Spatiotemporal Trends of Legacy and Alternative Flame Retardants in Harbor Seals from the Coasts of California, the Gulf of Maine, andS weden

Temporal trends of polybrominated diphenyl ethers(PBDEs) have been extensively studied in various environmentalcompartments globally. However, despite the increasing use ofalternativeflame retardants following PBDE bans, the spatiotempo-ral trends of these replacements have rarely been studied, and theavailable results are often inconsistent. In the present study, weretrospectively investigated the spatiotemporal trends of PBDEs anda suite of alternative brominated FRs (aBFRs) and chlorinated FRs(i.e., dechloranes or DECs) in three harbor seal (Phoca vitulina)populations from the coasts of California, the Gulf of Maine, andsouthern Sweden during 1999-2016. We observed significantlydecreasing trends of Sigma PBDEs in all the three populations at anannual rate of 9-11%, which were predominantly driven by thedeclining concentrations of tetra- and penta-BDEs. The levels of Sigma aBFRs decreased significantly in seals from California (mainly 1,3,5-tribromobenzene) and Sweden (mainly hexabromobenzene),while no trend was observed for those from Maine. By contrast, DECs (dominated by DEC 602) did not decrease significantly inany population. Compared with the consistent PBDE congener profiles across regions, aBFRs and DECs exhibited varyingcompositional profiles between regions, likely indicating region-specific sources of these alternative FR mixtures. Spatial analysis alsorevealed regional differences in the concentrations of PBDEs, aBFRs, and DECs in harbor seals. Our reconstructed spatiotemporaltrends suggest the effective regulation of commercial penta-BDE mix in these regions and warrant further monitoring of the higher brominated BDEs and alternative FRs.