Consequences of the radiation accident at the Mayak production association in 1957 (the 'Kyshtym Accident').

This paper presents an overview of the nuclear accident that occurred at the Mayak Production Association (PA) in the Russian Federation on 29 September 1957, often referred to as 'Kyshtym Accident', when 20 MCi (740 PBq) of radionuclides were released by a chemical explosion in a radioactive waste storage tank. 2 MCi (74 PBq) spread beyond the Mayak PA site to form the East Urals Radioactive Trace (EURT). The paper describes the accident and gives brief characteristics of the efficacy of the implemented protective measures that made it possible to considerably reduce doses to the exposed population. The paper also provides retrospective dosimetry estimates for the members of the EURT Cohort (EURTC) which comprises approximately 21 400 people. During the first two years after the accident a decrease in the group average leukocyte (mainly due to neutrophils and lymphocytes) and thrombocyte count was observed in the population. At later dates an increased excess relative risk of solid cancer incidence and mortality was found in the EURTC.

Cancer Incidence after In Utero Exposure to Ionizing Radiation in Techa River Residents.

Health effects of in utero exposure to ionizing radiation, especially among adults, are still unclear. The aim of this study was to analyze cancer risk in a cohort of subjects exposed in utero due to releases of nuclear waste into the Techa River in the Southern Urals, taking into account additional postnatal exposure. Analysis for solid cancer was based on 242 cases among 10,482 cohort members, accumulating 381,948 person-years at risk, with follow-up from 1956-2009, while analysis for hematological malignancies was based on 26 cases among 11,070 persons, with 423,502 person-years at risk, with follow-up from 1953-2009. Mean doses accumulated in soft tissues and in red bone marrow during the prenatal period were 4 mGy and 30 mGy, respectively. Additional respective mean postnatal doses received by cohort members were 11 and 84 mGy. Poisson regression analysis was used to estimate the excess relative risk (ERR) of cancer incidence related to in utero and postnatal doses. No association was observed for in utero exposure with solid cancer risk [ERR per 10 mGy: -0.007; 95% confidence interval (CI): <-0.107; 0.148] or with hematological malignancy risk (ERR/10 mGy: -0.011; 95% CI: <-0.015; 0.099). However, ERR of solid cancer increased significantly with increasing postnatal dose (ERR/10 mGy: 0.11; 95% CI: 0.04; 0.22). The very wide confidence intervals in these ERR results are similar to those of studies performed on the LSS cohort and the offspring of the Mayak Female Worker Cohort, as well as case-control studies of effects after in utero medical exposure. There were limitations of this study, with decreased statistical power, due to the low prenatal doses received by most of the cohort members, the small number of cancer cases and the absence of cohort members over the age of 59 years (living cohort members had reached 49-59 years of age). Further aging of the cohort and extension of the follow-up period will enhance the statistical power of this study in the future. There is a shortage of cohort studies reporting on the effects of prenatal radiation exposure, as well as information on chronic exposure during the prenatal period. Therefore, further research of this unique cohort will be a useful addition to the published literature on this subject, and a valuable means of elucidating the long-term effects of low-dose radiation exposure in the fetus.

How much can we say about site-specific cancer radiation risks?

Studies of Mayak workers and people who lived along the Techa River have demonstrated significant associations between low-dose-rate radiation exposure and increased solid cancer risk. It is of interest to use the long-term follow-up data from these cohorts to describe radiation effects for specific types of cancer; however, statistical variability in the site-specific risk estimates is large. The goal of this work is to describe this variability and provide Bayesian adjusted risk estimates. We assume that the site-specific estimates can be viewed as a sample from some underlying distribution and use Bayesian methods to produce adjusted excess relative risk per gray estimates in the Mayak and Techa River cohorts. The impact of the adjustment is compared to that seen in similar analyses in the atomic bomb survivors. Site-specific risk estimates in the Mayak and Techa River cohorts have large uncertainties. Unadjusted estimates vary from implausibly large decreases to large increases, with a range that greatly exceeds that found in the A-bomb survivors. The Bayesian adjustment markedly reduced the range of the site-specific estimates for the Techa River and Mayak studies. The extreme variability in the site-specific risk estimates is largely a consequence of the small number of excess cases. The adjusted estimates provide a useful perspective on variation in the actual risks. However, additional work on interpretation of the adjusted estimates, extension of the methods used in describing effect modification, and making more use of prior knowledge is needed to make these methods useful.

Solid cancer incidence and low-dose-rate radiation exposures in the Techa River cohort: 1956 2002.

BACKGROUND: This is the first analysis of solid cancer incidence in the Techa River cohort, a general population of men and women of all ages who received chronic low-dose rate exposures from environmental radiation releases associated with the Soviet nuclear weapons programme. This cohort provides one of the few opportunities to evaluate long-term human health risks from low-dose radiation exposures. METHODS: Cancer incidence rates in this cohort were analysed using excess relative risk (ERR) models. The analyses make use of individualized dose estimates that take into account residence history, age and other factors. Cases are identified on the basis of continuing, active follow-up of mortality and cancer incidence. RESULTS: Based on 1836 solid cancer cases with 446 588 person years accrued over 47 years of follow-up, solid cancer incidence rates were found to increase with dose and about 3% of the cases were attributable to radiation exposure. The ERR was 1.0/Gy (P = 0.004 95% CI (0.3; 1.9) in a linear dose-response model. There was no significant non-linearity in the dose response and no indication of effect modification by gender, ethnicity, attained age or age at first exposure. CONCLUSIONS: The Techa River cohort provides strong evidence that low-dose, low-dose rate exposures lead to significant increases in solid cancer risks that appear to be linear in dose. The results do not suggest that risks associated with low-dose rate exposures are less than those seen following acute exposures such as were received by atomic bomb survivors.

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.