Environmental Engineering Reference
In-Depth Information
Lead decreases the production of vitamin D. Inhibition of vitamin D
production in children has been observed at BLLs as low as 12
g/dL.
In addition to lead's effect on blood, evidence from both epidemiological
and animal studies indicates that low-level lead exposure is related to
increases in blood pressure (hypertension). A relationship appears to exist
between diastolic blood pressure in middle-aged males and a range of BLLs
down to 7
µ
g/dL. Studies with females have shown a less consistent asso-
ciation. Recent studies which have focused on knee bone (patella) lead con-
centrations have shown a twofold increase of hypertension with an increase
from the 10th to the 90th percentile lead concentration in middle-aged female
nurses, with no association with BLLs.
The mechanism for this lead-hypertension association is unknown. It
has been proposed that the effect may be due to the interaction of lead with
membrane-bound enzyme systems responsible for transmembrane fluxes of
ions such as sodium, potassium, and calcium. Lead directly affects the cel-
lular transport of sodium and indirectly alters a number of calcium-regulat-
ing processes.
High blood pressure is a major risk factor for coronary artery disease,
stroke, and renal (kidney) insufficiency. The effect of childhood lead expo-
sures on subsequent risk of hypertension and cardiovascular disease in adult-
hood has not yet been evaluated; it should be of some public health concern.
Lead exposures have been associated with sperm abnormalities, reduced
fertility, and altered testicular function in male industrial workers with BLLs
in the range of 40 to 50
µ
g/dL. As more females enter the workforce in once
male-dominated industries, an elevated lead body burden in pregnant
females may pose a significant risk to developing fetuses. Because lead
readily passes through the placenta, the fetus can be exposed through its
mother. Blood lead levels in pregnant females appear to be higher than
population averages, presumably due to the mobilization of bone lead along
with calcium. Several epidemiological studies have reported associations
between maternal BLLs and preterm delivery and low birth weight. An
inverse relationship between maternal BLLs and birth weight with BLLs
down to 15
µ
g/dL has been reported. Other studies have failed to observe
such a relationship.
Lead is a potential carcinogen. It can cause mutations and cell transfor-
mation and interfere with DNA synthesis in mammalian cell cultures. Ani-
mal studies have shown that it can induce kidney tumors. Though not
definitive, epidemiological studies suggest a causal relationship between
lead exposures and cancer. Based on this evidence, USEPA has identified
lead as a Group 2B human carcinogen (carcinogenicity has been confirmed
in animal studies; human studies are inconclusive).
The nervous system appears to be the primary target organ system for
lead exposure. Lead causes encephalopathy (brain damage) at BLLs of
µ
≥
80
µ
g/dL. Children with BLLs in this range may experience permanent brain
damage characterized by severe mental retardation and recurrent convul-
