Lead is a soft, dense, bluish-gray metal used in piping, batteries, weights, gunshot, and crystal. Of the six criteria pollutants, lead is the most toxic. When ingested through food, water, soil, dust, or inhaled through the air, it accumulates in the body's tissues and is not readily excreted. Excessive exposure to lead can cause anemia, kidney disease, reproductive disorders, and neurological impairments such as seizures, mental retardation, and behavioral disorders.14
The highest concentrations of lead are found in the surrounding area of nonferrous and ferrous smelters, battery manufacturers, and other stationary sources of lead emissions. The decline in ambient lead concentration is the greatest success story in the effort to reduce air pollution.
Ambient lead concentrations in the United States decreased 97 percent between 1977-1996. Most of this reduction was achieved through the introduction of unleaded gasoline, and the elimination of lead compounds in paints, coatings, and from point sources such as smelters and battery plants.
Young children are the most vulnerable to blood lead and high blood-lead levels, which in small children retard brain and IQ development. Children who live in older housing that has lead-based paint are still at risk for high blood-lead levels, but the pervasive threat of lead from poor urban air is a problem of the past. Lead in blood samples is a much better indicator of the public health impact of lead than outdoor air quality. Between the late 1970s and 1991, the proportion of people with more than 10 micrograms of lead per deciliter of blood declined from 78 percent to 4.3 percent.15