3,3′,5-Triiodo-l-thyronine-like activity in effluents from domestic sewage treatment plants detected by in vitro and in vivo bioassays

Thyroid system-disrupting activity in effluents from municipal domestic sewage treatment plants was detected using three in vitro assays and one in vivo assay. Contaminants in the effluents were extracted by solid-phase extraction (SPE) and eluted stepwise with different organic solvents. The majority of the thyroid system-disrupting activity was detected in the dichloromethane/methanol (1/1) fraction after SPE in all three in vitro assays: competitive assays of 3,3′,5-[125I]triiodo-l-thyronine ([125I]T3) binding to the plasma protein transthyretin (TTR assay) and thyroid hormone receptor (TR assay) and T3-dependent luciferase assay (Luc assay). Subsequent reverse-phase high-performance liquid chromatography (RP-HPLC) of the dichloromethane/methanol (1/1) fraction separated contaminants potent in the TR and Luc assays from those potent in the TTR assay. The contaminants potent in the TR and Luc assays were also potent in an in vivo short-term gene expression assay in Xenopus laevis (Tadpole assay). The present study demonstrated that the effluents from domestic sewage treatment plants contain contaminants with T3-like activity of ∼ 10− 10 M T3-equivalent concentration (T3EQ) and that the TR and Luc assays are powerful in vitro bioassays for detecting thyroid system-disrupting activity in effluents. The availability and applicability of these bioassays for screening contaminants with thyroid system-disrupting activity in the water environment are discussed.