Variation between atolls in risk of radiation-induced thyroid cancer and
the difference when compared to other irradiated groups had become an
important sctlentific and health~related question with the considerable
political overtones. Early in 1977, Bond, Borg, Conard, Cronkite, Greenhouse,
Naidu, and Meinhold, all members of Brookhaven National Laboratory (BNL), and
Sondhaus, University of California, College of Medicine, initiated a
reexamination of the technical issues. In 1978, formal program objectives and
funding were supplied to BNL by the Department of Energy's Division of
Biological and Environmental Research.
In June 1978, the Meteorology Division at Lawrence Livermore National
Laboratory was subcontracted to provide a computer simulation of the
dispersion, transport, and deposition of fallout from the 1954 atmospheric
nuclear test, BRAVO,
A subcontract to provide neutron activation analysis of
archival soil samples was given to the Radiological Sciences Department,
Battelle-Pacific Northwest Laboratory.
Soil samples were provided by Seymour,
the director of the University of Washington's Laboratory of Radiation
Ecology.
Thyroid absorbed dose tabulated here was estimated from results on 131y
activity excreted in urine and the specific nuclide composition of BRAVO
fallout.
Surface and airborne activity, fallout granule size, and exposure
rate at times after the detonation were developed for 142 nuclides at Rongelap
and Utirik on the basis of the reported nuclide composition on day 26 postdetonation. Over 70 documents were reviewed for information regarding
exposure-rate readings, film-badge readings, fallout composition, dose and
dose rate, body burdens, urine analyses, gastrointestinal tract contents, bone
marrow and thyroid dose estimates, and activity measurements in soil, water,
marine life, and land animals.
Results from the meteorology study and
archival soil study were also reexamined and compared to fallout composition
results.
A tabulation of the estimates of thyroid absorbed dose, age at exposure
and specific nuclides was done for each location.
For an adult male, the
thyroid absorbed dose {yom iodine and tellurium nuclides was 7.7 times the
absorbed dose due to
I at Rongelap, 10 times at Sifo Island and 4.7 times
at Utirik Island. James gafumed the total thyroid absorbed dose was 2.6 times
the absorbed dose due to
I (Ja64). The factor 2.6 would be appropriate for
slightly older fallout than that experienced at Rongelap, Utirik or Sifo
Islands.
Thryoid absorbed dose was based on ingestion intake.
Inhalation
intake and absorption through skin could not be reconciled with measurements
of
I in urine or with external exposure rate measurements.
Observations of the range of 137¢, body burdens during protracted
exposure (Mi79) and the range associated with the contents of the stomach in
cases of sudden death (Ev66) were used to estimate maximum thyroid absorbed
dose. Thg average internal thyroid dose at Rongelap Island was hased on the
average
I activity collected in urine.
The contribution to thyroid dose
from external sources was estimated from the air exposure created by 142
nuclides which were estimated from results of BRAVO fallout composition.
external dose was similar to original estimates by Sondhaus for persons
exposed at Rongelap and Utirik Islands.
The
The original external dose estimates
at these islands, 1.75 gray and 0.14 gray (175 rad and 14 rad) respectively,
were derived from survey instrument readings taken after evacuation and film