26 
PACIFIC SCIENCE, Vol. XIV, January I960 
tion on the soil. Residual contamination from 
fallout a year or more old would have an in- 
significant effect on rate of decline during the 
first 150 days if the total contamination from 
each detonation were of the same order of mag- 
nitude or the first less than the second. This was 
the case following the Nectar test at Belle Island, 
which had residual contamination from the 
Mike test (1.5 years previous to Nectar). 
After approximately 150 days following fall- 
out, the rate of decline becomes less than the rate 
of decay of mixed fission products, reflecting the 
relative concentration by the island organisms 
of the long-lived isotopes Cs 137 and Sr 90 . Other 
isotopes, both fission products and neutron in- 
duced products, are involved, but Cs 137 and Sr 90 
with their daughters account for 80 per cent or 
more of the total activity in land organisms two 
years following the Nectar test. This is true even 
though these isotopes together contribute only 
18 per cent of the total activity from mixed fis- 
sion products at that time. On a basis of fission 
yields, Cs 137 and Sr 90 would contribute no more 
than 35 per cent of the total activity even if all 
of the activity at Belle Island were from the 
Mike test. Ce 144 activity is low ( 1 per cent in 
crabs) in the island organisms because of its 
low rate of uptake by land plants from soil 
(Neel, 1953). On the other hand, in marine 
organisms radiocerium does enter into the food 
chain in significant amounts, 26-71 per cent of 
the total /3-activity, according to AEG report 
UWFL-43, Bonham, MS. 
It appears, therefore, that in so far as the 
long-lived radioactive fission products strontium, 
cesium, and cerium are concerned there is what 
might be called a strontium-cesium food cycle 
on land and a cerium food cycle in the lagoon. 
SUMMARY 
1. Periodic determinations of radioactivity in 
land crabs from Belle Island, Eniwetok Atoll, 
were made over a period of nearly two years fol- 
lowing the 1954 atomic testing program. 
2. Radioactivity in the exoskeleton was found 
to be due almost entirely to radiostrontium and 
the Y 90 daughter of Sr 90 and remained at a 
nearly constant level, excepting physical decay. 
3. An estimate of contributions of radiostron- 
tium from previous tests to a crab skeleton at 
Belle Island is given. 
4. Long-lived fission products in muscle tissue 
consisted of 84 per cent Cs 137 , 10 per cent 
Sr 9o + Y", and 1 per cent Ce 144 + Pr 144 . 
5. A possible association between the avail- 
ability of cesium and rainfall is suggested. 
6. During the first 150 days following a nu- 
clear detonation the rate of decline of radio- 
activity in organisms on an atoll island may be 
considered to approximate the rate of decay of 
mixed fission products. 
7. In so far as the long-lived fission products 
strontium, cesium, and cerium are concerned 
there appears to be a strontium-cesium food 
cycle on land and a cerium food cycle in the 
lagoon. 
REFERENCES 
Biddulph, O., and R. Cory. 1952. The relation- 
ship between Ca 45 , total calcium and fission 
product radioactivity in plants of Portulaca 
oleracea growing in the vicinity of the atom 
bomb test sites on Eniwetok Atoll. Washing- 
ton State College. U. S. Atomic Energ. Comm. 
Rep. UWFL-31. 
Bonham, Kelshaw. Radioactivity of inverte- 
brates and other organisms at Eniwetok Atoll 
during 1954-55. Applied Fisheries Labora- 
tory, University of Washington. MS. 
Donaldson, L. R., et al. 1948. Concentration 
of active materials by hydroids in the Bikini 
lagoon during the summer of 1947. Applied 
Fisheries Laboratory, University of Washing- 
ton. U. S. Atomic Energ. Comm. Rep. UWFL- 
11 . 
Donaldson, L. R., A. H. Seymour, and J. R. 
Donaldson. 1949. Radiological analysis of 
biological samples collected at Eniwetok May 
16, 1948. Applied Fisheries Laboratory, Uni- 
versity of Washington. U. S. Atomic Energ. 
Comm. Rep. UWFL-18. 
Donaldson, Lauren R., et at. 1956. Survey 
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Eniwetok atolls, June 11-21, 1956. Applied 
Fisheries Laboratory, University of Washing- 
ton. U. S. Atomic Energ. Comm. Rep. UWFL- 
46. 
Gross, Warren J., Janice F. Taylor, and 
James C. Watson. 1954. Some factors in- 
