21
Internal Radiation
Long-term effects of internally deposited isotopes
from the fallout would result largely from the
bone-seeking isotopes, of which Sr®° with a halflife of 28 years is by far the most important. Bone
deposition does not impose a genetic hazard,since
radiation is almost entirely confined to bones, with
little or no gonadal irradiation. As with radium,
Sr®° irradiation of the bone mayresult in osteoporosis, sarcoma, and possibly leukemia if depos-
ited in sufficient amounts. The Sr®activity of the
Rongelap urine samples at two vears post-exposure
was calculated to be 0.6 d/m/24 hr, and of bone
samples on the deceased to be 1.60.06 d/m/g
ash. Both values indicate the body burden ofSr°°
to be well below the accepted tolerance levels and
within the limits of American samples.
Cs‘? is distributed generally in thesoft tissues
and so might cause some gonadal radiation and
present a genetic hazard. However,the levels in
the Marshallese, though several times higher than
those found in Americans, are far below thetoler-
ance level. It was estimated that the individual
with the highest level of Cs**’ probably received
an additional amountof radiation equal to about
one-fifth that ordinarily received as cosmic radiation.
It is quite reassuring that such lowlevels of
body burden of radionuclides were reached so
quickly, when one considers the extreme degree of
contamination that these peoplelived with for two
days with little or no effort to avoid internal deposition. The original body burdens have dwindled rapidly over the three-year period. Indeed,
at this time such low levels are present that evaluation of the componentdueto the original fallout
becomesdifficult to differentiate from the added
components dueto subsequent world-widefallout.
The fact that the Cs'*’ level in the Marshallese
man not exposed to the original fallout was nearly
as high as that in the exposed Rongelap people
makesit seem plausible that additional sources of
fallout are now contributing more to the body
burden than the original exposure. Therelatively
muchhigherlevels observed in the Utirik people
are due either to the fact that these people have
been living continuously on their slightly contaminated island since four months after the accident, or that furtherfallout has occurred since the
original event. Probably both factors are involved.
Thepresence of detectable Zn** peaks on gamMma spectroscopyis ofinterest, since this isotope is
not a fission product. The isotope may haveoriginated from metallic structures involved in the
nuclear detonations. Zinc has been foundto be
concentrated in marine life.** The large consumption bythese peopieoffish containing Zn*
would therefore accountfor the zinc peaks. Co*
has been found to be concentrated in clams in the
Marshall Islands. Presumably since these are not
eaten to any great extent, Co®° peaks were not
detected.
REPATRIATION OF THE RONGELAP PEOPLE
The decision to move the Rongelap people back
to their homeisland was madeafter careful consideration of the hazards associated with theslight
residual contaminationofthe island to which the
people would be subjected ona lifetime basis. The
evaluation of the hazard resolveditself primarily
into a consideration of the gammadose and Sr”
levels. Extensive radiological surveys of Rongelap
Atoll with radiochemical analysis of samples have
been carried out by several agencies sponsored by
the Atomic Energy Commission.**** The results
of the surveys have been summarized by Dunning.”
External gamma readings on theisland at two
years post-contamination showedlevels (at 3 ft
above the ground) varying from 0.2 to 0.5 mr hr
with an average of 0.4 mr/hr. However,since part
of this dose was dueto relatively recent fallout of
slight degree (at that time), it was expected that
the dose rate at the time of repatriation ; Julv
1957) would be less than 30 mr/week, and at the
endof the first vear the accumulated dose would
probably not exceed 0.5 rem with lower doses in
succeeding years.
Radiochemical analyses of food sources of the
island revealed that in spite of some degree of
uncertainty, the estimated future body burdensof
the Rongelap people would beless than 100 uuC
Sr°° provided that land crabs (whichselectively
concentrate Sr°° ) were eliminated from thediet.
This is the value (100 sunshine units) that has
been considered allowable by the U.S. National
Academyof Sciences report. In view of the present
low levels of body burdenof radionuclides, and
since the added radiation burden imposedbyliv-