The Simulation of the dynamics of 137Cs accumulation by freshwater fish

The study aimed to simulate the dynamics of 137Cs accumulation by freshwater fish under conditions of hypothetical radioactive contamination of water reservoirs in different seasons. The subject of research is the regularities of 137Cs accumulation by non-predatory fish species in eutrophic and oligotrophic water bodies. The dynamics of the 137Cs content in freshwater fish was calculated according to the content of radionuclides in water masses. The results of modeling the volumetric activity of 137Cs in water masses were used as an input parameter for the radionuclide accumulation in fish model. The fish organism was represented in the form of 3 independent related only by the balance equation; seasonal changes in the fish feeding intensity were taken into account in the modeling. The parameter that takes into account the contribution of the feeding intensity to the process of 137Cs intake into the fish organism has been determined. The features of the dynamics of 137Cs accumulation in eutrophic and oligotrophic water bodies fish are analyzed for cases of a hypothetical accidental input of 137Cs into ecosystems at the beginning of different periods of the annual life cycle of fish: 1st - from 1 to 31 March; 2nd - from 1 to 30 April; 3rd - from May 1 to September 19; 4th - from September 20 to October 19; 5th - from October 20 to November 30; 6th (freeze-up period) - from December 1 to February 28. The study has found that for a eutrophic water body the highest levels of 137Cs content in peaceful fish will be formed in the case of 137Cs entering ecosystems in spring (options 1–3). The maximum levels of 137Cs content in fish will be observed in the contamination period mentioned in option 3. Under hypothetical pollution in the autumn-winter period (options 4–6), the levels of 137Cs in peaceful fish will be approximately 2 times lower than in the case of pollution of the reservoir in spring. It has been found that the maximum value of the specific activity of 137Cs in fish from an oligotrophic water reservoir is not related to the season of pollution. However, the levels of fish pollution in the oligotrophic reservoir will be 1.5–2 times higher than those of the eutrophic one in options 1–3 and 3–4 times higher in options 4–6 . In the event of an emergency density of 137Cs fallout at the level of 4 kBq /m2 on the surface of different types of closed water reservoirs, its specific activity in peaceful fish will exceed the currently established permissible levels of fish products contamination. If the fallout density is twice as low (2kBq/ m2), the accumulation levels 137Cs by fishes of eutrophic water bodies will exceed the permissible standards in case of emergency inflows in spring. For oligotrophic water reservoirs, the guaranteed non-excess of the established standards in fish products is possible if the 137Cs fallout density is under 0.5 kBq /m2.