Environmental Engineering Reference
In-Depth Information
contains less than half as much lead as it did a few decades ago. Lead
poisoning causes learning disabilities and antisocial behavior, among
other maladies. Most of the larger car-owning nations of the world have
either banned leaded gas or restricted its use.
Late in 2008, the EPA tightened the regulatory limit on airborne
lead for the fi rst time in thirty years, lowering the legal maximum to
a tenth of what it had been on the grounds that it poses a more serious
threat to young children than had been realized.
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More than 300,000
American children show adverse effects from lead poisoning, and ele-
vated lead can result in increased blood pressure and decreased kidney
function in adults.
The vast majority of airborne lead, a neurotoxin that reduces chil-
dren's IQ, now comes from lead smelters. The lead eventually falls to
the ground, and most of a child's exposure comes from soil and indoor
dust. However, there are fewer than 200 air lead monitoring stations
nationwide, so it is not clear that airborne lead can be suffi ciently
monitored to make the new law enforceable. According to the EPA,
there are 16,000 sources across the country emitting 1,300 tons of lead
into the air each year, a sharp decrease from 74,000 tons emitted three
decades ago.
Rubber
Car tires do not last forever, as all drivers are aware. But few people
consider what happens to the rubber dust that has been ground off by
friction between the rolling tires and the highway. The answer is that
most of it fl ies upward and becomes an unwanted constituent in the air
we breathe. Approximately 13 million cubic feet of rubber have been
lost from wear on the 300 million tires that enter the scrap heap every
year. Some of the rubber sticks to the highway and does not enter the
air (skid marks), but the amount has never been determined. However,
there can be no doubt that our lungs are partly coated with tiny rubber
particles. A study in England in 2005 found that about a quarter of the
particulate emissions from nonexhaust sources was from tire and brake
wear.
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In the United States, rubber is not a category in air pollution
studies.
In addition to microscopic particles of rubber, tire wear releases large
amounts of chemicals called polycyclic aromatic hydrocarbons into the
air, and these chemicals are suspected of being carcinogenic. The volume
of these chemicals released from tires as we drive is unknown.
