Photochemical degradation of polyhalogenated carbazoles in hexane by sunlight

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.

Presence of carbazole and polyhalogenated carbazoles in human urine

Exposure to carbazole (CZ) and polyhalogenated carbazoles (PHCZs) may pose a threat to human health, owing to their potential dioxin-like toxicity. Until now, the presence of these chemicals in the human urine from the general population is still unclear. Human urine samples (n = 210) were taken from the general population in Quzhou, China in this study, and were analyzed for CZ and 14 PHCZs. CZ and nine PHCZs were detected in collected human urine. CZ (detection frequency 100 %), 3-chlorocarbazole (3-CCZ; 88 %), 3,6-dichlorocarbzole (36-CCZ; 84 %), and 3-bromocarbazole (3-BCZ; 80 %) were more frequently detected. Among detected PHCZs, 3-CCZ (mean 0.49 ng/mL, < LOD-4.3 ng/mL) had comparatively higher urinary levels, followed by 3-BCZ (0.30 ng/L, < LOD-1.9 ng/mL) and 36-CCZ (0.20 ng/L, < LOD-1.4 ng/mL). Urinary concentrations of CZ in male participants (1.3 ± 0.26 ng/mL) were significantly (p < 0.05) higher than that in female participants (0.92 ± 0.24 ng/mL). No obvious trend in urinary concentrations with the age of participants was found for CZ and detected PHCZs. The mean daily excretion was found highest for CZ (31 ng/kg bw/day), followed by 3-CCZ (19 ng/kg bw/day) and 3-BCZ (8.5 ng/kg bw/day). This study provides the first data, to our knowledge, on the presence and levels of CZ and PHCZs in human urine, which is necessary for conducting the human exposure risk assessment.

Analysis of a novel strain Brevundimonas KX-1 capable of degrading 3-chlorocarbazole based on the whole genome sequence

In this study, a strain was isolated from a sewage treatment plant in Jiangsu Province, China. The strain was identified as Brevundimonas sp. KX-1. After 5 days, 50.2% 3-chlorocarbazole (3-CCZ) was degraded under the optimum condition as follows: 1 g/L starch, 30 °C, pH 6.5 and 50 mg/L 3-CCZ. The degradation of 3-CCZ by KX-1 conformed to the first-order kinetic model under different initial concentrations in this experiment. The intermediate product of 3-CCZ degradation was identified as (2E,4Z)-6-(2-amino-5-chlorophenyl)-2-hydroxy-6-oxohexa-2,4-dienoic acid. The activities of the meta-cleavage enzymes for biphenyl-2,3-diol (the analogs of intermediate product 2'-amino-5'-chloro-[1,1'-biphenyl]-2,3-diol) were measured with the crude extracts of cells grown in the presence of 3-CCZ. The complete genome of KX-1 was sequenced and compared with the Brevundimonas diminuta BZC3. BZC3 and KX-1 belonged to the same species, displaying the genetic similarity of 99%. But BZC3 could efficiently degrade gentamicin for the potential microbial function analysis. Compared with BZC3, KX-1 possessed the primary function annotations about transportation and metabolism of amino acids (6.65%) and the transportation and metabolism of carbohydrates (5.96%). In addition, KX-1 was rich in sucrose and starch metabolism pathways (ko00500) compared with the genome of BZC3, indicating the high efficiency of KX-1 for starch utilization during degradation. This article reveals the difference between strain KX-1 and bacteria of the same genus in terms of the whole genome sequence, demonstrating that KX-1 is a novel strain Brevundimonas with the ability to degrade 3-CCZ.

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.

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.

Degradation of 3-chlorocarbazole in water by sulfidated zero-valent iron/peroxymonosulfate system: Kinetics, influential factors, degradation products and pathways

As an emerging class of organic contaminants, polyhalogenated carbazoles (PHCZs) have been increasingly detected all over the world since 1980s. Due to the environmental persistence, bioaccumulation, and dioxin-like toxicity, PHCZs have aroused widespread concerns in recent years. However, efficient approach for the degradation of PHCZs is quite limited so far. Therefore, in this study, an advanced oxidation process (AOP), sulfidated zero-valent iron/peroxymonosulfate (S-ZVI/PMS) system was used to degrade 3-chlorocarbazole (3-CCZ), which is one of the mostly detected PHCZs congeners. The degradation of 3-CCZ was systematically studied under different conditions by varying the molar ratio of S/Fe, the dosage of S-ZVI or PMS, pH and temperature. The results indicated that S-ZVI/PMS was an effective strategy for PHCZs treatment. The 20-min degradation efficiency of 3-CZZ was up to 96.6% with the pseudo-first-order rate constant of 0.168 min^-1 under the conditions of 5 mg/L 3-CZZ, 0.3 g/L S-ZVI (S/Fe = 0.2), 1.0 mM PMS, pH 5.8 and 25 °C. HCO₃^-, Cl^- and humic acid (HA) showed inhibitory effects to different degrees. Results of the electron paramagnetic resonance (EPR) and scavenging experiments clarified the dominant role of •OH, followed by ¹O₂ and SO₄^•─. The product analysis and DFT calculation revealed three degradation pathways of 3-CCZ, namely hydroxylation, dechlorination and C-N bond cleavage, which largely alleviated the toxicity of the parent compound. This study showed the effectiveness of S-ZVI/PMS system in PHCZs treatment and provided a comprehensive investigation on the degradation behaviors of PHCZs in AOPs.

Enhanced PAHs-contaminated site soils remediation by mixed persulfate and calcium peroxide

Polycyclic aromatic hydrocarbons (PAHs) remain in the site soils after relocated coking plants and oil refineries pose huge constraints to the subsequent land utilization. However, single persulfate (PS) or calcium peroxide (CP) remediation strategies can only inefficiently oxidize some PAHs in soil. This work sought to optimize PS/CP oxidation remediation strategy and verify its practical application effect in soil samples spiked with PAHs. The results showed that the mixed PS/CP oxidation remediation was better than the single oxidants strategies; it had high remediation performance in different particles and pollution loads of PAHs-contaminated soils. Simultaneously, reactive radicals (SO₄·^- and ·OH) were detected, and one side-product (CaSO₄) was characterized. This work optimized the mixed PS/CP system (0.3 mol/L PS, and 8 g/kg CP, together with 0.18 mol/L Fe²⁺ and 0.11 mol/L C₂O₄^2-), and the corresponding Total-PAHs removal rate was 85.41%. Compared to the cost based on benzopyrene (BaP) removal, the study provided a cost-effective mixed PS/CP oxidation remediation technique (1.22 $/ton), widely applicable in soils polluted with various organic contaminants represented such as PAHs.

Effects of 3,6-dichlorocarbazole on microbial ecology and its degradation in soil

The emerging contaminants polyhalogenated carbazoles (PHCZs) have been verified to be present in soils and sediments globally, and they show dioxin-like toxicity. However, there is a lack of soil ecological risk assessments on PHCZs despite their high detection rate and concentration in soils. The present study investigated the degradation and soil microbial influence of 3,6-dichlorocarbazole (3,6-DCCZ, a frequently detected PHCZ) in soil. The results showed that the half-lives of 3,6-DCCZ at concentrations of 0.100 mg/kg and 1.00 mg/kg were 7.75 d and 16.73 d, respectively. We found that 3,6-DCCZ was transformed into 3-chlorocarbazole (3-CCZ) by dehalogenation in soil. Additionally, intermediate products with higher molecular weights were detected, presumably because the -H on the carbazole ring was replaced by -CH₃, -CH₂-O-CH₃, or -CH₂-O-CH₂CH₃. 3,6-DCCZ exposure slightly increased the soil bacterial abundance and diversity and clearly changed the soil bacterial community structure. Through a comprehensive analysis of FAPROTAX, functional gene qPCR and soil enzyme tests, we concluded that 3,6-DCCZ exposure inhibited nitrification and nitrogen fixation but promoted denitrification, carbon dioxide fixation and hydrocarbon degradation processes in soil. This study provides valuable data for clarifying the PHCZ ecological risk in soil.

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.

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.

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.

Assessment of endocrine-disrupting effects of emerging polyhalogenated carbazoles (PHCZs): In vitro, in silico, and in vivo evidence

Polyhalogenated carbazoles (PHCZs) are an emerging class of persistent, bioaccumulative compounds that are structurally and chemically related to dioxins. They have been detected widely in sediment, river, and soil samples, but their environmental risks are largely unknown. Therefore, seven common PHCZs were tested for their endocrine disrupting potential in silico, in vitro, and in vivo. A dual-luciferase reporter gene assay was used to detect receptor-mediated (agonist or antagonistic) activity (concentration range: 10^-9-10^-5 M) against the estrogen receptor α (ERα), glucocorticoid receptor α (GRα), and mineralocorticoid receptor (MR). The alterations in the steroidogenesis pathway were investigated in H295R cells. Antagonistic effects against GRα were observed with five PHCZs, along with an increase in the cortisol levels of H295R cells. The most common effect observed was that of the agonistic activity of ERα, with the molecular docking analysis further indicating that hydrogen bonding and hydrophobic interactions may stabilize the interaction between PHCZs and the estrogen receptor binding pocket. In addition, a seven-day exposure of young female rats to three PHCZs (27-BCZ, 3-BCZ, and 36-BCZ) resulted in changes in serum E2 levels, uterine epithelium cell heights, and relative uterus weights. In conclusion, endocrine-disrupting effects, especially the estrogenic effects, were observed for the tested PHCZs. Such adverse effects of PHCZs on humans and wildlife warrant further thorough investigation.