THE CURRENT STATUS OF CHILDHOOD LOW-LEVEL LEAD TOXICITY

Lead's toxicity has been recognized since antiquity, and certain themes recur during the history of its understanding. Warnings have been frequently pronounced, and frequently followed by statements that these warnings were exaggerated. Childhood lead poisoning was first discovered in Brisbane, Australia in 1894. The cause, lead on the rails of the porches was demonstrated by J.L. Gibson, and promptly derided by the business and medical communities. The first lead paint prevention act was passed in Australia in 1920. In the United States, it was believed that if a lead-poisoned child did not die, they recovered with no residua. This was disproved by R. K Byers in 1943, and the modern era of childhood lead poisoning was begun. In the 1960's, the defined toxic level of lead in the blood was 60 mug/dl. In some areas, as many as 20% of children had blood lead levels above 40 mug/dl. Questions about silent toxicity at these doses were raised. Studies of lower lead exposure began to be published in the early 1970's. Some reported an effect, others did not. Many of these early studies were of small sample size, used crude measures of outcome, relied on a short term markers of exposure, and had limited control of covariates. In the latter part of the 1970's, studies of better quality reported positive relationships between lead and IQ. We used tooth lead levels to classify asymptomatic 1st and 2nd grade children and, controlling for socioeconomic status, mother's IQ and other potential confounders, demonstrated that high lead in the teeth was associated with decreased IQ, impaired attention, and impaired speech performance. Twelve years later, children with elevated lead had increased school failure and reading disabilities. All investigations must balance Type I versus Type II risks in designing and executing the study. This paper examines six flaws encountered in many studies that increase the Type II bias, and examines some of the forces, economic and political, that condition the bias. The newer data on lead's neurotoxicity argue strongly that the current definition of toxicity requires downward revision. As expected the same industrial forces encountered over history continue to assert that the threat of lead is exaggerated. (C) 1993 Intox Press, Inc.