The effect of radioactive contamination of the Yenisei river on cytogenetic characteristics of aquatic plants

The Yenisei River, one of the world's largest rivers, is contaminated with artificial radionuclides released by one of the Russian facilities producing weapons-grade plutonium (the Mining-and-Chemical Combine, MCC), which has been in operation for many years. Aquatic plants are an important component of water ecosystems, which can accumulate high levels of radionuclides and, thus, can be used in bio-monitoring and bioremediation. The purpose of the study was to assess levels of radionuclides and to evaluate the frequency of chromosomal aberrations in samples of submerged plants collected in different parts of the Yenisei River. The following species were studied: Fontinalis antipyretica, Batrachium kauffmanii, Myriophyllum spicatum, Elodea canadensis, Ceratophyllum demersum and various Potamogeton species. Samples were collected at positions in the vicinity of the MCC discharge point, at a distance of 330 km downstream of Krasnoyarsk, and upstream of the MCC, during sampling campaigns in 2003-2012. Detailed analysis of radioactive contamination of aquatic plants of the Yenisei River revealed large-scale contamination of aquatic plants as far as 250 km downstream of the MCC. Before the last MCC reactor was shut down in 2010, about 30 radionuclides, including uranium and transuranium elements, were detected in the biomass of aquatic plants. The highest concentration factors of the major radionuclides were obtained for Fontinalis antipyretica and Potamogeton lucens. Samples of the plants collected after the shutdown of the reactor contained considerably lower activity levels of artificial radionuclides, and their diversity was significantly decreased. Results of cytogenetic investigations of aquatic plants collected when the reactor was still operating (2003-2009) suggest that at the MCC discharge site and downstream the occurrence of chromosomal aberrations in ana-telophase and metaphase cells of the plants was considerably higher (up to 30%) than in the control areas (4-6%). The cytogenetic investigations of aquatic plants collected in the area affected by the MCC in 2011-12 also showed a significantly higher frequency of chromosomal aberrations in ana-telophase cells compared to the control samples. The frequency of chromosomal aberrations in the cells of aquatic plants in the control areas has remained nearly the same for almost a decade. The frequency of aberrant ana-telophases in Elodea canadensis cells has been found to be positively correlated to the total activity of artificial γ-radionuclides in Yenisei sediments of the study area and to 137Cs concentration in the sediments. The range of chromosomal aberrations in cells of Elodea collected in the area affected by the MCC was wider than in cells of the plant samples collected in the control areas (there were ring chromosomes and residual nucleoli in dividing cells). These data suggest that the radiation factor still affects the Yenisei River ecosystem, even several years after the MCC nuclear reactor was shut down. The possible reasons for this may be both discharges of the MCC Radiochemical Plant, which is still operating, and the effect of artificial radionuclides accumulated in sediments on submerged plants. Document available in abstract form only. (authors)