soil.
Large-scale leaching with sea water by the Lawrence Livermore group
(Appendix B) has not yet proved effective (24).
In most continental soils,
cesium is very firmly fixed to clay minerals (25, 26).
soils
of the Marshall
Islands,
however,
the
fixation
In the coralloid
may
be
to
organic
matter, but the nature of the process is undefined (Appendix B).
4.2.2
Biological
Extraction (Cropping).
Since cesium may be
concentrated in plants, the possibility exists of removing cesium from soil
_ by cropping.
The method does not seem practical.
For example, assume that
the plant specific-activity is three times that in soil, and that 1.5 kg/m*
of plant material
can
be harvested annually.
Then for Bikini's 2.4 km,
some 3500 metric tons per year of plant material would have to be removed
for 50 years to reduce rooting-zone cesium-137 activity from 29 pCi/g (the
present level) down to 4.6 pCi/g (the liminal level).
4.2.3
Topping.
A
clean
rooting
zone
may
be
created
by
topping contaminated soil with a fresh layer 50 cm or more thick, as might
be needed.
of
roots
If the topping layer is thick enough and fertile, large numbers
of
the
edible
plants
contaminated layer below.
will
not
penetrate
from
it
into
Nor would the tightly bound cesium-137 of the
contaminated layer be expected to diffuse upwards into it.
The plan would
involvé removing and disposing of the vegetation currently in place
$3 million),
the -
(cost,
topping with 50 cm of dredged sediment from the lagoon,
only practical
the
source (cost, $55 million), and conditioning and replanting
the area thus treated (cost, $6-8 million), for a total cost of about $65
million.
Two
engineering,
to
after
four
years
which,
would
with
be
required
adequate
to
planning
complete
and
the
care,
civil
mature
revegetation would develop over a period of 10 years.
aad
Topping,
water.
however,
would
not
decontaminate
the
Furthermore, the roots of such plants as Messerschmidia,
and mature breadfruit would penetrate
result, the
falling leaves of these
Pisonia,
into the contaminated depth.
plants would contaminate the
soil.
3000024
ground
31
As
a
surface