Method for Evaluating the Impact of Radioactivity on Phytoplankton

Abstract

Concentration factors are often used to assess the impact that radionuclides may have on aquatic organisms. The use of literature values or even measured concentration factors may not be appropriate for a given situation, since these factors are dependent on many environmental parameters. However, if the environmental stresses that affect a concentration factor are known and quantified, a better and potentially more efficient estimate of impact assessment can be made. The authors report here the use and results of a laboratory technique that could be used to evaluate the environmental impact of radioactive effluents on phytoplankton. The target alga is Chlamydomonas reinhardii, a common green flagellate that is amenable to growth in the laboratory. The model radionuclide is cesium-137, an important constituent of the radioactive liquid effluents from nuclear power plants. The organisms are grown in a chemostat, which consists of four growth chambers. The chemostat allows algae to be maintained in their log growth phase while various environmental parameters are manipulated. It was found that the cesium-137 concentration factors are controlled by the phosphate concentration, the sodium concentration, and the algal biomass. Temperature, algal reproduction rate, potassium concentration, and chloride concentration have no effect on the observed concentration factors. The cesium concentration factor ranges from 115 to 586 on a dry weight basis under the various environmental conditions studied.