Strontium-90 and Gross Beta Activity in the Fat and Nonfat Fractions of 
the Liver of the Coconut Crab ( Birgus latro ) Collected at 
Rongelap Atoll during March 1958 
Diptiman Chakravarti and Ronald Exsler 1 
There has been a large individual variability 
in the levels of radioactivity per unit weight of 
biological samples collected in the vicinity of 
the Eniwetok Test Site (Applied Fisheries Lab- 
oratory, 1949, 1953, 1955*, 1955*; Held, I960). 
This variability may be great enough to mask 
or obscure differences which might exist be- 
tween species or with time or locality of col- 
lection. In most cases, practical considerations 
do not permit increasing the number of samples 
in an attempt to elucidate possible differences. 
The work reported in this paper points out a 
source of variability that exists in comparing 
the radioactivity of various samples of coconut 
crab liver. 
Birgus latro, the coconut crab, is of particular 
interest since it is edible and is known to con- 
centrate strontium-90. In the course of preparing 
samples of B. latro liver for radioassay, it ap- 
peared that the fat content varied considerably 
from specimen to specimen. A crude determi- 
nation indicated that the fat contained little or 
no radioactivity, which was expected because of 
the low mineral content of fat. 
It was therefore decided to determine ac- 
curately the fat content and the proportions of 
strontium-90 and gross beta activity in the fat 
and nonfat fractions. The objective was to deter- 
mine whether more uniform results could be 
obtained when radioisotopic content was ex- 
pressed on a basis of nonfat solids rather than 
total solids as had been done in the past. 
MATERIALS AND METHODS 
Liver samples of the coconut crab were col- 
lected from Kabelle, Rongelap, and Eniaetok 
1 Laboratory of Radiation Biology (formerly Ap- 
plied Fisheries Laboratory), University of Washington, 
Seattle, Washington. Operated under Contract No. 
AT (45-1 ) 540 with the United States Atomic Energy 
Commission. Manuscript received September 8, 1959- 
islands at Rongelap Atoll in March, 1958. The 
samples were oven-dried at 98 ± 2° C. and 
partially pulverized. The fat was extracted from 
the dried samples by a modification of the John- 
son method (Winton and Winton, 1945). Pe- 
troleum ether was used as the extracting solvent. 
The fat-free solids were wet-ashed with concen- 
trated HNO;r and H 2 0 2 . The ash obtained from 
nonfat solids was dissolved in a known volume 
of 1 N HNO'a and the strontium -90 levels of 
the samples were determined by the method of 
Kawabata and Held (1958). The gross beta 
activity was also measured from an aliquot of 
the solution. The fat content was determined on 
a dry weight basis by weighing and on a wet 
weight basis by using the wet weight to dry 
weight ratios shown in Table 1. The fat samples 
were dry-ashed in a muffle furnace at 550° C. 
overnight. The ash obtained from the fat frac- 
tion was dissolved in a small volume of 1 N 
HNGh and was transferred to a plate for de- 
termining the gross beta activity. The gross 
beta activity of the fat fraction was less than 
1 per cent of that in the nonfat fraction, making 
strontium-90 determinations impractical with 
the facilities available. 
All counting was done with an Anton end- 
window Geiger tube, number 1001-T, which 
was standardized against a National Bureau 
of Standards strontium-90 standard. 
RESULTS AND DISCUSSION 
The ratio of wet to dry weight and the fat 
content of the liver samples are presented in 
Table 1. The fat constituted an average of 47 
per cent by weight on a wet basis, with a stand- 
ard deviation of 9.71; and of 74 per cent by 
weight on a dry weight basis, with a standard 
deviation of 9.29. The average ratio of wet to dry 
weight was 1.603, with a standard deviation of 
0.156, indicating that the moisture level of the 
samples was relatively constant. 
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