RMI Nuclear Justice Documents

45

been reflected in an increase in body burdensof

some radionuclides. As will be shown, the in-

creases, though manyfold, have remainedfar below maximum permissiblelevels.

ESTIMATION OF THE INTERNAL
RADIATION HAZARD

so low thatlittle effort was made to quantify these
elements in the Marshallese until whole-body
counting techniques madeit feasible.
The body burden of fission products can be
determined in three ways. The methodofchoice
is the direct zm vivo measurement by whole-body
spectrometry. Thelimitations of this method are
that few whole-body counters are in existence,

‘duced by specific quantities of internally-deposited

théy require enormously bulky shielding and thus
are not easily transported to various sites, and

clinically observed effects of known amounts of internally-deposited radium. These effects do not

isotopes, since, to date, a whole-body beta counter

The potential radiation effects that may be pro-

radioisotopes can be only roughly predicted from

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 critical ele-

ment. Particular effort was therefore made to
determineits levels in the urine of the Marshallese, and thusto estimate the body burdens.
Of the gamma-emittingfission products, Cs!” is

of the greatest interest, even thoughit is of minor

significance as an internal radiation hazard. Like
Sr°°, Cs’97 has a gaseous precursor with a half-life
sufficiently long to avoid early condensation in the

fireball. Cs'*” thus follows Sr®° into the stratosphere. 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 though it, too, does

not appearin levels hazardous to human beings.
The interest centers chiefly around thefact thatit
is definitely transmitted through marinelife, and
thus provides a clear example of the transmission
of a radioelementthrough the food chain to man.
Other fission.products and neutron-induced
activities (Fe®?°®, Co™58 6) Mn>4, Cel##-Pri#t,
Zr°°-Nb*, and Ru'**-Rh’?"*) also appear in small
amountsin the soil and the food chain, and thus

may appearultimately in man, but the levels are

their absolute calibration is difficult. Further, this

methodis restricted to analysis of gamma-emitting

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 may becalled 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 togetherin the various componentsofthe
ecological chain, Ca is 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-rayactivity from the internallydeposited fission products and the neutron-inducedactivities in 227 of the Marshallese people
were measured with a whole-body gammascintillation spectrometer. The technique of tn vivo
gamma-ray measurement of human beings was