Johan Maervoet,1 Griet Vermeir,2 Adrian Covaci,1 Nicolas Van Larebeke,3 Gudrun Koppen,4 Greet Schoeters,4 Vera Nelen,5 Willy Baeyens,6 Paul Schepens,1 and Maria K. Viaene2,7
1Toxicological Centre, University of Antwerp (UA), Wilrijk, Belgium; 2Neurotoxicity Expertise Centre, Governmental Psychiatric Hospital, Geel, Belgium; 3Study Centre for Carcinogenesis and Primary Prevention of Cancer, Ghent University Hospital, Ghent, Belgium; 4Centre of Expertise in Environmental Toxicology, Flemish Institute of Technological Research (VITO), Mol, Belgium; 5Provincial Institute for Hygiene, Antwerp, Belgium; 6Laboratory of Analytical and Environmental Chemistry, Vrije Universiteit Brussel (VUB), Brussels, Belgium; 7Department of Occupational and Environmental Health, Katholieke Universiteit, Leuven, Leuven, Belgium
Background: Thyroid hormones are important regulators of brain development. During critical periods of development, even transient disorders in thyroid hormone availability may lead to profound neurologic impairment. Animal experiments have shown that certain environmental pollutants, including heavy metals and organochlorine compounds such as polychlorinated biphenyls (PCBs) and dioxins, can interfere with thyroid hormone homeostasis. Whether these contaminants can affect circulating levels of thyroid hormones in humans is unclear, however, because the results of available studies are inconsistent.
Objectives: The aim of the present study is to examine the possible relationships between concentrations of environmental pollutants and thyroid hormone levels in human umbilical cord blood.
Methods: We measured concentrations of environmental pollutants [including selected PCBs, dioxin-like compounds, hexachlorobenzene, p,p´-DDE (dichlorodiphenyldichloroethylene) , cadmium, lead] and thyroid hormones in the cord blood of 198 neonates.
Results: A statistically significant inverse relationship between concentrations of organochlorine compounds and levels of both free triiodothyronine (fT3) and free thyroxine (fT4) , but not thyroid-stimulating hormone, was observed. We found no association between concentrations of heavy metals and thyroid hormone levels.
Conclusions: Our results suggest that environmental chemicals may affect the thyroid system of human neonates. Although the differences in fT3 and fT4 levels associated with the organochlorine compounds were within the normal range, the observed interferences may still have detrimental effects on the neurologic development of the individual children, given the importance of thyroid hormones in brain development.
Key words: brain, cord blood, development, endocrine disruption, heavy metals, neonates, organohalogens, PCBs, thyroid. Environ Health Perspect 115:17801786 (2007) . doi:10.1289/ehp.10486 available via http://dx.doi.org/ [Online 27 September 2007]