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Table 1.
Dosimetric conclusions for the protracted exposure of Rongelap and
Utirik adults from day of return to 50 years.
Rongelap
Committed Effective
Utirik
Committed Effective
Dose Equivalent, Sv+S.E.
Dose Equivalent, SvtS.E.
Nuclide
Fe-55
4.8xl07) + 2.5x107/
Co-6n
zZn-65
Sr-90
Cs-137
External External
3.4x10_,
1.9x10_;,
5.3x10_,
2.2x10_,
1.7x10
+
+
+
+
+
3.6x107/ + 2.0x1077
1.3x10_,
1.0x10_7
&.0x10_,
1.1x10_,
3.4x10
4.4x10_,
3.0x10_,
1.9x10_,
1.3x19_,
4.1x1n
+
+
+
+
+
3.3x10_,
4.4x10_¢
5-9x10_5,
1.0x10_3
&.2x10
A decline in the daily activity ingestion rate greater than that due solely to
radioactive decay was estimated to be 9 % per year for Cs-137, 8% per year for
Sr-90, 80% per year for Zn-65 and 60% per year for Co-60.
A tentative value of
3% per year for Pu was estimated from sparse data.
Current studies are ained
at determining more accurately the dosimetric impact of Pu.
These values for
the % per year decline in activity ingestion rate were observed at both atolls
and do not account for the additional decline due to radioactive decay.
The accidental acute exposure during March 1 and 2, 1954 was considered
separately from the protracted post-return exposure.
The thyroid absorbed dose
was reevaluated due to the fact that incidence of thyroid nodules, benign and
malignant, in the exposed populations of Utirik and Rongelap has indicated
critical differences relative to that reported for other radiation exposed
groups. Reanalyses of thyroid absorbed dose was based on a conprehensive
fallout model in conjunction with dietary and living pattern data at the tine
of acute exposure.
Four studies were used to generate thyroid absorbed dose
estimates,
they
were:
(1)
archival
soil-sample
analysis
for
1-129,
(2)
evaluation of radiochemical analyses data for “Bikini Ash", the BRAVO fallout
which fell on a Japanese fishing vessel in the vicinity of RongePap Atoll on
March 1, 1954,
(3) weather and source-tem data for BRAVO coupled with current
fallout transport and deposition models and (4) evaluation of the radioiodine
analysis of the single initial pooled urine sample reported for the Rongelap
people.
Tentative
results
indicate
thyroid
doses
were
underestimated
for
the
Rongelap people by a factor of 2 to 10.
Thyroid nodule incidence will be
evaluated in terms of new estinates for thyroid absorbed dose for both atoll
populations.
ACKNOWLEDGEMENTS
Research
carried
out
under
the
auspices
of
the
Contract NO. DE-~ACO2-76CHOOO16.
The full text of
printed as a Brookhaven National Laboratory report.
U.S.
Deparment
of
Energy,
this communication will be