Phytoplankton is the fundamental autotrophic link of aquatic ecosystems. Due to a large total sorption surface, it is able to absorb, retain and transmit radionuclides along the food chains, leading to a deterioration of the environmental position of the reservoir. Phytoplankton was sampled in the summer of 2019 at 5 sites along the course of the Zaporizke reservoir. The specific radioactivity of phytoplankton samples was determined using generally accepted radiochemical methods and gamma spectrometry. The content of radionuclides in the phytoplankton of the Zaporizke reservoir averaged as follows: 137Cs – 7.61±0.501 Bq/kg; 90Sr – 1.13±0.242 Bq/kg; 226Ra – 95.45±7,010 Bq/kg; 232Th – 85.66±4,013 Bq/kg; 40K – 185.26±23.74 Bq/kg. It has been found that the specific activity of natural radionuclides 226Ra, 232Th and 40K was 80-320 times higher than that of the artificial ones (90Sr and 137Cs). According to the accumulation coefficients with respect to water, the sequence of accumulation of radionuclides in the phytoplankton of the Zaporizke reservoir has been arranged in descending order: 137Cs>232Th>226Ra> 40K> 90Sr. For most of the radionuclides studied, the maximum values of accumulation coefficients have been recorded in phytoplankton in the area of the Festivalnyi pier (137Cs, 90Sr, 232Th) and the creek of the Mokra Sura river (226Ra, 40K). The data obtained indicate that there is a potential threat of accumulation of radionuclides in phytoplankton and their transfer further along food chains.
radionuclides, phytoplankton, Zaporizke reservoir, specific activity, accumulation coefficient