Spatial and temporal trends of polyhalogenated carbazoles in sediments of the Yangtze river: insights into the origin

Fifteen surface sediments and three sediment cores were sampled in the Yangtze River (YR) of China to study the composition and temporal distribution trends of 10 selected polyhalogenated carbazoles (PHCZs) and gain insight into their origin. The total concentrations of PHCZs in the surface sediments ranged from 1.58 to 5.45 ng g(-1) dry weight (dw), with an average of 3.11 ng g-1 dw. The composition profiles of PHCZs in the surface sediments were dominated by 1,3,6,8-tetrabromocarbazole, 1,3,6-dibromocarbazole, and 3,6-dichlorocarbazole. The variation trends of PHCZs in the sediment cores showed an apparent peak concentration and subsequently a significant decreasing trend in recent years. A strong correlation exists between PHCZs and sediment physicochemical properties. Furthermore, human activities directly or indirectly affected PHCZ concentrations. The evaluation of the potential toxic effect suggested that the toxic equivalent of PHCZs was less than the safe sediment value.