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PRELIMINARY TEST OF RADIOACTIVITY IN COCONUT CRA!3S AT EN I}!ETOK ATOLL Samples of skeleton and muscle from two specimens of coconut crabs (BIrgus latro L.) collected on 21,January 1972, Glenn Islet, Eniwetok were dried, pulverized and placed in liquid scintillation vials with lnsta-Gel as a suspending and scintillation medium. These tissues from the crab Pachygrapus crassipes California in June 1972. These latter spec significant an-ount of radioactive nucleides samples were compared with similar collected near Laguna Beach, mens are assumed to not contain Table I gives a description of Samples were compared using a Packard Series 2000 Liquid Scintillation Spectrometer. For total radioactivity a winc!ow of 50 (on a 1000 maximum scale) to infinity was used, using the 20, 60, and 80% gain values of the instrument. For characterization of the spectrum a 10% window width (50-150) was employed at various gain leveis. Preliminary tests indicated that there is definite excess of radioactivity in the coconut crabs for Eniwetok. However, it is so small that considerable amounts of sample had to be used to permit detection and characterization of the spectral distribution. Tests on the total count are reported in Table 1. Analysis of this data also gives considerable evidence of quench;ng as the weight of the sample tised increases. This was tested further (following spectrum analysis) by adding a standard amount of Ca to each tube. The increase in counts was inversely proportional to the size of the sample. Quenching (in sample 5) was no~ed :0 Scintillation vials without any crab tissue present but with a standard ‘ ~ , amount of 90Sr or “5 Ca were used for comparison.
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Because of this excessive amount of quenching, total radioactivity is estimated only by comparing Eniwetok and California crab samples of 416 to 616 mg in weight. On this basis one can get estimates that suggest that the Eniwetok crabs contain an excess of 3 to 33 counts Per minute Per 9ram of tissue. This figure could easily be doubled or quadrupled because of quenching and also to allow for a safety factor. One specimen (No. 4) of Eniwetok crab skeleton gave the same count rate as California crab tissue. Since this specimen had three times as much tissue and it quenched a 45ca standard by over 90% it is assumed that the sample is truly radioactive. All other Eniwetok samples gave count rates h;gher (57.7-78.6 wm) than California crab samples regardless of weights which were both less and more than the California crab tissue specimens. See Table 1. The maximum of 33 (x2-4) counts per minute per gram dry weight obtained is about ?00 times less than the figures of 104 per gram of wet weights given for Cenob;ta crab specimens collected at Eniwetok in 1955. (See Held, H. E., 1960, Pacific Science 14:18-27). The difference may be due to species difference, time for dilution, and lccal collecting sights.. The Cenobita specimens came . -— from Bell islet in the north part of the atoll, Birgus from Glenn in the south. Analysis of the spectral distribut’ graphs following) gives further ev’ the Eniwetok crabs compared to Cal on of the counts (see the 5 pages of dence of the excess of radioactivity of fornia crabs. One can compare samples 1, 3, 5, 7, 8, 9, 10, from Eniwetok with samples 11 and 12 from California for the skeleton. Also samples 2 and 6 with sample 11 respectively for muscle tissue which shows that muscle tissue of the Eniwetok crabs also contains above normal levels of radionucleides. The spectral distribution for scintillation vials that are blank and vials containing gosr 137C5 s Co, and 3H is also given for comparison. This indicates that the increase in radioactivity of the Eniwetok crabs is due to medium to low energy nucleides. However, it is suspected that the high degree of quenching evident may have shifted the peaks of the crab specimens to the right and probably the radioactivity present is due to Sr and Cs, as ‘found in 1960, Pacific Science, 14:18-27). The habit of the coconut crabs of eating their exuviae (molted shell) would favor the perpetuation of radioactivity
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within this species. Further study with such low levels of radioactivity would require a different system then the one used here in order to overcome the quenching problem which is due to having to use large samples of tissue in the scintillation vials. Special acknowledgement for assistance is due to Gene Helfman who provided . the samples and to Larry Roth, Lance Hodges, and Lanny Fisk who helped in the preparation and analysis of the samples. Loma Linda University
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