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PLUTONIUM
3. HEALTH EFFECTS
The relatively long retention kinetics of inhaled plutonium particles in
the lung is thought to reflect, in
part, rates of physical transformation and dissolution of the particles. Various estimates have been made
for these rates, based on modeling of data on urinary excretion and tissue burdens of plutonium following
inhalation exposures (James et al. 2003; Khokhryakov et al. 2005). Based on an analysis of data from
535 autopsies of plutonium workers, particle dissolution half-times were estimated to range from
approximately 5–6 years, for exposures to highly insoluble plutonium oxides, to 1–2
years for exposures
to more soluble forms (e.g., plutonium nitrate; Khokhryakov et al. 2005). James et al. (2003) estimated
the lung dissolution half-time to be approximately 7 years in a subject who inhaled PuO
2
ceramic
particles.
Absorption of inhaled PuO
2
has been studied in various nonhuman primate species (Brooks et al. 1992;
LaBauve et al. 1980; Lataillade et al. 1995; Metivier et al. 1974, 1978b; Stanley et al. 1982). Observed
lung retention kinetics were biphasic. The slow-phase retention half-time in baboons exposed to
238
PuO
2
(count median aerodynamic diameter [CMAD]=2.1 μm±1.3 standard deviation [SD]) was estimated to be
approximately 400 days (range: 200–600 days), based on measurements made during the first 30–
170 days after exposure (Metivier et al. 1974); however with longer observation periods (>200–
300 days), the half-time was estimated to be approximately 1,000 days (Metivier et al. 1978b). Lataillade
et al. (1995) estimated the lung retention half-time in baboons that inhaled an
aerosol of an industrial
PuO
2
(AMAD=1.9 μm1.7 SD) consisting primarily of
239
Pu and
240
Pu (≈94 w%, 0.2 w%
238
Pu); the
estimated half-time was approximately 66 days, for an observation period of 180 days. Slow-phase lung
retention half-times measured in Cynomolgus monkeys exposed to an aerosol of
239
PuO
2
(AMAD=1.6 μm; GSD=1.6) ranged from 300 to 1,800 days (LaBauve et al. 1980). In Rhesus monkeys
exposed to
239
PuO
2
from industrial ball milling processes (AMAD=1.5 μg±1.6 SE), the slow-phase lung
retention half-time was estimated to be approximately 300 days (Stanley et al. 1982).
Lung plutonium
burdens have also been measured at various times in Cynomolgus monkeys exposed to aerosols of
239
Pu(NO
3
)
4
(AMAD=06 μm; GSD=2.1); based on these data, the slow-phase retention half-time was
approximately 200–300 days (Brooks et al. 1992).
Numerous studies have examined the lung deposition and kinetics of absorption of inhaled plutonium in
dogs (Bair et al. 1962b; Dagle et al. 1996; Guilmette et al. 1984, 1987; Mewhinney and Diel 1983;
Muggenburg et al. 1996; Park et al. 1997). Inhaled aerosols of
238
PuO
2
were
more rapidly cleared from
the lung than aerosols of
239
PuO
2
of similar particle size distributions (Guilmette et al. 1984; Park et al.
1997). This difference has been attributed to radiolytic fragmentation of particles in the lung, resulting in
more enhanced particle dissolution and absorption from the lung (Mewhinney and Diel 1983). Lung
75
PLUTONIUM
3. HEALTH EFFECTS
retention half-times following exposure of young adult beagles to aerosols of
239
PuO
2
(AMAD=1.6 μm1.2 SD) were 86 days (32%) and 1,386 days (Guilmette et al. 1984).
In comparison,
lung retention half-times following exposure of young adult beagles to aerosols of
238
PuO
2
(AMAD=1.8 μm1.9 SD) were 174 days (84%) and 908 days (Park et al. 1997). The corresponding
times to achieve 50% of initial lung burdens are approximately 500 days for exposure to
239
PuO
2
and
250 days for exposure to
238
PuO
2
(Park et al. 1997). Mewhinney and Diel (1983) analyzed
data on lung
retention in beagles exposed to
238
PuO
2
of various particle sizes (AMAD 0.7, 1.7, 2.7 μm) in order to
estimate fragmentation rates of the deposited particles. Estimated fragmentation rates appeared to
increase with time after exposure and particle size. Corresponding fragmentation half-times at 100 days
postexposure were 100–250 days and, at 500 days postexposure were 50–120 days. Particle size (AMAD
0.7–2.7 μm) had little effect on long-term lung retention (Mewhinney and Diel 1983). In beagles, short-
term (i.e., <1 month) lung retention of inhaled
239
PuO
2
was influenced by aerosol particle size
distribution, with faster clearance from the lung as particle size decreased (Bair et al. 1962b).
Long-term
lung retention in beagles is also influenced by particle size. In beagles that were exposed to
239
PuO
2
, the
slow phase lung retention half-times were 700 days (90%, AMAD=0.9 μm1.4 SD), 1,400 days (68%,
AMAD=1.6 μm1.2 SD), and 1,800 days (78%, AMAD=2.8 μm1.2 SD) (Guilmette et al. 1984). The
method used to produce PuO
2
also appears to affect the absorption of inhaled PuO
2
. Oxides produced at
high temperature (i.e., high-fired, e.g., 1,000 °C) had longer lung retention than oxides produced at low
temperature (i.e., low-fired, e.g., 350 °C) (Bair et al. 1973).
Inhaled aerosols of
238
Pu(NO
3
)
4
are also more rapidly cleared from the lung than aerosols of
239
Pu(NO
3
)
4
(Dagle et al. 1983, 1996). In beagles, this difference was most pronounced in the first 30 days
postexposure, during which approximately 80% of the initial lung burden from
238
Pu(NO
3
)
4
was
cleared
compared to approximately 40% from
239
Pu(NO
3
)
4
. Retention half-times were similar (≈130–150 days)
for the two isotopes, for observations extending from 30 days to 1 year.
3.4.1.2 Oral Exposure
Absorption of plutonium accumulated in shellfish (mollusks) has been studied in humans. Adult subjects
ingested winkles (six males, two females) or cockles (five males, one female) containing
239,240
Pu that
were collected from marine waters near the British Nuclear Fuels facility at Sellafield, Cumbria (Hunt
1998; Hunt et al. 1986, 1990). The range of the ingested activity of
239+240
Pu was 6–16 Bq.
Serial
24-hour urine samples were collected from each subject for up to 7 days after they ingested the mollusks.
The fraction of the activity absorbed was estimated as the ratio of the observed cumulative urinary