Early life Exposure to Triclosan Impacted Thyroid Follicular Structure and Decreased Thyroid Hormone Levels in Zebrafish

Abstract Background: Triclosan (TCS) is an antimicrobial chemical widely used in personal care products. Most of TCS is discharged into aquatic ecosystem after usage. While TCS has potential thyroid-disrupting effect, it is unknown whether early exposure to TCS affects thyroid grand and thyroid hormone levels. We used zebrafish model to examine this topic.Methods: The fertilized zebrafish eggs were exposed to TCS. We inspected hatching and mortality of larvae. The total triiodothyronine (TT3), total thyroxine (TT4), free triiodothyronine (FT3), and free thyroxine (FT4) levels were measured at 7, 14 and 120 days post fertilization (dpf). Thyroid histopathological analysis was conducted at 120 dpf of zebrafish.Results: The hatching rate of embryos decreased from 95.8% in control group to 18.3% in TCS highest exposure in 3 days. In 900 ng/mL TCS exposure all larvae died within one day. With increasing concentration of TCS exposure, TT3 and FT3 level decreased after 14 days. FT4 decreased, and the height and nuclear area of thyroid follicular cell increased with TCS exposure after 120 days.Conclusions: High TCS exposure decreased the hatching rate of zebrafish embryos, and also decreased thyroid hormone levels owing to structural change of thyroid follicles. Our study raised the concern that TCS exposure in early life may profoundly affect neurodevelopment.