Biomonitoring of radioactive contamination of the Yenisei River using aquatic plants

New data on mobility of transuranium elements in sediments of the Yenisei River

The inflow of transuranium elements to the Yenisei River was previously associated with the production of weapons-grade plutonium at the Mining-and-Chemical Combine (MCC, Zheleznogorsk, Russia), but the source of transuranium elements in the River today is fabrication of MOX fuel that started recently at the MCC. The current study presents results of sequential chemical extraction of radionuclides from sediment samples collected in 2014 and 2020 in two areas near the MCC discharge site and compares these results with the data obtained previously by sequential extraction of sediments collected during 1999-2007. Over the study period, the strength of binding of 137Cs and 60Co in the Yenisei River sediments was high (up to 100%) and remained so, while the percentages of 241Am and 152Eu in residual solids after sequential extraction increased considerably and the percentage of 239,240Pu in residual solids decreased in samples from all study areas. In samples collected at the position located close to the MCC discharge site, the percentages of the strongly bound 241Am and 152Eu as well as 239,240Pu were lower than in the samples from the other positions. The study demonstrated an enormous increase in 239,240Pu activity concentration in the top sediment layers collected at all positions in 2020 relative to 2014. In the same period, as literature data suggest, 239,240Pu activity concentrations also increased in aquatic organisms of the Yenisei River, which can be indicative of the growing potential bioavailability of plutonium in the aquatic ecosystem, which could be caused by the presence of the mobile form of plutonium in the routine discharges from the MCC.

The use of the aquatic plant Elodea canadensis to assess the effects of low-dose gamma irradiation

Responses of cytogenetic and growth endpoints of the aquatic plant Elodea canadensis were studied using the plants collected from non-contaminated control areas of the Yenisei River and exposed to external γ-radiation for 11-13 days in the laboratory. Elodea canadensis was exposed to 0.5-25 mGy/day γ-radiation dose rates from a ¹³⁷Cs source. The total number of aberrant cells and total root length were more sensitive elodea endpoints to γ-radiation than total shoot length and mitotic index of elodea. Radiation sensitivity of elodea can be compared with the sensitivity of such a Reference Plant as Wild Grass (1-10 mGy/day) recommended by the ICRP. Thus, the aquatic plant Elodea canadensis can be used as a radiation bioindicator.

Со-60 as a time marker to date sediment layers and estimate sediment transport distances during the 2006 flood event on the Yenisei River

The study of bottom sediments collected from the Yenisei River downstream of the Mining-and-Chemical Combine (MCC) conducted from 2006 to 2016 revealed increased concentrations of ⁶⁰Co, which was present in dispersed form and in the form of radioactive microparticles, in the upper core layers. The increase in ⁶⁰Co activity concentration occurred when the 2006 extreme flood on the Yenisei washed away the radionuclide-containing soil from the riverbank at the MCC. The ¹³⁷Cs/⁶⁰Co ratio in the upper layers of bottom sediments after the 2006 flood varied between 0.2 and 1.5 and differed considerably from the ¹³⁷Cs/⁶⁰Co ratio in the upper sediment layers before the flood (2.5-6.0). Because of the increased concentrations of ⁶⁰Co, especially in the form of microparticles, in some sediment layers, ⁶⁰Co was used as a time marker (2006) enabling calculation of sedimentation rates and radionuclide sediment chronology. The ¹³⁷Cs sediment chronology calculated using ⁶⁰Co showed that the major ¹³⁷Cs peak was dated to the most extreme flood on the Yenisei, which occurred in 1966. Those calculations confirmed the appropriateness of using ⁶⁰Co as a time marker. Our findings suggest that during the 2006 flood, ⁶⁰Co was washed away from the MCC area to the Yenisei and transported as a component of suspended particles as far as 245 km downstream of the MCC.

Effect of Gamma Radiation on Cytogenetic and Growth Endpoints of Allium cepa Seedlings in Long-Term Experiments

The effect of γ-radiation on the growth and cytogenetic endpoints of Allium cepa L. seedlings in a long period after irradiation in absorbed doses from 1.0 to 10.7 Gy were examined. The chromosome aberration rate was most sensitive to the radiation: it increased immediately after exposure at all doses. In the recovery period (up to 216 h) after irradiation, the chromosome aberration frequency naturally decreased but at the end of experiment in maximum doses remained above the control values. The impact of the initial level of chromosome aberrations on the inhibition of onion roots growth in the long terms after irradiation is discussed.

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

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.