Distributions and transformation of polyhalogenated carbazoles in environmental matrices contaminated by printing and dyeing plants

Abstract

As emerging organic contaminants, Polyhalogenated carbazoles (PHCZs) have caused wide concerns due to their wide distribution in the environment and dioxin-like toxicity. Nevertheless, research on the distribution and formation mechanisms of PHCZs in polluted environment of printing and dyeing plants is lacking. Here, 11 PHCZs were detected in samples from the Cao'e River, China, a typical river heavily polluted by printing and dyeing. The PHCZs concentrations in the soil, sediment, and water samples were 8.3–134.5 ng/g (median: 26.3 ng/g), 17.7–348.8 ng/g (median: 64.2 ng/g), and 1.2–41.4 μg/L (median: 4.8 μg/L), respectively. 3,6-dichlorocarbazole was the dominant congener, proved by both analysis results and formation mechanisms. PHCZ migration patterns in water-sediment systems indicated that highly halogenated PHCZs tend to be transferred to sediment. Furthermore, PHCZs are persistent, can undergo long-range transport, and pose high risks to aquatic organisms by models. PHCZs released from dye production into environment can be form through halogenation of carbazole or PHCZs formed during the dye synthesis, heating of halogenated indigo dyes, and photolysis of highly halogenated PHCZs. This is the first comprehensive study to reveal the impact of printing and dyeing plant activities on PHCZs in the environment.