added to determine whether or not there was selective uptake of strontium 

 or yttrium by the organisms. After 48 hours of exposure during the active 

 growth phase, aliquots of cells were filtered onto Millipore filter discs 

 washed, dried and counted. Table 3 shows the differential uptake by the 

 various phytoplankton . The two organisms, G. simplex and K. rotundata grown 

 in unialgal cultural showed remarkable ability to select nuclides. Nearly 

 all the radioactivity (95 to 99 percent) found in G. simplex was due to 

 yttrium while that found in K. rotundata was only from strontium. Confirmation 

 of the results of this experiment were obtained with a duplicate experiment 

 in which carrier-free yttrium-90 was used. Similar results to these were 

 obtained by Rice (1956) when he found that 10 out of 12 species of algae 

 investigated selected yttrium from the medium. 



Figure 1 through 5 show the concentration of strontium-90 accumulated 

 per gram of cells that were grown in media containing up to 200 microcuries 

 per liter. Here it can be seen that during the 48-hour exposure the accumulation 

 of strontium-90 by the organisms is proportional to the concentration of the 

 radionuclide in the medium. 



The concentration factors for strontium-90 are shown in table 4. Here 

 the differences in selectivity are indicated by their abilities to accumulate 

 strontium. K, rotundata concentrated the strontium exclusively while G_^ simplex 

 and the other three cultures indicated their preference for yttrium by their 

 small factors. During the 48-hour study K. rotundata was able to concentrate 

 strontium-90 about 382 times that of the medium in which they were grown, while 

 the 4000A culture which contained mainly diatoms had a concentration factor of 

 only 21.5. These results are similar to those obtained by Rice (1956) where 

 he found a concentration factor of 17 for Nitzchia, 



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