Prenatal PCB and PBDE Exposure and Thyroid Hormones

Abstract

ISEE-663 Objective: Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are organohalogen chemicals that have been applied commercially to insulate and reduce product flammability. Studies examining the health effects of PCBs and PBDEs have focused on their propensity to disrupt the endocrine system, in part because of their structural and functional similarity to the thyroid hormone, thyroxine (T4). This study was designed to investigate the relationship between prenatal exposure to PCBs and PBDEs and thyroid hormone levels in newborns. Materials and Methods: Prenatal exposure to PCBs and PBDEs was estimated from levels measured in umbilical cord blood collected from women delivering at the Johns Hopkins Hospital. Thyrotropin (TSH) and total and free T4 were measured in cord serum and total T4 was also assessed in newborn blood spots. Demographic and biological measures, including medical history, were abstracted from maternal medical records. Results: After adjustment for relevant confounders, we found that none of the compounds we studied showed a positive association with higher TSH levels, as hypothesized. There appeared to be no observable relationship between free T4 and PCB and PBDE levels in the overall population. Higher levels of all PCBs, BDE-100, and BDE-153 tended to be associated with lower total T4 levels in cord blood; for total T4 in blood spots; however, the trend between PCBs and T4 was positive. We found evidence of effect modification, such that associations between PCBs and PBDEs and cord total T4 and associations between PCBs and free T4 were stronger when restricted to spontaneous unassisted vaginal deliveries. Conclusions: Although the results observed are not consistent with reported relationships between PCBs, PBDEs, and thyroid hormones in animal models, there is evidence for thyroid perturbations involving a reduction in T4 without a commensurate increase in TSH production associated primarily with PCB but also with selective PBDE congeners.