Int. J. Environ. Res. Public Health 2009, 6 186 two-year period and that the commonly accepted inventory was biased toward longer-lived radionuclides i.e., a large proportion of the discharges in this period were likely to be radionuclides with relatively short half-lives, as yet unaccounted for in the previous discharge estimates. A scientific workshop to evaluate these findings concluded that while the TRDS-2000 dose reconstruction system was basically sound additional work was necessary such as a re-evaluation of the releases of radioactivity, and that any results based on the TRDS-2000 system should therefore be stated as being preliminary [34]. 2.2. Internal and External Doses Sr-90, with it’s half-life of 29.1 years, was the main contributor to internal exposure, as it accumulates in bone tissues and is retained for many years. Therefore, absorbed doses from 90Sr in red bone marrow and bone surfaces have been calculated for all age cohorts. As 90Sr accumulates in bone tissues, children and adolescents accumulate more 90Sr than adults. Reconstruction of internal dose depends on estimates of intake and models for metabolism of ingested radionuclides. In vivo measurements of 90Sr in teeth enamel, performed since 1959, have given information about the annual intake of 90Sr. Measurements of 90Sr whole body content have been necessary for estimating the metabolism of the radionuclide in the human body and thereby find realistic dose conversion factors. Monitoring people living along the Techa River began in 1951, including an extensive program for measuring whole body contents of long-lived radionuclides. Over half of the members of the ETRC have had individual measurements of whole body content of 90Sr. In the early 1950’s, analyses involved radiometric measurements of bioassay and autopsy samples. This program continued up to 1993, with over 7,500 analyses performed on bone samples from 5,400 autopsies. In vivo measurements started in 1959 by measuring beta activity in front teeth. Since 1974, a special whole body counter has been used to measure whole body contents of 90Sr and 137Cs [35]. About 30,000 measurements have been collected on more than 14,000 people. Further description of the internal dose reconstruction systems can be found in Degteva et al., [35]. Other radionuclides contributing to internal doses were predominantly 89Sr and 137Cs. Intake rates of 89Sr and 137Cs have been derived from estimates of ingestion of 90Sr scaled in terms of the radionuclide composition of river water. The TRDS database contains age-dependent mean-annual-intake levels for 89Sr, 90Sr, 95Zr, 95Nb, 103Ru, 106Ru, 137Cs and 141,144Ce [30]. Organ dose conversion factors for 89Sr and 90Sr were calculated for different time periods after intake using biokinetic models developed from 90Sr measurements of Techa River residents. Similar models from ICRP Publication 67 [36] were used for the other radionuclides. TRDS-2000 contains dose-conversion factors for red bone marrow (RBM), bone surface (BS), walls of the upper and lower parts of the large intestine (ULI and LLI), the wall of the small intestine (SI), stomach wall (ST), ovaries, testes and uterus. Dose rate measurements on the Techa River shoreline have been used to reconstruct external dose to the population along the Techa River [e.g., 25]. Typically, the highest dose rates measured are on the river shoreline and/or on the floodplain areas by the riverside. Absorbed doses due to external exposure can then be estimated on the basis of systematic measurements of gamma dose rates along the banks of the river and the typical living patterns of inhabitants in riverside villages. However,