Mutation Research, 262 (1991) 209-217 © 1991 Elsevier Science Publishers B.V. (Biomedical Division) 0165-7992/91/$ 03.50 ADONIS 016579929100023L
209
MUTLET 0471
The effect on lymphocyte chromosomes of additional radiation burden due to fallout in Salzburg (Austria) from the Chernobyl accident J. Pohl-Rfiling 1, O. Haas 2, A. Brogger a, G. Obe 4, H. Lcttncr 1, F. Daschil 1, C. Atzmiiller 1, D. Lloyd s, R. Kubiak 6 and A.T. Natarajan 7 1Division of Biophysics, University of Salzburg (Austria), 2St. Anna Children's Hospital, Vienna (Austria), 3Department of Genetics, Institutefor Cancer Research, Montebello, Oslo (Norway), 4Department of Genetics, University of Essen ( F.R.G.), SNational Radiological Protection Board, Chilton, Didcot ( U.K.), ~Instituteof Systematic and Experimental Zoology, Polish Academy of Science, Cracow (Poland) and 7Department of Radiation Genetics and Chemical Mutagenesis, State University of Leiden ( The Netherlands) (Received 28 May 1990) (Revision received 12 November 1990) (Accepted 16 November 1990)
Keywords: Chromosome aberration; Chernobyl fallout; Radiation burden
Summary An investigation has been carried out to determine whether chromosome aberrations in peripheral blood lymphocytes reflect the elevated environmental dose of low-LET ionising radiation, mainly due to radiocesium from Chernobyl fallout, to the population living in Salzburg city. Sixteen volunteers were sampled 1 year after the Chernobyl accident. Two of these persons were also sampled before the accident, and then in 1988 and 1990. The radioactive environment of Salzburg city and the radiation burden of its inhabitants have been frequently determined before and after the accident. The Cs-137 content of the volunteers was measured by whole-bodY counting. The additional external plus internal radiation doses in the year 1987 to the tested individuals ranged between 15 and 68% of the former normal environmental burden. The aberration frequencies showed a sharp increase of about a factor 6 from the pre-Chernobyl dose rate (0.9. mGy/year) to the post-Chernobyl dose rate (about 2 mGy/year total) but then decreased again with higher additional dose. In the two persons analysed before and up to 4 years after the accident the aberration yield showed a significant increase from 1984/85 to 1987, a decrease in 1988 and a further decrease in 1990. If these last 2 values are plotted against additional dose they fit the curve of the pooled 1987 values. The dose-effect curves revealed the same tendency as we found in various previous investigations and support the assumption that repair enzymes could be triggered by a certain amount of damage to the DNA.
Correspondence: Dr. J. Pohl-Rfiling, Division of Biophysics, University of Salzburg, Hellbrunnerstr. 34, A-5020 Salzburg
(Austria).
An increase in chromosome aberrations in peripheral blood lymphocytes of persons living and/or working in an environment with elevated
210
radioactivity has been found in various parts of the world (for reviews see Pohl-Riiling, 1990, 1989; Pohl-Riiling and Fischer, 1983; Pohl-Riiling et al., 1978). The goal of this work was to find out whether such an increase occurs even when the lowLET irradiation from the environment rises by less than a factor of 2. In a previous investigation of the population living in the area of Badgastein (Austria) the aberration frequencies rose strongly to twice the lowest environmental burden, but the increase in low-LET irradiation was mixed with an increase of high-LET a irradiation from radon and its decay products (Pohl-Riiling and Fischer, 1979). After the Chernobyl reactor accident (April 26, 1986) Salzburg province in Austria was one of the areas with the highest fallout deposition within Western Europe (WHO, 1986). The mean 3" dose rates outdoors and indoors in Salzburg city were measured frequently and the dose contribution due to incorporated radionuclides was assessed. These studies had commenced many years before the accident and are still going on. Thus there are good data on the doses received by the inhabitants of this city. Materials and methods
The pre-Chernobyl mean natural terrestrial 3" dose rates in Salzburg city were low compared to world-wide averages, because of the predominance of limestone in the subsoil and the low content of natural radionuclides in the local building materials, sand and bricks. They were outdoors 3.4 and indoors 4.5 ttR/h (e.g., Steinh~iusler et al., 1980). From this and the typical seasonal indoor/outdoor lifestyles of the inhabitants and organ shielding factors an average annual blood dose due to external 3' and cosmic irradiation of about 0.7 mGy/y could be estimated. It is not possible to estimate doses to peripheral lymphocytes of which at any time about 2-3070 are in circulating blood. Nevertheless we have assumed the dose to blood to be equivalent to the dose to lymphocytes (Pohl-Riiling and Fischer, 1979). Most of the internal radiation burden from naturally occurring radioactivity is due to the in-
halation of radon and its decay products. The internal ot dose, however, is very inhomogeneously distributed within the various organs and tissues of the body. The ratio between the oe doses to the blood, alveolar tissue and basal ceils of the bronchial epithelium is about 1:20:200 (Pohl and PohlRiiling, 1977). For the inhabitants of Salzburg city the absorbed a dose to blood varies from 0.001 to 0.075 with a mean value of 0.007 mGy/year (Steinh~iuser et al., 1980). Other incorporated radionuclides, mainly K-40 and C-14, contribute about 0.2 mGy/year to the blood dose. From these data plus the external dose the total mean preChernobyl absorbed annual dose to blood of Salzburg citizens was 0.9 mGy/year. The plume emitted from Chernobyl arrived at Salzburg on April 30, 1986. Heavy rainfall washed out radionuclides causing a high contamination of soil and plants. One year after the initial deposition the additional dose rate due to the external 3'-irradiation for the average Salzburg city inhabitant was 0.12+0.02 mGy/year (Steinh/iusler, 1987; Steinh/iusler et al., 1988). It had decreased by April 1988 to 0.08 + 0.02 mGy/year and by January 1990 to 0.07 ± 0.02 (Lettner, 1990, personal communication). The additional internal dose resulted from incorporation of the cesium isotopes Cs-137 and Cs-134 via the food chains grass-milk-meat and soil-vegetables. A small part was also contributed by inhalation (Daschil and Hofmann, 1987). The incorporated cesium is stored in muscle tissue with a biological half-life of 70-100 days. The cesium burden was measured in a whole-body counter with a 7 x 7 inch NaI detector and chair geometry. The measurement for Cs-137 carried errors of 15-30~70. The content of Cs-134 (with a radioactive half-life of 2 years) was measured in the first weeks after the accident to be about half that of Cs-137. From the Cs-137 plus Cs-134 content per kg body weight the dose commitment to the tissue can be calculated by the UNSCEAR (1982) model with the transfer coefficient: P45=2.4×10 -6 G y / B q x k g -1. The sum of the additional mean external and internal 3' dose during the first year (May 1, 1986 to May 1, 1987) for an average Salzburg citizen was assessed
211 TABLE 1 CHROMOSOME ABERRATION FREQUENCIES FROM 2 SALZBURG CITIZENS (A, female and B, male) IN THE YEARS 1984/85, 1987, 1988 AND 1990
Person,
Met,phases
Cs-137 +
Total aberrations
Year
scored
Cs- 134 (mGy/year)
D
R
A 84/85 B 84/85
1314 2956
-
0 3
85 pooled a
4270
-
A 87 B 87
1716 I191
87 pooled a
Aberrations/100 metaphases D + R + ID
D + R + ID + TD
Gaps
2 2
0.08 ± 0.08 0.20 ± 0.08
0.23 ± 0.13 0.27 ± 0.I0
0.23 ± 0.11 0.08 ± 0.08 not scored
4
4
0.16 ± 0.06
0.26 ± 0.08
7 5
4 0
17 II
0.93 ± 0.23 0.92 ± 0.28
1.92 ± 0.33 1.85 ± 0.39
2.05 ± 0.37 0.73 ± 0.26
1.25 ± 0.22 0.55 ± 0.22
II
12
4
28
0.93 ± 0.18
1.89 ± 0.26
1.44 ± 0.23
0.92 ± 0.18
0.037 0.095
I 3
0 0
0 0
0 3
0.39 ± 0.39 0.60 ± 0.35
0.39 ± 0.39 1.20 ± 0.49
0.78 ± 0.55 1.60 ± 0.57
0.78 ± 0.55 0.60 ± 0.35
756
0.075
4
0
0
3
0.53 ± 0.26
0.93 ± 0.35
1.32 ± 0.42
0.66 ± 0.30
A 90
1619
0.011
0
0
4
5
0.25 ± 0.12
0.56 ± 0.19
B 90
805
0.031
1
0
0
5
0.12 ± 0.12
0.75 ± 0.30
0.37 + 0.15 1.24 ± 0.39
0.31 ± 0.14 0.75 ± 0.30
2424
0.018
1
0
4
10
0.21 ± 0.09
0.62 ± 0.16
0.66 ± 0.17
0.45 ± 0.14
ID
TD
0 0
I 3
3
0
0.142 0.239
5 6
2907
0.182
A 88 B 88
256 500
88 pooled a
90 pooled"
Chr.tid Br.
" The means in the pooled values are weighted according to the numbers of scored metaphases. D, dicentrics; R, centric plus acentric rings; ID, interstitial deletions; TD, terminal deletions; Chr.tid Br., chromatid breaks.
2.00
.o q) J~ q)
1.50
1.00
E
+
o
o
E 2
0.50
6
0.00
~4
1965
1966
1987
19bB
1Q89
19b0
1961
Years of measurement
Fig. 1. Chromosome aberrations per 100 metaphases, mean values from persons A and B, in the years 1984/1985 to 1990. (The curves are based on 10,357 metaphases scored.) • Total chromosomal aberrations (dicentrics + rings + interstitial deletions + terminal deletions); • 2-break events (totals minus terminal deletions).
at 0.32 + 0.10 mGy/year, and for high-risk persons (e.g., farmers living at the city periphery handling highly contaminated grass and hay) 1.0+0.30 mGy/year. These values are respectively 36 and 110% higher than the previous normal environmental value (0.9 mGy/year). The Cs-137 contents of the subjects were measured at the time of blood sampling for cytogenetics and varied from 4 to 154 Bq/kg body weight. These values together with the Cs-134 contents, calculated with respect to its initial amount and its half-life, were converted as given above into dose per year. For the 16 persons sampled in 1987 these ranged from 0.013 to 0.492 mGy/year. To this dose the mean external dose rate of 0.12 mGy/year must be added. Blood samples from 7 volunteers were taken on June 9, 1987 and from one of these (A) also on August 25, and from a further 9 persons on July 27, 1987. They were all non-smokers, took no drugs and had no diagnostic X-rays within the last year. The procedures of lymphocyte culture, slide
212
preparation and scoring followed standard methods (e.g., Pohl-Riiling and Fischer, 1979), with 48 h culture time, and different coded slides were distributed for scoring to chosen laboratories. The scientists of these (with the exception of one) had collaborated for about 10 years, and their scoring variabilities had been cross-checked in detail in former investigations and been found to differ only within statistical errors. In all the different slides 23,060 metaphases were analysed. The 16 persons ranged in age from 24 to 69 years. In previous work (Pohl-Riiling et al., 1976) it was shown that induc-
ed aberration yields vary with age and the relationship is probably not linear. We have examined the effect of applying an age (over and under 50 years) correction factor to the present results but this did not change the dose-effect curves derived from the mean values. Therefore in the present work we used the uncorrected values. From 2 of the volunteers we have chromosome aberration data from the years 1984/85 and also 1988 and 1990. These are control values when their blood was used for other investigations. Their mean external plus internal additional dose rates in April 1988 and in
1 o0
4
a) 0.80
0.60
+
0 40
0 20
0o0
000
................... 010
, ......... , ................... 0,20 0,30 0.40
Additional e x t e r n a l
and
000
, ......... , 0.50 0.60
000
........
, ......... , ......... , ......... , ......... , ......... , 0.10 0.20 0.30 0.4-0 0.50 0.60
Additional e x t e r n a l
internal dose in mGy/yr
25O
oo 000 080
2.00
++
1 5O 070060 ~
@
E 2 O50
-~
internal dose in mGy/yr
+
i
C)
t
and
+
1.00
©
!
0.50
oso0 . 0~-~ . . . . . . . . ]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 0.1~0 0.20 0.30 0.4-0 0.50 Additional external and internal dose in mGy/yr
0.00 0.60
0.00
0.10
0.20
0.30
0.40
0.50
0.60
Adtiitional external and internal dose in mGy/yr
Fig. 2. Chromosome aberration per 100 metaphases, versus mean additional external and internal dose (the additional external doses in 1987, 1988 and 1990 were 0.12, 0.08 and 0.07 mGy/year respectively). (The curves are based on 23,060 metaphases.) (a) Total chromosomal aberrations (dicentrics + rings + interstitial deletions + terminal deletions). • from persons A and B; Q from 16 test persons. (b) Two-break events (totals minus terminal deletions). • from persons A and B; [] from 16 test persons. (c) Chromatid breaks. • from persons A and B; e from 16 test persons. (d) Chromatid gaps. * from persons A and B; O from 16 test persons.
213 January 1990 were 0.155 and 0.088 mGy/year, respectively.
Results
The aberration frequencies per 100 metaphases from the 2 persons (A, female, and B, male, aged 38 and 24 years in 1985) who were investigated before and up to 4 years after the accident are summarised in Table 1. The frequencies of the pooled results are weighted according to the numbers of metaphases scored. Because of these low doses and the resulting low effects, for statistical purposes we summarised all chromosomal aberrations (as 'totals') and all the '2-break events' (dicentrics + centric and acentric rings + interstitial deletions). They are plotted against the years of blood sampling in Fig. 1. The increase from the preChernobyl values to those of 1987, by a factor of about 6, is followed by a significant decrease from 1988 until 1990. Although the mean additional radiation burden in 1990 is only about 10°70 higher than the mean annual pre-Chernobyl dose the aberration frequencies are elevated. All pooled values from these 2 persons are included in Fig. 2. Not only the 1987 point but also the 1988 and 1990 values fit very well into the other points with respect to their annual doses. The results for the 16 persons investigated in 1987 are presented in Table 2. The 4 pooled points, each based on 3-5 persons with similar doses, are plotted in relation to annual dose in Fig. 2. The second point contains person A with a large number of scored metaphases as she was bloodsampled twice in 1987. But despite the large weighting factor the pooled results are not much influenced by the yields of person A alone. The third point contains person B but the weighting factor of his results is less than half of the others. Therefore the results of persons A and B are not exceptional and can be regarded together with those of all the other volunteers. From Fig. 2 it can be seen that all aberration frequencies increase from the pre-Chernobyl values derived from persons A and B until an additional
dose rate of about 0.30 mGy/year which corresponds, together with the pre-Chernobyl normal mean environmental dose rate of 0.9 mGy/year, to a total radiation burden of 1.2 mGy/year. At higher doses the frequencies of total chromosomal aberration remain constant or perhaps even decrease, although this cannot be distinguished within the statistical uncertainties shown. The plots of 2-break events, however, show a significant decrease. The curve for chromatid breaks increases and then decreases significantly with a shape qualitatively similar to that of the 2-break events. The gaps, however, did not show any significant correlation with dose. Table 3 presents the slopes and the corresponding correlation coefficients of the best straight lines through the dose-response points over the rising and falling parts of the curve and the entire range. From this table it can be seen that the correlation between the additional dose and the totals as well as the 2-break events is very significant in the rising range with slopes of 5.31+0.46 and 2.40+0.43 aberrations per 100 metaphases per mGy/year, respectively. If, however, we consider the slopes for the entire dose range it is clear that the correlation coefficients are lower and less significant. Discus~on
There have been a few other investigations of the effect of elevated body cesium content on lymphocyte chromosome aberrations. A region in the South of West Germany, bordering Salzburg province, experienced fallout from Chernobyl similar to Salzburg city. An independent investigation of the blood lymphocytes from 10 persons from the town of Berchtesgaden, situated in this area, was carried out by Stephan and Oestreicher (1988, personal communication). About 10,000 metaphases showed 0.38 + 0.06 dicentrics + rings and 1.48 + 0.13 total chromosome aberrations in 100 metaphases. These numbers agree very well with the overall mean value for the 16 Salzburg citizens studied in 1987 of 0.41 +0.05 for dicentrics and rings and 1.40 + 0.09 for total aberrations. Stephan and Oestreicher (1990, personal communication)
214
1.26_+ 0.08. For 11 Berchtesgaden subjects the blood doses were estimated. The pre-Chernobyl environmental dose was 1.35 mGy/year. The highest and the lowest aberration frequencies with 2.2°70 and 0.507o for the totals were found for additional internal dose rates from Cs-137 of 0.27 and from Cs-134 of 0.48 mGy/year. These 2 points fit very well within the statistical error in our Fig. 2a. The results of this absolutely unrelated investigation are perfectly in accord with those presented here.
continued their investigations and have so far scored 14,775 metaphases from 15 persons. They altogether yielded 0.25 _+0.04070 dicentrics + rings and 1.10_+0.09°70 total aberrations. These mean values are lower than those measured before 1988, as the additional dose to the inhabitants also decreased. If we include the results from the 2 persons blood-sampled in 1988 and 1990 to those of 1987 then our corresponding entire mean values also decrease and be,-ome 0.38_+ 0.05 and
TABLE 2 A B E R R A T I O N FREQUENCIES IN T H E BLOOD OF 16 SALZBURG CITIZENS PER 100 METAPHASES A N D CESIUM DOSE IN 1987 Person
Metaphases
Cs-137 +
Total aberrations
No., sex age
scored
Cs-134 (mGy/year)
D
1370 1365 2126
0.013 0.077 0.103
4861
Aberrations/100 metaphases
Ra
ID
TD
D+R+ID
D+R+ID+TD
Gaps
Chr.tid Br.
5 1 7
2 7 1
0 0 0
9 6 12
0.51 ± 0.19 0.59 ± 0.21 0.38 ± 0.13
1.17 ± 0.30 1.03 ± 0.27 0.94 ± 0.21
0.51 ± 0.19 1.42 ± 0.34 0.84 ± 0.20
0.80 ± 0.24 1.03 ± 0.29 0.25 ± 0.11
0.070
13
10
0
27
0.47 ± 0.10
1.02 ± 0.15
0.92 ± 0.14
0.64 ± 0.11
418 683 1716 510
0.118 0.139 0.142 0.151
0 2 5 1
0 2 7 0
3 0 4 2
3 3 17 9
0.71 0.59 0.93 0.59
1.44 1.02 1.92 2.35
2.87 2.20 2.05 2.16
1.67 0.59 1.25 0.20
3327
0.140
8
9
9
32
0.78 ± 0.15
1.74 ± 0.23
2.14 ± 0.26
0.96 ± 0.17
8, m, 65 186 9 = B , m, 26 1191 10, f, 62 328 11, m, 49 2142
0.229 0.239 0.263 0.267
0 6 0 4
0 5 0 2
0 0 1 1
2 II 5 20
0.92 ± 0.28 0.30 ± 0.30 0.32 ± 0.12
1.09 1.85 1.83 1.25
3.80 0.67 4.27 0.73
3.26 0.50 0.30 0.44
Pooled b
3847
0.256
10
7
2
38
0.49 ± 0.11
1.48 ± 0.20
1.21 ± 0.18
0.60 ± 0.13
12, 13, 14, 15,
2050 144 164 736
0.367 0.387 0.388 0.399
6 0 0 1
1 0 0 1
l 0 0 6
18 l 1 10
0.39 ± 0.14 1.09 ± 0.38
1.27 0.69 0.61 2.45
0.67 1.39 2.44 3.26
0.18 0.98 1.23 0.67
0.56 ± 0.17
481
0.492
0
0
3
6
0.27 + 0.19 0.62 ± 0.36
1.63 ± 0.47) 1.87 ± 0.62
4.37 ± 0.95
0.42 ± 0.29
3575
0.392
7
2
10
36
0.53 ± 0.12
1.54 ± 0.21
1.84 ± 0.23
0.49 ± 0.12
7
2
4
36
0.42 +_ 0.10
1, f, 69 2, f, 69 3, m, 41 Pooled b 4, f, 51 5, f, 27 6 = A , f, 40 7, f, 57 Pooled b
m, m, m, m,
44 65 24 53 c
(diploid cell removed: 16, m, 63 Pooled b (diploid cell removed:
± ± ± ±
0.41 0.29 0.23 0.34
± ± ± ±
± ± ± ±
± ± ± ±
0.72 0.39 0.33 0.68
0.78 0.39 0.75 0.24
0.25 0.69 0.61 0.58
± ± ± ±
± ± ± ±
± ± + ±
0.83 0.57 0.37 0.65
1.44 0.24 1.14 0.19
± ± ± ±
± ± ± ±
0.63 0.29 0.22 0.20
1.33 0.21 0.30 0.15
0.54 ± 0.27
1.37 ± 0.20)
a The relatively high numbers of rings occurring in some persons were checked and confirmed. b The means are weighted according to the numbers of metaphases scored. c This person had 6 ID in one diploid cell. As it is debatable whether to include this cell, the values with it removed are also given.
215
TABLE 3 S L O P E A N D C O R R E L A T I O N C O E F F I C I E N T OF C H R O M O S O M E A B E R R A T I O N F R E Q U E N C I E S Range of additional radiation burden (mGy/year)
Aberration
Background up to 0.30
Total D+R+ID Chromatid gaps Chromatid breaks
5.3 2.4 5.8 6.0
± ± ± ±
0.5 0.4 3.9 2.0
0.99 0.94 0.65 0.87
0.25-0.55
Total D+R+ID Chromatid gaps Chromatid breaks
- 1.0 -1.5 1.0 -4.3
± ± ± +
1.0 0.9 5.1 1.8
-0.51 0.70 0.11 -0.82
Background up to 0.55
Total D+R+ID C h r o m a t i d gaps C h r o m a t i d breaks
2.0 0.2 2.8 - 0.4
+ ± ± +
0.7 0.5 2.1 1.3
0.74 0.18 0.47 - 0.12
Stephan and Oestreicher (1989) also investigated the lymphocyte chromosomes of people who returned from 5 towns in the U.S.S.R. and Poland to West Germany soon after the Chernobyl accident. In the range up to 0.5 mSv effective dose equivalent the frequencies of dicentrics were up to a factor of about 100 higher than excpected if extrapolated from in vitro dose-response data obtained at higher doses. The dicentric yields in subjects exposed to higher doses, 0.5 and 2.0 mSv, were lower. Work has also been carried out on chromosome aberrations in Norwegian Lapp reindeer breeders exposed to fallout from the atomic bomb tests between 1965 and 1977 (Evensen et al., 1989). Two groups of persons were studied differing in the amount of reindeer meat consumption and hence levels of incorporated radiocesium. The higherburden group had about twice the additional blood dose and their mean aberration yield was approximately doubled. The results presented in this work reinforce the statement of Pohi-Riiling et al. (1978) on the shape of the dose-response curve for blood lymphocyte chromosomal aberration frequencies at low doses. They described a steep increase in the dose range up to the limit of normal environmental radiation ex-
Slope in % mGy/ycar
Correlation coefficient
posure, followed by a plateau and then by another increase. The explanation proffered for the plateau was that a certain amount of damage to the DNA induced repair mechanisms. This hypothesis has been supported by several investigations published in the last decade (see review by Pohl-Riiling, 1990). The recently found 'adaptive response' in mammalian cells and plants could be an indication that low doses of X-rays are able to induce repair processes (see e.g., Olivieri, 1990; Wolff et al., 1990; Rieger and Takeshisa, 1990). An analysis of inducible repair reactions in living organisms at low dose levels has recently been discussed on the basis of experimental and epidemiological data by Oftedal (1990). Specific examples in the low-dose range lead to an assumption of 2 categories of inducible repair mechanisms. In contrast to the investigations mentioned above, where the plateau starts at about 3-4 mGy/year, there seems to be a repair mechanism which is triggered at an increase above the continuous environmental dose of about 30-40070. This corresponds to an entire dose of 1.2-1.3 mGy/year for the blood of the population investigated in this work. According to different pre-Chernobyl environmental burdens estimated in Salzburg and Berchtesgaden the entire dose for the Berchtes-
216
gaden inhabitants is 1.6 mGy/year (Stephan and Oestreicher, 1990, personal communication). From several papers dealing with repair mechanisms occurring in living cells after damages due to ionising irradiations it could therefore be concluded that there are most probably quite different repair mechanisms, appearing at different dose levels. It can be concluded from this and previous work that the usual method of dose assessment from chromosome aberration frequencies, by linear extrapolation from measurements at high doses to doses in the range or at the border of the normal environment, is not appropriate. Doses estimated in this manner could be 1-2 orders of magnitude too high! Acknowledgement We thank Dr. Margarita Kokoschinegg for sampling the blood from the volunteers and acting as blood donor (person A) many times throughout this and previous work.
References Bosi, A., and G. Oliveri (1989) Variability of the adaptive response to ionizing radiations in human, Mutation Res., 211, 13-71. Daschil, F., and W. Hofmann (1987) Long-term inhalation dose due to resuspension of radionuclides deposited in an urban environment, Workshop on Consequences of an Accidental Contamination of the Urban Environment, Book of Abstracts, Ris6, Denmark. Evensen, J.F., J. Reitan, E.A. Westerlund and A. Brogger (1989) Caesium-137 body burden and chromosome aberrations in Norwegian Lapps, 1965-1978, in: T. Brustad, F. Langmark and J.B. Reitan (Eds.), Radiation and Cancer Risk, Hemisphere, New York, pp. 21-30. Oftedal, P. (1990) A holistic view of low level radiation effects in biological systems, Can. J. Physics, in press. Olivieri, G., and A. Bosi (1990) Possible causes of variability of the adaptive response in human lymphocytes, in: G. Obe and A.T. Natarajan (Eds.), Chromosomal Aberrations, Basic and Applied Aspects, Springer, Heidelberg, in press. Pohl, E., and J. Pohl-Riiling (1977) Dose calculations due to the inhalation of Rn 222, Rn 220 and their daughters, Health Physics, 32, 552-555. Pohl-Riiling, J. (1989) Chromosome aberrations in man in areas
with elevated natural radioactivity, in: Proceedings of the XVth Berzelius Symposium on Somatic and Genetic Effects of Ionizing Radiation, Umea, pp. 103-111. Pohl-Riiling, J. (1990) Chromosome aberrations of blood lymphocytes by low level doses of ionizing radiation, in: G. Obe (Ed.), Advances in Mutagenesis, Vol. I1, Springer, Berlin, pp. 155-190. Pohl-Riiling, J., and P. Fischer (1979) The dose effect relationship of chromosome aberrations to alpha- and gammairradiation in a population subjected to an increased burden of natural radioactivity, Radiat. Res., 80, 61-81. Pohl-Riiling, J., and P. Fischer (1983) Chromosome aberrations in inhabitants of areas with elevated radioactivity, in: T. Ishihara and M.S. Sasaki (Eds.), Radiation-lnduced Chromosome Damage in Man, Liss, New York, pp. 527-560. Pohl-R~ling, J., P. Fischer and E. Pohl (1976) Chromosome aberrations in peripheral blood lymphocytes dependent on various dose levels of natural radioactivity, in: Proceedings of Biological and Environmental Effects of Low-Level Radiation, Vol. I1, IAEA, Vienna, pp. 317-324. Pohl-Riiling, J., P. Fischer and E. Pohl (1978) The low-level shape of dose response for chromosome aberrations, in" Proceedings of International Symposium on the Late Biological Effects of Ionizing Radiation, Vol. II, IAEA, Vienna, pp. 315-326. Pohl-Riiling, J., O. Haas, G. Obe, A. Brogger, E. Roscher, F. Daschil, C. Atzmiiller and A.T. Natarajan (1988) The Chernobyl fallout in Salzburg/Austria and its effects on blood chromosomes, in: Proceedings of the International Symposium on DNA Repair, Chromosome Alterations and Chromatin Structure under Environmental Pollutions, USSR Academy of Science, Moscow, Acta Biol. Hung., in press. Rieger, R., and S. Takeshisa (1990) Adaptive response of plant meristem cells in vivo: protection against induction of chromatid aberrations, in: G. Obe and A.T. Natarajan (Eds.), Chromosomal Aberrations, Basic and Applied Aspects, Springer, Heidelberg, in press. Steinh~iusler, F. (1982) Long-term investigations in Austria of environmental natural sources of ionizing radiation and their impact on man, Ber. Naturw. Med. Vereins Salzburg, 6, 7-50. Steinh~iusler, F. (1987) The effect of fallout deposition on indoor gamma radiation levels in single family dwellings, Proceedings Workshop on Consequences of an Accidental Contamination of the Urban Environment, Roskilde, Denmark, Radiat. Protect. Dosimetry, 21, 103-105. Steinh~iusler, F., W. Hofmann, E. Pohl and J. Pohl-RiJling (1980) Local and temporal distribution pattern of radon and daughters in an urban environment and determination of organ dose frequency distributions with demoscopical methods, in: Proceedings of the Symposium on Natural Radiation Environment III, Houston, TX, Vol. 2, pp. 1145-1161.
Steinh~iusler, F., W. Hofmann, F. Daschil and B. Reubel (1988) Chernobyl and its radiological consequences for the province
217 of Salzburg, Austria, in: The Chernobyl Accident: Regional and Global Impact, Environ. Int., 14/2. Stephan, G., and U. Oestreicher (1989) An increased frequency of structural chromosome aberrations in persons present in the vicinity of Chernobyl during and after the reactor accident. Is this effect caused by radiation exposure?, Mutation Res., 223, 7-12. UNSCEAR (1982) Ionizing Radiation: Sources and Biological Effects. Report to the General Assembly, with Annexes, UNSCEAR, New York.
WHO (1986) Summary Report No. ICP/COR 129 (S) Rev. 1.5134 V, WHO, Geneva. Wolff, S., G. Olivieri and V. Afzal (1990) Adaptation of human lymphocytes to radiation or chemical mutagens: differences in cytogenetic repair, in: G. Ohe and A.T. Natarajan (Eds.), Chromosomal Aberrations, Basic and Applied Aspects, Springer, Heidelberg, in press. Communicated by F.H. Sobels
209
MUTLET 0471
The effect on lymphocyte chromosomes of additional radiation burden due to fallout in Salzburg (Austria) from the Chernobyl accident J. Pohl-Rfiling 1, O. Haas 2, A. Brogger a, G. Obe 4, H. Lcttncr 1, F. Daschil 1, C. Atzmiiller 1, D. Lloyd s, R. Kubiak 6 and A.T. Natarajan 7 1Division of Biophysics, University of Salzburg (Austria), 2St. Anna Children's Hospital, Vienna (Austria), 3Department of Genetics, Institutefor Cancer Research, Montebello, Oslo (Norway), 4Department of Genetics, University of Essen ( F.R.G.), SNational Radiological Protection Board, Chilton, Didcot ( U.K.), ~Instituteof Systematic and Experimental Zoology, Polish Academy of Science, Cracow (Poland) and 7Department of Radiation Genetics and Chemical Mutagenesis, State University of Leiden ( The Netherlands) (Received 28 May 1990) (Revision received 12 November 1990) (Accepted 16 November 1990)
Keywords: Chromosome aberration; Chernobyl fallout; Radiation burden
Summary An investigation has been carried out to determine whether chromosome aberrations in peripheral blood lymphocytes reflect the elevated environmental dose of low-LET ionising radiation, mainly due to radiocesium from Chernobyl fallout, to the population living in Salzburg city. Sixteen volunteers were sampled 1 year after the Chernobyl accident. Two of these persons were also sampled before the accident, and then in 1988 and 1990. The radioactive environment of Salzburg city and the radiation burden of its inhabitants have been frequently determined before and after the accident. The Cs-137 content of the volunteers was measured by whole-bodY counting. The additional external plus internal radiation doses in the year 1987 to the tested individuals ranged between 15 and 68% of the former normal environmental burden. The aberration frequencies showed a sharp increase of about a factor 6 from the pre-Chernobyl dose rate (0.9. mGy/year) to the post-Chernobyl dose rate (about 2 mGy/year total) but then decreased again with higher additional dose. In the two persons analysed before and up to 4 years after the accident the aberration yield showed a significant increase from 1984/85 to 1987, a decrease in 1988 and a further decrease in 1990. If these last 2 values are plotted against additional dose they fit the curve of the pooled 1987 values. The dose-effect curves revealed the same tendency as we found in various previous investigations and support the assumption that repair enzymes could be triggered by a certain amount of damage to the DNA.
Correspondence: Dr. J. Pohl-Rfiling, Division of Biophysics, University of Salzburg, Hellbrunnerstr. 34, A-5020 Salzburg
(Austria).
An increase in chromosome aberrations in peripheral blood lymphocytes of persons living and/or working in an environment with elevated
210
radioactivity has been found in various parts of the world (for reviews see Pohl-Riiling, 1990, 1989; Pohl-Riiling and Fischer, 1983; Pohl-Riiling et al., 1978). The goal of this work was to find out whether such an increase occurs even when the lowLET irradiation from the environment rises by less than a factor of 2. In a previous investigation of the population living in the area of Badgastein (Austria) the aberration frequencies rose strongly to twice the lowest environmental burden, but the increase in low-LET irradiation was mixed with an increase of high-LET a irradiation from radon and its decay products (Pohl-Riiling and Fischer, 1979). After the Chernobyl reactor accident (April 26, 1986) Salzburg province in Austria was one of the areas with the highest fallout deposition within Western Europe (WHO, 1986). The mean 3" dose rates outdoors and indoors in Salzburg city were measured frequently and the dose contribution due to incorporated radionuclides was assessed. These studies had commenced many years before the accident and are still going on. Thus there are good data on the doses received by the inhabitants of this city. Materials and methods
The pre-Chernobyl mean natural terrestrial 3" dose rates in Salzburg city were low compared to world-wide averages, because of the predominance of limestone in the subsoil and the low content of natural radionuclides in the local building materials, sand and bricks. They were outdoors 3.4 and indoors 4.5 ttR/h (e.g., Steinh~iusler et al., 1980). From this and the typical seasonal indoor/outdoor lifestyles of the inhabitants and organ shielding factors an average annual blood dose due to external 3' and cosmic irradiation of about 0.7 mGy/y could be estimated. It is not possible to estimate doses to peripheral lymphocytes of which at any time about 2-3070 are in circulating blood. Nevertheless we have assumed the dose to blood to be equivalent to the dose to lymphocytes (Pohl-Riiling and Fischer, 1979). Most of the internal radiation burden from naturally occurring radioactivity is due to the in-
halation of radon and its decay products. The internal ot dose, however, is very inhomogeneously distributed within the various organs and tissues of the body. The ratio between the oe doses to the blood, alveolar tissue and basal ceils of the bronchial epithelium is about 1:20:200 (Pohl and PohlRiiling, 1977). For the inhabitants of Salzburg city the absorbed a dose to blood varies from 0.001 to 0.075 with a mean value of 0.007 mGy/year (Steinh~iuser et al., 1980). Other incorporated radionuclides, mainly K-40 and C-14, contribute about 0.2 mGy/year to the blood dose. From these data plus the external dose the total mean preChernobyl absorbed annual dose to blood of Salzburg citizens was 0.9 mGy/year. The plume emitted from Chernobyl arrived at Salzburg on April 30, 1986. Heavy rainfall washed out radionuclides causing a high contamination of soil and plants. One year after the initial deposition the additional dose rate due to the external 3'-irradiation for the average Salzburg city inhabitant was 0.12+0.02 mGy/year (Steinh/iusler, 1987; Steinh/iusler et al., 1988). It had decreased by April 1988 to 0.08 + 0.02 mGy/year and by January 1990 to 0.07 ± 0.02 (Lettner, 1990, personal communication). The additional internal dose resulted from incorporation of the cesium isotopes Cs-137 and Cs-134 via the food chains grass-milk-meat and soil-vegetables. A small part was also contributed by inhalation (Daschil and Hofmann, 1987). The incorporated cesium is stored in muscle tissue with a biological half-life of 70-100 days. The cesium burden was measured in a whole-body counter with a 7 x 7 inch NaI detector and chair geometry. The measurement for Cs-137 carried errors of 15-30~70. The content of Cs-134 (with a radioactive half-life of 2 years) was measured in the first weeks after the accident to be about half that of Cs-137. From the Cs-137 plus Cs-134 content per kg body weight the dose commitment to the tissue can be calculated by the UNSCEAR (1982) model with the transfer coefficient: P45=2.4×10 -6 G y / B q x k g -1. The sum of the additional mean external and internal 3' dose during the first year (May 1, 1986 to May 1, 1987) for an average Salzburg citizen was assessed
211 TABLE 1 CHROMOSOME ABERRATION FREQUENCIES FROM 2 SALZBURG CITIZENS (A, female and B, male) IN THE YEARS 1984/85, 1987, 1988 AND 1990
Person,
Met,phases
Cs-137 +
Total aberrations
Year
scored
Cs- 134 (mGy/year)
D
R
A 84/85 B 84/85
1314 2956
-
0 3
85 pooled a
4270
-
A 87 B 87
1716 I191
87 pooled a
Aberrations/100 metaphases D + R + ID
D + R + ID + TD
Gaps
2 2
0.08 ± 0.08 0.20 ± 0.08
0.23 ± 0.13 0.27 ± 0.I0
0.23 ± 0.11 0.08 ± 0.08 not scored
4
4
0.16 ± 0.06
0.26 ± 0.08
7 5
4 0
17 II
0.93 ± 0.23 0.92 ± 0.28
1.92 ± 0.33 1.85 ± 0.39
2.05 ± 0.37 0.73 ± 0.26
1.25 ± 0.22 0.55 ± 0.22
II
12
4
28
0.93 ± 0.18
1.89 ± 0.26
1.44 ± 0.23
0.92 ± 0.18
0.037 0.095
I 3
0 0
0 0
0 3
0.39 ± 0.39 0.60 ± 0.35
0.39 ± 0.39 1.20 ± 0.49
0.78 ± 0.55 1.60 ± 0.57
0.78 ± 0.55 0.60 ± 0.35
756
0.075
4
0
0
3
0.53 ± 0.26
0.93 ± 0.35
1.32 ± 0.42
0.66 ± 0.30
A 90
1619
0.011
0
0
4
5
0.25 ± 0.12
0.56 ± 0.19
B 90
805
0.031
1
0
0
5
0.12 ± 0.12
0.75 ± 0.30
0.37 + 0.15 1.24 ± 0.39
0.31 ± 0.14 0.75 ± 0.30
2424
0.018
1
0
4
10
0.21 ± 0.09
0.62 ± 0.16
0.66 ± 0.17
0.45 ± 0.14
ID
TD
0 0
I 3
3
0
0.142 0.239
5 6
2907
0.182
A 88 B 88
256 500
88 pooled a
90 pooled"
Chr.tid Br.
" The means in the pooled values are weighted according to the numbers of scored metaphases. D, dicentrics; R, centric plus acentric rings; ID, interstitial deletions; TD, terminal deletions; Chr.tid Br., chromatid breaks.
2.00
.o q) J~ q)
1.50
1.00
E
+
o
o
E 2
0.50
6
0.00
~4
1965
1966
1987
19bB
1Q89
19b0
1961
Years of measurement
Fig. 1. Chromosome aberrations per 100 metaphases, mean values from persons A and B, in the years 1984/1985 to 1990. (The curves are based on 10,357 metaphases scored.) • Total chromosomal aberrations (dicentrics + rings + interstitial deletions + terminal deletions); • 2-break events (totals minus terminal deletions).
at 0.32 + 0.10 mGy/year, and for high-risk persons (e.g., farmers living at the city periphery handling highly contaminated grass and hay) 1.0+0.30 mGy/year. These values are respectively 36 and 110% higher than the previous normal environmental value (0.9 mGy/year). The Cs-137 contents of the subjects were measured at the time of blood sampling for cytogenetics and varied from 4 to 154 Bq/kg body weight. These values together with the Cs-134 contents, calculated with respect to its initial amount and its half-life, were converted as given above into dose per year. For the 16 persons sampled in 1987 these ranged from 0.013 to 0.492 mGy/year. To this dose the mean external dose rate of 0.12 mGy/year must be added. Blood samples from 7 volunteers were taken on June 9, 1987 and from one of these (A) also on August 25, and from a further 9 persons on July 27, 1987. They were all non-smokers, took no drugs and had no diagnostic X-rays within the last year. The procedures of lymphocyte culture, slide
212
preparation and scoring followed standard methods (e.g., Pohl-Riiling and Fischer, 1979), with 48 h culture time, and different coded slides were distributed for scoring to chosen laboratories. The scientists of these (with the exception of one) had collaborated for about 10 years, and their scoring variabilities had been cross-checked in detail in former investigations and been found to differ only within statistical errors. In all the different slides 23,060 metaphases were analysed. The 16 persons ranged in age from 24 to 69 years. In previous work (Pohl-Riiling et al., 1976) it was shown that induc-
ed aberration yields vary with age and the relationship is probably not linear. We have examined the effect of applying an age (over and under 50 years) correction factor to the present results but this did not change the dose-effect curves derived from the mean values. Therefore in the present work we used the uncorrected values. From 2 of the volunteers we have chromosome aberration data from the years 1984/85 and also 1988 and 1990. These are control values when their blood was used for other investigations. Their mean external plus internal additional dose rates in April 1988 and in
1 o0
4
a) 0.80
0.60
+
0 40
0 20
0o0
000
................... 010
, ......... , ................... 0,20 0,30 0.40
Additional e x t e r n a l
and
000
, ......... , 0.50 0.60
000
........
, ......... , ......... , ......... , ......... , ......... , 0.10 0.20 0.30 0.4-0 0.50 0.60
Additional e x t e r n a l
internal dose in mGy/yr
25O
oo 000 080
2.00
++
1 5O 070060 ~
@
E 2 O50
-~
internal dose in mGy/yr
+
i
C)
t
and
+
1.00
©
!
0.50
oso0 . 0~-~ . . . . . . . . ]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 0.1~0 0.20 0.30 0.4-0 0.50 Additional external and internal dose in mGy/yr
0.00 0.60
0.00
0.10
0.20
0.30
0.40
0.50
0.60
Adtiitional external and internal dose in mGy/yr
Fig. 2. Chromosome aberration per 100 metaphases, versus mean additional external and internal dose (the additional external doses in 1987, 1988 and 1990 were 0.12, 0.08 and 0.07 mGy/year respectively). (The curves are based on 23,060 metaphases.) (a) Total chromosomal aberrations (dicentrics + rings + interstitial deletions + terminal deletions). • from persons A and B; Q from 16 test persons. (b) Two-break events (totals minus terminal deletions). • from persons A and B; [] from 16 test persons. (c) Chromatid breaks. • from persons A and B; e from 16 test persons. (d) Chromatid gaps. * from persons A and B; O from 16 test persons.
213 January 1990 were 0.155 and 0.088 mGy/year, respectively.
Results
The aberration frequencies per 100 metaphases from the 2 persons (A, female, and B, male, aged 38 and 24 years in 1985) who were investigated before and up to 4 years after the accident are summarised in Table 1. The frequencies of the pooled results are weighted according to the numbers of metaphases scored. Because of these low doses and the resulting low effects, for statistical purposes we summarised all chromosomal aberrations (as 'totals') and all the '2-break events' (dicentrics + centric and acentric rings + interstitial deletions). They are plotted against the years of blood sampling in Fig. 1. The increase from the preChernobyl values to those of 1987, by a factor of about 6, is followed by a significant decrease from 1988 until 1990. Although the mean additional radiation burden in 1990 is only about 10°70 higher than the mean annual pre-Chernobyl dose the aberration frequencies are elevated. All pooled values from these 2 persons are included in Fig. 2. Not only the 1987 point but also the 1988 and 1990 values fit very well into the other points with respect to their annual doses. The results for the 16 persons investigated in 1987 are presented in Table 2. The 4 pooled points, each based on 3-5 persons with similar doses, are plotted in relation to annual dose in Fig. 2. The second point contains person A with a large number of scored metaphases as she was bloodsampled twice in 1987. But despite the large weighting factor the pooled results are not much influenced by the yields of person A alone. The third point contains person B but the weighting factor of his results is less than half of the others. Therefore the results of persons A and B are not exceptional and can be regarded together with those of all the other volunteers. From Fig. 2 it can be seen that all aberration frequencies increase from the pre-Chernobyl values derived from persons A and B until an additional
dose rate of about 0.30 mGy/year which corresponds, together with the pre-Chernobyl normal mean environmental dose rate of 0.9 mGy/year, to a total radiation burden of 1.2 mGy/year. At higher doses the frequencies of total chromosomal aberration remain constant or perhaps even decrease, although this cannot be distinguished within the statistical uncertainties shown. The plots of 2-break events, however, show a significant decrease. The curve for chromatid breaks increases and then decreases significantly with a shape qualitatively similar to that of the 2-break events. The gaps, however, did not show any significant correlation with dose. Table 3 presents the slopes and the corresponding correlation coefficients of the best straight lines through the dose-response points over the rising and falling parts of the curve and the entire range. From this table it can be seen that the correlation between the additional dose and the totals as well as the 2-break events is very significant in the rising range with slopes of 5.31+0.46 and 2.40+0.43 aberrations per 100 metaphases per mGy/year, respectively. If, however, we consider the slopes for the entire dose range it is clear that the correlation coefficients are lower and less significant. Discus~on
There have been a few other investigations of the effect of elevated body cesium content on lymphocyte chromosome aberrations. A region in the South of West Germany, bordering Salzburg province, experienced fallout from Chernobyl similar to Salzburg city. An independent investigation of the blood lymphocytes from 10 persons from the town of Berchtesgaden, situated in this area, was carried out by Stephan and Oestreicher (1988, personal communication). About 10,000 metaphases showed 0.38 + 0.06 dicentrics + rings and 1.48 + 0.13 total chromosome aberrations in 100 metaphases. These numbers agree very well with the overall mean value for the 16 Salzburg citizens studied in 1987 of 0.41 +0.05 for dicentrics and rings and 1.40 + 0.09 for total aberrations. Stephan and Oestreicher (1990, personal communication)
214
1.26_+ 0.08. For 11 Berchtesgaden subjects the blood doses were estimated. The pre-Chernobyl environmental dose was 1.35 mGy/year. The highest and the lowest aberration frequencies with 2.2°70 and 0.507o for the totals were found for additional internal dose rates from Cs-137 of 0.27 and from Cs-134 of 0.48 mGy/year. These 2 points fit very well within the statistical error in our Fig. 2a. The results of this absolutely unrelated investigation are perfectly in accord with those presented here.
continued their investigations and have so far scored 14,775 metaphases from 15 persons. They altogether yielded 0.25 _+0.04070 dicentrics + rings and 1.10_+0.09°70 total aberrations. These mean values are lower than those measured before 1988, as the additional dose to the inhabitants also decreased. If we include the results from the 2 persons blood-sampled in 1988 and 1990 to those of 1987 then our corresponding entire mean values also decrease and be,-ome 0.38_+ 0.05 and
TABLE 2 A B E R R A T I O N FREQUENCIES IN T H E BLOOD OF 16 SALZBURG CITIZENS PER 100 METAPHASES A N D CESIUM DOSE IN 1987 Person
Metaphases
Cs-137 +
Total aberrations
No., sex age
scored
Cs-134 (mGy/year)
D
1370 1365 2126
0.013 0.077 0.103
4861
Aberrations/100 metaphases
Ra
ID
TD
D+R+ID
D+R+ID+TD
Gaps
Chr.tid Br.
5 1 7
2 7 1
0 0 0
9 6 12
0.51 ± 0.19 0.59 ± 0.21 0.38 ± 0.13
1.17 ± 0.30 1.03 ± 0.27 0.94 ± 0.21
0.51 ± 0.19 1.42 ± 0.34 0.84 ± 0.20
0.80 ± 0.24 1.03 ± 0.29 0.25 ± 0.11
0.070
13
10
0
27
0.47 ± 0.10
1.02 ± 0.15
0.92 ± 0.14
0.64 ± 0.11
418 683 1716 510
0.118 0.139 0.142 0.151
0 2 5 1
0 2 7 0
3 0 4 2
3 3 17 9
0.71 0.59 0.93 0.59
1.44 1.02 1.92 2.35
2.87 2.20 2.05 2.16
1.67 0.59 1.25 0.20
3327
0.140
8
9
9
32
0.78 ± 0.15
1.74 ± 0.23
2.14 ± 0.26
0.96 ± 0.17
8, m, 65 186 9 = B , m, 26 1191 10, f, 62 328 11, m, 49 2142
0.229 0.239 0.263 0.267
0 6 0 4
0 5 0 2
0 0 1 1
2 II 5 20
0.92 ± 0.28 0.30 ± 0.30 0.32 ± 0.12
1.09 1.85 1.83 1.25
3.80 0.67 4.27 0.73
3.26 0.50 0.30 0.44
Pooled b
3847
0.256
10
7
2
38
0.49 ± 0.11
1.48 ± 0.20
1.21 ± 0.18
0.60 ± 0.13
12, 13, 14, 15,
2050 144 164 736
0.367 0.387 0.388 0.399
6 0 0 1
1 0 0 1
l 0 0 6
18 l 1 10
0.39 ± 0.14 1.09 ± 0.38
1.27 0.69 0.61 2.45
0.67 1.39 2.44 3.26
0.18 0.98 1.23 0.67
0.56 ± 0.17
481
0.492
0
0
3
6
0.27 + 0.19 0.62 ± 0.36
1.63 ± 0.47) 1.87 ± 0.62
4.37 ± 0.95
0.42 ± 0.29
3575
0.392
7
2
10
36
0.53 ± 0.12
1.54 ± 0.21
1.84 ± 0.23
0.49 ± 0.12
7
2
4
36
0.42 +_ 0.10
1, f, 69 2, f, 69 3, m, 41 Pooled b 4, f, 51 5, f, 27 6 = A , f, 40 7, f, 57 Pooled b
m, m, m, m,
44 65 24 53 c
(diploid cell removed: 16, m, 63 Pooled b (diploid cell removed:
± ± ± ±
0.41 0.29 0.23 0.34
± ± ± ±
± ± ± ±
± ± ± ±
0.72 0.39 0.33 0.68
0.78 0.39 0.75 0.24
0.25 0.69 0.61 0.58
± ± ± ±
± ± ± ±
± ± + ±
0.83 0.57 0.37 0.65
1.44 0.24 1.14 0.19
± ± ± ±
± ± ± ±
0.63 0.29 0.22 0.20
1.33 0.21 0.30 0.15
0.54 ± 0.27
1.37 ± 0.20)
a The relatively high numbers of rings occurring in some persons were checked and confirmed. b The means are weighted according to the numbers of metaphases scored. c This person had 6 ID in one diploid cell. As it is debatable whether to include this cell, the values with it removed are also given.
215
TABLE 3 S L O P E A N D C O R R E L A T I O N C O E F F I C I E N T OF C H R O M O S O M E A B E R R A T I O N F R E Q U E N C I E S Range of additional radiation burden (mGy/year)
Aberration
Background up to 0.30
Total D+R+ID Chromatid gaps Chromatid breaks
5.3 2.4 5.8 6.0
± ± ± ±
0.5 0.4 3.9 2.0
0.99 0.94 0.65 0.87
0.25-0.55
Total D+R+ID Chromatid gaps Chromatid breaks
- 1.0 -1.5 1.0 -4.3
± ± ± +
1.0 0.9 5.1 1.8
-0.51 0.70 0.11 -0.82
Background up to 0.55
Total D+R+ID C h r o m a t i d gaps C h r o m a t i d breaks
2.0 0.2 2.8 - 0.4
+ ± ± +
0.7 0.5 2.1 1.3
0.74 0.18 0.47 - 0.12
Stephan and Oestreicher (1989) also investigated the lymphocyte chromosomes of people who returned from 5 towns in the U.S.S.R. and Poland to West Germany soon after the Chernobyl accident. In the range up to 0.5 mSv effective dose equivalent the frequencies of dicentrics were up to a factor of about 100 higher than excpected if extrapolated from in vitro dose-response data obtained at higher doses. The dicentric yields in subjects exposed to higher doses, 0.5 and 2.0 mSv, were lower. Work has also been carried out on chromosome aberrations in Norwegian Lapp reindeer breeders exposed to fallout from the atomic bomb tests between 1965 and 1977 (Evensen et al., 1989). Two groups of persons were studied differing in the amount of reindeer meat consumption and hence levels of incorporated radiocesium. The higherburden group had about twice the additional blood dose and their mean aberration yield was approximately doubled. The results presented in this work reinforce the statement of Pohi-Riiling et al. (1978) on the shape of the dose-response curve for blood lymphocyte chromosomal aberration frequencies at low doses. They described a steep increase in the dose range up to the limit of normal environmental radiation ex-
Slope in % mGy/ycar
Correlation coefficient
posure, followed by a plateau and then by another increase. The explanation proffered for the plateau was that a certain amount of damage to the DNA induced repair mechanisms. This hypothesis has been supported by several investigations published in the last decade (see review by Pohl-Riiling, 1990). The recently found 'adaptive response' in mammalian cells and plants could be an indication that low doses of X-rays are able to induce repair processes (see e.g., Olivieri, 1990; Wolff et al., 1990; Rieger and Takeshisa, 1990). An analysis of inducible repair reactions in living organisms at low dose levels has recently been discussed on the basis of experimental and epidemiological data by Oftedal (1990). Specific examples in the low-dose range lead to an assumption of 2 categories of inducible repair mechanisms. In contrast to the investigations mentioned above, where the plateau starts at about 3-4 mGy/year, there seems to be a repair mechanism which is triggered at an increase above the continuous environmental dose of about 30-40070. This corresponds to an entire dose of 1.2-1.3 mGy/year for the blood of the population investigated in this work. According to different pre-Chernobyl environmental burdens estimated in Salzburg and Berchtesgaden the entire dose for the Berchtes-
216
gaden inhabitants is 1.6 mGy/year (Stephan and Oestreicher, 1990, personal communication). From several papers dealing with repair mechanisms occurring in living cells after damages due to ionising irradiations it could therefore be concluded that there are most probably quite different repair mechanisms, appearing at different dose levels. It can be concluded from this and previous work that the usual method of dose assessment from chromosome aberration frequencies, by linear extrapolation from measurements at high doses to doses in the range or at the border of the normal environment, is not appropriate. Doses estimated in this manner could be 1-2 orders of magnitude too high! Acknowledgement We thank Dr. Margarita Kokoschinegg for sampling the blood from the volunteers and acting as blood donor (person A) many times throughout this and previous work.
References Bosi, A., and G. Oliveri (1989) Variability of the adaptive response to ionizing radiations in human, Mutation Res., 211, 13-71. Daschil, F., and W. Hofmann (1987) Long-term inhalation dose due to resuspension of radionuclides deposited in an urban environment, Workshop on Consequences of an Accidental Contamination of the Urban Environment, Book of Abstracts, Ris6, Denmark. Evensen, J.F., J. Reitan, E.A. Westerlund and A. Brogger (1989) Caesium-137 body burden and chromosome aberrations in Norwegian Lapps, 1965-1978, in: T. Brustad, F. Langmark and J.B. Reitan (Eds.), Radiation and Cancer Risk, Hemisphere, New York, pp. 21-30. Oftedal, P. (1990) A holistic view of low level radiation effects in biological systems, Can. J. Physics, in press. Olivieri, G., and A. Bosi (1990) Possible causes of variability of the adaptive response in human lymphocytes, in: G. Obe and A.T. Natarajan (Eds.), Chromosomal Aberrations, Basic and Applied Aspects, Springer, Heidelberg, in press. Pohl, E., and J. Pohl-Riiling (1977) Dose calculations due to the inhalation of Rn 222, Rn 220 and their daughters, Health Physics, 32, 552-555. Pohl-Riiling, J. (1989) Chromosome aberrations in man in areas
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217 of Salzburg, Austria, in: The Chernobyl Accident: Regional and Global Impact, Environ. Int., 14/2. Stephan, G., and U. Oestreicher (1989) An increased frequency of structural chromosome aberrations in persons present in the vicinity of Chernobyl during and after the reactor accident. Is this effect caused by radiation exposure?, Mutation Res., 223, 7-12. UNSCEAR (1982) Ionizing Radiation: Sources and Biological Effects. Report to the General Assembly, with Annexes, UNSCEAR, New York.
WHO (1986) Summary Report No. ICP/COR 129 (S) Rev. 1.5134 V, WHO, Geneva. Wolff, S., G. Olivieri and V. Afzal (1990) Adaptation of human lymphocytes to radiation or chemical mutagens: differences in cytogenetic repair, in: G. Ohe and A.T. Natarajan (Eds.), Chromosomal Aberrations, Basic and Applied Aspects, Springer, Heidelberg, in press. Communicated by F.H. Sobels
