Occurrence, non-target screening, and sediment-water partitioning of traditional and novel polyhalogenated carbazoles in the Yangtze River.

Polyhalogenated carbazoles (PHCZs) are emerging halogenated contaminants, yet their occurrence and sediment-water partitioning remain poorly characterized. Based on paired surface water and sediment samples collected from 56 sites along the Yangtze River, this study quantified twelve traditional PHCZ congeners, while simultaneously screening and characterizing novel PHCZs. In Yangtze River water, 3,6-dichlorocarbazole (mean 2.28 ng/L) and 3,6-dibromocarbazole (36-BCZ; 2.17 ng/L) were the dominant traditional PHCZs. In sediment, 3-chlorocarbazole (6.23 ng/g dw) was the predominant traditional PHCZ. Furthermore, non-target screening identified 14 novel PHCZ congeners, including fluorinated, iodinated, and mixed-halogenated PHCZs. Fluorinated congeners 3-fluorocarbazole (mean 2.15 ng/L and 8.65 ng/g dw, respectively) and 3,6-difluorocarbazole (1.45 ng/L and 1.35 ng/g dw, respectively) were the most prevalent novel PHCZs in water and sediment. The 1,3,6-tribromocarbazole showed the highest mean field-derived log Koc value (3.33, 1.18-6.05), followed by 3-bromocarbazole (3.27, 1.63-5.68) and 36-BCZ (3.25, 1.42-5.11). The mean log Koc values of PHCZs increased with increasing log Kow. These findings expand the known environmental occurrence of PHCZs and provide new field evidence on their congener-specific sediment-water partitioning, highlighting the importance of incorporating previously overlooked PHCZs into environmental fate and exposure assessment.