Long-term trends and speciation of artificial radionuclides in two submerged macrophytes of the Yenisei River: A comparative study of Potamogeton lucens and Fontinalis antipyretica

Highlights: • Contents of ⁶⁰Co, ¹³⁷Cs, and ¹⁵²Eu were 2–7.5 times higher in F. antipyretica than in P. lucens. • Trends of artificial radionuclides in F. antipyretica and P. lucens were similar. • Effective half-lives were estimated for ⁵⁴Mn, ⁵⁸Co, ⁶⁰Co, ⁶⁵Zn, ¹³⁷Cs, and ¹⁵²Eu. • Considerable percentages of ⁶⁰Co, ¹³⁷Cs, and ¹⁵²Eu were recorded in epiphytic biofilm. • ⁶⁰Co, ⁶⁵Zn, and ¹⁵²Eu in plants correlated with discharges of these radionuclides. Long-term trends of artificial radionuclides, from 2003 to 2018, in two abundant species of macrophytes, shining pondweed, Potamogeton lucens, and water moss, Fontinalis antipyretica, have been analyzed to estimate the indicative reliability of these two species as biomonitors of radioactive contamination in a river system and to quantify the decrease in the content of artificial radionuclides in the Yenisei River. Time-dependent trends of artificial radionuclides in the biomass of these species were similar, resulting in estimates of effective half-lives for ⁵⁴Mn, ⁵⁸Co, ⁶⁰Co, ⁶⁵Zn, ¹³⁷Cs, and ¹⁵²Eu similar for both species. Concentrations of artificial radionuclides in biomass of shining pondweed and water moss correlated with annual discharges of the radionuclides to the Yenisei at different levels of significance, and the strongest (R² > 0.7) positive correlation (p < 0.05) was obtained for ⁶⁰Co, ⁶⁵Zn, and ¹⁵²Eu. Concentrations of ⁶⁰Co, ¹³⁷Cs, and ¹⁵²Eu in water moss were 2–7.5 times higher than in shining pondweed, and considerable percentages of those isotopes were recorded in extracellular particulate matter, which was largely represented by epiphytic diatoms. Higher concentrations of artificial radionuclides in the biomass of water moss can be considered as an advantage of water moss as a monitor of radioactive contamination of the Yenisei, while shining pondweed is more useful for estimation of annual deposits of radionuclides in vegetation of the Yenisei and spatial transfer of radionuclides downstream of the discharge site. Despite differences in concentrations of artificial radionuclides, both species can be considered as reliable indicators of radioactive contamination of the river on a long-term scale.