Not So Hot for Tots

PCBs

The letters PCB stand for polychlorinated biphenyl, a group of now-banned but still ubiquitous environmental contaminants that often give fish a bad name. But perhaps they ought to stand for Poor Cognitive Behavior. A team of researchers has found that children exposed prenatally to the substances have cognitive deficits that can adversely affect their learning abilities.

Specifically, reports psychologist Joseph L. Jacobson, Ph.D., and colleagues of Wayne State University in Detroit, it takes such children a longer than normal time to process information, limiting general intelligence. PCBs seem to target short-term memory processes and visual discrimination. Both are essential for mastering reading and arithmetic.

For infants, PCB exposure occurs throughout gestation via the umbilical cord, which transports nutrients from mother to growing baby. Acquired by the mother primarily through consumption of contaminated foods, such as freshwater fish in some regions, PCBs are stored in body-fat deposits until mobilized by demands such as development of a fetus.

Jacobson and company tested the cognitive functions of 224 four-year-olds from western Michigan. And they tested the PCB levels of their mothers, as measured in samples of the umbilicus at birth. Some of the women had consumed large amounts of contaminated Lake Michigan fish during their pregnancies; others had low PCB levels.

In tests of short-term memory and visual acuity, kids with lower PCB exposure as measured at the time of birth performed significantly better than those with high exposure. The higher the PCB level, the more errors on the memory test and the longer it took them to reach correct solutions of visual discrimination problems. In a test of attention span, there were no noticeable differences between the two groups.

Following birth, many infants get an even larger wallop of PCBs through breast milk. However, there was no consistent pattern of deficits among infants who were breast-fed, and cognitive deficits correlated only with PCB exposure in utero.

In fact, as a group, those breast-fed as babies outperformed their bottle-fed brethren on tests of sustained attention. The researchers believe breast-fed children become quick learners because their mothers are usually more highly educated and spend more time teaching them. They may also be spared PCB effects after birth because the blood-brain barrier has matured enough to protect the brain.

Pregnant women have some control over the amount of PCBs they take in; they can easily avoid eating fish from water known to be contaminated, such as the Great Lakes. Trouble is, many women just don't know when they're being exposed.

And it still isn't clear whether PCBs affect cognitive powers over the long haul. A follow-up study on 10-year-olds who were exposed in utero is now under way to determine whether PCBs still have an adverse affects their ability to learn later on in their lives.