Neurobehavioral function and tibial and chelatable lead levels in 543 former organolead workers

Objective: To evaluate the associations between tibial lead, dimercaptosuccinic acid (DMSA)-chelatable lead, and neurobehavioral function in former organolead manufacturing workers with past exposure to organic and inorganic lead. Methods: Data were collected from 543 subjects with a mean age of 58 years and an average of 17.8 years since last lead exposure. Years since last exposure to lead was used to estimate tibial lead levels in the year of last occupational lead exposure, termed “peak tibial lead.” Current tibial lead levels, measured by x-ray fluorescence, were extrapolated back using a clearance half-time of lead in tibia of 27 years, assuming first-order clearance from tibia. Results: Peak tibial lead levels ranged from −2.2 to 105.9 μg Pb/g bone mineral, and DMSA-chelatable lead levels were between 1.2 and 136 μg. After adjustment for confounding variables, peak tibial lead was a significant negative predictor of performance on the Wechsler Adult Intelligence Scale–Revised vocabulary subtest (p = 0.02), serial digit learning test (p = 0.04), Rey Auditory-Verbal Learning Test (immediate recall and recognition, p = 0.03 for each), Trail Making Test B (p = 0.03), finger tapping (dominant hand [p = 0.02] and nondominant hand [p < 0.01]), Purdue pegboard (dominant hand, nondominant hand, both hands, and assembly, p < 0.01 for each), and Stroop Test (p < 0.01). Moreover, with one exception, average neurobehavioral test scores were poorer at higher peak tibial lead levels. DMSA-chelatable lead was only significantly associated with choice reaction time (p = 0.01). Conclusion: Peak tibial lead was consistently associated with poorer neurobehavioral test scores, particularly in the domains of manual dexterity, executive ability, verbal intelligence, and verbal memory.