Int. J. Environ. Res. Public Health 2009, 6 191 • Group 2. People, who visit the river floodplain in accordance with average occupancy factor values (0.03), consume 10% of their average annual milk consumption from cows pastured on the floodplain and 10% of their average annual consumption of fish from the river Techa. This population group receives doses that correspond to the average weighted dose in the settlement. • Group 3. People, who visit the river floodplain with occupancy factor values for herdsmen (0.10), consume 100% of their milk from cows pastured on the river floodplain and 30% of their average annual consumption of fish from the river Techa. This can be defined as the critical population group. The data in Table 9 shows that the contribution of calculated external exposure to the total dose varied between 40% and 80% depending on the population group, less than compared to earlier assessments [25]. Contributions from 90Sr and 137Cs to internal doses were similar: the main dietary components contributing to internal dose were fish (29-61%) and milk (11-63%) [24]. Results of this dose assessment suggested that the established dose limit for a population (1 mSv per year) would probably be exceeded by a critical group in Muslyumovo. Further comparison with earlier dose assessments [25] where the lowest dose category (minimum level in Table 8, i.e., are not using riverbank areas for pasture, fishing and recreation) are assumed to compare with Group 1 in Table 9 shows the two dose assessments to compare quite well for low dose populations, though the later assessment [24] indicates a more rapid decline in doses moving downstream from Muslyumovo to Brodokalmak. The later dose assessment [24] predictions for the critical group (Group 3) compared to maximum level predictions made earlier for teenagers who were assumed to use the Techa River flood bank areas most often [25]. The positive effects of restrictions on activities and/or usage of areas closely associated with the Techa River on calculated doses are in agreement with other studies [40]. Table 9. Distribution of individual annual doses received by the population of Muslyumovo and Brodokalmak in 1998 (adapted from [24]). Village Muslyumovo Group1 Group2 Group3 Brodokalmak Group1 Group2 Group3 mean 0.05 0.28 0.89 0.03 0.09 0.27 External geom. 5% Mean conf. 0.04 0.23 0.67 0.03 0.08 0.21 0.03 0.08 0.19 0.02 0.03 0.06 95% conf. 0.07 0.70 2.34 0.04 0.21 0.67 Annual effective dose (mSv) Internal geom. 5% 95% mean mean conf. conf. 0.07 0.09 0.25 0.05 0.05 0.10 0.06 0.07 0.20 0.04 0.04 0.08 0.02 0.03 0.06 0.01 0.02 0.03 0.16 0.19 0.62 0.12 0.12 0.20 mean 0.12 0.39 1.13 0.08 0.15 0.37 Total geom. 5% Mean conf. 0.11 0.34 0.93 0.07 0.13 0.31 0.05 0.15 0.34 0.03 0.06 0.12 95% conf. 0.21 0.78 2.57 0.15 0.29 0.81 The most recent published assessment of external and internal doses to Techa residents is based on similar data sets regarding environmental levels of radioactivity [41], consumption patterns and occupancy factors as the studies mentioned here. The main findings were consistent: only a