a1 tea, it became even moredifficult to extrapolate to body burden from food. It is obvious that further data are required on the transport of low levels of Sr®° and other products through the ecological cycle in this and other communities to make possible assessmentfrom environmental data alone of the internal radiation hazard to human beingsliving in a falloutcontaminated area. More reliable estimates of the Marshallese body burdens can be obtained by whole-body gamma spectrometry and by radiochemical urinalysis. The excretion rate of Sr°° may be expressed as the sum of two exponential functionsfor the first 3 years following exposure. The majorfraction of Sr* is excreted early, with a biological half-life of 40 days. The smaller fraction is excreted witha half-life of 500 days. These excretion rates correspond to those reported by Cowan®! in a case of accidental inhalation of Sr®°°, and were used in extrapolating back to the one-day Sr®* body burden of the Marshallese.**. The 1958 Rongelap body burdens of Sr®, Cs'*", The urinary excretion levels of and Zn® are presented in Table 32, and also figures for percent of equilibnum and equilibrium value, estimated by Woodward*from urinary excretion data. These values are subject to some un- higher by a factor of 20 in March 1958 than in of other methods. For example, the estimated body burden of Sr*° in March 1958 was 2 puC/g Ca, based on the 24-hr Sr®° outputin urine(1 liter Radiochemica! Analysis of Urine Strontium-90. Sr®° for the 5 years following exposure to fallout are shown in Figure 55. The 4- and 5-yearlevels were muchhigher,after the return of the Marshallese to Rongelap in July 1957, the mean being March 1957. certainties, since they are based on a numberof assumptions; however, they can be checked by use per 24 hr), and this appeared to be ofthe right order of magnitude compared with data from bone analysis. Two bone samples of vertebra and it Lt ileum from a deceased 35-year-old Rongelap male at this time indicated a level of about 3.7 uuC/g zation factor of 2 from vertebra to average skele- Ca, which gives, upon application of the normali- ton,’ an average skeletal value of 2 puC/g. Thus the mean body burden of Sr*° for exposed Rongelap people in 1958 was estimated to be =2 muC, or about 9% of the estimated equilibrium value of 23 muC.*° The estimated Sr*" body burdenincreased from 2 mpC in 1958 to 6.0 muC in 1959, or 26% ofthe estimated equilibrium value. The 1959 Sr® mean urinary value in the exposed Rongelap inhabit- 4 a_i $190 EXCRETION ( pC/LITE R) o th~40 Days iY R 5 ‘ Oo 300 YR ‘ 600 RETURN TO RONGELAP SYR, 900 4 1200 ayYR 5 YR a 4 ‘ i500 1800 TIME IN DAYS — AFTER MARCH |, 1954 Figure 55. Urinary excretion of Sr*° ants was 6.3 wuC/I or 10.5 weC/24-hr urine, based in exposed Marshallese. Table 32 Estimation*®’ of Body Burden,in muC, of Rongelap Population From Urinary Excretion Levels, 1958 Cs137 Sr®°, Exposed Body burden Equilibrated body burden Percent of equilibrium Daily intake 2* 23 9 0.015** *3.7 Strontium units (SU) determined by bonebiopsy. **15 SU assuming daily calcium intake = 1 g. Zn®™ Exposed Control Exposed Control 900 1300 1200 1600 280 330 540 650 69 2(?) 75 85 2.1-4.1 83