Ingestion doses from 609 are negligible and therefore do not appear in any of the
tables. It is observed at low concentrations in soil samples, but incorporation in plants is
such that concentrations rarely exceed the detection limit. The
60
~~Co contribution to the
external gamma dose is about 5% or less.
905, 1376, and 60
Doses from
Co via the inhalation pathway are two to four orders
of magnitude smaller than doses from the transuranic radionuclides and are therefore not
listed in the dose tables.
The global deposition of 1376, in the 10 to 15° N. latitude of the Pacific region
through 1974 was about 30 mCi/kmn? (Ref. 45). Adjusting this to 1978 and comparing it
with the concentrations of 13"Cs determined here, we see that 30% of the 13 7Cs soil
concentration (and therefore the dose) listed for Likiep, Wotho, Ailuk, Mejit, Ujelang,
Bikar, Jerno, and Taka is from worldwide fallout and is not specific to the Marshall
Islands. The worldwide fallout of
137 Cs
137.65 at Utirik and
1376,
and 98% of the
accounts for about 7% of the
about 2% at Rongerik and Rongelap Islands.
The other 70, 93,
concentrations, respectively, is due to intermediate range and global fallout.
The global deposition of 13 7Cs between 30 and 50° N., which includes the United
States, is greater by more than a factor of 3 than that in the 10 to 15° N. latitude. Thus,
the deposition of 1376, from global fallout between 30 to 50° N. is nearly equal to the
total 1376. observed at Likiep, Wotho, Ailuk, Mejit, Ujelang, Bikar, Jemo, and Taka. The
deposition of other radionuclides follows a similar pattern.
Another comparison for this latitude and this area of the Pacific is the background
concentrations of
137 Cs
in the soils at Ponape, Truk, Palau, and Guam.
6
concentration averaged over !0 cm range from 0.1 to 0.5 pCi/g.*
The
1376s soil
The range of
1376,
concentrations in the 0- to 10-cm soil averaged for Likiep, Wotho, Ailuk, Ujelang, Mejit,
and Jemo is 0.2 to 0.7 pCi/g, very similar to the background levels at the other areas of
Micronesia, although slightly higher.
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.
First, the distributions of radionuclide concentration data
in
relatively large
vegetation and soil sample populations from Bikini and Eneu Islands at Bikini Atoll is
discussed in Ref. 5.
The distributions are log-normal; the arithmetic mean x includes
some 68% of the population, 2 x includes 88% of the population, and 3 X includes better
51