ky
been reflected in an increase in body burdens of
sume radionuclides. As will be shown, the in-
creases, though manyfold. have remained far below maxununm permissible levels.
su low that little eHort was made to quanufy these
elements in the Marshallese unel whote-body
counting techniques made it feasible.
The body burden of fission products can be
determined in three ways. UVhe method of choice
ESTIMATION OF THE INTERNAL
RADIATION HAZARD
The potential radiation elects that maybe pro-
duced byspecie quantties of internally-de posited
radioisotopes can be only roughly predicted from
clinically observed effects of known amounts of in-
ternally-de posited radium. These effects do not
appear until a period of years (LO to 15) has
elapsed. Thus, although it is possible to estimate
the potential hazard in terms of the concentration
of internal emitters, clinical observations niade
within a lew years after contamination yield no
data on the degree of damage that may ultimately
be produced.
In evaluating the long-terin cllects produced by
an acute internal exposure and exposure to residual contamination, Sr“4 is clearly the critical elenient. Particular effort was therefore made to
determine tts levels in the urine Of the Marshallese, and thus to estimate the body burdens.
Of the gamnta-emitting fission products, Cs? ¢ is
of the greatest interest, even though it ty of minor
signiicance as an internal radiavon hazard. Like
seo" Cs! has a gaseous precursor with a halllite
sufficiently long to avoid early condensation tn the
lireball. Cs'* thus follows Sr’ into the stratesphere. Since the fission yields and the half-lives
ol the two radioelements are nearly equal, they
are present in the fallout in hike quantities. While
they have different ecolagical cycles because of
their dillerent chemical properties, Cs‘ nevertheless provides 4 useful tracer for studying the movement of Sr’ through the biosphere, since its gamMa-cmituing properties atake it readily detectable.
There is also some interest ia the neutron-in-
duced radivelement Zn’', even though it, tov, does
not appear in levels hazardous to human beings.
Vhe interest centers chiefly around the fact that it
is definitely trausmitted through marine life, and
isthe direct a cree measurement by whole-body
speetromeiry. “Phe limitations of this method are
that few whole-body couiters are in existence,
they require cnurmously bulky shielding and thus
are not easily transported to vartous sites, and
therr absolute calibration is difficult. Further, this
mnethod is restricted to analysis of ganna -enicuine
lsutopes, since, to date, a whole-body beta counter
has not been developed.
Asecond method tur calculating body burden,
particularly for counting beta eoiiters such as
Srv is the estimation of the internal deposition
trom data obtained by radiochemical aialysis of
the urine,
Finally, it is pussible to make a Completely in-
direct estimate of the huiman beds burden of
radigisotopes by what may be called the environmental approach. In this method. the esutnate of
the body burden ts based on the couccotrauvons of
the fission products present in the environment,
chiefly che soil and the important components of
the diet. In order to make this estimate, data must
be obtained on the transfer of the fsstom 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 tn the various components of the
ecological chain, Ca is taken up preferentially by
plants and animals so that it is necessary to determine the discrimination factor for each step. When
these factors are known, it ts possible to estimate
the concentration of a radionuclide in man trom
ils concentrauon in any step of the ecological
chain.
All three of these approaches to the estimation
of the body burdens in the Marshallese people will
be considered in this report.
EXPERIMENTAL PROCEDURES
thus provides a clear example of the transmussign
Whole-Body Counting
af a radioelement through the food chain to man.
Vhe gamma-ray activity from the internallydeposited fission products and the neutron-induced activiges 1 227 of the Marshallese people
Other fisston products and neutroa-induced
woliviuies (Feo) Coton) Mint) Celle Pree,
At’ Nb cand Rut’ RAY) atse appear in small
wHHOdtS in Lhe saib and che food chin, and thus
Hay appear aitimately in man. but the levels are
were measured with a whole-body ganna scin-
ulation spectrometer. The technique oface
#alita-ray measurement of human bens was