An additional factor which may accentuate the condition found in
Birgus is currently under study at this Laboratory in cooperation with
the Department of Botany, University of Washington
The low potas-
sium levels in the soils at Rongelap represent a potassium
for at least some of the plants.
Greenhouse experiments
deficiency
in
which
Rongelap soil was used as well as field trials at Rongelap have demonstrated that potassium fertilization decreases cesium-137 uptake
plants (Walker and Held, 1959).
by
This observation is in agreement with
the reported increase in cesium-137 uptake by plants in other soils as
the potassium concentration in the soil is reduced by prolonged cropping
(Nishita et al., 1953 and i959).
It appears possible that if a surplus of
potassium were present in the soils at Rongelap, potassium levels in
Birgus muscle would be more uniform and cesium-137 levels lower.
The simplest system studied at Rongelap with respect to cesium-137
and potassium was the soil.
Cesium-137 and potassium in rain water
which had percolated through undisturbed soils were found to be present
in approximately proportional amounts under changing conditions of precipitation and fertilization (Cole et al.,
or higher trophic
level,
1959).
However, at the second
represented by Birgus, if any such :elationship
exists between the uptake of cesium and potassium,
it is masked by several
unknown variables in the ecosystem.
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