INTRODUCTION 



Since the first nuclear explosion in 1945, the open-sea environment 

 has been subject to an everincreasing supply of radio-chemicals through 

 expanded programs of weapon- testing, accidental sinkings of nuclear-powered 

 ships, and the wastes from land-based and ship-board reactors. While most 

 of these products have extremely short half- lives there are several whose 

 half- lives are of sufficient length to be biologically important. The 

 radionuclides of strontium and cesium are such products. The concentration 

 and vertical distribution of Sr^*-' and Cs^-^7 have been determined (Bowen and 

 Sugihara, 1960; Miyake , £t aj., 1962; Rocco and Broeckar, 1963). Both Bowen 

 and Sugihara, and Miyake and his group reported more or less continuous 

 decrease in activity from the surface to great depth, while Rocco and Broecker 

 found an absence of activity between 400 and 1300 meters except in the Anarctic. 

 The highest surface concentration and the greatest penetration was reported 

 by Miyake; they reported concentrations of Sr-90 and Cs-137 in the surface 

 waters of the Pacific of 3.1 mmc/L and 4.8 |j,)j,c/L respectively, and a vertical 

 penetration to 5000 m. Since the distribution and final disposition of these 

 radionuclides can be greatly influenced by marine organisms as they can be 

 utilized along with stable isotopes in their metabolic processes, a study 

 was made of the uptake, accumulation and exchange of these radionuclides 

 by open- sea phytoplankton . 



While our knowledge of the mechanisms for the uptake and accumulation 

 of radioisotopes by phytoplankton is still vague and incomplete, studies of 

 organisms found in the effluent from nuclear reactors and in the radioactive 

 sea water following a nuclear explosion have shown plankton capable of 

 concentrating certain radioisotopes from water. Lackey (1957) found that 

 Oedognonium in a settling basin at Oak Ridge National Laboratory had a 



