Biological indicators of occupational radiation exposure

The report presents results on finding appropriate biomarkers applicable in molecular epidemiological surveys of occupationally exposed individuals and/or population to study low dose effects. Blood samples were collected from the “strict regimen” area personnel (exposed) and the administrative staff (controls) of NPP-Kozlodui. Two levels of evaluation were used: molecular spontaneous and induced DNA repair by UDS, protein synthesis evaluated radio-metrically, DNA damage by SCGE – all of them in white blood cells, concentration of malonedialdehyde in blood serum; and cellular – the Ly-subsets by flow cytometry, using a FacScan analyzer and immunofluorescent stained mouse monoclonal antibodies. A significant decrease of potentially lethal damage was found in persons with “mean annual dose” lower or equal to 5 mSv/a. The highest repair capacity and protein synthesis after a challenging dose of 2,0 Gy gamma rays as well as a significant decrease in the level of oxidative stress were evaluated for persons from the same group. At doses below 200 mSv statistically different decrease of the index of СD3+4+, CD4+25+, СD4+62L+ lymphocyte populations and СD4/СD8 cell ratio was established, and increased levels of NK cells, CD57+8+, CD8+28+ and CD8+38 were recorded. The present investigation showed that annual doses lower than twice the natural radiation background exert positive effects on DNA damage and repair, increase cellular resistance and decrease oxidative stress. It is possible that the positive correlation between the dose and the cells with phenotype CD4+25+ and CD57+8+, as well as the negative one with CD4+62L+, CD8+28+ and CD8+38+, could reflect adaptive processes and compensatory activated immune system due to low dose irradiation. Further investigations allowing analysis of the molecular endpoints, increase the sensitivity of studies and help to search effects of low radiation exposures, are needed.