[Application of the EPR and FISH Methods to Dose Reconstruction for People Exposed in the Techa River Area].

Release of liquid radioactive waste into the Techa River from the Mayak Production Association during 1949-1956 resulted in a significant exposure of about 30000 people who lived in downstream settlements. The residents were exposed to internal and external radiation. The article discusses the capability of two methods that were used 50 years after the termination of radioactive discharges for the dose reconstruction, namely EPR measurements of tooth enamel, and FISH measurements of stable chromosome aberrations in circulating lymphocytes. The Main issue in the application of these methods for the dose reconstruction was local irradiation from strontium radioisotopes incorporated in teeth and bones. The EPR and FISH assays were supported by measurements of the 90Sr content in the skeleton and teeth in order to estimate and subtract internal doses from incorporated 89, 90Sr. The resulting dose estimates obtained from EPR and FISH mea- surements were found to be consistent The settlement-averaged values in the upper-Techa Region varied from 550-570 mGy to 130-160 mGy and showed a reduction with the distance from the release site. The EPR- and FISH-based dose estimates were in agreement with the doses calculated with the dosimetry system TRDS that uses data on radionuclide contamination of the Techa River floodplain and individual residential histories.

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.

Trabecula: A Random Generator of Computational Phantoms for Bone Marrow Dosimetry.

This study was motivated by the efforts to evaluate radiation risk for leukemia incidence in the Techa River cohort, where the main bone marrow dose contributors were Sr (bone-seeking beta emitters). Energy deposition in bone marrow targets was evaluated by simulating radiation particle transport using computational phantoms. The present paper describes the computer program Trabecula implementing an algorithm for parametric generation of computational phantoms, which serve as the basis for calculating bone marrow doses. Trabecula is a user-friendly tool that automatically converts analytical models into voxelized representations that are directly compatible as input to Monte Carlo N Particle code.

Possibilities of using human teeth for retrospective dosimetry: analysis of the Techa River data.

Different methods for utilising teeth were applied for the reconstruction of internal and external doses for the population of the Techa riverside area contaminated as a result of radioactive releases from the Mayak plutonium-production facility. Information on 90Sr content in the enamel of teeth obtained from the Techa River residents has been used for the reconstruction of intakes of this nuclide. Analyses of dosimetric investigations on dental tissues performed in the Techa River region provide an understanding of the possibilities and limitations of using human teeth in retrospective dosimetry studies.

An approach to reduction of uncertainties in internal doses reconstructed for the Techa River population.

A methodology was developed for reduction of uncertainties in estimates of internal dose for residents of the Techa Riverside communities, who were exposed as a result of releases of radionuclides from the Mayak plutonium production facility in 1949-56. The 'Techa River Dosimetry System' (TRDS) was specifically elaborated for reconstruction of doses. A preliminary analysis of uncertainty for doses estimated using the current version of the TRDS showed large ranges in the uncertainty of internal absorbed dose and led to suggestions of methods to reduce uncertainties. The new methodological approaches described in this paper will allow for significant reduction of uncertainties of 90Sr-dose. The major sources of reduction are: making use of individual measured values of 90Sr and through development of a Household Registry to associate unmeasured persons with measured persons living in the same household(s).

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.

Evaluation of uncertainties in 90Sr-body-burdens obtained by whole-body count: application of Bayes' rule to derive detection limits by analysis of a posteriori data.

A whole body counter (WBC) designed to measure bremsstrahlung from 90Y, the short-lived daughter of 90Sr, has been used since 1974 to measure 90Sr-body burdens in residents along the Techa River, which was contaminated by releases from the Mayak Production Association. Bayes' rule has been applied to the a posteriori WBC data in order to derive the uncertainties associated with the data: The lower limit of reliable detection is 2.0 kBq and the uncertainty of routine measurements is 1.6 kBq.