Exposure before birth to relatively small amounts of PCBs, a kind of industrial pollutant, can result in long-lasting deficits in a child's intellectual development, a new study has shown.
The researchers found higher than expected rates of "low normal" IQ scores, poor reading comprehension, memory problems and difficulty paying attention in 11-year-old children who had been prenatally exposed to polychlorinated biphenyls, or PCBs, in concentrations only slightly higher than those found in the general population.
Children with the highest levels of exposure were three times as likely to have low normal IQ scores and twice as likely to be behind in reading comprehension as the group as a whole.
The researchers, Dr. Joseph L. Jacobson and his wife, Dr. Sandra W. Jacobson, psychologists at Wayne State University in Detroit, concluded that the fetal brain damage caused by environmental exposure to PCBs was comparable to the damage found in children exposed to low levels of lead.
But exposure to these chemicals after birth, through breast milk, did not seem to cause any further harm to the children's mental abilities, the study showed.
In their report, published in today's issue of the New England Journal of Medicine, the researchers concluded that "the developing fetal brain is particularly sensitive to these compounds."
A pregnant woman with PCBs in her body can transfer the chemicals through the umbilical cord to her fetus. Even if she eats no contaminated foods during her pregnancy, PCBs from foods eaten before she becomes pregnant will remain in her body for years and can be transferred to her unborn children, Joseph Jacobson said in an interview.
The Jacobsons had previously linked prenatal PCB exposure to poor short-term memory in infants and young children. The new findings, in older children, are consistent with reports of reduced IQ scores among more heavily contaminated children in Taiwan whose mothers, while pregnant with them, ingested rice oil accidentally laced with PCBs and other chemicals.
Dr. Walter Rogan, an epidemiologist with the National Institute for Environmental Health Sciences at Research Triangle Park, N.C., said the new study had been very carefully done and had used highly refined measures to detect the effects of the PCBs.
"There's no question that PCBs are deleterious to the developing mammalian nervous system; the only question is dose," Rogan said in an interview.
PCBs were once widely used in the manufacture of electrical equipment and in paper recycling. Although their production and their use in newly manufactured equipment have been banned in hTC the United States and most other Western nations since the 1970s, and although environmental levels have since declined, they still contaminate the sediments of many lakes and rivers, including the Hudson, and remain prominent in diminishing pollutants in some freshwater fish.
Once ingested, they are stored in body fat, and they dissipate only slowly after ingestion ceases.
Pub Date: 9/12/96