Cytogenetic analysis of peripheral blood lymphocytes of occupational workers exposed to low levels of ionising radiation

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Abstract

The incidence of chromosomal aberrations was analysed in peripheral blood lymphocytes of occupationally exposed people having cumulative doses of 500 mSv. The exposed individuals showed higher frequencies of dicentrics as well as acentrics than normal controls. Absorbed radiation dose was calculated by using in vitro dose response curve established for Cobalt-60 gamma rays. In the control constituting 17 healthy individuals, two dicentrics were detected among 3700 metaphases analysed. In the exposed group 27 dicentrics and one centric ring was detected among 8400 metaphases analysed. Due to small number of dicentrics scored in each individual, the dose estimate suffers from a large statistical uncertainty. The collective dose was found to be 1.89 Gy. This is in good agreement with the corrected physical doses, assuming a mean life of 10 years for the disappearance of lymphocytes. The physical doses accumulated during the last 10 years of occupation were also in good agreement with the biological dose estimate.

Introduction

Cytogenetic studies conducted on peripheral blood lymphocytes of occupationally exposed workers have shown that it is possible to detect significant levels of chromosomal damage from the analysis of a few hundred metaphase cells. Evans et al. [1]found elevated numbers of unstable aberrations and also a dose–effect relationship in nuclear-dockyard workers. Many investigators have reported significant increases in chromosomal aberrations among radiation workers 2, 3, 4, 5, 6, 7, 8, 9.

The dose-yield kinetics of chromosome aberrations and their implications for dose assessment are not well established in the case of exposure to low level radiation encountered in occupational exposures. In the present study the yield of chromosomal aberrations in occupational workers exposed to γ radiation with cumulative life time dose of 500 mSv, have been analysed. The data was compared with that of age, and sex matched controls. An attempt has been made to estimate the absorbed radiation dose.

Section snippets

Choice of subjects

Peripheral blood samples were collected from 15 male individuals, who had cumulative doses of ≅500 mSv. The subjects were exposed to γ radiation and were routinely monitored with film badges or thermoluminiscent dosimeters (TLD). These radiation workers were occupationally exposed over a period of 20–25 years. Their average age was 50.1±1.5 years. None had ever exceeded the permissible dose limit. Blood samples from age, and sex matched normal individuals who had not been exposed to radiation

Results and discussion

Details of cytogenetic analysis, individual's age, accumulated dose, and biological dose are given in Table 1. Table 2 shows the accumulated physical dose over 5 years and 10 years, corrected physical dose and biological dose. Calculation of the corrected physical dose was made by applying the decay correction to the annual doses, assuming the mean life of lymphocytes as either 4.3 years or 10 years. The corrected dose was arrived at by using the formula:Annual dose×exp−(0.693×t/T1/2),where t

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