Multi-residue determination of polyhalogenated carbazoles in aquatic sediments
Introduction
The greatest proportion of organic nitrogen in petroleum is found in the form of the nonbasic pyrrolic ring systems such as carbazole and its derivatives [1]. Carbazole and derivatives (e.g., alkylated and benzo[a]carbazole) are also abundant in source rocks and sediments, although the compositions vary with facies and maturation [2]. Recently, a number of polyhalogenated carbazoles (PHCZs) were discovered in environmental matrixes and subject to increasing reports in soil and aquatic sediments. For example, 3-chlorocarbazole (3-CCZ) and 3,6-dichlorocarbazole (36-CCZ) were found in soils from Germany and Greece [3], [4]. 1,3,6,8-Tetrachlorocarbazole (1368-CCZ) and 1,3,6,8-tetrabromocarbazole (1368-BCZ) were found in sediments from the Buffalo River, New York (USA) and Lake Michigan (USA), respectively [5], [6]. Carbazoles substituted with a combination of chlorine and bromine atoms (e.g., 1,8-dibromo-3,6-dichlorocarbazole or 18-B-36-CCZ) were also found in sediments from Southern Ontario, Canada, and the Laurentian Great Lakes of North America [7], [8]. The latter study identified a number of PHCZs with various combinations of halogen (bromine, chlorine, and iodine) substitutions, including Br2-, Br3-, Br4-, Br3Cl-, Br3ClI-, Br4Cl-, Br4I-, and Br5-carbazole [8]. Recently, about 1600 bromine-containing compounds were identified in sediments from Lake Michigan [9], and PHCZs were found among those with the greatest peak intensities [10].
In addition to the discovery of PHCZs in environmental matrixes, studies also revealed toxicological potentials of carbazole and a few halogenated carbazoles. Treatment of adult male mice resulted in the induction of dominant lethal mutation and abnormal sperm heads [11]. Dioxin-like toxicity was reported for carbazole and a variety of PHCZs [3], [12], [13], [14]. Riddle et al. investigated the induction of cytochrome P450 1A1 (CYP1A1) and CYP1B1 gene expression in aryl hydrocarbon (Ah)-responsive MDA-MB-468 breast cancer cells by PHCZs [14]. The results clearly suggest that PHCZs act through the Ah receptor [14]. For PHCZs with a 1,3,6,8 substitution pattern, their relative effect potencies (REPs) compared to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) ranged from 0.00031 to 0.00066 for CYP1A1 induction and from 0.0058 to 0.0097 for CYP1B1 induction [14]. These estimated REPs overlap with the toxic equivalency factor (TEF) for higher chlorinated dibenzofurans, dibenzo-p-dioxins, and some coplanar PCBs [14], [15]. A TEF of 0.0016 was also reported for 18-B-36-CCZ [13], which ranges between that of 1,2,3,4,6,7,8- heptachlorodibenzodixoin (0.001) and 3,3′,4,4′,5-PentaCB (0.005) for fish [15].
Given the increasing reports of these chemicals in the environment and their potential persistent, bioaccumulative, and toxic characteristics, PHCZs have attracted mounting environmental concerns [16]. Although a couple most recent studies have determined PHCZs in sediments, both of them were subject to qualitative or semi-quantitative measurement due to lack of reference standards for most PHCZs [7], [8]. To date there is a lack of analytical methodology studies addressing the quantitative determination of these compounds with detailed quality assurance and control procedures. Very recently, reference standards of a suite of environmentally relevant PHCZs were commercially available due to increasing interests in these emerging contaminants. Therefore, the main goal of this study was to develop a highly efficient and sensitive analytical method, as well as an efficient extraction and cleanup procedure, for a broad suite of PHCZs of known or expected environmental relevance. The developed method was then applied to investigate these emerging contaminants in sediments from the Saginaw River system (Michigan, USA) and the Saginaw Bay of Lake Huron.
Section snippets
Chemicals and reagents
The reference standards of 3-CCZ, 36-CCZ, 1368-CCZ, 2,3,6,7-tetrachlorocarbazole (2367-CCZ), 1,3,6-tribromocarbazole (136-BCZ), 1-bromo-3,6-dichlorocarbazole (1-B-36-CCZ), and 18-B-36-CCZ were purchased from Wellington Laboratories (Guelph, ON, Canada). The standards of 3-bromocarbazole (3-BCZ), 2,7-dibromocarbazole (27-BCZ), and 3,6-dibromocarbazole (36-BCZ) were purchased from Sigma–Aldrich (St. Louis, Missouri). The reference standards of carbazole and 1368-BCZ were purchased from
SIM ions and instrumental performances
Table 1 lists m/z values of the SIM ions collected for the quantification of carbazole and PHCZs using ECNI- or EI–MS analyses, respectively, as well as the ions collected for confirmation purposes. The EI–MS full scan revealed that the most abundant ion fragment of each PHCZ was usually its molecular ion, agreeing with the previously published qualitative analysis/identification of PHCZs in sediments [8]. Hence for each PHCZ, the two most intense isotope ions of its molecular ion cluster were
Conclusions
In response to the increasing interest in these emerging contaminants, we developed an efficient and sensitive analytical methodology for the quantitative determination of a suite of most common and environmentally relevant halogenated carbazoles in sediments. Compared to the common sample cleanup techniques employed in a number of laboratories, our method avoided the usage of acid media which may damage some PHCZ substances. Our method also reduced solvent and time consumption, and resulted in
Acknowledgments
This study was financially supported in part by a Grant Agreement from the United States Department of the Interior, Fish and Wildlife Service with funding from the Great Lakes Restoration Initiative (GLRL) and the Faculty Collaborative Seed Grant of the Southern Illinois University Carbondale (SIUC). Mention of trade names or commercial products does not constitute their endorsement by the United States Government. We thank Molly McCool of the U.S. Geological Survey (USGS), and James Boase,
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