EXPERIMENTAL INVESTIGATIONS
5.
UPTAKE STUDIES
A number of studies which might relate to the uptake of sr® by plants and animals have been
run as field experiments. It must be emphasized that these are not controlled laboratory experiments and that the data are subject to more variability than if strict controls were possible. However, they are part of the data available for interpretation of sr*® analyses and can
be of some assistance in predictions of Sr® pehavior.
5.1
HASL PASTURE SITE SURVEYS
A series of annual samples has been taken at five sites in the United States by Dr. Lyle
T. Alexander of the U. 8. Department of Agriculture. The sampling program was begun in
1953, and samples of vegetation, animal bone, and soil have been collected. The intention was
to study the relative uptake of Sr*™ from soils to plant to animal under the most favorable
conditions possible. The animal bones in most cases represent yearling lambs or calves that
grazed in the same pasture from which the soil and vegetation samples were taken.
It is believed that the major problem in this uptake study is the variability of the sr®
content of the vegetation. The contribution of activity retained on the leavesto the total activity
of the plant is quite variable, depending on timing of the collections with respect to the test
periods. There is a noticeable general increase in the level of the animal bone from year to
year, and this program is continuing.
5.2
CHICAGO MILKSHED AREA SURVEY
Dr. Lyle T. Alexander has collected samples of vegetation and soil at a number of farms
in the Chicago area since 1955. In addition, milk samples were also taken in 1956. Since these
farms are in active use, it is increasingly difficult to sample soils in unplowed areas and ob-
tain values for top layers and lower layers of the soil.
The vegetation data, as mentioned in the previous section, appear to be more indicative of
the Sr® retained on the leaves than of uptake from the soil, since there is no increase with
time in the vegetation levels.
5.3.
UPTAKE OF Sr® BY BEAN PLANTS
During the summer of 1956, three types of bean plants —snap beans, lima beans, and
black-eyed peas——-were grown at the Beltsville Laboratory of the U. S. Department of Agriculture. The leaf, stalk, pod, and fruit of each were analyzed separately, and the snap bean
and black-eyed peas samples were run in duplicate. The results are given in Table 56.
Normalizing the data to stalk = 1, the mean Strontium Unit (S.U.) values for leaf, fruit,
and pod become 0.85, 0.52, and 0.54, respectively. The mean Ssr®/sr® ratios are 1.9, 0.2, 0.7,
and 1.4 for the leaf, fruit, stalk, and pod. Although such averaging may not be completely
justified, it would lead to the following conclusions: (1) The high stalk activity may indicate
uptake that is partially blocked from the rest of the plant. (2) The leaves show higher S.U.
values than the pod and fruit, indicating some leaf retention. (3) The Sr® values indicate that
the leaf and pod activity is younger than the fruit activity.
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