Island, the estimated annual dose-equivalent rate is about 140
mrem/y when imported foods are available and the corresponding 30y integral dose equivalent is about 3 rem. Again, the annual dose
equivalents results for both islands were multiplied by 3 and presented
to the Bikini people along with the associated risk analysis. After
evaluating this information, a segment of Bikini population is pursuing, with the U.S. Government, resettlement of Eneu Island. The U.S.
has not agreed to resettlement and currently no agreement or plans
have been adopted.
Uncertainty in the final dose values can result from uncertainty in
three sources of input data: (1) radionuclide concentration in food (or
soil); (2) dietary intake; and (3) the biological parameters such as
radionuclide turnover times in the body, fractional deposition in
various organs, and body or organ weight. However, evaluation of
these data indicates that a value three times the meanis a reasonable,
maximum value.
First, the distributions of radionuclide concentration data in relatively large vegetation and soil sample populations from Bikini and
Eneu Islands at Bikini Atoll are lognormal {15]. The numberof food
plants with a concentration three times the mean valueis Jess than
5% of the total. Therefore, the probability of a person finding his
entire diet for 1, 5, 10, or 30 y from food crops with a concentration
three times the mean value is very small. The observed lognormal
distribution of radionuclide concentrations in soils and plants at the
atolls is consistent with most elemental distributions in nature. Also,
the observation that three times the mean value includes more than
95% of the population distribution is consistent with other observations, several of which have recently been summarized by Cuddihyet
al. [55].
The ”’Sr concentration distributions in bone have been specifically
addressed by Kulp and Schulert [56]. They found that “Sr from fallout
was distributed lognormally and that the 98th percentile value was 2.3
times the mean value. Maximum values observed for *'Sr in bone by
Bennett were three times the mean; that is, most of the data fell below
three times the mean [10-12]. These data also reflect the combined
variability of the “Sr concentration in food products and in dietary
intake.
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show that the maximum exposure rate at an isolated point on the
island is, for most islands, less than three times the mean value. In
many cases, the maximum observed value is only two times the mean
value. Because of the movement of people around their residence
76
istand, the vanation of individual doses around the average cose is
probably minimized and would not add much vanability to the distr
bution of doses calculated for the ingestion pathway. In addition, we
have not included in the external doses the reduction in external
exposure that would occur from spreading crushed coral around the
houses and shielding by the houses.
Second, the dietary intake of local foods is a major source of input
data that is somewhat uncertain and could lead to higher average
doses than presented here if the average intake were significantly
greater than we have assumed. For example, if the atoll current
lifestyle should change drastically with a total reliance on local foods,
the average doses would be higher than those listed here. This is a
very unlikely occurrence because the people have a source of income
and imported foods are now considered a staple and a necessity, not. a
luxury. The people will have access to outside goods and will trade
with either the United States or other world governments. Conversely,
if the diets were to include more imported foods, the doses would be
lower than listed here.
Third, the range of values observed for the retention of ‘Cs in
humans has been summarized by the ICRP [19,20] and the NCRP
[21}. For example, the range of observed values for the retention time
for the short-term compartment is 0.5 to 2.1 d with a mean of 1 d; the
upper limit that has been observed is greater than the mean byonly a
factor of 2. For the long-term compartment, the data range from 60 to
165 d with a mean value of 110 d; the maximum value in this case is
less than twice the mean value. The fraction of the intake that has
been observed to go to the short-term compartment(i.e., 2 d) ranges
from 0.02 to 0.22 with a meanof 0.1; for the long-term compartment
(i.e., 110 d), the range is 0.78 to 0.97 with a mean value of 0.9. For
both cases, the maximum valueis less than twice the mean.
There are several reasons why the average doses we present might
be lower. First, the doses are calculated assumingresidence since 1978.
For uninhabited atolls, doses would be expected to be about 2.3%
lower per year until resettlement occurs based on the radiological
decay of cesium and strontium. Second, we still do not know the
environmental residence time of cesium in the atoll ecosystem. If it
were 30 y (i.e., equal to the radiological half life), the estimated doses
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Wr wrest we
.
.
=
mental residence time were as long as 50 y, the doses would be 34%
lower, and if it should be as short as 20 y, the estimated doses would
be 64% lower. We have experiments underway to determine the
environmental residence time. Third, we have not included shielding
77