Seasonal changes in uptake and depuration of 137Cs and 90Sr in silver Prussian carp (Carassius gibelio) and common rudd (Scardinius erythrophthalmus)

Dynamic transfer of radionuclides to fish was studied in a series of experiments under field condition in two lakes within the Chernobyl exclusion zone during 2016–2020. “Clean” common rudd (Scardinius erythrophthalmus) and silver Prussian carp (Carassius gibelio) were transported to the contaminated Glubokoye Lake and kept in cages during several months of exposure, while contaminated Glubokoye fish were kept in cages in the “clean” Starukha Lake. Radiocaesium (¹³⁷Cs) and radiostrontium (⁹⁰Sr) were determined in intestine contents, muscle and bone tissues based on repeated samples during several months of exposure.During summer, the activity concentrations of ¹³⁷Cs and ⁹⁰Sr increased with time of exposure in clean fish caged in the contaminated lake. During autumn and winter, however, minor changes in fish uptake occurred during several weeks of exposure to the contaminated water. Furthermore, depuration in the contaminated fish was significant during summer, while insignificant during winter when exposed in the «clean» water. The rate constant of ¹³⁷Cs uptake in muscle was between 8.0 and 22 day⁻¹ during summer, while 0.2 to 1.0 day⁻¹ during autumn-winter. Similarly, the rate constant of ⁹⁰Sr uptake in bone was between 1.4 and 1.6 day⁻¹, while 0.08–0.52 day⁻¹ during autumn-winter. Biological half-lives of ¹³⁷Cs in fish muscle tissue in summer were 77 ± 10 days, while exceeded 230 days during seasons at low water temperature.The results demonstrated that the transfer of ¹³⁷Cs and ⁹⁰Sr to fish was highly dependent upon seasons, in particular the water temperature. The transfer data obtained during low water temperature seasons deviated significantly from transfer data in literature and handbooks. Thus, seasonal changes in radionuclide transfer to fish should be taken into account when radiological impact to fish is assessed.