Lead is ubiquitous in the urban environment. Emissions from vehicles burning leaded gasoline constitute an important source of dispersed lead in many urban areas. Industrial emissions, particularly from smelters and battery recycling plants, are also a significant source.

Humans are exposed via the inhalation of contaminated air, ingestion of contaminated water and foods, and, especially among children in North America, ingestion of lead-based paint. Contact with and ingestion of contaminated soil provide another important route of exposure, particularly among children. Serious occupational exposures occur among adults involved in metal industries, electronics industries, construction trades, and battery manufacturing.

The adverse effects of lead on health have been recognized for centuries. Lead's principal threat, other than acute lead poisoning, is neurological damage in children. A 1988 study in Mexico City, where ambient lead levels are high because of the use of leaded gasoline, found that more than one quarter of newborns had blood lead levels high enough to impair neurological and motor-physical development[1].

Studies conducted in North America, Western Europe, and Australia report that elevated levels of exposure to lead in infancy cause intellectual impairment, although quantifying this impairment is still somewhat controversial[2]. Children with elevated dentine lead levels are reported to have a deficit in intelligence scores, speech, and language processing skills compared with children with low lead levels[3]. A 1990 study in Bangkok, Thailand, a city heavily polluted with lead, suggested that 30,000 to 70,000 children risked a loss of four or more IQ points because of high lead levels, and many more risked lesser reductions in intelligence[4].

Moreover, it has been suggested that exposure to high lead levels in childhood may be associated with dropping out of high school, reading disability, absenteeism, and neurodevelopmental deficits later in life[5]. Some studies have also linked increases in blood lead levels in adults with elevated blood pressure, although this finding has not been borne out in all studies[6][7].

The findings of neurological impairment in children sparked the effort in the 1970s and 1980s to reduce lead levels in gasoline and other sources in the United States and Europe -- an effort that has resulted in lower ambient and blood lead levels in these areas. Blood lead concentrations in the United States, for instance, have dropped substantially since the late 1970s, when the use of leaded fuel was phased out. Many countries in developing regions, however, have yet to enact such regulations, and the risk of exposure to lead remains dangerously high.

References and notes

1. David Satterthwaite, "The Impact on Health of Urban Environments," Environment and Urbanization, Vol. 5, No. 2 (October 1993), p. 93.

2. Peter Baghurst et al., "Environmental Exposure to Lead and Children's Intelligence at the Age of Seven Years," New England Journal of Medicine, Vol. 327, No. 18 (1992), pp. 1279-1284.

3. Herbert Needleman et al., "Deficits in Psychologic and Classroom Performance of Children with Elevated Dentine Lead Levels," New England Journal of Medicine, Vol. 300, No. 13 (1979), pp. 689-695.

4. U.S. Agency for International Development (U.S. AID), Office of Housing and Urban Programs, Ranking Environmental Health Risks in Bangkok, Thailand, Vol. 2, Technical Appendices (U.S. AID, Washington, D.C., December 1990), p. E-15.

5. Herbert Needleman et al., "The Long-Term Effects of Exposure to Low Doses of Lead in Childhood: An 11-Year Follow-Up Report," New England Journal of Medicine, Vol. 322, No. 2 (1990), pp. 83-88.

6. J.A. Staessen et al., "Hypertension Caused by Low-Level Lead Exposure: Myth or Fact?," Journal of Cardiovascular Risk (1994), pp. 87-97.

7. James Pirkle et al., "The Relationship Between Blood Lead Levels and Blood Pressure and Its Cardiovascular Risk Implications," American Journal of Epidemiology, Vol. 121, No. 2 (1985), pp. 246-258.