Kashparova O. Parameters for modeling the uptake and excretion of 90Sr and 137Cs in fish.

The PhD thesis is devoted to the study of the dynamics of uptake and excretion of radionuclides in the body of fish that will help in obtaining values of the rate of uptake from water (kw) or feed (kf), as well as the excretion of radionuclides from the body (kb) of fish in natural conditions at different water temperatures. The results are of practical importance when for predicting the dynamics of radioactive contamination of fish in the event of radiation accidents at different times of the year. They also have significant value in the development of protective measures. Determining the values of the rate of excretion (kb)/biological half-lives of radionuclides from fish, as well as the use of additional "clean" feed are considered as a countermeasure to reduce the level of radioactive contamination in the fish-human food chain. Seasonal changes in the content of radioactive isotopes in fish may depend on a number of abiotic and biotic habitat factors. The lack of information on the quantitative relationship between these phenomena does not allow to predict the dynamics of contamination of fish with radioactive contamination of water at different times of the year at different water temperatures. Therefore, experimental study and mathematical modelling of the prediction of radioactive contamination of fish is an important issue for radiation protection of the population and the environment. It has been proven that the oral contamination with 137Cs through the digestive system with food is the main way of its receiving in case of radioactive contamination of fish in natural conditions, even in winter at water temperatures below 8–10°С and when food consumption is minimal. For this reason, keeping fish in cages and using "clean" feeding is an effective countermeasure to reduce the content of cesium radioisotopes in fish. It has been confirmed that 90Sr uptake in the body of fish occurs mainly from water but not from food. There was a statistically significant acceleration of the rate of 90Sr from the water into the bone tissue of the fish with an increase in fish weight due to additional feed consumption. Obtained in aquarium experiments, the values of the rate of uptake and excretion of 90Sr and 137Cs from fish and its biological half-life in fish muscle and bone tissue correspond to our data from natural conditions of ChEZ. It allows us to use them to establish maximum permissible concentrations of radionuclides as much smaller in comparison with hygienic standards for drinking water (2 Bq l-1). On the basis of the received parameters of rate of uptake and excretion of radionuclides from an organism of fishes at various temperature and feeding mode, forecast estimations of dynamics of pollution of fish in radioactively contaminated reservoirs are made. The obtained results showed that in case of radioactive contamination of water bodies in winter and summer, the level of radioactive contamination of fish can differ up to 2 orders of magnitude.