Reversible neurobehavioral performance with reductions in blood lead levels--a prospective study on lead workers

Lead poisoning remains an occupational hazard in Taiwan. Many studies, based on crossed-section design, have focused on changes in lead-associated neurobehavioral dysfunctions that occur at increased blood lead levels. This study evaluates the changes in neurobehavioral performance of lead workers as blood levels are reduced. We tested 27 lead workers in a lead glaze factory using the computer-based and automated Chinese edition of Neurobehavioral Evaluation System 2 (C-NES II) in 1994, 1996, and 1997. The association of blood lead levels and C-NES II results were analyzed by longitudinal data analysis methods, repeated ANOVA and mixed model analyses after adjustment for potential confounders. Over these 4 years, the mean lead blood levels of workers were reduced from 26.3(SD=12.0) to 8.3(SD=6.9) microg/dL. Based on a mixed model analysis, we found that the negative effects of exposure to lead on neurobehavioral performance can be reversed to some extent with lowering levels of blood lead. During this period, we found significant improvements in 3 subtests: finger tapping, pattern comparison reaction time, and memory. This study tentatively concluded that reversibility of the neurobehavioral performance after reduction of the lead exposure, which encourages industrial hygiene and personal health promotion to reduce their body lead burden. However, though use of NES is more sensitive to detect the changes, the chronic symptoms (using standardized questionnaire) were found to decline slowly when blood lead level is reduced, with no statistically significant difference. The result means that to avoid the lead exposure primarily is essential to prevent chronic symptoms. We conclude that the most important way to prevent and possibly reverse chronic symptoms of lead poisoning remains to be the avoidance of exposure to lead.