32
the mortality data suggest that exposureof the
population to this factor has decreased recently.
Schwartz and Upton” have considered the role
of ionizing radiation in the general incidence of
leukemia and lymphomas. Amongotherfactors
considered ar€ age, race, sex, geographicalloca-
tion, climate, genetic factors, constitutional factors,
and other extrinsic agents such as chemicals and
infectious agents. These authors consider the increase in radiation background from all causes
(medical, dental, fallout, etc.) to be “clearly not
sufficient to accountfor the tremendous rise in the
recorded incidence ofleukemia. ..”” Burnet’! points
out that the present peak of incidence of leukemia
at age 3 to 4 is a relatively recent development
and suggests the possibility that exposure to some
new mutagenic agent at the timeof birth is the
cause. He cites data which indicate that at most
5 to 10% of leukemia incidence in the United
States can be ascribed to radiation from all sources,
and points out that the etiology of the other 90%
is unknown.
Otherconstituents of fallout have not received
as much publicity as Sr®°, but their study has not
been neglected.*?-’* Anderson” reports an extensive series correlating Cs'*’ and K*?° levels in
people and in milk supplies. He states that the
importanceof Cs'*" relative to Sr®° is increasing.
The levels in both people and milk representing
various locales in the United States ranged up to
60 puC Cs'*"/g K, with fairly good correlation between the twolevels. These results are consistent
with those reported by Miller and Marinelli,”
who have further data suggesting a rather uniform
distribution of fallout in the Northern Hemisphere.
The significance of low doses of radiation has
not been evaluated fully, the chief reason being
the absence of positive data on low-doseeffects,
particularly in humans. Perhaps more subtle
methods will be found by means of which low-dose
effects can be documented, butit is to be hoped
that the radiation dose can be maintained below
the level at which effects appear with any method.
{n the meantime, the Rongelap people provide
an interesting groupof subjects exposed to level
of radiation appreciably above the world average.
Present indications are that the body burdens of
radionuclides will not reach levels which, from
known data, will result in morbid processes. As
pointed out before, the developmentof leukemia
associated with their exposure to a sublethal dose
of gammaradiation in March 1954, based on ex-
periences with the exposed Japanese,°’-** is held
to be improbable, particularly in view of the small
numberof people involved. The superimposition
of the low level body burdens from environmental
contamination would not seem likely to be sufficient to increase this possibility substantially.
The habitation of these people on Rongelap
Island affords the opportunity for a most valuable
ecological radiation study on human beings. Since
only small amounts of radioisotopes are necessary
for tracer studies, the various radionuclides pres-
ent on the island can be traced from thesoil
through the food andinto the human being, where
the tissue and organ distributions, biological haiftimes, and excretion rates can be studied.
Summary
The medical survey of the Rongelap people in
March 1958, 4 years after exposure to accidental
fallout radiation, was carried out at Rongelap
Island, to which these people had been returned
in July 1957 after the radiation level of the island
was declared safe for habitation. They were adjusting satisfactorily to life in their newly reconstructed village.
No apparent acute or subacute effects were
foundatthis time related to the gammadose of
175 r received, with the possible exception of
hemopoietic findings indicating a persisting lag in
complete recovery of platelet levels of the peripheral blood. In the males these mean levels were
11 to 16% and in the females 9% below thecorresponding meanlevels of the comparison population. The lymphocytes had recoveredto level
about the sameas in the comparison population,
although manyof these counts were lower than in
the latter group. Thestress of childbearing and
menstruation did not appear to be reflected in any
lowered hemopoietic reserve in the exposed women,
based on comparative studies of the levels ofpe-
ripheral blood elements. The suggestive incidence,
previously reported,of slight lag in growth and
developmentofthe irradiated children at 2 and 3
years after exposure, based on height, weight, and
bone age studies, needs re-evaluation in the light
of the finding that the ages of someof the children
were not as firmly established as previously thought.
History and physical examinations revealed no
clinical evidence of any illnesses or findings during
the past year or at the time of the present survev
which could be related to whole-body exposure.