Spatial and Temporal Trends of Polyhalogenated Carbazoles in Sediments of Upper Great Lakes: Insights into Their Origin

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).

Polyhalogenated carbazoles contamination in East China Sea sediments: Spatial distribution, source apportionment, and ecological risk assessment

Polyhalogenated carbazoles (PHCZs), an emerging class of halogenated organic pollutants, have been widely detected in various environmental media, including sediments, soil, air, and organisms. The East China Sea (ECS) is a vital region for marine and fishery resource development in China, yet research on the pollution levels and sources of PHCZs in its sediments remains limited. This study reports the occurrence of seven PHCZs in the surface sediments of the ECS, with detection rates exceeding 90%. The concentrations of Σ7PHCZs ranged from 3.5 to 27 ng/g, with an average of 9.9 ng/g. The predominant congeners were 1368-BCZ and 3-ICZ. The sources of PHCZs included a non-specific source transported via terrestrial runoff (39%), industrial wastewater discharge (35%), and optoelectronic material pollution (26%), as identified by the positive matrix factorization model. The ecological risk assessment, based on TEQ, indicated a range of 0.18-5.0 pg TEQ/g across the study area. These findings highlight the potential ecological concerns associated with PHCZs in the ECS and emphasize the need for enhanced environmental monitoring and source mitigation efforts to reduce their potential environmental impacts.

Polyhalogenated carbazoles in the environment: Analysis, origins, occurrence, and toxicity

Polyhalogenated carbazoles are a class of emerging organic compounds characterized by the substitution of one to eight hydrogen atoms in the carbazole structure with halogen atom(s). Polyhalogenated carbazoles originate from natural and anthropogenic sources and are widely distributed in the environment. They are persistent in the environment and present a range of toxic effects, notably dioxin-like activity. This review focused on recent progress in determining their distribution, analytical methodologies, toxicity, origins, and transformation in the environment, highlighting their potential ecological and health risks. It confirmed the critical need for ongoing research regarding their environmental behavior and fate, to ensure a comprehensive understanding of the resulting environmental risks. This review also identified future research needs regarding these compounds.

Dioxin-like effects of an emerging contaminant 1,3,6,8-tetrabromocarbazole on the myogenic differentiation of mouse C2C12 cells

1,3,6,8-Tetrabromocarbazole (1368-BCZ) has been proposed as an emerging environmental contaminant which has aryl hydrocarbon receptor (AhR) activating properties analogous to those of dioxins. Skeletal muscle development is a critical target of dioxin toxicity. However, the impact of 1368-BCZ on muscle development is inadequately understood. The C2C12 mouse myoblast cell is extensively utilized as an in vitro model for studying myogenesis. In the present study, we observed that treatment with 1368-BCZ inhibited myogenic myoblast differentiation in a concentration-dependent manner, without inducing cytotoxicity. Using flow cytometry analysis and a wound healing assay, we found that the cell cycle exit and migratory activity were blocked in 1368-BCZ-treated cells at the early stage of C2C12 differentiation. In line with this alteration, 1368-BCZ significantly upregulated the expression of cell cycle regulators and migration-related genes, whereas it suppressed the expression of myogenic regulatory factors (MRFs) and skeletal muscle myosin isoforms (MYH3 and MYH4), marker genes for myogenesis. Furthermore, treatment with 1368-BCZ activated the AhR signaling pathway, leading to the transcriptional upregulation of AhR-target genes, CYP1A1 and CYP1B1. Silencing AhR mitigated the inhibitory effects of 1368-BCZ on C2C12 differentiation and significantly enhanced the formation of multi-nucleated myotubes through the upregulation of MRFs expression. Taken together, our study suggests that 1368-BCZ exerts an inhibitory effect on myogenesis in C2C12 cells through an AhR-dependent regulatory mechanism, which is highly similar to the observed dioxin effect.

The necessity of enhancing the human health risk assessment of 1,3,6,8-tetrabromocarbazole: Based on in vitro experiments, theoretical calculations, and model predictions

Industrial emissions have been identified as significant contributors to polyhalogenated carbazoles (PHCZs), a novel pollutant in the environment. Enhancing the health risk assessment of PHCZs is imperative, particularly for 1,3,6,8-tetrabromocarbazole (1368BCZ), the most commonly detected PHCZs in the environment. This study revealed that 1368BCZ could bind to the important transporters, human serum albumin (HSA), with high binding constant (KA: 1.02 × 105 L/mol). 1368BCZ primary bound to the HSA binding site 2, and the impact of 1368BCZ on HSA structure was minimal, indicating 1368BCZ may has strong accumulation in human. Theoretical analysis indicated that the uniformly distributed molecular surface electrostatic potential of the 1368BCZ molecule was crucial for its strong binding affinity to HSA. van der Waals forces serve as the primary interaction force stabilizing this binding. Further model predictions results showed that 1368BCZ may cause various toxic effects including hepatotoxicity, neurotoxicology, mutagenicity, etc. In summary, this study revealed the potential human health risks associated with 1368BCZ, providing an important basis for the formulation of relevant environmental control standards.

Non-negligible Polyhalogenated Carbazoles in Arctic Soils and Sediments: Occurrence, Target and Suspect Screening, and Potential Sources

The presence of polyhalogenated carbazoles (PHCZs), which are emerging as dioxin-like contaminants, in remote polar regions has not been reported. This study investigated 11 target PHCZs (Σ11PHCZs) and 25 unknown PHCZs (Σ25UNPs) in soil and sediment samples collected from Ny-Ålesund in the Arctic. The findings revealed that Σ11PHCZs concentrations reached 165.6 ng/g dry weight (dw), with 3,6-dichlorocarbazole and 3-chlorocarbazole being the predominant congeners. The Σ25UNPs concentrations ranged from 1.4 to 92.4 ng/g dw (median: 17.0 ng/g dw), primarily comprising a 1,3,6,8-tetrabromocarbazole isomer. The sediment contained ∼6 times more Σ25UNPs than Σ11PHCZs. Long-range atmospheric transport, oceanic transport, and human activity can potentially affect soils and sediments concurrently. For the first time, halogen substitution patterns in PHCZs, including ClI, ClI2, and ClI3, were detected in soil and sediment. Using the toxic equivalent (TEQ) approach, the potential toxic effects linked to the target PHCZ levels were assessed. The TEQPHCZs in Arctic soils and sediments indicated low risk, ranging from 8.0 × 10-3 to 17 pg TEQ/g dw (median: 2.8 pg TEQ/g dw) and 0.1 to 0.4 pg TEQ/g dw (median: 0.3 pg TEQ/g dw), respectively. This study marks the first report on the occurrence, composition, sources, and potential risks posed by PHCZs in the Arctic region.

Environmental behavior and risk of the emerging organic contaminants halogenated carbazoles in chemical industrial park clusters

Polyhalogenated carbazoles (PHCZs) are emerging organic contaminants and have attracted extensive concern because of their widespread occurrence and dioxin-like toxicity. However, the distribution characteristics, environmental behavior, and fate of PHCZs are still poorly understood. In this study, 74 composite environmental samples from 21 Chinese cities were collected around industrial parks in the Yangtze River Delta. The PHCZ concentration ranges in sediment and soil samples were 12.7-5.21 × 103 and 34.6-1.81 × 103 ng/g, respectively, which is equivalent to or higher than those of well-known persistent organic pollutants in the similar areas. The dominant congeners of PHCZs in sediment and soil were 3-chlorocarbazole and 3,6-dichlorocarbazole. Industrial emissions, especially from printing and dyeing textiles, were the main contributors to the high PHCZ environmental concentrations. Potential toxic effects of the PHCZs were evaluated using the toxic equivalent (TEQ) method. The TEQs of PHCZs in sediment and soil were up to 550 and 554 pg TEQ/g dry weight, respectively. The estimated TEQ value of sediment and soil exceeded the corresponding safety guideline, which indicated that PHCZs in the Yangtze River Delta posed high health risks. This study provides an important theoretical basis for controlling and reducing the ecological risks of PHCZs in the chemical industry. At the same time, it also provides reference for the priority control and revision of discharge standards for PHCZs in sewage treatment plants in future.

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

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.

Spatial distribution characteristics of carbazole and polyhalogenated carbazoles in water column and sediments in the open Western Pacific Ocean

Polyhalogenated carbazoles (PHCZs), an emerging persistent halogenated organic pollutant, have been detected in the environment. However, our understanding of PHCZs in the ocean remains limited. In this study, 47 seawater samples (covering 50 - 4000 m) and sediment samples (49 surface and 3 cores) were collected to investigate the occurrence and spatial distribution patterns of carbazole and its halogenated derivants (CZDs) in the Western Pacific Ocean. In seawater, the detection frequencies of CZ (97.87%) and 3-CCZ (57.45%) were relatively high. In addition, the average concentration of ΣPHCZs in the upper water (< 150 m, 0.23 ± 0.21 ng/L) was significantly lower than that in the deep ocean (1000 - 4000 m, 0.65 ± 0.56 ng/L, P < 0.05), which may indicate the vertical transport of PHCZs in the marine environment. The concentration of ΣCZDs in surface sediment ranges from 0.46 to 6.48 ng/g (mean 1.54 ng/g), among which CZ and 36-CCZ were the predominant components. Results from sediment cores demonstrate a noteworthy negative correlation between the concentration of CZDs and depth, indicating the ongoing natural degradation process occurring in sediment cores over a long period. This study offers distinctive insights into the occurrence, composition, and vertical features of CZDs in oceanic environments.

Occurrence, distribution, and ecological risks of polyhalogenated carbazoles in sediments from Daya Bay and Pearl River Estuary, China

Polyhalogenated carbazoles (PHCZs) are a group of emerging organic pollutants attracting increasing concern. In this study, 32 sediment samples were collected from the Pearl River Estuary (PRE) and adjacent Daya Bay (DYB) in China and were investigated for the occurrence and distribution of PHCZs. Total concentration of sedimentary PHCZs (∑PHCZs) ranged from 0.79 to 3.08 ng/g in PRE and 0.89 to 1.95 ng/g in DYB, both containing 3,6-dichlorocarbazole as the main component. Higher concentrations of ∑PHCZs were found in the rivers-mouth and inner part of the PRE indicating their main origins from anthropogenic activities. Notably, concentrations of brominated carbazoles (BCZs) gradually increased offshore, which suggests the potential bio-transformation of BCZs under a saline environment. The toxic equivalent of PHCZs was estimated at 0.13-0.34 pg TEQ/g suggesting limited dioxin-like effects on local organisms.

Combined toxic effects of polystyrene microplastics and 3,6-dibromocarbazole on zebrafish (Danio rerio) embryos

Microplastics (MPs) and polyhalogenated carbazoles (PHCZs) are widely detected in the aquatic environment, and their ecological risks have become a research focus. Although there is an extensive co-distribution of MPs and PHCZs, their combined toxicity to aquatic organisms is still unclear. This study investigated the toxic effects of polystyrene microplastics (PS-MPs) and 3,6-dibromocarbazole (3,6-DBCZ) on zebrafish embryos by individual/combined exposure. This study showed that individual or combined exposure of PS-MPs (10 mg/L) and 3,6-DBCZ (0.5 mg/L) could significantly increase the rate of zebrafish embryo deformity, whereas no significant effect was observed on mortality and hatching rate. Furthermore, exposure to 3,6-DBCZ or PS-MPs increased reactive oxygen species (ROS) levels in zebrafish embryos, and the resulting oxidative stress induced apoptosis. Comparably, the levels of oxidative stress and apoptosis in zebrafish embryos were significantly reduced with the combined exposure of 3,6-DBCZ and PS-MPs. These observations suggest that the combined exposure of 3,6-DBCZ and PS-MPs has an antagonistic effect on oxidative stress and apoptosis. Fluorescence PS-MPs tracing and 3,6-DBCZ enrichment analysis showed that, with the protection of chorion, the entry of PS-MPs (5 and 50 μm) into the embryonic stage (55 hpf) of zebrafish was prevented. Moreover, after exposure for 96-144 hpf, PS-MPs served as a carrier to promote the 3,6-DBCZ accumulation and its dioxin-like toxicity in zebrafish larvae through ingestion. Compared with 5-μm PS-MPs, 50-μm PS-MPs promoted higher accumulation and dioxin-like toxicity of 3,6-DBCZ in zebrafish larvae. These findings provide that MPs can be used as an important carrier of PHCZs, influencing their toxicity and bioaccumulation in the organisms.

Exploring the adverse effects of 1,3,6,8-tetrabromo-9H-carbazole in atherosclerotic model mice by metabolomic profiling integrated with mechanism studies in vitro

Given its wide distribution in the environment and latent toxic effects, 1,3,6,8-tetrabromo-9H-carbazole (1368-BCZ) is an emerging concern that has gained increasing attention globally. 1368-BCZ exposure is reported to have potential cardiovascular toxicity. Although atherosclerosis is a cardiovascular disease and remains a primary cause of mortality worldwide, no evidence has been found regarding the impact of 1368-BCZ on atherosclerosis. Therefore, we aimed to explore the deleterious effects of 1368-BCZ on atherosclerosis and the underlying mechanisms. Serum samples from 1368-BCZ-treated atherosclerotic model mice were subjected to metabolomic profiling to investigate the adverse influence of the pollutant. Subsequently, the molecular mechanism associated with the metabolic pathway of atherosclerotic mice that was identified following 1368-BCZ exposure was validated in vitro. Serum metabolomics analysis revealed that 1368-BCZ significantly altered the tricarboxylic acid cycle, causing a disturbance in energy metabolism. In vitro, we further validated general markers of energy metabolism based on metabolome data: 1368-BCZ dampened adenosine triphosphate (ATP) synthesis and increased reactive oxygen species (ROS) production. Furthermore, blocking the aryl hydrocarbon receptor (AhR) reversed the high production of ROS induced by 1368-BCZ. It is concluded that 1368-BCZ decreased the ATP synthesis by disturbing the energy metabolism, thereby stimulating the AhR-mediated ROS production and presumably causing aggravated atherosclerosis. This is the first comprehensive study on the cardiovascular toxicity and mechanism of 1368-BCZ based on rodent models of atherosclerosis and integrated with in vitro models.

Effects of exposure to 3,6-DBCZ on neurotoxicity and AhR pathway during early life stages of zebrafish (Danio rerio)

Polyhalogenated carbazoles (PHCZs) are emerging environmental pollutants, yet limited information is available on their embryotoxicity and neurotoxicity. Therefore, the current work was performed to investigate the adverse effects of 3,6-dibromocarbazole (3,6-DBCZ), a typical PHCZs homolog, on the early life stages of zebrafish larvae. It revealed that the 96-hour post-fertilization (hpf) median lethal concentration (LC50) value of 3,6-DBCZ in zebrafish larvae was determined to be 0.7988 mg/L. Besides, 3,6-DBCZ reduced survival rates at concentrations ≥ 1 mg/L and decreased hatching rates at ≥ 0.25 mg/L at 48 hpf. In behavior tests, it inhibited locomotor activities and reduced the frequency of recorded acceleration states in response to optesthesia (a sudden bright light stimulus) at concentrations ≥ 160 μg/L. Meanwhile, 3,6-DBCZ exposure decreased the frequency of recorded acceleration states in the startle response (tapping mode) at concentrations ≥ 6.4 μg/L. Pathologically, with the transgenic zebrafish model (hb9-eGFP), we observed a strikingly decreased axon length and number in motor neurons after 3,6-DBCZ treatment, which may be ascribed to the activation of the AhR signaling pathway, as evidenced by the molecular docking analysis and Microscale thermophoresis (MST) assay suggested that 3,6-DBCZ binding to AhR-ARNT2 compound proteins. Through interaction with AhR-ARNT, a striking reduction of the anti-oxidative stress (sod1/2, nqo1, nrf2) and neurodevelopment-related genes (elavl3, gfap, mbp, syn2a) were observed after 3,6-DBCZ challenge, accompanied by a marked increased inflammatory genes (TNFβ, IL1β, IL6). Collectively, our findings reveal a previously unrecognized adverse effect of 3,6-DBCZ on zebrafish neurodevelopment and locomotor behaviors, potentially mediated through the activation of the AhR pathway. Furthermore, it provides direct evidence for the toxic concentrations of 3,6-DBCZ and the potential target signaling in zebrafish larvae, which may be beneficial for the risk assessment of the aquatic ecosystems.

Occurrence of polyhalogenated carbazoles and the combined effects with heavy metals on variation in bacterial communities in estuarine sediments

Carbazole (CZ) and eight polyhalogenated carbazoles (PHCZs) were quantified by GC-MS in sediments of 12 estuaries, the interface linking large industrial and living areas to the Bohai Sea, China. These pollutants, heavy metals, and environmental factors caused integrated exposure to sediment bacteria. Four PHCZ congeners were detectable, with ΣPHCZs ranging from 0.56 to 15.94 ng/g dw. The dominant congeners were 3,6-dichlorocarbazole (36-CCZ) and 3-chlorocarbazole (3-CCZ), with a mean contribution of 72.6 % and 20.2 %. Significant positive correlations were found between 36-CCZ and both total organic carbon and heavy metals. Redundancy analysis of microbial variation implicated no impacts from PHCZs. Correlation analysis demonstrated an increase in abundance of Rhodocyclaceae but a decrease in Bacteroides-acidifaciens-JCM-10556 with presence of PHCZs, suggesting that these bacteria can be used as potential contamination indicators. The combined exposure of heavy metals, nutrients, and PHCZs may also increase toxicity and biological availability, adversely affecting the ecosystem and human health.

Tissue-specific accumulation, depuration and histopathological effects of 3,6-dichlorocarbazole and 2,7-dibromocarbazole in adult zebrafish (Danio rerio)

Although polyhalogenated carbazoles have been detected with increasing frequency in aquatic ecosystems, their bioaccumulation in fish and corresponding pathological effects related to bioaccumulation are still unclear. Here, we investigated the tissue-specific accumulation, depuration, and histopathological effects of two typical PHCZs, 3,6-dichlorocarbazole (36-CCZ) and 2,7-dibromocarbazole (27-BCZ), in adult zebrafish at three levels (0, 0.15 μg/L (5 × environmentally relevant level), and 50 μg/L (1/10 LC50). The lowest concentrations of 36-CCZ (1.2 μg/g ww) and 27-BCZ (1.4 μg/g ww) were observed in muscle, and the greatest concentrations of 36-CCZ (3.6 μg/g ww) and 27-BCZ (4 μg/g ww) were detected in intestine among the tested tissues. BCFww of 36-CCZ and 27-BCZ in zebrafish ranged from 172.9 (muscle) to 606.6 (intestine) and 285.2 (muscle) to 987.5 (intestine), respectively, indicating that both 36-CCZ and 27-BCZ have high potential of bioaccumulation in aquatic system. The 0.15 μg/L level of 36-CCZ or 27-BCZ caused lipid accumulation in liver, while 50 μg/L of 36-CCZ or 27-BCZ induced liver lesions such as fibrous septa, cytolysis, and nuclear dissolution. Brain damage such as multinucleated cells and nuclear solidification were only observed at 50 μg/L of 27-BCZ. This study provided valuable information in assessing the health and ecological risks of 36-CCZ and 27-BCZ.

Pollution characteristics, distribution, and source analysis of carbazole and polyhalogenated carbazoles in coastal areas of Bohai Bay, China

Polyhalogenated carbazoles (PHCZs) are a class of emerging environmental contaminants formed by the substitution of hydrogen on carbazole (CZ) benzene rings with halogens (Cl, Br, I) with potential dioxin-like toxicity, and they have been frequently detected in various environmental media and organisms recently. Nevertheless, co-research of CZ/PHCZs with PAHs is very limited. In addition, I-PHCZs, which are believed to be much more toxic than CZ, Cl-PHCZs and Br-PHCZs, have a few data in sediments previously. The concentration and distribution of CZ/PHCZs and PAHs were analyzed in 18 surface sediments of Bohai Bay, China. There is a significant correlation (R = 0.64, P＜0.05) between PHCZs and PAHs, and principal component analysis (PCA) also indicating that they may have a certain similarity in origin. Additionally, total CZ and PHCZs was up to 230.57 ng/g dw in the studied samples, which was approximately 1-2 orders of magnitude lower than PAHs and other common persistent organic pollutants (POPs). The compositions of the CZ/PHCZs in our study were dominated by CZ (2.74-18.28, median 2.92 ng/g dw), 3,6-dichlorocarbazole (n.d-6.78, median 0.97 ng/g dw) and 3,6-iodocarbazole (n.d-12.68, median 1.65 ng/g dw). Results of this study discovered the varying origins of CZ and PHCZs and/or a complexity of anthropogenic influences and natural sources processes, and revealed a wide distribution of CZ/PHCZs across the studied. Moreover, more attention should be paid by comparing CZ/PHCZs with other widely distributed POPs.

Identification and Prioritization of Environmental Organic Pollutants: From an Analytical and Toxicological Perspective

Exposure to environmental organic pollutants has triggered significant ecological impacts and adverse health outcomes, which have been received substantial and increasing attention. The contribution of unidentified chemical components is considered as the most significant knowledge gap in understanding the combined effects of pollutant mixtures. To address this issue, remarkable analytical breakthroughs have recently been made. In this review, the basic principles on recognition of environmental organic pollutants are overviewed. Complementary analytical methodologies (i.e., quantitative structure-activity relationship prediction, mass spectrometric nontarget screening, and effect-directed analysis) and experimental platforms are briefly described. The stages of technique development and/or essential parts of the analytical workflow for each of the methodologies are then reviewed. Finally, plausible technique paths and applications of the future nontarget screening methods, interdisciplinary techniques for achieving toxicant identification, and burgeoning strategies on risk assessment of chemical cocktails are discussed.

Mutual interference between 3,6-dichlorinated carbazole and p,p'-dichlorodiphenyltrichloroethane in gas chromatography mass spectrometry analysis

The widespread contamination of the environment by polyhalogenated carbazoles (PHCZs) has been increasingly observed during the past decade. Among numerous PHCZ congeners, 3,6-dichlorocarbazole (36-CCZ) is often among the most frequently detected at higher concentrations. Although the environmental level of the legacy pesticide p,p'-dichlorodiphenyltrichloroethane (p,p'-DDT) has been declining, it continues to be ubiquitously detected. These two compounds were found to interfere with each other during analyses using gas chromatography (GC) coupled with single- or triple-quadrupole low-resolution mass spectrometry (MS or MS/MS). The base peak in the mass spectra was that of m/z 235 for both compounds. In MS/MS with multiple reaction monitoring (MRM), the same transitions (235 → 200 and 235 → 165) were often used. Under the same GC operating conditions, the SH-I-5MS capillary column used in this work did not resolve the two compounds at baseline. Pre-treatment using cleanup column chromatography can fractionate the sample extract, with the two compounds separated in different fractions before instrumental analyses. Reversed-phase HPLC columns also work for resolving 36-CCZ and p,p'-DDT. Possible overlaps in GC retention and similarity in MS spectra might have caused data inaccuracy for 36-CCZ as well as p,p'-DDT in some studies published to date, and steps to avoid the interference should be taken into quality control protocols in future research and environmental monitoring.

PM2.5-bound polyhalogenated carbazoles (PHCZs) in urban Beijing, China: Occurrence and the source implication

Polyhalogenated carbazoles (PHCZs) are recently raising much attention due to their toxicity and ubiquitous environmental distribution. However, little knowledge is known about their ambient occurrences and the potential source. In this study, we developed an analytical method based on GC-MS/MS to simultaneously determine 11 PHCZs in PM_2.5 from urban Beijing, China. The optimized method provided low method limit of quantifications (MLOQs, 1.45-7.39 fg/m³) and satisfied recoveries (73.4%-109.5%). This method was applied to analyze the PHCZs in the outdoor PM_2.5 (n = 46) and fly ash (n = 6) collected from 3 kinds of surrounding incinerator plants (steel plant, medical waste incinerator and domestic waste incinerator). The levels of ∑₁₁PHCZs in PM_2.5 ranged from 0.117 to 5.54 pg/m³ (median 1.18 pg/m³). 3-chloro-9H-carbazole (3-CCZ), 3-bromo-9H-carbazole (3-BCZ), and 3,6-dichloro-9H-carbazole (36-CCZ) were the dominant compounds, accounting for 93%. 3-CCZ and 3-BCZ were significantly higher in winter due to the high PM_2.5 concentration, while 36-CCZ was higher in spring, which may be related to the resuspending of surface soil. Furthermore, the levels of ∑₁₁PHCZs in fly ash ranged from 338 to 6101 pg/g. 3-CCZ, 3-BCZ and 36-CCZ accounted for 86.0%. The congener profiles of PHCZs between fly ash and PM_2.5 were highly similar, indicating that combustion process could be an important source of ambient PHCZs. To the best of our knowledge, this is the first research providing the occurrences of PHCZs in outdoor PM_2.5.

Industrial source identification of polyhalogenated carbazoles and preliminary assessment of their global emissions

Polyhalogenated carbazoles (PHCZs) are emerging global pollutants found in environmental matrices, e.g., 3000 tonnes of PHCZs have been detected in the sediments of the Great Lakes. Recognition of PHCZ emissions from ongoing industrial activities worldwide is still lacking. Here, we identify and quantify PHCZ emissions from 13 large-scale industries, 12 of which previously have no data. Congener profiles of PHCZs from investigated industrial sources are clarified, which enables apportioning of PHCZ sources. Annual PHCZ emissions from major industries are estimated on the basis of derived emission factors and then mapped globally. Coke production is a prime PHCZ emitter of 9229 g/yr, followed by iron ore sintering with a PHCZ emission of 3237 g/yr. China, Australia, Japan, India, USA, and Russia are found to be significant emitters through these industrial activities. PHCZ pollution is potentially a global human health and environmental issue.

Polyhalogenated carbazoles induce hepatic metabolic disorders in mice via alteration in gut microbiota

Polyhalogenated carbazoles (PHCZs) have been widely accepted as emerging pollutants, whereas their ecological and health risks remain uncertain. Herein, female and male Sprague-Dawley (SD) mice were treated with four typical PHCZs to investigate their negative consequences, along with alternations in gut microbiota to indicate underlying mechanisms. In female mice, the relative liver weight ratio increased after four PHCZs exposure; 2-bromocarbazole (2-BCZ) increased urine glucose level; 3-bromocarbazole (3-BCZ) decreased the glucose and total cholesterol levels; 3,6-dichlorocarbazole (3,6-DCCZ) decreased glucose level. The only disturbed biochemical index in male mice was the promoted alkaline phosphatase (ALP) level by 3,6-DCCZ. We also found that the differential blood biochemical indices were correlated with gut microbiota. 3-BCZ and 3,6-DCCZ altered Bacteroidetes and Proteobacteria phyla in female and male mice, which were correlated with metabolic disorders. Our findings demonstrated the correlation between PHCZs induced potential hepatotoxicity and metabolic disorders may be due to their dioxin-like potentials and endocrine disrupting activities, and the gender differences might result from their estrogenic activities. Overall, data presented here can help to evaluate the ecological and health risks of PHCZs and reveal the underlying mechanisms.

Insight into the formation of polyhalogenated carbazoles during seawater chlorination

Although polyhalogenated carbazoles (PHCZs) have been widely detected in the marine environment, their origin is far from clear. In this study, the formation of PHCZs in the chlorination of seawater containing carbazole and its derivatives was investigated. A total of 14 PHCZs including six commonly found and eight unknown congeners were identified in the chlorination of seawater with carbazole. In addition, this study for the first time demonstrated the production of common PHCZs from the chlorination of seawater with 3-methyl carbazole and 3-formyl carbazole, especially 1,8-dibromo-3,6-dichlorocarbazole from 3-methyl carbazole. The formation of PHCZs in the reaction resulted from the halogenation of carbazole by reactive chlorine species (RCS) and mainly reactive bromine species (RBS), forming from the oxidation of bromide by RCS. Results also indicated that the reaction followed a successive halogenation pattern. A higher content of free chlorine and bromide facilitated the generation of RBS, while a higher concentration of DOC exhibited an inhibitory effect. The effects of free chlorine, bromide, DOC, and temperature on the formation of PHCZs were congener-specific. Given the widespread use of chlorination in seawater disinfection, seawater chlorination might be a potential source of PHCZs in the marine environment.

Production of Polyhalogenated Carbazoles in Marine Red Alga Corallina officinalis: A Possible Natural Source

Polyhalogenated carbazoles (PHCZs) have been increasingly detected in the environment as a result of anthropogenic and natural origin. However, it is unclear how PHCZs are naturally produced. In this study, the formation of PHCZs from bromoperoxidase (BPO)-mediated halogenation of carbazole was investigated. A total of six PHCZs were identified in reactions under different incubation conditions. The presence of Br^- significantly influenced the formation of PHCZs. The products were first dominated by 3-bromocarbazole and then 3,6-dibromocarbazole as the reactions proceeded. Both bromo- and chlorocarbazoles were identified in the incubations with trace Br^-, suggesting the co-occurrence of BPO-catalyzed bromination and chlorination. However, BPO-catalyzed chlorination of carbazole was much weaker than that of bromination. The formation of PHCZs could be attributable to the halogenation of carbazole by reactive halogen species generated from BPO-catalyzed oxidation of Br^- and Cl^- by H₂O₂. The halogenation was found to follow a successive substitution order of C-3, C-6, and C-1 on the carbazole ring, forming 3-, 3,6-, and 1,3,6-isomers. Similar to the incubation experiments, six PHCZs were for the first time detected in red algal samples collected from the South China Sea, China, suggesting the biogenesis of PHCZs in marine red algae. Given the widespread distribution of red algae in the marine environment, BPO-catalyzed halogenation of carbazole may be a natural origin for PHCZs.

Sediment-water distribution and potential sources of polyhalogenated carbazoles in a coastal river locating at a north metropolis, China

The fate and transformation of PHCZs in the coastal river environment are not yet comprehensively understood. Paired river water and surface sediment were collected, and 12 PHCZs were analyzed to find out their potential sources and investigate the distribution of PHCZs between river water and sediment. The concentration of ∑PHCZs varied from 8.66 to 42.97 ng/g (mean 22.46 ng/g) in sediment and 17.91 to 81.82 ng/L (mean 39.07 ng/L) in river water. 18-B-36-CCZ was the dominant PHCZ congener in sediment, while 36-CCZ was in water. Meanwhile, the logK_oc values for CZ and PHCZs were among the first calculated in the estuary and the mean logK_oc varied from 4.12 for 1-B-36-CCZ to 5.63 for 3-CCZ. The logK_oc values of CCZs were higher than those of BCZs, this may suggest that sediments have a higher capacity for accumulation and storage of CCZs than highly mobile environmental media.

Spatial and temporal distribution of polyhalogenated carbazoles in sediments from the Yangtze River estuary and adjacent East China Sea

Polyhalogenated carbazoles (PHCZs) have been increasingly detected in marine sediment, raising concerns in recent years. In this study, sediment samples (42 surface and one core) were collected from the Yangtze River estuary and the adjacent East China Sea, and eleven PHCZs and unsubstituted carbazole were measured. The total concentration of PHCZs in surface sediments ranged from 0.19 to 2.49 ng/g dry weight (d.w.) (median 1.03 ng/g d. w.). The congener compositions of PHCZs in the surface sediment were dominated by 3,6-dichlorocarbazole (36-CCZ, 53.2%), followed by 3-chlorocarbazole (14.9%) and 3,6-dibromocarbazole (36-BCZ, 11.8%). Carbazole in the surface sediment ranged from not detected to 9.89 ng/g (median 1.25 ng/g), with a detection frequency of 81.0%. The spatial distribution of 36-CCZ in surface sediments exhibited a clear decline from the coast to offshore, while 36-BCZ showed the opposite trend. The depth profile of 36-CCZ was maintained at a relatively low and stable concentration (about 0.36 ng/g) in core segments from 1903 to 1951, followed by a steady increase to 1.5 ng/g in 2006. This increase coincides with the industrial and agricultural development in China that began in the 1950s. In contrast, the other detected PHCZs and carbazole maintained stable, low concentrations over time. These spatial and temporal patterns suggest that 36-CCZ in this area is predominantly from anthropogenic sources, while 36-BCZ has a natural origin. Toxic equivalent estimations indicated that dioxin-like effects for the observed PHCZs were low. These results provide useful information for understanding the origin of PHCZs and carbazole in this area.

Carbazole and polyhalogenated carbazoles in the marine environment around the Zhoushan Archipelago: Distribution characteristics, environmental behavior, and sources

The distribution characteristics and drivers of carbazole (CZ) and polyhalogenated carbazoles are still poorly understood. In this study, 96 samples were collected around the Zhoushan Archipelago, and their distribution characteristics were assessed. The results showed that CZ, 36-CCZ, and 36-BCZ were the top three abundant congeners in most collected samples. The bioaccumulation analysis revealed that marine plants prefer to accumulate CZ and bromocarbazoles rather than chlorocarbazoles. Both the mean concentrations of total carbazole and its derivants (ΣCZDs), as well as individual congeners, are the highest in sediments around the berthing areas of cargo ships and oil tankers. Meanwhile, ΣCZDs of these sediments are significantly influenced by the geo-weighted displacement of ships (r = 0.61; p < 0.05), indicating the ballast water from these ships as potential contributor for marine CZDs. Moreover, the accumulation of CZ in plankton, planktonic origin of sedimentary organic matter, and relationship between CZ and C/N ratio (p < 0.05) in sediments support the scenario that plankton absorbs and takes CZ into the sediments. These findings will promote the understanding of the sources, environmental behaviors, and fates of marine CZDs.

Soil to earthworm bioaccumulation of polyhalogenated carbazoles and related compounds: Lab and field tests

Polyhalogenated carbazoles (PHCZs) are an emerging group of organic contaminants that have attracted attention because of their ubiquity, resistance to biodegradation, and toxicities. However, studies on the bioaccumulation of PHCZs in terrestrial organisms are limited. In the present study, bioaccumulation of 11 PHCZs and two related compounds, carbazole (CZ) and benzocarbazole (BZCZ), from soil to earthworms was investigated by paired soil-earthworm samples from Hangzhou, China and a laboratory bioaccumulation test. The sum of the concentrations of the 11 polyhalogenated carbazoles (Σ₁₁PHCZs), CZ and BZCZ in soils from Hangzhou were 1.78-67.27 ng/g dry weight, 1.11-57.90 ng/g dry weight, and 22.87-171.98 ng/g dry weight, respectively, while those in the earthworms were 179.49-892.90 ng/g lipid weight, 42.90-2140.42 ng/g lipid weight, and not detectable-2514.76 ng/g lipid weight, respectively. The average in situ biota-to-soil accumulation factors (BSAFs) ranged from 0.38 to 13.23, comparable to those in some reports for polychlorinated biphenyls and polybrominated diphenlethers. Site-independence of BSAFs and no correlation between log C_worm and log C_soil together support the hypothesis that distribution of PHCZs between soil and worms in Hangzhou didn't reach equilibrium. In the laboratory test, the accumulation trends of CZ, BZCZ, 3-bromocarbazole, 3,6-dichlorocarbazole, and 2,7-dibromocarbazole well fit to the first-order kinetics, with r² ranging from 0.796 to 0.997. The BSAFs under two exposure concentration groups at steady-state conditions were 38.8-56.0 and 2.1-4.4, respectively, suggesting the capacity of bioaccumulation for these compounds. Enhancement of concentrations and resident time of the chemicals in soil would reduce the BSAF values, which may be related to the change of uptake process of the compound or redistribution of compound between soil and earthworm. A comparison of the theoretical steady-state concentrations with the nonlinear regression-based concentrations indicates that increasing the exposure time beyond 28 days is beneficial for studying the bioaccumulation of PHCZs.

Effects of the emerging contaminant 1,3,6,8-tetrabromocarbazole on the NF-κB and correlated mechanism in human hepatocellular carcinoma cells

1,3,6,8-Tetrabromocarbazole (1368-BCZ) is identified as an emerging contaminant that exerts angiogenic effects. Multiple studies indicated there was a positive correlation between angiogenesis and nuclear factor kappa B (NF-κB) activation. While the role of NF-κB in inflammation and apoptosis has been well known, the potential biological effects of 1368-BCZ on NF-κB signaling and related mechanism remain unclear. We, therefore, explored the possible effects of 1368-BCZ on the NF-κB pathway at the gene and protein levels and confirmed that NF-κB activation by 1368-BCZ exposure caused an augmented phosphorylated protein level, induction of NF-κB response element (κBRE)-driven luciferase activity and upregulation of transcriptional level of downstream responsive genes. Although 1368-BCZ did not produce detectable changes in hepatic fibrosis in vivo, it obviously altered the apoptosis in human hepatocellular carcinoma (HepG2) cells. Furthermore, the induction of apoptosis was confirmed by the increased cleaved caspase-3 level. These data revealed the activating effects of 1368-BCZ on NF-κB and its involvement in the underlying mechanisms, providing additional information for toxicology studies of emerging contaminants and introducing a mechanism-based toxicological evaluation of emerging pollutants.

Method development for determination of polyhalogenated carbazoles in industrial waste through gas chromatography/triple quadrupole tandem mass spectrometry

RATIONALE

Polyhalogenated carbazoles (PHCZs) are dioxin-like compounds that are ubiquitous in the environment. However, their unintentional emissions from industrial sources have received little attention and there is no method available for determination of PHCZs in industrial waste. This research develops a method for determination of PHCZs in industrial waste.

METHODS

In this research, a glass column packed with activated silica serves as a rapid and efficient clean-up pretreatment for purification. An isotope dilution gas chromatography/triple quadrupole tandem mass spectrometry method was established for simultaneous determination of eleven PHCZs in industrial samples.

RESULTS

The regression coefficients of the standard curves for the congeners were all >0.99. The method detection limit ranged from 1.46 to 3.82 ng/mL for liquid samples and from 0.009 to 0.021 ng/g for solid samples. The precision described by the relative standard deviation ranged from 2.4% to 18.4% for liquid samples and from 5.5% to 35.8% for solid samples. The recovery ranges for the liquid and solid samples were 82%-123% and 83%-137%, respectively. 3-Chlorocarbazole (3-CCZ) and 36-dichlorocarbazole (36-CCZ) can be detected in both chemical bottom liquid from vinyl chloride production and fly ash from medical waste incineration by this method.

CONCLUSIONS

An efficient method is established for determination of PHCZs from industrial waste. The discovery of 3-CCZ and 36-CCZ highlights the importance of identification of potential industrial sources of PHCZs and clarification of their contribution to environmental risks. Our method could be applied to investigate industrial emission of PHCZs.

Occurrence and distribution of polyhalogenated carbazoles in eastern Tibetan Plateau soils along the slope of Mt. Qionglai

Polyhalogenated carbazoles (PHCZs), are considered as potential persistent organic pollutants (POPs), which have been frequently detected in the environment. However, the altitudinal distribution characteristics and possible sources of PHCZs in high mountain soils are still unknown. The present study was the first to analyze PHCZs in soil samples collected along the eastern slope of Mt. Qionglai (MQ), the east edge of the Tibetan Plateau. The concentration of ΣPHCZs (based on dry weight) ranges from 14.4 to 107 ng/g (median value of 40.9), which was at high end of the range reported in soils and sediments to date in the literature. The composition profiles of PHCZs in the soils of MQ were dominated by 3,6-dichlorocarbazole (36-CCZ), 3-chlorocarbazole (3-CCZ), and 2-bromocarbazole (2-BCZ). The mean TOC-normalized concentrations of ΣPHCZs in soil samples from below-treeline (2092 ng/g TOC) were higher than those from alpine meadow (1124 ng/g TOC), probably due to the forest filter effect. The decreasing trend of the PHCZs TOC-normalized concentrations with altitude shows that accumulation of PHCZs from the alpine meadow samples was not affected by the mountain cold-trapping effect. Significantly positive correlations were observed between the concentrations of more than half of detected PHCZ congeners and TOC. In addition, PHCZs show the potential to represent a class of POPs with the frequent occurrence and wide distribution, as the abundance and environmental behavior of PHCZs are similar to some POPs in MQ.

HIF-1alpha/VEGF pathway mediates 1,3,6,8-tetrabromo-9 H-carbazole-induced angiogenesis: a potential vascular toxicity of an emerging contaminant

The dioxin-like substances polyhalogenated carbazoles (PHCZs) may trigger the aryl hydrocarbon receptor (AhR) signaling pathway. Although the crosstalk between AhR and the hypoxia inducible factor-1 (HIF-1) pathways is generally believed to occur, the exact mechanisms of the HIF-1 pathway in PHCZ toxicity have not been determined. We aimed to elucidate the effect of PHCZs on the HIF-1 pathway and its involvement in the regulation of target genes of HIF-1. Herein, we employed human HepG2 cells transiently transfected with a hypoxia response element (HRE) luciferase reporter to identify PHCZs that could influence HIF-1 pathway. We found that exposure to one of the four selected PHCZs, specifically 1,3,6,8-tetrabromo-9 H-carbazole (1368-BCZ), induced a significant enhancement of the activity of HRE activity. In silico data supported 1368-BCZ-induced HIF-1α activity preferentially. Moreover, 1368-BCZ significantly upregulated the expression of HIF-1 target genes, including endothelial growth factor (VEGF) and erythropoietin. Importantly, the stimulated secretion of VEGF by 1368-BCZ promoted the angiogenesis in human umbilical vein endothelial cells. Therefore, the present experimental and computational studies provide new and direct evidence of 1368-BCZ - HIF-1 interaction, which sheds light on the HIF-mediated cardiovascular toxicity and allows a knowledge-based risk assessment of emerging pollutants.

Occurrence, bioaccumulation and potential risk of polyhalogenated carbazoles in marine organisms from the East China Sea

As well-known emergent environmental contaminants, polyhalogenated carbazoles (PHCZs) have recently received increasing attention. In this study, we investigated the concentrations of carbazole (CZ) and PHCZs in 70 marine organisms from the East China Sea (ECS). CZ and 9-11 PHCZs were detected in organisms from the ECS, with concentrations in the range of 0.75-33 ng/g lipid weight, lw and 4.3-113 ng/g lw, respectively. Among the PHCZs, there were 3-4 major components in zooplankton, fish, shrimp, crabs, snails and shellfish, and the sum of these major components accounted for 59% to 67% of ∑PHCZs. The bioaccumulation potentials of 1,3,6,8-tetrachlorocarbazole (1368-CCZ) and 3-chlorocarbazole (3-CCZ) from water were observed. The logarithmic bioaccumulation factor (logBAF) values of the CZ and PHCZs increased significantly with increasing logK_OW values (R = 0.449-0.784, p < 0.01). The trophic magnification factor (TMF) values of the CZ, 9 PHCZs and ∑PHCZs were calculated to be 3.32, 1.87-4.06 and 2.36, respectively, indicating the potential biomagnification of the CZ and PHCZs in the zooplankton-shrimp-fish food web. The toxic equivalents (TEQs) of PHCZs in organisms from the ECS were in the range of 0.78-36 pg TEQ/g lw. Overall, for the first time, this study systematically examined the occurrence, bioaccumulation and potential risk of PHCZs in the marine food web of the East China Sea.

Occurrence and potential sources of polyhalogenated carbazoles in farmland soils from the Three Northeast Provinces, China

Polyhalogenated carbazoles (PHCZs) have been detected in various environments frequently and have attracted increasing attention for their multiple toxicities. However, only a few reports record the occurrence of PHCZs in farmland soils, and the sources of which were not yet been implemented. In this study, 12 PHCZs and carbazole (CZ) were screened in farmland soil samples from the Three Northeast Provinces, and the ∑PHCZs were in the range of 18.16-219.67 ng/g dw. 36-CCZ was the dominant congener (40.67%) in farmland soils, followed by 3-CCZ (14.51%), and average percentages of other congeners were lower than 10%. A concrete analysis of the sources of PHCZs in the soil was conducted, revealing the diversity of PHCZs sources. Potential toxic effects associated with the levels of PHCZs were evaluated via the toxic equivalency (TEQ) approach, and the TEQs of PHCZs (TEQ^PHCZs) were in the range of 2.24-14.06 pg TEQ/g dw. Notwithstanding the 1368-CCZ with a low concentration level, the mean contribution to TEQ^PHCZs was up to 24.24%, preceded only by 36-CCZ (39.69%), showing the congeners with low concentration also may pose potential risks to the environment. Partial PHCZs congeners (2-BCZ, 3-BCZ, 36-CCZ, 136-BCZ, and 2367-BCZ) showed significant correlations (r = 0.45-0.63, p < 0.05) with the total organic carbon (TOC). Significant correlations were shown between PHCZ congeners replaced by halogens of the same species and quantity (r = 0.40-0.99, p < 0.01). In view of the fact that the high concentration level of PHCZs in the soil and their source diversity, more environmental monitoring and risk assessments of PHCZs should be of particular concern.

Polyhalogenated carbazoles in freshwater and estuarine sediment from China and the United States: A multi-regional study

The present study represents a multi-regional investigation of polyhalogenated carbazoles (PHCZs) contamination in estuarine and freshwater systems from the United States and China. Although recent studies have suggested that PHCZs are persistent and bioaccumulative, available data are not sufficient to understand their large-scale spatial and temporal distributions in the environment. The present study investigated spatial distributions of PHCZs in surface sediment from multiple freshwater and estuarine systems located in China and the United States (U.S.) during the period of 2012-2017, as well as temporal distributions from vertical trends in selected sediment cores. The results demonstrated large variations of PHCZ contamination across regions, with median concentrations of ΣPHCZs in surface sediment ranging from 3.1 to 134 ng/g. Profiles of PHCZ congener composition also exhibited regional variations and estuarine-freshwater differences. These differences likely reflect the relative contributions of different natural and industrial sources among the locations. Vertical profiles of concentrations and compositions in one Chinese estuarine sediment core and two freshwater sediment cores from the U.S. all demonstrated clear anthropogenic influences to varying degrees. Toxic equivalents (TEQ) of PHCZs were estimated based on their dioxin-like activities, which ranged from <0.001 to 4.94 pg TEQ/g in all sites. The results suggest that PHCZs could add additional ecological risks to the benthos and other aquatic organisms. Our findings constitute an essential contribution to the knowledge body of PHCZ contamination in global aquatic systems and congener-specific contamination characterizations.

Determination of polyhalogenated carbazoles in waters at low nanogram-per-liter concentrations with solid-phase disk extraction

Polyhalogenated carbazoles, a class of emerging contaminants with persistence and dioxin-like toxicity, have received increasing attention in recent years. In this study, a simple, rapid, sensitive, and high throughput method based on solid-phase disk extraction and gas chromatography-mass spectrometry was described for the determination of polyhalogenated carbazoles in low nanogram-per-liter range in water samples. The proposed solid-phase disk extraction method was initially optimized, and the optimum experimental conditions found were 1 L water sample (pH 6-9) extracted and enriched by Empore 3-stn octadecyl disk at flow rate of 5 to 50 mL/min and eluted by 5 mL of acetone and 3 × 10 mL methylene dichloride. The linearity of the method ranged from 0.2 to 50 ng/L for carbazole and 11 polyhalogenated carbazoles, with correlation coefficients ranging from 0.9951 to 0.9996. The limits of detection were in the low nanogram per liter level, ranging from 0.018 to 0.12 ng/L. Finally, the optimized method was applied for determining trace levels of carbazole and 11 polyhalogenated carbazoles in tap water and seawater samples with good recovery of 86.6-112.8%. Carbazole and 3-7 polyhalogenated carbazoles were detected, and 3,6-dichlorocarbazole was the predominant congener both in tap water and seawater.

Occurrence and partitioning of polyhalogenated carbazoles in seawater and sediment from East China Sea

Polyhalogenated carbazoles (PHCZs) have received great concern due to their environmental persistence and potential dioxin-like toxicities. Their presence in the marine sediment had been well characterized, but limited studies had investigated their environmental behaviors in the marine environment. In this study, we collected paired seawater (n = 48) and surface sediment samples (n = 48) from East China Sea and analyzed for carbazole (CZ) and 11 PHCZs to investigate the occurrence and spatial distribution of CZ and PHCZs in seawater and sediment, as well as to explore the partitioning behaviors of CZ and PHCZs between seawater and sediment. In seawater samples, CZ and nine PHCZs were detected, with the concentrations of ∑PHCZs ranging from 0.21 to 11 ng/L (mean 2.7 ng/L). CZ (94%), 3-CCZ (89%), 1368-CCZ (65%), and 36-CCZ (57%) had relatively higher detection frequencies. Among PHCZs, 36-CCZ (mean 1.1 ng/L) had the highest mean seawater concentration, followed by 3-CCZ (0.51 ng/L) and 1368-CCZ (0.19 ng/L). In sediment, CZ and 11 PHCZs were detected, with the concentrations of ∑PHCZs ranged from 0.34 to 2.0 ng/g (mean 1.0 ng/g). CZ, 3-CCZ, 3-BCZ, 36-CCZ, 27-BCZ, and 36-BCZ were measurable in all sediment samples, and 36-CCZ was the predominant PHCZ (0.47 ng/g, 0.025-1.1 ng/g), followed by 1368-BCZ (0.16 ng/g, <LOD-0.29 ng/g) and 3-BCZ (0.11 ng/g, 0.016-0.33 ng/g). This study first calculated the field-based log K_oc values for CZ and PHCZs in marine environment. CZ (mean 2.8, range 1.4-3.6) had the highest log K_oc value, followed by 36-CCZ (2.7, 1.7-3.8), 1-B-36-CCZ (2.7, 2.3-3.1), and 36-BCZ (2.5, 2.2-2.9). The results of study may contribute to the better understanding of the environmental occurrence and behaviors of these chemicals in the marine environment.

High throughput extraction strategy for simultaneous analysis of 19 tetrabromobisphenol A and halogenated carbazole analogs in seafood

Tetrabromobisphenol A (TBBPA), halogenated carbazole (HCZ), and their analogs are the emerging pollutants invading the marine environment. So far, a few methods have been reported for the simultaneous analysis of these pollutants due to their large polarity difference. In this study, an effective extraction and cleanup strategy was developed for the simultaneous determination of 19 TBBPA and HCZ congeners in seafood. The 19 analytes could be directly analyzed through high performance liquid chromatography after ultrasonic extraction (methanol, duplicate ethyl acetate-acetone (1:1, v/v)) and gel permeation chromatography cleanup. The acceptable spike-recoveries were within 65.7-118.3%; the precision was intra-/inter-day RSDs: 0.0-6.7%/0.0-8.5%; and the matrix effects were between -14.1% and 12.4%. The detection limits and quantification limits were 0.002-0.014 and 0.020-0.200 µg g^-1 dw, respectively. Additionally, this method successfully analyzed the seafood samples and the concentrations of these analytes were in range of nd-5.4 µg g^-1 dw.

Occurrence and distribution of polyhalogenated carbazoles (PHCs) in sediments from the northern South China Sea

Polyhalogenated carbazoles (PHCs) have been frequently detected in various environments and have gained increasing attention due to their dioxin-like toxicity. In this study, 28 surface sediments and three sediment cores were collected from the northern South China Sea (SCS) to investigate the spatial and temporal distribution trends of PHCs. The total concentrations of PHCs in the surface sediments ranged from 0.25 ng/g to 3.10 ng/g, with a median concentration of 1.50 ng/g. The composition profiles of PHCs in the surface sediments were dominated by 3,6-dichlorocarbazole (36-CCZ), 3,6-dibromocarbazole (36-BCZ), and 1,3,6,8-tetrabromocarbazole (1368-BCZ). The total organic carbon (TOC) based concentrations of 36-CCZ, 1-bromo-3,6-dichlorocarbazole, 1,3,6,8-tetrachlorocarbazole, and 1368-BCZ showed significant positive correlation with water depth (r = 0.58-0.88, p values < 0.01). On the contrary, the TOC based concentration of 2,3,6,7-tetrachlorocarbazole displayed a significant negative correlation with the water depth (r = -0.52, p < 0.01). However, no significant correlation was observed for 3-chlorocarbazole, 36-BCZ, and 1,3,6-tribromocarbazole (p values > 0.05). PHCs in sediment cores showed that congener profiles and concentrations of PHCs remained largely stable throughout the 1890s and 2010s. In addition, all the detected PHCs displayed a significant positive correlation with TOC content of the sediments. These unique spatial and temporal distribution patterns suggest that both terrigenous and natural marine sources contributed the observed PHCs in sediments of the northern SCS.

Environmental behavior and safety of polyhalogenated carbazoles (PHCZs): A review

Polyhalogenated carbazoles (PHCZs) are well-known as emergent environmental contaminants. Given their wide distribution in the environment and structural similarity with dioxins and dioxin-like chemicals (DLCs), the environmental behavior and ecological risks of these chemicals have become the major issue concerned by the governments and scientists. Since the initial report of PHCZ residues in the environment in the 1980s, over 20 PHCZ congeners with different residual levels had been identified in various environmental media all over the world. Nevertheless, researches concerning the toxicological effects of PHCZs are of an urgent need for the relatively lagging study of their ecological risks. Currently, only limited evidence has indicated that PHCZs would pose dioxin-like toxicity, including developmental toxicity, cardiotoxicity, etc; and their toxicological effects were partially consistent with AhR activation. And yet, much remains to be done to fill in the knowledge gaps of their toxicological effects. In this review, the research progresses in environmental behavior and toxicology study of PHCZs were remarked; and the lack of current research, as well as future research prospects, were discussed.

Occurrence and exposure risk evaluation of polyhalogenated carbazoles (PHCZs) in drinking water

Although polyhalogenated carbazoles (PHCZs) can be generated and detected in drinking water, their occurrence and potential health risks to humans via drinking water ingestion are not well known. In this study, 11 PHCZs were screened in drinking water samples from Wuhan, the most populous city in central China. The total concentration of PHCZs could be up to 53.48 ng/L with a median level of 8.19 ng/L, which was comparable to polychlorinated biphenyls and poly- and perfluoroalkyl substances reported in the literatures for drinking water. Composition profiles revealed that 3,6-dichlorocarbazole, 3-chlorocarbazole, 3-bromocarbazole and 3,6-dibromocarbazole were the predominant PHCZ congeners in the tested samples. Regional differences in the levels and patterns of PHCZs suggested that anthropogenic releases should be the dominant source compared to natural generation. Boiling of the water samples caused no significant change in PHCZs concentrations after correcting the volume change due to evaporation. Potential health risks associated to the levels of PHCZs in drinking water were assessed using the toxic equivalent (TEQs) method. The estimated daily intake of PHCZs via drinking water ingestion is up to 0.38 pg-TEQ/kg body weight/day for infants, nearly 4.5 times higher than that for adults, and appears to reach the maximum permissible concentration set by certain authority agencies. Overall, drinking water ingestion represents an important exposure pathway for PHCZs. This is the first comprehensive study on the abundance and health risks of PHCZs in drinking water.

Emerging contaminant 1,3,6,8-tetrabromocarbazole induces oxidative damage and apoptosis during the embryonic development of zebrafish (Danio rerio)

Since polyhalogenated carbazoles (PHCs) have been widely detected at high concentrations in multiple environmental media in recent years, the health risk of exposure to these compounds has drawn increasing attention. Most studies have mainly focused on their dioxin-like toxicity, which is induced through the AhR pathway, because PHCs have structures similar to those of polychlorinated dibenzofurans (PCDFs). In addition, most xenobiotic compounds induce oxidative stress in organisms, which is a more common mechanism of toxicity induction. However, there is limited information regarding the oxidative stress and damage induced by PHCs in vivo. The PHC 1,3,6,8-tetrabromocarbazole (1368-TBCZ) is detected at high concentration and frequency. In the present study, the toxic effects (acute toxicity, developmental toxicity, oxidative stress, and apoptosis) induced by 1368-TBCZ at three different concentrations were investigated using zebrafish embryos. It was concluded that the 96 h median lethal concentration (LC₅₀) of 1368-TBCZ for zebrafish embryos was greater than 2.0 mg L^-1. The results showed that 1368-TBCZ had little effect on the hatching rate of zebrafish embryos. However, 1368-TBCZ at 0.5 and 2.0 mg L^-1 inhibited skeletal and cardiac development. It promoted ROS production, CAT enzyme activity, lipid peroxidation, DNA damage, and apoptosis, even at the lowest dose (0.1 mg L^-1). In addition, 1368-TBCZ influenced oxidative stress-related gene expression, upregulating the expression of caspase 3 and p53 at 2.0 mg L^-1 and inhibiting the expression of caspase 9, FoxO3b, and Bcl-2/Bax. The present study comprehensively evaluated 1368-TBCZ-induced toxicity in zebrafish, providing valuable data for better evaluation of the potential risks posed by this PHC.

Complex network dynamics of the topological structure in a geochemical field from the Nanling area in South China

The topological classification of geochemical elements is widely used as a reference for regional prospecting prediction. In this study, we analyze the topological correlation structures of 39 representative geochemical elements from the Nanling area of South China by implementing the complex networks theory. The topological correlation structures of geochemical elements have a high clustering coefficient (0.8120–0.8880), but the magnitude of the shortest path (1.2950–2.3600) is small. In combination with the analysis of complex networks characteristics, we report that the topological correlation structures of the geochemical elements in this area have small-world characteristics, which reveals the self-organized criticality. As shown in the topological network, two random elements have some level of associations, which present a specific community feature. Our preliminary result shows that with changing the control parameter (k) of “coarse-graining”, the topological correlation structures undergo two critical phase transitions. As the control parameter (k) reaches 0.44, the entire element system evolves into two parts. When the control parameter (k) reaches 0.63, the system forms three “communities”. It is worth noting that the three “communities” are basically consistent with the Goldschmidt’s geochemical classification of the elements, which are lithophile, siderophile, and chalcophile groups, respectively. In these “communities”, we also found that a small level of component units is nested.

Will Climate Change Influence Production and Environmental Pathways of Halogenated Natural Products?

Thousands of halogenated natural products (HNPs) pervade the terrestrial and marine environment. HNPs are generated by biotic and abiotic processes and range in complexity from low molecular mass natural halocarbons (nHCs, mostly halomethanes and haloethanes) to compounds of higher molecular mass which often contain oxygen and/or nitrogen atoms in addition to halogens (hHNPs). nHCs have a key role in regulating tropospheric and stratospheric ozone, while some hHNPs bioaccumulate and have toxic properties similar those of anthropogenic-persistent organic pollutants (POPs). Both chemical classes have common sources: biosynthesis by marine bacteria, phytoplankton, macroalgae, and some invertebrate animals, and both may be similarly impacted by alteration of production and transport pathways in a changing climate. The nHCs scientific community is advanced in investigating sources, atmospheric and oceanic transport, and forecasting climate change impacts through modeling. By contrast, these activities are nascent or nonexistent for hHNPs. The goals of this paper are to (1) review production, sources, distribution, and transport pathways of nHCs and hHNPs through water and air, pointing out areas of commonality, (2) by analogy to nHCs, argue that climate change may alter these factors for hHNPs, and (3) suggest steps to improve linkage between nHCs and hHNPs science to better understand and predict climate change impacts.

Phytotoxicity and metabolic responses induced by tetrachlorobiphenyl and its hydroxylated and methoxylated derivatives in rice (Oryza sative L.)

Polychlorinated biphenyls (PCBs) and their biotransformation products, hydroxylated (OH-PCBs) and methoxylated derivatives (MeO-PCBs), have been detected in the environment and biota, especially crops. However, to date, little information is available on the phytotoxicity and metabolic responses induced by these chemicals in crops. In this study, we exposed rice (Oryza sative L.) seedlings to 2,3,4,5-tetrachlorobiphenyl (CB-61) and its hydroxylated (4'-OH-CB-61) and methoxylated derivatives (4'-MeO-CB-61) at 0, 10, 50, 100 and 500 μg/L, respectively. After exposure for 14 days, significantly growth inhibition and oxidative damage were observed, among which the toxicities of 4'-OH-CB-61 and 4'-MeO-CB-61 were greater than that of the parent PCBs. Metabolomics analysis indicated that exposure to the three chemicals induced different metabolic responses. 4'-MeO-CB-61 mainly affected the saccharide catabolism, including pyruvate metabolism, the TCA cycle, the transfer of acetyl groups into mitochondria and the Warburg effect, resulting in a greater energy consumption. Moreover, both CB-61 and 4'-OH-CB-61 promoted several amino acid metabolism and fatty acid biosynthesis, thereby alleviating the potential ROS damage. This study for the first time evaluates and reveals the phytotoxicity of OH-PCBs and MeO-PCBs at the metabolic level, which attempts to provide important information for accurately evaluating the environmental risks of PCBs from the perspective of metabolism.

Halogenated flame retardants in sediments from the Upper Laurentian Great Lakes: Implications to long-range transport and evidence of long-term transformation

Most hydrophobic halogenated flame retardants (HFRs) are highly accumulative and persistent in aquatic sediments. The objective of this study was to reveal spatial distributions, temporal trends, and transformation of selected legacy and emerging HFRs in sediments of Lakes Superior, Michigan, and Huron. We collected Ponar grab samples at 112 locations and sediment cores at 28 sites in the three lakes, and measured concentrations of 19 brominated FRs and 12 chlorinated FRs. Based on grab samples, concentrations were higher at southeastern and sites near Sleeping Bear Dunes of Lake Michigan, and Saginaw Bay and the North Channel of Lake Huron. The annual loadings of polybrominated diphenyl either (PBDEs) and Dechlorane Plus (DPs) to sediment have leveled off or been declining since 2000, while loadings of DBDPE and Dec604 have increased since the 1960s in most cores. The concentration ratio of BB101 to BB153 increased with sediment depth, suggesting the occurrence of in situ debromination of BB153. The ratio of dechlorinated anti-Cl₁₁DP over anti-DP increases with the increasing latitude of sampling locations, suggesting the occurrence of dechlorination of anti-DP to anti-Cl₁₁DP during transport. This ratio also increases with increasing sediment age in most cores, implying in situ dechlorination over time.

Molecular insights into the formation and remobilization potential of nonextractable anthropogenic organohalogens in heterogeneous environmental matrices

Anthropogenic organohalogens (AOHs) are toxic and persistent pollutants that occur ubiquitously in the environment. An unneglectable portion of them can convert into nonextractable residues (NER) in the natural solid substances. NER-AOHs are not detectable by conventional solvent-extraction, and will get remobilized through changes of surrounding environment. Consequently, the formation and fate of NER-AOHs should be investigated comprehensively. In this study, solvent extraction, sequential chemical degradation and thermochemolysis were applied on different sample matrices (sediments, soils and groundwater sludge, collected from industrial areas) to release extractable and nonextractable AOHs. Covalent linkages were observed most favorable for the hydrophilic-group-containing monocyclic aromatic AOHs (HiMcAr-AOHs) (e.g. halogenated phenols, benzoic acids and anilines) incorporating into the natural organic matter (NOM) as NER. Physical entrapment mainly contributed to the NER formation of hydrophobic monocyclic aromatic AOHs (HoMcAr-AOHs) and polycyclic aromatic AOHs (PcAr-AOHs). The hypothesized remobilization potential of these NER-AOHs follow the order HiMcAr-AOHs > HoMcAr-AOHs/ aliphatic AOHs > PcAr-AOHs. In addition, the NOM macromolecular structures of the studied samples were analyzed. Based on the derived results, a conceptual model of the formation mechanisms of NER-AOHs is proposed. This model provides basic molecular insights that are of high value for risk assessment and remediation of AOHs.

AhR Agonist Activity Confirmation of Polyhalogenated Carbazoles (PHCZs) Using an Integration of in Vitro, in Vivo, and in Silico Models

Polyhalogenated carbazoles (PHCZs) are a kind of rising environmental pollutant that has been reported to pose high risk to human beings and the natural environment. PHCZs are of a similar molecular structure with of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and exhibited some dioxin-like toxicity. Dioxin-like compounds (DLCs) are banned by the Stockholm Convention due to their potential adverse impacts to the environment and public health. However, a few efforts have been made toward the regulation of PHCZs. Herein, we initiated multimodels to systematically determine and validate the dioxin-like effects of PHCZs on a large scale. Transgenic zebrafish line-Tg(cyp1a-12DRE:EGFP) and stably transfected HepG2 cell line with luciferase reporter plasmids were used to screen and evaluate the aryl hydrocarbon receptor (AhR) agonist effects of the target PHCZs, which were then verified by application of molecular docking and expression levels of AhR downstream genes. Results of the two bioassays showed that most of the tested PHCZs could pose dioxin-like AhR agonist effects, change the expression levels of AhR downstream genes, and interact with AhR in accordance with TCDD. In summary, data presented here can help to guide the safe use and regulation of PHCZs.

Determination of carbazole and halogenated carbazoles in human serum samples using GC-MS/MS

Carbazole and halogenated carbazoles have been widely detected throughout the environment in soil, river deposits, and lake sediments. Human exposure to these compounds may occur through inhalation, drinking water, dietary intake and/or skin contact, and exposure levels in the body may be evaluated by measuring them in serum or blood. This paper reports the method development and validation for the analysis of carbazole and 11 halogenated carbazoles in human blood and/or serum samples. A small sample size of 100 μL of blood or serum was employed for the analysis. The samples were prepared through salting-out liquid-liquid extraction (LLE) by using hexane/ethyl acetate (4:1, v/v) as the extraction solvent and aqueous MgSO₄ (37.5 wt%) as the salting-out regent, respectively. Sample analysis was performed using gas-chromatography (GC) coupled with a tandem mass spectrometer (MS/MS) in an electron impact (EI) mode. The developed method demonstrated low detection limits in the range of 0.02-0.27 ng/mL, intra-day accuracy ranging from 81.2% to 125%, and inter-day accuracy from 91.0% to 117%. The intra- and inter-day precisions, calculated by relative standard deviations (RSDs), were in the ranges of 1.0-16.0% and 1.8-16.4%, respectively. The developed method was applied to the analysis of 50 human serum samples collected from pregnant women in Southern California in 2012. Low concentrations of carbazole were measured in 18 samples, while halogenated carbazoles were not detected in any of the samples.