Assessment of mouse rodents’ dose from the CHNPP contaminated territories

The main feature of the nearest 5-km zone of the Chernobyl nuclear power plant is the maximum concentration of fuel fallouts due to the accident in 1986. It is a unique testing ground for radiobiological research in the natural habitat of animals. At present, the background radiation level in the 5-km zone of the Chernobyl nuclear power plant fluctuates from 0.1 to 20 μSv/h. Besides, electrons from the decay of 90Sr and 137Cs add a significant contribution to the radiation background. Even though a large amount of experimental data on dose loads on the fauna of affected areas has been accumulated to date, the results obtained do not give an unambiguous idea of the dose dependences of radiobiological effects in natural ecosystems. In this work, we studied the total dose of irradiation of two murine rodents species: the bank vole (Clethrionomys glareolus) and the yellow-necked mouse (Apodemus flavicollis), living in territories of different levels of pollution near the destroyed power unit 4 of the Chernobyl nuclear power plant. We have assessed the density of radioactive contamination of the territory and study the isotopic composition of the fallout. Soil samples were taken to a depth of 30 cm, considering the depth of burrowing of mouse-like burrows is 10-15 cm. The 90Sr, 90Y, and 137Cs concentrations were measured using β- and γ-spectrometric methods for the selected soil samples. The 90Sr, 90Y, and 137Cs βactivity spectra were measured using a developed scintillation beta-spectrometer with a thin entrance window. Soil samples' gamma spectrometric studies were carried out using an anti-Compton device with an HPGe detector. The method for processing complex Xray and gamma-spectra in the energy range of 10-100 keV is developed. It takes into account the complexity of describing X-ray lines and providing a processing error of ≤1%. We calculated the murine rodents' radiation doses using the obtained data on the concentration of 90Sr, 90Y, and 137Cs activities in soil samples and animal bodies. The doses were calculated due to external irradiation with γ-quanta and electrons and internal irradiation with 137Cs and 90Sr electrons. For the first time, we obtained data on external electrons' contribution to the total dose of irradiation of murine rodents living in the contaminated territories of the 5-km zone of the Chernobyl nuclear power plant. Doses of internal irradiation and external γ-quanta are in good agreement with the data obtained for these territories earlier. It was found that the radiation dose is formed mainly due to external electrons for most rodents. Since many studies, including genetic and biochemical ones, are tied to the radiation dose, the correct account of the contribution of electrons to the radiation dose is, in many cases, critical.