average concentration of 233py in the soils of contaminated areas at NTS which
would result in a predicted dose rate of 1.5 rems/year to the lung is about
3 nCi/g dry. They use this rate as a "maximum permissible concentration" of
2339p in soil (MPC_; plotted with the soil concentrations in Figure 3). The
rate of 1.5 rems/year is the dose rate for individual members of the public
that the ICRP (1966) has recommended should not be exceeded.
Our interest here is to use this model for estimating hypothetical 239py
concentrations in lung, skeletal bone, and kidney of Standard Man for soil
concentrations at the MPC level (3 nCi/g dry) and for the average soil concen-
trations existing within fhe outer and inner compounds of Area 13 (0.07 and
0.55 nCi/g dry, respectively). These hypothetical human tissue concentrations
are obtained for one or more of the following exposure (residence) times of
Standard Man: 180 days, 433 days, 720 days, and 55 years. The results of the
model for residence time 180 days and soil concentration 0.55 nCi/g can presumably be compared with tissue burdens from cow 2 that grazed the inner fence
area for 176 days. Similarly, it is of interest to compare the model results
for 0.07 nCi/g and 433 days with the observed average tissue concentrations
for cows 3 and 8 since they grazed the outer compound for 433 days.
These results for Standard Man were obtained by first dividing total organ
burdens® (in units of curies) as estimated by the model, by the mass in grams
of each organ (500, 7000, and 300 grams for lung, bone, and kidney, respectively;
from Martin and Bloom, Figure 3).
These concentrations were converted to an
ash weight basis by multiplying by the average ratio of received? weight to
ash weight obtained for the lung, bone, and kidney tissues of cows and calves
grazed in Area 13; the assumption being made that these ratios also apply to
man. These average! ® ratios were estimated to be (average + approximate SE)
36 + 2.5, 4.6 + 0.7, and 37 + 3 for lung, bone, and kidney. Multiplying the
239pu concentrations (nCi/g ash tissue per 1 pCi/g dry of soil) by the concentration in soil (pCi/g dry) gives the estimates plotted for hypothetical
Standard Man in Figure 3.
Before discussing these results, we quote from Martin and Bloon:
“The present model is but one of several that have been investigated in
the course of the NAEG plutonium study. It presents our best effort to
judge and interpret the information currently available.
The design of
the model as well as the assumptions and parameter values selected for
its implementation comprise what we believe to be a reasonable working
hypothesis which is subject to continuing reappraisal as new information
comes to light.
While it is not the last word on the subject,
it does
provide a provisional method for evaluating potential health hazards
associated with Pu-contaminated areas at NTS."
SObtained from W. E. Martin.
Bloom (1976).
Also available from Figure 4 in Martin and
‘Tissue samples were frozen until analyzed.
1 Oaverage ratio computed as x/y, where x = average received weight, y = average
ash weight; n was 8, 11, and 7 for lung, bone (femur, vertebra), and kidney.
SE approximated using formula given in footnote to Table 17 in Gilbert et al.
(1975).
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