Note: EPA no longer updates this information, but it may be useful as a reference or resource.
Please see www.epa.gov/airtrends for the latest information on Air Quality Trends.
Nature and Sources of the Pollutant: In the past, automotive sources were the major contributor of Pb emissions to the atmosphere. As a result of EPA's regulatory efforts to reduce the content of Pb in gasoline, the contribution from the transportation sector has declined over the past decade. Today, metals processing is the major source of Pb emissions to the atmosphere. The highest concentrations of Pb are found in the vicinity of nonferrous and ferrous smelters, battery manufacturers, and other stationary sources of Pb emissions.
Health and Environmental Effects: Exposure to Pb occurs mainly through the inhalation of air and the ingestion of Pb in food, water, soil, or dust. It accumulates in the blood, bones, and soft tissues. Because it is not readily excreted, Pb can also adversely affect the kidneys, liver, nervous system, and other organs. Excessive exposure to Pb may cause neurological impairments such as seizures, mental retardation, and/or behavioral disorders. Even at low doses, Pb exposure is associated with damage to the nervous systems of fetuses and young children, resulting in learning deficits and lowered IQ. Recent studies also show that Pb may be a factor in high blood pressure and subsequent heart disease. Lead can also be deposited on the leaves of plants, presenting a hazard to grazing animals. Animals do not appear to be more susceptible to adverse effects from Pb than humans however, nor do adverse effects in animals occur at lower levels of exposure than comparable effects in humans. For these reasons, the secondary standard for lead is identical to the primary standard.
Trends in Pb Levels: Between 1987 and 1996, ambient Pb concentrations decreased 75 percent, and total Pb emissions decreased 50 percent. Since 1987, Pb emissions from highway vehicles have decreased 99 percent due to the phase-out of leaded gasoline. The large reduction in Pb emissions from transportation sources has changed the nature of the pollution problem for Pb in the U.S. While there are still violations of the Pb air quality standard, they tend to occur near large industrial sources such as Pb smelters. Between 1996 and 1996, Pb concentrations remained unchanged, total Pb emissions decreased 2 percent, and Pb emissions from transportation sources did not change.