| 45 been reflected in an increase in body burdensof some radionuclides. As will be shown, the in- creases, though manyfold, have remainedfar below maximum permissible levels. ESTIMATION OF THE INTERNAL RADIATION HAZARD The potential radiation effects that may be pro- duced byspecific quantities of internally-deposited radioisotopes can be only roughly predicted from so low thatlittle effort was made to quantify these elements in the Marshallese until whole-body counting techniques madeitfeasible. The body burden of fission products can be determined in three ways. The method ofchoice is the direct zn 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 varioussites, and their absolute calibration is difficult. Further,this ternally-deposited radium. These effects do not appear until a period of years (10 to 15) has elapsed. Thus, althoughit is possible to estimate method is restricted to analysis of gamma-emitting 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 within a few years after contamination yield no data on the degree of damagethat mayultimately the urine. clinically observed effects of known amounts ofin- the potential hazard in termsof the concentration of internal emitters, clinical observations made be produced. In evaluating the long-term effects produced by an acute internal exposure and exposure toresid- from data obtained by radiochemicalanalysis of Finally, it is possible to make a completely indirect estimate of the human body burden of radioisotopes by what maybe called theenviron- . ual contamination, Sr’? is clearly the criticalele- mental approach. In this method, the estimate of lese, and thusto estimate the body burdens. the fission products present in the environment, chiefly the soil and the important components of ment. Particular effort was therefore made to determine its levels in the urine of the MarshalOf the gamma-emittingfission products, Cs'*" is the body burden is based on the concentrations of the diet. In order to makethis estimate, data must of the two radioelements are nearly equal, they be obtained on the 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 componentsof the ecological chain, Ca is taken up preferentially by plants and animals so thatit is necessary to deter- duced radioelement Zn*, even thoughit, too, does the concentration of a radionuclide in man from its concentration in any step of the ecological chain. All three of these approaches to the estimation of the body burdensin the Marshallese people will be considered in this report. 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 stratosphere. Since thefission yields and the half-lives are presentin thefallout 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. Thereis also someinterest in the neutron-innot appearin levels hazardous to humanbeings. The interest 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 minethe discrimination factor for each step. When these factors are known, it is possible to estimate EXPERIMENTAL PROCEDURES Whole-Body Counting The gamma-ray activity from the internally- Zr°°-Nb**, and Ru'®*-Rh**) also appear in small deposited fission products and the neutron-inducedactivities in 227 of the Marshallese people were measured with a whole-body gammascin- may appearultimately in man,but the levels are gamma-ray measurement of human beings was activities (Fe®5°°, Co57-58.80, Mn**, Ce!**_ Pris, amountsin thesoil and the food chain, and thus tillation spectrometer. The techniqueof in vivo