Land Crabs and Fission Products— Held 
25 
Fig. 6. Counts per minute per gram in Coenobita 
tissues as of 600 days after May 14, 1954, plotted for 
each collection date. 
surface contamination and not all crabs would 
feed on the same thing at any one time. 
Initially, following the Nectar test, the gut 
had the highest level of activity of all tissues 
(5 X 10 6 d/m/g). The activity in the gut also 
had the shortest ecological half life of all tissues 
during the first 100 days post-Nectar. By 100 
days, the levels of activity in gut and liver ap- 
proached each other and their ecological half 
lives were about the same, although the gut re- 
mains so variable from collection to collection 
that only an approximation can be made. The 
activity in the carapace by 100 days was higher 
than that in the gut even though the latter had 
the highest initial activity. This variation is, of 
course, due to the different rates of decline, 
which reflect selection of the long-lived isotope 
Sr 90 by the carapace. 
No chemical analyses of gut samples were 
made. 
Gill 
The rate of decline of activity of the gill of 
the crab is more rapid than the rate of decay of 
mixed fission products during the first 10 to 20 
days post-Nectar, but thereafter approximates 
the same rate until the 200th day. The early high 
levels may be due to contamination of the sur- 
face of the gills and possibly to excretion of 
salts through the gills. From the tenth day on, 
the pattern of decline of the gill is the same as 
that of muscle. The activity level was generally 
higher in the gill than in the muscle by less than 
a factor of two on a wet weight basis. 
No chemical analyses of gill tissue were made. 
DISCUSSION 
During the first 150 days following a nuclear 
detonation the rate of decline of radioactivity in 
organisms on atoll islands may be considered to 
approximate the rate of decay of mixed fission 
products. This conclusion is supported by data 
from collections at Rongelap Atoll in 1954 
(AEG reports UWFL-42, -43). Errors in the 
estimate of future levels based on this approxi- 
mation would tend toward the prediction of 
higher levels than would actually be attained 
in the first 150 days. The wide spectrum of 
available radionuclides present in the early 
period following a detonation may be available 
to individual organisms in extremely minute 
amounts; consequently, differences in the rate of 
decline reflecting selectivity by an organism are 
masked, since various combinations of the short- 
lived nuclides could result in an approximation 
of mixed fission products decay. The availability 
of a wide spectrum of radionuclides during the 
first few days might be due not only to the 
presence of these nuclides, but also to the fact 
that they could potentially be absorbed directly 
by the leaves of plants and thus circumvent fixa- 
FlG. 7. Rainfall at Eniwetok Island (from records 
of Detachment 2, 57 th Strategic Reconnaissance 
Squadron, Medium, Weather, USAF). 
