What can the study of lead teach us about other toxicants?

The history of knowledge about lead toxicity may serve as a useful template to judge and predict progress in understanding other toxicants. A paradigm shift has occurred in which toxicity has been recognized at levels long held to be harmless. This shift has been accelerated by the use of newer tools for measuring outcome. Lead effects have been identified in children at blood lead levels as low as 15 micrograms/dL. They include impaired psychometric intelligence, language function, attention, and classroom behavior. Lead exposure during pregnancy results in increased risk for minor malformations and lowered infant IQ scores until at least 2 years of age. Understanding of this toxicant has been blurred by seven unrecognized Type II errors frequently encountered in the lead literature. These errors are discussed. A meta-analysis of thirteen informative lead studies in children is presented. The joint probability of the findings occurring by chance under the null hypothesis is less than 3 x 10(-12).