days postdetonation increased the excretion rate of internally deposited fission products, but
the over-all effect on decreasing the body burden was insignificant, as the excretion rates
were very low at this time.
2.5
SUMMARY AND CONCLUSIONS
The first instance of internal deposition of mixed fission products in humans occurred as
a result of the contaminating event of 1 March. This internal contamination resulted from
both inhalation and ingestion of contaminated material, the latter being the more important.
Few of the fission products present in the environment were readily absorbed from the
lungs and the gastrointestinal tract. Radiochemical analysis of the urine samples from the
Rongelap group indicates that strontium, barium, and the rare-earth group together con-
stituted 75 per cent of the total beta activity of the urine at 45 days postdetonation. Strontium89 was the predominant radionuclide at this time,-contributing 42 per cent of the total beta
activity. Assays for fissile material in the pooled urine samples wereall negative.
The human body burden of individual radionuclides was estimated from radiochemical
analysis of the human urine and of the tissues and urine of animals from Rongelap. The mean
body burdens of the radionuclides in the Ailinginae group were approximately one-half those
of the Rongelap group, and the mean body burdens of the American group were about onefourth those of the Rongelap group. While the activity excreted per unit volume of urine was
the same for adults and children of the Rongelap group, the total activity excreted in the urine
in 24 hr by children under 15 years of age was significantly lower than that excreted by the
adults.
The total amount of radioactive material in the gastrointestinal tract at 1 day postdetonation was estimated to be 3 mc in members of the Rongelap group. This activity was contributed
chiefly by isotopes of short radiological and biological half life and limited solubility, and 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 of the exposed individuals.
The estimated dose to the thyroid from I'*! and other short-lived iodine isotopes was 100
to 150 rep for the Rongelap group. Iodine is probably the most hazardous internal radioemitter
at early times after exposure. The dose to the thyroid, while appreciable, was low compared
to the partially or totally ablating doses of I'*! used in the treatment of hyperthyroidism or
carcinoma.
At 1 day postdetonation, the concentration of Sr® was calculated to be near the maximum
permissible level for this nuclide. At later times following exposure, this longer lived fission
product presents the greatest potential internal hazard.
Oral administration of calcium EDTA beginning 7 weeks postdetonation to a representative
group of individuals from Rongelap increased the rate of excretion of activity 2.5 times. However, the decrease of the body burden was insignificant, as the excretion rate was very low
at this time.
Analysis of the internal contamination indicates that the dose to the tissues of the body
was near but did not exceed the maximum permissible dose levels. The activity fixed in the
body decreased rapidly as a function of time. The contribution of the effects of internal contamination to the total radiation response observed appears to be small on the basis of the
estimated body burden of the radioelements. In view of the short half life of the most abundant
fission products in the situation, the possibility that chronic irradiation effects will occuris
quite small.
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