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(2) Animal boneslie in the range of a few Sunshineunits.
(3) Milk and cheese have an activity of 1-2 S.U.
(4) Chicago humanstillborns at 0.14 $.U. are lower in activity than the local milk by a
factor of 10, a part of which is undoubtedly caused by a placental barrier to Sr transfer.
(Comar found the Sr/Ca ratio in rat fetuses to be about % that of the mother at
equilibrium.)
No direct measurements are yet available on the current animal intake of Sr-90 produced
in the 1954 test series. However, for purposes of comparison of the body burden of this Sr—90
Cumulative Sr-—90
fallout in the U.S. from the 1954 series is thought to be very roughly 50 dpm/ft*. By analogy with
previous tests, it is expected that grazing animals would acquire a body burden of the order of
1-Sunshine unit from this quantity of Sr—90 fallout.
The interpretation of all these data for long term hazard evaluation is made difficult by
uncertainties in the current route of entry of Sr-90 into the food chain. If the present picture
is dominated by external leaf contamination with current fallout, present data would give an
exaggerated estimate of the long term hazard.
c. Stable Sr measurements.—Measurements on the stable Sr content of human bones have
been made as part of the picture of the soil-plant-animal Sr chain under equilibrium conditions.
Tipton *° studied bones from 28 individuals by activation analysis, finding an average Sr/Ca
ratio of 2x10—* by weight (range 0.2-7x10-*). Hodges, et al,?! made spectrographic analyses
on the bones of 26 individuals ranging in age from fetus to 75 years, and of 12 cadavers preserved
since 1914. The fetuses had an average Sr/Ca ratio of 4.5x10-‘ by weight (range 4.2-5.3 x
et eneResa
with that of the 1954 I-131, discussed later, a rough estimate can be made.
10-4), the others 7 x 10-* (range 4.5-15). No significant differences were observed between the
Sr/Ca ratios of different bones in the same individual, nor between the 1949 and 1914 series of
specimens.
It appears that the stable Sr/Ca ratio of bone is very roughly 10% that of soil. This correlates well with expectations of cumulative discrimination between the 2 elements in the food
chain. Estimates of discrimination against Sr are: soil-plant, factor of 2, cow feed-milk, factor
of 6; food-bone, factor of 2. In the U.S., 75% of food Ca is in milk, 25% in plants. Weighted
discrimination is then [ (25%) (42) + (75%) (4%) (%)] [42] ~10%.
2. Fission products other than strontium:
Observations, both by the United Kingdom and by the United States on quantities of radio-
iodine in human urine, animal thyroids, etc., and of radioruthenium in bomb debris have directed
of the spring, 1954, Pacific tests.
Thyroids from some 50 cattle and 25 sheep raised in the
Great Plains, Florida, Kentucky, and Massachusetts have been analyzed. Slaughter took place
during the last 3 weeks of June. As of June 12, the values were in the range of 0.4-4 x 10°
vc 1-131 per gram thyroid. A few hogs and dogs were found to contain considerably less I-131.
Thyroids from 4 human autopsies in Chicago were collected and analyzed during the first 2
weeks of July. They showed measurable levels of activity, but the possibility of laboratory
contamination has not been definitely ruled out. Two N. Y. human thyroids showed less than
Y% dpm I-131/thyroid at the end of July.
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attention to the relative importance of these materials to GABRIEL.
Accidental exposure of personnel to short-range fallout from one of the Pacific tests, 1954,
provided some data on this subject. Urine sampies taken from natives exposed on one island
and Americans on another were brought to Los Alamos Scientific Laboratory for analyses.
From the results LASL suggested the relative initial average body contents (uc basis) of the
principal radioisotopes involved to be as shownin table 4.
I~131 activity has also been observed in American animal and human thyroids as a result
Footnote references on pp. 42-43.
14
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