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

AX6-7
Table AX6-2.1 (cont’d). Prospective Longitudinal Cohort Studies of Neurocognitive Ability in Children
Reference, Study
Location, and Period Study Description Pb Measurement Findings, Interpretation
Latin America (cont’d)
Téllez-Rojo et al.
(2006)
Mexico
Australia
Baghurst et al. (1992);
McMichael et al.
(1994); Tong et al.
(1996)
Australia
294 one and two yr-olds residing in Mexico City
followed since birth. The Bayley Scales of Infant
Development-II (MDI and PDI) were used to index
developmental status. There was extensive
assessment of medical and sociodemographic
covariates.
400-500 subjects residing in and near Port Pirie,
Australia and followed since birth were re-evaluated
at 7 to 8 and 11-13 yrs of age. WISCR was used to
index intellectual status at both ages. Extensive
assessment of medical and sociodemographic
covariates.
Umbilical cord blood Pb and
postnatal blood Pb at 12 and
24 mos
Umbilical cord blood Pb 4.8
(SD 3.0) µg/dL
Blood Pb at 1 yr 4.27 (SD
2.1) µg/dL
Blood Pb at 2 yrs 4.3 (SD
2.2) µg/dL
Maternal prenatal, umbilical
cord and serial postnatal blood
Pb
Antenatal avg blood Pb
10.1 (SD 3.9) µg/dL
Umbilical cord blood Pb
9.4 (SD 3.9) µg/dL
Blood Pb at 2 yrs
geometric mean 21.3
(SD 1.2) µg/dL
Deciduous central incisor
whole tooth Pb
Tooth Pb geometric 8.8
(SD 1.9) µg/g
Blood Pb at 12 mos was not associated with MDI at either
age. Blood Pb at 24 mos was significantly associated with
24 mo MDI. An increase of one logarithmic unit in 24 mo
blood Pb level was associated with a reduction of ~5 points
in MDI. Findings for PDI were similar. In comparison to
a supplemental subsample of 90 subjects with blood Pb
levels >10 µg/dL, the coefficient for blood Pb was
significantly larger for infants never exceeding that level
of internal dose. A steeper inverse slope was observed
over the blood Pb range up to 5 µg/dL (!1.71 points per
1 µg/dL increase in blood Pb, p = 0.01) compared to the
range between 5 and 10 µg/dL (!0.94 points, p = 0.12);
however, these slopes were not significantly different
(p = 0.34). In conclusion, a major finding of this
prospective study was that a significant inverse
relationship between blood Pb concentration and
neurodevelopment was observed among children whose
blood Pb levels did not exceed 10 µg/dL at any age.
Significant decrements in covariate-adjusted full scale IQ
were observed in relationship to postnatal blood Pb levels
at both ages. At 7 to 8 yrs of age a loss of 5.3 points was
associated with an increase in blood Pb from 10 to
30 µg/dL. At 11-13 yrs, mean full scale IQ declined by 3.0
points for an increase in lifetime avg blood Pb
concentrations from 10 to 20 µg/dL. Pb levels in central
upper incisors were also associated with lower 7-8 yr IQ
following covariate adjustment. Adjusted estimated
decline in IQ across the range of tooth Pb from 3 to
22 ppm was 5.1 points.