Polyhalogenated carbazoles in freshwater and estuarine sediment from China and the United States: A multi-regional study.

The present study represents a multi-regional investigation of polyhalogenated carbazoles (PHCZs) contamination in estuarine and freshwater systems from the United States and China. Although recent studies have suggested that PHCZs are persistent and bioaccumulative, available data are not sufficient to understand their large-scale spatial and temporal distributions in the environment. The present study investigated spatial distributions of PHCZs in surface sediment from multiple freshwater and estuarine systems located in China and the United States (U.S.) during the period of 2012-2017, as well as temporal distributions from vertical trends in selected sediment cores. The results demonstrated large variations of PHCZ contamination across regions, with median concentrations of ΣPHCZs in surface sediment ranging from 3.1 to 134 ng/g. Profiles of PHCZ congener composition also exhibited regional variations and estuarine-freshwater differences. These differences likely reflect the relative contributions of different natural and industrial sources among the locations. Vertical profiles of concentrations and compositions in one Chinese estuarine sediment core and two freshwater sediment cores from the U.S. all demonstrated clear anthropogenic influences to varying degrees. Toxic equivalents (TEQ) of PHCZs were estimated based on their dioxin-like activities, which ranged from <0.001 to 4.94 pg TEQ/g in all sites. The results suggest that PHCZs could add additional ecological risks to the benthos and other aquatic organisms. Our findings constitute an essential contribution to the knowledge body of PHCZ contamination in global aquatic systems and congener-specific contamination characterizations.