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Margit L. Bleecker, D. Patrick Ford, Christopher G. Vaughan, Karen N. Lindgren, Michael J. Tiburzi, and Karin Scheetz Walsh

Center for Occupational and Environmental Neurology, Baltimore, Maryland, USA

Abstract
In this study we investigated the effect of recent and chronic lead exposure, and its interaction with ergonomic stressors, on peripheral nerve function. In a cross-sectional design, we used retrospective exposure data on 74 primary lead smelter workers. We measured blood and bone lead levels and, from historical records, calculated lead dose metrics reflecting cumulative lead exposure: working-lifetime integrated blood lead (IBL) and working-lifetime weighted-average blood lead (TWA) . We additionally created five metrics related to IBL that cumulated exposure only above increasing blood lead levels ranging from 20 to 60 µg/dL (IBL20-IBL60) . Current perception threshold (CPT) assessed large myelinated (CPT₂₀₀₀) , small myelinated (CPT₂₅₀) , and unmyelinated (CPT₅) sensory nerve fibers. Using multiple linear regression, we modeled CPT on the different measures of lead dose after adjusting for relevant covariates. CPT had a curvilinear relationship with TWA, with a minimum at a TWA of 28 µg/dL. Both TWA and IBL accounted for a significant percentage of the variance of CPT₂₀₀₀ (R² = 8.7% and 3.9%, respectively) . As the criterion blood lead level increased from IBL20 through IBL60, so did the percentage of CPT₂₀₀₀ variance explained, with R² ranging from 5.8% (p < 0.03) for IBL20 to 23.3% (p < 0.00) for IBL60. IBL60 also significantly contributed to the explanation of variance of CPT₂₅₀ and significantly interacted with ergonomic stressors. Measures of chronic blood lead exposure are associated with impairment of large and small myelinated sensory nerve fibers. This effect is enhanced at the highest doses by ergonomic stressors. Key words: bone lead, cumulative lead dose, ergonomic stressors, lead dose thresholds for peripheral nerve, peripheral nerve fiber size. Environ Health Perspect 113: 1730-1734 (2005) . doi:10.1289/ehp.8106 available via http://dx.doi.org/ [Online 8 August 2005]

Address correspondence to M.L. Bleecker, Center for Occupational and Environmental Neurology, 3901 Greenspring Ave., Suite 101, Baltimore, MD 21211 USA. Telephone (410) 669-1101. Fax: (410) 669-1103. E-mail: coen@msn.com

We thank F. McNeill for performing the bone lead measurements.

This work was supported by the New Brunswick Occupational and Safety Commission.

The authors declare they have no competing financial interests.

Received 10 March 2005 ; accepted 8 August 2005.