Authors
Daniels JL, Longnecker MP, Klebanoff MA, Gray KA, Brock JW, Zhou H, Chen A, Needham LL

Title
Prenatal Exposure to Low-Level Polychlorinated Biphenyls in Relation to Mental and Motor Development at 8 Months

Source
American Journal of Epidemiology: 157(6):485-492, 2003.

Summary
Polychlorinated biphenyls (PCBs) are a mixture of toxic chemicals. Some congeners of this mixture are highly persistent both in the environment and in humans. Although PCBs have not been used commercially since about 1977, they are still detected in human blood and tissues. A number of epidemiological studies have shown predictive relationships between prenatal exposure to PCBs and subtle deficits in neurodevelopment in infancy. However, since not all studies have demonstrated these relationships, debate regarding the role of prenatal PCB exposure in cognitive and motor development continues. The current study was designed to provide additional data to assist in resolving this question.

Approximately 42,000 pregnant women and 55,000 children from 12 centers across the United States were enrolled in the Collaborative Perinatal Project between 1956-1966. Most of the mothers were between 21-30 years of age, were either black or white, were nonsmokers during pregnancy, and did not breastfeed their infants. The mental and psychomotor development of 1,207 live born children, who had a maternal serum sample available, was assessed at 8 months of age using the Bayley Scales of Infant Development (BSID). Results were converted to age-standardized scores and to the related mental development index (MDI) and psychomotor development index (PDI). Eleven PCB congeners (PCBs 28, 52, 74, 105, 118, 138, 153, 170, 180, 194, 203) were measured in maternal blood taken during third trimester of pregnancy using gas chromatography. Total PCB exposure, which represented the sum of the 11 measured congeners, was expressed as µg/liter (µg /L) of serum and categorized by concentration intervals of 1.25µg /L. Serum cholesterol and triglyceride levels, which affect serum PCB levels, were also analyzed using standard enzymatic assays. Other covariates evaluated included: study center, maternal race, education, socioeconomic index, intelligence quotient, marital status, prenatal smoking, pregnancy body mass index, third trimester serum triglyceride, total cholesterol, dichlorodiphenyldichloroethylene (DDE) levels, child's birth order, gestational age, and whether the child was ever breastfed.

Both linear and multilevel (random-effects) regression models were used to estimate the association between maternal PCB levels and the child's standardized MDI and PDI and to assess heterogeneity in the PCB-neurodevelopment relation across study centers.

Maternal serum PCB levels were detectable in 99.9 percent of samples. Ninety-five percent of maternal total PCB concentrations were below 6.25µg/L, with a range of 1.24 µg /L to 16.3µg/L. Overall, this study did not demonstrate any relation between maternal prenatal PCB level and child's mental or motor development at 8 months of age. However, statistically significant heterogeneity existed among centers for the association between total PCBs and PDI (p<0.05). Elevated levels of PCBs were associated with a decreased PDI in New Orleans and Baltimore but an increased PDI in Richmond and Providence.

The authors analyzed several possible factors which could have contributed to the differences in results across study centers including variations in the testing protocol, timing of children examinations, assessment and analytical methods, exposure variability, nutritional factors and the presence of additional environmental toxicants which may modify the effect of PCBs. They believed the existing variation in results was likely not attributable to differences in the measurement of neurodevelopment or maternal PCB exposure as these procedures and the analytical methods were standardized across centers and conducted by trained personnel.

The present study is important because it represents a combined analysis of a large multicenter study that evaluated the relation between low-level prenatal maternal PCB exposure and children's mental and psychomotor development. Additional maternal exposures, such as DDE, which may confound the PCB effect, were also taken into account. Unfortunately, the heterogenicity in results across the centers within this study and among other distinct studies, and the relation between low-level prenatal PCB exposure and the infant's neurodevelopment remains unexplained. Further research would help to further assess and clarify the impact that PCBs and other organochlorine compounds may exert on the neurodevelopment of young children.