of removing the radionuclides from the sea water. In addition, not only 

 were they in able to remove nuclides, but they were also capable of selecting 

 the desired nuclide. For example, K. rotundata selected only strontium while 

 G. simplex took up the yttrium when exposed to Sr^^-Y^^ solution. 



The ability to accumulate and concentrate the cesium and strontium from 

 the sea water medium was primarily through absorption with adsorption playing 

 only a very minor role. Hence, when radioactive cells were placed in fresh 

 media the loss of radioactivity to the medium was msall and a steady state 

 was established very quickly, usually with 24 hours. Since absorption seems 

 to be primarily responsible for the accumulation strontium and cesium by the 

 phytoplankton it is of the utmost importance that more is learned, of the 

 basic mechanisms involved. Before an ion can be absorbed, transport across 

 the cell membrane must take place. Several mechanisms have been proposed 

 for such a penetration but each involves an expenditure of energy, either 

 directly or indirectly. The energy required for active transport which is 

 linked with metabolic reactions is unknown. Scott (1954) stated that the 

 mechanisms for IC*" and Na"*" in Ulva were independent of each other. It is 

 also very probable that each ion requires a specific organic compound to 

 act as a carrier for membrane penetration. For the most part, these are 

 also unknown. Recently, Greenfield (1962) has found, in his investigation 

 of a Pseudomonas, that alanine acts as such a carrier for calcium. A study 

 of these mechanisms in the microorganisms will not only enrich our knowledge 

 of them but may serve as a guide for the study of more complex forms. Since 

 phytoplankton serves as food for other organisms, the site of the accumulation 

 of the radioisotope will help predict its accumulation at other trophic levels. 

 And now that it is known that phytoplankton are not confined to the euphotic 

 zone (Kimball, Corcoran, Wood, 1963) and that the radioisotopes of cesium 



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