Abstract
South districts of Belarus are still highly radiocontaminated even after 23 years from the Chernobyl catastrophe in 1986, and consequent environmental changes are stored in the soil, plants and animals. The major radionuclides in the contaminated areas are 137Cs and 90Sr, and their physical half-lives are 30.2 and 28.9 years, respectively. It is easily predicted that the radionuclides are concentrated by the food chain into the living organisms in the contaminated area, and radionuclides remain in the irradiated organisms not only externally but also internally for long periods.
To simulate the radiocontamination in middle contaminated areas of Belarus (1997, 2005), mice were maintained for 8 months in the radioisotope facility with free access to drinking water containing 137CsCl (0Bq/ml, 10Bq/ml and 100Bq/ml).
Mice were assessed the long term low dose rate and low dose internal and external radiation effect by the quantitative measurement of the contaminated radionuclides-induced DNA double-strand breaks by γ-H2AX foci in the organs. The micro nuclei test and the tumorigenicity of mouse lung were also examined under the same condition.
The number of γ-H2AX focus per hepatic cell was 1.4 (0Bq/ml), 9.5(10Bq/ml), 10.7(100Bq/ml), respectively. It was suggested that the genome damage caused internal low dose 137Cs radiation were occurring chronically even in low dose contaminated area. But no significant difference was observed in the micro nuclei test. In addition, progress data (by 6 animals in each dose groups) is showing that the number of lung tumors per mouse induced by urethane under the same condition is 34.8 (0 Bq/ml), 41.2 (10Bq/ml), 44.2 (100Bq/ml), and the average of tumor diameter (mm) is 1.70, 1.71, 1.74, respectively. (Supported by JSPS)
