The reader is referred to their paper for details concerning the assumptions
and parameter values used in the model.
Turning to Figure 1, we see that the hypothetical 239pu concentrations in
lung, bone, and kidney of Standard Man for 433 days residence in an area with
soil concentrations of 0.07 nCi/g are less by factors of (roughly) 2, 22, and
6 than the mean 2739pu concentrations in these same tissues for the beef cattle
The hypothetical values for human
that grazed 433 days in the outer compound.
of soil are factors of 5
nCi/g
lung and bone for 180 residence days at 0.55
and 8 less than obtained for cow 2, which grazed 176 days in the inner compound
(no data are available for the kidney of cow 2).
Factors of 2 and 5 are perhaps not unexpected for lung since in the model the
inhalation rate of plutonium (pCi/day) for beef cattle is taken to be (based
on NTS studies) 5.5 times greater than that of man (see eq. 1 and the discussion
on cattle inhalation rates in Martin and Bloom).
tions in lung and bone at the MPC_
Hypothetical human concentra-
level (3 nCi/g of dry soil) for 180 residence
days are about equal to concentrations found in these two tissues of cow 2.
According to the model, human tissue concentrations in lung, bone, and kidney
increase by factors of 3, 6, and 6 in the time span from 180 to 720 residence
days when soil is at the MPC_
level.
The 239pu concentrations in these human
organs increase by factors of roughly 2, 80, and 70, respectively (according
to the model), between residence times 720 days and 55 years for soil at MPC...
The greater increases for bone and kidney between 720 days and 55 years occur
because the model assumes no losses of plutonium from these organs (see Figures 3
and 4, Martin and Bloom).
Discussion
We don't have now, nor are we likely to have in the near future, estimates of
the accuracy (bias) of these hypothetical human tissue concentrations since no
humans live in these contaminated areas. We also do not have any precise
knowledge of the precision (variability) of these model estimates. We presume
this variability is largely due to the high variability of most estimates of
parameters used in the model.
As new information becomes available from the
continuing NAEG studies, and we learn how to design better field studies and
extract more information from the data collected (see next section), the model
will undoubtedly be modified and improved.
As Martin and Bloom stress, the
present model is not the last word on the subject.
More data are clearly needed to obtain better estimates of plutonium burdens
in tissues of small vertebrates and grazing cattle, particularly for GZ areas.
Considerably more data will soon be available, at which time Figure 3 should
be revised.
Information is also available on concentrations of 238py, 238y ,
and *4lam that needs to be related to concentrations for soil, vegetation, and
small vertebrates.
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