PLUTONIUM
110
3. HEALTH EFFECTS
and Polig 2000). Sensitivity and uncertainty analyses of model predictions have been reported (Luciani et
al. 2001, 2003).
Risk Assessment.
The model could be used to establish the radiation dose (Sv) per unit of ingested
or inhaled plutonium (Bq) in adults if linked to radioactive decay and radiation dose models.
Target Tissues.
The model is designed to calculate radiation dose coefficients (Sv/Bq) corresponding
to specific inhalation or ingestion exposures to plutonium isotopes.
Species Extrapolation.
The model is intended for applications to human dosimetry.
Applications to
other species would require consideration of species-specific adjustments in model parameters.
The Luciani and Polig (2000) model is designed to simulate kinetics of
absorbed plutonium, and includes gastrointestinal tract compartments for simulating absorption from
ingestion. If combined with a respiratory tract model (e.g., ICRP 1994b), the model can be used to
simulate inhalation exposures to plutonium. The model has been applied to injection exposures (Luciani
and Polig 2000) and can be applied to any other route of exposure for which the transfer rate to
blood is
available.
First Branch of the First Institute of Biophysics (FIB-1) Biokinetic Plutonium Model
Description of the Model.
Khokhryakov et al. (1994, 2000, 2002) developed a biokinetics model for
predicting the accumulation of plutonium in the lungs (and corresponding radiation doses) of workers at
the Mayak Production Association (Russian Federation), based on exposure information and
biomonitoring of urinary plutonium. The model included
a lung clearance model, which delivered
plutonium into a multi-compartment elimination (urinary and fecal) model (Figure 3-9). In the lung
clearance model shown in Figure 3-9, inhaled plutonium was distributed to three lung clearance
pathways: rapid clearance, slow clearance (to systemic compartments and lymph nodes), or fixed
(permanently retained in the lung). Plutonium compounds were assigned specific distributions to the
three pathways according to estimates of “biological transportability” (S) as
determined by dialysis
through a semi-permeable membrane (Khokhryakov et al. 1998). Compounds in the low transportability
class (S=0.3%; e.g., PuO
2
) were assigned larger distribution fractions to fixed and slow clearance
pathways, compared to higher transportability classes (e.g., S=3%, Pu[NO
3
]
4
). For PuO
2
, lung retention
PLUTONIUM
112
3. HEALTH EFFECTS
half-times are assumed to be approximately 4.4 days (fast) and 2,000 days (slow; corresponding half-
times for Pu(NO
3
)
4
are 31 and 1,500 days, respectively.
Plutonium absorbed from the lung enters a systemic compartment composed of 10 sub-compartments
from which plutonium is transferred to urine (5) or feces (5). The sub-compartments
represent kinetically
similar pools of plutonium in the body, rather than specific tissues (i.e., the model was intended to
simulate lung retention and excretion, not plutonium burdens in other tissues),
and are assigned unique
excretion rate constants. Summing the outflow from all five compartments provides the estimated total
excreted plutonium per day. Distribution fractions and transfer rates, and half-times for the various
compartments are presented in Table 3-10. A recent configuration of the model (Khokhryakov et al.
2005) replaced the FIB-1 lung clearance model with the ICRP Human Respiratory Tract Model for
Radiological Protection (ICRP 1994b).
Validation of the Model.
The FIB-1 model has been evaluated with data on plutonium excretion and
postmortem lung and total body burdens in 543 Mayak workers (Khokhryakov et al. 2002). An
adaptation of the FIB-1 model, with the lung clearance model replaced by the ICRP Human
Respiratory
Tract Model for Radiological Protection (ICRP 1994b), has also been evaluated against the same data
(Khokhryakov et al. 2005; Suslova et al. 2003). An uncertainty analysis of model predictions has been
reported (Krahenbuhl et al. 2005).
Risk Assessment.
The model has been used to establish the lung radiation dose (Sv) per unit of
plutonium intake (Bq) in plutonium production workers (Khokhryakov et al. 2002, 2005).
Target Tissues.
The model is designed to calculate radiation dose coefficients (Sv/Bq) to the lung
corresponding to specific inhalation exposures to plutonium isotopes or from urine plutonium
biomonitoring data (Khokhryakov et al. 2002, 2005).
Species Extrapolation.
The model is based on both human and animal data. However, it is intended
for applications to human dosimetry. Applications to other species would
require consideration of
species-specific adjustments in modal parameters.
Interroute Extrapolation.
The FIB-1 model was constructed to simulate kinetics of inhaled
plutonium. The systemic portion of the model is an empirical model (compartmental with no assignments
of compartments to physiological entities) for which parameter values were derived from data on