a
by Libby.* His results have been reported in Sunshine Units, where 1 S.U.—10-'* curies
Sr—90/gm Ca, or approximately 1/1000 of the present maximum permissible body burden for
man (1 »c/1000 gm Ca in adult skeleton). The average content of 11 alfalfa samples was
9 S.U. (range 4.3-21 S.U.). The top inch of the associated soils averaged 12 8.U., and the
1”-6” depth averaged 4S.U. A similar alfalfa-soil pair from near Ankara, Turkey, on October
6, 1953, yielded values of 2.1 S.U. for the alfaifa and 1.2 S.U. for the top inch ofsoil.
Detailed comparison of individual alfalfa-soil pairs showslittle correlation between Sr uptake
and quantity of available Ca. This lack of correlation between Sr and Ca uptake, and the
excessively high activity of the alfalfa compared with soil, both indicate that the contamination
of the alfalfa was by direct fallout on the leaves rather than by root uptake. (American weapon
test series ended 4 months, and the Russian series two or three weeks, before sample collection.)
- Kulp * at the Lamont Geological Observatory (Columbia U.) New York, made preliminary
tests which also indicate the dominance of leaf over root uptake in the first months after weapon
detonations. Corn (maize) leaves from Wisconsin (Sept. 1953) were first leached 5 minutes
in 50% HCl, then ashed.
From the leachate was recovered 1.2 gm Ca of 0.5 S.U., and from the
ash 5.6 gm Ca of <0.05S.U. The inference is that most of the activity was adhering to the outside
of the leaves.
2, Barium:
Ba-140, a 12-day fission product of high fission yield, might be expected to behave similarly
to Sr. However, its uptake by roots appears to be lower, as demonstrated by the low ky, in
Menzel’s experiments listed in Table 1. The distribution factor ky, is defined as (Ba/Ca) piant/
Ba/Ca).ou. The question of root uptake may be academic because the short life of Ba—140 would
not allow serious concentration by this path. No experiments on leaf uptake and retention are
yet available.
3. Ruthenium:
Several experiments have been performed on a laboratory scale which permit comparison of
root uptake of Ru with that of Sr.
Nutrient solution experiments by Menzel at the U.S. Department of Agriculture have shown
that under some conditions Ru uptake is controled by iron content according to the relationship
(Ru/Fe) mant=0.1 (Ru/Fe) .oiutio. The Fe and presumably Ru was complexed with versene. If
this relationship held underfield conditions (which it may not, because of the complex chemistry
of Ru) root uptake of Ru would be far lower than uptakeof Sr: soil usually contains more Fe
than Ca (which controls Sr uptake), while plants contain about 1% as much Fe as Ca.
Kermit Larson’s © group at UCLA carried out-greenhouse experiments on the comparative
root uptake of Ru and Sr by barley and several vegetables. Carrier free isotopes (chemical form
of Ru ambiguous) were mixed into soils. The ratio of Ru to Sr taken into the plant tops varied
from 0.02 to 0.002 of the ratio in the soil.
Menzel !7 grew 9 different crops. (forage crops and vegetables) on soil contaminated with
close-in fallout from a weapon test: The soil was comparatively rich in Ca, with resultant suppression of Sr uptake. The ratio (Ru/Sr) pn/ (RU/STP) .i==0.02.
Experiments on leaf uptake of Ru have not been performed.
4, Yttrium and rare earths:
Several experiments on root uptake of Y and the rare earths have been performed forsoil
contaminated with separated isotopes and with actual weapon debris.
Kermit Larson’s ** group at UCLA compared the uptake of Sr-90, Y-91, and Ce-144 by barley,
carrot, lettuce, bean, and radish plants from artificially contaminated soils. Uptake to plant
tops of both Y and Ce was less than that of Sr by a factor greater than 100.
Footnote references on pp. 42-43.
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