Chemical Mixtures Isolated from House Dust Disrupt Thyroid Receptor β Signaling

House dust is a source of exposure to chemicals that can impact hormone regulation. This study was designed to evaluate the potential of house dust mixtures ( n = 137) to disrupt thyroid hormone nuclear receptor signaling in a cell-based reporter assay and to examine associations with thyroid hormones (TH) measured in residents of the homes. Approximately 41% of the extracts (ranging from 10.5 to 4.097 μg of dust/mL) significantly antagonized thyroid receptor β (TRβ) signaling by 20-67% relative to the hormone control. The concentrations of 12 flame retardants (FRs) quantified in the mixtures were significantly correlated with TRβ antagonism; however, they were inactive when tested individually. We hypothesize that the observed antagonism is due to mixture effects or unidentified compounds that co-occur with FRs. Dust extract potency was significantly associated with free thyroxine (FT4, rs = -0.64, p < 0.001), suggesting that more potent dust samples are associated with higher FT4 levels in residents. Overall, these results suggest that house dust is a significant source of exposure to TH-disrupting chemicals, and TRβ may have a role in mediating effects of exposure on TH levels. Additional studies are needed to identify the chemical(s) driving the observed effects on TRβ and to determine if these changes lead to any adverse outcomes.