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The East Urals Radioactive Trace (EURT) was formed after a chemical explosion in the radioactive waste-storage facility of the Mayak Production Association in 1957 (Southern Urals, Russia) and resulted in an activity dispersion of 7.4 × 10 16 Bq into the atmosphere. Internal exposure due to ingestion of radionuclides with local foodstuffs was the main factor of public exposure at the EURT. The EURT cohort, combining residents of most contaminated settlements, was formed for epidemiological study at the Urals Research Center for Radiation Medicine, Russia (URCRM). For the purpose of improvement of radionuclide intake estimates for cohort members, the following data sets collected in URCRM were used: (1) Total β-activity and radiochemical measurements of 90 Sr in local foodstuffs over all of the period of interest (1958-2011; n = 2200), which were used for relative 90 Sr intake estimations. (2) 90 Sr measurements in human bones and whole body (n = 338); these data were used for average 90 Sr intake derivations using an age- and gender-dependent Sr-biokinetic model. Non-strontium radionuclide intakes were evaluated on the basis of 90 Sr intake data and the radionuclide composition of contaminated foodstuffs. Validation of radionuclide intakes during the first years after the accident was first carried out using measurements of the feces β-activity of EURT residents (n = 148). The comparison of experimental and reconstructed values of feces β-activity shows good agreement. 90 Sr intakes for residents of settlements evacuated 7-14 days after the accident were also obtained from 90 Sr measurements in human bone and whole body. The results of radionuclide intake reconstruction will be used to estimate the internal doses for the members of the EURT cohort.

Radioactive contamination of the Techa River (Southern Urals, Russia) occurred from 1949-1956 due to routine and accidental releases of liquid radioactive wastes from the Mayak Production Association. The long-lived radionuclides in the releases were Sr and Cs. Contamination of the components of the Techa River system resulted in chronic external and internal exposure of about 30,000 residents of riverside villages. Data on radionuclide intake with diet are used to estimate internal dose in the Techa River Dosimetry System (TRDS), which was elaborated for the assessment of radiogenic risk for Techa Riverside residents. The Sr intake function was recently improved, taking into account the recently available archival data on radionuclide releases and in-depth analysis of the extensive data on Sr measurements in Techa Riverside residents. The main purpose of this paper is to evaluate the dietary intake of Cs by Techa Riverside residents. The Cs intake with river water used for drinking was reconstructed on the basis of the Sr intake-function and the concentration ratio Cs-to-Sr in river water. Intake via Cs transfer from floodplain soil to grass and cows' milk was evaluated for the first time. As a result, the maximal Cs intake level was indicated near the site of releases in upper-Techa River settlements (8,000-9,000 kBq). For villages located on the lower Techa River, the Cs intake was significantly less (down to 300 kBq). Cows' milk was the main source of Cs in diet in the upper-Techa River region.

More accurate reconstruction of the radioactive contamination of the Techa River system in 1949-1951 has been made on the basis of refined data on the amounts and the rate of discharge of radionuclides into the Techa River from the Mayak Production Association; this has led to the development of a modified Techa River model that describes the transport of radionuclides through the up-river ponds and along the Techa River and deposition of radionuclides in the river-bottom sediments and flooded areas. The refined Techa River source-term data define more precisely the time-dependent rates of release and radionuclide composition of the releases that occurred during 1949-1951. The Techa River model takes into account the time-dependent characteristics of the releases and considers (a) the transport of radionuclides adsorbed on solid particles originally contained in the discharges or originating in the up-river ponds as a result of stirring up of contaminated bottom sediments and (b) the transport of radionuclides in soluble form. The output of the Techa River model provides concentrations of all source-term radionuclides in the river water, bottom sediments, and floodplain soils at different distances from the site of radioactive releases for the period of major contamination in 1950-1951. The outputs of the model show good agreement with historical measurements of water and sediment contamination. In addition, the river-model output for (90)Sr concentration in the river water is harmonized with retrospective estimates derived from the measurements of (90)Sr in the residents of the Techa Riverside villages. Modeled contamination of the floodplain soils by (137)Cs is shown to be in agreement with the values reconstructed from late measurements of this radionuclide. Reconstructed estimates of the Techa River contamination are being used for the quantification of internal and external doses received by residents of the Techa Riverside communities.

Dynamics of soil contamination, food chain, and radiation doses to population at the East-Urals Radioactive Trace (EURT) and the Karachay Radioactive Trace (KRT) are reviewed. Gamma spectrometric analysis of samples was performed according to standard methodology; 90Sr was determined by the extraction method. Over 80% of radionuclides in soil are contained in the upper 20-cm layer. Biologically available forms of Sr and insoluble forms of 137Cs are predominant. The main reasons for reduction in milk contamination are radioactive decay and sequestration of radionuclides in soil. Current annual intake of radionuclides with food: EURT--310 Bq (90Sr), KRT--324 Bq (90Sr) and 732 Bq (137Cs).

Releases of radioactive materials from the Mayak Production Association in 1949-1956 resulted in contamination of the Techa River; a nuclide of major interest was 90Sr, which downstream residents consumed with water from the river and with milk contaminated by cows' consumption of river water and contaminated pasture. Over the years, several reconstructions of dose have been performed for the approximately 30,000 persons who make up the Extended Techa River Cohort. The purpose of the study described here was to derive a revised reference-90Sr-intake function for the members of this cohort. The revision was necessary because recently discovered data have provided a more accurate description of the time course of the releases, and more is now known about the importance of the pasture grass-cow-milk pathway for the members of this cohort. The fundamental basis for the derivation of the reference-90Sr-intake function remains the same: thousands of measurements of 90Sr content in bone with a special whole-body counter, thousands of measurements of beta-activity of front teeth with a special tooth-beta counter, and a variety of other measurements, including post mortem measurements of 90Sr in bone, measurements of 90Sr in cow's milk, and measurements of beta activity in human excreta. Results of the new analyses are that the major intake started in September 1950 and peaked somewhat later than originally postulated. However, the total intake for adult residents has not changed significantly. For children of some birth years, the intake and incorporation of Sr in bone tissue have changed substantially.

Operation of "Mayak" plutonium production complex resulted in radioactive contamination of the part of Chelyabinsk Region in 1950-60s. Significant gas-aerosol emissions of 1311 occurred since 1948; in 1957, a radiation accident resulted in 90Sr contamination of large territories. This paper presents comparison of bone mineral density of persons lived on territories with different levels of soil 90Sr-contamination with a control group. It was found that in 1970-1975 the bone mineral density, estimated from mineral content in bone samples, in residents of contaminated areas born in 1936-1952 was significantly lower compared with the control group. For persons born in 1880-1935 such differences were not found. It was shown that the decrease in bone mineral density was not related to 90Sr exposure of osteogenic cells in the dose range from 0.1 to 1300 mGy: the coefficient of correlation between individual 90Sr-doses and bone mineral contents was not significant. The decrease in bone mineral density of persons born in 1936-1952 could be associated with exposure of thyroid and parathyroid glands (systemic regulators of calcium turnover) by 131I from gas-aerosol emissions from "Mayak". Maximum gas-aerosol emissions occurred in 1948-1954 and coincided with growth and development of thyroid gland, characterizing by intensive accumulation of 131I, and with growth and maturation of the skeleton of persons born in these calendar years.

The river Iset belongs to the Techa-Iset-Tobol-Irtysh-Ob system contaminated by liquid radioactive wastes from Mayak plutonium facility in 1949-1956. This study represents the first retrospective analysis of postmortem measurements of 90Sr in bones from residents of the Iset riverside settlements in 1960-1982. It was shown that 90Sr concentration in bones of residents lived in settlements located downstream from the Techa river mouth (Shadrinsk, Isetskoye, Yalutorovsk) was 5 times higher than average 90Sr concentration in bones of the Russian residents. There was not statistically significant difference in accumulated 90Sr in bones between residents of the considered Iset' settlements indicating similar levels of 90Sr ingestion. Dietary 90Sr intake was reconstructed from the measurements of the radionuclide in bones. Total 90Sr dietary intake in 1950-1975 was 68 kBq; and 90% of the intake occurred in 1950-1961. In 1960s, 90Sr-contamination of the diet in settlements located downstream from the Techa river mouth was mostly (by 70%) due to global fallouts. Absorbed dose in the red bone marrow cumulated over 25 years of exposure was equal to 14 (4.7-42) mGy.

Bone mineral content in rib samples from Ural region residents was analyzed depending on donors' gender, age and year of birth. Bone mineral content, that reflects the mineral density, was estimated as gram of minerals per 1 kg of wet bone mass. The period of sampling and measurements covered 1958-1988, the age of donors ranged from newborn to 99 years, birth years varied from 1872 to 1984, and the total number of samples was equal to 4685. A decrease in bone mineral density during 1958-1988 period was found in groups of close ages but different years of birth indicating an existence of the secular trend. For people born before 1920, the trend was insignificant. For people born in later years, a continuous decrease in bone mineral content was observed in groups of the same ages with an average rate of 3 g/kg per year, which is about 1% per year. Longitudinal and cross-sectional studies of bone mineral density provide different estimates of age dependent rate of bone mineral loss, and these values may differ by a factor of two. Different generations, i.e. people born in different periods of the XX century, have age-dependent features of bone mineral density specific for their groups.

This paper presents the results of radioecological study of the Iset River and riverside settlements in 1961-2002. In 1961, specific activity of 90Sr in the Iset River water below the Techa River mouth was 44.4 Bq/l and decreased to 3.2 Bq/l in 2002. Annual Techa River run-offinto the Iset River was, on average, 2 x 10(12) Bq of 90Sr in 2000-2004. Density 90Sr-contamination of floodplain soils decreased downstream the Iset River from 146.1 to 37.1 kBq/m2 near the Iset River mouth. In 1977, 90Sr-specific activity of fish muscles was 18 Bq/kg and decreased to 2 Bq/kg in 2002. An average 90Sr-specific activity in milk in settlements located at distances of 12-26 km from the Techa River mouth was 10.2 Bq/l in 1961 and 1.2 Bq/l in 2001. The rate of 90Sr transfer in chain "floodplain soils --> milk" was 2 x 10(-5) (Bq/l)/(Bq/m2). Annual dietary 90Sr-intake by adult residents of the Iset riverside settlements did not exceed an annual limit of intake in 1964-2002.

The concentration of radionuclides in the upper river water depends on radionuclides flow from the Techa Cascade of Reservoirs (TCR) with filtration waters and water of bypass canals. Further concentration dynamics over the river depends on floodplain and bottom sediments contamination level. Perennial concentration dynamics of 90Sr and 137Cs in the Techa River water is stably decreases. At present time concentration of 90Sr in the water depends on TCR inflow mainly and concentration of 137Cs depends on the outflow from contaminated swampy floodplain of the upper rive. From the dam-11 to the river entry radionuclides content in the silt, as well as in the water is stably decreases. Specific activity of 137Cs in the silts is 5 rates higher than in the water and 90Sr - 3 rates higher. In the silts 137Cs prevails in the difficult of access forms, 90Sr prevails in the exchangeable and moveable forms. The highest contamination density of floodplain soils is registered in the Asanov and Muslyumov swamps area. With time content of 90Sr and 137Cs planes along the soil septh, so overall deposits are decreases. The floodplain soils contains 66.5% of 90Sr in water soluble and exchangeable forms and 94.3% of 137Cs in difficult of access forms.

The Techa River (Southern Urals, Russia) was contaminated as a result of radioactive releases by the Mayak plutonium production facility during 1949-1956. The persons born after the onset of the contamination have been identified as the "Techa River Offspring Cohort" (TROC). The TROC has the potential to provide direct data on health effects in progeny that resulted from exposure of a general parent population to chronic radiation. The purpose of the present investigation is the estimation of (90)Sr intake from breast milk and river water in the period from birth to 6 months of life, necessary for an infant dose calculation. The investigation is based on all available data concerning radioactive contamination due to global fallouts and Mayak releases in the Southern Urals where extensive radiometric and radiochemical investigations of human tissues and environmental samples were conducted during the second half of the twentieth century. The strontium transfer factor from mother's daily diet to breast milk was estimated as 0.05 (0.01-0.13) d L(-1). Based on this transfer factor and data on (90)Sr water contamination, the average total (90)Sr intake for an infant born in the middle Techa River region was found to be equal to 60-80 kBq in 1950-1951. For the same period, calculations of (90)Sr intake using ICRP models gave values of 70-100 kBq. From 1952 onwards, the differences in intakes calculated using the two approaches increased, reaching a factor of 2-3 in 1953. The Techa River data provide the basis for improving and adapting the ICRP models for application to Techa River-specific population.

A number of radiation accidents occurred at the "Mayak" plutonium production complex (Southern Urals, Russia) in 1950-60s that resulted in environmental contamination of large territories in the Southern and Middle Urals with long-lived radionuclides (90Sr, 137Cs). The results of long-term radiological monitoring were compiled into special databases at the Urals Research Center for Radiation Medicine, which allow the study of 90Sr behaviour in the environment and its accumulation in the human body. Retrospective analysis of the data on postmortem measurements of 90Sr in bones performed on residents of the Urals region over 1957-1988 were conducted for the first time. A time-dependence of 90Sr accumulation in the human body upon its density in soils was observed. Age and gender characteristics of 90Sr retention in bones were studied. It was shown that the levels of 90Sr in residents of large territories north and north-east of Chelyabinsk region, and of bordering territories of Sverdlovsk region were several times higher than the average values for the Russian Federation. Based on the measurements the direct dependence of 90Sr content in the skeleton on 90Sr density in soils was observed 30 years after the 1957 accident (the so called "Kyshtym accident"). However, for individual settlements this dependence may be weakened as a result of the influence of different biological and social factors. No influence of gender on 90Sr accumulation in the skeleton was found in the study. The analysis of age characteristics of 90Sr accumulation in bone, as influenced by skeleton growth and maturation, showed maximal levels of 90Sr from global fallout to be accumulated in bones of the persons born in 1949-1955.

Mineral content in samples of ribs, cranium, vertebra, sternum, diaphyses of long bones of lower extremities was analyzed in Urals residents in association with their age and gender. Bone mineral content was estimated in terms of gram per kilogram of wet weight of the sample. The period of sampling and measurements was 1958-1998, ages of persons studied varied form 0 to 99 years, the range of their years of birth was 1872-1984, total number of samples was 6901. The following regularities were found: 1) the rate of increase in bone mineral density in the period of childhood and youth varied from 1.3-1.5% per year in the rib to 0.5-0.9% per year in cranium and fibula; 2) for some bones (vertebrae, fibula, sternum, cranium) a period of insignificant changes of bone mineral content was observed; 3) the rate of bone mineral loss in elderly persons was dependent on gender and bone type, the rate was estimated in the range from 0.8% per year (fibula, in females after the age of 50) to 0.2-0.3% per year for other regions of the skeleton in both men and women. The comparison of data on bone mineral content obtained with different methods, is presented.

During the years 1949-1952, the Mayak Production Association (MAYAK), which was processing weapons-grade plutonium, was discharging radioactive wastes into the Techa River. As a result, all components of the river system (water, bottom soils, and flood plains) were exposed to massive radioactive contamination. The protective measures taken in the 1950's resulted in the improvement of the radioecological conditions in the Techa River. After 1952, the radioecological conditions in the area were mostly determined by the long-lived radionuclides 9OSr and 137Cs. This article focuses on the dependencies governing the migration of radionuclides along the vertical and horizontal planes in different components of the river system over a 40-y period. Until the 1990's, a decrease in 90Sr and 137Cs contents was noted in environmental samples and foodstuffs produced in riverside villages. In the subsequent years, the radioecological situation on the Techa stabilized. The sources of the current contamination of the river are represented by the runoffs from by-pass canals and swampy upper reaches.