CUMULATIVE EXPOSURE TO INORGANIC LEAD AND NEUROBEHAVIORAL TEST-PERFORMANCE IN ADULTS - AN EPIDEMIOLOGIC REVIEW

Objectives-To evaluate the current evidence that cumulative exposure t o inorganic lead is associated with decreased performance in neurobeha vioural tests in adults. Methods-21 unique studies were reviewed from 28 published manuscripts. An algorithm was developed to determine the usefulness of each study on the basis of exposure assessment, control of confounding variables, methods of subject selection, test condition s, and data analysis. Highest emphasis was placed on the use of cumula tive measures of exposure or absorption. Results-Only three studies us ed a measure of cumulative exposure to or absorption of lead, and two others used duration of exposure as a surrogate for cumulative exposur e. Ah other studies used a measure that did not adequately estimate cu mulative exposure to lead, most often current blood lead concentration . 20 of the studies controlled for age as a confounding variable, alth ough in several studies the possibility for residual confounding by ag e remained. 16 studies controlled for intellectual ability before expo sure; all of them used educational level for this purpose. Of the five studies that used direct or surrogate measures of cumulative exposure to or absorption of lead, two were thought to be of low usefulness be cause of inadequate duration of exposure. The three remaining studies found stronger associations of neurobehavioural performance with recen t exposure measures than with those of cumulative exposure. Conclusion -The current scientific literature provides inadequate evidence to con clude whether or not cumulative exposure to or absorption of lead adve rsely affects performance in neurobehavioural tests in adults. The cur rent evidence is flawed because of inadequate estimation of cumulative exposure to or absorption of lead and inadequate control for age and intellectual ability before exposure.