together with data on the activity of the various fission products at this same time’® and
animal isotope absorption and retention data.’-!8
LASL has also estimated the body burden at 1 day on the basis of radiochemical analysis
of polled urine samples from a representative number of Rongelap and American individuals
(Harris*). These calculations were based on the analysis of I'*! in the early samples of urine
(15 days postdetonation), as well as the above-mentioned physical and biological data on fis-
sion products (Hamilton,’ National Bureau of Standards Handbook 52,'° and Hunter and Bal-
lou’), Their findings are presented in Table 2.5.
On the basis of an assumed uptake of 20 per cent per 24 hr, the integrated dose to the
thyroid from I'*! and other shorter lived iodine isotopes was calculated by NRDLto be about.
100 rep. LASL has estimated (Harris®) that this dose was about 150 rep for the Rongelap
group and 50 rep for the Americans.
The differing approaches used by NRDL and LASL for estimating the body burden gave
results which, except for Ba!40, are very close.
The mean body burdens of the individual nuclides presented in Table 2.5 were calculated
for the Rongelap group. Values for the Ailinginae group were approximately one-half those
of the Rongelap group, and values for the Americans were about one-fourth those of the Rongelap group.
The total amount of radioactive material present in the gastrointestinal tract at 1 day
postdetonation in members of the Rongelap group was estimated as approximately 3 mc. This
activity was contributed 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 postdetonation 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 (Harris*). The dose to the thyroid was appreciable, but it was
low comparedto the partially or totally ablating doses of I'*! used in therapy of hyperthyroidism
or carcinoma, At 1 day postdetonation Sr® was calculated to be near the maximum permissible
level'® for this nuclide. At later times following exposureof this group, this longer lived fission product presents the greatest potential internal hazard.
The present study confirms 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 by the bloodstream from the lungs and the gastrointestinal tract. Only iodine, strontium, barium, and a few of the rare-earth elements were absorbed to any significant degree.
An attempt to measure bone-fixed radioactive emitters by means of sensitive film badges
taped below the knee, over the epiphysis of the tibia, on a number of persons yielded no posi-
tive results.
No correlation could be obtained between the degree of internal contamination and the
clinical and hematological findings. In view of the short half life of the most abundant fission
products deposited internally in this situation, the possibility that chronic irradiation effects
will occur is 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 in-
habitants of the Marshall Islands is minimal both from the acute and the long-range point of
view.
2.3
ROUTE OF ENTRY OF INTERNAL CONTAMINATION
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.
Theactivity in the air settles out fairly rapidly, but contaminated food, water, and utensils
retain their activity for long periods of time.
The particles with which the activity was associated were considerably larger than the
optimum size for deposition in the alveolar tissue of the lung (see Chap. 4). Thus the probability of the retention of inhaled airborne contamination was not appreciable during the exposure period.
19