b2Z
of Table 26 shows that the body burdensof '*’Cs
and °°Coare notsignificantly different among the
various subdivisions by age and sex of the Rongelap resident population. The values given for the
children may be overestimates, because the calibrations were in termsof an adult-size phantom
only and the countifig geometry is such that a
higher efficiency obtains for the children, espe-
cially the smaller ones.
Prior to 1962, the concentration of °°Sr in the
urine was used asa basis for estimating *°Sr body
burdens. Subsequently, the ratio of *°Sr to Ca in
the urine has been used. Onthis basis the 1965
mean concentrations of 10.1 pCi °"Sr/liter and
0.093 g Ca/liter correspond to a body burden of
11.4 nCi. Data were not obtained on children in
1965. In previous years the urinary °°Sr to Ca
ratios in children have been about twice that for
adults. Urines for °°Sr analysis were not collected
in 1966.
Comparison of the 1965 survey data with the
results from previous surveys (Figure 70) shows
that the mean levels of '*’Cs and °°Sr have remained nearly constant since 1961, and that '*’Cs
is at about the 1958 level. Further comparison
with the 1954 and 1957 results indicates that the
activities now being seen are almost entirely due
to intake subsequentto the return of the Rongelap
population to their homeatoll in 1958.
If the ecological cycle were in equilibrium, it
would be expected that, by virtue of physical de-
cay, the specific activities of '°*Cs and °°Sr in the
food and the corresponding body burdens of these
radionuclides would have decreased about 9%
during the interim 1961 to 1965. Actually there
may have been a small decrease that is masked by
the unknownoverestimationerror in the children.
Even with a correction for this, the sustained levels
suggest that increasing amountsofthe originally
contaminated materials are getting into the food
chain and thus maintaining the specific activity at
the previous levels. This hypothesis is supported
by data obtained from E. Held, University of
Washington,* to the effect that soil and plant surveysindicate that the '*’Cslevels in plants haveremained about the same since 1961. There is no
ready explanation of the mechanism for this. These
findings are to be contrasted with those cited be-
low for an Eskimo population.
Table 28 showsthe relationship between ‘*'Cs
body burden andits excretion rate for those resi-
Table 28
Comparison of Body Burdens and Excretion Rates
"Cs
body
burden,
nCi
''Cs,
nCi/
liter
8
508.9
15
51
33
38
405.6
484.8
971.2
575.0
773.9
Subject
No.
39
11
20
27
40
+1
30
7
835
843
928
932
942
822
833
840
833
855
732.7
325.5
1326.0
1047.0
1209.0
728.9
1861.0
644.8
419.8
491.4
549.6
1058.0
694.6
636.9
1453.0
814.9
606.2
Urine
volume,|
Cs,
nCi/
day
Fraction;
day
5.0
0.730
3.65
0.007 17
6.2
23.0
4.4
3.4
0.730
0.289
0.630
0.710
4.526
6.647
2.86
2.414
O.OLLI5
0.01343
0.00294
0.00419
6.0
0.500
3.600
1.2
2.1
3.1
4.7
2.2
0.6
19.0
3.2
L.3
6.5
97
18.0
4.5
3.4
6.0
2.0
3.6
0.645
0.940
1.320
0.560
0.890
1.800
0.630
0.350
1.340
1.040
0.350
0 40
0.035
1.000
0.800
1.750
0.500
0.774
1.974
6.732
2.63
1.958
1.08
12.35
2.86
2.01
6.76
3.395
972
3.758
5,10
4.80
3.50
1.80
Mean
0.00105
0.00373
0.00387
0.00507
0.00251
OQ.00161
0.00148
0.00663
0.00443
0.00478
0.01375
0.00617
0.00918
0.00549
0.00800
0.00329
0.00429
0.00296
9.004533
dents of Rongelap for whom individual urine
specimens were analyzed. An average of 0.553%of
the body burdenis excreted per day, the range being
0.105% to 1.375%. These values correspond to
turnoverhalf-times of 120 days, 660 days, and 50
days, respectively. Except for some of the very
slow turnover rates, these values fall within the
ranges cited or reported for other populations. in
which the means were 75, 74, 87, 115, and 135
days.*? Someof the lowest turnover rates in the
Rongelap population may be ascribed to uncer-
tainties in the completeness of the urine collections. Thusit is to be expected that the '*’Cs value
would fall to near-zero levels in a yearofliving in
a noncontaminated environment. That this fall
does occur is shown bythe results with the Ebeve
population, who have been absent from Rongelap
for various times from | to 18 months.
Becauseit is not a gamma-ray emitter, “"Sr is
not detected by the whole-body counting method.
(Theoretically it might be possible to estimate “Sr