with non-radioactive iodine; this should rarely produce anyserious side effects and would beof particular value in children and pregnant women.
When exposure of the thyroid has already occurred, prophylactic treatment with thyroid hormone, now being used in the Marshallese, may
help prevent development of thyroid tumors, and
even after tumor development,surgical excision
may reduce mortality due to malignancy.
The thyroid effects in the Marshallese were not
anticipated at the timeofthe accident or during the
early years afterwards. In retrospectthis is not surprising, for several reasons. At that time the thyroid was thoughtto be relatively radioresistant,
particularly with regard to radioiodine exposure
(on the basis of animal studies and diagnostic and
therapeutic use of 151] in peaple), and the calcu-
lated thyroid doses in the Marshallese were considered to be below thelevels likely to produce
_ tumors. In addition, neither the importanceof the
exposureto short-lived iodine isotopesin fallout
nor the thyroid dose differential in children due to
the smallersize of their gland was fully appreciated.
It is quite likely that the final results of thyroid
lesions in the Marshallese are incompleteat this
time since newlesions are still occurring. The
been seen as late as 40 years after exposure. Fur-
thermore, on the basis of the present data the risk
of developing radiation-induced thyroid neoplasia
is probably underestimated, since surgical removal
of potentially malignanttissues may have occurred
and the hormone treatment may haveinhibited
the development of some tumors, althoughthelatter is questionable. As has been pointed out, also,
the true carcinogenic potential of the exposure,
particularly in the children receiving the higher
dose, may have been masked by excessive cellular
destruction. The recent finding that subclinical
thyroid deficiency is present in some of the exposed people who have not shown any thyroid abnormalities indicates that the thyroid effects in the
Marshallese may not yet be completely manifest,
and continuedcareful surveillance of this population is necessary.
Acknowledgments
Because of the broad scope of the surveys and
the complexity of operations it would be impossible to acknowledge all the individuals and organizations that have contributed to the success of the
surveys over the past 20 years. We wouldlike,
however, to express thanks to some whohave contributed vitally in more recent years.
Ourforemost appreciation is to the people of
Rongelap and U-irik who have participated in the
examinations, including the unexposed people
comprising the control population. Wetreasure
the friendship andtrust of these people. We are
grateful to many Rongelap and Utirik peopie for
assisting the examining teams over the years, in-
cluding the Magistrates of both islands - at Ron-
gelap: John Anjain,Billiet Edmond, Jabwe Jorju,
and Niktimos Antak; at Utirik: Kabto Campus,
Maja Lena, Harold, the school principal, and
Joata, the health aide.
Thesenior author is most grateful to the many
fine medical and otherspecialists (listed in Appendix 2) who haveso willingly given of their time
andtalents, without remuneration,to participate
in the surveys. Without their dedicated efforts the
surveys could never have succeeded. Heis also
greatly indebted to the many technical assistants
who have contributed muchto the success of the
surveys, particularly to Mr. W. Scott and Mr. D.
ee a
radioiodines by isotope dilution and saturation
mean latent period for radiation-induced thyroid
tumors may be as long as 30 years. Cases have
_
posure under extreme conditions, with no corrective measures taken to reduceinternal absorption
of radioisotopes prior to evacuation of the exposed
people from thefallout area. {t did not involve the
contaminated pasture-cattle-milk cycle, which
might be an important pathwayof radioiodine to
man in other types of accidents (such as the Windscale accident).1"6
Civil Defense planning can provide for several
measures that will reduce the hazard of thyroid
exposure dueto radioiodine absorption and thus
largely preclude the degree of thyroid injury sustained by the Marshallese. Since the hazard from
radioiodine is acute for a period only of days,
early protective measures are extremely important. These include avoiding inhalation of radioiodines by shelter protection; consuming food and
water only from closed containers; feeding cows in
contaminated areas protected fodder; and temporarily withholding contaminated milk supplies and diverting them into processed products
with a shelflife longer than thelife of the isotope.
The addition ofstable iodine to food or water during the first week woulld provide a relatively inexpensive method of reducing thyroid uptake of
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