Accumulation and temporal trends (2002-2023) of legacy and emerging persistent organic pollutants in common dolphins (Delphinus delphis) from Korean coastal waters.

Elevated accumulation of persistent organic pollutants (POPs) in marine mammals remains a concern for the health and conservation of marine ecosystems. Long-term monitoring of POPs in marine mammals is essential to evaluate the effectiveness of regulations and to understand their environmental behavior in marine ecosystems. We investigated accumulation patterns and temporal trends of legacy and emerging POPs in the blubber of common dolphins (Delphinus delphis) from Korean coastal waters over the past two decades (2002-2023). Polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane and its metabolites (DDTs) were the dominant contaminants, whereas emerging compounds, such as novel brominated flame retardants (NBFRs) and dechlorane plus (DP), were detected at low concentrations and detection frequencies. Bioaccumulation of POPs was pronounced in mature male dolphins, whereas mature females exhibited lower concentrations, explained by maternal transfer via placenta and lactation. Temporal trend analysis using body length-adjusted concentrations revealed that PCBs, DDTs, and polybrominated diphenyl ethers (PBDEs) significantly declined over the study period, reflecting the effectiveness of domestic and global regulatory efforts. PCB concentrations decreased gradually, whereas PBDE concentrations exhibited the most rapid decline. Concentrations of BDE 184 showed an increasing trend, which is explained by debromination of highly brominated congeners. Unlike legacy POPs, NBFRs and DP did not show any predictable temporal trend in dolphin tissues. Despite declining trends, some dolphins are still exposed to PCB and DDT concentrations above the thresholds for endocrine disruption. These results highlight the need for continued long-term monitoring to better understand the fate and ecological effects of legacy and emerging POPs in marine ecosystems. Crucially, these monitoring data should be utilized to refine environmental quality standards and inform regional conservation policies for marine apex predators.