2. Actions taken to reduce exposures should be those which
show promise of significant exposure reduction when
weighed against total expected exposures and the "costs"
of the actions.
''Costs,'' in this context, are measured
primarily in terms of costs to the Enewetak people as
constraints on their activities or as dollar costs for
cleanup or remedial action.
In these evaluations, it should be emphasized that dosages
through various pathways are estimated on the basis of
environmental data and considerations of expected living
patterns and dietary habits. While "radiation standards"
ad
do not exist for environmental contamination levels in substances such as soil and foodstuffs, there is general agree-
ment in terms of conservative models of these pathways and
the relationships between a certain level in the environment
and the likely dose to result from the pathway exposure.
The area of plutonium in soils, however, is one for which
there is no general agreement as to the quantitative relationship
between levels in soils and dosages to be expected through the
inhalation pathway, the primary one through which man can
receive a significant dose from plutonium. The ICRP recommends
a maximum permissible average concentration (MPC) of 1
picocurie per cubic meter (pCi/m3) of air for "insoluble"
plutonium and 0.06 pCi/m3 for "soluble" plutonium for unrestricted areas. While the plutonium in the soil at Enewetak
is thought to be typical of world-wide fallout, and therefore
insoluble, 0.06 pCi/m3 will be used for the sake of conservatism.
Appendix A of Enewetak Radiological Survey, NVO-140, presents
two possible methods for deriving the exposures that may occur
through the inhalation pathway for plutonium in soil. (This is
the pathway of interest for the present although it is recognized
that for the very distant future,
important by comparison.
ingestion may become more
Table 250 of Appendix IZ shows that
exposure to bone, liver, and lung from 239Pu is
expected to
be a few hundredths of a rem in 30 years for pathways other than
inhalation.)
section.
This material is produced as Attachment I of this
The two methods presented are the ''resuspension-factor"
approach and the mass-loading'' approach.
Soil concentrations
of 739Pu that would be associated with the standard for °39Pu
in air (0.06 pCi/m3) by the two methods are:
II~7