—
the Atoll have shown that there i¢ essentially no resuspended material at 10'
to 50'
in height, where most of these food samples are collected (Shinn
et al., 1980).
Thus, uptaky via jear absorption is highly unlikely.
The structure of the cora} soi] provides a very large sink in which the
90sr can be immobilized.
Cora} 03) is composed primarily of CaCO3 in which
90sr is able to replace Ca in the crystal structure.
As a result, a large
fraction of the Sr is unavailable for dissolution in the soil solution or
for absorption by plants. Moreover. plants in general tend to accumulate Ca
in the leafy portion of the plants tdja greater degree than they do in the
edible
fruit.
The
plants at the Atoll also tend to have higher 90Sr
concentrations in the leaf portion of the plants than in the fruits.
As a result of these unique features of coral soil, the relative
availability of '37cs and 90s 4, the reverse of the availability in aluminum
Silicate clay soils common jn the U.S., Canada, and Europe and reported in
most of the literature (Ng et al., 1982; Cline and Rickard, 1972).
In
silicate soils, especially when the organic content is low, the !37cs is found
in the clay matrix and is relatively unavailable to plants (Barber, 1964:
Kaddah, 1968; kihn et al., 1984: Menzel, 1965: Fredriksson, 1963:
Fredriksson
et al., 1958, 1966; D'Souza at al., 1972, 1980; Tamura and Jacobs, 1960).
In
contrast,
the !37Cs js mobile and relatively available in coral
soils.
Correspondingly, %0Sr is relatively available in silicate-type soils but is
bound in the carbonate matrix and js relatively unavailable to plants in coral
soils.
This
information
has
important
ramifications,
if
radionuclide
concentrations in soil are to be used to estimate the concentration of the
radionuclide in edible foods for radiological dose assessment. If C.R.s based
on silicate soils were used for such a purpose, the estimated 137Cs
concentration in plants at coral] islands would be in serious error and would
underestimate the potential effective dose to people residing on an island,
and the concentration of %sr would be greatly overestimated and its
contribution to the bone marrow dose would be
exaggerated.
The transfer of Pu and Am from the coral soil to plants is very low,
similar to that observed in other soi] systems. The C.R. for Pu and
Am ranges
between 10-4 and 10-5.
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