External radiation exposure of residents living close to the Mayak facility: main sources, dose estimates, and comparison with earlier assessments

External dose reconstruction for the former village of Metlino (Techa River, Russia) based on environmental surveys, luminescence measurements, and radiation transport modelling

In the first years of its operation, the Mayak Production Association, a facility part of the Soviet nuclear weapons program in the Southern Urals, Russia, discharged large amounts of radioactively contaminated effluent into the nearby Techa River, thus exposing the people living at this river to external and internal radiations. The Techa River Cohort is a cohort intensely studied in epidemiology to investigate the correlation between low-dose radiation and health effects on humans. For the individuals in the cohort, the Techa River Dosimetry System describes the accumulated dose in human organs and tissues. In particular, organ doses from external exposure are derived from estimates of dose rate in air on the Techa River banks which were estimated from measurements and Monte Carlo modelling. Individual doses are calculated in accordance with historical records of individuals' residence histories, observational data of typical lifestyles for different age groups, and age-dependent conversion factors from air kerma to organ dose. The work here describes an experimentally independent assessment of the key input parameter of the dosimetry system, the integral air kerma, for the former village of Metlino, upper Techa River region. The aim of this work was thus to validate the Techa River Dosimetry System for the location of Metlino in an independent approach. Dose reconstruction based on dose measurements in bricks from a church tower and Monte Carlo calculations was used to model the historic air kerma accumulated in the time from 1949 to 1956 at the shoreline of the Techa River in Metlino. Main issues are caused by a change in the landscape after the evacuation of the village in 1956. Based on measurements and published information and data, two separate models for the historic pre-evacuation geometry and for the current geometry of Metlino were created. Using both models, a value for the air kerma was reconstructed, which agrees with that obtained in the Techa River Dosimetry System within a factor of two.

Monte Carlo-based calculation of imaging plate response to (90)Sr in teeth: experimental validation of the required correction on sample thickness

Recently, a numerical method was proposed to correct the imaging plate (IP) response to (90)Sr concentration in tooth samples, depending on the sample thickness. This is important to quantify any (90)Sr concentration in teeth, which in turn is necessary to determine any (90)Sr incorporation of a person retrospectively. Although the final goal will be to evaluate the (inhomogeneous) spatial distribution of (90)Sr inside tooth samples precisely, the present study was restricted -- as a first step -- to the evaluation of (90)Sr in teeth assuming a uniform (90)Sr distribution. A numerical method proposed earlier was validated experimentally in the present study by measuring the IP response to standard sources of various thicknesses and (90)Sr concentrations. For comparison, the energy deposition of the beta-rays emitted by (90)Sr in the IP -- which is considered to be proportional to the IP luminescence signal -- was calculated for the various sample thicknesses involved, by means of the MCNP-4C code. As a result, the measured IP response could be reproduced by the calculations within the uncertainties, depending on the thickness of the standard sources. Thus, the validity of the proposed numerical method to correct the IP response for sample thickness has successfully been demonstrated.

Risk analysis of leukaemia incidence among people living along the Techa River: a nested case-control study

Large quantities of radioactive materials released over time from the Mayak nuclear weapons facility caused significant internal and external exposure for people living along the banks of the Techa River (Southern Urals, Russia). We conducted a nested case-control study in the Extended Techa River Cohort to determine whether the risk of leukaemia incidence increased with protracted exposure to ionising radiation or with other non-radiation risk factors. The study included 83 cases identified over 47 years of follow-up and 415 controls matched for sex, age at diagnosis, age (within a 5 year age group), and date of initial residence in the riverside area. External and internal doses have been calculated using the Techa River Dosimetry System 1996 (TRDS96). Conditional logistic regression was used to calculate odds ratios per Gray (OR/Gy) and 95% confidence intervals (95% CI). After excluding cases of chronic lymphoid leukaemia, the OR/Gy of total, external, and internal doses were 4.6 (95% CI: 1.7-12.3), 7.2 (95%CI: 1.7-30.0) and 5.4 (95%CI: 1.1-27.2), respectively. A history of solid tumour, either malignant or benign, before the leukaemia diagnosis was associated with a 2.5-fold increase in the leukaemia risk (95% CI: 1.1-5.9). Even though the analysis of confounders was less useful than expected because of missing data, multivariate analyses that took the exposure dose into account confirmed the association between leukaemia incidence and tumour history.

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.

Dose assessment for the Metlino and Muslyumovo populations who lived along the Techa river from 1949 to 1954

In the period from 1949 to 1956, liquid radioactive waste was routinely and accidentally discharged by the Mayak Production Association, Southern Urals, Russia, into the Techa river. Based on a novel approach, the contamination of the Techa river water, the bottom sediments and the adjacent flood plains was modelled, and internal and external doses were estimated for two villages located downstream of the site of liquid radioactive waste release. Altogether, 11 radionuclides that occurred in the liquid radioactive waste were included in the calculations. The results suggest significantly higher doses than previously assumed, with the major contribution in the year 1951. Radionuclides with half-lives of less than 1 year, such as 89Sr, 131I, 95Zr+95Nb, 103Ru+103mRh, 140Ba+140La, and 144Ce+144Pr, represent the major sources and, in contrast, long-lived radionuclides, such as 90Sr and 137Cs that have so far been assumed to be most important, did not dominate the doses. For adults from the village Metlino, located 7 km downstream of the site of liquid radioactive waste discharge, the committed effective doses due to intake of radionuclides were calculated to be about 2.3 Sv, while the external doses were between about 1.2 Sv and 6.9 Sv. On the other hand, for adults from Muslyumovo, located 75 km downstream, the committed effective doses due to intake of radionuclides were calculated to be about 0.5 Sv, while the external doses were between 0.5 Sv and 2.0 Sv. The values for the skin doses to the Metlino and Muslyumovo populations were about 7.1 Sv and 1.3 Sv, respectively. It is concluded that the current dose estimates for the residents of the Techa river need, therefore, reevaluation.