Identification of brominated and chlorinated phenols as potential thyroid-disrupting compounds in indoor dusts

Our previous study demonstrated that compounds in indoor dusts strongly inhibit thyroxine (T4) binding to the human thyroid hormone transport protein transthyretin (TTR) in vitro. Exposure assessment indicated that house dust is an important medium of exposure of children to TTR-binding compounds when binding potency and dust ingestion rates are high. Here, we used chemical fractionation with in vitro competitive human TTR-binding assay and GC-MS to analyze the TTR-binding compounds in a sulfuric-acid-treated dust extract. 2,4,6-Tribromophenol (TriBPh) and 2,3,4,5,6-pentachlorophenol (PeCPh) were potent TTR-binding compounds in all dust samples. 2,4,6-TriBPh- and 2,3,4,5,6-PeCPh-derived theoretical T4 equivalents (T4EQs), calculated arithmetically from the concentrations and relative potencies, accounted for about 40-70% of experimental T4EQs detected in indoor dusts, indicating that these compounds contributed strongly to the TTR-binding potency of indoor dust. Indoor sources of 2,4,6-TriBPh might be brominated flame retardants currently used in household materials such as electrical appliances. In contrast, the 2,3,4,5,6-PeCPh might be trace evidence of past use in agricultural chemicals and preservatives in indoor or outdoor environments, because its use has been banned since 1990 in Japan. 2,4,6-TriBPh and 2,3,4,5,6-PeCPh are ubiquitous potential thyroid-disrupting compounds in the home and work environments of Japan and other countries.