Polybrominated diphenyl ethers, hydroxylated polybrominated diphenyl ethers, and measures of thyroid function in second trimester pregnant women in California

Abstract

Prenatal exposure to polybrominated diphenyl ethers (PBDEs) may disrupt thyroid function and contribute to adverse neurodevelopmental outcomes. We conducted a pilot study to explore the relationship between serum concentrations of lower-brominated PBDEs (BDE-17 to -154), higher-brominated PBDEs (BDE-183 to -209), and hydroxylated PBDE metabolites (OH-PBDEs) with measures of thyroid function in pregnant women. Concentrations of PBDEs, OH-PBDEs, thyroid-stimulating hormone (TSH), total thyroxine (T(4)), and free T(4) were measured in serum samples collected between 2008 and 2009 from 25 second trimester pregnant women in California. Median concentrations of lower-brominated PBDEs and OH-PBDEs were the highest reported to date in pregnant women. Median concentrations of BDE-47 and the sum of lower-brominated PBDEs (ΣPBDE(5)) were 43.1 ng/g lipid and 85.8 ng/g lipid, respectively, and the sum of OH-PBDEs (ΣOH-PBDE(4)) was 0.084 ng/mL. We observed a positive association between the weighted sum of chemicals known to bind to transthyretin (ΣTTR binders) and TSH levels. We also found positive associations between TSH and ΣPBDE(5), ΣOH-PBDE(4), BDE-47, BDE-85, 5-OH-BDE47, and 4'-OH-BDE49, and an inverse association with BDE-207. Relationships with free and total T(4) were weak and inconsistent. Our results indicate that PBDE exposures are elevated in pregnant women in California and suggest a relationship with thyroid function. Further investigation is warranted to characterize the risks of PBDE exposures during pregnancy.

Figure 1

Molecular structures of thyroid hormones (TH) and PBDEs.

Figure 2

Comparison of serum PBDEs levels in pregnant women from three study populations

Figure 3

Association between serum levels of TSH and the weighted sum of transthyretin-binding PBDEs and OH-PBDEs (ΣTTR binders) after adjustment for parity and lipid content in second trimester pregnant women in Northern and Central California (Adjusted R² = 0.14; p = 0.03). ΣTTR binders is a weighted sum of BDE-47, 5-OH-BDE47, 6-OH-BDE47, and 4′-OH-BDE49. Concentrations are weighted according to their potencies to compete with T₄ for binding to transthyretin (TTR) as determined by Hammers et al. [23].