Potassium and Cesium-137 in Birgus Latro (Coconut Crab) Muscle Collected at Rongelap Atoll

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Biology and Medicine POTASSIUM AND CESIUM - 137 IN BIRGUS LATRO (COCONUT cRAB)—— MUSCLE COLLECTED AT RONGELAP ATOLL Diptirnan Chakravarti and Edward E. Held Laboratory :f Radiation Biology University of Washington Operated by the University of M’ashington under Contract No AT(45- 1)540 with the United States Atomic Energy Commission +?3-41*

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Radio cesium and stable potassium levels were determined in samples of muscle tissue of 13irgus latro, the coconut crab, collected at Rongelap Atoll, Marshall Islands, during March and August, 1958, and March 1959, and at Utirik Atoll in March 1959. Levels of cesium-137 ranged between 731 d/m/g dry weight at Kabelle Island, Rongelap Atoll, and 28 d/m/g dry weight at Utirik Island, Utirik Atoll. The average potassium value for all samples was 13.05 mg/g dry weight with a standard deviation of 3.66. No significant correlation between cesium - 137 and potassium levels was found. There in the average levels of cesium - 137 times at the same island. was no significant difference in crabs collected at different

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POTASSIUM AND CESIUM - 137 IN BIRGUS LATRO (COCONUT CRAB) MUSCLE COLLECTED AT RONGELAP ATOLL Rongelap Atoll was contaminated with radioactive fallout resulting from the Bravo test on March 1, 1954, to the extent that it was neces - sary to evacuate the population of 82 Rongelapese. Some 200 Marshallese returned to Rongelap in June 1957, after the afiea 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 initi - ated 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 and stable potassium content in the muscle of 13irguk latro (coconut crab) and to evaluate the relationship between the two, if any, under the ex - isting conditions at Rongelap Atoll. Birgus latro, the coconut crab, is of particular interest because it is edible and is a land crab known to contain cesium - 137 in its muscle tissue. Cesium - 137 is also the principal long-lived (27 years half life) fission product found n plants on contaminated islands in the Marshall

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1 slands. There have been conflicting reports in the literature concerning the relationship of potassium to cesium -137 uptake in plants (Auerbach and Crossley, 1958; Nishita, et al. , 1958; Uhler, 1959; Nishita et al. ,—— . . 1959) , Apparently the uptake of cesium- 137 by plants is directly associated with potassium uptake in some cases and not in others. I t 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 MATERIALS AND METHODS 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 sampies were wet ashed with concentrated HN03 and H202, The ash was dissolved in a known volume of lN HN03 and the potassium content determined by flame photometry. Details of the method used have been reported by Chakravarti and Joyner (1959). The levels of cesium - 137 were determined by gamma spectroscopy. Five to ten-gram samples of dried muscle were counted. The counting

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equipment consisted of a three-inch thallium- activated scdium iodide crystal used in conjunction with a 256-channel analyzer with digital print out. The total counts per minute under the photopeak were calculated by summing counts per minute of all channels included in the peak and subtracting the background counts. The counting efficiency for the gamma energy measured was determined by calibrating the instrument with a cesium - 137 standard with an error of ~ 10 per cent. The factor used for converting counts per minute to disintegrations per minute was derived from the counting efficiency and from the fraction of the disintegrations giving rise to the gamma radiation being counted. The factor used for cesium - 137 - barium-137 was 18.0. Detailed used have been the counting equipment and standardization procedures RESULTS AND DISCUSSION The individual values for potassium and cesium - 137 in Birgus muscle collected at Rongelap Atoll and Utirik Island are presented in Table 1. Average values and their standard deviations for each col - lection also are given, The levels of cesium - 137 found in tween 731 d/m/g dry weight at Kabelle individual samples ranged beIsland, Rongelap Atoll, and 28 d/m/g dry weight at Utirik Island, Utirik Atoll. The individual

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variation at any one island was large. Range in values in d/m/g dry weight at three islands at Rongelap Atoll was as follows: Kabelle 324-731, Eniaetok 369-498, and Rongelap 199-330. However, the average cesium - 137 levels were highest at Kabelle Island, which lies in the northern part of the atoll, and lowest at Rongelap Island, in the southern part. Analysis of variance gave an F value cent level), indicating that the difference in these two islands is statistically significant lies about half way between Rongelap Island samples were obtained, two in March 1958, of 23.98 (significant at 1 per At Eniaetok Island, which and Kabelle Island, only three and one in August 1958. In the former collection the levels were higher than at Kabelle while in the latter collection the level was lower than at Kabelle for the corresponding dates. This apparent inconsistency is probably a result of individual variation. At Utirik Atoll, which lies some 200 miles to the east (Fig. 1), the levels were about one-tenth of the lowest levels at Rongelap. The gamma dose rates give an indication of the relative levels of radioactive contamination of the different islands. The average gamma dose rates measured three feet above ground in Wiarch 1959 at these islands were, Rongelap .031, expressed as milliroentgens Determinations of other radionuclides in 13irgus muscle indicate that over 90 per cent of the radioactivity is from cesium -- 137.

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For comparison with cesium - 137 levels, the average potassium value for each collection is given in Table 1. The average potassium value for all samples was 13.05 mg/g with a standard deviation of 3.66. The range in values was 2.96 to 21.2 mg K/g dry weight, but 83 per cent of the 30 samples analyzed fell in the range of 10 to 15 mg K/g dry weight. The two lowest values of 2.96 and 3.48 mg K/g dry weight appear to be completely out of line. Repetition of the analysis of these samples gave essentially the same results and no explanation for the disparity is offered. A significant difference in potassium levels associated either with island or season of collection is not apparent (March falls in the dry season and August in the wet season). Nor is there any correlation between potassium and cesium - 137 levels at any one island. In this regard, the data should not be pooled since it has been established that there are differences in cesium - 137 levels from island to island. The cesium-137 on potassium in the crab muscle, as determined in the largest sample from Kabelle Island, indicated no relation between these elements, Cesium-137 levels have been reported as cesium units, micro microcuries of cesium- 137 per gram of potassium { U,. S. AEC reports on fallout). This unit is based on metabolic similai-ity of cesium and potassium and is used to facilitate comparison of different types of materials in a manner similar to the use of the strontium unit adopted by Libby (1956). Anderson, Schuchj Fisher and Langham (1957) have used

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the gamma ratios of cesium - 137 to potassium-40 in place of the cesium unit. Cesium units for Birgus muscle are given in Table 1 for comparison with other published data on fallout given in the same units. However, since the potassium and cesium levels are both highly variable in Birgus muscle, there is some doubt as to the usefulness of the unit in this case. For example, the comparatively high value for cesium units of samples from Rongelap Island is due to the exceptionally low potassium content of one of the samples On the other hand, the high value for the March 1959 collection at Kabelle Island is due to high levels of cesium - 137, while the potassium levels are about average. These differences are not surprising when the following facts are considered. Gross (1959) has reported that Coenobita, which has habits similar to those of Birgus, obtains blood salts from its food. From work in progress at this Laboratory it is known that Pandanus fruit, which form a Dart of the diet of Biraus. varv by as much as a factor of five in. ~“ “. cesium - 137 content and a factor of four in potassium range in potassium levels in soils on which Pandanus is O. 1 to 1. 5 milliequivalents per 100 grams. range of gross beta activity in the top inch of differ by more than a factor of ten On a cesium - 137 and potassium levels found in the content and that the grows at Rongelap the extremes in the soil at a single island can basis of the variability in environment alone, one might expect the high degree of variability found in Birgus, 4’$$

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An additional factor which may accentuate the condition found in Birgus is currently under study at this Laboratory in cooperation with— the Department of Botany, University of Washington The low potassium levels in the soils at Rongelap represent a potassium deficiency for at least some of the plants. Greenhouse experiments in which Rongelap soil was used as well as field trials at Rongelap have clernonstrated that potassium fertilization decreases cesium - 137 uptake by plants (Walker and Held, 1959) This observation is in agreement with the reported increase in cesium - 137 uptake by plar; ts in other soils as the potassium concentration in the soil is reduced by prolonged cropping ( Nishita et al. , 1958 and 1959) . It appears possible that if a surplus of—— potassium were present in the soils at Rongelal~, patassiurn levels in Birgus muscle would be more uniform and cesium - 137 levels lower. The simplest system studied at Rongelap with respect to cesiurn - 137 and potassium was the soil. Cesium - 137 and potassium in rain water which had percolated through undisturbed soils were found to be present in approximately proportional amounts under changing conditions of preexists between the level, represented by -, if any such relationship uptake of cesium and potassium, it is rr. ~skecl by several in the ecosystem.

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Table 1, Potassium and cesium - 137 in Birgus latro (coconut crab) muscle collected at Rongelap Atoll and Utirik Island, Utirik Atoll. Cesium- 137 Potassium Cesium Unit no dry weight dry weight /g K ratio

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Cesium - 137 Potassium Cesiurn Unit no dry weight dry weight /g K ratio

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1956. Radioactivity in people and foods. Science 125: and cesium - 137 uptake by vegetation under natural conditions. Second United Nations I nternational Conference on Peaccfal Uses of Atomic Energy Paper No. A/ Conf. 15/P401, Chakravarti, D. and T. Joyner. 1960. Potassium as an index of naturally occurring radioactivity in tuna muscle. Transactions of the American Fisheries Society. (In press) .—— tension lysimeter in coral atoll and glacial till soils. Proceedings of Soil Science Society of America. (In pre8s) . Dunning, G. M. 1957. Radioactive contamination of certain areas in the Pacific Ocean from nuclear tests. U. S. Atomic Energy Commission report, U. S. Government Printing Office, Gross,. W. J, 1959 The effect of osmotic stress on the ionic exchange of a shore crab. Biological Bulletin 116:248-257. Held, E. E. 196b’ Land crabs and fission products at Eniwetok Libby, W. F. 1956 Radioactive fallout and radioactive strontium. 1958, The biological and geographical distribution of V?185 in the vicinity of the Eniwetok Test Site, April-September, 1958. University of Washington, Laboratory of Radiation Biology, 1959. The influence of K and Cs on the release of Cs 137 from t hree soils. University of California at Los Angeles, Atorni$@#%

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of strontium-90 and cesiurn- 137 from Vina loam, upon prolonged cropping. Soil Science 86: 195-201. 12. Uhler, R. L. 1959. Strontium and cesium plant studies. Meeting of the 13io-Medical Program Directors of the U. S. Atomic Energy Commission June 8-9, 1959, Hanford Laboratories, Hanford Atomic Products Operation, Richland, Washington. S. Atomic Eneregy Commission Quarterly Statement on Fallout, October 1959, (Release to public) on Rongelap Atoll soils. Oral presentation No I X International Botanical Congress, Montreal.