MARSHALLESE EXPERIENCE
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exposed to radioactive contamination by mixed fission products from a
nuclear detonation.
In the Marshallese experience, 239 individuals were accidentally ex-
posed to local fall-out for periods up to two days. The levels of the asso-
ciated radiation fields were estimated to vary between 14 and 175 r for the
different Marshallese groups [1-3]. The radiation exposure from the internal emitters following this acute exposure was insignificant compared with
the dose received from the external radiation, but nevertheless it is of great
interest and importance to follow the course of the isotopes in humans. As
part of the continuing medical care and follow-up of these people, aistudy
of the metabolism of internal emitters, inhaled or ingested, by the inhabitants of Rongelap Island (the group receiving the highest exposure) has been
carried out [4,5].
;
In addition to the investigation of the acute exposure situation, it is
of considerable importance to obtain data on the metabolism of fission products and neutron-induced radionuclides encountered in low-level chronic
exposures. This report will review the pertinent findings of the Marshall
Island studies on the levels of the various radionuclides in the Marshallese
in relationship to their environment over the past eight years. This relationship is of particular interest inasmuch as the Marshallese, since their
return to Rongelap in June 1957, have lived in an environment of persisting
low levels of contamination. These levels are far below the value considered
to be hazardous, but are nevertheless readily detectable with the whole-body
counter,
Laboratory and field studies have indicated that relatively few of the
250 radioisotopes formed in the fission process are significant from the
biological point of view. Only those products which are produced in significant quantity and which are sufficiently long-lived to become integrated
into the ecological environment are listed in Table I, Since fall-out consists
of various neutron-induced radionuclides in addition to fission products,
they are also listed in the table. The presence of radionuclides in man depends first on their physical availability in the environment. All of the radionuclides listed in Table I were found in plants and animals on the Marshall
Islands or in the lagoon. The biological availability of an element to a plant
or animal and ultimately to man is also dependent to a large extent upon
the solubility and physical state of the element. Of these fission products
listed in Table I, only the first seven are absorbed from the gastro-intestinal
tract in amounts exceeding 1% of the quantity available. The remaining
fission products have been assigned (ICRP-1959) a high absorption via the
respiratory tract even though the GI absorption is quite low.
In the present situation, in which the nuclear device was detonated on
or near the ground of a Pacific Island, the bulk of the radioactivity resided
as insoluble oxides on particles of CaO or Ca(OH)2g made by the heat of the
fireball acting on the coral of the Islands. A large amount of activity was
also carried on NaCl particles. A different physical-chemical nature of
fall-out in another situation would modify the metabolism of the fission
products to some extent.
In general, the radionuclides that form strong complexes with organic
matter (such as the transition elements) and those present as particulate
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or colloidal matter are found in marine organisms, These are Cot. 58, 80