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

AX6-12
Table AX6-2.3 (cont’d). Cross-Sectional Studies of Neurocognitive Ability in Children
Reference, Study
Location, and Period Study Description Pb Measurement Findings, Interpretation
Latin America
Kordas et al. (2004,
2006)
Mexico
Counter et al. (1998)
Ecuador
Asia
Rabinowitz et al.
(1991)
Taiwan
Bellinger et al. (2005)
India
602 1st grade children in public schools in a highly
industrialized area of northern Mexico. Premise of
study was that effects of Pb could be explained by
correlated nutritional factors such as iron status,
anemia, and growth. Peabody Picture Vocabulary
Test-Revised (PPVT-R), Cognitive Abilities Test
(CAT), and an abbreviated form of the WISC-R were
administered to assess intellectual status. Medical and
sociodemographic covariates were assessed.
77 chronically Pb-exposed children living in
Ecuadorian villages where Pb is used extensively in
commercial ceramics production. Ravens Colored
Progressive Matrices (RCPM) used to index
intellectual status. Only half of the sample was
assessed. No assessment of medical or
sociodemographic covariates.
443 children in grades one to three in Taipei City and
three schools near Pb smelters. Ravens Colored
Progressive Matrices (RCPM) used to index
intellectual status. Medical and sociodemographic
covariate factors were assessed.
74 four to fourteen yr-old children residing in Chennai,
India were enrolled in the study, 31 of which were
assessed with the Binet-Kamath Intelligence test. Data
were collected on sociodemographic features of
subjects’ families.
Blood Pb at time of testing
Blood Pb 11.5
(SD 6.1) µg/dL
Blood Pb at time of testing
Blood Pb 47.4 (SD 22)
µg/dL
Dentin tooth Pb
Taipei City 4.3 (SD 3.7)
µg/g
Smelter areas 6.3 (SD 3.3)
µg/g
Blood Pb at time of testing
Blood Pb 11.1 (SD 5.6)
µg/dL
Following covariate adjustment blood Pb levels were
significantly associated with poorer performance on the
PPVT-R, WISC-R Coding, and Number and Letter
Sequencing, a Math Achievement Test, and the Sternberg
Memory Test. Authors concluded that Pb’s association
with iron deficiency anemia or growth retardation could
not explain relationship between Pb and cognitive
performance. Non-linear analyses of selected
neurocognitive outcomes revealed that dose-response
curves were steeper at lower than at higher blood Pb
levels. Moreover, the slopes appeared negative at blood
Pb levels below 10 µg/dL, above which they tend to
plateau. Effects of Pb on neurocognitive attainment
appeared to be greatest among the least advantaged
members of the cohort.
Simple regression analysis revealed a correlation between
blood Pb and RCPM of only borderline significance.
Results difficult to interpret because there was no attempt
to age-adjust. When analysis restricted to children 9 to
11 yrs of age, a highly significant negative correlation was
obtained. Study has little relevance to the question of Pb
hazards in the U.S. because of unusually high levels of
exposure.
Scores on the RCPM were negatively correlated with tooth
Pb concentrations. In multivariate analyses, parental
education was the most important predictor of RCPM
scores, but tooth Pb concentrations still significantly
predicted lower scores in females residing in low-income
families.
Covariate-adjusted blood Pb coefficient was negative but
nonsignificant, perhaps due to small sample size and
highly variable performance of subjects with the least
elevated blood Pb concentrations.