specific cases.
The soluble plutonium during the May 17, 1974, and
July 10, 1974, trials could possibly have a considerably greater efficiency
of absorption than the soluble plutonium from the dioxide form, in which
case the predicted tissue retentions and milk secretion shown in lable 4
for July 10, 1974, would be minimal.
Predictions of tissue retention and milk secretion were not calculated for
field-ingested plutonium-239 because the in vitro purified plutonium studies
and the metabolism studies employed plutonium-238 only and there appear to
be possible differences in the availability of plutonium-238 and plutontum-239
due to factors other than particulate solubility. Hanson (1974) states
that another physical process that appears to emerge from several studies
is the changing availability of plutonium-238, This is indicated by a
changing plutonium-238/plutonium-239 ratio in soils, vegetation, and
animal components of the Trinity-site ecosystem from 0.05 (in soils) to
0.10 (in plants) to 1,0 (in mammals), respectively, as we go up the food
chain,
FUTURE PLANS
A study is necessary to compare the in vitro solubility of purified forms
of plutonium-238 dioxide and plutonium-239 dioxide. Other studies are
planned to determine the in vitro behavior of americium-241 and
curtum-243,
Future soil microorganisms-artificial rumen joint studies have been designed
to compare the biological availability of biologically incorporated plutonium
with nonbiological plutonium, and to determine the effects of soil
microbiological activity on the solubility of plutonium-238, plutonium—239,
and americium-241 present in contaminated soil.
Both tn vitro and in vivo studies are necessary to compare the
in vitro solubility of purified forms of plutonium-238 dioxide and
plutonium239 dioxide, and to compare the metabolism of the effective dose
of each.
So that americium-241 tissue retention and milk secretion predictions can
be made from the available data from the field-ingestion study, both
in vitro and metabolism trials of purified americium-241 are necessary.
An examination of the data presented in Table 3 indicates a very wide
variation throughout the year in both plutonium and americitum ingested and
their availability for absorption.
In evaluating soil-plant-animal
relationships at Area 13, the data from any single trial or season, alone,
could be very misleading, Variations between years have not been assessed.
An important characteristic of the field-ingested transuranics study is the
specificity of the data in regard to the field conditions under which the
rumen contents were collected. Some of these varying field conditions are
season, predominant species of vegetation ingested, stage of growth of
vegetation ingested, and distance of grazing area from the point of
detonation.
In the case of Area 13, NTS, Eurotia lanata frequently made up a
considerable portion of the vegetation ingested. There were drastic seasonal
variations {n the concentrations of plutonium in the rumen contents
coinciding with the reproductive or “woolly” stage of Eurotta lanata in
which its particulate collection efficiency 1s presumed to be hign.
Due to the specificity of the data, results obtained from these studies in
Area 13 may be applied to other areas only with reservations, The field
conditions mentioned above are factors which should be taken into consideration,
The results indicate the importance of conducting trials during field
studies throughout the year so that all field conditions affecting radionuclide collection efficiency of the vegetation and radionuclide availability
for absorption by livestock will be covered.
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