[INTRODUCTION Iron-55 is currently the most abundant fallout radionuclide in marine organisms. ‘The radionuclide has been studied intensive- ly because of its widespread occurrence since 1963, nuclear test series in 1962. data on 5 Fe Brill (1968) : levels in the environment, considerations for human populations. the mode of production of . . +4 summarized reported emphasizing dosimetric Persson (1969) reviewed . oy gs . . its distribution in the biosphere, (1970) reviewed the occurrence of cussed its distribution and possible on pe VY) 5 Qu Zz aa in marine n : Fe Fh 55 Fe, Preston oy and its dosimetry. 55. following the . : tas relative to other fallout v stratospheric anomalics leading to heavy depositions of radionuclides in northern “ (1968) suggested LQ. Jennings that much of the 55 Fe 55 Fe latitudes. from the USSR tests of 1962 was deposited as tropospheric fallout in narrow bands related to the test sites at 75°N and 52°N, In a review of radionuclides in marine organisms at the .fic 2. Pa . test site in 1956 to 1968, . as viisms were By or wo in plankton anc fish. Lowman (1960) . 55 Other early reports of those of Rema, Koide and Goldberg reported a . . Fe in marine (1961), who found the radionuclide in the livers and hearts of Pacific Ocean tuna 3: 1961, and Seymour (1963), who reported its presence in in skiptyack tune from the North Pacific. acre aw “<K be ak