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

AX6-17
Table AX6-2.5. Effects of Lead on Specific Cognitive Abilities in Children — Attention/Executive Functions, Learning, and
Visual-spatial Skills
Reference, Study
Location, and Period Study Description Pb Measurement Findings, Interpretation
United States
Bellinger et al. (1994a)
U.S.
Stiles and Bellinger
(1993)
U.S.
Canfield et al. (2003b,
2004)
U.S.
Design: Prospective cohort. 79 subjects from the
original Chelsea and Somerville, MA Pb study were
re-evaluated at 19-20 yrs of age with the Mirsky
battery of attentional measures. Extensive measures
of medical and sociodemographic covariates.
Design: Prospective longitudinal. 148 subjects from
the Boston Pb Study were re-evaluated at 10 yrs of
age with an extensive neuropsychological battery.
Tests included the California Verbal Learning Test,
Wisconsin Card Sorting Test, Test of Visual-Motor
Integration, Rey-Osterieth Complex Figure, Story
Recall, Finger Tapping, and Grooved Pegboard.
Extensive measures of medical and
sociodemographic covariates.
Design: Prospective longitudinal. 170-174 children
from the Rochester Pb Study were administered a
number of learning and neuropsychological
functioning at 48, 54, and 66 mos of age. At 48 and
54 mos the Espy Shape School Task was
administered while at 66 mos the Working Memory
and Planning assessment protocols of the Cambridge
Neuropsychological Test Automated Battery
(CANTAB) was given. Extensive measures on
medical and sociodemographic covariates.
Tooth (dentin) Pb
Tooth Pb 13.7 (SD 11.2)
µg/g
KXRF Bone Pb
Tibial bone Pb
(range 10) µg/g
Patellar bone Pb
(range 15) µg/g
Cord and serial postnatal
blood Pb assessments
Cord blood Pb grouping 10 µg/dL
Blood Pb at 2 yrs 6.5
(SD 4.9) µg/dL
Serial postnatal blood Pb
Blood Pb at 2 yrs 9.7 µg/dL
Lifetime avg blood Pb 7.2
(range 0-20) µg/dL
Higher tooth Pb concentrations were significantly
associated with poorer scores on the Focus-Execute and
Shift factors of the Mirsky battery. Few significant
associations were observed between bone Pb levels and
performance. Authors conclude that early Pb exposure
may be associated with poorer performance on
executive/regulatory functions, which are thought to
depend on the frontal or prefrontal regions of the brain.
Authors point out that the number of significant
associations was about equal to those that would be
expected by chance. However, tasks that assess attentional
behaviors and executive functions tended to among those
for which Pb was a significant predictor of performance.
Following covariate adjustment, higher blood Pb
concentrations at two yr were significantly associated with
lower scores on Freedom from Distractibility factor of the
Wechsler scales, increase in percentage of perseverative
errors on the Wisconsin Card Sorting Test and the
California Verbal Learning Test.
Following covariate adjustment, blood Pb level at 48 mos
was negatively associated with children’s focused attention
while performing the Shape School Tasks, efficiency at
naming colors, and inhibition of automatic responding.
Children with higher blood Pb concentrations also
completed fewer phases of the Espy tasks and knew fewer
color and shape names. On the CANTAB battery, children
with higher lifetime avg blood Pb levels showed impaired
performance on spatial working memory, spatial memory
span, and cognitive flexibility and planning. Authors
conclude that the effects of pediatric Pb exposure are not
restricted to global measures of intellectual functioning and
executive processes may be at particular risk.