74
EFFECTS OF IONIZING RADIATION
Onthe basis of an assumed uptake of 20 per-
cent per 24 hours, the integrated dose to the
thyroid from I** and other shorter-lived iodine
isotopes was calculated by the USNRDLto be
about 100 rep. The LASL hasestimated that
this dose was about 150 rep for Rongelap group
and 50 rep for the Americans.
The differing approaches used by the
USNRDL and the LASL for estimating the
body burden gave results which, except for
Ba, are veryclose.
The menn body burdens of the individual
nuclides presented in Table 5.6 were calculated
for the Rongelap group. Values for the
Allinginne group were approximately half
those of the Rongelap group, and values for
Americans, about one-fourth those of the
Rongelap group.
The total amount of radioactive material
present in the G. I. tract at one day post detonation in the members of Group I was estimated
as approximately 3 mc. This activity was con-
tributed chiefly by isotopes of short radiological
and biological half-life and limited solubility.
Thus the levels of activity in the tissues of the
body were relatively low. The concentration
of radioisotopes at 6 months post detonation
was barely detectable in the urine of most exposed individuals,
Iodine, which is quite soluble, is probably
the most hazardous internal radioemitter in the
early period following exposure (10). The
dose to the thyroid was appreciable, but low
compared to the partially or totally ablating
doses of ['*! used in therapy of hyperthyroidism
or carcinoma. At one day post detonation Sr®
was ctleulated to be near the maximum permissible level (5) for this nuctide. At later
times following exposure, this longer-lived fisston product presents the greatest potential internal hazard,
The present study contirms the observation
made in animal experiments that most of the
radioactive elements formed in fission as well
as the fissile material itself, are not readily absorbed from the lings and the G, I. tract. Only
{, Sr, Ba and a fewof the rare earth elements
were absorbed to any significant degree.
An attempt to measure bone-fixed radioactive
emitters by meansof sensitive film badges taped
below the knee, over the epiphysis of the tibia
on a number of persons, yielded no positive
results.
No correlation could be obtained between the
degree of internal contamination and the clini-
cal and hematological findings.
In view of the
short half-life of the most abundant fission
products deposited internally in this situation,
the possibiJity that chronic irradiation effects
will occur 1s quite small. Thus, an evaluation
of the data on the internal contamination, in-
cluding that of Sr®, leads to the conclusion that
the internal hazard to the contaminated inhabitants of the Marshall Islands is minimal both
from the acute and the long rangepoint of view.
5.33
Source of Internal Contamination
The fallout material consisted largely of
calcium oxide and calcium carbonate. The
fission products were adsorbed muinly on fairly
large particles. The material was 10 percent
soluble in water, and completely soluble in acid.
Internal deposition of fission products resulted from inhalation and ingestion of the fallout material. Ingestion appears to be the more
important of the two routes of entry into the
body. The activity in the air settles out fairly
rapidly, but contaminated food, water and
utensils retain their activity for long periods of
time,
The amount offission products reaching the
bloodstream through the respiratory tract is a
function of particle size and solubility of the
airborne contaminants. The particles with
which che activity was associated were considerably Jarger than the optimum size for
deposition in the alveolar tissue of the ling.
Thus, the probability of the retention of inhaled
airborne contamination was not appreciable
during the exposure period.
The hypothesis that ingestion was the chief
source of internal contamination is supported
by the finding that the gastro-intestinal tract,
its contents, and the liver of autopsied chickens
and pigs sacrificed at early (ntervals following