Scenario 

      The nuclear-industrial complex known as Mayak Production Association (PMA) was constructed in May 1946 in the province of Cheryabinsk (Southern Urals). MPA was comprised of a radiochemical separation plant (Facility B), isotope plants and uranium-graphite reactors (Facility A), and started the production of weapon-grade plutonium in 1948. The drainage of the area is primarily via Techa River (237 km length). The radiation exposures to the inhabitants alongside the Techa River were in complex pictures.

     (1) Discharge of radioactive wastes: While natural lakes and dammed ponds at the plant site were employed as reservoirs to manage radioactive effluents, direct discharges of large amount of radionuclides to the Techa River system occurred between 1949 and 1956; approximately 98% of the total radioactivity being released during 1949-1951. For instance, over 100 PBq of radioactive material was discharged during the whole period, causing severe contamination down the entire length of the Techa River. Of the total activity, ruthenium isotopes (¹⁰³Ru, ¹⁰⁶Ru) account for over 50% and estimated 12 PBq of ⁹⁰Sr, 13 PBq of ¹³⁷Cs, and alpha emitters (Pu and U isotopes) of 2 TBq were discharged during 1949-1957. The Techa River system was only water source for the residents of the riverside villages. A total of 124,000 people received external exposure from ¹³⁷Cs, ¹⁰⁶Ru, ⁹⁵Zr and other radionuclides, and internal exposure from ingestion of ⁸⁹Sr, ⁹⁰Sr and ¹³⁷Cs as well. It has been estimated that about 8% of this population received doses higher than 1 Gy.
     (2) Redistribution of radionuclides by flood: An extrardinary flood in April 1951 resulted in substantial contamination of floodplain soil, which continued to increase through October 1951.
     (3) Explosion of radioactive wastes (Kyshtym accident): On 29 September 1957, a chemical explosion of highly radioactive wastes in 300 m³ tank at the plutonium production center caused approximately 7.4×10¹⁶ Bq of nuclear fission products to be dispersed in the atmosphere exposing 270,000 people to radiation. Five years after the accident, the main source of long-term exposure to humans and the environment was predominantly by ⁹⁰Sr.
     (4) Redistribution of radioactive deposits by wind: Furthermore, in 1967, the radioactive wastes deposited in the slit of the dry bed of the lake Karachay was redistributed by the wind over a wide area previously affected by the 1957 contamination, irradiating about half a million people with 2.2×10¹³ Bq.

     With these nuclear disasters, a large number of residents of the riverside area have been exposed externally to ¹³⁷Cs and internally predominantly to ⁹⁰Sr. In 1952, the discharge of radioactive wastes into the river was prohibited. At the same time, the utilization of river water for living and industry use was prohibited and people were evacuated. (cited from Salassidis et al., Int. J. Radiat. Biol., 74:431-439, 1998; Testa et al., Mutation Res., 401:193-197, 1998).

     Excess cancer occurrence has been noticed in the riverside people as early as in 1960. It called international interest first in 1990, when Japan-USSR binational symposium was held in Tokyo, 25-29 June, 1990 and later in the International Symposium on "Chronic radiation exposure: Risk of late effects", Cheryabinsk, 9-13 January, 1995.
     Several studies have been performed to examine chromosome aberration frequencies in peripheral blood lymphocytes of the residents in the riverside villages of Techa River. Again as in the case of residents in the contaminated areas due to Chernobyl NPS accident and cleanup workers, they are unanimously raised a problem of discrepancy between chromosome-based dose and reconstructed dose, such as no significant elevation of aberration frequencies, absence of dose-response relationship and/or severely suppressed chromosome aberration level as compared to reconstructed physical estimate. 

Chromosome aberration analysis 

     Lymphocyte chromosome analysis was carried out in 73 radiation-exposed residents from villages along the Techa River located 7-148 km downstream the site of discharge of radioactive waste from the plutonium production facility of Mayak. Chromosome aberrations were studied by FISH painting using whole chromosome painting probes of chromosomes 1, 4 and 12. Blood sampling was made during the years between 1994 and 1996. Thirty-nine unexposed persons from non-contaminated areas were used as controls.
     As compared with controls, mean translocation frequencies were significantly higher in the exposed group. Individual translocation frequency in 40 subjects with known whole body counter data and calculated red bone marrow dose below 0.6 Gy was within 95% limits of the calibration curve constructed in vitro. 

References 

     Bauchinger, M., Salassidis, K., Braselmann, H., Vozilova, A., Pressl, S., Stephan, G., Snigiryova, G., Kozheurov, V. P. an Akleyev, A. (1998): FISH-based analysis of stable translocations in a Techa River population. Int. J. Radiat. Biol., 73:605-612.  

Dose evaluation in villages along the Techa River

Commentary added at compilation of data 

Figure 1A is reproduced from the scattered plots of F_G translocation frequencies presented by the authors for persons from the villages 7-148 km downstream from the waste discharge as plotted against red marrow dose (RBM dose). They concluded that the aberration frequencies were significantly elevated and were within the limits of 95% prediction levels of the in vitro linear dose-response relationship. The dose-dependent increase is more clearly seen when the data are smoothed by moving window averaging, MWA=(w5,s1), as seen in Figure 1B.

     Research was collaborative study between Ural Research Center for Radiation Medicine (URCRM), Chelyabinsk, Russia, and Radiation Effects Research Foundation (RERF), Hiroshima, Japan, was conducted 43 years after the beginning of radioactive waste discharge to Techa River. The study cohort was selected from persons cumulative doses accounting for radionuclides ⁹⁰Sr and ¹³⁷Cs in 90-95% of cases. The dose to the red bone marrow (RBM) was reconstructed from the dose rate throughout the follow-up period and the measurement of whole body counter.
     Blood sampling was made for the analysis of stable-type chromosome translocations, glycophorine A (GPA) mutations in erythrocytes and T-cell receptor (TCR) mutations. Chromosome translocations were analyzed by HISH painting technology with whole chromosome DNA probes for chromosomes 1, 2 and 4. Controls were taken from age-matched persons living in Urals.
     The analysis of chromosome translocation frequencies failed to find any significant difference between exposed and control cohorts. No difference was also the case for GPA and TCR mutations. 

     Akleyev, A. V., Kossenko, M. M., Silkina, L. A., Degteva, M. O., Yachmenyov, V. A., Awa, A., Akiyama, M., Veremeyeva, G. A., Vozilova, A. V., Kyoizumi, S., Kozheurov, V. P. and Vyushkova, O. V. (1995): Health effects of radiation incidents in Southern Urals. Stem Cells, 13 (Suppl. 1):58-68. 

Chromosome aberrations 

     Figure A is the scattered plots of the translocation frequencies, replotted from Figure 10 of Akleyev et al. 1995, indicating no positive correlation with the RBM dose. Figure B shows the data smoothing by moving window averaging, MWA=(w5s1), of the same data. The dose-response is suggestive. 

     Fifteen children born and raised in riverside village Myslyumovo (78 km from the site of radioactive waste discharge) subjected to radioactive contamination over a period of 45 years. They came to Italy for a one-month stay, where they underwent medical check. Blood sampling was carried out to examine chromosome aberrations. Control group consisted of 11 Russian children (10-14 yrs old) from uncontaminated locality of Smolensk (Russia) which had been selected for previous study on the Chernobyl accident (Padovani et al. Mutation Res., 395:249-254, 1997).
     Chromosomes were analyzed in the preparations prepared wit conventional Giemsa staining method. Aberration frequencies, particularly acentric aberrations, were significantly elevated in the Techa River cohort (p<0.05, two-tailed Mann-Whitney U test). 

     Testa, A., Padovani, L., Mauro, F., Appolloni, M., Anzidei, P. and Stronati, L. (1998): Cytogenetic study on children living in Southern Urals contaminated areas (nuclear incidents 1948-1967). Mutation Res., 401:193-197. 

     Degteva, M. O., Anspaugh, L. R., Akleyev, A. V., Jacob, P., Ivanov, D. V., Wieser, A., Vorobiova, M. I., Shishkina, E. A., Shved, V. A., Vozilova, A., Bayanskin, S. N. and Napier, B. A. (2005): Electron paramagnetic resonance and fluorescence in situ hybridization-based investigations of individual doses for persons living at Metlino in the upper reaches of the Techa river. Health Phys., 88:139-153. 

     External dose was estimated by electron paramagnetic resonance (EPR) on teeth enamel obtained from 16 exposed donors born between 1928 and 1952 in Metlino (7 km from the release site). Metllino is the closest village to the site of release. The residents were exposed both externally to gamma-rays from the contaminated river bank and internally from dietary intake of radionuclides (^89/90Sr). In the residents of Metlino, the external dose is estimated to contribute up to 45% of the total red bone marrow dose. In this study, a total of 36 EPR measurements were performed; 13 at the Institute for radiation protection, GSF-National Research Center for Environment and Health, Munich, Germany (GSF), and 20 at the Institute of Medical Physics, Ekaterinburg, Russia (IMP). The inter laboratory comparison of EPR dosimetry systems was made on the same samples obtained from Ural donors. 

     Chromosome analysis was carried out on peripheral lymphocytes from 31 exposed persons (residents of Metlino born between 1918 and 1953). Blood samples were collected between 1994 and 1998. Lymphocyte culture and chromosome preparation were made at the Urals Research Center for Radiation Medicine (URCRM), and FISH analysis was performed at GSF. Whole chromosome-painting probes for chromosomes 1, 4 and 12 were used together with pancentromeric probe. 

Chromosome translocations and EPA measures of external dose (c.f., Genome equivalent frequencies, F_G(Tr), were calculated and shown in figure at the time of data compiling.) 

     Vozilova, A. V., Shagina, N. B., Degteva, M. O., Anisbury, E. A., Moquet, J. E., Hone, P., Lloyd, D. C., Fominar, J. N. and Darroudi, F. (2012): Preliminary FISH-based assessment of external dose for residents exposed on the Techa river. Radiat. Res., 177:84-91.

     Blood samples were collected from 18 persons residing in middle Techa regions, and translocation frequencies were studied by FISH paining method three laboratories; Urals Research Center for Radiation Medicine (URCRM), Health Protection Agency (HPA), UK, and Leiden University Medical Center (LUMC).
    The residents were exposed predominantly to the internal doses from ingestion of radionuclides (mostly ⁹⁰Sr) in river water and local foodstuffs. Contribution of external exposure and internal exposure to non-strontium radionuclides to the red bone marrow (RBM) dose was less than 5 %.