EVIDENCE FOR PCBS AS NEURODEVELOPMENTAL TOXICANTS IN HUMANS

Neurobehavioral effects of prenatal exposure to polychlorinated biphen yls (PCBs) have been investigated most extensively in two prospective longitudinal studies-one in North Carolina, the other in Michigan. Bas ed on the Webb-McCall methodology available when these studies were in itiated, a majority of the cord serum PCB concentrations in both cohor ts were below laboratory detection limits. Prenatal exposure was, ther efore, assessed in North Carolina in terms of maternal body burden and , in a recent Ii-year follow-up in Michigan, by averaging detectable P CB values from cord and maternal serum and maternal milk samples. The new composite prenatal exposure measure used in Michigan at 11 years w as more valid in relation to maternal contaminated fish consumption an d more sensitive in detecting 4-year cognitive deficits than the cord serum measure used in earlier phases of the study. During infancy, the North Carolina study found poorer gross motor function in relation to prenatal PCB exposure; the Michigan study found poorer infant visual recognition memory, an effect confirmed in a sample of Taiwanese infan ts exposed to PCBs and polychlorinated dibenzofurans (PCDFs) due to ma ternal ingestion of highly contaminated rice oil. Cognitive deficits f ound at 4 years in Michigan were not seen in North Carolina, possibly due to a different pattern of exposure or a different congener mix. An examination of the incidence of functionally-significant impairment ( defined as > 1 SD below the sample mean) showed that the more highly e xposed Michigan children were twice as likely to perform poorly than o thers in the sample and that there are marked individual differences i n vulnerability to this exposure. Thus, a small reduction in a mean IQ score may reflect little effect on a majority of the sample, accompan ied by a substantial deficit in a small number of more vulnerable chil dren. (C) 1997 inter Press, Inc.