ABSTRACT
The goals were to determine if lead exposure is associated with cerebral white matter changes (WMC) and if so, does WMC mediate the relation between lead and psychomotor slowing as measured by Grooved Pegboard (GP). In the literature, age is the strongest predictor of WMC and therefore 61 lead smelter workers age 50 and under were included in the study population. Mean (range) age was 40 (23-50) years, years of education was 9 (0-13), duration of employment was 19 (1-26), current blood lead (PbB) was 29 (16-42) microg/dl, working lifetime weighted integrated blood lead (IBL) was 826 (65-1451) microg year/dl, working lifetime weighted average blood lead (TWA) was 42 (17-59) microg/dl, and bone lead (PbBn) was 39 (-12-90) microg Pb/g bone mineral. WMC, recorded as hyperintensities on T2-weighted MRI of the brain were graded. Lead variables were entered in a logistic regression attempting to differentiate normal versus abnormal MRI, after controlling for age and cerebrovascular risk factors. Direct effects of lead on GP and indirect effects of lead on GP through WMC was modeled using multiple linear regression analyses after controlling for the covariates. WMC were present in 23% of MRIs. Logistic regression of WMC on lead exposure metrics demonstrated significantly elevated odds ratios for IBL, TWA, and PbBn after the covariates. Of the lead exposure variables, IBL (beta=0.339, p<0.10) had a larger direct effect on GP after adjusting for the covariates than PbBn (beta=0.265, p<0.10). After adjusting for the lead term and covariates WMC accounted for an additional effect on GP performance after PbBn (beta=0.261, p<0.10) and after IBL (beta=0.278, p<0.05). Path analysis demonstrated that some of the relationship of both PbBn and IBL with GP is mediated by WMC.
Subject(s)
Air Pollutants/adverse effects , Lead Poisoning/etiology , Lead/adverse effects , Magnetic Resonance Imaging , Motor Skills/drug effects , Nerve Tissue/drug effects , Occupational Diseases/chemically induced , Occupational Exposure , Adult , Air Pollutants/blood , Air Pollutants/metabolism , Bone and Bones/metabolism , Canada , Humans , Image Interpretation, Computer-Assisted , Lead/blood , Lead/metabolism , Lead Poisoning/metabolism , Lead Poisoning/pathology , Lead Poisoning/psychology , Logistic Models , Male , Metallurgy , Middle Aged , Nerve Tissue/pathology , Occupational Diseases/metabolism , Occupational Diseases/pathology , Occupational Diseases/psychology , Odds Ratio , Reproducibility of Results , Risk Assessment , Risk FactorsABSTRACT
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 microg/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 microg/dL. Both TWA and IBL accounted for a significant percentage of the variance of CPT2000 (DeltaR2 = 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 DeltaR2 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.
