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

Radioactivity and radionuclides in deciduous teeth formed before the Fukushima-Daiichi Nuclear Power Plant accident

The Fukushima-Daiichi Nuclear Power Plant (FNPP) accident in March of 2011 released substantial amounts of radionuclides into the environment. We collected 4,957 deciduous teeth formed in children before the Fukushima accident to obtain precise control data for teeth formed after the accident. Radioactivity was measured using imaging plates (IP) and epidemiologically assessed using multivariate regression analysis. Additionally, we measured ⁹⁰Sr, ¹³⁷Cs, and natural radionuclides which might be present in teeth. Epidemiological studies of IP showed that the amount of radioactivity in teeth from Fukushima prefecture was similar to that from reference prefectures. We found that artificial radionuclides of ⁹⁰Sr and ¹³⁷Cs, which were believed to have originated from past nuclear disasters, and natural radionuclides including ⁴⁰ K and daughter nuclides in the ²³⁸U and ²³²Th series contributed to the generation of radioactivity in teeth. We also found no evidence to suggest that radionuclides originating from the FNPP accident significantly contaminated pre-existing teeth. This is the first large-scale investigation of radioactivity and radionuclides in teeth. The present findings will be indispensable for future studies of teeth formed after the FNPP accident, which will fall out over the next several years and might be more contaminated with radionuclides.

Eurados review of retrospective dosimetry techniques for internal exposures to ionising radiation and their applications

This work presents an overview of the applications of retrospective dosimetry techniques in case of incorporation of radionuclides. The fact that internal exposures are characterized by a spatially inhomogeneous irradiation of the body, which is potentially prolonged over large periods and variable over time, is particularly problematic for biological and electron paramagnetic resonance (EPR) dosimetry methods when compared with external exposures. The paper gives initially specific information about internal dosimetry methods, the most common cytogenetic techniques used in biological dosimetry and EPR dosimetry applied to tooth enamel. Based on real-case scenarios, dose estimates obtained from bioassay data as well as with biological and/or EPR dosimetry are compared and critically discussed. In most of the scenarios presented, concomitant external exposures were responsible for the greater portion of the received dose. As no assay is available which can discriminate between radiation of different types and different LETs on the basis of the type of damage induced, it is not possible to infer from these studies specific conclusions valid for incorporated radionuclides alone. The biological dosimetry assays and EPR techniques proved to be most applicable in cases when the radionuclides are almost homogeneously distributed in the body. No compelling evidence was obtained in other cases of extremely inhomogeneous distribution. Retrospective dosimetry needs to be optimized and further developed in order to be able to deal with real exposure cases, where a mixture of both external and internal exposures will be encountered most of the times.

Radiological impact assessment for workers on treatment of radioactive spent resin from heavy water reactors

In heavy water reactors, radionuclides are generated, then removed and treated by ion exchange resin. The disposal cost of spent resin is expected to increase because of the saturation of the existing storage capacity. In this study, a spent resin treatment process using microwaves is proposed, and a radiological safety assessment and cost evaluation of the spent resin treatment process are performed. A dose assessment was conducted by using the established exposure scenarios and the RESRAD-Build software. A sensitivity analysis was conducted to identify the main contributory radionuclide of the dose according to each exposure pathway because a spent resin consists of various radionuclides. The main exposure pathway was identified, and sensitivity analysis was applied to the working time and radioactivity concentrations of ¹⁴C, ⁶⁰Co and ¹³⁷Cs to confirm their effect on the dose. Finally, an optimal shielding system for a safe work environment was proposed. The disposal cost of the spent resin is reduced by lowering its radioactivity level via a treatment process using microwaves. The treatment process can reduce the radioactivity level through the desorption of ¹⁴C and can also recycle the ¹⁴C nuclide. These characteristics have great economic advantages from the viewpoint of the entire nuclear energy cycle. Thus, this study evaluates the radiological safety of the spent resin treatment process for actual application in a heavy water reactor power plant.

IN-VIVO RADIATION DOSIMETRY USING PORTABLE L BAND EPR: ON-SITE MEASUREMENT OF VOLUNTEERS IN FUKUSHIMA PREFECTURE, JAPAN

The aim of this study was to make direct measurements of the possible radiation-induced EPR signals in the teeth of volunteers who were residents in Fukushima within 80 km distance from the Fukushima Nuclear Power plant at the time of the disaster, and continued to live there for at least 3 month after the disaster. Thirty four volunteers were enrolled in this study. These measurements were made using a portable L-band EPR spectrometer, which was originally developed in the EPR Center at Dartmouth. All measurements were performed using surface loop resonators that have been specifically designed for the upper incisor teeth. Potentially these signals include not only radiation-induced signals induced by the incident but also background signals including those from prior radiation exposure from the environment and medical exposure. We demonstrated that it is feasible to transport the dosimeter to the measurement site and make valid measurements. The intensity of the signals that were obtained was not significantly above those seen in volunteers who had not had potential radiation exposures at Fukushima.

External dose reconstruction in tooth enamel of Techa riverside residents

This study summarizes the 20-year efforts for dose reconstruction in tooth enamel of the Techa riverside residents exposed to ionizing radiation as a result of radionuclide releases into the river in 1949-1956. It represents the first combined analysis of all the data available on EPR dosimetry with teeth of permanent residents of the Techa riverside territory. Results of electron paramagnetic resonance (EPR) measurements of 302 teeth donated by 173 individuals living permanently in Techa riverside settlements over the period of 1950-1952 were analyzed. These people were residents of villages located at the free-flowing river stream or at the banks of stagnant reservoirs such as ponds or blind river forks. Cumulative absorbed doses measured using EPR are from several sources of exposure, viz., background radiation, internal exposure due to bone-seeking radionuclides (⁸⁹Sr, ⁹⁰Sr/⁹⁰Y), internal exposure due to ¹³⁷Cs/^137mBa incorporated in soft tissues, and anthropogenic external exposure. The purpose of the present study was to evaluate the contribution of different sources of enamel exposure and to deduce external doses to be used for validation of the Techa River Dosimetry System (TRDS). Since various EPR methods were used, harmonization of these methods was critical. Overall, the mean cumulative background dose was found to be 63 ± 47 mGy; cumulative internal doses due to ⁸⁹Sr and ⁹⁰Sr/⁹⁰Y were within the range of 10-110 mGy; cumulative internal doses due to ¹³⁷Cs/^137mBa depend on the distance from the site of releases and varied from 1 mGy up to 90 mGy; mean external doses were maximum for settlements located at the banks of stagnant reservoirs (~500 mGy); in contrast, external doses for settlements located along the free-flowing river stream did not exceed 160 mGy and decreased downstream with increasing distance from the site of release. External enamel doses calculated using the TRDS code and derived from the EPR measurements were found to be in good agreement.

(90)Sr in teeth of cattle abandoned in evacuation zone: Record of pollution from the Fukushima-Daiichi Nuclear Power Plant accident

Here we determined the ⁹⁰Sr concentrations in the teeth of cattle abandoned in the evacuation area of the Fukushima-Daiichi Nuclear Power Plant (FNPP) accident. ⁹⁰Sr activity concentrations in the teeth varied from 6–831 mBq (g Ca)⁻¹ and exhibited a positive relationship with the degree of radioactive contamination that the cattle experienced. Even within an individual animal, the specific activity of ⁹⁰Sr (Bq (g Sr)⁻¹) varied depending on the development stage of the teeth during the FNPP accident: teeth that were early in development exhibited high ⁹⁰Sr specific activities, while teeth that were late in development exhibited low specific activities. These findings demonstrate that ⁹⁰Sr is incorporated into the teeth during tooth development; thus, tooth ⁹⁰Sr activity concentrations reflect environmental ⁹⁰Sr levels during tooth formation. Assessment of ⁹⁰Sr in teeth could provide useful information about internal exposure to ⁹⁰Sr radiation and allow for the measurement of time-course changes in the degree of environmental ⁹⁰Sr pollution.

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 (90)Sr 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 (90)Sr intake was different in different settlements located downstream the river. An additional factor influencing (90)Sr 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 (90)Sr 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 (90)Sr 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 (90)Sr 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.

Review of reconstruction of radiation incident air kerma by measurement of absorbed dose in tooth enamel with EPR

Electron paramagnetic resonance dosimetry with tooth enamel has been proved to be a reliable method to determine retrospectively exposures from photon fields with minimal detectable doses of 100 mGy or lower, which is lower than achievable with cytogenetic dose reconstruction methods. For risk assessment or validating dosimetry systems for specific radiation incidents, the relevant dose from the incident has to be calculated from the total absorbed dose in enamel by subtracting additional dose contributions from the radionuclide content in teeth, natural external background radiation and medical exposures. For calculating organ doses or evaluating dosimetry systems the absorbed dose in enamel from a radiation incident has to be converted to air kerma using dose conversion factors depending on the photon energy spectrum and geometry of the exposure scenario. This paper outlines the approach to assess individual dose contributions to absorbed dose in enamel and calculate individual air kerma of a radiation incident from the absorbed dose in tooth enamel.

Review of retrospective dosimetry techniques for external ionising radiation exposures

The current focus on networking and mutual assistance in the management of radiation accidents or incidents has demonstrated the importance of a joined-up approach in physical and biological dosimetry. To this end, the European Radiation Dosimetry Working Group 10 on 'Retrospective Dosimetry' has been set up by individuals from a wide range of disciplines across Europe. Here, established and emerging dosimetry methods are reviewed, which can be used immediately and retrospectively following external ionising radiation exposure. Endpoints and assays include dicentrics, translocations, premature chromosome condensation, micronuclei, somatic mutations, gene expression, electron paramagnetic resonance, thermoluminescence, optically stimulated luminescence, neutron activation, haematology, protein biomarkers and analytical dose reconstruction. Individual characteristics of these techniques, their limitations and potential for further development are reviewed, and their usefulness in specific exposure scenarios is discussed. Whilst no single technique fulfils the criteria of an ideal dosemeter, an integrated approach using multiple techniques tailored to the exposure scenario can cover most requirements.

Reconstruction of long-lived radionuclide intakes for Techa riverside residents: strontium-90

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.

EPR dosimetry with tooth enamel: A review

When tooth enamel is exposed to ionizing radiation, radicals are formed, which can be detected using electron paramagnetic resonance (EPR) techniques. EPR dosimetry using tooth enamel is based on the (presumed) correlation between the intensity or amplitude of some of the radiation-induced signals with the dose absorbed in the enamel. In the present paper a critical review is given of this widely applied dosimetric method. The first part of the paper is fairly fundamental and deals with the main properties of tooth enamel and some of its model systems (e.g., synthetic apatites). Considerable attention is also paid to the numerous radiation-induced and native EPR signals and the radicals responsible for them. The relevant methods for EPR detection, identification and spectrum analyzing are reviewed from a general point of view. Finally, the needs for solid-state modelling and studies of the linearity of the dose response are investigated. The second part is devoted to the practical implementation of EPR dosimetry using enamel. It concerns specific problems of preparation of samples, their irradiation and spectrum acquisition. It also describes how the dosimetric signal intensity and dose can be retrieved from the EPR spectra. Special attention is paid to the energy dependence of the EPR response and to sources of uncertainties. Results of and problems encountered in international intercomparisons and epidemiological studies are also dealt with. In the final section the future of EPR dosimetry with tooth enamel is analyzed.

Development of in vivo tooth EPR for individual radiation dose estimation and screening

The development of in vivo EPR has made it feasible to perform tooth dosimetry measurements in situ, greatly expanding the potential for using this approach for immediate screening after radiation exposures. The ability of in vivo tooth dosimetry to provide estimates of absorbed dose has been established through a series of experiments using unirradiated volunteers with specifically irradiated molar teeth placed in situ within gaps in their dentition and in natural canine teeth of patients who have completed courses of radiation therapy for head and neck cancers. Multiple measurements in patients who have received radiation therapy demonstrate the expected heterogeneous dose distributions. Dose-response curves have been generated using both populations and, using the current methodology and instrument, the standard error of prediction based on single 4.5-min measurements is approximately 1.5 Gy for inserted molar teeth and between 2.0 and 2.5 Gy in the more irregularly shaped canine teeth. Averaging of independent measurements can reduce this error significantly to values near 1 Gy. Developments to reduce these errors are underway, focusing on geometric optimization of the resonators, detector positioning techniques, and optimal data averaging approaches. In summary, it seems plausible that the EPR dosimetry techniques will have an important role in retrospective dosimetry for exposures involving large numbers of individuals.

The neutron dose conversion coefficients calculation in human tooth enamel in an anthropomorphic phantom

In the present study, MCNP4B simulation code is used to simulate neutron and photon transport. It gives the conversion coefficients that relate neutron fluence to the dose in tooth enamel (molars and pre-molars only) for 20 energy groups of monoenergetic neutrons with energies from 10-9 to 20 MeV for five different irradiation geometries. The data presented are intended to provide the basis for connection between EPR dose values and standard protection quantities defined in ICRP Publication 74. The results of the calculations for critical organs were found to be consistent with ICRP data, with discrepancies generally less than 10% for the fast neutrons. The absorbed dose in enamel was found to depend strongly on the incident neutron energy for neutrons over 10 keV. The dependence of the data on the irradiation geometry is also shown. Lower bound estimates of enamel radiation sensitivity to neutrons were made using obtained coefficients for the secondary photons. Depending on neutron energy, tooth enamel was shown to register 10-120% of the total neutron dose in the human body in the case of pure neutron exposure and AP irradiation geometry.

Radiation dose measurement by electron spin resonance studies of tooth enamel in lime and non-lime consuming individuals from the Silchar region of northeast India

Electron spin resonance (ESR) dosimetry of teeth is used extensively for dose estimation following exposure to radiation. The population inhabiting the northeast region of India is prone to different cancers of the head and neck, and their prevalence is several times the national average. The objective of this study was to determine the role of radiation in the causation of this high cancer incidence by performing ESR spectroscopic measurements of tooth samples collected from the general population living in and around the city of Silchar. Nineteen tooth samples were used, and the age of the patients was 13-60 years. The excess dose, determined by subtraction of the natural background dose from the dose absorbed by the enamel, was found to the extent of 123 +/- 43 mGy. However, the individual excess dose was found to be higher in subjects who consumed lime (5/6) than in non-lime-consuming subjects (2/13). It is not entirely clear if radiation is the cause of this excess cancer in this region of India. Therefore there is a need for wider studies including consideration of tobacco consumption as well as a larger number of samples for tooth enamel dosimetry.

Development of an Improved Dose Reconstruction System for the Techa River Population Affected by the Operation of the Mayak Production Association

The Techa River Dosimetry System (TRDS) has been developed to provide estimates of dose received by approximately 30,000 members of the Extended Techa River Cohort (ETRC). Members of the ETRC were exposed beginning in 1949 to significant levels of external and internal (mainly from (90)Sr) dose but at low to moderate dose rates. Members of this cohort are being studied in an effort to test the hypothesis that exposure at low to moderate dose rates has the same ability to produce stochastic health effects as exposure at high dose rates. The current version of the TRDS is known as TRDS-2000 and is the subject of this paper. The estimated doses from (90)Sr are supported strongly by approximately 30,000 measurements made with a tooth beta-particle counter, measurements of bones collected at autopsy, and approximately 38,000 measurements made with a special whole-body counter that detects the bremsstrahlung from (90)Y. The median doses to the red bone marrow and the bone surface are 0.21 and 0.37 Gy, respectively. The maximum doses to the red bone marrow and bone surface are 2.0 and 5.2 Gy, respectively. Distributions of dose to other organs are provided and are lower than the values given above. Directions for future work are discussed.

Parameters affecting EPR dose reconstruction in teeth

The aim of this paper is to analyze the lower limit of detection (LLD), linearity of dose response, variation of radiation sensitivity between different tooth enamel samples, and time/temperature stability of EPR biodosimetry in tooth enamel. The theoretical LLD is shown to be 0.46 mGy, which is far lower than the measured value of about 30 mGy. The main issues to lowering LLD are the differentiation of the radiation-induced component against the total EPR spectrum and the complex nature of the dose dependence of the EPR signal. The following questions are also discussed in detail: need for exfoliated or extracted teeth from persons of interest, accounting for background radiation contribution; conversion of tooth enamel absorbed dose to effective dose; accounting for internal exposure specifically from bone-seeking radionuclides. Conclusions on future development of EPR retrospective biodosimetry are made.

Comparison of gamma- and UV-light-induced EPR spectra of enamel from deciduous molar teeth

From previous work, it is known that CO2- radicals in tooth enamel are induced by gamma as well as by UV-light exposure. The parameters of the EPR signal of the CO2- radical were found to be independent of the source of exposure. However, it would be desirable for retrospective dosimetry to identify other characteristic features of the EPR spectrum of tooth enamel, which would allow differentiation between the two sources of exposure. In the present work, enamel of deciduous molars was exposed to gamma-radiation from a 60Co-source and 254 nm UV-light from a low-pressure mercury lamp. The resulting EPR spectra were deconvoluted, and the native spectrum simulated from spectra of the CO2- radical, and two further EPR lines. Both EPR signals of the native spectrum were located at g=2.0046, but were different in line shape and width. One was a 1 mT wide isotropic signal of Gaussian line shape while the other was a 0.7 mT wide axial signal of Lorentzian line shape. A comparable study of the amplitudes of the native and CO2- signals was done before and after gamma- and UV-light exposure. While the native signals were found to be only slightly sensitive to gamma-radiation, their amplitude increased significantly on UV-light exposure. Feasibilities are discussed to distinguish different radiation sources by exposure-induced alterations of the native EPR spectrum.

The 3rd international intercomparison on EPR tooth dosimetry: Part 1, general analysis

The objective of the 3rd International Intercomparison on Electron Paramagnetic Resonance (EPR) Tooth Dosimetry was the evaluation of laboratories performing tooth enamel dosimetry below 300 mGy. Participants had to reconstruct the absorbed dose in tooth enamel from 11 molars, which were cut into two halves. One half of each tooth was irradiated in a 60Co beam to doses in the ranges of 30-100 mGy (5 samples), 100-300 mGy (5 samples), and 300-900 mGy (1 sample). Fourteen international laboratories participated in this intercomparison programme. A first analysis of the results and an overview of the essential features of methods applied in different laboratories are presented. The relative standard deviation of results of all methods was better than 27% for applied doses in the range of 79-704 mGy. In the analysis of the unirradiated tooth halves 8% of the samples were identified as outliers with additional absorbed dose above background dose.

Electron paramagnetic resonance and fluorescence in situ hybridization-based investigations of individual doses for persons living at Metlino in the upper reaches of the Techa River

Waterborne releases to the Techa River from the Mayak Production Association in Russia during 1949-1956 resulted in significant doses to persons living downstream; the most contaminated village was Metlino, about 7 km from the site of release. Internal and external doses have been estimated for these residents using the Techa River Dosimetry System-2000 (TRDS-2000); the primary purpose is to support epidemiological studies of the members of the Extended Techa River Cohort. Efforts to validate the calculations of external and internal dose are considered essential. One validation study of the TRDS-2000 system has been performed by the comparison of calculated doses to quartz from bricks in old buildings at Metlino with those measured by luminescence dosimetry. Two additional methods of validation considered here are electron paramagnetic resonance (EPR) measurements of teeth and fluorescence in situ hybridization (FISH) measurements of chromosome translocations in circulating lymphocytes. For electron paramagnetic resonance, 36 measurements on 26 teeth from 16 donors from Metlino were made at the GSF-National Research Center for Environment and Health (16 measurements) and the Institute of Metal Physics (20 measurements); the correlation among measurements made at the two laboratories has been found to be 0.99. Background measurements were also made on 218 teeth (63 molars, 128 premolars, and 27 incisors). Fluorescence in situ hybridization measurements were made for 31 residents of Metlino. These measurements were handicapped by the analysis of a limited number of cells; for several individuals no stable translocations were observed. Fluorescence in situ hybridization measurements were also made for 39 individuals believed to be unexposed. The EPR- and FISH-based estimates agreed well for permanent residents of Metlino: 0.67 +/- 0.21 Gy and 0.48 +/- 0.18 Gy (mean +/- standard error of the mean), respectively. Results of the two experimental methods also agreed well with the estimates derived from the use of the TRDS-2000. For all persons investigated according to each technique, the EPR-measured dose to enamel was 0.55 +/- 0.17 Gy, and the TRDS-2000 prediction for the dose to enamel for these individuals is 0.55 +/- 0.07 Gy. The fluorescence in situ hybridization-based dose, 0.38 +/- 0.10 Gy, compared well to the TRDS-2000 prediction of external dose, 0.31 +/- 0.03 Gy, to red bone marrow for these persons. Validation of external doses at the remaining villages is an active area of investigation.

Estimation of radiation levels by EPR measurement of tooth enamel in Indian populations

Enamel from 34 molars from 22 individuals in the general population are used to evaluate the background radiation in six cities in India. The estimation of the background dose for each tooth is evaluated using two EPR methods: the calibration-curve method and the additive-dose method. The variation of the estimated EPR dose with tooth position is investigated by using eight teeth taken from the same person. Contribution of the dental X-ray treatments to the enamel-absorbed dose was evaluated using another 17 teeth exposed from 1 to 10 times.

Age dependencies of 90Sr incorporation in dental tissues: comparative analysis and interpretation of different kinds of measurements obtained for residents on the Techa River

Human teeth have been considered as dosimeters for decades. Methods include the in vivo measurement of 90Sr/90Y in teeth with a tooth-beta counter, the radiochemical determination of 90Sr in whole teeth, and the measurement of dose in teeth by use of electron paramagnetic resonance. Presented in this paper are results of 2,514 tooth-beta counter measurements, 334 radiochemical measurements, and 218 electron paramagnetic resonance measurements for residents living in settlements along the Techa River. All three kinds of measurements indicate a sharp peak that corresponds to the uptake of 90Sr by tooth tissue. The results can be interpreted in terms of an intake function for 90Sr only if the period of calcification of each individual tooth is considered--such detail on a tooth-by-tooth basis is presented in this paper. The conclusion is reached that the tooth-beta counter data are the most reliable in terms of reconstruction of 90Sr intake; this is due in part to the fact that the tooth-beta counter measures four teeth (all at position 1) with essentially the same time periods of mineralization and because there are a large number of tooth-beta counter measurements. The main utility of electron paramagnetic resonance measurements is considered to be the validation of estimates of external dose; but for this purpose teeth with 90Sr taken up into enamel must be avoided.

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.

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.

Correction factors in the EPR dose reconstruction for residents of the Middle and Lower Techa riverside

During 1949-1956, the first Soviet nuclear weapons plant, Mayak, released about 7.6 x 10(7) m(-3) of liquid radioactive waste with a total activity of 10(17) Bq into the Techa River (Southern Urals, Russia). 90Sr contributed 11.6% to the total waste radioactivity. As a result of these radioactive discharges, about 28,000 local residents were exposed to ionizing radiation, and some of them received relatively high doses. Internal exposure of the population residing at the Middle and Lower Techa riverside was mostly from 90Sr deposited in bone and tooth tissues. In order to reconstruct radiation doses to this population group, a study of 35 teeth extracted from local residents was carried out using electron paramagnetic resonance measurements. A total of 73 samples from these 35 teeth (tooth enamel, 33; crown dentin, 20; and root dentin, 20) were prepared and measured with electron paramagnetic resonance. The study revealed high doses (up to 15 Gy) absorbed in tooth enamel of the individuals born during 1945-1949, which was attributed to very high local 90Sr concentration in tooth enamel of this particular age group in the population. The analysis presented here takes into account (a) the time courses both of the release/intake of 90Sr and of the tooth formation, and (b) expected variations in measured absorbed doses due to differing geometric sizes of tooth structures. This methodology enables a more consistent picture to be developed of the 90Sr intake by the Middle and Lower Techa riverside population, based on electron paramagnetic resonance tooth dosimetry.

A mathematical model for calculation of 90Sr absorbed dose in dental tissues: elaboration and comparison to EPR measurements

A mathematical model for calculation of the 90Sr absorbed doses in dental tissues is presented. The results of the Monte-Carlo calculations are compared to the data obtained by EPR measurements of dental tissues. Radiometric measurements of the 90Sr concentrations. TLD and EPR dosimetry investigations were performed in animal (dog) study. The importance of the irregular 90Sr distribution in the dentine for absorbed dose formation has been shown. The dominant dose formation factors (main source-tissues) were identified for the crown dentine and enamel. The model has shown agreement with experimental data which allows to determine further directions of the human tooth model development.