examined with respect to ingestion was the ingestion to inhalation ratio
(H_/Am).
The ingestion model takes the form (Martin and Bloom, 1976;
1977);
HL
= ©,
2 1, D,
(24)
I.
is the ingestion rate for substance i (g/day)
where
D.
is the discrimination factor which is the ratio of
concentration of 23%Pu in substance i to the concentration of 239Pu in soil.
The principal item to note from Equation (24) is that H_
is directly
ANALYSIS OF THE EFFECTS OF VARIATIONS
The simplified model given by Fquations (19) through (24) allows us to
examine the effects of variations in the significant parameters in a
relatively easy manner.
The parameters subject to the most variation
are (a) the average soil concentration: (C_), (b) the mass loading factor
(L_), (c) the various fractions and biological half-times involved in
the lung model (Equations (20) and (21)), (d) the ingestion to inhalation ratio (Hm/Am) » and (e) the biological elimination rate for bone
OA, = in(2)/T>) and fraction from blood to bone.
Statistical summaries
of soil inventory data by Gilbert et al. (1975) show large variations
of soil concentration within a particular area.
This variation is compounded by uncertainties as to the proper size and boundaries to assign
to the ecosystem model.
The mass ltoading factor is also quite variable and
depends on wind velocities and frequencies as well as the size of soil
particles and whether the soil has been mechanically disturbed (e.g.,
plowed).
The various fractions and half-times in the lung model are
subject to considerable uncertainty because we are generally ignorant of
the particle size which affects the initial deposition fractions (D,,
Dis
and D.)
as well as
the chemical and physical form of the plutonium
(which affects the translocation class).
The ingestion to inhalation
ratio is uncertain because of the potential variation in the parameters
of the ecosystem model that predicts ingestion as well as uncertainties
in L, and C_.
The biological elimination rate (or half-time) of bone
and the fraction from blood to bone can be significant because bone does
not reach equilibrium within the time period of interest (50~70 years)
and because a range of values has been proposed for these two parameters
(ICRP 19, 1972).
525
SF Ane Ace RO AO SOI, lA enti
proportional to C.> but varies with respect to the composition of the
diet.