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Ibxicology letters

Toxicology Letters 76 ( 1995) 113- I I7

Chromosomal damage in workers occupationally exposed to chronic low level ionizing radiation

Alfred0 H. Hagelstriim, Nora B. Gorla*, Irene B. Larripa

Departamento de GenPtica, Institute de Investigaciones Hematoldgicas. Academia National de Medicina,

J.A Pacheco de Melo 3081, 1425 Buenos Aires. Argentina

Received 18 March 1994; revision received 2 September 1994; accepted 5 September 1994

Abstract

Chromosomal aberrations were evaluated in cultures of peripheral lymphocytes from subjects working in diagnostic X-ray and nuclear medicine areas, exposed to electromagnetic ionizing radiation and particulate ionizing emissions, respectively. A 4-fold increase in the level of chromosomal aberrations was found between the exposed and control groups without qualitative or quantitative cytogenetic differences between X-rays and nuclear medicine-exposed workers. Results are discussed in view of the early damage detection from chronic exposures particularly related to biological controls, hygienic improvements and overwork in a developing country.

Keywords: Biomonitoring; Occupational radiation exposure; Chromosomal damage

1. Introduction

Chromosomal aberrations, as a measurement of human exposure to ionizing radiation, have become a well-established methodology during the past 2 or 3 decades. Human lymphocytes exposed to radiation in vitro account for almost the entire literature in the area. Fewer data are available on the genetic effects of human in vivo exposure to radiation, except the observations of genetic con- sequences after acute accidental exposures, i.e.

l Corresponding author, Genetica, Departamento de ProducGn Animal, Facultad de Agronomia y Veterinaria, Universidad National de Rio Cuarto, ruta 36, km 601, Rio Cuarto (Cba), Argentina.

evaluations in survivors of the nuclear attacks on Hiroshima and Nagasaki [ 1,2] and, more recently and to a lesser extent, the Chernobyl and Goiana nuclear accidents [3,4]. Thus, the supposed effects of radiation used for diagnostic purposes in medi- cal practice are extrapolations from the unequi- vocal effects observed at high doses. Evaluations of the cytogenetic impact of chronic low dose radi- ation exposure are scarce. The literature shows cytogenetic effects in radiological technologists exposed to low level radiation [5,6] and there are limited data linking radiation doses from diagnos- tic procedures in nuclear medicine with deleterious genetic effects [7].

In the present study, chromosomal aberrations were evaluated from cultures of peripheral lym-

0378-4274/95/XJ9.50 0 1995 Elsevier Science Ireland Ltd. All rights reserved

SSDI 0378-4274(94)03204-K

114 A.H. Hagelstriim er al. / Toxicol. ht. 76 (1995) 113-117

phocytes of subjects working in diagnostic X-ray and nuclear medicine areas exposed to elec- tromagnetic ionizing radiation and particulate ion- izing emissions, respectively.

2. Materials and methods

2.1. Subjects Blood samples were obtained from 20 hospital

workers exposed to low level ionizing radiation in nuclear medicine and radiodiagnostic areas at 4 different hospitals of Buenos Aires, Argentina. Of these, 10 subjects (3 physicians and 7 technicians) belonged to nuclear medicine areas and were ex- posed to particulate ionizing radiation (Table 1) and 10 subjects (3 physicians and 7 technicians) worked in radiodiagnostic areas and were exposed to predominantly electromagnetic ionizing radia- tion (Table 2). All of them gave their oral consent to participate in this study. We have also cytogenetically studied 2 groups of unexposed controls. The 20 control subjects used in this study, and the 20 exposed subjects, were selected on the basis of a questionnaire detailing habits, sex and age. Only individuals without concurrent in- fections and medications and no general and den- tal X-rays in the last 6 months were admitted. Individuals did not consume more than 3 cups of coffee per day and 10 cigarettes per day. Each ex- posed subject culture was set up with a control one with the same sex and range age (approximately 25-40 or 40-60 years old).

Data concerning the total 40 subjects are shown in Tables 1 and 2. All the workers of nuclear medi- cine areas were exposed to particulate emissions from radioactive isotopes (32P, 67Ga, In 201T1, 59Fe, 57Co, SICr, 99mTc, 131, 1921r). Thk dose absorbed in exposed subjects film badges indicated a mean of 47 mrads (nuclear medicine areas workers) and 180 mrads (radiodiagnostic areas workers) over the prior 6 months.

2.2. Cytogenetics Blood samples were obtained by venipuncture

and collected into heparinized tubes. Lymphocytes were cultured for 72 h at 37C according to the method of Moorhead et al. [S]. Cultures were set up with 0.8 ml whole blood, 8.5 ml FlO nutrient

mixture medium (Gibco Laboratories), 15% heat- inactivated fetal bovine serum, certified grade (Gibco Laboratories) and 0.1 ml phytohemag- glutinin-M (Gibco Laboratories). Colcemid solu- tion (Gibco Laboratories), 0.1 ml, was present in the cultures for the final 1.5 h. The cells were harvested by exposure to hypotonic shock with potassium chloride 0.075 M for 20 min at 37C, and fixation in methanol and acetic acid 3: 1. Slides were prepared and conventionally stained with Giemsa. The coded slides were scored blind by 2 observers. At least 100 cells per individual were analyzed for the number and type of chromosomal aberrations. Chromosome aberrations were classified according to ISCN [9]. Cells with less than 44 chromosomes were not included. Students t-test was performed to determine the difference between exposed and control groups.

The significance of differences was assessed using a two-way ANOVA model with multifac- torial experiment for sex, radiation exposure and their interactions. In order to normalize the chro- mosomal aberrations distribution and to equalize the variances, a logarithmic transformation was applied.

3. Results and discussion

Tables 1 and 2 give data on the age, sex, and re- sults of the chromosome aberration analysis per- formed in blood lymphocytes of the 4 groups studied. In the control groups, the mean frequency of chromosomal aberrations1100 cells was 3.6 f 0.5 and 2.8 f 0.3 in the particulate and elec- tromagnetic studies, respectively. In the radiation- exposed groups the mean value was 13.6 f 1.5 for the nuclear medicine-, and 13.6 f 1.3 for the X- ray-exposed groups, respectively. These frequen- cies were statistically different (P < 0.0001) between control and exposed groups. Statistically, no differences were observed between female or male exposure to either type of ionizing radiation.

The 4-fold increase in the level of chromosomal aberrations due to an occupational exposure to ionizing radiation is biologically significant. We did not find differences in the level of chromo- somal aberrations induced by either type of ioniz- ing radiation, (electromagnetic or predominantly

A.H. Hagelstriim et al. / Toxicol. Lett. 76 (1995) 113-117 115

Table I Chromosomal aberrations in blood lymphocytes from subjects occupationally exposed to particulate ionizing radiation and controls

Group Chromosomal aberrations

No. Sex Age ctg csg ctb csb

Mean aberrations/ 100 cells

end ace qr

Nuclear medicine I M 35 2 F 41 3 F 30 4 M 28 5 M 32 6 M 54 I F 44 8 F 46 9 M 28 IO F 60 Mean f S.D.

Controls II F 28 I2 M 38 I3 M >20 I4 M >20 I5 F >20 I6 F 32 I7 M 48 I8 M 25 I9 F 32 20 F 26 Mean f S.D.

8 I3 3 2 5 2 0 0 0 0

0

0

0

2 I I 0 I 0 0

0

3 2 I 0 0 I 0 0 0

0 0 I 0 0 0 0 0 0 0

9 I5 5 3

IO I6 IO 8

I2 I2

4 0 4 I 4 3 4 2 I 3

I 5 2 0 I 0 I 0 I 0

2 0 0 0 0 0 0 0 I 0

I 0 0 0 0 0 0 0 0 0

0 3 0 0 0 0 0 0 0 0

I 0 0 0 0 0 0 0 0 0

0

0

I

0

0

0

0 0

0

0

0

0

0

0

0

0

0

0

I 0

0

0

0

0

0

0

0

0

0

0

20 I8 I2 6

I6 I8 12 8

I4 I2 13.6 f l.5*

3 3 6 3 5 4 4 3 2 3 3.6 * 0.5

ctg, chromatid gap; csg, chromosome gap; ctb, chromatid break; csb, chromosome break; end, endoreduplication; ace, acentric frag- ment; qr, quadriradial. *P < 0.0001 (Students t-test) for the difference between control and nuclear medicine groups.

particulate) despite their different mechanisms of action. All of the charged particles from radioac- tive isotopes are directly ionizing, i.e, they can directly disrupt the atomic structure of the ab- sorber through which they pass and produce chemical and biological changes [lo]. On the other hand, electromagnetic radiations (X- and gamma rays) are indirectly ionizing. They do not produce chemical and biological damage themselves, but when absorbed in the material through which they pass they give up their energy to produce fast- moving charged particles. Indirectly ionizing radi- ation is usually more penetrating than directly ion- izing particulate radiation [ 111.

Next to be considered are the different types of aberrations found and their distribution, sum-

marized in Tables 1 and 2. Stable aberrations, principally chromatid gaps and chromatid breaks, predominate the distribution. No dicentrics or ring figures were seen. Other authors in long-term radi- ation exposure studies have also found a majority of stable aberrations [12]. In spite of this, it is im- portant to discuss that dicentrics and ring figures are the unstable chromosome aberrations general- ly observed as a consequence of an in vitro or an acute in vivo ionizing radiation exposure [13,14]. In our population, dicentrics and rings were not found probably due to the low level of ionizing radiations chronically received. In the case of long-term chronic exposures, aberrations can be induced in Go lymphocytes and will accumulate in the long-lived lymphocyte population. The fre-

116 A.H. Hagelstdm er al. IToxicol. Lurt. 76 (1995) 113-117

Table 2 Chromosomal aberrations in blood lymphocytes from subjects occupationally exposed to electromagnetic ionizing radiation and controls

Group Chromosomal aberrations Mean aberrations/

No. Sex Age I00 cells

ctg csg ctb csb end ace qr

X-rays 21 M 44 22 M 61 23 M 30 24 F 35 25 F 25 26 F 28 27 M 42 28 F 56 29 F 36 30 F 32 Mean f S.D.

Conlrols 31 F 52 32 M 41 33 M 36 34 F 28 35 F 33 36 M 28 37 F 35 38 M 58 39 F 24 40 F 21 Mean * SD.

6

4 4 3 5

3 2 2 3

0

0 0 0 0 0 0 0

0

0

0

0 0 0

0

I

2 0 0 0

0

0 1 0 0 0 0 1 0 0 0

IO 8 8

14 7 9 3

13 8

12

2 0 3 0 4 3 3 0 2 4

2

1 0 2 1 2 0 1 0 0

0 1 0 2

0 0 0 1 1 0

0

0 0

0

0

0 0

0

0

0

0

0

0

0

0 0

0

0

0

0

0

0 0 0 0

0

0 0

0

0

0 0

0

0

0

0

0

0 0 0

0 0

0

0 0

0

0

0

0

0

0

0

0 0

0

0

0

0

0

0

18 13 12 19 14 16 5

16 II 12 13.6 f 1.3;

2 2 3 2 4 3 4 I 3 4 2.8 f 0.3

ctg, chromatid gap; csg, chromosome gap; ctb, chromatid break; csb, chromosome break; end, endoreduplication; ace, acentric frag- ment; qr, quadriradial. *P < 0.0001 (Students r-test) for the difference between control and radiodiagnostic groups.

quency can therefore be used to indicate an expo- sure [15]. In general, chronic exposure involves breakage of 1 chromatid, whereas those that pro- duce breakage of 2 chromatids (rings, dicentrics, translocations) require increases approximately as the square of the dose [16].

The purpose of this work was to provide data on the genetic hazards due to the occupational expo- sure to ionizing radiation, since the potential risks and biological consequences of nuclear medicine, namely mutagenesis, carcinogenesis and terato- genesis, have been attained through the extrapola- tion from acute exposures. Our results are also particularly interesting for a developing country such as ours, where biological security controls are

not so strict and extended work days are common. Biomonitoring of occupationally exposed people appears to be a sensitive way to evaluate the genotoxic effects of radiation exposures. This type of monitoring may be used as an indicator to detect early damage and to demand more controls in radiation protection. Unfortunately, it is not possible to compare the exposed radiation dose (mean 47 and 180 for the last 6 months) to re- sponse relationship with that found by other authors as many of the workers have confessed that they have not used the film badges periodical- ly. Thus, the reported values are not an exact esti- mation of the exposure dose and are only taken as hypothetical minimum exposure doses.

A.H. Hagelsrriim et al. /Toxicol. L&t. 76 (1995) 113-117 117

Biomonitoring for somatic mutations in human populations is also important as it is believed that somatic mutations contribute to cell lethality, loss in specific functions (171 and diseases such as cancer. There is an association between an increas- ed rate of chromosome aberrations and cancer risks [ 181. For health surveillance, the detection of early genotoxic effects may permit the adoption of preventive biological controls such as hygienic improvements in the workplace or the reduction of hours of occupational exposure.

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