by a factor of 1.5-5. This was a considerably lower factor than obtained in experiments on
water contaminated artificially by pile produced isotopes.
G. V. Alexander ™ at UCLA has measured the Ca and stable Sr content of the water supplies
of 50 American cities, both before and after purification. The Ca and Sr were in general found
to be removed in equal percentage. For chemical treatment (alum or FeSO,, sometimes plus
lime, lime-soda ash, or lime-phosphates) the Sr was removed in the range of 10-70%. Water
softeners only (phosphates-zeolite) removed about 70% in the 2 cities examined. The observed
Sr/Ca ratio (by weight) had a mean of 6 x 10(range 0.9—-30 x 10°).
3. Soil:
Measurements on the distribution of fallout with depth of soil indicate that it is held
fairly firmly in the top inches of soil. Thomas found the following relative gross activities at
various depths in Boston soil in 1953: 14’-5, 1-3, 4”-1. Libby® has obtained data on the
Sr—90 content of the layers 0-1” and 1-6” for 7 Chicago milkshed alfalfa fields in October 1953.
The total content of the 1-6” layer averaged 1.7 times as great as that of the 0-1’’ layer (range
0.6-3.5). (Activity per gram soil in the 1-6” layer therefore averaged 14 that in the 0-1”
layer.) Approximately half of this Sr-90 had fallen on the soil at 1% years before measurement, and approximately half at 4% year before measurement.
Data available at present indicate that the major portion of the long range fallout is in
a State readily available to plants. M. M. Weiss* at Brookhaven observed that about half the
activity in rain was filterable through papers which passed particles of less than % micron
diameter. Libby® analyzed successive extracts of the same sample of soil, the first extraction
with ammonium acetate containing the available Sr-90, the second with dilute HCl containing
a part of the unavailable Sr-90. (A third extract, namely complete solution of the soil, will
be analyzed in the future.) The ratio of available to total observed Sr-90 (ammonium acetate
fraction to ammonium acetate + HCi fractions) was 0.8, 0.7, and 0.4, respectively, on the 3
different soil samples measured.
Harley 12 compared extraction of bomb debris Sr—89, 90 from soil by the 3 methods of
complete solution of the soil, 10 minutes leaching with 6N HCl, and 10 minutes leaching with
ammonium acetate. Limited data indicate that in 2 of the 3 soils, leaching removed more than
half the Sr—89, 90, but in one case only 10%.
A program has been undertaken to determine the natural (stable) Sr content of soil. These
measurements will be correlated with similar datafor plants, animals, and humansas an analogy
to the Sr-90 uptake problem under equilibrium conditions. Preliminary data obtained by Menzel
and Heald of the U. S. Department of Agriculture show a mean Sr/Ca ratio (by weight) of about
2-4 x 10-* for ammonium acetate leachates from a set of Wisconsin and Illinois alfalfa fields.
Further measurements on these and other sites will be forthcoming. G. V. Alexander’s raw
water data, which presumably are indicative of the Sr/Ca ratio of the associated watershed, are
consistent with these soil analyses.
E. Uptake and metabolism of fission products by plants: The uptake of bomb debris by plants has been considered significant only as a step toward
the contamination of humans through the food chain. Sr, which has been generally considered
to be the most hazardous, has been studied most extensively.
1. Strontium:
Plant uptake of Sr has been examined by two different approaches: (1) Controlled laboratory
or field experiments, and (2) observations on the actual atomic test debris now disseminated
throughout the world.
10
Footnote references on pp. 42-43.
So
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