cme
particularly with regard to the thyroi:. More information would be desirable
concerning certain aspects of thyroid exposure. More data are needed on the
contribution of short-lived iodine racioisotopes, including relative abundance
and distribution as a function of time, dose fractionation, etc.
Also,
the
dose-response relationship of these isotopes in the thyroid compared with 13ly
and gamma radiation needs further investigation; such studies should be done
in large animals, perhaps sheep or swine, having thyroid glands comparable in
size to human glands.
Since radioelements other than iodine may have been involved in the thyroid exposure of the Marshallese, further information is needed on such elements that might be present in fallout. Certain elements are known to show
relatively greater affinity for deposition in the thyroid than in other organs. Radium and thorium (226,227), barium (226), americium (228,229), plutonium (228-230), and calcium (226,231,232) have been found in animal thyroid
glands. Robison et al. (231) have shown that calcium is concentrated in the
lining of thyroid follicles with small localized areas of calcification in
human thyroid glands. Haeberli et al. (232) have reported rapid incorporation
of “Sta in the rat thyroid. In view of the abundance of calcium in the atoll
environment, perhaps consideration - ould be given to the possibility of a neutron-induced calcium isotope that might have been involved in the thyroid exposure of the Marshallese. Autoradiographic and other studies of animal thyroids removed at surgery or autopsy might he helpful in this regard. It
should be noted that the elements referzed to above are absorbed by the thyroid to a much smaller degree than iodine, and it seems unlikely that they
would contribute significantly to the thyroid dose.
Very little is known about the 2ffects of low doses of radioiodine radiation on the thyroid. One source of information comprises thyroid studies on
people given diagnostic doses of 131] in che early days, when doses were
higher than now used. It is hoped that further information from such studies
will be forthcoming so that a better evaluation can be made of low-dose effects and of the relative importance of 1311 exposure on the thyroid.
The development of thyroid nodules in two of three Rongelap children
exposed in utero emphasizes the probable importance of radioiodine absorption
by the fetus from the mother. More precise information regarding fetal iodine
uptake at various stages of gestation is needed.
1297, a long-lived isotope
with low radioactivity and a high cross section for neutron activation, might
be administered to prgsnant women in cases where abortion is indicated. Neu-~
tron activation of 4/29] in the thyroid gland removed from the fetus would provide precise information on uptake of iodine by the gland at the given stage
of gestation.
In view of the greater relative sensitivity of the child's thyroid, further information on thyroid weights and thyroid function in children of various ages would be heipful.
In conclusion, in view of the possible further development of thyroid
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abnormalities and other late effects of radiation in the exposed Marshallese
people, it is necessary that regular examinations and provision for adequate
health care be continued throughout their lifetime.