Relationship between BDE 209 metabolites and thyroid hormone levels in rainbow trout (Oncorhynchus mykiss)

Decabromodiphenyl ether (BDE 209), the primary component in a commonly used flame retardants, has recently been shown to be metabolized by organisms. In the present study, juvenile rainbow trout (Oncorhynchus mykiss) were exposed to BDE 209 at five nominal gradient concentrations from 50 to 1000 ng/g wet weight for 21 days via a single intraperitoneal injection. Then the liver, kidney and blood samples were collected to analyze for its debrominated, hydroxylated and methoxylated metabolites. The relationships between levels of BDE 209 metabolites in different tissues and thyroid hormone (TH) levels in plasma were evaluated. The results showed that BDE 209 could be metabolized into debrominated BDEs, methoxylated BDEs (MeO-BDEs) and hydroxylated BDEs (OH-BDEs). Levels of these three metabolites were tissue-dependent. The TH levels, including total thyroxine (TT4), free thyroxine (FT4), total triiodothyronine (TT3) and free triiodothyronine (FT3) in plasma, were significantly affected by BDE 209 metabolism. However, only FT4 levels showed a negative correlation with MeO-BDE and OH-BDE metabolites, among which the correlation between FT4 and OH-BDEs was the most significant.

► BDE 209 could be metabolized into debrominated BDEs, MeO-BDEs and OH-BDEs in rainbow trout.
► TH levels in plasma were significantly affected by BDE 209 metabolism.
► OH-BDEs were negatively correlated with the plasma FT4 levels.
► OH-BDEs acted as the main disruptors of TH homeostasis.