Studies on the Concentration of Radioactive Substances by Plankton, Chlorella pyrenoidosa

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The uptake and accumulation of 60Co, 106Ru, and 144Ce by a phytoplankton, chlorella, in seawater, as well as the particulate behavior of these radionuclides, were studied. The following results were obtained. (1) The uptake and accumulation of 60Co increased during the logarithmic growth phase and reached an equilibrium at stationary phase, while those of 106Ru and 144Ce reached the maximum level after one day, followed by reduction during the logarithmic growth phase and an equilibrium at stationary phase. (2) The adsorption of 60Co on dead cells showed a similar pattern to that in live cells, but no change was noted in 106Ru and 144Ce. (3) The examination of particulate formation of the radionuclides using HAWP Millipore filters demonstrated that most of 60Co was contained in the filtrate, while about 4% of 106Ru and 18% of 144Ce were captured on the filters. (4) The concentration factors were 2.6×102 for 60Co, 3×102 for 1106Ru, and 6.5×103 for 144Ce. (5) The different patterns for the uptake of 60Co and 106Ru or 144Ce were attributed to the changes of radioactivity concentration due to their particulate formation in the media.