Evaluation of the bioaccumulation potential of selected alternative brominated flame retardants in marine fish using in vitro metabolic transformation rates

Abstract

The global consumption of alternative brominated flame retardants (BFRs) has increased with the restriction of the first generation BFRs such as polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecanes (HBCDs). However, many alternative BFRs are suspected to be persistent in the environment and possibly bioaccumulative after their release into the environment because of their chemical properties, which are similar to those of the already banned BFRs. In this study, the bioaccumulation potential of selected alternative BFRs (1,2-bis(2,4,6‑tribromophenoxy)ethane (BTBPE), 1,2,3,4,5,6‑hexabromobenzene (HBB), pentabromoethylbenzene (PBEB), 2,3,4,5,6‑pentabromotoluene (PBT), 2‑ethylhexyl-2,3,4,5-tetrabromobenzoate (TBB), and 2,3,4,5‑tetrabromo-6-chlorotoluene (TBCT)) was evaluated. The in vitro depletion rate constants (k_depl) were measured for the alternative BFRs using liver S9 fractions isolated from five marine fish species (Epinephelus septemfasciatus, Konosirus punctatus, Lateolabrax japonicus, Mugil cephalus, and Sebastes schlegelii) that inhabit the oceans off the Korean coast. The measured k_depl values were converted to in vitro intrinsic clearance rate constants (CL_{in vitro}) to estimate whole-body metabolic rate constants (k_MET) using an in vitro to in vivo extrapolation (IVIVE) model. Finally, the bioconcentration factors (BCF) were determined using a one-compartment model. The transformation kinetics for obtaining k_depl agreed well with first-order chemical kinetics, regardless of initial BFR concentrations. The values of CL_{in vitro} were lower in the selected marine fish species than those in freshwater fish species, implying slower metabolic transformation. The derived BCF values based on the total concentration in water (BCF_TOT) ranged from 16 (TBB in M. cephalus) to 27,000 (HBB in K. punctatus). The BCF values for HBB and PBT were >2000 except for those in M. cephalus suggesting further investigation of BCF values of BFRs whose log K_OW is between 6 and 7.

Keywords: Alternatives; Bioconcentration; Biotransformation; Marine fish.