Ultra-trace carbazoles in sediment samples of the Weser and Elbe Rivers and the North Sea in 2012 to 2014

Carbazole and some of its derivatives may possess dioxin-like toxicity and could be persistent in the environment, but information on their distribution and environmental fate is limited. This study developed and validated an ultra-trace targeted-analysis method for the determination of carbazole, 1,2-benzocarbazole, and 13 halogenated carbazoles in sediments from the river, coast, and North Sea. An 8-g sediment sample was extracted using accelerated solvent extraction combined with in-cell cleanup and analyzed using gas chromatography-tandem mass spectrometry. The method was sensitive and reliable with method detection limits ranging from 4.54 to 52.9 pg/g, and most of the quantification biases and relative standard deviations were <20 and <15%, respectively. Carbazole and 1,2-benzocarbazole were the predominant substances in the sediments (median 565 and 369 pg/g, respectively) followed by 3,6-dichlorocarbazole (median 196 pg/g). The detection frequencies of carbazole, benzo-, 3-chloro-, and 3,6-dichlorocarbazole were >75%, while those of 3,6-dibromo-, 1-bromo-3,6-dichloro-, and 1,8-dibromo-3,6-dichlorocarbazole were approximately 50%. Brominated carbazoles occurred more frequently in marine than river-influenced sediments, which could indicate halogenation after discharge into the river. This is the first study regarding these substances in coastal environments without apparent contamination history. The ubiquity and bioaccumulative potential of these substances needs to be considered.