Air Quality Criteria for Lead Volume II of II - (NEPIS)(EPA) - US ...

AX5-140
Table AX5-8.4 (cont’d). Bone Lead as a Potential Source of Toxicity in Altered Metabolic Conditions
Compound
Dose/Concentration
Duration Exposure
Route Species Effects Blood Level Reference
Pb acetate
50 ppm
11 mo
Drinking water
Pb acetate
0, 2, or 10 mg/kg/d
9.5 mo
Drinking water
Pb acetate
7 yrs total
Drinking water
Pb (type unidentified)
occurring naturally in
diet (0.258 ng/mg dry
wt) and water
(5.45 ppb).
Exposure from age
1 mo up to 958 days.
Drinking water and diet
Rat Studied differences in tissue distribution of Pb in adult and old rats. Adult
(8 mo old) and old (16 mo old) rats were exposed to 50 ppm Pb acetate in
drinking water for 11 mo at which time the experiment was completed. Bone
(femur) Pb levels in older rats were found to be less than those in younger rats,
however, blood Pb levels were higher in the older rats. Brain Pb concentration
in the older rats exposed to Pb were significantly higher, and brain weight
significantly less than the brain Pb concentration and weights of unexposed
older control rats or adult rats exposed to Pb, suggesting a potential
detrimental effect. Authors suggested that a possibility for the observed
differences in tissue concentrations of Pb was due to changes in the capacity of
bone to store Pb with advanced age.
Rat Examined kinetic and biochemical responses of young (21 days old), adult
(8 mo old), and old (16 mo old) rats exposed to Pb at 0, 2, or 10 mg Pb
acetate/kg/d over a 9.5 mo experimental period. Results suggested older rats
may have increased vulnerability to Pb due to increased exposure of tissues to
Pb and greater sensitivity of the tissues to the effects of Pb.
Nonhuman
primate
In studies of bone Pb metabolism in a geriatric, female nonhuman primates
exposed to Pb ~10 yrs previously, there were no significant changes in bone
Pb level over a 10 mo observation period as measured by 109 CD K X-ray
fluorescence. The mean half-life of Pb in bone of these animals was found to
be 3.0 ± 1.0 yrs, consistent with data found in humans, while the endogenous
exposure level due to mobilized Pb was
0.09 ± 0.02 µg/dL blood.
Mice The Pb content of femurs increased by 83% (values ranged from 0.192 to 1.78
ng Pb/mg dry wt), no significant relationship was found between Pb and bone
density, bone collagen, or loss of calcium from bone. The results suggest
against low levels of bone Pb contributing to the osteopenia observed normally
in C57BL/6J mice.
Approximate median
values after 6 mo of
exposure:
Adult rats : 23 µg/dL
Old rats: 31 µg/dL
After 11 mo of exposure:
Adult rats: 16 µg/dL
Old rats: 31 µg/dL
Various from ~1 µg/dL
up to 45 µg/dL
Historic concentrations
during exposure: 44 to
89 µg/100 mL.
Cory-Slechta et al.
(1989)
Cory-Slechta
(1990b)
McNeill et al.
(1997)
None given Massie and Aiello
(1992)