The relationship between prenatal PCB exposure and intelligence (IQ) in 9-year-old children

Abstract

Background: Several epidemiologic studies have demonstrated relationships between prenatal exposure to polychlorinated biphenyls (PCBs) and modest cognitive impairments in infancy and early childhood. However, few studies have followed cohorts of exposed children long enough to examine the possible impact of prenatal PCB exposure on psychometric intelligence in later childhood. Of the few studies that have done so, one in the Great Lakes region of the United States reported impaired IQ in children prenatally exposed to PCBs, whereas another found no association.

Objectives: This study was designed to determine whether environmental exposure to PCBs predicts lower IQ in school-age children in the Great Lakes region of the northeastern United States.

Methods: We measured prenatal exposure to PCBs and IQ at 9 years of age in 156 subjects from Oswego, New York. We also measured > 50 potential predictors of intelligence in children, including repeated measures of the home environment [Home Observation for Measurement of the Environment (HOME)], socioeconomic status (SES), parental IQ, alcohol/cigarette use, neonatal risk factors, and nutrition.

Results: For each 1-ng/g (wet weight) increase in PCBs in placental tissue, Full Scale IQ dropped by three points (p = 0.02), and Verbal IQ dropped by four points (p = 0.003). The median PCB level was 1.50 ng/g, with a lower quartile of 1.00 ng/g and an upper quartile of 2.06 ng/g. Moreover, this association was significant after controlling for many potential confounders, including prenatal exposure to methylmercury, dichlorodiphenyldichloroethylene, hexachlorobenzene, and lead.

Conclusions: These results, in combination with similar results obtained from a similar study in the Great Lakes conducted 10 years earlier, indicate that prenatal PCB exposure in the Great Lakes region is associated with lower IQ in children.

Keywords: IQ; Oswego; PCBs; WISC-III; Wechsler; children; cognitive; intelligence; mercury; polychlorinated biphenyls.

Figure 1

Dose–response functions for PCB–IQ effect expressed in true exposure intervals: Full Scale IQ (A), Verbal IQ (B), Freedom from Distractibility (C), and Verbal Comprehension Index (D). Adjusted means ± SE are plotted against the median PCB concentration within each interval, nondetectable to 0.99, 1.00–1.49, 1.50–1.99, 2.00–2.49, and ≥ 2.50 ppb. Linear F-tests (Braver and Sheets 1993) showed significant linear dose–response relationships between PCB concentrations and Full Scale IQ, Verbal IQ, and Freedom from Distractibility (all p < 0.05).

Figure 2

Dose–response functions for PCB–IQ effect expressed ordinally, in exposure quintiles (31–32 subjects per group). Linear F-tests (Braver and Sheets 1993) showed significant linear dose–response relationships between PCB concentrations and Full Scale IQ (A), Verbal IQ (B), and Freedom from Distractibility (C) (all p < 0.05). (D) Verbal Comprehension Index.