By Janet Raloff
Men and woman who accumulated large amounts of polychlorinated biphenyls (PCBs), primarily through eating Great Lakes fish, exhibit subtle memory problems, according to a new study.
PCBs are oily fluids that have been used principally as insulation in electrical transformers. Because these toxic dioxinlike compounds break down slowly, they persist in the environment for decades and are now slated for a global phaseout (SN: 6/2/01, p. 343: Nations sign on to persistent-pollutants ban).
Studies have shown that children exposed to fairly small amounts of PCBs in the womb can develop learning problems and IQ deficits that persist at least into their preteen years (SN: 9/14/96, p. 165). However, far larger exposures after birth–from breast milk–had no discernable effect, notes Joseph L. Jacobson of Wayne State University in Detroit, a coauthor of those studies.
“So, if a baby isn’t vulnerable after birth, we wouldn’t have expected that an adult would be,” he says.
To verify that assumption, Susan L. Schantz of the University of Illinois in Urbana-Champaign and her colleagues compared mental tasks in adults who’d had relatively high or low exposures to PCBs.
The researchers measured blood concentrations of PCBs in 180 adults over age 50–79 of whom had eaten little or no Lake Michigan fish and 101 who for decades ate at least 24 pounds each year. Because top-predator fish can accumulate high concentrations of PCBs, people eating such fish can also build up high body burdens of the pollutants. In fact, each study participant’s PCB load roughly correlated with his or her history of fish consumption.
Some 40 percent of people with high PCB concentrations scored relatively poorly on memorization tests, while only 8 percent of people with low PCB loads did, Schantz’s group reports in the June Environmental Health Perspectives. These poor performers had trouble recalling grocery lists or details of a paragraph read to them 30 minutes earlier.
Ordinarily, people categorize related items to aid recall, Schantz says. For example, they mentally link all listed fruits and recall them as a group. Although people with low blood concentrations of PCBs did just that, those with the highest concentrations often didn’t. In other tests of abstract reasoning and visual attention, however, everyone performed comparably.
“These deficits on memory and verbal learning,” Schantz says, “are consistent with what had been seen in children [prenatally] exposed to PCBs.”
The findings may point to increasing neural vulnerability to toxicants with age. Through young adulthood, the brain has extra cells to back up small losses, explains Bernard Weiss of the University of Rochester (N.Y.) Medical Center. With age, the size of this reserve diminishes, he notes, increasing the chance that damage to remaining cells will cause neural problems.
Though states recommend that pregnant women and children avoid eating tainted fish, Weiss says that Schantz’s new data show “that we have to be just as sensitive to the vulnerability of the aging brain, like mine.”
