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

AX5-139
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
1100 to
1300 µg/Common
Pb/kg/d
~14 yrs, replaced by a
204 Pb-enriched dose,
206 Pb-enriched dose,
and/or finally a
207 Pb-enriched dose of
varied durations and
concentrations.
Orally, in gelatin
capsule
Pb acetate
250 mg/L
Exposure began either
at 5, 10, or 15 wks of
age and continued for a
total of 5 wks.
Drinking water
Nonhuman
primate
Using the method of sequential stable isotope administration examined flux of
Pb from maternal bone during pregnancy of 5 female cynomolgus monkeys.
Blood Pb levels in maternal blood attributable to Pb from mobilized bone were
reported to drop 29 to 56% below prepregnancy baseline levels during the first
trimester of pregnancy. This was ascribed to the known increase in maternal
fluid volume, specific organ enlargement (e.g., mammary glands, uterus,
placenta), and increased metabolic activity that occurs during pregnancy.
During the second and third trimesters, when there is a rapid growth in the
fetal skeleton and compensatory demand for calcium from the maternal blood,
the Pb levels increased up to 44% over pre-pregnancy levels. With the
exception of one monkey, blood Pb concentrations in the fetus corresponded to
those found in the mothers, both in total Pb concentration and proportion of Pb
attributable to each isotopic signature dose (common = 22.1% vs. 23.7%,
204 Pb = 6.9% vs. 7.4%, and 206 Pb = 71.0% vs. 68.9%, respectively). Between
7 and 25% of Pb found in fetal bone originated from maternal bone, with the
balance derived from oral dosing of the mothers with isotope during
pregnancy.
In offspring from a low Pb exposure control monkey (blood Pb