~36-
On the basis of the increase in background levels of
radioactivity at Eniwetok Atoll after the March 1954 tests
at Bikini Atoll,
and the steep slopes of decay plots of in-
dividual plant samples,
it is believed that the relatively
high amounts of radioactivity in the Eniwetok pre-Nectar
samples were due to contamination from the Bikini fallout
material.
After the Nectar test the levels of beta radioactivity
of land plants at the various islands were directly related
to geographical distance from ground zero and to time after
detonation.
Uptake of Radioisotopes by the Plants
A comparison of the rates of decline of radioactivity
of the soils and plant tissues shows that the radioactivity
of some of the land plant tissues declined at the same rate
as that of the soil samples.
The rate of decline for the
first 100 days was similar to the decay of mixed fission products.
This similarity indicates that the radioactive
ma-
terial had adhered to the external surfaces of the leaves of
the tall plants such as Scaevola and Messerschmidia during
fallout.
Splattering of contaminated soil particles on the
low plants such as Triumfetta,
Boerhaavia and Portulaca may