Refuse leachate exposure causes changes of thyroid hormone level and related gene expression in female goldfish (Carassius auratus)

- The effects of leachate on thyroid system of female fish remain unknown.
- Leachate exposure induced elevated plasma T3 and TSH levels.
- The expression profiles of HPT axis-responsive genes were altered.
- After treatment, the leachate still possesses potential thyroid disrupting activity.
- The thyroid system in female seems to be more sensitive than that of the male.

To elucidate the potential thyroid disrupting effects of refuse leachate on females, female goldfish (Carassius auratus) were exposed to 0.5% diluted leachates from each step of a leachate treatment process (i.e. raw leachate before treatment, after membrane bioreactor treatment, and the final treated leachate) for 21 days. Raw leachate exposure caused disturbances in the thyroid cascade of female fish, as evidenced by the elevated plasma 3,3ʹ,5-triiodo-l-thyronine (p < 0.05) and thyroid-stimulating hormone (p < 0.01) levels as well as up-regulated hepatic and gonadal type I deiodinase (p < 0.01), type II deiodinase (p < 0.01) and thyroid receptor (p < 0.05) mRNA levels. Thyroid disrupting potency decreased markedly as raw leachate progressed through the “membrane bioreactor + reverse osmosis” treatment but could still be detected in the treated leachate. As our results indicated, thyroid system in female goldfish was more sensitive to leachate exposure than that of the male fish.