The Techa River Cohort: study design and follow-up methods.

Residents living on the banks of the Techa River in the Southern Urals region of Russia were exposed to radioactive contamination from the Mayak plutonium production and separation facility that discharged liquid radioactive waste into this river. This paper describes the methods used to establish and follow the Extended Techa River Cohort (ETRC), which includes almost 30,000 people living along the Techa River who were exposed to a complex mixture of radionuclides, largely 90Sr and 137Cs. The system of regular follow-up allows ascertainment of vital status, cause of death and cancer incidence. With over 50 years of follow-up and over 50% deceased, the ETRC now provides a valuable opportunity to study a wide range of health effects, both early and late, associated with protracted internal and external radiation exposures. The wide range of doses allows analysis of the nature of the dose-response relationship based on internal comparisons. Other features of the cohort are the high proportion (40%) exposed under age 20, and the inclusion of both sexes. The limitations of the study include loss to follow-up due to difficulties in tracing some cohort members and migration and incomplete ascertainment of cause of death.

Protracted radiation exposure and cancer mortality in the Techa River Cohort.

In the 1950s many thousands of people living in rural villages on the Techa River received protracted internal and external exposures to ionizing radiation from the release of radioactive material from the Mayak plutonium production complex. The Extended Techa River Cohort includes 29,873 people born before 1950 who lived near the river sometime between 1950 and 1960. Vital status and cause of death are known for most cohort members. Individualized dose estimates have been computed using the Techa River Dosimetry System 2000. The analyses provide strong evidence of long-term carcinogenic effects of protracted low-dose-rate exposures; however, the risk estimates must be interpreted with caution because of uncertainties in the dose estimates. We provide preliminary radiation risk estimates for cancer mortality based on 1,842 solid cancer deaths (excluding bone cancer) and 61 deaths from leukemia. The excess relative risk per gray for solid cancer is 0.92 (95% CI 0.2; 1.7), while those for leukemia, including and excluding chronic lymphocytic leukemia, are 4.2 (CI 95% 1.2; 13) and 6.5 (CI 95% 1.8; 24), respectively. It is estimated that about 2.5% of the solid cancer deaths and 63% of the leukemia deaths are associated with the radiation exposure.

Issues in the comparison of risk estimates for the population in the Techa River region and atomic bomb survivors.

Plutonium production in the former Soviet Union began in 1949 at the Mayak Production Association located between the cities of Chelyabinsk and Ekaterinbourg in the southern Ural mountains about 1200 km east to Moscow. During the first few years of Mayak's operation, almost 30,000 people living on the banks of the Techa River received significant internal and external exposures as a consequence of the release of large quantities of radioactive materials from Mayak. Studies of levels of radioactive contamination and health effects in this population began in the early 1950s. A systematic follow-up of a fixed cohort that includes all people who were living in Techa River villages in 1949 was begun about 30 years ago. In this paper we describe the Techa River cohort, outline the nature of the exposures and discuss the status of follow-up for the period from 1950 through 1989. While noting the limitations of the current epidemiological follow-up data, we also compare the demographic and mortality structure of the Techa River cohort with the Life Span Study cohort of Japanese atomic bomb survivors. It is seen that, despite a number of limitations, the current data suggest that the risks of mortality from leukemia and other cancers increase with increasing radiation dose in the Techa River cohort. This finding suggests that, with continued improvements in the quality of the follow-up and dosimetry, the Techa River cohort has the potential to provide quantitative estimates of the risks of chronic low-dose-rate radiation exposures for an unselected general population that will be an important complement to the estimates based on the Life Span Study that are used as the primary basis for numerical assessments of radiation risk.

Analysis of strontium metabolism in humans on the basis of the Techa river data.

Age and sex features of strontium metabolism have been analyzed on studies of the population residing on the banks of the Techa river which was contaminated by fission products during the years 1949-1956. Measurements of 90Sr body burden have been performed since 1974 using a whole-body counter, and these have made it possible to estimate age-specific long-term retention and elimination rates for men and women. Regarding the retention that correlated with the respective maturation ages, distinct sex differences have been observed for adolescents, whereas only postmenopausal women showed a sharp increase of their elimination rates. There were no differences concerning the reproductive ages. Our experimental findings have a clear physiological interpretation and can be used to develop metabolic models for bone-seeking radionuclides.

Pregnancy outcome and early health status of children born to the Techa River population.

As a result of contamination of the river Techa by fission products in 1949-1956, the residents of the riverside villages were exposed to external and internal irradiation. The average gonadal dose in the study cohort of 28,100 people is estimated to be 0.16 Sv. No decrease in fertility and birth rate was detected. The gonadal doubling dose ranges calculated for the incidence of stillbirths, miscarriages, early neonatal mortality and lethal developmental defects was found to be rather high, ranging from 0.2 to 4.8 Sv.