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The discussion in the following pages of “Thyroid
Irradiation in Utah Infants Exposed to Iodine 131”
by Charles Mays, which appeared in our last issue,
centers around these two questions and the problems
involved in trying to answer them.
Obviously, it is desirable to find and treat any malignancies that might develop in any of these children.
It is also important to find answers to the questions because of the light this could throw on the more general
questions: How much iodine 131 produces thyroid
camage of any kind? Thyroid cancer? In what proportion of exposed children? These questions are important,
not only for past exposure, but for the evalution of
possible future exposure from underground testing,
atmospheric testing by other nations, Plowshare projects
(nuclear explosions for peaceful purposes) or from reactor accidents.
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carbon {4—as an indicator of the age of archeological
findings.
.
Tissue preserved after autopsies performed on people
who died shortly after nuclear tests in the fifties could
therefore be tested for iodine 129. This would tell us
how much iodine 131 was in the same thyroids prior
to death, and the approximate level of iodine 131 exposure to others still living, who were subject to fallout
in the same locality in the same year. Autopsy tissue
is probably available in Salt Lake City, if not in the
smaller towns (CNI has not checked with Salt Lake
hospitals, but such tissue would be available in St.
Louis, and presumably also in other metropolitan
medical centers). Such a study would not have to cover
the whole geographical area of high exposure in order
to serve as a check on estimates—such as those of
Tamplin and Fisher—based on external radiation
measurements.
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A recent paper from the Lawrence Radiation Laboratory (reviewed on page 4 ) presents new estimates of
the size of the dose anc the numberof children exposed;
estimates which underscore the need for expanding the
search for radiation effects. A procedure for checking
these estimates, proposed in the Appendix to Dr. Mays’
article Jast month, would use the long-lived iodine 129
as an indicator of the amount of iodine 131 originally
present. This proposal is discussed further by Dr. Tamplin on page 3.
The question has been asked: If iodine 129 has a
half-life of millions of years, why aren’t we concerned
about its biological effects? Doesn’t it do more damage than the short-lived iodine 131? The answer is
“No.” Because it cecays slowly, iodine 129 gives off
much less radioactivity in a given amount of time than
does iodine 131. Also, although it takes about seventeen
million years for half the radioactivity of iodine 129 to
decay ‘a physical half-life of 17,250,000 years), it is
excreted from the body fast cnough to makcits biological half-life (the time it takes for half of it to disappear
from the hody) only about three months.
In pathological tissue from autopsy, the excretory
process would have ceased with death. Because there
is a known ratio of iodine 131 to iodine 129 at the
time they are created in a nuclear explosion, the iodine
129 still present in the tissue can vive a clue to the
amount of ‘odine 131 that was formerly present. This
is not unlixe the use of another long-lived isotope—
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Want effects ?
Dr. Conard, who has been studying the Marshall
Islanders exposed to fallout from the Bikini test of
March 1, 1954, summarizes the thyroid abnormalities
found in these people (page 1 ). With one exception,
all the abnormalities found have been in the group
exposed to 700 or more rads of radiation from iodine
131. The children exposed to the lesser doses, and
showing no abnormalities are too few in number, as
Conard points out, to establish a threshold dose (a dose
below which no abnormalities would be produced).
They are also too few to draw conclusions from the
Marshall Island experience that are applicable to the
Utah-Nevada experience.
Six children in the Marshall Islands were exposed
to 300-600 rads. On the basis of the assumption used by
Mays (35 cancers per million children exposed to one
rad of x-rays), one would expect only one case of thy-
roid cancer per hundred children exposed to 300 rads,
or onecase per50 children exposed to 600 rads. If iodine
131 is one-tenth as effective as x-rays in producing
thyroid damage, one case of thyroid cancer per thousand children exposed to 300 rads would be expected,
or one case in 500 children exposed to 600 rads. It is
therefore not surprising that no cancer has been found
in the six children exposed to doses in this range.
Forty children were exposed to 55-125 rads. In this
exposure range, one would expect a maximum of one
Copyriekt 1983, Greater St, Loute Citizens’ Committee for Nuclear Information
5