Contrasted occurrence and temporal trends of legacy and alternative flame retardants in marine shellfish from the French coasts over 10 years of monitoring.

Following regulations on flame retardant usage during the last few decades, alternative flame retardants (a-FRs) have been introduced to the market, increasing the diversity and quantities of FR use, and raising concerns about their occurrence in the marine environment. In this study, both legacy and alternative brominated and chlorinated FRs were determined in filter-feeding shellfish over a ten-year period (2012-2022) at 20 sites located on the French coastline. The studied contaminants included some legacy FRs, such as polybrominated diphenylethers (PBDEs), hexabromobenzene (HBB), hexabromocyclododecane (HBCDD), and Dechlorane Plus, as well as various a-FRs, such as decabromodiphenylethane (DBDPE), 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), 2,3,4,5,6-pentabromoethyl benzene (PBEB), pentabromotoluene (PBT), 1,2-dibromo-4-(1,2-dibromoethyl)-cyclohexane (DBE-DBCH), bis(2-ethylhexyl) 3,4,5,6-tetrabromophthalate (BEH-TEBP), and dechlorane-related compounds. In addition, compounds of mixed natural and anthropogenic origins were investigated, namely, 2,4,6-tribromoanisole (TBA), 2,4-dibromophenol (DBP) and 2,4,6-tribromophenol (TBP). The results showed widespread contamination of the shellfish, with most compounds detected in more than 50% of the samples. The median concentrations recorded at the end of the study period ranged from <1 pg g-1 dw for HBB and PBEB to 154 pg g-1 dw for α-HBCDD. The median concentrations of TBP, DBP and TBA were in the 1545-4991 pg g-1 dw range. Temporal variations revealed significant decreasing levels over 2012-2022 for ∑8 PBDE, BTBPE, and HBB median concentrations, while DBDPE was the only FR showing an increasing trend. PBDE profiles display significant differences between oysters and mussels, indicating a higher metabolism of these contaminants in oysters.