5
INTERNAL IRRADIATION
Radiochemical analyses of numerous urine samples of the exposed population showed internal
absorption of radioactive materials, probably
brought about largely through eating and drinking
contaminated food. and water and to a lesser extent through inhalation. During the first few days
when the body levels were at their highest, the
maximum permissible concentrations were approached or slightly exceeded only in the case of
strontium-89 and the isotopes of iodine. The concentrations were believed to be too low to result in
any serious effects. Body levels fell rapidly, so that
by 2 and 3 years post exposure, they were far below
the accepted maximum permissible level; by 6
monthsactivity in the urine was barely detectable.
In 1958 analyses of bone samples on one of
the men who died showed 3.7 strontium-90 units/g
calcium. Beginning in 1957, gammaspectroscopy
by use of a low-level counting chamber was added
to the techniques of radiochemical analysis. The
return of the Rongelapese’ to their home island
(which after careful survey was considered safe for
habitation, despite a persisting low level of radioactive contamination) was reflectedin a rise in their
body burdens and increased urinary excretion of
certain radionuclides. During the years since the
original contaminating event, additional weapons
tests held in the area have contributed to thefission
products in the environment.Since the diet includes
a variety of imported foods, the people are not
living in a “closed” environment, and therefore
may not be rapidly approaching equilibrium with
the environmental fission products, as might be
expected under other circumstances.
Body burdens of gamma-emitting fission products (such as Cs'47 and Zn**) were measured in a
whole-body counter and checked by radiochemical
analysis of urine specimens. The levels of internal
contamination per unit weight appeared to be
about the same for juveniles as for adults, male
and female. Wide variationsin levels of contamination in any group were found, apparently due to
differences in diet and metabolism.
Body burdens of Sr* were estimated from urinary excretion as determined by radiochemical
analyses. Both the external dose measurements on
Rongelap Island and the levels of radioactive isotopes in the food on the island indicated that some
increase in Cs**7, Zn®*, and Sr°° body burdens was
to be expected when the people returned there in
1957. The Cs'** body burden in 1958 was about
0.68 uC, about 60 times as great as in 1957, and
the urinary Cs'** level rose by a factor of 140; the
mean body burden for 1959 was 0.57 uC. The
mean body burden of Zn* estimated from wholebody counting data was, in 1958, after the return
to Rongelap, 0.36 uC, 8 times as high as in 1957,
and 0.44 uC in 1959. In 1961 the mean Cs*3* body
burden in adult males was 14.7 myC/kg, whichis
not significantly different from the mean value of
a similar group obtained in 1959; it was 300 times
that of the medical team, who were measured at
the same time for comparison. The Zn* level in
adult males (1.51 mzC/kg) dropped to 17% of
the mean value measured in 1959. With a larger
detector and a longer counting time than previously
employed, it was possible to identify and quantify
Co® for the first time in these people; the mean
level of Co® was about 11% of the Znlevel. A
small amount of residual activity was still present
after the subtraction of K‘* and the above radionuclides from the total spectrum. The mean levet
of urinary excretion of Sr* was 7.2 uuC/1 or 14%
higher than measured in the 1959 medical survey.
Little of the body burden of the exposed group is
apparently due to their initial exposure, since at
present thereis little difference between the levels
of the exposed and unexposed populations living
on Rongelap Island. The body burdensare of small
significance in terms of radiation hazard.
OTHER STUDIES
Studies of genetically inherited characteristics.
Blood grouping studies in the Marshallese showed
a relatively high B gene frequency, a high N gene
frequency, an extremely high R* gene frequency,
and total absence of Kell and Diego factors. These
characteristics differ from those of Polynesians and
suggest relationship with Southeast Asians and
Indonesians. Haptoglobin studies showed the frequency of the Hp’ gene to be higher than in European populations thus far tested and consistent with
populationsliving near the equator. The distribution of haptoglobin types showed the population
to be relatively homogeneous. Transferrins in ail
sera were type CC, the common European type.
B-A mino-iso-butyric acid urinary levels showed the
Marshallese to be the highest excreters of this acid
of any population thus far reported. Levels in the
exposed group were about the same as in the unexposed group, and no correlation was found with