Cytogenetic Effects of the Action of Ionizing Radiations on Human Populations
Vladimir A. SHEVCHENKO1, Galina P. SNIGIRYOVA2
1

2

N. I. Vavilov Institute of General Genetics, Russian Academy of Sciences, Moscow
Moscow Research Institute of Diagnostics and Surgery, Ministry of Health and Medical
Industry of the Russian Federation
exposure (8, 9). In this connection, the retrospective
assessment of absorbed doses (this primarily concerns
cases of emergency and accidents) by the frequency ofdicentrics without additional investigations ispractically unfeasible, if years have passed since theexposure occurred. More promising for the purpose of
biological dosimetry is the analysis of stable
aberrations (translocations) the frequency of which
remains constant for a long time after exposure toradiation (months, years). The probability ofoccurrence of stable (translocations) and unstable(dicentrics) aberrations after exposure is the same (10,11). However, translocations are not subjected to
selection during cell proliferation, in contrast to
dicentrics. In some works, the data for exposed
individuals undergoing radiotherapeutic treatment andfor Hiroshima survivors confirm this fact (9, 12).
The use of biological dosimetry, and, in particular,
cytogenetic analysis, makes it possible to fill in the
gap in the knowledge about absorbed doses in people
exposed as a result of large nuclear catastrophes,
which was repeatedly demonstrated in studies of the
impacts of the accidents at the Chernobyl nuclear
power plant in 1986 (13-19), in Goiania (Brazil) in
1987 (20) and other radiation situations (21, 22). In
their turn, the data on absorbed doses refined with thehelp of cytogenetic methods permit assessing thegenetic risk from radiation for future generations.
The objective of the present work is the analysis ofavailable materials on practical application of thecytogenetic method for dose assessment in people
participating in the post-accidental rescue andclean-up operations in Chernobyl (so-called“liquidators”). These materials will be compared withthe results of cytogenetic investigations performed inother regions of Russia exposed to radiation (thevillage Muslyumovo in the Chelyabinsk region,
several localities of the Altai Territory in the vicinityof the Semipalatinsk nuclear test site) as well as withthe results of cytogenetic monitoring in the population
living around the Three Mile Island (TMI) nuclear
power plant (Pennsylvania, USA) where a nuclear
accident occurred in 1979. The work presents theresults of cytogenetic investigations obtained by the
traditional method of analysis of the frequency of
unstable chromosome aberrations and by the FISH

Introduction
The methodology for assessing the genetic risk
from the action of ionizing radiations on humanpopulations has been elaborated by the United
Nations Scientific Committee on the Effects ofAtomic Radiation (1-3). On the basis of over 30-year
international experience of investigation of genetic
effects of ionizing radiations in experimental objects(microorganisms, plants, animals) as well as relatively
rare investigations of genetic effects in man,
UNSCEAR made an estimate of expected genetic
effects of radiation in future generations per dose unit
- 1 Sv.
The main source of information on absorbed doses
has been accepted to be physical dosimetry. Thismethod makes it possible to obtain evidence on thetype of ionizing radiation, dose rate, duration of
exposure and dose distribution in space. However,evidence on genetically important doses based on
physical dosimetric measurements in the case ofwide-scale accidents, such as in Chernobyl, is mostoften very limited.
A promising method for estimating absorbed doses
is biological dosimetry, namely cytogenetic analysis(4). Radiation can induce two types of chromosome
aberrations: unstable - dicentrics, centric rings,
acentric fragments; and stable - reciprocaltranslocations and other types of translocations.
Most often absorbed doses are assessed on thebasis of the frequency of unstable aberrations(dicentrics) (5). Centric rings can also be used for thispurpose, but the frequency of their occurrence makes
up only 5-10% as compared to the rate of dicentricchromosomes (6). By comparing the rate of dicentricchromosomes with a standard dose-effect curve
obtained in an experiment in vitro, it is possible todetermine a radiation dose. This method has been
recommended for practical use by the documents ofWHO, IAEA and UNSCEAR (1, 4, 7). Dicentricchromosomes are easily recognized without using
special staining techniques. However, the use ofdicentrics as well as other aberrations of the unstable
type for the purposes of biological dosimetry is notalways possible since the frequency of cells
containing such chromosomes declines in time post203

Table 1

Cytogenetic results obtained in 1986 in the liquidators of the Chernobyl Nuclear Power
accident[ (M ± SEM) ×10-3]

Group
Chernobyl Nuclear
Power Plant staff
Physicians
Dosimetrists
Drivers
Builders of the“Sarcophagus”
Pripyat population
Control

NumberNumberofof cells
personsscoredNumberof chromosome
aberrations

Dicentric
Absorbed whole body dose **s+
mGy ± SEM
centric
1
2
rings

83

6015

23.7 ± 2.0*

5.8 ± 1.0*474 ± 315

303 ± 199

37
23
60

2590
1641
5300

13.1 ± 2.3*
31.1 ± 4.3*
14.7 ± 1.7*

2.7 ± 1.0*
4.8 ± 1.7*
3.2 ± 0.8*

198 ± 212381 ± 345
264 ± 211125 ± 123
243 ± 214
168 ± 124

71

4937

32.4 ± 2.5*

4.4 ± 0.9*347 ± 260

221 ± 159

35
19

2593
3605

14.3 ± 2.4*
1.9 ± 0.7*

1.9 ± 0.8*0131 ± 168-81 ± 92-

Level of significance* - p< 0.05;
SEM, standard error of the mean;** - dose estimations on the basis of: 1 - reference 15, 2 - reference 23, on the basis of the sum of dicentrics and centricrings (0.011 and 0.018 dicentrics per 1 Gy per 1 cell).

consumer's co-operatives, etc.).
Blood samples were collected within several days
(groups 1, 3, 4, 5) and within 1-3 months (groups 2, 6)
after the evacuation of people from the 30 km zone.
The results of cytogenetic examination are presented
in Table 1. They demonstrate that the frequency ofchromosome aberrations in the examined liquidators
significantly exceeds (up to 17-fold) the control level.
The highest frequency of cytogenetic injuries wasrecorded in the builders of the sarcophagus, CNPP
personnel and in the dosimetrists. The greatest spreadin the frequency of chromosome aberrations between
individuals was observed among the sarcophagusbuilders (up to 16%). A more homogeneous
distribution was noted in the group of inhabitantsfrom Pripyat (from 1 to 6%) and in the CNPP
personnel (from 0 to 10%).
Absorbed doses were assessed by the frequency ofdicentrics and centric rings using a calibration
dose-effect curve generated in vivo (analysis of
dosimetric data for the liquidators whose absorbed
dose was precisely measured by the physical method)(15) and linear coefficients of calibration dose-effectcurves obtained in vitro for acute exposure in the lowdose range (23). Table 1 presents the values of
average absorbed doses calculated on the basis of
cytogenetic data. These values are from 81 to 474
mGy in the groups of people exposed to radiation in1986. The highest level of absorbed doses wasrecorded for the CNPP personnel, dosimetrists andsarcophagus builders.
It should be noted that the results of dose
assessment obtained from the dose-effect curve in
vivo (15) completely agree with the real dose situationin Chernobyl while the dose estimate by thecalibration curve of Lloyd et al. (23) generated underhigh dose rate conditions needs correction in view ofmethod based on the frequency of stable chromosome
aberrations.

Cytogenetic examination of the victims of
nuclear accidents
A. Cytogenetic examination of the liquidators
working in Chernobyl
Cytogenetic examination of the liquidators working in
Chernobyl was started in 1986 in the laboratoryorganized by the N. I. Vavilov Institute of General
Genetics of the Russian Academy of Sciences directlyin Chernobyl in accordance to the resolution of theGovernmental Commission on the liquidation of theconsequences of the accident (13, 14, 15).
All examined people working in the zone of theaccident in 1986 were grouped as follows:
employeers from the Chernobyl nuclear power plant(CNPP) who participated in the liquidation of theconsequences of the accident and in decontaminationof the territory in 1986-1987; physicians of the
medical station in Pripyat who examined the workersof the Chernobyl nuclear power plant before theaccident and participated in the evacuation of the
population of Pripyat and the personnel of unit ¹4 andlater in medical examination of the liquidators
working in the 30 km control zone; a group of
dosimetrists who participated in the dosimetric control
on the CNPP territory during decontamination works;
drivers who transported concrete and other materials
for constructing the "sarcophagus" around unit 4;builders of the "sarcophagus" who directly
participated in its construction;
part of the population of Pripyat evacuated after
the accident but remaining in the 30 km zone andparticipating in the liquidation works (members of thelocal administration, militiamen, workers of204

Table 2 gives the main results of cytogenetic
examination obtained using the conventional method.
Throughout the whole follow-up period, beginningfrom 1990, the level of cells with unstable aberrations- dicentrics and centric rings - significantly differedfrom the control. Only in 1995 the frequency of cellswith dicentrics and centric rings was at the control
level (group 6).
Thus, despite a long period of time after the
exposure, a high level of cells with unstable
aberrations was preserved in peripheral blood of theexamined people.
Analysis of the frequency of stable translocations
with the FISH method was carried out in 53
liquidators who worked in Chernobyl in 1986 and in
12 persons from the control group. The cytogenetic
study was performed in 1994-1995, i.e. 8-9 years after
the accident. The data of this study are presented inTable 3. In the group of liquidators, the frequency ofcells with translocations exceeds that in the control
group nearly 4-fold. On this basis of the data obtained,
an absorbed dose was assessed using the calibration
dose-effect curve for acute radiation exposure
generated after 137Cs gamma-irradiation of whole
blood in the range of 0 to 3 Gy (33). This dose madeup 200 mGy. 32 out of 53 examined liquidators had
official data on absorbed doses, but no dependence ofthe frequency of cells with translocations on theradiation dose value was revealed (r=0.143, p=0.44).
Table 4 demonstrates the results of cytogenetic
examination with the FISH method for a group ofliquidators who had dosimetric data and for
liquidators for whom such information was not

the peculiarities of dose formation in Chernobyl. The
correction factor is apparently equal to the ratio of
α coefficients in corresponding regression
equations: 0.018 (15) and 0.011 (23) dicentrics per 1
Gy per cell. This ratio in the given case is 1.6. Itshould also be stressed that according to the data
presented in the report of UNSCEAR 1982 (1) the
accepted coefficients for different genetic effects are
2.0 upon transition from acute exposure conditions toprolonged exposure and 3.0 upon transition fromacute exposure to chronic exposure.
Beginning in 1990, the cytogenetic examination of
the liquidators was continued in the Moscow
Research Institute of Diagnostics and Surgery of the
Ministry of Health and Medical Industry of theRussian Federation (16, 24-26). Over 400 individuals
involved in reconstruction works in 1986-1987 havebeen examined. As a rule, the dose officially recordedin the documents did not exceed 250 mSv. For asignificant part of the liquidators (about 30%)
information on absorbed doses was lacking. Particularattention was given to the formation of a control
group. This group consisting of 82 persons included
those who had never had contact with ionizing
radiation and had never been subjected to therapeuticand serious diagnostic irradiation. The frequency ofdicentrics and centric rings in the control group madeup 0.2 ± 0.1 per 1,000 cells (26,849 metaphases
analyzed). Cytogenetic examination involved analysisof the frequency of unstable aberrations (dicentrics
and centric rings) by the conventional method andanalysis of the frequency of stable translocations by
the FISH method.

Table 2

Results of cytogenetic analysis of lymphocytes in the liquidators and the control group[ (Mean ± SEM) × 10-3 ]Group
Number of
Number of
Number of cells(year of
Cdr
persons
cells scoredwith aberrations
sampling)
I (1990)234268
14.9 ± 1.9*
1.0 ± 0.5*
II (1991)
110
20077
19.7 ± 1.0*
0.9 ± 0.2*
III (1992)
136
32000
31.8 ± 1.0*
1.4 ± 0.2*
IV (1993)
75
18581
34.8 ± 1.4*
0.9 ± 0.2*
V (1994)60
18179
31.8 ± 1.3*
1.8 ± 0.3*
VI (1995)
41
12160
18.8 ± 1.2*
0.4 ± 0.2
Control
82
26849
10.5 ± 0.6
0.2 ± 0.1
Level of significance* - p< 0.05;
SEM, standard error of the mean;Cdr, cells containing dicentrics and/or centric rings; ace, acentrics.

Table 3ace
5.3 ± 1.1
6.8 ± 0.6*
9.0 ± 0.5*
11.9 ± 0.8*
10.3 ± 0.8*
7.3 ± 0.8*
3.9 ± 0.4

Frequency of symmetrical translocations in a group of liquidators (pooled data) and in thecontrol group

Number of
Number of Number ofstable(FP ± SEM)
persons
cells scoredtranslocations
×10 -2Liquidators
53
45007
166
0.37 ± 0.03*
Control
1213586
130.10 ± 0.03
Level of significance* - p< 0.05;
SEM, standard error of the mean;FP, translocations/cell; FG, genomic translocation frequency.
Group

205

(FG ± SEM)
×10 -2
1.17 ± 0.05
0.32 ± 0.05

Estimateddose(mGy)
200 (100,300)-

chromosomes - decreases in time but over 8 years
after the exposure it exceeded the control level. The
use of unstable aberrations for the purposes of
biological dosimetry in case years have passed since
the exposure occurred requires an experimental
determination of a temporal parameter characterizing
the dynamics of reduction of the level of such
aberrations.
Analysis of the frequency of stable translocations
with the FISH method is more promising forbiological dosimetry since it permits estimating
absorbed doses irrespective of the time post exposure.
The cytocenetic examination (analysis of stabletranslocations) of the liquidators working in
Chernobyl demonstrates the possibility of assessing
absorbed doses within 8-9 years after the action ofionizing radiations. It should be pointed out that theindividual doses were not always in agreement withthe dosimetric data presented in the official
documents of these people. The scatter in the dosevalues in the group of examined liquidators

available. A higher level of cells with translocations
was established in the second group including
liquidators whose absorbed doses were not officially
documented.
Table 5 presents the data of individual cytogenetic
analysis with the FISH method for 10 liquidators inwhom the frequency of cells with translocations
significantly differed from the control level. For thesepatients, the absorbed radiation doses were estimatedin the range from 300 to 1,000 mGy.
It is important that all the above estimates ofabsorbed doses based on the FISH method were madewithout corrections for prolonged and chronic
exposures.
Thus, the liquidators examined immediately after
the exposure to radiation displayed a high level of
unstable chromosome aberrations which permitted us
to estimate average absorbed doses depending on thecharacter of their work in the range of 81-474 mGy. It
was revealed that the level of cells with unstable
chromosome aberrations - dicentrics and ring

Table 4

requency of symmetrical translocations in two groups of liquidators (with and without
official doses)

Official
Number of
Number of Number of stable
dose
persons
cells scoredtranslocations
I
YES
32
26947
84
II
NO
21
18060
82
FP, translocations/cell; FG, genomic translocation frequency.
SEM, standard error of the mean.
Group

Table 5(FP ± SEM)
×10 -20.31 ± 0.03
0.45 ± 0.05

(FG ± SEM)
Estimateddose(mGy)
×10 -2100 (0,200)
0.98 ± 0.06
300
(200,400)
1.43 ± 0.09

Frequency of translocations (detected by FISH), dicentrics and rings (obtained withconventional scoring) and individual dose estimates (95% CL)
FIS H m e t h o dPat-ient
No

Docum-ented
dose
(mGy)

cells
scoredtranslocations

1

-

583

6

2

-

1016

15

5

145

1297

8

6

170

1314

10

9

-

473

11

12

-

1161

9

34

-

1157

6

35

-

1209

7

44

800

1688

45

293

857

11*
6

FP±SEM
×10-2

FG±SEM×
10-2

Estimateddose(mGy)

1.03
±0.42
1.48
±0.38
0.62
±0.22
0.76
±0.24
2.33
±0.69
0.77
±0.25
0.52
±0.21
0.58
±0.22
0.59
±0.19
0.70
±0.29

3.27
±0.75
4.70
±0.68
1.97
±0.39
2.42
±0.43
7.40
±1.25
2.44
±0.46
1.65
±0.38
1.84
±0.39
1.87
±0.33
2.22
±0.51

600
(400,800)
700(600,800)
400(300,500)
400(300,500)
1000(800,1200)
400(300,500)
300(200,400)
300(200,400)
300(200,400)
400(300,500)*;10 cells.

206

Conventional method(dic+Rc)cells
Dic+/cell±SEM×scored
Rc
10-2
250

0

0

1000

8

0.80
±0.28

300

0

0

300

0

0

300

3

300

2

300

0

0

300

0

0

300

0

0

300

0

0

1.00
±0.58
0.67
±0.47

Table 6 Frequency of unstable chromosome aberrations in blood lymphocytes in the Altai population[ (M ± SEM) ×10-3]
No ofCells with
Total
No of
dic + Rc
Group
per-sonaberr-atio
number of
ace
cells
s
ns
aberrations
Tyumentsevo
30
7831
10.2
10.7
0.3
5.7
(control)
±1.1
±1.2
±0.2
±0.9
Ugly
15
1958
7.8
16.8
3.7
9.2
±2.0
±2.9
±1.4*
±2.2
Ozernoye12
1523
12.0
12.0
0.7
6.0
Kuznetsovo
±2.8
±2.8
±0.7
±1.9
Zelenaya
24
2749
31.6
32.0
1.1
8.1
Dubrava
±3.4*
±3.4*
±0.6*
±1.7
Laptev
84
22195
14.4
16.5
3.1
5.3
Log
±0.8*
±0.9*
±0.4*
±0.5
Naumovka
26
4275
16.8
17.5
2.6
6.2
±2.0*
±1.9*
±0.7*
±1.3
Belenkoye
35
9069
13.6
16.9
1.3
7.3
±1.2*
±1.4*
±0.4*
±0.9
Topolnoye
30
6530
20.4
20.5
1.7
6.2
±1.8*
±1.8*
±0.5*
±1.0
Level of significance * - p<0.05; SEM, standard error of the mean;dic, dicentrics; R , ring chromosomes; ace, acentrics; Cdr, cells containing dic+Rc.
c

Chromatid
Cdr
0.3
±0.2
1.0
±0.7
0.7
±0.7
1.1
±0.6*
1.9
±0.3*
2.6
±0.7*
1.2
±0.4*
1.7
±0.5*

aberra-tions
4.7
±0.8
3.1
±13
5.4
±1.9
22.1
±2.8*
7.6
±0.6*
8.8
±1.4*
7.5
±0.9*
12.3
±1.4*

exposure. This fact creates a unique situation inestimating genetic effects in the exposed part of the
population - it is necessary to choose approaches
enabling the study of genetic effects within such along time after the exposure.
In this section, we present the materials ofcytogenetic examination of people from 7 settlementsof the Altai region (226 individuals) that suffered
most greatly from the explosion in 1949 (21, 22, 28).
In 1992, blood samples were collected in thefollowing settlements: Uglovskoye (average dose about 0.1 Sv), Ozernoye-Kuznetsovo (about 0.1 Sv),
Laptev Log (0.97 Sv) and Topolnoye (2.43 Sv). Lateron, in 1993 and in 1994, cytogenetic examinations
were continued in the villages Zelyonaya Dubrava(0.18 Sv), Belenkoye (1.87 Sv) and Naumovka (1.86
Sv). The village Tyumentsevo was chosen as a control
(0.05
Sv).
The
social-economic
andclimatic-geographic conditions were analogous for all
examined groups.
The results of these cytogenetic studies arepresented in Table 6. In addition to chromatidaberrations (mainly single fragments), the spectrum ofaberrations included chromosome aberrations:
acentric fragments, centric rings, dicentric and eventricentric chromosomes. Atypical monocentricchromosomes resulting from translocations were also
detected. In some exposed individuals cells withmultiple chromosome aberrations were found.

constituted up to 1 Gy. However these values may
appear to be underestimated as the calculations weremade without corrections for prolonged and chronic
exposures.

B. Cytogenetic examination of the Altai
population exposed to ionizing radiations as aresult of nuclear explosions on the Semipalatinsk
nuclear test site
As a result of nuclear tests in the air on the
Semipalatinsk nuclear test site in 1949-1962, a
number of regions of the Altai Territory were exposedto the action of high doses of ionizing radiations
capable of inducing serious genetic effects. According
to the data of the Semipalatinsk nuclear test site (27),radioactive products from more than 50 explosions
made in the air and on the earth for a period from1949 till 1962 spread in the direction of the Altai
Territory. A collective effective dose from the firstnuclear explosion in 1949 made up 32,000 man-Sv. A
total dose for the Altai population from all subsequent
explosions is estimated at 10,000 man-Sv. Thus, thecontribution from the explosion in 1949 constitutes
about 80% of the total collective effective dose
received by the Altai population as a result of nuclear
tests on the Semipalatinsk test site (27).
The dotted line indicates the rates of cells withchromosome aberrations in a group of Moscow
citizens. Absciss - dose, Sv; ordinate - the numberof cells with dicentrics and rings per 1,000
cells.The study of genetic impacts from nuclear
explosions for the Altai population was started only
when several decades had passed since the radiation

In the populations of Zelyonaya Dubrava, Laptev
Log, Naumovka, Belenkoye and Topolnoye thefrequency of aberrant metaphases significantly

207and rings per 1000 cells

Num ber ofcells with dicentric

10

1

0.1
0.01

Control

0.1

1

10

Dose (Sv)Fig. 1. The frequency of cells with dicentrics and centric ring chromosomes in theexamined groups of the Altai population depending on the effective dose of irradiation
caused by the nuclear explosion on the Semipalatinsk nuclear test site in 1949.
relationship. Approximating equation coefficientswere determined by the method of maximum
likelihood assuming Poisson distribution. The
following linear regression equation was derived:y = (08. ± 02.)× 10−3 + (06. ± 02.)× 10−3 × Sv−1D ,where y is the frequency of cells containing
dicentrics and centric rings (Cdr), D - dose. The levelof significance of the linear regression coefficient isp<0.05. The results of the study clearly demonstratethat despite a long post-exposure time (several
decades) an increased number of cells with unstable
chromosome aberrations, the level of which depends
on the effective dose value, is observed in peripheral
blood of the examined people. It can be inferred thatthe source of such cells carrying dicentrics and centricring chromosomes are radiation-injured stem cells ofblood-forming tissue.
Among 40,777 cells analyzed in the examinedgroups of the Altai population 10 cells were found tohave multiple chromosome aberrations. The
distribution of multiaberrant cells among these groups
and their characteristics are shown in Table 7. One
multiaberrant cell containing five acentric fragments
was found in peripheral blood of the examined
persons from Tyumentsevo (control group).
Multiaberrant blood cells, including dicentrics,
tricentrics and centric rings, were discovered in theexamined inhabitants from the settlements exposed toionizing radiations. The frequency of multiaberrant
cells in them is higher than in the control group.

exceeds the control level. In the same populations, astatistically significant excess over the control level by
the frequency of chromatid aberrations was observed.
No differences were found by the frequency ofacentric fragments (non-associated with dicentrics andcentric rings), except an increased frequency ofacentric fragments in the inhabitants of the village
Belenkoye (p<0.05).
Most informative in respect of biologicaldosimetry are dicentrics and centric ring
chromosomes as recognized markers of radiation
effects (5). For all examined populations, except thevillage Ozernoye-Kuznetsovo, the average rate ofcells with dicentrics and centric rings (Cdr)significantly exceeds the control level. The frequencyof these chromosomes in the examined groups ofpeople from the villages Uglovskoye, Naumovka,
Laptev Log, Topolnoye, Belenkoye and Zelyonaya
Dubrava exceeds the control level 12-fold, 9-fold,
6-fold, 6-fold, 4-fold and 3.5-fold, respectively.
Fig. 1 shows the frequency of cells with dicentrics
and centric rings in the inhabitants of several
settlements of the Altai region depending on thevalues of effective doses presumably absorbed bythem. These doses were estimated on the basis ofexperimental measurements and with the help ofmathematical simulation performed by the Central
Physical-Technical Institute of the Ministry of
Defence of the Russian Federation (29).
Statistical analysis of the results presented in Fig. 1
was performed on the basis of linear dose-effect208

organism caused the appearance of multiaberrant cells.
This hypothesis is confirmed by the data of A. M.
Marenny et al. (32) who detected hot particles (asource of alpha-radiation) in the lungs and in thelymph nodes of ten patients from theradionuclide-contaminated regions of Altai who wereoperated from lung cancer.
Thus, within 43-45 years after the first nuclear
explosion on the Semipalatinsk nuclear test site in1949, the inhabitants of all examined settlements
revealed an increased frequency of unstable

The nature of such multiaberrant cells is notcompletely understood yet (30, 31). Probably they are
induced by chemical or biological mutagenic factors.
One of possible explanations of the nature of suchcells is the action of densely-ionizing radiations, andfirst of all, of alpha-particles of various radionuclides,
assuming their high concentration in the human body.
Since 239Pu, a source of alpha-particles, is acomponent of the mixture of products of the nuclear
explosion that affected the Altai population, it can beinferred that the entry of plutonium into the human

Table 7Frequency of multiple cells in blood lymphocytes of people from different radionuclidecontaminated areasGroup

Muslyumovo(116 persons)Altai(178 persons)Patients *
1
2
3
4
5
6
1
2
3
4
5
6
7
8
9
10
1

Age
(Year of birth)
1949
1975
1950
1980
1915
1958
1947
1945
1930
1941
1956
1949
1935
1949
1961
1946
1962

Sex
f
m
f
m
f
f
m
m
m
m
m
f
m
f
m
m
f

Control(30 persons)dic, dicentric; tric, tricentric; tet, tetracentric;Rc, centric ring;ace, acentric (double fragment); SF, single fragment; t-translocation;* people with multiple aberrations

Table 8Description ofmultiple cells
tric-2; dic-3
tric-2
dic-8; ace-4
dic-2
tet-1; tric-1; dic-1
dic-2
dic-2
ace-9; SF-1
tric-5;dic-5;Rc-1;t-2
dic-3; ace-1
dic-1; ace-2;
dic-2;tric-2; ace-11
tric-2;dic-2;t-1;ace-5
dic-2; ace-7
dic-2
dic-1; ace-2
ace-5

Frequency of symmetrical translocations (FISH method) in blood lymphocytes
Altai populationin the

Group

No of
No of cells
No of
-2
-2
(FP ± SEM)×10(FG ± SEM)×10
personsscoredtranslo-cations
Laptev Log
14
7026
29
0.41 ±0,08*
1.29 ±0,11
Belenkoye
63213
18
0.56 ±0,13*
1.76 ±0,19Topolnoye
42762
110.40 ±0,12*
1,26 ±0,17
Altai region (Total)
24
13001
58
0.45 ±0.06*
1.42 ±0.10
Control
1213586
130.10 ± 0,03
0.32 ±0,05
Level of significance * - p<0.05; SEM, standard error of the mean;FP, translocation/cell; FG , genomic translocation
frequency; m, standard error of the mean.

Table 9Frequency of symmetrical translocations (FISH method) in blood lymphocytes in the Laptev
Log (Altai region) populationGroup

No. ofpersons

I (born before 1949)
II (born after 1949ã)Control
Level of significance * -8612
p<0.05;

No.of cells
scoredNo. oftranslocations

4271
25
2755
4
13586
13
SEM, standard error of the mean;

209(Fp ± SEM) ×
10-2
0.58 ± 0.12*
0.14 ± 0.01
0.10 ±0.03(FG ± SEM) ×10-2
1.82 ±0.17
0.44 ± 0.10
0.32 ±0.05

test period and after it. A correction factor 3 is usuallyused for assessing chronic irradiation doses (1).
Hence it follows that in the case of the exposure thattook place in the Altai region the linear-quadraticmodel yields underestimated dose values. In view of
the above-stated, the average dose for the examinedgroups of the population calculated on the basis of
cytogenetic analysis makes up about 1 Gy.
It is obvious that the values of absorbed doses forthe part of the Altai population exposed to ionizing
radiations from nuclear explosions on the
Semipalatinsk nuclear test site will be corrected withaccumulation of cytogenetic data obtained by the
FISH method.

chromosome aberrations, mainly dicentrics andcentric rings. The frequency of cells with such
chromosome aberrations was linearly related toeffective doses presumably accumulated by the
populations of the examined settlements. At present, it
is hard to say anything about the initial level ofdicentrics and centric rings immediately after the
explosion since the dynamics of these chromosome
aberrations for a period of several decades is unknown.
This hinders the use of the presented data for thereconstruction of absorbed doses in the Altai
population.
The results of cytogenetic examination of the Altai
population with the FISH method are presented inTable 8. The average levels of translocations for the
populations of Laptev Log, Belenkoye and Topolnoye
are 0.41 per 100 cells, 0.56 per 100 cells and 0.40 per
100 cells, respectively. These values significantly
exceed our control level and therefore it is safe toassume the presence of radiation-induced changes in
the cell chromosome apparatus in the examined
persons. As noted above, about 80% of the externalradiation dose falls on the explosion made in 1949;
therefore people born before 1949 received thehighest doses. In connection with this, the results of
examination of this group of the population should beanalyzed separately. For example, the group of
examined persons from the village Laptev Log
included those born before and after 1949. As seen in
Table 9, the average level of stable translocations for
8 individuals born before 1949 is 0.58 per 100 cells
and for 6 individuals born after 1949 it is 0.14 per 100
cells. In the first group, the frequency of stabletranslocations is more than 5 times higher than in thecontrol, and in the second group the frequency ofstable translocations does not differ from the control
level. The data obtained are far from being sufficient
to make any final conclusions, however even theseresults confirm the fact that the most affected part ofthe population are people born before 1949 and thatthey must be, in the first turn, in the focus of attention
when undertaking medical and preventive measures.
The absorbed dose value estimated by thefrequency of stable translocations for three villages,
Laptev Log, Belenkoye and Topolnoye, is about 300
mGy. It should be mentioned that this value wasobtained using the linear-quadratic dose-effect model
for acute exposure (33). The situation observed in the
Altai region due to surface nuclear explosions is much
more complicated in terms of dosimetry than that
could be assessed with the use of this model. It is
important to take into account the long-term chronic
irradiation from external and internal radiation
sources (29). A true estimate of effective doses basedon the frequency of stable aberrations can be obtained
only given clear-cut data on the dynamics ofirradiation of the population both during the nuclear

C. Cytogenetic examination of the population of
Muslyumovo located on the banks of theradionuclide-contaminated Techa river
In 1949-1951, the plutonium-producing plant(“Mayak”) in the Chelyabinsk region discharged
radioactive waste products (a total of 2.76 mln Ci)
into the open hydrosystem of the rivers Techa, Iset,
Tobol (34). 124,000 people, including 28,100 of thoseliving on the Techa banks, were exposed to radiation.
The doses of exposure were rather high - a collective
dose made up about 6,000 man-Sv. Nearly 7,500
individuals evacuated from 20 settlements received,
according to official data, average effective equivalentdoses from 3.5 to 170 cSv (34). The highest radiation
doses were recorded for the evacuated population of
the village Metlino (170 cSv, 1,200 people). Among
non-evacuated settlements, the most serious radiation
situation remains in Muslyumovo (30 km from the
Mayak plant). In 1949, the population of thissettlement was 4,000 people, and at present it is about
2,500 people. The level of exposure here is critical an average bone marrow dose is 0.25 Gy. In nearly
5% of the population an average bone marrow dose is
1 Gy (35). The first medical examinations wereorganized within 2 years after the discharge ofradioactive waste products into the Techa river only
for the population of one settlement in the upper
reaches of the river - Metlino. In other settlements the
medical examination was started only after 3-6 years.
The register of exposed people living along the river
was initiated only in 1968. These facts in combination
with a high migration of the exposed population has
created a situation in which the assessment of remoteradiation effects becomes rather difficult.
At the same time, even the first studies showedthat the exposure of people in the upper reaches of the
Techa river had led to the development of chronic
radiation sickness (particularly in Metlino where thisdisease was diagnosed in 1956 in 64.7% of the adult
population and in 63.15% of examined children) (36).
Chronic radiation sickness was revealed in a total of935 people. An increase in the incidence of leukoses
210

contamination.
Table 10 presents the results of cytogenetic
examination by the conventional method (analysis ofunstable chromosome aberrations). In all groups, thefrequency of chromosome aberrations exceeded thecontrol level. It is worth noticing that the value of thisfrequency was higher in the second and third groups.
In all examined groups exchange aberrations(dicentrics and centric rings) were revealed, and theirfrequency significantly exceeded (5-10-fold) that in
the control group. The highest frequency of dicentrics
and centric rings, as well as cells containing such
aberrations, was noted in the second and third groups.
These results are presented in Fig. 2. The frequency ofacentric fragments did not differ significantly in thegroups of examined people from Muslyumovo and in
the control group. In all examined groups an excess
over the control level by the frequency of chromatidaberrations was observed.
Cells with multiple chromosome aberrations were
found in the examined persons from Muslyumovo(Table 7). On the whole, 6 multiaberrant cells werediscovered among 32,203 analyzed metaphases,
including tricentric and tetracentric cells which are notpractically found normally.
It can be assumed that the appearance of cells withmultiple aberrations is the result of the action ofalpha-radiation from plutonium and its fission
products (30, 31, 37). According to A. V.
Trapeznikov et al. (38), the Techa river contains about
8 Gbq 239, 240Pu. This estimate was made within theriver section from 50 km to 240 km from the Mayakplant, i.e. up to the place of confluence with the Isetriver.
Thus, the cytogenetic study carried out in
Muslyumovo revealed an increased level ofin the examined population was established. For aperiod of 33 years, 52 cases of hemoblastoses wererecorded, including 37 leukosis patients among
17,200 people examined since 1950, which is by 15
cases more than expected without irradiation.
Besides chronic radiation sickness, a decrease inimmunologic reactivity, depression of hemopoiesis,
an increase in cases of vegetovascular dystonia,
hypertensive disease, pathologic pregnancy and labor,
and increased infantile mortality were recorded in the
inhabitants of the riverside settlements. As shown in
the work by M. M. Kosenko and M. O. Degteva (36),the mortality from cancer increased in 1950-1982 ascompared to a group of people living in
non-contaminated areas with similar social-economic
conditions.
Cytogenetic examinations of the population of
Muslyumovo were performed in 1993-1994. The
examination was carried out on a total of 116 persons.
The data of the cytogenetic analysis were comparedwith the results of examination of the control group(30 individuals, 7,831 metaphases analyzed) formedof the inhabitants from a non-contaminated region of
the Altai. In view of the tasks of the examination, allpeople were divided in several groups. The first group
included all examined people. The second groupunited inhabitants of Muslyumovo born before 1949
(beginning of the contamination of the Techa river)and living there permanently. The third group wascomposed of people born from 1949 till 1956 (thistime is characterized by the highest level ofcontamination of the Techa river). The fourth groupconsisted of people born after 1957, and the fifthgroup was formed of migrants, i.e. people who cameto Muslyumovo at different times, including thoseevacuated from villages exposed to radioactive

Table 10

Cytogenetic results obtained in a human population continually exposed to low doses ofradiation in the South Urals, Chelyabinsk area, Muslyumovo(M ± SEM) x 10-3]
Total
No of
No of
Cells with
dic + Rc
Group
number oface
personscells
aberrations
aberrations
14.4
15.3
2.2
5.4
1
116
32203
±0.7*
±0.7*
±0.3*
±0.4
19.3
19.4
2.7
6.6
2
23
6730
±1.7*
±1.7*
±0.6*
±1.0
15.8
17.2
3.2
7.6
3
46
5730
±1.7*
±1.7*
±0.7*
±1.1
11.9
12.4
1.5
3.3
4
49
14052
±0.9
±0.9
±0.3*
±0.5
13.3
15.4
2.2
6.7
5
21
5691
±1.5
±1.6*
±0.6*
±1.1
10.2
10.7
0.3
5.7
Cont-rol
30
7831
±1.1
±1.2
±0.2
±0.8
1, total; 2, born before 1949; 3, born in 1949-1956; 4, born in 1957-1988; 5, migrants.
Level of significance * - p<0.05; SEM, standard error of the mean;

211

Cdr

Chromatid
aberrations

1.4
±0.2*
1.9
±0.5*
2.1
±0.6*
1.1
±0.3*
0.9
±0.4
0.3
±0.2

7.6
±0.5*
9.8
±1.2*
6.3
±1.1*
7.6
±0.7*
6.4
±1.1
4.7
±0.8

Dic/rings per 1000 cells

2.5
2
1.5
1
0.5
0

1

2

3
4
Exam ined group5

6

Fig. 2. The frequency of cells with dicentrics and centric ring chromosomes in theexamined groups of the population of Muslyumovo (Chelyabinsk region).
1 - control group; 2 - all examined individuals; 3 - born before 1949;4 - born in the period
from 1949 to 1956; 5 - born in the period from 1957 to 1988; 6 - evacuated from othersettlements.
nuclear power plant were carried out. The aim of thisstudy was to analyze the level of unstable and stable
chromosome aberrations in people assumed to be
exposed to ionizing radiations due to the TMI
accident. The basis for such assumption were thesigns of radiation damages in people (skin reddening,
peculiar metallic smack in the mouth, irritation of
mucous membranes, vestigo, vomiting, diarrhea, etc.)
at the moment of the accident and also a number of
diseases that occurred some time later.
The cytogenetic study was carried out in
July-August, 1994 and in January-February, 1995. In
selecting a group of patients, their possible diagnostic
and therapeutic irradiation as well as a number of
additional factors that might influence the results ofcytogenetic analysis were taken into account. The
results of the study are presented in Table 11 and in
Fig. 3. Given a relatively normal general level ofchromosome aberrations, a significant increase in thefrequency of cells containing chromosome aberrations,
namely dicentrics, was recorded. In the group of
examined people from the TMI region this rate
exceeded 10-fold the control level (0.2 × 10-3
dicentrics per 1,000 cells). Dicentrics were found in
20 persons, i.e. in 70% of cases. The rate of cells
containing exchange aberrations (dicentrics) varied
from 0.2 to 0.8% and exceeded the control level
10-40-fold, respectively. In one patient, a cell withtricentric was discovered.
The obtained results suggest that the group of
examined individuals from the TMI neighborhood
presumably exposed to the action of ionizing
radiations as a result of the accident at the nuclear

chromosome aberrations of the exchange type dicentrics and centric rings - which are characteristicof ionizing radiation exposures. The highest level ofsuch aberrations (9-10 times exceeding the control)
was detected in the people born before 1949 or in the
period of the most significant contamination of the
Techa river with radionuclides. Cells with multiple
chromosome aberrations detected in the blood of theexamined inhabitants of Muslyumovo seem to be theresult of organism exposure to densely-ionizing
alpha-radiation from plutonium and its radioactive
products.

D. Cytogenetic examination of the populationfrom the neighborhood of the Three Mile Island
nuclear power plant in USA
In 1979, an accident occurred at the Three Mile
Island (TMI) Nuclear power plant (unit ¹2) locatedwithin several miles from the capital of Pennsylvania,
Harrisbugr (USA). The extent and consequences ofthis accident have not been uniquely assessed yet.
According to the official data stated in the NUREG
report in 1980 (39), no impact from this accident on
the population, flora and fauna is expected. At thesame time, the discovery of radioactive iodine in theair, calculations of experts concerning the extent ofpossible discharges of radioactive inert gases,
publications of scientists on radiation effects in trees
and animals observed after the accident prompt the
public and scientists to perform new studies forassessing the impacts from this nuclear incident (40).
In 1994-1995, cytogenetic examinations of the
population living in the neighborhood of the TMI
212

Table 11

Frequency of unstable chromosome aberrations in blood lymphocytes from persons
living in the neighborhood of TMI[(M ± SEM) × 10-3]
GroupsNumber of
Number of
Total number of
Cdr
persons
cells scoredaberrations
Population2914854
14.0±1.0*
2.0±0.4*
Control8226849
10.9±0.6
0.2±0.1
Level of significance * - p<0.05; SEM, standard error of the mean;Cdr, cells containing dicentrics and/or centric rings.

Table 124.0±0.5
3.9±0.4

Chromatid
aberrations
7.0±1.0
6.6±0.5

Frequency of symmetrical translocations detected by FISH and results of conventional
cytogenetic examination of persons living in the neighborhood of TMI.

FISH method
Cells(FG±SEM) ×(Fp±SEM) ×
scored-2-2
10
10
Population
3468
17
3024
0.49±0.12*
1.55±0.21
Control
13586
13
26849
0.10±0.03
0.32±0.05
FP, translocations/cells; FG, genomic translocation; Level of significance* p<0.05; SEM, standard error of the mean; Cdr, cells containing dicentric
and/or centric rings.
Groupsace

Cells
svoredTranslocations

Conventional scoring
Cdr(Cdr ± SEM) ×10-2
1450.46±0.12
0.02±0.01

dose-effect curves (33) a dose estimate of 0.30 ± 0.10
Gy was obtained. This dose is consistent with thesituation of acute radiation exposure. In the case of
prolonged and chronic exposure, which is more real
for the situation observed after the TMI accident, thedose assessment should involve the use of correction
factors 2-3. In this case an estimated dose for the
exposed group of people is 0.6-0.9 Gy.
Thus, the cytogenetic examination of people livingin the vicinity of the TMI nuclear power plant andpresumably exposed to radiation as a result of theaccident that took place in 1979 revealed in them anincreased level of stable and unstable chromosome
aberrations. This finding undoubtedly indicates thatthe examined group of people was affected byionizing radiation. The preliminary data on thefrequency of translocations obtained with the FISH
method made it possible to estimate an averageabsorbed dose for the given group of examined
persons. This value is 0.6-0.9 taking into account the
prolonged or chronic character of the exposure.

power plant is characterized by an increased
frequency of chromosome exchange aberrations dicentrics.
In 6 persons from the examined group the rate ofstable translocations was analyzed with the FISH
method. Cells with translocations were found inperipheral blood of all examined people, and the levelof these cells exceeded the control; in 3 persons thesedifferences were statistically significant. Table 12
demonstrates the data on the frequency oftranslocations in the group of examined people fromthe TMI neighborhood. It is seen that its value
exceeds 5-fold the control level. Here the frequency oftranslocations per genome (FG) and the results oftraditional cytogenetic analysis (analysis of unstable
aberrations) are also presented.
The ratio of stable and unstable aberrations is
assumed to be 1:1 (10, 11). The prevalence of cellswith translocations indicates that for a period of 15
years after the accident the level of cells with unstable
chromosome aberrations decreased due to theirelimination from the blood channel. Despite a rather
high level of cells with dicentrics, the retrospective
dose assessment in this case is hardly feasible.
The frequency of cells with translocations inperipheral blood of the examined individuals living in
the neighborhood of TMI is 0.49 ± 0.06 per 100 cells.
This value is close to the level of cells withtranslocations observed in the Altai population (seeTable 8). This fact permits the comparison of thesegroups with respect to absorbed radiation doses. Inview of a limited amount of data (the number of
examined persons, the number of metaphases
analyzed), an average absorbed dose was determined
for the whole examined group of people. On the basisof the obtained cytogenetic data and using calibration

Conclusion
The presented cytogenetic data obtained from theexamination of different groups of people exposed toionizing radiations permit us to make the following
conclusions.
The use of the cytogenetic method for examining
people exposed to radiation as a result of theChernobyl accident, nuclear explosions on the
Semipalatinsk nuclear test site, radioactive
contamination of the Techa river (Chelyabinsk region)
and as a result of the accident at the TMI nuclear
power plant (USA) revealed increased levels of
unstable and stable chromosome aberrations ascompared to the control.
213

Num ber ofobserved person

10
9
8
7
6
5
4
3
2
1
0

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Num ber ofcells with dicentrics per 100 cells
Fig. 3. The distribution of the inhabitants from the TMI region depending on the numberof cells with dicentrics.
dicentrics and centric rings. Otherwise, particularly
Dose estimations in the liquidators working inupon exposure to low doses, when much time has
Chernobyl made on the basis of the frequency ofpassed since the exposure occurred, the use of thisunstable chromosome aberrations (dicentrics andmethod of biological dosimetry is of low efficiency
centric rings) using the materials of examinations
and practically unfeasible in most cases.
carried out in 1986 yielded values from 81 to 474
Analysis of stable translocations is presently themGy.
most promising method in retrospective assessment of
The level of cells with unstable chromosome
irradiation doses. The efficiency of this methodaberrations was found to decline in time. At the same
particularly increased after the development of thetime, during 8 years after the accident in Chernobyl
technology for scoring stable translocations this level in the examined people exceeded the control
fluorescence in situ hybridization (FISH) - whichlevel.
permits the cytogenetic analysis to be performed
The examination of the populations living in therather easily (41, 42).
Techa river region (Muslyumovo), in the Altai region
The presented results of cytogenetic examinationand in the neighborhood of the TMI nuclear powerof the liquidators in Chernobyl demonstrate theplant (USA) revealed high levels of cells withpossibility of dose assessment within 8-9 years after
dicentrics and centric rings significantly exceeding thethe accident. The range of absorbed doses in thecontrol values. The detection of such chromosome
group of examined people appeared to be up to 1 Gyaberrations within 15-45 years after the action of
from the background level.
ionizing radiations suggests the preservation of a
Retrospective assessment of individual doses,
certain portion of cells with unstable chromosome
particularly in the low dose range, based on the FISH
aberrations in people with rather high doses.
method is impeded by the fact that in order to obtain
Multiaberrant cells found in the Altai population andreliable results it is necessary to analyze a rather large
in the population of Muslyumovo apparently suggest
number of cells, which is impossible for several
their exposure to densely-ionizing alpha-radiation
reasons. This task is simplified when we deal withfrom plutonium and its fission products.
retrospective assessment of a dose for a definite group
As has already been noted, the most widelyof people. The obtained cytogenetic data are a good
accepted and sufficiently accessible method of
illustration of that. The absorbed dose estimated withbiological dosimetry based on the analysis of thethe FISH method, taking into account the character of
frequency of unstable chromosome aberrations
exposure for the populations of three villages of the(dicentrics and centric rings) cannot be effectively
Altai region, is about 1 Gy and for the population of
employed for retrospective assessment of absorbed
the TMI region (USA) it varies from 0.6 to 0.9 Gy.
doses without clear-cut knowledge about the character
It should be noted in conclusion that theand rate of temporal elimination of cells containing
importance of analysis of stable translocations forsuch chromosome aberrations. Only when there is aretrospective dose assessment by no means minimizes
possibility of reconstructing the picture of an exposure
the role of cytogenetic examination with the use of the(dose range, exposure conditions, post-exposure time)
conventional method (analysis of unstableusing mathematical simulation one can try to makechromosome aberrations) that remains to be decisive
dose estimates by the frequency of cells with214

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