and phosphate- phosphorus . Research was continued in development of a good 

 phytoplankton medium until at present a very successful medium has been 

 developed. The formula for this synthetic medium is shovm in table 11 below. 



Slightly better growth from certain organisms has been realized when 

 2,54 grams of sodium chloride was substituted for 1.8 grams. 



SUMMARY AND CONCLUSIONS 



A 2 1/2 year study has been made of the uptake, accumulation and 

 exchange of the radioisotope Sr90.Y90^ Y^O, Sr^O and Cs^^y.^glB? ^y 

 tropical oceanic phytoplankton and many of the parameters which influence 

 these phenomena. It was apparent after reviewing much of the literature 

 which concerned the uptake of various nuclides by microorganisms that the 

 conditions and procedures varied from laboratory to laboratory. In fact, 

 so many different procedures, or lack of procedures and condition were 

 reported that comparison of results was very difficult. It was therefore, 

 necessary to investigate the parameters which affect the uptake, accumulation 

 and loss of radionuclides by phytoplankton as the study progressed. Such 

 parameters as light, temperature, and medium were kept constant while retention 

 of the radioisotopes by filter discs, the adsorption of the isotope on glass- 

 ware have been investigated. Every effort has been made to describe the 

 procedure developed and the results obtained in these investigations so that 

 this information might be utilized in future studies. 



All the organisms used in these studies are representative of the open 

 sea environment. While in the early work the cultures contained some bacteria, 

 their affect was minimized through selected conditions. In all later research, 

 the cultures were free of bacteria. All experiments were conducted with healthy, 

 actively growing organisms usually during their logarithmic growth phase. 



The results of this study show that all the organisms tested were capable 



-25- 



