Legacy and alternative halogenated flame retardants in sediment and bivalves along Korean coast: geographic distribution, temporal trends, contamination sources, and ecological risk

Following the global and domestic regulations on brominated flame retardants (BFRs), including polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecanes (HBCDDs), novel halogenated flame retardants (HFRs) have been introduced in industrial markets. Legacy and alternative HFRs, such as PBDEs, HBCDDs, novel BFRs (NBFRs), and dechlorane plus, were measured in sediment and bivalves collected from 50 locations along the Korean coast to investigate geographic distribution, contamination sources, and ecological risks. All HFRs were detected in sediment and bivalves, with the highest contamination spots close to industrial complexes, harbors, and aquaculture farms. A shift in HFR usage was observed in bivalves, characterized by the replacement of octa-BDE with 1,2-bis (2,4,6-tribromophenoxy) ethane and deca-BDE with decabromodiphenyl ethane. This trend suggests a clear transition toward the use of alternative HFRs. BDE 47 and α-HBCDD exhibited a biota-sediment accumulation factor exceeding 1, indicating bioaccumulation potential from sediment-associated exposure. Temporal trends between 2004 and 2019 showed a decline in PBDE contamination in sediment and an increase in bivalves, with deca-BDE remaining dominant. The ecological risks of PBDEs and HBCDDs were generally low, though high localized concentrations of BDE 209 posed significant ecological risks in certain coastal regions.