MARSHALLESE EX PERIENCE
Fe55.59,
239
Zn65, Mn54 and the fission products Zr% -~-Nb%, Rul06 - Rh1°6, and
Cel44 -pr14 , In the terrestrial environment, the fall-out material taken
up in greatest amounts by land plants and man are those which are most
highly soluble, i.e. Cs}®7 and Sr”,
While few of the neutron-induced activities were present in the island
soil or in plants, they make up to 100%of the activity in plankton and fish.
Thus the neutron-induced activities and the fission products listed above
are taken up by marine forms andget into the diet of man via fish, clams
and crabs [5]. Both these radionuclides are incorporated into plants via
root or foliar absorption, or as external contamination on the leaves of
plants. There are many factors that determine the uptake of these two
nuclides by plants, such as solubility, soil chemistry and soil structure,
competing ions, etc. The levels of these radionuclides in various plants
and animals vary considerably, and consequently the body burdens of the
people living in this environment vary greatly as a function of the composition of their varied diets.
Since the half-lives of the various fission products differ widely, the
time of exposure after fission will determine the composition of the remaining fission product mixture. Immediately following the acute exposure,
most of the radioactivity is contributed by short-lived radionuclides.
A. ACUTE EXPOSURE
In the Marshallese experience, the acute exposure lasted less than
two days. The diagnosis of internal radioactive contamination was made
early from the appearance of high levels of radioactivity in urine assays
of the Marshall Islanders. The highest levels were found in the 82 inhabitants of Rongelap Island. During the two days that the people remained on
Rongelap, before their evacuation, they lived in a radioactively contaminated
environment and took no precautionary measures to avoid ingestion or inhalation of the material. The initial body burdens of internal emitters in
the Rongelap people were estimated from data obtained by radiochemical
analysis of the tissues of two pigs, which had been simultaneously exposed,
and subsequent comparison of human and animal urinalysis data [4]. The
mean body burden at one day was estimated (inuc) as Sr89-1.6, Bal? -2. 7,
1131 _6, 4 and the rare-earth group together-1. 2.
Information on the tissue distribution of fission products was obtained
from the radiochemical analyses of the pigs living on Rongelap for one month
and sacrificed two months later (Table II). 95% of the internal activity is
localized in the skeleton. The alkaline earths, Sr®? and Ba14° , and the
rare earths together constitute 75% of the gross B-activity at 82 d. The
activity in the pig was tenfold higher than that estimated in the people, reflecting the 30-d longer exposure of the animals. The pattern of deposition
of the fission product mixture in the skeleton, as seen in an autoradiograph
of a tibia of one of these pigs, resembles that seen after administration
of alkaline earths, i.e. dense deposition in the epiphyseal region (Fig. 1).
In the first few months following this acute exposure, Sr®® and I!3!
(plus the shorter-lived iodine isotopes) contributed the greatest internal
radiation dose to the Marshallese. Sr®8? contributed the major portion of