Legacy and emerging halogenated organic pollutants in sediments of the Pearl River Delta: Spatial distribution, source implications, and mass inventories

A comprehensive assessment of the environmental occurrence and spatial distribution of legacy and emerging halogenated organic pollutants (HOPs), including polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethanes (DDTs), halogenated flame retardants (HFRs), and per- and polyfluoroalkyl substances (PFAS) was conducted. Concentrations of PCBs (0.15-30 ng/g dry wt) and DDTs (0.028-54 ng/g dry wt) have declined significantly compared with historical data, demonstrating the effectiveness of long-term regulatory interventions. HFRs such as polybrominated diphenyl ethers (PBDEs, 0.01-3,700 ng/g dry wt) and decabromodiphenyl ethane (DBDPE, ND-250 ng/g dry wt) have become the dominant contaminants, collectively accounting for over 90% of the total HOPs burden, with BDE-209 as the predominant congener. The PFAS concentrations (0.07-3.3 ng/g dry wt) were relatively lower than other HOPs. Industrial-derived HOPs exhibited strong correlations with each other but were not associated with agricultural-derived HOPs. Guangzhou and Dongguan emerged as the primary contamination hotspots. Total organic carbon (TOC) was a key factor governing the spatial distribution of HOPs, complemented by hydrodynamic processes and compound-specific partitioning behavior. Mass inventory estimation indicated a total HOPs burden of approximately 20,860 kg, with PBDEs and DBDPE contributing 74.3% and 19.6%, respectively. These residual contaminants will act as persistent long-term exposure sources in local aquatic environments. Ecological risk assessment revealed high risks for penta-BDE and deca-BDE at multiple sites, particularly in Dongguan and Guangzhou. This study highlights the persistence and coexistence of legacy and emerging HOPs in complex contamination systems and provides insights for pollutant prioritization and management in rapidly industrializing coastal regions.