Polychlorinated biphenyls (PCBs), once widely used in insulation and other products, were banned in 1977. However, the chemicals continue to contaminate water supplies, and a new German study adds to evidence that this contamination can affect young children's brain development.
Gerhard Winneke and colleagues followed 171 mothers and their healthy babies, testing the babies at seven, 18, 30, and 42 months of age. The researchers measured the babies' exposure to PCBs by analyzing samples of umbilical cord blood and breast milk, and by testing their blood levels of PCBs at 42 months. They controlled for many factors including parent education and IQ, maternal smoking during pregnancy, and maternal body mass index.
Winneke et al. report that babies whose mothers had high concentrations of PCBs in their breast milk had significantly lower mental and motor development scores at 30 months and beyond. "Everybody thought that, if anything, PCBs had prenatal effect, but we have shown that they can also produce post-natal effects," Winneke told BBC News. "Perhaps this is not surprising as the amount of PCB to which a newborn is exposed is much higher than that which acts on a fetus."
The researchers note that PCB concentrations in breast milk are decreasing over time. "However," they note, "the human infant by way of breastfeeding is exposed to PCB doses which, on a bodyweight basis, exceed those of adults by at least two orders of magnitude."
Winneke et al. speculate that PCBs may interfere with prenatal and post-natal development by reducing thyroid function. They note that hypothyroidism is linked to mental retardation, and that studies show that PCBs interfere with thyroid hormone function both by competing with these hormones for uptake by the blood and by increasing metabolism of the hormones by the liver.
In earlier research (see related article, Crime Times, 1996, Vol. 2, No. 4, Page 5), Joseph Jacobson and Sandra Jacobson studied more than 200 11-year-old children whose PCB exposure had been determined by measuring PCB levels in umbilical cord serum and maternal serum and milk at the time of delivery. The researchers found that prenatal PCB exposure was associated with lower overall and verbal IQ scores, even when the researchers controlled for socioeconomic factors. In that study, children with the highest PCB exposure had an average 6.2-point IQ deficit, similar to the effects reported for low- level lead exposure.
"Environmental exposure to polychlorinated biphenyls and quality of the home environment: effects on psychodevelopment in early childhood," Jens Walkowiak, Jörg- A Wiener, Annemarie Fastabend, Birger Heinzow, Ursula Krämer, Eberhard Schmidt, Hans-J Steingürber, Sabine Wundram, and Gerhard Winneke, The Lancet, Vol. 358, No. 9293, November 10, 2001. Address: Gerhard Winneke, Medical Institute of Environmental Hygiene, Heinrich-Heine-Universität Düsseldorf, Auf'm Hennekamp 50, D-40225 Düsseldorf, Germany, email@example.com.