source. During removal the source was dislodged and fell to
the ground. One of the men picked it up and placed it in his
pocket. Before leaving the repository, he began to feel ill. A
few hours later he began to vomit. He took the source to hishome in the nearby village of Kiisa. Subsequently he wasadmitted to a hospital with severe injuries to his leg and hip,and he died on 2 November 1994.
86. The injury and subsequent death were not initiallyattributed to radiation exposure, and the source remained in
the man’s house with his wife, his stepson and the boy’s greatgrandmother. The boy was hospitalized on 17 ­November
with severe burns on his hands, and a ­doctor ­identified theburns as being induced by radiation. The authorities werealerted, and the Estonia Rescue Board recovered the sourcefrom the house. The occupants of the house and one of
the man’s two brothers were hospitalized and diagnosedas ­suffering from radiation-induced injuries of varying­severity. All were subsequently released from the hospitaland continued to receive outpatient treatment for at least four
years. Studies conducted on other people living in the area
where the source was discovered revealed no ­symptoms ofradiation sickness [I13].
87. Russian Federation, 1995. In 1995, a 48 GBq 137Cs
source was discovered in the cabin door pocket on the

12

UNSCEAR 2008 REPORT: VOLUME IIdriver’s side of a truck near Moscow. The driver of the truck
was apparently overexposed over a period of about fivemonths. The dose rate at the left side of the driver’s seat wasestimated to be about 50 mGy/h. An estimate of the average whole-body dose of 7.9 ± 1.3 Gy was made on the basisof cytogenetic studies of chromosomal aberrations in thedriver’s blood lymphocytes. The driver was hospitalized in
Moscow in July 1995 with complaints of fatigue and shortness of breath. Epilation was evident on the lateral surfacesof the left thigh and buttock. Pancytopenia, myelodysplasia
and anaemia progressed over the next several months, eventually leading to myelomonocytic leukaemia. The individual
died 22 months after the source was discovered [B7, S7].
88. Islamic Republic of Iran, 1996. In July 1996, ­industrial
radiography was under way at the Gilan ­combined cycle­fossil fuel power plant located 600 km north of Tehran.
After making a series of radiographs, the radiography
team failed to notice that the 185 GBq 192Ir source was­m issing from the container. A 33-year-old plant employee
found the source, handled it and then placed it in his shirt
pocket, where it remained for about 90 minutes. Over the
next few weeks the irradiated individual demonstrated­haematological ­depression and was treated with anti­biotics,
platelet trans­fusions, and the haematological growth ­factor
granulocyte-colony-stimulating factor (G-CSF). He also
developed lesions to the right thorax, right elbow, rightthigh and left palmar surface. He was treated in Tehranand ­subsequently transferred to Paris for treatment of hisskin lesions. His chest and thigh lesions were successfully treated with a free graft from the undamaged thigh.
About 16 months after ­exposure, the skin lesions healed,
although there was ­thickening of the skin on the hand, slight­retraction on the right side due to the fibrotic chest graft andcontracture of the right elbow. The estimated whole-bodydose was 2–4 Gy, while the ­maximum skin doses did notexceed about 40 Gy [I21].
89. Georgia, 1996–1997. Numerous sources were­abandoned when Soviet troops turned over the Lilo ­Training
Centre to the Georgian army in 1992. From April to August
1997, several Georgian soldiers sought medical care becauseof skin lesions. After radiation injury was diagnosed,
high-activity sources were found 30 cm below the surface
of a ­soccer field, 10 cm below ground in an area used for­smoking, stored in lead containers and in the pocket of asoldier’s ­winter jacket. In addition, 200 discarded sighting
devices containing 226Ra and a 60Co source were found. In
total, 12 137Cs sources were located. Eleven persons ­sufferedlocal and systemic effects as a result of their ­exposures. The
estimated doses for protracted exposures ranged from 4.2
to 0.6 Gy. Seven patients remained under treatment in 1999
[I20].
90. Peru, 1999. In February 1999, an 192Ir industrial radio­
graphy source with an estimated activity of 1.37 TBq was lostat the Yanango hydroelectric power plant in the San Ramon
district 300 km east of Lima. A few hours later a welder
found the source and placed it in the right back pocket of

his trousers. Over the next several hours the welder worked
in a pipe and then took a minibus home. He changed clothing, placing his trousers (with the source still in the pocket)
on the floor, and sought local medical assistance becauseof pain in his right thigh. He was diagnosed with an insect
bite. Meanwhile his wife sat on the trousers while breastfeeding her 18-month-old child. Authorities recovered thesource at 1 a.m. the following morning, and the welder wastransferred to Lima for medical care. The estimated 1 cm
depth dose to his thigh was 9,966 Gy, and over the next threemonths he developed an extensive severe lesion on the rightthigh. He was then transferred to Paris for skin grafts using
porcine xenografts. The grafts failed, and the right leg was
disarticulated at the hip. Additional surgeries were required
after the welder’s return to Peru. His wife developed moist
desquamation and ulcerative and fibrotic lesions of her lower
back [I8].
91. Thailand, 2000. In 1999, unauthorized teletherapy
sources were relocated to an unsecured site in Samut Prakarn.
In January 2000, four scrap collectors gained access to thefacility, partially disassembled a teletherapy head and took
the device home for further disassembly. On 1 ­February
two of the individuals sold the components to a junk dealer.
­During further disassembly of the device at the junkyard,
the source fell out of its housing but was not noticed. By
mid-February several individuals had sought medical­attention, and suspicion of radiation injury was reported tothe authorities. The 15.7 TBq 60Co source was recovered on
20 February. Ten people were hospitalized. Three junkyard
employees died of ARS-associated ­infections in March.
Four other individuals suffered local injuries; one required
hand amputation. G‑CSF and GM‑CSF were used in the
medical management of these patients [I9].
92. Egypt, 2000. In May 2000, a farmer from Meet Halfa
village found a 1.17 TBq 192Ir industrial gamma radio­graphysource that had been lost by a worker testing pipe welds.
The farmer took the source to his home, where he lived withhis wife, a sister and four children. In the ­following weeks
the source was handled by family ­members and moved
to ­various locations within the ­family home. The 9-yearold son died in June, and death was reported to be due tobone marrow ­failure and inflammation caused by a viral or­bacterial infection. Other family members were also foundto be sick with skin lesions, bone marrow ­failure and gastro­
intestinal symptoms, but the diagnosis again was ­incorrect.
On 16 June the farmer died. On 25 June, a ­fact-finding­mission detected high radiation levels at the family home,
and the source was recovered. Family ­members were
­hospitalized with skin lesions and bone marrow depression.
G-CSF was used in their treatment. Dose estimates were:father, 7.5–8 Gy; 9-year-old son, 5–6 Gy; five other family
members, 3.5–4 Gy. Between 200 and 300 neighbours andrelatives were monitored, and the affected family received
continuing treatment and surveillance [E1, I10].
93. Georgia, 2001. In December 2001, three ­woodsmen
found two heat-emanating ceramic objects near theirANNEX C: RADIATION EXPOSURES IN ACCIDENTS

campsite in the remote Inguri River Valley of Georgia. Twoof the woodsmen carried the containers on their backs, andexperienced nausea, vomiting and dizziness within hours of
exposure. The third carried the source attached to a wire.
At a hospital in Tbilisi, the woodsmen were ­diagnosed
with radiation sickness and severe radiation burns, and at
least two of the three men were in serious condition. A
Georgian team recovered the sources in early 2002 withthe ­assistance of the International Atomic Energy Agency(IAEA). They were unshielded ceramic sources from two
Soviet-era radioisotope thermoelectric generators (RTGs),
each containing about 30,000 Ci (1 PBq) of 90Sr. Two of thepatients were treated in hospitals in Paris and Moscow forIV.

many months before recovering from their severe radiation
burns [I23].
A. Summary
94. Table 4 presents information on 34 accidents involving orphan sources. These accidents resulted in 42 early
deaths and in disfiguring injuries to both children andadults. Significant environmental contamination and theinternal contamination of 129 persons occurred in one ofthese accidents. The Committee considers it probable thatsome radiation accidents involving orphan sources and that
resulted in deaths or injuries have not been reported.

ACCIDENTS AT ACADEMIC AND RESEARCH FACILITIES

95. Table 5 summarizes information about 22 radiation accidents at academic and research facilities, seven­involving sealed radioactive sources and 15 involving
machine-­generated radiation (i.e. from accelerators and
X-ray devices). Some examples of these accidents aredescribed briefly below to illustrate the nature of these
events.
A.

13

Sealed radioactive sources

96. USSR, 1962. A 60Co source of about 1.9 PBq was used at
a research institute in Moscow for irradiating metal ­samples.
A researcher opened the locked door and entered the irradiation room, believing the time to change the ­sample would
be so short as to be not dangerous. However, she received
a whole-body dose (non-uniform) of about 2.5–3.0 Gy, and
12 Gy to her right hand. She survived a moderate ARS withmild local skin injury [G5].
97. United States, 1971. In February 1971, a 32-year-oldt­ echnician was performing seed irradiation ­experiments atthe ­Variable Dose Rate Irradiation Facility at the ­Universityof ­Tennessee Comparative Animal Research Facility in
Oak Ridge. Because of an interlock failure, the ­technician
was able to enter the facility with a 285 TBq 60Co source
unshielded. He was within 50 cm in front of an unshielded
source for about 40 seconds. When the ­technician left
the facility, the operator noticed that the source wasunshielded and ­notified the authorities. The technician was­hospitalized within two hours, and experienced episodesof nausea and vomiting starting 2.25 hours after exposureand lasting for about 24 hours. Maximum haematologicaldepression lasted from day 24 to day 34 after exposure.
The estimated whole-body and bone marrow doses were1.27 Gy and 1.18 Gy. The patient was treated with ­standard
antibiotic and haematological ­support, and returned towork 11 weeks after exposure [V2].

B.

Accelerators and X-ray devices

98. USSR, 1977. In March 1977, a 40 MeV proton­accelerator in the Institute of Nuclear Physics, Kiev, wasactivated for the first time. A physicist—who had fosteredits construction—decided to demonstrate the presence ofthe beam. He inserted a luminescent lamp by hand “into thebeam”, and it illuminated. However the physicist received anabsorbed dose within the hands’ tissues ranging from 12 Gyon the surface to more than 30 Gy at the depth of 0.5 cm
at some points. This led to a complicated clinical course of
local radiation injury to both hands, and several surgicalinterventions were performed in order to save some of thehands’ functionalities [A5, B12].
99. United States, 1977. In April 1977, a graduate student
at the ­Donner Laboratory of Lawrence Berkeley Laboratory, ­University of California at Berkeley, was conducting a
research experiment involving the effects of X-rays (about
30 kVp) on yeast cultures. On the day of the accident the­student was to expose 60 Petri dishes of yeast cultures. Aninterlock failure resulted in the student’s hands ­receiving
about 70 Gy. There was noticeable erythema within 12hours, followed by blistering and desquamation over a
period of several months. Two fingers on the left hand and
one finger on the right hand were amputated [T2, U3].
100. USSR, 1978. A powerful 70 GeV proton accelerator
was used at the Institute of High Energy Physics, ­Protvino,
for a broad spectrum of scientific experiments. In June
1978, after a long chain of procedure violations and errors,a researcher was accidentally exposed to a needle-thin beamof protons, which pierced his head from left occipital lobeof the brain to the left nostril. His middle ear was destroyed,
and facial nerve injured. He survived, and the function of
the facial nerve was restored. However, deafness in his left
ear and a scar on the left nostril remained; and brain damage
caused mild epilepsy six years later [B13].

14

UNSCEAR 2008 REPORT: VOLUME II

101. USSR, 1978. An accident occurred in an electron­linear accelerator in Leningrad, involving a 12.7 MeV ­electron
beam. A worker entered the experimental room after irradiation was complete and a timer had cut the ­voltage to the controlling electrode. She stood with her back to the exit window
and then turned 180°. It appeared that she was exposed twice
owing to so-called “dark current”, because the high voltage
to the accelerating tube was still on. The ­localized doses toher back and chest were ­estimated as more than 20 Gy and8 Gy respectively. Skin ­reactions ­corresponded to these doses;
however, signs of severe ­radiation damage to the spinal cord
appeared six months later [A5].
102. Vietnam, 1992. In November 1992, an accident­involving a research X-ray accelerator occurred at the Hanoi
Institute of Health Physics. One individual entered the irradiation room without supervision and subsequently exposed
his hands to the X-ray beam. The dose to the individual’sleft hand was estimated to be 10–25 Gy, and the whole-bodydose was estimated to be 1–2 Gy. The individual’s hands
were seriously injured, and one hand had to be amputated[I4].
103. United States, 1994. In June 1994 two ­graduate students at the University of California at Davis were ­analysing­samples using a water-cooled Enraf-Nonius X-ray ­diffraction

unit operating at 45 kVp, 25 mA, with the timer mode set
in the “continuous” position. On previous ­occasions, the­students and a faculty member had dismantled the unit toclean ­corrosion that had built up between the X-ray tube
column and the primary shutter. Procedures called forthe unit’s electrical power to be in the “off” position. The­students had, however, adopted the practice of expediting
sample changing by bypassing the cabinet door safety interlock rather than turning the power to the “off” position. This
led to significant exposure to areas of both hands of one of
the students. The skin entrance dose rate was 960 Gy/min.
The clinical course over one year after exposure included­tightness and paraesthesiae in the student’s fingers, swelling,erythema, bullae, hyperkeratosis and significant pain [B4].
C. Summary
104. Table 5 lists accidents in academic and research facilities. Twenty-two accidents have been reported in the use ofaccelerators, research reactors, radiochemistry laboratories,
small irradiation facilities, and with the use of X-ray diffraction, spectroscopy, crystallography and fluorescence units.
The hands were commonly the area injured. The ­Committee
considers it probable that some radiation accidents in­academic and research work have not been reported.

V. ACCIDENTS ASSOCIATED WITH THE MEDICAL USE OF RADIATION
105. A summary of nearly 100 radiotherapy accidents has
been presented by the IAEA [I25], and a similar number
have been reported by the International Commission on
Radiological Protection (ICRP) [I24]. Table 6 summarizes
information on 32 serious radiation accidents associatedwith the medical use of radiation. Some examples of accidents associated with the diagnostic and therapeutic usesof radioactive materials and machine-generated ionizing
radiation are described briefly below. More discussion on
accidents in radiotherapy is provided in annex A, “Medical
radiation exposures”.
A.

Nuclear medicine

106. United States, 1968. In August 1968 a 73-year-old
woman was scheduled for a diagnostic nuclear medicine
liver/spleen scan at a hospital in Wisconsin. The radio­
pharmaceutical being used was colloidal 198Au, administered intravenously. The intended activity was 7.4 MBq, but
because of an error, the patient received 1,000 times moreof the radionuclide, or 7.4 GBq. The estimated bone marrowdose was 4–5 Gy, and the dose to the liver was 70–90 Gy.
The patient died 69 days after exposure [M3].

B.

Sealed radioactive sources

107. United States, 1974–1976. This accident involved
426 patients being treated with a 60Co teletherapy unit overa 16-month period (1974–1976) at the Riverside Hospital in­Columbus, Ohio. Dose rates had been underestimated by
10–45% owing to an error in calculating the source decay
and to a lack of routine periodic calibration. Of the 183 who­survived beyond one year, 34% had severe complications,some of which led to death. Fifteen years after the accident, 18 ­individuals remained alive, with 50% experiencing
severe complications [M1].
108. France, 1981. During the initial loading of a radiation therapy device in a new radiotherapy department inSaintes, the 137 TBq 60Co source had become jammed in
the loading channel instead of being in its retracted, shielded
position. Unaware of this, an assistant operator placed hishands in contact with the device in an area where the source
was jammed. On removal of the source transport apparatus that contained a dummy source, both the dummy source
and the 60Co source fell on to the floor. Despite 25 years ofexperience, the main operator picked up the source with hisbare hands and put it in a safe position. Doses to the hands

ANNEX C: RADIATION EXPOSURES IN ACCIDENTS

of both the operator and his assistant exceeded 25 Gy at thewrists. The amputations of both hands of both victims wereunavoidable. A third operator received an unexplained highlevel exposure of one hand, leading to amputation of a large
portion of the hand [N7].
109. United States, 1992. An accident occurred in­November 1992 in Indiana, Pennsylvania, involving a female
patient scheduled for a high-dose-rate brachytherapy procedure using a 159 GBq 192Ir source. The treatment was to begiven in three fractions of 6 Gy each. During the first procedure the source broke off the guide wire and remained inside
one of the catheters surgically implanted into the patient’s
tumour. A radiological survey of the patient was not performed, and she was returned to a local nursing home. The
source became dislodged from the catheter on day 4 and was
discarded in the biohazard waste. It was discovered somedays later when a waste truck passed through a radiation
detector installed at an incinerator facility.
110. The estimated dose at 1 cm in tissue was 16,000 Gy.
Death occurred four days after the procedure, but wasthought to be associated with the patient’s disease and age.
The patient’s remains were later exhumed and an autopsy
was performed, resulting in the death certificate beingchanged to reflect death from ARS. Ninety-four additional
individuals, including staff, visitors, family members andother nursing home residents, were exposed, although thedoses were not medically significant [N4].
111. Costa Rica, 1996. In August 1996, a 60Co radio­
therapy source was replaced at a hospital in San José.
­Following the replacement, a calibration error was made.
Over the next 37 days, radiation doses 50–60% greater thanthose prescribed were delivered to 115 patients under treatment for neoplasms. These overexposures were confirmedby recalibration of the source and review of ­individual
patient charts. In July 1997, an IAEA investigation teamevaluated 70 of the 73 patients who were still living. The
team concluded that 20 patients were suffering from major
adverse effects due to their overexposures, with 26 other
patients experiencing less severe effects. Twenty-two had
no discernible effects, because of incomplete therapy. Twopatients were underexposed and three were not examined.
Seventeen deaths associated with the radiation exposures
were reported [I14, I24].
112. Panama, 2000. At the Instituto Oncológico Nacional
in Panama, a computerized treatment planning system wasused to calculate the dose distribution and determine treatment times. In August 2000, medical physicists changed themethod for entering data on shielding blocks in the computer
program in order to overcome limitations for treatments that
required more than four blocks. Soon thereafter, the radiation oncologists started to observe prolonged diarrhoea insome patients. In March 2001, physicists identified a problem
with the calculation of exposure times, and the treatment of

15

patients with abnormal symptoms was suspended. Further
studies revealed that 28 patients had received a proportionately higher dose than prescribed. Further investigations
were undertaken, although eight patients had already died.
At least five of these deaths were probably radiation related.
The 20 surviving patients were examined, and a number
were found to be suffering from bloody diarrhoea, necrosis,
ulceration and anaemia [B10, I15].

C.

Accelerators and X-ray devices

113. United States and Canada, 1985–1987. In 1985,
1986 and 1987, several serious overexposures occurred
when patients were being treated for carcinoma using a
Therac-25 ­electron linear accelerator. The device was firstmanufactured in 1982, and 12 units were in use within the
United States and ­Canada. Accidents occurred in UnitedStates hospitals located in Marietta, Georgia; Tyler,
Texas; and Yakima, Washington; as well as at a hospitalin ­Hamilton, Ontario, Canada. Control of the device wasachieved using a small digital computer. Unfortunately,
the computer had a software problem such that when thetechnician made an error in the treatment procedure, thecomputer screen displayed a “malfunction 54”, which was
the code for “dose input error”. This resulted in the patient
receiving a direct electron beam at 25 MeV.
114. Six patients were irradiated during machine malfunction and received severe burns. Two of the patients diedas a result of their injuries following therapy in Texas. In
March 1986, a 33-year-old man with a liposarcoma on his
left upper back was treated; owing to the machine malfunction, the patient experienced severe damage to the cervicalcord, resulting in death five months after exposure. In April
1986, a 66-year-old man with a multifocal skin cancer on theleft side of the face was treated during machine malfunction.
He died three weeks later from damage to the right temporal
lobe of the brain and the brain stem [N2].
115. Spain, 1990. In Zaragoza, 27 patients received higher
radiotherapy doses than those prescribed, because of a malfunction in a linear accelerator. During a repair procedure,
the electron energy of the accelerator was ­modified, and thischange was not noted by the therapists, who thought thatthe meter on the control panel was faulty. The increased
energy resulted in greater penetration of energy and effects
on deeper tissues. In addition, the electrons were focused ina smaller cross-section of the beam. This resulted in doses
three to seven times higher than intended. Patients ­developed
injuries in the lungs, pharynx and spinal cord, complicatedby vascular and skin injuries. As the victims of this malfunction were suffering severe tumours for which they werebeing treated with radiation, it is difficult to ­accurately assess
the contribution of the accident to the number of deceased.
It was estimated that 15 patients died with radiation as theprimary or major cause of death, while others had severe
disabilities [I24, S5].

16

UNSCEAR 2008 REPORT: VOLUME II

116. Poland, 2001. In February 2001, at the Bialystok
Oncology Centre, a serious accidental overexposure injured
five female patients undergoing post-operative radio­therapy
for breast cancer. The accident involved a NEPTUN 10P linear accelerator. A transitory electrical power loss occurred,and following restart of the device, the patients received
considerably higher doses than planned. Prescribed doses
were 2–2.5 Gy per fraction from an 8 MeV electron beam.
EPR assessment of rib samples resulted in dose estimates of
60–80 Gy. Medical examination revealed local injuries in
the five patients, which worsened over time. Surgical intervention was necessary in all cases. The condition of four
patients improved with the use of hyperbaric oxygen therapy[I22].
117. United Kingdom, 2006. In January 2006, a 15-yearold female patient was receiving radiotherapy for a brain
tumour at an oncology centre in Glasgow. Twenty planned
fractions of 1.75 Gy (35 Gy total) were to be delivered using
a linac system, but owing to a dose planning error undiscovered until the 19th fraction, the estimated delivered dose was55.5 Gy [J5].

VI.
A.

D.

Summary

118. Those at risk in the medical use of radiation include
patients, physicians and staff, as well as those involved inchanging sources, repairing devices, and so on. Humanerror has been a common cause of these accidents in the
medical field. Examples of errors include delivering theradiation dose to the wrong patient or to the wrong location, giving the wrong dose because of errors in treatment
planning and failure to use survey equipment/monitors as
intended. The IAEA [I25] and ICRP [I24] have catalogued
over 100 radiotherapy accidents, and table 6 lists 32 examples of serious radiation accidents in the medical field.
It is noteworthy that such accidents were sometimes notrecognized, because injuries were not always evident until
some time after a procedure, or symptoms were masked by
the severity of the underlying disease process. Both under­
exposure and overexposure to radiation have had serious
consequences. Only overexposures have been included inthis annex. The Committee considers it likely that somedeaths and many injuries in the medical use of radiation
have not been reported.

OTHER ACCIDENTS

Transport accidents

119. Millions of packages of radioactive material aresafely transported throughout the world each year. Most ofthese materials are for medical or general industrial use.
Many packages are manually handled and are transported
by road, or sometimes by air, sea or rail. Some packages
require remote handling because of their weight. Road andrail traffic is often through urban areas, and members of
the public may be in close proximity to the packages. In theevent of an accident, there could be a local release with some
atmospheric or aquatic dispersion [H1, I16].
120. Accidents do occur during transport, although any
consequences are normally limited by built-in safety ­featuresof the packages/containers and by adherence to ­regulatory
controls, including emergency response ­procedures. (See­reference [I17] for detailed information regarding ­accident
frequency, types and consequences.) A recent United­K ingdom study of accidents and incidents over the period
1958–2004 concluded that the most serious radiological consequences occurred as a result of transporting ­improperly
packaged industrial radiography sources [H10].
121. Less commonly, accidents have occurred during­military and civilian movement of radiological or nuclear
materials by aircraft, ship, submarine or spacecraft (seetable 7). These accidents have involved small nuclear­reactors, RTGs, nuclear weapons, nuclear waste and otherradioactive shipments [B1, I16, I18, T1]. A number of these

accidents have resulted in loss of life due to causes otherthan radiation. Again, consequences have been limitedby the substantial built-in safety features, by adherence tothe controls required for transport, and by the emergency
response and recovery procedures utilized.
122. Table 7 summarizes 24 accidents involving sea, air andspace vehicles. With the exception of the submarine ­accidents
in the former Soviet Union (see table 1), these ­accidents did
not lead to early acute effects of radiation exposure. Some ofthem, however, did lead to widespread dispersion of radioactive material in the environment. Military activities have
involved at least two documented serious transport accidents
that led to environmental contamination: the accidents at
Palomares, Spain, and Thule, Greenland. These accidents
were described in the UNSCEAR 1993 Report [U6]. Moredetailed information on accidents and losses in the marine
environment can be found in reference [I18].
B.

Suspected malicious act

123. While malicious acts are clearly not accidental, they
are in principle of interest for the Committee’s assessments ifthey lead to early acute health effects of radiation or to widespread significant population exposures. The ­Committee has
not reviewed such events comprehensively in the context of
this report. Nevertheless, it considered it appropriate to notea recent suspected malicious act that received much media
attention.

ANNEX C: RADIATION EXPOSURES IN ACCIDENTS

124. On or about 1 November 2006, a Russian living in the
United Kingdom was allegedly poisoned with 210Po [H9]. He
died on 23 November 2006 [H6]. The death caused widespread
public interest. An extensive public monitoring ­programme
revealed no public health consequences for open public spaces.

17

More than 700 persons in the United ­Kingdom were tested forPo ­contamination. Of these, more than 100 showed 210Po concentrations in urine indicating some contamination from theincident, but fewer than 20 had results ­indicating committed
effective doses of greater than 6 mSv [H7, U17].
210

VII. Summary
125. Early acute (deterministic) health effects of ­radiation
exposure have occurred as a result of accidents or ­malicious
acts. Some serious accidents have additionally led to­significant population exposures (at levels below that for
deterministic effects) owing to widespread dispersion ofradioactive material in the environment.
126. This annex categorizes and summarizes radiation
accidents that have resulted in early acute health effects,
deaths and/or major environmental contamination ­during
the past 60 years (tables 2–6). Selected examples of eachaccident type have been briefly described in the text to­provide insight into the nature of the reported accidents,
their medical consequences and the associated radiation
doses that resulted in injuries and deaths.
127. Table 8 presents an overall summary of the numberof accidents reported in each category over time. Table 9
presents published estimates of the collective doses for aspectrum of accidents that have led to significant population
exposures owing to environmental contamination. Table 10
presents a summary of the numbers of deaths and early
health effects that have been reported owing to radiation­accidents over the last 60 years. These summaries cannot
be deemed complete. For example, it was not possible to use
fully the summary information in table 1.
128. In more than 60 years (1945–2007) of work at nuclear
facilities there have been 35 serious radiation ­accidents
reported. Seven of these caused off-site releases of radioactive ­materials, with potential for significant ­population
exposures. Of the 35 reported accidents, 24 were in­facilities related to nuclear weapons research, ­developmentand ­production, and to the reprocessing of nuclear fuel for­weapons ­programmes. Other accidents occurred in powerreactor research, ­development and operation, and in the­reprocessing of nuclear fuel. Excluding the 1986 accident
at Chernobyl, 32 deaths are known to have occurred as aresult of radiation exposure in accidents at nuclear facilities,
and 61 workers suffered radiation injuries ­requiring medicalcare. The ­incidence of accidents in these facilities has fallen;
most of the deaths and injuries occurred in the early years of
research and development in the ­context of nuclear weapons
programmes. Only one criticality ­accident, with the death of
two workers, has occurred in the past 20 years.
129. Eighty accidents were reported at other industrial
facilities utilizing radiation sources, accelerators and X-ray

devices. Nine deaths were reported in these accidents, and120 workers were injured, with the hands being a commonsite of injury. Serious injuries frequently led to amputations.
Acute radiation syndrome developed in some injured workers, and multiple amputations were necessary in some cases.
130. Thirty-four accidents have been attributed to lost,
stolen or abandoned sources (orphan sources) since 1960.
These accidents are known to have resulted in the deathsof 42 members of the public, including children. In addition, ARS, serious local injuries, internal contamination or
psychological problems necessitated medical care for hundreds of persons. The number of reported accidents involving orphan sources has increased in the past 20 years (seetable 8). It is noteworthy that six accidents were associatedwith abandoned medical therapy units.
131. Reports of accidents in academic and researchfacilities have been rare, with 22 accidents since 1960 andonly four within the past 20 years. Most of these accidents
resulted in injuries to the hands.
132. The Committee considers that accidents associatedwith the medical use of radiation in diagnosis and treatment
may have been under-reported. There have been relatively
few reports of serious accidents, considering the extremely
large number of procedures performed annually throughout
the world (annex A). Since 1967, 32 accidents with 46 deaths
have been considered here. However, there have been a large
number (623) of persons who developed early acute (deterministic) health effects as a result of these accidents. Delays
in recognizing errors led to greater numbers of persons
being injured. The 32 accidents considered here involved
serious overexposures to radiation, but underexposures canalso have serious consequences for patients.
133. The extensive worldwide civilian transport of radio­
active materials has not resulted in any human injuries related
to radiation exposure. Accidents have occurred during military transport of radioactive materials. Some resulted in, or
had the potential for causing, environmental contamination,and some have resulted in the loss of lives (although not­necessarily because of the radioactivity). A limited numberof spacecraft carrying radioactive material have burned up
on re-entry into the earth’s atmosphere or have crashed,resulting in significant releases of radioactive material to theenvironment. However, there is no documented evidence ofanyone sustaining injury from these events.

18

UNSCEAR 2008 REPORT: VOLUME II

134. This annex does not explicitly address observable
late effects due to ionizing radiation exposure. However, for­comparative purposes, table 9 presents estimates for ­collective
doses sustained by local and regional ­populations from a­spectrum of accidents that led to dispersion of radioactive
material in the environment. One accident dominates the collective dose, namely the 1986 Chernobyl accident, on which
the Committee has prepared a dedicated annex, annex D,“Health effects due to radiation from the ­Chernobyl accident”.

remains unreported in the literature. Human error, carelessness, failure to follow procedures and safety guidelines, defective equipment or defective repair, inadequate­training, loss of control and source abandonment, and other­conditions have led to accidents in the past 60 years, and willprobably lead to accidents in the future.

135. Serious radiation accidents have been rare occurrences. Much information has been published about these
accidents, but information about some less serious accidents

136. The Committee wishes to express its gratitude for the
support provided by M.-E. Berger and E. Rochedo to thelead author, R. Ricks.

Acknowledgements

ANNEX C: RADIATION EXPOSURES IN ACCIDENTS

19

Table 1. Major types of radiation accident on the territory of the former USSR and the nature of their early effects
As recorded up to 30 June 2003 [I27]TypeRadioisotope units and their sources(total)Number of people with significant clinical symptoms
ARS severity gradeb

Number of radiation
accidents

Total(ARS + LRI)a

I

II

III

IV

Died

92

170

49

27

11

6

16

Co

17

28

15

9

6

3

3

137

Cs

19

59

13

7

1

—

9

192

Ir

60

37

54

10

3

—

—

1

Other gamma emitters

8

10

2

1

—

—

—

beta/gamma emitters

2

2

—

—

—

—

—

beta emitters

9

17

9

7

4

3

3

X-ray units and accelerators (total)

39

43

—

—

—

—

—

27

30

—

—

—

—

—

Electron accelerators

9

10

—

—

—

—

—

Proton accelerators

3

3

—

—

—

—

—

33

82

73

39

25

13

13

X-ray units

Reactors and critical fissile materials(total excluding Chernobyl accident)
Criticality

16

42

42

30

20

10

10

Reactors (other than criticality)

17

40

31

9

5

3

3

Mayak Production Association(1949–1956) with LRI

168 c

168

—

—

—

—

—

Nuclear submarine

4

133

85

29

19

12

12

Others

12

17

7

3

2

2

2

Total excluding Chernobyl accident

348 c

613

214

98

57

33

43

1

134

134

93

43

21

28

349 c

747

348

191

100

54

71

Chernobyl accident
Total

a Acute radiation syndrome (ARS) and local radiation injuries (LRI).
b ARS severity grades: I – mild, II – moderate, III – severe, IV – extremely severe.
c Each LRI case at Mayak Production Association (1949–1956) is considered as a separate accident.

Year

Accidents at nuclear facilities: Related to nuclear weapons programmes
Location

Operation/
installation

20

Table 2A.

Early

Main cause of accident
DeathsNature of exposure/health consequences

Ref.

Effects

Criticality accidents
United States:
Los Alamos, New
MexicoNuclear researchfacility

Unsafe procedure; during a critical assembly
experiment, a scientist’s hand slipped, allowing atungsten carbide brick to fall into the assembly11Experimenter received 5.1 Gy whole-body dose and died 28 days after
exposure; a guard received 0.5 Gy

[L1]

1946

United States:
Los Alamos, New
MexicoNuclear researchfacility

Unsafe procedure; a critical assembly reflected byberyllium was being demonstrated; the reflector
slipped, allowing a criticality excursion

1

6

Man performing demonstration died nine days after exposure of 21 Gy;seven others had doses of between 0.37 and 3.6 Gy

[L1]

1952

United States:
Argonne,Illinois

Nuclear researchfacility

Failure to follow operating procedure during
replacement of control rod

3

Radiation doses to four workers were 1.36, 1.27, 0.6 and 0.09 Gy

[L1]

1953

USSR:
Chelyabinsk

Nuclear research andreprocessing facility

Poor design; unfavourable geometry used for
mixing, dilution, storage, etc. of plutonium nitrate
products

2

Chief operator received 10 Gy non-uniform whole-body exposure withmaximum dose of 30 Gy to legs; survived moderate ARS, and both legs
were amputated; another worker survived moderate ARS (1.5–2.0 Gy)[G5, L1, V1]

1957

USSR:
Chelyabinsk a

Nuclear research andreprocessing facility

Poor design; accumulation of uranyl oxalate inunsafe geometry

1

5

Operator exposed for approximately 10 minutes, dose estimate was morethan 10 Gy, died 12 days after exposure; five others had ARS (2.0–6.0 Gy)
but recovered[G5, L1, V1]

1958

USSR:
Chelyabinsk

Nuclear research andreprocessing facility

Unsafe geometry during draining of uranium solution; neutron reflector contributed to criticality

3

1

Three workers died in 5–6 days; doses estimated at 40–50 Gy; a fourth
person was approximately 3 m away and survived, with continuing healthproblems and loss of eyesight[B11, G5,
K2, L1, V1]

1958

United States:
Oak Ridge,
Tennessee

Nuclear processing
facility

Valve leakage led to an unplanned transfer ofenriched uranium solution to a 55-gallon (208 L)
drum. Unsafe geometry resulted in a criticality

8

Doses of the eight injured ranged from 0.7 to 3.65 Gy; all survived

[A1]

1958

United States:
Los Alamos, New
MexicoNuclear researchfacility

Unsafe geometry occurred when plutonium solids
were washed from two vessels into one

1

Operator died 36 hours after the accident; dose to upper torso wasestimated to be 120 Gy; two others had whole-body doses of 1.34 and0.53 Gy but no ill effects

[L1]

1961

United States:
Idaho Falls, Idaho

Reactor researchfacility

Evidence suggests control rod was manually pulled
out too fast, causing power rise3
(trauma)

Two men were killed instantly from a steam explosion; a third man died
two hours later as a result of head injury

[L1]

1961

USSR:
Seversk, Siberia

Chemical processing
facility

Criticality controls were not in place during condensing and evaporation of uranium hexafluoride

1

Process operator received a dose of about 2 Gy, with mild radiation­sickness symptoms[L1, V1]

1962

United States:
Hanford,
Washington

Processing facility

Improper control of solutions led to unfavourable
geometry1

One person received 1.1 Gy

[L1]

1963

USSR:
Arzamas,
Sarov

Nuclear weapons
research facility

Violation of operating procedures

2

Two operators received doses of 3.7 and 5.5 Gy; both developed radiation
sickness but survived; four others working in adjacent areas received low
doses (0.07–0.0002 Gy)[L1]UNSCEAR 2008 REPORT: VOLUME II

1945

Year

Location

Operation/
installation

Main cause of accident

Early

Nature of exposure/health consequences

Deaths

Effects2

United States:
Wood River Junction, Rhode Island

Chemical processing
facility

Human factors; labelled bottle indicated highc­ oncentration of U; contents were transferred tovessel and unsafe geometry resulted

1

1968

USSR:
Chelyabinsk-70

Reactor

Violation of procedures; failure to reposition areflector

2

1968

USSR:
Chelyabinsk-40

Plutonium extraction
facility

Inadequate design leading to unfavourable­geometry of plutonium solution

1

1978

USSR:
Siberia

Plutonium processing
facility

Unfavourable geometry of plutonium ingots during
packaging; deficient box design

1997

RussianFederation:
Sarov

Nuclear weapons
research facility

Criticality; experimenter violated safety
requirements

Radiation dose to the operator was estimated to be 100 Gy; he died 49
hours after the accident; two individuals who entered the room received
doses of 1 and 0.6 Gy[K1, L1]

One technician received 20–40 Gy from gamma and neutron exposuresand died three days later; a second technician received 5–10 Gy and died
54 days after the excursion

[L1]

1

Shift supervisor died on day 34 after receiving whole-body dose of morethan 7 Gy and 50 Gy to the legs; the operator survived moderate ARS andsubsequently had both legs and one arm amputated[V1, V4]

1

Operator received approximately 2.5 Gy whole-body dose and 70 Gy
to the hands, he survived moderate ARS, but with amputation of both
hands; seven others received doses of between 0.05 and 0.6 Gy[B11, L1,V1]

45 Gy neutrons and 3.5 Gy gamma whole-body dose; death in 66.5 hours[I5, L1]

External gamma and beta exposure causing local and/or ARS injury

[S2]
[S2]

1

Other accidents with only on-site consequences
1951

USSR:
Chelyabinsk-40

Nuclear research andreprocessing facility

Unknown

1

1952

USSR:
Chelyabinsk-40

Nuclear research andreprocessing facility

Unknown

2

Internal contamination with tritiated water

1954

USSR:
Arzamas, Sarov

Nuclear weapons
facility

Unknown

1

210

1976

United States:
Hanford,
Washington

Research processing
facility

Chemical explosion in glovebox

1986

United States:
Gore, Oklahoma b

Uranium processing
facility

Accidental rupture of a 14 ton (1 270 kg) cylinderof UF6

1(trauma)4

Po internal exposure; ARS

[S2]

1

Worker injured by glass, nitric acid and intake of 241Am; 8.6 Gy dose tobone marrow; death 11 years later of cardiovascular disease

[H2]

7

Internal contamination of workers as well as low-level internal contamination of seven members of the public[N3]

Accidents with releases to the environment and potential public health consequences
Year

Location

Operation/
installation

Main cause and nature of accident

Ref.

1957

USSR: Mayak Complex, Kyshtym aRadiochemical plant

Overheating and resulting explosion of a storage tank led to release of 740 PBq of radioactive products

1957

United Kingdom: Windscale,
Cumbria

Graphite reactor

Overheating and fire resulted in release of 740 TBq

1986

United States: Gore, Oklahoma b

Uranium processing facility

Accidental rupture of a 14-ton (1 270 kg) UF 6 cylinder resulting in a trauma death as well as low-level contamination of sevenmembers of the public and of the environment

[N3]

1993

Russian Federation: Tomsk, Siberia

Reprocessing facility

Largest occupational group exposed were 1 920 persons involved in clean-up; build-up of gases in vessel followed by explosive
rupture and explosion of flammable cloud[I19]

I; other radionuclides also released

131

[U6]
[C2, G4,
U6, U9]21

a This accident is listed twice in this table under two categories: Criticality accidents and Accidents with releases to the environment and potentially significant population exposures.
b This accident is listed twice in this table under two categories: Other accidents with only on-site consequences, and Accidents with releases to the environment and potentially significant population exposures.

ANNEX C: RADIATION EXPOSURES IN ACCIDENTS

1964

Ref.

Year

Accidents at nuclear facilities: Not related to nuclear weapons programmes
Location

Operation/
installation

22

Table 2B.

Early

Main cause of accident
DeathsNature of exposure/health consequences

Ref.

Effects

Criticality accidents
Yugoslavia:
Vinca

Zero power reactor

Equipment failure (controls) caused nuclear
excursion

1965

Belgium:
Mol

Experimental reactor

1971

USSR:
Moscow1971

1

5

Five individuals recovered from severe cases of radiation sickness;radiation doses ranged from 2.07 to 4.36 Gy[L1, M4]

Failure to follow safety procedures, resulting in
criticality excursion

1

Technician received non-uniform exposure of 3–40 Gy, with highest
exposure to left foot; medical therapy was successful but left footrequired amputation[J3, L1, P2]

Power reactor researchfacility

Violation of operating procedures; control rods not
actuated when water was added to tank containing
fuel rods3

Three persons received whole-body doses of about 3 Gy; two of themalso received doses of about 20 Gy to the legs

[L1, V4]

USSR:
Moscow

Power reactor researchfacility

Faulty construction of the fuel assembly in the reactor; fuel rods fell into highly supercritical geometry2

2Technician received approximately 60 Gy and died in five days;s­ upervisor received 20 Gy and died within 15 days; two others received
7–8 Gy and survived with long-term health effects[L1, S2]

1983

Argentina:
Buenos Aires

Critical facility

Failure to follow procedures in removing water fromtank containing fissile material

1

Acute whole-body dose (17 Gy neutron and 20 Gy gamma); death twodays after the accident from ARS (neurological) with radiopneumonitis
in right lung

[L1, N1]

1999

Japan:
Tokai-mura a

Fuel conversion plant

Workers unknowingly added higher enriched uranium into a tank bypassing criticality controls2

Two fatalities (uneven exposures of 10–20 Gy Eq and 6–10 Gy Eq) and
one person with whole-body dose of 1.2 to 5.5 Gy Eq[A2, I6]

1

Other accidents with only on-site consequences
1977

Argentina:
Atucha1985

Czechoslovakia:
Petrvald

1989

Hungary:
Paks

Nuclear power plant

Nuclear power plant

Worker not wearing lead gloves

1

Wound contaminated with 3 800 Bq; mean beta dose of 364 Gy inperiod 1977–1985 and annual gamma dose of 0.04 Gy in 1 cm 3 of soft
tissue[U3]

Carelessness and inadequate equipment for workwith transuranics

1

Intake through wound of 600 Bq of 241Am; surgical excision of wound
and administration of DTPA

[U3]

Careless handling of detectors from reactor vessel

1

Whole-body dose of 29 mGy; 1 Gy to fingers of left hand; slight increasein chromosomal aberrations[U3]

Accidents with releases to the environment and potentially significant population exposures
Year

1979

Location

United States:
Three Mile Island,
Pennsylvania

Operation/
installation
Nuclear power plant

Early
DeathsMain cause and nature of accident

Ref.

Effects
Low water levels in reactor led to severe damage to fuel elements; 550 GBq 131I released to the atmosphere.
Limited evacuation of local population[U6, U9]UNSCEAR 2008 REPORT: VOLUME II

1958

Year

Location

Operation/
installation

Early

Main cause of accident
DeathsNature of exposure/health consequences

Ref.

Effects

1986

USSR: Chernobyl

Nuclear power plant

28 radiationinduced,
2 trauma106

Breach of operating rules and violation of safety procedures, combined with a flawed design resulted in a steame­ xplosion, fire and destruction of the reactor. Whole-body doses of 1–16 Gy and localized doses to skin among
plant staff and emergency personnel; 30 deaths; 106 others with ARS; medical treatment, including bone marrowtransplants (101 others initially examined for ARS). Significant release of radionuclides into the environment (including
1 760 PBq of 131I and 86 PBq of 137Cs). Major evacuation and relocation of populations in the area. See annex D, “Healtheffects due to radiation from the Chernobyl accident” for more details

[U7]

1999

Japan:
Tokai-mura a

Fuel conversion plant2

1

Overfilling of tank led to criticality, neutron and gamma irradiation of people in the vicinity of the facility, and a verysmall release of fission products into the air. Limited evacuation of local population[A2, I6]

a This accident is listed twice in this table under two categories: Criticality accidents and Accidents with releases to the environment and potentially significant population exposures.

ANNEX C: RADIATION EXPOSURES IN ACCIDENTS
23

Accidents at industrial facilities

Year

Location

24

Table 3.

Industrial source/
installation

Early

Main cause of accident
DeathsNature of exposure/health consequences

Ref.

Effects

Sealed radioactive sources
Worker carried a 0.5 TBq source in pocket for 18
hours

1

Whole-body dose of 0.5 Gy; maximum dose to thigh of 17 000 Gy;
both legs amputated[B6, B16]

192

Ir source

Worker picked up a source that had fallen off acamera and kept it in his pocket for two hours

1

Skin dose of 130 Gy; ulcer took one year to heal

[A3]

Germany192

Ir source

Worker carried source in jacket pocket

1

Whole-body dose of 1 Gy; maximum dose to pelvis and thigh of
40–60 Gy

[S4]

1969

United Kingdom:
Scotland192

Ir sourceRadiographer travelled with unshielded source

1

Whole-body dose of 0.6 Gy; dose to chest of 20–200 Gy; skin graft
to chest required

[H4]

1972

China:
Sichuan60

Co irradiation facility

Accidental entry into the irradiation room

Unknown

0.5–1.47 Gy whole-body exposure to workers

[P1]

1973

USSR, Moscow
area

4.2 PBq 60Co industrial
sourceOperator entered room while source was in“on” mode1

Operator survived whole-body dose of about 4 Gy

[B11]

1974

United States:
New Jersey

4.4 PBq 60Co industrial
sourceFailure to use survey meter prior to entering­irradiation room1

Non-uniform exposure estimated to be 4.1 Gy

[B2]

1975

Italy:
Brescia60
Co industrial irradiation facility

Lack of safety systems on conveyer entry point

Non-uniform exposure with mean whole-body dose of 12 Gy;­haematopoietic syndrome; death 12 days after exposure[J3, U3]

1975

USSR: Kazan

60

1975

Iraq

1976

Argentina

60

1968

India

1968

1

Co irradiation facility

Deterioration of safety system and improper actions
to regain control

2Whole-body doses of 3 and 5 Gy; dose to hands of 30 Gy and morethan 50 Gy[N10, U3]

192

Ir radiography source

Unknown

1

Whole-body dose of 0.3 Gy plus localized exposure of hand

[U3]

United States:
Pittsburgh,
Pennsylvania

192

Ir radiography source

Unknown

1

Dose of 10 Gy to hand

[U3]

1976

USSR: Moscow
region60

Co irradiation facility

Technical failure of the equipment and improper
entry

1

Whole-body dose of 4 Gy; moderate ARS

[U3]

1977

Czechoslovakia:
Pardubice192

Ir industrial irradiation
sourceTechnical failure of the equipment and improper
actions to bring source back under control

1

Whole-body dose of about 5 mGy; data insufficient for estimating
local doses; bullous dermatitis of the thumb of the right hand; plastic
surgery two years later

[U3]

1977

United States:
Rockaway, New
Jersey60
Co industrial irradiation source of 18.5 PBq

Construction in the facility, lack of safety precautions
and interlock failure

1

Whole-body dose of 2 Gy

[B2]UNSCEAR 2008 REPORT: VOLUME II

Co source

1968

Year

Location

Early

Industrial source/
installation

Main cause of accident

Ir radiography source

Operator working in a confined area held source for
90 seconds while conducting radiography on a weld

1

Equivalent whole-body dose of <0.1 Gy estimated on the basis of
cytogenetic dosimetry; radiation burns on three fingers[U3]

DeathsNature of exposure/health consequences

Ref.

Effects

192

1977

Hungary:Györ

Industrial defectoscope

Failure of equipment to withdraw source into its
container

1

Whole-body dose of 1.2 Gy; slight nausea, changes in blood andincreased frequency of chromosomal aberrations

[U3]

1977

United Kingdom

Filling gaseous tritium
light source

Broken inlet manifold led to the release and escapeof 11–15 TBq of tritium

2

Whole-body doses of 0.62 and 0.64 Gy

[U3]

1977

South Africa:
Sasolburg,
Transvaal

192

Ir source

Faulty operation of pneumatically operated container
and monitor; carelessness of operator

1

Whole-body dose of 1.16 Gy; amputation of two fingers, rib removal
and skin grafts

[U3]

1977

Peru:
Ona del Oleoducto

192

Ir source

Untrained personnel and lack of supervision;­equipment neither registered nor authorized3

Maximum doses of 164 Gy to hands; 0.9 Gy to lens of the eye; 2 Gy to
the whole body; amputation of fingers of two people and effects on
the left hand of another person

[U3]

1978

Argentina:
Buenos Aires

192

Ir industrial source

Manual handling of source

1

Dose of 12–16 Gy, causing radiation burns on two fingers of left hand

[U3]

1978

United States:
Monroe, Louisiana

192

Ir radiography source

Radiography of pipe welds on barge (off-shore
drilling)

1

Localized exposure of hand; amputation of finger

[S1]

1979

Czechoslovakia:
Sokolov

192

Technical failure of the equipment and inadequate
monitoring during and after work

1

Whole-body dose of about 5 mGy; data insufficient for estimating
local doses; bullous dermatitis of the third finger of the left hand andadjacent areas; plastic surgery two years later

[U3]

1979

France:Montpelier

192

Ir radiography source

Unknown

1

Whole-body and localized exposure; amputation of left arm

[U3]

1980

USSR:
Leningrad60

Co irradiation facility

Failure of safety device and improper entry

Whole-body dose of more than 12 Gy

[S2]

1980

China:
Shanghai60

Co irradiation facility

Entry into the irradiation chamber during power
failure and with defective interlocks

1

Whole-body dose of 5.22 Gy and localized exposure[U3, Y1]

1980

USSR

60

Co irradiation facility

Unknown

1

Dose of 50 Gy to lens of eye

[U3]

1981

Argentina:
Buenos Aires

192

Ir industrial source

Source became detached and lodged in the delivery
tube

2

Doses were not specified; radiation burns on fingertips

[U3]

1982

Norway:Kjeller60

Co irradiation facility

Failure of safety device and failure to follow
procedures

Mean whole-body dose estimated to be slightly higher than 20 Gy;
death 13 days after exposure[R1, S3]

1983

United Kingdom

Gamma radiographysourceInadvertent exposure to radiographer

1

Whole-body dose of 0.56 Gy

[U3]

1983

German Democratic Republic:
Schwarze Pumpe

192

Technical defect and inappropriate handling

1

Dose to the right hand of about 5 Gy; acute and chronic radio­
dermatitis (1st degree)[U3]

Ir industrial
radiography

Ir industrial source

1

1

25

United Kingdom

ANNEX C: RADIATION EXPOSURES IN ACCIDENTS

1977

Location

Industrial source/
installation

Early

Main cause of accident
DeathsNature of exposure/health consequences

Ref.

Effects

India:
Muland, Bombay

192

Ir radiography
projector

Operation by untrained personnel

1

Dose to the skin of 20 Gy and whole-body dose of 0.6 Gy; severed­ amage to fingers; four were amputated

[U3]

1984

Hungary:
Tiszafured

192

Ir industrial
defectoscope

Failure of equipment and careless handling of source

1

Whole-body dose of 46 mGy; 20–30 Gy estimated to fingers of left
hand; irreversible necrosis at tip of one finger, surgically removed;slight increase in chromosomal aberrations

[U3]

1984

Argentina:
Mendoza

192

Operator pushed source into camera using a finger

1

Dose of 18 Gy to finger (radiation burn on finger) and whole-body doseof 0.11 Gy

[U3]

1985

India:Yamunanager

192

Ir radiography
projector

Violation of safe working practices associated withpower failure in the workplace

2

Doses of 8–20 Gy to hands of both operators; damage to fingers; twofingers amputated from each individual

[U3]

1985

India:
Visakhapatnam

60
Co radiography
projector

Violation of safe working practices and lack ofmaintenance2

Skin dose of 10–20 Gy to operator and 0.18 Gy to an assistant;d­ amage to fingers; one finger amputated

[U3]

1986

China:
Harran60

Co irradiation facility

Power loss occurred and source was ­manuallyraised; workers entered room with source
unshielded2

Doses to workers of 3.5 and 2.6 Gy

[U3]

1986

China:
Beijing60

Co irradiation facility

Workers entered irradiation room when source wasunshielded; failed drive system; door open2

Doses to workers of 0.7 and 0.8 Gy

[U3]

1986

China:
Kaifun City

60

Co source

Accidental exposure for about 1.5–2 minutes

2

Whole-body doses of 2.6–3.5 Gy; haemopoietic type of ARS[W2, Y1]

1987

China:
Zhengzhou City

60

Co irradiation facility

Accidental entry into irradiation room, 10–15
seconds

1

Estimated whole-body dose of 1.35–1.45 Gy; anorexia and nausea
four hours later; severe damage to haemopoietic system with­relatively slow restoration of white blood cells

[Y1]

1988

China:
Liaoning

Radiography source

Workers handled source with hands

6

Local exposure of 0.1–12.6 Gy

[Z2]

1988

Czechoslovakia:
PragueManufacturing of foils
containing 241Am for use
in fire alarms

New rolling methods untested; poor radiation
protection practice1

Inhalation of 50 kBq of dispersed 241Am; hospitalization and administration of DTPA; no clinical manifestations

[U3]

1988

China:
Zhao Xian60

Co irradiation facility

Accidental entry into irradiation room, about 40
seconds

1

Estimated whole-body dose of 5.2 Gy; ARS (bone marrow syndrome);
after three years of follow-up, condition good

[U3]

1989

India:
Hazira Gujarat

192

Ir radiography
projector

Failure of safety management and improper
maintenance1

Dose of 10 Gy to fingers and whole-body dose of 0.65 Gy; radiation
burns on fingers of both hands; fingers amputated

[U3]

1989

South Africa:
Witbank,
Transvaal

192

Ir industrial radiography source

Detached source; negligence of radiographer (source
improperly attached) and failure of portable monitor
to register detached source

3

Whole-body doses to three workers were 0.78, 0.1 and 0.09 Gy;computed effective dose to the most exposed worker was 2.25 Gy;
this worker had amputation of right leg at the hip six months after
exposure and amputation of three fingers one year after exposure

[U3]

1989

China

192

Ir radiography source

Unknown1

Localized dose of 18.37 Gy

[U3]

1989

Bangladesh192

Ir source

Unknown

1

Whole-body dose of 2.3 Gy[U3]UNSCEAR 2008 REPORT: VOLUME II

1983

Ir radiography source

26

Year

Year

Location

Industrial source/
installation

Early

Main cause of accident
DeathsChina:
Beijing60

Co source

Accidental exposure to source for about four minutes

1989

El Salvador:
San Salvador

60

Co irradiation facility

Deterioration of safety system and lack of understanding of radiation hazards

1990

South Africa:
Sasolburg,
Transvaal

60
Co industrial radiography source

Source left behind after radiography work; loss
undetected because of inadequate monitoring;source handled by six people

1990

Israel:Soreq

60

Co irradiation facility

Improper entry and maintenance

1

1990

China:
Shanghai60

Co irradiation facility

Entry into the irradiation chamber during power
failure and with defective interlocks

2

1991

Belarus:Nesvizh60

Co irradiation facility

Improper entry with source exposed

1

1991

United Kingdom

Industrial radiography

Chronic incidents over 14 years

1

1992

China

Irradiation facility

1992

Switzerland

192

1993

United Kingdom

1998

Ref.

2

Whole-body doses of 0.87 and 0.61 Gy; two workers suffered mild
haemopoietic radiation sickness; recovered

[U3]

2

Three workers developed ARS after whole-body doses of 3–8 Gy;
all three had local radiation injuries; one patient had both legs
­amputated; the most seriously irradiated patient had one leg­amputated and died 197 days after exposure

[I1]

6

One individual had right hand amputated above the wrist; three others
had local radiation injuries; whole-body doses were less than 0.55 Gy[U3]

10–20 Gy whole-body dose; death 36 days after exposure; bone­marrow transplant and growth factors administered[I2]

Workers received doses of 2–12 Gy; the two who received 11 and12 Gy died

[L2, P1]

11–18 Gy whole-body dose; death in 113 days; haematopoietic growth
factor administered

[I3]

1

30 Gy to fingers, parts of two fingers amputated; estimated wholebody dose (chronic) of <10 Gy; death from acute myeloid leukaemia[U3]Power loss and safety interlocks out of order4

One worker with ARS[P1]Jammed 700 GBq source; released by hand

1

Erythema of fingers: 3.5–10 Gy[U3]Gamma radiography unit

Improper procedures

1

Overexposure caused erythema and subsequent necrotic ulceration;
hand dose of 30 Gy[U3]China:
HarbinUnknown

Safety equipment failure1

One worker with ARS

[P1]

2000

Brazil:Rio de Janeiro

60
Co industrial gamma
radiography

Exposure during a routine service

1

Serious injuries to left hand

[D1]

2006

Belgium:
Fleurus60

Malfunction of a command/control hydraulic systemand failure of safety system

1

Worker entered an irradiation area and stayed approximately 20
seconds; he developed nausea and vomiting but did not seek medical
attention until he developed massive hair loss; estimated whole-bodydose of 4.4–4.8 Gy

Ir radiography source

Co irradiation facility

1

5

ANNEX C: RADIATION EXPOSURES IN ACCIDENTS

1989

Nature of exposure/health consequences
Effects[S9]

Accelerators and X-ray devices
United States:
Lockport, NewYork

Klystron tube
X-irradiation

Shielding not in place during maintenance/repair

7

Non-uniform exposures; two individuals seriously injured, five otherswith less severe injuries

[H5]

1965

United States:
Rockford, Illinois

Accelerator (10 MeV
electrons)

Unknown1

Man received 290 Gy to right ankle, 420 Gy to right hand and 0.05 Gy
whole-body dose; amputations necessary[G2, L3]

1967

United States:
Pittsburgh,
Pennsylvania

Linear accelerator

Failure of safety interlock system

3

One individual with severe radiation syndrome and multiple­amputations; two other individuals had exposures of 3 and 1 Gy

[G2, G3]
27

1960

Location

Industrial source/
installation

Early

Main cause of accident
DeathsNature of exposure/health consequences

Ref.

28

Year

Effects

Germany

X-ray fluorescence unit

Carelessness and technical faults during repair

1

Estimated dose of 30 Gy to the fingers; reddening of two fingers tendays after exposure

[U3]

1975

Germany

X-ray equipment

Carelessness and technical defects

1

Welding seam test; estimated dose of 2 Gy to the stomach region

[U3]

1976

Germany

X-ray equipment

Inexpert handling of equipment

1

Estimated whole-body dose of 1 Gy; reddening of skin after 24 hours
and radiation after-effects

[U3]

1977

Argentina:
La Plata

X-ray crystallography

Shutter removed from crystallography set

3

Dose of 10 Gy to hands of one operator (radiation burns); doses to two
workers not specified

[U3]

1978

France:Nancy

X-ray equipment

Unknown1

Localized exposure of hand; amputation of finger

[U3]

1979

German Democratic Republic:
Freiberg

X-ray fluorescence unit

Violation of safe working practice1

Dose of 10–30 Gy to right hand and whole-body dose of 0.2–0.5 Gy;acute and chronic radiodermatitis (2nd and 3rd degree)

[U3]

1980

German Democratic Republic:
BohlenAnalytical X-ray unit

Violation of safe working practice1

Dose of 15–30 Gy to left hand; acute and chronic radiodermatitis(2nd and 3rd degree)

[U3]

1980

Germany

Radiography

Defective equipment

2

Estimated dose of 23 Gy to the hand and an effective dose of 0.2 Gy

[U3]

1981

Germany

X-ray fluorescencedeviceViolation of safe working practice1

Partial-body exposure with 20–30 Gy dose to the right thumb;­extensive tissue damage developing over several months

[U3]

1983

Germany

X-ray equipment

Defective equipment

1

Partial-body exposure of approximately 6–12 Gy to regions of thebody; localized physical changes

[U3]

1985

China:
ShanghaiAccelerator

Entry into irradiation area while main motor was
running

1

Worker incurred local radiation injury with dose of 25–210 Gy

[Z1]

1991

France:ForbachIrradiation accelerator

Exposure to dark current

3

Severe skin lesions to one worker; less serious injury to two others[C1, U3, Z3]

1991

United States:
Baltimore,
MarylandAccelerator

Exposure to dark current during maintenance1

55 Gy to fingers; most required amputation

[D3]

1992

Italy

X-ray spectrometer

Improper procedure during maintenance1

Acute radiodermatitis of fingers of both hands

[S6]

1993

United Kingdom~160 kV radiography
unit

Improper procedures

1

Erythema of hands leading to necrotic ulceration

[I26]

1994

Mexico:Lazarus Cardenas

X-ray spectrometer

Failure to de-energize device prior to repair

1

Amputation of portion of finger necessitated

[B8]

1995

Brazil

X-ray diffraction unit

Poor maintenance of device allowing open backwindow

3

Acute radiodermatitis of hands caused by low-energy X‑rays

[V3]

1999

United States

Electron beam device

Residual beam exposed operator’s hand during
manufacture testing

1

Skin dose to hand estimated to be 50 Gy[M1]

UNSCEAR 2008 REPORT: VOLUME II

1975

Table 4.

Accidents involving orphan sources

Year

Location

Operation/
installation

1960

USSR: Moscow

137

1962

Mexico:Mexico City

1963

Cs source

Early

Main cause of accident
Deaths1

60

Co source(0.2 TBq)

Unsecured source removed from site

4

China:
Hefei City, Sanli’an

60
Co source(0.43 TBq)

Abandoned source taken to farmer’s home

2

1971

Japan:
Chiba

192

Ir source

1973

Mexico:Tula, Hidalgo

137

Cs source

1975

USSR:
Sverdlovsk

60
Co medical source(17 TBq)

1977

South Africa

192

Ir source

1978

China:
Herran137

1978

Algeria

1979

Ref.

Effects[D2]

1

Family died as a result of exposure. The 10-year-old boy had a protracted(four months) exposure of 47 Gy; the 3-year-old child received a dose of
28.7 Gy, the 27-year-old pregnant mother 35 Gy and the 57-year-old grandmother 30 Gy; the father’s exposure over approximately seven months was
120 Gy and he survived

[M6]

4

Farmer’s dose was 80 Gy; source was in his pocket for approximately 52
hours; his 7-year-old brother had the source in his pocket for 18 hours,
receiving a dose of 40 Gy; both failed to respond to medical treatment; theother four people exposed had doses of 8, 6, 4 and 2 Gy and survived[P1, W2]

Lost source picked up by worker

6

Three patients had minimal blood changes and were hospitalized for twomonths; three others had ARS and local radiation injuries[H3]

Source fell out of its container in truck and was
picked up and put in pocket

1

One person suffered injury to hand, thigh and buttock, leading to amputation of left leg and one finger; estimated local dose to thigh of 1 386 Gy

[N5]

2

Driver died from very severe ARS (7 Gy) on day 33; two others (about 3 Gy)
survived moderate ARS[B11, S2]

Source picked up from factory floor and taken home

1

Burns of hands and chest; skin graft on chest required; whole-body dose of
1.1 Gy; maximum skin dose of 50–100 Gy; three individuals with low-level
symptoms[L5]

Cs source

Unused source was taken to worker’s home29

Doses of 0.01–0.53 Gy to bone marrow of individuals

[U3]

192

Ir radiographysourceSource fell out of truck and was picked up

6

One fatality (member of public); source found by boys aged 3 and 7 years;
one foetus also aborted[J2]

United States:
Los Angeles,
California

Lost 192Ir radiography source

Failure of radiographer to check source storage

5

Individual who carried source in hip pocket developed severe lesion to theright buttock from a dose at the skin surface of 800–4 000 Gy; whole-bodydose was 0.75–1 Gy; four individuals had minor skin injuries; 11 persons
were involved

[R2]

1980

USSR:
Yuzhno-Sakhalinsk

192

Ir radiographysourceTaken from improper storage by 2 children for play;
one put it in jacket pocket

1

1First boy received more than 15 Gy to the hands, and two spots on abdomen received more than 20 Gy; he died after 3 months from poor liverfunction; second boy received 8 Gy to the hand, and developed not severe
local radiation injury

[N11]

1982

China:
Hanzhong

60

Co source

Source was stolen

Not specified

Doses ranged from 0.42 to 3 Gy

[W1]

Source fell unnoticed during transport for burial

1

1

29

Whole-body dose of 14.8 Gy; maximum dose to several points of skin of
1 650 Gy; death on day 18

ANNEX C: RADIATION EXPOSURES IN ACCIDENTS

Person deliberately placed source in belt of trousers
and around body for suicide

Nature of exposure/health consequencesLocation

Operation/
installation

Main cause of accident

Cs military source

Two abandoned sources circulated among soldiers

Co medical source

Abandoned device containing the source wasdismantled by hospital patients; a man found thesource and took it home; on the next day, 11 otherpeople touched it

Early

Nature of exposure/health consequences

Ref.

Deaths

Effects

5

17

Five of the most exposed had very severe radiation injury to one or boththighs and lower abdomen (doses from 500 to 900 Gy); one died on day 26,
three others in spite of treatment within 3-4 months; the fifth died after ayear. Seventeen people developed local radiation injuries

[N11]

13

A patient who dismantled the device and the man discovering the source
received whole-body doses of 2 Gy and 6 Gy, and doses to the hands of
30 Gy and 700 Gy respectively. Both hands of the latter person were amputated. Eleven other people developed local radiation injuries to the hands

[N11]

2

ARS and local injuries

[S2]

10

Source contained 60Co in tiny pellets of 2.77 GBq each; total activity was
16.6 TBq[B3]

USSR: Azerbaijan

137

1982

USSR:
Turkmenistan

60

1982

USSR: Ukraine

137

1983

Mexico:Ciudad Juarez

60
Co teletherapy
sourceDevice disassembled and sold to a scrapyard; lackof control

1984

Morocco192

Ir radiographysource (603 GBq)

Source was taken home, kept in family bedroom
and discovered after 80 days

8

3

Protracted exposures resulted in deaths of four adults and four children(ages 4, 5, 7 and 8)[M2, M5]

1985

China:
Mudanjiang

137

Cs source

370 GBq source was found and taken home12

Accumulated local doses were 8–10 Gy; one person died after 22 months

[Y1]

1987

Brazil:Goiânia137

Cs radiotherapy
deviceAbandoned device containing caesium source,disassembled

4129

21 persons had doses in excess of 1.0 Gy (up to 7 Gy); 50 persons wereadmitted to hospital or primary care units; 79 persons received dispensarycare. ARS, skin injuries and internal contamination were problems. Local
environmental contamination occurred[I11, I12]

1988–
1991

USSR:
Ukraine137

Cs source(2.6 TBq)

Source found embedded in bedroom wall

2

1

Chronic exposure. Young boy had radiation injury of foot skin witht­ ransformation into sarcoma, and died; his 9-year-old brother had radiation
injury of the foot and bone marrow depression with transformation into
leukaemia, and died; a third person incurred mild chronic skin radiation
injury and survived[M2, S2]

1992

China:
Xinzhou

Former 60Co irradiation facility

Farmer working on the site demolishing the facility
picked up source; it went with him to the hospital3

11

14 persons were exposed to doses of >0.25 Gy; three received doses of>8 Gy and died

[P1]

1993–
1998

Turkey:Istanbul

Two 60Co medical
therapy sources

Poor source security

18

Five persons with ARS (up to 3 Gy), one with lesions on one hand

[I7]

1994

Estonia:
Tammiku

1.6 TBq 137Cs sourcefrom part of an
irradiator

Theft of source and poor source security

1

5

Whole-body exposure of up to 4 Gy, variety of localized exposures of up to
1 800 Gy

[I13]

1995

RussianFederation

137

Cs source(48 GBq)

Unshielded source in truck for approximately fivemonths1

Source located in door pocket of truck; protracted dose of 7.9 Gy(­whole-body); local dose of approximately 65 Gy; death at 22 months
after discovery[B7, S7]

1995

France192

Ir gamma radiography source

Direct handling of 1 TBq source

Erythema of hands; estimated local dose of >30 Gy[U3]

Cs source

2

1

UNSCEAR 2008 REPORT: VOLUME II

1982

30

Year

Year

Location

Operation/
installation

Early

Main cause of accident
DeathsNature of exposure/health consequences

Ref.

Effects

France137

Cs density gaugesourceUnknown1

Erythema of hands

[U3]

1996

Islamic Republicof Iran: Gilan

192

Ir radiographysourcePoor procedures; failure of lock on radiography
container

1

Labourer found source and put it in breast pocket; 2–4 Gy whole-body dose,
40 Gy to chest

[I21]

1996–
1997

Georgia:
Lilo137

Cs training
sources, 60Co
source and sighting
devices

Abandoned sources at a military training centre

11

12 sources (137Cs) were found; later 200 discarded sighting devices (226Ra)
were found; local injuries and some individuals with systemic effects

[I20]

1999

China:
Henan60

Co “ex-service”
therapy source

Source found in residence of farmer

7

Seven persons received high doses (1.0–6.0 Gy)

[X1]

1999

Peru:
Yanango1.37 TBq 192Ir source

Welder found industrial radiation source2

Source found and placed in trouser pocket; severe exposure to right thigh,perineum and hip led to amputation, colostomy; welder’s wife received
local injury while sitting on trousers containing source

[I8]

2000

Thailand:Samut Prakarn

60
Co radiotherapy
sources

Poor source security leading to three old therapy
units ending up in scrapyard

3

7

Ten persons were hospitalized; three died

[I9]

2000

Egypt:
Meet Halfa

192

Ir radiographysourceSource lost by worker testing pipe welds was foundby farmer

2

5

Abandoned source was taken home by farmer; he died 40 days later; hisson died after 30 days of exposure. Dose estimates were: father 7.5–8 Gy;
son 5–6 Gy; and five others 3.5–4 Gy[E1, I10]

2000

RussianFederation:
Samara Oblast

192

Ir radiographysourceInsufficient safety training of radiographers

3

Three radiographers received whole-body doses of 1–3 Gy; one of them had
hand burns due to localized doses of 30–70 Gy

[S8]

2001

Georgia:
Lia

90
Sr radioisotope
thermoelectric
generator

Two abandoned sources3

Woodsmen found thermally hot objects and used them as heaters. They
suffered systemic effects; two developed severe local injuries[I23, J1]

ANNEX C: RADIATION EXPOSURES IN ACCIDENTS

1995

31

Year

Accidents at academic and research facilities
Location

Operation/
installation

32

Table 5.

Early

Main cause of accident
DeathsNature of exposure/health consequences

Ref.

Effects

Sealed radioactive sources
Co source

1

Graduate student exposed to 7 TBq 60Co whole-body dose of 2.5–3 Gy;
maximum skin dose of 30 Gy[R3]Violation of safe working practices, improper entry
to irradiation room

1

Whole-body dose of 2.5-3.0 Gy and 12 Gy to the hand[G5]

Co irradiation

Equipment malfunction and operational error

1Technician was in front of unshielded source for approximately 40 seconds;
whole-body dose of <2 Gy, dose to hand of 12 Gy[V2]Sweden:Nykoping

Research reactor

Instructions for work not followed

1

Dose of 30 Gy to skin of hand; radiation burn to skin

[U3]

1979

Germany:
Rossendorf

Research reactor

Neutron activation of a sample grossly
underestimated1

Dose of 20–30 Gy to right hand; acute and chronic radiodermatitis(2nd and 3rd degree) and oedema

[U3]

1980

Germany:
Rossendorf

Radiochemicallaboratory

Defect in protective glove led to contamination with
32
P

1

Dose of 100 Gy to skin of left hand; no clinical symptoms

[U3]

1983

GermanDemocratic
Republic:
Leipzig

Radiochemicallaboratory

Explosion of vial containing 241Am solution

1

Committed effective dose of 0.076 Gy[U3]

United States

60

1962

USSR:
Moscow

60
Co source(1.9 PBq)

1971

United States:
Tennessee

60

1978

Accelerators and X-ray devices
1972

UnitedKingdom

X-ray crystallography

Shutter was removed prior to and during servicing

1

Dose to two fingers of 15–20 Gy, resulting in burns

[L4]

1974

United States:
Davis,
California

X-ray diffraction unit

Safety interlock bypassed; failure to note warning
light

2

Localized exposure of hands; one person had serious injuries

[B4]

1975

Germany

X-ray fluorescence unit

Violation of safe working practice1

Dose of 1.2–2 Gy to finger; acute radiodermatitis

[U3]

1977

USSR: Kiev

Proton accelerator(40 MeV)

Violation in beam testing examinations

1

Localized doses to hands of 12–30 Gy[A5, B12]1977

United States:
Berkeley,
California

X-ray

Safety interlock failure1

Loss of two fingers on one hand and one finger on the other hand

[T2, U3]

1978

USSR:
Protvino

Proton accelerator(70 GeV)

Improper entry to adjust sample in beam

1

Beam pierced man’s head; middle ear destroyed, facial nerve injured,­abortive epilepsy developed

[B13]

1978

United States

Accelerator

Unknown1

Localized exposure to abdomen, hands, thighs[U3]

UNSCEAR 2008 REPORT: VOLUME II

Source detached during irradiation of samples

1960

Year

Location

Operation/
installation

Early

Main cause of accident
DeathsNature of exposure/health consequences

Ref.

Effects

USSR:
LeningradElectron accelerator(12.7 MeV)

Improper entry

1

Localized doses to back and chest of more than 20 Gy and 8 Gy
­respectively. Local radiation injury of skin and spinal cord

[A5]

1981

Germany:
BerlinAnalytical X-ray unit

Violation of safe working practice1

Dose of 5 Gy to the left hand; acute radiodermatitis (1st degree)

[U3]

1982

Germany:
BerlinAnalytical X-ray unit

Violation of safe working practice1

Dose of 6–18 Gy to the right forefinger; acute radiodermatitis (2nd degree)

[U3]

1984

Peru:
Lima

X-ray diffraction
equipment

Fault of supervision, deliberate exposure from lackof knowledge of risk; equipment not registered withauthorities

6

Localized doses of 5–40 Gy to fingers; skin burns and blistering leaving
residual scar tissue

[U3]

1988

GermanDemocratic
Republic:
Trustetal

Analytical X-ray unit

Technical defect2

Maximum dose of 4 Gy to the hand of one person; acute radiodermatitis(1st degree) in one person

[U3]

1988

GermanDemocratic
Republic:
Jena

Analytical X-ray unit

Violation of safe working practice1

Dose of 3 Gy to left hand; acute radiodermatitis (1st degree)

[U3]

1992

Vietnam:
Hanoi

Research accelerator

Improper entry to adjust sample in beam

1

Individual unknowingly exposed hands; dose to left hand of 10–25 Gy, toright hand 20–50 Gy; fingers and one hand amputated; whole-body dose
estimated to be 1–2 Gy

[I4]

1994

United States:
Davis,
California

X-ray diffraction
equipment

Bypass of safety interlock to effect repair

1

Exposure of both hands with formation of bullae[B4]

ANNEX C: RADIATION EXPOSURES IN ACCIDENTS

1978

33

Accidents associated with the medical use of radiation

Year

Location

Operation/
installation

34

Table 6.

Early

Main cause of accident
DeathsUSSR: Kaluga

X-ray equipment (50 kV)

Poor maintenance

1967

India

60

Co teletherapy

Source gain during transfer

1968

United States:
Wisconsin

Nuclear medicine,1972

China:
Wukan

60

Co radiotherapy

Source fell from holder and was unnoticed
for 16 days; design of device did not meetinternational standards

United States:
Riverside, Ohio60

Co teletherapy

1975

Germany

1975

Argentina:
Tucumán

60

1977

Germany

192

1977

United Kingdom

1979

Ref.

Localized dose to face and head of more than 20 Gy.
Local radiation injury developed into atrophy and scars of face, loss ofleft eye; bone necrosis; death in year 7 of late radiation encephalitis[B14, G5]Skin dose to hand of 80 Gy[B5]Acute whole-body radiation exposure from internal source; patientdied 69 days after the misadministration[B9, M3]28

20 patients and eight workers received doses in the range
0.5–2.45 Gy[W1]

Use of incorrect decay curve, lack of periodic
calibration of output

426

Overexposure of 426 patients; dose rates had been underestimatedby 10–45%[M1]

X-ray equipment

Probable violation of safe working practice inmaintenance1

Dose in excess of 1 Gy to head and upper torso[U3]

Co teletherapy

Failure of source mechanical mechanism

2

Technician and physician both received high doses to fingers; radiation
burns on fingers[U3]

Ir radiography

Defective equipment

1

Estimated dose to hand of about 5 Gy and effective dose of 0.01 mGy;
temporary reddening of fingers[U3]

Laboratory

Accidental contamination of laboratory
workers2

Thyroid dose of 1.7 Gy to one person from a 125I intake of about 1 MBq;a low dose to another person[U3]

Argentina:
Paraná

Diagnostic radiology

Faulty wiring led to emission of X-rays when
the top of the fluoroscope was open

1

Nurse received a whole-body dose of 0.94 Gy; slight bone marrowdepression

[U3]

1981

France:Saintes60
Co radiotherapy
sourceDirect hand contact with 137 TBq 60Co source
during source loading3

Two victims had both hands amputated owing to severe injury causedby exposures estimated at >25 Gy; a third victim had a large portionof his right hand amputated

[N7]

1982

Argentina:
La Plata

X-ray therapy facility

Operator looked through window while changing tubes without recognizing system wasenergized

1

Whole-body dose of 0.12 Gy and dose of 5.8 Gy to lens of eye;c­ ataracts in both eyes

[N2]

1985

United States:
Marietta, Georgia

Therac-25 accelerator

Problem of integration of hardware andsoftware of system

1

Loss of function of one arm and shoulder

[N2]

1985

Canada:Hamilton, Ontario

Therac-25 accelerator

Problem of integration of hardware andsoftware of system

1

Severe burn on hip; patient died of cancer four months after theaccident

[N2]

1985

United Kingdom

Laboratory

Technician cut finger; poor technique

1

Technician cut his finger while wearing a glove contaminated with 125I;
sucked cut finger, which resulted in an intake of about 740 MBq and athyroid dose of 400 Gy[U3]

1974–1976

198

Au

Higher than prescribed dose administered

1

1
1

UNSCEAR 2008 REPORT: VOLUME II

1966

Nature of exposure/health consequences
Effects

Year

Location

Operation/
installation

Main cause of accident

Early
DeathsUnited Kingdom

60

Co radiotherapy

Exposure during source changing

1986

United States:
Tyler, Texas

Therac-25 accelerator

Problem of integration of hardware andsoftware of system

1986

United States:
Tyler, Texas

Therac-25 accelerator

Problem of integration of hardware andsoftware of system

1987

United States:
Yakima, Washington

Therac-25 accelerator

Problem of integration of hardware andsoftware of system; operator error

1987–1988

United States:
Maryland60

Co therapy

1988

Netherlands:
Rotterdam

1990

Ref.

[U3]

1

Loss of function of arm and both lower extremities; skin injuries;p­ eriodic nausea and vomiting; radiation-induced myelitis at C5, C6level of cervical cord; death five months after the accident

[N2]

1

Victim died three weeks after the accident; acute high dose radiation
injury to the right temporal lobe of the brain and brain stem

[N2]

1

90–100 Gy accidentally delivered to chest of patient; the patient
subsequently died of oesophageal carcinoma[N2]

Treatment planning; computer file was not
updated after source change

33

33 patients received whole-brain doses 75% greater than prescribed;
20 patients died either during or after completion of therapy[I24]

Sagittaire accelerator

Leakage of radiation during therapy

1

Severe skin reactions of thorax, head and upper arm; dose estimatedat 10–20 Gy[W3]Spain:
Zaragoza

Linear accelerator

Assumption that meter on control panel wasstuck, although electron energy had been
modified by technician

15

12

27 patients received doses 3–7 times higher than intended; 15
died with radiation exposure as primary cause; others had majordisabilities[I24, S5]

1992

United States:
Indiana, Pennsylvania

Brachytherapy source

Source dislodged; failure to check for source’s
return to shielded holder

1

Source remained in patient for four days; 94 other individuals were
exposed at the clinic, nursing home and other areas[I24, N4]

1994

United States

High-dose-ratebrachytherapy

Treatment planning errors

1

Patient was given a dose of 12 Gy to the vaginal area instead of theprescribed dose

[N6]

1996

Costa Rica:
San José

60

Co teletherapy

Error in calculating dose rate

46

Exposures were significantly higher (50–60%) than prescribed[I14, I24]

1996

Russian Federation,
Moscow

Accelerator accident

Accidental dose rate increase1

Localized dose of more than 100 Gy. Acute, high dose radiation injury
to left part of chest[B11]

Panama:Panama City

60

Co teletherapy

Misuse of treatment planning system

23

Patient doses were doubled; five died of radiation injuries; two deaths
were questionable; nine of 16 survivors had marked or catastrophic
complications[B10, I15]

2001

Russian Federation:
Nizhny Novgorod

X-ray cosmetic therapy

Systematic errors in dose rate calculations

9

Local radiation injuries to facial skin – dry and moist desquamation

[B11]

2001

Poland:Bialystok

Linear accelerator

Power failure causing equipment damage

5

Local radiation injuries were present in five patients; severely injured
patients required surgery and skin grafts

[I22]

2004

France:ÉpinalHospital/therapy

Errors in treatment planning; operator’s
instructions not in language understood

19

23 patients received overdoses (20% more than intended); onepatient died of radiation exposure; three died of severe radiationinduced complications

[A4]

2006

United Kingdom:
Glasgow, Scotland

Linear accelerator

Inexperienced treatment planner

1

Critical error made in data used during treatment delivery; 15-year-old
female was given 58% higher dose than planned

[J5]

2007

United States:
Detroit, Michigan

Gamma knife
radiotherapy

Image reversal on MRI led to wrong side ofbrain being treated1

Small area of normal brain tissue and 7% of lesion treated with 18 Gy
exposure, rather than whole lesion volume being treated

[N9]

17

5

4

35

Dose of 15 Gy to hand; erythema, blistering at two weeks

2000–2001

1

ANNEX C: RADIATION EXPOSURES IN ACCIDENTS

1986

Nature of exposure/health consequences
Effects

Summaries of sea, air and space vehicle accidents

Year

Country

Vehicle type36

Table 7.

Accident location

Identifying nameCause and result

Reference

Sea
USSR

Nuclear submarine

North-west Atlantic

K-19

Leakage in heat transfer circuit with fuel overheating; submarine towed to base[B1, I18]

1963

United States

Nuclear submarine

Atlantic (unspecified)ThresherUnknown cause; lost at sea with entire crew

[I18]

1968

USSR

Diesel submarine

Pacific near Hawaii

K-129

Submarine sank carrying two nuclear warheads that were subsequently
recovered[B1, I18]

1968

United States

Nuclear submarine

Atlantic (unspecified)

Scorpion

Unknown cause; lost at sea with entire crew

[I18]

1970

USSR

Nuclear submarine

Bicay Bay

K-8

Fire; rubber seals in hull failed and seawater entered; sank north-west of Spain[B1, I18]

1978

Unspecified

Surface vessel

South-east Barents Sea

Nikel

Lighter carrying encapsulated waste was lost at sea during storm

[I18]

1984

FranceSurface vessel

North Sea

Mont Louis

Collision of vessel and ferry; ship carrying 30 containers of <1% enriched UF 6
sank off Zeebrugge; all containers recovered

[I18]

1985

USSR

Nuclear submarine

Chazma Bay

K-431

Explosive criticality occurred during refuelling; environmental contamination in
Russia resulted[B1, I18]

1986

USSR

Nuclear submarine

North-east Atlantic

K-219

Fire and explosion damaged hull; towed to 6 000 m depth and sunk (Bermuda)[B1, I18]

1989

USSR

Nuclear submarine

Norwegian Sea

K-278

Fire in the stern compartment while submerged; submarine sank

[B1, I18]

1989

USSR

Nuclear submarine

Ara Bay

Unknown member ofNorth Fleet

Unknown problem; largest reported release of radioactive material

[I18]

1997

PanamaSurface vessel

Atlantic, Azores

MSC Carla

Three Type B packages containing 137Cs involved

[I18]

2000

Russian Federation

Nuclear submarine

Barents Sea

Kursk

Cause unknown; two seismic events occurred on the day of the accident; thesubmarine sank with 118 crew members on-board; subsequently, the reactors
on-board were found to be intact

[I18]

Air
1965

United States

AircraftNear Okinawa, Japan

Skyhawk jet

Jet carrying nuclear weapon rolled off aircraft carrier

[I18]

1966

United States

Aircraft

Palomares, Spain

Bomber (B-52)

Aircraft collision during refuelling; four nuclear weapons involved; two recovered
intact, two destroyed on impact with land; significant ongoing plutonium­contamination of the environment resulted

[I18]

1968

United States

AircraftThule, Greenland

Bomber (B-92)

Aircraft crashed; four nuclear weapons destroyed, spreading plutoniumc­ ontamination over large area of marine environment

[I18]

1987

USSR

Aircraft

Sea of Okhotsk

Helicopter emergency resulted in drop of RTG equipped with 90Sr source (12.95–
25.3 PBq) at sea in 30 m of water; attempts to locate it have been unsuccessful

[I18]

1997

Russian Federation

Aircraft

Sea of Okhotsk

Helicopter emergency resulted in disposal of RTG containing 1.3 PBq 90Sr

[I18]

UNSCEAR 2008 REPORT: VOLUME II

1961

Year

Country

Vehicle type

Accident location

Identifying nameCause and result

Reference

Space vehicle
United States

SpacecraftWest Indies Ocean

SNAP-9A Transit-5BN3

Satellite containing 630 TBq of 238Pu failed to achieve orbit and vaporized during
re-entry in the Southern Hemisphere

[I18]

1968

United States

Spacecraft

Santa Barbara, California

Nimbus BI

Spacecraft failed to achieve orbit; two RTGs recovered intact

[I18]

1970

United States

Spacecraft

South Pacific

Apollo 13

Malfunction in oxygen supply led to emergency return to Earth in the lunar­landing module; an RTG on-board re-entered intact and is at a depth of not lessthan 6 000 m in the Tonga Trench

[I18]

1978

USSR

Spacecraft

Northern Canada

Cosmos 954

Research satellite carrying small nuclear reactor re-entered atmosphere andspread radioactive fragments over wide area

[I18]

1983

USSR

Spacecraft

South Atlantic

Cosmos 1402

Satellite failed to boost nuclear reactor into higher orbit after completion of mission; reactor core and fission products re-entered atmosphere east of Brazil

[I18]

1996

United States

Spacecraft

Pacific Ocean

Mars 96

Unsuccessful burn of booster resulted in re-entry into Earth’s atmosphere westof Chile; 18 RTGs onboard with total 238Pu activity of 174 TBq[I18]

ANNEX C: RADIATION EXPOSURES IN ACCIDENTS

1964

37

38

UNSCEAR 2008 REPORT: VOLUME IITable 8. Number of accidents resulting in early acute health effects or significant population exposures
Based on published information; excludes malicious acts and nuclear testingType of accident

1945–1965

1966–1986

1987–2007

Accidents at nuclear facilities

19

12

4

Industrial accidents

2

50

28

Orphan source accidents

3

15

16

Accidents in academic/research work

2

16

4

Unknown

18

14

Accidents in medical use aa The IAEA [I25] and ICRP [I24] have reported more than 100 accidents in radiotherapy. This table considers only serious radiation accidents in medicine.

Table 9. Estimated collective doses for a spectrum of accidents increasing population exposure
Not comprehensive, an illustrative selection; excludes malicious acts and nuclear testingYear

Accident

Local and regional collective effective dose (man Sv)
320 000 a

1986

USSR: Chernobyl (see annex D)

1964

SNAP-9A [U6]1957

United Kingdom: Windscale, Cumbria [U6]

2 000

1957

USSR: Mayak Complex, Kyshtym [U6]

1 200

1983

Mexico: Ciudad Juarez [U6]

150

1987

Brazil: Goiânia [U6]

60

1979

United States: Three Mile Island, Pennsylvania [U6]

40

1966

Spain: Palomares [U6]

3

1999

Japan: Tokai-mura<0.6 c1993

Russian Federation: Tomsk, Siberia [I19]0.02 b

a Sum of collective dose estimates for 1986–2005 for evacuees and inhabitants of Belarus, the Russian Federation and Ukraine, and of the rest of Europe (annex D) multipliedby 1.25 to take account of dose yet to be delivered. The 61 000 man Sv received by the recovery workers is not included here.
b Estimated collective dose to the recovery workers was 13.3 man Sv [I19].
c Based on reference [M7].

Table 10.

Numbers of deaths and early acute health effects due to radiation accidents

Based on published information; excludes malicious acts and nuclear testingType of accident
Accidents at nuclear
facilities

1945–1965

1966–1986

42 early effects
13 deaths

Industrial accidents

8 early effects

Orphan source accidents

61 early effects

5 early effects

Accidents in medical use

205 early effects

22 early effects

308 early effects
42 deaths

5 early effects
0 deaths

470 early effects
4 deaths

119 early effects
9 deaths

16 deaths

0 deaths
Unknown

Unknown

51 early effects

98 early effects

2 early effects
0 deaths

167 early effects
50 deaths

6 deaths

19 deaths

Total

2 early effects
3 deaths

3 deaths

7 deaths
Accidents in academic/
research work

123 early effects
34 deaths

0 deaths

1987–200729 early effects
0 deaths

153 early effects
42 deaths

623 early effects
46 deaths

ANNEX C: RADIATION EXPOSURES IN ACCIDENTS

39

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ANNEX C: RADIATION EXPOSURES IN ACCIDENTS

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Corrigendum to Sales No. E.11.IX.3

18 May 2016

Sources and Effects of Ionizing Radiation: United Nations
Scientific Committee on the Effects of Atomic Radiation
2008 Report
Volume II
Annex D (Health effects due to radiation from the Chernobyl accident)
Corrigendum
1.

Page 55, figure V, heading

For references in the heading of the figure, for [I14, K22, K25, L4, Z4] read
[K8, L4, R6, Z4]
2.

Page 182, footnote 1
For kBq/km 2 read kBq/m2

3.

Page 183, paragraph D251
The fourth and final sentence of the paragraph should readThis is the position formulated by UNSCEAR in annex G, “Biological effectsof low radiation doses”, of the UNSCEAR 2000 Report [U3], which states“For most tumour types in experimental animals and in man a significant
increase in risk is only detectable at doses above about 100 mGy.”

V.16-02701 (E)*1602701*

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. 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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

64
64
65
65
66

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

Table 2.

UNSCEAR 2008 REPORT: VOLUME II

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Figure 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 Federationand Ukraine [K8, L4, R6, Z4]

District average
thyroid doses (Gy)<0.01
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

Ukraine
Kiyev

Orel

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

0.01–0.03

Zhytomyr55

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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

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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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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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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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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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UNSCEAR 2008 REPORT: VOLUME II

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

74

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.

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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

82

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

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

Borisov

Baranovichi

R

I
R

U

S

Kirov

I

O

PlavskMtsenskEfremov

OREL

Desna

Soligorsk

YeletsNovozybkov

Sosna

Pinsk
Mozyr

Pr i p y at

Khoyniki
Braginod

Narovlya

Shostkakh

CHERNIGOV

Goryn

Seym

Slavutich

Des

na

SUMY

re

Ps e lv

BELGORODTe

te

Novograd Volynskiy

KIEV

ZHITOMIR
Berdichev

TernopolU
Belaya Tserkov

Rosk aKhmelnitskiy

VINNITSA

Dn

ep

r

CHERKASSY

K

R

A

I

Vo r s k l arSty

PripyatPolesskoje
Chernobyl
Narodichi’

Sto

OvruchKorosten

ROVNO

KURSK

Oskol

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

Sarny

Novomoskovsk
Kimovsk

Lyudinovo

BRYANSK

GOMEL

TULA

N

Bolkhov

Bobruysk

SlutskN
T

Dyatlovo

Krichev

Cherikov

Bykhov

A
A

a

A

S
E
Roslavl

MOGILEV

Berezina

L

S
D

POLTAVANE

KHARKOV-2

1 480–3 700 kBq m

555–1 480 kBq m-2

185–555 kBq m-2

37–185 kBq m-2

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

Novogrudok

E

U
E

So

MINSK

R
F

Aleksin

KALUGA

Ok

Lida

Gorki

SMOLENSK

pr

ka

ORSHA

Molodechno

B

e
Dn

O

VILNIUSzh

Figure A-II.

<37 kBq m-2

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
103

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UNSCEAR 2008 REPORT: VOLUME II

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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UNSCEAR 2008 REPORT: VOLUME II

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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(a)

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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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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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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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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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

122

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.

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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
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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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UNSCEAR 2008 REPORT: VOLUME II

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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UNSCEAR 2008 REPORT: VOLUME II

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.
1.
(a)

UpdateRegistration 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. Registration of mortality and diseasein the general population(a) 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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UNSCEAR 2008 REPORT: VOLUME II

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) ssessment of current evidence of risk for the emergencyAand 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. Leukaemia(a)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

UNSCEAR 2008 REPORT: VOLUME II

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

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

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 the­follow‑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) ther recent studies of low‑dose radiation exposure andOcataracts

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

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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/m2 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
morbid-ity and mortality due to radiation exposure ofcohorts of individuals with an acute average dose of
the order of 100 mSv and above. So far, neither themost informative LSS study nor any other studies haveprovided conclusive evidence of carcinogenic effects ofradiation at smaller doses. This is the position
formulated by UNSCEAR in annex G, “Biological effectsof low radiation doses”, of the UNSCEAR 2000 Report[U3], which states “For most tumour types in experimental
animals and in man a significant increase in risk is only
detectable at doses above about 100 mGy”.
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 effect 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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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

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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

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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

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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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ANNEX E
effects of ionizing radiation
on non-human biota
Contents
Page

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 A. Background. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 B. Scope of annex. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 C. Effects of exposure to ionizing radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
1. Individual level effects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
2.	Population and ecosystem level effects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
3. Multiple stressors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
4. Commentary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 D. Observations from case studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 E. Structure of this annex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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I. ESTIMATING doseS to non-human biota. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 A. Assessing exposures of biota. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
1. Choice of reference organisms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
2. Radioecological models. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
3. Transfer of radionuclides in the environment and resulting exposures. . . . . . . . . . . . . . . . . . . . . . . . .
		 B. Transfer of radionuclides in the terrestrial environment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
1. Dry deposition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
2. Interception of radionuclides deposited from the air. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
3. Weathering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
4. Distribution of radionuclides within plants. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
5. Uptake of radionuclides from soil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
6. Migration in soil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
7. Resuspension. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
8. Transfer to animals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 C. Transfer to freshwater organisms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 D. Transfer of radionuclides to marine organisms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 E. Evaluating doses to biota. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
1. Fraction of radiation absorbed by organism. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
2.	Principal relationships for internal and external exposure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
3. Doses to non-human biota. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
4. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

229
229
229
230
231
232
232
233
233
233
233
236
237
237
238
241
242
242
244
253
254

II. Summary of dose–effects data from the UNSCEAR 1996 Report. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 A. Dosimetry for environmental exposures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 B. Effects of radiation exposure on plants and animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
1. Terrestrial plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
2. Terrestrial animals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
3. Aquatic organisms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

255
255
258
259
260
261

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		 C.
		 D.

Effects of radiation exposure on populations of plants and animals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261
Effects of major accidents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262

III. Summary of dose–effects data from the Chernobyl accident. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 A. Radiation exposure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 B. Effects of radiation exposure on plants. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 C. Effects of radiation exposure on soil invertebrates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 D. Effects of radiation exposure on farm animals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 E. Effects of radiation exposure on other terrestrial animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 F. Effects of radiation exposure on aquatic organisms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 G. Genetic effects in animals and plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 H. Overall observations on the effects of the Chernobyl accident. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

263
263
263
265
265
266
266
268
269

IV. Effects of radiation EXPOSURE on NON-HUMAN BIOTA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 A. Overall conclusions of the UNSCEAR 1996 Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 B. Evaluations since 1996. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
1. United States Department of Energy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
2. Canada. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
3. FASSET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
4. ERICA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
5. Observations from recent literature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
			
6. Effects on populations and ecosystems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

272
272
273
273
274
275
278
282
288

V. summary and conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 A. Estimating dose to non-human biota. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 B. Summary of dose–effects data from the UNSCEAR 1996 Report. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 C. The current evaluation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
		 D. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

291
291
292
293
294

ACKNOWLEDGEMENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297

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Introduction
A.

Backgroundharm. Furthermore, it also concluded that it was unlikely thatradiation exposures causing only minor effects on the most
exposed individual member of a population would have significant effects at the population level; that chronic exposures to low-LET radiation at dose rates of less than
100 mGy/h to the most highly exposed individuals would be
unlikely to have significant effects on most terrestrial animal
populations; and that maximum dose rates of 400 mGy/h toa small proportion of the individuals in aquatic populationsof organisms would not have any detrimental effects at the
population level.

1. The estimation of human exposure to ionizing radiationfrom radionuclides of natural and artificial origin is an important and ongoing function of the Committee. The Committee
has used simplified generic models of the dispersion andtransfer of radionuclides through the environment to estimate
the internal and external exposure of humans and the resulting doses. Owing to the complexity and interactions of theunderlying processes, special attention has been given toradionuclide transfer via human food chains and the assessment of ingestion doses. The underlying model assumptions
and parameters are kept under review and revised as necessary. The last revision was documented by the Committee inannex A, “Dose assessment methodologies” of the UNSCEAR
2000 Report [U3].

4. The International Commission on Radiological Protection (ICRP), the International Atomic Energy Agency(IAEA) and other international organizations have encouraged the exchange of information on the effects of radiation
exposure on non-human biota [I19, N6]. The IAEA’s action
plan on the protection of the environment was discussed atthe 2003 Stockholm Conference [I1], which concluded that
“While accepting that there remain significant gaps inknowledge and that there needs to be continuing research …
there was an adequate knowledge base to proceed and (theConference) strongly supported the development of a framework for environmental radiation protection”. It also foundthat “the time is ripe for launching a number of international
initiatives to consolidate the present approach to controllingradioactive discharges to the environment by taking explicit
account of the protection of species other than humans”.

2. In the past decades, scientific and regulatory activities
related to radiation protection focused on the radiation exposure of humans. The prevailing view has been that, if humans
were adequately protected, then “other living things are also
likely to be sufficiently protected” [I8] or “other species are
not put at risk” [I5]. Over time, the general validity of thisview has been questioned on occasion and therefore consider­ation has been given to the potential effects of exposure toionizing radiation of non-human biota. This has occurred, inpart, as a result of the increased worldwide concern over thesustainability of the environment, including the need to maintain biodiversity and protect habitats and endangered species[U22, U23]; in part, because it has increasingly been recognized that the exposure scenarios and pathways for assessing
human exposure may not apply to non-human biota; and, inpart, as a result of various efforts to assess the effects of exposure to ionizing radiation on plants and animals [C1, D1, F5,
I1, I2, I3, I4, I9, N6, P13, R9, T1, W16].

5. In 2000, the ICRP, recognizing that environmental protection is a global matter, set up a Task Group to examine
the issues. It considered that an approach to environmental
protection from ionizing radiation “should relate as closely
as possible to the current system for human radiologicalprotection, and that these joint objectives could therefore
best be met by the development of a limited number of Reference Animals and Plants” [I9]. Subsequently, the ICRP
decided to establish a new Committee (ICRP Committee 5)on the Protection of the Environment. The ICRP further
noted that “as radiation effects at the population level—or
higher—are mediated via effects on individuals of that population, it seems appropriate to focus on radiation effects on
the individual for the purpose of developing a framework ofradiological assessment that can be generally applied toenvironmental issues” [I10].

3. The Committee initially addressed the effects of radiation exposure on plant and animal communities in a scientific annex, “Effects of radiation on the environment”, of the
UNSCEAR 1996 Report [U4]. Prior to this, the Committee
had considered living organisms primarily as part of theenvironment in which radionuclides of natural or artificial
origin may be present and contribute to the internal exposureof humans via the food chain. Like man, however, organisms
are themselves exposed internally to radiation from radio­
nuclides that have been taken up from the environment andexternally to radiation in their habitat. In general terms, theCommittee, in its 1996 report, considered that populationlevel effects were of primary interest and, of those, that
reproductive effects were the most sensitive indicator of

6. Since the preparation of the UNSCEAR 1996 Report[U4], the approaches to evaluating radiation doses to nonhuman biota have been reviewed and improvements made[C1, E1, F1, F5, U26]. Information on the levels of radiation
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exposure below which biological effects are not expected or,alternatively, above which such effects might be expected,
has been developed. This has been obtained, in part, for the
projects on the Framework for Assessment of Environmental
Impact (FASSET) [F1] and the Environmental Risk from
Ionising Contaminants: Assessment and Management(ERICA) [E1], in particular, as part of the development of
the FASSET Radiation Effects Database (FRED) [F3]. This
information was subsequently integrated with the databaseon the effects of radiation exposure from the project on Environmental Protection from Ionising Contaminants in the
Arctic (EPIC) [B26] resulting in the so-called FREDERICA
database [F20].
B.

Scope of annex

7. The scientific information given in the FRED [F20]combined with that obtained in the subsequent ERICA programme [G11, J6] and that from more recent studies, especially those undertaken around the site of the Chernobyl
accident, provided the basis for the Committee’s review ofthe effects of exposure to ionizing radiation on non-humanbiota given in this annex. In particular, the Committee used
the information from its review to re-evaluate its recommendations on dose rates below which exposure to ionizing
radiation is unlikely to result in detrimental effects on populations of non-human biota, given in the UNSCEAR 1996
Report [U4].
8. This annex only provides the Committee’s overview of
the current data and methods to assess doses to non-humanbiota and a brief discussion of the nature of effects of­radiation exposure on individual organisms and populations.
Detailed discussion of these topics is beyond the scope of
this annex.
C.

metabolic impairment and changes in genetic diversity)
can be traced to events at the cellular or subcellular level in
specific tissues or organs.
1.

Individual level effects

11. Even though mutational events in somatic cells are primarily responsible for cellular transformation and tumour
formation, the occurrence of cancer in individual organisms
is normally of low relevance to the ecosystem as a whole,
except in the case of endangered or protected species [A13].
However, mutational effects in germ cells may lead to reproductive impairment [A14]. Genotoxic stressors, including
ionizing radiation, may alter reproductive success bydecreasing fertility via clastogenic and mutagenic effects ingerm cells resulting in a decrease of the number of gametes.
Such stressors may also increase the frequency of developmental abnormalities, e.g. when mutations are induced ingerm cells and the progeny of exposed parents develop
abnormally.
12. There are a number of weaknesses in the data on which
to base estimates of the dose rates below which effects on
non-human biota are not considered likely. In addition,
there are also issues in extrapolating from the effects
observed at cellular and subcellular levels to effects thatmight be observed in individual organisms, populations andeco­systems. Moreover, it is only under controlled conditions in the laboratory that organisms can be exposed to asingle stressor. This presents a further source of uncertainty
in extrapolating the results to real ecosystems where multiple stressors exist. Although beyond the scope of this annex,
the Committee acknowledges that improved understandingof the mechanisms of radiation damage, of how to extrapolate information from lower to higher trophic levels, and of
the possible consequences of multiple stressors is of great­interest and worthy of further study.

Effects of exposure to ionizing radiation

9. Since the preparation of the UNSCEAR 1996 Report[U4], a number of radiobiological phenomena have been
described, including genomic instability (genomic damage
expressed post irradiation after many cell cycles) and the
bystander effect (whereby non-irradiated cells in proximity
to irradiated cells exhibit effects similar to those seen in theirradiated cells). These phenomena were discussed inannex C, “Non-targeted and delayed effects of exposure toionizing radiation”, of the UNSCEAR 2006 Report [U1].
While such phenomena are relevant to understanding mechanisms for the development of effects on non-human biota
after exposure to ionizing radiation, a discussion of suchphenomena is beyond the scope of this annex.
10. The immediate effects of ionizing radiation exposure
may be seen at various levels of organization from the subcellular through individual organisms to populations andecosystems [G16]. Responses of various biological functions to radiation exposure (e.g. reproductive success,13. The scientific literature provides many examples ofadaptive responses to and hormetic effects of exposure toionizing radiation. Annex B of the UNSCEAR 1994 Report[U5] provided a comprehensive discussion of adaptive
responses. In that report, the Committee concluded that there
was evidence of an adaptive response in selected cellular
processes following exposure to low doses of low-LET
radia­tion but went on to suggest that it was premature to conclude that adaptive cellular responses had beneficial effects
that outweighed the harmful effects of exposure. Subsequent
to the UNSCEAR 1994 Report [U5], there have been numerous papers and considerable discussion concerning the­possibility of hormetic responses to low doses of gamma
radiation. For example, Boonstra et al. [B39] reported possible hormetic effects of gamma radiation exposure on populations of meadow voles. These authors suggested that
increases in glucocorticoid levels associated with chronic
gamma irradiation at a rate of about 1 mGy/d may be an
important factor in the increased longevity of exposed
meadow voles compared to non-exposed ones. Mitchel et al.

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

[M9] found that a single dose of 10 mGy to radiation-­
sensitive mice (Trp53 heterozygous) reduced the risk of both
lymphoma and spinal osteosarcoma by greatly delaying theonset of malignancy. Further discussion of adaptive
responses and potential hormetic effects of low dose and low
dose-rate gamma radiation exposure is beyond the scope of
this annex.
14. The various life stages of organisms differ in their sensitivity to exposure to ionizing radiation. It is often assumed
that a population will be protected if the most sensitive
stage of the life cycle is protected. For a large number ofstressors, this assumption seems to be widely true [F9].
However, the most sensitive life stage is often difficult to
identify a priori. Consequently, if data on effects only exist
for one or two life stages, it may not be possible to know for
certain if these data represent information for the most sensitive life stage, even though most of the available infor­
mation indicates that gametogenesis and embryonicdevelopment are among the most radiosensitive stages ofthe life cycle [I4]. For example, Anderson and Harrison[A15] showed that the synchronous spawning in polychaete

225

worms rendered the organisms susceptible to low-level
cumulative impact of ionizing radiation exposure. Because
they spawned synchronously and died, oocytes were formed
all at once, and damaged gametes could not be replaced.
15. The propagation of effects on individuals to the population as a whole depends greatly on the characteristics of thespecific life history. The relative importance of each stage inthe life history also varies between species, depending on thespecific reproductive characteristics (short generation time
versus long generation time, iteroparous versus semelparous, sexual versus asexual reproduction, etc.). Changes inthe value of an individual parameter such as age of reproduction (i.e. generation time) often have much stronger consequences for species with fast population growth rates (i.e.
with short generation time and high fecundity rate) than for
those with slow population growth rates [G3]. On the other
hand, the National Council of Radiation Protection andMeasurements (NCRP) [N8] noted that when natural causesof deaths are considered collectively on a biologically comparable time scale, natural mortality occurs at a biologicallycomparable age, as illustrated in figure I.

Figure I. Cumulative survival curves of the mouse, beagle and human for natural causes of death

CUMULATIVE SURVIVAL

1.0
Human

0.8
Beagle

0.6
0.4
0.2

Mouse

0
100

300

1 000

500
1 100
700
900
AGE AT DEATH (mouse days)

1 300

1 500

5 000

6 000

7 000

2 000

3 000

4 000

AGE AT DEATH (dog days)
20

40

60

80

100

120

AGE AT DEATH (human years)

2. Population and ecosystem level effects
16. Whatever the stressor considered, population-level
effects are valuable indicators of ecological hazard (e.g.
[F9]). However, because of experimental constraints, mostavailable data describe the effects on the individual traits ofirradiated organisms. Many studies have documented theeffects of radiation exposure at the cellular, tissue and individual levels. The consequences have been found to be

increases in morbidity and mortality, decreases in fertility
and fecundity, and increases in mutation rate [W10]. Thesetypes of effect, observed at the individual level, may haveconsequences for a population of a species.
17. Matson et al. [M12] and Baker et al. [B29] investigatedthe possible genetic and population effects resulting fromthe chronic radiation exposure of bank voles, Clethrionomys
glareolus, inhabiting contaminated sites near Chernobyl.

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UNSCEAR 2008 REPORT: VOLUME II

Both groups reported that genetic diversity was elevated in
the contaminated sites when compared to relatively uncontaminated sites but were unable to attribute any significant
detrimental effects among the bank vole populations to­radiation exposure.
18. Ionizing radiation does not appear to have any direct
effects at the population or higher ecological levels (i.e.
community or structure and function of ecosystems). At
present, it appears that all such effects are mediated byeffects at the individual or lower levels. In addition, indirect effects through food-web mediated processes may
occur [G16]. One approach to extrapolating from theeffects on individuals to effects at the population level is tointegrate the effects on survival and reproduction in termsof population growth rate. Population growth rate is one of
the most important characteristics of a population and isdefined as the population increase per unit time divided by
the number of individuals in the population. Population
models are used to extrapolate from the toxic effects on
individuals, expressed as modifications to values of lifecycle parameters, to effects at the population level. Thismethod has been used, for example, by Woodhead [W10]in a theoretical way and was implemented through experiments within the ERICA project for the chronic exposureof two invertebrates exhibiting contrasting life cycles: theearthworm and the daphnid [A26, G3].
19. An ecosystem has complex interactions between biotic
and abiotic components and among biotic components. The
latter are called interspecific interactions and include competition, predation and association. These interactions contribute to the flow or cycle of energy, materials and informationin the ecosystem, and thus provide the ecosystem with its
fundamental property of self-organization. It is possible that
if one species is directly damaged by a toxic agent, anotherspecies more resistant to that agent is also indirectly affectedby the depletion of interactions with the directly damaged
species. As a result, the entire ecosystem can be affected in
extreme cases. These indirect effects have been observed inecosystems exposed to ultraviolet radiation [B37] and somechemicals [C23, H24, M24, T24, W20]. Similarly, someindirect effects through inter-species interactions have been
observed in irradiated ecosystems, as reviewed in the
UNSCEAR 1996 Report [U4]. Given this backdrop, theimportance of indirect effects has been considered in reviewsof the effects of exposure to ionizing radiation on ecosystems [B38, C21, I2, I3, I4, N1, U4]. Since these indirect
effects cannot necessarily be deduced from effects on individuals and populations, ecosystem-level effects are evaluated using mathematical modelling, model ecosystem
experiments and field irradiation experiments.
3.

Multiple stressors

20. In general terms, the modifying effects of multiple
stressors can be considered in one of two broad categories,
namely (a) the modification by the other stressors of theorganism’s uptake of radioactive material and the distribution of radioactive material within the organism, and (b) the
influence of the other stressors on the radiosensitivity of thespecies [A18, B28, F5, G18, L8, P9, R19, S17, S18].
21. Metabolic manifestations of exposure to ionizing radiation include impairment in enzyme function, altered protein
turnover, impairment in general metabolism and inhibitionof growth. Sugg et al. [S17] showed that the body conditionof largemouth bass exposed to mercury and 137Cs in different
lakes near the Savannah River site could be related to DNA
damage. Changes in lipid metabolism in fish liver and astimulation of the ventilation rate of a lamellibranch species
have also been shown to occur at low doses in this mixed
exposure scenario [P22, P23].
22. Experiments involving multiple exposures to metals(cadmium and zinc), organic pollutants, such as polychlorinated biphenyl (PCB), polycyclic aromatic hydrocarbon(PAH), endocrine disruptors, and radionuclides (radioactive
isotopes of cobalt, caesium, and silver) have been conductedboth under controlled conditions and in the field [G17].
Experiments using a freshwater bivalve (Dreissena polymorpha) and a carnivorous fish (Oncorhynchus mykiss)
exposed under chronic conditions to water containing concentrations of 1–4 µg/L of cadmium and/or 170–250 µg/L ofzinc showed a 60% decrease in the bioaccumulation of theisotopes of silver and caesium in the bivalve and a 30%
decrease in the fish. However, no effect was observed forother radionuclide/organism pairs (such as cobalt for thefish). On the other hand, prior exposure to organic micro­
pollutants enhanced both the uptake and retention of 57Co
and 134Cs in the fish. Several possible explanations, linked toa modification of the health status of the animal by the presence of stable pollutants, were advanced by the authors andsupported by biomarker measurements: an increase in respiratory activity by alteration of the global metabolism; adecrease in the Na+/K+-ATPase in gills and therefore modification of the ionic flux; or an alteration of the epithelium
permeability [A16, A17, F15].
23. Genotoxic/cytotoxic damages are not specific to ionizing radiation and may also be initiated by other toxins [S18].
Indeed, most biochemical techniques for detecting DNA
damage at the molecular or cellular level lack specificity forradiation-induced DNA damage [T9]. However, Tsytsugina[T8] and Tsytsugina and Polikarpov [T6] analysed the distribution of chromosome aberrations in cells and the frequencyof the different types of aberrations in order to discriminate
between the contributions of radiation and chemical factors
to the total damage to natural populations in aquatic organisms. These studies showed that the chromosome damage
observed in aquatic worm populations exposed to dose ratesof 10 µGy/h or more in lakes located in the vicinity of the siteof the Chernobyl accident was mainly caused by radioactive
contamination. Hinton and Bréchignac [H20], however, cautioned that, while there is a great potential value in using
biomarkers for assessing risks to non-human biota, there
remain many challenges in linking changes in biomarkers at

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

the molecular or cellular levels to effects on individual­organisms and populations of organisms.
24. The antioxidant status modified by exposure to various
stressors may influence the radiosensitivity of organisms.
The cellular damage due to radiation exposure is mainly
associated with oxidation. This oxidative stress may also be
caused by other stressors, such as chemical pollutants, andcellular defence mechanisms against reactive oxidative­species (ROS) that may be solicited are not stressor specific[S27]. Therefore, the interaction of heavy metals and radionuclides, and the resulting modification of radiosensitivity,
may depend on the capability of the antioxidant defence­systems of the organism [C13, C14, C15, S27, V1].
25. The potential effects of exposure to uranium in theenvironment may arise from the chemical toxicity of themetal and its radiotoxicity (arising from the uranium alphaparticles) and thus, such situations can be regarded as being
due to a mixture of stressors coming from a single element[B30, C19, P24]. Thus, while an evaluation of the chemical
toxicity of uranium to non-human biota is beyond the scopeof this annex, it is important to recognize that the chemical
toxicity and the radiological effects of uranium occur concurrently, and that both may need to be considered in apractical assessment of risks to non-human biota.
4.

Commentary

26. Most of the data on the effects of exposure to ionizing
radiation on non-human biota are from observations made on
individual organisms. Radiation effects on populations occur
as a result of the exposure of individual organisms. The
propa­gation of effects from individual organisms to populations is complex and depends on a number of factors. However, as suggested in the UNSCEAR 1996 Report [U4], themost important effects appear to be those on reproduction

Table 1.

227

and reproductive success. Many questions remain withrespect to the following: the mechanisms whereby radiation
exposure can cause harm; inter-species extrapolation; propagation of harm from nuclear DNA to the population; and theeffects of multiple stressors. Moreover the possibility ofhormetic effects at low doses and dose rates of gamma radiation, the relation between changes in biomarkers at themolecular and cellular level and the effects on individualorganisms or populations of organisms, and the effects ofmultiple stressors continue to be of ­considerable interest.
D. Observations from case studies
27. Ecological risk assessments (ERAs) have been conducted for a wide variety of situations where non-humanbiota are exposed to enhanced levels of radiation or radio­
active material. ERA studies are available for a wide varietyof nuclear fuel cycle activities from uranium mining to waste
management, as well as for sites with enhanced levels ofnaturally occurring radioactive materials, and for sites contaminated as a result of accidents. Table 1 outlines the key
elements of an ERA framework for assessing the effects of
exposure to ionizing radiation on non-human biota. Various
approaches for performing ERAs have been outlined including those of the IAEA [I2, I3, I4], NCRP [N1], the UnitedStates Department of Energy (DOE) [U26], Jones et al. [J1],
Environment Canada and Health Canada [E2], FASSET [F1,L4] and ERICA [B17]. All of the approaches necessarily
involve simplifications of the knowledge about the actual
environment. A common approach to the assessment of theeffects of radiation exposure on non-human biota involves
the use of a screening index (SI), where SI is simply a dimensionless ratio of the estimated dose rate (to an individualorganism) to the reference radiation dose rate, viz.:SI =estimated dose rate
reference dose rate

(1)

Key elements of a framework for the assessment of the effects of radiation exposure on non-human biota
Element

Considerations

Exposure of biota• Spatial and temporal patterns of radionuclide concentrations in environmental material• Uptake by organism• Non-uniform distribution within organism

Reference biota• Not possible to evaluate all biota• Need to select reference biota or indicator species appropriate for area of interest and desirable basis for selection• Possible need to consider individual biota per se when species are endangered

Dosimetry model for (reference) biota• Absorbed dose (to whole body or to tissue/organ)• Geometry corrections• Relative biological effectiveness (RBE): the effects of different qualities of radiation on biota

Endpoints in radiological assessment• Selection of appropriate population-level (deterministic) “umbrella” effects such as mortality or reproductive capacity and­corresponding reference doses

Effects on biota• Connection between radiation effects on “umbrella” endpoint in individual, and consequent “possible” effects on population• Role of background radiation levels• Natural population variability

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UNSCEAR 2008 REPORT: VOLUME II

28. The reference dose rate refers to the chronic dose rate(commonly expressed in milligray per day) below which
potential effects on populations of organisms are notexpected. The ratio, SI, assumes that the estimated dose rate
and the reference dose rate relate to the same endpoint (e.g.
mortality, reproductive capacity). The estimation of dose
rate to an individual organism is discussed in section I of thisannex. As there are many complex factors involved, caution
is needed in extrapolating from the effects of radiation exposure on an individual organism to those on a population oforganisms [B17].
29. The reference radiation dose rates for particular endpoints developed by the Committee in the UNSCEAR 1996
Report [U4] have been the most commonly used for thedenominator of the SI calculation. However, other guidance
has also been developed [C1, E1, E2, F5, I4, N1] and, more
recently, the concept of species sensitivity distributions(SSDs) has been introduced [B17, G3]. These developments
may necessitate a re-evaluation of the reference dose rates
obtained in the ERA case studies.
30. Because of the sparsity of peer-reviewed literature, allof the various sources of information on reference dose rates(e.g. various reports and supporting environmental assessments in Canada, technical reports of government agencies
in various countries and conference proceedings) have been
considered in this annex.
31. Of the numerous reports [A24, A25, B17, C1, C2, C20,
C22, E2, E3, E5, E22, E23, F2, G2, G3, G27, J2, S10, S11,
S32, S33, U26, W19], only a few provide studies of the radia­
tion exposure of non-human biota arising from radio­active
waste management activities or accidents involving dose
rates close to or exceeding the reference dose rates [A25, E8,E22]. For example, one study [S39] which involved investigation of the risks to biota from exposure to ionizing radiation from nuclear fuel cycle activities in Canada concluded
that the largest risk is associated with past uranium mining
activities; that discharges of radioactive material from powerreactors under normal operating conditions are not expected
to cause environmental harm; that organisms within one of
the waste management areas examined may be harmed byexposure to ionizing radiation; and that current radioactive
discharges from uranium refineries and conversion plants are
not expected to cause environmental harm. Similar results
can be derived from a consideration of the case studies
reported in ERICA [B17] of a wide ­variety of nuclear fuelcycle and other activities.
32. One study in which the estimated dose rates to biota
exceeded the reference dose rates, at least over a limited area,
was of the radioactive waste management site at the ChalkRiver Laboratories (CRL) located on the shore of the Ottawa
River, 160 km north-west of Ottawa, Ontario, Canada [E23].
The CRL site was established in the mid-1940s and has a history of various nuclear operations and facilities, primarily
related to research. An ERA was conducted to assess thedoses to biota arising from elevated levels of tritium, 14C,

41

Ar, 90Sr, 131I, 137Cs and 239Pu and from radionuclides that are
naturally present in the environment, for example, the uranium series radionuclides, using standard methods for evaluating the uptake of these radionuclides by biota from theaffected aquatic and terrestrial environments [B12]. A reference dose rate of 1 mGy/d was used for all organisms [B36].
Dose rates to some aquatic organisms such as frogs, small
fish, snails and aquatic plants within the on-site waste management areas were estimated to be above the reference dose
rate of 1 mGy/d; however, outside of the actual waste management areas, dose rates were estimated to be below the reference dose rate. The main contributor to the estimated dose
rates to invertebrates and terrestrial plants was 90Sr in surface
soil, while that to the woodchuck (estimated at 51 mGy/d)was inhalation in the burrow of 222Rn decay products frombackground levels of 226Ra in the soil. A few individual invertebrates and terrestrial plants actually within the confines ofsmall on-site waste management facilities were also estimated to have been subjected to dose rates above 1 mGy/d.
Based on the limited spatial extent of the estimated dose rates
that exceeded the reference dose rate and environmental
observations, the authors considered that significant effects at
the population level were unlikely.
33. Much of the new information on the effects of exposure
to ionizing radiation on organisms has arisen from studies in
the area surrounding the site of the Chernobyl accident,
where dose rates to organisms were above the reference dose
rate suggested in the UNSCEAR 1996 Report [U4]. A summary of the results of these studies up to 1996 is provided inthis annex. Section III of this annex provides a comprehensive review of the more recent data from studies of nonhuman biota in the area surrounding the site of the Chernobyl
accident.
E. Structure of this annex
34. The prime purpose of this annex is to build on theinformation reported in the UNSCEAR 1996 Report [U4];to compile data that has since become available on theeffects of exposure to ionizing radiation on non-humanbiota; and to determine if the reference dose rates need to be
updated. However, it is necessary first to provide some general information on the relationships between the levels ofradiation in the environment in which the biota live and theconsequent dose (or dose rate) to biota as a whole or selected
tissues and organs. Table 1 provides a summary of five key
elements that form the basis for assessing the effects of
exposure to ionizing radiation on non-human biota.
35. The relationships between the levels of radiation exposure and the activity concentration of radioactive material in
the environment and the dose to an organism living in thatenvironment is the subject of section I.
36. Section II provides a summary of the information considered in the UNSCEAR 1996 Report [U4] and the key
observations from that report.

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

37. Section III provides an overview of the findings of thestudies of non-human biota in the area surrounding the siteof the Chernobyl accident. It includes the work of the­Chernobyl Forum [E8].
38. Section IV provides a summary of the effects of
exposure to ionizing radiation on non-human biota derived
from the material given in earlier sections and reviews
carried out by other scientific organizations and groups,
namely, the IAEA [I4], Bird et al. [B1], the DOE [J1,U26], Environment Canada and Health Canada [E2],I.

Canada’s former Advisory Committee on RadiologicalProtection (ACRP) [A1], the UK Environment Agency[C1], the FASSET group [F1, F5, L1, L4], and the ERICA
group [E1, G11, G15]. The published literature was also
reviewed.
39. Section V provides an overall summary of the data
reviewed and, based on these data, the Committee’s evaluation of the dose rates below which effects on non-humanbiota are not considered likely. A few important areas forpotential future study are also noted.

ESTIMATING doseS to non-human biota

40. Data on the effects of radiation exposure on non-humanbiota have been obtained from experimental studies carriedout in the laboratory and in the field. Additional data havebeen obtained from the results of studies on environmentswith elevated levels of radiation or of radioactive material
resulting from normal operations of nuclear facilities, waste
management activities, or accidents. The interpretation of
the results of these studies requires an understanding of therelationship between the levels of radiation and the activity
concentrations of radionuclides in the various environmental
media in which the organism resides, the consequent dose
rate to an organism (or a tissue or organ of the organism) thatlives in the environment, and the biological effect of interest.
For example, radionuclides in the ambient environment may
lead to external irradiation and internal irradiation as a resultof radionuclides being taken into the organism via inhalation, ingestion, or uptake through its skin or membrane.
Empirically determined concentration factors and transfer
factors are commonly used to estimate contaminant concentrations in the organism (e.g. expressed for wet or dry weightin units of Bq/kg) from concentrations in the ambient environment (e.g. expressed in units of Bq/kg for sediment orsoil, or Bq/L for water). Dosimetric models can then be used
to derive, for selected organisms, dose conversion coefficients (DCCs) that relate ambient concentrations to internalor external exposure, as appropriate, and hence to dose.
A.

229

Assessing exposures of biota

1. Choice of reference organisms
41. In view of the enormous variety of living organisms, itwould be impossible to consider all species of flora andfauna as part of an environmental impact assessment evenfor a limited area. Instead, a concept has been developed
involving the selection of reference organisms that are representative of large components of common ecosystems andfor which models are adopted for the purpose of deriving
doses and dose rates to organisms, tissues, or organs fromradionuclides in the environment. The results of such dose
assessments for these predefined reference organisms willallow a basic assessment to be made concerning the possible
biological effects. This approach provides a strategy thatallows the modelling effort to be reduced to a manageablelevel. It further provides information on the exposures of different organisms under varying exposure conditions, whichallows the estimation of the impacts on those components ofthe environment for which data may be sparse or absent.
42. The reference organism approach of the ICRP had its
genesis in some earlier publications [P6, P13]. In the framework of the FASSET project [F20, L4], reference organisms
were defined as “a series of entities that provide a basis forthe estimation of radiation dose rate”. The idea was that theseorganisms would provide a basis for assessing the doses toorganisms and consequential effects in general due to radionuclides in the environment. The main criterion for the selection of reference organisms within the FASSET project wasthat the habitats and feeding habits should be such that theexternal and internal exposures are maximized.
43. The ICRP is assembling databases that relate to a limited
number of “reference animals and plants”. These are defined
as “hypothetical entities with the assumed basic charac­teristics
of a specific type of animal or plant, as described to the generality of the taxonomic level of family, with defined anatomical, physiological, and life-history properties that can be used
for the purposes of relating exposure to dose, and dose toeffects, for that type of living organism” [I12].
44. Both the FASSET and the ICRP approaches wereintended to simplify the process of estimation and evaluationof exposures to ionizing radiation of non-human biota.
Whereas reference organisms in FASSET were specificallyselected for different ecosystems (e.g. agricultural, semi-­
natural, freshwater, and marine), ICRP [I10] described thereference animals and plants in groups (family or taxonomic
level). The reference organisms selected cover a range of ecosystems and taxonomic families (table 2). The generic (reference) organisms that are explicitly considered in this annex
are summarized in table 2. Organisms similar to those adopted
by the ICRP were selected for consistency. The features ofthe selected organisms are described in reference [I10].

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Table 2.

UNSCEAR 2008 REPORT: VOLUME II

Comparison of reference organisms defined by different international bodies
Defined by

Reference organisms

FASSET
Terrestrial ecosystems [L1]

Soil microorganisms
Soil invertebrates
Plants and fungi
Bryophytes
Grasses, herbs and crops
ShrubsAbove ground invertebrate
Burrowing mammal
Herbivorous mammals
Carnivorous mammals
ReptileVertebrate eggs
Amphibians
Birds
Trees

FASSET
Aquatic ecosystems [L1]

Benthic bacteria
Benthic invertebrates
Molluscs
Crustaceans
Vascular plants
Amphibians
Fish
Fish eggs
Wading birds
Sea mammals
Phytoplankton
Zooplankton
Macroalgae

ICRP
Proposal on Reference Animals and Plants [I10]This annex

2. Radioecological models
45. Three classes of radioecological model can be distinguished and are presented here in terms of increasing complexity—equilibrium models, dynamic models and researchmodels.

Deer
Rat
Duck
Frog
Trout
FlatfishBee
CrabEarthworm
Pine tree
Wild grass
Brown seaweed
Earthworm/soil invertebrate
Rat/burrowing mammal
Bee/above ground invertebrate
Wild grass/grasses, herbs and crops
Pine tree/tree
Deer/herbivorous mammal
Duck/bird
Frog/amphibian
Brown seaweed/macroalgae
Trout/pelagic fish
Flatfish/benthic fish
Crab/crustaceans

46. Equilibrium models are primarily intended for theassessment of exposures due to routine discharges of radio­
active material into air or water. They are based on two fundamental assumptions: (a) the emission rates of the radionuclides
are constant in time; and (b) the duration of the discharges islong compared to the time needed for radionuclide transfer

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

along the environmental pathways considered. With theseassumptions, the radionuclide concentrations reach equilibrium within each of the compartments into which the environment is subdivided for modelling purposes, and the transfers
between compartments are easily characterized by time-­
invariant ratios of concentrations between the acceptor anddonor compartments.
47. Since equilibrium radionuclide concentrations in theenvironment are typically attained after considerably long
operational times of a nuclear facility, the equilibrium­models are likely to give conservative exposure estimates.
This type of radioecological model has been used to determine compliance of routine discharges from nuclear ­facilities
with authorized limits [H4, I11, N3, U3].
48. Ciffroy et al. [C22] tested the influence of the timedependence assumption frequently used in radioecologicalmodels in a case study conducted on the Loire River inFrance. For routine discharges of radionuclides from
nuclear power plants, their main conclusions were that:(a) attention must be paid to the temporal variations in the
discharges, and gaps between actual instantaneous discharges and maximum discharges on a yearly time scalemust be analysed; (b) the equilibrium assumption at thewater-suspended matter interface must be justified andeventually corrected when equilibrium conditions are notexpected; and (c) for organisms showing slow uptake/elimination rates, a kinetic approach to the bioaccumulation
process can avoid some overestimation of radionuclide
concentrations. The assumption of equilibrium led to overestimations of one to two orders of magnitude in predicting60
Co concentrations in invertebrates.
49. A number of inherent advantages have contributed tothe proliferation of equilibrium models. The model structure
can be kept simple, but there is flexibility to allow moredetailed structure, if necessary. Under equilibrium conditions, dispersion of trace amounts of radionuclides in theatmosphere or rivers is adequately represented by analyticalsolutions of more general physical models; transfer via foodchains is represented by simple multiplicative chains of­concentration ratios.
50. A major conceptual limitation of radioecologicalmodels is that many of the parameters involved (e.g. concentration ratios) have to be established empirically.
Experience gained during recent decades has amply demonstrated that numerical values of many of these parameters may vary by several orders of magnitude; this has
been well documented, for example, for plant–soil relationships of radiocaesium and radiostrontium concentrations [F7, F8, N4]. While for the purposes of screening or
environmental protection as may be established by the
ICRP or required by a national regulator, representative
parameter values can be selected that ensure that themodel assessments are conservative, obvious difficulties
exist if a realistic assessment of exposures in specific­ecosystems is needed.

231

51. Dynamic radioecological models [M4, S13, W3] areapplied if the time dependence of exposures that result fromvarying or instantaneous releases has to be taken into
account. Examples of their use include the assessment of
the time-dependent radionuclide concentrations in the environment, such as those resulting from accidental radio­
nuclide releases varying over time, and the simulation ofseasonal effects, which are of major importance in terrestrial environments during the first year following depositionof radionuclides after an accidental release [M7].
52. Research models are characterized by a high degree ofcomplexity and longer computation times, and presently are
limited to simulating a few of the important processes inanalyses of environmental pathways for radionuclides [C7,P9]. Currently, therefore, they do not offer an alternative toequilibrium and dynamic radioecological models for environmental assessments, although they do constitute animportant tool for improving understanding of the sources ofvariability observed empirically.
53. The scope of this annex is limited to providing a broad
overview of the approach to estimating radiation exposureand subsequent doses to non-human biota. The reader interested in these topics is referred to the extensive literature.
Exposure assessments are generally based on equilibrium
models. However, for case studies at specific locations contaminated by accidental releases of radionuclides, information on the levels of exposure of local biota taken from theliterature is sometimes based on simulations using dynamic
radioecological models.

3.

Transfer of radionuclides in the environmentand resulting exposures

54. The major pathways of radiation exposure of biota
in the environment are summarized in figure II. In thisschematic representation, the physical components of theterrestrial environment are air, soil and sediment; the­biological components include plants, invertebrates, andvertebrates (mammals, birds, reptiles, and land-based
amphibians). The physical components of the freshwateraquatic environment include streams, rivers, lakes andsediments; the biological components are phytoplankton,
zooplankton, macroinvertebrates, sessile aquatic plants
and vertebrates (fish, water-based amphibians and someaquatic mammals). In a marine environment, the physicalcomponents include tidal zones, coastal waters andmarine sediments; and the biological components include
phytoplankton, zooplankton, macroinvertebrates, sessile
aquatic plants, and vertebrates (fish and marine mammals), molluscs, crustaceans and marine birds. The terrestrial and aquatic environments are not totally separate.
Some birds and terrestrial mammals eat fish and shellfish; moose and waterfowl feed on aquatic plants; andterrestrial animals ingest drinking water from the aquatic
environment.

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UNSCEAR 2008 REPORT: VOLUME II

Figure II. Major environmental transfer routes for evaluating radiation exposure of biota
Activity in air and rain

Activity in water/sediment

PlantsSoil/sediment

Biota
External
exposureInternal
exposure

External
exposure

Radiation exposure of biota

55. The total radiation dose received by an organism (orsome organ or tissue of the organism) is the sum of the contributions from both external and internal exposure. External
exposure results from complex non-linear interactions ofvarious factors, such as the levels of the radionuclides in the
habitat, the geometrical relationships between the radiation
source and the target, the shielding properties of the materials in the environment, the size of the organism and theradio­nuclide-specific decay properties (characterized by thetype and energy of the radiations emitted and their emission
probabilities).
56. Internal exposure is determined by the activity concentrations of the radionuclides in the organism, the size of theorganism, the radionuclide distributions within the organism
and the specific decay properties of the radionuclides. In
addition, the relative biological effectivenesses (RBE) ofalpha, beta and gamma radiation need to be taken into
account in assessing the consequences of the exposure.

B.

Transfer of radionuclides in the terrestrial environment

57. Radioactive material released into the atmosphere isdispersed and transported by the wind. Exposures ofbiota are calculated from the activity concentrations ofradionuclides in the environmental media, such as air,soils and vegetation, and in the organisms under consideration. The principal processes involved in the transportof radionuclides in the terrestrial environment include
dry deposition, wet deposition, interception by vegetation, loss of radionuclides from plants due to weathering,
resuspension, the systemic transport of radionuclides
within plants, uptake from soil, run-off to water bodies
and the transfer to animals. This section discusses thefactors that affect the behaviour of radionuclides in a terrestrial environment and the uptake of radionuclides
from the environment to plants and animals.

1.

Dry deposition

58. Dry deposition per unit time is proportional to the nearsurface concentration of the material in air. Usually, the dry
deposition of a radionuclide from the atmosphere to soil andvegetation is expressed in terms of the deposition velocity,vg (m/s), which is defined as the ratio of the activity deposition rate per unit area and the local activity concentration in
air of the radionuclide at a reference height. This empiricalquantity depends on a variety of factors such as the size of
any associated particles, the characteristics of the surface–air
interface, the meteorological conditions and the chemical
form of the radionuclide.
59. Typical estimates of deposition velocities for grass andforests are summarized in table 3. These values are used forthe calculation of the exposures of biota resulting from theatmospheric release of radionuclides.

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

Table 3.

233

Typical estimates of deposition velocities for grass and forest [P14, R11]
Chemical/physical form

Deposition velocity (m/s)
Foresta

Grass

Particles, 0.1–1 µm
Elemental iodine
Methyl iodide

0.001
0.01
0.000 1

Crown

Trunk

Soil

0.005
0.05
0.000 50.000 50.005
0.000 05

0.000 8–0.003
0.006–0.02
0.000 08–0.000 3

a Coniferous trees and deciduous trees with fully developed foliage.

2.

3.

Interception of radionuclides deposited from the air

Weathering

60. Interception defines the fraction of radioactivity deposited by wet and dry deposition processes that is initiallyretained by the plant. There are several possible ways toquantify the interception of deposited radionuclides. The
simplest is the interception fraction, f, which is defined as theratio of the activity initially retained by the standing vegetation, Ai, immediately subsequent to the deposition event to
the total activity deposited. A full description of the interception process is beyond the scope of this annex and the reader
interested in this topic is referred to the extensive literature(e.g. see reference [H26]).

63. Following deposition on vegetation, radionuclides are
removed by wind and rain. In addition, the increase of biomass
during growth leads to a reduction in the activity concentration.
Since growth is subject to seasonal variations, the post-­
deposition reduction of the activity concentration of radio­
nuclides in plants depends on the season. These processes of
reduction in the activity concentration of radionuclides in plants
occur simultaneously after deposition. As it is difficult to quantify the exact contribution of each process, the net reduction in
the activity concentration with time is usually called “weathering” and expressed by the empirical weathering half-time, Tw.

61. Radioactive material in air can be washed out by rain
and snow. A fraction of the radionuclides deposited with
precipitation is retained by the vegetation, and the rest
falls through the canopy to the ground. Although theradio­active material retained eventually transfers to soil
through weathering and is retained only temporarily byvegetation, the fraction initially intercepted is important
owing to the fact that the concentration of radioactive
material will be at its highest at this time. Interception of
wet deposits is the result of a complex interaction of theamount of rainfall, the chemical and physical form of thedeposit and the actual stage of development of the plant[M4] and thus, interception fractions for a single event
may vary from 0 to 1.

64. The chemical form of the contaminant seems to be ofminor importance in weathering. After the Chernobyl accident, the median weathering half-times observed for iodine
and caesium on grass were approximately 8 and 10 days,
respectively [K5]. Shorter half-times were observed primarily in regions with fast growing vegetation, while longer
half-times were found in Scandinavia, where the growth
rates were lower because of the later spring in the area [K5].
In general, longer weathering half-times are observed forslowly growing or dormant vegetation [M8].

62. To account for its dependence on biomass in somemodels, the interception of wet deposited activity is model­
led as a function of the biomass density, according to theapproach of Chamberlain [C8]. The chemical form is a key
factor; since the plant surface is negatively charged, theabsorption of anions is less effective than that of cations [H6,H7, K4, M4, P11]. Differences between plants seem to be ofminor importance compared to those between radionuclides,
e.g. the interception of polyvalent cations is higher than thatfor anions by as much as a factor of 8 [H5]. However, ingeneral, for the estimation of interception following the routine discharge of radioactive material, very simple approaches
are used in the models [P10]. Anspaugh [A22] suggested adefault value for the interception fraction of the order of 0.3
for all elements, plants and precipitation events for routinedischarges of radionuclides.

65. In forests, weathering is more complex because of the
canopy structure, which comprises several vegetation layers, such as crown, trunk and understorey vegetation. Radio­
nuclides lost from the crown may be retained by theunderstorey vegetation, thus reducing the overall loss rate ofradionuclides from vegetation to soil.
4.

Distribution of radionuclides within plants

66. The currently available dosimetric models for theassessment of the exposure of biota do not take into accountheterogeneous radionuclide distributions within plants.
Hence, any information on these distributions cannot­currently be used in the assessment.
5.

Uptake of radionuclides from soil

67. Soil is the main reservoir for long-lived radionuclides deposited on terrestrial ecosystems. The behaviour of radionuclides in234

UNSCEAR 2008 REPORT: VOLUME II

soils controls their migration in soil, the possible transport togroundwater, and the long-term radionuclide concentration invegetation and thus the exposure of soil organisms. As for all
minerals, the uptake of radionuclides by plants mainly takes
place via dissolution from soil. The concentration of radio­
nuclides in soil solutions is the result of complex physical–
chemical interactions with the soil matrix, with ion exchange
being the dominant mechanism. Ion exchange by its very
nature is a competitive mechanism. The concentrations andcomposition of the major competing elements present in soil
thus are of primary importance in determining the distributionof radio­nuclides between soil, soil solution and plant roots(which are able to influence the microspace in their vicinity inorder to provide and maintain conditions that favour the uptakeof nutrients) [E6].
68. The physical chemistry of sorption and desorption ofradionuclides in the soil–soil solution system and their possible uptake by plants are the result of complex interactions
between soil type, pH, redox potential, sorption capacity,
clay content, content of organic matter and soil management practice. Although these factors are qualitatively
known, they are difficult either to quantify or to integrate
into a universal model applicable to a wide range of soil
conditions. Consequently, the approaches used include
classifying the transfer according to soil types (e.g. peat,sand, loam and clay) and other physical and chemicalparameters. In addition, various biological factors should
be considered, especially whether or not the radionuclide isan essential element.
69. For the quantification of the root uptake of radio­
nuclides, empirically derived (aggregated and greatly simplified) parameters—soil–plant transfer factors or concentration

Table 4.

ratios—are usually applied despite their inherent limitations[E6]. In this case, these parameters are the ratios of theactivity concentrations in the plant to those in the soil within
the uppermost layer of a standardized thickness. Transfer
factors were originally defined for agricultural ecosystems
within which radionuclides are distributed homogeneously
within the rooting depth of agricultural plants because ofploughing.
70. The aggregated transfer factor is defined as the activity
concentration of a radionuclide in a material (Bq/kg) divided
by the total deposition—activity per unit area (Bq/m2)—atequilibrium. The concept of aggregated transfer factors wasdeveloped as a simplification of detailed physical and chemical processes to a single value, inter alia, to avoid difficulties
with determining radionuclide concentrations in soils with amulti-layered structure, such as in forests.
71. Alternatively, concentration ratios that relate to theactivity concentrations of radionuclides in specific soil horizons exploited by the mycelium or the root system were proposed in the late 1980s and proved to be useful, especially inconnection with the prediction of the transfer of 137Cs tofungi [G4, R8, Y1, Y4, Y5].
72. Illustrative ranges of soil–plant transfer factors for anumber of elements are summarized in table 4 [T11]. This
table shows that the uptake of caesium from soil usually
does not result in a simple proportional accumulation inplants. Radiocaesium is effectively sorbed by micaceous
clay minerals that are present in almost all soils in varying
amounts. A detailed compilation of soil–plant transfer factors including data for specific plant groups, plant organs
and soil types can be found elsewhere [I14].

Typical ranges of soil–plant transfer factors [T11]
Element

Concentration ratio
Bq/kg plant (d.m.) per Bq/kg soil (d.m.)

Aggregated transfer factora
Bq/kg plant (d.m.) per Bq/m2 soil

Sr
Cs
Csb
I
Tc
Pb
Ra
U
Np
Pu
Am
Cm

0.01–10.001–0.1
0.1–100.001–1
0.1–100.001–0.01
0.001–0.1
0.001–0.1
0.001–0.1
10‑5–10‑3
10‑5–10‑3
10‑5–10‑3

4 × 10‑5–4 × 10‑3
4 × 10‑6–4 × 10‑4
4 × 10‑4–4 × 10‑2
4 × 10‑6–4 × 10‑3
4 × 10‑4–4 × 10‑2
4 × 10‑6–4 × 10‑5
4 × 10‑6–4 × 10‑4
4 × 10‑6–4 × 10‑4
4 × 10‑6–4 × 10‑4
4 × 10‑8–4 × 10‑6
4 × 10‑8–4 × 10‑6
4 × 10‑8–4 × 10‑6

a Calculated from the concentration ratio assuming a mass density for dry matter (d.m.) in the soil rooting zone of 280 kg/m2 taking account of the mass of the soil within therooting zone.
b Observed range in natural and semi-natural ecosystems on acid sandy soils poor in potassium.

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

73. Caesium uptake is particularly high from organic soils
with a low pH and pronounced potassium deficits [F11].
Such soils are frequently found in the Russian Federation,
Belarus and Ukraine, as well as in Scandinavia, the uplandareas of the UK and the alpine areas of Europe. For organic
matter, the cation exchange capacity decreases with increasing acidity owing to the saturation of carboxyl groups withhydrogen ions. Furthermore, the availability of caesium for
uptake is enhanced in soils that are poor in potassium. Additionally, the clay content of organic soils is low and this prevents strong sorption and leads to persistently high caesium
levels in plants [A7, F12, F13, K6]. Another important aspectis that the bioavailability of radionuclides and their uptake
after deposition may change with time. This was observed inareas close to the site of the Chernobyl accident and wascaused by the degradation of fuel particles, the fixation of
caesium within the soil and changes in the sorption strengthof the soil for caesium [N5, S14, S15].
74. In recent years, a number of experiments have been
performed to determine soil–plant transfer factors for tropical and subtropical environments [C9, F11, R6, T12, T13,

235

U24, U25, W12, W13]. The anaerobic soil conditions inflooded paddy fields change the solubility of some elements,
such as I and Tc, and thus possibly their soil–plant transfer
factors [M25, T26, Y3]. In general, however, the results do
not indicate any systematic impact of climatic conditions on
the transfer of radionuclides from soil to plants, although thenumbers of data are still small. Further data on the tropicaland subtropical environments are therefore needed [M25].
75. In forest ecosystems, the transfer of radionuclides fromsoil to plants and fungal fruit bodies depends on the depth
profile of the radionuclides and the vertical distribution of fineroots and fungal mycelia in soil. At least in the case of fungi,
the use of transfer factors referring explicitly to the soil layer
exploited by fungal mycelia seems to be the best approach forquantifying the uptake to radionuclides, balancing overall
simplicity with mechanistic considerations of the dynamic
processes [S37]. However, the concentrations of radionuclides
in understorey vegetation, trees and fungal fruit bodies can be
estimated roughly in a simplified manner using aggregatedtransfer factors. The ranges of aggregated transfer factors
given in table 5 summarize the available observations.

Table 5. Typical ranges of aggregated transfer factors for 137Cs from soil to vegetation and fungal fruit bodies in forest
ecosystems [A8, B27, G7, I16, I17, K15, L7, Z1]
Data are given on a dry weight basis unless otherwise noted
Species or genus

TFagg (Bq/kg organism (d.m.) per Bq/m2 soil)
Fungal fruit bodies

Agaricus
Amanita
Armillaria
BoletusCantharellus
Clitocybe
Collybia
Coprinus
Cortinarius
HydnumHygrophorus
Laccaria
Lactarius
Leccinum
Lepista
Lycoperdon
Macrolepiota
Paxillus
Ramaria
Rozites
RussulaSarcodonSuillus
Tuber
Xerocomus

0.002–0.007
0.008–5
0.001–0.2
0.001–10
0.01–20.01–2
0.03–0.3
0.004a
0.02–103a0.2–7
0.4–100.006–5
0.005–0.9
0.002a0.009–0.5
0.000 7–0.1
0.01–50.05–0.6
0.08–10
0.04–5
0.3–0.4
0.02–20.000 3–0.008b
0.002–7

236

UNSCEAR 2008 REPORT: VOLUME IISpecies or genus

TFagg (Bq/kg organism (d.m.) per Bq/m2 soil)
Understorey vegetation

Rubus chamaemorus (cloudberry), fruit
Vaccinium vitis-idaea (lingonberry), fruit
Vaccinium myrtillus (bilberry), fruit
Rubus idaeus (raspberry), fruit
Fragaria vesca (strawberry), fruit
Rubus fruticosus (blackberry), fruit
Green parts of understorey vegetation, including
the stems of berry plants

0.002–0.2
0.03–0.07
0.02–0.1
0.001–0.004
0.004–0.01
0.006–0.05
0.001–1
Trees

Fagus sp. (beech)
Bole wood
Leaves0.001–0.002
0.002–0.003

Picea sp. (spruce)
Bole wood
Needles

0.000 3–0.002
0.000 6–0.02

Pinus sp. (pine)
Bole wood
Needles

0.000 2–0.003
0.001–0.04

Quercus sp. (oak)Bole wood
Leaves

0.002–0.004
0.008–0.01

Betula sp. (birch)
Bole wood
Leaves0.000 03–0.001
0.000 3–0.04

Populus sp. (aspen)
Bole wood
Leaves0.000 5–0.002
0.008aAlnus sp. (alder)
Bole wood
Leaves0.001a0.008aa Only a single value available.
b Data are given on a fresh weight basis and refer to the top 10 cm of soil.

76. Fungi are able to accumulate radiocaesium in theirfruit bodies [G14, H8]. Some species exhibit activity levels
that exceed those of green plants by more than one order ofmagnitude. On average, the radiocaesium levels in symbiotic fungi are higher than those in saprophytic species [R7,Y4, Y5].
77. Radionuclides in growing wood originate from twosources: the initial atmospheric deposits that enter the plantby foliar absorption, and root uptake from the soil. Theirrelative contributions depend on the type of tree (coniferous
versus deciduous) and the age [B20, E7, G5, H9], the season
at the time of deposition and the time elapsed after deposition, with root uptake being the dominant pathway for growing wood in the long term. Transfer factors or concentration
ratios that are calculated on the basis of the total content ofradionuclides in wood inevitably include both uptake pro­
cesses and therefore are likely to overestimate root uptake(table 5) [G5].

6.

Migration in soil

78. Vertical migration of radionuclides in the soil column
is driven by various transport mechanisms, such as convection, dispersion, diffusion and bioturbation. The long-term
consequences of downward migration differ considerably,
however, depending on the dominant mechanism. For­convective-driven migration, for example, the radionuclide
input due to the Chernobyl accident moves down the soil asa marked peak and shows broadening with time as a result ofdispersive mixing. Convective transport of radionuclides
usually dominates in soils showing high hydraulic conductivities, e.g. sandy soils. For further discussion of the importance of downward migration of radionuclides in soil andforest litters, see section III and the references cited.
79. For diffusive transport, the concentration is always at a
maximum at the surface with a close to exponential decrease
with depth. For this type of transport, which is typical inANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

soils of low hydraulic conductivity, the bulk of the radio­
nuclides deposited from the atmosphere thus remains within
the rooting zone of plants.
80. Agricultural practices have a major impact on radio­
nuclide behaviour. Depending on the intensity and type ofsoil cultivation, mechanical redistribution of radionuclides
may occur. This causes, in arable soils, a rather uniform distribution of radionuclides in the tilled horizon. Fertilization
shifts the ratio of radionuclide to nutrient concentrations insoil and soil solution and thus may influence plant root
uptake of the radionuclides [E6].
81. Some investigations indicate [B21, S16] that elementindependent transport mechanisms, such as the transport ofradionuclides attached to clay particles or soil colloids, may
play a relevant role in determining the migration rate of radio­
nuclides in soil. Furthermore, the activity of soil animals thatcause a turnover of soil, e.g. earthworms, cannot be neglected.
The authors of references [B21, S16] suggest that a value of
100 years for the default residence half-time for the upper
25 cm layer is adequate for all elements with low mobility,
such as radium, lead, uranium, plutonium and americium.
Iodine under aerobic conditions is strongly bound to organic
matter and therefore a residence half-time of 100 years canalso be assumed [K7]. On the other hand, iodine can bereleased from soil to soil solution under anaerobic conditions,such as in a flooded paddy field [M25].
82. The situation with forest soil is more complex owing to
the more pronounced soil horizons. Radionuclides deposited
directly onto forest soil or washed from the canopy andunderstorey vegetation initially infiltrate the soil rather rapidly. They are therefore initially assigned to a labile pool. In
the long term, they will become immobilized through fungal
or microbial activity or by mineral constituents of the soil.
The radionuclides in the non-labile pool may be available forroot uptake, e.g. via symbiotic fungi, but are assumed not tobe leached to deeper soil layers. The rate of downward migration is correspondingly reduced considerably over time, and,in the organic horizons, is determined mainly by the rates ofdecomposition of the organic material, and litter accumulation. Subsequently, downward migration of radionuclides israther slow and partially offset by upward translocation byfungal mycelia and roots [R4]. Fungal and microbiologicalactivity is likely to contribute substantially to the long-term
retention of radionuclides, notably radiocaesium, in organic
layers of forest soil. In this phase, radiocaesium is well mixed
and almost equilibrated with stable caesium within the biologically connected compartments [Y6]. When radionuclides
reach the mineral horizons of forest soil, essentially the sameprocesses may occur as in arable soils, e.g. radiocaesium canbe fixed by micaceous clay minerals.
7.

Resuspension

83. Resuspension refers to the removal of deposited material from the ground to atmosphere as a result of wind, traffic,

237

soil cultivation and other activities. Potentially, resuspension
is a persistent source of radionuclides in air subsequent totheir deposition on the ground. Furthermore, it may lead toredistribution of radionuclides and their deposition onto cleansurfaces. Resuspension is influenced by a variety of factors,
such as the time since deposition, meteorological conditions,surface characteristics and human activities. For biota, resuspension is of low importance. For animals living in the soil, it
is not relevant. The contribution of resuspension to the activity concentration of radionuclides in plants in humid eco­systems usually is negligible compared to that of dry­deposition and interception [G6, H10].
8.

Transfer to animals

84. The transfer of radionuclides to animals is usuallyestimated using element-dependent concentration ratios ortransfer factors. The transfer factor is defined either as theratio of the activity concentration in an organism or tissue
and the intake rate under equilibrium conditions, or as theratio of the activity concentration in an organism or tissue
and the deposition density (activity per unit area). It isonly applicable to an intake of a radionuclide by adult animals that is constant over long periods. To account for
time-dependent (dynamic) intakes, one or more biologicalhalf-lives are considered [M4].
85. In recent decades, many data have been accumulatedon the transfer factors for domestic animals. They depend on
animal mass, performance level, feeding regimes and feed
components. However, these data are not generally applicable to estimating activity concentrations in biota, since they
were determined in order to estimate activity concentrationsin animal products for human food (such as meat, milk andeggs) while this annex is concerned with the estimation ofactivity concentrations in whole animals. Furthermore, theapplication of transfer factors presumes knowledge of thefeed intake as well as the activity concentrations of the feed
components. It has been demonstrated that highly contaminated feed components may determine the activity levels ofgame, even if consumed in low quantities. The seasonal peak
activity concentration of 137Cs in roe deer, for example, hasbeen attributed to the ingestion of mushrooms [Z1]. Fungal
fruit bodies can show radiocaesium levels exceeding thoseof green plants by one order of magnitude or more. Wildboar ingest deer truffle (Elaphomyces granulatus), a preferred “delicacy”, which dominates the radiocaesium uptake,despite being only a few per cent of the boar’s total diet [F14,P12]. However, the relevant data are not available for wild
animals in general.
86. In most cases, the activity concentrations of radio­
nuclides in game are calculated in a simplified manner using
aggregated transfer factors. This transfer factor neither takes
into account the time-dependent intake rates nor can reproduce the time-dependent activity concentrations in game.
Values for aggregated transfer factors for different species
are compiled in table 6.

238

UNSCEAR 2008 REPORT: VOLUME IITable 6. Aggregated transfer factors (soil-to-game) for 137Cs [A9, I16, J3, K8, S19, Z1]
Data are given on a fresh mass basis unless otherwise noted
Species

TFagg (Bq/kg organism (dry mass) per Bq/m2 soil (dry mass))
Default value

Range of literature data

0.02
0.05
0.03
0.03
0.004
0.3
0.02

0.006–0.03
0.001–0.2
0.02–0.04
0.009–0.1
0.002–0.05
0.01–10a

Alces alces (moose)
Capreolus capreolus (roe deer)
Cervus elaphus (red deer)
Lepus arcticus (arctic hare)
Lepus capensis (brown hare)
Lynx lynx (lynx)
Game except roe deera Data are given on a dry weight basis.

87. Table 7 summarizes the equilibrium concentration
ratios for the reference organisms considered. The values are“order-of-magnitude” estimates based on the compilation inreference [F4]. Some of the original values were given as
aggregated transfer factors and have been converted to concentration ratios. At least in temperate environments, concentration ratios are higher in forest and semi-natural
ecosystems than in agricultural systems, because of theiroften lower nutrient supply and pH values. Furthermore, thehigh content of organic matter in forests is accompanied byhigh concentrations of fulvic and humic acids, which act as

Table 7.

complexing agents and increase the mobility of cationicradionuclides in soil.
88. The nominal values of transfer factors provided in table
7 have been suggested for use [E10, F4], in the absence ofsite-specific information, to estimate the exposure rates forbiota after the release of radionuclides to atmosphere andtheir subsequent transfer to soil. As such, these transfer­factors were intended to be applied for screening purposes toobtain an order of magnitude estimate, but they may not beappropriate for application to specific sites.

Nominal values of transfer factors for reference organisms (adapted from [E10, F4])

Element

Transfer factors (Bq/kg (fresh weight) per Bq/kg soil)
Earthworm

Rat

Deer

Duck

Frog

Bee

Grass

Pine tree

H

150

150

150

150

150

150

150

150

Cl

0.2

7

7

7

7

0.3

20

1

Sr

0.01

2

2

0.6

1

0.06

0.2

0.5

Tc

0.4

0.4

0.4

0.4

0.4

0.4

20

0.3

I

0.2

0.4

0.4

0.4

0.4

0.3

0.1

0.1

Cs

0.09

3

3

0.8

0.6

0.06

0.7

0.2

Np

0.1

0.04

0.04

0.04

0.04

0.1

0.02

0.3

Pu

0.03

0.02

0.02

0.02

0.02

0.06

0.01

0.03

Am

0.1

0.04

0.04

0.04

0.04

0.1

0.005

0.000 1

Pb

0.03

0.04

0.04

0.06

0.1

0.06

0.07

0.08

Ra

0.09

0.03

0.03

0.04

0.04

0.04

0.04

0.000 7Th

0.009

0.000 10.000 10.000 40.000 4

0.009

0.04

0.001

U

0.009

0.000 10.000 10.000 50.000 5

0.009

0.02

0.007

C.

Transfer to freshwater organisms

89. Radionuclides can enter water bodies as a result of discharges to the aquatic environment (e.g. directly from anuclear facility), by deposition of airborne radioactive material onto the water surface and by run-off of material

deposited onto soil. For a point source of emission into aswiftly flowing stream, the flow rate of the stream can bedivided by the flow rate of the effluent discharge to obtain
the dilution factor. A certain mixing distance must be
assumed, which could vary from a few tens of metres for asmall stream to a few kilometres for a large river. Beyond theANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

mixing distance, a uniform concentration of the radionuclidein water can be assumed. Suspended material may be deposited as sediment. The deposited material may become lockedin the sediments and, over time, migrate to deeper sediments
or be redissolved by physical and biological processes andre-enter the water column. Dissolved or finely suspended
material may be transported over large distances, being progressively diluted by water from other streams and rivers,
eventually reaching the oceans.
90. The movement of radionuclides in rivers is often model­
led using the diffusion–transport equation and the behaviourof radionuclides in the “water column–river bed sediment”
system is often assessed using compartment ­models [M23].
At present, although the structures of the models have notbeen subjected to significant revisions, the scope of the transfers modelled (physical, chemical and biological) and of theassociated radionuclide specific parameters has been considerably enlarged. For instance, the previous state-of-the-art
publication of the IAEA, “Handbook of parameter values forthe prediction of radionuclide transfer in temperate environments” [I16], listed solely values of water–­sediment partition
coefficients and concentration factors for edible portions offish. The most recent version also incorporated equations andparameters for representing transfer by wash-off from watersheds of deposited radionuclides, interaction between liquidand solid phases, migration to and from sediments, and­transfers to freshwater biota [I14].
91. The mixing of radionuclides discharged into a lake orpond is much slower than is the case for rivers. As a first239

approximation, a uniform radionuclide concentration throughout the pond could be assumed, with a dilution factor equal tothe pond outflow rate divided by the effluent input rate. In alarge lake or coastal environment, a uniform concentration
would never be reached. Plume models have been developed
for lake-shore environments analogous to atmospheric transport models. The lake-shore environment is often complicated by thermal layering within the water column, which
impedes vertical mixing. Moreover, removal of material fromthe water column via sedimentation is an important longterm process which results in an approximately exponential
decline with time of the radionuclide concentrations present
in the water column.
92. Sedimentation and attachment to suspended particulates
are the main processes influencing the residence times ofradionuclides in freshwater. Fractions of dissolved and ofparticle-bound radionuclides are usually determined by the
distribution coefficient, Kd, which is defined as the ratio of theradionuclide concentration in water and the concentration of
the radionuclide attached to particulate matter, under equilibrium conditions. Values of Kd are element-dependent. Low Kdvalues and concentrations of suspended matter indicate highdissolved fractions, whereas high Kd values and suspended
load values indicate a considerable sorption of radionuclides
by particles and favour sedimentation. Once deposited, radionuclides may migrate down within the sediment or may
become involved in resuspension processes. These processes
may create additional sources or sinks with potential impact
on the long-term behaviour. The distribution coefficients forvarious elements in freshwater are given in table 8.

Table 8. Distribution coefficients Kd in freshwater ecosystems [I14]
Element

Kd (m3/kg)
Geometric mean

Geometric standard deviation

Be

42

3.6

Mn

130

12

Co

43

9.5

Sr

0.18

4.6

Ru

32

1.9

Ag

85

2.3

Sb

5

3.8

I

4.4

14

Cs

8.5

6.7

Ba

2

3.6

Ce

220

2.8

Th

180

21

Ra

7.4

3.1

Pu

240

6.6

Am

850

3.7

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UNSCEAR 2008 REPORT: VOLUME II

93. Aquatic organisms may be directly irradiated byradio­nuclides present in their habitats (e.g. water, sediment). They may also take up radionuclides from water
and/or the food chain and incorporate them into their­tissues. External irradiation of most aquatic organisms,with the exception of burrowing invertebrates and benthic
organisms, is limited by the shielding provided by the­surrounding water or sediment.

that in water expressed in units of Bq/L, under equilibrium
conditions) for 137Cs ranging from 500 to 9,500 L/kg for
freshwater fish, compared to values of 3 to 25 L/kg formarine fish. The lower values for marine fish were thought tobe as a result of the competition for uptake from potassium
and other cations. Freshwater amphibians can also showhigh values of CR (1,000 to 8,000 L/kg) in the aqueous
environment.

94. Considerable attention has been focused on fish because
they are at a higher trophic level in aquatic food chains andserve as food for humans and predators. ­Polikarpov [P2] hasgiven concentration ratios, CR, (CR here is the ratio of theactivity concentration in fish expressed in units of Bq/kg and

95. Table 9 gives values of CR for 137Cs in fish in Canadianlakes in the Northwest Territories [L5] and for the upper
Great Lakes [T15]. High trophic level fish such as trout,pike and cisco show an especially high accumulation ofradiocaesium.

Table 9.

Concentration ratios for 137Cs in freshwater fish
Species

Concentration ratio (L/kg)
NWT Lakes [L5]

BurbotGreat Lakes [T15]800

Lake whitefish

400–1 000Round whitefish

1 000–1 800

Sucker700

1 500–2 500

Chub

1 900

Alewife

1 800–2 300

Bullhead

2 300

Cisco

1 600–5 000

Pike

2 500–5 500

Lake trout

3 000–6 000

6 100

96. Swanson [S20] has summarized concentration ratios for water to fish tissues for the naturally occurring radionuclides ofuranium, 226Ra, 210Pb, and 228Th (table 10).
Table 10.

Concentration ratios for natural radionuclides in freshwater fish [S20]

Element/
radionuclide

Concentration ratio (L/kg)
Bone

Flesh

Liver

Kidney

Gonad

Gut

U

20–8000.1–25<0.04–0.5

0.1–0.5

0.01–0.35

0.05–0.5Ra

35–1 800

1–60

1–45

3–30

5–115

7–45

Pb

100–2 500

4–100

3–420

6–780

10–150

11–206Th

15–160

4–32

4–36

5–46

13–50

23–50

226

210

228

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

D.

Transfer of radionuclides to marine organisms

where A is the activity of the radionuclide discharged perunit time to a specific part of the sea (Bq/a), V is the­volume of this part (m³), τ is the mean residence time (a),lr is the radioactive decay constant (a-1), Kd is the distribution coefficient (m³/kg), and S is the concentration ofsuspended particles (kg/m). The steady-state activity
concentration of the ­radionuclide in ­suspended particles,
Cs (Bq/kg), is then:

97. The main processes that modify the activity concentrations of radionuclides in marine water are (a) dilution due toconvective and dispersive mixing during transport, driven by
local, regional and global currents, (b) sedimentation after
attachment to suspended particles and (c) radioactive decay.
98. For a given continuous discharge rate into a specific section of the marine system, the steady-state concentration of adissolved radionuclide in water, Cw (Bq/m3), can be calculated
according to:

Cw =



A
V ⋅ (τ

−1

1+ λr ) 1 + K d ⋅ S
⋅

241



Cs =

A
V ⋅ (τ

−1

Kd+ λr ) 1 + K d ⋅ S⋅(3)The distribution coefficients for a number of elements inmarine waters are summarized in table 11.

(2)

Table 11. Distribution coefficients Kd for open ocean and ocean margins [I20]
Element

Kd (m3/kg)
Open ocean

Ocean margins

H

0.001

0.001

Cl

0.001

0.000 3

Sr

0.2

0.008

Tc

0.1

0.1

I

0.2

0.07

Cs

2

4

Pb

1 × 104

1 × 102

Ra

4

2

Th

5 × 103

3 × 103
1

U

0.2

Np

1 × 102

1Pu

2 × 103

1 × 102Am

2 × 103

2 × 103

99. A value of 3 years was given in reference [U3] for themean residence time, t, in a specified part of the marine system,
for all radionuclides in coastal waters with the exception of
239
Pu, for which a value of 3.5 years was assumed. These values
took account of radionuclide losses from water to sediment.

Table 12.

From simulations of the transport of radionuclides discharged
from the reprocessing plants at Sellafield and La Hague throughthe North Atlantic and its marginal seas, the mean residence
times given in table 12 were estimated using the North ­Atlantic–
Arctic Ocean Sea Ice Model (NAOSIM) [I21].

Residence times in different parts of the North Atlantic according to the NAOSIM modelPart of ocean

Volume (km³)

Mean residence time (a)North Sea

41 0002.5 ± 0.36

Norwegian Sea

59 0000.37 ± 0.11

Barents Sea

220 000

2.4 ± 0.24

Kara Sea

38 0004.5 ± 1.2

Central Nordic Seas

44 0000.52 ± 0.18

242

UNSCEAR 2008 REPORT: VOLUME II

100. As for freshwater aquatic biota, activity concentrations of radionuclides in marine biota can be estimated using
a concentration ratio approach. Concentration ratios for various elements in marine biota are compiled in table 13. For
Table 13.

Concentration ratios for marine biota [I20]
Element

Concentration factors (L/kg fresh weight)
Fish

Macroalgae

Crustaceans

H

1

1

1

Cl

0.06

0.05

0.06

Sr

3

10

10

Tc

80

30 000

1 000

I

9

10 000

100

Cs

100

50

30

Np

1

50

100

Pu

100

4 000

200

Am

100

8 000

400

Pb

200

1 000

9 000

Ra

100

100

100

Th

600

200

1 000

U

1

100

10

E.
1.

most elements, these data are based on concentrations inmuscle (fish) and soft tissue (crustaceans). For the boneseeking elements such as strontium, however, the entries intable 13 are based on whole body concentrations.

Evaluating doses to biota

Fraction of radiation absorbed by organism

101. Radionuclides distributed in the environment lead toexternal exposure of an organism living in or close to a
medium that contains radionuclides. The external exposureof biota is the result of complex and non-linear interactionsof various factors:– The geometrical relation between the source of theradiation and the target;– The activity levels of the radionuclides in theenvironment;– The materials in the environment and their shielding
properties;– The radionuclide-specific decay properties characterized by the radiation type, the energies emitted
and their emission probabilities; and103. The exposure due to radionuclides incorporated into
the organism is determined by the activity concentrations in
the organism, the size of the organism, and the type and theenergy of the emitted radiation. A key quantity for estimating internal doses is the absorbed fraction of energy, f(E),which is defined as the fraction of energy emitted by a radiation source that is absorbed within the target tissue, organ ororganism. In the simplest case, the organism is assumed to
be in an infinite homogeneous medium and to have a uniform activity concentration throughout its body. The densities of the medium and the organism’s body are assumed tobe identical. Under these conditions, both internal (Dint) andexternal (Dext) dose conversion coefficients (DCCs; the DCC
is defined as either the absorbed dose or the absorbed doserate, according to the circumstances, per unit activity concentration of the relevant radionuclide in the organism or
medium) for monoenergetic radiation can be expressed as afunction of the absorbed fraction [N1, V2]:

Dint = E ⋅φ ( E )and  Dext = E ⋅(1 − φ( E ))(4)

– The habitat and size of the organism.
102. The geometric relationship between the radiation source
and the exposed organism is an important factor in relation to
the absorbed dose rate incurred. The intensity of the radiation
field around a source decreases with distance and is influenced
by the material between the radiation source and the target.
The number of possible source target configurations is infinite;
therefore, a number of limited and representative situations
need to be selected for detailed consideration.

104. Absorbed fractions for photon and electron sources
uniformly distributed in soft-tissue spherical bodies
immersed in an infinite water medium have been systematically calculated by Monte Carlo simulation [U17]. The calculations covered a particle energy range of 10 keV to
5 MeV, a range for the mass of the body from 10−6 to 103 kg,
and shapes from spheres to ellipsoids with varying degrees
of non-sphericity. Figures III and IV show, respectively, theresults for electrons and photons.

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

Figure III. Absorbed fraction, φ(E), for electrons of different
energy uniformly distributed in spheres of different mass ina water medium

10-1

105. For electron energies below 100 keV, the absorbed
fraction is close to unity, even for very small organisms. The
mean free path of electrons in living tissue increases from
160 µm for 100 keV electrons to 5 mm for 1 MeV electrons.
Thus, even above 100 keV, the absorbed fraction is close tounity if the diameter of the target is much greater than therange of the electron. Only for very small targets and highenergies does the absorbed fraction become considerably
smaller than 0.5.
106. The mean free path of photons is considerably longer
than that of electrons. The absorbed fractions cover a range
from nearly unity for low photon energies and large organisms to less than 0.0001 for small organisms and high photon
energies. Absorption is a non-linear function of target sizeand energy. The main processes causing absorption of photon energy are the Compton effect, the photoelectric effectand pair production; their contributions to absorption dependon the energy of the emitted photons. As a result, theabsorbed fraction of photons in the energy range from 20 to
100 keV decreases by a factor of 10–15 for small organisms,
but is relatively constant for photons with energies between
100 keV and 1 MeV. Beyond energies of 1 MeV, the absorbed
fraction decreases steeply with energy.

(g)

106
105
104
103
102
101
100

SS

10-2
10-1
E (Me

100

V)

10-1
10-2

MA

Φ(E)

100

243

10-3

Figure IV. Absorbed fraction, φ(E), for photons of different
energy uniformly distributed in spheres of different mass ina water medium

100

107. The range of alpha particles in living tissue is very
short, increasing from 16–130 µm within the energy range of
3–10 MeV. Therefore, with the exception of bacteria, it isassumed for all organisms that all the energy emitted isabsorbed. Since the dimensions of bacteria are well below
the range of alpha particles, the absorbed fraction is assumed
to be zero.
108. Re-scaling factors have been derived from the computed absorbed fractions for spheres to determine the dosecoefficients for ellipsoidal shaped organisms, using the massand proportions of the organism. The relationship between there-scaling factors and the non-sphericity parameter of theorganism’s body are described analytically in reference [U17].
Owing to the short range of alpha particles, the internal exposure due to incorporated alpha emitters is independent of the
shape of the organism.

10-1

109. The approach was also applied to the calculation of
the absorbed fractions for non-aquatic animals and theirinternal exposures. With the use of the absorbed fractions forspheres and the suggested re-scaling and interpolation techniques, a set of internal DCCs has been calculated for allreference animals and plants [U17].

Φ(E)

10-2

10-3

10
105
4
10
103
2
10
101
100
10-1
10-2
10-3

6

10

g)

-4

MA
SS
(

10-2
10-1

E (Me

V)

100

110. The estimation of external exposures of terrestrial reference animals and plants is more complex than that of biota
in the aquatic environment. The intrinsically different density and composition of soil, air and organic matter cannot,
in general, be adequately taken into account by the application of analytical solutions. Dosimetric models for estimating external doses to biota in the terrestrial environment
were developed within the FASSET project [F4, T10]. A key
factor for determining external exposure is the geometric

244

UNSCEAR 2008 REPORT: VOLUME II

relationship between the radiation source and the exposedorganism. A number of limited and representative exposure
situations were selected for detailed consideration.
111. Simple three-dimensional phantoms, i.e. ellipsoids
and cylinders, were defined as model geometric equivalentsof reference organisms based on their average mass and size
characteristics. The dimensions ranged from a millimetre toa metre and the respective masses range from 0.2 g to
550 kg. The ellipsoids represented organisms such as woodlouse, earthworm, mouse, mole, snake, fox, deer and cattle.
Details of the assumed exposure conditions are given in reference [T10]. The fur and the outer layers of skin consist of
non-active tissue, and therefore shield the living organism.
112. Herbaceous vegetation, shrubs and trees were considered as reference plants. Exposure of the meristem and buds
was calculated because these organs are characterized byvery intensive cell division, which may make them highly
radiosensitive.
113. In order to take account of the distribution of radio­
nuclides in the canopy, a distinction was made between
alpha, beta and gamma radiation because of their different
ranges. For gamma radiation, the whole canopy was considered to have a homogeneous activity concentration. For
high-energy beta radiation, the irradiation of the target wasalso assumed to result from a canopy with a homogeneous
activity concentration. However, owing to the much shorter
range of alpha and low-energy beta radiation, the irradiation
resulting from external deposits on, or internal activity of,
the target organ had to be considered explicitly. Because of
the very short range of alpha particles in air, only the exposure due to the external deposits on, or internal exposure of,the target needed to be taken into account [T10].

114. The elemental composition and density of the materials involved have an important impact on the radiation transport calculation. All organisms were assumed to be composedof skeletal muscle alone with the characteristics/parameters
given in reference [I15]. The DCCs were derived using
Monte-Carlo techniques; all relevant processes of radiationtransport and interaction with matter were included. For
electrons, a thick-target bremsstrahlung model was usedinstead of an electron-transport simulation. For the calculation of DCCs for a species in the soil, a volume source withuniform activity concentration was assumed. For the calculation of DCCs for a species on the ground, a planar radiation source on top of the soil with a surface roughness of
3 mm and a volume source with a depth of 10 cm wereassumed. Calculations were made for monoenergetic gamma
energies of 50 keV, 300 keV, 662 keV, 1 MeV and 3 MeV.
Data for other energies were obtained by interpolation.

2.

Principal relationships for internal and external exposure(a)External exposure

115. Although the simulations cover only a limited numberof possible exposure conditions, they allow the relationships
between organism size, radiation energy and habitat to be
deduced. The DCC (Gy per photon per kg) increases in proportion to the photon energy as illustrated in figure V for a
volumetric source with a thickness of 0.5 m and target organisms that live at a depth of 0.25 m. Whereas the DCCs varyby a factor of 200 between photon energies of 50 keV to
3 MeV, the variation between the organisms does not exceeda factor of 2, even for low-energy photons (for high-energy
photons, the difference is a factor of only 1.5).

Figure V. Dose conversion coefficients for various soil organisms at a soil depth of 25 cm, for monoenergetic photons from a
uniformly distributed source in the upper 50 cm of soil (soil density: 1,600 kg/m³) [F4]DCC (Gy per photon/kg)

10-12

10-13

Woodlouse
Earthworm
Mouse
Mole
Snake
Rabbit
Fox

10-14

10-15
0.01

0.1

1

PHOTON SOURCE ENERGY (MeV)10

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

116. The DCC (Gy per photon per kg) for an earthworm as
a function of soil depth for monoenergetic photons is shownin figure VI. The upper 50 cm of the soil was assumed tohave a homogeneous activity concentration. The maximum

245

DCC was found to be at a depth of 25 cm and the lowest, at
depths of 0 cm and 50 cm. The maximum DCC is a factor of
2 higher than the lowest.

Figure VI. Dose conversion coefficients for an earthworm at various depths in soil, for monoenergetic photons from a
uniformly distributed source in the upper 50 cm of the soil (soil density: 1,600 kg/m3) [F4]DCC (Gy per photon/kg)

10 -12

10 -13Depth = 0.00 m
Depth = 0.05 m
Depth = 0.25 m
Depth = 0.50 m

10 -1410 -15
0.01

10

1

0.1

PHOTON SOURCE ENERGY (MeV)

117. The DCC at a depth of 5 cm is only about 20% lower
than the maximum. This is because of the relatively shortmean free path of photons in soil, which is about 0.2, 2 and10 cm for photon energies of 20 keV, 100 keV and 3 MeV,
respectively. Thus, an organism in soil would be irradiatedby photons originating within a surrounding shell of, at
most, 10 cm radius.
118. The DCCs (Gy per photon per m2) for different reference organisms for a planar source on the soil surface are

given in figure VII. The DCCs decrease as the photon energy
increases from 10 to 100 keV by a factor of about 5 for small
animals and 2 for large animals. Above 100 keV, the DCCs
gradually increase by approximately two orders of magnitude; the DCCs for small animals are greater than those forlarge animals owing to the more effective self-shielding inlarge organisms. Such differences are more pronounced at
low energies; for example, the difference between the mouseand the cow is a factor of about 6 for 50 keV photons,
whereas it is a factor of 3 for 3 MeV photons.

Figure VII. Dose conversion coefficients as a function of the source energy for various reference organisms for a planarsource on top of the soil [F4]-142DCC (Gy per photon/m )

10

10

-15

10

-16

10

-17

Cow
Roe deer
Wolf
Rabbit
Mole
Mouse

0.01

0.1

1

PHOTON SOURCE ENERGY (MeV)1010-14(a) Mouse
10-15

UNSCEAR 2008 REPORT: VOLUME II

119. The DCCs for different animals as a function of thedepth of a planar source in the soil are summarized in figure VIII. The results show that the DCCs for low-energy

DCC (Gy per photon/m2)

246

10-16

photons
for animals living on soil are low. Relatively shal10-17
low depths of soil over the planar source suffice to attenuate
the photons
completely.
10-18
Source depth:
0 g/cm2
1 g/cm2

10-19

10 g/cm2and depth of a planar source in the soil for (a) the
Figure VIII. Dose conversion coefficients as a function of the source energy
10-20
0.01
0.1
10
1
mouse and (b) the cow living on the soil
PHOTONfor soil densities of
The source depth quantifies the amount of soil by which the photon source is covered (e.g. the source
depthSOURCEof 10ENERGY
g/cm2 (MeV)
1.0 and 1.6 g/cm2 are equivalent to a depth of the source in the soil of 10 and 6.25 cm, respectively) [F4]
10-14

10-14

(a) Mouse(b) Cow
10-15
DCC (Gy per photon/m2)

DCC (Gy per photon/m2)

10-15
10-16
10-17
10-18

Source depth:
0 g/cm2

1 g/cm2

10-19

10-16
10-17
10-18

Source depth:

10-19

1 g/cm2

0 g/cm2

10 g/cm2
10-20

0.01

0.1

1

10 g/cm2
10-20

10

0.01

PHOTON SOURCE ENERGY (MeV)

0.1

1

10

PHOTON SOURCE ENERGY (MeV)

10-14

DCC (Gy per photon/m2)

120. The(b)data
indicate that the relationship between the
Cow
DCCs,
-15 the size and habitat of the organism and the energy
10and type of the radiation is complex. Nevertheless, these
data10provide
an appropriate basis for deriving data, either by-16
interpolation or by extrapolation, for other exposure conditions
10-17that were not explicitly considered. They were used toderive radionuclide-specific DCCs (µGy/h per Bq/kg) forinternal
and external exposure of a numberSourceof reference
10-18
depth:
organisms, taking into account the type of radiation
as well
0 g/cm2
as theenergyandintensityoftheemission,asspecifiedby
1 g/cm2
10-19
the ICRP [I13]. Table 14 summarizes the DCCs10(µGy/h
g/cm2 perBq/kg)
for external exposure. The data are provided accord10-20
ing to the 0.01
habitat of organisms
considered.
0.1
1 Animals living
10
in soil were assumed to PHOTON
be at a SOURCE
depth ENERGY
of 25 cm
in
a
soil
layer
(MeV)
that is homogeneously contaminated by radionuclides to adepth of 50 cm. Above ground organisms were assumed tobe irradiated by a source homogeneously distributed in thesoil layer to a depth of 10 cm. For the terrestrial organisms,
only the contribution of photons was included, whereas foraquatic organisms, exposure due to electrons (including
bremsstrahlung) was also implicitly taken into account.
This has the effect of causing the DCCs for 3H, 90Sr and135

Cs to appear to be inconsistent: the DCCs for 3H and 135Cs
for terrestrial organisms are zero, whereas the values foraquatic organisms are very small. Aquatic organisms are in
direct contact with the contaminated medium, whereas electrons emitted from soil are attenuated by the surface roughness of the soil, the air and the fur of terrestrial organisms.
So, this apparent inconsistency is of no significant practicalconsequence.
(b)

Internal exposure121. The DCCs (µGy/h per Bq/kg) for internal exposure
are provided in table 15 [U17]. The values are given interms of weighted absorbed dose rate per unit activity concentration in the organism, assuming homogeneous distribution of the radionuclides. The DCCs have been weighted
to take account of the different RBEs of the different qualities of radiation; a factor of 10 to reflect the RBE has beenused for alpha radiation and a factor 1 to reflect that for
gamma and beta radiation including that from tritium (seethe next subsection).

1.5 × 10‑100

3.5 × 10‑6

1.9 × 10‑4

8.3 × 10‑40

3.0 × 10‑4

6.0 × 10‑7

9.0 × 10‑4

1.4 × 10‑7

1.2 × 10‑7

7.6 × 10‑6

8.5 × 10‑8

1.6 × 10‑7

6.1 × 10‑6

Sr

Tc

I

I

Cs

Cs

Cs

Pb

Ra

Th

U

Np

Pu

Pu

Am

In soil a

5.5 × 10‑6

1.3 × 10‑7

7.2 × 10‑8

7.0 × 10‑6

1.0 × 10‑7

1.2 × 10‑7

8.5 × 10‑4

5.2 × 10‑7

2.8 × 10‑40

7.8 × 10‑4

1.8 × 10‑4

3.0 × 10‑60

1.2 × 10‑100Rat

9.2 × 10‑7

1.4 × 10‑8

9.5 × 10‑9

1.4 × 10‑6

1.0 × 10‑8

1.3 × 10‑8

1.8 × 10‑4

7.7 × 10‑8

5.6 × 10‑50

1.6 × 10‑4

3.7 × 10‑5

4.0 × 10‑70

4.6 × 10‑12

0

Deer

2.4 × 10‑6

5.4 × 10‑8

3.0 × 10‑8

3.3 × 10‑6

4.3 × 10‑8

3.9 × 10‑8

3.2 × 10‑4

2.6 × 10‑7

1.1 × 10‑40

2.9 × 10‑4

7.1 × 10‑5

1.1 × 10‑60

1.5 × 10‑11

0

Duck

2.6 × 10‑6

6.0 × 10‑8

3.3 × 10‑8

3.6 × 10‑6

4.8 × 10‑8

4.3 × 10‑8

3.4 × 10‑4

2.8 × 10‑7

1.1 × 10‑40

3.2 × 10‑4

7.7 × 10‑5

1.1 × 10‑60

1.6 × 10‑11

0

Frog
0

Bee

2.6 × 10‑6

6.2 × 10‑8

3.3 × 10‑8

3.6 × 10‑6

5.0 × 10‑8

4.4 × 10‑8

3.5 × 10‑4

2.9 × 10‑7

1.2 × 10‑40

3.2 × 10‑4

7.8 × 10‑5

1.1 × 10‑60

1.6 × 10‑11

On soil b

2.6 × 10‑6

6.1 × 10‑8

3.3 × 10‑8

3.6 × 10‑6

4.9 × 10‑8

4.3 × 10‑8

3.4 × 10‑4

2.9 × 10‑7

1.1 × 10‑40

3.2 × 10‑4

7.8 × 10‑5

1.1 × 10‑60

1.6 × 10‑11

0

Grass

2.6 × 10‑6

6.1 × 10‑8

3.3 × 10‑8

3.6 × 10‑6

4.9 × 10‑8

4.3 × 10‑8

3.4 × 10‑4

2.9 × 10‑7

1.1 × 10‑40

3.2 × 10‑4

7.8 × 10‑5

1.1 × 10‑60

1.6 × 10‑11

0

Pine
tree

Absorbed dose rates per activity concentration (µGy/h per Bq/kg)

a Organisms are assumed to live at 25 cm depth of a soil with radionuclides distributed homogeneously to a depth of 50 cm.
b Organisms are assumed to live on a soil layer with radionuclides distributed homogenously to a depth of 10 cm.
c Organisms are assumed to be immersed in water.

241

240

239

237

238

232

226

210

137

135

134

131

129

99

90

3

0

Earthworm

H

Radionuclide

Table 14. Dose conversion coefficients for external exposure of reference organisms [E10, T10, U17]

1.1 × 10‑5

1.4 × 10‑7

8.2 × 10‑8

1.2 × 10‑5

1.0 × 10‑7

1.5 × 10‑7

9.1 × 10‑4

2.7 × 10‑6

2.7 × 10‑4

4.5 × 10‑8

7.6 × 10‑4

1.9 × 10‑4

7.7 × 10‑6

1.2 × 10‑7

2.2 × 10‑5

7.9 × 10‑12Pelagic
fish

1.2 × 10‑5

1.9 × 10‑7

1.0 × 10‑7

1.3 × 10‑5

1.3 × 10‑7

1.8 × 10‑7

9.6 × 10‑4

4.7 × 10‑6

2.9 × 10‑4

4.5 × 10‑8

8.0 × 10‑4

2.0 × 10‑4

9.2 × 10‑6

1.2 × 10‑7

4.9 × 10‑5

7.8 × 10‑12

Benthic
fish

Brown
seaweed

1.7 × 10‑5

6.8 × 10‑7

3.0 × 10‑7

1.8 × 10‑5

5.1 × 10‑7

5.0 × 10‑7

1.1 × 10‑3

4.7 × 10‑5

3.4 × 10‑4

4.3 × 10‑7

8.9 × 10‑4

2.3 × 10‑4

1.3 × 10‑5

1.5 × 10‑6

2.0 × 10‑4

8.2 × 10‑11

In water c

1.1 × 10‑5

1.6 × 10‑7

8.7 × 10‑8

1.3 × 10‑5

1.1 × 10‑7

1.6 × 10‑7

9.1 × 10‑4

3.0 × 10‑6

2.8 × 10‑4

5.2 × 10‑8

7.6 × 10‑4

1.9 × 10‑4

7.9 × 10‑6

1.4 × 10‑7

2.2 × 10‑5

1.0 × 10‑11

Crab

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA
247

1.6 × 10‑4

6.2 × 10‑4

5.8 × 10‑5

4.2 × 10‑4

1.4 × 10‑4

1.9 × 10‑4

3.9 × 10‑5

1.8 × 10‑4

2.4 × 10‑4

1.3 × 10‑1

5.3 × 10‑4

5.8 × 10‑5

3.8 × 10‑5

1.1 × 10‑4

1.1 × 10‑4

3.9 × 10‑5

1.5 × 10‑4

2.3 × 10‑4

1.3 × 10‑1

Sr

Tc

I

I

Cs

Cs

Cs

Pb

Ra

Rat

1.5 × 10‑4

Earthworm

3.0 × 10‑2
3.0 × 10‑2
3.2 × 10‑2

Pu

Pu

Am

a Assumes a homogeneous activity distribution in the organism.
b Assumes an RBE of 10 for alpha and 1 for beta.

241

240

239

237

238

232

2.7 × 10‑2

1.3 × 10‑1

2.3 × 10‑4

1.4 × 10‑4

3.9 × 10‑5

1.1 × 10‑4

1.1 × 10‑4

3.8 × 10‑5

5.8 × 10‑5

5.1 × 10‑4Np

1.4 × 10‑1

2.2 × 10‑4

1.4 × 10‑4

3.8 × 10‑5

9.9 × 10‑5

1.1 × 10‑4

3.7 × 10‑5

5.7 × 10‑5

4.4 × 10‑4

2.4 × 10‑2

1.3 × 10‑1

2.4 × 10‑4

1.6 × 10‑4

3.9 × 10‑5

1.4 × 10‑4

1.2 × 10‑4

3.9 × 10‑5

5.8 × 10‑5

5.9 × 10‑4Grass

1.5 × 10‑4

3.3 × 10‑6

1.5 × 10‑4BeeU

1.4 × 10‑1

2.5 × 10‑4

2.0 × 10‑4

3.9 × 10‑5

2.5 × 10‑4

1.5 × 10‑4

4.4 × 10‑5

5.8 × 10‑5

6.3 × 10‑4

1.6 × 10‑4

Frog

2.3 × 10‑2

1.4 × 10‑1

2.5 × 10‑4

3.7 × 10‑4

3.9 × 10‑5

7.1 × 10‑4

2.6 × 10‑4

5.0 × 10‑5

5.8 × 10‑5

6.5 × 10‑4

1.6 × 10‑4

Duck

Th

226

210

137

135

134

131

129

99

90

1.6 × 10‑4Deer

1.4 × 10‑1

2.5 × 10‑4

3.5 × 10‑4

3.9 × 10‑5

6.5 × 10‑4

2.5 × 10‑4

5.0 × 10‑5

5.8 × 10‑5

6.5 × 10‑4

1.6 × 10‑4

Pine tree

Weighted absorbed dose rates per activity concentration (µGy/h per Bq/kg)a,b

Weighted dose conversion coefficients for internal exposure of reference organisms [T10, U20]

Cl

36

3

H

Radionuclide

Table 15.

1.4 × 10‑1

2.5 × 10‑4

1.9 × 10‑4

3.9 × 10‑5

2.3 × 10‑4

1.4 × 10‑4

4.3 × 10‑5

5.8 × 10‑5

6.3 × 10‑4

1.6 × 10‑4Pelagic
fish

1.3 × 10‑1

2.4 × 10‑4

1.8 × 10‑4

3.9 × 10‑5

1.9 × 10‑4

1.3 × 10‑4

4.2 × 10‑5

5.8 × 10‑5

6.0 × 10‑4

1.6 × 10‑4

Benthic
fish

1.4 × 10‑1

2.0 × 10‑4

1.3 × 10‑4

3.8 × 10‑5

9.7 × 10‑5

1.0 × 10‑4

3.8 × 10‑5

5.7 × 10‑5

4.5 × 10‑4

1.4 × 10‑4

Brown
seaweed

1.4 × 10‑1

2.5 × 10‑4

1.9 × 10‑4

3.9 × 10‑5

2.3 × 10‑4

1.4 × 10‑4

4.3 × 10‑5

5.8 × 10‑5

6.3 × 10‑4

1.6 × 10‑4

Crab

248
UNSCEAR 2008 REPORT: VOLUME IIANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

(c)Relative biological effectiveness122. The effects of radiation exposure on biota depend not
only on the absorbed dose, but also on the type or quality of
the radiation. For example, alpha particles and neutrons can
produce observable damage at much lower absorbed doses
than beta or gamma radiation. Thus, the absorbed dose (ingray) is often multiplied by a factor in order to account for
the RBE of the quality of the radiation.
123. A number of authors have evaluated the data on the
RBE of different types of radiation [A1, C1, E2, F4, T7,
U4, U26]. Nominal values for the factor to reflect theRBE of alpha particles derived from these reviews are249

summarized in table 16. The experimental values of RBE
are specific to the endpoint studied, the biological, environmental and exposure conditions (e.g. reference radiation,dose rate, and dose) amongst other factors. Thus, as noted
in a FASSET report [F4], it is difficult to develop a generally valid factor to reflect the RBE for different radiation
qualities for use in an environmental risk assessment. The
ACRP [A1] and FASSET [F4] have therefore proposed
ranges of values for general application. Both selected afactor of 10 to reflect the RBE for alpha particles, the
ACRP, citing references [K2, T7, U4], referring to it as a
notional central value, and FASSET as a value “to illustrate” the impact of the RBE for an internally depositedalpha emitter.

Table 16. Modifying factors to reflect the RBE of alpha radiation for deterministic effects on non-human biota (relative to
low-LET radiation)
SourceNominal value

Comment[N1]

1

Built-in conservatism in dose model

[I4]

20

Numerically the same as the radiation weighting factor used in the protection of humans

[B22]

2–10

Non-stochastic effect of neutrons and heavy ions

[U4]

5

Average for deterministic effects

[T7]

10

Deterministic population-relevant endpoints

[C1]

20

Likely to be conservative for deterministic effects

[E3]

40

Includes studies with high RBE values

[E12]

<35

Based on concentrations in the whole body

[A1]

5–20 (10)

5–10 deterministic effects (cell-killing, reproductive)
10–20 cancer, chromosome abnormalities
10 nominal central value[F4]

5–50 (10)10 to illustrate the effect of the alpha RBE[K19]<7 to <35

Upper bound of estimate of RBE

124. Chambers et al. [C5] reported a review of the literature on experimentally determined RBEs for internallydeposited alpha-emitting radionuclides. The relevance ofeach experimental result in selecting a factor to reflect theRBE for alpha particles was judged on the basis of pre-­established criteria. They recommended a nominal factor of
5 to reflect the RBE for alpha particles for population-­
relevant deterministic and stochastic endpoints but, to reflect
the limitations in the experimental data, they also suggested
uncertainty ranges of 1–10 and 1–20 for population-relevant
deterministic and stochastic endpoints, respectively. The

data developed by Chambers et al. [C5] after application of
their evaluation criteria are summarized in figure IX. Threeevaluation criteria were used in reference [C5]. Criterion 1
required the dosimetric conditions to be sufficiently welldefined and not peculiar to the source of radiation. Criterion 2 required the dose–effect relationships to be sufficiently well known so that the results from the dose rates
used experimentally can be applied to effects that may occur
with environmental dose rates. Criterion 3 required theexperimental uncertainties to be discussed by the authors of
the original studies.

250

UNSCEAR 2008 REPORT: VOLUME II

Figure IX. Application of the criteria to the distribution of RBEs (all endpoints) [C5]80
RBEs eliminated by criterion #3 only

70

NUMBER OF RBE VALUESRBEs eliminated by criterion #2 only
60

RBEs eliminated by criterion #1 only
RBEs remaining after all criteria applied

50
40
30
20
10
0

<5

5-10

11–20

21–40

41–80

81–160>160

RBE RANGE

125. Knowles [K19] reported on experimental studies ongroups of zebra fish that were exposed from an early age todifferent dose rates of gamma and alpha radiation (the latter
was from 210Po). Among the gamma-irradiated fish, only
those in the highest dose-rate group (7,400 mGy/h) showedradiation-related damage. No groups of alpha-irradiated fish
showed evidence of radiation-induced reduction in egg production even though autoradiographs showed concentrationsof 210Po in the testes and ovaries. Since the highest alphadose rate (214 mGy/h) showed no effect, comparison withthe gamma dose rate of 7,400 mGy/h, which caused egg production to cease, resulted in only upper limits to the RBE.
These were calculated to be in the range of <7 to <20 basedon ovary concentrations and <35 based on whole body concentrations. The authors suggested that the RBEs derived
from their work provide the best available (upper bound)estimates for a population-relevant effect for fish.
126. The ACRP [A1] considered tritium beta radiation
because the low velocity of the beta particles (maximum
energy = 18.6 keV) results in a relatively high LET over ashort path length. It has an LET very similar to that of 70 keV
photons, which are representative of the X‑rays used inradio­biological research and in diagnostic medicine [M6]. In
their review of the effects of tritiated water (HTO) in mammals and fish, Environment Canada in their Priority Substances List (PSL2) [E3] listed tritium RBE values ranging
from 1.7 to 3.8, with gamma rays from 60Co or 137Cs being
used as the reference radiation. Based on this, they recommended a factor of 3 to reflect the RBE of beta radiationfrom tritium. Research conducted at Atomic Energy of Canada Ltd. on breast cancers in female rats [G1] and on myeloid leukaemia in male mice indicated an RBE value of 1.2
for tritium, with X‑rays being used as the reference

radiation. The difference between these values is largely the
result of the choice of reference radiation. Sinclair [S8] has
shown that, at low doses, X‑rays are about twice as effective
as gamma rays in producing damage. Hence, the radiationfrom tritium has an effectiveness for biological damage inthe higher part of the range expected for the gamma and
X‑ray photon energies likely to be experienced in the environment. Citing Straume and Carsten [S9] amongst others,
the ACRP concluded that for the dosimetry of non-humanspecies, where the endpoints are usually deterministic innature, a reasonable average factor to reflect the RBE of beta
particles may be 2 with a range of 1–3, depending on theendpoint being assessed [A1].
127. A number of studies suggested that beta radiation
with energies below 10 keV has a higher RBE than electrons
with energies above 10 keV [M10, S9]. Straume and Carsten[S9] reviewed 33 studies of the RBE of tritium beta particles
and found arithmetic means of 1.8 based on X‑rays as thereference radiation, and 2.3 with 137Cs or 60Co gamma rays as
the reference radiation. Most of these studies related todeterministic effects. Moiseenko et al. [M10] considered an
appropriate factor to reflect the RBE of beta particles fromtritium (mean beta energy <10 keV) to be between 2 and 3.
The UK Health Protection Agency (HPA) [H21] reviewed
the RBE studies on tritium beta particles along with a wide
variety of experimental studies using X‑rays and gamma
rays as reference radiations and noted that the RBEs generally ranged from 1 to 2 when compared to orthovoltage
X‑rays and from 2 to 3 when compared to gamma rays
[H21]. Little and Lambert [L9] also reviewed the experimental studies of cancer induction, chromosomal aberration, cell
death and various other endpoints and arrived at similar­conclusions for the RBE of tritium in water.

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

128. In order to illustrate the effect of the radiation quality ofemissions from internally deposited radionuclides, the ­FASSET
programme recommended the use of a factor of 10 to reflect
the RBE of alpha radiation, 3 for low-energy beta radia­tion(E < 10 keV), and 1 for both beta radiation with energies
greater than 10 keV and for gamma radiation [F4, L4].

results are particularly sensitive to the choice of factor,
especially for radiation from the actinides and tritium. The
contributions of weighted internal doses to the total normalized doses are close to or above 90%, which indicates thatinternal exposure is the dominant pathway.
131. These annual doses took account of external exposure
as well as internal exposure via inhalation and ingestion.
They are compared with the weighted absorbed doses to biota
in table 19. The ranges given in the table for biota reflect thevariations between the different reference organisms considered. This comparison has however some inherent limitations. The values for humans are expressed in terms of annual
effective dose, whereas the values for biota are in terms ofweighted absorbed dose and were estimated assuming ahomogeneous distribution of the radionuclide in the organism. Furthermore, the annual effective doses per unit deposition to humans were based on a radiation weighting factor of
20 for alpha particles, whereas the weighted absorbed doses
to biota were based on a factor of 10 to reflect the RBE foralpha particles. Further still, the values for humans reflectlargely the transfer of radionuclides through agricultural ecosystems, whereas the values for biota are more typical of thetransfer in forests and semi-natural ecosystems.

129. The Committee, in its UNSCEAR 1996 Report [U4],recommended a nominal factor of 5 to reflect the RBE forinternally deposited alpha emitters. The Committee now­recommends a nominal (generic) factor of 10 to reflect theRBE for internally deposited alpha radiation. For beta andgamma radiation, the Committee recommends a nominal(generic) factor of 1 to reflect the RBE. However, it should beunderstood that the most appropriate factor to reflect the RBE
for low-energy (<10 keV) beta radiation remains an open
question and ought to be the subject of future research. These­recommended values to reflect the RBE are intended to apply
on a generic basis across all organisms and endpoints. Where
appropriate scientific information specific to a particularorganism and endpoint exists, such information is preferred.
(d)

251

Dose rates for internal exposure132. Despite these differences, the estimated normalized
effective doses to humans and the weighted absorbed doses tobiota are about the same order of magnitude, except in thecases of 129I and 131I. These exceptions are probably due to thespecial importance of radiation exposure of the human thyroid in evaluating effective dose, which has no counterpart in
the dosimetry for biota. Thus, apart from these exceptions,the comparison indicates that for similar levels of radio­
nuclides in the environment, the effective doses to humans
and the weighted absorbed doses to biota are comparable.

130. The dose from unit exposure of the selected reference
organisms is estimated from the weighted absorbed dose
rate due to external exposure arising from deposits in the
ground and that due to internal exposure. Weighted absorbed
dose rates to the reference organisms normalized for continuous exposure to 1 Bq/m3 in air for each radionuclide are
given in table 17. These weighted absorbed dose rates were
calculated assuming the factors to reflect the RBE recommended by the Committee. Table 18 summarizes the ratiosof weighted to non-weighted normalized total doses. The

Table 17. Normalized weighted absorbed dose rates per unit activity concentration to various biota from internal exposureRadionuclide

Weighted dose rate per unit activity concentration (µGy/h per Bq/m3)
Earthworm

Rat

H

1.7 × 10‑19

1.7 × 10‑19

1.7 × 10‑19

1.7 × 10‑19

1.7 × 10‑19

1.7 × 10‑19

1.7 × 10‑19

1.7 × 10‑19Cl

5.6 × 10

3.3 × 10

3.3 × 10

3.3 × 10

3.3 × 10

9.3 × 10

5.4 × 10

5.5 × 10‑14

Sr

‑15

6.1 × 10

1.2 × 10

1.3 × 10

7.3 × 10

7.5 × 10

5.1 × 10

1.8 × 10

4.3 × 10‑13

Tc

4.4 × 10‑15

4.4 × 10

4.4 × 10

4.4 × 10

4.4 × 10

4.4 × 10‑13

2.4 × 10

4.8 × 10‑15

129I

2.3 × 10‑14

4.8 × 10‑14

4.9 × 10‑14

4.5 × 10‑14

4.0 × 10‑14

2.9 × 10‑14

1.7 × 10‑14

2.1 × 10‑14I

4.6 × 10‑16

1.3 × 10‑15

1.8 × 10‑15

4.2 × 10‑16

3.4 × 10‑16

1.9 × 10‑16

1.6 × 10‑15

2.8 × 10‑15Cs

1.7 × 10

2.7 × 10

4.5 × 10

9.7 × 10

8.1 × 10

6.6 × 10

8.7 × 10

1.2 × 10‑13

Cs

8.3 × 10

2.7 × 10

2.7 × 10

7.1 × 10

5.4 × 10

5.0 × 10

6.7 × 10

1.7 × 10‑14Cs

4.7 × 10

4.4 × 10

1.1 × 10

1.9 × 102.0 × 102.0 × 10‑13

1.9 × 10

2.3 × 10‑13

3

36
90

99

131
134
135
137

‑13
‑15
‑13

‑13
‑12
‑15

‑13
‑13
‑13

Duck

‑13
‑12
‑15

‑13
‑13
‑13

Frog

‑13
‑13
‑15

‑14
‑14
‑13

Bee

‑13
‑13
‑15

‑14
‑14
‑13

Grass

‑15
‑14
‑15

‑14
‑15
‑13

Pine tree

‑13
‑13

‑14
‑14

Pb

2.9 × 10‑14

9.4 × 10‑15

9.2 × 10‑15

1.2 × 10‑14

1.2 × 10‑14

1.1 × 10‑14

1.3 × 10‑14

8.7 × 10‑16Ra

5.0 × 10‑12

2.1 × 10‑12

4.7 × 10‑13

8.9 × 10‑13

9.3 × 10‑13

3.7 × 10‑12

1.5 × 10‑11

1.3 × 10‑12Th

4.9 × 10

6.4 × 10

5.6 × 10

2.8 × 10

2.8 × 10

4.9 × 10

8.4 × 10

4.0 × 10‑13U

5.8 × 10

2.4 × 10

2.4 × 10

2.4 × 10

2.4 × 10

7.5 × 10

9.9 × 10

1.8 × 10‑11

210
226

‑15

Deer

232

238

‑13
‑12

‑15
‑12

‑15
‑12

‑14
‑12

‑14
‑12

‑13
‑12

‑13
‑13

Np

1.9 × 10

1.5 × 10

1.5 × 10

1.5 × 10

1.5 × 10

4.0 × 10

4.1 × 10

4.9 × 10‑12

239

Pu

2.1 × 10

1.7 × 10

1.7 × 10

1.7 × 10

1.7 × 10

4.4 × 10‑12

4.5 × 10

5.4 × 10‑12

240

Pu

7.2 × 10‑12

2.9 × 10‑12

2.9 × 10‑12

2.9 × 10‑12

2.9 × 10‑12

9.3 × 10‑12

3.9 × 10‑12

3.1 × 10‑12Am

8.8 × 10‑14

8.6 × 10‑14

7.6 × 10‑14

7.9 × 10‑14

8.0 × 10‑14

8.0 × 10‑14

3.7 × 10‑12

3.3 × 10‑12

237

241

‑12
‑12

‑12
‑12

‑12
‑12

‑12
‑12

‑12
‑12

‑12
‑12

‑12

252

UNSCEAR 2008 REPORT: VOLUME IITable 18.

Ratio of weighted and unweighted doses
Ratio of weighted dose/unweighted dosea

Radionuclide
Earthworm

Rat

Deer

Duck

Frog

Bee

Grass

Pine tree

H

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

3

Cl

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

Sr

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

36
90

Tc

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

129

I

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

99

I

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

Cs

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

Cs

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

Cs

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

131
134
135
137

Pb

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

Ra

2.0

1.0

1.1

1.2

1.1

3.3

7

2

Th

9.9

7.1

9.5

9.7

9.7

10

10

10

U

10

10

10

10

10

10

10

10

Np

9.1

8.9

9.6

9.4

9.3

9.6

9.6

9.7

Pu

10

10

10

10

10

10

10

10

210
226

232

238
237

239

Pu

10

10

10

10

10

10

10

10

Am

4.1

4.3

7.9

6.1

5.9

5.9

10

10

240
241

a Factors to reflect the RBE: alpha radiation, 10; beta and gamma radiation, 1.

Table 19.

Comparison of doses to biota and humans, normalized for unit deposition to terrestrial ecosystems
Radionuclide

Biota (range)a
Normalized weighted absorbed dose rate
(Gy a‑1 per Bq m‑2 a‑1)

Humansb
Normalized effective dose rate
(Sv a‑1 per Bq m‑2 a‑1)

Minimum

MaximumSr

6.2 × 10‑9

1.3 × 10‑6

4.7 × 10‑7Tc

4.4 × 10‑9

2.5 × 10‑7

1.8 × 10‑8129I

1.7 × 10‑8

5.0 × 10‑8

6.3 × 10‑7I

2.0 × 10‑10

2.8 × 10‑9

1.0 × 10‑7

134

Cs

6.7 × 10‑8

4.6 × 10‑7

1.3 × 10‑7

135

Cs

5.1 × 10‑9

2.8 × 10‑7

1.2 × 10‑8

137

Cs

1.1 × 10‑7

4.8 × 10‑7

1.3 × 10‑7Pb

8.9 × 10‑10

2.9 × 10‑8

2.5 × 10‑6Ra

4.8 × 10‑7

1.5 × 10‑5

1.6 × 10‑6Th

5.6 × 10‑9

8.5 × 10‑7

1.2 × 10‑6U

1.0 × 10‑6

1.8 × 10‑5

6.0 × 10‑7Np

1.5 × 10‑6

5.0 × 10‑6

4.9 × 10‑7Pu

1.7 × 10‑6

5.5 × 10‑6

6.8 × 10‑7Pu

3.0 × 10‑6

9.5 × 10‑6

6.8 × 10‑7Am

7.7 × 10‑8

3.8 × 10‑6

5.8 × 10‑7

90

99

131

210
226

232

238
237

239
240
241

a Range represents the minimum and maximum among the organisms considered.
b Calculated according to [I11].

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

3. Doses to non-human biota(a)

TFflora,r is the transfer factor from soil to flora (Bq/kg flora per
Bq/kg soil).

Calculation of doses to biota

133. In terrestrial environments, the most important sourceof radiation exposure as a consequence of discharges ofradio­nuclides to the environment is due to deposition on soil.
Radionuclides present in soil are generally a persistent radiation source for all terrestrial biota. Aquatic organisms areirradiated externally by the activity in water and, in the casesof bottom dwellers and benthic organisms, the activity insediments, and internally by incorporated radionuclides. The
dose rate, D, can be calculated according to:

D = ∑  DCCext ,r ⋅ Csoil ,water ,r + DCCint,r ⋅ Cbiota ,r 
r(5)where DCCext,r is the DCC for external exposure to radio­
nuclide r (µGy/h per Bq/kg); Csoil,water,r is the activity concentration of radionuclide r in soil or water (Bq/kg); DCCint,r isthe DCC for internal exposure to radionuclide r (µGy/h per
Bq/kg); and Cbiota,r is the internal activity concentration ofradionuclide r in biota (flora or fauna) (Bq/kg).
(b)

Activities in environmental media

134. In the absence of measurements, in order to evaluate
equation (5), the activity concentrations, Csoil,water,r , and Cbiota,r ,have to be estimated. Assuming a constant discharge of radionuclides over a period of 50 years, the activity in soil for thelast year of that period is calculated as indicated in reference[I11]:
C s ,r =Dtot ,r(lr + lm ) ⋅ ms

253

⋅ [1 − exp(−(lr + lm ) ⋅ te )] (6)where Cs,r is the activity concentration in soil (Bq/kg); Dtot,ris the total (wet plus dry) deposition rate to soil (Bq m‑2 a‑1);
ms is the mass of the upper soil layer (kg/m2); lr is the radioactive decay constant (a‑1); lm is the loss rate from the upper
soil layer (a‑1); and te is the discharge period (50 a).
135. The total deposition is calculated as the sum of dry(Ddry,r) and wet deposition (Dwet,r). The activity concentrationin flora, Cflora,r, is estimated by taking into account direct
deposition on the foliage and uptake from soil according toreference [I11]:

136. The activity concentration in reference fauna is estimated from the soil concentration and the soil–fauna transfer
factor as follows:C fauna ,r = Cs,r ⋅ TFfauna ,r(8)

where TFfauna,r is the soil–fauna transfer factor (Bq/kg fauna
per Bq/kg soil).
137. The habitats of the reference fauna are differentiatedaccording to whether the organisms live in or above soil.
DCCs for species living in soil are expressed in units ofµGy/h per Bq/kg and are based on the assumption that theorganism lives in the centre of a slab containing radio­
nuclides uniformly distributed to a depth of 50 cm. For
organisms living on soil, it is assumed that radionuclides arehomogeneously distributed to a depth of 10 cm; the DCCs inthis case have units of µGy/h per Bq/m2.
138. The estimation of the activity concentration of a radio­
nuclide in aquatic biota (Caqua biota) is usually obtained fromthe activity concentration in water (Cwater) and the concentration factor (CFwater–biota) according to:Caqua biota = Cwater ,r ⋅ CFwater −biota ,r(9)139. As outlined above, the exposure due to incorporated
radionuclides is determined by the size and geometry of theorganism, the radionuclide distribution, and the type andenergy of the emitted radiation. Currently, DCCs are notavailable for specific target organs in the reference organisms; the DCCs for internal exposure are therefore based on
the assumption that the radionuclides are homogeneously
distributed throughout the organism [T10].
(c) oses to marine organisms and to humans due toDc­ onsumption of marine food

140. As an example of the calculations of exposures ofaquatic organisms, the exposures to marine organisms arecalculated assuming a radionuclide concentration in water of
1 Bq/m3 and applying the appropriate concentration factor
for water–biota in table 13 and the appropriate DCCs given
in tables 14 and 15. The weighted absorbed dose rates toDdry ,r + fw ⋅ Dwet ,rflatfish, crab and brown seaweed are summarized in table 20.
C flora ,r =⋅ [1 − exp(−(lw,r + lr ) ⋅ t w )] + Cs,r ⋅ TFflora ,rFor all radionuclides considered, the dose rates to biota are(lw,r + lr ) ⋅ balmost completely a result of internal exposure. For comparison, the effective dose rates to an adult human are given− exp(−(lw,r + lr ) ⋅ t w )] + Cs,r ⋅ TFflora ,r(7)
assuming an annual fish intake of 20 kg. In general, thewhere fw is the interception fraction (dimensionless); b is theeffective dose rates to humans are much less than thestanding biomass (kg/m2); lw is the activity loss rate fromweighted absorbed dose rates to biota for a unit activity
plants due to weathering (a-1); tw is the exposure time (a); and­concentration of a radionuclide in marine water.

254

UNSCEAR 2008 REPORT: VOLUME IITable 20.
1 Bq/m3Comparison of doses to non-human biota and humans, normalized to an activity concentration in marine water ofRadionuclide

Non-human biota

Humansa

Weighted absorbed dose rate (µGy/h per Bq/m3)

Normalized effective dose rate(µSv/h per Bq/m3)

FlatfishCrabMacroalgaeH

3.3 × 10‑9

3.3 × 10‑9

3.3 × 10‑9

4.1 × 10‑11Cl

9.6 × 10

9.6 × 10‑9

7.0 × 10

1.3 × 10‑10Sr

1.8 × 10‑6

6.3 × 10‑6

4.5 × 10‑6

1.9 × 10‑7Tc

4.6 × 10

5.8 × 10‑4

1.7 × 10

1.2 × 10‑7I

3.8 × 10‑7

4.3 × 10‑6

3.8 × 10‑4

2.3 × 10‑6I

1.2 × 10

1.4 × 10‑3

1.0 × 10

4.5 × 10‑7

134

Cs

1.9 × 10‑5

6.9 × 10‑6

4.9 × 10‑6

4.3 × 10‑6

135

Cs

3.9 × 10‑6

1.2 × 10‑6

1.9 × 10‑6

4.6 × 10‑7

137

Cs

1.8 × 10

5.7 × 10

‑6

6.5 × 10

3.0 × 10‑6Pb

4.8 × 10‑5

2.3 × 10‑3

8.0 × 10‑4

3.2 × 10‑4Ra

1.3 × 10

1.4 × 10‑2

1.4 × 10

6.4 × 10‑5Th

1.4 × 10‑2

2.3 × 10‑2

4.6 × 10‑3

3.2 × 10‑4U

2.4 × 10

2.4 × 10‑3

2.4 × 10

1.0 × 10‑7Np

2.7 × 10‑3

2.7 × 10‑3

1.4 × 10‑3

2.5 × 10‑5Pu

3.0 × 10

6.0 × 10‑1

1.2 × 10

5.7 × 10‑5Pu

3.0 × 10‑3

6.0 × 10‑3

1.2 × 10‑1

5.7 × 10‑5Am

3.2 × 10

1.3 × 10

2.5 × 10

4.6 × 10‑5

3

36
90

99

129
131

210

‑5

‑2

238

‑5

237

239

‑3

240
241

‑6

‑6

226

232

‑9

‑3

‑9

‑5

‑5

‑6

‑2

‑4

‑3

‑2

‑1

a For an intake of marine fish of 20 kg/a.

4.

Conclusions

141. In this section, approaches have been described for theassessment of exposures of flora and fauna to radiation fromnatural background levels of radionuclides or regulated discharges of radionuclides to the environment. The models cover
two major fields. One is concerned with the transport processesof radionuclides from the source to plants and animals, to whichapproaches may be applied that are similar to those used toassess the exposures of humans. In the terrestrial environment,these are mainly atmospheric dispersion, deposition, interception, weathering and uptake from soil. For discharges to aquatic
systems, models can be used that describe dispersion, dilution,
sedimentation and uptake by freshwater or marine organisms.
142. There are major differences in the dosimetry involved in
the assessment of the exposures of humans and non-humanbiota. The current approaches for biota rely on the mean activity
concentrations in the whole organism rather than on those in distinct organs or tissues. Thus, the calculated absorbed doses are to
the whole organism. There is an ongoing discussion about theappropriate factors to be applied in order to account for the different RBEs of the different kinds of radiation involved. Example calculations in this annex show that the estimated weighted
absorbed doses from exposure to alpha radiation are sensitive tothe value of the factor used. This is relevant to the assessmentof doses to biota both as a result of radioactive discharges froma nuclear site and as a result of exposure to radiation fromradio­nuclides that are naturally present in the environment.
143. The estimated doses to biota are compared in thisannex with those to humans in accordance with the approachgiven in reference [U3]. The comparison shows that theweighted absorbed doses to terrestrial non-human biota andthe effective doses to humans are generally of a similar orderof magnitude, for a given level of environmental contamination by radionuclides. The weighted absorbed doses to marine
biota are, in general, considerably higher than the effective
doses to humans (for whom an annual consumption of marine
fish of 20 kg is assumed for illustrative purposes).
144. The results of the dosimetric calculations presented inthis annex are based on stylized models of ecosystems using
average values for most of the model parameters. Thus, they do
not accurately reflect the variability of ecosystems and the pro­
cesses present in nature that control the environmental mobilityof radionuclides. In addition, the exposures due to the various
sources of natural background radiation and their variabilities
would have to be included if the results presented in this annex
were to be used in a site-specific assessment. As indicated earlier, there are substantial uncertainties associated with the estimation of dose rates to non-human biota, including those
associated with the environmental pathways (such as in the values of the transfer factors) and those related to dosimetric issues.

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

II.

255

Summary of dose–effects data from the UNSCEAR 1996 Report145. In the absence of reports of obvious deleterious
effects on other organisms from exposure to environmental
radiation, whether of natural origin or due to the controlled
discharges of radionuclides to the environment, it had generally been accepted that priority should be given to evaluating the potential consequences for humans (which areamong the most radiosensitive mammalian species) and toproviding a sound basis for protecting human health. By
1996, this position had, however, been questioned [D1, T1],
and at least one situation (namely deep-sea sediments, anenvironment very remote from man) had been identified
where the above accepted priority could be incorrect [I3]. In
response to such concerns, the Committee noted that the
impact of radiation exposure of non-human biota had beenstudied in a number of situations [I2, I3, I4, M1, N1, W1,
W2] and considered that it was appropriate to conduct an
independent review of the matter and to summarize the stateof knowledge existing at that time. The UNSCEAR 1996
Report [U4] took account of the earlier reviews and studies
and the Committee’s summaries of the radiobiological work
carried out over the previous 50 years.
146. In its 1996 report, the Committee noted that there wasa fundamental difference in the approaches to the protectionof humans and non-human biota from the effects of exposure
to ionizing radiation. For humans, ethical considerations had
made the individual the principal object of protection. This
meant, in practice, that any incremental risk to the individual
arising from increased radiation exposure was to be constrained below some level that society judged to be acceptable; this level of risk, although small, was not zero [I5]. For
non-human biota, the populations of the biota were considered to be important and protection from a significantly
increased risk to each population arising from radiation
exposure might be the appropriate objective. Exceptions
might be populations of small size (rare species) or those
reproducing slowly (i.e. with long generation times and/or
low fecundity) for which protective measures might be more
appropriately targeted at the level of the individual organism. The Committee noted that there could not be any effectat the population level (or at the higher levels of communityand ecosystem) if there were no effects on the individualorganisms constituting the different populations. It went on
to suggest that radiation-induced effects on some membersof a population would not necessarily have any significant
consequences for the population as a whole.
147. The Committee noted that natural populations oforganisms existed in a state of dynamic equilibrium within
their communities and environments and that exposure toionizing radiation was but one of the stresses that may affectthis equilibrium. The incremental radiation exposure fromhuman activities could not, therefore, be considered in isolation from other sources of stress, whether natural (e.g. climate, altitude, or volcanic activity) or of human origin (e.g.
synthetic chemical toxins, oil discharges, exploitation forfood or sport, or habitat destruction). When (as is not uncommon) ionizing radiation and chemicals, both resulting fromhuman activities, acted together on a population, the difficult
problem arose of correctly attributing any observed response
to a specific cause.
148. The objective of the UNSCEAR 1996 Report on the“Effects of radiation on the environment” [U4] was tosummarize and review information on:– The exposures (actual or potential) of organisms in their natural habitats to the natural background radiation, to radionuclides discharged
into the environment in a controlled mannerfrom industrial activities, and to radionuclides
released as a consequence of accidents; and– The responses of plants and animals, both as individuals and as populations, to acute and chronic
irradiation.
149. The Committee hoped that its review would assist
national and international bodies to select appropriate ­criteria
for the radiological protection of natural populations, communities and ecosystems. The following paragraphs recapitulate
the information available to the Committee in 1996.

A. Dosimetry for environmental exposures150. As discussed in the annex to the UNSCEAR 1996
Report [U4], reliable determination of the dose rate to organisms is essential for assessing the potential or actual impacts
of contaminant radionuclides in the environment. The Committee noted that “this simple statement conceals a multitudeof difficulties that prevent the easy achievement of that estimation”. In practice, it is necessary to make simplifying
assumptions, with the degree of simplification depending on
the purpose of the assessment. For example, for the purposeof screening, the concept of a single generic biota that represented all plants and animals had been used [A2]. Moresophisticated models attempted to account for the dose distributions within reference organisms of assumed shapes andsizes and the fraction of radiation being absorbed within theorganism [W2]. The Committee’s views on dosimetry for
estimating the exposure of biota based on what was known
in the UNSCEAR 1996 Report [U4] are summarized below.
151. A dosimetric model is essentially a mathematical construction that allows the energy deposition in a defined target
to be estimated from a given radionuclide (source) distribution. The model was often derived using theoretical or
empirical functions that described the distribution of doseabout a point source [B2, B3, L1, W2]. The dose at a point in
the target was then obtained by integrating the point source
dose distribution function over the defined radionuclide
source, either internal or external to the organism. This

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procedure was frequently simplified by using ideal
geometries (spheres, ellipsoids, etc.) of appropriate size torepresent the target and by assuming that the radionuclide
distribution was uniform (over a surface or through a volume) or varied in a way that could be described by a simple
mathematical expression (e.g. an exponential decline in radionuclide concentration with depth in soil or sediment).
Alternatively, Monte-Carlo calculations had been used todetermine the absorbed fractions of energy for a variety ofsource and target geometries [B4, E2]. These data could be
used, either directly or with interpolation (or, to a lesser
extent, with extrapolation) for geometries that could represent targets of environmental concern. In principle, these procedures could be adapted for use in estimating doses toterrestrial and aquatic organisms, from both the plant and animal kingdoms, for both internal and external sources ofradiation.
152. Dosimetric models had been developed to takeaccount of the radiation type; the specific geometry of thetarget (e.g. the whole body, the gonads, the developing
embryo or the plant meristem); and the source of exposure(e.g. radionuclides accumulated in body tissues, adsorbed
onto the body surface or distributed in the underlying soil).
Clearly, it was not possible to consider all organisms, andthere were limitations in the basic data that were available as
input to the models (e.g. the spatial and temporal distributions of radionuclides both within the organism and in theexternal environment). Additional sources of complexity
arose from the behaviour of mobile organisms, particularly
some aquatic organisms and many insects, which inhabit different environmental niches at different stages of their life
cycles. Thus, the models had to be simplified and generalized without undue loss of the realism that is essential for avalid estimation of dose.
153. The presence of an alpha particle component in the
total absorbed dose rate to a tissue in a plant or animal raised
the question of how to take account of the probably greater
effectiveness of this type (quality) of radiation in producing
biological damage. The RBEs of different qualities of radiation had been very critically examined for the purposes ofhuman radiation protection. Each component of the absorbed
dose to a tissue or organ was weighted by a factor which
took account of the RBE of the radiation involved [I5]. It
seemed reasonable to apply a similar approach to the radiation dosimetry for organisms other than man. In practice,
however, there were circumstances that altered the detailed
application of this approach. In the human case, the major
concern had been with the induction of stochastic effects(principally cancer) at low doses and dose rates. For alpharadiation, experimental determinations of the RBE had led toa recommended radiation weighting factor of 20 for the purpose of human radiation protection. In the case of wild animals, however, the Committee assumed that it was likely that
deterministic effects were of greater significance. For alpharadiation, the experimental data for animals indicated that alower factor to reflect the RBE would be more appropriate;
the factor to reflect the RBE of beta and gamma radiations

would however be numerically the same as the radiation
weighting factor used in human radiation protection. On theassumption that mammals are the most sensitive species,
these values could be applied to other taxonomic groups.
154. In its 1996 UNSCEAR Report [U4], the Committee
assumed that these factors would also apply to effects onplants, although there were no definitive experimental data
to support this. In the absence of protection quantities(equivalent and effective dose) for non-human organisms,
the absorbed doses from low-LET radiation (beta particles,
X‑rays and gamma rays) and from high-LET radiation (alphaparticles) were assessed and specified separately in the
UNSCEAR 1996 Report [U4]. The absorbed doses retained
the unit, joule per kilogram (J/kg), with the special namegray (Gy).
155. An IAEA technical report [I4] provided estimates ofthe dose rates to terrestrial plants due to radionuclides deposited following discharges to the atmosphere. The model,
PATHWAY [W3], developed to estimate doses to humans,
had been used to derive the equilibrium concentrations ofradionuclides in plants and animals for the limiting case inwhich humans, while living on the land, breathing the air
over it and eating the food produced from it, would receive
an annual effective dose of 1 mSv. To estimate the dose toplants from internal sources, it was assumed that the energyof alpha and beta particles would be totally absorbed (except
for emissions from 32P, which would be 50% absorbed) andthat 10% of the gamma-ray energy would be absorbed. An
additional degree of conservatism was provided by using
estimates of the radionuclide concentrations in plant tissue
on a dry weight basis (which are 5–10 times higher than ona wet weight basis) to calculate the absorbed dose rates toliving (i.e. “wet”) plant tissue. The results are given intable 21. As these estimates had been made using a radio­
ecological model and a scenario designed for calculating
exposures to humans, the calculated exposures of nonhuman species should be interpreted cautiously.
156. The annex of the UNSCEAR 1996 Report [U4] notedthat there have been fewer estimates of the potential exposures of fully terrestrial animals than of animals occupying
semi or fully aquatic niches. This was thought to be a reflection of the greater use that had been made of aquatic systems
for the discharge of radioactive waste.
157. The annex of the UNSCEAR 1996 Report [U4] suggested that naturally occurring alpha-emitting radionuclides
appeared to be the most significant sources of backgroundradiation exposure for the majority of wild organisms.
158. In its 1996 report, the Committee considered that thedata on the radiation exposures of non-human biota due toboth natural background radiation and contaminant radio­
nuclides were incomplete, more in some areas than in others.
The Committee also noted that the aquatic environment wasprobably the most thoroughly studied environment up to thattime [I2, I3, I7, N1, N2, W1], even with the substantial

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

generalizations that had had to be made, particularly withrespect to the range of organisms that could reasonably beconsidered [I3]. As had been emphasized elsewhere [I3, I6],
the limiting factor was not the development of an appropriate dosimetric model for a particular organism but rather theacquisition of essential input data on the temporal and spatial distributions of the radionuclides both external to andwithin the organism. Although dynamic models had been
employed to describe the dispersion and dilution of radio­
nuclides in a water body, related phenomena (e.g. transfers
to sediments and biological tissues) were almost always

257

modelled as equilibrium processes, i.e. using simple distribution coefficients and (whole-body) concentration factors.
This simplification largely neglected the temporal variations
in dose rate due, for example, to short-term fluctuations indischarge rate, differing stages in the life cycle, and behavioural and short-term environmental processes (e.g. seasonality). As a consequence, while the estimated absorbed dose
rate might be a reasonable indication of the general magnitude of the actual environmental value, the Committee considered that it did not provide a very secure basis forevaluating total doses over time.

Table 21. Estimated dose rates to organisms from controlled discharges of radionuclides that would each result in an annual
dose of 1 mSv to humans residing in the same environment
Table 6 of UNSCEAR 1996 Report [U4]; based on [I4, N1]
Radionuclide

H
C
32
P
60
Co
90
Sr
95
Zr
99
Tc
131
I
137
Cs
226
Rad
235 d
U
238 d
U
239 d
Pu
241
Amd
3

14

Dose rate (µGy/h)Plantsa

Animalsa,b

Fishc

5.8
18
32

5.8
11
28

0.59

2.0
38

0.042
2.0

1.2
5.4

0.058
3.1

0.023

0.000 55

4.8
0.53
67
3.8
0.72
3.6
2.6
4.7
0.49
0.71

a Discharges to atmosphere.
b Domestic sheep.
c Discharges to water (lakes).
d High-LET radiation.

159. The Committee also noted that accident situations
were by nature quite different from routine situations, particularly in their potential to produce high dose rates anddoses to the environment. It concluded that generalization isdifficult because the actual exposure regime depends on thetypes and quantities of radionuclides released, their initialdispersal and deposition patterns, and their redistribution
over time in the environment. Following the accident at the
Chernobyl nuclear power plant, large quantities of shortlived radionuclides were released, leading to high dose rates
in the local area. Total doses up to 100 Gy were delivered totrees (and, by inference, to most other organisms in the locality) over a period of a few days [K1]. This radiation regime
might have been characterized as “acute” in that the doses
were delivered in periods that were shorter than or comparable to the time taken for severe damage to become apparent.
During this initial (acute) phase, the dose rates declined rapidly as the very short-lived radionuclides decayed. The
release following the accident in 1957 in the south-eastern
Urals was dominated by 144Ce–144Pr (approximately 66%;t½ = 285 d) and 95Zr–95Nb (approximately 25%; t½ = 65 d). In
that case, the dose rates locally were also relatively high during the initial phase (more than 4 mGy/h) but declined more
slowly, such that high total doses (causing severe effects,
including mortality) could still be accumulated from essentially chronic exposure. Close to the release point, total doses
up to 2,000 Gy were experienced [T4]. In the longer term,
the exposure regime for the Chernobyl release was dominated by 137Cs (t½ = 30 a) and 90Sr (t½ = 28.6 a), and that forthe south-eastern Urals accident area by 90Sr. In both cases,
the exposures were chronic and moderately high, withresponses other than mortality becoming significant.
160. Radioactive waste discharges to atmosphere, landfills
or aquatic systems from man-made practices entail increased
radiation exposure of wild organisms. The incremental
radia­tion exposures are chronic (i.e. continuing) at absorbed
dose rates of generally no more than 100 μGy/h, but, very
exceptionally, they may reach several thousand microgray
per hour. The Committee [U4] noted that these additional

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radiation exposures may be greater than the normal range ofnatural background exposures but generally are within theextreme range of background exposures, if the exceptional
cases of areas of uranium and thorium mineralization are
included. Given that radioactive waste discharged to theenvironment will normally be dispersed and diluted, dose
rates higher than those due to normal natural backgroundexposure are likely to apply to only a small proportion of
the individual organisms in any population and the average
dose rate to the population would probably be much lower[W8, W9].
B.

direct or indirect interactions among its members are more
important than those between its members and members ofother populations” [B6]. Notwithstanding this definition, it
has to be understood that a population of a particular species
is always linked to its environment. Such a population would(or could) be a self-sustaining unit, independent of other,geographically separate populations of the same species.
However, protection of this population would require that
increased radiation exposure did not significantly affect the
attributes mentioned in the definition on which the population depended for its maintenance within the normal dynamic
range of variation dictated by the interactions of natural
physical, chemical and biological factors.

Effects of radiation exposure on plants and animals

161. Studies of the effects of ionizing radiation exposure
on plants and animals were started immediately following
the discovery of X‑rays and radioactivity (see, for example,
reference [A4]). Since 1945, when the first nuclear detonations were conducted, there was widespread concern about
the impact of environmental radiation exposures and interestin the environmental behaviour of radioactive materials. As
a result, studies using a wide variety of plant and animal­species were performed [A4, B5, C3, P1].
162. The Committee, in its 1996 report [U4], noted that the
responses of organisms to radiation exposure were varied
and may become manifest at all levels of organization, fromindividual biomolecules to ecosystems. The significance of agiven response depended on the criterion of damage adopted,
and it was not to be concluded that a response at one level oforganization would necessarily produce a consequential,
detectable response at a higher level of organization.
163. The Committee also noted that a population might bedefined as all members of a population species [U4]. Alternatively, a population might be considered as an aggregate ofinter-breeding individuals of a species occupying a specificlocation in space and time [S5]. The latter definition is perhaps more useful given the Committee’s observation thatradiation fields, such as those arising from radioactive waste
discharges, generally show large spatial variability, not least
because of the often discrete nature of the source, and therefore many members of a population might not receive any
significant exposure from a particular source. The natural distributions of most species are inhomogeneous because of thevariations in physical, chemical and biological conditions
under which the individuals of the species are able to survive,
i.e. species are geographically restricted. Thus, it is probablethat a more limited, and relevant, definition of a population
could be developed for the purposes of environmental impact
assessment.
164. The following definition (developed for use in population ecology) has been suggested as a useful basis for discussion and progress [I4]: “A population is a biological unit forstudy, with a number of varying statistics (e.g. number, density, birth rate, death rate, sex ratio, age distribution), andwhich derives a biological meaning from the fact that some165. These attributes, which could be defined only for
popu­lations of organisms and might be taken to be indicatorsof their health, are nevertheless amalgamations of properties
that relate to individuals (in no sense was this meant to imply
simple addition). The Committee concluded, in effect, thatfor a response to radiation exposure at the population level(or, indeed, at any higher level of organization) some clearly
detectable effect in individual organisms (i.e. at lower levelsof organization) would be expected. This clearly implied thatthe protection of the population (as the ultimate objective)
might be achieved by restricting the exposure of individualorganisms to the extent that there are no significant radiation
effects on those processes necessary for the maintenance ofthe population. It is therefore necessary to consider the available information on the effects of radiation exposure (mainly
at chronic low dose rates) on the relevant processes in individual organisms, to consider how these responses mighttranslate to an impact on the population, and to examine theresults of studies of population responses to deliberate
experimental irradiation or to exposure in the environment
due to controlled or accidental releases of radionuclides.
166. Examination of the population attributes indicatedthat the individual responses to radiation exposure likely to
be significant at the population level are mortality (affecting
age distribution, death rate and density), fertility (birth rate),
fecundity (birth rate, age distribution, number and density)and the induction of mutations (birth rate and death rate).
These individual responses can be traced to events at thecellular level in specific tissues or organs. An extended summary discussing the processes involved was provided inannex J, “Non-stochastic effects of irradiation”, of the
UNSCEAR 1982 Report [U9]. There was a substantial bodyof evidence indicating that the most radiosensitive sites areassociated with the cell nucleus, specifically the chromosomes, and that, to a lesser extent, damage to intracellular
membranes is additionally involved. The end result is thatthe cells lose their reproductive potential. For most cell
types, at moderate doses, death occurs when the cellattempts to divide; death does not, however, always occur at
the first post-exposure division: at doses of a few gray, seve­ral division cycles might be successfully completed before
death eventually occurs. It was also well known that radiosensitivity varies within the cell cycle, with the greatest sensitivities being apparent at mitosis and the commencement

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

1.

of DNA synthesis [U9]. It followed that the greatest radiosensitivity is likely to be found in cell systems undergoing
rapid cell division for either renewal (e.g. spermatogonia) or
growth (e.g. plant meristems and the developing embryo);these examples clearly underlie the processes in individualorganisms that are important for the maintenance of the
population.

259

Terrestrial plants

168. Radiation injury in plants expresses itself as abnormal
shape or appearance, reduced growth or yield, loss of reproductive capacity, wilting and (at high exposures) death [S1].
Acute lethal doses to higher plants ranged from 10 to about
1,000 Gy (approximate mean absorbed doses averaged over
the whole plant). The Committee concluded that plants suchas mosses, lichens and unicellular species are at one extremeof radiosensitivity being highly resistant to radiation exposure; woody species are at the other extreme being the mostsensitive. In 12 species of woody plants assessed 10–14 months
after exposure, the lethal doses were found to be in the range
of 8–96 Gy [S2]. The pine tree was the most sensitive, experiencing mortality following short-term absorbed doses ofabout 10 Gy [W5]; growth was severely inhibited at 50–60%
of the lethal dose. Floral inhibition was observed at 40–50%
of the lethal dose, and failure to set seed at 25–35%. Thus, thecapacity of the plant population to maintain itself could bedamaged at acute doses lower than those required to cause
mortality. Below 10% of the lethal dose, effects were not soapparent and the plants maintained a normal appearance.
These general observations for several herbaceous plant species are illustrated in figure X [S3]. Another general relationship was that the dose that reduced survival by 10% (LD10)
was roughly equivalent to the dose that reduced the yield by
50% (YD50) [S1].

167. Fractionation or protraction of exposure to low-LET
radiation increases the total dose required to produce a given
degree of damage since at low dose rates, the factors responsible for mitigating the response come into play. These
include the repair of sublethal damage, the repair of potentially lethal damage, the replacement of killed cells throughproliferation of survivors, and other slow repair processes
not related to cell repopulation [U9]. Although it was clear to
the Committee that repair, in the general sense, is possible,
the existence and extent of residual injury was less clear.
While such an outcome might be demonstrated for moderate, acute doses, it was not possible to extrapolate theseresults in order to predict the likely response to low-level
exposures extending over a significant fraction of the lifetime of an organism. However, given that genetic mutations
might be passed from generation to generation, it was reasonable to suppose that somatic mutations individually consistent with cell survival could occur and accumulate overtime until the combined impact might reduce cell viability.

Figure X. General ranges of response to radiation exposure by herbaceous plants as a percentage of the lethal dose (LD100) [S3]Mortality in 50% of plants
Severe growth inhibition
Floral inhibition
Pollen sterility
Mortality in 10% of plants
Yield reduced by 50%
Failure to set
Yield reduced by 10%
Normal appearance
0

10

20

30

40

50

60

70

80

PERCENTAGE OF LETHAL DOSE

169. The Committee, in the UNSCEAR 1996 Report [U4],noted that protraction of radiation exposures increased thetotal doses required to kill plants [S4].
170. A range of sensitivities to radiation exposure was
exhibited by the components of plants, ranging from dryseed (least sensitive) to apical meristems (most sensitive).
Various crop plants showed different reductions in yieldfollowing radiation exposures, with further modifications
being caused by external factors (e.g. temperature andhumidity).

171. Plant species also varied in their tolerance to chronic
radiation exposures. For the more sensitive pine species, dose
rates of more than 3 mGy/h over 3–4 years reduced needle
growth; in one‑year-old saplings, needle length was substantially reduced when subjected to a dose rate of 7 mGy/h over a
single growing season. Trunk growth was reduced in maturepine trees by dose rates in the range 0.4–2 mGy/h over a 9‑year
period. Delayed bud burst and an extended period of leafing
out was demonstrated in white oaks chronically exposed to
gamma radiation. At dose rates greater than 4 mGy/h, the trees
were more susceptible to aphid infestation.

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172. In view of the effects on the most sensitive plants evident with chronic exposure at dose rates of 1–3 mGy/h andof some specific changes noted at dose rates of 0.4–2 mGy/h,the Committee [U4] suggested that chronic dose rates at or
below 400 μGy/h (10 mGy/d) should have only slight effects
on sensitive plants but would be unlikely to produce any significant deleterious effects on the wider range of plants
present in natural plant communities.
2.

176. While acknowledging that the numbers of mammalian species that had been (or indeed were likely to be)­studied were extremely limited and probably atypical, theCommittee noted [U4] that, even taking account of substantial interspecific variability, the available data provided very
little evidence that chronic dose rates below 400 μGy/h(approximately 10 mGy/d) to the most exposed members of
the population would seriously affect their mortality (and,thus, the death rate in populations of these species) fromeither deterministic or stochastic responses.

Terrestrial animals

173. The effects of radiation exposure on mammals had been
extensively studied in radiobiological experiments using laboratory animals (mice, rats, dogs and monkeys) and domestic
livestock (pigs, sheep, goats, burros and cattle) [B7, B8].
Except in the case of exposure involving unusually high doses,
radiation damage or lethality in mammals results from disturbances in the haematopoietic system and the gastro­intestinal
mucosa. These cell self-renewal systems contain stem cells,
differentiating cells and functional end cells, with the stem
cells being the most radiosensitive and thus having the predominant influence on the radiation response. Symptoms
become apparent when end cells are not replaced.
174. Protraction of a given total exposure generally reduces
the extent of injury, as it allowed two distinct processes tointervene. First, sublethal damage is reparable at the cellularlevel, which is particularly important for exposures to lowLET radiation. Secondly, cell proliferation could replacelethally damaged cells and maintain the cell population at a
new level, which is determined by the dynamic interaction
between the dose rate and the rate of cell death, and by the
total reserve proliferative capacity.
175. The Committee noted that at reduced dose rates (protraction of a given total dose) of low-LET radiation, all species
showed a gradual increase in LD50, i.e. higher total doses were
tolerated. This changing response was attributed to the increasingly effective influence of cellular repair of sublethal damage
at the lower dose rates. As the dose rate was further reduced, asharply increasing trend in the values for the median lethal
dose was apparent for mice, pigs, dogs, goats and sheep; theapproximate threshold dose rates for this change in response
corresponded to the accumulation of an LD50 dose within periods ranging from 0.2 days (mouse) to 9 days (goat). This rapidchange in LD50 with dose rate was interpreted as being theconsequence of a shifting balance in the dynamic interaction
between the dose-rate-dependent cell loss and the cell proliferation and maturation kinetics in the haematopoietic system;
the latter processes are under homeostatic control, i.e. theirrate constants can alter in response to radiation-induced cellloss. The data for the burro (donkey) and primates did notshow any sharp increase in the median lethal dose at dose rates
down to 8.3 mGy/h (LD50 in 18 days) and 5.4 mGy/h (LD50 in
60 days), respectively. There did not appear to be any data for
LD50 values at dose rates of less than 4 mGy/h or for exposure
periods exceeding 60 days, although studies had been madeoutside these levels for other purposes.

177. The effects of radiation exposure on reproduction had
also been much studied, with most of the results suggestingthat natality is a more radiosensitive parameter than mortality in species other than man and therefore of more relevancein an environmental context. The Committee considered thatthe minimum dose required to depress reproduction rates
might be less than 10% of the dose required to produce directmortality [W6].
178. The Committee suggested that damage to the developing mammalian embryo appeared to be a potentially significant criterion for assessing the impact of contaminantradionuclides in the natural environment. Dose rates of
420 μGy/h throughout gestation produced readily detectablereductions in the populations of germ cells in the developing
gonads of a number of mammalian species, and the lowest
dose rate at which damage had been seen was 10 μGy/h fromtritium (as HTO in drinking water) incorporated in female
mouse embryos. In addition, dose rates of the order of
420 μGy/h induced reductions in neonatal brain weight,
although the significance of this deficit was unknown infunctional or behavioural terms. The wider significance of
these responses at the population level had not been investigated. Even recognizing that only very limited data wereavailable, the Committee concluded that maximum dose
rates of 100 μGy/h (2.4 mGy/d) to pregnant members of a
mammalian population were unlikely to have any consequences for the population as a whole from the induction ofdamage in the developing embryos.
179. The Committee noted that the data on the radiosensitivity of terrestrial animals were dominated by data on mammals, the most sensitive class of organisms. Acute lethal
doses (LD50/30) were 6–10 Gy for small mammals and 1.5–
2.5 Gy for larger animals and domestic livestock. When atotal dose of magnitude similar to the LD50/30 was delivered
over a lifetime—for example, 7 Gy to the mouse (420 μGy/h,or 10 mGy/d)—the average loss of lifespan had been estimated to be about 5% and resulted from the induction ofneoplastic disease [U9]. There was substantial inter-species
variability, but, in general, little indication that dose rates
below about 400 μGy/h to the most exposed individual
would seriously affect mortality in the population.
180. The Committee noted that reproductive capacity was
more sensitive to the effects of radiation exposure than life
expectancy (mortality) and felt that the reproductive rates ofmammals might be depressed at doses that were 10% ofANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

those leading to mortality. It also felt that some loss ofoocytes might occur at 1% of the lethal dose, but because ofexcess oocyte production, fecundity should be affected to alesser extent. Mice, exposed from conception to a dose rateof 800 μGy/h, could be made sterile at 25 weeks. In the mostsensitive mammal studied, the beagle dog, a dose rate of
180 μGy/h caused progressive cell depletion and sterility
within a few months, but a dose rate of 36 μGy/h over thewhole life produced no damaging response. The Committee
concluded that a radiation dose rate of less than 40 μGy/h tothe most exposed individual in a population (and most probably, therefore a lower mean dose rate to individuals in the
population as a whole) would be unlikely to have an impact
on the overall reproductive capacity of a mammalian population as a consequence of the effects of radiation exposure on
fertility, fecundity or the production of viable offspring.
181. The effects of radiation exposure on birds had beenshown to be similar to those on small mammals. Reptiles
and invertebrates were less radiosensitive, although physio­
logical differences began to make direct comparisons withother species less appropriate. The chronic exposure of one
short-lived species of lizard in enclosures had shown noevident effects when exposed over 5 years at a dose rate of830 μGy/h. In two longer-lived species of lizard, some individuals had been made sterile after 3.5 years at a dose rateof 630 μGy/h in one species and after 5.5 years at a dose
rate of 210 μGy/h in another species. Adult invertebrates
were seemingly quite insensitive to the effects of radiation
exposure in terms of induced mortality, but the process ofgametogenesis, developing eggs and juvenile stages weremore sensitive.
3.

Aquatic organisms

182. A number of reviews of the studies of the effects of
exposure to ionizing radiation on aquatic organisms wereavailable to the Committee [A3, B9, C3, E2, I2, I3, N1, N2,
P2, T5, W9] during the preparation of the annex of the
UNSCEAR 1996 Report [U4]. Some of these had been prepared specifically to provide a basis for assessing the potential effects of discharges of liquid radioactive effluents onaquatic organisms in their natural environment [I2, I3, N1,
N2, W1].
183. Among aquatic organisms, fish were the most sensitive to the effects of radiation exposure; the developing fishembryos were particularly sensitive. The LD50 for acute irradiation of marine fish was in the range 10–25 Gy for assessment periods of up to 60 days following exposure. The upper
end of the range of LD50 for marine invertebrates had beenfound to be several hundred grays. Embryos, on the other
hand, were affected at much lower doses, for example, theLD50/90 for salmon embryos was 0.16 Gy [B10].
184. Chronic exposures at dose rates of 10–30 mGy/h had
no effect on the mortality of snails, marine scallops, clams
and blue crabs. Dose rates somewhat above this range had

261

some effects on food-limited populations of Daphnia pulex.
Short-term (40 days) exposure of mosquito fish at dose rates
in the range 14–54 mGy/h showed no radiation-induced
mortality, but, for the closely related guppy, there was someindication that long-term exposure (>470 days) at dose rates
above 1.7 mGy/h reduced the normal lifespan, particularly
for males.
185. Reproductive effects are a more sensitive indicator ofradiation response for aquatic organisms. Chronic dose rates
in the range 3.2–17 mGy/h reduced the reproductive capa­
city in the freshwater snail, Physa heterostropha, and in themarine polychaete worms, Ophriotrocha diadema and Neanthes arenaceodentata. Exposure at a dose rate of 7.3 mGy/hrendered male freshwater fish (Ameca splendens) effectively
sterile after 50 days, and exposure at a dose rate of 1.7 mGy/hover the lifespan of pairs of guppies (the freshwater fish,
Poecilia reticulata) significantly reduced the lifetime production of offspring [W7]. It had been concluded that significant effects on fish gonads from chronic radiation
exposure would be unlikely at dose rates less than 1 mGy/h[I3, W1]. Overall consideration of the data available led tothe conclusion that chronic irradiation at dose rates up to400 μGy/h to a small proportion of the individuals in an
aquatic population (and, therefore, with correspondingly
lower average dose rates to the whole population) would nothave any detrimental effects at the population level [I4, N1].
C. Effects of radiation exposure on populationsof plants and animals
186. The Committee noted in the annex of the UNSCEAR
1996 Report [U4] that one of the difficulties in evaluating theeffects of radiation exposure on populations and ecosystems
was the determination of the parameters to measure. Typically measured attributes at the population level included
numbers of individuals, mortality rate, reproduction rate andmean growth rate. The Committee also noted that measurable changes in populations and communities required rather
severe effects to be induced at the cellular and individualorganism levels [e.g. W8]. The Committee also noted thatgenetic or somatic mutations that could be produced by relatively low levels of exposure might have little or no impact
on population or community performance because of natural
selection [B10, C4, M2, P3, T5] and the convergence ofgenetic information among adjacent populations [R1, T5].
187. The Committee also noted that the effects of radiation
exposure at the population and community levels were manifest as a combination of direct changes due to radiation damage and indirect responses to the direct changes. This
seriously complicated the interpretation of the effects ofradiation exposure on organisms in the natural environment.
The wide range of radiosensitivities of the organisms thatmake up most natural communities creates a situation where,
if doses are such that the sensitive species, but not the moreresistant ones, are affected, the latter might gain a significant
competitive advantage and increase in abundance or vigour.

262

UNSCEAR 2008 REPORT: VOLUME IIThis could erroneously be interpreted as a hormetic response;such a response might not however be produced if the resistant species alone were irradiated. This is but one of many
examples of indirect response to the direct effects of ­radiation
exposure.
188. Because of the compensation and adjustment possible
in animal species, the Committee considered that it isunlikely that radiation exposures causing only minor effects
on the most exposed individual would have significant
effects on the population. Reproductive changes are a moresensitive indicator of the effects of radiation exposure thanmortality, and mammals are the most sensitive animal organisms. On this basis, chronic dose rates of less than 100 μGy/h
to the most highly exposed individuals would be unlikely tohave significant effects on most terrestrial animal communities. The Committee also concluded that maximum dose
rates of 400 μGy/h to a small proportion of the individuals inaquatic populations of organisms would not have any detrimental effect at the population level. These conclusions
referred to the effects of low-LET radiation exposure. Wherea significant part of the incremental radiation exposure
comes from high-LET radiation (alpha particles), the Committee considered that it is necessary to take account of thedifferent RBEs.
D.

Effects of major accidents

189. The UNSCEAR 1996 Report [U4] discusses theeffects of two accidents in the former Soviet Union (at­Chernobyl and at Mayak in the south-eastern Urals) leading
to major releases of radioactive material into the environment [A28, G19, I23, I24, K1, K22, K23, N9, S29, S34, S40,
T4, T27]. These accidents provided opportunities to observe
radiation-related changes in plant and animal communities.
The Committee noted however that any major accident islikely to be unique in terms of the quantity and compositionof the radioactive material released, the time course of therelease, the dispersal and deposition patterns, which are governed by local and regional meteorological or hydrologicalconditions, and the biochemical and geochemical characterof the areas subject to contamination. Where long-lived
radio­nuclides are released, biochemical and geochemical
processes would determine the long-term behaviour andredistribution of the radionuclides in the environment. Given
this multiplicity of factors, any major nuclear accident would
be expected to yield new radioecological information. However, the primary concern following an accidental release ofradionuclides is to ensure that the radiation risks to humanpopulations are controlled and minimized. Consequently,
the only environmental information likely to be collected isthat which is immediately necessary to meet this objective.
Such information is unlikely to be sufficient for the purposesof developing a complete radioecological description of thesituation. The larger the incident and the greater its potential
human impact, the more limited would be the resources
available to collect radioecological information, particularlyin the early phase following the accident.

190. In particular, the data required to develop estimatesof the radiation exposure of wild organisms (i.e. the space
and time-dependent variations of the radionuclide concentrations, especially of the short-lived radionuclides bothwithin the organisms and in their external environment
immediately following an accident) would not be known.
These variations would result in substantial intra-species
and inter-­species inhomogeneities in exposure and would
pose considerable difficulties for establishing a clear andreliable relationship between cause (the accumulated radiation dose) and any observed effect. In practice, it is likelythat estimates of the dose rates in the early period following
the release would be calculated subsequently from theobserved distribution of deposition densities of the longerlived radionuclides, from a knowledge of the relative quantities of the radionuclides released, and using models ofradionuclide behaviour in the environment. Such dose-rate
estimates are inevitably imprecise and could be subject tosignificant systematic error.
191. The highly variable habits and target geometries of
the wild organisms are additional complicating factors.
These range, for example, from soil bacteria to single-celledalgae and protozoa, and include a wide variety of terrestrial
and aquatic invertebrates, mammals (ranging from shrews todeer) and large deciduous or evergreen trees. Plants provide
a very high surface area to mass ratio (compared with animals) for deposition/adsorption of a radioactive aerosol.
Because the leaves, flowers and terminal buds of plants are
responsible for energy absorption, growth and reproduction,a coincidence arises between radionuclide accumulation(and hence radiation dose) and potential radiosensitivity.
Other examples of coincidence are the surface litter layer
and its populations of invertebrate decomposers in terrestrial
environments, and surface sediments and benthic organisms
in aquatic systems.
192. Depending on the quantities of specific radio­
nuclides released following an accident, the radiation
exposures might range from low (a few multiples of thenatural background) to high (absorbed doses greater than
1 Gy). Different phases of biological response to thehigher total doses might be distinguished. Initially, and, inparticular if short-lived radionuclides made up a significant proportion of the release, there might be an acutephase in which total doses sufficient to produce immediate
or relatively early detectable biological responses areaccumulated. In the intermediate phase, dose rates would
decrease owing to the decay of the short-lived radio­
nuclides and possibly, but not necessarily, owing to theredistribution of the longer-lived radionuclides by naturalprocesses. Even in this phase, the slower accumulation ofradiation dose might still result in total integrated doses
sufficient to prevent recovery of organisms damaged in theinitial phase or lead to the appearance of medium-term
damage. In the long-term phase, post-irradiation recovery(and adaptation) becomes apparent, provided that the initial and medium-term damage had not been large enoughto radically alter the population or community structure.

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

III.

263

Summary of dose–effects data from the Chernobyl accident

193. A great deal of scientific information concerning theeffects of exposure to ionizing radiation has been developed
from studies of non-human biota in the area surrounding thesite of the Chernobyl accident. The follow-up studies provided the main source of new information on the effects ofradiation exposure on non-human biota since the UNSCEAR
1996 Report [U4]. This area has a temperate climate andflourishing flora and fauna. Much of the new information,
originally reported in Russian, has been summarized in areport prepared for the Committee [A5] and by the work of theChernobyl Forum [E8]. The following discussion of radia­tionlevels and effects on biota observed in the region around theChernobyl nuclear power plant is based on information­presented in reference [E8] and in other recent reviews [G26].
A.

Radiation exposure

194. The Chernobyl Forum Expert Group on Environment(EGE) [E8] noted that the effects of the Chernobyl accident
should be studied within specific time periods. Three distinct
phases of radiation exposure have been identified in the area
local to the accident [U4]. In the first 20 days, radiation
exposures were essentially acute because of the large quantities of short-lived radionuclides present in the passing cloud(99Mo, 132Te/I, 133Xe, 131I and 140Ba/La). Most of these shortlived, highly radioactive nuclides deposited onto plant andground surfaces, resulting in gamma radiation dose rates of
up to about 20 Gy/d. However, for surface tissues and small
biological targets (e.g. mature needles and the growing budsof pine trees) there was a considerable additional dose rate
due to the beta radiation from the deposited radionuclides.
High doses to the thyroids of vertebrate animals also
occurred during the first days/weeks following the accident
owing to the inhalation and ingestion of radioactive isotopesof iodine and their radioactive precursors.
195. The second phase of radiation exposure extended
through the summer and autumn of 1986, during which time
the short-lived radionuclides decayed and the longer-lived
radionuclides were transported to different components ofthe environment by physical, chemical and biological pro­
cesses. Dominant transportation processes included raininduced transfer of radionuclides from plant surfaces onto
soil, and bioaccumulation through plant tissues. Dose rates
at the soil surface declined to much less than 10% of theinitial values owing to radioactive decay of the short-lived
radionuclides, but damaging total doses were still accumulated. Approximately 80% of the total radiation dose accumulated by plants and animals was received within 3 monthsof the accident, and over 95% of this was due to beta radiation exposure [E8]. Measurements made with thermoluminescent dosimeters on the soil surface at sites within the
30‑km exclusion zone indicated that the ratio of beta to
gamma dose was about 26:1, (i.e. 96% of the total dose wasdue to beta radiation exposure) [P18].

196. The EGE [E8] also defined a third (and continuing)phase of radiation exposure with chronic dose rates less than
1% of the initial values and derived mainly from 137Cs. With
time, the decay of the short-lived radionuclides and themigration of much of the remaining 137Cs into the soil meantthat the contributions to the total radiation exposure from thebeta and gamma radiations tended to become more comparable. Reference [E8] noted that the balance depended on the
degree of bioaccumulation of 137Cs in organisms and the
behaviour of the organism in relation to the main source of
external exposure resulting from the 137Cs in the soil.
B. Effects of radiation exposure on plants
197. The report of the EGE was a great advance on previous publications describing the follow-up work on theeffects of the Chernobyl accident. In particular, the reportgave considerable attention to evaluating the dosimetry of,and consolidating the information on the effects on nonhuman biota. Thus, given both the greatly improved qualityof the data and the comprehensive nature of the evaluation
provided by the EGE, much of the following discussion isadapted from reference [E8].
198. Doses received by plants arising from the depositedradionuclides resulting from the Chernobyl accident were
influenced by the physical properties of the various radio­
nuclides (i.e. their half-lives, radiation emissions, etc.), thephysiological stage of the plant species at the time of theaccident, and the different species-dependent propensities totake up radionuclides into critical plant tissues [E8]. The
occurrence of the accident in late April 1986 was thought tohave enhanced the damaging effects of the deposition
because it coincided with the period of accelerated growth
and reproduction of plants.
199. The deposition of beta-emitting radionuclides onto
critical plant tissues resulted in their having received a significantly larger dose than animals living in the same environment [P18, P19]. According to reference [G9], large
apparent inconsistencies in the dose–response observations
occurred when the beta‑irradiation component was not
appropriately taken into account.
200. Within the 30‑km zone around the Chernobyl plant,
the doses to plants associated with the deposition of total beta
activity (0.7–3.9 GBq/m2) were sufficient to cause short-term
sterility and reduction in productivity of some species [P19].
By August 1986, crops that had been sown prior to the accident began to emerge. Growth and development problems
were observed in plants in fields with deposition densities of
0.1–2.6 GBq/m2 of total beta activity, and with estimateddose rates initially received by the plants having reached
300 mGy/d. Spot necroses on leaves, withered tips of leaves,
inhibition of photosynthesis, transpiration and metabolite

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UNSCEAR 2008 REPORT: VOLUME II

synthesis were detected, as well as an increased incidence ofchromosome aberrations in meristem cells [S22]. The frequency of various anomalies in winter wheat exceeded 40%
in 1986–1987, with some abnormalities apparent for several
years afterwards [G12].
201. Coniferous trees were already known to be among themore radiosensitive plants, and the pine forests, 1.5–2 km
west of the Chernobyl nuclear power plant, received sufficient doses, more than 80 Gy, at dose rates that exceeded
20 Gy/d, to cause mortality [T18]. The first signs of radiation
injury were yellowing and needle death in pine trees in close
proximity to the nuclear power plant and appeared during
the summer of 1986. The colour of the dead pine stands
resulted in the forest being referred to as the “red forest”.
202. Tikhomirov and Shcheglov [T18] and Arkhipov et al.
[A11] found that mortality rate, reproduction anomalies, standviability, and re-establishment of pine-tree canopies weredependent on absorbed dose. Acute irradiation of Pinus silvestris at doses of 0.5 Gy caused detectable cytogenetic damage;at doses of more than 1 Gy, growth rates were reduced andmorphological damage occurred; and, at more than 2 Gy, thereproductive abilities of trees were altered. Doses of less than
0.1 Gy did not cause any visible damage to the trees. Table 23
shows the variation in activity concentration and dose amongpine trees within the 30‑km zone. The radiosensitivity of
spruce trees was observed to be greater than that of pines. At
absorbed doses as low as 0.7–1 Gy, spruce trees had ­malformed
needles, buds and shoot growth [K1].
203. About 90% of the absorbed dose to critical parts of thetrees was due to beta irradiation from the deposited radio­
nuclides with the remaining 10% from gamma irradiation.
Table 22 summarizes the external gamma dose rates and theinternal radionuclide concentrations in the conifers around theChernobyl plant. By 1987, recovery processes were evident in
the surviving tree canopies and the forests were re-­establishingthemselves where the trees had perished [A11]. In the decimated pine stands, a sudden invasion of pests occurred thatlater spread to adjoining areas. Grassland, with a slow invasion of self-seeding deciduous trees, has now replaced thedeceased pine stands. Four distinct zones of radiation-induced
damage to conifers were discernable (table 23).

Table 22. Activity concentration in needles of coniferous trees and estimated external gamma dose rates in October 1987 as
a function of distance from the Chernobyl nuclear power plant
For azimuth 205 to 260 degrees (adapted from reference [K12])
Distance from NPP(km)

External exposure rate
(μGy/h)a

Accumulated external dose(mGy)a

2

2 500

4
16

Activity concentration in needles (kBq/kg)
144

Ce

106

Ru

95

Zr

95

Nb

134

Cs

137

Cs

126 000

13 400

4 100

800

1 500

1 500

4 100

120

5 000

150

60

8

15

17

72

0.4

14

1.5

0.6

0.1

0.17

0.18

0.55

a Based on gamma radiation levels at 1 m height above the soil surface. The values given in the original reference were in mR/h and have been converted assuming 1 mR/h isequivalent to 10 μGy/h.

Table 23. Zones and corresponding damage to coniferous forest in the area around the Chernobyl nuclear power plant (fromreference [K1])
Zone and classification

External gamma dose
(Gy)

Exposure rate
(μGy/h)aInternal dose to needles(Gy)over 80–100

over 5 000

over 100Sublethal (38 km2)
Death of most growth points
Partial death of coniferous trees
Morphological changes to deciduous trees

10–20

2 000–5 000

50–100Medium damage (120 km2)
Suppressed reproductive ability
Dried needles, morphological changes

4–5

500–2 000

20–50

Minor damage
Disturbances in growth, reproduction and morphology
of coniferous trees

0.5–1.2<200<10Conifer death (4 km2)
Complete death of pines
Partial damage to deciduous trees

a The values given in the original reference were in mR/h and have been converted assuming 1 mR/h is equivalent to 10 μGy/h.

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

C.

Effects of radiation exposure on soil invertebrates

265205. A fourfold reduction in earthworm numbers wasfound in arable soils, but no catastrophic mortality in anygroup of soil invertebrates was observed. The dose to invertebrates in forest litter was 3–10 fold higher than that tothose residing in unploughed surface soil since the radio­
nuclides deposited on the surface had not migrated downwards. The result was no reduction in the numbers of soil
invertebrates below a depth of 5 cm in the soil as they wereshielded by the overlying soil [K11].

204. Between 60% and 90% of the initial fallout of radionuclides was captured by the forest canopy and other plants[E8]; however, within weeks to a few months, the processesof wash-off by rain and leaf fall removed most of the initialdeposition to the litter and soil layers, where soil and litter
invertebrates were exposed to high radiation levels for protracted time periods. The timing of the accident coincidedwith the most radiosensitive life stages of the soil invertebrates: reproduction and moulting following their winterdormancy [T18]. Within two months after the accident, thenumbers of invertebrates in the litter layer of forests 3–7 kmfrom the nuclear power plant were reduced by a factor of
30 [K11], and reproduction was strongly impacted (larvaeand nymphs were absent). These effects corresponded todoses of approximately 30 Gy (estimated from TLDs
placed in the soil) resulting in mortality of eggs and earlylife stages, as well as reproductive failure in adults.
­However, within a year of the accident, reproduction of
invertebrates in the forest litter resumed, due, in part, to themigration of invertebrates from less contaminated sites.
After 2–3 years, the ratio of young to adult invertebrates in
the litter layer, as well as the total mass of invertebrates perunit area, were no different from those in control sites;
however, species diversity remained markedly lower [K11].
As noted in the report of the EGE [E8], this is importantsince the diversity of invertebrate species within the soil
facilitates an analysis of the community-level effects ofradiation exposure (i.e. changes in species composition andabundance). For example, only five species of invertebrates
were found in 10 soil cores taken from pine stands in July
1986, 3 km from the Chernobyl nuclear power plant, compared to 23 species at a control site 70 km away. The meandensity of litter fauna was reduced from 104 individuals
per 225 cm2 core at the control location to 2.2 at the 3‑km
site. Six species were found in all 10 cores taken from thecontrol site, whereas no one species was found in all
10 cores from the 3‑km location [K13]. The number of
invertebrate species found in the heavily contaminated sites
was only half that of controls in 1993, and complete species diversity did not recover until 1995, almost 10 years
after the accident [K11].

206. Although, the researchers were unclear if sterility of
invertebrates occurred in the heavily contaminated sites aroundthe Chernobyl nuclear power plant [K11], the 30 Gy cumulative dose reported in the field studies was within the range ofexperimental doses used to control pest insects by external irradiation. A recent review indicated that most insect, mite andtick families require a sterilization dose of less than 200 Gy[B40], although the sterilization dose for some insects andrelated arthropods is much lower than this and varies widely.
As was found for plants [S2], the radiosensitivity of insects is
related to the average interphase nuclear volume [B40].
D. Effects of radiation exposure on farm animals
207. Ruminants, both domestic (cattle, goats and sheep)
and wild (elk and deer), generally receive relatively highdoses in radioactively contaminated environments, because
they consume large amounts of vegetation, and many radionuclides accumulate in their bodies. For example, a single
cow consumes about 75 kg of fresh grass each day.
208. In the period shortly after the accident, domestic livestock within the 30‑km zone were exposed to high levels ofradioactive iodine (131I and 133I with half-lives of 8 days and21 hours, respectively). This resulted in significant internaland external doses due to beta and gamma radiation exposure (table 24). A dose of about 76 Gy is sufficient to cause
harm to the thyroid gland [B23]. Soils of Ukraine and­Belarus are naturally low in stable iodine, cobalt and manganese. In conditions of endemic deficiency of stable iodine,
the transfer of radioactive iodine from blood to the thyroid
gland may be 2–3 times greater than normal [P19]. These
conditions accentuated the consequences of the accident.

Table 24. Doses to cattle that stayed in the 30‑km zone around the Chernobyl plant from 26 April to 3 May 1986 [K12]Distance from nuclear
power plant (km)Surface activity(108 Bq/m2)

3

Absorbed dose (Gy)Thyroid

GI tract

Whole body internal

8.4

300

2.5

1.4

10

6.1

230

1.8

1.0

14

3.5

260

1.0

0.6

12

2.4

180

0.7

0.4

35

1.2

90

0.4

0.2

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209. Depressed thyroid function in cattle was related to thedose received (69% and 82% reductions in function withthyroid doses of 50 Gy and 280 Gy, respectively). The concentration of thyroid hormones in the blood of animals was
lower than the physiological norm during the whole lactation
period. Radiation damage to the thyroid gland was confirmed by histological studies (i.e. hyperplasia of connective
tissue and sometimes adipose tissue, vascular hyperaemia
and necrosis of epithelium). Animals with practically no thyroid tissue were observed in Ukraine. Disruptions of the hormonal status in calves born to cows with irradiated thyroid
glands were especially pronounced [A12]. Similar effects
were observed in cattle evacuated from the Belarusian­portion of the 30‑km zone [I18].
210. Although most livestock were evacuated from thearea after the accident, several hundred cattle were maintained in the more contaminated areas for a 2–4 month
period. By autumn 1986, some of these animals had died;others showed impaired immune responses, lowered bodytemperatures and cardiovascular disorders. Hypothyroidism
lasted until 1989, and may have been responsible for reproductive failures in animals that received thyroid doses ofmore than 180 Gy [I18]. Offspring of highly exposed cows
had reduced weight, reduced daily weight gains, and signsof dwarfism. Reproduction returned to normal in the springof 1989. Haematological parameters were normal for animals kept in areas with 137Cs deposition densities of 0.2–
1.4 MBq/m2 (5–40 Ci/km2) [A12].
211. No increase in the rates of birth defects were detected
above background levels at annual doses below about
0.05 Gy [P17].
E. Effects of radiation exposure onother terrestrial animals
212. Surveys and autopsies of wildlife and of abandoned
domestic animals that remained within 10 km of the­Chernobyl nuclear power plant were conducted four months
after the accident. [K11]. Fifty species of birds were identified, including some rare ones; all appeared normal inappearance and behaviour. No dead birds were found. Swallows and house sparrows were found to be producing progeny that also appeared normal. Forty-five species ofmammals from six orders were observed and no unusual
appearances or ­behaviours were noted.
213. In a review of thirty-three studies of the biologicalconsequences of the Chernobyl accident, Møller and­Mousseau [M19] commented on various increases in mutations and cytogenetic abnormalities attributed to elevatedradiation levels. They noted that the fitness consequencesof such increases were largely unknown and cited a studyof differences in phenotypes in barn swallows from near
Chernobyl and those from relatively uncontaminated control areas [M18]. The authors suggested that mutations
with slightly negative fitness effects could have been
exported from the contaminated zones and potentiallyaffected unexposed populations. In an exchange of views,
Møller et al. [M17, M20] challenged the hypothesis ofSmith [S26] that the impacts on barn swallows arose fromfactors other than radiation exposure, namely the change inhabitat and wildlife community arising from changes inagricultural practices resulting from efforts to reduce thespread of radioactively contaminated food. Smith however
noted that the most contaminated sites were located within
abandoned lands, which had large differences in both land
use and ecology from the control sites.
214. Some wildlife and domestic animals were shot andautopsied in August and September 1986. Dogs and­chickens showed signs of chronic radiation syndrome(reduced body mass; reduced fat reserves; increased massof lymph nodes, liver and spleen; haematomas present inliver and spleen; and thickening of the lining of the lower
intestine). No eggs were found in the nests of chickens,nor in their ovaries.
215. During the autumn of 1986, the number of smallrodents on highly contaminated research plots decreased bya factor of 2–10. Estimates of absorbed doses during the first
five months after the accident ranged from 12–110 Gy for
gamma and 580–4,500 Gy for beta irradiation. By the springof 1987, the numbers of animals were recovering, mainly
due to immigration from less affected areas. In 1986 and1987, the percentage of pre-implantation deaths in rodents in
the highly contaminated areas was 2–3 fold greater than thatin the controls. Resorption of embryos also increased markedly in rodents from the impacted areas; however, thenumber of progeny per female did not differ from that of thecontrols [T16].
F. Effects of radiation exposure on aquatic organisms
216. Cooling water for the Chernobyl nuclear power plant
was obtained from a 21.7 km2 man-made reservoir located tothe south-east of the plant site. The cooling reservoir becameheavily contaminated following the accident with a total
activity of over 6.5 ± 2.7 PBq of a mixture of radionuclides(alpha and beta emitters) in the water and sediments [K14].
Aquatic organisms were exposed to external radiation fromthe radionuclides in the water, contaminated bottom sediments, and aquatic plants. Internal irradiation occurred asorganisms took up radionuclides in their food and water or
inadvertently consumed contaminated sediments. The resultant doses to aquatic biota over the first 60 days following theaccident are depicted in figure XI.

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

267

Figure XI. The dynamics of absorbed dose rate to organisms within the Chernobyl nuclear power plant cooling pond during
the first 60 days following the accident
Data are model results based on concentrations of radionuclides in the water column and lake sediments (adapted from reference [K12])
1 000

Benthicorganisms

Macroalgae

mGy/d

100

Fish

10

Zooplankton

Phytoplankton
1
0

10

20

30

40

50

60

DAYS POST ACCIDENT

217. The maximum dose rates to aquatic organisms(excluding fish) were reported in the first two weeks after
the accident, when short-lived radionuclides (primarily
131I) contributed 60–80% of the dose. During the second
week, the contribution of short-lived radionuclides to thedoses of aquatic organisms decreased by a factor of two.
Maximum dose rates to fish were delayed (see figure XI)
owing to the time required for their food webs to becomecontaminated with longer-lived radionuclides (largely
134,137
Cs, 144Ce/Pr, 106Ru/Rh and 90Sr/Y). The dose rates tofish depended on their trophic positions. Non-predatory
fish (carp, goldfish and bleak) incurred estimated peakdose rates of 3 mGy/d due to internal exposure in 1986,
followed by significant reductions in 1987. Dose rates topredatory fish (perch), however, increased in 1987 anddid not start to decline until 1988 [K12]. Accumulated
doses were greatest for the first generation of fish born in1986 and 1987. Bottom-dwelling fish (goldfish, silver
bream, bream and carp) that were significantly irradiatedby the bottom sediments accumulated total doses ofapproximately 10 Gy.

218. The reproductive capacity of young silver carp was
analysed in 1990 [R10]. The fish were in live boxes within
the cooling pond at the time of the accident. By 1988, the fish
had reached sexual maturity. Over the entire post-­accident
period, they received a dose of 7–8 Gy. Biochemical analysesof muscles, liver and gonads indicated no difference from thecontrols. The amount of fertilized spawn was 94%; 11% of
the developing spawn was abnormal. Female fertility was
40% higher than that of the controls, but 8% of the irradiatedsires were sterile. The level of fluctuating asymmetry in offspring did not differ from that of the controls, although thelevel of cytogenetic damage (22.7%) significantly exceededthat of controls (5–7%). In contrast, Pechkurenkov [P20]reported that the number of cells with chromosome aberrations in 1986–1987 in carp, bream flat and silver carp waswithin the norm. It is worth noting that the cooling pond was
subjected not only to radioactive contamination, but also tochemical pollution. Table 25 provides a summary of therecent reviews of the chronic effects of ionizing radiation
exposure on the reproduction in fish. The Chernobyl accident
data are included.

Table 25. Chronic effects of exposure to ionizing radiation on reproduction in fish
Derived from the FASSET database [C11]
Dose rate(μGy/h)Dose rate(mGy/d)Reproductive effects

0–99

0–2.4

Background dose group, normal cell types, normal damage and normal mortality observed

100–199

2.4–4.8

No data available

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UNSCEAR 2008 REPORT: VOLUME II

Dose rate(μGy/h)Dose rate(mGy/d)Reproductive effects

200–499

4.8–12

Reduced spermatogonia and sperm in tissues

500–999

12–24

Delayed spawning, reduction in testis mass

1 000–1 999

24–48

Mean lifetime fecundity decreased, early onset of infertility
Reduced number of viable offspring
Increased number of embryos with abnormalities

2 000–4 999

48–120

Increased number of smolts in which sex was undifferentiated
Increased brood size reported
Increased mortality of embryos

5 000–9 999

120–240

Reduction in number of young fish surviving to 1 month of age
Increased vertebral abnormalities
Inter-brood time tends to decrease with increasing dose rateSignificant reduction in neonatal survival
Sterility in adult fish

>10 000>240

Destruction of germ cells within 50 days in medaka fish
High mortality of fry, germ cells not evident
Significant decrease in number of male salmon returning to spawn; after 4 years, female salmon had
significantly reduced fecundity

G. Genetic effects in animals and plants
219. High quality data on the incidence of radiogenic
mutations in plants and animals as a result of the accident are
relatively sparse. An increased mutation level was apparent
in 1987 in the form of various morphological abnormalities
in Canada fleabane, common yarrow and mouse millet.
Examples of abnormalities included: unusual branching ofstems; doubling the number of racemes; abnormal colour
and size of leaves and flowers; and development of “witch’s
broom” in pine trees. Similar effects within 5 km of thenuclear power plant also appeared in deciduous trees (leafgigantism, and changes in leaf shapes). Morphologicalchanges were observed at an initial gamma dose rate of 4.2–
6.3 mGy/d. At a dose rate of 15.8–31.5 mGy/d, enhancementof vegetative reproduction (in heather) and gigantism ofsome plant species were observed [A11, K10, T17, T18].
220. Cytogenetic analysis of cells from the root meristem
of winter rye and wheat germ of the 1986 harvest demonstrated a dose dependency in the number of aberrant cells. A
significant excess over the control level of aberrations wasobserved at an absorbed dose of 3.1 Gy. Inhibition of mitotic
activity occurred at a dose of 1.3 Gy, and germination was
reduced at a dose of 12 Gy [G10]. The analysis of three successive generations of winter rye and wheat on the most contaminated plots revealed that the rates of aberrant cells in theintercalary meristem in the second and third generations
were higher than in the first.
221. From 1986–1992, mutation dynamics were studied in
populations of Arabidopsis thaliana Heynh. (L.) within the

30‑km zone [A10]. On all study plots during the first
2–3 years after the accident, Arabidopsis populations exhibited an increased mutation burden. In later years, the level oflethal mutations declined; nevertheless the mutation rate in1992 was still 4–8 times higher than the spontaneous level.
The dose dependence of the mutation rate was best approximated by a power function with an exponent value of lessthan one.
222. Zainullin et al. [Z2] observed elevated levels of sexlinked recessive lethal mutations in natural Drosophila melanogaster populations living under conditions of increased
chronic exposure to radiation resulting from the Chernobyl
accident. The mutation levels were increased during 1986–
1987 in flies inhabiting the more contaminated areas withinitial exposure rates of 2 mGy/h (expressed as 200 mR/h in
the original text) and more. During the subsequent two years,
mutation frequencies gradually returned to normal.
223. Shevchenko et al. [S21] and Pomerantseva et al. [P16]reported studies of adverse genetic effects in wild mice.
These involved mice caught during 1986–1991 within a
30‑km radius of the Chernobyl nuclear power plant with different levels of gamma radiation exposure and, during 1992–
1993, on a site in the Bryansk Oblast, Russia. The estimatedtotal doses of gamma and beta radiation varied widely; thedose rates reached 3–4 Gy per month in 1986–1987. One
endpoint was dominant lethality, measured by embryo mortality in the offspring of wild male mice mated with unexposed female laboratory mice. The dominant lethality rate
was elevated for a period of a few weeks following capturein mice sampled at the most contaminated site. At dose rates

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

of about 2 mGy/h, 2 of 122 captured males produced no offspring and were assumed to be sterile. The remainder showeda period of temporary infertility and reduced testis mass.
Fertility and testis mass, however, recovered with time after
capture.
224. The frequencies of reciprocal translocations in mouse
spermatocytes were consistent with previous studies. A
dose-rate-dependent incidence of increased reciprocal translocations (scored in spermatocytes at meiotic metaphase I)
was observed in all collected mice. The frequency of miceharbouring recessive lethal mutations decreased with timeafter the accident [P16]. Radiation-related gene mutation isunlikely to have any adverse effect on populations, at thedose rates that prevail now.
225. Increasing sophistication in the technologies for thedetection of molecular and chromosomal damage haveallowed researchers on the genetic consequences of theChernobyl accident to examine endpoints not previously
considered [E8]. Most prominent, and controversial, is thetechnique involving the measurement of mutation frequencies in repeat DNA sequences termed “minisatellite loci” or“expanded simple tandem repeats” (ESTR). These are repeat
DNA sequences that are distributed throughout the germline
and have a high background (spontaneous) mutation rate.
Presently, ESTRs are considered to have no function,although this is a matter of much interest and discussion[B33, C10, I9]. Minisatellite mutations have only rarely
been associated with recognizable genetic disease.
226. Although laboratory examination of mutations inmouse ESTR loci show clear evidence of a mutational dose
response [D4, F16], the EGE was not aware of any convin­cing data on elevated levels of minisatellite mutations inplants or animals residing in the contaminated areas having
been published in peer-reviewed scientific literature [E8]. In
general, quantitative interpretation of the ESTR data is difficult because of conflicting findings, their weak association
with genetic disease, dosimetric uncertainties and methodological problems [C10]. This is an area of science that
requires additional research.

269

occurred within this zone. As a result of the elevated radiation
doses associated with the contamination, human activities
such as agriculture, forestry, hunting and fishing within the
exclusion zone were stopped [E8]. After the accident, thefields continued to yield agricultural produce for a number ofyears and, in the absence of active management in the areasthat had been evacuated, many animal species, especiallyrodents and wild boars, consumed the abandoned cereal
crops, potatoes and grasses as an additional source of forage[E8]. This was advantageous to these animal species and,along with the special reserve regulations established in the
exclusion zone (e.g. a ban on hunting), tended to compensate
for the adverse biological effects of radiation exposure andpromoted an increase in the populations of wild animals,
including game mammals (wild boars, roe deer, red deer, elk,
wolves, foxes, hares, beaver, etc.) and bird species (black
grouse, ducks, etc.) [G8, S23]. In addition, the ­Chernobyl
exclusion zone has become a breeding area of white-tailed
eagles, spotted eagles, eagle owls, cranes and black storks[G9].
229. The high dose rates from ionizing radiation during thefirst few weeks following the Chernobyl accident affected
the balanced community by killing sensitive individuals,
altering reproduction rates, destroying some resources (e.g.
pine stands), making other resources more available (e.g.
soil water), and opening niches for immigration of new andsometimes negative organisms (e.g. negative entofauna).
These components and more, were interwoven in a complex
web of action and reaction that altered populations and­communities of organisms [E8].
230. Overall, the EGE [E8, H25] arrived at a number ofgeneral observations from their evaluation of the Chernobyl
data, namely that:– Radiation from radionuclides released as a resultof the Chernobyl accident caused numerous acute
adverse effects on the biota located in the areas ofhighest exposure (i.e. up to a distance of a few tensof kilometres from the release point). Beyond theexclusion zone, no acute radiation-induced effects
on biota have been reported;

227. According to the EGE [E8], prior to the accident,much of the area around the Chernobyl nuclear power plant
was covered by 30–40 year old pine stands that, from a successional standpoint, represented mature, stable ecosystems.
The high dose rates due to ionizing radiation exposure during the first few weeks following the accident altered the balance in the community and opened niches for immigrationof new individuals.

– The environmental response to the increased radiation exposure incurred as a result of the Chernobyl
accident was a complex interaction among radiation dose, dose rate and its temporal and spatial
variations, as well as the radiosensitivities of thedifferent taxons. Both individual and population
effects caused by radiation-induced cell death
were observed in plants and animals and included
increased mortality of coniferous plants, soil invertebrates and mammals; reproductive losses inplants and animals; and chronic radiation sickness
in animals (mammals, birds, etc.);

228. The ecological conditions within the 30‑km ­Chernobyl
exclusion zone arose from the complex interaction of anumber of factors. The highest level of contamination– No adverse radiation-induced effects were reported
in plants and animals exposed to a cumulative doseof less than 0.3 Gy during the first month after theaccident (i.e. <10 mGy/d, on average); andH.

Overall observations on the effectsof the Chernobyl accident

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UNSCEAR 2008 REPORT: VOLUME II– Following the natural reduction of exposure levels
due to radionuclide decay and migration, populations have been recovering from acute radiation
effects. By the next growing season following theaccident, the population viability of plants andanimals substantially recovered as a result of the
combined effects of reproduction and immigration.
A few years were needed for recovery from the
major radiation-induced adverse effects on plants
and animals.

and indicated that the minimum dose rate at which morphological changes have been seen in the Chernobyl zone wasabout 1.2 mGy/d. The authors also indicated that this dose
rate is about nine times lower than the reference dose rate
provided in reference [U4] but suggested that such discrepancies can be explained by the use of generic reference dose
rates for all terrestrial plants rather than for specific plants.
For herbaceous plants, they suggested a reference dose rate ofabout 8.2 mGy/d [F17] which is comparable to the value suggested in reference [U4]. For cattle, they suggested a reference dose rate of about 1.6 mGy/d based on data given inreferences [C16, S36] but go on to indicate that radiation
harm to farm animals in the Chernobyl zone was more related
to damage to the thyroid from internally deposited radio­
nuclides. Based on the assumption that impairment of reproduction usually occurs at doses about one order of magnitude
below the LD50 of about 0.8 Gy and on observed reductionsin the numbers of invertebrates, the authors [F17] suggested
a reference dose rate of about 2.5 mGy/d. Finally, for aquatic
systems, the authors [F17] suggested that fish are generally
more radiosensitive than plankton and zoobenthos and­proposed a reference dose rate of about 1.6 mGy/d.

231. Fesenko et al. have compared the relative radiologicalimpact on people and non-human biota arising from the
Chernobyl accident [F17]. They reviewed the data on reference dose rates for non-human biota (which they refer to as
critical exposure doses or CDVb below which an effect would
not be expected). The authors adopted the commonly used
endpoints of early mortality, morbidity, reduced reproductive
success and deleterious genetic effects. Their values of CDVb
for non-human biota near Chernobyl are summarized intable 26. They noted that coniferous trees were known to beamong the most radiosensitive components of the biosphere

Table 26. Review of CDVb for non-human species inhabiting the study area
(adapted from reference [F17])
Non-human species

CDVb (mGy/d)cited in [F17]

Literature data

Terrestrial ecosystems
Coniferous trees (pine)

1.1

1.1 [S35], 2.4 [C16], 10 [U4]Herbaceous plants (meadow grasses)

8.2

1.1 [S35, S36], 2.4 [C16], 10 [U4]Herbaceous plants (cereals)

8.2

1.1 [S35, S36], 2.4 [C16], 10 [U4]Cattle1.6 (137a)

1.1 [S36], 2.5 [C16]

Mouse-like rodents

1.1

0.1 [S35], 0.2 [S36], 1 [C16], 1 [U4], 2.7 [B31]

Soil invertebrates

2.5

1.1 [S35, S36], 2.4 [C16], 5.5 [B31]

Aquatic ecosystems
Phytoplankton

8.2

2.4 [C16], 2.7 [B31]

Zooplankton

6.8

2.4 [C16], 2.7 [B31]

Zoobenthos

2.5

1.6 [C16], 5.5 [B31]

Fish

1.6

0.3 [S35], 0.5 [C16], 0.5 [B31], 10 [U26]a Dose to the thyroid.

232. Another report provided a comprehensive evaluationof the effects of radiation exposure resulting from the Chernobyl accident on non-human biota along with corresponding dosimetry information [G26]. In total, 250 referenceswere evaluated. Of these, some 79 papers were considered tohave adequate information on environmental contaminationand doses to biota. The review focussed on the assessment of

the effects of radiation exposure on plants and animal populations inhabiting the contaminated areas around Chernobyl
at the time of, and following, the accident [G26]. As
described earlier, the radiation doses associated with the firstphase following the Chernobyl accident was a period ofshort-term quite high radiation dose rates followed by aperiod with a gradual decline in dose rate. The most severeANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

environmental effects were associated with the high dose
rates. Effects of radiation exposure were seen in both naturaland agricultural systems. The authors noted that the effects
depended on the radiosensitivity of the dominant species andobserved that coniferous trees were one of the most sensitiveplant species and mammals were the most radiosensitive animal species [G26]. To date, reference [G26] provides themost comprehensive evaluation of observations of the effectsof the Chernobyl accident on non-human biota. The key
observations from the review are summarized in table 27,
which shows various effects on non-human biota around
Chernobyl and the corresponding doses below which such
effects were not observed.

Forum [E8]. Table 27 provides a summary of the informationon the effects and associated doses and dose rates from studies of non-human biota around the Chernobyl nuclear power
plant. However, given the importance of this topic, a few
additional comments are appropriate. The available information indicates that the forest close to the Chernobyl power
plant captured much of the radioactive dust following theaccident, reducing the spread of radioactive material outside
the 10‑km zone [A11]. The dose rate within the 10‑km zone
showed an exponential decay, with the majority of the total
dose absorbed by the environment within the first month[A11, K20, S30]. Thus, the Committee has assumed, in table
27, that most (80% or so) of the dose would have been delivered in (about) the first month following the accident. Where
appropriate for comparison purposes, a notional daily dose
rate was derived by dividing the reported doses by 30.

233. The reliability of the estimated doses arising from the
Chernobyl accident has been examined by the Chernobyl

Table 27.

271

Effects on populations of non-human biota around the Chernobyl power plant [G26]
Species effect

Estimated minimum doses (or dose rates)
at which effect was observed

Estimated maximum doses (or dose rates)
at which effect was not observed

Scots pine
Death of weakened trees

8–12 Gy [A11, K20]

5 Gy

Mass death of young cones and anthers

10–12 Gy [S29]5 Gy

35–40 years old, mass yellowing of needles

8–12 Gy [K20]5 Gy

Inhibition of reproductive capacity (reduced number of seeds per cone andincreased fraction of hollow seeds)

1–5 Gy [F10]0.5 GyMorphological disturbances one year after accident

0.1–1.0 Gy [A11]0.05 Gy

Significant increase in cytogenetic effects in seedlings and needles

0.5 Gy [F10]0.05 Gy

Frequency of mutations of enzyme loci in seed endosperm

0.07 Gy [F10]0.01 Gy

Spruce10–15 years old. Death of trees

4–5 Gy [K20]

1 Gy

25 years old. Dying-off of young sprouts. Mortality of much of the trees within
2–3 years

8–10 Gy [K21]5 Gy

40 years old. Noticeable reduction in sprout mass

2.5–3 Gy [K21]

1 Gy

Mass yellowing of needles

3.5–5 Gy [K21]2 Gy

Herbaceous plants
Reduced density of plants and species diversity in following year

17 mGy/d [S30]

10 mGy/dMorphological changes

4.2–6.3 mGy/d [S30]

2 mGy/dEnhanced vegetative reproduction and gigantism of some herbaceous species

16–30 mGy/d [S30]

10 mGy/d

Sterility of seeds

40 Gy – vetch; 10 Gy – dandelion andarabidopsis [S30]

Decrease in the number of peas in pods of wild vetch, increase in bothf­raction of sterile pods and fraction of embryonic lethalities

0.4 mGy/d [S31]5 Gy
0.1 mGy/dSoil fauna
Drastic decrease in the population density and species composition of forest
litter mesofauna

Dose absorbed on the soil surface 9 Gy
[K13]

1 Gy

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UNSCEAR 2008 REPORT: VOLUME IISpecies effect

Estimated minimum doses (or dose rates)
at which effect was observed

Estimated maximum doses (or dose rates)
at which effect was not observed

Amphibians (brown frogs)
Dose rate, mGy/d: 0.01 from 90Sr tobone tissue, 0.038 from other sources
to the whole body, 0.013 from external
g-radiation exposure [E18, E19]

Increased yield of chromosome aberrations and damage severity in aberrant
cells

0.01 mGy/dHydrobionts
9–11 Gy for 5 years [B19, M21]

Silver carp. Higher occurrence of reproduction system alterations, reduced
viability of progeny

1 Gy/aSmall mammals
Inhibition of reproductive capacity (the significantly reduced testis mass aswell as irreversible or temporary sterility in some males)

Absorbed gonad doses of 3 Gy per month[P16]

1 Gy/aPathological changes in haemopoietic system, liver, adrenals and thyroid

Absorbed dose from external g‑radiation
exposure from the moment of accident
till animal catching in autumn 1986 was
1 Gy. Contribution of b‑radiation was
2–5 times higher than g and incorporated
radionuclides by 1–2 orders lower thanfrom external [E20, M22]

0.5 GyA dose-dependent increase in the frequencies of chromosome aberrations
in bone marrow cells and embryonic losses in bank voles, high frequency ofpolyploid cells and genome mutations

Whole-body absorbed dose rate in 1986:
approximately 6–600 µGy/d [R17]5 µGy/dCattleDestruction of thyroid, chronic radiation disease

Doses absorbed by thyroid >200 Gy, withdose to the whole body being no morethan 0.2 Gy [A24, B16]

20 Gy to thyroidaa Effect in the early days after the accident was mainly determined by 13II action and depended greatly on content of stable iodine in animal ration.

IV.

Effects of radiation EXPOSURE on NON-HUMAN BIOTA

234. This chapter provides an overview of the independent
evaluations of the published literature on the effects of radiation
exposure on non-human biota, briefly considers the relevant
observations from case studies where dose rates to non-humanbiota have been estimated and compared to reference dose rates(from, for example, reference [U4]), and extracts additional key
observations from the post-1996 literature.
A.

Overall conclusions of the UNSCEAR 1996 Report235. The main observations from the Committee’s 1996
evaluation [U4] are described in chapter III of this annex.

The Committee, while emphasizing that only limited data
were available for consideration, concluded that the production of viable offspring through gametogenesis and reproduction is a more radiosensitive population attribute than the
induction of individual mortality.
236. The Committee also noted that there was a wide dose
range over which organisms were sensitive to the lethal
effects of radiation exposure. A schematic representation of
the Committee’s qualitative assessment of the overall sensitivities of various taxa to an acute dose of radiation is shownin figure XII [U4].

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

273

Figure XII. Approximate acute lethal dose ranges for various taxonomic groups [S12, W6]
Reproduction of figure VII of reference [U4]
Viruses
Molluscs
Protozoa
Bacteria
Moss, lichen, algae
Insects
Crustaceans
ReptilesAmphibians
Fish
Higher plants
Birds
Mammals
100

101

102

103

104

ACUTE LETHAL DOSE (Gy)237. Overall, the Committee judged that for the most sensitive plant species, the effects of chronic radiation exposure
were noteworthy at dose rates of 1–3 mGy/h. It suggested thatchronic dose rates of less than 400 μGy/h (10 mGy/d) would
have effects, although slight, on sensitive plants but would be
unlikely to have significant deleterious effects on the wider
range of plants present in natural plant communities.
238. The Committee concluded that “for the most sensitive
animal species, mammals, there is little indication that dose
rates of 400 μGy/h to the most exposed individual would seriously affect mortality in the population. For dose rates of up to
an order of magnitude less (40–100 μGy/h), the same statement could be made with respect to reproductive effects. For
aquatic organisms, the general conclusion was that maximum
dose rates of 400 μGy/h to a small proportion of the individuals and therefore, a lower average dose rate to the remaining
organisms, would not have any detrimental effects at the population level. The radiation doses necessary to produce a significant deleterious effect are very difficult to estimate becauseof long-term recovery (including natural regeneration and themigration of individuals from surrounding less affected areas),
compensatory behaviour and the many confounding factors
present in natural plant and animal communities in both­terrestrial and aquatic environments”.

B.

Evaluations since 1996

239. Since the UNSCEAR 1996 Report [U4], several
national and international authorities have reviewed theavailable literature on the effects of ionizing radiation exposure on non-human biota [C1, E1, F5, W11, W17]. This section provides a short discussion of the recent work relevantto this annex.
1.

United States Department of Energy

240. The United States DOE has conducted a considerable
amount of work in developing a graded approach to radioecological risk assessments [H1, H2, J1, U26]. In developing their approach, the DOE considered a number of issues
relevant to the re-evaluation, including assessment endpoints, effort levels and dosimetry. The DOE noted thatradioecological risk assessments focused on population
rele­vant endpoints, such as reproduction, and cited guidance from national and international organizations [I4, N1,
U4]. The DOE went on to adopt screening dose rates corresponding to expected safe levels of exposure of populations of biota based on reviews of the data on the acute andchronic radiation effects of exposure to a dose rate of

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UNSCEAR 2008 REPORT: VOLUME II

10 mGy/d to populations of aquatic animals, 10 mGy/d topopulations of terrestrial plants and 1 mGy/d to populationsof terrestrial animals [I4, N1, R2, U4]. The DOE indicatedthat, if the dose rate to the most exposed individual in the
population does not exceed the expected safe dose rate, thepopulation should also be protected [B18].
2.

Canada241. In response to requirements under the Canadian Environmental Protection Act (CEPA), 1999 [C6], Environment
Canada and Health Canada carried out an assessment of the
impact of the discharge of radionuclides from nuclear facilities on non-human biota for all aspects of the uranium fuelchain, from mining and milling to power generation andwaste management [E5].
242. The approach used in reference [E5] for ecological risk
assessment required identifying “chronic toxicity values”(CTVs) from which “estimated no-effects values” (ENEVs)
were derived using appropriate application factors [E2].
The application factor was intended to address the uncertainties related to differences between observed effects on
endpoints and the success of organisms in the field. An
application factor (safety factor) of 1 was used to estimate
ENEVs for radiation exposure. The CTVs for the various
taxonomic groups reported in reference [E5] were based on
measures of effect applicable to the survival of populationsof sensitive species and on chronic exposures. In assessing
radiological risks, Environment Canada and Health Canada[E5] used factors of 1 for gamma and beta radiation and 40
for alpha radiation to account for the differences in the
RBEs of the different types of radiation. The ENEVs usedby Environment Canada and Health Canada are summarized in table 28 and were based on detailed evaluations of
the published literature [I4, R2, U4] as well as on evaluations specifically carried out in support of the assessment[E4, H3, M3].

Table 28. Summary of “estimated no-effects values” (ENEVs) used to assess the potential toxicity of exposure of non-humanbiota to radiation near Canadian nuclear facilities [E2]Taxa

ENEV (Gy/a)a

Fishb

0.2

Benthic invertebrates

2

Algae

1

Macrophytes1

Mammals

1

Terrestrial plants

1

Terrestrial invertebrates

2

a In all cases, the application factor used to convert the CTV to an ENEV was 1.
b The assessment given in reference [E2], citing the lack of data for Canadian fish, referred to effects on carp (species different from those found in Canada) in the Chernobyl
cooling pond, and acknowledged that the ENEV for fish may be conservative.

243. The (former) Advisory Committee on RadiologicalProtection (ACRP) to the Canadian Nuclear Safety Commission also reviewed the available information relevant to theprotection of non-human biota [A1]. The ACRP consideredthat the ultimate goal of “ecological protection” is to ensurethat communities and populations of organisms can thrive
and that all the component parts will be self-sustaining.
Simi­lar to the DOE [H1], the ACRP [A1] reported thegeneric dose-rate criteria summarized in table 29 for theeffects of ionizing radiation exposure on biota, which werebased on reviews by national and international authorities,
including UNSCEAR [U4], the NCRP [N1] and the IAEA
[I4]. The ACRP also suggested that overall, dose-rate criteria
in the range of 1–10 mGy/d were generally protective of
populations of non-human biota and, given current know­
ledge (and the associated uncertainties), that perhaps a single
nominal dose-rate criterion of about 3 mGy/d might be suitable on a broad basis for assessing risks to non-human biota.

Table 29. Generic dose-rate criteria for biota [A1]
Biota

IAEA [I4]

NCRP [N1]

UNSCEAR 1996 Report [U4]Terrestrial plants

10 mGy/d (4 Gy/a)—

10 mGy/d (4 Gy/a)Terrestrial animals

1 mGy/d (0.4 Gy/a)——   mortality—

10 mGy/d (4 Gy/a)   reproduction—

1 mGy/d (0.4 Gy/a)Aquatic organisms

10 mGy/d (4 Gy/a)

10 mGy/d (4 Gy/a)ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

244. The ACRP [A1] noted that radionuclides incorporated
in biota are not uniformly distributed and that some radio­
nuclides tend to concentrate in certain tissues or organs butthat for dosimetric calculations, radionuclides were often
assumed to be distributed uniformly throughout the organism. This assumption can result in underestimation of thedoses to specific tissues for those radionuclides that concentrate in these tissues (for example, bone-seeking radio­
nuclides in fish). The ACRP emphasized that, in practice,simplifying assumptions have to be made especially fordemonstrating compliance with regulatory standards or criteria and that the degree of simplification will depend on the
purpose of the application [A1]. For screening purposes, theconcept of a single “generic” biota, which represents allplants and animals irrespective of size, shape and composition, has been used [A2] while somewhat more sophisticatedmodels took account of the dose distributions within reference organisms of assumed shapes and sizes and the fractions of radiation energies absorbed in the organisms [W2].
The ACRP also recognized that it is impractical to addressorganisms individually and recommended the use of reference biota, typically developed in terms of simple physicalshapes and dimensions for the purpose of dosimetry [B14,
I2, N1, P7].
3.

275

– Morbidity (including growth rate, effects on the
immune system, and the behavioural consequences ofdamage to the central nervous system from radiation
exposure of the developing embryo);– Mortality (including the stochastic effect ofsomatic mutation and its possible consequence forcancer induction, as well as deterministic effects inparticular tissues or organs that would change theage-dependent death rate);– Reduced reproductive success (including fertility
and fecundity); and– Mutation (induced in germ and somatic cells).
246. Table 30 gives an overview of the quality and quantityof the available data within the FRED, based on a simplified
categorization (ecosystem type, exposure duration and irradiation pathway). The data on effects are strongly weighted
in favour of terrestrial ecosystems (73% of all data) and, foreach ecosystem, the available data appear to be biased
roughly 2:1 in favour of data of acute effects and an external
gamma radiation exposure situation. As a consequence, thedata on chronic effects are limited and largely dominated byexternal gamma radiation exposure conditions experimentally obtained using gamma sources (frequently either 137Cs
or 60Co); thus, mathematical modelling such as that describedin section I is needed to estimate doses for comparison withreference dose rates [G3, G15].

FASSET

245. The group working on the Framework for Assessmentof Environmental Impact (FASSET) [F1, F4, F6, L4]
reported on a wide range of issues relevant to the protectionof non-human biota from ionizing radiation, including dosimetric information and data on the effects of radiation on
non-human biota. The FASSET project developed a database (FASSET Radiation Effects Database—FRED) on theeffects of radiation exposure on non-human biota under four
broad effects categories, referred to by FASSET as “umbrella
effects”. These included:

247. Real et al. [R9] summarized the available informationfrom the FRED on the effects of continuous low dose-rateirradiation of plants, fish and mammals. The effects observedon plants, fish and mammals are shown in tables 31, 32 and33, respectively. Each of these tables provides a brief description of the effect, the corresponding endpoint and the dose
rate resulting in the effect. Table 34 provides an overall summary of the data on chronic effects of radiation exposure asprovided by reference [R9].

Table 30. Allocation of the data on effects within the FRED database to freshwater, terrestrial and marine ecosystems, andto the radiation exposure regimes (duration and irradiation pathways) [G3]
Ecosystem(number of references)

Terrestrial(579)

Freshwater(195)

Total number ofdata (%)

19 983(72.6)

6 067(22.0)

Number of data for each exposure duration

Number of data for each exposure irradiation pathway

Total number%

External

Internal

OtheraAcute

12 273

61.4

11 564288

421

Chronic

6 795

34.0

3 449

344

3 002

Transitoryb

913

4.57

670

40

203

Not stated

2

0.03

0

0

2

Acute

4 526

74.6

4 058

97

371

Chronic

1 484

24.5

970

20

494

Transitory

54

0.89

12

2

40

Not stated

3

0.01

0

0

3

Type

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UNSCEAR 2008 REPORT: VOLUME II

Ecosystem(number of references)

Marine(45)

Total number ofdata (%)

1 470
(5.4)

Number of data for each exposure duration

Number of data for each exposure irradiation pathway

Total number%

External

Internal

Othera

Acute

1 116

75.9

995

58

63

Chronic

353

24.1

286

0

67

Transitory

0

0

0

0

0

Not stated

1

0

0

0

1

Type

a “Other” means that the experiment reported in the literature was devoted to the study of the effects involved by mixed irradiation pathways, and/or not well characterized to
be used for the present analysis.
b “Transitory” means in between “acute” and “chronic” in terms of exposure duration.

Table 31.

Effects of chronic irradiation on plants [R9]Dose rate(µGy/h)SpeciesRadiation

100–1 000

Pine

Gamma

(1–5) × 103(5–10) × 10

3(1–2) × 104

Pine

Pine

Pine

Gamma

Gamma

Gamma

Effects described

Endpoint

Reference

Reduced trunk growth of mature trees

Morbidity[W4]

Death of some conifers; little changes in populations

Morbidity[A6]

Reduced canopy cover of individual conifers; whole canopy remains constantMorbidity[A6]

Decreased stem growth of saplings

Morbidity[A23]

Reduced photosynthetic capacity of pines and thus growth

Morbidity[B11]

Death of all conifers within 2–3 years

Mortality[A6]

Reduced seed production and germination

Reproduction[W11]

Morphological changes in leaves of some plants

Morbidity[W11]

Withered crowns

Morbidity

[W11]

Birch

Gamma

Underdeveloped leaves

Morbidity[W11]

Herbaceous

Gamma

Reduced reproductive potential

Reproduction

[U4]

Birch

Gamma

Death of trees

Mortality[A6, W11]

Grasses

Gamma

Death of grasses and forbs

Mortality[W11]>1 × 105

PlantsGamma

Death of all higher plants

Mortality[A6, W11]>1 × 106

LichenGamma

Reduced diversity of lichen communities after one year exposure

Mortality[B13, W18]

Endpoint

Reference>2 × 104

Table 32.

Effects of chronic irradiation on fish [R9]Dose rate(µGy/h)SpeciesRadiation(1–10) × 102

Plaice,Medaka,
Roach

Gamma

Reduction in testis mass and sperm production. Lower fecundity. Delayed
spawning

Reproduction[H11, K16,
N1](1–5) × 103

Plaice,Eelpout,
Medaka,Guppy,
Rainbow
trout

Gamma orbeta

Reduction in testis mass and sperm content. Severe depletion of s­ permatogonia.
Reduced fertility or complete infertility. Reduced fecundity. Reduced male­courtship activity. Reduced immune response

Reproduction
Morbidity[E10, G20,
H11, H16,
K16, K17, P5,
W7](5–10) × 103

MedakaGamma

Depletion of spermatogonia

Reproduction[H11](1–5) × 10

Medaka,
Guppy

Gamma

Sterility. Reduction in larval survival. Increase in vertebral anomalies

Reproduction[H17, W7]

>5 × 104

Guppy

Gamma

No impact on offspring survival following parental irradiation

Mortality[W7]

4

Effects describedANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

Table 33.

277

Effects of chronic irradiation on mammals [R9]Dose rate(µGy/h)SpeciesRadiation

<102

Mouse
Rat

Gamma

No detrimental effects have been described

Dog

Gamma

Mouse

(1–10) × 102

Endpoint

Reference

Morbidity
Mortality
Reproduction[C17, P8]
[C17, U21]
[L2, Y2]

Life shortening

Mortality

[C18]

Gamma

Life shortening

Mortality

[M13]

Mouse

Neutrons

Life shortening

Mortality

[M13]

Pig

Gamma

Prenatal irradiation decreased the number of primitive stem germ cells andthe ovary and testis weight

Reproduction[E14, E15]

Rat

Gamma

Reduction in number of A1 spermatogonia

Reproduction

[E16]

Mouse

Beta

Irradiation from conception to 14 days of age decreased the number ofprimary oocytes

Reproduction[D2]

Reduction of mean number of litters per female; higher mortality between
birth and weaning; reduction in number of primary oocytes

Reproduction[S6]

Irradiation during three consecutive generations increased the % of sterile
mice and the % of early deaths and decreased the mean litter size

Reproduction[M14, M15]

Field study. Increased % of sterile pairs; reduced mean offspring sired andweanedReproduction

[L3]

Mouse

Gamma

Effects described

Reindeer

Gamma

Natural forest. Increased number of chromosomal aberrations

Mutation

[R3]

Goat

Gamma

Life shortening

Mortality

[H18]

Mouse

Gamma

Increased mortality ratio (the effect was dependent on the mice strain used);decreased mean after survival

Mortality[G25, T2]

Mouse

Neutrons

Life shortening

Mortality

[U21]

Goat

Gamma

Reduced number of liveborn per female in the third generation and reduced
total sperm production

Reproduction[H19]

Irradiation during the 2nd week after birth reduced the fertility and the litter
size

Reproduction[R5]

Irradiation during 4–90 days reduced the fertility span, the germ cells per
ovary and the testis weight

Reproduction[M16, R12,
R13]

Prenatal irradiation reduced the litter size and increased the % of resorptions

Reproduction[L2, L6]

Reduced number of spermatogonia and testis weight

Reproduction[P15, P21]

Prenatal irradiation reduced the number of germ cells in females and males

Reproduction[E14](1–5) × 103
Mouse

Gamma

Rat

Beta

Rat

Gamma

Mouse

Gamma

Increased mutation frequency at seven specific loci in mouse spermatogonia

Mutation

[R14]

Sheep

Beta

Reduction in the number of leukocytes in peripheral blood

Morbidity

[B15]

Rat

Gamma

Reduced brain weight and cingulum volume

Morbidity[R15]Life shortening after exposures of 68 days or longer

Mortality[S7, S24]

Mouse

Gamma

Increased paternal expanded simple tandem repeat (ESTR) mutation rate andpaternal mutation per offspring band at loci MMS10 plus Ms6-hm plus Hm-2

Mutation[D3, D5]

Dog

Beta

Reduced survival

Mortality

[R16]

Mouse

Gamma

Increased mortality ratio (dependent on the strain used)

Mortality

[G25]
[C19]

Gamma

Prenatal irradiation reduced the length and weight of embryos and increased
the % mortality

Reproduction

Rat

Reduction in ovary and testis weight

Reproduction[E17](5–10) × 10

3

>10

4

278

UNSCEAR 2008 REPORT: VOLUME IITable 34. Overall summary of data on the effects of chronic irradiation for plants, fish and mammals, based on the FASSET
Radiation Effects Database (FRED) [R9]Wildlife groupMorbidity

Mortality

Reproductive capacity

Mutation

Plant

Plant growth begins to be affected
at more than 100 µGy/h.
Continued exposure at 21 µGy/h
for 8 years increases thesensitivity in pines

50% mortality at 8 years at~1 000 µGy/h in pines

A field study indicated a decrease
in seed weight of a herb at
5.5 µGy/h

The mutation rate in microsatellite
DNA increased at ~40 µGy/hFish

One experiment, but not another,indicates effects on the immune
system at 8.3 µGy/h

Too few data to draw conclusions

One study showing effects on
gametogenesis at 230 µGy/h.
Otherwise effects at more than
1 000 µGy/h

Radiation exposure increases themutation rate

Mammals

Rat growth not affected at
16 µGy/h but affected at morethan 3 000 µGy/h.
Some blood parameters affected
at 180–850 µGy/h. No effect on
thyroid function at 8 000 µGy/h

No effect on mouse lifespanat 460 µGy/h, but significant
reductions above ~1 000 µGy/hin the mouse, goat and dog

Threshold for effects at~100 µGy/h, with clear effects at
more than 1 000 µGy/h

Too few data to draw conclusions.
One of nine references gives an
LOEDR of 420 µGy/h for mice

248. Real et al. [R9] noted that plant morphology (size,
shape and density of plant stands) can alter the exposure andthe resulting radiation dose. They also noted that plants with
exposed meristems or buds can receive higher doses to thecritical tissues than those plants that grow and reproduce
underground or are protected by thick scales.
249. Real et al. [R9] concluded that chronic exposures up
to 4 × 103 µGy/h to developing fish embryos will not resultin significant effects on growth. Furthermore, they considered that the available data suggest that dose rates of lessthan 4 × 103 µGy/h at any life stage would not be expected toaffect survival. However, they felt that the limited amount ofdata further suggests that genetic damage caused by chronic
irradiation is likely to occur at all dose rates and that theradiosensitivity for this damage is similar to that of othervertebrates.
250. There are a large number of data on mammals available
within the FRED; therefore, Real et al. [R9] had to be selective in summarizing the information. Altogether, the authors
considered 183 references for mammals, which provided
more than 3,000 data points on effects. The authors concluded
that chronic radiation dose rates lower than 103 µGy/h do not
result in irreversible effects on mortality, morbidity and reproduction. A dose rate of 100 µGy/h (i.e. 2.4 mGy/d) had been
described for reproductive capacity impairment; however, thedetrimental effects observed were reversible [R9]. The authors
indicated that the majority of the work had been conductedusing mice and rats and that it would be beneficial to haveadditional information on the effects of chronic radiation
exposure on other species.
251. An overall summary of the effects due to chronic
exposure of plants, fish and mammals identified by FASSET
was reported in reference [R9] for the different endpointclassifications (morbidity, mortality, reproductive capacityand mutation) provided in table 34. The authors concluded
that the amount of available information on the effects of low
dose rates (less than about 100 µGy/h) for continuous­radiation exposure is reasonable for both plants and animals
and that for chronic exposure conditions “the reviewed
effects data give few indications for readily observableeffects at chronic dose rates below 100 µGy/h”. However,they advised that “using this information for establishingenvironmentally ‘safe levels’ of radiation should be donewith caution, considering that the database contains large
information gaps for environmentally relevant dose rates andecologically important wildlife groups” [F5, R9].

4.

ERICA

252. The project on Environmental Risks from Ionizing
Contaminants: Assessment and Management (ERICA) carried out under the European Commission’s 6th Framework
Programme was the successor of the FASSET project.
Extensive quality assurance of the data was carried out andthis led to the development of an expanded effects database(referred to as FREDERICA). A database on the effects ofchronic radiation exposure of fish, which was developed in
the project on Environmental Protection from Ionising Contaminants in the Arctic (EPIC) [S25] was subsequently
incorporated into the FREDERICA effects database [C12].
253. The ERICA integrated approach adopted an Ecological
Risk Assessment tiered methodology that required values of
the risk assessment screening dose rates for risk characterization within Tiers 1 and 2. The screening values used within
Tiers 1 and 2 were derived on the basis of data taken from the
FRED and compared from some key data from the EPIC
project (making thus the best use of the FREDERICA database) [C12]. The method applied follows recommendations of
the European Commission for the estimation of Predicted

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

No-Effect Concentration (PNEC) for chemicals [E11]. A
three-step methodology was used. First, a coherent data subset
was extracted from each experiment, covering endpoints
related to mortality, morbidity and reproduction. Next, a systematic mathematical treatment was applied to reconstructdose-rate–effect relationships and to estimate critical toxicity
endpoints. For chronic exposure, the critical toxicity endpoint
was the estimated Effect Dose Rate (EDR10, expressed in
μGy/h), the dose rate that gives rise to a 10% change in
observed effect. The final step of the method consisted inusing these estimated critical toxicity data to derive a Predicted No-Effect Dose Rate (PNEDR) by means of the species
sensitivity distribution method (SSD) [E11, G15, G27].

279

separate analyses of the data available for different ecosystems, the authors [G15] concluded there was no statisticaljustification for attempting to derive ecosystem-specificscreening dose rates and all data were therefore analysed
together as a generic ecosystem. The resultant HDR5 was
82 µGy/h (with 95th percentile confidence intervals of 23.8
and 336 µGy/h). To derive the final dose rate for screening(i.e. PNEDR), a safety factor (SF) of 5 was used to allow for
any remaining extrapolation and the resultant number
rounded down to the nearest one significant figure. Basedon this approach, the authors suggested a reference dose
rate for incremental exposure of 10 μGy/h for “screening forpotential radiological effects”. The methodology and pro­
cess used to derive this screening value are documented
within references [G3, G11, G15] where the value is shown
to be similar to that derived using alternative methods to
SSD (figure XIII).

254. The SSD method was used to estimate the Hazardous
Dose Rate (HDR5), the dose rate at which 95% of the species in the aquatic/terrestrial ecosystem are protected. After

CUMULATIVE WEIGHTED PROBABILITY(%)

Figure XIII. Species sensitivity distributions for generic ecosystems and chronic external gamma irradiation conditions
The log-normal distribution with its associated 95% confidence interval is fitted to geometric means per effect category for each species
calculated on critical ecotoxicity data (EDR10) [G3]
100
80
60
Number of data = 24
Number of species = 18
HDR5 = 81.8 Gy
CI95% = [23.8–336] µGy/h

40
20
0
1

10

103

102

104

105

106

107

DOSE RATE (µGy/h)Plants255. At the ecosystem level, the value of the ERICA
integrated approach screening dose rate lies in the range
giving rise to minor effects [F5, G3, G15, G27]. The
authors suggested that such effects are not expected to be
directly relevant at higher organizational levels, such as
the structure and functioning of ecosystems.
256. The same method was also applied to acute exposure conditions to guide interpretation of accidental situations; however, in this case, the authors [G11, G15] did
find a difference between marine ecosystems compared toterrestrial and freshwater ecosystems. The values derived

Invertebrates

Vertebrates

from an SSD analysis on the set of Effect Doses giving a
50% change in observed effect (ED50) for limiting thepotentially affected fraction to 5% of the species underacute external gamma irradiation conditions varied fromabout 1 to 5.5 Gy, according to the ecosystems type, withassociated 95% confidence intervals covering less than
one order of magnitude (see figure XIV). To derive screening values, an SF of 5 was applied and the results rounded
down to the nearest one significant figure. This resulted in
Predicted No-Effect Doses (PNED) of 900 mGy for marine
ecosystems and 300 mGy for terrestrial and freshwater
ecosystems [G3, G15, G27].

280

UNSCEAR 2008 REPORT: VOLUME II

Figure XIV. Species sensitivity distributions for generic ecosystems and acute external gamma irradiation conditions
The log-normal distribution with its associated 95% confidence interval is fitted to geometric means per effect category for each species
calculated on critical ecotoxicity data (ED50) [G3]Generic continental ecosystem (freshwater and terrestrial)
100

CUMULATIVE WEIGHTEDPROBABILITY
(%)

90
80
70
60

Number of data = 60

50

Number of species = 50
HD5 = 1.86 Gy

40
30

CI95% = [1.16–2.98] Gy

20
10
0
0.1

1

10

102

103

104

DOSE (Gy)Marine ecosystem

CUMULATIVE WEIGHTEDPROBABILITY
(%)

100
80
60

Number of data = 13
Number of species = 8
HD5 = 4.84 Gy
CI95% = [0.64–12.7] Gy

40
20
0
0.1

1

10

102

103

104

105

DOSE (Gy)

Plants257. Dose rates below which no significant effects are
expected at various levels of organization (population, wildlife group or ecosystem) were compared by different organizations/authors [G3, G15], and are summarized in table 35.
The selection was mainly based on observations of effects

Invertebrates

Vertebrates

and expert judgement. The approach using SSD provides analternative methodology for assessing radiation risks byderiving, for the first time for radioactive substances, protection thresholds using a rational and transparent process basedon the approach adopted for chemicals in Europe [G15].

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

281

Table 35. Dose-rate values proposed by various organizations/programmes to support effect analysis for chronic exposure
to radiation [G3, G11]
Targeted protected level as describedin the source

Method/justification of the value

Dose rate(µGy/h)Sourcereference

Terrestrial ecosystems
Generic ecosystems

SSD-95% species protected plus SF of 5
SSD giving an HDR5 of 81.8 mGy/h divided by an SF of 5 and rounded down

10

[G3]

Generic ecosystems

SF method: SF of 10 applied to the lowest critical radiotoxicity value EDR10

0.6

[G3]

PlantsBackground

0.02–0.7[U4]

Plants

Review, SF on the lowest critical radiotoxicity value

110[B31, E5]

Plants

Review based on NCRP 1991; IAEA 1992; UNSCEAR 1996

400

[O1, U26]

Plants

Critical review for screening purpose from IAEA 1992

400

[E12]

Organisms

Background – external irradiation and non-weighted

0.01–0.1[G21]

Animals

Background0.01–0.44[U4]

Animals

Review based on NCRP 1991; IAEA 1992; UNSCEAR 1996

40

[O1, U26]

Animals

Critical review for screening purpose from IAEA 1992

40

[E13]

Small mammals

Review, SF on the lowest critical radiotoxicity value

110[B31, E5]

Invertebrates

Review, SF on the lowest critical radiotoxicity value

220[B31, E5]

Vertebrates and cytogenetic effects

Review contaminated environments

4–20

[S28]

Vertebrates and effects on morbidity

Review contaminated environments

20–80

[S28]

Vertebrates and effects on reproduction

Review contaminated environments

80–200[S28]

Aquatic ecosystems
Generic freshwater ecosystems

SSD-95% species protected plus SF of 5
SSD giving an HDR5 of 81.8 mGy/h divided by an SF of 5 and rounded down

10This annex

Generic freshwater ecosystems

SF method: SF of 50 applied to the lowest critical radiotoxicity value EDR10

10This annex

Generic marine ecosystems

SSD-95% species protected plus SF of 5
SSD giving an HDR5 of 81.8 mGy/h divided by an SF of 5 and rounded down

10

[G3]

Generic marine ecosystems

SF method: SF of 50 applied to the lowest critical radiotoxicity value EDR10

3.7

[G3]

Freshwater organisms

Background0.022–0.18[U4]

Freshwater organisms

Background–external irradiation and non-weighted

0.02–6[B32]

Aquatic algae/macrophytes

Review, SF on the lowest critical radiotoxicity value

110[B31, E5]

Aquatic animals

Review based on NCRP 1991; IAEA 1992; UNSCEAR 1996

400

[O1, U26]

Freshwater and coastal marine organisms

Critical review for screening purpose from IAEA 1992

400

[E12]

Amphibians/reptiles

Review, SF on the lowest critical radiotoxicity value

110[B31, E5]

Benthic invertebrates

Review, SF on the lowest critical radiotoxicity value

220[B31, E5]

Fish

Review, SF on the lowest critical radiotoxicity value

20[B31, E5]

Marine organisms

Background–external irradiation and non-weighted

0.03–1[B32]

Marine mammals

Critical review for screening purpose from IAEA 1992

40

[E13]

Deep ocean organisms

Critical review for screening purpose from IAEA 1992

1 000

[E13]

Aquatic and terrestrial flora and fauna

Review concluded that few indications of readily observable effects at chronic dose
rates below

<100

[F5]

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UNSCEAR 2008 REPORT: VOLUME II

258. As indicated elsewhere in this annex, few new data on
the effects of ionizing radiation exposure on non-human biota
have been developed since 1996. In all the recent literature
reviews [C1, F5, G16, R9, W11]), the specificities of the environmental situations of interest (chronic low-level exposure
regimes) consistently emphasized the importance of all reproductive parameters to the population within a given ecosystem
to the structure and functioning of that ecosystem. These
reviews clearly argued for the need of a research programme
to acquire specific data related to chronic low-level exposureand the effects on reproductive capacity in such a way as to beable to shift from observations on individual organisms toobservations on populations. A brief summary of the data on

Table 36.

effects from the FRED is given in table 36 along with assigned
weight ratios based on the numbers of data sets available
related to acute versus chronic exposure and, for chronic
exposure data, to external versus internal exposure and reproductive endpoints. The extrapolation on the basis of the existing knowledge will become increasingly critical as the relative
weights increase. In reviewing these data, ­Garnier-Laplace etal. [G16] concluded that operationally for any site-specificrisk assessment, the present state-of-the-art on extrapolation
issues allows the relative magnitudes of the various sources of
uncertainty to be ordered as follows: one species to another >acute to chronic = external to internal = mixture of stressors >individual to population > ecosystem structure to function.

Brief overview of the data on effects from FRED (adapted from reference [G16])

Wildlife group

Number of data

Weight data ratio
All data: acute/chronic

Chronic data: (external)/(internal+mixed)
All endpoints

Reproduction

Aquatic plants

616

2.7

4.1

0/0a

Aquatic invertebrates

542

1.2

4.1

8.3

Amphibians

749

1.3

0.02

0/0

Bacteria

171

0.5

2.4

0/0

Birds

1 732

3.4

3.4

5.5

Crustaceans

850

3.7

180

20/0

Fish

2 802

2.8

1.0

0.8

Fungi

120

0/120

120

0/0

Insects

1 237

5.2

5.4

0.8

Mammals

4 112

2.5

4.7

3.3

Molluscs

484

2.4

1.7

0.4

Moss/lichen

44

0/44

0.5

0/0

Plants11 984

1.6

0.7

0.5

Reptiles

271

6.7

0/35

0/0

Soil fauna

398

1.6

0.15

0/0

Zooplankton

111

4.3

21/0

9/0

a (number of data devoted to reproduction endpoints and chronic external irradiation) / (number of data devoted to reproduction endpoints and chronic internal or mixed irradiation): for example, 0/0 means that no data exist.

5. Observations from recent literature
259. The European Commission (EC) has been supporting
research on the effects of ionizing radiation exposure on
non-human biota for the past several years. This included thedevelopment of the FRED. More recently, the ERICA project
conducted a review of the quality of the data in the FRED
and merged the FRED with the Russian EPIC database toform a new database, FREDERICA, with several hundredadditional references [C12]. This database includes references to over 1,200 papers that focus on the effects of radiation exposure on non-human biota and is a valuable sourceof information. General information on the new data on
effects or new interpretations of the data on effects isprovided in the previous section. Additional observations
from the literature identified in the ERICA database as wellas the open literature are provided in the following section in
an attempt to supplement the previous information in several
areas of current interest.
(a)Terrestrial biota

260. Hingston et al. have described the effects of low dosesof ionizing radiation on terrestrial invertebrates and reported
experiments on earthworms (Eisena fetida) and woodlice(Porcellioscaber) [H23]. Both species were continuously
exposed to gamma radiation from a 137Cs source over a rangeof dose rates with total exposures for each experimental group

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

of 0.5–20 Gy delivered over a total of 14 and 16 weeks,
respectively. The investigators considered a number of endpoints relevant to reproduction, growth and mortality. They
reported on the results for woodlice [H23]. They found nodele­terious effects for the endpoints studied up to a maximum
dose rate of approximately 8 mGy/h (192 mGy/d); the woodlice were unaffected by the doses given. However, they notedthat the results may, in part, have reflected the laboratory conditions, i.e. an environment protected from predation. HertelAas et al. reported the results from a study of the reproductive
capacity (numbers of cocoons, hatchability, etc.) of earthworms exposed chronically to gamma radiation [H22]. In thisstudy, earthworms (Eisena fetida) were exposed over two generations to gamma radiation from a 60Co source at five dose
rates, from 0.18–43 mGy/h. The lowest dose rates at whichan effect was observed was 4 mGy/h and 11 mGy/h in F0 andF1 worms, respectively. The experiments also suggested a
possible acclimatization in F1 worms.

283

neonates showed significantly reduced resistance to starvation
at every dose rate compared to the control.
264. Gilbin et al. [G22] reported effects on Daphnia magna of
external gamma radiation exposure at dose rates ranging from
0.4–31 mGy/h over a 23‑day period (i.e. 5 broods). Gamma
radiation exposure caused no significant change in somatic
growth. The mass-specific respiration rate was significantly
lower at dose rates of 31 mGy/h than for the control. Broods
were deposited earlier and fecundity was 20% lower at the highest dose rate than for the control. The combination of decreased
fecundity and unchanged individual offspring mass resulted in asmaller total mass of eggs produced per daphnid at dose rates of
4.2 and 31 mGy/h than for the control. A decreased resistance of
neonates to starvation was observed at every dose rate.

262. The great majority of the data on aquatic invertebrates
in the FRED concern the effects of chronic irradiation on
crustaceans. The data indicate that observable impacts atdose rates up to 103 mGy/h are unlikely and that a dose rateof ~104 mGy/h is probably the lower limit for the onset ofsignificant effects. However, effects were apparent in theembryonic development of the goose barnacle (Pollicipes
polymerus) following a 32‑day exposure to tritiated water atdose rates of 0.7, 6.5 and 64 mGy/h [F5].

265. Alonzo et al. [A27] tested the chronic effects of internalalpha irradiation on Daphnia magna respiration, somatic
growth and reproduction over three successive generations.
They showed that the toxicological effects of internal alphairradiation on life-history traits of Daphnia magna increased
across generations. A 70‑day experiment was performed with
Daphnia magna exposed to waterborne 241Am corresponding
to average dose rates of 0.3, 1.5 and 15 mGy/h. In the first
generation (F0), a reduction in body length (5%) and the dry
mass of females (16%) and eggs (8%) was observed after
23 days of exposure, while mortality and fecundity remained
unaffected. New cohorts were started with neonates of broods
1 and 5, to examine the potential consequences of the reduced
mass of the offspring for subsequently exposed generations.
At the highest dose rate, an early mortality of 38–90% affectedjuveniles while survivors showed delayed reproduction andreduced fecundity in F1 and F2. At dose rates of 0.3 and1.5 mGy/h, the mortality of daphnids in generation F1 ranged
from 31–38%. Reproduction was affected through a reductionin the proportion of breeding females occurring in the first
offspring generation at a dose rate of 1.5 mGy/h (to 62% of
total daphnids) and in the second generation at 0.3 mGy/h (to69% of total daphnids). Oxygen consumption remained significantly higher at dose rates ≥0.3 mGy/h than for the control
in almost every generation. Body size and mass continued
decreasing in relation to dose rate, with a significant reduction
in mass ranging from 15% at a dose rate of 0.3 mGy/h to 27%
at 15 mGy/h in the ­second offspring generation.

263. Concerning the effects of internal radiation exposure on
crustaceans, recent data exist on daphnids which were chronically exposed internally to alpha radiation from 241Am underexperimental conditions at dose rates up to 990 µGy/h [A19].
These authors reported that exposure to dose rates of 110 µGy/hor higher resulted in a significant (15%) reduction in bodymass. Daphnids also showed increased respiratory demand
after 23 days at the highest dose rate, suggesting increased
metabolic cost of maintenance resulting from the need to copewith the stress from alpha irradiation. Fecundity remained
unchanged over the 23‑day period, but individual masses of
eggs and neonates were significantly smaller compared to thecontrol. This suggested that increased metabolic expenditure inchronically alpha-­irradiated daphnids came at the expense of
their energy investment per offspring. As a consequence,

266. Dose rates above 0.1 mGy/h to developing mollusc
embryos affected the incidence of developmental abnormalities but not the subsequent overall survival of the resulting larvae. Significant detrimental effects are to be expected at dose
rates greater than 1 mGy/h [F5]. Recently, Jha et al. [J4]exposed mussels (Mytilus edulis) to a series of concentrationsof HTO equivalent to a dose rate ranging from 12–485 µGy/h
for 96 hours. The study revealed a dose-dependent increase in
the response for both the micronuclei test and the comet assay.
Dose rates below 500 µGy/h induced genetic damage in the
haemocytes. For the same species but another life stage (i.e.
one-hour-old embryos exposed during 12 to 24 hours to arange of HTO doses between 0.02 and 21.41 mGy), ­Hagger et
al. [H13] found that the embryo–­larvae showed dose or­concentration-dependent effects for mortality, developmental

261. Tanaka et al. [T3, T25] discussed the effects of chronic
exposure of mice (SPF B6C3F1) to gamma rays at low dose
rates. Mice of both sexes were divided into 4 groups, one ofwhich was not irradiated and the other three which were irradiated. The exposed mice were irradiated at dose rates of
0.05, 1.1 and 21 mGy/d for about 400 days using a 137Cs
source. All mice were maintained until natural death, after
which pathology was performed to identify the cause ofdeath. Females exposed to 1.1 mGy/d and both sexes exposed
to 21 mGy/d had significantly shortened lifespans compared
to non-exposed mice. The mean survival times of mice ofboth sexes exposed to 0.05 and 1.1 mGy/d were shorter thanfor non-exposed mice but not significantly so.
(b)Aquatic and marine biota

284

UNSCEAR 2008 REPORT: VOLUME II

abnormalities and induction of sister chromatid exchanges.
However, they reported that there was a lack of a clear dose
response for chromosomal aberrations and proliferative-rateindex.
267. For annelids, Knowles and Greenwood [K3] exposed
Ophryotrocha diadema to beta radiation at a dose rate of
7.3 mGy/h and observed that the number of eggs surviving
to the larval stage was reduced, but did not affect egg production. This is in contrast to previous studies related to
gamma irradiation where egg production is reduced but not
the number becoming larvae.
268. Kryshev and Sazykina [K18] reported an evaluation of
the radioecological effects on aquatic organisms exposed tohigh levels of radioactive contamination in lakes affected by
the Mayak reprocessing facility, in lakes affected by the
Kyshtym accident, in the cooling pond of the Chernobyl

nuclear power plant (NPP) and in the littoral area downstreamof the Leningrad NPP. The authors reported doses based on
the concentrations of radionuclides in water, sediments andfish and indicated that the highest dose rates, up to 300–
800 mGy/d, were to organisms in the lakes affected by the
Mayak complex. They also noted that the biota in the Mayaklakes were exposed to chemical contamination in addition toradiation but commented that the fish population had retained
its viability for the period of observation of 30 years. The
lowest dose rates were for the Leningrad NPP, where theauthors noted that, typically, aquatic organisms were exposed
to background levels of radiation. However, the dose rates toaquatic organisms in the liquid radioactive-waste canal of theLeningrad NPP were elevated. Here, the authors noted anincreased asymmetry of the soft rays of the pectoral fins ofroach and suggested that this was due to the combined effects
of exposure to radiation and elevated temperature. The overall observations from this study are summarized in table 37.

Table 37. Radioecological effects in water bodies exposed to radioactive contamination(adapted from reference [K18])
Water body (period of assessment) species under study

Dose rate assessment(µGy/d)Brief description of the effects

300 000–800 000
30–2 000

Total death of lake ecosystem
Mass death of fish in the upper reaches of the riverSouthern Urals [K24, K25, K26]
Lake Karachai (1951–1952)
Techa River (1951–1951)
Cooling pond of the Chernobyl NPP[B19, K12, K28] (1986–1992):
Silver carp Hypophthalmichthys molitrix

0.2–3

Increased anomalies of the reproductive system; disturbances in the stateof sexual cells to 47–90%; sterility of gonads

Waste channel of the Leningrad NPP[K27, R18] (1980–1983)
Roach Rutilus rutilus

0.007–2

Increase by a factor of 2.3 in the variance of fluctuating asymmetry of thenumber of soft rays of pectoral fins at different sides of the body of roach

269. Real et al. [R9] in their review of the information in the
FRED observed that the developing embryos of fish that were
subjected to chronic exposures at dose rates up to 4 mGy/hwill not result in significant effects on subsequent growth.
They also noted conflicting results for the effects of radiation
exposure of the immune system: for rainbow trout irradiatedas embryos, there was a threshold at dose rates between 8.3–
83 µGy/h from exposure to beta radiation from tritium, while
there was no effect at a dose rate of 9 mGy/h from exposure
to radiation from 137Cs. According to the authors [R9], thelimited data available on mortality effects of chronic irradiation indicated that dose rates less than 4 mGy/h at any life
stage were unlikely to affect survival and that there was little
consistent, significant evidence for any effects on reproductive capacity at dose rates of less than 0.2 mGy/h. Finally, theauthors [R9] suggested, based on a very limited amount of
data, that chronic irradiation-induced genetic damage probably occurs at all dose rates and that radiosensitivity for thisdamage is similar to that of other vertebrates.
270. An interesting recent study has been performed withzebrafish larvae by Jarvis and Knowles [J5]. Gamma radiation
was delivered externally from sealed sources (137Cs) at a dose
rate ranging from 0.3–7.4 mGy/h. The alkaline comet assay
was used to assess DNA damage on larvae (5–6 days post

laying, 2 days post hatching), exposed for 24 hours to dose rates
of 0.4, 1.2 or 7.2 mGy/h and for 1 hour to 0.4 or 1.2 mGy/h.
Entire larvae were macerated and their cells embedded in agarose gel. Larvae exposed at dose rates of 7.2 or 1.2 mGy/h for
24 hours (total dose of 173 and 29 mGy, respectively) showed asignificant increase in the percentage of DNA in the comet tail.
The same observation was made for larvae exposed at the samerates for 1 hour (total dose of 7.2 and 1.2 mGy, respectively).
The increase in tail movement was not correlated to the exposure time, indicating that DNA damage was repaired with time.
No information was available on DNA repair in long-term irradiated or contaminated fish. It must be noted that for a similardose rate (1 mGy/h), no effect on reproduction in adults after
exposure of more than 12 months could be observed [E12].
(c)

Genotoxicity

271. Data on genotoxicity are summarized in table 38.
Knowles [K16] irradiated plaice under laboratory-controlled
conditions using sealed 137Cs sources to investigate potential
genotoxic effects. No effect on the coefficient of variation(CV) of the DNA content, aneuploidy or polyploidy, measured
by flow cytometry (FC), was observed even for the maximum
exposure period (197 days) and maximum dose rate (1 mGy/h).

n.d.
n.d.

125 µGy/hb
80 µGy/hc
400–25 000 Gy/h
260 µGy/h

3 000 µGy/h (24 d)
6 000 µGy/h (48 d)

1 000 µGy/h to >100 Gy/h
Background
5 × 10‑3 to 0.5 µGy/hd
240–1 000 µGy/h

In situ, Chernobyl, cooling pond, 137Cs

In situ, Savannah River site, 134,137Cs +89, 90
Sr + Hg

Lab in vivo, external, 60Co

In situ, Savannah River site, 134,137Cs +89,90
Sr + Hg

Lab in vivo, external, 60Co

Lab, external, 137Cs

Various conditions (literature review)

Lab, in vivo, external, 137Cs

In situ, Swedish lake, Chernobyl fallout
1988, external + internal, 137Cs

In situ, Swedish lake, Chernobyl fallout
1988, external + internal, 137Cs

In situ, Siberian (Tomsk‑7) nuclear site

Channel catfish (I. Punctatus), adults

Largemouth bass (M. salmoides),adultsMarine polychaete worm (N. arenaceodentata), larvae

Midge (C. tentans), larvae

Marine polychaete worm
(N. arenaceodentata), larvae

Slider turtle (T. scripta), fibroblasts andlymphocytes

18 different fish species

Plaice, (P. platessa), adult

Pike (E. lucius), perch (P. fluviatis),roach (R. rutilus) and bream (A. brama)

Pike (E. lucius), perch (P. fluviatis),roach (R. rutilus) and bream (A. brama)

Pike (E. lucius), adults

n.d.
n.d.
n.d.

10 000 Bq/kg d.w. 137Cs
10 µGy/hd
18 000 Bq/kg d.w. 137Cs
Ext. dose rate : 10 µGy/hd
57 000 µGy/hd
1 200 Bq/kg
w.w.

MN per 1 000 erythrocytes

MN per 1 000 erythrocytes

MN per 1 000 erythrocytes

MN per 1 000 erythrocytes

MN per 1 000 erythrocytesn.d.

197 days

CA (symmetrical translocations)

CA (metaphase)

24 days
48 days

n.d.

CA

SCE

Alkaline unwinding (hepatocytes,
gill cells, erythrocytes)

Alkaline unwinding (hepatocytes,
gill cells, erythrocytes)

Agarose gel electrophoresis(hepatocytes, erythrocytes)

Alkaline and neutral unwinding(hepatocytes)

Alkaline comet (tail moment)

Assay(parameter)

Lifetime

12 hours
24 hours

49 years

External dose rate:
50 µGy/hIn situ, (Oak Ridge) external + internal,
235
U, 239,240Pu, 137Cs, 60Co, 90Sr, Hg, HAP, PCB

Mosquitofish (G. affinis), adults

1 hour;24 hours

Exposure
durationn.d.

In situ, (White Oak Lake) external +internal, 235U, 239,240Pu, 137Cs, 60Co, 90Sr, Hg,
HAP, PCB

Pond slider (T. scripta)
Snapping turtle (C. serpentina), adults

400, 1 200,
7 200 µGy/h

Dose rate, dose orinternal concentration

External dose rate:
50 µGy/ha

Lab in vivo, external, 137Cs

Type of exposure

Zebrafish (D. rerio),
larvae (2 d)Species(life stage)

Table 38. Genotoxicity in aquatic species exposed to radionuclides in the laboratory or in situ [A13]++57 000 µGy/h

=

=

=

+
Mean [min; max] : 3 [0; 13]
5 × 10‑3 to 0.5 µGy/h

230 000 µGy/h (LNOEDR)+
3 000 µGy/h+
6 000 µGy/h+++ : inversion+ : deletion
260 µGy/h+
400 µGy/h==+
50 µGy/h+
50 µGy/h+
1 200 µGy/h

EffectLOEDR (µGy/h)(LNOEDR or LOED)

[I22]

[A21]

[A20]

[K16]

[G23]

[H14, U18]

[P4]

[B34]

[H15]

[S17]

[S18]

[T21]

[M5]

[J5]

Reference

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA
285

n.d.

n.d.

n.d.

n.d.

9 months

125 µGy/hb

125 µGy/hb

80 µGy/hc

80 µGy/hc

80 µGy/hc

In situ, Chernobyl, cooling pond, 137Cs

In situ, Chernobyl, cooling pond, 137Cs

In situ, Savannah River site, 134,137Cs +Sr + Hg

In situ, Savannah River site, 134,137Cs +89,90
Sr + Hg

In situ, Savannah River site, 134,137Cs +89,90
Sr + Hg

Crucian carp (Carassius carassius),
adults

Crucian carp (Carassius carassius), carp
(Cyprinus carpio), tench (Tinca tinca),channel catfish (I. punctatus), adults

Slider turtles (P. scripta), adults

Slider turtles (P. scripta), adults

Mallard (A. platyrhynchos), ducklings

FC erythrocytes(DNA CV, aneuploidy and cellproliferation)

FC erythrocytes(DNA CV and aneuploidy)

FC erythrocytes(DNA CV and aneuploidy)

FC whole blood, erythrocytes,
leukocytes (DNA CV, aneuploidy,
cell proliferation)

FC (DNA CV, aneuploidy)

FC erythrocytes (DNA CV, aneuploidy
and CV distribution)

FC (DNA CV, aneuploidy, polyploidy)

MN per 1 000 erythrocytes

Assay(parameter)= : aneuploidy= : cell proliferation+ : CV
80 µGy/h= : aneuploidy+ : CV
80 µGy/h= : aneuploidy+ : CV
80 µGy/h= : aneuploidy+ : CV blood & erythrocytes++ : CV leukocytes+ : cell proliferation
125 µGy/h= : aneuploidy+ : CV125 µGy/h= : aneuploidy+ : CV+ : CV distribution
80 µGy/h=-EffectLOEDR (µGy/h)(LNOEDR or LOED)

[G24]

[L11]

[B35]

[D8]

[L10]

[L8]

[K16]

[S18]

Reference

Symbols and abbreviations: Dose rates are either those indicated in the article or those taken from other studies (a from reference [T21]; b from reference [K9]; c from reference [H14]; d from reference [T6]). SCE : sister chromatid exchange;
CA : chromosomal aberration; MN : micronuclei; FC : flow cytometry. Effect description: + : increase; ++ : strong increase (>3 fold the value of the control group); +++ : very strong increase; = : no significant response; - : decrease; -- : strong
decrease (>3 fold the value of the control group). LOEDR (µGy/h) : Lowest Observed Effect Dose Rate; LNOEDR (µGy/h) : Lowest No Observed Effect Dose Rate; LOED (µGy) : Lowest Observed Effect Dose. By default, the endpoint is LOEDR. If notavailable, LNOEDR or LOED are given.

89,90

n.d.

80 µGy/hc

In situ, Savannah River site, 134,137Cs +89,90
Sr + Hg

Largemouth bass (M. salmoides),adults197 days

240–1 000 µGy/hLab, in vivo, external, 137Cs

Plaice, (P. platessa), adultn.d.

Exposure
duration

125 µGy/hb

Dose rate, dose orinternal concentration

In situ, Chernobyl, cooling pond, 137Cs

Type of exposure

Channel catfish (I. Punctatus), adults

Species(life stage)

286
UNSCEAR 2008 REPORT: VOLUME IIANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

272. To date, experiments have failed to demonstrate aclear correlation between micronucleus (MN) induction andthe 137Cs concentration in fish muscle. Al‑Sabti [A20] collected blood samples from pike, perch, roach and bream in
Swedish lakes contaminated by Chernobyl fallout. Even if
the 137Cs concentrations in the muscle were high, up to
18 kBq kg–1 (dry weight), and MN induction significant, they
were not correlated and the highest MN frequency (42 per
1,000 erythrocytes) was observed in the control lake. A similar observation was made in another study on Swedish lakes[A21]. In another in-situ study conducted by Sugg et al.
[S18] on catfish from the Chernobyl area, the highest MN
frequency (6 per 1,000 erythrocytes) was found in fish fromthe control site, although alkaline unwinding assay showed
an increase (non-significant) of single-strand breaks (SBs) inthe cooling pond. The authors hypothesized that other pollutants might have been present in the control lake or that thefish might have displayed an adaptive behaviour andincreased defence mechanisms against ionizing radiation
exposure. On the other hand, Ilyinskikh et al. [I22] found apositive correlation between the 137Cs concentration in pikemuscle (up to 1.2 kBq/kg wet weight) and the frequency of
micronucleated erythrocytes, for fish caught in Siberian
nuclear facilities. A positive correlation was also foundbetween micronuclei frequency and age.
273. Gustavino et al. [G23] exposed carp to acute doses of
X‑rays (250 kV, 6 mA, 0.75 Gy/min). They found a dose andtime-dependent response of MN to irradiation, the peak
being 21 days after treatment. The lowest dose tested, forwhich there was a significant MN induction, was 0.1 Gy. It isinteresting to remark that the baseline of micronuclei induction ranges over 2–3 orders of magnitude between different
fish species. In the medaka (Oryzias latipes), an X‑ray doseof 4 Gy (0.5 Gy/min) increased the frequency of MN toapproximately 7 per 1,000 gill cells. Knowles [K16] irradiated plaice using 137Cs sealed sources. He did not observe
any MN induction, even for the highest dose tested (1 mGy/hover 197 days, total dose of 4.6 Gy). The lack of sensitivityof this assay for fish could be linked to its application to nondividing cell populations or to dividing cell populations inwhich the kinetics of cell division are not well understood orcontrolled.
274. Ulsh et al. [U18, U19] used the fluorescence in situ
hydridization (FISH) technique in a study involving slider
turtles. They showed for Trachemys scripta fibroblasts andlymphocytes, that the dose rate below which no reduction in
effect per unit dose was observed with further dose protraction was about 230 mGy/h. Interestingly, they also showedthat this species had a much lower spontaneous backgroundof symmetrical translocations in lymphocytes than humans(30‑fold less), which makes it a sensitive species for the
study of low doses and dose rates.
275. Theodorakis and Shugart [T21, T22] found different
allele frequencies for mosquitofish populations exposed toradionuclides within the Oak Ridge nuclear site compared tofish in reference lakes. They showed that heterozygotes for287

the allozyme locus nucleoside phosphorylase (NP), an
enzyme involved in nucleoside synthesis, were more prevalent in fish in the radionuclide-contaminated sites and, moreover, that they had fewer DNA strand breaks than thehomozygotes. Finally, they showed that NP heterozygotes
had a greater fecundity than homozygotes.
276. Genetic adaptation, i.e. the genetic basis for resis­
tance, can be evaluated in populations exposed to a contaminant. The individuals that are not resistant are naturally
eliminated, while tolerant individuals can be bred. Subsequently, F1 and F2 generations can be tested for resistance.
If tolerance persists or increases in F1 and F2 generations,then the response can be said to be genetic. Further analyses can be conducted using molecular techniques to­investigate thoroughly the mechanisms involved. Suchexperiments have been scarcely performed, probably
because they are costly and time consuming. In a series of
papers, ­Theodorakis et al. used such an integrated approach,and demonstrated the effects of contaminants (mostly
radio­nuclide) on genetic patterns [T20, T21, T22, T23].
The bacterium Escherichia coli population became radio­
resistant after daily X‑­irradiation over many generations[E21], and it was shown that the most radioresistant strain
isolated from this population has the mutation(s) in genes
involved in ­inducible DNA repair [E9].
(d)Effects of acute exposure277. For primary producers, the information is still rather
limited (only 10 papers in the FRED), mainly describing
morphological changes and growth inhibition for green
microalgae at high doses (approximately 100–1,000 Gy).
Chromosome aberration at doses from 1–5 Gy was evident
in the macroalgae Nitella flagelliformis (as discussed in­reference [F5]).
278. From the information in the FRED, acute doses up to
1 Gy have no significant effects on species representative ofannelid, mollusc and crustaceans. Acute doses as low as
0.5 Gy can significantly decrease the percentage of live
embryos in broods of the particularly radiosensitive polychaete worm, Neanthes arenaceodentata. This radiosensitivity is confirmed by the finding of an increased incidence ofradiation-induced sister chromosome exchanges in juvenile
worms exposed at total doses greater than 0.17 Gy. The
explanation was that the response was due to the inductionof dominant lethal mutations in gametes of irradiated adultworms [F5].
279. For fish, the existing knowledge mainly relates toacute exposures greater than 5 Gy. Acute doses below 1 Gy
are unlikely to have any significant influence on their general
health (morbidity). Fish embryos are much more radiosensitive than free swimming larvae, juveniles and adults. Dosesless than 2 Gy are likely to have little effect on mortality. The
lowest dose reported in the FRED with significant effect, is
as low as 0.16 Gy delivered in the early 1‑cell stage of288

UNSCEAR 2008 REPORT: VOLUME II

development and the consequent mortality is scored overlong periods—150 days post fertilization. The developing
fish embryo is very sensitive to the effects of acute irradiation, particularly at the very early stages just prior to, or
immediately after the actual fertilization and during theprocess of division of the single cell. Irradiation of silver
salmon embryos at this stage gave an estimated LD50 of
0.16 Gy when assessed at 150 days post-irradiation. Apartfrom this critical period in embryonic development, ­FASSET[F5] concluded that it appears unlikely that significant effects
will follow doses below 0.5 Gy. An acute dose of this magnitude at any later stage of development will be unlikely tohave any significant influence on adult male and female fertility. Mutagenic damages (specific locus mutations, dominant and recessive lethal mutations, polygenic characters,
and chromosome aberrations) have been observed at allradia­tion doses used in the relevant studies. Where comparisons of relative radiosensitivity have been made, it has beenconcluded that fish show a sensitivity similar to, and mostoften less than, that of the mouse. There is a single example
of apparently greater sensitivity—for specific locus mutations induced in medaka sperm [R9]. Although there are nodata relating to radiation-induced mutagenesis in marine
fish, there is no reasonable basis for expecting them torespond differently from freshwater fish.
6.

Effects on populations and ecosystems

280. Ecosystems consist of various organisms that have awide range of radiosensitivities and interact with one anotherin a complex fashion. As a result, indirect responses to thedirect effects of radiation exposure are observed in the­natural environment. Since these indirect responses cannot
neces­sarily be deduced from the effects on individuals andpopulations, effects at the community level are evaluated bymathematical modelling, model ecosystem experiments andfield irradiation experiments.
281. In mathematical modelling, physical, chemical andbiological components of natural ecosystems and interactions among them are mathematically defined, and ecosystems are simulated in computers. Effects on the entire
ecosystems are evaluated by applying single-species effectdata to the mathematically constructed ecosystems. For
example, Bartell et al. developed a comprehensive aquaticsystems model (CASM) [D6]. The CASM model is a bio­energetic ecosystem model that simulates the daily production
dynamics of populations (including predator–prey interactions) with time, in relation to daily changes in light intensity,
water temperature, and nutrient availability. This model has
been adopted for estimating the ecological risks of chemicals
for aquatic ecosystems in Quebec [B24], central Florida[B25] and Japan [N7]. In time, this type of model will also be
useful for the evaluation of the effects of radiation exposure.
282. Model ecosystem experiments provide biotic or ­abiotic
simplicity, controllability and replicability, which cannot be
expected in field experiments. At the same time, they

simulate the inter-species interactions of natural ecosystems.
It is therefore expected that model ecosystem experiments
can investigate the indirect effects of radiation exposure,which cannot be evaluated by conventional single-species
experiments. Model ecosystem experiments can therefore be
regarded as a bridge between single-species experiments andfield experiments. Some model ecosystem experiments havebeen performed to investigate the effects of radiation exposure. For example, Williams and Murdoch [W14] made studies using two different types of marine model ecosystems.
However, no effects for 23 possible effect endpoints wereobserved at dose rates of up to 0.79 Gy/d.
283. Ferens and Beyers [F18] acutely irradiated aquaticmodel ecosystems derived from a sewage oxidation pondconsisting of various kinds of microorganisms. Effects onbiomass, chlorophyll content and gross-community meta­bolism were more severe at doses of 1,000 Gy than at
10,000 Gy. This unexpected phenomenon might arise fromthe disappearance of inhibitory inter-species interactions
after elimination of certain species at doses of 10,000 Gy.
284. Fuma et al. [F19] studied effects of acute gamma irradiation on the aquatic model ecosystem consisting of theflagellate alga, Euglena gracilis, as a producer, the ciliate
protozoan, Tetrahymena thermophila, as a consumer and thebacterium, Escherichia coli, as a decomposer. After a doseof 1,000 Gy, the cell density of T. thermophila was increased
temporarily, and then decreased compared with controls.
This complicated change in T. thermophila might be an indirect response to direct effects on the other species, i.e. extinction of E. coli and decrease in Eu. gracilis. Doi et al. [D7]mathematically simulated a dose–effect relationship for thisexperimental model ecosystem with a particle-based model,
in which inter-species interactions were taken into consideration. This suggests that experimental model ecosystems
are useful for validation of mathematical models.
285. Hinton et al. [H12] constructed a Low Dose-Rate Irradiation Facility (LoDIF) in the Savannah River Ecology
Laboratory (Aiken, South Carolina, USA). This facility consists of outdoor open-air tanks and is designed to house avariety of aquatic organisms. Gamma irradiation is conducted with an irradiator placed over each tank. Each irradiator contains a 0.74, 7.4 or 74.0 MBq sealed 137Cs source. The
7.4 MBq source delivers a mean dose rate of approximately
10 mGy/d. The LoDIF is now used only for studies of theeffects of chronic irradiation on the reproduction of small
fish (Japanese medaka; Oryzias latipes), but can be used as
an experimental model ecosystem.
286. Some field irradiation experiments have been performed, though these have already been terminated. The
Brookhaven Irradiated Forest Experiment is a typical example. This experiment was designed to study the effects ofradia­tion exposure on plant and animal communities [W15].
In 1961, a 350 TBq 137Cs source was placed in an oak–pine
forest at the Brookhaven National Laboratory (Upton, New
York, USA). The dose rate within a few metres from theANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

source was in the order of 10 Gy/d; it decreased to backgroundlevels beyond 300 m. After commencement of irradiation,
biomass, species composition, densities and other ecologicalpara­meters were measured for plants, insects, fungi, lichensand soil algae. Many examples of the indirect effects describedin the UNSCEAR 1996 Report [U4] were observed in a seriesof experiments conducted with this source.

289

radiation had not shown any individual or population effectfrom chronic exposure to low-LET external radiation in therange of 10–100 mGy/d and that the current guidelines in therange of 1–10 mGy/d appeared suitable as benchmarks forgeneral environmental protection purposes [M11].
288. Simulation can be used to illustrate population-level
effects arising from individual effects with different endpoints.
By modelling the delay in population growth on the basis of
the observed effects on individual traits (figure XV), simulation of the effects of chronic exposure to radionuclides at the
population level appeared to be mediated through individualeffect endpoints as follows: (a) effects on the hatchability of
cocoons and the number of hatchlings per hatched cocoon forearthworms; and (b) effects on larval resistance to starvation
for daphnids. Ultimately, effects increase the early mortalityof larvae in both species (offspring are produced but they
never reach reproduction age) which are, with regard to population dynamics, equivalent to not producing those offspring.
Observed effects can be assimilated to a reduction in fecundity in every case: 10% reduction in fecundity in earthworms
at a dose rate of 4 mGy/h (point A on figure XV), 55% reduction in fecundity in earthworms at a dose rate of 11 mGy/h(point B on ­figure XV), 70% reduction in starved control
daphnids and up to 100% reduction (i.e. extinction) in starved
contaminated daphnids independent of the dose rate (point C
on figure XV). The last result indicates that this species
becomes more vulnerable to food depletion for the radio­
nuclide-contaminated environment than for non-contaminatedhabitats [G3].

287. Two field-irradiation experiments were conducted at
the Whiteshell Laboratories in Manitoba, Canada. One is the
Field-Irradiated Gamma (FIG) experiment in which a boreal
forest was chronically irradiated from 1973–1986 to study
the effects on plant communities [G13]. The radiation source
was 370 TBq 137Cs, and the dose rates ranged from 0.12–
1,560 mGy/d. The effects of radiation exposure were investigated for tree canopy, naturally growing shrubs, groundcover species, germination of seeds, morphological change
and tree-ring growth. One experimental observation was thatthe seed germination of Jack Pine showed deleterious effects
at a dose rate of 1.1 mGy/h [S38]. In contrast, reference[S38] reported hormetic effects (increased germination) at
dose rates up to 0.6 mGy/h. The other experiment was the
Zoological Environment Under Stress (ZEUS) that was performed from 1981–1985 to study the effects on the individual or population characteristics of meadow voles [M11].
Vole populations were irradiated at nominal dose rates of200, 9,000 and 40,000 times that from natural backgroundradiation. No effects on individual or population-level characteristics were observed at a dose rate up to 81 mGy/d, thehighest dose rate used. Mihok noted that experiments with

Figure XV. Relationship between effects at the individual level and their relative consequence at the population level (fromreference [G3])Earthworms chronically exposed to external gamma radiation: A: 10% reduction in fecundity at 3.3–3.6 mGy/h; B: 55% reduction in fecundity
at the dose rate of 9–9.5 mGy/h. Daphnids chronically exposed to internal alpha radiation (241Am); C: 70% reduction in starved control and up
to 100% reduction (i.e. extinction) independent of the dose rate
Delay in population growth(up to 50,000 daphnids)

Delay in population growth(up to 50,000 worms)
1

RELATIVE CHANGE IN
INDIVIDUAL ENDPOINT

RELATIVE CHANGE IN
INDIVIDUAL ENDPOINT

1
0.8
0.6
0.4

C

0.2
0
0.0

A

0.8
0.6

Survival
Fecundity
Age of reproduction

B

0.4
0.2
0

0.2

0.4

0.6

0.8

RELATIVE DELAY
IN POPULATION GROWTH

1.0

0.0

0.2

0.4

0.6

0.8

RELATIVE DELAY
IN POPULATION GROWTH

1.0

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289. The consequences of radiation exposure at the population level depend on the particular stage in the life historyof the organism. Small effects on individual endpoints critical for population dynamics may impair population growthrate to a greater extent than large effects on neutral individual endpoints. The impact of chronic exposure to radio­
nuclides at the population level depends on which stage inthe life history is impaired. Individual endpoints do not show
the same importance at the population level, population
growth being by far more sensitive to changes in age ofreproduction than changes in fecundity or survival [A26,G3] (figure XV).

radiation damage to individuals to an acceptable degree will
also provide a sufficient degree of protection for populations. However, in situations where the most sensitive life
stage has not been positively identified, or where there is alack of data on the most sensitive life stage, there may be aneed to introduce a margin of safety when using the available dose–effect information on individual life stages todevelop measures to protect field populations. Furthermore,
population-level consequences of hereditary mutations
might in some cases need to be allowed for in these extrapolations. If and how this might be done requires additional
research and scientific review [G16].

290. Specific studies have provided evidence linking
geno­toxic syndrome to population-level changes [T20, T21,
T22, T23]. Trabalka and Allen [T19] raised 2 generations ofmosquitofish collected from a radionuclide-contaminatedsite. They showed that fish from the F2 generation were lesstolerant to thermal stress than fish from the control site.

294. Most studies of the effects of exposure to ionizing
radiation have been performed under non-limiting growth
conditions (i.e. sufficient food and space were available).
In contrast, wild organisms are often regulated by various
types of density-dependent factors such as competition forresources. Based on current knowledge, it is hard to draw
general conclusions on how density-dependent factors
may influence the propagation of effects on individuals to
populations [G16].

291. Mutations occur at the molecular level, but heritable
mutations in germ cells are capable of affecting the genetic
diversity of populations, and can lead to increased or
decreased genetic diversity, as well as to changes in phenotype that can affect Darwinian fitness. Increases in mutation
rate can increase genetic diversity of the population by producing new alleles or genotypes, but they can also result in
decreased genetic diversity, since the mutations could reducethe viability or fertility of the individuals [T14]. Consequently, increases in mutation rate can affect the genetic
structure of the population, and thereby have ecologically
relevant effects.
292. Exposure to contaminants can lead to alterations in
the genetic makeup of populations, a process termed evolutionary toxicology. It is generally hypothesized that there isan alteration of genotype frequencies and a reduction in
genetic variation in genotoxicant-contaminated environments. These changes may occur as a result of selection on
specific alleles, selection for multi-locus genotypes, mortality in specific life stages, and changes in breeding period.
They may induce reduction in population size, alterations in
the degree of inbreeding, alteration of the level of gene flow
and changes in age or class structure. Potentially, these shifts
may alter population viability and fitness. Theodorakis andShugart [T21] observed a higher percentage of polymorphism and heterozygosity in mosquitofish from the radio­
nuclide-contaminated site, correlated with a higher fitness
and lower level of DNA strand breaks. These findings suggest that there is a selective advantage in radionuclide-­contaminated areas. More surprisingly, they found a higher
genetic diversity in the radionuclide-contaminated populations, for which no definite explanation was given. The
authors hypothesized that the higher diversity was linked togenomic rearrangements or different life-history processes.
293. Even though several factors complicate extrapolationsof individual-level effects to populations, current knowledge
supports the conclusion that measures intended to limit

295. In its 2008 report, the ICRP [I10] suggested that, in
considering the potential effect of exposure to ionizing radia­tion, context should be provided by comparing the estimateddose rates to multiples of the dose rates experienced by thevarious biota in their natural environment. In this regard, the
ICRP proposed the use of the concept of “Derived Consideration Levels” (DCLs) which were intended to serve as
points of reference for assessing the potential effects of
exposure to ionizing radiation on non-human biota. In doing
this, the ICRP compiled available information for their various biota categories and summarized the data into bands ofdose rate from less than 0.1 to more than 100 mGy/d. In
commenting on the available data, the ICRP emphasized thatthe data are both incomplete and of varied quality and that
their summary tables represent “an extreme oversimplification of existing data”. The range of DCLs (dose rates) for
various biota categories (e.g. mammals, birds, and trees)summarized by ICRP were:– With regard to the mammals (“higher vertebrates”),
deer and rat, the ICRP suggested that at dose rates
in the region of 0.1–1 mGy/d, there was only avery low probability of certain effects occurringthat could result in reduced reproductive success or
morbidity. At dose rates in the band of 1–10 mGy/d,there was some potential for reduced reproductive
success;– For birds (the reference bird was the duck), the
ICRP suggested that based on metabolism, longevity, and reproductive behaviour, it was reasonable
to assume similar results to those for mammals;– With regard to the “lower” poikilothermic vertebrates (frog, trout and flatfish), data are generally
lacking below about 1 mGy/d. However, considering the general lack of physiological data on

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

amphibians, the ICRP suggested a lower DCL(dose-rate) band of 0.01–0.1 mGy/d for frogs
compared to the two types of fish. For dose rates
in the range of 1–10 mGy/d, the ICRP suggested
that some reduction in reproductive capacity mightoccur in frogs and possibly also in fish species;– The ICRP indicated that there are essentially nodata for the invertebrates, bee, crab and earthworm,

V.

291

but suggested that invertebrates are less sensitiveand recommended a DCL of 10–100 mGy/d; and– The data for trees, plants and seaweeds are highlyvariable across species, the best data being for pinetrees. The ICRP suggested DCLs of 1–10 mGy/dfor grasses and seaweeds but a 10‑times lower
value for pine trees, which they attribute in part totheir potential for very long periods of exposure.

Summary and conclusions

296. All living organisms have existed and developed inenvironments where they are exposed to ionizing radiationfrom the natural background and, recently, to radiation
resulting from global fallout of radioactive material following the atmospheric nuclear weapons tests. In addition, biota
are exposed, generally in areas of limited spatial extent, toradiation from man’s activities, such as the controlled discharge of radionuclides to the air, ground or aquatic systems,
or from accidental releases of radionuclides.
297. Prior to the development of the annex, “Effects ofradiation on the environment” of the UNSCEAR 1996
Report [U4], the Committee had not specifically addressed
the effects of radiation exposure on plant and animal communities. Living organisms had been considered primarily
as part of the environment in which radionuclides might bedispersed and as resources that, if they took up radio­
nuclides, might contribute to human exposures via thehuman food chains. Like humans, however, organisms arethemselves exposed internally from radionuclides that they
may have taken up from the environment, and externally
due to radiation from radionuclides in the environment.
298. In the past decades, scientific and regulatory activities
related to radiation protection focused on the radiation exposure of humans arising from both artificial and natural
sources. The prevailing view was that, if humans were adequately protected, then “other living things are also likely tobe sufficiently protected” [I8] or “other species are not put atrisk” [I5]. Over time, the general validity of this view has
been challenged on occasion and more attention has therefore been given to the potential effects of exposure to ionizing radiation on non-human biota. In part, this has occurred
as a result of the increased worldwide concern over sustainability of the environment, including the need to maintainbiodiversity and protect habitats or endangered species (e.g.
[U22, U23]), and, in part, as a result of various efforts toassess the effects of exposure to ionizing radiation on plants
and animals [D1, I1, I2, I3, I4, I9, N6, T1].
299. Since the Committee issued its first report in 1996
[U4] on the doses and dose rates of ionizing radiation below
which effects on populations of non-human biota areunlikely, the approaches to evaluating radiation doses havebeen reviewed and progress has been made (e.g. by the DOE[U26], the Environment Agency [C1], FASSET [F1], ERICA[E1]). In addition, the continuing follow-up of the consequences of the Chernobyl accident has provided a great dealof new information on the radiobiological effects of ionizing
radiation exposure on non-human biota (e.g. [E8, G26]).
Similarly, information not previously available to the Committee on the levels of radiation exposure below whichradio­biological effects on non-human biota are unlikely has
been further compiled and evaluated, in part, through thework carried out in support of the development of the­FASSET effects database, FRED, and the subsequent­FREDERICA effects database [B26, E1, F1]. The Committee undertook a review of the new scientific information that
had become available since its previous report and assessed
whether it needed to modify its previous recommendations
concerning the dose rates below which effects on non-humanbiota are considered unlikely.

A. Estimating dose to non-human biota
300. The radiation dose received by an organism (or someorgan or tissue of the organism) is the sum of both the external and internal exposure. Absorbed doses are calculated as
the dosimetric endpoint; however, for radionuclides taken
into the organism, an appropriate factor may be applied inorder to account for the different RBEs of the different kindsof radiation.
301. External exposures of biota are the result of complex
and non-linear interactions of various factors, such as thelevels of radionuclides in the habitat, the geometrical relationship between the radiation source and the target, theshielding properties of materials in the environment, the sizeof the organism and the radionuclide-specific decay properties (characterized by the radiation type, the energies emitted
and their emission probabilities).
302. Internal exposures of plants and animals are determined by the activity concentration in the organism, the sizeof the organism, the radionuclide distribution and the specificdecay properties of the radionuclide.
303. In considering the potential effects of ionizing radiation exposure on non-human biota, the Committee assumed

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that natural populations of non-human biota are in a state ofdynamic equilibrium within their environment. Equilibrium
models assume that radionuclide concentrations reach equilibrium within various environmental compartments and thattransfer between compartments is reasonably characterizedby time-invariant ratios of concentration between the compartments. One of the advantages of the equilibrium model is
its simplicity. Such models are widely used by national regulators for assessment purposes. However, when it is necessary to assess a time-dependent response—for example,
when considering an accidental release of radio­nuclides—
dynamic radioecological models are needed. Within the context of this annex, equilibrium ­models have been assumed in
the exposure assessments, unless otherwise indicated. Readers interested in dynamic radioecological models are referredto the published ­literature [M4, M7, S1, W3].
B. Summary of dose–effects datafrom the UNSCEAR 1996 Report304. Notwithstanding the limitations of the data available
in 1996, the Committee considered it unlikely that radiation
exposures causing only minor effects on the most exposed
individual would have significant effects on the population.
It also suggested that the effects of radiation exposure at the
population and community levels are manifest as somecombination of direct changes due to radiation damage andindirect responses to the direct changes [U4].
305. The Committee considered that the individual
responses to radiation exposure likely to be significant at
the population level are mortality (affecting age distribution, death rate and density), fertility and fecundity (bothaffecting birth rate, age distribution, number and density)and the induction of mutations (birth rate and death rate).
The response of these individual functions to radiation
exposure could be traced to events at the cellular level in
specific ­tissues or organs. An extended summary discussing the pro­cesses involved had been provided in annex J,“Non-­stochastic effects of irradiation”, of the UNSCEAR
1982 Report [U9]. The Committee also considered there
was a substantial body of evidence indicating that the mostradiosensitive sites are associated with the cell nucleus,
specifically the chromosomes, and that, to a lesser extent,
damage to intracellular membranes was additionallyinvolved. The end result is that the cells lose their reproductive potential. For most cell types, at moderate doses,
death occurs when the cell attempts to divide; death does
not, however, always occur at the first post-exposure division: at doses of a few gray, several division cycles might
be successfully completed before death eventuallyoccurred. It was also well known that radiosensitivity varies within the cell cycle, with the greatest sensitivities
being apparent at mitosis and the commencement of DNA
synthesis [U9]. It followed that the greatest radiosensitivity is likely to be found in cell systems undergoing rapid
cell division for either renewal (e.g. sperma­togonia) or
growth (e.g. plant meristems and the developing embryo);these examples clearly underlie the processes in individualorganisms that are important for the maintenance of the
population. Effects of radiation exposure on populations
occur as the result of exposure of individual organisms.
The propagation of effects from individual organisms topopulations is complex and depends on a number of factors; however, the Committee considered that of the various effects on populations of non-human biota, the key
effects are those that affected reproductive success.
306. The Committee noted that the responses of organisms
to radiation exposure are varied and might become manifest
at all levels of organization, from individual biomolecules toecosystems. The significance of a given response depends onthe criterion of damage adopted, and it was not to be concluded that a response at one level of organization would
necessarily produce a consequential, detectable response at ahigher level of organization.
307. In its 1996 assessment, the Committee considered that
reproductive changes are a more sensitive indicator of theeffects of radiation exposure than mortality, and mammals
are the most sensitive animal organisms. On this basis, theCommittee concluded that chronic dose rates of less than
100 μGy/h to the most highly exposed individuals would be
unlikely to have significant effects on most terrestrial animal
populations. The Committee also concluded that maximum
dose rates of 400 μGy/h to a small proportion of the individuals in aquatic populations of organisms would not haveany detrimental effect at the population level. These conclusions refer to the effects of low-LET radiation. Where a significant part of the incremental radiation exposure comesfrom high-LET radiation (especially alpha particles) that isinternal to the organism, it is necessary to apply an appropriate factor to adjust for the different RBEs of the different
radiations.
308. Acute lethal radiation doses to plants had been noted
to range from 10–1,000 Gy. In general, larger plants are
more radiosensitive than smaller plants, with radiosensitivity
decreasing in the order coniferous trees, deciduous trees,
shrubs, herbaceous plants, lichens [U4]. The data on radiosensitivity of terrestrial animals were dominated by data on
mammals, the most sensitive class of organisms. Acute lethal
doses (LD50/30) were 6–10 Gy for small mammals and 1.5–
2.5 Gy for larger animals and domestic livestock [U4]. The
Committee concluded [U4] that the effects of radiation
exposure on birds are similar to those in small mammals.
Separately, it [U4] found that reptiles and invertebrates areless radiosensitive than birds, with studies of acute radiation
exposures of adult amphibians indicating LD50 values ofbetween 2–22 Gy. With respect to aquatic organisms, fish are
the most sensitive to the effects of radiation exposure; thedeveloping fish embryos are particularly so. The LD50 for
acute irradiation of marine fish is in the range of 10–25 Gy
for assessment periods of up to 60 days following exposure[U4]. Overall, a notional range of dose of 1–10 Gy fromacute radiation exposure is unlikely to result in effects on
populations of non-human biota.

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTAC.

The current evaluation

309. Many of the new data subsequent to the Committee’s
1996 report [U4] arose from follow-up studies of the consequences of the Chernobyl accident. Prior to the accident,much of the area around the Chernobyl nuclear power plant
was covered in 30–40-year old pine stands that, from a successional standpoint, represented mature, stable ecosystems[E8]. The high dose rates during the first few weeks following the accident altered the balance in the community andopened niches for immigration of new individuals. All thesecomponents and many more, were interwoven in a complex
web of action and reaction that altered populations and communities of organisms. In addition to the effects from theradiation exposure, activities such as agriculture, forestry,hunting and fishing within the 30‑km zone were stopped[E8]. Moreover, after the accident, the agricultural fields
remained productive for a number of years and, in theabsence of active management of areas that had been evacuated, many animal species, especially rodents and wild boar,
consumed the abandoned cereal crops, potatoes and grasses
as an additional source of forage [E8]. This advantage, alongwith the special reserve regulations established in the exclusion zone (i.e. a ban on hunting) tended to mask potential
adverse biological effects of radiation exposure and led to anincrease in the populations of wild animals, including gamemammals (wild boar, roe deer, red deer, elk, wolves, foxes,
hares, beaver, etc.) and bird species (black grouse, ducks,etc.) [G8, S23]. The exclusion zone has become a breedingarea of the white-tailed eagle, spotted eagle, eagle owl, craneand black stork [G9].
310. Overall, based on an evaluation of the available dataarising from studies of plants and animals in the zone
around the Chernobyl nuclear power plant, the Chernobyl
Forum [E8] arrived at a number of general observations,
including:– Radiation from radionuclides released as a resultof the Chernobyl accident caused numerous acute
adverse effects on the biota located in the areas ofhighest exposure (i.e. up to a distance of a few tensof kilometres from the release point);– The environmental response to the increased radiation exposure incurred as a result of the Chernobyl
accident was a complex interaction among radiation dose, dose rate and its temporal and spatial
variations, as well as the radiosensitivities of thedifferent taxons. Both individual and population
effects caused by radiation-induced cell death
were observed in plants and animals and included
increased mortality of coniferous plants, soil invertebrates and mammals; reproductive losses inplants and animals; and chronic radiation sickness
in animals (mammals, birds, etc.);– No adverse radiation-induced effects were reported
in plants and animals exposed to a cumulative doseof less than 0.3 Gy during the first month after theaccident (i.e. <10 mGy/d, on average); and293– Following the natural reduction of exposure levels
due to radionuclide decay and migration, populations have been recovering from acute radiation
effects. By the next growing season following theaccident, the population viability of plants andanimals substantially recovered as a result of the
combined effects of reproduction and immigration. A few years were needed for recovery frommajor radiation-induced adverse effects in plants
and animals.
311. Another, and even more recent comprehensive
review of the effects of radiation exposure arising from the
Chernobyl accident on non-human biota compiled andexamined the data on effects along with the associateddosimetric information [G26]. The authors evaluated
250 references in total, of which, some 79 papers wereconsidered to have adequate information on environmental
contamination and doses to biota as well as information on
the associated effects. The effects of radiation exposure
were seen in both natural and agricultural systems. Consistent with the Committee’s 1996 report [U4], the authors
noted that the effects depended on the radiosensitivity ofthe dominant species and observed that coniferous trees
are one of the most sensitive plant species and mammals
are the most radiosensitive animal species. Table 27 summarizes the various effects seen in non-human biota
around the Chernobyl nuclear power plant and the corresponding doses or dose rates below which such effects
were not observed.
312. Alexakhin et al. [A29] reported on the environmental and agricultural impact of the Chernobyl accident.
These authors described the effects of countermeasureson the doses to ecosystems and the public. High radiation
doses within the 30‑km exclusion zone led to numerous
effects on biota ranging from subtle effects at the molecular and subcellular levels, to significant degradation of
ecosystems, pine stands for example. On the other hand,evacuation of people from the 30‑km zone reduced
stresses arising from human use of the environment.
Exclusion of people, along with the special reserve regulations established in the exclusion zone (i.e. a ban on
hunting) overcame potential adverse biological effects ofradiation exposure and led to an increase in the populations of wild animals and birds. Based on an evaluation of
the FRED database, FASSET concluded that the information available on the effects of radiation exposure on nonhuman biota from low dose rates (less than about
100 µGy/h or 2.4 mGy/d) for continuous irradiation isreasonable for both plants and animals and that, forchronic exposure conditions, “the reviewed effects data
give few indications for readily observable effects at
chronic dose rates below 100 µGy/h”. However, it advisedthat “using this information for establishing environmentally ‘safe levels’ of radiation should be done with caution, considering that the database contains large
information gaps for environmentally relevant dose rates
and ecologically important ­wildlife groups” [F5, R9].

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313. For chronic exposures, the ERICA project used statistical methods to estimate the dose rates below which 95% of
species in the aquatic/terrestrial ecosystems should be protected. Their analysis of the data on effects from external
gamma irradiation of species of different ecosystems concluded that there was no statistical justification to attempt toderive ecosystem specific screening dose rates and hence alldata were analysed together as a “generic” ecosystem. The
resultant dose rate that would protect 95% of the species in
the generic ecosystem was estimated at 82 µGy/h (with 95th
percentile confidence intervals of 23.8 and 336 µGy/h). Thisis generally consistent with the Committee’s 1996 assessment [E11, G27]. It should be noted that these authors
implicitly adopted a further safety factor of 5 in an attempt toaccount for data limitations.

and shoot growth at absorbed doses as low as 0.7–1 Gy[K1]. Information has been reported [G3] that shows adecrease in population density and species composition offorest litter mesofauna at doses in the range of 1–9 Gy.
Based on a review of the FRED, FASSET concluded that
acute doses of up to 1 Gy have no significant effect onannelids, molluscs and crustaceans, that acute doses below
about 1 Gy are unlikely to have a significant effect on general health (morbidity), and that doses below about 0.5 Gy
are unlikely to have any significant effect on adult maleand female fertility [F5]. When the SSD method wasapplied to data on the effects of acute exposures, HDR5
values in the range of about 1–5.5 Gy were estimated.
Thus, on the basis of the available data, the Committee
continues to recommend a nominal reference dose of about
1 Gy, within a factor of 2 or so, as a reference value below
which population-­level effects on non-human biota areunlikely in the event of an acute exposure.

314. ERICA also applied the same statistical methods tothe data on effects for acute exposure conditions but in thiscase, a statistically significant difference was seen between
marine ecosystems compared to terrestrial and freshwater
ecosystems. The values derived from a statistical analysisof the set of doses giving a 50% change in the observed
effect for limiting the potentially affected fraction to 5% of
the species under acute external gamma irradiation varied
from about 1–5.5 Gy, according to the ecosystems type,with the associated 95% confidence intervals covering lessthan one order of magnitude. For screening purposes,
ERICA applied a further SF of 5 and reported Predicted
No-Effect Doses (PNED) of 900 mGy for marine ecosystems and 300 mGy for terrestrial and freshwater ecosystems [G3, G15, G27]. The application of such additionalsafety factors is of great interest in developing regulatory
approaches for the protection of non-human biota; however, such judgements are beyond those of the Committee
and properly lie in the domain of the ICRP and national
authorities.

D. Conclusions
316. As discussed in the UNSCEAR 1996 Report, theCommittee considered it unlikely that radiation exposurescausing only minor effects on the most exposed individual
would have significant effects on the population. It also
considered that reproductive changes are a more sensitive
indicator of the effects of radiation exposure than mortality,
and that mammals are the most sensitive animal organisms.
Since 1996, new data on the effects of exposure to ionizing
radiation have been developed from follow-up observationsof non-human biota in the zone around the Chernobyl
nuclear power plant (section III) and various organizations
have carried out comprehensive reviews of the scientific
literature on the data on effects and, in some cases, developed new approaches to the assessment of the potential
risks to non-human biota (section IV). There is a considerable range of endpoints and corresponding effects levels(dose or dose rate) presented in the literature and also considerable variation in how different researchers have evaluated these data. Table 39 provides a summary of the data on
the effects of radiation exposure for aggregated categories
of biota. Details of endpoint effects are described in thecorresponding references.

315. Information on the effects of acute doses of radiation has also been reviewed. For example, soil fauna areunlikely to be affected at doses below about 1 Gy [G3].
The same authors reported data that suggested that the
reproductive capacity of Scots pine is inhibited at doses in
the range of 0.5–5 Gy. The radiosensitivity of spruce isgreater than that of pines with malformed needles, buds,

Table 39.

Overall summary of data on chronic effects of radiation exposure for plants, fish and mammals

Category

Dose rate(μGy/h)Plant

100–1 000Fish

Effects

Endpoint

Reference

Reduced trunk growth of pine trees

Morbidity[W4]

400–700

Reduced numbers of herbaceous plants

Morbidity[G26]

100–1 000

Reduction in testis mass and sperm production, lower fecundity,
delayed spawning

Reproduction[H11, K16, N1]

200–499

Reduced spermatogonia and sperm in tissues

Reproduction[C11]

ANNEX E: EFFECTS OF IONIZING RADIATION ON NON-HUMAN BIOTA

Category

Dose rate(μGy/h)Mammals<100

Generic ecosystems(terrestrial and aquatic)

about 80

Effects295

Endpoint

Reference

No detrimental endpoints have been described

Morbidity,
mortality,
reproduction[C17, L2, P8,
R9, U21, Y2]

A new statistical approach (species sensitivity distribution, SSD) wasapplied to the data on radiation effects to estimate HDR5 , the dose
rate at which 95% of the species in the ecosystem are protected

Morbidity,
mortality,
reproduction[G3, G11, G15]

317. Overall, the Committee concluded that chronic dose
rates of less than 100 μGy/h to the most highly exposed
individuals would be unlikely to have significant effects onmost terrestrial communities and that maximum dose rates
of 400 μGy/h to any individual in aquatic populations oforganisms would be unlikely to have any detrimental effectat the population level. For acute exposures, significant
effects on populations of non-human biota are unlikely atdoses below (about) 1 Gy. These conclusions refer to theeffects of exposure to low-LET radiation. Where a significant part of the incremental radiation exposure comes fromhigh-LET radiation (alpha particles), the Committee concluded that it is necessary to take account of the different
RBEs of the radiations.
318. In addition to new data on the levels at which theeffects of radiation exposure have been observed, notably
from follow-up studies of the consequences of the ­Chernobyl
accident, various authors have investigated new analyticalmethods, notably that of species sensitivity distribution[G3, G11], which involves meta-analysis of the variations inradiosensitivity among species. However, at this time, insufficient data are available for the application of such methods. It is anticipated that as new information is developed in
the future, the application of these new methods of analysis
will facilitate future re-evaluations of the effects of ionizing­radiation exposure on non-human biota.

319. A great deal of work has been done since 1996 to
improve the data and methods for evaluating pathways throughwhich biota are exposed to radiation from radioactive material
in the host environment and many improvements in biota
dosimetry have been made. However, many opportunities still
remain to improve our understanding of the relation between
the levels of radioactive material in the environment and thepotential effects on biota residing in that environment.
320. Based on the new information described in this annex,
and considering the overall limitations of the available data,
the Committee considered that there is no need to change its
previous conclusions of the values of nominal chronic dose
rates below which direct effects on non-human species areunlikely at the population level. Nonetheless, where data ofsuitable scientific quality are available for a specific species
endpoint and/or other level of biological organization, theCommittee would encourage their use in assessments of thepotential effects of radiation exposure. However, there arevery limited data for many taxa and therefore many assumptions are needed to extrapolate between species. There is aneed to better understand the chronic effects at a multigenerational time scale, chronic effects for multiple stressors, andthe propagation of effects at the molecular and cellular levels
to higher levels of ecological organization. In this respect, theapplication of so-called “-omic” techniques (transcriptomic,
proteomic and so on) will help in future assessments.

ACKNOWLEDGEMENTS
321. The Committee gratefully acknowledges the considerable help received by the principal consultants, D. Chambers

and G. Kirchner, from M. Doi, J. Garnier-Laplace, J‑J. Leguay,
G. Pröhl, K. Sakai and D. Woodhead.

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