Radioactive contamination of fish in the flooding lake Starukha in the Chornobyl exclusion zone

After the accidents at the Chornobyl NPP in 1986 and the Fukushima-1 NPP in 2011, the specific activity of radionuclides in fish in radioactively contaminated freshwater bodies reached hundreds of kBq kg-1 and exceeded international and national permissible levels. The work aimed to determine the content of radionuclides in different fish species in "the semi-closed" flooding Starukha Lake, which is located in the north-western trace of radioactive fallout in the Chornobyl Exclusion Zone (ChEZ). The experimental studies were conducted during 2000 - 2018. The values of 137Cs and 90Sr specific activities in different fish species were obtained. The maximum levels of 137Cs specific activity in fish muscle tissue of 3.7 and 3.6 kBq·kg-1 were in pikes, which weighed 6.2 and 1.65 kg and were caught on 04.10.2000 and 30.08.2006, respectively. In 2016 and 2018, the specific activity of 137Cs in muscle tissue and 90Sr in bone tissue did not exceed 800 Bq·kg-1. The effective half-lives of 137Cs specific activities in muscle tissue of pike, pike perch, and common whitefish were estimated to be in the range of 19 - 30 years. The radioactive decay of the radionuclide is the main process governing the activity decreasing. The geometric mean of 137Cs specific activity in the muscle tissue of pike, pike perch, and whitefish in Starukha Lake will decrease below the permissible level of 150 Bq kg-1 by 2043 - 2072. At the same time, the non-exceeding specific activity of 137Cs in the muscle tissue of individual fish with a probability of 95 % will be achieved in 50 - 100 years. Thus, there is a potential threat that fish may migrate during flooding from "semi-closed" lakes in the ChEZ to the Pripyat River and the Kyiv Reservoir.