J. Mar. biol. Ass. India, 1960, 2 (1): 75-81 POTASSIUM AND CESIUM-137 IN BIRGUS LATRO (COCONUT CRAB) MUSCLE COLLECTED AT RONGELAP ATOLL* By DipTIMAN CHAKRAVARTI AND EDWARD E. HELD Laboratory of Radiation Biology, University of Washington, Seattle, Wash., U.S.A. INTRODUCTION RONGELAP Atoll was contaminated with radioactive fallout resulting from the Bravo test on March 1, 1954, to the extent that it was necessary to evacuate the population of 82 Rongelapese. Some 200 Marshallese returned to Rongelap in June 1957, after the area had been declared safe for human habitation. Since 1954, there have been several surveys to determine the level of radioactive contamination of the biota at Rongelap Atoll (Dunning, 1957). In March 1958, a long-term study of the ecology of the atoll, relative to radioactive contamination, was initiated at the request of the U.S. Atomic Energy Commission, Division of Biology and Medicine. The objective of this investigation was to determine the radiocesium andstable potassium content in the muscle of Birgus latro and to evaluate the relationship between the two, if any, under the existing conditions at Rongelap Atoll. Birgus latro, the coconout crab,is of particular interest because it is edible and also the principal long-lived (27 years half life) contaminated islands in the Marshall Islands. in the literature concerning the relationship of plants (Auerbach and Crossley, 1958 ; Nishita, Cesium-137 is fission product found in plants on There have been conflicting reports potassium to cesium-137 uptake in et a/., 1958; Uhler, 1959 ; Nishita nee is a land crab known to contain cesium-137 in its muscle tissue. et al., 1959). Apparently the uptake of cesium-137 by plants is directly associated with potassium uptake in some cases and not in others. It was suggested from the results of studies of Coenobita at Eniwetok Atoll that seasonal differences in precipitation might influence cesium-137 levels in muscle tissue (Held, 1960) ; the data presented here do not support this suggestion. Samples of Birgus muscle were collected from Kabelle, Rongelap, and Eniaetok Islands at Rongelap Atoll during March 1958, August 1958 and March 1959. Two samples were also collected at Utirik Island, Utirik Atoll (Fig. 1) in March 1959. The samples were oven-dried at 98°C and the wet weight to dry weight ratios were determined. For potassium analysis, the samples were wet ashed with concentrated HNO, and H,0,. The ash was dissolved in a known volume of 1N HNOg and * Report No. UWFL-64. Operated by the University of Washington under Contract No. AT (45-1) 540 with the United States Atomic Energy Commission. From EW? CL, “Box = Wr2fS /e, fole= '/960" Sor eyperenne erence MATERIALS AND METHODS