Thyroid function and plasma concentrations of polyhalogenated compounds in Inuit adults

Area of Science:

• Environmental Health
• Endocrinology
• Toxicology

Background:

• Ubiquitous polyhalogenated compounds (PHCs) are known to affect thyroid function in experimental studies.
• Previous epidemiological research has primarily focused on polychlorinated biphenyls (PCBs) and organochlorines (OCs), neglecting other significant PHCs.

Purpose of the Study:

• To investigate the relationship between exposure to various PHCs and thyroid hormone homeostasis in Inuit adults from Nunavik.
• To assess the impact of a wide range of contaminants on thyroid parameters in a vulnerable population.

Main Methods:

• Plasma samples from 623 Inuit adults were analyzed for 41 contaminants, including PCBs, organochlorine pesticides (OCPs), polybrominated diphenyl ethers (PBDEs), and perfluorooctanesulfonate (PFOS).
• Thyroid parameters measured included thyroid-stimulating hormone (TSH), free thyroxine (fT(4)), total triiodothyronine (tT(3)), and thyroxine-binding globulin (TBG).

Main Results:

• Negative associations were observed between tT(3) levels and 14 PCBs, 7 hydroxylated PCBs (HO-PCBs), methylsulfonyl metabolites of PCBs (MeSO(2)-PCBs), and 2 OCPs.
• fT(4) levels showed negative associations with hexachlorobenzene, while TBG concentrations were inversely related to 8 PCBs, 5 HO-PCBs, and 3 OCPs.
• Perfluorooctanesulfonate (PFOS) was negatively associated with TSH, tT(3), and TBG, and positively with fT(4); BDE-47 showed a positive association with tT(3).

Conclusions:

• Exposure to multiple PHCs is associated with altered thyroid parameters in adult Inuit, primarily characterized by reduced circulating tT(3) and TBG.
• The specific effects of PFOS and BDE-47 on thyroid homeostasis warrant further investigation, given their presence in other human populations.