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

AX6-38
Table AX6-3.3 (cont’d). Neurobehavioral Effects Associated with Occupational Lead Exposure in Adults
Reference, Study
Location, and Period Study Description Pb Measurement Findings, Interpretation
Canada (cont’d)
Bleecker et al. (1997a)
New Brunswick
1992-1993
Bleecker et al. (1997b)
New Brunswick
1992-1993
The performance of the 467 current and retired
smelter workers as described in Lindgren et al.
(1996) administered a screening
neuropsychological battery by testers blinded
to the degree of Pb exposure of the worker had
their performance compared to age matched
norms. If performance on two or more tests in
any functional domain was below 1.5 standard
deviations the worker was invited for a
complete clinical evaluation. Eighty current
workers were identified by this criterion.
Mean yrs - age 44 (8.4) yrs, education 8 (2.8)
yrs and duration employed 20 (5.3) yrs. Five
neuropsychological tests commonly associated
with Pb exposure were examined for a
differential association with blood Pb,
IBL,TWA and bone Pb.
Of the 80 current smelter workers described
above 78 completed a simple visual reaction
time (SRT) and had mean yrs age 44 (8.2) yrs,
education 8 (7.2) yrs and duration employed
20 (5.6) yrs.
Mean (SD) blood Pb 26
(7.07) µg/dL
Mean (SD) TWA 42
(8.4) µg/dL
Mean (SD) IBL 903
(305.9) µg·yr/dL,
Mean (SD) tibial bone Pb
41 µg/g bone mineral
Mean (SD) blood Pb, 26
(7.2) µg/dL
Mean (SD) blood Pb from
bone 7 (4.2) µg/dL
Mean (SD) blood Pb from
environment 19
(7.0) µg/dL
Mean (SD) bone Pb 40
(25.2) µg/g bone mineral
Relationship of 5 neuropsychological tests with 4 measures of Pb dose
after adjusting for age age 2 and education, education 2 found RAVLT trial
V and Verbal Paired Associates were associated with blood Pb
(♠R 2 = 6.2%, p = 0.02; ♠R 2 = 5.5%, p = 0.07) and TWA (♠R 2 = 3.2%,
p = 0.09; ♠R 2 = 13.9%; P = 0.00) while Digit Symbol and Grooved
Pegboard were associated with TWA (♠R 2 = 6.1%, p = 0.00; ♠R 2 = 5.5%,
p = 0.02) and IBL (♠R 2 = 4.8%, p = 0.01; ♠R 2 = 5.7%, p = 0.02). Only
grooved pegboard was associated with bone Pb (♠R 2 = 4.2%, p = 0.05).
Block design was not associated with any measures of Pb dose. Age was
an effect modifier with grooved pegboard. There was enhanced slowing in
older workers when compared to younger workers with the identical IBL.
SRT consisted of 44 responses to a visual stimulus at interstimulus
intervals (ISI) varying between 1 through 10 seconds with a mean SRT
(median) of 262 (179 to 387) ms. Blood Pb and median SRT had a
curvilinear relationship R 2 = Pb + Pb 2 , 13.7%, p < 0.01) after adjusting for
age and education with slowing of SRT beginning at a blood Pb of
~30 µg/dL. No relationship existed between bone Pb and SRT. There was
a stronger association between Pb and Pb 2 and SRT for the longer ISIs of 6
to 10 seconds (R 2 = 13.9%, p < 0.01), as age was significantly related to
the shorter ISI = s but not the longer ones. In this population the
contribution of bone Pb to blood Pb had been previously where estimated
where for a bone Pb level of 100 µg Pb/g bone mineral, 17 µg Pb/dL of the
blood Pb was derived from internal bone stores with the remainder from
the environment. Blood Pb was fractionated to that from bone (blood Pbbn)
vs. blood Pb from the environment (blood Pb-en). Regression analysis
to examine the relationship of blood Pb-bn and blood Pb-en and SRT after
adjusting for the covariates found significant contribution to the variance
of SRT only for blood Pb-en (R 2 for blood Pb-en + blood Pb-en 2 = 14.4%,
p < 0.01). The absence of a contribution by age and more stable responses
with ISIs of 6 to 10 sec supports using this component of SRT.