45
been reflected in an increase in body burdens of
some radionuclides. As will be shown, the in-
so low thatlittle effort was made to quantify these
elements in the Marshallese until whole-body
low maximum permissible levels.
The body burden offission products can be
determined in three ways. The method of choice
is the direct in vivo measurement by whole-body
spectrometry. The limitations of this method are
that few whole-body counters are in existence,
they require enormously bulky shielding and thus
are not easily transported to various sites, and
their absolute calibration is difficult. Further, this
methodis restricted to analysis of gamma-emitting
ESTIMATION OF THE INTERNAL
RADIATION HAZARD
The potential radiation effects that may be produced by specific quantities of internally-deposited
radioisotopes can be only roughly predicted from
ee]
clinically observed effects of known amounts of in-
ternally-deposited radium. These effects do not
appear until a period of years (10 to 15) has
elapsed. Thus, althoughit is possible to estimate
the potential hazard in terms of the concentration
of internal emitters, clinical observations made
within a few years after contamination yield no
data on the degree of damage that mayultimately
be produced.
In evaluating the long-term effects produced by
an acute internal exposure and exposureto residual contamination, Sr®is clearly the criticalelement. Particular effort was therefore made to
determineits levels in the urine of the Marshallese, and thusto estimate the body burdens.
Of the gamma-emitting fission products, Cs’*’ is
of the greatest interest, even thoughit is of minor
significance as an internal radiation hazard. Like
Sr°°, Cs'3* has a gaseous precursor with a half-life
sufficiently long to avoid early condensation in the
fireball. Cs'*’ thus follows Sr®° into the strato-
sphere. Since thefission yields and the half-lives
of the two radioelements are nearly equal, they
are presentin the fallout in like quantities. While
they have different ecological cycles because of
their different chemical properties, Cs'*’ nevertheless provides a useful tracer for studying the movement of Sr*° through the biosphere, since its gamma-emitting properties makeit readily detectable.
There is also some interest in the neutron-induced radioelement Zn®, even thoughit, too, does
not appearin levels hazardous to humanbeings.
Theinterest centers chiefly around the fact thatit
is definitely transmitted through marinelife, and
thus provides a clear example of the transmission
of a radioelement through the food chain to man.
Other fission products and neutron-induced
activities (Fe®§-5*, Co%?-58-69°) Mn**, Celtt-Pri,
Zr-Nb*®, and Ru'**-Rh'°*} also appear in small
amountsin the soil and the food chain, and thus
mayappearultimately in man, butthe levels are
counting techniques madeit feasible.
isotopes, since, to date, a whole-body beta counter
has not been developed.
A second methodfor calculating body burden,
particularly for counting beta emitters such as
Sr®’, is the estimation of the internal deposition
from data obtained by radiochemical analysis of
the urine.
Finally, it is possible to make a completely indirect estimate of the human body burden of
radioisotopes by what maybecalled the environmental approach. In this method, the estimate of
the body burdenis based on the concentrations of
the fission products present in the environment,
chiefly the soil and the important components of
the diet. In order to makethis estimate, data must
be obtained onthe transfer of the fission products
between successive elements of the ecological
chain leading from soil to bone. For example, although Sr and Ca are chemically similar and thus
appear together in the various components of the
ecological chain, Cais taken up preferentially by
plants and animals so that it is necessary to determinethe discrimination factor for each step. When
these factors are known, it is possible to estimate
the concentration of a radionuclide in man from
its concentration in any step of the ecological
chain.
All three of these approachesto the estimation
of the body burdens in the Marshallese people will
be consideredin this report.
EXPERIMENTAL PROCEDURES
Whole-Body Counting
The gamma-ray activity from the internallydeposited fission products and the neutron-inducedactivities in 227 of the Marshallese people
were measured with a whole-body gamma scin-
tillation spectrometer. The technique ofzn vwo
gamma-ray measurement of human beings was
aor
creases, though manyfold, have remainedfar be-