PLUTONIUM
113
3. HEALTH EFFECTS
Table 3-10. Parameters of the First Branch of the First Institute of Biophysics
(FIB-1) Biokinetic Plutonium Model
a
Parameter
Symbol Unit
S=0.3%
S=1.0%
S=3.0%
Fraction of inhaled
V(T)
percent Particle size-dependent
deposited in lung
Fraction to fast lung
percent 26.5
±
46.5
71.7
±
9.1
90.1
±
3.5
clearance
Fraction to fixed lung
K
f
percent 15.4
±
4.2
4.3
±
0.7
1.8
±
0.2
compartment
Fraction
to slow lung
percent 58.0
±
46.4
24.0
±
9.1
8.1
±
3.5
clearance compartment
Fraction to lymph nodes
K
n
percent 26.0
±
4.2
21.0
±
1.6
11.0
±
0.9
Clearance rate from slow
year
-1
0.134
±
0.103 0.133
±
0.045 0.170
±
0.063
lung compartment
Urine
Feces
a
i
x
i
a
i
x
i
Systemic compartment 1 a
1
, x
1
day
-1
4.1x10
-3
5.634x10
-1
6.0x10
-3
3.465x10
-1
Systemic compartment 2 a
2
, x
2
day
-1
1.2x10
-3
1.26x10
-1
1.6x10
-3
1.05x10
-1
Systemic compartment 3 a
3
, x
3
day
-1
1.3x10
-4
1.65x10
-2
1.2x10
-4
1.24x10
-2
Systemic compartment 4 a
4
, x
4
day
-1
3.0x10
-5
2.31x10
-3
2.0x10
-5
1.8x10
-3
Systemic compartment 5 a
5
, x
5
day
-1
1.3x10
-5
2.0x10
-5
5.2x10
-6
2.0x10
-5
a
See Figure 3-9 for schematic representation of model.
Source: Khokhryakov et al. 2002
PLUTONIUM
114
3. HEALTH EFFECTS
plutonium excretion and postmortem lung and total body burdens in Mayak workers. The model cannot
be directly extrapolated to predicting the kinetics of systemic plutonium following exposures by other
routes (e.g., dermal, oral).
Leggett et al. (2005) Plutonium Biokinetics Model
Description of the Model.
Leggett et al. (2005) developed a modification of the ICRP (1994a)
model. A schematic diagram of the model and list of parameter values are presented in Figure 3-10 and
Table 3-11, respectively. The major important features introduced into the Leggett et al. (2005) model
are the simulations of blood and urinary excretion from blood, liver, and bone. The blood compartment in
the Leggett et al. (2005) model is divided into two sub-compartments (blood 1, blood 2).
Absorbed
plutonium enters blood 1, from where it distributes to other tissues and is excreted into urine. Plutonium
in tissues returns to blood 2 (recycled plutonium), from where it distributes to blood 1, the rapid soft
tissue compartment (ST0), and is excreted in urine.
The two blood compartments, with both contributing
to urinary bladder contents, provides a simulation of a relatively fast pathway for urinary excretion of
recycled plutonium (blood 2
to urine, t
1/2
≈
5 hours) and a slower excretion pathway for initially-absorbed
plutonium (blood 1 to urine, t
1/2
≈
45 days). The liver is divided into three compartments (liver 0, 1, and
2). Liver 0 receives plutonium from blood 1 from where it can be secreted into the gastrointestinal tract
(e.g., bile), or transferred to liver 1 and liver 2. The latter sub-compartments simulate faster and slower
transfers of plutonium from liver to blood 2 (liver 1 to blood, t
1/2
≈
460 days; liver 2 to blood,
t
1/2
≈
5,500 days). This configuration (i.e., fast and slower liver compartments) results in a
gradual shift in
the systemic plutonium distribution from liver to skeleton, with the liver burden being greater than
skeletal burden, initially after absorption, and the liver contribution diminishing, relative to skeletal, over
time. As in the ICRP (1994a) model, the skeleton is divided into trabecular and
cortical components,
with each further divided into surface bone, bone volume, and bone cavity (marrow) compartments. In
the ICRP (1994a) model, initial deposition of plutonium is assumed to occur from blood directly to bone
surfaces, where it can be transferred to bone marrow or to bone volume (i.e., burial). In the Leggett et al.
(2005) model, plutonium in blood 1 is directly transferred to
both bone surface and volume
compartments. This configuration simulates faster and slower components of burial of plutonium in bone
volume. The fast component is represented by direct transfer from blood 1 to bone volume (t
1/2
≈
50 days
and 150 days for trabecular and cortical volume, respectively) and the slower component is represented
by transfer from bone surface to volume (t
1/2
≈
15 and 93 years for trabecular and cortical, respectively).