Lead is one of the six common pollutants--referred to by the Environmental Protection Agency (EPA) as "criteria pollutants"--for which the EPA sets air quality standards under the mandates of the Clean Air Act. Lead is a naturally occurring metal that has unique properties and has been used almost throughout civilization for a wide variety of purposes even though its highly toxic nature has been recognized for thousands of years. Lead compounds are emitted into the air primarily from metal-processing operations, large incinerators, lead-acid battery manufacturers, and gasoline combustion.
Lead is highly toxic to humans. At sufficient concentrations in the blood, it can cause kidney damage, brain damage, and death. At lower concentrations, lead affects the gastrointestinal system, blood, and the nervous system. Because lead affects brain and nervous system development, pregnant women and children are at particular risk from lead exposure. Gastrointestinal symptoms include abdominal discomfort and pain, nausea, and lack of appetite. Chronic lead poisoning can also cause anemia, irritability, headaches, sleeplessness, and dizziness. Severe symptoms of lead poisoning include hallucinations, bizarre behavior, seizures, and coma. In addition, because lead dust settles on vegetation and on water, it can be ingested by wildlife and fish, which can suffer many of the same health effects.
In the 1920's, chemical engineers discovered that adding tetraethyl lead to gasoline increased gasoline's octane and eliminated engine pre-detonation, commonly known as "engine knock." The combustion of leaded gasoline results in dust containing lead that can be breathed in or settle on the ground or water. In 1970, there were 221,000 tons of lead emissions in the United States, 82 percent of which came from vehicle exhaust. The recognition that vehicle emissions were posing an ever-growing health hazard led to federal efforts to reduce vehicle-based lead emissions. In addition, the EPA's mandate that catalytic converters be included in vehicles to reduce other types of emissions required the elimination of lead from gasoline because lead stops catalytic converters from functioning properly.
In the 1970's, the EPA directed that there be a gradual phase-out of the use of lead as an additive in gasoline, and as of 1996 it is illegal to sell leaded gasoline in the United States or sell new vehicles that require it. In 1997, lead emissions in the United States had dropped to 3,915 tons, only 26 percent of which were attributable to fuel combustion, most of which by airplanes. Currently, most lead emissions come from the processing of metals and from waste incineration, which have been reduced only six percent since 1988.
The EPA's national air quality standard for lead requires that lead levels not exceed 1.5 micrograms per cubic meter for any three-month period. In 2004, 10 of 13 counties in the United States previously classified as areas not meeting the national standard sought reclassification as meeting the standard. Therefore, as of August, 2004, only 10,000 people in three counties in the United States lived in areas with lead levels that exceeded national standards. Copyright 2013 LexisNexis, a division of Reed Elsevier Inc. |