The Effects of Prenatal Exposure to PCBs and MeHg on Memory and Learning in School-Aged Children

Abstract

ISEE-0464 Background and Objective: Polychlorinated biphenyls (PCBs) and methylmercury (MeHg) are environmentally persistent neurotoxicants with adverse effects on neurodevelopment at high exposure levels. However, findings at lower level exposures are inconsistent. Methods: 355 children, born between 1993–1998 to mothers residing near a PCB-contaminated harbor in New Bedford, Massachusetts, and participating in a longitudinal study of child development, were studied. Cord serum PCB and maternal peripartum hair mercury (a MeHg proxy) levels were measured to estimate exposure. Memory and learning abilities were assessed at age 8 years (range: 7–10 years) using the Wide Range Assessment of Memory and Learning (WRAML), age-standardized to a mean of 100 and standard deviation of 15. Associations with each WRAML index–Visual Memory, Verbal Memory, and Learning–were examined with multivariable linear regression, controlling for potential confounders and predictors of the outcome. Results: While cord serum PCB levels were low and comparable to population-based background levels (mean: 0.3 ng/g serum; range: 0.01, 4.4), hair Hg levels were slightly higher than U.S. population norms (mean: 0.6 ppm; range: 0.1, 5.1). There was no significant association of PCBs with WRAML indices. However, in multivariable models, each ppm increase in hair Hg was associated with −3.3 (95% CI: −5.8, −0.7) and −2.5 (95% CI: −5.2, 0.1) respective decrements in Visual Memory and Learning indices. Stratified analysis suggested an adverse hair Hg effect on Verbal Memory but only among children with higher PCB levels ( > 0.3 ng/g serum, the upper tertile of the exposure distribution) with a −3.1 (95% CI: −5.9, −0.3) decline in Verbal Memory per ppm hair Hg in this group. Conclusions: This study supports a relation of modest prenatal MeHg exposure with subsequent decrements in memory and learning at school age, and suggests potential enhancement of this association with modest elevations in prenatal PCB exposure.