Long term substantial impacts of historic Chlor-Alkali production as a newly recognized source of polyhalogenated carbazoles in aquatic environments

Bottom sediments of the North American Great Lakes are characterized by a high loading (over 3,000 tonnes) of polyhalogenated carbazoles (PHCZs). The origin of this environmental contaminant loading is unclear. Here, we first examined PHCZs levels and profiles in sediment, lotus, and fish from the Ya-Er Lake (China) that has been under the influence of an obsolete chlor-alkali facility for forty years and discovered substantial PHCZs contamination. Among the PHCZs determined, 3,6-dichlorocarbazole (36-CCZ) and 3-chlorocarbazole (3-CCZ) were the most frequently detected. Sediments from backfilled land exhibited Σ11PHCZs at median concentration of 973 ng/g (dry weight), suggesting the chlor-alkali industry as an important source. Even after 20 years of dredging treatment, the concentration of Σ11PHCZs in the sediment of the oxidation ponds (median = 41.1 ng/g) remained substantially higher than in other areas globally. Furthermore, the concentration of Σ11PHCZs was found to be higher in surface sediments (median) at 66.7 ng/g if compared to middle (14.1 ng/g) and lower layers (18.2 ng/g), indicating the potential availability of PHCZs from surface sediments to aquatic plants and animals. Notably, this study detected PHCZs in both fish (26.3 ng/g lipid weight) and lotus (14.5 ng/g dry weight), with significant enrichment of 3-monobromocarbazole (3-BCZ) observed in both lotus root systems (bio-soil accumulation factor, BSAFroot = 5.04) and fish muscle (BSAFfish = 3.04).