Long-term health effects of persistent exposure to low-dose lr192 gamma-rays.

The aim of the present study was to investigate the effect of persistent low-dose iridium-192 (Ir192) exposure on immunological function, chromosome aberration and the telomerase activity of bone marrow mononuclear cells (BMNCs), in order to increase clinical knowledge of the late effects of persistent low-dose Ir192 gamma-ray exposure. Patients (n=54) accidentally exposed to persistent low-dose Ir192 were included in this 10-year follow-up study. Clinical symptoms, peripheral blood, bone marrow, cellular and humoral immune status, chromosome aberrations and the telomerase activity of BMNCs were analyzed in this study. Exposure to low-dose Ir192 resulted in different degrees of clinical symptoms and significantly lowered complement C3 and C4 levels, CD3+, CD4+ and CD8+ T cell levels, the lymphocyte transformation rate and the percentage of natural killer (NK) cells. It also led to increases in peripheral blood and bone marrow abnormality rates, chromosome aberration rate and BMNC telomerase activity. Exposure to persistent low-dose Ir192 radiation resulted in different degrees of immune dysfunction, and abnormalities of blood cells and bone marrow, which recovered within 1-3 years. Chromosome aberrations were observed to take 5-10 years to recover. However, it would take >10 years for the telomerase activity of BMNCs to be reduced to normal levels. A prolonged follow-up time is required in order to monitor clonal proliferative diseases such as leukemia.