ABSTRACT
Man has mined and used lead since antiquity. Despite its widespread utility and its commercial importance, lead has long endured a low status among metals as the above verses cited from the Old Testament, where lead is metaphorically compared negatively to sin, attest. This negativity has persisted to the present day, when the recognized toxicity of lead is the premier environmental health issue for children in the United States and in many other countries. There is a common misconception that adverse health effects due to environmental lead exposure are a problem of the past. However, based onnew scientific data it is believed that human populations are potentially affected at lower levels than previously thought to be toxic, and organ systems, such as the immune system, are also potentially affected. It is estimated that 3 to 4 million American children exhibit excessive blood lead levels as defined by the Centers for Disease Control (i.e. less than 10µg Pb/dl of whole blood, CDC, 1991),
and the World Health Organization has concluded, based on prospective logitudinal studies in human pediatric populations and experimental animal studies in rodents and non-human primates, that exposures producing blood lead levels as low as 10µg Pb/dl adversely impact cognitive functions (WHO, 1995). The positions of the CDC and the WHO are based on many epidemiological findings which collectively assert that intoxication with lead at subclinical levels, previously thought to be harmless, significantly impairs intelligence and neurobehavioral development, particularly in young children. Although most concern and emphasis has been placed on the dangers of lead exposure among preschool-aged children, there has also been a gradual lowering of the occupational toxicological standards in many countries. No comparable epidemiological database either in a pediatric lead-exposed population or an occupationally exposed cohort exists which characterizes the human immune system as a target for lead toxicity. However, based on animal studies and the available information indicating that lead affects human immune parameters, the immune system as a target for subclinical lead toxicity has been proposed and investigated by several laboratories. Detailed epidemiological data on the potential immunotoxicity of lead are lacking and are obviously needed.
