78 



Afom/c Radiation and Oceanography and Fisheries 



algae. On the other hand, oysters fed upon 

 other phytoplankters that contained no more ra- 

 diophosphorus than the Chlorella accumulated 

 relatively large amounts of radiophosphorus and 

 incorporated that element into their tissues as 

 organic phosphorus compounds. It appears that 

 the particular food web used by any organism 

 is of primary importance in the transfer of ra- 

 diomaterials from one trophic level to another. 



Problems for further research 



One of the fundamental questions to be an- 

 swered concerns the mechanism of incorpora- 

 tion of the heavier elements, such as the fission 

 products, in aquatic organisms. To date, no 

 metal heavier than molybdenum has been shown 

 to be necessary for metabolic processes. Spe- 

 cifically, we need to know: 



1. How are the radioactive elements passed 

 through membranes and where and why do they 

 concentrate in the organisms ? 



2. What are their biological half-lives of the 

 different radioactive elements in different or- 

 ganisms ? 



3. What are the average and extreme concen- 

 tration levels of these elements in various or- 

 ganisms and in the biosphere ? 



The revolution in biological thought brought 

 about by the use of labelled atoms is manifest 

 in all branches of biological research today. 

 Radioisotopes have permitted the study of rate 

 processes that could not have been investigated 

 in any other way. Such processes include the 

 pumping rates of water and other biological 

 fluids, and the transfer of molecules or portions 

 of molecules from tissue to tissue, or, on the 

 ecological level, from organism to organism. 



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