CHAPTER 4
THE RADIOIODINE PROBLEM -- INHALATION
The discovery a decade later of severely damaged thyroids in those
Marshallese who were exposed as children to the fallout from the March 1,
1954, BRAVO shot, in two ins tances amoun ting to complete ablation, and
almost surely due to radioiodine,
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raised the question of the pathway
by which that exposure occurred.
In earlier analyses, it was generally
assumed that ingestion through food and drinking water was the principal
pathway, and not inhalation.
Direct data on the thyroid exposure were
not available, partly because the problem was not appreciated then, and
partly because gamma spectral analysis was in its infancy. Direct
measurement of thyroid burden was not possible as it is today. On the
other hand , it is readily demonstrable that there were massive external
and internal exposures to a wide mix of fission products, including
the radioiodines.
The severity of the thyroid damage suffered by the Marshallese has
raised the specter of a possible neglected but important danger from
radioiodine in fallout particles.
It also became important to investigate
the possible routes of_entry--ingegtion or inhalation. This has led to
recent studies by Cole”? and Norman’ on the threat of inhalation of
radioiodine.
In the fission process, the iodine radionuclides (I-131, 132, 133 and
135) are mainly produced as decay products of the precursor nuclides
of Sb and Te, Although these precursors are less volatile than iodine
itself, almost all the iodine radionuclides would be expected to
condense late in the temperature history of the nuclear cloud and thus
on the surface of the fallout particles, This tendency for surface
condensation would make the radioiodines liable to leaching and later
assimilation by plants and animals.
In addition, significant volatilization of iodine takes place in the evaporation of water solutions of iodide,
and when moist warm air is passed over iodine-coated, pseudo-fallout
particles. This effect can be orders of magnitude greater on coral
(carbonate) than on siliceous particles.
Cole found one set of circumstances in which he concluded that
inhalation of radioiodine would be a real and significant hazard
following nuclear attack: where people are in a fallout
the most intense part of a fallout field,* and there is
standing water near the shelter ventilator intakes, and
thermal inversion. Fallout in rain he excluded because
occurs in coincidence with a strong inversion.
shelter near
appreciable
an extended
rain seldom
Examination of data from atmospheric tests does not yield a basis
for clear-cut conclusions about
the hazard of
iodine inhalation.
The
*Because iodine is usually fractionated out of the larger particles that
fall in the intense part of the fallout field, these circumstances are
generally limited to overlapping fallout fields.
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