Chevrier, J; Eskenazi, B; Holland, N; Bradman, A; Barr, D
Objective: To determine whether polychlorinated biphenyls (PCBs), p,p′-dichlorodiphenyl trichloroethane (DDT), p,p′-dichlorodiphenyl trichloroethylene (DDE), o,p′-DDE and/or hexachlorobenzene (HCB) body burdens are associated with thyroid function in pregnant women.
Materials and Methods: Serum samples were collected during the second and third trimester of pregnancy in 334 women participating in the Center for the Health Assessment of Mothers and Children of Salinas (CHAMACOS), a birth cohort study investigating the health effects of environmental exposures on pregnant women and their children. A total of 34 PCB congeners as well as p,p′-DDT, p,p′-DDE, o,p′-DDE, and HCB were measured in maternal serum using HRGC/MS-MS. Thyroid-stimulating hormone (TSH) as well as total and free thyroxine (T4) were measured concurrently by immunochemiluminometric assay (TSH and total T4) and radioimunnoassay preceded by direct equilibrium dialysis (free T4). Data were analyzed by multiple linear regression controlling for a large number of demographic characteristics and environmental exposures.
Results: Despite low serum concentrations compared with national levels, 7 of the 19 PCB congeners detected in ≥75% of participants were negatively associated with free T4 levels (PCBs 18, 28, 44, 49, 52, 183, and 199; β = −0.14 to −0.09). Only PCB 44 was associated with total T4 (β = −0.57; 95% CI = −1.07 to −0.07). The sum of PCBs with detection frequencies ≥75% was also negatively associated with free T4 (β = −0.01; 95% CI = −0.02 to −0.00) but not total T4 (β = −0.04; 95% CI = −0.11 to 0.02). HCB levels were associated with both free T4 (β = −0.08; 95% CI = −0.15 to −0.01) and total T4 levels (β = −0.51; 95% CI = −0.98 to −0.05). None of the exposures under study were associated with TSH.
Conclusions: Exposure to PCBs and HCB may affect thyroid function during pregnancy. Thyroid hormones are essential for normal brain development. Our results suggest that neurodevelopmental effects of PCBs and HCB reported by previous studies may be mediated in part through TH disruption even at background levels of exposure. This will be examined in a future analysis of neurodevelopment in the CHAMACOS birth cohort.
© 2007 Lippincott Williams & Wilkins, Inc.