Association of prenatal exposure to an environmental contaminant with intellectual function in childhood.

Polychlorinated biphenyls are a family of synthetic hydrocarbon compounds that were used historically for a broad range of industrial purposes. Although banned in the 1970s, they continue to be ubiquitous in landfills, sediments, and wildlife. Prenatal polychlorinated biphenyl exposure was evaluated in a sample of children born to women who had eaten relatively large quantities of polychlorinated biphenyl-contaminated Lake Michigan fish. This exposure was found to be associated with poorer intellectual function after controlling statistically for a broad range of potential confounding variables. Deficits included poorer recognition memory in infancy, lower scores on a preschool IQ test, and poorer verbal IQ and reading comprehension at 11 years of age. Although breast-fed children were exposed postnatally to elevated levels of polychlorinated biphenyls from maternal milk, the adverse effects associated with prenatal exposure were markedly stronger in the children who were not breast-fed. It is not clear whether the adverse effects were attenuated in the breast-fed children due to certain nutrients in the breast milk or due to better quality of intellectual stimulation provided by the breast-feeding mothers. Virtually no adverse effects were found in relation to postnatal exposure to polychlorinated biphenyls from breast-feeding, indicating that the fetus is particularly vulnerable to this exposure.