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.

Stochastic effects of environmental radiation exposure in populations living near the Mayak Industrial Association: preliminary report on study of cancer morbidity.

The Mayak Industrial Association, located in the South Ural Mountains, began operation in 1948 and was the first Russian site for the production and separation of plutonium. During the early days of operation, technological failures resulted in the release of large amounts of radioactive waste into the Techa River. Residents who lived in villages on the banks of the Techa and Iset Rivers were exposed to varying levels of radioactivity. The objective of this study is to assess stochastic (carcinogenic) effects in populations exposed to offsite releases of radioactive materials from the Mayak nuclear facility in Russia. Subjects of the present study are those individuals who lived during the period January 1950 through December 1960 in any of the exposed villages along the Techa River in Chelyabinsk Oblast. Death certificates and cancer incidence data have been routinely collected in the past from a five-rayon catchment area of Chelyabinsk Oblast. The registry of exposed residents along the Techa River assembled and maintained by the Urals Research Center for Radiation Medicine for the past 40 y is the basis for identifying study subjects for this project. Specific study objectives are to evaluate the incidence of cancer among current and former residents of Chelyabinsk Oblast who are in the exposed Techa River cohort; integrate results from the dose-reconstruction study to estimate doses for risk assessment; and develop a structure for maintaining continued follow-up of the cohort for cancer incidence. In the earlier part of our collaborative effort, the focus has been to enhance the cancer morbidity registry by updating it with cancer cases diagnosed through 1997, to conduct a series of validation procedures to ensure completeness and accuracy of the registry, and to reduce the numbers of subjects lost to follow-up. A feasibility study to determine cancer morbidity in migrants from the catchment area has been proposed. Our preliminary analyses of cancer morbidity underscore the importance of examining both cancer mortality and cancer morbidity in conducting a comprehensive analysis of the occurrence of cancer in this important cohort.

Mortality in the offspring of individuals living along the radioactively contaminated Techa River: a descriptive analysis.

From 1949 onwards, radioactive waste was released into the Techa River in the southern Urals and the population living along the river was exposed to ionising radiation. Relocation of these people did not start until several years later, causing many individuals to be exposed to substantial doses from internal and external radiation. The identification and follow-up of the exposed individuals started more than 40 years ago and is still continuing. The Techa River offspring cohort (TROC) that has recently been established, comprises 10,459 children born to at least one parent living along the Techa River during the period 1950-1992. Of these children, 3,897 were born during the period of highest release, i.e. between 1950 and 1956 and might thus have been exposed in utero. A total of 1,103 individuals have since died mainly due to infectious and respiratory diseases, injury and poisoning. Only 25 cases were identified as having died of a malignant condition. The radioactive contamination of the Techa River in the southern Urals gives a unique possibility to study the adverse effects of protracted exposure to ionising radiation in a large well-described cohort. The Techa River offspring cohort will make it possible to study the effects on those exposed in utero or early in life and the follow-up of the cohort in the future is, therefore, of great importance. Comparisons with other cohorts of humans exposed early in life, will increase our knowledge in this field of research.

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.

Cancer mortality among Techa River residents and their offspring.

This paper analyzes the data on leukemia and solid cancers of all types among 28,000 people exposed due to discharges of radioactive waste into the Techa River in the South Urals. Cancer mortality rates for the 33-y period since the beginning of the exposure have been estimated. In addition, the paper discusses malignancy cases among the first generation offspring of the exposed people. In comparison with matched control groups, an increased incidence of malignant neoplasms was observed among the exposed population. The leukemia risk, estimated on the basis of the linear model of absolute risk, was 0.85 per 10,000 person-y Gy of the dose accumulated in red bone marrow. Solid cancer risk (except osteosarcoma), estimated using linear model of relative risk, was 0.65 per Gy of dose accumulated in soft tissues. No increase in cancer mortality has been documented for the offspring of the exposed individuals.

Cancer mortality in the exposed population of the Techa River area.

Radioactive contamination and population exposure resulted from the operation of the Mayak complex, a plutonium-production facility in the Southern Urals. The highest doses were received by residents along the Techa River into which wastes from the complex leaked between 1949 and 1956. A registry was established containing data on 29,528 persons and information on deaths (9426 by 1982; 6439 death certificates) and cancer cases. Six groups differing in exposure levels were set up for the cohort analysis. The range of doses to red bone marrow in these cohorts was from 1.64 to 0.176 Sv. Leukaemia and solid cancer mortality over the 33-year period of exposure was analysed. The age-standardized total cancer mortality rates and their 95% confidence intervals account for 140 (131-150) and 105 (101-109) per 100,000 person-years for the entire exposed and entire control population. The analysis of cancer mortality in different organs has shown increased rates for leukaemia in one exposed group and for cancers of the uterine corpus and cervix in the other exposed group, as compared to the identical control groups.

Health effects of radiation incidents in the southern Urals.

This article discusses the most important information on health effects in the Urals region (Russia) of residents exposed to radiation from activities of a weapon plutonium separation plant. The population residing on the contaminated territory was exposed to chronic combined irradiation (external gamma-irradiation and internal irradiation due to Sr-90 and Cs-137). The red bone marrow (RBM) was the critical organ affected as a result of radiation events in the Urals. In the early period, after the discharges of radioactive wastes into the river Techa (about 3 M Ci) started, cases of chronic radiation sickness (CRS; 940 cases, in total), postirradiation reactions manifested by changes in blood parameters (e.g., leukopenia, thrombocytopenia, granulocytopenia), nervous system disorders, immunity changes and ostealgic syndrome were registered in a portion of those riverside village residents who had received the highest doses. Increased leukemia and cancer mortality and morbidity rates were noted among this population in later periods. No late effects were observed in residents exposed to an explosion in a radioactive waste depot in September, 1957 when radioactive wastes with about 20 M Ci of activity were released into the environment. Similarly, the offspring of the residents exposed on the Techa also did not display any late effects. The data about the possibilities of long-term (43-45 years after the start of exposure) biological indication of chronic internal exposure are presented. The methods used in the study include in situ fluorescent hybridization, analysis of mutations in the TCR gene of peripheral blood lymphocytes and erythrocyte mutations in the glycophorine A system. No dependence of genomic translocations and mutations in glycophorine A on cumulative exposure dose to RBM was traced.

Cancer mortality and radiation risk evaluation for the Techa River population.

The current nominal risk coefficients for radiation induced cancer are predominantly based on the follow-up of the atomic bomb survivors, i.e. a collective of persons exposed to a short duration, high dose rate exposure. It is one of the central issues in radiation protection, whether these data are representative also for protracted, low dose rate exposures. The International Commission for Radiological Protection has postulated a dose and dose rate reduction factor in the derivation of the nominal risk coefficients; but this factor has been debated. Direct observations on populations that were subjected to prolonged low dose exposures are, therefore, of special interest, and a major contribution to the problem may result from the long term observation of the population exposed at the beginning of the 1950s as a result of massive releases of fission products by a plutonium producing facility into the Techa river in the southern Urals. The present article deals with the cancer mortality in this population during the period 1950-1982.

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.