62
PLUTONIUM
3. HEALTH EFFECTS
bronchoalveolar carcinomas and papillary adenocarcinomas (Muggenburg et al. 1996; Park et al. 1997).
No single histopathological type of liver tumor was identified as the most frequent.
Bile duct tumors
were also observed in the
238
PuO
2
-exposed ITRI and PNL dogs (Muggenburg et al. 1996; Park et al.
1997).
Exposure of Dogs to
239
PuO
2
.
In contrast to the high incidences of bone tumors in the dogs exposed to
238
PuO
2
or
239
Pu(NO
3
)
4
aerosols, cancer deaths in dogs exposed to aerosols of the relatively insoluble
239
PuO
2
were predominantly associated with lung tumors, as reported in a 20-year lifespan composite
study (Muggenburg et al. 2008). The study included 18 control dogs and 108
239
PuO
2
-exposed
dogs per
sex, including seven dose groups with average ILBs of 0.16, 0.63, 1.6, 3.7, 6.4, 14, and 29 kBq/kg lung.
A total of 125 of the
239
PuO
2
-exposed dogs developed primary lung tumors and died between days 1,086
and 6,123 after receiving radiation lung doses between 1.7 and 80 Gy. The lowest absorbed dose for
radiation pneumonitis in the dogs was in excess of 10-fold higher than that reported for humans by
Newman et al. (2005).
Most of the lung cancers were papillary adenocarcinomas (n=70) followed by bronchiolo-alveolar
carcinomas (n=40) and adenosquamous carcinomas (n=22). The frequency of lung cancer occurrence
exceeded that of radiation
pneumonitis at the lower doses, but radiation pneumonitis dominated at doses
above an ILB of 3.7 mBq/kg; there was insufficient time for cancer development at ILBs >14 kBq/kg
(Muggenburg et al. 2008). Earlier and shorter studies reported bronchiolo-alveolar carcinoma as the most
frequently identified cancer type. (DOE 1987f, 1988a, 1990a; Hahn et al. 1999; Weller et al. 1995b). At
exposure levels used in those studies, surviving dogs were at high risk for lung tumors. In the dog study
performed at PNL (DOE 1988a, 1990a; Weller et al. 1995b), death due at least in part to lung tumors was
noted in 52/116 plutonium-exposed dogs versus 4/20 control dogs.
Among the various studies, few dogs died
from tumors of the bone, liver, or kidney where the respective
radiation doses to those organ systems were approximately 2, 4, or 5 orders of magnitude lower than that
to the lungs. Although up to 10 and 1% of the plutonium deposited in the lung relocated to liver and
skeleton, respectively, tumor incidences in liver and skeleton of plutonium-exposed were not significantly
different from those of controls (Muggenburg et al. 2008). Although bone tumors were reported as a
primary cause of death in three PNL dogs from the two lowest exposure groups (mean ILBs of 0.01 or
0.064 kBq/kg (DOE 1988a), they were not observed in dogs with higher ILBs and may not have been
239
PuO
2
-induced. Death due to radiation pneumonitis in dogs with higher ILBs would
be expected to
preclude late-developing lung tumors or tumors in organs where significantly lower radiation doses would
63
PLUTONIUM
3. HEALTH EFFECTS
make them relatively unlikely to occur. Time-to-death in dogs with primary lung tumors ranged from
1,086 days for a bronchioloalveolar carcinoma at 1.7 Gy to 6,123 days for a squamous cell carcinoma at
80 Gy. Neither bone nor liver tumors were reported in the
239
PuO
2
-exposed ITRI dogs (Hahn et al. 1999;
Muggenburg et al. 2008).
Exposure of Dogs to
239
Pu(NO
3
)
4
.
The pattern of tumor development in PNL dogs exposed to
239
Pu(NO
3
)
4
was similar to
that of dogs exposed to
238
PuO
2
, with tumors observed in lung, bone, and liver
(principally of bile-duct epithelium) (Dagle et al. 1996; DOE 1988b, 1994a). Bone tumors were the main
cause of death in the exposure groups with mean initial lung burdens of 1.02 and 5.91 kBq/kg, exposure
levels at which incidences of dogs with bone tumors were 10/20 and17/20, respectively (DOE 1994a).
Three of 20 dogs in the next lower exposure group (initial lung burden of 0.19 kBq/kg) also
exhibited
bone tumors. No bone tumors were observed in the lowest exposure groups (mean initial lung burdens of
0.028 or 0.0069 kBq/kg) or control dogs. Bone tumors were found in axial and appendicular skeleton and
primarily consisted of osteogenic sarcomas arising from endosteal surfaces (DOE 1994a). In an interim
report (DOE 1988b), lung tumors were a main cause of early death in 2/20, 6/20, and 11/20 dogs in the
groups with mean initial lung burdens of 0.19, 1.02, and 5.91 kBq/kg, respectively.
Final lung tumor
incidences were not located in available reports of
239
Pu(NO
3
)
4
-exposed PNL dogs. Incidences of liver
tumors were 1/20, 0/20, 3/20, 3/20, 3/20, 5/20, and 0/20 in unexposed controls, vehicle controls, and low-
to-high exposure groups (mean initial body burdens of 0.0069, 0.030, 0.19, 1.02, and 5.91 kBq/kg),
respectively (DOE 1994a). At the highest exposure level, early deaths from other causes may have
precluded the development of liver tumors.
Exposure of Other Laboratory Animal Species.
Lung tumors have been associated
with exposure to
239
PuO
2
aerosols in rats (Dudoignon et al. 2001, 2003; Herbert et al. 1993; Lundgren et al. 1995; Oghiso
and Yamada 2003a; Oghiso et al. 1994b, 1998; Sanders and Lundgren 1995; Sanders and Mahaffey 1979;
Sanders et al. 1988a, 1988b, 1993b), mice (Lundgren et al. 1987), and primates (Hahn et al. 1984;
Metivier et al. 1974). Two of 32 baboons developed lung tumors following exposure to
239
PuO
2
aerosols
at levels resulting in initial
239
Pu lung burdens ranging from 10.6 to 267 kBq/kg lung (Metivier et al.
1974). Lung tumors have also been reported in rats exposed to
238
PuO
2
aerosols (Sanders et al. 1977).
Hamsters appear to be resistant to lung tumor induction following inhalation of plutonium. No
statistically significant increases in tumor incidence occurred in lifetime studies of Syrian hamsters
exposed once or repeatedly (seven exposures during 12 months) to
238
PuO
2
or
239
PuO
2
aerosols at levels
resulting in initial or reestablished
238
Pu or
239
Pu lung burdens ranging from 52 to 130 kBq/kg (Sanders