SPECIES-SPECIFIC AND STRUCTURE-DEPENDENT DEBROMINATION OF POLYBROMINATED DIPHENYL ETHER IN FISH BY IN VITRO HEPATIC METABOLISM

To explore the cause of species-specific differences and structure-activity relationships in the debromination of polybrominated diphenyl ethers (PBDEs) in fish, a series of in vitro measurements of hepatic metabolism of PBDE were made using crucian carp (Carassius carassius) and catfish (Silurus asotus) and the activity of deiodinase in liver microsomes was measured. Debromination was observed in the crucian carp but not in the catfish. No difference was found in total deiodinase activity despite the activity of type 1 deiodinase in crucian carp being twice that of catfish. It is difficult to determine whether the differences in deiodinase activity were responsible for the species-specific differences observed. In crucian carp, penta-brominated diphenyl ether congeners exhibited the highest debromination rates, and the transformation rate decreased with an increasing number of substituted bromines. Adjacent bromine substitution in the phenyl ring was a necessary, but insufficient, condition for debromination in crucian carp. Doubly flanked bromine was always preferentially removed, while single-flanked bromine, meta-substituted bromine, was debrominated the most, followed by para- and then ortho-bromine. No debromination was observed for single-flanked bromine when there was a symmetrical structure with (2, 4, 6) bromine substitutions in 1 phenyl ring, indicating that this structure can improve resistance to debromination metabolism. (C) 2017 SETAC