Occupational lead exposure and longitudinal decline in neurobehavioral test scores

Background: No previous longitudinal studies have compared and contrasted associations of blood lead and tibia lead with declines in cognitive function over the course of time in a large sample of subjects with current and past occupational exposure to inorganic lead. Methods: From 1997 through 2001, we conducted a longitudinal study of 803 current and former lead workers in South Korea to evaluate effects on the central and peripheral nervous systems. Three study visits occurred during a mean follow-up duration of 2.20 years. Neurobehavioral test scores, peripheral nervous system function, and blood lead were measured at each of the 3 study visits, whereas tibia lead was measured by x-ray fluorescence at the first and second visits. We limited our analysis to the 576 lead workers who completed testing at all 3 visits. We performed regression analyses using generalized estimating equations. Results: There were consistent associations of blood lead with test scores at baseline and of tibia lead with declines in test scores over the next year, mainly in executive abilities, manual dexterity, and peripheral vibration threshold. Conclusions: The results support the inference that occupational lead exposure can cause declines in cognitive function over the course of time. Lead likely has an acute effect on neurobehavioral test scores as a function of recent dose and a longer-term (possibly progressive) effect on cognitive decline as a function of cumulative dose.