Assessment of radioecological situation in the areas of the “Chernobyl footprint” in Russia (1986-2020)

The current environmental situation in areas located in the “Chernobyl footprint” in Russia is considered in the paper. Radiation contamination in different parts of the “footprint” varies from the maximum level in the exclusion zones to the level close to the background in areas with low level of radioactive contamination. Environmental monitoring data and calculated density of soil contamination with radionuclides in the vicinities of residential areas in Bryansk, Kaluga, Tula, Orel and Novgorod regions were used as reference data for assessment of radiation dose rates and ecological risks for the reference biological species: the elk ( Alces alces ), red-backed mouse ( Myodes glareolus ), the Archangel fir ( Pinus sylvestris ), brandling ( Lumbricus terrestris ), the pike ( Esox lucius ), and the fresh-water soldier ( Stratiotes aloides ). The integrated contamination index, that is the sum of ratios of registered radionuclides contamination density to the reference levels, was used as the indicator of territory radioecological safety. The calculation was made in accordance with the Roshydromet Recommendations R-52.18.853-2016. The highest doses to the biota and ecological risks were registered in 1986. Radiation dose rates to some vertebrates in the most contaminated districts of the Bryansk region in May 1986 exceeded ecologically safe radiation level of 1 mGy/day. Doses to reference biological species inhabited outside exclusion zones within the period of May-December 1986 were lower than the radioecological safety level. After decay of 131I and other short-lived radionuclides 137Cs became the basic contributor to the biota dose. Radiation dose rate to the terrestrials and radio-ecological safety index gradually decreased due to radionuclides physical decay over the period of 1986-2020. Current radiation doses to the terrestrials inhabited the most contaminated districts were, on average, one order below the safe radiation dose to the vertebrates, two orders below the safety radiation level to the Archangel fir and three orders below the safety radiation dose to the soil invertebrates. Current radiation dose rates to inhabitants of the lake of Kozhanovskoe, one of the most contaminated areas due to the radioactive fallout, current radiation dose rates to the lake fish were two orders below the safe level, radiation dose rates to algae were three orders below the safety level, however, they still are above the background level. Current indices of integrated contamination in areas of the Chernobyl radioactive “footprint” are inhomogeneous. Current indices of integrated contamination in the majority of contaminates areas are dozens times and the indices in low radiation contaminated areas are hundreds times lower than ecological safety level. The highest indices occur in a number of districts of Bryansk region but they are lower than ecological safety level, however in some sites in exclusion zones the indices exceed the ecological safety level. These sites are unique natural testing grounds for radio-ecological research and monitoring of the environment and radiation protection development. In this connection it is recommended to continue long term research and development of radiological protection of the environment.