sa ance ve atedAPAeo ta oe i, GARResBT ad aw "tethe . Topp as oe Beak LCE AL RADIOACTIVITY OF INVERTEBRATES AND OTHER ORGANISMS AT ENIWETOK ATOLL DURING 1954-55 Introduction Levels of radioactivity in living forms have been determined at almost all of the Pacific Proving Ground tests, both immediately before and shortly after the detonations, as well as at occasional relatively great intervals of & year or more later (UWFL-33, 42, and 43) The present study traces the trends in the beta radioactivity of invertebrates by means of repeated observations from shortly before the Nectar detonation (May 14, 1954) for a period of nearly two years. For comparison with the inverte- brates similar observations on other substances and organisms are included, using some information given more fully in reports by other members of the Applied Fisheries Laboratory who deal with their problems from different points of view. Palumbo (1957) reported on the radioactivity in algae and land plants. Held (1957) studied the trends of radioactivity in the land hermit crab and discovered the preponderance of radiostrontium in the exoskeleton. the trends of radioactivity Welander (1957) described for the reef fishes of Belle Island. Lowman, Palumbo, and South 11957) reported the identity of the radioactive non-fission products remaining in certain samples collected itn 1954-55 and in 1956 as determined in late 1956 and early 1957. Although the emphasis of the present paper is on inverte- brates, certain data from many of the other areas are brought together here in order to compare the trends in levels of radioactivity in a unified form and by as nearly identical methods as is practicable. It should be possible in this way to observe the general pattern of change of radioactivity in living and non-living materials, and to detect divergences from the pattern. study of the trends in this manner has proved useful in pointing out materials of interest for radioisotopic analysis by gamma- ray spectrometry.