Lead

Sources: Atmospheric lead is emitted from a variety of stationary
sources. Smelters and battery plants are the most significant
contributors. Other sources include electric utilities, fuel
combuststion from transportation and industry, lead production,
waste oil and solid waste incineration. According to National Air
Pollutant Emission Trends (1995), total lead emissions from all
sources dropped from 219,000 short tons in 1970 to 5,000 short
tons in 1994.
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Until recently, alkyl lead compounds used as anti-knock additives
in gasoline accounted for about 90 percent of all lead emissions.
In the early 1970s, EPA required gradual reduction in lead
content of gasoline. In 1985, the lead content of leaded gasoline
was reduced from 1.0 gram (gm) per gallon, to 0.5 gm/gallon and,
one year later, further declined to 0.1 gm/gallon. In 1993, it
became illegal in the U.S. to manufacture vehicles required
leaded gasoline. By 1994, 99.4 percent of gasoline in the U.S.
was unleaded. In 1996, lead will be totally banned from
motor-vehicle use. As a result of this tremendous drop in leaded
gasoline use, automobile-related lead emissions into the
atmosphere have been virtually eliminated.
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Concentration: Except in the immediate vicinity of mining,
smelting and manufacturing facilities, where lead concentrations
are locally high, ambient air concentrations of lead are higher
in urban locations than rural. Lead concentrations in rural areas
range between 0.008 - 0.01 ug/m3. Before the removal of lead in
gasoline, typical lead levels in urban areas were 0.1-10 ug/m3,
rising as high as 8-18 ug/m3 near freeways. Very high lead levels
can exist in small areas near lead smelters.
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Health Effects: Exposure to lead can occur by inhalation through
the air and ingestion of lead in food, paint, water, soil and
dust. When lead enters the body, it is absorbed in the
bloodstream and transported to all parts of the body. Although
significant amounts of lead may be found in blood and soft tissue
(liver and kidney), it tends to accumulate in the bones, where it
is immobilized. About 20-40 percent inhaled ambient lead
particles are deposited in the lungs, where 50 percent or more
are absorbed into the bloodstream.
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In children, about 50 percent of ingested lead is absorbed,
compared to 8-10 percent for adults. Lead ingestion in children
is particularly serious, given the possibility that lead competes
with calcium in the skeletal system. Poor children seem most at
risk because their diets contain less calcium from milk and other
dairy products. Similar amounts of lead would therefore affect
poor children more than those with good nutrition available.
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Based on the extent of exposure, individuals may develop symptoms
of acut4e or chronic lead poisoning. Target organs and systems
are the circulatory system, brain and nervous system, kidneys and
reproductive system. Symptoms of acute lead exposure include
colic, shock, severe anemia, acute nervousness, kidney damage and
irreversible brain damage. With a sufficiently high dosage, death
may result. Chronic exposure may result in severe brain damage
and damage to the kidneys and blood-forming systems. Lead is also
gametotoxic (causes sterility) and embryotoxic (causes abortions
and stillbirths).
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A child with blood lead levels over 10 ug/dl (micrograms of lead
per deciliter of blood) is considered lead poisoned. Childhood
lead poisoning results in lower IQs and abnormal behavior.
Exposure to air containing 1 ug/m3 of lead is associated with 5
ug/dl increase in lead levels in the bloodstream. Therefore,
long-term exposure to air contaminated with 2 ug/m3 could cause a
child to be lead poisoned.
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Women of child-bearing age are also at high risk. High blood lead
levels in a mother may expose the fetus to lead, resulting in
postnatal mental retardation.
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Ecological Effects: At low ambient concentrations, plants and
animals are not seriously affected by lead poisoning. Exposure to
high lead levels, however, adversely affects domestic animals,
wildlife and aquatic life. Lead poisoning resulting from air
pollution has been reported in the vicinity of major sources,
such as smelters, battery manufacturers and urban areas with
heavy automobile emissions. Lead in the air does not damage
materials or property.