PCBs adversely affect mental development in infants

Prenatal and postnatal exposure to polychlorinated biphenyls (PCBs) both have negative effects on the mental development of infants, becoming significant from 30 months onwards, according to new research published in The Lancet.

Previously, it was thought that PCBs only affected early childhood development through prenatal exposure – due to the greater sensitivity to damage of the foetus, and not through postnatal exposure, even if relatively large quantities were transferred to infants through breast milk. The new study shows that both prenatal and neonatal PCB exposure in breast milk has a significant negative association with mental and motor development between the ages of seven and 42 months. Although prenatal exposure has the greatest effect on later development, it is likely that postnatal exposure through breastfeeding has an additional effect. The report notes that by way of breastfeeding, PCB exposure in infants, on a bodyweight basis, exceeds that of adults by at least two orders of magnitude.

Past research programmes include one carried out in Michigan, where children whose mothers had consumed various quantities of fish were studied. The research revealed a memory deficit in infants at seven months old and at four years old, associated with prenatal PCB concentrations. A follow-up study of 11 year olds revealed that there were still negative associations related to the PCB concentrations.

This latest research shows that after a child is 30 months old, its home environment has a positive effect on its development, and the quality of parental stimulation and socioenvironmental factors become more strongly related to development than are prenatal exposure to small quantities of PCBs. The research suggests that a favourable home environment might even counteract the adverse developmental effects of PCBs.

It is still unclear as to how PCBs cause these negative effects, say the researchers.

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