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* CATTLE (853 samples)
1.0
o HUMAN (1!65 samples)
E
—4
2
20.1
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TESTS”
* BRITISH
currence of occasional high values re- |
quires further study to determine how
muchreliance can be placed on the ideas
of uniform distribution or uniform accessibility’ of fallout materials. Similar
interpretation of occasional high values
could not be made for the human samples because any such value was automatically suspect on accountof the widespread medical uses of iodine-131; in
compilation, such values were eliminated
from averages after the institution of
origin confirmed that the individual had
been treated with iodine-131.
Milk
4 RUSSIAN
me U.S.(PACIFIC)
1 U.S. (CONTINENTAL)
WH
u
bbe
$
JFMAMJJASONOJFMAMJ JASOND
1955
i956
Fig. 1. Summaryof iodine-13! levels in human andcattle thyroids as correlated with
nuclear weaponstests during 1955-1956.
nation for cattle; indirect evidence (3)
implicating food as the principal source
of iodine-131 in cattle provides support
for the findings presented in this paper.
A comparison of cattle values shown
in Table 2 and the average humanlevel
is of interest. If the concentration in the
thyroids of the barn-fed animals is corrected by’a factor of 5 to accountfor the
difference in respiratory tidal volume between the two species, a value of 0.0024
millimicrocurie per gram is obtained. As
noted from Fig. 1, this is in fair agreement with the human values for this
period (late June 1955). Since it is reasonable to assume that the iodine-131
burden in the barn-fed animals resulted
primarily from inhalation, this supports
the idea that the human burden may in
large measure result from inhalation.
Table 1 presents the data for May
1955, a peak month. For ease of interpretation, the results have been lumped
by geographical regions. Despite the fact
that generalizations about regional differences are not particularly meaningful
in Table 3, which presents the percentile
distribution of samples for May 1955
and August 1956, two peak months. For
instance, during the May peak, 30 percent of the human samples hadless than
0.0008 millimicrocurie per gram, whereas
11 percent had more than 0.01 millimicrocurie per gram; the spread was
even greater for the cattle samples. As a
further example, out of ten cattle sam-
are apparent. As expected, the levels
from the region near the Nevadatest sitc
were higher than those from the rest of
the country. The human values were essentially the same all over the country
except for the Nevada-Urah area. The
cattle samples, in contrast, appeared to
show more differences between regions,
with lowest values from the West Coast
and highest from the Southwest. This
maybe related to the different routes of
assimilation of fallout iodine-131 by man
and grazing animals. Cattle samples from
abroad ‘were generally low.
Particular attention is called to the
large spread of values. This is illustrated
and Portland; five cattle samples from
California and Washington)
because of arbitrary factors, some trends
ples during the period 1 to 15 October
1956, eight ranged between 0.004 and
0.09, whereas the other two samples were
1.6 and 2.0 millimicrocuries per gram.
There are obvious reasons for variations
within sample groups; however, the oc-
It seemed important to consider milk
as a route by means of which fallout
radioiodine could be transmitted to the
human population, especially to children, since appreciable amounts (up to
.6 percent) of radioiodine ingested by the
dairy cow appears in the milk (7). Sam-
ples of milk (100 milliliters) from the
same areas as the sources of the cattle
thyroids were collected from February
to June 1955. No activity was detectable
in these milk samples, indicating that
the concentration of iodine-131 must
have been less than about 0.01 millimi-.
crocurie per 100 milliliters when the
milk was secreted. From some unpublished experiments by F, W. Lengemann,
it was shown that in two dairy cows receiving iodine-131 every day there was,
at steady state, 0.74 and 1.3 percent of
the daily dose per kilogram of milk and
30 and 65 percent of the daily dose in
the thyroid gland, respectively. It is estimated from these values that the levels
of iodine-131 in milk from dairy cows
———-
Table 1. Iodine-131 content of human andcattle thyroid glands during May 1955.
_,
Human
Location
(mpc/g)
Nevada-Utah (eight human samples from Salt
Lake City; two cattle samples from Nevada
and southern Utah)
0.030
West (27 human samples from Los Angeles
-
Louisville, Oak Ridge, and New Orleans;
nine cattle samples from Louisiana,
Tennessee, Texas, and Florida)
North and Northeast (37 human samples from
Minneapolis, Chicago, Boston, and New
York: ‘six cattle samples from South Dakota,
Missouri, anid Massachusetts)
Abroad
Panama(two cattle samples)
Hawaii (two cattle samples )
Germany (two cattle samples)
Greece (one cattle sample)
French Morocco (one cattle sample)
Tokyo, Japan (one cattle sample)
:
\
aN
0.0048
South and Southeast (39 human samples from
Cattle
(mpc/g)
Lo
>
4630.15
0,086
0.0055
0.46
0.0032
0.18
0.10; 0.082
0.11; 0.081
0.0019; 0.0056
0.013
0.047
0.0092