SECT. 1] ARTIFICIAL RADIOACTIVITY IN THE SEA 83 



skeletal structures. While living, some of the organisms may make vertical 

 migrations which could transport a part of the radioisotopes from a contaminated 

 to an uncontaminated layer. The net effect of such processes depends on the 

 concentration factors or enrichment factors of radioelements in marine pro- 

 ducts. Generally the concentration factors of radioelements cover a range 

 from less than unity to values as large as 10 6 (see Tables III and IV). 



The concentration factors of some radionuclides such as iron, cadmium, zinc, 

 etc. are exceedingly high (Tables III and IV). The concentration of rare-earths 

 has been confirmed; Ketchum and Bowen (1958) gave the value of the order 

 of 10 3 as a concentration factor of Ce. As to the concentration of cadmium in 

 marine organisms, Kawabata and others determined 0.9 \j.[xc of 113m Cd/g wet 

 tissue in the liver of albacore caught in the tropical North Pacific in 1956. 

 The presence of 115m Cd in fish organs was confirmed by Shirai et al. (1957). The 

 concentration factor of cesium is low, which is attributed to the hold-back 

 action by the stable alkali elements in sea-water. 



Yamagata (1957) gave the values of 0.021 ^c of 137 Cs/g wet weight of the 

 total body of a squid and 0.016 fAfxc/g wet weight in the flesh of a bonito both 

 caught near Japan in the early summer of 1957. The nuclidic differentiation of 

 fission products in plankton was observed by A. H. Seymour et al. (1957) in 

 the sample collected near the Bikini-Eniwetok proving ground. The averaged 

 results are given in Table V in which the relative concentrations of cerium, 

 praseodymium and ruthenium-rhodium are observed. 



Table V 



The Nuclidic Differentiation of Fission Products in Planktonic Organisms 

 Collected near Ujelang Island (Seymour et al., 1957) 



Isotope Observed % Expected % Observed/Expected 



They also observed that there was a difference in nuclidic content of plankton 

 collected 90 miles north of Eniwetok and plankton collected 470 miles west of 

 Eniwetok. They reported the presence of non-fission products such as 57 Co, 

 58 Co, 60 Co, 65 Zn in plankton and in the liver of flying fish caught near Eniwetok. 



3. Artificial Radioactivity as a Tracer of Water Movements in the Ocean 



Up to now, artificial radioactivity, as a tracer, has not been employed to any 

 great extent to investigate water movements in the ocean. Miyake, Sugiura 



