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

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AX6-11<br />

Table AX6-2.3. Cross-Sectional Studies <strong>of</strong> Neurocognitive Ability in Children<br />

Reference, Study<br />

Location, and Period Study Description Pb Measurement Findings, Interpretation<br />

United States<br />

Lanphear et al. (2000)<br />

U.S.<br />

Emory et al. (2003)<br />

U.S.<br />

Chiodo et al. (2004)<br />

U.S.<br />

Europe<br />

Walkowiak et al.<br />

(1998)<br />

Germany<br />

Prpic-Majic et al.<br />

(2000)<br />

Croatia<br />

4,853 U.S. children ages six to 16 yrs enrolled in<br />

NHANES-<strong>II</strong>I. Two subtests <strong>of</strong> the WISC-R (Block<br />

Design and Digit Span) used to assess intellectual<br />

status. Medical and sociodemographic covariates were<br />

assessed<br />

77 healthy, lower-risk African-American infants age 7<br />

mos. The Fagan Test <strong>of</strong> Infant Intelligence (FT<strong>II</strong>) was<br />

administered to assess intellectual status. Birth weight<br />

and gestational age examined as potential<br />

covariates/confounders.<br />

237 African-American inner-city children assessed at<br />

7.5 yrs <strong>of</strong> age. Cohort was derived from a larger study<br />

<strong>of</strong> the effects <strong>of</strong> prenatal alcohol exposure on child<br />

development. 83% <strong>of</strong> children in Pb study had little or<br />

no gestational exposure to alcohol. WISC-<strong>II</strong>I was<br />

administered to assess intellectual status. Medical and<br />

sociodemographic covariates were assessed.<br />

384 six-yr-old children in three German cities. Two<br />

subtests <strong>of</strong> the WISC (Vocabulary and Block Design)<br />

used to estimate IQ. Both subscales were combined to<br />

<strong>for</strong>m a “WISC Index.” Medical and sociodemographic<br />

covariate covariates were assessed.<br />

275 3rd and 4th grade students in Zagreb, Croatia.<br />

WISC-R was administered to assess intellectual status.<br />

Covariate factors limited to parents’ educational status<br />

and gender <strong>of</strong> child.<br />

Blood Pb at time <strong>of</strong> testing<br />

Geometric blood Pb 1.9<br />

(SE 0.1) µg/dL<br />

2.1% with blood Pb<br />

∃10 µg/dL<br />

Maternal blood Pb<br />

Blood Pb 0.72 (SD 0.86)<br />

µg/dL<br />

Blood Pb at time <strong>of</strong> testing<br />

Blood Pb 5.4 (SD 3.3)<br />

µg/dL<br />

Blood Pb at time <strong>of</strong> testing<br />

Blood Pb 4.2 µg/dL<br />

95th percentile 8.9 µg/dL<br />

Blood Pb at time <strong>of</strong> testing<br />

Blood Pb 7.1 (SD 1.8)<br />

µg/dL<br />

Multivariate analyses revealed a significant association<br />

between blood Pb levels and both WISC-R subtests.<br />

Associations remained statistically significant when<br />

analyses were restricted to children with blood Pb levels<br />

below 10 µg/dL. Authors caution that lack <strong>of</strong> control <strong>for</strong><br />

parental intelligence and variables like the HOME scale<br />

should temper any conclusions regarding observed effects.<br />

Infants scoring in the upper 5th to 15th percentiles <strong>for</strong> the<br />

FT<strong>II</strong> had mother with significantly lower maternal blood<br />

Pb levels when compared to those scoring in the lower<br />

5th or 15th percentile. Findings <strong>of</strong> this study should be<br />

considered preliminary due to small sample size and lack<br />

<strong>of</strong> covariate assessment or control.<br />

Following covariate adjustment statistically significant<br />

relationships between blood Pb and full-scale, verbal and<br />

per<strong>for</strong>mance IQ were observed. Significant effects <strong>of</strong> Pb<br />

on full-scale and per<strong>for</strong>mance IQ was evident at blood Pb<br />

concentrations below 7.5 µg/dL.<br />

Following covariate-adjustment, WISC Vocabulary was<br />

significantly associated with blood Pb but combined WISC<br />

index was borderline. Authors conclude that findings<br />

roughly correspond with those <strong>of</strong> other studies that find<br />

effects below 10 µg/dL but caution that potentially<br />

important covariates such as HOME scores were not<br />

controlled.<br />

Following covariate adjustment, no statistically significant<br />

associations were observed <strong>for</strong> Pb or other indicators <strong>of</strong><br />

toxicity (ALAD, EP) on WISC-R. Authors argue that<br />

study had sufficient power and that the “no-effect”<br />

threshold <strong>for</strong> Pb must be in the upper part or above the<br />

study’s range <strong>of</strong> exposures.

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