34 - Lead

Abstract

Human activities have led to significant contamination of the environment with lead, arising from emissions to the atmosphere, especially from motor vehicles. The impact of these emissions can be detected in increased levels of lead in environmental media throughout the world and elevations in blood lead levels during the middle part of the 20th century. Interventions by governments to reduce lead emissions have brought about a decline in blood lead levels in recent years in many parts of the world. This has been achieved, in part, by controls on lead in food and drinking water, but much of the decline in lead exposure is a result of the elimination of lead from gasoline. While the ability of lead to cause severe morbidity and mortality in heavily exposed individuals has been well documented, its effects on the general population, who are exposed to lower levels, have been the subject of considerable debate and controversy. Of most concern are a series of population studies of lead on measures of childhood intelligence, but there is also evidence of a possible effect on blood pressure in adults. Uncertainties in both the measurement of lead exposure and the health endpoints, as well as the profound difficulties in controlling adequately for confounding social and environmental factors in epidemiological investigations, restrict the interpretation of the causal nature of these associations.