SECT. 1] ARTIFICIAL RADIOACTIVITY IN THE SEA 81 



between the retention of 144 Ce by microplankton and its removal by sedi- 

 mentation is in favor of the former. 



Yamagata and Matsuda (1959) gave the value of 0.07 to 0.15 [Xfxc/1. for 

 radioactive cesium ( 137 Cs) in the coastal waters of Japan in early 1958. Folsom 

 (1960) reported that the average content of 137 Cs was 0.097 ^.fxc/1. in coastal 

 waters in Southern California during the period from November, 1959, to 

 April, 1960. In surface waters of the western North Pacific 137 Cs from 0.8 to 

 4.8 [xu.c/1. was given by Miyake et al. (1961). 



2. Enrichment of Radioactive Substances in Marine Products 



It was rather astonishing to find considerable amounts of 65 Zn, 55 Fe and 

 59 Fe, which are not fission products but induced radionuclides, in the marine 

 organisms collected in June, 1954, in the tropical North Pacific by Amano, 

 Kawabata and other Japanese workers. The maximum activities of 65 Zn and 

 55 Fe were respectively 3.8 mp.c/g and 7.7 mjxc/g of wet tissue of a liver of 

 albacore. 



Since then, 54 Mn, 57 Co, 58 Co, 60 Co have been found in the internal organs of 

 fishes caught in the western tropical region of the North Pacific. The same 

 kinds of non-fission products were also detected in zooplankton and pelagic 

 sediments collected in the central equatorial Pacific by Martin (1957) in 1956. 

 The high levels of activity in the pelagic sediments are attributed to the enrich- 

 ment of these radionuclides in the benthic organisms. 



The 90 Sr concentration in the marine products was studied by Hiyama and 

 others (1960) whose results showed a remarkable increase in 90 Sr from 1954 

 to 1959. 90 Sr in clam shells was 0.08 fi^c/g of Ca in 1954 while it increased to 



Table III 



Concentration Factors in Some Marine Organisms (wet weight volume basis). 

 Values in parentheses are for analyses made on closely related genera (Ketchum 



and Bowen, 1958) 



Elements Cesium Strontium Iron Cobalt Zinc Cadmium Iodine 



Sea-water, g/ml 5x10 10 9 x 10~ 6 4xl0" 9 2.5 x lO" 10 1.4 x 10" 9 5 x 10" 11 5 x 10" 8 



Organism 



Limacina (0.2) « (5 x 10 4 ) 10 4 (3 x 10 4 ) (7 x 105) (5 x 10 4 ) 



Centropages 0.1-1 600 — (6 x 10 3 ) 



Calanus 0.1-1 0.28& 2.5 xlO 4 200 100 



Ommastrephes (0.1)° (0.3) 6 104 200 (2 x 10 4 ) 2 x 10 5 (10 4 ) 



Sagitta 70 5 x 10 4 10 4 — 



Euphausia (0.3) b 800 



Salpa — — — 60 — — — 



° Based upon analyses for potassium, assuming the Cs/K ratio in the organisms to be 

 the same as that in sea-water. 



b Derived from Ca analysis and Sr/Ca ratio given by Thompson and Chow (1956). 

 4 — s. ii 



