Radiation-hygienic assessment of the concentration and distribution of ⁹⁰Sr and ¹³⁷Cs in ichthyofauna of the Ob’-Irtysh river system

The aim of the work is the radiation-hygienic assessment of 90Sr and 137Cs content in fish of the Ob-Irtysh river system and the study of the basic laws of the radionuclides accumulation in the ichthyofauna of these rivers. To perform this task, long-term results of radioecological studies of fish from the Techa, Irtysh and Ob rivers for the period 2004-2016 were used. Fish as a food product was evaluated according to two criteria: a) permissible levels of radionuclides specific activity (SanPiN 2.3.2.1078-01); b) using the indicator of conformity В and uncertainty of its definition ΔВ (GOST 32161-2013 and GOST 32163-2013). It is shown that a higher content of radionuclides is observed in the ichthyofauna of the Techa river (1379.1 Bq/kg for 90Sr and 41.9 Bq/kg for 137Cs). On the Ob and Irtysh rivers, the average specific activity of radionuclides in fish was significantly lower and slightly changed during the surveyed area: for 90Sr in the range of 6.0 ÷ 8.1 Bq/kg (mean 6.8), for 137Cs – 0.6 ÷ 1.9 Bq/kg (mean 1.3). Assessment for compliance with radiation safety criteria using the indicator of compliance and its uncertainty (В+ΔВ) confirmed the unsuitability of use for food purposes by the radiation factor of all studied fish species from the Techa river (45÷55 >1). Fish from all other studied areas of the Ob-Irtysh river system can be used for food without restrictions (0,06÷0,53 < 1). The distribution of 90Sr and 137Cs in the ichthyofauna of the Ob-Irtysh river system part over a 2400 km is presented in the form of empirical regression models. The models describe a sharp decrease in the radionuclides specific activity in fish in the Techa and Iset rivers by two orders for 90Sr (from 2000 to 20 Bq/kg), and by one order for 137Cs (from 40 to 2 Bq/kg). With a high degree of reliability (R2>0.86 for 90Sr and R2>0.92 for 137Cs), the presence of power relationships between the content of radionuclides in the ichthyofauna and their content in water was shown, with adequacy confirmed by Fisher’s F-criteria. This can be used for a preliminary assessment of the radionuclides level in fish based on the results of measurements of the average annual concentrations of these radionuclides in water