Radioecological consequences of radioactive discharges into the Techa River on the Southern Urals

The sources and levels of radioactive contamination of the Techa River are analyzed. Dose assessments are made for humams and biota. The highest radionuclide concentrations in the river water were observed in the period 1950–1951. In 1951, at a distance of 78 km from the site of radioactive discharges, the content of 90Sr in the water was 2.7 × 104 Bq l−1 and that of 137Cs was 7.5 × 103 Bq l−1. Subsequently, the radionuclide activity in the river water decreased considerably. In the period 1991–1994, the average annual content of 90Sr in the water varied between 6 and 20 Bq l−1. The average annual content of 137Cs in the river water varied from 0.06 to 0.23 Bq l−1, i.e. was lower than that of 90Sr approximately by two orders of magnitude. The concentration of 239,240Pu in the water varied between 0.004 and 0.019 Bq l−1. The radioactive contamination of the Techa floodplain is highly nonuniform. With increasing distance from the river sources, the contamination density of the floodplain decreases, remaining, however, considerably higher than the background values. At present, the average annual dose rates in contaminated areas are (0.1–2) × 10−3 Sv year−1, which is considerably lower than in the periods of ‘acute’ exposure (1950–1951). The doses to aquatic biota were much higher than those to humans.