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Renée Dallaire,¹ Éric Dewailly,¹ Daria Pereg,¹ Serge Dery,² and Pierre Ayotte¹

¹Public Health Research Unit, Centre hospitalier universitaire de Québec-CHUL, Québec, Canada; ²Nunavik Regional Board of Health and Social Services, Kuujjuaq, Canada

Abstract
Background: Several ubiquitous polyhalogenated compounds (PHCs) have been shown to alter thyroid function in animal and in vitro studies. So far, epidemiologic studies have focused on the potential effect of a small number of them, namely, polychlorinated biphenyls (PCBs) and some organochlorines (OCs) , without paying attention to other important PHCs.

Objectives: We investigated the relationship between exposure to several PHCs and thyroid hormone homeostasis in Inuit adults from Nunavik.

Methods: We measured thyroid parameters [thyroid-stimulating-hormone (TSH) , free thyroxine (fT₄) , total triiodothyronine (tT₃) , and thyroxine-binding globulin (TBG) ] and concentrations of 41 contaminants, including PCBs and their metabolites, organochlorine pesticides (OCPs) , polybrominated diphenyl ethers (PBDEs) , perfluorooctanesulfonate (PFOS) , and a measure of dioxin-like compounds, detected in plasma samples from Inuit adults (n = 623) .

Results: We found negative associations between tT₃ concentrations and levels of 14 PCBs, 7 hydroxylated PCBs (HO-PCBs) , all methylsulfonyl metabolites of PCBs (MeSO₂‑PCBs) , and 2 OCPs. Moreover, we found negative associations between fT₄ levels and hexachlorobenzene concentrations. TBG concentrations were inversely related to 8 PCBs, 5 HO-PCBs, and 3 OCPs. Exposure to BDE‑47 was positively related to tT₃, whereas PFOS concentrations were negatively associated with TSH, tT_3, and TBG and positively with fT₄ concentrations.

Conclusion: Exposure to several PHCs was associated with modifications of the thyroid parameters in adult Inuit, mainly by reducing tT₃ and TBG circulating concentrations. The effects of PFOS and BDE‑47 on thyroid homeostasis require further investigation because other human populations display similar or higher concentrations of these chemicals.

Key words: dioxin-like compounds, hydroxylated metabolites, Inuit, organochlorines, perfluorooctanesulfonate, polybrominated diphenyl ethers, polychlorinated biphenyls, polyhalogenated compounds, thyroid hormones. Environ Health Perspect 117:1380–1386 (2009) . doi:10.1289/ehp.0900633 available via http://dx.doi.org/ [Online 12 May 2009]

Address correspondence to P. Ayotte, Unité de recherche en santé publique, Centre hospitalier universitaire de Québec-CHUL, 2875 boulevard Laurier Édifice Delta, 2 bureau 600, Québec, G1V 2M2 Canada. Telephone: (418) 656-4141 ext. 46519. Fax: (418) 654-2726. E-mail: pierre.ayotte@crchul.ulaval.ca

Supplemental Material is available online (doi:10.1289/ehp.0900633.S1 via http://dx.doi.org/) .

We are grateful to the Nunavik population for their participation in this research.

This study was made possible by grants from the Québec Health and Social Services Ministry, the Nunavik Regional Board of Health and Social Services, Indian and Northern Affairs Canada (Northern Contaminants Program) , the Network of Centres of Excellence of Canada (ArcticNet) , the Canadian Foundation for Innovation, and the Fonds de Recherche en Santé du Québec.

The authors declare they have no competing financial interests.

Received 30 January 2009 ; accepted 12 May 2009.