186
Health Physics
Table 19. Comparison of estimates of acute and chronic internal
doses (mGy) with external dose (mGy) for representative adults of
four population groups.
Population groups
Organ/Mode of
exposure
Majuro
residents
Kwajalein
residents
Utrik
community
Rongelap
Island
community
Thyroid
Acute
Chronic
RBM
Acute
Chronic
Stomach wall
Acute
Chronic
Colon
Acute
Chronic
Whole body
(external
dose)
22
0.76
66
1.3
740
25
7,600
14
0.11
0.98
0.25
1.7
2.3
33
0.32
0.75
1.1
1.3
16
24
530
14
180
2,800
4.4
0.99
9.8
12
1.7
22
32
130
25
17
17
1,600
August 2010, Volume 99, Number 2
Uncertainties in D/Q. The uncertainties in the thyroid
dose per unit '*'I intake, D/Q, are relatively well documented
(for example, Dunning and Schwarz 1981; Zvonova 1989;
NCI 1997; Apostoaei and Miller 2004). They depend essentially on the uncertainties on the fractional thyroidal uptake and
on the thyroid mass, as well as on the degree of correlation
between the two parameters. Considering that the quantity of
interest 1s the average thyroid dose per unit intake for adults of
the Rongelap Island community, a direct approach was taken:
the six possible sets of parameter values for the thyroid
biokinetic model that are presented in Table Al were used to
quantify the variations of the value of D/Q for '*'l. The
obtained range of values is from 4.3 to 6.1 X 10°’ Gy Bq|,
resulting in a GSD of1.2.
Using values of 1.0, 1.6, and 1.2 for the GSDs of C,
O/C, and D/O,respectively, the GSD for D('*'I, Bravo,
adults) is estimated to be 1.7.
There are additional uncertainties involved in the
estimation of the overall uncertainty in the annual doses
received by representative persons of the Rongelap
Island community. They include:
where
K =the correction factor corresponding to the
radioactive decay of '*'I between time of
sampling and time of counting;
® uncertainties in the contributions of ‘I (20.8 h) and I (6.6
h) to the thyroid dose to adults from the Bravo test, which
are estimated to be 4,200 and 1,300 mGy,respectively, and,
V=the 24-h urine volume (mL) averaged
therefore, of the same order of magnitude as the thyroid dose
EF(t) = the urinary excretion fraction for '*'I on day
© uncertainties in the estimation of the thyroid dose to
over the sample population; and
of sampling, t being the time elapsed between intake and sampling.
Because of the relatively long half-life of '*'T (8 d),
the uncertainty for K is very small. Uncertainties on V are
discussed in the Appendix and in Harris et al. (2010): the
mean 24-h urine volumes averaged over the sample
population are 427 and 448 mL for the samplings on
March 16 and 17, respectively (Table 7); the distributions
of the mean are assumed normal with standard errors of
the mean of 42 and 37 mLfor the two days of sampling.
For this analysis, the mean and the standard error of the
mean were taken to be 440 and 40 mL,respectively. The
uncertainties in EF(f) are related to those in the parameter
values of the biokinetic model. In Appendix A, six
possible sets of parameter values for the thyroid biokinetic model were used to quantify the variations of the
value of EF(t). Results, presented in Table Al, suggest
for the Rongelap Island community a range of values
from 0.92 to 2.3 X 10 * around an arithmetic mean value
from '*'I (1,700 mGy);
children; and
© uncertainties related to small components of the thy-
roid dose due to acute intakes of '*’Te and '*"I from the
Bravotest, thyroid doses due to chronic intakes from
Bravo, and to acute and chronic intakes from other
tests of the Castle series.
The contributions of "I (20.8 h) and '*I (6.6 h)
account for about 75% of the thyroid dose from the
Bravotest to adults of the Rongelap Island community.
As all other radionuclides collectively contribute no
more than 25% of the thyroid dose from Bravo, a good
approximation of the thyroid doseis:
D(total) = D?"'1D + DUD) + DUD
133
O(!**1)
= D(3!]) x f + om
of 1.7 X 10 4, leading to a GSD of1.6, assumingthat the
range of values correspond to one GSD. Using the
numerical estimates of the GSDs for V and for EF(t)
indicated above, the GSD for Q/C for adults of the
Rongelap Island community exposed to acute intakes of
'S'T from the Bravo test is found to be 1.6.
135
=D(""'1) x r + a
+ aT
D(3'T)
ox
O(!?'T)
aT
D(3'D/OC3D)
|
DC3'1veC3!1
14)
.
Becausethe values of Q('*"1) and Q(’"I) are correlated to Q('**1), and the values of [DC*D/OC*D] and