Radioactive Contamination of Coastal Regions due to Aqueous Aerosol Entrainment from the Techa River Area

The study is aimed at reconstruction of the parameters of the source from which the Techa River was contaminated in the period 1949–1956 and deals with the migration of γ-emitting nuclides (GENs), namely, of ⁹⁵Zr and ⁹⁵Nb, in the river system. The archive (1951) results of measuring the specific activity of the sum of β-emitting nuclides (BENs), A_Σ (μCi/kg), in the soil and plants in the Techa riverside regions that are not flooded by floodwaters are analyzed. Analysis shows that the radioactive contamination of riverside territories is not associated with atmospheric discharges from the enterprise stacks and that the measurement results do not correspond to the commonly accepted views on the contamination distribution. In particular, contamination of the riverside soil and plants varied nonmonotonically with increasing distance from the river bank and along the river (spotty contamination pattern was observed), whereas the absolute values of BEN specific activities were constant throughout the territory within an order of magnitude. Furthermore, the depth distribution of BEN specific activities in soil up to 0.5 m was virtually uniform, and in some cases the activity increased with the depth. Finally, the plants had both external (on leaves) and internal (in roots) contamination, and in some cases the BEN specific activity in stems and leaves was lower than in roots. Presumably, the radioactive contamination of the soil and plants was determined by ⁹⁵Nb and was due to entrainment of an aqueous aerosol from the river water surface with the wind. The model calculations explain all the unusual distribution patterns observed and allow estimation of the upper boundary of the mean (for summer 1951) ⁹⁵Nb activity concentration in the river water.