62
of Table 26 showsthat the body burdensof '*’Cs
Table 28
and ©°Co are not significantly different among the
various subdivisions by age and sex of the Ronge-
lap resident population. The values given for the
children may be overestimates, because the calibrations were in terms of an adult-size phantom
only and the counting geometry is such that a
higher efficiency obtains for the children, especially the smaller ones.
Prior to 1962, the concentration of *°Sr in the
urine was used as a 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 thatfor
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 '°7Cs
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 burdensof 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 unknown overestimation errorin 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 maintainingthe specific activity at
the previouslevels. This hypothesis is supported
by data obtained from E. Held, University of
Washington,”to the effect that soil and plant surveys ind.vate that the ’*’Cs levels in plants have remained about the samesince 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 shows the relationship between '*’Cs
body burden andits excretion rate for those resi-
Comparison of Body Burdens and Excretion Rates
NICs
Subject
No.
8
15
51
53
58
59
11
20
27
40
41
50
73
835
843
928
932
942
822
833
840
853
855
body
7Cs,
burden,
nCi/
nCi
508.9
405.6
484.8
971.2
575.0
732.7
525.5
773.9
1326.0
1047.0
1209.0
728.9
1861.0
644.8
419.8
491.4
549.6
1058.0
694.6
636.9
1455.0
814.9
606.2
liter
5.0
6.2
23.0
4.4
3.4
1.2
2.1
6.0
5.1
4.7
2.2
0.6
19.0
3.2
1.5
6.5
97°
18.0
4.5
3.1
6.0
2.0
3.6
NICs,
Urine
nCi/_
-Fraction/
0.730
0.730
0.289
0.650
0.710
0.645
0.940
0.500
1.320
0.560
0.890
1.800
0.650
0.550
1.340
* 040
.350
0.540
0.835
1.000
0.800
1.750
0.500
3.65
4.526
6.647
2.86
2.414
0.774
1.974
3.000
6.732
2.63
1.958
1.08
12.35
2.86
2.01
6.76
3.395
9.72
3.758
5.10
4.80
3.50
1.80
0.00717
0.01115
0.01343
0.00294
0.00419
0.00105
0.00375
0.00387
0.00507
0.00251
0.00161
0.00148
0.00663
0.00443
0.00478
0.01375
0.00617
0,00918
0.00540
0.00800
0.00329
0.00429
0.00296
volume, |
day
Mean
day
0.00553
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 turnoverrates, these values fall within the
ranges cited or reported for other populations, in
which the means were 75, 74, 87, 115, and 135
days."? Some of the lowest turnover rates in the
Rongelap population may be ascribed to uncertainties in the completeness of the urine collections. Thusit is to be expected that the '°'Cs value
would fall to near-zero levels in a yearof living in
a noncontaminated environment. That this fall
does occur is shown bythe results with the Ebeye
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