Int. J. Environ. Res. Public Health 2009, 6 194 excess relative risk per Gy for solid cancers of 0.92 (95 % CI 0.2; 1.7). For leukemia the corresponding values reported are 4.2 (CI 95 % 2.1; 13) and 6.5 (CI 95 % 1.8; 24), including and excluding lymphocytic leukemia, respectively. Furthermore, they associate about 2.5 % of solid cancer deaths and about 63 % of leukemia deaths to exposure to radiation. During 1994-1996 a research team of the Siberian Medical University conducted an investigation of chromosome aberrations and whole body doses in the radiation exposed population of four settlements in the Techa River Region. The methods used were chromosome analysis, electron spin resonance (ESR) of tooth enamel and whole body measurements of 137Cs and 90Sr [52]. Approximately 60 individuals from each of the four most exposed remaining settlements in the Techa River Region participated in the survey. Compared to the control group there was a significant increase in frequencies of chromosome aberrations in the peripheral blood of inhabitants of all the four exposed villages. A high frequency of lymphocytes with dicentric and ring chromosomes was observed, corresponding to whole body activity levels of 90Sr measured by the whole body counter. The highest whole body 90Sr activity levels and frequency and chromosome aberrations were found in Muslyumovo: highest levels of both chromosome aberrations and whole body 90Sr activity were found in adults, born between 1949 and 1957 when the largest exposures took place [52]. This indicates that chromosome aberrations can still be found a long time after irradiation that occurred around the time of birth. The Techa River Cohort data has also been used to study the malignant neoplasms among the progeny of exposed people [53]. The study group comprised children aged 0-4 years during the period from 1950 to 1954, children aged 0-9 years during the period from 1955 to 1959 and persons aged 0 - 29 years by the end of the year of the follow-up study. The progeny were divided in 6 groups after the estimated doses to parental gonads. The average doses to parental gonads in the six groups were from 0.032 Gy to 1.3 Gy. The study showed that there was no increased number of cancer deaths in the progeny of exposed persons compared to the persons in the control group. However, the small number of deaths by the time of the study was deemed to make the conclusions regarding dose dependencies rather uncertain. Studies of chromosome aberrations in the child population of Muslyumovo have also been reported [44]. Here, a significant difference between Muslyumovo children (n = 15) and an age- matched control group (n = 11) from an uncontaminated Russian village was reported, where 0.56 ± 0.08 chromosome aberrations per 100 cells were recorded in Muslyumovo compared to 0.29 ± 0.07 in the controls [44]. 4. Conclusions Although contamination has greatly reduced since the period of maximum discharges of radioactivity from the Mayak PA, external and internal exposure of Techa riverside residents resulting from the initial discharges are still measurable. The reconstruction of the historic discharge inventory from the Mayak PA has proved to be an important part of dose reconstruction work. Average external dose rates in the settlements are lower than within the sanitary zones, with maximum dose rates observed on the floodplain, though many studies have shown that dose rates are heterogeneous. External dose rates are higher in Muslyumovo compared to Brodokalmak. This is to be expected due to the former’s closer proximity to the source of radioactive discharges. Estimates of the contribution