whole-body and bone-marrow doses. The “Sr is the next most signifi-
cant radionuclide contributing principally to the bone-ma
rrow dose.
The transuranic radionuclides contributed the least to the lung
and
bone-marrow doses. The contribution to the estimated dose
for "Co
only occurs through the external gamma pathway and at most atolls
is insignificant: even at those atolls where it does make
a minor
contribution, it is rapidly becoming insignificant because of
its short
radiological half-life (5.7 y).
Exposure Pathways
External and internal pathways are the sources of exposure for
persons living at or resettling anatoll.
(1) External exposure
(a) Natural background
(b) Man-made gamma and heta ravs
(2) Internal exposure
(a) Radionuclides inhaled
(b) Radionuclides in drinking water
(c) Radionuclides in terrestrial foods
(d) Radionuclides in marine foods
The exposure pathways in order of their contribution to the total
estimated doses are: terrestrial food chain, external gamma,
marine
food chain, inhalation, and cistern water and groundwater. The
terrestrial food chain accounts for between 50 and 80% of the estimat
ed
doses, the external gamma between 45 and 15%, and the other
pathways the remainder,
samples in the U.K. gives similar results [t4]. The
concentrations in
the diet are the concentrations expected to result
from worldwide
fallout. The models use as input the actual dietary “Sr
concentration
and the output is the actual "Sr concentration
In mineral bone
determined from analvsis of autopsy samples. They also
include agedependent variations to make dose estimates for childr
en as well as
adults. Figure 4 shows the comparative results of
the models. ‘The
major differences occur between the ages of 5 and 15
where the ratio
of Papworth and Vennart to Bennett ranges from
1.2 to about 1.6.
The two models are essentially the same from age
18 through adulthood.
The estimated calcium content of the normal Marsha
llese diet is
more than 0.8 g/d, which is very similar to the
0.9 g/d estimated for
U.S.diets [15]. Therefore, the similar intake of calciu
m of the overall
Marshallese and U.S. diets would indicate no major
problems in
applying the “Sr model to the Marshallese population.
2.0
T
T
.
S
3
*
°
g
*
— slat
6
~
i
seseees
b
o\
/ a‘\
r
= Papworth and Vennart
~——-—==_ = Bennett
—*™=*— = Ratio of Papworth
and Vennart to
B enne tt
*
2
°
@
es
¥
&
3
.
o
.
he
o
2
£ 1.0/-
Models Used for Dose Calculations
The "Sr Methodology
Bone-marrow doses and dose rates are calculated in two steps.
First,
the model of Bennett {10-12} is used to correlate the Sr concent
ra-
tions in diet with that in mineral bone. Second, the dosimet
ric model
developed by Spiers [13] is used to calculate the bone-m
arrow dose
rate from the c
2
o
ho
7a
E
o
Cc
°
8
.
> 0.5
2
z
°
a
rati
Bennett's empirical model is developed from "Sr concentrations
found in foods and autopsy bone samples from New York
and San
Francisco from 1951 through 1981. A similar model develop
ed by
Papworth and Vennart based on the "Sr content of the
diet and bone
44
£
0
0
1
5
10
15
Age of intake of 1 uci (y)
20
Fig. 4. Comparison of Bennett and Papwor
th and Vennart ™Sr bone-dose models.
45