during centrifugation which should be considered as adding to the exposure 

 time. By cell counts it was found that more than 907o of the cells are spun 

 out of the medium after one minute at 1500 rpm plus 45 seconds of deceleration 

 time and that 417„ of the cells are removed after 30 seconds of centrifugation 

 at 1500 rpm and 45 seconds deceleration. Therefore, it was decided to add 

 one minute of the centrifugation time to the total exposure time of the cells. 



The experiments to determine the uptake of Sr-89 by adsorption to G, 

 simplex and K. rotundata were conducted in a manner similar to that used with 

 cesium except the organisms were grown in culture tubes instead of Erlenmeyer 

 flasks. For the study with G. simplex fourteen culture tubes were used. They 

 were grown to a dense population then three tubes were counted to determine 

 the number of cells per mm . Ten milliliters of cell suspension was used for 

 each experiment. After counting, the cell suspension was filtered onto tared 

 filters, dried, weighed and the cell count related to weight. 



In this experiment the cells were exposed to a concentration of 0.2 |j,c/ml 

 of Sr-90 for the following times: 2, 4, 10, 20, 40, 60, 80, and 160 minutes. 

 The cells were centrifuged from the medium and duplicate one-ml aliquots of 

 the medium were assayed for loss in radioactivuty . After this the remainder 

 of the medium was removed, and the cells were resuspended in fresh medium and 

 then filtered out of suspension onto tared Millipore filter discs. 



No-cell controls were used throughout the experiments and all experiments 

 were made in duplicate. The uptake of Sr-89 by adsorption studies for K. 

 rotundata were conducted in the same manner. 



EXPERIMENTAL RESULTS 



1. Uptake of Strontium-Yttrium by Various Phytoplankton 



The five cultures of open sea phytoplankton were grown in an enriched 

 natural sea water medium to which various amounts of Sr^^-Y'^ solution was 



-11a- 



