- 57 The radioisotopes found in fish, clam, plankton and algae samples are given in Table V. The samples were collected in the vicinity of the test site at Bikini and Eniwetok Atolls within a month or two after the test series and were selected for their high level of radioactivity. Within the limits of the available data, the radioisotopes of elements with high concentration faetors in Table IV were the radioisotopes taken up by fish as shown in Table V. Practically all of the radioisotopes found in fish were non-fission products -- those isotopes listed in Table Vt the left of sr99, Either the fission products are not available to fish or fish do not have a physiological need for the elements of fission products. Also to be noted in Table V is that the amount of radioactivity in plankton is greater than in fish and that the species ofisotopes are somewhat different in the two groups of organisms, although the samples are not strictly comparable in time and place. Contrary to some opinions, this observation indicates that although marine organisms concentrate certain radioisotopes, the concentration will not increase necessarily as the isotopes are transferred upward through the food chain. To determine the hazard to man from fish and clam samples with high levels of radioactivity, the ratio of the