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3. HEALTH EFFECTS
and reduction in radio-resistance in mouse-rat (hybrid) cell line (Robertson and Raju 1980).
Results were
negative for plutonium-induced gene mutation in several strains of
Salmonella typhimurium (DOE
1980h).
3.4 TOXICOKINETICS
Studies of the toxicokinetics of plutonium have focused on two general classes of compounds:
highly
insoluble compounds (e.g., PuO
2
) and soluble compounds (e.g., Pu[NO
3
]
4
, plutonium citrate complexes).
However, factors other than solubility affect the behavior of plutonium in biological systems. These
include: (1) hydrolysis reactions at physiological pH that yield highly insoluble polymers from soluble
Pu(IV); (2) particle size, which affects deposition characteristics in the respiratory tract and absorption
rates from the lung and gastrointestinal tract; (3) firing temperature at which the PuO
2
was formed, which
may affect particle surface characteristics and susceptibility to physical transformation reactions that
increase mobility and absorption; and (4) isotope specific activity, which can affect the
intensity of
radiation of the particles and rates of radiolytic fragmentation of particles in tissues. These various
factors give rise to toxicokinetics of the various plutonium compounds that are not easily distinguished
solely on the basis of water solubility. The toxicokinetics of inhaled
238
PuO
2
is distinctly different from
that of inhaled
239
PuO
2
having a similar particle size range (>1 μm). Inhaled
238
PuO
2
that deposits in the
lung is much more rapidly absorbed and distributed to liver and skeleton (predominantly) compared to
239
PuO
2
. As a result, deposition of similar initial lung burdens of the two isotopes will result in long-term
(e.g., chronic) radiation doses to liver and skeleton (i.e., bone and marrow) that are higher,
and lung doses
that are lower, following exposures to
238
PuO
2
compared to
239
PuO
2
. The consequences of these different
radiation doses are distinct patterns of health effects that have been observed in controlled lifetime studies
in animals, with more prominent lung effects following exposures to
239
PuO
2
.and more prominent effects
on bone, marrow, and liver following exposures to
238
PuO
2
(see Section 3.2.1). The kinetics,
distribution,
and health outcomes of inhaled
239
Pu(NO
3
)
4
are similar to those of
238
PuO
2
.
3.4.1
Absorption
3.4.1.1 Inhalation Exposure
Evidence for absorption of inhaled plutonium in humans derives from several types of measurements:
(1) measurements of fecal and urinary excretion of plutonium following occupational inhalation
exposures (Carbaugh and La Bone 2003; DOE 1985k, 1991c; James et al. 2003; Kathren and McInroy
1991; Kurihara et al. 2002; McInroy et al. 1991; Voelz et al. 1979; Woodhouse and Shaw 1998);
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PLUTONIUM
3. HEALTH EFFECTS
(2) postmortem plutonium levels in tissues of workers exposed to airborne plutonium (Filipy and Kathren
1996; Filipy et al. 1994; Hahn et al. 2003, 2004; Kathren and McInroy 1991; Khokhryakov et al. 2005;
McInroy et al. 1989, 1991; Romanov et al. 2003; Voelz et al. 1997); (3)
in vivo chest radiation
measurements (
241
Am) following occupational exposures to
airborne
241
Pu (Carbaugh and La Bone 2003;
DOE 1991c); and (4) experimental studies in which
in vivo blood, urine, and organ x-ray emission were
measured in subjects who inhaled
237
Pu nitrate (Etherington et al. 2003; Hodgson et al. 2003).
Inhaled plutonium particles that deposit in the respiratory tract are subject to three general distribution
processes: (1) bronchial and tracheal mucociliary transport to the gastrointestinal tract; (2) transport to
thoracic lymph nodes (e.g., lung, tracheobronchial, mediastinal); or (3) absorption by blood and/or lymph
and transfer to other tissues (e.g., bone, liver). The above processes apply to
all forms of deposited
plutonium, although the relative contributions of each pathway and rates associated with each pathway
vary with the physical characteristics (e.g., particle size), chemical form (degree of water solubility), and
radiological characteristics (e.g., specific activity). The various processes that contribute to the
elimination of plutonium from the respiratory tract give rise to multi-phasic lung retention kinetics. In
most studies of lung retention, at least two kinetic components are evident. The faster phase is thought to
be contributed by relatively rapid mechanical clearance mechanisms (e.g., mucociliary transport) and
absorption to blood of soluble or relatively rapidly dissolved insoluble material deposited in the lung.
The slower phase is contributed by the transformation and dissolution and/or mechanical clearance (e.g.,
phagocytic) of highly insoluble particles.
Etherington et al. (2003) measured plutonium kinetics in two adult subjects who inhaled an aerosol of
237+244
Pu(NO
3
)
4
(activity median aerodynamic diameter [AMAD]=1.1 μm; geometric standard deviation
[GSD]=1.2). Lung, liver, and urine plutonium levels were estimated from K x-ray emission from the
decay of
237
Pu; blood plutonium levels were measured by mass
spectrometry of
244
Pu. Initial lung
burdens were estimated to be 8 kBq
237
Pu and 35 ng
244
Pu. Lung retention half-times, estimated from
observations made up to 120 days following the exposure, were 1.6–3.0 days (20%) for the fast phase,
and 280–430 days (80%) for the slow phase. Longer-term observations of lung retention
kinetics are
available from studies of accidental inhalation exposures to plutonium oxide containing
241
Pu (Carbaugh
and La Bone 2003; DOE 1991c). In these studies, lung plutonium burdens were inferred from
measurements of external radiation emitted by
241
Am, a gamma-emitting daughter of
241
Pu. Estimated
lung retention half-times for 10 subjects ranged from 14 to 80 years.