Differential contribution of current and cumulative indices of lead dose to neuropsychological performance by age.

We examined measures of lead dose that reflect intensity of exposure and cumulative exposure for differential association with neuropsychological functional domains and with neuropsychological performance by age. Eighty active lead smelter workers assessed for verbal memory and visuomotoric skills had a mean (range) age of 44 (24-64) years, duration of employment of 20 (4-26) years, education of 8 (0-13) grades, current blood lead (B-Pb) of 26 microgPb dl(-1) (13-43), working lifetime weighted average blood lead (TWA) of 42 microgPb dl(-1) (17-57), working lifetime integrated blood lead (IBL) of 903 microgPb-yr dl(-1) (81-1,436) and bone lead (bone-Pb) of 41 microgPb (g bone mineral)(-1) (-12-90). Multiple linear regression after adjusting for age and education showed a significant amount of variance in verbal memory (Rey Auditory Verbal Learning Test and Verbal Paired Associates) explained only by measures of lead dose intensity, B-Pb, and TWA. Visuomotoric ability (Grooved Pegboard [GP] and Digit Symbol) had significant variance accounted for by measures of both lead dose intensity, TWA, and of cumulative lead dose, IBL, and bone-Pb. The relationship between bone-Pb and GP was curvilinear in older workers, with increasingly slower performance above a bone-Pb threshold of 20 microgPb (g bone mineral)(-1). Examination of age-related change in GP with exposure using IBL, a surrogate for cumulative lead dose in the brain, showed enhanced age-related change in older workers with high IBL. These findings suggest that the older nervous system provides a substrate more susceptible to the effects of chronic lead exposure.