Heavy prenatal exposure to PCBs linked
to lower IQ scores

A new study strongly links heavy prenatal exposure to PCBs (polychlorinated biphenyls) to lower IQs and greater distractibility in young children. Both reduced IQ and high distractibility are risk factors for serious behavioral and learning problems.

Prior to 1977, when they were banned, PCBs were used extensively for lubricating and cooling electrical equipment. PCBs break down slowly and persist in the environment, with fish from heavily contaminated lakes being a primary source of exposure.

The new study, by Paul Stewart and colleagues, involved 156 nine-year-old children in the New York region of Oswego, located in the basin of Lake Ontario. The researchers measured PCB levels in placental tissue and cord blood samples collected at the time of the children’s birth and evaluated the children’s full-scale, verbal, and performance IQs as well as their levels of distractibility. High distractibility levels can be a warning sign of attention deficit hyperactivity disorder.

Children with higher placental PCB levels had lower scores on full-scale and verbal IQ tests and had poorer distractibility scores than mildly-exposed children. The findings remained significant when the researchers controlled for a wide range of demographic and biological factors. (One of these factors, mercury exposure, also contributed to higher distractibility.) Cord blood PCB levels were not related to IQ scores

Their analysis, the researchers say, reveals a three-point drop in full-scale IQ for every 1 ng/g increase in PCBs in placental tissue. They note, “Within the exposure ranges of this study, this translated roughly into a six- to seven-point decline in full-scale IQ from the least exposed group (average of 0.75 ng/g) to the most highly exposed group (average of 3.15 ng/g PCB).” Verbal IQ dropped four points for each 1ng/g increase in PCBs.

The study’s findings add support for a 1996 study by Joseph Jacobson and Sandra Jacobson (see related article, Crime Times, 1996, Vol. 2, No. 4, Page 4) which found lower full-scale and verbal IQs in PCB-exposed children of mothers in the Lake Michigan area. However, they are inconsistent with a 2005 study by Kimberly Gray et al. in 2005, which evaluated PCB exposure in the general population and found no link between PCB exposure and IQ.

Commenting on the conflicting findings, reviewers Martha Susiarjo and Wendy Hessler note, “Stewart et al.’s findings, which support the previous Great Lakes study [by Jacobson and Jacobson], but at PCB levels almost half the levels as those reported then, suggest that geography plays a role in how exposures affect mental development. More highly chlorinated types and mixes of PCBs pollute this region than other areas…. Thus, children from this region may be exposed to a more harmful mix and possibly higher ‘pulse’ levels during the time when their mothers ate fish during pregnancy. These factors could increase prenatal exposure in this regional population when compared to children who live in other parts of the country.”

“The relationship between prenatal PCB exposure and intelligence (IQ) in 9-year-old children,” Paul W. Stewart, Edward Lonky, Jacqueline Reihman, James Pagano, Brooks B. Gump, and Thomas Darvill, Environmental Health Perspectives, Vol. 116, No. 10, October 2008, 1416-22. Address: Paul Stewart, 304 Mahar Hall, State University of New York at Oswego, Oswego, NY 13126, pstewar1@oswego.edu.