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Release of liquid radioactive waste into the Techa River from the Mayak Production Association during 1949-1956 resulted in a significant exposure of about 30000 people who lived in downstream settlements. The residents were exposed to internal and external radiation. The article discusses the capability of two methods that were used 50 years after the termination of radioactive discharges for the dose reconstruction, namely EPR measurements of tooth enamel, and FISH measurements of stable chromosome aberrations in circulating lymphocytes. The Main issue in the application of these methods for the dose reconstruction was local irradiation from strontium radioisotopes incorporated in teeth and bones. The EPR and FISH assays were supported by measurements of the 90Sr content in the skeleton and teeth in order to estimate and subtract internal doses from incorporated 89, 90Sr. The resulting dose estimates obtained from EPR and FISH mea- surements were found to be consistent The settlement-averaged values in the upper-Techa Region varied from 550-570 mGy to 130-160 mGy and showed a reduction with the distance from the release site. The EPR- and FISH-based dose estimates were in agreement with the doses calculated with the dosimetry system TRDS that uses data on radionuclide contamination of the Techa River floodplain and individual residential histories.

The parameters characterizing the state of hemopoietic cells obtained from chronically exposed residents of the Techa riverside villages studied at late time after the exposure included: the level of somatic mutations in the TCR gene, the level of chromosome aberrations, the intensity of peripheral blood lymphocyte apoptosis. Exposed versus unexposed subjects (controls) showed an increased frequency of CD3-CD4+ T-lymphocytes, chromosome aberrations of stable type (translocations) and unstable type (dicentrics, rings), and also increased intensity of lymphocyte apoptosis. The findings of tests using a standard additional gamma-irradiation (1 Gy) accompanied by 24-hour incubation indicated that the rate of apoptosis of lymphocytes was significantly higher in exposed individuals in comparison with unexposed ones. It was suggested basing on the obtained data that at late time the chronic (for over 50 years) exposure at RBM doses from 0.01 to 3.22 Sv was a factor inducing the damage to the genetic apparatus of hemopoietic cells. Evidently, the initial chronic low-intensity irradiation in the above-indicated dose range activates adaptive processes at the cellular level in hemopoietic cells. Late time after the onset of exposure the adaptation reserves are depleted in chronically exposed persons which brings about its failure in the case of a challenge by additional external exposures.

The evaluation of remote cytogenetic consequences was studied in population, irradiated at low level during 40 years and more preferentially internally. Mean level of exposure was in 1950 year at maximum--0.2 Sv/year. In 1993 year it was equal 1.95 mSv/year. It was revealed statistically significant increasing of chromosome type of aberrations in lymphocytes of irradiated people in comparison with control ones. The incidence of chromosome type exchanges in irradiated individuals comprised 0.43 per 100 cells, and 0.17 per 100 cells in the control.