Comparative Study of Plutonium and Radiocaesium Content in the Muscle of Fish of the Yenisey River

This work reports the first data on the content of plutonium (^239+240Pu) in the muscle tissues of the Northern pike (Esox lucius) and the Siberian dace (Leiciscus baicalensis) inhabiting the middle reaches of the Yenisey River in the vicinity of the radioactive discharge site. An increase in the content of ^239+240Pu and radiocaesium (¹³⁷Cs) in pike muscles followed an increase in the volume of controlled discharges of these radionuclides to the Yenisey in 2018. The content of ^239+240Pu in the muscles of pike (2-11 mBq/kg dry weight) and dace (1-4 mBq/kg dry weight) of the Yenisey fall within the range of values obtained by other authors for the ichthyofauna from water bodies contaminated with radioactive discharges from nuclear power plants and spent nuclear fuel processing plants. The ratio of the activity concentrations ^239+240Pu/¹³⁷Cs in fish muscles, compared with the similar ratios in other hydrobionts, indicates a significantly lower bioavailability of plutonium for fish. The obtained preliminary results make it possible to consider the Northern pike as a more prospective indicator of biologically available plutonium in the Yenisey than the dace.