Does the cortical bone resorption rate change due to <Superscript>90</Superscript>Sr-radiation exposure? Analysis of data from Techa Riverside residents

The Mayak Production Association released large amounts of ⁹⁰Sr into the Techa River (Southern Urals, Russia) with peak amounts in 1950–1951. Techa Riverside residents ingested an average of about 3,000 kBq of ⁹⁰Sr. The ⁹⁰Sr-body burden of approximately 15,000 individuals has been measured in the Urals Research Center for Radiation Medicine in 1974–1997 with use of a special whole-body counter (WBC). Strontium-90 had mainly deposited in the cortical part of the skeleton by 25 years following intake, and ⁹⁰Sr elimination occurs as a result of cortical bone resorption. The effect of ⁹⁰Sr-radiation exposure on the rate of cortical bone resorption was studied. Data on 2,022 WBC measurements were selected for 207 adult persons, who were measured three or more times before they were 50–55 years old. The individual-resorption rates were calculated with the rate of strontium recirculation evaluated as 0.0018 year⁻¹. Individual absorbed doses in red bone marrow (RBM) and bone surface (BS) were also calculated. Statistically significant negative relationships of cortical bone resorption rate were discovered related to ⁹⁰Sr-body burden and dose absorbed in the RBM or the BS. The response appears to have a threshold of about 1.5-Gy RBM dose. The radiation-induced decrease in bone resorption rate may not be significant in terms of health. However, a decrease in bone remodeling rate can be among several causes of an increased level of degenerative dystrophic bone pathology in exposed persons.     

Reconstruction of 90Sr intake for breast-fed infants in the Techa riverside settlements

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.     

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 commited 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.     

Fetal dose assessment for the offspring of the Techa Riverside residents

Massive releases of fission products from the plutonium facility Mayak (Southern Urals, Russia) resulted in the contamination of the Techa river and its floodlands (1949–1956). The results of long-term studies of exposure populations have been used for different purposes of retrospective dosimetry. The riverside residents were exposed via various pathways and their progeny were exposed in utero both to external radiation and to internal radiation from radionuclides ingested by the mothers prior to conception and during pregnancy. Fetal doses due to ⁹⁰Sr from the maternal skeleton were estimated and compared with doses from other pathways. Individual red bone marrow (RBM) doses to the late fetuses were calculated on the basis of ⁹⁰Sr contents measured in the maternal skeleton and the ⁹⁰Sr transfer coefficients (TC) to the fetal skeleton were determined on the basis of the Techa river data. Two values of TC were assumed depending on the mothers’ maturation status in the period of maximum releases: TC=0.2 for group 1 (adulthood of mothers in 1950) and TC=0.02 for group 2 (mothers not yet in menarche age in 1950). Fetal doses in both groups that resulted from the different TC values varied by a factor of about 5–8. Furthermore, the fetal RBM doses due to ⁹⁰Sr from the maternal skeleton were found to depend on the distances from the site of release and the time after major ⁹⁰Sr intake. The average fetal RBM doses in the population of the upper, middle and lower Techa riverside regions were close to the ratio 3:2:1 and 20 years after the onset of contamination, the fetal doses have decreased by a factor of about 3–5. The distance from the site of release determined the relative contribution of different pathways to the fetal dose. For the settlements that are located closest to the site of release, the external exposure was of major concern up to the date of evacuation. For the non-evacuated settlements, the contribution of internal doses was higher and after 1956, external exposure is assumed to be negligible. From 1956 on, ⁹⁰Sr that has been transferred from the maternal skeleton was practically the single source of in utero exposure. Received: 8 December 2000 / Accepted: 1 July 2001     

Concentrations of 90Sr in the tooth tissues 60 years after intake: results of TL measurements and applications for Techa River dosimetry

This article focuses on the study of ⁹⁰Sr in the tooth tissues of Techa riverside residents 60 years after intake. The Techa River was contaminated by radioactive wastes in the 1950s. Contamination of the river system, including water, bottom sediment, floodplain soil, and grass, depended on the distance from the source of releases. Therefore, the average ⁹⁰Sr intake was different in different settlements located downstream the river. An additional factor influencing ⁹⁰Sr accumulation in the teeth is the rate of tissue mineralization at the time of intake which depended on the donor’s age at the time of releases. Measurements of ⁹⁰Sr concentration in various dental tissues (enamel, crown, and root dentin) of 166 teeth were performed about 60 years after the main intake using the method of thermoluminescence passive beta detection. The paper presents the current levels of tooth tissue contamination, and the tooth-to-tooth variability of ⁹⁰Sr concentration in tooth tissues was assessed for the tissues which were matured at the time of massive liquid radioactive waste releases into the Techa River. A model describing the expected levels of ⁹⁰Sr in matured dental tissues depending on age and intake has been elaborated for the population under study. The results obtained will be used for calculation of internal dose in enamel and for interpretation of tooth doses measured by means of the electron paramagnetic resonance method, among the population of the Techa River region.     

Reconstruction of radionuclide intakes for the residents of East Urals Radioactive Trace (1957–2011)

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?×?10¹⁶ 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 ⁹⁰Sr in local foodstuffs over all of the period of interest (1958–2011; n?=?2200), which were used for relative ⁹⁰Sr intake estimations. (2) ⁹⁰Sr measurements in human bones and whole body (n?=?338); these data were used for average ⁹⁰Sr intake derivations using an age- and gender-dependent Sr-biokinetic model. Non-strontium radionuclide intakes were evaluated on the basis of ⁹⁰Sr 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. ⁹⁰Sr intakes for residents of settlements evacuated 7–14 days after the accident were also obtained from ⁹⁰Sr 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.     

Strontium metabolism in teeth and enamel dose assessment: analysis of the Techa river data

People living on the banks of the Techa river were exposed to ⁹⁰Sr in the early 1950s. Data obtained by radiochemical measurements of extracted permanent teeth, ⁹⁰Sr autopsy measurements in bone and tooth samples, in vivo measurements of surface beta activity of the anterior teeth and whole-body counter (WBC) measurements of ⁹⁰Sr in the skeleton have been analyzed. Surface beta activity measurements indicate a biological half-life of ⁹⁰Sr of about 35 years in enamel. The WBC measurements have been performed since 1974 and a model for the age-dependent strontium retention in human bone has been used to extrapolate to previous time periods when the other measurement results were obtained. For the first decade after the intake, the ratio of the ⁹⁰Sr concentrations in teeth and bones were found to decrease with age at the time of major intake, from about 10 for 1-year-old children to about 0.3 for adults. There was a considerable variability of individual data within each age group. For adults, the correlation between ⁹⁰Sr in skeleton and teeth was not high at 0.47 according to radiochemical data for posterior teeth (molars and premolars) and 0.43 according to measurements of surface beta activity for anterior teeth. For children and adolescents there was no correlation between individual measurements in the skeleton and teeth. The absorbed dose in enamel due to ⁹⁰Sr in dentine has been calculated by Monte Carlo simulations of the electron transport. The results are in agreement with EPR measurements of the absorbed dose in the enamel of persons exposed, mainly due to ⁹⁰Sr ingestion. Received: 19 July 1999 / Accepted: 5 May 2000     

Chronic low-dose exposure in the Techa River Cohort: risk of mortality from circulatory diseases

The aim of the present study was to analyze the mortality from circulatory diseases for about 30,000 members of the Techa River cohort over the period 1950–2003, and to investigate how these rates depend on radiation doses. This population received both external and internal exposures from ⁹⁰Sr, ⁸⁹Sr, ¹³⁷Cs, and other uranium fission products as a result of waterborne releases from the Mayak nuclear facility in the Southern Urals region of the Russian Federation. The analysis included individualized estimates of the total (external plus internal) absorbed dose in muscle calculated based on the Techa River Dosimetry System 2009. The cohort-average dose to muscle tissue was 35 mGy, and the maximum dose was 510 mGy. Between 1950 and 2003, 7,595 deaths from circulatory diseases were registered among cohort members with 901,563 person years at risk. Mortality rates in the cohort were analyzed using a simple parametric excess relative risk (ERR) model. For all circulatory diseases, the estimated excess relative risk per 100 mGy with a 15-year lag period was 3.6 % with a 95 % confidence interval of 0.2–7.5 %, and for ischemic heart disease it was 5.6 % with a 95 % confidence interval of 0.1–11.9 %. A linear ERR model provided the best fit. Analyses with a lag period shorter than 15 years from the beginning of exposure did not reveal any significant risk of mortality from either all circulatory diseases or ischemic heart disease. There was no evidence of an increased mortality risk from cerebrovascular disease (p > 0.5). These results should be regarded as preliminary, since they will be updated after adjustment for smoking and alcohol consumption.     

Reconstruction of the contamination of the Techa River in 1949–1951 as a result of releases from the “MAYAK” Production Association

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 ⁹⁰Sr concentration in the river water is harmonized with retrospective estimates derived from the measurements of ⁹⁰Sr in the residents of the Techa Riverside villages. Modeled contamination of the floodplain soils by ¹³⁷Cs 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.     

Evaluation of age and gender dependences of the rate of strontium elimination 25-45 years after intake: analysis of data from residents living along the Techa river

The Mayak Production Association released large amounts of 90Sr into the Techa River with peak amounts in 1950-1951. Residents near the Techa River ingested an average of approximately 3,000 kBq of 90Sr. The affected people have been followed by scientists at the Urals Research Center for Radiation Medicine. The whole-body content of 90Sr of approximately 15,000 individuals has been measured over a period of 24 years (1974-1997) using a special whole-body counter. This report evaluates the gender and age dependences of individual rates of strontium elimination. Data on persons who had been measured 12 or more times were selected for study. There were 108 men and 81 women older than 30 years who met this criterion. Individual measurement results were fitted to an exponential function and grouped mean averages of the rate of strontium elimination as a function of age for each sex were derived. For men, a significant increase (from 2.8% year(-1) to 3.2% year(-1)) in the rate of strontium elimination after age 55 years is seen. For women, the increase in the rate of elimination was significant at age 45 and reached 5.8% year(-1) after the age of 60. The results may be used to develop a gender- and age-dependent model of strontium metabolism.     

The characteristics of 90Sr accumulation and elimination in residents of the Urals region in the period of 1957-1988

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.     

Pilot study of the Urals population by tooth electron paramagnetic resonance dosimetry

During 1949–1956, about 76 × 10⁶ m³ of radioactive liquid waste containing a total activity of 10¹⁷ Bq was discharged into the Techa River by the first Russian industrial nuclear facility Mayak. As a consequence, the population living in the river valley received considerable internal and external radiation doses. The results of a first application of electron paramagnetic resonance (EPR) of tooth enamel for a retrospective individual dose evaluation of the residents of the Techa riverside are presented. Three main contributions to the dose absorbed in tooth enamel have been considered: external exposure mainly from the Techa River sediments, internal exposure mainly due to ⁹⁰Sr; and background radiation including all other sources of exposure except the Techa River. The teeth of 86 inhabitants of the town Kamensk-Uralskii were analysed to determine the age-dependent contribution of the background radiation to the enamel dose. For 22 residents of the middle and lower Techa riverside, measurements of the ⁹⁰Sr whole-body content and EPR measurements of the absorbed dose in enamel were used to establish a correlation between these two quantities. Finally, absorbed doses in the enamel of five residents of the upper Techa riverside were determined by the EPR method. Contributions of the background radiation and the internal ⁹⁰Sr contamination were subtracted to determine the external exposure of the residents.     

Mapping the distribution of (90)Sr in teeth with a photostimulable phosphor imaging detector

The present communication describes the technical aspects of the first application of an imaging plate for visualization of (90)Sr deposited in human teeth. The teeth were obtained from Techa River area residents who were exposed as a result of releases of radioactivity into the Techa River by the first Soviet nuclear plant Mayak in the early 1950s. The investigations form the basis for an experimental procedure for accurate mapping of the distribution of (90)Sr in teeth with an imaging plate. This new method can be used as an individual indicator of radionuclide intake. Its advantages are its high sensitivity (0.02 Bq/g mm(-2) of (90)Sr), it ability to examine small detectable cross-sectional areas of dental tissue (dentin) contaminated with (90)Sr (from 0.01 mm(2)), the nondestructive method of analysis, and the simplicity of use. The combined application of this method with EPR tooth biodosimetry can provide more accurate dose reconstruction and may lead to more effective radiation risk assessment.     

Measurements of radioactivity in environmental samples from the Southern Urals

A region between Chelyabinsk and Ekaterinburg in the Southern Urals has been heavily contaminated due to operational and accidental releases from the first Soviet plutonium production facility Mayak. In 1992 and 1993, the German Federal Office for Radiation Protection organized a measuring campaign involving two Russian institutes to assist with the validation of former Soviet measurement data. The results of this measuring campaign are reported here. Environmental samples were collected from areas affected by significant radioactive releases into the Techa river, which started in 1948, and by fallout from the explosion of a fission product storage tank in 1957. Soil, sediment, water, milk and food samples were independently analysed for ⁹⁰Sr, ¹³⁷Cs and plutonium by the three institutes involved. This paper presents data on the present levels of environmental radioactivity. The highest contamination of areas accessible to the local population was found in the vicinity of the Techa river around Muslumovo. Activity concentration of floodplain samples reached up to 37 000 Bq ⋅ kg^{–1 137}Cs, 5 600 Bq ⋅ kg^{–1 90}Sr and 9.9 Bq ⋅ kg^–1 Pu. Milk and potatoes from private farms in Muslumovo showed low activity in the range from 0.7 Bq ⋅ kg^–1 to 25 Bq ⋅ kg^{–1 90}Sr. The results of the three independent measurement teams showed sufficient agreement. One Russian laboratory obtained plutonium activities that exceeded the results of the other laboratories by about 20%. Contrary to the International Chernobyl Project, there was no overestimation of ⁹⁰Sr activities in the Russian analyses. Therefore, the validity of earlier data sets acquired with same methodology and quality control can be considered a valuable basis for further assessments and for dose reconstruction in epidemiological projects. Received: 18 July 1997 / Accepted in revised form: 19 December 1997     

Preliminary FISH-based assessment of external dose for residents exposed on the Techa River

This paper presents the results of a feasibility cytogenetic study using the fluorescence in situ hybridization (FISH) translocation assay for residents of villages located on the Techa River (Southern Urals, Russia) contaminated with liquid radioactive wastes from the Mayak plutonium facility in 1949-1956. The study was conducted with two groups of donors that differed in their main pathways of exposure. The first group comprised 18 residents of the middle Techa region who were exposed predominantly from ingestion of radionuclides (mostly (89,90)Sr) via the river water and local foodstuffs. The second group included 20 residents of Metlino, the closest village to the site of releases, who were exposed to external γ radiation from the contaminated river bank and exposed internally from dietary intake of radionuclides. A significant linear dependence between the radiation-induced translocation frequency and individual red bone marrow dose from incorporated (89,90)Sr, calculated with the Techa River Dosimetry System (TRDS), was found in the first group of donors. This allowed us to take the contribution of (89,90)Sr to the total radiation-induced translocation frequency into account for the second group of donors and to analyze translocations resulting from external γ-ray exposure. Individual doses from external exposure derived from the corrected translocation frequency for the second group of donors (Metlino residents), using a linear dose-response coefficient of 0.015 translocation/cell/Gy recommended by Edwards et al. in 2005, were shown to vary up to 2.1 Gy, with an average value of 0.48 Gy, which was in agreement with TRDS-based external dose estimates for Metlino residents.     

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.     

The application and adaptation of ICRP internal dosimetry models to the calculation of bone marrow tissue doses from 90Sr for epidemiological studies of Techa River populations

The operation of the Mayak Production Association in the Southern Urals region of Russia, resulted in releases of large amounts of radioactive effluent into the Techa River during the period 1949-1956. The residents of the riverside communities were thus exposed to both external radiation, and internal radiation following ingestion of contaminated water and foodstuffs. One of the most important radionuclides for internal exposure was 90Sr. This paper gives a brief overview of the models provided by International Commission on Radiological Protection (ICRP), which are of interest for assessing internal doses from 90Sr. The application of these models to the calculation of red bone marrow doses for the fetus and infant from 90Sr intakes by the mother and the infant is illustrated by an example. A hypothetical individual born in 1951 is used as an example for dose calculations. The following doses due to intakes of 90Sr are taken into account: received in utero due to maternal intakes during pregnancy; received after birth from 90Sr accumulated by the fetus in utero; from intakes in breast milk; from intakes in the infant's diet after weaning. It is shown that doses to the fetus following maternal ingestion and subsequent transfer to the fetus via the placenta dominate the doses received for this particular individual for the first two years of life. Doses to the infant from intakes in breast milk are substantially lower but do make significant contributions to total doses in the first two years after birth. By about the age of two years residual 90Sr from placental transfer still contributes about the same dose as do intakes by the infant, but in later years doses from intakes by the infant dominate.     

Analysis of solid cancer mortality in the techa river cohort using the two-step clonal expansion model

In this study the solid cancer mortality data in the Techa River Cohort in the Southern Urals region of Russia was analyzed. The cohort received protracted exposure in the 1950s due to the releases of radioactive materials from the Mayak plutonium complex. The Extended Techa River Cohort includes 29,849 people who resided along the Techa River between 1950 and 1960 and were followed from January 1, 1950 through December 31, 1999. The analysis was done within the framework of the biologically based two-stage clonal expansion (TSCE) model. It was found that about 2.6% of the 1854 solid cancer deaths (excluding 18 bone cancer cases) could be related to radiation exposure. At age 63, which is the mean age for solid cancer deaths, the excess relative risk (ERR) and excess absolute risk (EAR) were found to be 0.76 Gy(-1) (95% CI 0.23; 1.29) and 33.0 (10(4) PY Gy)(-1) (95% CI 9.8; 52.6), respectively. These risk estimates are consistent with earlier excess relative risk analyses for the same cohort. The change in the ERR with age was investigated in detail, and an increase in risk with attained age was observed. Furthermore, the data were tested for possible signs of genomic instability, and it was found that the data could be described equally well by a model incorporating effects of genomic instability. Results from the TSCE models indicated that radiation received at older ages might have stronger biological effects than exposure at younger ages.     

Cytogenetic consequences of chronic irradiation in rodent populations inhabiting the Eastern Ural Radioactive Trace zone

Chromosome instability in bone-marrow cells and ⁹⁰Sr accumulation in the bone tissue are studied in rodents (Apodemus (Sylvaemus) uralensis Pall., 1811 and Apodemus agrarius Pall., 1771)* inhabiting the Eastern Ural Radioactive Trace (EURT) zone (Kyshtym radiation accident 1957) and adjacent areas of the Urals. Intensive mutagenic process in both species from impact plots (soil pollution by ⁹⁰Sr, 2322–16690 kBq/m²) is found. Significant positive correlation of the frequency of aberrant cells and the concentration of ⁹⁰Sr is shown. Possible causes of the lack of resistance to long-term mutagenic factors (over 100 generations in the 50 years since the accident), such as migration of animals and the specific configuration of the EURT zone (an extended narrow territory with a sharply falling gradient of radionuclide pollution), which considerably decrease the probability that certain changes will be fixed and inherited in a series of generations of rodents, are discussed.