SIMULATION OF PLUTONIUM INGESTION BY GRAZING CATTLE
W.
E.
Martin and §S.
G.
Bloom
Battelle's Columbus Laboratories
Columbus, Ohio
ABSTRACT
A simple model of plutonium ingestion by cattle grazing a uniformly
contaminated pasture is I
=IC +t1C_ where I
is the plutonium
ingestion rate (pCi/day), Y and ¥ are vegetation and soil ingestion
rates (g/day), C_ and C_ are plutonium concentrations (pCi/g) in vegeta-
tion and soil. In a ground zero area such as the inner compound of
Area 13 (NTS), where the spatial distribution of plutonium is nonuniform
and highly variable, the simple ingestion model seems to require a
stochastic interpretation.
This paper provides evidence for assuming that the five factors of the
ingestion model are lognormally distributed.
Estimates of the geometric
means and standard deviations of the four factors on the right side of
the model equation were used to generate synthetic random samples of I>
I_, C_, and C_.
The means of these synthetic samples were then used to
obtain iterative solutions of the model equation in which the factors on
the right were varied randomly and independently within the limits
specified by the synthetic geometric means and standard deviation.
The
resulting synthetic composite random sample of I
(n = 500 days) indicated an average plutonium ingestion rate, for a hypothetical 410-kg cow
grazing the inner compound of Area 13, of 557 + 526 nCi/day.
Subsamples
{n = 100 days) ranged from 486 * 330 to 629 + 526 nCi/day.
This result
compares favorably with previous estimates:
565 nCi/day based on fistu-
lated steer rumen contents (Smith et @l., 1976), 620 nCi/g based on an
assumed diet of winterfat and shadscale (Gilbert et al., 1977), and 585
nCi/day based on general theoretical considerations (Martin and Bloom,
1977).
(1) that
the grazing, soil, and plant studies conducted in Area 13 were apparently
well designed; (2) that a repetition of the study would probably yield
results similar to those already obtained; (3) that given an adequate
sampling design, reasonably accurate estimates of plutonium ingestion
rates by grazing cattle can be obtained in spite of the extreme variability of the contributing factors; and (4) that given site-specific
483
a
The conclusions to be drawn from these simulation studies are: