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Reprinted *from Scrence, July 5, 1957, Vol. 126, No. 3262, pages 16-18.
minute; 1 millimicrocurie of iodi
Thyroid Radioactivity after
“Nuclear Weapons Tests
C. L. Gomar, Bernard F, Trum, U. S. G. Kuhn IT],
R. H. Wasserman, M. M. Nold, J. G. Schooley
2
nt
In 1954 it was shown that nuclear
weapons tests had produced radioactive
materials (primarily iodine-131) that
were accumulated and detectable in the
thyroid glands of livestock in the United
States (1). Further survey values for
both man and animals have been presented in U.S. Atomic Energy Commission reports and in the open literature
(2-4). The magnitude and pattern with
time of radioactivity levels in the thyroids are of interest because (i) there is
provided an alert to any build-up of
potentially hazardous levels; (ii) as relationships are developed, radioiodine
measurements could serve as a sensitive
monitoring system for other fallout nu-
clides less easily detected in the hio-
sphere; (iii) information may be obtained on the movementof radioiodine
particularly in the biological system; and
(iv) there could be an interference with
medica! diagnostic tests that employ low
levels of radioiodine. This paper (5)
summarizes the information that has
been obtained onthe levels of iodine-131
in human and cattle thyroids and pre-
sents an estimate of milk levels in the
United States during the period from
January 1955 to December 1956. Correlation with known bombtests is noted,
and some inferences are drawn about
routes of exposure.
Procedure
Human thyroids from autopsies were
submitted by pathologists from locations
as noted by acknowledgment (6). In
general, the thyroids were predominantly
from persons more than 50 years old, and
it was necessary to determine whether
the radioiodine content was affected by
the age of the person. Samples from the
Dr. Comar and Dr. Wasserman are on the staff
of the Medical Division, Oak Ridge Institute of
Nucleat Studies, Oak Ridge, Tenn. Lt. Col. Trum,
Lt. Col. Kuhn, and Maj. Nold, were on assignment from the Veterinary Corps of the U.S. Army
and U.S. Air Force for this study. Mr, Schooley
is presently in the department of physiology, Unisersity of California, Berkeley.
MO
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. New. Orleans area permitted comparisons of thyroid radioactivity in various
age groups; thyroids from older persons
showedslightly higher values than those
from younger, and the few samples from
children were not generally higher than
those from other age groups. In addition,
no differences were observed between
samples from accident cases and those
from patients hospitalized for a matter
of weeks prior to autopsy. Thus, the
sampling was considered as conservatively representative of the total population. Cattle samples were taken at the
slaughter house, usually from calves or
yearlings.
All thyroid glands were. shipped in
formalin and were processed in a standard manner upon receipt. The thyroids
were washed, blotted dry, trimmed of
extraneous tissue, cut into small pieces,
placed in a tared aluminum cup, and
weighed. The samples were dried for
several hours at 100°C, reweighed, and
then pelieted in a Carver laboratory hydraulic press into a cylinder about 16
millimeters in diameter. The pellet was
placed in a test tube for counting. The
dried pellets gave more uniform samples
than did fresh tissue and permitted more
sample to be presented to the sensitive
volume of the detector. Recovery experiments showedthat losses during processing did not exceed 10 percent; formalinfixed weights were about 5 percent higher
than wet weights. The results are expressed as millimicrocuries per gram of
tissue (fresh weight) (muc/g) calculated back to the date of death. The
counting was usually done between 1 and
2 weeks after death. The samples as
counted represented, on the average,-
about 10 to 15 grams of fresh tissue,
ranging from 3 to 30 grams for both man
and cattle.
For the most part, a commercial well
crystal (background, 300 counts per min-
ute; | millimicrocurie of iodine-131, 909
counts per minute) was employed, although some samples were counted with
a 3-inch crystal and a_ single-channel
analyzer (background, 19 cunts per
ty
Jf oY
394 counts per minute). Counts
considered significant when the cou.
rate was 2 to 3 times its standard devi.
tion. As a rule, the counting rate was not
significant when the sample contained
less than 0.005 millimicrocurie of iodine131. The usual calibration and standatdization procedures were employed.
Occasionally, the gamma-ray spectrum
and half-life were determined and were
found to be in agreement with the characteristics of iodine-131. Muscle sam-
ples showed no detectable activity under
the conditions of measurement that
could not be ascribed to radiopotassium.
Results
The over-all results are presented in
Fig. 1 and represent the human andcat-
tle samples averaged by 2-week periods.
The curves were drawn by inspection to
aid in the visualization of the general
pattern; broken lines indicate periods
during which samples were not taken.
All the human samples were averaged
except those from the Salt Lake City
station, The cattle samples up to June
1955 represent averages of all continental stationslisted in Table 1 except those
from the Nevada-Utah area; thereafter,
coliections were made only from Omaha,
Nebraska.
It is first noted that the pattern of
levels is correlated with known weapons
tests. The peak in mid-1955 was undoubtedly a result of the United States
continental tests in the spring of 1955.
The smaller rise with a peak near January 1956 presumably reflected a contribution from Soviet tests. The general
rise during the latter half of 1956 could
haveresulted from United States, British,
and Soviet activities.
From comparison of the pattern of
cattle and human values, there seems
little question about the commonsource
of radioactivity. The cattle values were
Significantly greater than those of man
(P < 0.01) and were increasingly higher
at the higher levels. An indication of the
route of entry of the radioiodine into
cattle is given in Table 2. Through the
cooperation of George K. Davis of the
Florida Experiment Station, it was possible to obtain thyroids from six animals
that had been barn-fed in central Florida
for about 3 months on feed that could
have contributed only small amounts of
iodine-131,
For
comparison,
thyroids
were sent from two animals that had
been allowed to graze normally on nearby
pastures. It is apparent that at least 70
percent of the jodine-i31 in the grazing
animals had been contributed by the pasture. This observation is in disagreement
with other reports (2) that suggest inhalation as the major source of contami-
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