Issues in developmental neurotoxicology: interpretation and implications of the data.

The potential for environmental contaminants to produce neurological, cognitive, or other behaviour deficits as a result of developmental exposure has received increasing attention. The focus has shifted from description of frank neurotoxicity observed in a relatively few individuals to more subtle impairment in a much greater number of children. With this shift has come the recognition that subtle deficits such as a small decrease in IQ can have important societal impact when large numbers of children are affected. For example, the result of a 1 microgram/dL decrease in blood lead concentration in children in the United States with blood lead concentrations between 10 and 20 micrograms/dL would translate into a savings of 5-7.5 billion U.S. dollars a year in increased earning power alone. In addition, behavioural problems such as increased aggression and poor social adjustment identified early in childhood may escalate to serious antisocial behaviour such as delinquency as the child approaches puberty. Exposure to neurotoxic agents during development or over a significant portion of the lifespan may also result in acceleration of age-related neurodegenerative diseases. Such changes in the functional abilities of a significant proportion of a population have potentially serious consequences for society as well as for affected individuals.