238
Health Physics
the U.S. NRDL data (acronym for U.S. Naval Radiological Defense Laboratory, cited as U.S. AEC 1956), and
(3) the Harris data (Harris 1954), for purposes of deter-
mining the availability and alimentary tract absorption of
fallout radionuclides at close-in distance (the sites of
exposure being between 150 km and 210 km from the
detonation point). Only intake by ingestion is considered,
as it is the primary pathway of acute internal exposure
due to the dominance oflarger particles in local fallout
(Simonet al. 2010).
Amongthe three data sets, there were six radionu-
August 2010, Volume 99, Number 2
that is excreted in urine on day of sampling, ¢ s?
following intake.
Combining eqns(1) and (2) allowsusto estimate f,
for any radionuclide i that was assayed in the urine
samples:
—
(3)
DO = GX ENG1)’
where the intake, Q(i), for any radionuclide i, was
calculated as:
clides assayed though no single data set reported all of
them. Our evaluation of the validity and quality of the
three sets of urine measurements suggested that '°'],
'’Cs, and *°Sr from Walter Reed and from Harris were of
AG, BY
Vii)
—
7131
Qi) = QO
Dep(i) |
(4)
0)pansmy
good quality and had reasonably low uncertainties. Mea-
and Dep(i) is the deposition density (Bg m°) of radionuclide i from fallout, calculated according to Becket al.
(2010), while ETC, t,) was derived from ICRP models
satisfactory but had significantly larger relative uncer-
for Sr, 11, “°Ba, and ‘Rul.
surements of *’Sr by U.S. NRDL and Harris were
tainties. Both '“°Ba and '’Rudata were likely notreliable
due to the lack of specific radiochemical separations and
the detection methods used in the bioassay.
Weselected the measurement of '*'I in urine as
likely to have been the most precise because of reliable
measurement techniques which verified the half-life of
the activity (Harris 1954; Harris et al. 2010). Moreover,
''T measurements were selected because all literature
supports the notion of complete absorption of radioiodines in the alimentary tract (presented later) for all
commonly occurring forms [ie., f,(°'1) = 1), thus
giving us a basis for interpreting the bioassay measurements of other radionuclides. As indicated in Harriset al.
(2010) and Simon et al. (2010), the bioassay measure-
mentsof '*'T in pooled urine samples were used to derive
a population average acute intake, QO (Bq), of ‘I at
Rongelap as follows:
AC*'T, t,)
OU") = Fras,py:
y
(131
—_
(1)
[ICRP Report 56 (1989) for '*’Cs and Report 67 (1993)
Using the ICRP models to estimate the excretion
fractions for total absorption of '°’Cs, °Sr, '°Ba, and
‘Ru on the days of sampling, the bioassay data from
Woodwardet al. (1959), U.S. Atomic Energy Commis-
sion (U.S. AEC 1956), and Harris (1954), as well as the
assumption that f, for '’I is equal to unity (even when
ingested as fallout particles), we estimated the f, values
for '°’Cs, Sr, *’Sr, “°Ba, and '°’Ru ingested in the form
of fallout particles at close-in distances from ground
zero. The bioassay data are discussed in Harris et al.
(2010) and the deposition data are presented in Becket
al. (2010). The results of calculations to estimate f, for
those four radionuclides are presented in Table 4.
As shown in Table 4, we estimated an f, value for
"Cs of 0.44 and an average f, value for both *’Sr and
°Sr equal to 0.02. In addition, we estimated an f, of
0.031 for “Ba similar to that for Sr and a value of ~1
10* for ‘Ru. The f, value estimated for '*Ru is much
smaller than literature values (presented later). However,
as discussed earlier, the reliability of the '“°Ba and '’Ru
where A(’*'I, f,), in Bq,is the activity of '’'T in urine ina
24-h urine sample at the time of sampling, ¢,, in days, and
EF("'l, t,, unitless, is the fraction of ingested '*']
excreted in urine on day of sampling, 7,, following the
intake of fallout particles, and is inferred from the
metabolic model of iodine described in Simon et al.
(2010).
For radionuclides other than '*'l, denoted asi in eqns
(2), (3), and (4), the f, values cannot be assumed to be
equal to unity. In that case,
EF(i, ts) = fiX ETG, t),
(2)
where ET(i, t,) is the fraction of ingested radionuclide
i that is totally absorbed in the alimentary tract and
Table 4. Estimated f, values based on urine bioassay measurements of the Marshallese population on Rongelap Atoll following
the Bravotest.
Data set (see text)
Radionuclide
USNRDL
Walter Reed
BICs
—
0.440
—
Sr
0.020
—
0.020
1317
—
—
1 0?
Sr
—
0.021
Harris
—
M0Ba
0.031°
—
0.031°
Ru
—
—
~0.0001°
* Assumed based on literature information.
> Estimates may not bereliable since bioassay measurements may not be
reliable (see text).