SOURCES AND EFFECTS
OF IONIZING RADIATION
United Nations Scientific Committee on the Effectsof Atomic Radiation
UNSCEAR 2000 Report to the General Assembly,
with Scientific Annexes

VOLUME II: EFFECTS

UNITED NATIONSNew York, 2000

NOTE
The report of the Committee without its annexes appears as Official Records of theGeneral Assembly, Fifty-fifth Session, Supplement No. 46 (A/55/46).
The designation 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 the data 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.00.IX.4
ISBN 92-1-142239-6

ANNEX J
Exposures and effects of the Chernobyl accident

CONTENTSPage

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

453

I.

PHYSICAL CONSEQUENCES OF THE ACCIDENT . . . . . . . . . . . . . . . . . . .
A. THE ACCIDENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B. RELEASE OF RADIONUCLIDES . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1. Estimation of radionuclide amounts released . . . . . . . . . . . . . . . . . .
2. Physical and chemical properties of theradioactive materials released . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C. GROUND CONTAMINATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1. Areas of the former Soviet Union . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. Remainder of northern and southern hemisphere . . . . . . . . . . . . . . .
D. ENVIRONMENTAL BEHAVIOUR OF
DEPOSITED RADIONUCLIDES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1. Terrestrial environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. Aquatic environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
E. SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

454
454
456
456

RADIATION DOSES TO EXPOSED POPULATION GROUPS . . . . . . . . . . .
A. WORKERS INVOLVED IN THE ACCIDENT . . . . . . . . . . . . . . . . . . . .
1. Emergency workers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. Recovery operation workers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B. EVACUATED PERSONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1. Doses from external exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. Doses from internal exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3. Residual and averted collective doses . . . . . . . . . . . . . . . . . . . . . . . .
C. INHABITANTS OF CONTAMINATED AREAS
OF THE FORMER SOVIET UNION . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1. Doses from external exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. Doses from internal exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
D. INHABITANTS OF DISTANT COUNTRIES . . . . . . . . . . . . . . . . . . . . .
1. Thyroid doses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. Bone-marrow doses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
E. COLLECTIVE DOSES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1. Collective doses from external exposure . . . . . . . . . . . . . . . . . . . . . .
2. Collective doses from internal exposure . . . . . . . . . . . . . . . . . . . . . .
3. Total collective doses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
F. SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

467
468
468
469
472
473
474
474

II.

457
458
458
465
465
465
466
466

475
476
479
485
486
486
486
486
486
486
487

452

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT
Page

III. EARLY HEALTH EFFECTS IN REACTOR AND EMERGENCY WORKERS 488
IV. REGISTRATION AND HEALTH MONITORING PROGRAMMES . . . . . . . .
A. REGISTRATION AND MONITORING
OF EXPOSED POPULATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1. The Chernobyl registries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. Specialized registries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B. REGISTRATION OF MORTALITY AND DISEASE
IN THE GENERAL POPULATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1. Mortality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. Cancer incidence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3. Specialized cancer registries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C. QUALITY AND COMPLETENESS OF REGISTRATION . . . . . . . . . . .
1. Registers of exposed populations . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. Registers of the general population . . . . . . . . . . . . . . . . . . . . . . . . .
D. INTERNATIONAL COLLABORATIVE SCREENING PROJECTS . . . .
1. The International Chernobyl Project . . . . . . . . . . . . . . . . . . . . . . . .
2. The IPHECA project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3. The Chernobyl Sasakawa Health and Medical Cooperation Project .
E. SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
V.

LATE HEALTH EFFECTS OF THE CHERNOBYL ACCIDENT . . . . . . . . . .
A. CANCER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1. Thyroid cancer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. Leukaemia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3. Other solid tumours . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B. OTHER SOMATIC DISORDERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1. Thyroid abnormalities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. Somatic disorders other than thyroid . . . . . . . . . . . . . . . . . . . . . . . .
3. Immunological effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C. PREGNANCY OUTCOME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
D. PSYCHOLOGICAL AND OTHER ACCIDENT-RELATED EFFECTS . .
E. SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

490
490
490
491
491
491
492
492
493
493
494
495
495
495
495
496
497
497
497
504
507
508
508
510
511
512
513
514

CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 515

Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 518
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

453

INTRODUCTION
1. The accident of 26 April 1986 at the Chernobyl
nuclear power plant, located in Ukraine about 20 km southof the border with Belarus, was the most severe ever tohave occurred in the nuclear industry. The Committee
considered the initial radiological consequences of that
accident in the UNSCEAR 1988 Report [U4]. The shortterm effects and treatment of radiation injuries of workers
and firefighters who were present at the site at the time of
the accident were reviewed in the Appendix to Annex G,“Early effects in man of high doses of radiation”, and theaverage individual and collective doses to the population of
the northern hemisphere were evaluated in Annex D,“Exposures from the Chernobyl accident”, of the 1988
Report [U4]. The objective of this Annex is (a) to review ingreater detail the exposures of those most closely involvedin the accident and the residents of the local areas mostaffected by the residual contamination and (b) to consider
the health consequences that are or could be associatedwith these radiation exposures.
2. The impact of the accident on the workers and local
residents has indeed been both serious and enormous. The
accident caused the deaths within a few days or weeks of
30 power plant employees and firemen (including 28
deaths that were due to radiation exposure), brought about
the evacuation of about 116,000 people from areas surrounding the reactor during 1986, and the relocation, after
1986, of about 220,000 people from what were at that time
three constituent republics of the Soviet Union: Belorussia,
the Russian Soviet Federated Socialist Republic (RSFSR)
and the Ukraine [K23, R11, V2, V3] (these republics will
hereinafter be called by their present-day country names:
Belarus, the Russian Federation and Ukraine). Vastterritories of those three republics were contaminated, andtrace deposition of released radionuclides was measurable
in all countries of the northern hemisphere. Stratosphericinterhemispheric transfer may also have led to someenvironmental contamination in the southern hemisphere[D11]. In addition, about 240,000 workers (“liquidators”)
were called upon in 1986 and 1987 to take part in major
mitigation activities at the reactor and within the 30-km
zone surrounding the reactor; residual mitigation activities
continued until 1990. All together, about 600,000 persons
received the special status of “liquidator”.
3. The radiation exposures resulting from the Chernobyl
accident were due initially to 131I and short-lived radionuclides and subsequently to radiocaesiums (134Cs and
137Cs) from both external exposure and the consumption offoods contaminated with these radionuclides. It wasestimated in the UNSCEAR 1988 Report [U4] that, outside
the regions of Belarus, the Russian Federation and Ukrainethat were most affected by the accident, thyroid doses
averaged over large portions of European countries were at
most 25 mGy for one-year old infants. It was recognized,
however, that the dose distribution was veryheterogeneous,especially in countries close to the reactor site. For
example, in Poland, although the countrywide populationweighted average thyroid dose was estimated to beapproximately 8 mGy, the mean thyroid doses for the
populations of particular districts were in the range from
0.2 to 64 mGy, and individual values for about 5% of thechildren were about 200 mGy [K32, K33]. It was also
estimated in the UNSCEAR 1988 Report [U4] that
effective doses averaged over large portions of European
countries were 1 mSv or less in the first year after theaccident and approximately two to five times the first-yeardose over a lifetime.
4.
The doses to population groups in Belarus, theRussian Federation and Ukraine living nearest the accidentsite and to the workers involved in mitigating the accident
are, however, of particular interest, because these people
have had the highest exposures and have been monitored
for health effects that might be related to the radiation
exposures. Research on possible health effects is focussed
on, but not limited to, the investigation of leukaemia
among workers involved in the accident and of thyroid
cancer among children. Other health effects that areconsidered are non-cancer somatic disorders (e.g. thyroid
abnormalities and immunological effects), reproductive
effects and psychological effects. Epidemiological studies
have been undertaken among the populations of Belarus,
the Russian Federation and Ukraine that were mostaffected by the accident to investigate whether dose-effectrelationships can be obtained, notably with respect to the
induction of thyroid cancer resulting from internal
irradiation by 131I and other radioiodines in young children
and to the induction of leukaemia among workers resulting
from external irradiation at low dose rates. The dose
estimates that are currently available are of a preliminary
nature and must be refined by means of difficult and timeconsuming dose reconstruction efforts. The accumulationof health statistics will also require some years of effort.
5.
Because of the questions that have arisen about the
local exposures and effects of the Chernobyl accident, theCommittee feels that a review of information at this stage,
almost 15 years after the accident, is warranted. Of course,
even longer-term studies will be needed to determine thefull consequences of the accident. It is the intention toevaluate in this Annex the data thus far collected on thelocal doses and effects in relation to and as a contribution
to the broader knowledge of radiation effects in humans.
Within the last few years, several international conferenceswere held to review the aftermath of the accident, andextensive use can be made of the proceedings of these
conferences [E3, I15, T22, W7]; also, use was made ofbooks, e.g. [I5, K19, M14, M15], and of special issues ofscientific journals, e.g. [K42], devoted to the Chernobyl
accident.

454

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

6. The populations considered in this Annex are (a) the
workers involved in the mitigation of the accident, either
during the accident itself (including firemen and power
plant personnel who received doses leading to deterministic effects) or after the accident (recovery operation
workers); (b) members of the general public who were
evacuated to avert excessive radiation exposures; and (c)inhabitants of contaminated areas who were not evacuated.

The contaminated areas, which are defined in this Annex
as being those where the average 137Cs ground deposition
density exceeded 37 kBq m2 (1 Ci km2), are found mainly
in Belarus, in the Russian Federation and in Ukraine.
Information on the contamination levels and radiation
doses in other countries will be presented only if it isrelated to epidemiological studies conducted in thosecountries.

I. PHYSICAL CONSEQUENCES OF THE ACCIDENT
7. The accident at the Chernobyl nuclear power station
occurred during a low-power engineering test of the Unit
4 reactor. Safety systems had been switched off, andimproper, 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. An accountof the accident and of the quantities of radionuclides
released, to the extent that they could be known at the time,
were presented by Soviet experts at the Post-Accident
Review Meeting at Vienna in August 1986 [I2]. The
information that has become available since 1986 will besummarized in this Chapter.
8. The radionuclide releases from the damaged reactor
occurred mainly over a 10-day period, but with varying
release rates. An initial high release rate on the first day
was caused by mechanical discharge as a result of the
explosions in the reactor. There followed a five-day period
of declining releases associated with the hot air and fumes
from the burning graphite core material. In the next few
days, the release rate of radionuclides increased until day
10, when the releases dropped abruptly, thus ending theperiod of intense release. The radionuclides released in theaccident deposited with greatest density in the regions
surrounding the reactor in the European part of the former
Soviet Union.

accident with unexpected and unknown events andoutcomes, many questions remain to be satisfactorily
resolved.
10. The events leading to the accident at the Chernobyl
Unit 4 reactor at about 1.24 a.m. on 26 April 1986 resulted
from efforts to conduct a test on an electric control system,
which allows power to be provided in the event of a station
blackout [I2]. Actions taken during this exercise resulted
in a significant variation in the temperature and flow rateof the inlet water to the reactor core (beginning at about
1.03 a.m.). The unstable state of the reactor before theaccident is due both to basic engineering deficiencies (large
positive coefficient of reactivity under certain conditions)and to faulty actions of the operators (e.g., switching off
the emergency safety systems of the reactor) [G26]. The
relatively fast temperature changes resulting from theoperators’ actions weakened the lower transition joints thatlink the zirconium fuel channels in the core to the steel
pipes that carry the inlet cooling water [P4]. Other actions
resulted in a rapid increase in the power level of the reactor[I7], which caused fuel fragmentation and the rapidtransfer of heat from these fuel fragments to the coolant(between 1.23:43 and 1.23:49 a.m.). This generated ashock wave in the cooling water, which led to the failure ofmost of the lower transition joints. As a result of the failureof these transition joints, the pressurized cooling water inthe primary system was released, and it immediately
flashed into steam.

A. THE ACCIDENT
9. The Chernobyl reactor is of the type RBMK, which
is an abbreviation of Russian terms meaning reactor ofhigh output, multichannel type. It is a pressurized water
reactor using light water as a coolant and graphite as amoderator. Detailed information about what is currently
known about the accident and the accident sequence has
been reported, notably in 1992 by the International Atomic
Energy Agency (IAEA) [I7], in 1994 in a report of the
Massachusetts Institute of Technology [S1], in 1995 by the
Ukrainian Academy of Sciences [P4], and in 19911996 by
the Kurchatov Institute [B24, C5, K20, K21, S22, V4]. A
simplified description of the events leading to the accident
and of the measures taken to control its consequences isprovided in the following paragraphs. As is the case in an

11. The steam explosion occurred at 1.23:49. It issurmised that the reactor core might have been lifted up by
the explosion [P4], during which time all water left thereactor core. This resulted in an extremely rapid increase
in reactivity, which led to vaporization of part of the fuelat the centre of some fuel assemblies and which wasterminated by a large explosion attributable to rapid
expansion of the fuel vapour disassembling the core. This
explosion, which occurred at about 1.24 a.m., blew the core
apart and destroyed most of the building. Fuel, corecomponents, and structural items were blown from thereactor hall onto the roof of adjacent buildings and theground around the reactor building. A major release ofradioactive materials into the environment also occurred asa result of this explosion.

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

12. The core debris dispersed by the explosion started
multiple (more than 30) fires on the roofs of the reactor
building and the machine hall, which were covered withhighly flammable tar. Some of those fires spread to themachine hall and, through cable tubes, to the vicinity of theUnit 3 reactor. A first group of 14 firemen arrived on thescene of the accident at 1.28 a.m. Reinforcements werebrought in until about 4 a.m., when 250 firemen wereavailable and 69 firemen participated in fire control activities.
These activities were carried out at up to 70 m above theground under harsh conditions of high radiation levels anddense smoke. By 2.10 a.m., the largest fires on the roof of themachine hall had been put out, while by 2.30 a.m. the largest
fires on the roof of the reactor hall were under control. By
about 4.50 a.m., most of the fires had been extinguished.
These actions caused the deaths of five firefighters.
13. It is unclear whether fires were originating from thereactor cavity during the first 20 h after the explosion.
However, there was considerable steam and water because of
the actions of both the firefighters and the reactor plant
personnel. Approximately 20 h after the explosion, at 9.41
p.m., a large fire started as the material in the reactor became
hot enough to ignite combustible gases released from thedisrupted core, e.g. hydrogen from zirconium-water reactions
and carbon monoxide from the reaction of hot graphite withsteam. The fire made noise when it started (some witnesses
called it an explosion) and burned with a large flame that
initially reached at least 50 m above the top of the destroyed
reactor hall [P4].
14. The first measures taken to control the fire and theradionuclide releases consisted ofdumping neutron-absorbing
compounds and fire-control materials into the crater formed
bythe destruction of the reactor. The total amount of materials
dumped on the reactor was approximately 5,000 t, including
about 40 t of boron compounds, 2,400 t of lead, 1,800 t ofsand and clay, and 600 t of dolomite, as well as sodium
phosphate and polymer liquids [B4]. About 150 t of materials
were dumped on 27 April, followed by 300 t on 28 April,
750 t on 29 April, 1,500 t on 30 April, 1,900 t on 1 May, and
400 t on 2 May. About 1,800 helicopter flights were carriedout to dump materials onto the reactor. During the first flights,
the helicopters remained stationary over the reactor while
dumping the materials. However, as the dose rates received by
the helicopter pilots during this procedure were judged to be
too high, it was decided that the materials should be dumped
while the helicopters travelled over the reactor. This
procedure, which had a poor accuracy, caused additional
destruction of the standing structures and spread thecontamination. In fact, much of the material delivered by thehelicopters was dumped on the roof of the reactor hall, wherea glowing fire was observed, because the reactor core waspartially obstructed by the upper biological shield, broken
piping, and other debris, and rising smoke made it difficult tosee and identify the core location (see Figure I). The material
dumping campaign was stopped on day 7 (2 May) throughday 10 (5 May) after the accident because of fears that thebuilding support structures could be compromised. If that
happened, it would allow the core to be less restrained from455

possible meltdown, and steam explosions would occur if thecore were to interact with the pressure suppression poolbeneath the reactor. The increasing release rates on days 7
through 10 were associated with the rising temperature of thefuel in the core. Cooling of the reactor structure with liquid
nitrogen using pipelines originating from Unit 3 was initiatedonly at late stages after the accident. The abrupt ending of thereleases was said to occur upon extinguishing the fire andthrough transformation of the fission products into morechemically stable compounds [I2].

Reactor coverCore region(empty)Materials dropped
from helicopter

Spent
fuel
pool

Location offuel "lava"

69 m

Figure I. Cross-section view of damaged Unit 4
Chernobyl reactor building.

15. The further sequence of events is still somewhat
speculative, but the following description conforms with theobservations of residual damage to the reactor [S1, S18]. It issuggested that the melted core materials (also called fuelcontaining masses, corium, or lava) settled to the bottom of
the core shaft, with the fuel forming a metallic layer below thegraphite. The graphite layer had a filtering effect on therelease of volatile compounds. This is evidenced by a concentration of caesium in the corium of 35% [S1], somewhat
higher than would otherwise have been expected in the highly
oxidizing conditions that prevailed in the presence of burning
graphite. The very high temperatures in the core shaft would
have suppressed plate-out of radionuclides and maintained
high release rates of penetrating gases and aerosols. Afterabout 6.5 days, the upper graphite layer would have burned
off. This is evidenced by the absence of carbon or carboncontaining compounds in the corium. At this stage, without
the filtering effect of an upper graphite layer, the release ofvolatile fission products from the fuel may have increased,

456

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

although non-volatile fission products and actinides would
have been inhibited because of reduced particulate emission.
16. On day 8 after the accident, it would appear that the
corium melted through the lower biological shield (LBS)and flowed onto the floor of the sub-reactor region (seeFigure I). This rapid redistribution of the corium andincrease in surface area as it spread horizontally would
have enhanced the radionuclide releases. The corium
produced steam on contact with the water remaining in thepressure suppression pool, causing an increase in aerosols.
This may account for the peak releases of radionuclides
seen at the last stage of the active period.
17. Approximately nine days after the accident, thecorium began to lose its ability to interact with thesurrounding materials. It solidified relatively rapidly,
causing little damage to metallic piping in the lower
regions of the reactor building. The chemistry of thecorium was altered by the large mass of the lower
biological shield taken up into the molten corium (about
400 of the 1,200-t shield of stainless steel construction andserpentine filler material). The decayheat was significantly
lowered, and the radionuclide releases dropped by two to
three orders of magnitude. Visual evidence of thedisposition of the corium supports this sequence of events.
18. On the basis of an extensive series of measurements
in 19871990 of heat flux and radiation intensities andfrom an analysis of photographs, an approximate massbalance of the reactor fuel distribution was established(data reported by Borovoi and Sich [B16, S1]). The amountof fuel in the lower regions of the reactor building wasestimated to be 135 ± 27 t, which is 71% of the core loadat the time of the accident (190.3 t). The remainder of thefuel was accounted for as follows: fuel in the upper levelsof the reactor building (38 ± 5 t); fuel released beyond thereactor building (6.7 ± 1 t); and unaccounted for fuel(10.7 t), possibly largely on the roof of the reactor hall
under the pile of materials dumped by the helicopters.
19. Different estimates of the reactor fuel distribution havebeen proposed byothers. Purvis [P4] indicated that the amountof fuel in the lava, plus fragments of the reactor core under thelevel of the bottom of the reactor, is between 27 and 100 t andthat the total amount of the fuel in the reactor hall area isbetween 77 and 140 t. Kisselev et al. [K12, K15] reported that
only 24 ± 4 t were identified by visual means in the lower
region of the reactor. It may be that most of the fuel is on theroof of the reactor hall and is covered by the material that was
dropped on it from helicopters. Only the removal of this layerof material will allow making a better determination of thereactor fuel distribution.

B. RELEASE OF RADIONUCLIDES
20. Two basic methods were used to estimate the releaseof radionuclides in the accident. The first method consistsin evaluating separately the inventory of radionuclides in

the reactor core at the time of the accident and the fractionof the inventory of each radionuclide that was released into
the atmosphere; the products of those two quantities are theamounts released. The second method consists inmeasuring the radionuclide deposition density on the
ground all around the reactor; if it is assumed that all of
the released amounts deposited within the area where themeasurements were made, the amounts deposited are equal
to the amounts released. In both methods, air samples
taken over the reactor or at various distances from thereactor were analysed for radionuclide content to determineor to confirm the radionuclide distribution in the materials
released. The analysis of air samples and of fallout also led
to information on the physical and chemical properties of
the radioactive materials that were released into theatmosphere. It is worth noting, however, that the doses
were estimated on the basis of environmental and humanmeasurements and that the knowledge of the quantities
released was not needed for that purpose.
1. Estimation of radionuclide amounts
released
21. From the radiological point of view, 131I and 137Cs are
the most important radionuclides to consider, because they
are responsible for most of the radiation exposure received
by the general population.
22. Several estimates have been made of the radionuclide
core inventory at the time of the accident. Some of theseestimates are based on the burn-up of individual fuelassemblies that has been made available [B1, S1]. The
average burn-up of 10.9 GW d t1 [B1], published in 1989,
is similar to the originally reported value of 10.3 GW d t1[I2], but with non-linear accumulation of actinides, moredetailed values of burn-up allow more precise estimation of
the core inventories. In the case of 132Te and of the shortlived radioiodines, Khrouch et al. [K16] took into accountthe variations in the power level of the reactor during the
24 hours before the accident, as described in [S20]. An
extended list of radionuclides present in the core at thetime of the accident is presented in Table 1. The values
used by the Committee in this Annex are those presented
in the last column on the right. For comparison purposes,
the initial estimates of the core inventory as presented in1986 [I2], which were used by the Committee in the
UNSCEAR 1988 Report [U4], are also presented inTable 1; these 1986 estimates, however, have been decaycorrected to 6 May 1986, that is, 10 days after the
beginning of the accident. The large differences observed
between initial and recent estimates for short-lived
radionuclides (radioactive half-lives of less than 10 days)
are mainly due to radioactive decay between the actual dayof release and 6 May, while minor differences may havebeen caused by the use of different computer codes tocalculate the build-up of activity in the reactor core. For
137
Cs, the 1986 and current estimates of core inventory at
the time of the accident are 290 and 260 PBq, respectively.
For 131I, the corresponding values are 1,300 and 3,200 PBq,
respectively.

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

this Annex, are illustrated in Figure II; for comparison
purposes, the estimated daily releases of 137Cs are also
shown in Figure II.
10 3

131

DAILY RELEASE (PBq)

23. There are several estimates of radionuclides releasedin the accident based on recent evaluations. Three suchlistings, including two taken from the IAEA international
conference that took place at Vienna in 1996 [D8], aregiven in Table 2 and compared to the original estimates of1986 [I2]. The estimates of Buzulukov and Dobrynin [B4],as well as those of Kruger et al. [K37], are based on
analyses of core inventories [B1, B3]. There is generalagreement on the releases of most radionuclides, and inparticular those of 137Cs and 131I, presented in the 1996
evaluations. The values used by the Committee in thisAnnex are those presented in the last column on the right.
The release of 137Cs is estimated to be 85 PBq, about 30%of the core inventory and that of 131I is estimated to be
1,760 PBq, about 50% of the core inventory.

457

I

10 2
132

Te

137Cs

10 1

10 0
133

I

24. In the UNSCEAR 1988 Report [U4], estimates weremade of the release of 137Cs and 131I in the accident. Fromaverage deposition densities of 137Cs and the areas of landand ocean regions, the total 137Cs deposit in the northernhemisphere was estimated to be 70 PBq, which is in fairly
good agreement with the current estimate.
25. The release of 131I was estimated in the UNSCEAR
1988 Report to be 330 PBq on the basis of the reported 131I
inventory of 1,300 PBq [I2] and of a release fraction of
25% [U4]. This, however, was the inventory of 131I at theend of the release period (6 May 1986). It would have been
higher at the beginning of the accident. The 131I inventory
is now estimated to be 3,200 PBq, as shown in Table 1, andbecause the fractional release of 131I is likely to have been
about 50%, the 131I release given in the UNSCEAR 1988
Report is lower than the current estimate by a factor of
about 5.
26. The results presented in Table 2 are incomplete withrespect to the releases of 132Te and of the short-lived
radioiodines (132I to 135I). In this Annex, the releases of
those radionuclides have been scaled to the releases of 131I,
using the radionuclide inventories presented in Table 1 andtaking into account the radioactive half-lives of theradionuclides. The following procedure was used: (a) the
release rates at the time of the steam explosion were
estimated from the radionuclide inventories presented inTable 1, assuming no fractionation for the short-lived
radioiodines (133I, 134I and 135I) with respect to 131I, a valueof 0.85 for the ratio of the release rates of 132Te and of 131I,
and radioactive equilibrium between 132I and 132Te in thematerials released. The activity ratios to 131I in the initial
release rates are therefore estimated to have been 1.5 for
133
I, 0.64 for 134I, 0.9 for 135I, and 0.85 for 132Te and 132I; (b)the variation with time of the release rate of 131I over the
first 10 days following the steam explosion was assessedusing published data [A4, I6]. The estimated daily releasesof 131I are presented in Table 3; and (c) the variation withtime of the release rates of the short-lived radioiodines andof 132Te has been assumed to be the same as that of 131I, but
a correction was made to take into account the differencesin radioactive half-lives. The variation with time of thedaily releases of 131I, 133I and 132Te, which are adopted in

10-1
26 April 27 April 28 April 29 April 30 April 1 May 2 May 3 May 4 May 5 May

DATE

Figure II. Daily release of iodine-131, iodine-133, tellurium132 and caesium-137 from the Chernobyl reactor.

27. The overall releases of short-lived radioiodines andof 132Te are presented in Table 4; they are found to be
substantially lower than those of 131I. This is due to the factthat most of the short-lived radioiodines decayed in thereactor instead of being released.
28. Additional, qualitative information on the pattern of
release of radionuclides from the reactor is given in
Figure III. The concentrations of radionuclides in air were
determined in air samples collected by helicopter above thedamaged reactor [B4]. Although the releases wereconsiderably reduced on 5 and 6 May (days 9 and 10 after
the accident), continuing low-level releases occurred in thefollowing week and for up to 40 days after the accident.
Particularly on 15 and 16 May, higher concentrations wereobserved, attributable to continuing outbreaks of fires or to
hot areas of the reactor [I6]. These later releases can becorrelated with increased concentrations of radionuclides
in air measured at Kiev and Vilnius [I6, I35, U16].
2. Physical and chemical properties of theradioactive materials released
29. There were only a few measurements of the aerodynamic size of the radioactive particles released during thefirst days of the accident. A crude analysis of air samples,taken at 400600 m above the ground in the vicinity of theChernobyl power plant on 27 April 1986, indicated that large
radioactive particles, varying in size from several to tens of
micrometers, were found, together with an abundance ofsmaller particles [I6]. In a carefully designed experiment,
aerosol samples taken on 14 and 16 May 1986 with a device
installed on an aircraft that flew above the damaged reactor
were analysed by spectrometry [B6, G14]. The activity
distribution of the particle sizes was found to be well
represented as the superposition of two log-normal functions:

458

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

CONCENTRATION (kBq m-3)

35

95Zr
131I

30
25
20
15
10
5
0
1 2 3 4 5 6 7 8

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
TIME AFTER ACCIDENT (days)

Figure III. Concentration of radionuclides in air measured above the damaged Chernobyl reactor [B6].

one with an activity median aerodynamic diameter (AMAD)
ranging from 0.3 to 1.5 µm and a geometric standard
deviation (GSD) of 1.61.8, and another with an AMAD of
more than 10 µm. The larger particles contained about
80%90% of the activityof non-volatile radionuclides such as
95
Zr, 95Nb, 140La, 141Ce, 144Ce and transuranium radionuclides
embedded in the uranium matrix of the fuel [K35]. The
geometric sizes of the fuel particles collected in Hungary,Finland and Bulgaria ranged from 0.5 to 10 µm, with anaverage of 5 µm [B35, L40, V9]. Taking the density of fuelparticles to be 9 g cm3, their aerodynamic diameter therefore
ranged from 1.5 to 30 µm, with an average value of 15 µm.
Similar average values were obtained for fuel particles
collected in May 1986 in southern Germany [R20] and for
those collected in the 30-km zone in September 1986 [G27].
30. It was observed that Chernobyl fallout consisted of hot
particles in addition to more homogeneouslydistributed radioactive material [D6, D7, K34, S26, S27, S28]. These hotparticles can be classified into two broad categories: (a) fuelfragments with a mixture of fission products bound to amatrix of uranium oxide, similar to the composition of the fuelin the core, but sometimes strongly depleted in caesium,
iodine and ruthenium, and (b) particles consisting of one
dominant element (ruthenium or barium) but sometimes
having traces of other elements [D6, J3, J4, K35, K36, S27].
These monoelemental particles may have originated fromembedments of these elements produced in the fuel during
reactor operation and released during the fragmentation of thefuel [D7]. Typical activities per hot particle are 0.11 kBq for
fuel fragments and 0.510 kBq for ruthenium particles [D6];a typical effective diameter is about 10 µm, to be comparedwith sizes of 0.40.7 µm for the particles associated with theactivities of 131I and 137Cs [D6, D7]. Hot particles deposited in
the pulmonary region will have a long retention time, leading
to considerable local doses [B33, L23]. In the immediate
vicinity of a 1 kBq ruthenium particle, the dose rate is about
1,000 Gy h1, which causes cell killing; however, sublethal
doses are received by cells within a few millimetres of the hotparticle. Although it was demonstrated in the 1970s thatradiation doses from alpha-emitting hot particles are not moreradiotoxic than the same activity uniformly distributed in thewhole lung [B28, L33, L34, L35, R15], it is not clear whether
the same conclusion can be reached for beta-emitting hot
particles [B33, S27].

C. GROUND CONTAMINATION
1. Areas of the former Soviet Union
31. Radioactive contamination of the ground was found tosome extent in practically every country of the northernhemisphere [U4]. In this Annex, contaminated areas aredefined as areas where the average 137Cs deposition densities
exceeded 37 kBq m2 (1 Ci km2). 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 longradioactive half-life, and its ease of measurement. As shownin Table 5, the contaminated areas were found mainly in
Belarus, in the Russian Federation and in Ukraine [I24].
32. The radionuclides released in the accident depositedover most of the European territory of the former Soviet
Union. A map of this territory is presented in Figure IV.
The main city gives its name to each region. The regions(oblasts) are subdivided into districts (raions).
33. The characteristics of the basic plume developments
were illustrated in the UNSCEAR 1988 Report [U4]. Further
details have been presented by Borzilov and Klepikova [B7]and are illustrated in Figure V. The important releases lasted
10 days; during that time, the wind changed direction often,
so that all areas surrounding the reactor site received somefallout at one time or another.
34. The initial plumes of materials released from the
Chernobyl reactor moved towards the west. On 27 April, thewinds shifted towards the northwest, then on 28 April towards the east. Two extensive areas, Gomel-Mogilev-Bryansk
and Orel-Tula-Kaluga, became contaminated as a result of

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

459

LATVIA
LITHUANIAMOSCOW

RUSSIANFED.
VILNIUS
Smolensk

POLAND

Kaluga

MINSK

Tula

MogilevB E L A R U S

BryanskWARSAW

Orel

Brest
Gomel

LublinR U S S I A N
F E D E R A T I O N

Chernigov

Chernobyl
Rovno

Sumy
Zhitomir

Lvov

KIEV
Kharkov

KIA
VA
O
SL

Vinnitsa
Cherkassy

Y
GAR
HUN R O M A N I A

U K R A I N E

Chernovtsy

REP. OFMOLDAVIA

Kirovograd
0

50

100

150

200

250

300 kmFigure IV. Administrative regions surrounding the Chernobyl reactor.

LATVIA
LITHUANIARUSSIANFED.

1

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

VILNIUS
Smolensk

POLAND

KalugaMINSK

1MogilevTula

B E L A R U S

BryanskWARSAW
Brest

3

Gomel

2
LublinSumy
Zhitomir

Lvov

Chernovtsy

4

KIEV

VinnitsaY
GAR
HUN R O M A N I A

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

Chernigov

Chernobyl
Rovno

KIA
VA
SLO

Orel

6
REP. OFMOLDAVIA

Kharkov

5
Cherkassy

U K R A I N E
Kirovograd
0

50

100

150

200

250

300 kmFigure V. Plume formation by meteorological conditions for instantaneous releases
on dates and times (GMT) indicated [B7].

deposition of radioactive materials from the plume that passed
over at that time (Figure V, trace 3). The contamination of
Ukrainian territorysouth of Chernobyl occurred after 28 April(Figure V, traces 4, 5 and 6). Rainfall occurred in an

inhomogeneous pattern, causing uneven contamination areas.
The general pattern of 137Cs deposition based on calculations
from meteorological conditions has been shown to match themeasured contamination pattern rather well [B7].

r-BuTernopol

ROVNO

Pinsk

g ski C anal

PripyatDn
ep

E

Baranovichi

B

Novogrudok

Lida

od

kh

St o

r

St y

’

Goryn

VILNIUSL

Khmelnitskiy

Mozyr

Narodichi

epr

CHERKASSY

Dn

U

K

Novozybkov

U

R

A

I

E

185-555 kBq m-237-185 kBq m-2

555-1480 kBq m<37 kBq m

Yelets-2

Kimovsk

Novomoskovsk

Efremov

BELGORODKHARKOV-2-2

Plavsk

TULA

Aleksin

Mtsensk

OREL

KURSK

Bolkhov

KALUGA

1480-3700 kBq m

N

SUMY

POLTAVA

ShostkaA
Lyudinovo

Kirov

I

Dyatlovo

S

BRYANSK

RoslavlS

SMOLENSK

Krichev

CHERNIGOV
Slavutich

Belaya Tserkov

Roska

CherikovR

pr

Figure VI. Surface ground deposition of caesium-137 released in the Chernobyl accident [I1, I3].

VINNITSA

Berdichev

KIEV

Chernobyl

ZHITOMIR

Korosten

PripyatPolesskoje

BraginKhoynikie
Dn

MOGILEV

Gorki

GOMEL

ORSHA

Bykhov

Bobruysk

NarovlyaS

Borisov

OvruchPripyatU

Novograd Volynskiy

SarnySlutskR

MINSKSoligorsk

A

Molodechno

ev
er
Te
t

na
Des

Desna

460
ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

Mikhalki

Loev

Khoynikinepr

BELARUSD

Mikulichi

Radul

Narovlya

Yelsk

461

BraginDobryny
Malozhin
Chemerisy

DronykiDernovichi

LyubechSavichi

Vystupovichi
Dovlyady

KirovoZhelonPirki
SlavutichPr
Denisovichi
ip
y a Zimovishche
Novo ShepelichitPripyatKomarinNov. Radcha
ep

KovpytaDn

Ilyincyr

Gdeny
Polesskoye

Chernobyl

Narodichi

Volchkov
Bazar
Skuraty

Nedashki

Krasilovka

Stracholese
Gornostaypol

Termakhovka

UKRAINE

Kiev

Reservoir

Bogdany

Ivankov

Varovskt
TeMorovsk

er

Oster

ev

Kukhari<37 kBq m-2

37-185 kBq m-2

185-555 kBq m-2

555-1480 kBq m-2

1480-3700 kBq m-2> 3700 kBq m-2

Figure VII. Surface ground deposition of caesium-137 in the immediate vicinity of the Chernobyl reactor [I1, I24].
The distances of 30 km and 60 km from the nuclear power plant are indicated.

35. The detailed contamination patterns have been
established from extensive monitoring of the affected
territory. The contamination of soil with 137Cs in the mostaffected areas of Belarus, the Russian Federation and Ukraine
is shown in Figure VI, and the 137Cs contamination of soil in
the immediate area surrounding the reactor is shown in
Figure VII. The deposition of 90Sr and of nuclear fuelparticles, usuallyrepresented as the deposition oftheir marker,
95
Zr or 144Ce, were relatively localized. The contamination
maps for these radionuclides are illustrated in Figures VIII
and IX. An important deposition map to be established is thatof 131I. Estimated 131I deposition in Belarus and the westernpart of the Russian Federation is shown in Figure X. Because
there were not enough measurements at the time ofdeposition, the 131I deposition pattern can be only
approximated from limited data and relationships inferredfrom 137Cs deposition. Because the 131I to 137Cs ratio was
observed to vary from 5 to 60, the 131I deposition densities
estimated for areas without 131I measurements are not very
reliable. Measurements of the current concentrations of 129I in
soil could provide valuable information on the 131I deposition
pattern [S45].
36. The principal physico-chemical form of the depositedradionuclides are: (a) dispersed fuel particles, (b) condensation-generated particles, and (c) mixed-type particles, including the adsorption-generated ones [I22]. The radionuclide

distribution in the nearby contaminated zone (<100 km), also
called the near zone, differs 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, and therefractory elements (Zr, Mo, Ce and Np) were to a large
extent deposited in the near zone. Intermediate elements (Ru,Ba, Sr) and fuel elements (Pu, U) were also deposited largelyin the near zone. The volatile elements (I, Te and Cs) in theform of condensation-generated particles, were more widelydispersed into the far zone [I6]. Of course, thischaracterization oversimplifies the actual dispersion pattern.
37. Areas of high contamination from 137Cs occurred
throughout the far zone, depending primarilyon rainfall at thetime the plume passed over. The composition of the depositedradionuclides in these highly contaminated areas was
relatively similar. Some ratios of radionuclides in different
districts of the near and far zones are given in Table 6.
38. The three main areas of contamination have been
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 thereactor. Caesium-137 was deposited during the active
period of release, and the deposition density of 137Cs was
greater than 37 kBq m2 (1 Ci km2) in large areas of theANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT
Rogachev
Sidorovichi
Chechersk
Zabolotje
Svetilovichi

Chernin

r ez

i na

Vetka

BELARUS

GOMEL
Dn
e pr

Rechitsa

Dobrushh

Svetlogorsk

S oz

Be

Vasilevichi

Terekhovka

Kalinkovichi
Mozyr
Pr
ip
ya
t

Loev

Khoyniki
Mikulichi

Dobryny
Narovlya

MalozhinDronykiChemerisy

Dernovichi

Polesskoye

Chernobyl

Kraslikovka
Varovsk

Stracholese

UKRAINE

IvanovkaPrna

Kovpytaeerv

Bogdanyy a Yurovichit

Borscevka

Khoyniki>111 kBq m-2
74-111 kBq m-2
Oster

ip

Mikhalki

KrasnojeMorovsk

TermakhovkatTeSlavutich

Des

Gdeny

Nov. Radcha
Ilyincy

CHERNIGOV

Pirki

Denisovichi
Zimovisce
Novo Shepelichi
Komarin
Pripyat

Bazar

LyubechSavichi
Dovlyady

KirovoRepki

Bragin-237-74 kBq m

Mikulichi

BELARUS

Narovlya

BraginMalozhin
Chemerisy

Dobryny
Slovecna

Dronykir

Zhlobin

41. Outside these three main contaminated areas there weremanyareas where the 137Cs deposition densitywas in the range
37200 kBq m2. Rather detailed surveys of the contamination of the entire European part of the former Soviet Union
have been completed [I3, I6, I24]. A map of measured 137Cs
deposition is presented in Figure VI. The areas affected by137
Cs contamination are listed in Table 7. As can be seen,
146,100 km2 experienced a 137Cs deposition density greaterthan 37 kBq m2 (1 Ci km2). The total quantity of 137Cs
deposited as a result of the accident in the contaminated areasof the former Soviet Union, including in areas of lesser
deposition, is estimated in Table 8 to be 43 PBq. A 137Cs
background of 24 kBq m2 attributable toresidual levels fromatmospheric nuclear weapons testing from earlier years mustbe subtracted to obtain the total deposit attributable to theChernobyl accident. When this is done, the total 137Cs deposit
from the accident is found to be approximately 40 PBq(Table 8). The total may be apportioned as follows: 40% in
Belarus, 35% in the Russian Federation, 24% in Ukraine, andless than 1% in other republics of the former Soviet Union.
The amount of 137Cs deposited in the contaminated areas (>37
kBq m2) of the former Soviet Union is estimated to be 29 PBq,
and the residual activity there from atmospheric nuclear
weapons testing is about 0.5 PBq.

Dernovichi

Savici
Pirki

Dovlyady

39. The Gomel-Mogilev-Bryansk contamination area iscentred 200 km to the north-northeast of the reactor at theboundary of the Gomel and Mogilev regions of Belarus andof the Bryansk region of the Russian Federation. In someareas contamination was comparable to that in the Central
area; deposition densities even reached 5 MBq m2 in somevillages of the Mogilev and Bryansk regions.
40. The Kaluga-Tula-Orel area is located 500 km to thenortheast of the reactor. Contamination there came fromthe same radioactive cloud that caused contamination in
the Gomel-Mogilev-Bryansk area as a result of rainfall on
2829 April. The 137Cs deposition density was, however,lower in this area, generally less than 500 kBq m2.

Denisovichi
Zimovishche
Novo-Sepelichi
PripyatNov. Radcha

Slavutich
Komarin
Gdeny

Ilyincy

Kovpyta

Chernobyl
Polesskoye
Volchkov

K i ev

Krasilovka
Gornostojpol

Bazar

Morovsk

Termakhovka
Ivankovna

Kiev, Zhitomir, Chernigov, Rovno and Lutsk regions of
Ukraine and in the southern parts of the Gomel and Brest
regions 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 m2 (40 Ci km2) in this zone and also in some areasof the near zone to the west and northwest of the reactor,
in the Gomel, Kiev and Zhitomir regions (Figure VII).

KirovoVarovskDes

Figure VIII. Surface ground deposition of strontium-90
released in the Chernobyl accident [I1].

Dne p

462

KuchariteTe

Chernin

Dymer

Zarudjere v

UKRAINE
Bujan

Brovary

Vorzely
IrpenyKIEVMotyzhinBojarka

Figure IX. Surface ground deposition of plutonium-239
and plutonium-240 released in the Chernobyl accident
at levels exceeding 3.7 kBq m -2 [I1].

r-B
u

-2

L

-2

-2

Khmelnitskiy

Narodichi

Roska

Belaya Tserkov

KIEV

ep

r

U
CHERKASSY

Dn

K

S
Kirov

A

SUMY

I

KALUGA

N

E

PlavskBELGORODKHARKOV

Kimovsk

Novomoskovsk

YeletsEfremov

TULA

Aleksin

Mtsensk

OREL

KURSK

Bolkhov

Lyudinovo

POLTAVAA

ShostkaR

I

Dyatlovo

S

BRYANSK

RoslavlNovozybkov

U

SMOLENSK

Krichev

R

pr

CHERNIGOV
Slavutich

BraginChernobyl

ZHITOMIRVINNITSA

Berdichev

PripyatCherikov

MOGILEV

Gorki

GOMEL
Khoyniki

Polesskoje

Narovlya

Korosten

Bykhov

Bobruysk

Mozyr

S

OvruchPripyatU

Borisov

ORSHA
e
Dn

Figure X. Estimated surface ground deposition in Belarus and western Russia of iodine-131 released in the Chernobyl accident [B25, P19].

37-185 kBq m-2

185-370 kBq m-2

370-1850 kBq m-2

1850-5550 kBq m-25550-11100 kBq m-211100-18500 kBq m

SlutskR

MINSKSoligorsk

A

Sarny

18500-37000 kBq m>37000 kBq m

Pinsk

g ski C anal

PripyatDn
ep

E

Baranovichi

B

Novogrudok

Lida

od

kh

St o

r

St y

’

Goryn

Molodechno

ev
er
Te
t

na
Des

Desna

VILNIUSANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT
463

Figure XI. Surface ground deposition of caesium-137 released in Europe after the Chernobyl accident [D13].

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

465

42. During the first weeks after the accident, most of theactivity deposited on the ground consisted of short-lived
radionuclides, of which 131I was the most important radiologically. Maps of 131I deposition have been prepared for
Belarus and part of the Russian Federation (Figure X). As
indicated in paragraph 35, these maps are based on thelimited number of measurements of 131I deposition density
available in the former Soviet Union, and they use 137Cs
measurements as a guide in areas where 131I was notmeasured. These maps must be regarded with caution, as theratio of the 131I to 137Cs deposition densities was found to vary
in a relatively large range, at least in Belarus.

by the surveillance networks of environmental radiation.
Interhemispheric transfer also occurred to a small extent
through human activities, such as shipping of foods ormaterials to the southern hemisphere. Therefore, only very
low levels of radioactive materials originating from the
Chernobyl accident have been present in the biosphere of
the southern hemisphere, and the resulting doses have been
negligible.

43. Deposition of 90Sr was mostly limited to the near zoneof the accident. Areas with 90Sr deposition density exceeding 100 kBq m2 were almost entirely within the 30-km
zone, and areas exceeding 37 kBq m2 were almost allwithin the near zone (<100 km). Only a few separate sites
with 90Sr deposition density in the range 37100 kBq m2
were found in the Gomel-Mogilev-Bryansk area, i.e. in the
far zone (Figure VIII) [A9, B25, H13].

47. The environmental behaviour of deposited radionuclides depends on the physical and chemical characteristics of the radionuclide considered, on the type of fallout(i.e. dry or wet), and on the characteristics of theenvironment. Special attention will be devoted to 131I, 137Cs
and 90Sr and their pathways of exposure to humans.
Deposition can occur on the ground or on water surfaces.
The terrestrial environment will be considered first.

44. Information on the deposition of plutonium isotopes is
not as extensive because of difficulties in detecting theseradionuclides. The only area with plutonium levels exceeding
4 kBq m2 was located within the 30-km zone (Figure IX). In
the Gomel-Mogilev-Bryansk area, the 239,240Pu deposition
density ranged from 0.07 to 0.7 kBq m2, and in the KalugaTula-Orel area, from 0.07 to 0.3 kBq m2 [A9]. At Korosten,located in Ukraine about 115 km southwest of the Chernobyl
power plant, where the 137Cs deposition density was about 300
kBq m2, the 239,240Pu deposition density due to the Chernobyl
accident derived from data in [H8] is found to be only about
0.06 kBq m2, which is 48 times lower than the 239,240Pu
deposition density from global fallout.

1. Terrestrial environment

2. Remainder of northern and southernhemisphere
45. As shown in Table 5, there are also other areas, inEurope, where the 137Cs deposition density exceeded 37
kBq m2, notably, the three Scandinavian countries (Finland, Norway and Sweden), Austria and Bulgaria. In thosecountries, the 137Cs deposition density did not exceed 185
kBq m2 except in localized areas (for example, a 24 km2
area in Sweden within the commune of Gävle [E6] andmountainous areas in the Austrian Province of Salzburg[L24]). The pattern of 137Cs deposition density in the wholeof Europe is shown in Figure XI [D13, I24].
46. Small amounts of radiocaesium and of radioiodine
penetrated the lower stratosphere of the northernhemisphere during the first few days after the accident [J6,K43]. Subsequently, transfer of radiocaesium to the lower
atmospheric layers of the southern hemisphere may haveoccurred as a result of interhemispheric air movementsfrom the northern to the southern stratosphere, followed bysubsidence in the troposphere [D11]. However, radioactive
contamination was not detected in the southern hemisphere

D. ENVIRONMENTAL BEHAVIOUR OF
DEPOSITED RADIONUCLIDES

48. For short-lived radionuclides such as 131I, the main
pathway of exposure of humans is the transfer of theamounts deposited on leafy vegetables that are consumed
within a few days, or on pasture grass that is grazed bycows or goats, giving rise to the contamination of milk.
The amounts deposited on vegetation are retained with ahalf-time of about two weeks before removal to the groundsurface and to the soil. Long-term transfer of 131I from
deposition on soil to dietary products that are consumed
several weeks after the deposition has occurred need not be
considered, because 131I has a physical half-life of only
8 days.
49. Radionuclides deposited on soil migrate downwards
and are partially absorbed by plant roots, leading in turn to
upward migration into the vegetation. These processes
should be considered for long-lived radionuclides, such as
137
Cs and 90Sr. The rate and direction of the radionuclide
migration into the soil-plant pathway are determined by anumber of natural phenomena, including relief features,the type of plant, the structure and makeup of the soil,hydrological conditions and weather patterns, particularly
at the time that deposition occurred. The vertical migrationof 137Cs and 90Sr in soil of different types of natural
meadows has been rather slow, and the greater fraction ofradionuclides is still contained in its upper layer(010 cm). On average, in the case of mineral soils, up to
90% of 137Cs and 90Sr are found in the 05 cm layer; in thecase of peaty soils, for which radionuclide migration isfaster, only 40% to 70% of 137Cs and 90Sr are found in thatlayer [I22]. The effective half-time of clearance from theroot layer in meadows (010 cm) in mineral soils has been
estimated to range from 10 to 25 years for 137Cs and to be
1.23 times faster for 90Sr than for 137Cs; therefore, theeffective clearance half-time for 90Sr is estimated to be 7 to
12 years [A11, A14].

466

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

50. For a given initial contamination of soil, thetransfer from soil to plant varies with time as theradionuclide is removed from the root layer and as its
availability in exchangeable form changes. The 137Cs
content in plants was maximum in 1986, when thecontamination was due to direct deposition on aerial
surfaces. In 1987, 137Cs in plants was 36 times lower
than in 1986, as the contamination of the plants wasthen mainly due to root uptake. Since 1987, the transfer
coefficients from deposition to plant have continued todecrease, although the rate of decrease has slowed: from1987 to 1995, the transfer coefficients of 137Cs decreasedby 1.5 to 7 times, on average [I22]. Compared with 137Csfrom global fallout, 137Cs from the Chernobyl accident in
the far zone was found to be more mobile during thefirst four years after the accident, as the water-soluble
fractions of Chernobyl and fallout 137Cs were about 70%
and 8%, respectively [H15]. Later on, ageing processes
led to similar mobility values for 137Cs from the
Chernobyl accident and from global fallout.
51. The variability of the transfer coefficient from
deposition to pasture grass for 137Cs is indicated in Table 9
for natural meadows in the Polissya area of Ukraine [S40].
The type of soil and the water content both have an
influence on the transfer coefficient, the values of whichwere found to range from 0.6 to 190 Bq kg1 (dry grass) per
kBq m2 (deposition on the ground) in 19881989 [S40].
The variability as a function of time after the accident in
the Russian Federation has been studied and reported on by
Shutov et al. [S41].
52. Contrary to 137Cs, it seems that the exchangeability of90
Sr does not keep decreasing with time after the accident
and may even be increasing [B36, S41]. In the RussianFederation, no statistically significant change was found in
the 90Sr transfer coefficient from deposition to grass during
the first 4 to 5 years following the accident [S41]. This is
attributable to two competing processes: (a) 90Sr conversion
from a poorly soluble form, which characterized the fuelparticles, to a soluble form, which is easily assimilated byplant roots, and (b) the vertical migration of 90Sr into
deeper layers of soil, hindering its assimilation byvegetation [S41].
53. The contamination of milk, meat and potatoes usuallyaccounts for the bulk of the dietary intake of 137Cs.
However, for the residents of rural regions, mushrooms andberries from forests occupy an important place. The
decrease with time of the 137Cs concentrations in thosefoodstuffs has been extremely slow, with variations fromone year to another depending on weather conditions [I22].
2. Aquatic environment
54. Deposition of radioactive materials also occurred onwater surfaces. Deposition on the surfaces of seas andoceans resulted in low levels of dose because theradioactive materials were rapidly diluted into very large
volumes of water.

55. In rivers and small lakes, the radioactive contamination resulted mainly from erosion of the surface layers ofsoil in the watershed, followed by runoff in the water
bodies. In the 30-km zone, where relatively high levels ofground deposition of 90Sr and 137Cs occurred, the largest
surface water contaminant was found to be 90Sr, as 137Cs
was strongly adsorbed by clay minerals [A15, M19]. Muchof the 90Sr in water was found in dissolved form; low levelsof plutonium isotopes and of 241Am were also measured in
the rivers of the 30-km zone [A15, M19].
56. The contribution of aquatic pathways to the dietaryintake of 137Cs and 90Sr is usually quite small. However, the137
Cs concentration in the muscle of predator fish, like perchor pike, may be quite high in lakes with long water retention
times, as found in Scandinavia and in Russia [H16, K47, R21,
T23]. For example, concentration of 137Cs in the water of lakes
Kozhanyand Svyatoe located in severely contaminated part ofthe Bryansk region of Russia was still high in 1996 because of
special hydrological conditions: 1020 Bq l1 of 137Cs and
0.61.5 Bq l1 of 90Sr [K47]. Concentration of 137Cs in themuscles of crucian (Carassius auratus gibeio) sampled in thelake Kozhany was in the range of 515 kBq kg1 and in pike
(Esox lucius) in the range 2090 kBq kg1 [K47, T23].
Activity of 137Cs in inhabitants of the village Kozhany locatedalong the coast of lake Kozhany measured by whole-bodycounters in summer 1996 was 7.4 ± 1.2 kBq in 38 adults who
did not consume lake fish (according to interviews performed
before the measurements) but was 49 ± 8 kBq in 30 people
who often consumed lake fish. Taking into account seasonalchanges in the 137Cs whole-body activity, the average annualinternal doses were estimated to be 0.3 mSv and 1.8 mSv inthese two groups, respectively. Also, the relative importanceof the aquatic pathways, in comparison to terrestrial pathways,
may be high in areas downstream of the reactor site where
ground deposition was small.

E. SUMMARY
57. The accident at the Chernobyl nuclear power station
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 thereactor building and completely destroyed the reactor.
58. The radionuclide releases from the damaged reactor
occurred mainly over a 10-day period, but with varying
release rates. From the radiological point of view, 131I and137
Cs are the most important radionuclides to consider,because they are responsible for most of the radiation
exposure received by the general population. The releasesof 131I and 137Cs are estimated to have been 1,760 and
85 PBq, respectively (1 PBq = 1015 Bq). It is worth noting,however, that the doses were estimated on the basis ofenvironmental and thyroid or body measurements and thatknowledge of the quantities released was not needed forthat purpose.

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

59. The three main areas of contamination, defined as
those with 137Cs deposition density greater than 37 kBq m2(1 Ci km2), are in Belarus, the Russian Federation andUkraine; they have been designated the Central, GomelMogilev-Bryansk and Kaluga-Tula-Orel areas. The Central
area is within about 100 km of the reactor, predominantly
to the west and northwest. The Gomel-Mogilev-Bryansk
contamination area is centred 200 km to the northnortheast of the reactor at the boundary of the Gomel andMogilev regions of Belarus and of the Bryansk region of
the Russian Federation. The Kaluga-Tula-Orel area islocated in the Russian Federation, about 500 km to thenortheast of the reactor. All together, as shown in Table 7
and in Figure XI, territories with an area of approximately
150,000 km2 were contaminated in the former Soviet
Union.
60. Outside the former Soviet Union, there were many
areas in northern and eastern Europe with 137Cs deposition

467

density in the range 37200 kBq m2. These regions
represent an area of 45,000 km2, or about one third of thecontaminated areas found in the former Soviet Union.
61. The environmental behaviour of depositedradionuclides depends on the physical and chemical
characteristics of the radionuclide considered, on the typeof fallout (i.e. dry or wet), and on the characteristics of theenvironment. For short-lived radionuclides such as 131I, themain pathway of exposure to humans is the transfer ofamounts deposited on leafy vegetables that are consumedby humans within a few days, or on pasture grass that isgrazed by cows or goats, giving rise to the contaminationof milk. The amounts deposited on vegetation are retainedwith a half-time of about two weeks before removal to theground surface and to the soil. For long-lived radionuclides
such as 137Cs, the long-term transfer processes from soil tofoods consumed several weeks or more after depositionneed to be considered.

II. RADIATION DOSES TO EXPOSED POPULATION GROUPS
62. It is convenient to classify into three categories the
populations who were exposed to radiation following theChernobyl accident: (a) the workers involved in the accident,
either during the emergency period or during the clean-up
phase; (b) inhabitants of evacuated areas; and (c) inhabitantsof contaminated areas who were not evacuated. The available
information on the doses received by the three categories of
exposed populations will be presented and discussed in turn.
Doses from external irradiation and from internal irradiation
will be presented separately. The external exposures due togamma radiation were relatively uniform over all organs andtissues of the body, as their main contributors were 132Te-132I,
131
I and 140Ba-140La for evacuees, 134Cs and 137Cs forinhabitants of contaminated areas who were not evacuated,
and radionuclides emitting photons of moderatelyhigh energy
for workers. These external doses from gamma radiation havebeen expressed in terms of effective dose. With regard tointernal irradiation, absorbed doses in the thyroid have been
estimated for exposures to radioiodines and effective doses
have been estimated for exposures to radiocaesiums.
63. Doses have in almost all cases been estimated by meansof physical dosimetrytechniques. Biological indicators of dose
has been mainly used, within days or weeks after the accident,
to estimate doses received by the emergency workers, whoreceived high doses from external irradiation and for whom
dosemeters were either not operational nor available. Unlike
physical dosimetry, biological dosimetric methods are
generally not applicable to doses below 0.1 Gy and reflect
inter-individual variations in radiation sensitivity. Soon after
the accident, biological dosimetry is usually based on themeasurement of the frequency of unstable chromosome
aberrations (dicentric and centric rings). By comparing therate of dicentric chromosomes and centric rings with astandard dose-effect curve obtained in an experiment in vitro,
it is possible to determine a radiation dose. This method has
been recommended for practical use in documents of WHO
and IAEA. However, the use of dicentric as well as otheraberrations of the unstable type for the purposes of biologicaldosimetry is not always possible, since the frequency of cells
containing such aberrations declines in time after exposure.
64. For retrospective dosimetry long after the exposure,biological dosimetry can be a complement to physical dosimetry, but only techniques where radiation damage to the
biological indicator is stable and persistent and not subject tobiochemical, physiological or immunological turnover, repair
or depletion are useful. In that respect, the analysis of stable
aberrations (translocations), the frequency of which remains
constant for a long time after exposure to radiation, is promising. The probability of occurrence of stable (translocations) and unstable (dicentrics) aberrations after exposure is
the same. However, translocations are not subjected to
selection during cell proliferation, in contrast to dicentrics.
Fluorescence in situ hybridization (FISH) or Fast-FISH in
conjunction with chromosome painting may be useful inretrospective dosimetry for several decades after exposure.
65. Other biological (or biophysical) techniques formeasuring doses are electron spin resonance (ESR) or
opticallystimulated luminescence (OSL). These techniques
are used in retrospective dosimetry to measure theradiation damage accumulated in biological tissue such as
bone, teeth, fingernails and hair. Also, the gene mutation
glycophorin A that is associated with blood cells may be
used. Currently, the detection limits for FISH, ESR and
OSL are about 0.1 Gy [P28]. At low dose levels, however,
the estimation of the dose due to the radiation accident is468

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT(26 April 1986), i.e. the staff of the plant, the firemen
involved with the initial emergency, the guards and the staffof the local medical facility. Most of them were at the reactorsite at the time of the accident or arrived at the plant during
the few first hours. In the Russian literature, two othercategories of people are referred to: (a) the “accident
witnesses”, who were present at the plant at the time of theaccident and who may or may not have been involved inemergency operations (so that part of them are also classified
as “emergency workers”) and (b) the “accident victims”, whowere sent to the local medical facility and then transferred to
special hospitals in Moscow and Kiev. All accident victims
were emergency workers and/or accident witnesses. The
numbers of accident witnesses and emergency workers arelisted in Table 10. According to Table 10, on the morning of
26 April, about 600 emergency workers were on the site of theChernobyl power plant.

highly unreliable because of the uncertainty in the
background dose resulting from other radiation exposures(medical irradiation, natural background, etc.) or, in thecase of FISH, from other factors such as smoking.

A. WORKERS INVOLVED IN THE
ACCIDENT
66. The workers involved in various ways in the accident
can be divided into two groups: (a) those involved inemergency measures during the first day of the accident(26 April 1986), who will be referred to as emergency
workers in this Annex, and (b) those active in 19861990
at the power station or in the zone surrounding it for thedecontamination work, sarcophagus construction and otherclean-up operations. This second group of workers isreferred to as recovery operation workers in this Annex,
although the term liquidator gained common usage in theformer Soviet Union.

68. The power plant personnel wore only film badges that
could not register doses in excess of 20 mSv. All of thesebadges were overexposed. The firemen had no dosimeters andno dosimetric control. Dose rates on the roof and in the roomsof the reactor block reached hundreds of gray per hour.
Measured exposure rates in the vicinity of the reactor at thetime of the accident are shown in Figure XII.

1. Emergency workers
67. The emergency workers are the people who dealt
with the consequences of the accident on the very first day

TOWN OF PRIPYATRIVER PRIPYAT

0.1

COOLING POND

10
1

100
100
REACTOR

100

1
1 km

Figure XII. Measured exposure rates in air on 26 April 1986 in the local area of the Chernobyl reactor.

  

69. The highest doses were received by the firemen and thepersonnel of the power station on the night of the accident.
Some symptoms of acute radiation sickness were observed in
237 workers. Following clinical tests, an initial diagnosis ofacute radiation sickness was made in 145 of these persons. On
further analysis of the clinical data, acute radiation sickness
was confirmed later (in 1992) in 134 individuals. The healtheffects that were observed among the emergency workers are
discussed in Chapters III and IV.

  


70. The most important exposures were due to external
irradiation (relatively uniform whole-body gamma
irradiation and beta irradiation of extensive body surfaces),as the intake of radionuclides through inhalation was
relatively small (except in two cases) [U4]. Because all of
the dosimeters worn by the workers were overexposed, they
could not be used to estimate the gamma doses received via
external irradiation. However, relevant information was
obtained by means of biological dosimetry for the treatedANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

persons. The estimated ranges of doses for the 134
emergency workers with confirmed acute radiation
sickness are given in Table 11. Forty-one of these patients
received whole-body doses from external irradiation of lessthan 2.1 Gy. Ninety-three patients received higher doses
and had more severe acute radiation sickness: 50 persons
with doses between 2.2 and 4.1 Gy, 22 between 4.2 and
6.4 Gy, and 21 between 6.5 and 16 Gy [I5]. As shown in
Table 12, the relative errors were 10%20% for doses
greater than 6 Gy; they increased as the dose level
decreased, to about 100% for whole-body doses of about
1 Gy, and were even greater for doses of less than 0.5 Gy.
The skin doses from beta exposures evaluated for eightpatients with acute radiation sickness ranged from 10 to 30
times the dose from whole-body gamma radiation [B10].
71. Internal doses were determined from thyroid and wholebody measurements performed on the persons under treatment, as well as from urine analysis and from post-mortem
analysis of organs and tissues. For most of the patients, morethan 20 radionuclides were detectable in the whole-body
gamma measurements; however, apart from the radioiodines
and radiocaesiums, the contribution to the internal doses fromthe other radionuclides was negligible [U4]. Internal doses
evaluated for 23 persons who died of acute radiation sickness
are shown in Table 13. The lung and thyroid doses, calculated
to the time of death, are estimated to have ranged from
0.00026 to 0.04 Gy and from 0.021 to 4.1 Gy, respectively.
Some of the low thyroid doses may be due to the fact thatstable iodine pills were distributed among the reactor staff lessthan half an hour after the beginning of the accident. It is also
speculated that the internal doses received by the emergency
workers who were outdoors were much lower than thosereceived by the emergency workers who stayed indoors. For
comparison purposes, the estimated external doses are alsopresented in Table 13. The external doses, which range from
2.9 to 11.1 Gy, are, in general, much greater than the internal
doses.
72. Internal dose reconstruction was also carried out for 375
surviving emergency workers who were examined in
Moscow; the results are presented in Table 14. The average
doses were estimated to vary from 36 mGy to bone marrow to
280 mGy to bone surfaces, the maximum doses being about
10 times greater than the average doses. Also, thyroid doses
were estimated for the 208 emergency workers admitted to
Hospital 6 in Moscow within 34 weeks after the accident(Table 15); most of the thyroid doses were less than 1 Gy, butthree exceeded 20 Gy. It is interesting to note that themeasurements of 131I and 133I among the five emergency
workers with the highest thyroid doses showed that 133I
contributed less than 20% to the thyroid dose. The specificvalues of the contributions from 133I were 18% (with 74%
from 131I), 11% (81% from 131I), 6% (86% from 131I), 10%(82% from 131I) and 14% (78% from 131I) for the five workers[G12]. The thyroid doses due to internal exposures are
estimated to be in the range from several percent to several
hundred percent of the external whole-body doses. The
median value of the ratio of the thyroid to the whole-bodydose was estimated to be 0.3 [K19]. Finally, information is469

available for the relative intakes of 16 radionuclides of 116
patients, determined from measurements in urine and in
autopsy materials [D12]; according to these measurements,
the average intake of 132Te was found to be about 10% that of131
I [D12].
2. Recovery operation workers
73. About 600,000 persons (civilian and military) havereceived special certificates confirming their status asliquidators, according to laws promulgated in Belarus, theRussian Federation and Ukraine. Of those, about 240,000
were militaryservicemen [C7]. The principal tasks carried out
by the recovery operation workers (liquidators) included
decontamination of the reactor block, reactor site, and roads(19861990) and construction of the sarcophagus (MayNovember 1986), a settlement for reactor personnel (MayOctober 1986), the town of Slavutich (19861988, 1990),
waste repositories (19861988), and dams and water filtration
systems (July-September 1986, 1987) [K19]. During the entire
period, radiation monitoring and securityoperations were also
carried out.
74. Of particular interest are the 226,000 recoveryoperation
workers who were employed in the 30-km zone in19861987, as it is in this period that the highest doses werereceived; information concerning these workers is provided inTable 16. About half of these persons were civilian and half
were military servicemen brought in for the special and shortterm work. The workers were all adults, mostly males aged
2045 years. The construction workers were those participating in building the sarcophagus around the damaged
reactor. Other workers included those involved in transportand security, scientists and medical staff. The distributions of
the external doses for the categories of workers listed in Table
16, as well as for the emergency workers and accident
witnesses, are shown in Table 17.
75. The remainder of the recovery operation workers(about 400,000), who generally received lower doses,
includes those who worked inside the 30-km zone in19881990 (a small number of workers are still involved),those who decontaminated areas outside the 30-km zone,
and other categories of people.
76. In 1986 a state registry of persons exposed to radiation
was established at Obninsk. This included not only recovery
operation workers but evacuees and residents of contaminatedareas as well. The registry existed until the end of 1991.
Starting in 1992, national registries of Belarus, the RussianFederation and Ukraine replaced the all-union registry. The
number of recovery operation workers in the national
registries of Belarus, the Russian Federation and Ukraine islisted in Table 18. Some 381,000 workers from these countries
were involved in the years 19861989. To this must be added
the 17,705 recovery operation workers recorded in theregistries of the Baltic countries, including 7,152 from
Lithuania, 5,709 from Latvia and 4,844 from Estonia [K13].
More detailed information on the registries is provided in
Chapter IV. The total number of recovery operation workers

470

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

recorded in the registries appears to be about 400,000. This
number is likely to increase in the future, as someorganizations may not have provided all their information to
the central registries; in addition, individuals may on theirown initiative ask to be registered in order to benefit fromcertain privileges. However, the number of recoveryoperation
workers recorded in the national registries is well below thefigure of about 600,000, which corresponds to the number ofpeople who have received special certificates confirming theirstatus as liquidators.
(a) External effective doses from gamma
radiation
77. The doses to the recovery operation workers who
participated in mitigation activities within two months
after the accident are not known with much certainty.
Attempts to establish a dosimetric service were inadequate
until the middle of June. TLDs and condenser-type dosimeters that had been secured by 28 April were insufficientin number and, in the case of the latter type, largely nonfunctioning, and records were lost when the dosimetricservice was transferred from temporary to more permanentquarters. In June, TLD dosimeters were available in large
numbers, and a databank of recorded values could beestablished. From July 1986 onwards, individual dosemonitoring was performed for all non-military workers,
using either TLDs or film dosimeters.
78. The dose limits for external irradiation varied with time
and with the category of personnel. According to national
regulations established before the accident [M1], for civilian
workers, during 1986, the dose limit, 0.05 Sv, could be
exceeded by a factor of up to 2 for a single intervention and by
a factor of 5 for multiple interventions on condition ofagreement by the personnel. The maximum dose allowed
during the year 1986 was, therefore, 0.25 Sv. In 1987, theannual dose limits for civilian personnel were lowered to 0.05
or to 0.1 Sv, according to the type of work performed on thesite. However, a dose of up to 0.25 Sv could be allowed by the
Ministry of Health for a limited number of workers for the
implementation ofextremelyimportant interventions. In 1988,
the annual dose limit was set at 0.05 Sv for all civilian
workers, except those involved in the decontamination of theengine hall inside the sarcophagus; for them, the annual dose
limit was set at 0.1 Sv. From 1989 onwards, the annual dose
limit was set at 0.05 Sv for all civilian workers, without
exception [M1, M12]. For military workers, a dose limit of
0.5 Sv, corresponding to radiation exposures during wartime,
was applied until 21 May 1986, when the Ministry of Defence
lowered the dose limit to 0.25 Sv [C7]. From 1987 onwards,
the dose limits were the same for military and civilian
personnel.
79. Estimates of effective doses from external gamma
irradiation were generally obtained in one of three ways: (a)individual dosimetry for all civilian workers and a small partof the military personnel after June 1986; (in 1987, they wereidentified as those working in locations where the exposure
rate was greater than 1 mR h1); (b) group dosimetry (anindividual dosimeter was assigned to one member of a groupof recoveryoperation workers assigned to perform a particulartask, and all members of the group were assumed to receive
the same dose; in some cases, no member of the group wore
an individual dosimeter and the dose was assigned on thebasis of previous experience); or (c) time-and-motion studies(measurements of gamma-radiation levels were made atvarious points of the reactor site, and an individual’s dose wasestimated as a function of the points where he or she worked
and the time spent in these places). Methods (b) and (c) wereused for the civilian workers before June 1986, when thenumber of individual dosimeters was insufficient, and for the
majority of the military personnel at any time. For example,
effective doses from external irradiation have been reconstructed by physical means for the staff of the reactor, as
well as for the workers who had been detailed to assist them,
exposed from 26 April to 5 May 1986 [K19]. Personnel
location record cards filled in by workers were analysed byexperts who had reliable information on the radiation
conditions and who had personally participated in ensuring
the radiation safety of all operations following the accident.
Using this method, two values were determined: the maximum possible dose and the expected dose. The maximum
possible effective doses ranged from less than 0.1 Sv to a few
sievert and were estimated to be about twice the expected
doses. It seems that in most cases the maximum possible
effective doses are those that were officially recorded.
80. The main sources of uncertainty associated with thedifferent methods of dose estimation were as follows: (a)individual dosimetry: incorrect use of the dosimeters (inadvertent or deliberate actions leading to either overexposure orunderexposure of the dosimeters); (b) group dosimetry: very
high gradient of exposure rate at the working places at thereactor site; and (c) time-and-motion studies: deficiencies indata on itineraries and time spent at the various working
places, combined with uncertainties in the exposure rates.
Uncertainties associated with the different methods of dose
estimation are assessed to be up to 50% for method (a) (if thedosimeter was correctly used), up to a factor of 3 for method(b), and up to a factor of 5 for method (c) [P15].
81. The registry data show that the annual averages ofthe officially recorded doses decreased from year to year,
being about 170 mSv in 1986, 130 mSv in 1987, 30 mSv
in 1988, and 15 mSv in 1989 [I34, S14, T9]. It is, however,difficult to assess the validity of the results that have beenreported for a variety of reasons, including (a) the fact thatdifferent dosimeters were used by different organizations
without any intercalibration; (b) the high number ofrecorded doses very close to the dose limit; and (c) the highnumber of rounded values such as 0.1, 0.2, or 0.5 Sv[K19]. However, the doses do not seem to have beensystematicallyoverestimated, because biological dosimetry
performed on limited numbers of workers produced resultsthat are also very uncertain but compatible nonethelesswith the physical dose estimates [L18]. It seems reasonable
to assume that the average effective dose from external
gamma irradiation to recovery operation workers in theyears 19861987 was about 100 mSv, with individual

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

effective doses ranging from less than 10 mSv to more than
500 mSv. Using the numbers presented in Table 18, thecollective effective dose is estimated to be about 40,000
man Sv.
82. A particular group of workers who may have been
exposed to substantial doses from external irradiation ismade up of the 1,125 helicopter pilots who were involved
in mitigation activities at the power plant in the first threemonths after the accident [U15]. The doses to pilots were
estimated using either personal dosimeters or, less reliably,
calculations in which the damaged reactor was treated asa collimated point source of radiation [U15]. The doses
obtained by calculation were checked against the results
derived from the personal dosimeters for about 200 pilots.
That comparison showed a discrepancy of (a) less 0.05 Sv
for about 10% of pilots, (b) from 0.05 to 0.1 Sv for about
33%, and (c) more than 0.1 Sv for about 57% [U15]. The
simplification used to describe the origin of the radiation
emitted from the damaged reactor is the main source of
uncertainty in the assessment of the doses received by thehelicopter pilots. The average dose estimates are 0.26 Sv
for the pilots who took part in the mitigation activities
from the end of April to the beginning of May, and 0.14 Sv
for the pilots who were exposed after the beginning ofMay.
83. Another group of workers that may have been
exposed to substantial doses from external irradiation is the672 workers from the Kurchatov Institute, a group that
includes those who were assigned special tasks inside thedamaged unit 4 before and after the construction of thesarcophagus [S36]. Recorded and calculated doses
available for 501 workers show that more than 20% ofthem received doses between 0.05 and 0.25 Sv, and thatabout 5% of them received doses between 0.25 and 1.5 Sv[S36]. A number of nuclear research specialists worked inhigh-radiation areas of the sarcophagus, without formal
recording of doses, on their own personal initiative, andwere exposed to annual levels greater than the dose limitof 0.05 Sv applicable since 1988. Doses for this group of
29 persons have been estimated using electron spinresonance analysis of tooth enamel as well as stable andunstable chromosome aberration techniques [S42, S47]. It
was found that 14 of those 29 persons received doses lower
than 0.25 Sv, 5 had doses between 0.25 and 0.5 Sv, 6
between 0.5 and 1 Sv, and 4 greater than 1 Sv [S42].
Additional analyses by means of the FISH technique forthree of those nuclear research specialists resulted in dosesof 0.9, 2.0 and 2.7 Sv [S48].
84. Biological dosimetry. Chromosome aberration levels
among Chernobyl recovery operation workers wereanalysed in a number of additional studies. In a pilot studyof a random sample of 60 workers from the RussianFederation, stratified on the level of recorded dose (31 withdoses <100 mGy, 18 with 100200 mGy, and 13 with>200 mGy), no association was found between thepercentage of the genome with stable translocations
measured by fluorescent in situ hybridization (FISH) and471

individual recorded physical dose estimates [C1, L18]. A
good correlation was found, however, for group (rather
than individual) doses. Blood samples of 52 Chernobyl
recovery operation workers were analysed by FISH [S32]and simultaneously by conventional chromosome analysis.
Based on FISH measurements, individual biodosimetry
estimates between 0.32 and 1.0 Gy were estimated for 18
cases. Pooled data for the total group of 52 workers
provided an average estimate of 0.23 Gy. For a group of 34
workers with documented doses, the mean dose estimate of
0.25 Gy compared well with the mean documented dose of
0.26 Gy, although there was no correlation between
individual translocation frequencies and documented doses.
Comparison between the conventional scoring and FISH
analyses showed no significant difference. In a study ofEstonian workers, Littlefield et al. [L41] did not detect anincrease of stable translocation frequencies with reported
doses and questioned whether the reported doses could
have been overestimated. In conclusion, FISH does not
currently appear to be a sufficiently sensitive and specifictechnique to allow the estimation of individual doses in the
low dose range received by the majority of recovery
operation workers.
85. Lazutka and Dedonyte [L30], using standard
cytogenetic methods, reported no significant overall
increase in chromosome aberrations over controls in 183
recovery operation workers from Lithuania with a meandose estimate of 140 mGy, although ~20% had elevatedfrequencies of dicentric and ring chromosomes, possibly
related to radiation exposure. Lazutka et al. [L31] also
evaluated the impact of a number of possible confounders
such as age, alcohol use, smoking, recent febrile illness,and diagnostic x-ray exposures on the frequency ofchromosome aberrations. When transformed data wereanalysed by analysis of variance, alcohol abuse made asignificant contribution to total aberrations, chromatid
breaks, and chromatid exchanges. Smoking was associatedwith frequency of chromatid exchanges, and age wassignificantly associated with rates of chromatid exchanges
and chromosome exchanges [L31]. In another study [S37],
the frequency of chromosomal aberrations was evaluated in
more than 500 recovery operation workers. Blood samples
were taken from several days to three months after
exposure to radiation. The mean frequencies of aberrations
for different groups of workers were associated with doses
varying from 0.14 to 0.41 Gy, with a good correlation
between the doses determined by biological and physicalmethods [S37].
86. Glycophorin A assay (GPA) was used as a possible
biological dosimeter on 782 subjects from Estonia, Latvia
and Lithuania with recorded physical dose estimates [B17].
Although a slight increase in the frequency of erythrocyteswith loss of the GPA allele was seen among these subjects
compared to control subjects from the same countries, thisdifference was not significant. The pooled results indicatethat the average exposures of these workers were unlikely
to greatly exceed 100200 mGy, the approximate
minimum radiation dose detectable by this assay.

472

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT(b) External skin doses from beta radiation
87. In addition to effective doses from external gamma
irradiation, recovery operation workers received skin doses
from external beta irradiation as well as thyroid andeffective doses from internal irradiation. The dose tounprotected skin from beta exposures is estimated to havebeen several times greater than the gamma dose. Ratios ofdose rates of total exposures (beta + gamma) to gamma
exposures, measured at the level of the face, ranged from
2.5 to 11 (average, around 5) for general decontamination
work and from 7 to 50 (average, 28) for decontaminationof the central hall of the Unit 3 reactor [O3].
(c) Internal doses
88. Because of the abundance of 131I and of shorterlived radioiodines in the environment of the reactor
during the accident, the recovery operation workers who
were on the site during the first few weeks after theaccident may have received substantial thyroid doses
from internal irradiation. Information on the thyroid
doses is very limited and imprecise. From 30 April
through 7 May 1986, in vivo thyroid measurements werecarried out on more than 600 recovery operation
workers. These in vivo measurements, which aremeasurements of the radiation emitted by the thyroid
using detectors held or placed against the neck, wereused to derive the 131I thyroidal contents at the time of
measurement. The thyroid doses were derived from themeasured 131I thyroidal contents, using assumptions on
the dynamics of intake of 131I and short-lived radioiodines and on the possible influence of stable iodine
prophylaxis. Preliminarythyroid dose estimates (assuming a single intake at the date of the accident and no
stable iodine prophylaxis) showed the following
distribution [K30]: 64% of workers were exposed to lessthan 0.15 Gy, 32.9% to 0.150.75 Gy, 2.6% to0.751.5 Gy, and the remaining 0.5% to 1.53.0 Gy.
The average thyroid dose estimate for those workers isabout 0.21 Gy. The thyroid doses from internal
irradiation are estimated to range from several percent
to several hundred percent of the effective doses fromexternal irradiation. The median value of the ratio of theinternal thyroid dose to the external effective dose wasestimated to be 0.3 Gy per Sv [K19].
89. It is important to note that information on the influenceof stable iodine prophylaxis is limited, as iodine prophylaxis
among the recoveryoperation workers was not mandatory nor
was it proposed to everybody. The decision to take stableiodine for prophylactic reasons was made by the individual
worker or by the supervisor. The results of interviews of 176
workers (including emergencyworkers and recoveryoperation
workers who arrived at the plant at the ealy stage of theaccident) concerning the time when theytook stable iodine forprophylaxis is presented in Table 19. According to this sample
of workers, only about 20% took stable iodine before being
exposed to radioiodine, while another 10% refused to takestable iodine.

90. The internal doses resulting from intakes ofradionuclides such as 90Sr, 134Cs, 137Cs, 239,240Pu, and others
have been assessed for about 300 recovery operation
workers who were monitored from April 1986 to April
1987 [K2, K8, P13, S11]. The majority of them were staffof the power plant who took part in the recovery work
starting on days 3 and 4 after the accident. The dose
assessment was based on the analysis of whole-bodymeasurements and of radionuclide concentrations in
excreta. The average value of the effective dose committed
by the radionuclide intakes was estimated on the basis of
ICRP Publication 30 [I17] to be 85 mSv. The part of theeffective dose received between June and September 1986
was estimated to have been about 30 mSv. Internal doses
from intakes in later years are expected to be much lower:
routine monitoring of the 134Cs + 137Cs body burdens
indicated average annual doses from 134Cs + 137Cs of about
0.10.2 mSv in 1987 and 1988 [V6].

B. EVACUATED PERSONS
91. The evacuation of the nearby residents was carriedout at different times after the accident on the basis of theradiation situation and of the distance of the populatedareas from the damaged reactor. The initial evacuations
were from the town of Pripyat, located just 3 km from thedamaged reactor, then from the 10-km zone and from the
30-km zone around the reactor (located mostly in Ukraine
but also in Belarus). In addition, a number of villages inBelarus, the Russian Federation and Ukraine beyond the
30-km-radius circle centred on the reactor were also
evacuated in 1986. The term “exclusion zone” is used inthis Annex to refer to the whole area evacuated in 1986,
which includes the 30-km zone.
92. In Ukraine, the residents of Pripyat (49,360 persons)and of the nearest railway station, Yanov (254 persons),
3 km from the reactor, were the first to be evacuated. On
the evening of 26 April 1986, the radiation exposures in
Pripyat were not considered too alarming. Exposure-rate
readings were in the range 110 mR h1 [I1], but with theseriousness of the accident becoming evident, the decision
to evacuate the residents of the town was taken at 22:00.
During the night, arrangements were made for nearly
1,200 buses that would be needed to transport the residents.
Around noon on 27 April the evacuation order was
broadcast to the people, and the evacuation began at 14:00
and finished at 17:00. The over 40,000 evacuees weretaken in by families who lived in settlements in thesurrounding districts, especially Polesskoe district of
Ukraine. Most people stayed with these families until
August 1986. After that they were resettled to apartments
in Kiev [I1].
93. Also in Ukraine, the evacuation of the residents fromthe southern part of the 10-km zone (10,090 persons) was
carried out from 30 April through 3 May. The otherUkrainian residents (28,133) inside the 30-km zone,

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

including Chernobyl town, were evacuated from 3 May
through 7 May. On the basis of exposure-rate criteria(520 mR h1 on 10 May 1986), 2,858 persons who resided
outside the 30-km zone in the Kiev and in Zhitomir
regions were evacuated from 14 May to 16 August. The
last Ukrainian settlement that was evacuated was Bober,with 711 inhabitants, in September 1986. Thus, 91,406
residents from 75 settlements were evacuated in Ukraine in1986 [S20, U14].
94. The evacuation in Belarus was conducted in threephases. During the first phase (27 May), 11,358 residents
of 51 villages were evacuated from the 30-km zone. In asecond phase (310 June), 6,017 residents of 28 villages
beyond the 30-km zone were evacuated. In the third phase(August and September 1986), 7,350 residents of 29
villages, also beyond the 30-km zone, were evacuated. In
villages evacuated during the second and third phases, theexposure rate was from 5 to 20 mR h1, corresponding to a
projected annual effective dose (26 April 1986 to 25 April
1987) of more than 100 mSv. The total number ofBelarusian residents who were evacuated in 1986 was
24,725 from 108 rural settlements. In the Russian Federation, only 186 residents from four settlements in the
Krasnaya Gora district of Bryansk region were evacuated,
mainly to other settlements of that district. In summary, by
the autumn of 1986, about 116,000 residents from 187
settlements had been evacuated (Table 20). By the sametime, about 60,000 cattle and other agricultural animals
had been relocated from the evacuated zone.
95. The figure of 116,000, adopted in this Annex as thenumber of evacuees in 1986, is somewhat lower than the
figure of 135,000 that was cited by the Committee in the
UNSCEAR 1988 Report [U4] and by IAEA in 1996 [I15].
It is believed that the figure of 135,000 was a roughpreliminary estimate that was not substantiated.
96. The extent of the exclusion zone was based on two
principles: geographical and radiological (dose criteria). A
detailed study of the radiation situation carried out in the
exclusion zone led to the resettlement of 279 residents of
two Ukrainian villages (Cheremoshnya and Nivetskoe) in
June 1986. In addition, it was recommended that theresidents of 27 other villages might move back after the
sarcophagus was constructed (15 settlements in Ukraine
and 12 settlements in Belarus). In accordance with theserecommendations, 1,612 residents of 12 villages in Belarus
had been resettled by December 1986. However, theUkrainian authorities considered that resettling theresidents inside the exclusion zone was economically andsocially undesirable. Nevertheless, some people, mainly
elderly, resettled by themselves to 15 settlements inside theexclusion zone. The population of those 15 settlements wasestimated to be about 900 by spring 1987; about 1,200 by
September 1988; and about 1,000 in 1990. In 19961997,
the number is estimated to be 600800. The decrease withtime is due to migration rather than death.

473

1. Doses from external exposure
97. The effective doses from external exposure for the
persons evacuated from the Ukrainian part of the 30-km
zone were estimated from (a) measurements of exposure
rates performed every hour at about 30 sites in Pripyat anddaily at about 80 sites in the 30-km zone and (b) responses
to questionnaires from about 35,000 evacuees from Pripyat
and about 100 settlements; the questionnaires asked for
information on their locations, types of houses, andactivities at the time of the accident and during a few days
thereafter [L9, M2, R10]. Individual effective doses werereconstructed in this way for about 30,000 evacuees fromthe city of Pripyat and settlements in the 30-km zone. The
average effective dose from external irradiation for thiscohort was estimated to be 17 mSv, with individual values
varying from 0.1 to 380 mSv [L9]. This value is concordant with the absorbed dose of 20 mGy estimated for theevacuees of Pripyat using Electron Spin Resonance (ESR)
measurements of sugar and exposure rate calculations[N1]. The collective effective dose for the approximately
90,000 evacuees from the Ukrainian part of the 30-km
zone was assessed to be 1,500 man Sv [R12].
98. The effective doses and skin doses from external
irradiation received by the evacuees from Belarusian territory
were estimated on the basis of (a) 3,300 measurements of
exposure rates performed in the settlements that were
evacuated; (b) 220 spectrometric measurements, carried out
mainly in May and June 1986, of the gamma radiation
emitted by radionuclides deposited on the ground; (c)measurements of the 137Cs ground deposition density for eachsettlement from the Belarusian data bank [D4]; and (d)responses of about 17,000 evacuees from the territory inside
the 30-km zone and from adjoining areas. It was assessed thatthe doses to evacuees from external irradiation were mainly
due to radionuclides deposited on the ground, because
external irradiation during the passage of the radioactive
cloud played a minor role. The method developed to assess thedoses included the reconstruction of the radionuclide
composition of the deposition in each of the 108 evacuatedsettlements in Belarusian territory and the estimation of thecontribution to the dose from each radionuclide [S29]. It was
assumed that 60%80% of the effective doses was contributedby the short-lived radionuclides 131I, 132Te+132I and
140
Ba+140La, while the contribution from the long-lived
radionuclide 137Cs was estimated to be only 3%5%. The
distribution of individual doses received by the residents of agiven settlement was found to be appropriately described by alog-normal function with a geometric standard deviation of
about 1.5. Overall, it is estimated that about 30% of the people
were exposed to effective doses lower than 10 mSv, about
86% were exposed to doses lower than 50 mSv, and only
about 4% were exposed to doses greater than 100 mSv, withthe average dose estimated to be 31 mSv. The highest average
effective doses, about 300 mSv, were estimated to be received
by the population of two villages located inside the 30-km
zone in Khoyniki district: Chamkov and Masany. The
uncertainty in the average dose for a settlement is estimated to
be characterized with a geometric standard deviation of about

474

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

1.3. The main source of uncertainty in the estimation of theaverage effective doses from external irradiation for the
Belarusian evacuees is the assessment of the activity ratios of132
Te and 131I to 137Cs in the deposition. The collective
effective dose from external irradiation for the 24,725
evacuees from Belarus is assessed to be 770 man Sv.
99. The average skin doses from beta and gamma
radiation are estimated to be 34 times greater than theeffective doses and to range up to 1,560 mGy. The
uncertainty of the average skin doses in a given settlement
is estimated to be characterized by a geometric standard
deviation of about 1.6.
2. Doses from internal exposure100. The thyroid doses received from intake of 131I by theevacuees from Pripyat were derived from (a) 4,969
measurements of radioiodine content of their thyroid
glands made, on average, 23 days after the accident and (b)responses to questionnaires by 10,073 evacuees on theirlocations and consumption of stable iodine [G8]. Average
individual and collective thyroid doses to the evacuees
from Pripyat are shown in Table 21. The thyroid doses
from 131I, which were for the most part due to inhalation,
were highest for 03-year-old children (about 1.4 Gy) andaveraged about 0.2 Gy. The main factor influencing theindividual dose was found to be the distance of theresidence from the reactor [G8].
101. Thyroid doses from intake of 131I to other evacuees
from the 30-km zone were also estimated on the basis ofmeasurements of thyroid contents in 10,676 persons [L12,R10]. When dose estimates obtained for the evacuees from
Pripyat are compared with those for the evacuees fromother settlements of the 30-km zone (Table 21), the doses
to the latter are seen to be somewhat higher than those to
the evacuees from Pripyat, especially for adults. This may
be because Pripyat was evacuated before the rest of the
30-km zone, giving the population of the 30-km zone moretime to consume foodstuffs contaminated with 131I. Usingfor the settlements of the 30-km zone the same age
structure as that for Pripyat in Table 21, the collective
thyroid dose from 131I intake for the entire population ofevacuees from Ukraine is tentatively estimated to be about
30,000 man Gy. Evaluation of thyroid doses to theevacuated population of Belarus is presented in Table 22.
The collective thyroid dose estimate for this population is
25,000 man Gy.
102. Inhalation of short-lived radioiodines and of 132Te
contributed somewhat to the thyroid dose received by
evacuees. According to Goulko et al. [G5], the mostimportant of these short-lived radionuclides is 133I,
amounting to about 30% of the contribution of 131I to thethyroid doses. This maximal value was obtained by taking
into account an inhalation for one hour occurring one hour
after the accident. Khrouch et al. [K16] estimated that thecontribution of all the short-lived radioiodines and of 132Te
could have represented about 50% of the dose from 131I if

the intake occurred by inhalation during the first day after
the accident and about 10% if the intake occurred by both
inhalation and the ingestion of contaminated foodstuffs.
103. Internal effective doses from 137Cs were estimated for
the Belarusian evacuees on the basis of 770 measurementsof gamma-emitting radionuclides in foodstuffs and of 600
whole-body measurements of 137Cs content, in addition to
the environmental measurements already mentioned in
Section II.B.1 [S29]. The main contribution to dose wasfrom inhalation (about 75% of total internal dose) andradiocaesium intake in milk. The average internal exposure
from radiocaesium in milk for the evacuated population isestimated to be 1.4 mSv. The main sources of uncertainty
in the assessment of the internal doses from 137Cs are
considered to be the dates when the cows were first put on
pasture in each settlement and the actual countermeasuresthat were applied in the settlement. The collective effective
dose for the 24,725 Belarusian evacuees from internal
exposure was assessed to be 150 man Sv [S29].
3. Residual and averted collective doses
104. Estimates of collective doses for the populations thatwere evacuated in 1986 from the contaminated areas ofBelarus, the Russian Federation and Ukraine are summarized in Table 23. The collective effective and thyroid
doses are estimated to be about 3,800 man Sv and 55,000
man Gy, respectively. Most of the collective doses werereceived by the populations of Belarus and Ukraine.
105. The evacuation of the residents of Pripyat (28 April)and of the rural settlements inside the 30-km zone
(beginning of May) prevented the potential occurrence ofdeterministic effects and resulted in collective doses
substantially lower than would have been experienced if
there had been no evacuation. A comparison of the external
effective doses for the Belarusians, calculated with andwithout evacuation from the 30-km zone, is presented inTable 24 [S24]. Because of the evacuation, the number of
inhabitants with doses greater than 0.4 Sv was reduced
from about 1,200 to 28 persons. The collective effective
dose from external exposure averted in 1986 for theapproximately 25,000 evacuated Belarusian inhabitants
was estimated to be 2,260 man Sv (or approximately 75%of the dose that would have been received without
evacuation). A similar assessment of averted collective
dose for the evacuated Ukrainian inhabitants led to a valueof about 6,000 man Sv. Therefore, the averted collective
dose from external exposure for the 116,000 persons
evacuated in 1986 is estimated to be 8,260 man Sv.
106. The thyroid collective dose was also reduced to someextent. Iodine prophylaxis was mostly effective in Pripyat,
where about 73% of the population received iodine tablets
on April 26 and 27, i.e. during the very first days after theaccident. It is estimated that a single intake reduced the
expected thyroid dose by a factor of 1.61.7 and that
intakes during two consecutive days reduced it by a factorof 2.3 [R10]. In the rural areas close to the nuclear powerANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

plant, about two thirds of the children used iodine tablets
for prophylactic reasons. However, they did not start taking
the tablets before 30 April, and about 75% of the children
who took iodine tablets began to take them on 24 May.
Thus, because there was a one-week delay in the use ofiodine tablets and because only part of the population wascovered, the averted collective thyroid dose from ingestionof contaminated milk was about 30% of the expectedcollective thyroid dose from that pathway, while thethyroid doses from inhalation remained unchanged. An
upper estimate of the averted collective thyroid dose for the
116,000 evacuees is about 15,000 man Gy [A10].

C INHABITANTS OF CONTAMINATED
AREAS OF THE FORMER SOVIET UNION
107. Areas contaminated by the Chernobyl accident havebeen defined with reference to the background level of137
Cs deposition caused by atmospheric weapons tests,
which when corrected for radioactive decay to 1986, isabout 24 kBq m2 (0.050.1 Ci km2). Considering
variations about this level, it is usual to specify the level of
37 kBq m2 (1 Ci km 2) as the area affected by the
Chernobyl accident. Approximately 3% of the European
part of the former USSR was contaminated with 137Cs
deposition densities greater than 37 kBq m2 [I3].
108. Many people continued to live in the contaminatedterritories surrounding the Chernobyl reactor, although
efforts were made to limit their doses. Areas of 137Cs
deposition density greater than 555 kBq m2 (15 Ci km2)
were designated as areas of strict control. Within theseareas, radiation monitoring and preventive measures weretaken that have been generally successful in maintaining
annual effective doses within 5 mSv. Initially, the areas ofstrict control included 786 settlements and a population of
273,000 in an area of 10,300 km2 [I3, I4]. The sizes andpopulations of the areas of strict control within Belarus, theRussian Federation and Ukraine are given in Table 25.
Those population numbers applied to the first few years
following the accident. Because of extensive migration outof the most contaminated areas and into less contaminatedareas, the current population in the areas of strict control
is much lower in Belarus and Ukraine and somewhat lower
in the Russian Federation. In 1995, the number of people
living in the areas of strict control was about 150,000[K23, R11]. The distribution of the population residing incontaminated areas in 1995 according to 137Cs deposition
density interval is provided in Table 26. The total
population is about 5 million and is distributed almost
equally among the three countries.
109. In the UNSCEAR 1988 Report [U4], the Committee
evaluated separately the doses received during the first year
after the accident and the doses received later on. The mostimportant pathways of exposure of humans were found tobe the ingestion of milk and other foodstuffs contaminatedwith 131I, 134Cs and 137Cs and external exposure from475

radioactive deposits of short-lived radionuclides (132Te, 131I,
Ba, 103Ru, 144Ce, etc.) and long-lived radionuclides(essentially, 134Cs and 137Cs).

140

110. In the first few months, because of the significant
release of the short-lived 131I, the thyroid was the most
exposed organ. The main route of exposure for thyroid
dose was the pasture-cow-milk pathway, with a secondary
component from inhalation. Hundreds of thousands ofmeasurements of radioiodine contents in the thyroids ofpeople were conducted in Belarus, the Russian Federationand Ukraine to assess the importance of the thyroid doses.
111. During the first year after the accident, doses fromexternal irradiation in areas close to the reactor arose
primarily from the ground deposition of radionuclides withhalf-lives of one year or less. In more distant areas, theradiocaesiums became the greatest contributors to the dosefrom external irradiation only one month after the accident.
112. Over the following years, the doses received by the
populations from the contaminated areas have comeessentially from external exposure due to 134Cs and 137Cs
deposited on the ground and internal exposure due tocontamination of foodstuffs by 134Cs and 137Cs. Other,usually minor, contributions to the long-term radiation
exposures include the consumption of foodstuffs
contaminated with 90Sr and the inhalation of aerosols
containing 239Pu, 240Pu and 241Am. The internal exposures
to 134Cs and 137Cs result in relatively uniform doses over allorgans and tissues of the body. A very large number ofmeasurements of exposure rates, as well as of radiocaesiumin soil and in foodstuffs, have been made in Belarus, theRussian Federation and Ukraine to assess the effective
doses and have been used to prepare compilations ofannual effective doses received by the most exposed
residents in the contaminated settlements. These compilations, which were prepared for regulatory purposes, tend tooverestimate the average doses that were received during
the years 19861990.
113. Since 1991, methods for average dose estimation
have been introduced to account for observed changes inradiation levels, as evidenced by experimental dose
determinations with TLD measurements and 134Cs/137Cs
whole-body counting. These methods were introduced inorder to make reasonable decisions regarding the radiation
protection of the population, and also to obtain dose
estimates for use in epidemiological studies, whereaccurate individual dose estimates are needed, or in risk
assessment studies, where collective doses over limitedareas are necessary, and they were an improvement in thegeneral state of knowledge in the field of dosereconstruction. These methods are based on as manymeasurements as possible, either in the area underconsideration or for the individual of interest.
114. The experience thus far acquired and the data
accumulated are allowing more realistic dose assessment
procedures to be formulated. For example, the external

476

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

dose estimates may be related to the contributions fromeach radionuclide present at the time of deposition, thereduction with time due to radioactive decay andpenetration of radionuclides into soil, and shielding andoccupancy for various types of buildings and populationgroups (urban, rural, agricultural workers, schoolchildren,etc.) [G1]. Data from whole-body counting of 134,137Cs haveallowed a better estimation of 137Cs retention times inrelation to sex for adults and in relation to age, body massand height for children [L1]. A careful analysis of the
thyroid activity measurements, along with theconsideration of 137Cs deposition densities and of relevant
environmental parameters, has improved the reliability of
estimated thyroid doses, although much work remains to bedone [G7].
115. When the above methods of dose estimation are used,
they may yield several estimates of dose, not necessarily
comparable, for example maximal projected doses, average
projected doses and actual doses. In local areas there could
also be wide deviations from the average settlement doseowing to particular control measures or individual
behaviour. Estimates of effective doses per unit deposition
density from external and internal exposure have been
derived for various districts and times following theaccident. These effective dose estimates, as well as the
thyroid doses from intake of radioiodines, are discussed
below.
1. Doses from external exposure116. Effective doses have been estimated in Belarus, theRussian Federation and Ukraine on the basis of (a) the
large number of measurements of exposure rates and ofradionuclide concentrations in soil carried out in thecontaminated areas and (b) population surveys on indoor
and outdoor occupancy as a function of age, season,
occupation and type of dwelling. The methodology that
was applied [B14] has some similarities to that used by theCommittee in the UNSCEAR 1988 Report [U4]. The
effective dose for a representative person of age k is
calculated as
Ek  Da Fk Σ Li,k Bi,kiwhere Da is the absorbed dose in air over the time period ofinterest at a reference location at a height of 1 m above flat,
undisturbed ground; Fk is the conversion factor fromabsorbed dose in air to effective dose for a person of age k;
Li,k is the location factor, which is the ratio of the absorbed
doses in air at location i and at the reference location for a
person of age k; and Bi,k is the occupancy factor, that is, thefraction of time spent at location i. The location i can beindoors (place of work, place of residence, etc.) or outdoors(street, forest, backyard, etc.).
117. The absorbed dose in air at the reference location, Da,
was usually inferred from the measured or assumed
radionuclide distribution in deposition. The conversion

factor from absorbed dose in air to effective dose, Fk, wasdetermined using anthropomorphic phantoms simulating
individuals from one year of age to adult, containing TLDs
in many organs, exposed to radiocaesium outdoors andindoors [E7, G1, G19]. The values of Fk were found to be
0.70.8 Sv Gy1 for adults, 0.80.9 Sv Gy1 for 717-yearold schoolchildren, and about 0.91.0 Sv Gy1 for 07year-old pre-schoolchildren [G1].
118. The term Σ Li,k Bi,k, called the occupancy/ shielding or
reduction factor, was derived from population surveys.
Values obtained for the reduction factor for rural and urban
populations in the Russian Federation [B14] are presented
in Table 27, along with the values used by the Committee
in the UNSCEAR 1988 Report [U4]. There is good
agreement between the two sets of values used for
representative groups. Detailed information on the locationand occupancy factors derived from surveys among the
populations of Belarus, the Russian Federation andUkraine is available [E7]; for example, values of occupancy
factors in the summertime for rural populations of the three
countries are presented in Table 28.
119. It is clear from Tables 27 and 28 that there aresubstantial differences in the reduction factor depending on
the type of dwelling and occupation. The values used forthe representative group are meant to reflect the age andsocioprofessional composition of the population living ina typical dwelling. Estimates of external effective doses for
specific groups can be obtained by multiplying the dose forthe representative group by a modifying factor, as given in
Table 29 [B14]. The values of the modifying factor werevalidated with data from individual dosimetry (TLD
measurements) [E8].
120. Values of the overall coefficient used to calculate theaverage external effective doses, Db, on the basis of theabsorbed dose in air, Da, are shown in Table 30. These
overall coefficients have different values for urban andrural populations, but for both populations, the values areaveraged over age, occupation, and type of dwelling.

(a) Doses from external irradiation received
during the first year after the accident
121. For times of less than one year after the accident, thereference absorbed dose rate in air was calculated assumingthat the radioactive deposit was a plane source below a soil
slab with a mass per unit area of 0.5 g cm2 [E7]. During
the first few months after the accident, the dose rate in air
varied according to the radionuclide composition of theactivity deposited, which, as shown in Table 6, varied
according to direction and distance from the reactor. As an
example, Figure XIII illustrates the variations in thecontributions to the absorbed dose rate in air of various
radionuclides from a contaminated area of the RussianFederation [G1]. In that case, the radiocaesiums became
the greatest contributors to the dose rate in air only one
month after the accident, because the short-lived radio-

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

477

from 11 µSv per kBq m 2 of 137Cs for urban areas of theRussian Federation to 24 µSv per kBq m2 of 137Cs for rural
areas of Ukraine.

80
70
132

Te + 132I

PERCENTAGE

60
50

134Cs

40

137Cs

30
20

131

I

106Ru

10

Other
140

Ba + 140La

00

10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
TIME AFTER ACCIDENT (days)

Figure XIII. Contributions of radionuclides to theabsorbed dose rate in air in a contaminated area of theRussian Federation during the first several months
after the Chernobyl accident [G1].

RELATIVE CONTRIBUTION TO DOSE RATE (%)

nuclides and the refractory elements were less important
than in areas closer to the reactor. As shown in Figure
XIV, the short-lived radioisotopes of refractory elements,
such as 95Zr, 106Ru, and 141Ce, played an important role inthe doses from external irradiation received during the firstyear after the accident in areas close to the reactor site[M3]. Following decay of the short-lived emitters, theannual doses per unit 137Cs deposition were similar in allareas, although a slight decrease was observed withincreasing distance from the reactor [J1]. Table 31 presents
published estimates of normalized effective doses fromexternal irradiation for various periods after the accident
and for rural and urban areas in the three countries thatwere most affected by the accident. The effective doses
from external irradiation are estimated to be higher in rural
areas than in urban areas by a factor of about 1.5. During
the first year after the accident, average values of thenormalized effective dose are estimated to have ranged
100
95Zr + 95m

Nb

137Cs

106Ru

134Cs

10

122. In summary, during the first year after the accident,
the average values of the normalized effective dose are
estimated to have been 1524 µSv per kBq m2 of 137Cs forrural areas and 1117 µSv per kBq m2 of 137Cs for urban
areas, the values for Belarus and Ukraine being higher
than those for the Russian Federation because of theircloser proximity to the reactor. These values are inagreement with the value of 10 µSv per kBq m2 of 137Cs
used by the Committee in the UNSCEAR 1988 Report [U4]for the normalized effective dose equivalent, because mostof the data used to derive the 1988 value came fromcountries further away from the reactor than Belarus, theRussian Federation and Ukraine.

(b) Doses from external irradiation received
after the first year following the accident
123. At times greater than one year after the accident, theabsorbed dose rate in air came essentially from the gamma
radiation from 134Cs and 137Cs. The models used in the three
countries (Belarus, the Russian Federation and Ukraine) toderive the variation with time of the normalized absorbed dose
rate in air at a height of 1 m above undisturbed ground in thesettlements of the contaminated areas are somewhat different.
In Belarus, a Monte Carlo method was used; the verticalprofile of 134Cs and 137Cs in soil was simulated by a set of
infinite isotropic thin sources placed at different depths of soil
and an exponential decrease with depth, with an initial
relaxation length of 0.5 g cm2 and a linear increase of thatvalue with time after the accident [K38]. In the RussianFederation, the vertical migration of 137Cs to deeper layers ofsoil was taken into account using a time-varying function r(t),which represents the ratio of the absorbed dose rates in air ata height of 1 m above ground at times t after deposition andat the time of deposition (t = 0), the latter being calculated
over flat, undisturbed ground. The variation with time of r(t)may be described asr(t)  a1 e

ln2t/T1

 a2 e ln2t/T2

144

Ce

95
103Ru
144

Ce

Nb
Ba +140La

140

1
155

Eu

131

I

132

110mAg

I

0
0

3

6

with T1 = 1.5 a, T2 = 20 a, and a1 and a2 equal to 0.4 and
0.42, respectively [B26, M17].

9
12
15
18
21
24
TIME AFTER ACCIDENT (months)

27

30

Figure XIV. Contributions of radionuclides to theabsorbed dose rate in air in areas close to theChernobyl reactor site [M3].

124. In Ukraine, the variation of the normalized absorbed
dose rate in air was determined both on the basis of routine
measurements of exposure rate at eight reference sites andmodelling of the vertical migration of 137Cs. The second
approach used the time-varying function given in the above
equation but with different parameter values: T1 = 0.5 a, T2= 10 a and a1 and a2 equal to 0.18 and 0.65, respectively[M16]. The difference in the estimates obtained for r(t) in
the Russian Federation [M17] and in Ukraine [M16] isdifficult to explain; it may be partly due to the fact that themeasurements were made in different conditions accordingANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

125. Average external normalized effective doses for the
populations living in contaminated areas are derived fromthe reference values of normalized absorbed dose rates in
air presented in Table 32 and the overall coefficients fromdose in air to effective dose presented in Table 30. Results
for several time periods are shown in Table 31. Values forrural areas of Belarus for the 19962056 time period are
estimated in this Annex to be the same as those for theRussian Federation and Ukraine in rural areas; on the basisof data in Table 30, values for urban areas of Belarus aretaken to be the same as in rural areas of that country. The
selected values of the average normalized external effective
doses for urban and rural populations are shown in
Table 33. On average, the external doses received during
the first 10 years after the accident represent 60% of the
lifetime doses (Table 33). The normalized lifetime doses
are estimated to range from 42 to 88 µSv per kBq m2 of137
Cs. These values are somewhat lower than the value of86 µSv per kBq m2 of 137Cs used by the Committee in the
UNSCEAR 1988 Report for the normalized effective dose
equivalent. This may be due to the fact that in the
UNSCEAR 1988 Report, the Committee used the conservative assumption that the vertical profile of 137Cs in soil
would be permanently fixed one year after the time ofdeposition.
126. Average effective doses from external irradiation
received during the first 10 years after the accident are
estimated to range from 5 mSv in the urban areas of theRussian Federation to 11 mSv in the rural areas of Ukraine.
The distributions ofthe collective effective doses from external
irradiation according to region of the country, dose interval,and 137Cs deposition densityare presented in Tables 3436 forBelarus, the Russian Federation and Ukraine. These
distributions have been estimated from the databases ofradionuclide depositions that are available for each settlementof the contaminated areas of Belarus, the Russian Federationand of Ukraine [B37, L44, M17, S46].
127. The variability of individual external doses can be
estimated from the analysis of TLD measurements.
Figure XV illustrates the relative distribution of external
doses in 1991 and 1992 for 906 inhabitants of 20
Belarusian villages in which the 137Cs deposition density
ranged from 175 to 945 kBq m2 [G9, G10]. The individual
doses were normalized to the median dose in eachsettlement. It was found that a log-normal distribution witha geometric standard deviation of 1.54 provides a good
approximation of the normalized individual doses fromexternal irradiation. The calculated doses that are recordedin the dose catalogues at that time were in good agreementwith the measured median doses, the maximum
discrepancy being ±30%.

99.9
99CUMULATIVE FREQUENCY (%)

to the type of fallout (wet or dry), the distance from thereactor and the type of soil. The values obtained in thethree countries for the normalized absorbed dose rate in air
are given in Table 32 for each year between 1987 and1995. The variation with time is fairly similar in the three
countries.

95
80
50
20
5
1
0.1
0.25

0.5
1.0
2.0
RATIO OF INDIVIDUAL TO MEDIAN DOSE

4.0

Figure XV. Distribution of ratios of measured external
individual doses to median settlement dose for 906
inhabitants of 20 rural settlements of Gomel region in
1991-1992 (geometric standard deviation: 1.54).

128. Figure XVI illustrates the distribution of external
doses obtained in 1987 in a smaller survey involving the
inhabitants of the village of Stary Vyshkov in the RussianFederation [S25]. In that particular case, it was found thata normal distribution with a coefficient of variation of
about 1.4 could be used. Individuals who received doses in
the upper or lower tenths of the distribution were examinedfurther. The two characteristics found to be important were
occupation and the construction of the building in which
the individuals spent a large proportion of time. None of
the individuals living or working in stone or brick buildings
received external doses in the upper tenth percentile of thedose distribution [S25]. In addition, the external dose
received as a function of age was also studied for the
inhabitants of that Russian village. The results, shown in
Figure XVII, indicate a great variability in external dose,30

25
NUMBER OF PERSONS

478

20

15

10

5

0
1

2
5
10
EXTERNAL WHOLE-BODY DOSE (mGy)20

Figure XVI. Distribution of external whole-body doses
among 124 residents of Stary Vyshkov, RussianFederation, in 1987 [S25]. The fitted normal curve issuperimposed.

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

with an overall trend that suggests an increase in external
dose with increasing age [S25]. This may reflect
differences in occupational activity, since young people
would be expected to spend a large proportion of timeindoors at school and, consequently, to receive low external
doses, while old people generally spend much time
outdoors or inside lightly shielded buildings [S25].
15
EXTERNAL WHOLE-BODY DOSE (mGy)

14

479

they may play a more important role in the future. Following the Chernobyl accident, about 350,000 measurementsof 131I in the thyroids of people [G7, L10, S17] and about 1
million measurements of 134,137Cs whole-body contents[B14, D3, L21] were conducted in the three republics bymeans of gamma radiation detectors placed outside thebody. In addition, thousands of analyses of 90Sr andhundreds of analyses of 239Pu were performed on autopsy
samples of tissues.

13
12
11
10
9
8
7
6
5
4
3
2
1
0
0

20

40

60

80

AGE (years)

Figure XVII. Variation with age of external whole-bodydoses among residents of Stary Vyshkov, RussianFederation, in 1987 [S25].

129. The effect of decontamination procedures on external
dose was also studied by the analysis of daily external doses
calculated from TLD measurements made before and after
decontamination of the Belarusian village of Kirov [S25].
Decontamination procedures included replacing road surfaces,
replacing roofs on buildings, and soil removal. The results,
presented in Table 37, suggest that the decontamination
measures were most effective for schoolchildren and field
workers (with dose reductions of 35% and 25%, respectively)
but had a limited effect on other members of the population[S25]. Similar estimates have been obtained with regard to thedecontamination of Russian settlements in 1989 [B38]. The
average external dose ratio measured after and before
decontamination was found to range from 0.70 to 0.85 fordifferent settlements [B38].
130. The averted collective dose attributable to decontamination procedures was estimated to be about 1,500 man Sv forthe first four years after the accident, taking into account thefact that decontamination was only conducted in areas with a137
Cs deposition density greater than 555 kBq m2 andassuming that the doses were reduced by about 20% as aresult of the decontamination procedures [A10, I30].
2. Doses from internal exposure131. The doses from internal exposure came essentiallyfrom the intake of 131I and other short-lived radioiodines
during the first days or weeks following the accident, andsubsequently, from the intake of 134Cs and 137Cs. Other
long-lived radionuclides, notably 90Sr and 239,240Pu, have so
far contributed relatively little to the internal doses, but132. The assessment of the internal doses from radioiodines
and radiocaesiums is based on the results of the measurementsof external gamma radiation performed on the residents of thecontaminated areas. Usually, individuals were measured only
once, so that only the dose rate at the time of measurement
can be readily derived from the measurement. To calculate thedose, the variation with time of the dose rate needs to beassessed. This is done by calculation, taking into account therelative rate of intake of the radionuclides considered, both
before and after the measurement, and the metabolism of theseradionuclides in the body, which in the case of thyroid doses
from radioiodines may have been modified by the intake ofstable iodine for prophylactic purposes. The age-dependent
values recommended by the ICRP [I36] for the thyroid massand the biological half-life of 131I in the thyroid were generally
used in thyroid dose assessments based on measurements,
although there is evidence of mild to moderate iodine
deficiency in some of the contaminated areas [A16].
(a) Thyroid doses from radioiodines andtellurium-132
133. The same methodology as described in the preceding
paragraph was used in the three countries to reconstruct
the thyroid doses of the persons with thyroid measurements[W7]. There were, however, practical differences related tothe quantity and quality of the thyroid measurements andthe assumptions used to derive the temporal variation of
the radioiodine intake. For the individuals who were notmeasured but who lived in areas where many persons had
been measured, the thyroid doses usually are reconstructedon the basis of the statistical distribution of the thyroid
doses estimated for the people with measurements, together
with the knowledge of the dietary habits of the individuals
for whom the doses are reconstructed. Finally, the thyroid
doses for people who lived in areas with very few or no
direct thyroid measurements within a few weeks after theaccident are being reconstructed by means of relationships
using available data on 131I or 137Cs deposition, exposure
rates, 137Cs whole-body burdens, or concentrations of 131I in
milk. The largest contribution to the thyroid dose was fromthe consumption of fresh cows' milk contaminated with
131
I. Short-lived radioiodines (132I and 133I) in general played
a minor role for the populations that were not evacuatedwithin a few days after the accident; the contribution of theshort-lived radioiodines and of 132Te is estimated to havebeen up to 20% of the 131I thyroid dose if the radionuclide
intake occurred only through inhalation and of the order of
1% if the consumed foodstuffs (milk in particular) were
contaminated [K16]. Although many initial estimates of

480

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

pills between 2 and 4 May 1986 [S43]. However, in a survey
performed in 1992 on about 10,000 individuals from 17
Ukrainian districts of the Chernigov region, only about 1% of
the respondents reported that they took stable iodine between
1 May and 20 May 1986 [L25].

thyroid doses are available, they need to be refined using
all the relevant and scientificallyreviewed information thatis available [L42, L43]. In order to obtain better
information on the pattern of deposition density of 131I,
measurements of the 129I concentrations in soil areenvisaged [P25, S45].

135. For several reasons, thyroid dose estimates were madeindependently of 137Cs measurements and not only in areas
where the 137Cs deposition density exceeded 37 kBq m2: (a)the thyroid measurements were carried out within a few weeks
after the accident, that is, in large part before an accurate anddetailed pattern of 137Cs deposition density was available; (b)the 131I to 137Cs activity ratio in fallout was markedly variable,
especially in Belarus (Figure XVIII); (c) the milk that was
consumed within a few weeks after the accident was notnecessarily of local origin, at least in urban areas; and (d)there is a large variability of the individual thyroid doses
according to age and dietary habits. The thyroid dose estimates reported in the scientific literature are for populations
with thyroid measurements, for populations that resided at thetime of the accident in ill-defined “contaminated areas”, andfor the entire populations of the three republics.

134. The influence of having taken stable iodine forprophylactic purposes has usually not been taken into accountin the determination of thyroid doses. Based on a survey
conducted in 1990 of 1,107 persons living in contaminatedareas, the number of persons who indicated that they actually
took potassium iodide (KI) for prophylactic purposes is about
one quarter of the population [M5]. Forty-five percent of those
who took KI indicated that they took it only once, 35% morethan once, and 19% could not remember details of their KI
prophylaxis [M5]. The exact day that administration of KI
was begun was poorly recalled by the subjects, making it
difficult to use these data for dose reconstruction purposes. In
another survey, conducted in the three most contaminateddistricts of the Gomel region of Belarus, it was found that
68% of the children who consumed fresh cow’s milk took KI
LATVIA

LITHUANIA

25

RUSSIAN
FED.

15

20

10

VILNIUS

Smolensk

POLAND

Kaluga60

MINSK

MogilevTula

B E L A R U S

540
WARSAW

Bryansk
Orel

5

Brest

RUSSIANFEDERATION

Gomel

30

10

25

Lublin7
Chernigov

Chernobyl
Rovno

Y
GAR
HUN R O M A N I A

10

Sumy
Zhitomir

Lvov

IA
AK
OV
L
S

MOSCOW

30

KIEV

Kharkov

15

20

Vinnitsa
Cherkassy

30 25

Chernovtsy

20

REP. OFMOLDAVIA15

U K R A I NE

Kirovograd
0

50

100

150

200

250

300 kmFigure XVIII. Estimated pattern of iodine-131/caesium-137 activity ratio over the European territory of theformer USSR resulting from the Chernobyl accident [S30]. (Values decay corrected to 1 May 1986).

136. The ratio of 131I to 137Cs deposited by dry processes(i.e. in the absence of precipitation) in Poland was assessedfrom measurements of air concentrations [K39]. From 28
April to 1 May, the measured time-integrated concentrations of 131I and 137Cs were 187 and 18.2 Bq d m3,
respectively. This ratio of about 10 for the time-integrated
concentrations of 131I and 137Cs is consistent with that foundin a previous estimation [Z5]. The measured physicochemical forms of 131I were 62% aerosol-bound, 34%elemental, and 4% organic. Assuming that (a) all of the
Cs is aerosol-bound, (b) the deposition velocity ofelemental iodine is five times greater than that of theaerosol-bound fraction, and (c) the deposition velocity oforganic iodine is negligible, the ratio of 131I to 137Cs
deposition can be estimated to be 23 [K39]. The
measurements of 131I and 137Cs in soil sampled in a few
locations in central and southern Poland yield a ratio of 20(95% CI: 2040). These values are in agreement with both137

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

137. Belarus. The main contaminated areas of Belarus arelocated in the Gomel and Mogilev regions. Within a few
weeks after the accident, direct thyroid measurements (i.e.
measurements of gamma radiation emitted by the thyroid
using detectors placed outside the body) were made on
approximately 130,000 persons, including 39,500 children,
living in the most contaminated areas of Gomel and Mogilev
regions, as well as in the city of Minsk [G6]. The content, atthe time of measurement, of 131I in the thyroid of these
130,000 persons was derived from the direct thyroid measurements. The thyroid dose estimation was then performed forthe measured individuals, supplementing the results of thedirect thyroid measurements with standard radio-ecologicaland metabolic models, for 131I intake with inhalation and withingestion of fresh milk following a single deposition of fallout
on pasture grass [G6, S44]. Unfortunately, most of the thyroid
measurements are of poor quality, as they were made byinexperienced people with uncollimated detectors. The uncertainties in the thyroid dose estimates obtained in this mannerin Belarus are reported to be characterized by a geometricstandard deviation of up to 1.7 [G7]. A detailed breakdown of
the thyroid dose distribution for approximately 32,000 children with thyroid measurements is presented in Table 38. In
each age category, the thyroid dose estimates are found to lie
in a very wide range (from <0.02 Gy to >2 Gy). As shown in
Figure XIX, doses to adults also show a large variability, even
if the samples are taken from a single village or town [G6].
138. Limited information is available on in utero thyroid
doses. In a study of 250 children born during the period fromMay 1986 to February 1987 from mothers who lived at thetime of the accident in areas with 137Cs deposition densities
greater than 600 kBq m2 in Gomel region (222 mothers), in
Mogilev region (14 mothers) and in Pripyat town (14 mothers
who were evacuated to Belarus), thyroid doses were estimatedto range up to 4.3 Gy, with 135 children exposed to less than
0.3 Gy, 95 children between 0.3 and 1.0 Gy, and 20 children
with doses greater than 1.0 Gy [I37]. Uncertainties in theestimated doses were characterized by a geometric standard
deviation of 1.7 to 1.8.
139. Average and collective thyroid doses for the rural andurban populations of the contaminated areas of the Gomel
and Mogilev regions were derived from an analysis of dose
estimates obtained from direct thyroid measurements [I28].

The results, presented in Table 39 for children 07 years
old and for the total population, show that the thyroid
doses are about two times greater in rural areas than inurban areas and also two times greater in Gomel region
than in Mogilev region.
0.999

Narovlya town
Khoyniki town
Pogonnoe (evacuated village)

0.99
CUMULATIVE FREQUENCY

the ratio derived from air concentrations and the values
shown in Figure XVIII. Measurements of deposition arelacking for the northeastern part of Poland, but the measured
concentrations in milk indicate that the ratio of 131I to 137Cs
deposition was greater there than in central and southern
Poland, again in agreement with Figure XVIII. There are also
other reports on the composition of 131I species in the air indifferent countries. Some of them were presented in the
UNSCEAR 1988 Report [U4]. The results indicate that the
distribution of the physico-chemical forms changed with time,
distance, and weather conditions. Because the transfer ofradioiodine from the air to vegetation is highly influenced byits chemical forms, it is important to consider the distributionof iodine species in the assessment.

481

0.9

0.5

0.1

0.01

10

-3

-2
-1
0
10
10
10
INDIVIDUAL THYROID DOSE (Gy)101Figure XIX. Cumulative distribution of individual
thyroid doses for adults of selected towns and villagesof Belarus [G6].

140. Because very few or no thyroid measurements wereavailable for many villages and towns, whereas 137Cs
deposition densities were measured in practicallyall inhabitedareas of Belarus, a model was developed to establish arelationship between the 137Cs deposition densities, F(137Cs),
and the mean thyroid doses to adults, Dad, in areas whereabundant thyroid measurements had been performed. Thismodel enabled the estimation of thyroid dose to be made forthe populations of any area in Belarus. In Figure XX, thevalues of Dad are plotted against those of F(137Cs) for 53
villages of the Khoyniki district. A proportional relationshipbetween the 137Cs deposition density and the mean thyroid
dose to adults seems to be inadequate; however, there is aweak tendencyshown bythe solid line, although characterized
by large uncertainties. Similar relationships were observed for
all areas of Belarus where abundant thyroid measurements
had been performed. That there is no proportional
relationship between Dad and F(137Cs) in Belarus is likely to be
partly due to the fact that the fraction of 131I intercepted by
pasture grass differs according to whether deposition occurs
with or without rainfall and varies also as a function of
rainfall intensity. The fraction of 131I intercepted by pasturegrass is greater when the deposition occurs in the absence ofrainfall (usually associated with low levels of deposition) thanwhen deposition occurs with rainfall (generally associatedwith high levels of deposition). Because of this, the thyroid
dose per unit 137Cs deposition density is found to decrease as
the 137Cs deposition density increases. A confounding factor isthat the ratio of 131I to 137Cs in deposition also varied
according to whether deposition occurred in the presence orabsence of rainfall. However, similar relationships areobserved when the thyroid dose is plotted against either 131I or
137
Cs deposition density, suggesting that the variation in theinterception coefficient is the dominant factor.

482

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

1.2

reactor. During this time period, most of the short-lived
iodine isotopes had decayed. Rainfall in the area decreased
the concentrations in air and reduced the inhalation intake.
Therefore, the dose to thyroid was due primarily to 131I
intake with milk and leafy vegetables, and the pattern ofdoses was similar throughout the region.

Semi-empirical model: y = 0.33 + 0.00032 x
Proportional model: y = 0.00081 x

1.1
MEAN THYROID DOSE (Gy)

1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0

200

400

600

800

1000

1200

CAESIUM-137 DEPOSITION DENSITY (kBq m-2 )Figure XX. Thyroid dose to adults in relation to
caesium-137 deposition density in the district ofKhoyniki (Gomel region, Belarus) [G17].

141. Using these relationships for areas with no or few
direct thyroid measurements, estimates of collective thyroid
dose have been calculated for the entire population of eachregion of Belarus and for the entire population of thecountry [G7]. The collective thyroid dose to the entire
population of Belarus is roughly estimated to be about
500,000 man Gy (Table 40).
142. Russian Federation. The main areas of contamination in the Russian Federation are located 150250 km to
the northeast of Chernobyl in the Bryansk region and at a
500 km distance in the Kaluga-Tula-Orel regions. The
ratio of 131I to 137Cs varied little in this area, whichindicated that the contamination originated from a single
plume. The plume arrived 12 days after release from the143. About 45,000 direct thyroid measurements were madein May-July 1986 in the Bryansk, Kaluga, Tula and Orelregions [B39, Z1]. These measurements showed a maximumon 16 and 17 May of up to 300 kBq in the thyroid of someindividuals in the villages of Barsuki and Nikolayevka in the
Krasnogorsk district of the Bryansk region. The 137Cs
deposition at these locations was 2.63 MBq m2 [Z1]. In
other areas, the content of 131I in the thyroid was considerably
less, owing to lower contamination and also to earlier implementation of protective measures, including the ban on
consumption of local milk and leafy vegetables and theadministration of stable iodine. Activities of 131I in the thyroid
were calculated from the results of direct thyroid measurements and were corrected for the contribution of the gamma
radiation due to radiocaesium incorporated in the entire body.
144. In the absence of protective measures, the temporalvariation of the 131I intake, taking into account inhalation andthe ingestion of contaminated milk, is calculated fromstandard radio-ecological models shown in Figure XXI (leftpanel). However, for the purposes of dose reconstruction, a
simplified representation has been adopted (Figure XXI, rightpanel) [B14]. The thyroid mass was determined from
autopsies in the Novozybkov district hospital in the Bryansk
region. The average value for adults was 26.7 g, suggesting amildly endemic goiter area. The Tula and Orel regions are notin endemic areas, and as direct measurements were
unavailable, the standard thyroid mass for adults of 20 g wasused in dose calculations [Z1].
Simplified model

INTAKE ( kBq d -1)

INTAKE ( kBq d -1)

Radiological model

T ½ = 5 days

T ½ = 5 days

T ½ = 1.5 days0

θ1 15 θ2
TIME (d)30

0θ1 15 θ2
TIME (d)30

Figure XXI. Models of iodine-131 intake to inhabitants of contaminated areas in Russia [B14].

145. Thyroid doses were estimated in this manner for six age
groups: <1, 12, 35, 711, 1217 and >18 years. Withineach age group the distribution of dose was asymmetrical,
approximately log-normal. The maximum individual doses
often exceeded the mean dose by a factor of 35. The
variations between age groups were different for towns andvillages, reflecting not only the age-related iodine metabolism
but also differences in social and nutritional habits. As

presented in Table 41, the average thyroid doses for children
less than one year old were greater than those for adults byfactors of 13 in towns and 5 in villages [B14, Z1].
146. Where measurements were insufficient or lacking,correlations were used to estimate the thyroid doses. The
uniformityof contamination allowed correlation analyses tobe
used to relate the thyroid doses to the deposition of 137Cs, theANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

air kerma rate on 1012 May 1986, the concentrations of 131I
in milk, and the body content of 137Cs in adults measured
within a few months after the accident. The analysis of theresults of the direct thyroid measurements for inhabitants of
the Kaluga region showed that the thyroid doses of people
who did not consume local milk was about 15% of the thyroid
doses received by the people who consumed local milk. The
type and number of data available in the Russian Federation
are presented in Table 42.
147. The analysis of the direct thyroid measurements and ofdata from personal interviews for 600 inhabitants of the
Bryansk region showed a significant correlation with milk
consumption. From 80% to 90% of 131I intake appeared to be
derived from this source and only 10% to 20% fromvegetables and inhalation. Thus, estimates of doses toindividuals could be derived by normalizing 80% of theaverage dose for the settlement by the actual volumes of milk
consumed (litres per day times days) relative to the average
consumed volume.
148. Estimates of thyroid doses in contaminated areas of theRussian Federation are presented in Table 43. In areas where
there were no limitations on 131I intake (e.g. Plavsk district ofTula region), the thyroid dose for children less than 3 years
old reached 0.35 to 0.7 Gy, on average, with individual doses
up to 4 Gy. In the most contaminated areas of the Orel region,
the thyroid doses were approximately 0.3 Gy, on average, foryoung children. The highest doses were received byinhabitants of the most contaminated areas of the Bryansk
region even though local milk consumption was banned inthose areas in early May 1986. In some villages average doses
in children exceeded 1 Gy and individual doses exceeded
10 Gy. Average thyroid doses of rural inhabitants were higher
than those received by urban populations in areas with similarradioactive contamination. The age distribution of thecollective dose for the population of the Bryansk region ispresented in Table 44. About 40% of the collective thyroid
dose in rural areas and 60% of the collective thyroid dose inurban areas were received by children under 15 years of age.
149. Ukraine. Over 150,000 direct thyroid measurements of
the radioiodine content of the thyroid gland were made in
May-June 1986 in the areas of Ukraine closest to Chernobyl.
Most of the thyroid measurements were made in eight districts
surrounding Chernobyl and the town of Pripyat: Polesskoe,
Ivanov, Chernobyl and Pripyat in the Kiev region; Kozeletsk,
Repkine and Chernigov in the Chernigov region; andNarodichi and Ovruch in the Zhitomir region [L12]. Between
30% and 90% of the children and 1% and 10% of the adults
from these areas were measured [L2, L11, L12, R4]. Whenthe quality of these measurements was reviewed, over 80%
were found to be of acceptably high quality [L13, L14].
150. Preliminary estimates of the thyroid doses received by
the persons with direct thyroid measurements were madeusing standard methods [A3, I13]. Except for the city of Kiev,
where the 131I concentrations in air, water and milk weremonitored extensively [L15], very few measurements of 131I in
the environment are available from Ukraine. Two models
have been used to describe the variation of the temporal intake

483

of 131I. According to the most conservative model, a single
intake of 131I was assumed to have occurred on the first day of
the accident, and a single exponential is used to describe theiodine retention in the thyroid gland. The more realistic model
for calculating thyroid doses assumes that 131I intake occurred
during the entire period of stay in the contaminated areas[L12]. The intake function was determined assuming a single
initial contamination event by 131I in an area. A two-exponential function is used to represent the dynamics of intake bymilk consumption. The effective decay constants from grass
and milk are 0.15 and 0.63 d1, respectively [A3]. The period
of intake was taken to be the period until relocation or, if there
was no relocation or the information is lacking, the whole
period until 131I decay.
151. Results of the thyroid dose evaluations for children
and adults of the Ukraine indicate that the highest absorbed
doses (1.52.7 Gy) were received by children of the
Narodichi and Ovruch districts of Zhitomir region and of
Pripyat and the Polesskoe districts of Kiev region. Doses tochildren 715 years old were, in general, 2.5 times lower
than doses to the 07-year-old group. The adult doses werelower by a factor of 28 [L2, L12, R4]. According to theconservative, single-exponential model, there were 38,000
children (>40%) with doses lower than 0.3 Gy and 79,500(nearly 90% of children) with doses lower than 2 Gy. Useof the more realistic model generally shifts the distribution
to lower doses. In this case, 63% of children had doses
below 0.3 Gy [L12]. The distribution of thyroid doses in asettlement usually was found to be log-normal.
152. The estimation of doses to individuals living in the cityof Kiev was performed using direct thyroid measurements forapproximately 5,000 residents and measured 131I concentrations in air, water and milk during May-June 1986 [L16,
L17]. The individual thyroid doses were found to vary by anenormously wide range of up to four orders of magnitude[L15]. The average thyroid doses to individuals of five agegroups were as follows: 0.10 Gy (birth years 19831986),
0.06 Gy (19791982), 0.2 Gy (19751978 and 19711974),
and 0.04 Gy (those born before 1974) [L15].
153. To estimate the thyroid doses received by the persons
without direct thyroid measurements living in areas other thanthe city of Kiev, two procedures were used, depending on theabundance of the thyroid measurements in the area
considered. In the three regions where most of the thyroid
measurements were performed (Chernigov, Kiev andZhitomir), the following empirical relationship between themeasured thyroid doses, D, and the 137Cs deposition density,
as well as the location relative to the Chernobyl reactor, wasdetermined to be D(n) = K at [L10, L25], where t = ebn, D is
the thyroid dose (Gy), n is the age of the individual (years),and K is a scaling parameter (Gy). The parameters a(dimensionless) and b (a1) describe the age dependence of the
thyroid dose in the locality considered.
154. The parameter values for K, a, and b were established
for the towns and villages of each district of the three regions.
As examples, Table 45 presents the values obtained for three
districts of the Chernigov region as well as the mean thyroid

484

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

doses for infants and adults [L25], while the measured
individual doses are compared in Figure XXII with thecalculated mean thyroid doses for various age groups in
Rudka village of the Chernigov district [L25]. As is the casein Belarus and the Russian Federation, the mean thyroid dosesin villages are about twice those in urban areas (Table 45).
However, the variability of the individual doses, within agiven village and a given age group, is very great(Figure XXII).

THYROID DOSE (Gy)

10 1

Individual doses

10 0

10 -1

Before1968

1968-1970

1971-1974

1975-1978

1979-1982

1983-1985

1986

10 -2

BIRTH YEARS

Figure XXII. Comparison of individual doses estimatedfrom thyroid measurements and of calculated meandoses (histogram) for the Ukrainian village of Rudka[L25].

155. Another method of thyroid dose assessment was used
for the regions of Cherkasy and Vinnytsia, where very few
thyroid measurements were carried out. Those regions
were subdivided into sectors and segments with relatively
uniform 131I intake functions [L10]. The relationships
established for areas with thyroid measurements were thenextrapolated to other areas.
156. The age-dependent thyroid dose distribution obtained
for the population of the five regions (Cherkasy, Chernigov, Kiev, Vinnytsia and Zhitomir) is given in Table 46.
Most of the thyroid doses are estimated to be less than
0.3 Gy. Doses exceeding 2 Gy are found only amongchildren less than 4 years old [L10]. An estimate of thecollective thyroid dose to residents of Ukraine is presented
in Table 47.
(b) Effective doses from caesium-134
and caesium-137
157. Internal effective doses from 134Cs and 137Cs have been
estimated by two methods: (a) estimation of dietary intake
from measured concentrations in foods and standard
consumption assumptions and (b) whole-body counting. The
foodstuffs that contribute the most to the effective dose aremilk, meat, potatoes and mushrooms [F4]. From 1986 to
1990, the internal doses were calculated from the measured
137
Cs concentrations in milk and potatoes, assuming that the

intake of radiocaesium by ingestion is adequately represented
by consumption rates of 0.8 l d1 of milk and 0.9 kg d1 ofpotatoes. The concentrations used to calculate the doses were
those corresponding to the 90th percentiles of the distributions[A12]. The relationship between the 90th percentiles to theaverage 137Cs concentrations in milk and potatoes was 1.7±0.1[B9]. Beginning in 1991, the average 137Cs concentrations inmilk and potatoes, rather than the 90th percentiles, were used
to estimate the effective doses from internal irradiation.
158. Calculated internal doses assuming consumption onlyof
locally produced foods (no imported, uncontaminated foods)
have been recognized to overestimate actual doses. The dose
estimates calculated in this manner are used only for decisionmaking purposes. The ratios of calculated doses using the90th percentiles of the distributions to the doses determined bywhole-body counting range from 2.5 to 25 for mostsettlements in the zone of strict control (where the 137Cs
deposition density is greater than 555 kBq m2), with a
median value of 7 [B9]. In areas with lower 137Cs deposition
density, where most of the consumed foodstuffs are of local
origin, this ratio is estimated to be in the range 1.515, witha median of 4. For this reason, the internal effective dose
estimates provided currently in the official dose catalogues inBelarus and the Russian Federation are based on whole-bodymeasurements. However, the dose estimates presented in the
Ukrainian dose catalogues are still based on the assessment of
the dietary intakes.
159. The transfer of radiocaesium from soil to milk depends
substantially on the type of soil. For example, in Ukrainian
territory, as a result of radio-ecological monitoring carried out
in 1991, four zones with typical values of soil-milk transfer
coefficient for radiocaesium ranging from less than 1 togreater than 10 Bq l1 per kBq m2 were delineated [K23].
The corresponding normalized effective doses from internal
irradiation are shown in Table 48 for the first 10 years after
the accident; the estimated normalized effective doses for thezone with highest values of the transfer coefficient are about
20 times greater than those obtained in the zone with thelowest values of the transfer coefficient. The territories with
peat-swampy soil that are characterized with the highest
values of soil-milk transfer coefficient are mainly located in
the northern part of the Rovno and Zhitomir regions(Ukraine) and in the eastern part of the Brest region and thesouthwestern part of the Gomel region (Belarus).
160. In the Russian Federation, normalized doses were
estimated for the sodic-podzol sand soil found in some areasof the Bryansk and Kaluga regions and for the chernozem soil
found in the Tula and Orel regions [B25, R9]. Here again, thevalues of the transfer coefficients and of the normalized
effective doses vary by factors of 1020 (Table 49).
161. Estimated internal effective doses, normalized to unit
deposition density of 137Cs (1 kBq m2), are given in
Table 50 for various periods after the accident and forareas with different degrees of contamination in the
Russian Federation. More detailed information for the
population of Belarus is presented in Table 51. It isANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

recognized that the internal effective doses normalized perunit deposition density of 137Cs have to be treated withcaution, because of the large differences in the transfer of137
Cs from soil to milk and because of the influence ofprotective measures. Estimates of projected doses frominternal exposures are highly uncertain, as they depend on
local soil conditions for the transfer to foodstuffs, on thecomposition of the diet, and on the extent to which local
foods are supplemented by imported foods [Z4]. In
particular, it is to be noted that the importance of forest
products (mushrooms, berries, wild game) increases withtime, since the 137Cs concentration in these products
generally have longer ecological half-times than foodproducts from agricultural systems (milk, vegetables, meatfrom domestic animals) [K7, S16]. Average internal
effective doses received during the first 10 years after theaccident are estimated to range from 4 mSv in the rural
areas of Tula region in the Russian Federation to 13 mSv
in the rural areas of Bryansk region in the RussianFederation. On average, the internal doses received during
the first 10 years after the accident represent 90% of the
lifetime doses (Table 50). The distributions of thecollective effective doses from internal irradiationaccording to the region of the country, dose interval, and137
Cs deposition density are presented in Tables 3436 forBelarus, the Russian Federation and Ukraine.
162. Several measures were taken to reduce the internal
exposure to the residents of the contaminated areas. During
the first year after the accident, the most important measures
were taken in the territories of strict control (territories with a137
Cs deposition density exceeding 555 kBq m2). In Belarus,
the resulting factor of decrease in the internal dose wasestimated to be 3.23.4 [S24], while in the Bryansk region it
was about 3.6. In the following years, the corresponding
factors of decrease were maintained at approximatelythe samelevels: 4.1 [I30] and 3.7 [I22], respectively. Therefore, theaverted collective dose for the strict control zone (inhabited by
273,000 residents) can be assessed to be 6,000 man Sv. For
the territories with a 137Cs deposition density from 185 to 555
kBq m2 (inhabited by about 1,300,000 people), the factor of
decrease in the internal dose was estimated to be approximately 2 [S24], resulting in an averted dose of 7,000 man Sv.
Thus, the averted collective dose for about 1,500,000
residents of the areas contaminated with a 137Cs levelexceeding 185 kBq m2 was assessed at nearly 13,000
man Sv. It should be noted that self-imposed measures also
led to a decrease in the internal doses [L21].
163. Within the framework of the Chernobyl Sasakawa
Health and Medical Cooperation Project, about 120,000
children, aged 010 years at the time of the accident, were
examined in two Belarusian centres, two Ukrainian centres
and one Russian centre [N2, S2, S7]. The examinations
were essentially of a medical nature but included ameasurement of the whole-body concentration of 137Cs.
Average values were similar from centre to centre andfrom year to year, with an overall average of about
50 Bq kg1 of 137Cs; the corresponding internal effective
dose rate from 137Cs is about 0.1 mSv a1.

485

164. The Ministry of the Environment, Protection of
Nature, and Reactor Safety of Germany also organized acampaign of whole-body counting in Belarus, the RussianFederation and Ukraine. About 300,000 persons weremonitored from 1991 to 1993 for their 137Cs whole-bodycontent [H1, H4, H5]. For 90% of the persons monitored,
the internal effective dose rates from 137Cs were found to beless than 0.3 mSv a1. The analysis of the results for Kirov,
in Belarus, shows that the population monitored could beclassified in one of five groups, according to the nature of
their diet and the origin of the consumed milk, withincreasing 137Cs content from one group to the next; thedietary characteristics of those groups are defined as (a) no
milk, no forest products; (b) local milk, no forest products;(c) non-local milk, forest products; (d) local milk, forest
products but no wild game; and (e) local milk and forest
products including wild game [S25].
(c) Internal doses from strontium-90
165. Because of the relatively small release of 90Sr andbecause a large fraction of the 90Sr activity released was
deposited within the 30-km zone, internal doses from 90Sr
are relatively small. It is estimated that the 90Sr
contribution to the effective dose from internal exposure
does not exceed 5%10%, according to intake calculations
based on measurements of 90Sr concentrations in foodstuffs,
as well as measurements of 90Sr in human bones [B15].
(d) Lung doses from transuranics
166. The fuel particles that deposited on the groundcontained alpha-emitting transuranics, such as 238Pu, 239Pu,
240
Pu and 241Am, as well as beta-emitting transuranics, suchas 241Pu. Lung doses from transuranics may be caused byinhalation of radioactive particles during the passage of thecloud and following resuspension of deposited materials. A
pathway of concern is the potential hazard from theresuspension from soil to air of radioactive aerosols
containing 239Pu. In an assessment of the equivalent doses
to lungs for agricultural workers, it was concluded thateven at sites inside the 30-km zone, lifetime committed
equivalent doses to the lungs per year of work will not
exceed 0.2 mSv for most individuals [J1]. In the future, therelative importance of 241Am among the alpha-emitting
transuranics is going to increase as a result of the decay of
its shorter-lived parent, 241Pu.

D. INHABITANTS OF DISTANT COUNTRIES
167. Information on doses received bypopulations other thanthose of Belarus, the Russian Federation and Ukraine is not ascomplete. In the UNSCEAR 1988 Report [U4], theCommittee estimated first-year thyroid and effective doses formost of the countries of the northern hemisphere and lifetime
effective doses for three latitude bands (northern, temperateand southern) of the northern hemisphere. These data havebeen used in this Annex to estimate crude average thyroid andbone-marrow doses received by the populations considered in

486

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

epidemiological studies of thyroid cancer and of leukaemia.
These populations usually resided in areas where thedeposition densities of 137Cs resulting from the Chernobyl
accident were the highest (except for contaminated areas ofBelarus, the Russian Federation and Ukraine).
1. Thyroid doses
168. Populations of Croatia, Greece, Hungary, Poland andTurkey have been considered in epidemiological studies ofthyroid cancer [S12]. The average thyroid doses received bythose populations have been estimated, using the approximation that the population-weighted average thyroid dose isthree times that to adults. Results are presented in Table 52.
The estimates of average thyroid dose range from 1.5 to
15 mGy.
2. Bone-marrow doses
169. Populations of Bulgaria, Finland, Germany, Greece,
Hungary, Romania, Sweden and Turkey have been
considered in epidemiological studies of leukaemia [S12].
The average bone-marrow doses received by those
populations have been estimated from data in the
UNSCEAR 1988 Report [U4], using the approximationthat the bone-marrow dose is numerically equivalent to theeffective dose equivalent from all radionuclides for external
irradiation and from radiocaesium for internal irradiation.
The values of effective dose equivalents per unit 137Cs
deposition density that are calculated in the UNSCEAR
1988 Report for the populations of three latitude bands
have been assigned in this Annex to the populations of thecountries considered, as appropriate. In each country, the137
Cs deposition density corresponding to the region ofhighest fallout has been selected, when that information isprovided in the UNSCEAR 1988 Report. The resulting
estimates of average bone-marrow dose for the populations
considered range from about 1 to 4 mGy (Table 52).

received during the first 10 years after the accident by theapproximately 5.2 million people living in thecontaminated areas of Belarus, the Russian Federation andUkraine is estimated to be 24,200 man Sv. Assuming that
this collective dose represents 60% of the lifetime
collective dose, on the basis of the data presented inTable 33, the lifetime collective dose from external
irradiation received by the inhabitants of the contaminatedareas of the three republics would be 40,300 man Sv.
2. Collective doses from internal exposure
172. Collective effective doses. The collective effective
doses from internal exposure received bythe inhabitants of thecontaminated areas during the first 10 years after the accident
have also been estimated using the average 137Cs deposition
densities in each district and estimated average annual
effective doses from internal exposure in each district. They
are found to be about 5,500 man Sv for Belarus [D3], 5,000
man Sv for the Russian Federation and 7,900 man Sv for
Ukraine [L7]. Detailed estimates of the collective effective
doses and of their distributions are presented in Tables 3436
for Belarus, the Russian Federation and Ukraine. Whether
those estimates were obtained using similar methodologies has
not been thoroughly clarified. From the data presented inTable 50, the doses from internal exposure received during thefirst 10 years after the accident represent about 90% of the
lifetime doses. The collective effective doses from internal
exposure received by the population of the contaminated areas
can thus be estimated to be about 18,400 man Sv for the first
10 years after the accident and about 20,400 man Sv overlifetime; this corresponds to an average lifetime effective doseof 3.9 mSv.
173. Collective thyroid doses. Estimated collective thyroid
doses, as reported for populations of Belarus, the RussianFederation and Ukraine, are presented in Table 40.
Collective thyroid doses are estimated to be about 550,000,
250,000 and 740,000 man Gy for the entire populations ofBelarus, the Russian Federation and Ukraine, respectively.

E. COLLECTIVE DOSES
3. Total collective doses
170. In this Section, the collective doses received by the
populations of the contaminated areas of Belarus, theRussian Federation and Ukraine are summarized.
1. Collective doses from external exposure
171. The collective effective doses from external exposure
received by the inhabitants of the contaminated areas
during the first 10 years after the accident have been
estimated using the average 137Cs deposition densities ineach district and estimated average annual effective doses
from external exposure in each district. Detailed estimatesof the collective effective doses and of their distributions
are presented in Tables 3436 for Belarus, the RussianFederation and Ukraine. The totals for each country arepresented in Table 53, while the distribution of thecollective effective doses for the three republics issummarized in Table 54. The total collective effective dose174. Estimated collective effective doses received during
the 19861995 time period by the inhabitants of thecontaminated areas of Belarus, the Russian Federation andUkraine are presented in Table 53. The collective effective
doses that were delivered during the first 10 years after theaccident are estimated to be about 24,200 man Sv fromexternal exposure and 18,400 man Sv from internal
exposure, for a total of 42,600 man Sv and an average
effective dose of 8.2 mSv. Assuming that the dosesdelivered during the first 10 years represent 60% of the
lifetime dose for external exposure and 90% of the lifetime
dose for internal exposure, the estimated lifetime effective
doses for the populations of the three countries living incontaminated areas are about 40,300 man Sv from external
exposure and 20,400 man Sv from internal exposure, for a
total of about 60,700 man Sv. This total corresponds to an
average lifetime effective dose of 12 mSv.

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

175. These figures do not include the collective thyroid
doses, which were delivered in their totality during 1986,
and which are estimated to be 1,500,000 man Gy in total
for the three countries. Taking the population size of thethree republics to be 215 million, the average thyroid dose
is found to be 7 mGy. Much larger thyroid doses, however,were received by a small fraction of the population. For
example, the distribution of the thyroid doses received in
Ukraine is such that very low thyroid doses were received
in a large part of the country, while average thyroid doses
greater than 500 mGy were received in twelve districts.

F. SUMMARY
176. Doses have been estimated for: (a) the workers
involved in the mitigation of the accident, either during theaccident itself (emergency workers) or after the accident(recovery operation workers) and (b) members of thegeneral public who either were evacuated to avert excessive
radiation exposures or who still reside in contaminatedareas, which are found mainly in Belarus, in the RussianFederation and in Ukraine. A large number of radiation
measurements (film badges, TLDs, whole-body counts,
thyroid counts, etc.) were made to evaluate the radiation
exposures of the population groups that are considered.
177. The highest doses were received by the approximately
600 emergency workers who were on the site of theChernobyl power plant during the night of the accident. The
most important exposures were due to external irradiation, as
the intake of radionuclides through inhalation was relatively
small in most cases. Acute radiation sickness was confirmed
for 134 of those emergency workers. Forty-one of thesepatients received whole-body doses from external irradiationof less than 2.1 Gy. Ninety-three patients received higher
doses and had more severe acute radiation sickness: 50
persons with 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
from beta exposures evaluated for eight patients with acuteradiation sickness ranged from 10 to 30 times the whole-bodydoses from external irradiation.
178. About 600,000 persons (civilian and military) havereceived special certificates confirming their status asliquidators (recovery operation workers), according to laws
promulgated in Belarus, the Russian Federation and Ukraine.
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, of a
town for reactor personnel, and of waste repositories. Thesetasks were completed by 1990.
179. A registry of recovery operation workers wasestablished in 1986. This registry includes estimates of doses
from external irradiation, which was the predominant
pathway of exposure for the recovery operation workers. The
registry data show that the average recorded doses decreased
from year to year, being about 0.17 Sv in 1986, 0.13 Sv in

487

1987, 0.03 Sv in 1988, and 0.015 Sv in 1989. It is, however,difficult to assess the validity of the results that have beenreported for a variety of reasons, including (a) the fact thatdifferent dosimeters were used by different organizations
without any intercalibration; (b) the high number of recorded
doses very close to the dose limit; and (c) the high number ofrounded values such as 0.1, 0.2, or 0.5 Sv. Nevertheless, it
seems reasonable to assume that the average effective dosefrom external gamma irradiation to recovery operation
workers in the years 19861987 was about 0.1 Sv.
180. The doses received by the members of the generalpublic resulted from the radionuclide releases from thedamaged reactor, which led to the ground contaminationof large areas. The radionuclide releases occurred mainly
over a 10-day period, with varying release rates. From theradiological point of view, the releases of 131I and 137Cs,
estimated to have been 1,760 and 85 PBq, respectively, arethe most important to consider. Iodine-131 was the main
contributor to the thyroid doses, received mainly via
internal irradiation within a few weeks after the accident,
while 137Cs was, and is, the main contributor to the doses
to organs and tissues other than the thyroid, from either
internal or external irradiation, which will continue to bereceived, at low dose rates, during several decades.
181. The three main areas of contamination, defined as thosewith 137Cs deposition density greater than 37 kBq m2(1 Ci km2), are in Belarus, the Russian Federation andUkraine; they have been designated the Central, GomelMogilev-Bryansk and Kaluga-Tula-Orel areas. The Central
area is within about 100 km of the reactor, predominantly to
the west and northwest. The Gomel-Mogilev-Bryansk
contamination area is centred 200 km to the north-northeastof the reactor at the boundary of the Gomel and Mogilev
regions of Belarus and of the Bryansk region of the RussianFederation. The Kaluga-Tula-Orel area is located in the
Russian Federation, about 500 km to the northeast of thereactor. All together, territories from the former Soviet Union
with an area of about 150,000 km2 were contaminated. Aboutfive million people reside in those territories.
182. Within a few weeks after the accident, approximately
116,000 persons were evacuated from the most contaminated areas of Ukraine and of Belarus. The thyroid
doses received by the evacuees varied according to theirage, place of residence and date of evacuation. For
example, for the residents of Pripyat, who were evacuatedessentially within 48 hours after the accident, thepopulation-weighted average thyroid dose is estimated tobe 0.17 Gy, and to range from 0.07 Gy for adults to 2 Gyfor infants. For the entire population of evacuees, thepopulation-weighted average thyroid dose is estimated tobe 0.47 Gy. Doses to organs and tissues other than the
thyroid were, on average, much smaller.
183. Thyroid doses have also been estimated for residentsof the contaminated areas who were not evacuated. In eachof the three republics, thyroid doses exceeding 1 Gy were
estimated for the most exposed infants. For residents of a

488

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

given 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 is estimated to be 7 mGy.
184. Following the first few weeks after the accident when131
I was the main contributor to the radiation exposures, doses
were delivered at much lower dose rates by radionuclides withmuch longer half-lives. Since 1987, the doses received by the
populations ofthe contaminated areas have resulted essentiallyfrom external exposure from 134Cs and 137Cs deposited on the
ground and internal exposure due to contamination offoodstuffs by 134Cs and 137Cs. Other, usually minor, contribu-

tions to the long-term radiation exposures include theconsumption of foodstuffs contaminated with 90Sr and theinhalation of aerosols containing isotopes of plutonium. Bothexternal irradiation and internal irradiation due to 134Cs and137
Cs result in relatively uniform doses in all organs andtissues of the body. The average effective doses from 134Cs and137
Cs that were received during the first 10 years after theaccident by the residents of contaminated areas are estimatedto be about 10 mSv. The median effective dose was about
4 mSv and only about 10,000 people are estimated to havereceived effective doses greater than 100 mSv. The lifetime
effective doses are expected to be about 40% greater than thedoses received during the first 10 years following the accident.

III. EARLY HEALTH EFFECTS IN REACTOR AND EMERGENCY WORKERS
185. The first information on the early manifestations andoutcomes of acute radiation sickness in persons who were
exposed to ionizing radiation in the earlyphase of the Chernobyl accident was provided to the international community in
Vienna in August 1986 [I2]. A detailed and comprehensive
review of these effects was included in the UNSCEAR 1988
Report (Appendix to Annex G, “Early effects in man of highdoses of radiation”) [U4]. This Chapter describes the healtheffects observed in this group in the years since the accident.
Dose estimations for those working at the Chernobyl nuclear
power plant on 26 April, 1986, are given in Section II.A.1.
186. Among the staff members of the reactor and emergency
workers at the site at the time of the accident, a total of 237
were initially examined for signs and symptoms of acuteradiation sickness, defined here as having at least minimalbone-marrow suppression as indicated by depletion of blood
lymphocytes. This diagnosis was later confirmed in 134
patients, the others being designated as unconfirmed. A
computerized questionnaire for patients with acute radiation
sickness was developed in 1990 [F11] and later extended,
incorporating other nuclear accidents [F3]. The fate of thewhole group of 237 patients has been monitored up to thepresent, although not always systematically, with accurate data
available for most patients for the acute phase and incomplete
information available for the follow-up period of 19861996.
187. The definition of acute radiation sickness is wellestablished and based on clinical observations and thedegree of pancytopenia [B22, K26]. A reliable assessmentof the severity of acute radiation sickness from mild (GradeI) to severe (Grade IV) is possible at three days following
exposure. To predict the likelihood of bone marrow
recovery, damage to the stem cell pool must be determined[F12]. Seven to ten days after exposure, patients in whom
prolonged myelosuppression was diagnosed were selected
for bone marrow transplantation.
188. Among 37 patients considered for transplantation
treatment, all had severe radiation damage to the skin and,in 15 cases, gastrointestinal tract symptoms. Cutaneous
lesions and/or oropharyngeal mucositis were the primarycauses of death in the majority of these patients who later
died as an immediate consequence of the accident. As
might be expected, there was a clear relationship between
the extent of local skin radiation injury, the grade of acuteradiation sickness and mortality. Patients not selected forbone marrow transplantation received supportive therapy
such as transfusions and antibiotics.
189. A total of 13 patients with estimated whole-bodydoses of 5.6 to 13 Gy received bone marrow transplants at
the Institute of Biophysics of the Ministry of Health andClinical Hospital, Moscow [B40]. Two transplant
recipients, who received estimated radiation doses of 5.6
and 8.7 Gy, were alive more than three years after theaccident. The others died of various causes, including
burns (n = 5), interstitial pneumonitis (n = 3), graft-vs-hostdisease (n = 2), and acute renal failure and respiratory
distress syndrome (n = 1).
190. Stable chromosome aberrations in circulating stem
cells, indicating residual damage in the stem andprogenitor cells, were used for retrospective dosimetry[K45]. Unstable chromosome aberrations seemed to be aless reliable proxy for average whole-body dose unlessevaluated shortly after exposure [T15].
191. The distribution of patients with acute radiation
sickness by severity of disease and range of absorbed dosefrom whole-body gamma radiation is given in Table 11.
Among the 134 cases, 28 died within the first four monthsof the accident. The causes of death are listed in the
UNSCEAR 1988 Report, Appendix to Annex G, “Early
effects in man of high doses of radiation” [U4]. In the early
period (1423 days after exposure), 15 patients died of skinor intestinal complications and 2 patients died ofpneumonitis. In the period 2448 days after exposure, six
deaths from skin or lung injury and two from secondary
infections following bone-marrow transplantation

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

occurred. Between 86 and 96 days following the accident,
two patients died from secondaryinfections and one patientfrom renal failure [U4]. Underlying bone marrow failure
was the main contributor to all of these deaths.
192. There have been eleven deaths between 1987 and1998 among confirmed acute radiation sickness survivors
who received doses of 1.35.2 Gy. The causes of death arepresented in Table 55. There were three cases of coronary
heart disease, two cases of myelodysplastic syndrome, twocases of liver cirrhosis, and one death each of lunggangrene, lung tuberculosis and fat embolism. One patient
who had been classified with Grade II acute radiation
sickness died in 1998 from acute myeloid leukaemia.
193. At exposures below 6 Gy, the bone-marrow depletion
was not the direct cause of death when prompt andadequate treatment of the complications could be provided.
The therapy decreased the incidence and severity of
infectious complications and haemorrhagic manifestations[G21, S33, W2].
194. Inflammation of the oropharynx (mucositis) wasapparent even at relatively low doses (12 Gy) of gamma
radiation 46 days following exposure. An unknown
influence of beta radiation could explain these findings. The
incidence of mucositis increased and reached 100% inpatients receiving gamma doses of 613 Gy. The pathogenesis of the oropharyngeal syndrome is complex, as it isdetermined by the initial radiation damage to the skin andmucosa and further complicated by infections of viral,bacterial and fungal species. Recovery of the mucosal epithelium was observed even in severe acute radiation sickness
survivors, which is typical of beta radiation effects [G22, P10].
Acute gastrointestinal symptoms were observed in 15 Chernobyl accident victims and were the most severe symptoms in 11
patients who received doses higher than 10 Gy.
195. Radiation skin burns were observed in 56 patients,
including 2 patients with combined radiation-thermalburns. Alopecia, onycholysis, mucositis, conjunctivitis andacute radiation ulcers were seen. There was a clear
correlation between extent of skin injury and severity ofacute radiation sickness. Skin damage varied from patientto patient in terms of occurrence, severity, course andextent. The clinical course of skin damage was shown to be
dependent on the skin exposure conditions, the beta/
gamma ratio, and the radionuclide contamination on skinand clothing and in the environment [B29]. Absorbed
doses in skin exceeded bone marrow doses by a factor of
1030 in some victims, corresponding to doses up to400500 Gy. From detailed analysis of clinical morphology

489

data, it can be stated that severe skin injury by beta
radiation of moderate energy (13 MeV) could be a major
cause of death if the damaged area exceeds 50% of the
body surface. Relatively smaller areas of injury (10%15%
of body surface) from high-energy beta exposure (134Cs,
137
Cs, 106Ru, 90Y, 90Sr) with early development of necrosisulceration require surgery and can cause long-term
disability [B29, G21, N3]. Surgical treatment was provided
to fifteen acute radiation sickness survivors with extensive
cutaneous radiation injuries, including ulcerations andfibrosis, at University of Ulm between 1990 and 1996.
Follow-up of these survivors has not shown a single case ofskin cancer.
196. Cataracts, scarring and ulceration are the mostimportant causes of persistent disability in acute radiation
sickness survivors. The consequence of severe skin ulceration
is cutaneous fibrosis, which has been successfully treated with
low-dose interferon [P26]. The recovery of physical ability isrelated to the severity of the initial symptoms of acuteradiation sickness. To limit occupational radiation exposuresof the acute radiation sickness survivors, legal measures
adopted in the Russian Federation and other countries of theformer Soviet Union have restricted their activities or caused
them to change their occupations.
197. Sexual function and fertility among acute radiation
sickness survivors was investigated up to 1996 [G2]. In the
majority of cases, functional sexual disturbances predominated, while fourteen normal children were born to acuteradiation sickness survivor families within the first five years
after the accident (in one family, the first newborn died fromsepsis, but a second, healthy child was born subsequently).
198. Patients with acute radiation sickness Grades III and IV
were severely immunosuppressed. Whereas haemopoietic
recovery occurs within a matter of weeks or, at most, months,
full reconstitution of functional immunity may take at least
half a year, and normalization may not occur for years after
exposure. This does not necessarily mean that after the acutephase, i.e. the first three months, recovering patients display
major immunodeficiency, and it is not surprising that studiesof immune status did reveal pattern of changes in the blood
cell concentrations without clinical manifestations of
immunodeficiency [N3]. Nineteen parameters of the immune
system were investigated five and six years after the accident
in acute radiation sickness survivors (19 Gy) and in persons
without acute radiation sickness (0.10.5 Gy) as well. For
higher doses of radiation, T-cell immunity may show
protracted abnormalities; however, these abnormalities are notnecessarily associated with clinically manifest immunodeficiency.

490

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

IV. REGISTRATION AND HEALTH MONITORING PROGRAMMES
199. In order to mitigate the consequences of the Chernobyl
accident, registration followed by continuous monitoring of
the exposed populations was one of the priorities set by the
Ministry of Health of the former Soviet Union. In the summerof 1986, Chernobyl registries were established for continuous
monitoring of the health status of the exposed populations[M7, T12, W1]. Specialized population-based disease registers
were created to monitor haematological tumours [I10, W1].
These activities have continued in Belarus, the RussianFederation and Ukraine since the dissolution of the USSR in
1991, with financial and technical support from many
countries of the world.
200. Following the first reports of an increased incidenceof thyroid cancer in children exposed to the radioactive
fallout during the early 1990s [B18, K11, P8], thyroid
cancer registries were developed in Belarus, the RussianFederation and Ukraine [D2, R2, T4]. More recently,
specialized childhood cancer registries began to be
developed in these countries [V7].
201. Considering the potential long-term health consequences of the Chernobyl accident, the existing general
population cancer surveillance systems in Belarus, theRussian Federation and Ukraine have attracted particularattention. International researchers started to assess thefunctioning of these systems as well as their quality andcompleteness in comparison with the cancer registries inmany Western countries and to evaluate their potential for
research purposes [S6, W10]. To provide a basis forinterpreting the health effects reported from epidemiological studies, this Chapter reviews the available
information on registers and their follow-up.

A. REGISTRATION AND MONITORING
OF EXPOSED POPULATIONS
1. The Chernobyl registries
202. In May 1986, the Ministry of Health of the USSR
convened a conference of Soviet experts on the treatment
and follow-up of radiation-exposed individuals [M7]. Thisconference recommended the establishment of a special
registry to assist in the delivery of primary health care,treatment, and follow-up and to provide a basis for the
long-term monitoring of the Chernobyl-exposed populations. Governmental orders issued by the Ministry of
Health in 1987 provided the basis for creating the AllUnion Distributed Clinico-Dosimetric Registry and forappointing the Medical Radiological Research Centre at
Obninsk as the institution responsible for the development
and maintenance of this registry [T12]. Compulsory
registration and continuous monitoring of the health status
was introduced for four population groups (primary
registration groups): group 1, persons engaged in therecovery operations following the accident (liquidators);group 2, persons evacuated from the most contaminatedareas (137Cs deposition >1,480 kBq m2); group 3, residentsof highly contaminated areas (137Cs deposition >555 kBqm2); and group 4, children born after the accident to thoseregistered in groups 13.
203. For the purpose of data collection, registries were
established at the national, regional and district levels, as wellas in certain ministries that provide health care for theiremployees independent of the general health care network.
Four special data collection forms were introduced [M7, W1]:
registration, clinical examination, dosimetry and correctionform.
204. Persons were registered in the All-Union Registry
upon presentation of their official documents of work or
residence in the Chernobyl zone, mainly during the compulsory annual medical examination in the outpatient
department of the district hospital responsible for theirplace of residence (see Section IV.A.2). In return, each
person obtained a special registration document enabling
him/her to obtain special Chernobyl-related social benefits.
At the time of the dissolution of the USSR, the All-Union
Registry had accumulated data on 659,292 persons, 43% ofwhom were recovery operation workers (group 1), 11% ofwhom were persons evacuated from the most contaminatedareas (group 2), and 45% of whom were persons living incontaminated areas (group 3); the remaining 1% werechildren of groups 13 (group 4) [W7].
205. Since 1992, the national Chernobyl registries havecontinued to operate, but independently, with only basic data
items in common. Although the registries continue to employ
the general registration techniques and categories developed
during the Soviet era, they have evolved separately in terms of
the population groups and/or data items that are covered, data
quality, dose-reconstruction methodology and follow-up
mechanisms [W12]. This must be kept in mind wheninterpreting and comparing results from the three countries
most heavily exposed as a consequence of the accident.
206. Successive publications using Chernobyl registrydata
sources show ever-increasing numbers of persons
registered. Whereas at the beginning, the Chernobyl
registry of Belarus contained information on 193,000
persons, 21,100 of whom were reported to have worked as
recovery operation workers [W7], at the beginning of 1995
this number had risen to 63,000 [O2]. Similarly, thenumber of persons registered in the Russian National
Medical and Dosimetric Registry as belonging to one of thefour primaryregistration groups has increased steadilyover
the years (Figure XXIII). The legal statute regulating
medical criteria for disability and invalidity has changed
over the years, and as a result the number of individuals
included in the registries has increased [O4, W7].

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT
500,000

491

termination of employment (other than retirement), after
which the person returns to the general health-care regime.

NUMBER OF PERSONS

400.000

211. The Registry of Professional Radiation Workers ismaintained by the Institute of Biophysics in Moscow. It
contains information on 22,150 professional radiation
workers who participated in recovery work. Approximately
18,600 of them currently live in the Russian Federation, and13,340 worked in the Chernobyl area in 19861987. The
radiation doses for these workers were monitored withpersonal dosimeters. The Registrycurrently contains doses forapproximately 50% of the workers; doses for the remainder
are being collected and entered into the database.

300.000

200.000

100.00001986 1987 1988 1989 1990 1991 1992 1993 1994 1995
YEAR

Figure XXIII. Number of persons registered in the
Russian National Medical and Dosimetric Registry as
exposed to ionizing radiation as a consequence of theChernobyl accident [I14].

207. All persons included in the Chernobyl registries
continue to receive active follow-up. This follow-up wascentralized for a number of years in the former Soviet
Union. Subsequently it has been performed in the threesuccessor countries. Originally, the Chernobyl registration
process was grafted onto an existing infrastructure, but thefollow-up of the exposed populations is more specific andconcerns all age ranges, including retired persons, who
would not normally have received medical follow-up, since
this is confined to the working population.
208. Compulsory annual medical examinations are conducted by a general practitioner in the outpatient department of the district hospital at the official place of residence.
The information ascertained during these examinations is
systematically reported to the Chernobyl registry by meansof the specially devised clinical examination form [T12,
W1]. In case a more severe health condition is suspected,
the patient is referred to specialized health-care institutions
for diagnosis and treatment.

2. Specialized registries
209. In addition to the Chernobyl registries, the RussianFederation keeps specialized registries of Chernobylexposed populations. Whereas the primary information on
persons included in these registries is systematicallyreported to the Russian National Medical and Dosimetric
Registry, the specialized registries generally contain moredetailed information on exposure and follow-up.
210. The follow-up mechanisms for the specialized registries
follow the same principles as those for the Chernobyl
registries. However, medical services and annual medical
examinations are provided at special medical facilities of therespective Ministry. The provision and quality of services atthese special facilities are generally considered to be better
than those offered by the general health-care network [W10].
Follow-up in the special medical facilities ceases with

212. Medical examinations of persons included in theRegistry of Professional Radiation Workers are carried out inabout 70 medical facilities of the Ministry of Health. The
oncology service of the Institute of Biophysics verifies thediagnosis of all cases of cancer and extracts information fromcase histories. Before 1993, no information was collected on
the date of diagnosis or cause of death. Of the 22,150 workers
registered at the beginning, only 18,430 are currently being
followed [T13].
213. The Registry of Military Liquidators, operated by the
Military Academy at St. Petersburg, contains information on
persons from all over the former USSR who were drafted by
the Ministry of Defence to help in the recovery work after theaccident. Their doses were mainly determined through timeand motion studies. Information on places and dates of workin the Chernobyl area has been recorded in the registers. The
medical follow-up of the approximately 15,000 servicemen
included in the registry is carried out at local polyclinics andspecialized dispensaries of the Ministry of Defence. Anothergroup of approximately40,000 persons who were sent to workin the Chernobyl area by the Ministry of Defence are followedin the general civilian network of health care.
214. Among the recovery operation workers, there areabout 1,250 helicopter pilots and crew. All individuals withdoses of more than 250 mGy were hospitalized for careful
medical examination as soon as their work was finished.
No sign of radiation sickness was found. A list of persons
is maintained by the Russian Aviation Medicine Institute[U15]. The Aviation Medicine Institute carries out periodic
examinations of helicopter pilots; results have been
published on groups of 80 to 200 of them, including
military pilots and crew members who flew over Unit 4 of
the Chernobyl reactor in April and May 1986 [U15].

B. REGISTRATION OF MORTALITY ANDDISEASE IN THE GENERAL POPULATION
1. Mortality
215. Mortality statistics are one of the main measures ofhealth outcome used in epidemiological studies. In the
countries of the former USSR, and throughout the world,
registration of death is the responsibility of vital statistics

492

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

departments. For each death, a medical death certificate(medical document) is completed by the attending physician
or by a medically trained person. The death is then registeredat the district vital registration department by completing adeath registration act (legal document), which provides
authorization for burial. The medical death certificate in use
in the countries of the former USSR has followed international
recommendations since the 1980s [W10]. The quality of thedeath certificates depends on the competency of the personcompleting them, and the validity of the death certificates has
probably changed over time.

number of cases according to sex, age group and cancer site,
and the cancer patient report provides basic information onprevalence as well as on the diagnosis, treatment and survivalof the patient. Death certificates and autopsy reports as
information sources have been used since 1961, but theregistration of leukaemia became compulsory only in 1965
[R1]. Thus, cancer statistics that meet the Western definitionof cancer registries have existed only since 1966 in the
countries of the former Soviet Union [W10].

216. A copy of the death registration act is forwarded to theregional vital registration department, which is in charge ofthe coding and the preparation of annual regional mortality
statistics. The cause of death is coded using a slightly
modified version of the Ninth Revision of the International
Classification of Diseases B-List [S6]. Regional mortality
statistics are submitted to the national statistical authority forthe compilation of annual national mortality statistics.

222. Haematological cancer registries were set up in Belarus,
the Russian Federation and Ukraine shortly after the accident,
but thyroid cancer registries only started to appear during theearly 1990s, after first reports of an increase in thyroid cancer
following the Chernobyl accident. Specialized childhood
cancer registries were set up only recently because the qualityof the general registration was questionable [V7].

217. As part of a general policy of censorship of demographic and health statistics, the use of mortality statistics
for research purposes was severely restricted during theSoviet era [R1]. The main use of the mortality statistics
was health planning. Since the dissolution of the Soviet
Union into independent countries, however, such data havebeen readily available.
2. Cancer incidence
218. Cancer diagnosis and treatment were the responsibilityof oncological dispensaries throughout the Soviet Union.
Cancer patients were followed by the district hospital at theofficial place of residence. Certain malignant neoplasms, suchas haematological neoplasms, childhood cancers, and certain
rare tumours, e.g. brain and eye, are diagnosed and treatedoutside the network of oncological dispensaries [W10].
219. Based on the existing oncological infrastructure, cancer
registration was made compulsory in 1953 throughout the
USSR [N6]. The cancer registration process, which still
applies today in the successor countries, involves the passive
reporting of newly diagnosed cancer cases and information on
their follow-up to regional cancer registries at the regional
oncological dispensaries in the patient’s place of residence[W10].
220. The patient cards maintained at the regional cancer
registries are continuously updated with the information
received from the cancer registration documents. After acancer patient dies, the card is removed from the active
cancer registry for storage in archives. Information on
cancer deaths is gathered at regular intervals from the vitalregistration departments, and trace-back procedures are
initiated for persons not registered during their lifetimes.
221. Annual cancer statistics are compiled at both theregional and national levels. Two basic reports are compiled
manually each year. The cancer incidence report provides the

3. Specialized cancer registries

223. These specialized cancer registries are for cancers thatare mainly diagnosed outside the network of regional
oncological dispensaries. The registration of these cancers in
the national cancer registries is likely to be less complete thanfor cancers directly diagnosed and registered in the
oncological dispensaries. An important difference between thenational cancer registries and the specialized cancer registries
is that case ascertainment is passive in the former and activein the latter. Active reporting systems generally achieve ahigher degree of completeness, as cancer registry personnel
directly and systematically abstract the information from thesource. Furthermore, specialized cancer registries generally
record more detailed information on the clinical features of thetumour than do general cancer registries.
(a) Haematological cancer registries
224. In Belarus, the National Register of Blood Diseases isoperated by the Institute of Haematology and Blood
Transfusion in Minsk. Although activities only started in
1987, data since 1979 have been collected retrospectively. The
registry covers the entire population of Belarus and receives
details of cases of leukaemia, lymphoma and related blood
diseases from haematological departments and oncologicaldispensaries and from autopsies. Information in this registryhas, however, only recently been computerized.
225. The Registry of Leukaemia and Lymphomas in the
Bryansk region (Russian Federation) records all relevantcases in all ages in this region, including a retrospective
assessment since 1979. Before 1986, however, the registry
is reported to be incomplete [W1].
226. Little is known about the Ukrainian Registry of
Haemoblastosis (term used in the Russian language) thatcovers leukaemia, lymphomas and related non-malignant
diseases, such as polycythaemia vera, aplastic anaemia andsideroblastic anaemia. The registry is operated by the
Ukrainian Centre for Radiation Medicine and is designed
to record all cases of haemoblastosis in the Ukrainian
resident population [W1].

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT(b) Thyroid cancer registries
227. In Belarus, the Thyroid Surgery Registry is operated by
the Scientific and Practical Centre for Thyroid Tumors at theInstitute of Medical Radiology and Endocrinology, Minsk[D2, P2]. This registry includes only patients with thyroid
disorders treated at the Centre. A comparison between theregistry data and data obtained from pathologists indicatedthat it is incomplete for thyroid cancers diagnosed duringadolescence and adulthood, as these are mostly diagnosed andtreated at the regional level [C6]. The number of thyroid
cancer cases reported from Belarus in different scientificpublications varies according to the age range considered anddepends on whether case series were abstracted from theThyroid Surgery Registry only [P2], whether they werecomplemented by incidence data [B11], or whether only cases
known to the national cancer registry were used [K40].
228. In the Russian Federation, the Thyroid Cancer Registry
has been created for the Bryansk and Tula regions; it includes
data on all cases of thyroid cancer since 1981 [R2]. In
Ukraine, a clinical morphological register of thyroid cancers
has been created at the Institute of Endocrinology andMetabolism in Kiev [T4]. This registry includes data on all
thyroid cancer cases in which the patients were under the ageof 18 years at the time of the Chernobyl accident, as well as
retrospective data since 1986. Information is gathered fromtwo sources: (a) data on all cases treated at the surgery
department of the Institute of Endocrinology and (b) data on
thyroid cancer cases from the national cancer registry,
diagnosed throughout Ukraine. In 19861994, one third ofthe
total of 531 cases recorded was identified from surgicalrecords. Data quality and the amount of detail available in thisregistry is likely to vary, depending on the data sources. Also,
thyroid cancer cases occurring in the Chernobyl-contaminatedareas are more likely to undergo surgery in Kiev than cases
occurring in other areas.
(c) Childhood cancer registries
229. Publications on childhood thyroid cancer or haematological malignancies generally are based on data from thecorresponding specialized cancer registries [D2, I10, I31,
T4] or, in the case of childhood thyroid cancers, from
population screening programmes [I26, T5]. A new
specialized registry, the Belarusian Childhood Cancer
Registry, was created at the Institute of Oncology andMedical Radiology in 1996. Data are reported from centres
diagnosing and treating children. Similarly, childhood
cancer registries are also being created for the Bryansk andTula regions of the Russian Federation [R2].
(d) Registers of hereditary disorders andcongenital malformation
230. A national monitoring system for hereditary diseases
exists in Belarus at the Institute for Hereditary and Congenital Diseases [L8]. Reporting is compulsory since 1979
for anencephaly, spina bifida, cleft lip and palate, polydactyly, limb reduction defects, oesophageal and anorectal

493

atresia and Down’s syndrome. In addition, reporting ofmultiple congenital malformations became compulsory in
1983. Morphogenesis defects in embryos and early fetuseshave been recorded since 1980.
231. The comparability of registries of congenital malformations with similar registries from countries outside the former
Soviet Union is generally considered to be poor owing to thegreat variation in definitions of the included parameters.
Differences are found in defining the geographical location(e.g. place of residence of the mother or place of birth ofthe child), in the definition and coding of the diagnosis,
and in coverage (live births, stillbirths, induced abortions,
fetal deaths, spontaneous abortions) [L8, L20]. There has
been no independent assessment of the quality andcompleteness of this registry, in particular for the period
before the Chernobyl accident.

C. QUALITY AND COMPLETENESS OF
REGISTRATION
1. Registers of exposed populations
232. The ever-increasing number of persons registered in
the Chernobyl registries raises the crucial question ofwhether and when the registration of the exposed population groups can ever be reasonably complete. The legal
statute regulating medical criteria for disability and invalidity
in citizens of the Russian Federation was promulgated in1991. According to this law, the causal association between
the Chernobyl accident and disease, death, or invalidity canbe established independently of the absorbed dose received
or the health status of the person before the accident. As aresult of this law, the number of individuals included in theregister has increased over the past years [O4, W7]. Someregistration increases occur as the people exposed as aresult of the accident grow older, become ill, and seekregistration to obtain social benefits. Any difference between
the health status of exposed persons registered in recent
years in the Chernobyl registries and that of exposed
persons registered in earlier years could introduce bias into
epidemiological studies using these data. However,preliminary analysis in Belarus and the Russian Federation
appears to indicate that the health status distribution of the
newly registered workers is similar to that of the workers
registered previously [P18].
233. To obtain a more reliable and complete enumerationof a cohort of Chernobyl recovery workers for epidemiological purposes, Estonian researchers used four independent data sources:(a) records of military personnel, both regular personnel
and reservists, who were sent to the Chernobyl area;(b) The Estonian Chernobyl Radiation Registry;(c) members of the Estonian Chernobyl Committee, anon-governmental organization that aims to obtaincompensation and health-care benefits for the recovery
workers;

494

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT(d) files from the Ministry of Social Welfare of Estonia,
which had conducted an independent registration ofrecovery operation workers for social benefits.
By using multiple data sources, the information on 83% of
the 4,833 Estonian men who worked in the Chernobyl area
could be ascertained from two or more sources [T6].
234. It remains unclear to what extent a verified diagnosis
in the more specialized institutions is actually reported to
the Chernobyl registries. One study indicated that almost
half of the leukaemia diagnoses in the Russian Federation
Chernobyl registry were not confirmed [O1]. By contrast,
in Belarus, where a national registry of haematologicalmalignancies was created following the Chernobyl
accident, this information has been periodically reported to
the Chernobyl registry in recent years.
235. Caution should be observed when comparing the
mortality experience in the Chernobyl registry populations
with national background mortality rates. The Chernobyl
registries obtain mortality information from next-of-kin
whenever the person under observation does not present
himself/herself for the annual medical examination and/orfrom official death certificates, which are screened for
information. The Chernobyl registry does not use the coding
rules implemented by the official demographic authorities but
often uses the existing medical information to code theappropriate cause of death in the Chernobyl registry. As aresult, the mortality information available in the Chernobyl
registries is often more specific and has a higher degree ofcompleteness than official demographic sources.
236. Understanding the registration processes, coding andquality changes over time is essential for researchers toappropriatelyconduct and interpret epidemiological studies
using Chernobyl related data. More research is needed to
document the methods of data collection and the quality ofdata collected in the framework of the Chernobyl registries.
2. Registers of the general population
237. Mortality. Very little information exists on the qualityof mortality statistics from countries of the former Soviet
Union. During the late 1970s, a study was conducted tocompare the quality of cause-of-death coding in sevencountries, including the USSR [P22]. The results showed thatfor a standard set of 1,246 causes of death related to cancer
there were no differences in the quality of coding in the USSR
and in the other participating countries. However, for thisparticular study, an expert pathologist performed the codingin the USSR, whereas in the rest of the countries a vitalstatistics official did the coding. A study is currently under
way comparing the coding for the same 1,246 cause-of-death
series as performed by the actual coders of a number ofregional vital registration departments in Belarus, the RussianFederation and Ukraine.
238. Mortality rates in the three countries declined in19841987, increased in 19871994 [L38], and were morestable in recent years [L37]. International comparisons ofmortality statistics show higher rates for deaths fromcardiovascular disease and violence in the Russian Federation.
[M8]. Although differences in data qualitycannot be excluded
entirely, recent evidence suggests that increased alcohol
consumption may account for a substantial portion of thedifference in mortality patterns between the countries of theformer Soviet Union and Western countries [L37, L38, W11].
239. Mortality data are used in epidemiological studies as
endpoints for individual follow-up of exposed populations
or in aggregated form as mortality rates in geographicallydefined populations. Although changes in mortality
patterns in the countries of the former Soviet Union are notrelated to radiation exposure, they must be taken into
account when interpreting epidemiological studies using
these data. In these countries, individual mortality data are
available only on paper at the district level. The absence ofcentralized, computerized mortality registries posesconsiderable difficulty, particularly in tracing subjects who
have moved from one area to another [O1].
240. Cancer incidence. A survey of cancer registration
techniques in the countries of the former Soviet Union [W10]showed a number of important differences compared toWestern countries. First, cancer registries in Westerncountries were created for research purposes, whereas in theSoviet Union they were created for health-planning purposes.
The system in operation in the countries of the former Soviet
Union functions as a public health surveillance system with
fast reporting of statistics (three months after the end of areporting year). The impact of the fast reporting on the qualityof the information is unknown. Second, many data items arecoded independently of the internationally recommended andaccepted classification schemes. This is particularly relevant
for one of the most important data items in cancer
registration: tumour pathology. This may have important
implications for the quality of the data recorded. Third,
standard concepts for verifying the quality and completenessof registries, widely used for Western cancer registries, arevirtuallyunknown in the countries of the former Soviet Union.
Finally, personal identification is based on names. Differencesin spelling, the increasing use of national languages rather
than the Russian language, and the increasing mobility of the
population raise questions about the correctness of the identifications. Whereas probabilistic record-linkage procedures areused for this purpose in Western cancer registries, theseprocedures remain unknown in the countries of the former
Soviet Union.
241. Of the countries most contaminated by the Chernobyl
accident, only Belarus had a centralized cancer registry inoperation before the accident. In the 1990s, the RussianFederation and Ukraine began developing computerizedcancer registration software and regional registration
networks, and Belarus worked to modernize the system inoperation there. This work of gradually adjusting the cancer
registration techniques in these countries to satisfy
international standards is being conducted within a framework
ofinternational collaboration to ensure adequate training [S6].

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

242. A computerized central cancer registry was establishedin Belarus as early as 1973, and computerized cancer
incidence data have been available since 1978 [O4]. However,owing to the lack of resources, the data were computerized
anonymously during the early years of operation. In 1985
personal-computer-based cancer registration was developed,
including appropriate information on the individuals. Since
1991 a computerized network has provided the basis forcancer registration in Belarus.
243. Efforts to computerize cancer registration in Ukraine
started at the beginning of the 1990s [W10]. By the end of
1997, computerized cancer registration had been
implemented in many regions. Approximately 82% of the
population of Ukraine was covered at that time, andnationwide coverage is expected by the year 2000. In recent
years, the Russian Federation has also started to develop a
computerized cancer registration system [W10]. Fullcoverage of the population of the Russian Federation withcomputerized cancer registration technology has to be seen
as a long-term goal. In any case, priority will be given tocomputerizing the Chernobyl-contaminated regions and anumber of control regions.

495

large-scale screening was not started until the early 1990s.
A description of the organization, completeness, and results ofthese efforts has not yet been published.
1. The International Chernobyl Project247. In 19901991, IAEA organized the International
Chernobyl Project [I1] at the request of the Government of
the USSR. International experts were asked to assess theconcept the USSR had developed that would enable thepopulation to live safely in areas affected by radioactive
contamination following the Chernobyl accident; theywere
also asked to evaluate the effectiveness of the steps takenin these areas to safeguard the health of the population.
The International Chernobyl Project investigated thegeneral health of the population of seven rural settlements
in Belarus, the Russian Federation and Ukraine and of six
control settlements using an age-matched study design[M10]. Psychological health, cardiovascular, thyroid andhaematological disorders, cancer, radiation-induced
cataracts and fetal anomalies were also investigated, andcytogenetic studies were carried out.
2. The IPHECA project244. Probably the main source of international cancer
incidence statistics is the series Cancer Incidence in Five
Continents, published by the International Agency for
Research on Cancer (IARC) at five-year intervals since thelate 1960s. Although cancer registries all over the world
are invited to contribute data, only data sets satisfying thedefined quality standards are accepted for publication. No
data from the USSR were included in any of the earlyvolumes, although a supplement to Volume III, “Cancer
incidence in the USSR”, was published jointly by IARC
and the USSR Ministry of Health in 1983 [N6]. The twomost recent volumes, presenting data for 19831987 and19881992, include data from Belarus, Estonia and Latvia,
and data from St. Petersburg and Kyrgyzstan were
published in the earlier of the two volumes. However, theeditors warned that all data from the countries of theformer Soviet Union (except data from Estonia) may
under-ascertain the number of cases, may lack validity, or
may be inaccurate with respect to the denominators of therates [P17, P23].

D. INTERNATIONAL COLLABORATIVESCREENING PROJECTS
245. For more than three years after the Chernobyl accident,
efforts to mitigate its consequences were considered by theSoviet Union to be exclusively an internal matter.
International collaborations started to develop in 1990 andhave since played a substantial role in the assessment of thehealth consequences of the Chernobyl accident.
246. Soviet health authorities initiated screening activities
in June 1986 throughout the areas most affected by theaccident. Initially, these activities were locally organized;

248. In 19921995, WHO conducted an International
Programme on the Health Effects of the Chernobyl
Accident (IPHECA). A number of pilot projects surveying
registration activities, radiation- dose reconstruction,haematological disorders, thyroid disorders, brain damage,and oral health were carried out. The IPHECA Dosimetry
Project reconstructed radiation doses from measurement
surveys of the populations of contaminated and evacuatedareas [W1, W13].
3. The Chernobyl Sasakawa Health andMedical Cooperation Project249. Between 1991 and 1996, the Sasakawa Memorial
Health Foundation sponsored the largest international
programme of screening of children following the Chernobyl
accident. The project aimed at assessing the anxiety andhealth effects in the people affected by the Chernobyl accident
through large-scale population screening. Children wereselected as the target population for the screening. Regional
diagnostic centres were set up in Gomel and Mogilev in
Belarus, in Klincy(Bryansk region) in the Russian Federation,and in Kiev and Korosten (Zhitomir region) in Ukraine toscreen children by means of mobile examination units [S38].
250. Standard examination protocols and questionnaires
focussing on thyroid disorders, haematological disturbancesand radiation dose were used. The examination included
collection of disease history and anthropometric data,
dosimetric measurements using whole-body counters,
ultrasonography of the thyroid, general blood count,determination of thyroid hormones in the serum,
determination of iodine and creatinine in the urine, andexamination by a paediatrician. When abnormalities were
found, the child was referred to the regional diagnostic

496

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

centre for comprehensive examination and appropriate
treatment. During the course of the project (May 1991April 1996), approximately 120,000 children were
examined. The results are given in Chapter V [H2, I16,
I21, I26, S7, Y1].
251. International collaborative efforts are continuing, andseveral studies of the effects of the accident are underway.
An example is a project to establish a tissue bank of thyroid
carcinomas from all of the three most affected countries,
which has as participating organizations the European
Union, National Cancer Institute of the United States, theSasakawa Memorial Health Foundation, the World HealthOrganization, and the health ministries of Belarus, theRussian Federation and Ukraine..

255. Health outcome registries are an important source of
information for assessing the consequences of theChernobyl accident. Their primary advantage is that the
information was collected in a systematic way before andafter the accident and that the criteria for data collection
are the same in all countries of the former Soviet Union.
However, most of these registries, whether related tomortality, cancer incidence, or special diseases, continue tobe largely operated manually, which seriously limits theiruse for epidemiological research purposes. The Chernobyl
accident led to major international efforts to computerize
cancer incidence and special disease registries and to
improve their registration methods so as to comply withinternational standards. However, mortality registration
systems have received little attention so far. Information on
the quality and completeness of these systems remains
scarce.

E. SUMMARY
252. Following the Chernobyl accident, compulsory
registration and continuous health monitoring of recovery
operation workers and residents of the most contaminatedareas, including their offspring, were initiated throughout theSoviet Union. Until the end of 1991, the All-Union
Distributed Clinico-Dosimetric Registryrecorded information
on 659,292 persons. After the dissolution of the Soviet Union
into independent states, national Chernobyl registries havecontinued to operate, but independently. Changes in national
registration criteria, compensation laws, dose-reconstruction
methods, and follow-up mechanisms increasingly limit thecomparability of data from the different national sources.
More detailed registries of exposed populations exist in the
Russian Federation (Registry of Professional Radiation
Workers, Registry of Military Workers and the cohort of
Helicopter Pilots and Crew). The quality and completeness ofthese registries remain largely unknown, however.
253. The number of people registered in the national
Chernobyl registries continues to increase, even in recent
years, which raises questions about the completeness andaccuracy of registration. Information on mortality andcancer incidence is collected from many different sources
and is coded independently of international guidelines.
Evidence from recent cohort studies suggests that the
Chernobyl health outcome data cannot be successfullycompared with health data obtained from official statisticalsources.
254. Systematic linkage of the Chernobyl registry
population data with existing mortality and/or cancer
incidence registries and the subsequent comparison of thehealth outcome experience in the cohort with thecorresponding national reference statistics could be avaluable tool for epidemiological research. Internal
comparisons, e.g. using a low-dose comparison group, arelikely to provide information on risks associated withionizing radiation in the future. However, complete
information on, e.g. previous exposure to ionizing
radiation in an occupational setting, will most probably
only be available for small sub-cohorts.

256. Compulsory cancer registration was introduced
throughout the former Soviet Union in 1953. The systemrelies on passive reporting of information on all newly
diagnosed cancer cases to the regional cancer registry forthe patient’s place of residence. Since the early 1990s,
there have been efforts to computerize the existing systems
and to gradually improve their quality to satisfy
international standards. Belarus has been covered with a
network of computerized cancer registries since 1991.
Computerization is well advanced in Ukraine, and full
population coverage is expected soon. In the RussianFederation, efforts to develop computerized cancer
registration started only recently and will be concentrated
in contaminated areas and control areas.
257. Specialized population-based registries for haematological malignancies and thyroid cancer were set up in thewake of the Chernobyl accident and in response to theunknown quality and lack of detail for these sites in thegeneral registries. Childhood cancer registries wererecently developed for the same reasons. Quality assessments of these registries are underway. Other registries forhereditary disorders and malformations exist, but their
quality and completeness have not so far been independently assessed.
258. Shortly after the Chernobyl accident, efforts weredevoted mainlyto developing adequate registration systems
for future follow-up of those population groups mostaffected by the radionuclide deposition. More recently,international collaborations have helped to modernize theexisting disease registration infrastructure. However,information on the quality and completeness of all theseregistries is still very scarce. The usefulness of the vast
amount of data collected will become clearer in the coming
decades as the long-term consequences of the accident arestudied. In particular, matching the health outcomes withthe dosimetric data described in Chapter II, will be of great
importance.

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

497

V. LATE HEALTH EFFECTS OF THE CHERNOBYL ACCIDENT
259. The studies of late health consequences of theChernobyl accident have focussed on, but not been restricted
to, thyroid cancer in children and leukaemia and other cancer
in recovery operation workers and residents of contaminatedareas. Many studies have been descriptive in nature, but until
individual dosimetryis completed, proper controlsestablished,
and methodological requirements satisfied, the results will bedifficult to interpret. Quantitative estimates and projections
will certainly be very unreliable without individual andreliable dose estimates.
260. The late health effects of the Chernobyl accident aredescribed in this Chapter. These effects include malignancies,
especially thyroid cancer and leukemia, non-malignant
somatic disorders, pregnancy outcome and psychologicaleffects. The focus will be on health effects in the mostcontaminated areas, but possible effects in other parts of theworld will also be considered.

A. CANCER
1. Thyroid cancer(a) Epidemiological aspects
261. Thyroid carcinomas are heterogeneous in terms ofhistology, clinical presentation, treatment response andprognosis. Although rare, they are nevertheless one of themost common cancers in children and adolescents. Thyroid
cancer is known to be more aggressive in children than in
adults, but paradoxically, the prognosis is supposed to bebetter in children [V8]. Several risk factors have beensuggested for thyroid cancer, but only ionizing radiation
has been found to have a causative effect, although ahistory of benign nodules, miscarriages, iodine deficiency
or excess, and an elevated level of thyroid-stimulating
hormones have been discussed as causative factors [F9,R18]. Risk factors for thyroid cancer are discussed in
Annex I, “Epidemiological evaluation of radiationinduced cancer”.
262. The childhood thyroid gland is, besides red bonemarrow, premenopausal female breast, and lung, one of themost radiosensitive organs in the body [U2]. Age at
exposure is the strongest modifier of risk; a decreasing risk
with increasing age has been found in several studies [R7,
T20]. Among survivors of the atomic bombings, the mostpronounced risk of thyroid cancer was found among those
exposed before the age of 10 years, and the highest risk
was seen 1529 years after exposure and was still
increased 40 years after exposure [T20]. The carcinogenic
effect of 131I is less understood, and the effects ofradioiodine in children have never been studied to any
extent, since medical examinations or treatments rarely
include children [H6]. Similar to the studies of atomic

bomb survivors, there is little evidence of an increasing
risk for exposures occurring after age 20 years [H6, T20].
263. As seen in Tables 5658 an increasing number ofthyroid cancers among children and adolescents living inareas most contaminated by the accident have been
diagnosed in the last 12 years. Among those less than 18
years of age at exposure, 1,791 thyroid cancers werediagnosed during 19901998 (complete information is notavailable for the Russian Federation). The increase in all
three countries for 19901998 was approximatelyfourfold,with the highest increase seen in the Russian Federation.
The increase in absolute numbers seems to have leveled
off, particularly for the older age-at-exposure cohorts. It
should be emphasized that the source population in Belarus
is approximately 1.3 million, in the Russian Federation
300,000 (only one region) and in Ukraine 9 million
children.
264. As previously discussed in this Annex, there areconsiderable uncertainties in the estimates of individual
thyroid doses to the population in the contaminated areas.
More than 80% of the dose from internal exposure wasestimated to be from 131I [Z1]; external exposure contributed
only a small proportion of the thyroid dose [M4] (seeSection II.C.2.a).
265. Two recent studies [F13, R17] found an elevated riskof thyroid cancer mortality following adult 131I treatment
for hyperthyroidism, which is in contrast to previous
studies of hyperthyroid patients [H14] or patients examinedwith 131I [H6]. The reason for referral, i.e. the underlying
thyroid disorder, could have influenced the risk, since thehighest risk was seen less than five years after exposure.
The thyroid dose (60100 Gy) received by most
hyperthyroid patients had previously been considered ashaving a cell-killing rather than a carcinogenic effect.
266. In a recent paper by Gilbert et al. [G23], thyroid
cancer rates in the United States were related to 131I doses
from the Nevada atmospheric nuclear weapons tests. The
analysis involved 4,602 thyroid cancer deaths and 12,657
incident cases of thyroid cancer. An elevated risk wasfound for those exposed before the age of one year and born
during the 1950s, but no association with radiation
exposure was seen in older children in the age range 115
years. It could be that migration complicated the dose
assessment and case identification. The authors concluded
that the increase was most likely due to the 131I exposure,but the geographical correlation approach, i.e. lack ofindividual doses and information on residency, precluded
them from making quantitative estimates of risk related to
exposure. Further, 131I exposures from nuclear weapon tests
in other countries were not taken into account, nor wereother releases such as those that occurred from the Hanfordsite [R22].

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

268. Prisyazhiuk [P8] described in 1991 three cases ofchildhood thyroid cancer in Ukraine that were diagnosed in
1990, in contrast to no diagnosed cases during the preceding
eight years. A screening effect was discussed, and it was
postulated that “these thyroid cancers might represent the
beginning of an epidemic”. In the following year, Kazakov etal. [K11] reported 131 cases of childhood thyroid cancer in
Belarus. The geographical distribution suggested a
relationship with the ionizing radiation caused byradionuclides released from the Chernobyl accident, but
unexplained differences existed. Most cases had been
confirmed by a panel of international pathologists [B18].
Increased risks of childhood thyroid cancer were later
reported in Ukraine [L6, T2] and, more recently, in the partof the Russian Federation most contaminated by the
Chernobyl accident [S19, T1].
269. The large number of cases appearing within five yearsof the accident was surprising, since it had been believed thatthyroid cancer needed an induction and latency period of atleast 10 years after exposure to ionizing radiation [U2]. The
findings were challenged, the major concerns being theinfluence of an increased awareness and of thyroid cancer
screening [B23, R8, S5].
270. The numbers of thyroid cancers in children born before
26 April 1986 and who were less than 15 years of age at thattime by country/region and year of diagnosis are given in
Table 56 and illustrated in Figure XXIV. The corresponding
incidence rates are given in Table 57 and Figure XXVChildhood thyroid cancers in heavily contaminated areas
show 510-fold increases in incidence in 19911994
compared to the preceding five-year period. The number ofchildhood thyroid cancers occurring from 1990 to 1998 in a
wider age range of children (017 years old at time of theaccident) is presented in Table 58. It should be noted thatmany of the cases were diagnosed in adolescents and young
adults and that only few of them have undergone
histopathological review. The numbers given in Tables 5658
are not entirely consistent, since various sources of
information have been used (see Section IV.B.3.b).
271. Kofler et al. [K41] recently described thyroid cancer
in children 014 years old at the time of the accident inBelarus. Through the Belarus cancer registry, 805 thyroid
cancers were found by the end of 1997. The distribution
with time and by age at exposure is presented in Figure
XXVI. It can be seen that children 04 years old at thetime of the accident still have an increase in absolute
numbers of thyroid cancers, while the number of thyroid
cancers diagnosed among those who were 59 years old

140

NUMBER OF THYROID CANCERS

267. Between 1944 and 1957, the Hanford site in the UnitedStates released large quantities of 131I into the atmosphere
during fuel processing. In the Hanford Thyroid Disease Study,
thyroid doses were estimated for 3,193 individuals, and themean thyroid dose was 186 mGy [R22]. Initial results of thestudy indicated that a diagnosis of thyroid cancer could bemade for 19 participants, but no dose-response relationshipwas apparent. The final report is yet to be published.

120

Belarus
Russian Federation
Ukraine

100
80
60
40
20
0
1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
YEAR OF DIAGNOSIS

Figure XXIV. Number of thyroid cancers in children
exposed before the age of 14 years as a result of theChernobyl accident [I23, K41, T2, T16].
NUMBER OF CANCERS PER 100,000 CHILDREN

498

12

Belarus
RussiaUkraine

10

8

6

4

2

0
1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
YEAR OF DIAGNOSIS

Figure XXV. Thyroid cancer incidence rate in children
exposed before the age of 14 years as a result of theChernobyl accident [I23, K41, T2, T16].

seems to decrease after 1995. In those 1014 years of age
at exposure, the number of thyroid cancers seems to bestable for the period 19911997.
272. In a recent report on the childhood thyroid cancer
cases in the Russian Federation, Ivanov et al. [I27]described findings similar to those revealed above. In total,
3,082 thyroid cancer cases in persons less than 60 years ofage at diagnosis were recorded between 1982 and 1996 in
the four most heavily contaminated regions of the RussianFederation (Bryansk, Kaluga, Orel and Tula). Among
those 017 years of age at the time of the accident, 178cases were found. A significantly lower incidence of
thyroid cancer in women in these four areas compared to
women in the Russian Federation as a whole was found forthe period 19821986 (Figure XXVII). In the next five
years, described as an induction period, the risk was, onANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

average, 1.6 times the Russian Federation baseline risk,
probably reflecting increased surveillance and screening.
Separate figures for those less than 14 years of age were
not given, but the elevated risk seen for the period
19921996 was said to reflect the high rates found in thoseless than 14 years old at the time of the Chernobyl
accident. A nearly 14-fold increased risk was found among
girls 04 years of age at exposure compared to adult rates.
273. Jacob et al. [J2] reported a correlation between
collective dose and incidence of thyroid cancer in 5,821
settlements in Belarus, the Russian Federation and Ukraine in19911995. Using the southern half of Ukraine as areference, the excess thyroid cancer risk was found to belinear in the dose interval 0.071.2 Gy. The study was
extended in an attempt to take thyroid surveillance, background incidence, age, gender and appropriate methods into
consideration [J5]. Thyroid doses in two cities and 2,122
settlements in Belarus and one city and 607 settlements in the
Russian Federation were reconstructed. Thyroid cancers
diagnosed during 19911995 in individuals between the ageof 018 years at the time of the accident were included in the
study. Information on residency at the time of the accident
was collected for all cases, and 243 thyroid cancers were
found, giving an excess absolute risk of 2.1 (95% CI: 1.04.5)
per 104 person-year Gy (Table 59).
274. In a pooled analysis of children exposed to external
photon radiation [R7], the excess absolute risk of thyroid
cancer was 4.4 cases per 104 person-year Gy (95% CI:
1.910.1). The excess relative risk found by Jacob et al.
[J5] was 23 Gy1 (95% CI: 8.682), which is nonsignificantly higher than the excess relative risk of 7.7 Gy1(95% CI: 2.128.7) found by Ron et al. [R7]. It could bethat indolent thyroid cancers detected only at screening
were included. The possible shortening of the latency
period by screening, which served to “harvest” thyroid
cancers, could partly explain the differences. Anotherexplanation for the differences could be the dosimetry,

4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
1996

Figure XXVI. Number of diagnosed thyroid cancer
cases in Belarus as a result of the Chernobyl accident[K41].

1995

YEAR OF DIAGNOSIS

1994

1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997

1993

0

1992

10

1991

20

1990

30

1989

40

275. A recent case-control study by Astakhova et al. [A6]included the initial 131 Belarus thyroid cancers presented
by Kazakov et al. in 1992 [K11] but excluded 24 cases fordifferent reasons. Eleven cases did not have pathologicalconfirmation, 8 cases were not in Belarus at time of theaccident, 2 cases had no information on pathology, 2 cases
were diagnosed before 1987 and 1 patient was deceased.
For the remaining 107 thyroid cancers included in the
study, the male:female ratio was 1:1.1, and 105 cancers(98%) were of papillary origin. Two sets of controls werechosen, both matched on age, sex, rural/urban residency,
taking reason for diagnosis and area of residency into
consideration. A strong relationship between estimatedthyroid dose and thyroid cancer was found, even whenreason for diagnosis, gender, age, year of diagnosis, and131
I level in soil were taken into consideration [A6]. The
mean doses were different for the cases and for the controls
selected to represent the general population of children
exposed to fallout from the accident (Table 60), and theodds ratio was 3.1 (95% CI: 1.75.8) when comparing thelowest and the two highest dose groups. The highest odds
ratio, based on 19 cases and controls, was seen for thosediagnosed incidentally (Table 60) when using the other setof controls, i.e. those having the same opportunity for
diagnosis as the cases. The odds ratio for those thyroid
cancers found at routine screening (OR = 2.1, 95% CI:
1.04.3) indicated that screening was conducted in highfallout areas, since no large difference in dose was noted.

1988

10-14 years

1987

50

1986

5-9 years

1985

60

1984

0-4 years

1983

70

since collective thyroid doses were used, and individual dose
measurements in Belarus were available for onlya minority ofthe study population. Dose calculations were based on
environmental measurements and radio-ecological models.

1982

Age at exposure in 1986

STANDARDIZED INCIDENCE RATIONUMBER OF CANCERS

80

499

Figure XXVII. Standardized incidence ratios (SIR) of
thyroid cancers among women less than 60 years ofage at diagnosis in the four most contaminated areas(Bryansk, Kaluga, Orel, Tula) of Russia to Russia as awhole [I27].

276. The Astakhova case-control study [A6] is one of themore reliable published to date. Individual thyroid doses
received by the children were inferred from established

500

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

relationships between adult thyroid doses and 137Cs
deposition on a village basis and then modified according
to age-adjusted intake rates and dose coefficients. Locationof the children before and after the accident wasestablished on the basis of interviews. Although thequestionnaire was designed to acquire individual information on milk-consumption rates and the administration of
thyroid-blocking agents, such information was incomplete
in many cases and could not be used. Age-dependent
default values of milk-consumption rates were therefore
used for all children in order not to introduce bias into thestudy; the use of blocking agents was assumed either not tohave occurred at all or to have occurred too late to havebeen effective. Uncertainty in the individual estimates ofthyroid dose is difficult to quantify, but is estimated to beat least a factor of three.
277. In a study of Ukrainian thyroid cancer patients lessthan 15 years old at diagnosis, registered at the Institute of
Endocrinology and Metabolism, Kiev, the thyroid cancer
rate for 19861997 exceeded the pre-accident level by afactor of ten [T18]. A total of 343 thyroid cancers occurredin patients born between 1971 and 1986, and the thyroid
cancer rate for this age cohort was 0.45 per 100,000
compared with 0.040.06 per 100,000 before the accident.
For the slightly older group of patients 1518 years old atdiagnosis in 19861997, 219 cases of thyroid cancers were
found, and the average incidence was three times higher
than that in the group diagnosed before the accident.
278. Descriptions of the dosimetric methods or doseresponse models are unavailable, but it was stated that 22%of the patients aged 014 years at the time of the accident
received a thyroid dose of >0.3 Gy [T18]. Thyroid cancer
rates were analysed for different areas, and a rate of 27 per
100,000 was found in children evacuated from the villages
closest to the accident (including Pripyat and Chernobyl).
The authors concluded that the highest risk was found in
those less than 5 years of age at the time of the accident,
but it is questionable whether the methods used allow sucha statement. Only cases below the age of 19 years at
diagnosis are registered, thus excluding those older than 7
years of age in 1986 to be registered in 1997.
279. In a recent paper, Shirahige et al. [S34] compared 26
children diagnosed with thyroid cancer in Belarus within
the framework of the Sasakawa project with 37 children
diagnosed with thyroid cancer in Japan between 1962 and1993. A peculiar finding was the peak incidence at 10
years of age at time of diagnosis and a drop thereafter
among the Belarus cancer cases compared with a steadyincrease between the ages of 8 and 14 among the Japanesecases. This could reflect a difference in age distribution,
since those exposed very early in life seemed to have an
increased risk many years after exposure [G23, K41]. The
differences could also indicate a different growth patterncaused by an alternative process of carcinogenesis,
differences in screening routines, or the manner in which
the children were selected for screening, since someregistries only follow children until the age of 15.

280. In a study of male recovery operation workers from
Belarus, the Russian Federation and Ukraine who worked
within the 30-km zone, an increased incidence of thyroid
cancer was noted, based on a total number of 28 cases [C2].
Significant thyroid doses may have been received from shortlived iodines during the first days after the accident, but
information on the period workers spent within the 30-km
zone was not taken into consideration. Histopathology andmode of confirmation were not available for the 28 thyroid
cancers. These results must therefore be interpreted withcaution, especially since the follow-up of recovery operation
workers is much more active than that of the general
population in the three countries (see Section IV.A.1 andIV.C.2). In a study of approximately 34,000 patients receiving
131
I for diagnostic purposes, 94% being older than 20 years at
exposure, no increased risk of thyroid cancer related toradioiodine exposure could be found [H6]. As previously
discussed, the intensity of screening may greatly influence theobserved incidence of thyroid cancer in adults [S4].
281. Ivanov et al. [I8, I14, I33] extensively studied the lateeffects in Russian recovery operation workers. The Russian
National Medical and Dosimetric Registry (the former
Chernobyl registry) was used, and a significantly increased
risk of thyroid cancer was found when the number ofobserved cases was compared to the number expected fromnational incidence figures. With the exception of the recent
papers by Ron [R17] and Franklyn [F13], this is the first time
an increased risk of thyroid cancer has been reported in adults
after exposure to ionizing radiation. The study has been
criticized for not using individual doses and internal comparisons [B30, B31]. The increased medical surveillance andactive follow-up of the emergency workers most likely
influenced the results, particularlywhen observed numbers arecontrasted to national background rates.
282. In a descriptive study of cancer incidence in the six
most contaminated regions of the Russian Federation [R2],the thyroid cancer incidence increased over time in adults,
and the increase was larger than that observed in the wholeof the Russian Federation. The highest values were foundin the Bryansk region in 1994; the thyroid cancer incidence
for women there was 11 per 100,000 compared with 4.0
per 100,000 for the Russian Federation as a whole. The
corresponding figures for males were 1.7 and 1.1 per
100,000, respectively. It was concluded that no correlation
was found between adult thyroid cancer and the levels ofradioactive contamination [R2]. A pronounced difference
was observed in children based on 14 cases; the incidence
was 2.5 in the Bryansk region compared with 0.2 per
100,000 for the whole of the Russian Federation. Before
the accident, the incidence of thyroid cancer in children in
Bryansk and in the Russian Federation was the same. The
registration and follow-up of the Russian population as awhole are probably not comparable to that in the highly
contaminated regions surrounding Chernobyl (see Section
IV.A.1 and IV.C.2), and this influences the results.
283. Thyroid examinations, including ultrasound and fineneedle aspiration, were conducted in 1,984 Estonian recovery

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

operation workers nine years after the accident [I19]. The
average age on arrival at Chernobyl was 32 years and at
thyroid examination, 40 years. The mean documented dosefrom external irradiation of the thyroid was 108 mGy, but apoor correlation was found with biological indicators of
exposures such as loss of expression of the glycophorin A
gene in erythrocytes. Doses from incorporated iodine were nottaken into consideration. Two cases of papillary carcinoma
were identified and referred for treatment. Both men withthyroid cancer had worked at Chernobyl in May 1986, when
the potential of exposure to radioactive iodine was highest.
284. In a study of 3,208 Lithuanian recovery operation
workers in 19911995, three thyroid cancers (two papillarycarcinomas and one mixed papillary-follicular carcinoma)
were detected [K9]. There was no significant differencecompared with the Lithuanian male population and noassociation with level of radiation dose or duration of stayin the area of Chernobyl.
285. Three years after the Chernobyl accident, Jewish
residents of the former USSR began to emigrate in large
numbers to Israel. Between 1989 and 1996, about 140,000
persons from contaminated regions of Belarus, the RussianFederation and Ukraine moved to Israel. The thyroid status of
300 immigrant children brought to the clinic voluntarily byparents was evaluated [Q1], and enlarged thyroid glands were
found in about 40% of subjects. One 12year-old girl from
Gomel was found to have a malignant papillary carcinoma of
the thyroid.
286. Several studies on the late health effects of theChernobyl accident were carried out in Europe and have been
critically reviewed and summarized [S12]. No increase inthyroid cancer among children was observed, although nostudy focussed specifically on childhood thyroid cancer, since
the disease is so rare and a small increase could have gone
undetected in these studies.
287. Screening programmes have increased the ascertainment of occult thyroid tumours through the use of ultrasoundexamination [B23, S5], a possibility discussed in one of theoriginal reports [B18]. Thyroid screening was locallyorganized in the most contaminated areas after the accident,
but large-scale screening with ultrasound examination,
supported bythe Sasakawa and IPHECA programmes, did notstart until 1991 and 1992. Soviet health authorities initiated anational screening programme shortly after the accident, andeach country later continued the thyroid screening [S19]. It is
anticipated that 40%70% of the diagnosed childhood thyroid
cancer cases have been found through these programmes. In
the case-control study of 107 childhood thyroid cancers [A6],63 cases were found through endocrinological screening(Table 60). In a survey of 50 thyroid childhood cancers in
Belarus [A5, C1], 12 cases were detected by targeted
screening and another 23 cases were found incidentally inother examinations (Table 61). A study by Ron et al. [R8]supports these findings of a screening effect. Increased
screening of a cohort given external photon radiation for
benign head and neck diseases in the United States resulted ina roughly sevenfold increase in thyroid cancers.

501

288. Although rarely fatal, the aggressiveness of the thyroid
cancers found in the Chernobyl area, which is frequently
present with periglandular growth and distant metastases [E1,K11, W8], argues against the findings being entirely a resultof screening. Although thyroid tumours in adults are usually
tumours of relatively low malignancy, they tend to be moreaggressive in children [S3], so it could be argued that thegrowth pattern would have led to the diagnosis of a thyroid
cancer sooner or later.
289. Although ultrasound screening is not sufficiently
widespread to explain the majority of the thyroid cancer
cases observed until now, it is clear that increased
awareness and medical attention to thyroid disorders
during routine medical examinations in the contaminatedterritories influence the findings. Enhanced examinationsin schools may have advanced the time at which sometumours were recognized [A5]. However, the continuing
increase in the number of cases [C4, I27, K41] and theobservation that the increase appears to be confined tochildren who were born before the accident support theconclusion that ascertainment bias could not fully explain
the increased rates. Rates among those conceived after theaccident appear to be similar to pre-accident rates in theaffected countries.
290. Factors other than screening and lack of individual
dosimetry may modifythe risk of radiation-induced thyroid
cancer, one of them being iodine saturation. The iodine
deficiency in some of the affected areas will affect not only
the level of dose received by the thyroid gland at the
moment of exposure but also, if continued, thyroid functionin the years after exposure [Y1]. The risk of thyroid cancer
may be enhanced when the excretion of radioactive iodine
is limited owing to reduced thyroid hormone synthesis andblocked thyroid hormone secretion [R6]. Iodide dietary
supplementation had been terminated in the former USSR
approximately 10 years before the accident. The relationship between iodine deficiency and goiter is discussed inparagraph 345.
291. Another risk-modifying influence might be a genetic
predisposition to radiation-induced thyroid cancer, perhaps
related to ethnicity. A recent survey indicated that cases
occurred in siblings in at least three families in Belarus[A5, C1], a finding unlikely to be explained by chancealone. In a study of children exposed in the Michael Reese
hospital in the United States, the risk of radiation-induced
thyroid cancer appeared to vary by ethnic origin of thechildren [S4]. The genetic susceptibility to thyroid cancer
and its familial aggregation were studied in relatives of 177
patients with thyroid cancer [V8]. No significantly
increased rate of thyroid cancer was seen compared with
controls. In a recent study, 7 of 119 patients with papillary
thyroid microcarcinoma had a family history of thyroid
carcinoma, and they experienced less favourable tumour
behaviour than patients without a family history of thyroid
carcinoma [L39]. The possible existence of a genetic
predisposition to radiation-induced thyroid cancer might beimportant.

502

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT(b) Clinical and biological aspects
292. A large proportion of the childhood thyroid cancers in
Belarus and Ukraine were reported to be locally aggressive;
extrathyroidal growth was seen in 48%61% of the cases,
lymph node metastases in 59%74% and distant metastases(mainly lung) in 7%24% [F5, P2, P6, T4, T18].
Comparisons with characteristics of tumours from othercountries (France, Italy, Japan, the United Kingdom and theUnited States) indicate a higher percentage of extrathyroidal
extension for tumours from Belarus and the RussianFederation but similar percentages of cases with metastases[N5, P2, P6, V8, Z3].
293. In a recent pooled analysis of 540 thyroid cancers
diagnosed before the age of 20 years (mean age at diagnosis,
14 years) that included nine Western centres, the average
male:female ratio was 1:3.2 and the mean follow-up was 20
years [F7]. Eighty-six percent were papillary thyroid
carcinomas, 79% showed evidence of lymph node metastases,
20%60% had extracapsular invasion and 23% werediagnosed with distant metastases. In nearly all cases thepresenting sign was a neck mass. Thirteen of the patients diedas a consequence of the disease.
294. Two of the above-mentioned centres participated ina study in which 369 Italian and French thyroid cancers
were compared to 472 Belarusian cancers [P2]. The
Belarusian cases were diagnosed between May 1986 andend of 1995 and included approximately 98% of the casesin the country diagnosed in that period. The Belarusianpatients were younger at diagnosis, and 95% of the cancers
were of papillary origin compared to 85% in Italy/France.
Extrathyroidal extension and lymph node metastases weremore frequent in Belarus, 49% and 65%, compared to
Italy/France, where the corresponding figures were 25%
and 54%, respectively. Thyroid lymphocytic infiltrationand circulating antithyroidperoxidase were more frequentin the Belarusian patients, possibly indicating a higher rateof autoimmune thyroid disorders. The male:female ratio
was 1:2.5 in Italy/France, in contrast to 1:1.6 in Belarus.
The low male:female ratio could be a screening effect,
since no difference in sex ratio of occult thyroid cancer was
found at autopsy in young individuals [F10]. The age
distribution could probably also explain some of thedifference in stage, the histopathological distribution andgender ratio.
295. A number of thyroid cancer cases in Belarus weretreated with radioiodine at the university clinics of Essen
and Würzburg [R23]. All 145 patients had undergone
operations at the Centre for Thyroid Tumors in Minsk;
lymph node metastases were found in 140 patients anddistant metastases in 74 of them. The mean age at
diagnosis was 12 years. Among 125 children subsequently
followed, 90 were classified as in complete remission andthe others had partial remissions.
296. In a study of 577 Ukrainian thyroid cancer cases
diagnosed in patients less than 19 years of age [T18],

histopathology was evaluated in 296 cases (123 wereanalysed by non-Ukrainian pathologists, who confirmed
the initial diagnosis in all cases). Ninety-three percent were
papillary carcinomas, and 65% were found to be of themore aggressive solid/follicular type. In 55% of cases,
lymph node metastases were found, and in 17% lungmetastases were found either at initial diagnosis or in later
follow-up. Difference in TNM classification [H17] overtime did not show a significant trend towards moreadvanced stages (Table 62), as could have been anticipatedif radiation-associated cancers are indeed more aggressive.
Cancers diagnosed in 1996 and 1997 were more likely to
be locally aggressive, stage T4, but they revealed the same
pattern of lymph node metastases and distant spread. The
male:female ratio was found to be influenced by age at thetime of diagnosis (Table 63): the ratio was 1.1:1 for thoseless than 5 years of age at time of diagnosis and 1:2.7 forthose 1518 years. However, age at time of the accident
did not seem to influence the male:female ratio (Table 63).
A possible sex difference in the susceptibility of the thyroid
tissue to ionizing radiation did not seem to influence thegender ratio, since age at diagnosis and not age at exposure
influenced the distribution.
297. In a study in the United States of 4,296 patientspreviously irradiated for benign disorders, 41 childhood(mean age at diagnosis, 16 years) and 77 adult (mean age
at diagnosis, 27 years) thyroid cancers were found [S4].
The childhood cancers more often presented themselveswith lymph node metastases and vessel invasion but weresignificantly smaller in adults and found incidentally whenbenign nodules were operated. Of the childhood cancers,
95% were papillary carcinomas compared with 84% of theadult cancers. Thirty-nine percent of the childhood cancers
relapsed compared with 16% of the adult cancers. After amean follow-up of 19 years, there was only one death dueto thyroid cancer, and this was in the adult group.
298. The histopathology of over 400 post-Chernobyl thyroid
cancers diagnosed in children under the age of 15 years wasreviewed by pathologists from the United Kingdom and fromthe countries where the children were diagnosed [E2].
Virtually all cases were papillary carcinomas, in contrast to
thyroid cancers in British children of similar age who were
not exposed to ionizing radiation, where 68% of the
carcinomas were of papillary origin [H3]. The solid variant ofpapillary carcinoma, indicating a low level of differentiation,
was particularly prevalent in those cases believed to haveresulted from radiation exposure following the Chernobyl
accident [E2]. This finding is not in agreement with a studyof 19 cases in the Gomel area carried out by the Chernobyl
Sasakawa Health and Medical Cooperation Project, where no
specific morphological evidence of radiation-induced thyroid
cancer was observed [I26].
299. Shirahige et al. [S34] examined 26 Belarusian and 37
Japanese children diagnosed with thyroid cancer and foundthe mean tumour diameter to be smaller in Belarus(1.4 cm) than in Japan (4.1 cm). The solid growth pattern
was seen in 62% of the Belarusian papillary carcinomas

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

compared to 18% of the Japanese carcinomas. All cancers
from Belarus showed a papillary growth pattern, comparedto 92% of the cancers found in Japan.
300. Recent advances in the field of molecular biology
have improved the understanding of the mechanisms
underlying the thyroid carcinomas. Cellular signalling has
become a major research area, and signalling via protein
tyrosine kinases has been identified as one of the mostimportant events in cellular regulation. Protein tyrosine
kinases are thus important in the development of cancer,
and the RET proto-oncogene is one of the genes coding fora receptor tyrosine kinase. Rearrangements of the tyrosine
kinase domain of the RET proto-oncogene have been foundin some thyroid cancers and at a higher rate among those
supposed to be associated with ionizing radiation [F2, I21,
K14]. Other mutations are those seen in the RAS gene,which probably represent an early event in the carcinogenic process; the mutations of the RAS gene therefore
possess an early gate-keeper function, as reflected by thefact that they are found in similar frequencies in boththyroid carcinomas and adenomas. Point mutations in the
TP53 gene are rare in differentiated thyroid carcinomas but
are found in anaplastic thyroid cancer [F8].
301. A number of studies have been carried out to determine
whether any specific molecular biological alterations
characterize the childhood papillary cancers in the Chernobyl
area. A high frequency of RET/PTC3-type rearrangement inpost-Chernobyl papillary carcinoma was suggested in two
early studies [F2, K14]. However, a study including morecases showed that a RET/PTC1 rearrangement was more
frequent than PTC3 [E2] and that there was no significant
increase in the proportion of papillary carcinomas showing
RET rearrangement, when compared with a non-irradiatedpopulation of a similar age [W3]. In a French study, a higher
frequency of RET/PTC rearrangements (84%) was foundamong 19 thyroid cancer patients who had received previous
external radiotherapy for a benign or malignant condition
than among 20 “sporadic” thyroid cancers (15%) [B12]. The
most frequently observed chimeric gene was RET/PTC1, andfor the first time RET/PTC rearrangements were found infollicular adenomas.
302. Recent findings indicate a strong dependence of age
at exposure and latency period in the distribution of
RET/PTC rearrangements [S35]. When comparing 51
Belarusian childhood papillary thyroid carcinomas (meanage at exposure: three years) with 16 Belarusian and 16
German adult thyroid cancers patients, only RET/PTC1
mutations were found in adults (Table 64), while similarfrequencies of RET/PTC1 and RET/PTC3 were found inchildren. The authors suggested that thyroid cancers
expressing RET/PTC3 may be a feature of cancers detectedsoon after exposure, while RET/PTC1 may be a marker oflater-occurring, radiation-associated papillary thyroid
carcinoma in both children and adults. It also seems like
RET/PTC3 rearrangements are more common in younger
individuals. These findings are supported by a study
comparing RET/PTC rearrangements in Belarusian

503

radiation-associated thyroid cancers diagnosed in19911992 and in 1996 [P27]. A switch occurred from
RET/PTC3 rearrangements in patients diagnosed in theearly 1990s to RET/PTC1 alterations in patients diagnosed
later on.
303. The morphological subtype may also influence thepattern of RET rearrangements in papillary thyroid
carcinomas, as shown by Thomas et al. [T19]. Among 116
Chernobyl-related childhood papillary thyroid cancers,
RET/PTC1 and RET/PTC3 mutations were found in 9% and19%, respectively, of the solid follicular subtype. The
corresponding figures for the non-solid follicular subtype(classic papillary carcinoma and diffuse sclerosing
carcinoma) were 46% and 0%, respectively. It could be thatthe solid, less differentiated, follicular subtype associated with
RET/PTC3 rearrangements have a shorter induction period.
304. Despite the large amount of information accumulated
on RET activations in radiation-associated thyroid cancers,
little is known about the clinical significance of thedeletions. No significant differences were found, e.g. intumour size, multicentricity, extrathyroidal growth,
vascular invasion, lymphocytic invasion, or lymph nodeinvasion, when eight RET positive thyroid cancers werecompared with 25 carcinomas not displaying the activation[S39]. A lower proliferation rate was, however, seen in the
RET-activated tumours.
305. Karyotype abnormalities were studied in 56
childhood thyroid tumours from Belarus, and clonal
structural aberrations were seen in 13 cases [Z2]. In
particular, aberrations in 1q, 7q, 9q and 10q were found. It
is interesting to note that the 10q chromosomal band
harbours the RET proto-oncogene.
306. Two new rearrangements have been described in three
post-Chernobyl thyroid carcinomas. One is the RET/PTC4,
which involves a different breakpoint in the RET gene [F6]and PTC5, which involves fusion of RET with anotherubiquitously expressed gene, rgf5 [K31]. However, PTC4 andPTC5 appear to be present in only a small number of postChernobyl papillary cancers. Just recently, two novel types
RET rearrangements have been described, RET/PTC6 andPTC7 in childhood papillary thyroid carcinomas [K27].
307. No association has previously been shown between
mutations of other types of genes, e.g. RAS, bcl-2, andTP53, and thyroid carcinogenesis [E2, S9]. However, in astudy of 22 papillary thyroid cancers associated withionizing radiation, four mutations of TP53 were foundcompared to none in the 18 thyroid cancers not known tohave been exposed to ionizing radiation [F8]. In three ofthe four mutation carriers, invasion beyond the thyroid
capsule was found compared with 2 out of 17 in the rest of
the radiation-associated thyroid cancer patients. In a studyof thyroid adenomas and of well and poorly differentiatedthyroid cancers, the rates of TP53 mutations were 0%, 11%
and 63%, respectively [P1]. However, no correlation withage, sex, stage, or survival was seen.

504

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT(c) Summary
308. There can be no doubt about the relationship between
the radioactive materials released from the Chernobyl
accident and the unusually high number of thyroid cancers
observed in the contaminated areas during the past 14 years.
While several uncertainties must be taken into consideration,
the main ones being the baseline rates used in the calculations,the influence of screening, and the short follow-up, thenumber of cases is still higher than anticipated based on
previous data. This is probably partly a result of age at
exposure, iodine deficiency, genetic predisposition, anduncertainty that surrounds the role of 131I compared with thatof short-lived radioiodines. The exposure to short-lived
radioiodines is entirely dependent on the distance from therelease and the mode of exposure, i.e. inhalation or ingestion.
It was only in the Gomel region, the area closest to theChernobyl reactor, that Astakhova et al. [A6] found asignificantly increased risk of thyroid cancer. It has beensuggested that the geographical distribution of thyroid cancer
cases correlates better to the distribution of shorter-lived
radioisotopes (e.g. 132I, 133I and 135I) than to that of 131I [A7].
309. The identification of a genomic fingerprint thatshows the interaction of a specific target cell with a definedcarcinogen is a highly desirable tool in molecularepidemiology. However, a specific molecular lesion isalmost always missing, probably because of the large
number of factors acting on tumour induction and progression. Signalling via protein tyrosine kinases has been
identified as one of the most important events in cellular
regulation, and rearrangements of the tyrosine kinasedomain of the RET proto-oncogene have been found inthyroid cancers thought to be associated with ionizing
radiation [F2, I21, K14]. However, the biological andclinical significance of RET activation remains controversial, and further studies of the molecular biology ofradiation-induced thyroid cancers are needed before the
carcinogenic pathway can be fully understood.
2. Leukaemia
310. As discussed in Annex I, “Epidemiological evaluationof radiation-induced cancer”, the risk of leukaemia has beenfound to be elevated after irradiation for benign and malignant
conditions, after occupational exposure (radiologists), as wellas among the survivors of the atomic bombings. Leukaemia,
although a rare disease, is the most frequently reported
malignancy following radiation exposure. However, not all
subtypes of leukaemia are known to be associated withionizing radiation, e.g. chronic lymphatic leukaemia and adult
T-cell leukaemia. The naturally occurring subtypes ofleukaemia have an age dependency, with acute lymphatic
leukaemia most common in childhood and acute myeloid
leukaemia predominating in adulthood.
311. The incidence of leukaemia was increasing incountries of the former USSR even before the accident.
Prisyazhiuk et al. [P7] found an increase starting alreadyin 1981, which was most pronounced in the elderly. The

increase may simply be the result of improved registrationand diagnosis, but this cannot yet be exactly quantified.
The underlying trend must, however, be taken into accountwhen interpreting the results of studies focussing on the
period after the accident. Most existing studies have notaddressed this problem and suffer from a number of otherlimitations and methodological weaknesses, making it
premature to attempt a quantitative risk assessment basedon the results.
312. A number of publications have presented details of
the medical and dosimetric follow-up of the large numberof workers who took part in recovery operations following
the Chernobyl accident [K6, O2, T3, T7, T8, T9, T10].
Cardis et al. [C2] analysed cancer incidence in 1993 and1994 among male recovery operation workers who worked
within the 30-km zone of the reactor during 1986 and1987. The observed numbers of cancers were obtained fromthe national cancer registry in Belarus and from the
Chernobyl registries in the Russian Federation andUkraine. In total, 46 leukaemia cases were reported in thethree countries in the two-year period (Table 65), and nonsignificant increases were observed in Belarus and in the
Russian Federation. In Ukraine, a significant increase wasreported (28 cases observed, 8 cases expected) [C2]. It is
most likely that the increase reflects the effect of increased
surveillance of the recovery operation workers and underregistration of cases in the general population, since nosystematic centralized cancer registration existed in thethree countries at the time of the accident (see Section
IV.A.1 and IV.C.2). It could also be that different registries
define haematological malignancies differently, including,for example, myelodysplastic syndrome, which could resultin a leukaemia.
313. Ivanov et al. [I8, I9, I14] studied the late effects in
142,000 Russian recovery operation workers. The Russian
National Medical and Dosimetric Registry (formerly the
Chernobyl registry) was used, and a significantly increased
risk of leukaemia was found when the observed cases werecompared with those expected from national incidence
rates. The studies have been criticized for not using individual doses and internal comparisons and for including
chronic lymphatic leukaemia, a malignancy not linked toradiation exposure [B30, B31]. The increased medical
surveillance and active follow-up of the emergency
workers, coupled with under-reporting in the general
population, most likely influenced the results.
314. In contrast to their findings for the above-mentioned
cohort of recovery operation workers, the sameinvestigators [I29] did not find an increased risk ofleukaemia related to ionizing radiation in a case-control
setting. From 1986 to 1993, 48 cases of leukaemia wereidentified through the Russian National Registry and 34 ofthese patients (10 cases were diagnosed as chronic
lymphatic leukaemia) were selected for the case-control
study. The same registry was used when four controls werechosen for each case, matched on age and region ofresidence at diagnosis. For cases occurring among thoseANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

who were working in 1986 and 1987, controls had to haveworked during the same period, which is a questionableapproach, since dose is highly dependent on the period ofwork in the Chernobyl area. The mean dose for the cases
was 115 mGy compared with 142 mGy for controls. No
association was found between leukaemia risk andradiation.
315. These studies [I8, I9, I14, I29] suggest that, at leastin the case of the Russian Federation, cancer incidence
ascertainment in the exposed populations differs from thatin the general population. Future epidemiologicalinvestigations might be more informative if they are basedon appropriate Chernobyl registry-internal comparison
populations, although care must be taken if recent
additions to the register have been made because of diseasediagnosis and compensation (see Section IV.C.1).
316. In discussing the discrepancy between the findings ofthe case-control and cohort studies, Boice and Holm [B31]
claimed that the increased incidence in the cohort analyses
reflected a difference in case ascertainment between
recovery operation workers and the general population andnot an effect of radiation exposure. Boice [B30] further
argued that the results of the case-control study and of astudy of Estonian recovery operation workers [R13]
indicate that leukaemia risk among recovery operation
workers is not consistent with predictions from atomic
bomb survivors. He postulated that this may be due to an
overestimation of official doses received by recovery
operation workers and/or to the effect of protracted
exposure. In response, Ivanov [I18] questioned theinterpretation of the case-control analyses because of theconsiderable uncertainty surrounding the accuracy andquality of the official estimates of radiation doses available
in the Chernobyl registry of the Russian Federation. Cardis
et al. [C2] estimated that 150 cases of leukaemia should
occur within 10 years of the accident among 100,000
recovery operation workers exposed to an average dose of
100 mSv. Such numbers have not been apparent in any
studies or reports.
317. Shantyr et al. [S31] examined 8,745 Russian recovery
operation workers involved in operations from 1986 to
1990. Dosimetry records were available for 75% of theworkers, and the doses generally fell in the range
0250 mSv. Although cancer incidence increased,
particularly 410 years after the accident, no evidence ofa systematic dose-response relationship was found, and it
was suggested that the aging of the cohort influenced thefindings. Tukov and Dzagoeva [T11] observed noincreased risk of haematological diseases, including acuteforms of leukaemia, in a careful study of Russian recovery
operation workers and workers from the nuclear industry.
318. Osechinsky et al. [O6] studied the standardized
incidence rates of leukaemia and lymphoma in the general
population of the Bryansk region of the Russian Federation
for the period 19791993 on the basis of an ad hoc registry of
haematological diseases established after the Chernobyl

505

accident. The results were not adjusted for age, and the rates
in the six most contaminated districts (more than 37 kBq m2
of 137Cs deposition density) did not exceed the rates in the restof the region or in Bryansk city, where the highest rates wereobserved. Comparisons of crude incidence rates before andafter the accident (19791985 and 19861993) showed asignificant increase in the incidence of all leukaemia and nonHodgkin’s lymphoma, but this was mainly due to increases in
the older age groups in rural areas. The incidence ofchildhood leukaemia and non-Hodgkin’s lymphoma was not
significantly different in the six most contaminated areas fromthe incidence in the rest of the region.
319. The health status of 174,812 Ukrainian recovery
operation workers (96% males) was examined by Buzunov
et al. [B21]. Information on diagnosis was obtained fromthe State register of Ukraine and on leukaemia from an ad
hoc registry for haematological disorders. The majority(77%) of the recovery operation workers were exposed in19861987, and information on radiation exposure wasavailable for approximately 50% of the workers. A total of
86 cases of leukaemia were reported in the period
19871992, and the highest number of cases was foundamong those employed in April-June 1986. The averagerate of leukaemia among male recovery operation workers
was 13.4 per 100,000 among those employed in 1986 and
7.0 per 100,000 among those employed in 1987. No
apparent trend over time was seen among those employed
in 1986. Eighteen cases of acute leukaemia among
recovery operation workers exposed to 120680 mGy wererecorded as occurring 2.53 years after exposure in19861987. No difference in histopathology or response totreatment was found compared with cases that occurred
before the accident [B20].
320. Leukaemia and lymphoma incidence among adults
and children in the regions of Kiev and Zhitomir, Ukraine,
during 19801996 was examined by Bebeshko et al. [B32].
Total incidence in adults increased from 5.1 per 100,000
during 19801985 to 11 per 100,000 during 19921996,
but there were no excess cases in contaminated areas of theregions. Likewise, no excess cases among children who
resided in contaminated districts were found.
321. The incidence of leukaemia and lymphoma in the threemost contaminated regions of Ukraine increased from 1980 to
1994 [P12]. This result should be viewed cautiously, since thefindings were based on only a few cases, and lymphomas havenot previously been known to be induced by radiation.
Increased awareness and better health-care facilities anddiagnosis most likely influenced the findings.
322. Childhood leukaemia in Belarus during 19821994
was investigated with regard to area of residency [I20].
Approximately 75% of the leukaemia cases were of theacute lymphatic subtype. No evidence of an increasing
number of childhood leukaemia cases over time was noted.
When the two most heavily contaminated areas, Gomel andMogilev, were compared with the rest of the country, nodifference was seen.

506

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

323. The incidence of leukaemia and lymphoma in thegeneral population of Belarus was studied for 19791985
and 19861992 [I11]. Among children, no difference wasobserved either over time or in relation to 137Cs groundcontamination. In adults, significant increases were notedin the post-accident period for most subtypes of leukaemia
and for lymphoma, but no relationship with the level ofradioactive contamination was found.
324. An analysis of the mortality and cancer incidence
experience of Estonian Chernobyl recovery operation
workers took a different approach. First, a cohort consisting of 4,833 recovery operation workers wasconstructed using multiple data sources not based solely on
Chernobyl registry data [R13, T6]. Second, mortality data
were ascertained from vital registration sources, and deathcertificates in the cohort were coded following the samecoding rules used by the Statistical Office of Estonia andcompared to the official national mortality statistics [T6].
Furthermore, cancer incidence data in the cohort, alongwith the corresponding national cancer incidence rates,
were obtained from the Estonian cancer registry. During19861993, 144 deaths were identified compared with 148
expected [R13, T6]. A non-significant excess of nonHodgkin’s lymphoma was observed, based on three cases,
while no case of leukaemia was found.
325. Fujimura et al. [F1] reported the results of haematological screening organized in the framework of the
Sasakawa project. By the end of 1994, 86,798 children who
were less than 10 years of age at the time of the accident
were examined, and four cases of haematologicalmalignancies were found. No correlation was observed
between the prevalence of any haematological disorder andeither the level of environmental contamination or 137Cs
measured by whole-body counting.
326. The European Childhood Leukaemia–Lymphoma
Incidence Study (ECLIS), coordinated by IARC, was set up
to monitor trends in childhood leukaemia and lymphoma[P5, P11]. Incidence rates from European cancer registries
were related to the calculated radiation dose in the large
geographical regions for which environmental dose
estimates were provided in the UNSCEAR 1988 Report[U4]. Thirty-six cancer registries in 23 countries arecollaborating in ECLIS by supplying an annual listing ofcases in children less than 15 years of age. Data for19801991 indicated a slight increase in the incidence ofchildhood leukaemia in Europe. This increase was,however, not related to the estimated radiation dose fromthe accident [P11, P21]. No indication of an increased
incidence among those exposed in utero was noticed.
327. A study of infant leukaemia incidence in Greece afterin utero exposure to radiation from the Chernobyl accident
was based on ad hoc registration of childhood leukaemia
cases diagnosed throughout Greece since 1980 by anational network of pediatric oncologists [P3]. Based on 12
cases, a statistically significant 2.6-fold increase in theincidence of infant leukaemia (from 0 to 11 months after

birth) was observed among the 163,337 live births exposed inutero (i.e. born between 1 January 1986 and 31 December
1987) compared with 31 cases among non-exposed children.
Those born to mothers residing in areas of high radioactive
fallout were at significantly higher risk of developing
leukaemia. The reported association, which is not consistent
with risk estimates from other studies of prenatal exposures,is based on the selective grouping of data. It is unclear how
the authors chose the group <1 year to represent “infantleukaemia”, as there is little a priori aetiologic reason for
limiting to this age group. No significant difference in theincidence of leukaemia among children aged 1247 months
born to presumably exposed mothers was found.
328. Michaelis et al. [M6] conducted a study of childhood
leukaemia using the population-based cancer registry inGermany. Cohorts were defined as exposed and nonexposed, based on dates of birth using the same criteria as
Petridou et al. [P3] in the Greek study. The cohorts were
subdivided into three categories based on level of 137Cs
ground deposition (<6, 610 and >10 kBq m2). These
categories corresponded to the estimated in utero doses of
0.55 mSv for the lowest exposure category and 0.75 mSv
for the highest exposure category. Overall, a significantly
elevated risk was seen (1.48, 95% CI: 1.022.15) for the“exposed cohort” compared with the “non-exposed”, basedon 35 cases observed in a cohort of 900,000 births.
However, the incidence was higher for those born in April
to December 1987 than for those born between July 1986
and March 1987, although in utero exposure levels in thelatter group would have been much higher than in theformer group. The authors concluded that the observed
increase was not related to radiation exposure from the
Chernobyl accident.
329. A cluster effect described several decades ago could
explain the Greek findings. A total of 13,351 cases ofchildhood leukaemia diagnosed between 19801989 in 17
countries was included in a study aimed at relating
childhood leukaemia to epidemic patterns of common
infectious agents [A2]. A general elevation of the incidence
was found in densely (but not the most densely) populatedareas, and weak, but significant, evidence of clustering was
found. When seasonal variation in the onset of childhood
leukaemia was studied in the Manchester tumour registrycatchment area, the onset of acute lymphatic leukaemia (n= 1,070) demonstrated a significant seasonal variation,with the highest peak found in November and December[W6]. Both studies provide supportive evidence for an
infectious aetiology for childhood leukaemia.
330. In a Swedish study of cancer incidence amongchildren [T21] in areas supposed to have been contaminated as a consequence of the Chernobyl accident, 151cases of acute lymphatic leukaemia were found during
19781992 in those 019 years at diagnosis. The areas
were divided into three exposure categories, and the lowest
risk was found in the supposedly highest exposure group.
A non-significant decreasing trend with calendar year was
also noted. A Finnish study covering nearly the same

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

period analysed leukaemia risks among those 014 yearsof age for the whole country [A13]. The estimatedpopulation-weighted mean effective dose was 0.4 mSv. No
increased incidence of childhood leukaemia could be seenfor 19761992, and no risk could be related to exposure toionizing radiation. These results are consistent with themagnitude of effects expected.
331. Summary. Although leukaemia has been found to be
one of the early carcinogenic effects of ionizing radiation
with a latency period of not more than 23 years [U4], no
increased risk of leukaemia related to ionizing radiation
has been found among recovery operation workers or in
residents of contaminated areas. Numerous reports havecompared incidence and mortality data from the registers
described in Chapter IV with national rates not taking thedifferences in reporting into consideration. A case-control
study would diminish this bias, and a recent paper by
Ivanov et al. [I29] failed to show an increased risk ofleukaemia related to ionizing radiation in 48 cases ofleukaemia in recoveryoperation workers identified throughthe Russian National Registry.
3. Other solid tumours
332. Given the doses received by the recovery workers,
described in Chapter II, and the previous data on radiationassociated cancer in exposed populations, reviewed in
Annex I, “Epidemiological evaluation of radiationinduced cancer”, an increased number of solid tumours
could be anticipated in the years to come. The induction
and latency period of 10 years [U4] and the protracted
nature of the exposure probably explain why no radiationassociated cancers have been noticed so far.
333. The numbers of observed and expected cases ofcancer in 19931994 among residents of the territories
with 137Cs contamination in excess of 185 kBq m2
included in the Chernobyl registries of Belarus, theRussian Federation and Ukraine are presented in Table 65[C2]. The observed numbers of cancer cases were obtained
from the national cancer registry in Belarus and from the
Chernobyl registries in the Russian Federation andUkraine. Age- and sex-standardized expected numbers
were based on rates for the general national population.
Fewer solid tumours than anticipated were seen in workers
in Belarus, while the workers in the Russian Federationand Ukraine revealed higher risks. The different registries
used in the three countries could probably explain thesedifferences. No increased risk was seen among thoseresiding in contaminated areas [C2].
334. The crude incidence of malignant diseases per 100,000
persons among Russian recoveryoperation workers, excluding
leukaemia, was estimated by Tukov and Shafransky [T13]. It
rose from 152 in 1989, 193 in 1991 and 177 in 1993, to 390
in 1995. This increase was interpreted as an effect of age, but
no attempt was made to adjust for age. The cause of death haschanged over time. Accidents and trauma were the maincause of death in 19891990, while cardiovascular diseases

507

were responsible for 43% of all deaths in 1996, followed bycancers (20%) and accident and trauma (15%) [T14]. The
increase found in the report is similar to and consistent withthat reported for the population of the Russian Federation asa whole [L26].
335. In a recent paper covering 114,504 of the approximately 250,000 Russian recovery operation workers, 983
cases of solid tumours were found during the years
19861996 [I32]. The observed number of cases was compared with the Russian national rates, and the overall
standardized incidence ratio was 1.23 (95% CI:
1.151.31), with a significant excess relative risk per grayof 1.13. The only individually elevated site was thedigestive tract (n = 301), and the corresponding figures
were 1.11 (95% CI: 1.011.24) and 2.41, respectively. No
increased risk of respiratory tract tumours was noticed.
Increased ascertainment could influence the data but
probably not explain the dose-response relationship. The
excess relative risk is higher than what has been reported
for survivors of the atomic bombings [T20], which might
indicate uncertainty in the individual dose estimates.
336. When the same investigators presented data on
individuals living in contaminated areas, somewhat
contradictory results were seen [I12]. Cancer risks in threeof the most contaminated districts of the Kaluga region
were compared with the region as a whole. The populationof the three regions contained approximately 40,000
individuals, and incidence rates before and after theaccident were compared. The increase over time wassimilar for almost all sites regardless of exposure status. No
increased risk of gastrointestinal cancer was seen for men,but an increased risk for respiratory tract cancers was
suggested for women, based on 31 cases. However, theoverall cancer risk among women in the contaminatedareas was only one third of the incidence for the region in19811985, a sign of previous under-reporting.
337. A descriptive studyof cancer incidence in 19811994
was performed for the six most contaminated regions of theRussian Federation (Bryansk, Kaluga, Orel, Tula, Ryazan
and Kursk) [R2]. Information on cancer incidence wasgathered from the local oncological dispensaries andcompared with Russian national statistics. It is unclear
whether the analyses were adjusted for age, and theabsolute number of cases was not reported. An increased
incidence of all cancers was observed over the study period,
both in the contaminated regions and for the RussianFederation as a whole. However, from 1987 onwards, theincrease was more pronounced in the six study regions
than in the rest of the country. The incidence rate of solidcancer among men in 1994 in Bryansk and Ryazan was
305 per 100,000 compared with 272 per 100,000 for theRussian Federation as a whole. The corresponding figures
for women were 180 per 100,000 and 169 per 100,000,
respectively.
338. An increase in dysplasia and urinary bladder cancer
was seen in 45 Ukrainian males living in contaminated508

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

areas and compared to 10 males living in uncontaminatedareas of the country [R16]. Forty-two of the exposed
individuals had signs of irradiation cystitis. It was reported
that the incidence of bladder cancer in the Ukrainian
population gradually increased, from 26 to 36 per 100,000,
between 1986 and 1996. Among other histopathologicalfeatures, increased levels of p53 were noted in the nucleusof the urothelium in the exposed individuals, indicating
either an early transformation event or an enhancement of
repair activities. Further analyses of the exposed patients,
including urine sediments collected 427 months after the
first biopsy, indicated a novel type of p53 mutation notseen in the first analyses and showed that the mutation
carriers could be identified [Y2]. The authors concluded
that screening would be required.

342. Summary. The occurrence of solid tumours otherthan thyroid cancers in workers or in residents ofcontaminated areas have not so far been observed. The
weaknesses in the scientific studies, the uncertainties in thedose estimates, the latency period of around 10 years andthe protracted nature of the exposures probably explain
why no radiation-associated cancers have been noticed sofar. Some increase in incidence of solid tumours might
have been anticipated in the more highly exposed recovery
operation workers.

339. The health status of the 45,674 recovery operation
workers from Belarus registered in the Chernobyl registry wasstudied by Okeanov et al. [O2]. Eighty-five percent of themwere men, and 31,201 (90%) had worked in the 30-km zone.
For 1993 and 1994, the overall cancer incidence was lower
than anticipated for both male (standardized incidence ratio(SIR) = 77; 95% CI: 6590) and female (SIR = 90; 95% CI:
59131) workers compared with the general population.
Among men, a significant excess of urinary bladder cancer
was seen (SIR = 219; 95% CI: 123361), and non-significant
increases were seen for cancers of the stomach, colon, andthyroid and for leukaemia. The numbers of cases on whichthese comparisons are based were small, particularly forthyroid cancer (n = 4). Recovery operation workers who
worked in the 30-km zone more than 30 days had a slightly
higher incidence of all cancers than other recovery operation
workers.

343. The first report of non-malignant thyroid disorders in
the Chernobyl area was published in 1992 [M10]. The
prevalence of thyroid nodules among individuals in sevencontaminated villages in Belarus, the Russian Federationand Ukraine was compared with the prevalence in six
uncontaminated villages, and 1,060 individuals, in total,
were examined. Ultrasound examinations revealed an
overall rate of discrete nodules of 15% in adults and 0.5%
in children, with a higher prevalence in women. No
difference related to exposure status was found, but it wassuggested that it might be helpful to screen selected groups
such as recovery operation workers and individuals living
in contaminated areas.

340. Breast cancer incidence data in different time periods
for the Mogilev region of Belarus were recently presented[O5]. A steadily increasing incidence was noted for the whole
follow-up period, 19781996, and when the period
19891992 was compared with 19931996, a difference wasfound, but only for those 4549 years at diagnosis, i.e. 3542
years at the time of the accident. The findings could be due toincreased awareness, documentation, or accessibility toscreening, since the rates are lower in all age categories
compared with the ages found in Western data. It is peculiarthat younger age groups were not affected, and continued
follow-up is warranted. However, as in all studies of radiationassociated cancer, individual dosimetry is essential, andindividual doses were not used in this study.
341. Several studies of the effects of the Chernobyl
accident outside the former Soviet Union have been carriedout [E5, P5, P11]. The evaluations have mainly been doneon a local or national level. Most studies have focussed on
various possible health consequences of the accident,
ranging from changes in birth rates to adult cancer. Studies
related to cancer have been critically reviewed andsummarized [S12]. Overall, no increase in cancer
incidence or mortality that could be attributed to theaccident has been observed in countries of Europe outside
the former USSR.

B. OTHER SOMATIC DISORDERS
1. Thyroid abnormalities

344. The Chernobyl Sasakawa Health and Medical
Cooperation Project started in May 1991 as a five-year
programme, and through April 1996, approximately
160,000 children had been examined [S2, S7, Y1]. The
examined children were all born in Belarus, the RussianFederation and Ukraine between 26 April 1976 and 26
April 1986. The thyroid examinations included ultrasound,serum free thyroxine, thyroid-stimulating hormone (TSH),
antithyroperoxidase, antithyroglobulin and urine iodine
concentration. A total of 45,905 thyroid abnormalities were
found in 119,178 examined children (Table 66) [Y1].
Ninety-one percent of the abnormalities were diagnosed asgoiter, and 62 thyroid cancers were found. The incidence
rates in Gomel, the area of Belarus with the highest
contamination, had the lowest incidence of goiter but thehighest incidence of abnormal echogenity, cystic lesions,nodular lesions, and cancer, the latter two known to berelated to radiation (Table 67). No association between
thyroid antibodies, hypo- or hyperthyroidism, and 137Cs
activity in the body or soil contamination was seen in
114,870 children examined [Y1].
345. The contaminated areas around Chernobyl have beenrecognized as iodine-deficient areas, but the influence on
the goiter prevalence has not been clear. In an extended
study of the 119,178 children included in the Chernobyl
Sasakawa Health and Medical Cooperation Project [A8],urinary iodine excretion levels were measured in 5,710
selected cases. The study did not reveal any correlation
between goiter and whole-body 137Cs content or 137Cs

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

contamination level at the place of residence either at thetime of examination or the time of the accident. However,a significant negative correlation was indicated between
prevalence of goiter and urinary iodine excretion levels.
The highest prevalence of goiter (54%) was found in Kiev,
where the incidence of childhood cancer was relatively
low. However, the Kiev area was also identified as anendemic iodine-deficient zone. The opposite was found in
Gomel, i.e. no profound iodine deficiency and a lower rateof thyroid nodules (18%) in an area with a higher rate ofchildhood thyroid cancer.
346. For inhabitants of the Bryansk region in the RussianFederation who were born before the accident and examinedwith ultrasound, the overall prevalence of thyroid abnormalities did not differ when contaminated and uncontaminatedareas were compared [K10]. A difference was revealed when
age was taken into consideration. For those 09 years of age
at the time of the accident, the prevalence of thyroid
abnormalities was 8.1% in the exposed cohort compared with
1.6% in the non-exposed. The corresponding figures forindividuals 1027 years in 1986 were 18.8% and 17.7%,
respectively. Approximately half of the pathological findings
identified through ultrasound were also noticed at palpation.
347. The prevalence of thyroid antibodies (antithyroglobulin
and antithyroperoxidase) in children and adolescents in
Belarus was measured in 287 individuals residing in contaminated areas (average 137Cs contamination, 200 kBq m2)
and compared to the findings in 208 individuals living in
uncontaminated areas (average 137Cs contamination, <3.7
kBq m2) [P20]. All individuals were younger than 12 years
at time of the accident. Significantly elevated concentrationsof thyroid antibodies were found among the exposed
individuals with most pronounced concentrations in girls ofpuberty age. No indication of thyroid dysfunction was found,but the future development of clinically relevant thyroid
disorders was thought to be a possibility.
348. Blood samples from 12,803 children living in the
Kaluga region were studied for antibodies to thyroid antigen
with a modifying reaction of passive haemoagglutination[S15]. In the sixth year after the accident, the reaction showed
positive results in only a small percentage of samples(1.2%4.8%). However, in children from contaminated areas,
the percentage of positive results was consistently higher thanin children from uncontaminated areas.
349. Similar results were found in a Russian study inwhich 89 exposed and 116 non-exposed children were
examined [K28]. There was no apparent alteration inthyroid function, but a higher rate of thyroid antibodies
was found in the exposed group. This group also had alower percentage of individuals with iodine deficiency, as
defined by urinary iodine excretion (76%), than groups
living in uncontaminated areas (92%), but at the same timea fivefold greater rate of thyroid enlargement was
identified by ultrasound. No sex difference was seen forgoiters in the exposed group compared with a 1:2 male tofemale ratio in the non-exposed group.

509

350. Fifty-three Ukrainian children (07 years of age at
the time of the accident) living in contaminated areas werecompared with 45 children living in supposedly
uncontaminated regions [V1]. The level of antithyroglobulin, thyroid-stimulating hormone and abnormal
findings at ultrasound were higher in the exposed
individuals, and it was concluded that there was a doseresponse relationship. In contrast, no difference in thyroid
function was noticed when 888 Belarusian schoolchildren
living in contaminated areas were compared with 521 agematched, non-exposed controls [S10]. Both groups lived in
iodine- deficient areas, and the prevalence of diffuse goiterwas significantly higher in the exposed group. Thyroid
antibodies were not measured.
351. When 143 children 5 to 15 years old at examination
living in a contaminated area were compared with 40 ageand sex-matched controls living in clean areas of the Tularegion of the Russian Federation, a higher prevalence of
thyroid autoimmunity was found in the exposed group[V10]. The difference was only noticed in those less than
5 years of age at the time of the accident, and no differencein thyroid function was noticed.
352. A total of 700,000 persons from the former Soviet
Union have immigrated to Israel, approximately 140,000
of whom come from territories affected by the Chernobyl
accident [Q1, Q2]. The thyroid status of 300 immigrantchildren voluntarily brought for thyroid examination by
their parents was evaluated. Enlarged thyroid glands were
found in about 40% of subjects, irrespective of whether
they came from the contaminated or uncontaminated areas,
i.e. 137Cs greater or less than 37 kBq m2 [Q1, Q2].
Thyroid-stimulating hormone levels, although within
normal limits, were significantly higher (p < 0.02) for girls
from the more contaminated regions.
353. Thyroid screening was performed in 1,984 Estonian
recovery operation workers through palpation of the neckbya thyroid specialist and high-resolution ultrasonography
by a radiologist [I19]. Fine- needle biopsy was carried out
for palpable nodules and for nodules larger than 1 cm
found by ultrasound; enlarged nodules were observed in
201 individuals. The prevalence of nodules increased withage at examination but was not related to recorded dose,
date of first duty at Chernobyl, duration of service at
Chernobyl, or the activities carried out by the recovery
operation workers. Two cases of papillary carcinoma andthree benign follicular neoplasms were identified andreferred for treatment [I19].
354. Thyroid examinations by ultrasound were performed
on 3,208 Lithuanian recovery operation workers in19911995, and thyroid nodularity (nodules > 5 mm) was
detected in 117 individuals [K9]. There was, however, nosignificant difference in the prevalence of thyroid
nodularity compared with the Lithuanian male population
as a whole and no association with level of radiation doseor duration of stay in the Chernobyl area.

510

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

355. The development of hypothyroidism following highlevel external or internal exposures to ionizing radiation iswell known. A change in hypothyroid rates in newborns
has been shown in some areas of the United States and was
supposed to be related to fallout from the Chernobyl
accident [M9]. These findings were challenged [W4] on
the grounds that the received doses were far too low to
induce hypothyroidism. Doses received in the northwesternpart of the United States were approximately 1/10,000 ofthat received in the Chernobyl area, and extensive
examinations of children in Belarus, the RussianFederation and Ukraine have not shown a relationshipbetween dose and either hyper- or hypothyroidism [Y1].
356. Summary. Other than the occurrence of thyroid
nodules in workers and in children, which is unrelated toradiation exposure, there has been no evidence of thyroid
abnormalities in affected populations following theChernobyl accident. Even the large screening programme
conducted by the Chernobyl Sasakawa Health and Medical
Cooperation Project in 19911996, involving 160,000
children, less than 10 years of age at time of the accident,
there was no increased risk of hypothyroidism, hyperthyroidism or goiter that could be related to ionizing
radiation. Neither was an increase in thyroid antibodies
noticed, which is in contradiction with some other minor
studies.

2. Somatic disorders other than thyroid
357. The first study of health effects other than cancer andthyroid disorders on a representative sample of the populations from contaminated and control districts was carriedout in the framework of the International Chernobyl
Project [I1]. The conclusion of this project was that,
although there were significant health disorders in the
populations of both contaminated and control settlements,
no health disorder could be attributed to radiation
exposure.
358. As discussed previously, between 1991 and 1996, theSasakawa Memorial Health Foundation of Japan funded thelargest international screening programme of children in five
medical centres in Belarus, the Russian Federation andUkraine [Y1]. In all, haematological investigations werecarried out for 118,773 children. White blood cells, red blood
cells, haemoglobin concentration, haematocrit, mean corpuscular volume and concentration, and platelets were measured.
The prevalence of anaemia was higher in girls than in boys
and ranged from 0.2% to 0.5 %. An extended examination of
322 children suggested that iron deficiency was the cause of
one third of these cases. The prevalence of leukopenia wassomewhat lower in girls than boys (overall range, 0.2%
1.1%), while no sex difference was seen for leukocytosis(range, 2.8%4.9%). No differences between sexes or centres
were seen for trombocytopenia (range, 0.06%0.12%),
trombocytosis (range, 1.0%1.3%), or eosinophilia (range,
12.2%18.9%). The prevalence of eosinophilia changed
dramatically during the five years of follow-up, from 25% in1991 to 11% in 1996. There are probably several reasons forthis decline, among them better socioeconomic conditions, agreater awareness ofhealth, and improved medical conditions.
The frequency of haematological disorders showed nodifference by level of 137Cs contamination at the place ofresidency at the time of the accident, current residency, or
137
Cs concentration in the body [Y1].
359. A number of studies have addressed the generalmorbidity of populations living in contaminated areas [I8,O2, W1]. When individuals in the contaminated areas werecompared with the general population in these countries,
increased morbidity due to diseases of the endocrine,
haematopoietic, circulatory and digestive systems wasfound. A higher rate of mental disorders and disability has
also been noted. It is difficult to interpret these results,
since the observations may be at least partly explained by
the active follow-up of the exposed populations and by thefact that age and sex are not taken into account in thesestudies. On the other hand, they may reflect a real increasein morbidity following the Chernobyl accident, which
would mainly be an effect of psycho-social trauma, since
existing epidemiological studies of radiation-exposed
populations are not consistent with these findings. Stressand economic difficulties following the accident are most
likely influencing the results.
360. The demographic situation in Belarus has changed
since the accident. People have moved to the cities to alarger extent, and the population is, on average, older as aresult of the low birth rate. Mortality due to accidents andcardiovascular diseases has increased, particularly amongevacuated populations and people living in zones
recommended for relocation [W1]. Mortality rates in the
Russian Federation regions of Kaluga and Bryansk areclose to those in the rest of the country and are relatively
stable over time; however, infant mortality is steadilydecreasing. Except for an increase in accidental deaths in
the contaminated areas, no significant difference in causeof death was found [W1]. Population growth in Ukraine, as
in other parts of the former Soviet Union, has become
negative. General mortalityin contaminated areas is higher(1418 per 1,000) than in the whole of Ukraine (1112 per
1,000). The pattern in causes of death in Ukraine is stable,with some decrease in cardiovascular mortality [W1].
361. Since 1990, 4,506 children (3,121 from Ukraine,
1,018 from the Russian Federation and 367 from Belarus)
from the Chernobyl area have received medical care at theCentre of Hygiene and Radiation Protection, in Cuba
[G18]. Measured body burdens of 137Cs were in the range
1.5565 Bq kg1 (90% of children had levels below 20
Bq kg1). Doses from external irradiation were estimated torange from 0.04 to 30 mSv (90% < 2 mSv), 2 to 5.4 mSv
from internal irradiation and thyroid doses from 0 to 2 Gy
(44% < 40 mGy). Assessment of overall health condition,
including haematological and endocrinological indicators,
did not differ when the children were divided into fivegroups on the basis of 137Cs contamination (<37, 37185,>185 kBq m2, evacuated, unknown).

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

362. The incidence of non-malignant disorders in children
was evaluated using the Belarus Chernobyl registry [L19].
The children were divided into three groups: evacuatedfrom the 30-km zone, residing (or previously residing) inareas with contamination >555 kBq m2, and born toexposed parents. Increased rates of gastritis, anaemia andchronic tonsillitis were found among all exposure
categories compared to Belarus as a whole, and the highest
rates were for children in the Gomel region. The authors
concluded that the increases were most probably due topsycho-social factors, lifestyle, diet and increased medical
surveillance and suggested that further analyses would beneeded to establish aetiological factors.
363. When hormonal levels, biologically active
metabolites and immunoglobulins in 132 Russian recovery
operation workers were stratified by absorbed doses, nodifferences related to ionizing radiation were seen except
for so-called biomarkers of oxidative stress, e.g. conjugateddienes [S8]. These biomarkers are, however, not specificfor radiation damage and can be seen in several
pathological conditions.
364. In an Estonian cohort of 4,833 recovery operation
workers, 144 deaths were identified in the period
19861993, compared with 148 expected [R13, T6]. A
relatively high number of deaths were due to accidents,
violence and poisoning. In nearly 20%, the cause of death
was suicide, and the relative risk of 1.52 (n = 28) was
statistically significant [R13, T6].
365. A Lithuanian cohort of 5,446 recovery operation
workers was followed regularly at the Chernobyl Medical
Centre during the years 19871995, and 251 deaths wereobserved [K3]. The major causes of death were injuries andaccidents, and the overall mortality rate of the recovery
operation workers was not higher than that of the total
population.
3. Immunological effects
366. Acute as well as fractionated exposures to low dosesof ionizing radiation have been reported to alter several
immunological parameters in experimental animals. It is,however, not clear what effects are found in humans. Many
papers have been published in the last decade on the
immunological effects of exposure to radiation from the
Chernobyl accident. Since it is unclear, however, if
possible confounding factors have been taken into account,
including, in particular, infections and diet, it is difficult tointerpret the results.
367. The immunological status of 1,593 recovery
operation workers was studied by Kosianov and Morozov[K24]. A moderate decrease in the number of leukocytes
was observed, as well as a decrease in T-lymphocytes andperiodic decreases in the number of B-lymphocytes and in
immunoglobulin level. These disturbances lasted for 46months in individuals with a dose <2.5 mGy and about ayear in those with doses from 2.5 to 7 mGy.

511

368. The immune status of 85 recovery operation workers
who were professional radiation workers from the Mayakplant was studied carefully between 9 and 156 days after
they finished work in the Chernobyl area [T17]. The
radiation doses were between 1 and 330 mGy. Only somedecreases in T-lymphocytes and increases in nulllymphocytes showed causal relations to the radiation dose.
369. A three-year study of 90 recovery operation workers
living in the town of Chelyabinsk [A1] showed that the
average numbers of leukocytes, neutrophyls and lymphocytes
in the whole period were the same as in the control group,
consisting of the general population of Chelyabinsk with thesame age and sex distribution. During the first and second
years, a moderate increase of IgM level in blood was found,while a slight decrease was seen in the first month; complete
recovery was seen in the third year [A1].
370. A five-year study of the immunological status of 62
helicopter pilots exposed to radiation doses from 180 to
260 mGy did not reveal significant quantitative changes infunctional characteristics of T- and B-lymphocytes [U15].
Among persons with the highest doses and with somechronic diseases, however, an increase in the functional
activity of B-lymphocytes and other non-specific changes
in immune status were observed.
371. A careful immunological study of 500 healthy
children evacuated from Pripyat with doses from 0.05 to
0.12 Gy did not show significant differences in comparison
with Kiev-resident children of the same age [B8]. This
study considered the T-lymphocyte subpopulation, naturalkiller activity, levels of immune complexes, and ofinterleukin-1 and -2. Some changes in immunoglobulin-A
with hypoglobulineaemia and other functional changes
were found in children who suffered from respiratory
allergy and chronic infections.
372. No differences in absolute and relative levels of
T-lymphocytes were found in more than 1,000 examinedchildren living in contaminated areas of the Gomel andMogilev regions [G20]. A slight increase in serum Ig-G
level and B-lymphocytes was observed in children 37
years old at the time of examination. The study was
conducted in the second year after the accident.
373. Immune status was studied in 84 children 714 years
old (at the time of the accident) and living in contaminatedareas of Belarus and in a control group of 60 children (withthe same age and sex distribution) living in uncontaminatedareas [K25]. The study was conducted four and half years
after the accident. A direct association was observed between
the T-lymphocyte levels in children from contaminated areas
and the average reconstructed dose from radioiodine to thethyroid in the settlements where the children resided.
374. While evaluating the significance of these various
findings, it must be borne in mind that the doses received by
the subjects were unlikely to directly affect constituents of theimmune system. The long period over which disturbances of

512

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

immune function were observed are not consistent with theunderstanding of recovery of immune functions following
acute exposure of experimental animals. It is quite likely,
therefore, that psychological stress mediated by neuroendocrine factors, cytokines, respiratory allergies, chronic
infections, and autoimmunity related imbalances could havecaused the fluctuations in some immunological parameters in
different groups of subjects.
375. Summary. With the exception of the increased riskof thyroid cancer in those exposed at young ages, nosomatic disorder or immunological defect could be
associated with ionizing radiation caused by the Chernobyl
accident.

C. PREGNANCY OUTCOME
376. In a group of Belarusian children born to exposed
mothers with in utero doses ranging from 8 to 21 mSv, norelationship between birth defects and residency incontaminated areas was seen [L5]. The observations thatthe defects were largely of multifactorial origin and varied
according to the residency of the mother appeared to reflect
the influence of complex and multiple non-radiation
factors. No consistent relationship was seen between thedetected rate of chromosome and chromatid aberrations inchildren and the level of radioactive ground contamination.
377. Later studies of birth defects and malformations in
Belarus yielded conflicting results [L8]. The studies conducted on all legal medical abortions from 1982 to 1994
revealed increased rates of polydactyly, limb reduction, andmultiple malformations in highly contaminated areas (>555
kBq m2) when pre- and post-accidental rates were compared[L8]. In the less contaminated areas (<37 kBq m2), increased
rates of anenchephaly, spina bifida, cleft lip/palate, polydactyly, limb reduction and multiple malformations werenoted. The city of Minsk was used as a control, and spina
bifida, polydactyly, multiple malformations, and Down’s
syndrome were found to have increased. No changes in birthdefects over time could be related to exposure to ionizing
radiation.
378. One explanation to the findings of Lazjuk [L8] could
be that classification of birth disorders has not been
consistent over time, probably reflecting the lack of clarityof diagnostic criteria and the significant improvement indiagnostic procedures. Only a few reliable clinical studies
have been undertaken in representative groups and regions[K5], and these studies suggest that the observed shifts in
the health status of children are unlikely to have beencaused by radiation exposure only.
379. Somewhat conflicting results have also been reported
when reproductive outcomes in contaminated areas of theRussian Federation were examined [B19, L27, L28, L29].

The outcomes before and after the accident were comparedin regions of different contamination levels. The results are
summarized in Table 68. Birth rates decreased in all three
regions and were related to severity of contamination,
while spontaneous abortions increased in two of the three
regions. Congenital malformations, stillbirths, prematurebirths and perinatal mortality were studied, but noconsistency or apparent relationship to ionizing radiation
was noticed.
380. The frequency of unfavourable pregnancy outcomesfor 19861992 was studied through interviews of 2,233
randomly selected women from 226 contaminatedsettlements of Belarus and the Russian Federation [G11].
In the contaminated areas of Gomel and Mogilev (Belarus)and of Bryansk (the Russian Federation), a decrease in thebirth rate in both urban and rural populations was reported.
This corresponds to an increase in the number of medical
abortions in both populations.
381. Studies of chromosomal aberrations in distantpopulations have been critically reviewed [L32, V5].
Increased numbers of cases of Down’s syndrome werereported in West Berlin in January 1987 [S23], in theregion of Lothian, in Scotland [R14] and in the mostcontaminated areas of Sweden [E4]. All studies were basedon a small number of cases and were later challenged[B13]. The doses in Berlin and Scotland reached 10% of
the natural background irradiation, and it is not likely that
this contribution was enough to cause the non-disjunction
in oocytes during meiosis that is needed for the specificaneuploidy of Down’s syndrome. The findings have notbeen confirmed in larger and more representative series in
Europe [D9, L32]. In particular, no peak in Down’s
syndrome among children exposed at time of conception
was observed in equally contaminated zones of Europe(e.g. Finland) or even in Belarus [B34, V5]. In a careful
study of birth defects in Belarus, no increased rate of
Down’s syndrome was found when pre- and post-accident
figures were compared in contaminated areas [L8].
382. According to a recent paper [K4], perinatal mortality
in Germany showed a statistically significant increase in
1987, and it was concluded that this was an effect of theChernobyl accident fallout. The findings were laterquestioned, since whole-body doses from incorporated
caesium were found to be 0.05 mSv [R19]. No effect of theChernobyl accident could be found when temporal patternsof perinatal mortality in Bavaria were correlated todifferent fallout levels and subsequent exposures [G24].
383. Summary. Several studies on adverse pregnancy
outcomes related to the Chernobyl accident have been
performed in the areas closest to the accident and in moredistant regions. So far, no increase in birth defects, congenital
malformations, stillbirths, or premature births could be linked
to radiation exposures caused by the accident.

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

D. PSYCHOLOGICAL AND OTHER
ACCIDENT-RELATED EFFECTS
384. Many aspects of the Chernobyl accident have beensuggested to cause psychological disorders, stress andanxiety in the population. The accident caused long-termchanges in the lives of people living in the contaminateddistricts, since measures intended to limit radiation doses
included resettlement, changes in food supplies andrestrictions on the activities of individuals and families.
These changes were accompanied by important economic,
social and political changes in the affected countries,
brought about by the disintegration of the former Soviet
Union. These psychological reactions are not caused byionizing radiation but are probably wholly related to thesocial factors surrounding the accident.
385. The decisions of individuals and families to relocate
were often highly complex and difficult. The people felt
insecure, and their lack of trust in the scientific, medical
and political authorities made them think they had lost
control [H9]. Experts who tried to explain the risks andmollify people were perceived as denying the risk, thus
reinforcing mistrust and anxiety.
386. The environmental contamination created widespreadanxiety that should be referred to not as radiophobia, as it
initially was, but as a real, invisible threat, difficult tomeasure and localize. The key to how people perceive risk
is the degree of control they exert over it. Once measures
are taken to improve the quality of life for those still living
in contaminated areas, the climate of social trust improves,probably because of the better cooperation between
inhabitants and local authorities [H9].
387. Psychological effects related to the Chernobyl
accident have been studied extensively [I1, L3, L4].
Symptoms such as headache, depression, sleep disturbance,
inability to concentrate, and emotional imbalance havebeen reported and seem to be related to the difficult
conditions and stressful events that followed the accident.
388. The psychological development of 138 Belarusianchildren who were exposed to radiation from the Chernobyl
accident in utero was compared with that of 122 age-matchedchildren from uncontaminated areas [K46]. The children were
followed for 612 years and the study included neurological,
psychiatric and intellectual assessments of children andparents. The exposed group was found to have a slightlylower
intellectual capability and more emotional disorders. A
correlation was found between anxiety among parents andemotional stress in children. It was concluded thatunfavourable psychosocial factors, such as broken social
contacts, adaptation difficulties, and relocation, explained thedifferences between the exposed and non-exposed groups. No
differences could be related to ionizing radiation.
389. Many individuals affected by the Chernobyl accident
are convinced that radiation is the most likely cause of theirpoor health [H7]. This belief may cause or amplify psycho-

513

somatic distress in these individuals. When studying theimpact of the accident in exposed areas of Belarus, Havenaar
et al. [H11, H12] found that depression, general anxiety andadjustment disorders were more prevalent among thoseevacuated and in mothers with children under 18 years of age.
It was concluded that the Chernobyl accident had had asignificant long-term impact on psychological well-being,
health-related quality of life, and illness in the exposed
populations [H10]. However, none of the findings could bedirectly attributed to ionizing radiation.
390. Post-traumatic stress is an established psychiatricdiagnostic category involving severe nightmares andobsessive reliving of the traumatic event. Although it is
widely perceived by victims of disasters, such stress is
supposed to occur only in those persons who were directly
and immediately involved. The uncertainty, threat andsocial disruption felt by the wider public has been termed
chronic environmental stress disorder by Lee [L3], who
compared the consequences of the Chernobyl accident withthe consequences of other destructive events and accidents.
391. Among recovery operation workers, those without
occupational radiation experience suffered a higher rate ofneurotic disturbances than the general population [R5,S13]. Clinically expressed disturbances with significant
psychosomatic symptoms were predominant in this group,
but the increased medical attention, which leads to thediagnosis of chronic somatic diseases and subclinicalchanges that persistently attract the attention of the patient,complicates the situation. The possibility of rehabilitation
decreased correspondingly, while unsatisfactory andunclear legislation exacerbated the conflicts and tended toprolong the psychoneurotic reactions of the patients [G4,S13]. The health status of recovery operation workers who
were nuclear industry professionals did not seem to bedifferent from that of the rest of the cohort [N3].
392. Social and economic suffering among individuals
living in contaminated areas has exacerbated the reactions
to stressful factors. Although the incidence of psychosomatic symptoms in the population of highly contaminated areas is higher than that in populations of lesscontaminated areas, no direct correlation with radiationdose levels has been observed. The self-appraisal of thisgroup is low, as is their general physical health, asobserved in systematic screening programmes, including
the International Chernobyl Project [I1]. This makes theindividuals functionally unable to solve complicated socialand economic problems and aggravates their psychologicalmaladaptation. The tendency to attribute all problems to
the accident leads to escapism, “learned helplessness”,
unwillingness to cooperate, overdependence, and a belief
that the welfare system and government authorities shouldsolve all problems. It also contributes to alcohol and drug
abuse. There is evidence of an increased incidence ofaccidents (trauma, traffic incidents, suicides, alcohol
intoxication and sudden death with unidentified cause) inthis population, as well as in recovery operation workers,
compared with the populations of unaffected regions.

514

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

393. A follow-up study of the psychological status of 708
emigrants to Israel from the former Soviet Union was
carried out over a two-year period [C3]. A total of 374
adults who had lived in contaminated areas and for whombody-burden measurements had been carried out and 334
non-exposed emigrants matched by age, sex and year of
emigration were compared. The subjects from exposed
areas were categorized into two exposure groups: high andlow (137Cs greater or less than 37 kBq m2) on the basis of
the map of ground caesium contamination [I1]. The
prevalence of post-traumatic stress disorders, depression,anxiety and psychosomatic effects, such as high bloodpressure and chronic illness, were measured. Interviews
were carried out during the initial contact andapproximately one year later with 520 of the original
respondents. The results obtained in the first interview
showed that psychological symptoms were much moreprevalent in the exposed groups than in the non-exposedgroup; in the second interview, a decline in the prevalenceof disorders was noted. The proportion of those whoreported three or more chronic health problems was 48%
among the high-exposure group, 49% in the low-exposuregroup, and 31% in the non-exposed group (p < 0.0003).
Based on these results, the authors concluded that the
Chernobyl accident had had a strong impact on both themental and physical health of the immigrants fromcontaminated areas of the former Soviet Union.
394. Summary. The Chernobyl accident caused long-termchanges in the lives of people living in the contaminatedareas, since measures intended to limit radiation dose
included resettlement, changes in food supplies, andrestrictions on the activities of individuals and families.
These changes were accompanied by important economic,
social, and political changes in the affected countries,
brought about by the disintegration of the former Soviet
Union. The anxiety and emotional stress among parents
most likely influenced the children, and unfavourable
psychosocial factors probably explain the differences
between the exposed and non-exposed groups.

E. SUMMARY
395. A majority of the studies completed to date on thehealth effects of the Chernobyl accident are of thegeographic correlation type that compare average population exposure with the average rate of health effects orcancer incidence in time periods before and after theaccident. As long as individual dosimetry is not performed
no reliable quantitative estimates can be made. The
reconstruction of valid individual doses will have to be a
key element in future research on health effects related to
the Chernobyl accident.
396. The number of thyroid cancers in individuals exposedin childhood, particularly in the severely contaminatedareas of the three affected countries, is considerably greaterthan expected based on previous knowledge. The highincidence and the short induction period have not been

experienced in other exposed populations, and factors otherthan ionizing radiation are almost certainlyinfluencing therisk. Some such factors include age at exposure, iodine
intake and metabolic status, endemic goitre, screening,short-lived isotopes other than 131I, higher doses thanestimated, and, possibly, genetic predisposition. Approximately 1,800 thyroid cancer cases have been reported in
Belarus, the Russian Federation and Ukraine in children
and adolescents for the period 19901998. Age seems to be
an important modifier of risk. The influence of screening
is difficult to estimate. Approximately 40%70% of thecases were found through screening programmes, and it isunclear how many of these cancers would otherwise havegone undetected. Taking the advanced stage of the tumoursat time of diagnosis into consideration, it is likely that mostof the tumours would have been detected sooner or later.
397. The present results from several studies indicate thatthe majority of the post-Chernobyl childhood thyroid
carcinomas show the intrachromosomal rearrangementscharacterized as RET/PTC1 and 3. There are, however,
several questions left unanswered, e.g. the influence of age
at exposure and time since exposure on the rate ofchromosome rearrangements.
398. The risk of leukaemia has been shown in epidemiological studies to be clearly increased by radiation exposure. However, no increased risk of leukaemia linked toionizing radiation has so far been confirmed in children, in
recovery operation workers, or in the general population of
the former Soviet Union or other areas with measurable
amounts of contamination from the Chernobyl accident.
399. Increases in a number of non-specific detrimental
health effects other than cancer in recovery operation
workers and in residents of contaminated areas have beenreported. It is difficult to interpret these findings without
referring to a known baseline or background incidence.
Because health data obtained from official statisticalsources, such as mortalityor cancer incidence statistics, areoften passively recorded and are not always complete, it is
not appropriate to compare them with data for the exposed
populations, who undergo much more intensive and active
health follow-up than the general population.
400. Some investigators have interpreted a temporary lossof ability to work among individuals living in cotaminatedareas as an increase in general morbidity. High levels ofchronic diseases of the digestive, neurological, skeletal,
muscular and circulatory systems have been reported.
However, most investigators relate these observations tochanges in the age structure, the worsening quality of life,and post-accident countermeasures such as relocation.
401. Many papers have been published in the last decadeon the immunological effects of exposure to radiation fromthe Chernobyl accident. Since it is unclear, however, if
possible confounding factors have been taken into account,
including, in particular, infections and diet, it is difficult tointerpret these results.

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

515

CONCLUSIONS
402. The accident of 26 April 1986 at the Chernobyl
nuclear power plant, located in Ukraine about 20 km southof the border with Belarus, was the most serious ever tohave occurred in the nuclear industry. It caused the deaths,
within a few days or weeks, of 30 power plant employees
and firemen (including 28 with acute radiation syndrome)and brought about the evacuation, in 1986, of about
116,000 people from areas surrounding the reactor and therelocation, after 1986, of about 220,000 people from
Belarus, the Russian Federation and Ukraine. Vastterritories of those three countries (at that time republics of
the Soviet Union) were contaminated, and trace depositionof released radionuclides was measurable in all countriesof the northern hemisphere. In this Annex, the radiation
exposures of the population groups most closely involvedin the accident have been reviewed in detail and the healthconsequences that are or could be associated with theseradiation exposures have been considered.
403. The populations considered in this Annex are (a) the
workers involved in the mitigation of the accident, either
during the accident itself (emergency workers) or after theaccident (recovery operation workers) and (b) members of thegeneral public who either were evacuated to avert excessive
radiation exposures or who still reside in contaminated areas.
The contaminated areas, which are defined in this Annex as
being those where the average 137Cs ground deposition density
exceeded 37 kBq m2 (1 Ci km2), are found mainly in
Belarus, in the Russian Federation and in Ukraine. A large
number of radiation measurements (film badges, TLDs,
whole-bodycounts, thyroid counts, etc.) were made toevaluate
the exposures of the population groups that are considered.
404. The approximately600 emergencyworkers who wereon the site of the Chernobyl power plant during the nightof the accident received the highest doses. The mostimportant exposures were due to external irradiation(relativelyuniform whole-bodygamma irradiation and beta
irradiation of extensive body surfaces), as the intake ofradionuclides through inhalation was relatively small(except in two cases). Acute radiation sickness was
confirmed in 134 of those emergency workers. Forty-one ofthese patients received whole-body doses from external
irradiation of less than 2.1 Gy. Ninety-three patients
received higher doses and had more severe acute radiation
sickness: 50 persons with 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 from beta exposures, evaluated for eightpatients with acute radiation sickness, were in the range of400500 Gy.
405. About 600,000 persons (civilian and military) havereceived special certificates confirming their status asliquidators (recoveryoperation workers), according to laws
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 thesarcophagus and of a town for reactor personnel. Thesetasks were completed by 1990.
406. A registry of recovery operation workers wasestablished in 1986. This registry includes estimates ofeffective doses from external irradiation, which was the
predominant pathway of exposure for the recovery
operation workers. The registry data show that the average
recorded doses decreased from year to year, being about
170 mSv in 1986, 130 mSv in 1987, 30 mSv in 1988, and
15 mSv in 1989. It is, however, difficult to assess thevalidity of the results that have been reported because (a)different dosimeters were used by different organizations
without any intercalibration; (b) a large number ofrecorded doses were very close to the dose limit; and (c)there were a large number of rounded values such as 0.1,
0.2, or 0.5 Sv. Nevertheless, it seems reasonable to assume
that the average effective dose from external gamma
irradiation to recovery operation workers in the years
19861987 was about 100 mSv.
407. Doses received by the general public came from theradionuclide releases from the damaged reactor, which led
to the ground contamination of large areas. The radionuclide releases occurred mainly over a 10-day period,
with varying release rates. From the radiological point ofview, the releases of 131I and 137Cs, estimated to have been
1,760 and 85 PBq, respectively, are the most important.
Iodine-131 was the main contributor to the thyroid doses,
received mainly via internal irradiation within a few weeks
after the accident, while 137Cs was, and is, the main
contributor to the doses to organs and tissues other than the
thyroid, from either internal or external irradiation, which
will continue to be received, at low dose rates, during
several decades.
408. The three main contaminated areas, defined as thosewith 137Cs deposition density greater than 37 kBq m2(1 Ci km2), are in Belarus, the Russian Federation andUkraine; they have been designated the Central, GomelMogilev-Bryansk and Kaluga-Tula-Orel areas. The Central
area is within about 100 km of the reactor, predominantly
to the west and northwest. The Gomel-Mogilev-Bryansk
contaminated area is centred 200 km north-northeast of thereactor at the boundary of the Gomel and Mogilev regionsof Belarus and of the Bryansk region of the RussianFederation. The Kaluga-Tula-Orel area is in the RussianFederation, about 500 km to the northeast of the reactor.
All together, territories from the former Soviet Union withan area of about 150,000 km2 were contaminated with 137Cs
deposition density greater than 37 kBq m2. About fivemillion people reside in those territories.

516

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

409. Within a few weeks after the accident, more than
100,000 persons were evacuated from the most contaminatedareas of Ukraine and of Belarus. The thyroid doses received by
the evacuees varied according to their age, place of residence,
dietary habits and date of evacuation. For example, for the
residents of Pripyat, who were evacuated essentially within 48
hours after the accident, the population-weighted average
thyroid dose is estimated to be 0.17 Gy and to range from0.07 Gy for adults to 2 Gy for infants. For the entire
population of evacuees, the population-weighted average
thyroid dose is estimated to be 0.47 Gy. Doses to organs andtissues other than the thyroid were, on average, much smaller.
410. Thyroid doses also have been estimated for the residentsof the contaminated areas who were not evacuated. In each of
the three republics, thyroid doses are estimated to haveexceeded 1 Gy for the most exposed infants. For residents ofa given locality, thyroid doses to adults were smaller thanthose to infants by a factor of about 10. The average thyroid
dose was approximately 0.2 Gy; the variability of the thyroid
dose was two orders of magnitude, both above and below theaverage.
411. Following the first few weeks after the accident, when131
I was the main contributor to the radiation exposures, doses
were delivered at much lower dose rates by radionuclides withmuch longer half-lives. Since 1987, the doses received by the
populations of the contaminated areas came essentially fromexternal exposure from 134Cs and 137Cs deposited on the
ground and internal exposure due to the contamination offoodstuffs by 134Cs and 137Cs. Other, usually minor, contributions to the long-term radiation exposures include theconsumption of foodstuffs contaminated with 90Sr and theinhalation of aerosols containing plutonium isotopes. Bothexternal irradiation and internal irradiation due to 134Cs and137
Cs result in relatively uniform doses in all organs andtissues of the body. The average effective doses from 134Cs and137
Cs that were received during the first 10 years after theaccident by the residents of contaminated areas are estimatedto be about 10 mSv.
412. The papers available for review by the Committee todate regarding the evaluation of health effects of theChernobyl accident have in many instances suffered frommethodological weaknesses that make them difficult tointerpret. The weaknesses include inadequate diagnoses andclassification of diseases, selection of inadequate control orreference groups (in particular, control groups with a different
level of disease ascertainment than the exposed groups),
inadequate estimation of radiation doses or lack of individual
data and failure to take screening and increased medical
surveillance into consideration. The interpretation of thestudies is complicated, and particular attention must be paid
to the design and performance of epidemiological studies.
These issues are discussed in more detail in Annex I,“Epidemiological evaluation of radiation-induced cancer”.
413. Apart from the substantial increase in thyroid cancer
after childhood exposure observed in Belarus, in the RussianFederation and in Ukraine, there is no evidence of a major

public health impact related to ionizing radiation 14 years
after the Chernobyl accident. No increases in overall cancer
incidence or mortality that could be associated with radiation
exposure have been observed. For some cancers no increase
would have been anticipated as yet, given the latency periodof around 10 years for solid tumours. The risk of leukaemia,
one of the most sensitive indicators of radiation exposure, has
not been found to be elevated even in the accident recovery
operation workers or in children. There is no scientific proofof an increase in other non-malignant disorders related toionizing radiation.
414. The large number of thyroid cancers in individuals
exposed in childhood, particularly in the severely
contaminated areas of the three affected countries, and theshort induction period are considerably different fromprevious experience in other accidents or exposure situations.
Other factors, e.g. iodine deficiency and screening, are almost
certainly influencing the risk. Few studies have addressed
these problems, but those that have still find a significant
influence of radiation after taking confounding influences into
consideration. The most recent findings indicate that the
thyroid cancer risk for those older than 10 years at the time of
the accident is leveling off, the risk seems to decrease since1995 for those 59 years old at the time of the accident, while
the increase continues for those younger than 5 years in 1986.
415. There is a tendency to attribute increases in cancer
rates (other than thyroid) over time to the Chernobyl
accident, but it should be noted that increases were also
observed before the accident in the affected areas. Moreover, a general increase in mortality has been reported inrecent years in most areas of the former USSR, and thismust also be taken into account in interpreting the resultsof the Chernobyl-related studies. Because of these andother uncertainties, there is a need for well designed, soundanalytical studies, especially of recovery operation workers
from Belarus, the Russian Federation, Ukraine and theBaltic countries, in which particular attention is given to
individual dose reconstruction and the effect of screening
and other possible confounding factors.
416. Increases of a number of non-specific detrimental healtheffects other than cancer in accident recovery workers havebeen reported, e.g. increased suicide rates and deaths due toviolent causes. It is difficult to interpret these findings without
reference to a known baseline or background incidence. The
exposed populations undergo much more intensive and active
health follow-up than the general population. As a result,using the general population as a comparison group, as has
been done so far in most studies, is inadequate.
417. Adding iodine to the diet of populations living in
iodine-deficient areas and screening the high-risk groups
could limit the radiological consequences. Most datasuggest that the youngest age group, i.e. those who wereless than five years old at the time of the accident,
continues to have an increased risk of developing thyroid
cancer and should be closely monitored. In spite of the factthat many thyroid cancers in childhood are presented at a

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

more advanced stage in terms of local aggressiveness anddistant metastases than in adulthood, they have a good
prognosis. Continued follow-up is necessary to allow
planning of public health actions, to gain a better
understanding of influencing factors, to predict theoutcomes of any future accidents, and to ensure adequate
radiation protection measures.
418. Present knowledge of the late effects of protracted
exposure to ionizing radiation is limited, since the doseresponse assessments rely heavily on high-dose exposurestudies and animal experiments. The Chernobyl accident
could, however, shed light on the late effects of protracted
exposure, but given the low doses received by the majorityof exposed individuals, albeit with uncertainties in the dose
estimates, any increase in cancer incidence or mortality
will most certainly be difficult to detect in epidemiologicalstudies. The main goal is to differentiate the effects of theionizing radiation and effects that arise from many othercauses in exposed populations.
419. Apart from the radiation-associated thyroid cancers
among those exposed in childhood, the only group thatreceived doses high enough to possibly incur statisticallydetectable increased risks is the recovery operation workers.
Studies of these populations have the potential to contribute to
the scientific knowledge of the late effects of ionizing
radiation. Many of these individuals receive annual medical
examinations, providing a sound basis for future studies of thecohort. It is, however, notable that no increased risk ofleukaemia, an entity known to appear within 23 years after

517

exposure, has been identified more than 10 years after theaccident.
420. The future challenge is to provide reliable individual
dose estimates for the subjects enrolled in epidemiologicalstudies and to evaluate the effects of doses accumulated overprotracted time (days to weeks for thyroid exposures ofchildren, minutes to months for bone-marrow exposures of
emergency and recovery operation workers, and months toyears for whole-body exposures of those living incontaminated areas). In doing this, many difficulties must be
taken into consideration, such as (a) the role played bydifferent radionuclides, especiallythe short-lived radioiodines;(b) the accuracy of direct thyroid measurements; (c) the
relationship between ground contamination and thyroid doses;and (d) the reliability of the recorded or reconstructed doses
for the emergency and recovery operation workers.
421. Finally, it should be emphasized that although those
exposed as children and the emergency and recovery
operation workers are at increased risk of radiationinduced effects, the vast majority of the population need
not live in fear of serious health consequences from the
Chernobyl accident. For the most part, they were exposed
to radiation levels comparable to or a few times higher
than the natural background levels, and future exposures
are diminishing as the deposited radionuclides decay. Liveshave been disrupted by the Chernobyl accident, but fromthe radiological point of view and based on the assessmentsof this Annex, generally positive prospects for the future
health of most individuals should prevail.

518

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

Table 1
Radionuclide inventory in Unit 4 reactor core at time of the accident on 26 April 1986

Activity (PBq)
Radionuclide

Half-life
1986 estimates a
[I2]

3

H
C
85
Kr
89
Sr
90
Sr
95
Zr
95
Nb
99
Mo
103
Ru
106
Ru
110m
Ag
125
Sb
129m
Te
132
Te
129
I
131
I
132
I
133
I
134
I
135
I
133
Xe
134
Cs
136
Cs
137
Cs
138
Cs
140
Ba
140
La
141
Ce
144
Ce
147
Nd
154
Eu
235
U
236
U
238
U
237
Np
239
Np
236
Pu
238
Pu
239
Pu
240
Pu
241
Pu
242
Pu
241
Am
243
Am
242
Cm
244
Cm
14

a
b
c
d
e
f

12.3 a5 730 a10.72 a50.5 d29.12 a64.0 d35 d2.75 d39.3 d368 d
250 d2.77 a33.6 d3.26 d
15 700 000 a
8.04 d2.3 h20.8 h52.6 min6.61 h5.25 d
2.06 a13.1 d30.0 a32.2 min12.7 d40.3 h32.5 d284 d11.0 d8.6 a
704 000 000 a
23 400 000 a
4 470 000 000 a
2 140 000 a2.36 d2.86 a87.74 a24065 a6537 a14.4 a376 000 a
432 a
7 380 a163 d18.1 aEstimates by[B1, I2]

33
2 000
200
4 400

33
2 330
200
4 810

4 800
4 100
2 100

5 550
4 810
2 070

320

2 700

1 300

3 180

1 700
190

6 290
190

290

280

2 900

4 810

4 400
3 200

5 550
3 260

140

49 600 c

1
0.8
1
170

1.0
0.85
1.2
170
0.002526

15 c

Decay-corrected to 6 May 1986.
Values used in this Annex.
Corrected to account for burnup of individual fuel assemblies.
Reference [K1].
Corrected value.
Reference [K16].

Estimates by
[S1]
1.4 d
0.1 d
28
3 960
230
5 850
5 660
6 110
3 770
860
1.3
15
1 040
4 480
0.000081 d
3 080
4 480
6 700

6 510
170
110 e
260
6 550
6 070
6 070
5 550
3 920
2 160
14
0.000096 d
0.0085 d
0.0023 d
0.00026
58,1000.0001
1.3
0.95
1.5
180
0.00290.17
0.009743
0.43

Estimates by[B2, B3, B4] b

220

850

4 200 f
3 200 f
4 200 f
4 800 f
2 050 f
2 900 f
150
260

3 920

58 100
0.93
0.96
1.5
190
0.00210.14
0.005631
0.18

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

519

Table 2Estimates of the principal radionuclides released in the accident
Activities released (PBq)
Radionuclide
1986 estimates a[I2]

1996 estimates b[B4, B27, D8]

1996 estimates[K37]

1996 estimates c d[D5, D8, N4]

33
6 500

6 500

1 800

~1 150~1 760

50

~54

86

~85

80
8
120
25
160

~115
~10
>168
>73
240

140

0.033
0.0334
0.053
6.3

196
>168
196
~116
945
0.035
0.03
0.042
~6

1.1

~0.9



5 300

Noble gases
85

Kr
Xe

133

33
1 700

33
6 500
Volatile elements

129m

Te
Te
131
I
133
I
134
Cs
136
Cs
137
Cs
132

48
260
19
38

240
1 000
1 2001 700
2 500
4 448367485Intermediate

89

Sr
Sr
103
Ru
106
Ru
140
Ba
90

80
8
120
63
170

81
8
170
30
170
Refractory (including fuel particles)

95

Zr
Mo
141
Ce
144
Ce
239
Np
238
Pu
239
Pu
240
Pu
241
Pu
242
Pu
242
Cm
99

Total
(excluding noble gases)
a
b
c
d
e

130
96
88
96
4.2
0.03
0.024
0.03
5.1
0.00007
0.78

170
210
200
140
1 700
0.03
0.03
0.044
5.9
0.00009
0.93

1 0002 000

8 000 e-120
90

Decay-corrected to 6 May 1986.
Estimate of release, decay-corrected to 26 April 1986.
Estimate of total release during the course of the accident.
Values used in this Annex.
Decay correction to beginning of accident allows more short-lived radionuclides to be included, giving a higher estimate of total release, which,however, is a probable overestimate since many of these radionuclides would have decayed inside the damaged core before any release to theatmosphere could occur.

520

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

Table 3
Estimated daily releases of iodine-131 during the accident

Day of release

Percentage(based on [A4, I6])

Daily releases (PBq)

26 April
27 April
28 April
29 April
30 April
1 May
2 May
3 May
4 May
5 May

40.0
11.6
8.5
5.8
3.9
3.5
5.8
6.1
7.4
7.4

704
204
150
102
69
62
102
107
130
130

Total

100

1 760

Table 4
Estimated amounts of radioiodines a and tellurium-132[K16]Radionuclide

Half-life

Amount in the reactor core at thetime of the accident (PBq)

Activity released b (PBq)

132

78.2 h2.3 h20.8 h52.6 min6.61 h

4 200
4 200
4 800
2 050
2 900

1 040
1 040
910
25
250

Te
I
133
I
134
I
135
I
132 c

a
b
c

The activity of iodine-131 in the reactor core at the time of the accident is taken to be 3,200 PBq. The release of iodine-131 is assumed to be 1,760 PBq.
With decay correction.
Iodine-132 is assumed to be in radioactive equilibrium with tellurium-132.

Table 5
Contaminated areas in European countries following the accident[I24]
Area in deposition density ranges (km2) a
Countrya37185 kBq m-2

185555 kBq m-2

5551 480 kBq m-2>1 480 kBq m-2

Russian Federation
Belarus
Ukraine49 80029 90037 2005 700
10 200
3 200

2 100
4 200
900

300
2 200
600

SwedenFinland
Austria
NorwayBulgaria
Switzerland
GreeceSlovenia
Italy
Republic of Moldova

12 00011 500
8 600
5 200
4 800
1 300
1 200
300
300
60


































The 137Cs levels include a small contribution (2-4 kBq m-2) from fallout from the atmospheric weapons tests carried out mainly in 1961 and 1962.

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

521

Table 6Composition of radionuclide deposition in the near and far zones around the reactor[B5, I6]

Radionuclide

89

Sr
Sr
Y
95
Zr
99
Mo
103
Ru
106
Ru
110m
Ag
125
Sb
131
I
132
Te
134
Cs
137
Cs
140
Ba
141
Ce
144
Ce
239
Np
90

Ratio to 137Cs deposition a

Ratio to137
Cs
releaseNear zone (<100 km)

[B4]

North

South

West

Northeast b

South cSoutheast d

1.0
0.1

0.7
0.13
2.7
3
3
2.7
1.0
0.01
0.02
17
17
0.5
1.0
3
4
2.3
7

12
1.5
8
10
25
12
5
0.01
0.1
30
13
0.5
1.0
20
10
6
140

4
0.5
5
5
8
4
1.5
0.005
0.05
15
18
0.5
1.0
7
5
3
25

0.14
0.014
0.06
0.06
(0.11)
1.9
0.7
0.008
0.05
10
(13)
0.5
1.0
0.7
0.11
0.07
(0.6)

0.3
0.03
0.17
0.3
(0.5)
2.7
1.0
(0.01)
0.1
(1)
(1)
0.5
1.0
(0.5)
0.5
0.3
(3)

1.0
0.1
0.6
1.0
(1.5)
6
2.3
(0.01)
0.1
(3)
(3)
0.5
1.0
(1.5)
1.8
1.2
(10)

91

a
b
c
d

Far zone

2.0
2.0
0.4

20
5
0.5
1.0
2.0
2.3
1.6
20

Decay-corrected to 26 April 1986; values from indirect data in parentheses.
Areas of higher 137Cs deposition in Belarus and Russian Federation.
District south of Kiev.
Northern Caucasus.

Table 7
Areal extent of 137Cs contamination from the accident in the European part of the former USSR
[G16, I3]
Area in deposition density ranges (km2)Country / Region

37185 kBq m2

185555 kBq m2

5551 480 kBq m2>1 480 kBq m2

Belarus
Gomel
Mogilev
Brest
GrodnoMinsk
Vitebsk

16 900
5 500
3 800
1 700
2 000
35

6 700
2 900
500
12
48

2 800
1 400

1 625
525

Total

29 900

10 200

4 200

2 200

6 750
3 500
10 3208 840
20 350

2 630
1 420
1 270
130

2 130

310

49 760

5 450

2 130

310

57 65037 200

3 200

900

600

41 900Russian Federation
Bryansk
Kaluga
Tula
Orel
Other
Total
UkraineOther republics
Total area

60
116 920

Total

46 50060
18 850

7 230

3 110

146 110

522

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

Table 8Estimated 137Cs deposit from the accident
Cs deposition density (kBq m2)

137

137

Range

Mean a

Area
[I3]
(km2)

7.4191937
371851855555551 480
>1 480

12
26
83
320
910
2 200

654 200
211 850
116 920
18 850
7 230
3 110

Total
a
b

Cs deposit (PBq)

Total

From fallout b

From Chernobyl
accident

7.8
5.6
9.7
6.0
6.6
6.8

1.32.6
0.40.8
0.20.4
0.050.1
0.020.04
0.0080.02

5.26.5
4.85.2
9.39.5
5.9
6.6
6.8

42.5

2.04.0

38.540.5

Assumed to be geometric mean of range.
The estimated residual range in 1986 of 137Cs deposition density from atmospheric nuclear weapons fallout is 24 kBq m2.

Table 9Measured transfer coefficients for 137Cs in natural meadows of the Polissya region in Ukraine, 19881989[S40]
Type of soilBlack soil loam
Loamy sandSoddic-podzolic loam
Soddic-podzolic sandPeaty-gleyaType of meadow

Transfer coefficient a

Floodplain humid
Dry valley normal
Floodplain humid
Dry valley normal
Dry valley normal
Dry valley, water-saturated
Floodplain humid
Peaty drained
Peaty flooded
Peaty callows

0.6
23
811
14
59
1322
2539
3045
5882
135190

Bq kg-1 of dry grass per kBq m2 deposited on the ground.

Table 10
Staff on site and emergency workers in initial hours of the accident[K23]

Professional group
Staff of the power plant (Units 1, 2, 3 and 4)
Construction workers at Units 5 and 6
Firemen
GuardsStaff of the local medical facilityabcAccident witnesses
176268
14 a, 10 b
23



Arrived on the site of the accident at 1.27 a.m.
Arrived on the site of the accident at 1.35 a.m.
Excluding the accident victims, the numbers of whom are given in Table 11.

Emergency workers(at 8 a.m. on 26 April 1986)
374 c



69
113
10

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

523

Table 11
Emergency workers with acute radiation sickness following the accident[I5]
Degree ofacute radiation
sickness
Mild
Moderate
SevereVery severe

(I)
(II)
(III)
(IV)

Total
a
b

Number of patients treated aRangeof dose(Gy)

Kiev

Numberofdeaths b

Numberofsurvivors

Moscow

0.8–2.1
2.2–4.1
4.2–6.4
6.5–16

23
44
21
20

18
6
1
1

0 (0%)
1 (2%)
7 (32%)
20 (95%)

41
49
15
1

0.8–16

108

26

28

106

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

Table 12Error range of estimated external doses evaluated by cytogenetic analysis to patients admitted to Hospital 6
in Moscow[P14]
Dose range (Gy)

Number of persons sampled

Number of counted cells per sample

Statistical error range (%)

10.113.7
6.19.5
4.05.8
2.13.8
1.01.9
0.50.9
0.10.4

7
12
16
33
19
17
25

191001910165630303003030065900503501118
1116
8.6362256
33100100; +100
100; +300

524

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

Table 13
Estimated internal and external doses to victims of the accidentInternal absorbed dose until time of death a (Gy) [K17, K18]
Personal code
25
18
22
5
9
21
8
2
19
23
1
15
16
3
17
4
7
10
11
14
20
24
13
a
b

Thyroid

Lungs

0.021
0.024
0.054
0.062
0.071
0.077
0.13
0.13
0.21
0.31
0.34
0.32
0.47
0.54
0.60
0.64
0.78
0.89
0.74
0.95
1.9
2.2
4.1

0.00026
0.00280.000470.00057
0.000770.000680.00150.00220.00350.00230.00870.00270.00410.00680.12
0.034
0.00470.0094
0.029
0.02
0.019
0.021
0.04

External dose b (Gy)
[G25]
8.2
6.4
4.3
6.2
5.6
6.4
3.8
2.9
4.5
7.5
11.1
6.4
4.2
7.2
5.5
6.5
10.2
8.6
9.1
7.2
5.6
3.5
4.2

The relative errors in the organ doses are estimated to be less than 30%.
Evaluated by chromosome analysis of peripheral blood lymphocytes.

Table 14
Estimates of internal doses received by surviving emergency workers a[K17, K18]
Absorbed dose (Gy)
TissueBone surface
Lungs
Wall of lower large intestine
Thyroid gland
Wall of upper large intestineLiver
Red bone marrowab

Average b

Maximum

0.28
0.25
0.22
0.096
0.090
0.056
0.036

3.6
2.4
2.9
1.8
1.2
0.73
0.46

Doses estimated from measurements with whole-body counters; the relative error does not exceed 45%.
The doses were averaged over 375 individuals.

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

525

Table 15
Distribution of thyroid doses in workers treated at Hospital 6 in Moscow during April and May 1986
[G12]

a

Thyroid dose range a(Gy)

Number of workers

01.2
1.23.7
3.76.1
6.18.6
8.611
1113
1316
1618
1821
2123
>23

173
18
4
4
2
2
0
2
0
1
2

Doses assessed by repeated in vivo thyroid counting, except for the two workers with estimated doses greater than 23 Gy; for those two workers, thedoses were assessed by repeated gamma spectrometry of bioassay samples (blood and urine). The relative error in the estimated individual thyroid
doses does not exceed 30%.

Table 16
Estimated effective doses from external irradiation received by recovery operation workers in the
30-km zone during 19861987[I25]
Number of workers

Average dose (mSv)

Collective dose (man Sv)

Group
1986

1987

1986

1987

1986

1987

Staff of nuclear power plant
Construction workers
Transport, security workers
Military servicemen
Workers from other power plants

2 358
21 50031 02161 7624 498
5 376
32 51863 751
3 458

87
82
6.5
110

15
25
27
63
9.3

210
1 760
200
6 800

70
130
870
4 000
30

Annual total or average

116 641

109 601

77

47

8 970

5 100

Total or average

226 24262

14 070

Table 17
Distribution of the external doses received by emergency and recovery operation workers
[K44]

Group

Emergency workers and accident witnesses
Staff of nuclear power plant 1986
Staff of nuclear power plant 1987
Construction workers 1986
Construction workers 1987
Military servicemen 1986
Military servicemen 1987
Workers from other power plants 1987a

Numberofpersons
a

820
2 358
4 498
21 5005 376
61 76263 751
3 458

Percentage in the dose interval (mSv)
010

1050

50100100200200250250500

>500





4
14
1
18
4
23
15

7
2

87

45
42
24
23
22
15
21

2
24
1
11
24
16
49
1



13
66
23
47
13
15
78

Number of persons included in the registry of the Institute of Biophysics in Moscow.



2





11
1
19
6

13
1
19
6













526

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

Table 18
Distribution of doses to recovery operation workers a as recorded in national registries[C2, M13]
Number ofrecoveryoperation
workers

Percentage
for whomdose
is known

MeanMedian75th
percentile

95th
percentile

Belarus19861987
19861989

31 00063 000

28
14

39
43

20
24

67
67

111
119

Russian Federation
1986
1987
1988
1989
19861989

69 00053 00020 500
6 000
148 000

51
71
83
73
63

169
92
34
32
107

194
92
26
30
92

220
100
45
48
180

250
208
94
52
240

Ukraine
1986
1987
1988
1989
19861989

98 00043 00018 000
11 000170 000

41
72
79
86
56

185
112
47
35
126

190
105
33
28
112

237
142
50
42
192

326
236
134
107
293

Total
1986
1987
1988
1989
19861989

187 000
107 000
45 50042 500381 000

45
65
80
80
52

170
130
30
15
113

Area
and periodaEffective dose (mSv)

Including those who worked outside the 30-km zone, but excluding those for whom the year of service is not recorded.

Table 19
Stable iodine prophylaxis among a sample of workers involved in early phases of the accident[K44]Time of iodine prophylaxis a (h)aNumber of workers

Percentage of sample

Before arrival at the plant
Upon arrival at the plant
01
13
310
1030
30100100300

19
22
22
16
27
22
23
3

11
12.5
12.5
9
15
12.5
13
2

Did not accept prophylaxis

22

12.5

Total

176

100

Counted from the time of arrival of the worker at the plant.

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

527

Table 20
Population groups evacuated in 1986 from contaminated areas
Country

Area

Belarus [M4, S24]

51 villages within the 30-km zone
28 villages outside the 30-km zone
29 villages outside the 30-km zone

Date

Number of evacuees

27 May
310 June
August/September

11 3586 017
7 350
24 725

Total of 108 villages
Russian Federation [S20]

4 villages of Krasnaya Gora district, Bryansk region

Ukraine [U14]

Pripyat town
Railway station Yanov
Burakovka village
15 villages within the 10-km zone
Chernobyl town
43 villages within the 30-km zone
8 villages outside the 30-km zone
4 villages outside the 30-km zone
Bober village

Former USSR

August186

27 April
27 April
30 April
3 May
5 May
37 May
1431 May
10 June16 August
September

49 360
254
226
9 864
13 591
14 542
2 424
434
711

Total of 75 settlements

91 406

Total of 187 settlements

116 317

Table 21
Estimates of thyroid doses from intake of 131I received by the Ukrainian evacuees of towns and villages within the
30-km zone
[G8, R12]
Age attime ofaccident(years)aChernobyl town a

Pripyat town [G8]Totalcollective
dose

Evacuated villages a

Numberofpersons

Arithmetic
mean dose(Gy)

Collective
dose(man Gy)

Numberofpersons

Arithmetic
mean dose(Gy)

Collective
dose(man Gy)

Numberofpersons

Arithmetic
mean dose(Gy)

Collective
dose(man Gy)(man Gy)

<1
13
47
811
1215
1618
>18

340
2 030
2 710
2 710
2 710
2 120
36 740

2.18
1.28
0.54
0.23
0.12
0.066
0.066

741
2 698
1 463
623
325
140
2 425

219
653
894
841
846
650
9 488

1.5
1
0.48
0.15
0.11
0.09
0.16

329
653
429
126
93
59
1 518

369
1 115
1 428
1 360
1 448
941
21 794

3.9
3.6
1.7
0.62
0.46
0.39
0.40

1 439
4 014
2 428
843
666
367
8 718

2 509
7 265
4 320
1 592
1 084
566
12 661Total

49 3608 315

13 591

3 206

28 45518 47529 996

Assumes same age distribution of population as Pripyat.

528

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

Table 22
Estimates of thyroid doses from intake of 131I received by the evacuees of Belarusian villages[G15]
Age at timeof accident a(years)Number ofmeasured
persons

Arithmetic mean
thyroid dose
(Gy)Medianthyroid dose
(Gy)

Estimated
number ofresidents b

Collective
thyroid dose(man Gy)

<1
1-3
4-7
8-11
12-15
16-17
>17

145
290
432
460
595
221
7 332

4.3
3.7
2.1
1.4
1.1
1.0
0.68

2.3
1.7
1.2
0.86
0.61
0.59
0.38

586
966
1 199
1 105
1 392
704
18 773

2 519
3 573
2 517
1 548
1 531
704
12 76624 72525 158

Total
a
b

9 475

Derived from information on year of birth; e.g. age <1 includes children born in 1986 and 1985.
Based on the age distribution available for 17,513 evacuees.

Table 23
Summary of estimated collective effective and thyroid doses to populations of areas evacuated in 1986

Number of persons
evacuated

CountryaCollective dose (man Sv)
Thyroida

External effective doseInternal effective dose

Belarus
Russian Federation
Ukraine24 725186
91 40625 000<1 00030 000

770
< 10
1 500

150
< 10
1 300

Total

116 31755 000

2 300

1 500

Units: man Gy.

Table 24
Distribution of the estimated first-year doses from external irradiation to inhabitants of Belarus evacuatedfrom the exclusion zone
[S24]

Dose interval
(mSv)
010
1020
2030
3040
4050
5060
6070
7080
8090
90100100150150200200250250300
300350350400>400

Number of persons in the dose interval
In the absence of evacuation (calculated)

In the evacuated population (actual)

1 956
4 710
3 726
2 552
1 795
1 226
961
726
565
453
1 513
1 015
814
646
494
371
1 204

7 357
7 652
3 480
1 764
1 094
761
556
416
314
239
605
195
109
67
42
26
28

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

529

Table 25
Inhabitants in 1986 and 1987 of the areas of strict control[I3, I4]
Country
Belarus

RegionPopulation

Gomel
Mogilev

Total population

85 70023 300109 000

Russian Federation

Bryansk

111 800

111 800

UkraineKiev
Zhitomir

20 80031 20052 000Total

272 800

Table 26
Distribution of the inhabitants in 1995 of areas contaminated by the Chernobyl accident[K23, R11, V3]137

aPopulation a

Cs deposition
density(kBq m-2)

Belarus

Russian Federation

UkraineTotal

37–185
185–555
555–1 480

1 543 514
239 505
97 593

1 654 175
233 626
95 474

1 188 800
106 700300

4 386 389
579 831
193 367

Total

1 880 612

1 983 275

1 295 600

5 159 487

For social and economic reasons, some of the populations living in areas contaminated below 37 kBq m-2 are also included.

Table 27
Values of occupancy/shielding factors used in evaluation of external exposure 01 year and >1 year after
the accident[B14]
Occupancy/shielding factor
Population
group

Rural areas01 year after accident

Urban areas>1 year after accident

01 year after accident>1 year after accident

0.23
0.29

0.29
0.25

0.15
0.23

0.13
0.20

0.22
0.18 a0.20
0.18

Wooden houses
Indoor workers
Outdoor workers
Schoolchildren

0.26
0.36
0.34

0.32
0.41
0.39

Brick houses
Indoor workers
Outdoor workers
Schoolchildren

0.22
0.31
0.29

0.24
0.34
0.31

Both types of houses
Representative value
UNSCEAR assessment [U4]a0.36
0.36 aEstimated for time period from one month to one year after the accident.

0.31
0.36

530

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

Table 28
Values of occupancy factor in the summer for rural populations of Belarus, Russian Federation, andUkraine[E7]
Occupancy factor
Location
Indoors

Outdoors in same village

Outdoors elsewhere

Belarus

RussiaUkraineBelarus

RussiaUkraineBelarus

RussiaUkraine

0.77
0.40
0.44
0.44

0.65
0.50
0.56
0.57
0.64

0.56
0.46
0.54
0.75
0.81

0.19
0.25
0.42
0.45

0.32
0.27
0.40
0.39
0.36

0.40
0.29
0.41
0.21
0.19

0.04
0.35
0.14
0.11

0.03
0.23
0.04
0.04
0

0.04
0.25
0.05
0.04
0

Indoor workers
Outdoor workers
Retired people
Schoolchildren
Preschool children

Table 29
Ratio of external effective dose of specific population groups to that of the representative group[B14]
Dose ratio to representative group
Population living in
Wooden dwellings
One- or two-storey brick houses
Multi-storey buildings

Indoor workers

Outdoor workers

Herders, foresters

Schoolchildren

0.8
0.7
0.6

1.2
1.0
0.8

1.7
1.5
1.3

0.8
0.9
0.7

Table 30
Estimated values of the overall coefficient used to calculate external effective dose on the basis of theabsorbed dose in air
Dose coefficient (mSv mGy1)
Country

1986 a19871995

Rural
Small town
Large town

0.28
0.19



0.28
0.19
0.14

Rural
Urban

0.19
0.12

0.12
0.12

Russian Federation [R9]

Rural
Small town
Large town

0.24
0.15
0.13

0.19
0.12
0.10

Ukraine [M16]

Rural
Small town
Large town

0.23
0.16
0.10

0.23
0.16
0.10

Former USSR [M11]

Belarus [K38]aType of settlement

Covers the time span from 26 April 1986 to 25 April 1987.

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

531

Table 31
Estimates of external effective doses per unit deposition density of 137Cs for the residents of contaminatedareas
Normalized effective dose (µSv per kBq m-2)
CountryabType of settlement
1986 a19871995

19861995

19962056

19862056

48
33

951086371

Former USSR b[A12, G3, M11]

Rural
Urban

1328
715

34
23

4762
3038

Belarus
[K38]

Rural
Urban

19
12

36
36

55
48

Russian Federation
[M17]

Rural
Urban

15
11

22
14

37
25

28
17

65
42

Ukraine [M16]

Rural
Urban

24
17

36
25

60
42

28
19

88
61

Covers the time span from 26 April 1986 to 25 April 1987.
The estimates were obtained mainly in the empirical manner by relating the results derived from monitoring the residents of settlements in Belarus,
Russian Federation, and Ukraine by means of TLD devices to the 137Cs deposition density in those settlements ( 372,200 kBq m-2 ).

Table 32
Reference values of absorbed dose rate in air per unit deposition density of 137Cs
Normalized absorbed dose rate in air a (nGy h-1 per kBq m-2)
Country
Belarus [K38] b
Russian Federation [B26, M17]
Ukraine [L36][M16]
Former USSR [A12, G3] b
a
b

1987

1988

1989

1990

1991

1992

1993

1994

1995

4.5
3.4
2.1
4.5
3.0

3.1
2.4
1.8
3.0
2.4

2.3
1.9
1.8
2.3
1.9

1.9
1.5
1.7
1.9
1.6

1.6
1.3
1.7
1.6
1.3

1.4
1.1
1.6
1.4
1.1

1.3
1.0
1.6
1.3
1.0

1.2
0.93
1.5
1.2
0.89

1.0
0.85
1.5
1.1
0.79

Estimated for May of the corresponding year.
In publications [A12, G3, K38], the normalized absorbed dose rate in air is expressed in µR h-1 per Ci km-2. The conversion from exposure to absorbed
dose in air was made using the relationship 8.7 nGy per µR.

Table 33
Selected values of external effective dose normalized to the deposition density of 137Cs for the residents ofcontaminated areas
Normalized effective dose (µSv per kBq m-2)
CountryType of settlement
1986

19871995

19861995

19962056

19862056

Belarus

Rural
Urban

19
12

22
14

41
26

28
17

69
43

Russian Federation

Rural
Urban

15
11

22
14

37
25

28
17

65
42

Ukraine

Rural
Urban

24
17

36
25

60
42

28
19

88
61

532

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

Table 34
Estimated collective effective doses to the populations of contaminated areas 19861995, (excluding thyroid
dose)
137

RegionCs deposition
density(kBq m2)

Collective effective dose (man Sv)
Population
External

Internal

Total

Belarus [S46]Brest

37185185555
Total

151 31216 183167 495

404
159
563

311
118
429

715
277
992

Gomel

37185185555
 555
Total

1 246 613
140 732
77 571
1 464 916

2 792
1 556
2 315
6 663

1 676
1 237
822
3 735

4 468
2 793
3 137
10 398Grodno37185185555
Total

28 060282
28 342

71
2.6
74

57
2.2
59

128
4.8
133

Minsk

37185185555
Total

23 809880
24 689

68
7
75

61
6
67

129
13
142

Mogilev

37185185555
 555
Total

93 65881 42820 022
195 108

347
796
1 118
2 261

302
584
328
1 214

649
1 380
1 446
3 475

Vitebsk

37185

62

0.12

0.11

0.23

Total

 37

1 880 612

9 636

5 504

15 140Russian Federation [B37, M17]
Belgorod3718573 350

114

48

162

Bryansk

37185185555
 555
Total

205 625
150 00295 462451 089

472
1 440
2 611
4 523

1 414
1 023
799
3 236

1 886
2 463
3 410
7 759

Kaluga37185185555
Total

91 801
12 654104 455

201
108
309

74
45
119

275
153
428

Kursk
Leningrad
LipetskMordovia

37185371853718537185

133 7208 434
50 73210 909

278
18
58
20

118
43
47
20

396
61
105
40

Orel

37185185555
Total

151 008
14 435
165 443

328
64
392

183
34
217

511
98
609

Penza
PyazanTambov

3718537185371859 910
199 687
16 832

16
275
23

16
313
23

32
588
46

Tula

37185185555
 555
Total

667 168
56 53512723 715

1 916
453
0.25
2 369

649
115
0.03
764

2 565
568
0.28
3 133

Ulyanovsk
Voronezh37185371852 805
32 194

4
55

4
23

8
78

Total

 37

1 983 275

8 454

4 991

13 445

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

533

Table 34 (continued)
Collective effective dose (man Sv)

137

RegionCs deposition
density(kBq m2)

Number of population
External
Rural

Urban

Rural

Internal

Total

Urban

Rural

Urban

Rural

Urban

UkraineVinnyts’ka
Volyns’ka

371853718566 00015 40017 100

261
49.7

34.5

73.6
214.3

36.0

335
264

70.5

Zhytomyrs’ka

37185185555555

207 200
21 300300

18 30066 300

1 012
332
10.8

81.2
769

1 785
264
13.7

38.7
140

2 797
596
24.6

120
909

Ivano-Frankivs’ka

37185

8 500

Kyivs’ka37185185555

243 500
11 500142 400

941
176

483

570
56.4

288

1 510
233

771

Rivnens’ka

37185185555

221 700
1 400

49 600

903
18.1

121

3 710
30.8

188

4 613
48.9

309

Sums’kaTernopils’ka

3718537185

4 500
7 400

22.7
29.6

21.2
11.7

44.0
41.2

Khmel’nyts’ka

37185185555

2 000
100

10.0
0.6

3.0
0.2

13.0
0.8

Cherkas’ka

37185185555

61 7002 900

Chernivets’ka

37185185555

18 500
3 000

Chernihivs’ka

37185185555

25 400
300

9 900

101
4.7

24.9

105
3.3

20.8

206
7.9

45.7

922 600

373 200

4 336

1 768

7 000

858

11 340

2 626

Total

69 600

252
43.2

60.5

15.4

45.1

255

70.7
10.7

147

401

119
45.6

31.3
10.2

87.2
35.5

323
53.9

534

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

Table 35
Distribution of estimated total effective doses received by the populations of contaminated areas,
19861995 (excluding thyroid dose)
Dose interval(mSv)

Number of persons
in dose interval

Percentage of persons
in dose interval

Cumulative percentageof persons in dose interval

Belarus [S46]
<1
12
23
34
45
510
1020
2030
3040
4050
50100100200>200

133 053444 709362 510221 068
135 203276 605
163 015
63 99732 271
17 52125 065
5 105
790

7.07
23.65
19.28
11.75
7.19
14.71
8.67
3.40
1.71
0.93
1.33
0.27
0.04

Total

1 880 912

100

7.07
30.72
50
61.75
68.94
83.65
92.32
95.72
97.43
98.36
99.69
99.96
100

Russian Federation [B37, M17, S46]
<1
12
23
34
45
510
1020
2030
3040
4050
50100100200>200

155 301445 326
383 334
258 933
165 537
317 251
156 925
50 01021 81811 04814 580
2 979
333

7.83
22.45
19.32
13.06
8.35
16
7.91
2.52
1.10
0.55
0.74
0.15
0.02

Total

1 983 375

100

7.83
30.28
49.60
62.66
71.01
87.01
94.92
97.44
98.54
99.09
99.83
99.98
100

Ukraine [L44]

Dose interval(mSv)

Number of persons
in dose interval
Rural

12
23
34
45
510
1020
2030
3040
4050
50100100200

26 10057 10097 200294 700
290 500
99 10031 40018 200
7 700
400

Total

922 400

Urban

38 800111 700
145 700
77 000373 200

Percentage of persons
in dose interval
Rural

2.0
4.4
7.5
22.7
22.4
7.7
2.4
1.4
0.59
0.03
71.2

Cumulative percentageof persons in dose interval

Urban

3.0
8.6
11.2
6.0

28.8

0
2.0
9.4
25.6
59.5
87.9
95.6
98.0
99.4
99.97
100
100

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

535

Table 36
Summary of estimated collective effective doses to the populations of contaminated areas, 19861995(excluding thyroid dose)137

Collective effective dose (man Sv)

Cs deposition
density(kBq m2)

Population
External

Internal

Total

Belarus [S46]37185185555555

1 543 514
239 505
97 593

3 682
2 521
3 433

2 409
1 945
1 150

6 091
4 466
4 583

Total

1 880 612

9 636

5 504

15 140Russian Federation [B37, M17, S46]
37185185555555

1 654 175
233 626
95 474

3 778
2 065
2 611

3 009
1 183
799

6 787
3 248
3 410

Total

1 983 275

8 454

4 991

13 445

Ukraine [L44]Collective effective dose (man Sv)
137

Population

Cs deposition
density(kBq m2)

External

Internal

Total

Rural

Urban

Rural

Urban

Rural

Urban

Rural

Urban

37185185555>555

881 800
40 400300

306 800
66 300

3 715
610
11.0

999
769

6 610
375
13.8

717
140

10 330
986
24.8

1 717
909

Total

922 500

373 100

4 336

1 768

7 000

857

11 340

2 626

Table 37
Distribution of external dose rates before and after decontamination measures in Kirov, Belarus, in 1989
[S25]
Measured mean dose rate (µGy d-1)
Before decontamination

After decontamination

External
dose ratio
after/before

Cattle breeders
Field workers
Office workers
Housewives and retired persons
Schoolchildren
Tractor drivers

12.3
17.5
12.1
12.9
15.0
12.8

11.9
13.2
11.8
12.8
9.7
12.7

0.97
0.75
0.98
0.99
0.65
0.99

Average

13.7

12.1

0.89

Population group

536

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

Table 38
Distribution of estimated individual doses in the thyroid of children in contaminated districts of Belarus[G13]
Absorbed dosein thyroid(Gy)

Number of children in age range a
13 years<1 year47 years

811 years

1215 years

1618 years

All children

Gomel district<0.05
0.050.1
0.10.3
0.31
12
>2

134 (6.7)
58 (2.9)224 (11)587 (30)318 (16)
3 667 (34)198 (6.1)
107 (3.3)
449 (14)963 (29)590 (18)965 (29)452 (7.4)
362 (5.9)
1 089 (18)2 023 (33)
1 075 (18)
1 095 (18)518 (8.4)
399 (6.5)
1 385 (22)2 365 (38)868 (14)643 (10)540 (8.8)
485 (7.9)
1 613 (26)2 364 (38)695 (11)464 (7.5)

596 (16)354 (9.4)
1 086 (29)
1 119 (30)383 (10)230 (6.1)

2 438 (8.9)
1 765 (6.4)
5 846 (21)9 421 (34)
3 929 (14)4 064 (15)Total

1 988 (100)

3 272 (100)

6 096 (100)

6 178 (100)

6 161 (100)3 768 (100)

27 463 (100)

Mogilev district

a

<0.05
0.050.1
0.10.3
0.31
12
>2

33 (13)31 (12)65 (26)74 (29)36 (14)14 (5.5)

43 (9.1)
93 (20)170 (36)127 (27)
28 (5.9)
14 (3.0)210 (19)215 (19)351 (31)275 (25)55 (4.9)
16 (1.4)273 (28)
157 (16)324 (33)
190 (20)24 (2.5)
1 (0.1)326 (29)207 (19)372 (33)
195 (17)15 (1.3)
1 (0.09)227 (37)103 (17)169 (28)
99 (16)14 (2.3)
1 (0.2)

1 112 (24)806 (18)
1 451 (32)960 (21)172 (3.8)
47 (1.0)

Total

253 (100)475 (100)

1 122 (100)969 (100)

1 116 (100)613 (100)

4 548 (100)Percent of total in parentheses.

Table 39
Thyroid doses to 07-year-old children and to the total population in contaminated areas of Belarus[I28]
Number of persons

Average absorbed dose (Gy)

Collective dose (man Gy)

RegionChildren

Total

Children

Total

Children

Total

Gomel
Rural
Urban

23 9008 600

238 600
85 600

1.1
0.4

0.4
0.2

25 0003 800

98 000
15 000

Mogilev
Rural
Urban

9 300
4 900

93 70048 700

0.4
0.2

0.2
0.08

4 100
1 100

17 000
4 000

Total

46 700466 600

0.7

0.3

34 000134 000

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

537

Table 40
Estimates of collective thyroid doses to populations of Belarus, the Russian Federation, and Ukraine
Country/region
Belarus [D1, G7]
Brest
Gomel
GrodnoMinsk
Mogilev
Vitebsk
Entire country
Russian Federation [Z1]Bryansk
Orel
Tula
Bryansk, Kaluga, Kursk, Leningrad,Orel, Ryaza, and Tula a[S21]
Entire country[B14]
UkraineKiev
Eight districts b plus Pripyat
Entire countryabc

Population

Collective thyroid dose (man Gy)

1 400 000
1 700 000
1 200 000
3 200 000
1 300 000
1 400 000
10 000 000

101 000
301 000
49 00068 00032 0002 000
553 000

1 500 000
900 000
1 900 000

55 000
15 00050 0003 700 000
150 000 000

234 000
200 000–300 000

3
0.5
55

110 000
190 000
740 000 c

[L15]
[L12]
[L6]

Only the territories with 137Cs deposition densities greater than 37 kBq m-2 were considered.
Situated around the Chernobyl nuclear power plant.
Derived from an estimated collective thyroid dose of 400,000 man Gy for children aged 0–18 years in the entire Ukraine.

Table 41
Ratios of the average thyroid doses in children and teenagers to those in adults for the populations ofcontaminated areas in the Russian Federation[Z6, Z7]
Age group (years)

Urban population

Rural population

<1
12
37
812
1317
>17

15±5
10±3
5±2
2.0±0.5
1.5±0.5
1

7±2
6±2
3±1
1.0±0.5
2.0±0.5
1

Table 42
Input data for internal thyroid dose reconstruction in the Russian Federation[B39]
Number of measurements
Region131

I in thyroid131

I in milk

137

Cs in soil

137

Cs in foodproducts

137

Cs in humanbody

Personal
interviews

Bryansk
Tula
Orel
Kaluga12 700644
3 600
28 000

2 100
2 157
872
256

2 081
2 308
1 577
578

217 000
2 000
17 00018 000300 000
17 000
10 00028 00017 000
1 800

Total

45 000

5 385

6 544

250 000

360 000

25 000



6 000

538

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

Table 43
Collective and average thyroid doses in population of the Russian Federation[R3, Z1]
Population (millions)Collective thyroid dose (man Gy)

Average thyroid dose (mGy)

Region

a

Urban

Rural

Total

Urban

Rural

Total

Urban

Rural

Total

Bryansk
KalugaOrel
Tula
Other regions a

1.0
0.8
0.6
1.5

0.5
0.3
0.3
0.4



1.5
1.1
0.9
1.9
16

33 000
4 000
8 000
14 00027 000
3 000
5 000
6 000

60 000
7 000
13 000
20 000110 000±30 000

33
5
13
9

54
10
17
15



40
6
15
11
7

Total





21





110 000±30 000





10









Other eleven contaminated regions: Belgorod, Voronezh, Kursk, Leningrad (without city of St. Petersburg), Lipetsk, Mordovia, Penza, Ryazanj,
Smolensk, Tambov, Uljanov.

Table 44
Age distribution of the collective thyroid doses to inhabitants of the Bryansk region in the Russian Federation[Z6]
Population

Collective thyroid dose (man Gy)

Age (years)
Urban

Rural

Urban

Rural

02
35
69
1015
1619
20

47 00047 00059 00085 00059 000694 000

21 000
19 000
23 00036 00017 000368 000

9 000
5 000
3 000
2 000
1 000
13 000

4 000
3 000
2 000
2 000
1 000
15 000Total

992 000

483 000

33 00027 000

Table 45
Calculated mean thyroid doses for infants and adults in three districts of the Chernigov region, Ukraine[L25]

District

Type ofsettlement

Parameter values

Mean thyroid doses (Gy)

K (Gy)ab (a-1)

Infants (1 a)Adults (20 a)

RepkineTowns
Villages

0.031
0.082

7.4
5.0

0.049
0.094

0.21
0.35

0.065
0.11

Chernigov

City
Villages

0.030
0.17

10
3.0

0.064
0.079

0.26
0.47

0.057
0.22

Kozelets

Towns
Villages

0.012
0.047

18
7.4

0.15
0.062

0.14
0.30

0.014
0.085

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

539

Table 46
Estimated age-dependent thyroid dose distribution in the population of the Ukrainian regions of Cherkassy,
Chernigov, Kiev, Vinnitsa, and Zhitomir a
[L10]

a

Age at thetime of theaccident (years)

Percentage of age groups within dose intervals
00.049 Gy

0.050.099 Gy

0.10.29 Gy

0.30.99 Gy

11.99 Gy

>2 Gy

<1
13
47
811
1215
1618
>18

2.8
3.2
10.8
19.3
35.3
45.7
54.6

10.4
10.3
27.2
39.6
35.2
26.8
21.0

55.5
58.6
47.7
34.0
24.4
23.5
21.6

23.3
24.9
13.4
6.1
4.3
4.1
2.8

7.4
2.1
0.9
0.9
0.7
0.0
0.0

0.5
0.9
0.0
0.0
0.0
0.0
0.0

Excludes the 30-km zone and city of Kiev.

Table 47
Distribution of absorbed dose in the thyroid of the population of Ukraine from the Chernobyl accident
[L12]

a

Absorbed dose (Gy)

Number of persons

Collective thyroid dose (man Gy)<0.01
0.010.05
0.050.1
0.10.3
0.30.5
0.51.0
1.01.5

7 325 000
3 400 000
1 312 000
228 000
131 000
26 00028 00036 625102 000
98 40045 60052 40019 50035 000Total

12 450 000

390 000 a

Estimate is less by a factor of 2 for more realistic intake model.

Table 48
Normalized effective doses from radiocaesium via internal exposure to rural inhabitants of Ukraine indifferent soil zones[K23]

Soil zone

I
II
III
IV

Normalized doses (µSv per kBq m-2)

Transfer coefficientfrom soil to milk in 1991
(Bq l1 per kBq m-2)

1986

19871995

19861995

<1
15
510
>10

9
42
95
176

26
144
320
591

35
186
415
767

540

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

Table 49
Values of the transfer coefficient and of the normalized effective dose from internal exposure for sodicpodzol sand and chernozem soils in the Russian Federation[B25, R9]Transfer coefficient (Bq kg1 per kBq m-2)
Milk

Type of soil

Sodic-podzol sandChernozem

Normalized effective dose(µSv per kBq m-2)

Potatoes

1987

1993

1987

1993

1986

19871994

19952056

5
0.07

0.2
0.01

0.16
0.03

0.04
0.004

90
28

78
2

16
1

Table 50
Rounded estimates of internal effective doses per unit of 137Cs deposition density for inhabitants ofcontaminated areas of the Russian Federation
Normalized effective dose (µSv per kBq m-2)
RegionBryansk a
Tula
Orel
a

1986

19871995

19962056

19862056

36 (10)151548 (13)
6
8

9 (9)
1.8
2.4

93 (32)
23
25

The values within parentheses correspond to areas with a 137Cs deposition density greater than 555 kBq m-2.

Table 51
Average effective doses from internal exposure per unit deposition density of 137Cs for population
subgroups in Belarus[D3, K22]
Normalized effective dose (µSv per kBq m-2)
Location

Age group
1986

19871990

19911995

19861995

Rural areas06 years
717 years>18 years

317
519
524

632
845
1262

37
26
310

1256
1570
2096

Towns

06 years
717 years>18 years

2
2
3

5
4
7

2
2
4

9
8
14

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

541

Table 52
Populations in Europe examined in epidemiological studies[S12]
Country

Age group

Average absorbed dose (mGy) a

All ages
20-60 years
All ages
All ages
All ages

15 b
5
3b
4b
1.5 b

AdultsChildren 0-14 years
Children 0-14 years
Children 0-14 years
Children 0-14 years
All agesChildren 0-14 years cChildren 0-14 years
All ages

2
2
2
4
1
0.7
3
4
0.7

Study region
Thyroid studies

Croatia
GreeceHungary
PolandTurkeyWhole country
Whole country
Whole country
Krakow, Nowy Sacz
Five most affected areas on Black Sea coastand Edirne province
Leukaemia studiesabc

Bulgaria

Whole country

FinlandGermany
GreeceHungary
Romania
SwedenTurkeyWhole country
Bavaria
Whole country
Six counties
Whole country
Whole country
Five most affected areas on Black Sea coastand Edirne province

To thyroid in thyroid studies and to bone marrow in leukaemia studies; assumes bone marrow dose is numerically equal to effective dose and dose inchildren is the same as in adults.
Assumes population-weighted thyroid dose is three times that to adults.
Age at death.

Table 53
Summary of estimated collective effective doses to populations of areas contaminated by the Chernobyl
accident (1986-1995)
Collective effective dose (man Sv)
Country

Population

Average effective dose (mSv)

External
exposureInternal
exposure

Total

External
exposureInternal
exposure

Total

Belarus
Russian Federation
Ukraine

1 880 000
1 980 000
1 300 000

9 600
8 500
6 100

5 500
5 000
7 900

15 10013 500
14 000

5.1
4.3
4.7

2.9
2.5
6.1

8.0
6.8
10.8

Total

5 160 000

24 20018 40042 600

4.7

3.5

8.2

542

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

Table 54
Distribution of the estimated total individual effective doses received by the populations of contaminatedareas, 19861995 (excluding thyroid dose)
Number of persons in dose interval in

Dose interval(mSv)

Belarus

Russian Federation

Ukraine

Total

<1
12
23
34
45
510
1020
2030
3040
4050
50100100200>200

133 053444 709362 510221 068
135 203276 605
163 015
63 99732 271
17 52125 0655 105790

155 301445 326
383 334
258 933
165 537
317 251
156 925
50 01021 81811 04814 580
2 979
333

0
0
26 10095 900208 900
440 400
367 500
99 10031 40018 2007 700
400
0288 804
890 035
771 944575 901509 640
1 034 056
687 440
213 10785 48946 76947 345
8 484
1 123

Total

1 880 912

1 983 375

1 295 600

5 159 887

Table 55
Deaths of survivors of acute radiation sickness during 19861998[W5]
Year of death

Grade of acute radiation sickness

1987
1990
1992
1993

II
II
III
I
III
I
II
I
III
II
II

1995

1998

Disease recorded and/or cause of death
Lung gangreneCoronary heart disease
Coronary heart disease
Coronary heart disease
Myelodysplastic syndrome
Lung tuberculosis
Liver cirrhosis
Fat embolism
Myelodysplastic syndrome
Liver cirrhosis
Acute myeloid leukaemia

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

543

Table 56
Thyroid cancer cases in children under 15 years old at diagnosis

Number of cases

Region
1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

9
3
28
6
7
8
1
62

28

19
2
38
4
3
7
4
77

20

16

16

41
5
9
2
5
82

37
4
1
6
3
67

17
2
33
5
4
8
4
73

4







5
1

2

Belarus [P9]Brest
Vitebsk
Gomel
GrodnoMinsk city
Minsk
Mogilev
Total







1
2

2
1

1




2
1
1
1

2
2





8
1
15
1
4












1



3

4

6

5

2
31

1

7
3
38
4
5
4
1
62



34
5
9
5
6
87







14
5
7
3
3
48

Russian Federation [I23]
Bryansk region
Novozybkovsky
Klintsovsky
Klimovsky
Sturodubsky
Unechsky
Komarichsky
Dyatkovsky
Surazhsky
Vygonechsky
Suzemsky
Total



















1




1


































1
1







1

1
1
1

1


























1

3

3
10
9
5
4
3
15
49






1








1

6

1
7

3
10
5
2
4
4
16
44

5
3
5

7
9
9

1




3















2

5

6
18
4
3
2
4
19
56

5
8
4
2
2
6
9
36

2





Ukraine [T2, T16]
Zhitomir
Kiev
Kiev city
Rovno
Cherkassy
Chernigov
Other regions
Total

















1







5
8

7
7

6
8

1
7
11

3
15
26

2
1

1





2
1

2
4
2

1
4
3
1
2
2
9
22





2
11
18
44

2
4
16
47

7
7
6
2
1
3
18
44

544

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

Table 57
Thyroid cancer incidence rates in children under 15 years old at diagnosis

Number of cases per 100 000 children

Region
1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

3.7
1.4
11.2
3.2
2.7
3.2
0.5
3.9

11.6

8.8

7.3

17.9
2.8
3.9
0.9
2.9
5.6

16.9
2.4
0.5
2.8
1.8
4.8

8.2
1.2
16.0
3.1
2.0
3.9
2.6
5.6

8.0

13.9
2.7
3.5
2.0
3.2
5.5

8.1
1.0
15.9
2.2
1.2
3.0
2.2
5.1

26.6

Belarus [P9]Brest
Vitebsk
Gomel
GrodnoMinsk city
Minsk
Mogilev
Total







0.4




0.4
1.1

0.7
0.6

0.7
0.5
0.4
0.4

0.7
1.1





0.2



0.4



0.3





0.4



3.3
0.5
5.6
0.6
1.5

0.4



0.3

1.0
1.9



2.9
1.4
15.0
2.2
1.9
1.7
0.5
3.9









7.1
3.3
3.7
1.6
2.0
3.9

Russian Federation [I23]
Bryansk region
Novozybkovsky
Klintsovsky
Klimovsky
Sturodubsky
Unechsky
Komarichsky
Dyatkovsky
Surazhsky
Vygonechsky
SuzemskyKrasnogorsky
Navlinsky
Karachevsky
Bryansk city
Total























9.1









0.3

















































4.3

4.3
12.1
9.9

4.3



















0.3

0.3

23.2

























0.9

0.3

0.9
2.5
1.7
1.7
1.3
1.2
0.2
0.5

1.0
2.5
1.0
0.7
1.3
1.6
0.2
0.4













21.7
12.1

8.6

12.9

10.5
10.0
2.8


















2.5

0.6

2.2

1.6
0.8
1.0

2.3
2.4
1.8

0.7
4.4
0.2
0.4

0.7
1.7
0.2
0.5

2.0
4.9
0.8
1.1
0.7
1.7
0.2
0.6

1.7
2.2
0.9
0.7
0.7
2.6
0.1
0.4

9.1



20.2












23.2
18.8






18.2






14.3
10.5



Ukraine [T2, T16]
Zhitomir
Kiev
Kiev City
Rovno
Cherkassy
Chernigov
Other regions
Total













0.2
0.3




0.1
0.2

0.1
0.1

0.1
0.1

0.4
0.1
0.1

0.5
0.2







0.5
0.2

0.6
1.0
0.4




1.1
0.2
0.2

0.3
1.0
0.6
0.3
0.7
0.8
0.1
0.2





2.5
2.0
1.4
0.7
0.4
1.4
0.2
0.5

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

545

Table 58
Thyroid cancer cases diagnosed among children 017 years old at the time of the Chernobyl accident
Number of cases in year of diagnosis
Region

Sex
1990

1991

1992

1993

1994

1995

1996

1997

1998

Total

9
27
25
37
4
4
4
15
3
5
3
7
4

10
23
16
41
3
7
5
10
5
6
1
4
1
4

8
18
24
42
3
5
5
11
9
5
1
8
2
5

14
20
19
34
1
8
9
22
2
8
3
12
2
6

77
146
156
283
26
47
39
100
33
51
17
44
13
35

147

136

146

160

1 067

6
11
1

6
15
1
2

8

1
9
5
8

3
7
2
1
1
14
1
7

9

27
61
7
7
6
46
12
39

47

41

36

35

205

Belarus [P9]
Brest
Gomel
GrodnoMinsk city
Minsk
Mogilev
Vitebsk

M
F
M
F
M
F
M
F
M
F
M
F
M
F

Total

3
4
9
7
1

3

6
5
13
35
3
4
5
5
2
3
1

5
5
19
15
6
6
5
5
4
8
2



8
3
14
2
11
2
5

5
5



2

2
2

2

11
18
16
41
5
5
2
14
5
5
1
8
1
5

35

86

90

130

137


1
4
1







11
26
15
31





Russian Federation [I23]
Bryansk
Kaluga
Orel
Tula

M
F
M
F
M
F
M
F

Total




1



1
2


1
1

2
4
1




4
5





2



2

3
2



6
1
3

5

10

12

19



3
2

5
17
2
2
3
10






2



Ukraine [T16]
Zhitomir
Kiev
Kiev city
Rovno
Cherkassy
Chernigov

Total

M
F
M
F
M
F
M
F
M
F
M
F

1
1
2
7
3
4

2
1
3
6
1
5
1
1









1
2
1

3
1
3

4
5
11
5
12
3
2
2
3
2
4

22

27

55

1
2
6
7
3
13
2
1
1
6
2
5

4
7
2
9
4
10
3
1
1
5
7
6

4
9
10
14
3
25
3
1
1
1
1
7

3
5
13
26
3
14
4
2
1
4
1
6

4
5
5
17
5
16
4
2

49

59

79

82

5
3
7

5
9
2
10
7
15
1
5
2
2
3
12

24
43
48
107
34
114
22
16
8
30
22
51

73

73

519



546

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

Table 59
Thyroid cancers and risk for children 018 years old at the time of the Chernobyl accident for the years
19911995 in three cities and 2,729 settlements in Belarus and the Russian Federation
[J5]

a
b

Thyroid dose

Person years at risk

Observednumber of cases

Expected
number of cases a

Excess absolute risk b(104 PY Gy)1

00.1 (0.05)
0.10.5 (0.21)
0.51.0 (0.68)
1.02.0 (1.4)>2.0 (3.0)

1 756 000
1 398 000
386 000
158 000
56 000

38
65
52
50
38

16
13
3.6
1.5
0.5

2.6 (0.56.7)
1.9 (0.84.1)
2.0 (0.94.2)
2.3 (1.14.9)
2.4 (1.15.1)

Calculated by multiplying the age-specific incidence observed in Belarus in 19831987 by three.
95% confidence intervals in parentheses.

Table 60
Odds ratio for thyroid cancer cases in Belarusian children compared with age-, location-, and exposurematched controls[A6]
Number of cases or controls at estimated thyroid dose from 131I
Pathway to diagnosisa<0.30 Gy0.300.99 Gy>0.99 Gy

Total

Odds ratio a

Routine endocrinological screening
Cases
Control

32
43

16
16

15
4

63
63

2.1
(1.04.3)

Incidental findings
Cases
Control

13
18

4
1

2
0

19
19

8.3
(1.158)

Enlarged or nodular thyroid
Cases
Control

19
23

6
2

0
0

25
25

3.6
(0.718)

Cases
Controls
Total

64
84
152

26
19
41

17
4
21

107
107
214

3.1
(1.75.8)

Comparing lowest and two highest groups. 95% confidence interval in parentheses.

Table 61
Circumstances of diagnosis of thyroid problems[A5]

Probable circumstanceof diagnosis
Formal screening programme
Incidental to other examination
Consulted since unwell
Consulted even though well
Total

Ultrasound diagnosis
Unknown

No

Yes

Total

2 (29%)
2 (29%)
1 (14%)
2 (29%)

7 (20%)
18 (51%)8 (23%)
2 (6%)

3 (38%)
3 (38%)
1 (13%)
1 (13%)

12
23
10
5

7

35

8

50

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

547

Table 62
Pathological types of thyroid cancers in Ukrainian children less than 15 years old at diagnosis[T18]
Number of cancers in relation to year of diagnosis b

Pathologicalclassification aab19861990

19911995

19961997

Total



T1
T2
T3
T4
N1
N2
M1

9 (18)
6 (12)
14 (29)9 (18)
9 (18)2 (4)4 (2)49 (20)27 (11)69 (28)45 (18)45 (18)
6 (2)

1 (1)
18 (16)6 (5)38 (35)22 (20)22 (20)
3 (3)

5 (1)
76 (19)39 (10)121 (30)
76 (19)76 (19)11 (3)Total

49 (100)

245 (100)110 (100)

404 (100)

Staging system of the World Health Organization [H17].
Percentage of total in parentheses.

Table 63
Age and sex distribution of Ukrainian children and adolescents who underwent surgery for thyroid
carcinoma during 19861997[T18]
NumberAge at time of surgery(years)
04
59
1014
1518
014

Females

Males

5
46
176
159
227

5
42
84
61
131

Ratio
female : male
1.0 : 1
1.1 : 1
2.1 : 1
2.7 : 1
1.7 : 1

NumberAge at time of exposure(years)
04
59
1014
1518
014

Females

Males

146
149
69
15
364

88
58
30
7
176

Ratio
female : male
1.7 : 1
2.6 : 1
2.3 : 1
2.1 : 1
2.1 : 1

Table 64
Frequency of RET rearrangements in thyroid papillary carcinomas in relation to age and radiation history[S35]

Patient groupChildren (Belarus)
Adults (Belarus)
Adults (Germany) aa

Number of cases

Mean ageat exposure(years)Mean ageat surgery(years)

2
22

12
31
48

51
16
16

Negligible radiation exposure from Chernobyl accident.



Number of caseswith RET/PTC1
mutationswith RET/PTC3
mutations

12 (23.5%)
11 (69%)3 (19%)

13 (25.5%)




548

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

Table 65
Incidence of leukaemia and all cancer during 19931994 among recovery operation workers and residentsof contaminated areas[C2]
Leukaemia cases a

All cancer cases aStandardized incidence ratio (SIR)

Country
Observed

Expected

Observed

Expected

Leukaemia

All cancer

136
405
329

200
108
339

75
111
121

9 387
16 80022 245

93
104
105

103
103
99

Recovery operation workers b
Belarus
Russian Federation
Ukraine

102
449
399

4.5
8.4
8

9
9
28

Residents of contaminated areas c
Belarus
Russian Federation
Ukraine
a
b
c

9 682
17 26022 063

302
328
562

281
340
592

ICD9 codes: 204-208 (leukaemia) and 140-208 (all cancer); expected cases are for age- and sex-matched members of the general population.
Males who worked in the 30-km zone during 1986 and 1987.
Areas with 137Cs deposition density > 185 kBq m-2.

Table 66
Thyroid abnormalities diagnosed by ultrasonography in children 010 years old at the time of the accident
screened by the Chernobyl Sasakawa project during 19911996[Y1]

RegionNumber ofchildrenscreened

Mogilev
Boys
Girls

23 531

Gomel
Boys
Girls

19 273

BryanskBoys
Girls

19 918

Kiev
Boys
Girls

27 498

Zhitomir
Boys
Girls

28 958Total

119 178

Number of children with diagnosis
GoitreAbnormalechogenity

CysticlesionNodularlesionCancerAnomaly

2 231
2 391

91
188

19
25

5
19

1
1

16
19

1 355
2 053

332
604

59
63

130
212

12
25

67
73

3 666
4 480

172
251

56
51

46
53

3
5

7
8

6 634
8 194

246
588

18
40

13
33

2
4

4
7

4 473
6 453

38
87

34
137

23
43

4
5

17
19

41 930

2 597

502

577

62

237

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

549

Table 67
Incidence of thyroid abnormalities diagnosed by ultrasonography in children screened by the Sasakawa
project during 19911996[Y1]
Incidence rate per 1000 children examined
RegionGoitreAbnormalechogenity

CysticlesionNodularlesionCancerAnomaly

Mogilev
Gomel
Bryansk
Kiev
Zhitomir

219
177
409
539
377

11.9
48.6
21.2
30.3
4.3

1.9
6.3
5.4
2.1
5.9

1.0
17.7
5.0
1.7
2.3

0.08
1.9
0.4
0.2
0.3

1.5
7.3
0.8
0.4
1.2

Total

352

21.8

4.2

4.8

0.5

2.0

Table 68
Comparison of reproductive effects in population groups in the Russian Federation during 19801993[B19, L27, L28, L29]
Ratio of effect before and after accident a
Bryansk region

Parameter / effectBirth rate
Spontaneous abortions
Congenital anomalies
Stillbirths
Perinatal mortality
Premature births
Overall diseases in newborns
Overall unfavourable pregnancy
outcomea

Tula region

Ryazan region<37
kBq m-2

37185kBq m-2

185555
kBq m-2<37
kBq m-2

37185kBq m-2

185555
kBq m-2<37
kBq m-2

37185kBq m-2

0.81
1.27
0.66
0.66
1.18
1.07
1.02

0.83
1.34
1.41
1.39
1.13
0.95
1.03

0.75
1.34
1.67
1.29
0.91
1.39
1.42

0.87
0.90
1.32
1.50
0.77
0.88
1.06

0.73
1.03
1.28
0.93
1.57
0.86
1.32

0.69
1.18
0.91
1.41
1.21
0.71
1.29

1.0
1.22
1.43
0.90
1.13
0.83
1.00

0.90
0.91
0.91
0.97
1.00
1.23
1.38

1.07

1.16

1.35

0.95

0.97

0.92

1.07

1.00

Number of women examined before and after accident: Byransk region: 3,5004,100 in each area; Tula region, 2,400 (<37 kBq m-2), 2,100 (37-185
kBq m-2) and 810860 (185555 kBq m-2); Ryazan region, 1,6001 ,00 (<37 kBq m-2) and 1,2001,400 (37185 kBq m-2).

ANNEX J: EXPOSURES AND EFFECTS OF THE CHERNOBYL ACCIDENT

551

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