- present in the environment. 1ents in samples collected at iptake of radioactive materials of the different radioisotopes ate the sites of deposition in ances give evidence concerning alyses on organs and tissues of n, agoon, taken during the testing lant isotope, with red muscle, 4, of the total radioactivity as was in the kidney, suggesting fish. ts a low excretion rate for this in the kidney is probably not licates a concentration of iron, fishes is a blood-forming organ. 1e spleen is probably the result Mleen, too, has haematopoietic 70 %of the total radioactivity, sle is known to contain greater nd therefore the depasition of 4 apparently is not concentrated een, and was found in the liver vity. ok Lagoon in September 1956, 33, Zn®> contributed 47% and ictive cobalt was present at a , about the same percentage as una collected during the tests. radioisotopes in the plankton and tuna samples gives some indication of the relative concentration factors for the different isotopes in the tuna fish. The two radioactive anions ruthenium and zirconium were present in the plankton at a level of approximately 11° but were absent in the fish samples; 100 °% of the radioactivity present in the fish samples was contributed by radioactive cations. Co*”. °8. 8 contributed 43% of the total radioactivity in the plankton, and on the average only 1.4% of that in the fish organs andtissues. Although Zn®5 contributed only 3 % of the total radioactivity in the plankton, it was present at an averagelevel of 88 % in thefish tissues. Fe*5-** contributed 16% of the total radioactivity in the plankton and an average of 9.5% in the tuna fish. Mn54 was not detected in the plankton samples and was present at an average level of 0.7% in the fish samples. The highest percentage of Zn®> in the tuna samples in comparison with that in the plankton suggests a low turnover rate for this radioelement in the fishes, and the very low percentage of radioactive cobalt in the tuna samples with respect to the percentage observed in the plankton suggests a high turnover rate for this element. The percentage of Fe®5—® in the tuna fish samples and in the plankton samples suggests a turnover rate for iron intermediate between that for radioactive cobalt and zinc. Indirect evidence concerning the relative turnover rates of the three radioelements iron, cobalt and zinc in fish was found in observations on the levels of these three radioelements in plankton samples collected at increasing time intervals following contamination of the sea during the 1956 test series (Fig. 8). The ratios of Co5’/Zn® and Co5?/Fe®+ were determined from plankton samples collected to the north and to the west of Eniwetok Test Site at distances of 15° BIKINI s after the test series in 1956, slightly lower than that found 958 test series. In the livers of July 1957, approximately three oisotopes were similar to those sted during the test period and 358, tuna samples taken in the fradioisotopes from those taken ‘ted 81—91 % of the total radiof Fe*5-59 ranged from 5 to 18%. ENIWETOK “Il 96 150° 15° sea, the level of Zn®5 in relation hat found in the lagoonfishes, espondingly lower. In addition, resent in some of the lagoon in the tuna samples from the ' Collett survey (Table I) were e tuna samples from the open somparison of the levels of the i 10° ENIWETOK 27 BIKINI ne 160° 165° 4 150° 155° Fig. g 8 Ratio of Co®’/Zn® (top) and of Co7/Fe® (bottom) in plankton taken approximately six weeks after the end of the test series in 1956 127 cg cere ene me ee etme