Banned pollutant's legacy: Lower IQs

One by-product of the United States' industrial culture is the ubiquitous contamination of the environment--and our bodies--with polychlorinated biphenyls (PCBs). Exposure to these persistent, now-banned chemicals begins before birth, as a woman's blood delivers to the fetus some of the PCBs stored in her fat. This legacy, even when not unusually large, can impair brain development.

 By fifth grade, a new study finds, its effects can show up as diminished IQs.

 Joseph L. Jacobson and Sandra W. Jacobson of Wayne State University in Detroit have followed several hundred Michigan children born in the early 1980s. They stratified the children into exposure groups, using PCBs in the mothers' breast milk as a gauge of how much of the pollutant the mothers carried.

 Once used primarily as insulators in electrical transformers, PCBs now taint most soils and water. Much of the pollutant in the most heavily exposed Michigan children traced to their mothers' having eaten large quantities of Great Lakes fish--notorious for their PCB contamination.

 Earlier studies had shown that children with the highest prenatal PCB exposures exhibited developmental delays, starting in infancy. Though breast-feeding sometimes added substantially to an infant's store of PCBs, only prenatal exposures appeared to affect a young child's development--especially his or her short-term memory.

 The Jacobsons now describe IQ and achievement test results for 212 Michigan children. While there was no "gross intellectual impairment," they report in the Sept. 12 New England Journal of Medicine, the average IQ was 6.2 points lower in the 30 11-year-olds who had the highest prenatal PCB exposures (based on at least 1.25 micrograms per gram of fat in their mothers' breast milk) than in children with smaller exposures.

 PCBs appear to exert their greatest effect on short-term memory, planning skills, and distractibility, says Joseph Jacobson. Although affected kids "are still in the normal range," he notes, high exposures "are just pulling a lot of them into the bottom of the normal range." In word comprehension, for example, the highly exposed children lagged 6 months behind the other group.

 Most of the children are middle-class, says Joseph Jacobson. "I thought that once they reached a structured school environment, whatever minor [PCB-induced] handicaps they had would be overcome. So I was quite surprised to find that, if anything, the effects were stronger and clearer at age 11 than they had been at age 4."

 While unexpected, the findings are "plausible," judging by recent data from children born to victims of PCB poisoning, observes Walter J. Rogan of the National Institute of Environmental Health Sciences in Research Triangle Park, N.C. He notes that even the highest exposures in the Michigan children could occur anywhere in the United States. "The notion of a background substance that everybody's exposed to doing that kind of detectable damage is disturbing."

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