Int. J. Environ. Res. Public Health 2009, 6 177 Figure 1. Map showing the Mayak Production Association (inset) and the Techa-Iset- Tobol-Irtysh-Ob river system, draining into the Kara Sea. Direct discharges of radionuclides to the Techa river system via sedimentation ponds (Reservoirs 3 and 4) occurred between 1949 and 1956, approximately 98 % of the total activity being released in the period between December 1949 and November 1951. Over 100 PBq of radioactive material was discharged during the whole period [e.g.1, 2, 6], causing severe contamination down the entire length of the Techa River. Ruthenium isotopes (103Ru, 106Ru) and rare earth nuclides accounted for over 50 % of total activity releases and an estimated 12 PBq 90Sr and 13 PBq 137Cs were discharged. Alpha releases (including Pu and U isotopes) were lower, amounting to about 2 TBq according to discharge records [1]. Discharges of 90Sr and 137Cs during the period 1949-1957 contaminated 240 km2 of the Techa River floodplain: an area of 80 km2 exhibiting concentrations above 3.7×1010 Bq km-2 [5]. In order to contain the activity and act as a storage basin for low level wastes, construction of dams along the Techa was initiated creating reservoirs containing high levels of radionuclides such as 137Cs, 90Sr, 60Co and plutonium isotopes [1]. A thermal explosion in a tank holding high-level liquid waste (HLW) in September 1957 created what has subsequently become known as the East Urals Radioactive Trace (EURT). Some 740 PBq was released as a result of the accident, an estimated 90 % settling in the immediate vicinity of the site. The remaining activity, about 74 PBq, was released in a plume that is assumed to have reached an altitude of 1 km and which became dispersed by the wind in a NNE direction to form the EURT [1, 7, 8]. The trace, with an initial contamination density of 3,700 Bq m-2 90Sr or above (twice that of global