For predictive purposes, we shall assume that the soil and vegetation compartMents are in steady state and that the mean vegetation/soil ratio is 0.1.
This ratio is somewhat conservative as it tends to overestimate the plutonium
content of vegetation in areas where soil concentrations are > 100 pCi/g.
INGESTION
RATE
CATTLE
:
INHALATION
RATE
Transport Pathways
For present purposes, the only herbivore assumed to contribute to man's plutonium intake is the cow.
Both dairy cattle and beef cattle are considered.
The principal plutonium inputs to these herbivores (Figure 1) are by tnhalation
and by ingestion of contaminated soll and vegetation.
Figure 2 illustrates
the assumed pathways of plutonium transport to man via beef cattle and dairy
cattle and provides estimates of some of the parameters required to estimate
potential concentrations of plutonium in the muscle, liver, and milk of beef
and dairy cattle maintained in a contaminated area at NTS.
Formulation of Cow Model
A general equation for the concentration of plutonium in the muscle, liver, or
milk compartment of Figure 2 can be derived as follows:
dy, /dt = m, (Tb! bi - huyy)
y,i (t} =
£ = muscle, Liver, mitk.
‘pfoi
f'1 - etait
my
LIVER
m= 125 kg
T = 2000 days
(18)
hy
where, y,; ts the concentration of plutonium in compartment i at time
t (pci/g),
and
MUSCLE
a7)
m, is the weight of compartment i (g),
r, is the rate at which plutonium enters blood (pCi/day),
fbi {s the fraction (dimension
to compartment i (Figure 2:
0.07, 0.12, and 0.007),
Ay is the effective elimination rate coefficient (day~*),
for plutonium in compartment i (based on effective half lives,
T, in Figure 2},
a
1
m= 3950 g
T = 30,000 days
m = 25 kg/day
T = 16 br
*Gastrointestinal Tract.
FIGURE 2.
PATHWAYS OF PLUTONIUM TRANSPORT TO MAN VIA
BEEF CATTLE AND DAIRY CATTLE
Estimated values for some of the parameters of Equations (17) and (18) are
given, as indicated above, in Figure 2.
The transfer fractions from the
gastrointestinal tract to blood and from blood to muscle, liver, and milk; the
645
644
MILK