Air Quality Criteria for Lead Volume II of II - (NEPIS)(EPA) - US ...

AX6-51
Table AX6-3.5. Neurophysiological Function and Occupational Lead Exposure in Adults
Reference, Study
Location, and Period Study Description Pb Measurement Findings, Interpretation
Canada
Bleecker et al. (2005b)
New Brunswick
1992-1993
Europe
Kovala et al. (1997)
Finland
74 current smelter workers, mean age
44 (8.4) yrs, education 8 (2.8) yrs and
employment duration 20 (5.3) yr had current
perception threshold (CPT) measured for
large and small myelinated and unmyelinated
nerve fibers in the finger. Linear regression
modeled CPT on metrics of Pb dose after
adjusting for covariates. Interaction of Pb
dose and ergonomic stressor on peripheral
nerve function was assessed.
60 workers in a Pb battery factory with a
mean age of 43 (9) yrs and mean exposure
duration of 16 (8) yrs. Nerve conduction
studies, vibration thresholds, and quantitative
EEG were performed. Relationship of Pb
exposure with peripheral nerve function and
quantitative EEG were examined by partial
correlation and regression analyses adjusting
for age.
Mean (SD) blood Pb 26
(7.1) µg/dL
Mean (SD) IBL 891
(298.8)
µg·yr/dL
Mean (SD) TWA 42
(8.4)µg/dL
Mean (SD) tibia bone 40
(23.8) µg/g
5 metrics relating to IBL
cumulated only exposure
above increasing blood Pb
ranging from 20 to
60 µg/dL
Mean (SD) tibial Pb 26
(17) mg/kg
Mean (SD) calcaneal Pb
88 (54) mg/kg
Mean (SD) IBL 546
(399)
µg·yr/dL
Mean (SD) TWA 34
(8.4) µg/dL
Mean (SD) maximum
blood Pb 53 (19) µg/dL,
Mean (SD) blood Pb 27
(8.4) µg/dL
Blood Pb and tibial bone Pb were not associated with any of the three
nerve fiber populations. IBL and TWA accounted for a significant
percentage of the variance only for the large myelinated nerve fibers
(♠R 2 = 3.9%, ♠R 2 = 8.7% respectively). The relationship of CPT and
TWA was curvilinear with a minimum at a TWA of 28 µg/dL.
Unique variance of CPT for large myelinated fibers explained by
different thresholds of IBL were IBL – 3.9%, p = 0.08; IBL20 – 5.8%,
p < 0.03, IBL30 – 7.8%, p < 0.02; IBL40, p < 0.005; IBL50,
p < 0.005; and IBL60, p < 0.005. IBL60 also explained significant
variance of CPT for small myelinated nerve fibers demonstrating an
increased impairment in peripheral nerve function. This effect on
myelinated sensory nerve fibers was enhanced when a measure of
ergonomic stress was added to the model for IBL60.
The sensory amplitude of the median and sural nerves had a negative
correlation with IBL and duration of exposure that was not related to
age. Vibration threshold at the ankle related significantly to IBL and
duration of exposure after adjusting for age. Vibration threshold in
the finger was associated with blood Pb and blood Pb avgs over the
past three yrs. The alpha and beta frequencies were more present in
workers with higher long term Pb exposure such as tibial and
calcaneal, IBL and TWA. Overall historical blood Pb measures were
more closely associated with peripheral nerve function than bone Pb
concentrations. The study had no comparison group and did not
account for the effect of smoking and alcohol use or give their usage
in this population.