Epidemiological Studies in Russia about the Consequences of the Chernobyl
APS Accident
Igor A. RYABZEVInstitute of Problem of Ecology and Evolution, Russian Academy of Sciences
Leninsky st. D-33, Moscow 117071, Russia
1. Introduction

1.1 General assessment of radionuclide release into
the environment by the Chernobyl accident

The final purpose of all efforts to study and mitigate
the consequences of the accident at the 4th reactor of
the Chernobyl atomic power station (ChAPS) is
protection of health of the people who were more orless exposed to radiation action. This situation has notanalogs in terms of scale and character. Certain
experience was accumulated earlier through the studiesof biological and medical effects of atomic bombing in
Hiroshima and Nagasaki, other radiation catastrophes,
diagnostic and therapeutic application of radiation, andthe control of health state of professionals in atomic
industries. However, these experiences can be usedjust partially in the assessment and the forecast of
possible negative after-effects of the Chernobyl
accident for the present and future generations.
The long-term irradiation of a large number of
population at low doses is to be considered theprincipal peculiarity of the Chernobyl accident. The
medical activities are complicated significantly by theabsence of verifiable individual dosimetric
information, natural or forced migration of the
population, insufficient development of radiation
epidemiology, complicated social-economic situationin the country, and other factors which are inevitable atlarge-scaled catastrophes. Besides, many fundamental
questions related to biological effects of action of low
doses of ionizing radiation are still being studied.

According to the official estimations, the total
release of radioactivity constituted 50MCi (without
noble gases) - near 4% of the total in the reactor. Thisis 1,000 times as high as it was at the accident atThree-Mile-Island APS (USA) in 1979.
Radionuclide releases were assessed by
calculations using models of admixtures transfer in theatmosphere. The input information for calculation was
taken from the results of study of radionuclide
composition of aerosol samples picked up over the 4threactor of ChAPS since 26 of April 1986, as well asfrom the results of gamma-aerosurvey around the APS
area,
analysisofprecipitation
samples,
meteo-observations in the areas of polluted air mass
moving. The data on radioactive pollution of theenvironment over the USSR territory were used
therewith. The precision of the results of calculation
was appraised in the report [1] as ± 50%. The
radioactive noble gases were not taken into accounthere. The composition of released radioniclides as awhole corresponded to the isotope structure of fuel inreactor. The short-living radionuclides were dominant
in them, first of all - 131I. From the long-living
radionuclides - 137Cs. The release of 90Sr was
significantly lesser. Much lesser was 239Pu which is themost dangerous in long-term aspect and enters into theTable 1. Estimation of composition of major radionuclides released from ChAPS [1]Release activity
Nuclide26.04.1986*
06.05.1986**
MCi
1015 BqMCi
1015 Bq
Iodine-131
167
4.5
270
7.3
Cesium-134
5.6
0.15
18.5
0.5
Cesium-137
11.1
0.3
37
1.0
Ruthenium-103
22.2
0.6
118
3.2
Ruthenium-106
7.4
0.2
59.2
1.6
Cerium-141
14.8
0.4
104
2.8
Cerium-144
16.7
0.45
88.8
2.4
Strontium-89
9.2
0.25
81.4
2.2
Strontium-90
0.6
0.015
8.1
0.22
Plutonium-238
3.7 x 10-3
0.1 x 10-3
0.03
0.8 x 10-3
Plutonium-239
3.7 x 10-3
0.1 x 10-3
0.026
0.7 x 10-3
-3-3
Plutonium-240
7.4 x 100.2 x 100.037
1 x 10-3
Plutonium-241
0.74
0.02
5.2
0.14
* Release on the 1st day of the accident. Activity is decay-corrected to 06.05.1986.
** Total release until 06.05.1986.
139

composition of hot particles with extraordinary highspecific activity (Table 1).
The assessment of released quantity of long-living
137
Cs is worth attention because it is determining now
the radioecological situation on the major part of theChernobyl trace territories. The report [1] - on the basisof data of radiocontamination on the USSR territory gives an estimation of the total release of 137Cs: 1 MCi(37 x 1015 Bq) or 13 ± 7% of its activity in the reactor
core. The UNSCEAR experts - on the basis of analysisof data on precipitation in the Northern hemisphere estimated 137Cs release from ChAPS as 1.9 MCi (70 x1015 Bq), i.e. 27% [2]. According to [3], up to 23% of
its activity in the reactor fell into the atmosphere. By
the estimation on the basis of analysis of quantity andradionuclide composition in the fuel remaining in“Shelter” object, 2.3 ± 0.7 MCi (85 x 1015 Bq) werereleased, or 33 ± 10% of primary activity of 137Cs in
the reactor [4].

creation of the Register, as well as a large number ofscientific and practical institutions [6].
At present, the National Radiation-Epidemiological
Register is acting in Russian Federation. The Russian
Ministry on Emergencies is the general customer of theRegister. The head organization is Medical
Radiological Scientific Center of RAMS (Russian
Academy of Medical Sciences). It fulfils collection ofprimary medical and dosimetric data through 24
regional centres [7].

2.1 Russian State Medical-Dosimetric RegisterThree principal data bases consist of the National
Radiation-Epidemiological Register:
Registration List of those who underwent
irradiation. It is created according to special
dosimetric categories;
Chernobyl Register. In 1992, it was officiallynamed Russian State Medical-Dosimetric Register(RSMDR);
Register of inter-institutional expert councils.
In the present paper we will dwell on theradiation-epidemiological analysis of data of theChernobyl Register of Russia.
During all years of functioning, the data bank of
RSMDR was filled constantly with medical-dosimetric
information. By 1 of December 1994, it comprehended
370,120 persons from all the Russian Federation. All
persons registered in RSMDR are divided into 5groups of primary account (GPA):
1 GPA - liquidators - 159,027 (43.0%);
2 GPA - evacuees - 8,091 (2.2%);
3 GPA - those who live or have lived on controlled
territories - 185,912 (50.4%);
4 GPA - children born by liquidators of 1986-1987- 16,226 (4.4%);
5 GPA - migrants from the zones of alienation(after 1986), resettlement and with right toresettlement - 864 (0.2%) [8].
Special attention is paid to observation of healthstate of the liquidators which have obtained the highest
radiation loading as a result of accident. RSMDR
contains data of external irradiation of 125,771
liquidators on the basis of certificates given in the zone
of works on liquidation of the accident consequences.
Regretfully, it is impossible now to establish types ofdose values- absorbed or exposure one - put down in
RSMDR. The maximum difference between exposureand absorbed doses for whole-body external
irradiation can reach 30%, i.e. absorbed dose canconstitute 0.7 exposure dose (this estimation was madeon the results of measurements by the Institute ofBiophysics of Minzdravmedprom of Russia in the
30-km zone of ChAPS). Considering that the error ofeach individual value of dose can be much higher than
30%, the mentioned possible difference due to dosetypes is not taken into consideration in further analysis.
The unit of absorbed dose (cGy) is used in the analysis.

1.2. Release of radioactive iodine as one of
peculiarities of the Chernobyl accident
The most important characteristic of this accident is
the release into the environment of significant quantityof radioactive iodine. However, there is uncertainty inthe assessments of the total release of this radionuclide
from the 4th reactor. The report [1] gives the value of
7.3 MCi or 20% of activity in core (calculation for6.05.1986). UNSCEAR experts [2] estimated the total
131
I release as 8.9 MCi being quite near to the data ofreport [1]. According to the proceedings of 1stInternational Task Force on severe accidents and theirconsequences, estimations of the total 131I release
ranged from 20 % to 60% of its content in the core of
the reactor [3]. By the WHO data, the release of thisradionuclide into the environment is equal to 44 MCi,
and, if we take into account the short-living 132I-135I
isotopes, this value is to be increased considerably [5].
Note that, due to the relatively short period of
half-decay, we have only the data on theseradionuclides which were obtained before July 1986.
Therefore, only the results of their analysis can be new
ones. Iodine and its isotopes affect thyroid, and theeffect on thyroid is one of principal consequences of
the Chernobyl accident.

2. Epidemiological studies in Russia after the
ChAPS accident
In 1986, immediately after the Chernobyl accident,
the USSR Ministry of Health undertook a large-scaled
programme to create All-Union Distributed Register of
persons affected by radiation. By 1992 (the moment of
USSR decay), the data base of the Register contained
medical and dosimetric information about 659,292
persons including 284,919 participants of liquidationof the accident consequences (liquidators). All the
republics of the former Soviet Union took part in the140equipped with necessary accident means of IDS as wellas the firemen which came to put out the fire on the 4threactor. Meanwhile, exposure dose rate (EDR) on the
ChAPS roof and in premises reached after the
explosion several hundreds of R/h.
The equipment and methodical provision of
dosimetric services of involved Ministries andinstitutions were different each other. The precision ofindividual dose values is thus different too. Besides,
nonuniformity of radioactive precipitation is to betaken into account, which complicated the radiation
situation significantly. In consequence, participants ofliquidation of the accident were situated in
non-uniform radiation field of β- and γ-radiation
during the works within and out of the 30-km zone
(especially in 1986-1987). Therefore, exposure dosecan be assessed with admissible precision only byusing IDS data, although they were practically absent
in first weeks after the accident.
By the level of reliability, the dosimetric data for
liquidators can be divided into three principal groups
in dependence of the used methods for dosage
assessment:
Exposure or absorbed dose obtained by using
individual dosimeter: maximum error is near 50%(supposing its correct use);
Group dose attributed to groups of people working
within the zone based on individual dosimeter of
one of them: maximum uncertainty by the group
can reach 300%;
Itinerary dose evaluated based on the average
exposure dose rate in the zone of works and theperiod of stay there of group of persons: maximum
uncertainty by the group can reach 500%.
At present, the quality of dosimetric data for asignificant number of liquidators can thus be low due
to absence in the Register of additional information
about the character, locality and time period of theworks by each liquidator. All this justifies the extreme
necessity to verify the dosimetric data for liquidatorsand other persons who underwent irradiation as a resultof the ChAPS accident [10]. In spite of the difficulty ofdosage assessment, some average statistical

2.2 Dosimetric data of Russian State
Medical-Dosimetric Register for liquidators
In order to understand clearly the character ofdosimetric information put down in RSMDR, it isuseful to describe briefly when and how the dosimetricsurveillance of radiation loading was organized in thezones of liquidation of the accident consequences.
After the ChAPS accident, the USSR Governmental
Commission charged on 28 of May 1986 with theindividual dosimetric surveillance (IDS) three
institutions: USSR Ministry of Defence (MD),Ministry of Middle Machine-Industry and Ministry ofEnergy. The dosimetric surveillance was also carriedout independently by USSR Ministry of Interior,
USSR KGB (until September 1987), Academy of
Sciences of Ukrainian SSR.
The staff of more than 600 organizations of 49
ministries and institutions of USSR was under IDS
since 1986. The biggest share of them fell on units of
USSR Ministry of Energy.
Since October 1986, the dosimetric data were put
down in data base of computer of SM 1634 type. The
automated information-reference system of IDS wasformed on the basis of Administration of Dosimetric
Surveillance (ADS) of science-production association“Pripyat” in April 1988. This system contained
information about 103,800 participants of liquidationof the accident consequences. Since 1987, IDS of
ChAPS personnel was carried out by the Service ofControl of Radiation Safety of ChAPS. IDS of
personnel engaged in works within alienation zone wascarried out by ADS of science-production association“Pripyat”.
Before the ChAPS accident, condenser dosimeterof KID type and individual film dosimeter (IFD) wereused for controlling irradiation of ChAPS staff. These
dosimeters were created at the Institute of Biophysics
of USSR Ministry of Health. The measured dose rangeof them was from 50 mR to 2 R. 400 persons were
working in ChAPS at night shift on 26 April of 1986.
They were equipped only with IFD [9]. Thereby, at the
moment of the accident, ChAPS personnel was not

Table 2. Average characteristics of dose commitments for liquidators [10]N -number of liquidators, men;D - average absorbed dose, cGy;
T - average period of stay in polluted zone, days;
R - average EEDR, mR/h;
σ - standard deviation of distribution D, T, R

Year ofentering
1986
1987
1988
1989
1990

N
men
46575
48077
18208
5475
1004

D,
cGy
15.9
9.0
3.3
3.2
3.7

σ
cGy
8.3
5.8
3.5
3.6
2.9
141

T,
days
70
79
106
102
86

σ
days
72
59
58
60
58

R,
mR/h
19.2
6.8
2.0
1.9
2.5

σ
mR/h
45.5
19.8
14.8
6.7
7.3

characteristics of dosage distribution contained in theRegister are used here, because average values are
considered to be more useful than individual values.
Table 2 contains average values and their standard
deviations of doses of liquidators, terms of their stay inthe zone of works, and “effective exposure dose rate”
in dependence of entering in the polluted zone.
The conclusion can be made by the data of Table 2
about the dynamics of average irradiation loading
during the principal works within the accident zone.
There was certain increase of average dose forliquidators who had come to the zone in 1990. This canbe explained by the next: the mass works in the zone
were concluded, therefore just professionals were sent
there in order to fulfil special tasks. This can be
confirmed also by the data on average period of stay (itis something less than that of 1989) and average EEDR
(it is by 50 % higher than that of 1988-1989). The
spread of D, T, R distributions is quite big because
standard deviations are close to mean values andsignificantly exceed it in the EEDR distribution. Thisfactor testifies also to the acceptable reliability of
dosimetric data of the Register on the whole. It is
impossible yet to make any conclusions about thereliability of every individual value [10]. Anotherestimations of irradiation dose for liquidators also
exist, e.g. in the data base of the register of All-Russia
Centre of Ecological Medicine (St. Petersburg).
According to these estimations, the average dose ofirradiation of liquidators constituted in 1986: 0.1207 ±0.0025 Sv, in 1987 - 0.0838 ± 0.0009 Sv, in 1989 0.0312 ± 0.0012 and in 1990 - 0.0494 ± 0.0022 Sv. As
a result of mathematical-statistical analysis, it wasestablished that the time of coming to the zone ofaccident works was the most significant factor in theirradiation dose formation. The coefficient ofcorrelation between irradiation dose and the time ofcoming constitutes 0.487 for all data. The dependence
of individual irradiation doses on the time of coming of
liquidators to the radiation zone turned out stepwise.
Irradiation doses vary substantially and significantly
by four time intervals: 0-15th day from the moment of
the accident, 16-350th day, 351-700th day and morethan 700 days. The average dose for liquidators whichcame in the first 15 days constituted 0.145 Sv, from16th to 350th day - 0.119 Sv, from 351st to 700th day 0.065 Sv, after 701 days - 0.03 Sv. The dependence
between dose and the time of coming within eachperiod is insignificant. From the point of view ofauthors [11], these time intervals must be the basis offorming risk groups of liquidators for scientificanalysis of biological consequences of the ChAPS
accident, and classification of medical and social
assistance.

As a result of the explosion of the 4th reactor of theChernobyl APS, the territory of Russia was intensively
polluted with radioactive substances released into theatmosphere. In the composition of mixture ofradionuclides precipitated over the Russian territory,
isotopes of iodine, cesium, strontium and transuranium
elements are the most radiologically significant. A spotof high radioactive pollution formed in 6 western
districts of the Bryansk region. The territory withdensity of soil pollution for 137Cs over 15 Ci/km2
stands out there. There are areas with radioactive
pollution density up to 5-15 Ci/km2 in the Bryansk,
Tula, Kaluga and Orel regions. Besides, separate areas
with pollution density from 1 to 5 Ci/km2 for 137Cs
were found in the Belgorod, Voronezh, Kursk,
Leningrad, Lipetsk, Penza, Ryazan, Smolensk,
Tambov, Ulianovsk regions and the Republic ofMordovia. The 90Sr content in soil of polluted areas of
Russia is 10-100 times as low as that of 137Cs. By thedata of State Committee of Russian Federation on
Hydrometeorology for 1991, the total area ofradioactive pollution (more than 1 Ci/km2 for 137Cs)
constituted in Russia 55,000 km2 being bigger thanthat in Ukraine or Belarus.
From the moment of radioactive pollution of area,
the population is subjected to external irradiation withgamma- and beta-radiation of mixture of radionuclides- products of nuclear fission and activation. The initial
dose rate in the air has decreased tens of times by July
1986 and is determined thereafter mainly by
gamma-radiation of 137Cs and 134Cs. 131I was theleading factor of internal irradiation of people in May
1986. It entered the organism with food, principallywith local milk and vegetables. Radioactive iodine
gathered in human thyroid and irradiated it selectively.
137
Cs and 134Cs are leading factors of internal
irradiation since the summer of 1986. They enter theorganisms of residents of polluted areas with milk andmeat, natural products (mushrooms, forest berries andfish) and - in lesser degree - with vegetables and fruits.
The content of cesium radionuclides in plant andanimal products made on "chernozem" soils (Tula,
Orel and other regions) is 10-100 times as low as thaton soddy-podzolic soils with the same pollution level(Bryansk, Kaluga regions). These indices decreased 2
times every 1-1.5 years, and, in general, from thesummer of 1986 to 1992 - tens of times.
Beside of cesium isotopes, 90Sr is transferred fromsoil to plants and then to animals. This radionuclide
also enters the organisms of habitants with milk (notwith meat) and plant products. Its quantity, however, ismuch smaller than the quantity of cesium isotopes.
Unlike the cesium and strontium isotopes,
transuranium radionuclides exist in soil in thecomposition of low-soluble fuel particles and do notparticipate almost in biological processes. Theseradionuclides can be inhaled with dust into humanorganisms in small quantities. The contribution of 90Srand radionuclides of transuranium elements into

2.3 Long-term irradiation of population of RussianFederation as a result of the Chernobyl APS
accident
142

irradiation doses of people is not big and constitutes intotal 1-5% [12].

measurements were carried out in Ulianovsk,
Khvastovichi and Zhizdrin districts using movable andstationary calibrated whole-body counters with
one-channel analysers, which gave calculation ofannual irradiation doses in the last years. Near 60,000
measurements were held by 1994. Children andadolescents were mainly studied. The results ofmeasurements show that the cesium radionuclides
content in organism on the whole has decreased
substantially in past years. The average doses ofinternal irradiation by different districts were nothigher than 0.8 mSv per year since 1987 and weredecreasing in the course of time. In 1990-1991, they
were not higher than 0.25 mSv even in the mostly
polluted Ulianovsk district. Nevertheless, individual
doses up to 3 mSv/year were registered for separate
persons (1990-1991). The highest irradiation levels
took place in 1986. Though the average annual doses
of internal irradiation did not overreach 20 mSv, theindividual doses for separate persons (near 2.5%) werehigher and reached 60 mSv [13].
By the estimations, the collective dose of external
and internal whole-body irradiation from the momentof the accident for the average duration of life can beequal to 5,000 man-Sv (for the districts of the Kaluga
region where radioactive precipitation took place).
This value constitutes near 10% of expected collective
dose for all Russian territories polluted by the accident.
Individual examinations with TL-dosimeters were
held also on the territory of western districts of the
Bryansk region with pollution density from 0.6 to 4.0
MBq/m2. 8,000 individual measurements were held in
1986-1993 in 44 settlements. This number of habitants

2.4 Doses of irradiation of thyroid of Russian
population
The results of calculations, based on the data of
direct measurements of 131I content in thyroid, show
strong age dependence of absorbed doses for thyroid.
The average thyroid doses estimated for different
age groups in dependence of the level of pollution ofareas in the Bryansk and Kaluga regions were within
the range from 10 mGy to 2.2 Gy. Individual thyroid
dose reached in separate cases 10 Gy and more. The
statistical distribution of individual doses ischaracterized by a long “tail” in the area of high dose
as well as by a big share of persons for which values ofthyroid dose were assessed as zero within the limits ofmeasurement errors. So far as the calculations in 1986of individual absorbed dose were pointwise, presently,
in order to determine the errors of calculations, theoverall assessment of factors able to influence doses
values is carried out. The results of assessment ofvalues of average and collective thyroid doses ofhabitants in various Russian settlements with pollution
density over 3.7 kBq/m2 are adduced in Table 3.

2.5 Doses of whole-body irradiation of Russian
population
The measurements of 137Cs and 134Cs radionuclides
content in human bodies were carried out during
annual examinations of the population in Kaluga
region of Russia since September 1986. The

Table 3. Doses of thyroid irradiation in different regions of Russian Federation [13]Soil pollution
Mean thyroid dose Collective thyroid dose
Population,
Regiondensity for 137Cs,
per population,
for all population,
thousands
kBq/m2mGy
103 man-Sv
Bryansk region:
3.7 - 37
670.0
12.4
94.34
37 - 185227.0
76.5
185 - 555
147.0
229.0
>= 55593.1
376.0
Tula region:
3.7 - 37
370.0
30.6
92.34
37 - 185770.0
77.4
185 - 555
170.0
126.0
Kaluga region:
3.7 - 37
120.0
28.4
10.12
37 - 18578.0
65.5
185 - 555
15.5
103.2
Orel region:
3.7 - 37
100.0
22.6
21.37
37 - 185330.0
54.5
185 - 555
18.0
95.1
Kursk region:
3.7 - 37
111.0
17.0
5.80
37 - 185
134.0
29.3
Ryazan region:
3.7 - 37
110.0
27.1
9.22
37 - 185
182.0
34.3
Leningrad region:
3.7 - 37
10.0
24.0
0.54
37 - 185
182.0
27.9
143

Table 4. Average accumulated doses for population of polluted districts of in Bryansk region [13]Average accumulated dose of external
Settlement with different levels
Districts
and internal whole-body irradiation
137
of pollution with Cs
for1986-1993 period, mSv
Novozybkov
t. Novozybkov
30
Zlynkav. Zlynka
50
villages with > 555 kBq/m2
90 - 140< 555 kBq/m2
20 - 90
Krasnaya Gorav. Krasnaya Gora
20
villages with > 555 kBq/m2
90 - 160< 555 kBq/m2
20 - 90
Gordeevka
v. Gordeevka
60
2
villages with > 555 kBq/m
90 - 130< 555 kBq/m2
20 - 90
Klintsyt. Klintsy
10
villages with > 555 kBq/m2
90 - 110< 555 kBq/m2
20 - 90
constituted 90% of all population in the strict controlzone.
The results of evaluation of accumulated doses ofexternal and internal irradiation in 1986-1993 period
are adduced in Table 4 for the territories of the Bryansk
region with various pollution levels. These evaluations
were made from one side - on the basis of results ofcalculations of internal irradiation using verified
measurements of 137Cs content in organism in various
years after the accident; from other side - on the basisof results of calculations using measurements ofγ-radiation dose rate in air in various years after theaccident and extrapolations of these results forsettlements with different levels of pollution with 137Cs[13].
The highest value of average irradiation dose for
adult population was registered in village Vyshkov of
the Zlynka district (236 mGy). This settlement issituated close to the zone of increased pollution (1480
kBq/m2) and is of interest in terms of dosimetricstudies. The averaged dose for children in given
settlement is substantially less (103 mGy).
Considerable differences between irradiation doses ofadults and children are observed also in other small
settlements where the activity of population isconnected mainly with agriculture, they do not differ
practically among children in different settlements..
For Klintsy town the values of averaged dose for
adults are considerably less than those for small
settlements (123 mGy) and differ few from the values
for children (105 mGy). Incidentally, low level ofpollution with radionuclides (near 100 kBq/m2 for137
Cs [14]) is registered in Klintsy town as a whole, andthe calculated averaged irradiation doses by thesettlement are much less than measured ones.

2.6 Mortality, morbidity and disability of liquidators
In the analysis of mortality of liquidators living in
Russian Federation, it is important to take into accountthat, in last years, negative demographic processes areobserved on the territory of the country on the whole(increase of death rate and decrease of birth rate). The
structure of principal causes of mortality of liquidators is
also important.
RSMDR contains reports on 78 territorial regions of
Russia: republics, lands, regions, Moscow, St. Petersburg,
and compiled reports (annual) for all Russian Federationand for 5 regions (Bryansk, Smolensk, Tula, Kaluga andOrel) entering the zone of radioactive pollution of Russia- so-called “Chernobyl zone”.
It is stated - on the basis of data of these reports - thatthe mortality of participants of the ChAPS accident
consequences liquidation from all causes (total mortality
or simple mortality) increased from 4.6 to 6.9 per 1,000
persons in 1990-1992 period, i.e. the mortality index
increased by 50%. This index increases by years for one
regions and decreases for other regions, but does not on
the average exceed the control level for Russia [13]. For
example, until 1991, the death rate among liquidators in
the Ryazan region was not higher than regional indices ofdeath rate for the same age. In 1992-1993, the death rate
among liquidators was higher than the regional indices1.3-1.5 times and constituted 12.4 and 15.3 per 1,000
persons per year [14].

144Table 5. Comparison of disease rate per 100,000 persons by the principal classes of diseases among Russian
population and among liquidators in 1993 [16]Population ofClasses of diseases
Liquidators
Ratio of indicesRussiaNeoplasms
788
747
0.9
Malignant neoplasms*
140
233
1.6
Endocrine system diseases
327
6036
18.4
Diseases of blood and blood-forming organs
94
339
4.3
Mental disorders
599
5743
9.6
Diseases of blood circulation organs
1472
6306
4.3
Diseases of digestion organs
2635
9739
5.7
All classes of diseases
50785
75606
1.5
* - The standardized index on age distribution of liquidators for 1993 is adduced for malignant neoplasms.
Table 6. Comparison of disease rate per 100,000 persons by principal classes of diseases among liquidatorsof different dose groups in 1993 [16]Classes of diseases
0-5 cGy
5-20 cGy
more than 20 cGy
Neoplasm
690
648
747
Malignant neoplasm
217
232
225
Endocrine system diseases
5270
6120*
6075*
Diseases of blood and blood-forming organs
213
354*
450*
Mental disorders
5178
5490
5472
Diseases of blood circulation organs
5287
6090*
6648**
Diseases of digestion organs
9106
9743
9515
All classes of diseases
69831
75346*
75785** - indices differ significantly (p < 0.001) from corresponding indices in group of 0-5 cGy;** - indices differ significantly (p < 0.01) from corresponding indices in group of 5-20 cGy.
Table 7. Dynamics of invalids (per 1,000 persons) among liquidators by dosage groups in 1990-1993. Data of
RSMDRYears of observation
0-5 cGy
5-20 cGy
more than 20 cGy
1990
6.0
10.3
17.3
1991
12.5
21.4
31.1
1992
28.6
50.1
57.6
1993
43.5
74.0
87.4
According to the results of study of 814 deaths in
1989-1995 of liquidators, the share of oncologicaldiseases (12%) among the causes of death is not higher
than the mean indices for Russian population.
Cardiovascular pathology occupies the first place among
somatic diseases (35%). The most frequent causes ofdeath (over 50%) are accidents among which suicides,
alcoholic intoxications and road accidents prevail. By thedata of study, 34% of liquidators were at the moment ofdeath in state of middle or strong stage of alcoholic
intoxication. Among those who committed suicide,alcohol was found in blood only in 28% of cases, another
72% did it consciously. These data indicate the necessityof deep examination of liquidators in the field of
psychoneurological sphere [15].
The forecast and interpretation of data on morbidityand disability indices of liquidators are much more
complicated. Comparison of morbidity indices by theprincipal classes of diseases among liquidators andRussian population as a whole is adduced in Table 5. This

table shows that the indices of morbidity amongliquidators in a number of cases are many times as high as
those among the population of Russia. Undoubtedly, thelevel, completeness and quality of medical examination ofliquidators differ significantly from all-Russia practice.
The most modern methods of diagnostics are applied in
examining liquidators, and mostly skilled and competentspecialists are engaged. By the data of MRSC RAMS, therevealing rate of primarily registered diseases by means ofspecialists of this institution is several times as high as thatby the means of local medical personnel. In such situation
it is quite difficult to pick up the adequate control groupfor comparing.
It is known that factors of social and psychologicalcharacter connected with the Chernobyl accident havegreat importance in the formation of pathological statesand morbidity among liquidators. All this combined withradiation influence can be determined as “Chernobyl
syndrome”. Attempts to analyse the weight of radiation
factor from this very complicated syndromes are of great145

importance. Therefore, the authors [16] evaluated theindices of morbidity and disability by dosage groups - 0-5
cGy, 5-20 cGy and more than 20 cGy - grounding on
dosimetric data of liquidators included in RSMDR. As
internal control group the contingents of liquidators
irradiated within 0-5 cGy interval were taken therewith.
As it is seen from Table 6, morbidity indices by anumber of classes of diseases in groups of 5-20 cGy andmore than 20 cGy turned out statistically higher thanthose in group of 0-5 cGy. It was established therewiththat the group of more than 20 cGy consisted by 99.1% ofliquidators of 1986-1987.
The liquidators of 1986-1987 constitute 91.2% of
dosage group of 5-20 cGy and the smaller half of group of
0-5 cGy (48.9%). Therefore, 2 factors were studied within
the framework of standard multifactor analysis: dosage(with 3 grades: 0-5 cGy, 5-20 cGy and more than 20 cGy)and date of entering the radiation zone (with 3 grades:
liquidators of 1986, of 1987 and of 1988-1990). By the
analysis of indices of rate of 3 classes of diseases(endocrine system, blood circulation organs and mental
disorders), it was established that the factor of date ofentering the radiation zone (1986, 1987, 1988-1990) is
undoubtedly the determining one as compared withdosage factor from the point of view of its influence on
morbidity. It means that first of all the health state ofliquidators of 1986 and 1987 is of special worry.
The indices of disability of liquidators in dependenceof obtained external irradiation doses are adduced inTable 7. The disability indices in second and third dosegroups are significantly higher than the corresponding
coefficients in first group (0-5 cGy). The fact is also worth
attention that the index of disability of liquidators on thewhole is 2.8-3.2 times as high as the index of all Russia.

radionuclides and, as a result, impetuous growth of
thyroid cancer cases among children and adolescents ofboth sexes and women of genital age.
In the process of screening of children and adolescentsfrom south-western districts of the Bryansk region in
1991-1995, the primary clinico-laboratoy information on
25,000 persons was obtained including the examinationof pediatrist, endocrinologist, ultrasonic investigation of
thyroid, analysis of TTH, FT4 content in serum as well asof antibodies to thyroglobulin and microsomal fraction,and the data on 137Cs content in organism.
It was stated that thyroid pathology in given groups of
persons occupies the leading place in general morbidity
structure. Out of all thyroid pathology, 75-80% fall on
euthyroid goiter, 0.2-3.7% - on nodal formations in
dependence of age group, 0.32-1.7% - on autoimmune
thyroidites, 0.1% - on hypothyrosis with clinicalmanifestation and 5.0-7.8% - on that with subclinicalcourse. As a result of screening, 14 cases of thyroid cancer
were first discovered and confirmed histologicallythereafter.
In total, 48 cases of thyroid cancer have beenverified presently in the Bryansk region among children
and adolescents who were children at the moment of the
ChAPS accident. 33 girls and 15 boys are among them
(Table 8).
Nearly 50% of children and adolescents withdiagnosed thyroid cancer have lived on areas with
pollution level as 15 and more Ci/km2 for 137Cs, i.e. in
the resettlement zones.
Medical-dosimetric investigation is carried out
concerning all cases of thyroid cancer. It has beenfound that the reconstructed individual dose on thyroid
due to radioactive iodine depends on the zone of living
and ranges from 1 to 270 cGy. Dose dependence wasdiscovered of thyroid cancer incidence on the densityof soil pollution with 137Cs. 11.9 cases per 100,000 ofchildren population were revealed on territories with
pollution density from 0.1 to 1.0 Ci/km2, 18.5 cases on the territories with 1.0-5.0 Ci/km2, 29.7 cases - on
the territories with 15 and more Ci/km2 [17].

2.7 Thyroid cancer among the population of the
Bryansk and Kaluga regions
Against the background of general aggravation ofhealth state, decrease of birth-rate and duration of life ofRussians in the last 10 years, Chernobyl brought a strong
additional factor of immediate and mediate effect ofionizing radiation on present and following generations.
The direct result of radiation influence on humanorganism - beside of acute and sub-acute radiation
sickness - is the injury of thyroid tissue by iodine

2.8 Malignant neoplasm on territories polluted as aresult of the ChAPS accident

Table 8. Number of cases of thyroid cancer in children and adolescents of Bryansk and Kaluga regions of
Russian Federation [13]RegionBryansk region
Kaluga region
Russia

1987
1
1

1988
-

1989
-

Year of diagnosing
1990 1991 1992 1993
4
4
8
12
1
4
4
8
13
146

1994
19
3
22

Total
48
4
52

Table 9. Standardized indices of general oncological morbidity per 100,000 persons in different
regions of Russian Federation [18]Increase in 1994
Region1994
compared with 1981, %Bryansk
336.2
38.6
Kaluga
294.3
29.6
Orel
313.3
40.1
Tula
339.3
21.4
Ryazan
357.1
Kursk
300.0
Russian Federation
278.0
19.1
on all radiocontaminated territories, and the pace ofincrease is much higher than in Russian Federation.
The highest levels of thyroid cancer incidence inRussian Federation were registered in 1994 in the
Bryansk, Orel and Ryazan regions; the indicesconstituted 7.8, 7.7, 7.7 per 100,000 of population
respectively [18].

Moscow Research Oncological P. A. Gertsen
Institute
analysedthedynamics
ofonco-epidemiological situation in the six polluted
regions by the Chernobyl accident: Bryansk, Kaluga,
Orel, Tula, Ryazan, Kursk, in 1981-1994 period.
Uninterrupted rise of malignant neoplasm incidence
was registered in all territories and the whole RussianFederation as well. Since 1987, the levels of malignant
neoplasm incidence were permanently higher in six
mentioned regions than in Russian Federation (Table
9).
The structure of malignant neoplasm incidence did
not change substantially in the post-accident period.
On all areas, except for the Bryansk region, neoplasmof lungs, trachea, bronchi occupied the first place inthe structure, and tumours of stomach - the second
place. In the Bryansk region, the most frequent
nosological form was cancer of stomach; and tumoursof respiration system organs were on the second place.
The malignant neoplasm of stomach, blood-forming
and lymphatic tissue, thyroid gland, and larynx have abigger specific weight in the morbidity structure of the
Bryansk region than in that of Russian Federation. The
share of malignant neoplasm of thyroid in morbidity
structure of the Orel region is more significant thanthat in Russian Federation.
The dynamics of disease incidence among the
population of studied territories with cancer of lungs,
trachea, bronchi is characterized by positive trend. The
highest levels of morbidity are characteristic of the
Bryansk, Tula and Ryazan regions. The stomach
cancer incidence which is higher than in RussianFederation was registered on radiocontaminatedterritories both in the pre- and the post-accident
periods although the uninterrupted trend of decrease ofthis index is observed. In 1994, the Bryansk region
occupied the second place in Russian Federation by thelevel of morbidity among men (index - 55.4; Russia 40.3) and the third place among women. The incidenceof malignant neoplasm of blood-forming andlymphatic tissue is higher in the Bryansk, Tula, Ryazan
regions than that in Russian Federation. The highest
indices in 1994 were registered in the Ryazan region:
18.0 for men and 13.5 for women. The rise ofincidence of thyroid malignant neoplasm is observed

Conclusion
More than 10 years passed since the Chernobyl
catastrophe. The biggest technogenic accident inmankind history attracted attention of the worldsociety. However, the problem of assessment of total
integral damages for life and health of the irradiatedpeople is still extremely complicated. The negative
influence of Chernobyl included the entire range offactors which are causing their mutual strengthening.
In particular, neither theoretical models nor practical
recommendations for the integral assessment of socialand psycho-emotional factors by radiation
catastrophes exist at present. From the other side, inorder to rehabilitate efficiently the sufferers, it isneeded to range and to determine objectively thecontribution of both radiation and non-radiation
components of influence. Therefore, it is of greatpractical value to continue many-years studies and toobtain new scientific data in the field of radiation
epidemiology .

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