Dioxin-like Toxicity Research Articles

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.

Characterizing persistent organic pollutants in seawater at a multifunctional international harbor influenced by industrial riverbank activities.

The objective of this study is to comprehensively characterize persistent organic pollutants (POPs) in seawater at Kaohsiung Harbor, focusing on their concentrations, partitioning behaviors, and profiles in both particle and liquid phases. We analyzed 100L seawater for each sample, finding total dioxin-like toxicity (PCDD/Fs+PCBs + PBDD/Fs) ranging from 0.00936 to 0.167pg WHO-TEQ/L, with PCDD/Fs accounting for 68% of total toxicity. POPs predominantly appeared in the particle phase, observed in over 80% of samples, except for PCBs. The observed correlations between particulate matter (PM) and chlorinated POPs at sites receiving river effluents suggest shared pollution sources. The liquid partition of PCDD/Fs, PCBs, and PBDEs in the seawater shows an inverse relationship with log Kow and a direct proportionality with solubility, particularly above 0.1μg/L. Furthermore, PBDEs in seawater can transform into PBDD/Fs upon UV light exposure, highlighting another potential pathway for the persistence and spread of these harmful contaminants in the environment. These findings emphasize the need for field-based investigations to assess PBDF formation in aquatic environments and underscore the importance of stronger mitigation strategies, including better wastewater treatment and stricter discharge regulations to reduce POPs in marine ecosystems.

Unveiling the Photodegradation Mechanism of Monochlorinated Naphthalenes under UV‒C Irradiation: Affecting Factors Analysis, the Roles of Hydroxyl Radicals, and DFT Calculation

Polychlorinated naphthalenes (PCNs) are a new type of persistent organic pollutant (POP) characterized by persistence, bioaccumulation, dioxin-like toxicity, and long-range atmospheric transport. Focusing on one type of PCN, monochlorinated naphthalenes (CN‒1, CN‒2), this study aimed to examine their photodegradation in the environment. In this work, CN‒1 and CN‒2 were employed as the model pollutants to investigate their photodegradation process under UV-C irradiation. Factors like the pH, initial concentrations of CN‒1, and inorganic anions were investigated. Next, the roles of hydroxyl radicals (·OH), superoxide anion radicals (O2•‒), and singlet oxygen (1O2) in the photodegradation process were discussed and proposed via theory computation. The results show that the photodegradation of CN‒1 and CN‒2 follows pseudo-first-order kinetics. Acidic conditions promote the photodegradation of CN‒1, while the effects of pH on the photodegradation of CN‒2 are not remarkable. Cl−, NO3−, and SO32− accelerate the photodegradation of CN‒1, whereas the effect of SO42‒ and CO32‒ is not significant. Additionally, the contributions of ·OH and O2•‒ to the photodegradation of CN‒1 are 20.47% and 38.80%, while, for CN‒2, the contribution is 16.40% and 16.80%, respectively. Moreover, the contribution of 1O2 is 15.7%. Based on DFT calculations, C4 and C6 of the CN‒1 benzene ring are prioritized attack sites for ·OH, while C2 and C9 of CN‒2 are prioritized attack sites.

Solid phase extraction coupled with gas chromatography-triple quadrupole mass spectrometry for the rapid and simultaneous determination of forty-nine parent and halogenated polycyclic aromatic hydrocarbons in human serum

Halogenated polycyclic aromatic hydrocarbons (H-PAHs) are the emerging organic pollutants in environment, which are ubiquitous in the atmosphere, soil and water. Some H-PAH congeners have been proven to have dioxin-like toxicity. However, the research on the human internal exposure of H-PAHs is still limited. A simple and efficient analytical method is essential for the study of human internal exposure, so a method for the rapid and simultaneous determination of 16 polycyclic aromatic hydrocarbons (PAHs) and 33 H-PAHs in human serum was established in this study. After 1.0 mL serum was extracted with ethyl acetate/acetonitrile (1:4) solution containing 1 % formic acid, samples were purified by Captiva EMR-Lipid solid phase extraction column, and then determined by gas chromatography tandem triple quadrupole mass spectrometer (GC-MS/MS). The results showed that the recoveries of PAHs and H-PAHs ranged from 71.2 % to 119 % and 68.8 % to 121 %, respectively. When 1.0 mL of serum sample is used, the method detection limit of PAHs and H-PAHs is 0.001–0.314 ng/mL. The method is simple and efficient, and suitable for the simultaneous determination of trace PAHs and H-PAHs in human serum. High concentrations of chlorinated polycyclic aromatic hydrocarbons were detected in pooled serum, of which 1,5-dichloranthracene was the main contributor congener, with a concentration of 204–328 ng/g lipid, which deserved more attention.

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.

A novel approach to assess the health risk of aryl hydrocarbon receptor-bound contaminants via inhalation exposure using CYP1A1 expression as a biomarker

Polycyclic aromatic hydrocarbons (PAHs) and dioxins are potential causes of multiple diseases by activating the aryl hydrocarbon receptor (AhR) pathway. Health risk assessment of chemicals primarily relies on the relative potency factor (RPF), although its accuracy may be limited when solely using EC50 values. The induction of cytochrome P4501A1 (CYP1A1) serves as a biomarker for AhR activation and is an integrator of dioxin-like toxicity. Here, we present a method for evaluating the risks associated with AhR activation using mathematical models of dose-CYP1A1 induction. The dose-effect curves for certain PAHs and dioxins, including Ant, BghiP, 1,2,3,4,7,8-HxCDD, and others, exhibited a non-classical S-shaped form. The toxic equivalent factor (TEF) profiles revealed a broad range of toxic equivalent factor values. The TEFs for PAHs ranged from approximately 0.01 to 6, with higher values being observed when the concentration was less than 10−10 M, with the exceptions of Ace, Phe, and BghiP. Most congeners of dioxins got the lowest TEF value at around 10−10 M, ranging from 0.04 to 1.00. The binding affinity of AhR to ligands did not display a strong correlation with the EC50 of CYP1A1 expression, suggesting that the AhR-mediated effects of PAHs and dioxins are not fixed but instead fluctuate with the dose. Air samples acquired from a parking area were used to compare the proficiency of RPF and our current approach. In the current method, naphthalene and chrysene were the primary contributors of PAHs to AhR-mediated risks in parking lots air samples, respectively. However, the contributions of naphthalene and chrysene could be disregarded in the RPF approach.

Analysis of 78 trace liquid crystal monomers in air by gas chromatography coupled with triple quadrupole mass spectrometry

Liquid crystal monomers (LCMs) comprise a class of organic pollutants that have garnered considerable attention because of their dioxin-like toxicity (i.e., modulation of genes) and presence in various environments. However, limited information about the identities, occurrence, and distribution of LCMs has highlighted an urgent need for a high-throughput and sensitive analytical method. In this study, we developed and validated a rapid, simple, sensitive method that involves minimal solvent consumption. The method was applied for the simultaneous detection and identification of 78 LCMs in atmospheric total suspended particulate samples (dae < 100 μm) using gas chromatography coupled with triple quadrupole mass spectrometry. The results showed high degrees of linearity with correlation coefficients >0.995 in the concentration range of 5.0–500 ng/mL. The instrumental detection limits ranged from 0.7 to 5.3 pg, and the method detection limits ranged from 0.1 to 0.9 pg/m3. The accuracy of the method was between 70 % and 130 % for most analytes, and the relative standard deviations of six replicates were <15 % at three levels of spiking (10, 50, and 200 ng/mL). The developed analytical method was applied to analyze real air particulate samples from Beijing, China. Overall, 45 LCMs ranged from 65.5 to 145.7 pg/m3, with a mean concentration of 92.5 pg/m3. Among them, (trans,trans)-4-propyl-4′-ethenyl-1,1′-bicyclohexane (PVB) was the most abundant, with an average concentration of 33.6 pg/m3. The total estimated daily intakes of LCMs for adults and children were 15.6 and 46.6 pg/kg bw/day, respectively. Accordingly, the method described herein is suitable for quantifying LCMs in atmospheric particulate samples. This study will be valuable for investigating LCM environmental occurrence, behaviors, and risk assessments.

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.

Polychlorinated Naphthalenes in Foods from the French Market: Occurrence, Dietary Exposure, and Evaluation of Relative Contributions to Dioxin-like Contaminants.

Despite the growing interest in PCNs and the dioxin-like toxicity exhibited by a number of congeners, a comprehensive assessment of their contribution to the cocktail of dioxin-like contaminants is still lacking. To address such a shortcoming, this study investigated the PCN contamination in foodstuffs recently acquired in France, together with that of the regulatory polychlorinated dibenzodioxins/furans (PCDD/Fs) and polychlorinated biphenyls (PCBs). PCNs were ubiquitous at levels (∑70 PCNs = 2.5-150 pg g-1 wet weight) similar to those reported in other countries, with maximum concentrations observed in fish and fishery products from the North-East Atlantic Ocean. Their congener patterns further suggested unintentional releases of PCNs, while those of the other foodstuffs were correlated to the historical PCN profiles. Low risk from dietary exposure was estimated (∑70 PCNs-EDIs of 60-360 pg kg-1 bw d-1, ∑24 PCNs-TEQ-EDIs of 8 × 10-3-2.2 × 10-2 pg TEQ kg-1 bw d-1), with milk and dairy products being the highest contributors, followed by meat and meat products. Finally, the rather high contributions of PCNs to the total PCNs+PCDD/Fs+PCBs concentrations (0.9-50%, average of 9%) and the toxic equivalents (0.2-24%, average of 5%) show that these substances are not minor components of the PCNs+PCDD/Fs+PCBs cocktail.

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.

Enrichment and distribution of 3,6-dichlorocarbazole in red crucian carp (Carassius auratus) and its hepatotoxicity

Polyhalogenated carbazoles (PHCZs) are a class of organohalogen compounds where the hydrogen atom on the carbazole ring is replaced by a halogen atom. In recent years, PHCZs have drawn increasing concern due to their persistence, dioxin-like toxicity, bioaccumulation, potential ecological hazards and widespread occurrence in the environment. Current research on the enrichment and depuration of PHCZs in biological tissues and organs is insufficient, and the liver toxicity is unclear. Herein, to understand the enrichment and elimination of 3,6-DCCZ in fish tissues and organs as well as the hepatotoxicity, we exposed the red crucian carp to 20 and 100 μg/L of 3,6-DCCZ for 20 days followed by a depuration period of 10 days. The 3,6-DCCZ enrichment in each organ tissue was classified from high to low: brain > liver, intestine, gill > muscle. For depuration, 3,6-DCCZ was quickly excreted in the various organs of the red crucian carp; however, the liver depuration was slow, with the concentration of 3,6-DCCZ was maintained at 0.25–0.35 μg/g. 3,6-DCCZ exposure at both tested concentrations induced oxidative stress in red crucian carp, causing lipid peroxidation and DNA damage, as well as some histopathological changes in the liver, such as cell vacuolization, nucleus pyknosis, nucleus pleomorphism, no nucleus areas. Additionally, the 3,6-DCCZ exposure at higher concentration (100 μg/L) caused more serious damage and abnormal lipid metabolism in the red crucian carp liver.

Genotoxicity of chlorinated hydrophobic organic compounds extracted from a source of drinking water

As precursors of disinfection by-products (DBPs), sediment hydrophobic organic compounds (HPOCs) derived from six reservoirs along the Dongjiang River were chlorinated (Cl-WS) and then fractionated into two polar components (hydrophobic organic compounds (Cl-HOCs) and hydrophilic organic compounds (Cl-HICs)) by solid phase extraction. Based on Caco-2 cell exposure study, the genotoxicity of Cl-WS, Cl-HOCs and Cl-HICs was analyzed by reactive oxygen species (ROS) analysis, comet assay and ethoxyresorufin-O-deethylase assay. Protective effects of antioxidants (catalase, vitamin C and epigallocatechin 3-gallate (EGCG)) on genotoxicity of the chlorinated samples were investigated. The results showed that Cl-WS and its two fractions (Cl-HOCs and Cl-HICs) induced ROS, DNA damage and dioxin-like toxicity (TEQbio), and Cl-HICs were a major contributor to oxidative damage and TEQbio compared with Cl-HOCs. Antioxidants significantly reduced Cl-HOCs- and Cl-HICs-induced ROS, but had insignificant effect on DNA oxidative damage and TEQbio. In addition, EGCG showed higher efficacy in reducing DNA damage induced by Cl-HICs than by Cl-HOCs. To our knowledge, this is the first study to investigate the genotoxicity of Cl-WS and its two polar components in Caco-2 cells, as well as the protective effects of antioxidants on Cl-HOCs and Cl-HICs-induced ROS, DNA damage, and TEQbio. This study provides important toxicity information for water treatment industries in differentiating DBPs of different polarity.

Risk assessment of sediment PAH, BTEX, and emerging contaminants in Chanomi Creek Niger Delta, Nigeria.

This study assessed the levels of polycyclic aromatic hydrocarbons (PAHs), benzene, toluene, ethylbenzene, and xylene (BTEX), and emerging contaminants in Chanomi Creek. Sediment samples were collected between March 2019 and July 2020 to evaluate the concentrations of PAH, BTEX, and emerging contaminants using GC-MS and GC-FID with Headspace extraction. Results indicated mean PAH concentrations were 22.691 ± 15.09µg/kg. The highest individual PAH concentrations were fluorene (7.085µg/kg), naphthalene (4.517µg/kg), and phenanthrene (3.081µg/kg). Carbazole (0.828µg/kg) was discovered as a novel environmental toxin with dioxin-like toxicity and widespread prevalence in sediments. The most common congener (25%) was ethylbenzene, followed by toluene and ortho- and meta-xylene (21%) and benzene (13%). The analysis of diagnostic ratios revealed that the main factors responsible for the presence of PAHs in the study area are the residential use of firewood, emissions from industrial activities, bush burning, and petroleum slicks. The risk assessment indicated that most PAHs exceeded the permissible risk quotient values, suggesting a moderate to high ecological risk. However, cutaneous exposure to PAHs and BTEX was found to have minimal impact on human health, with no significant hazards identified in adults and children. Nevertheless, the study revealed low cancer risks associated with PAH and BTEX compounds for both age groups. The continued discharge of PAHs and BTEX compounds into Chanomi Creek could have significant long-term negative effects on human and aquatic health. Thus, contamination risk awareness programs and the development of stringent contextual thresholds for identified contaminants could enhance environmental and public health protection.

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.

Partitioning behavior and mechanism of polyhalogenated carbazoles in water and suspended particulate matter

Polyhalogenated carbazoles (PHCZs), known as new dioxin-like compounds, are a new class of emerging environmental contaminants that have received increasing attention in recent years due to their wide distribution and dioxin-like toxicity. This study investigated the partition characteristics and adsorption mechanisms of eight PHCZs in the aqueous phase and suspended particulate matter (SPM). The competitive impact of humic acid (HA) on the adsorption of PHCZs was revealed when the effects of various environmental conditions (HA, temperature, perturbation disturbance, and pH) behavior were explored. The key finding of this study is that SPM, which is its effective vector, could adsorb 70.7 % of ΣPHCZs. The equilibrium adsorption amount is ranked as 3,6-ICZ > 3,6-BCZ > 2,7-BCZ > 3,6-CCZ > 1,3,6,8-BCZ > 3-BCZ > 2-BCZ > CZ. The halogen species, the degree of halogenation, and the substitution position of the PHCZs influence the amount of adsorption, where the log Kow values, the steric effect (Es), and the density contribute the most to the amount of adsorption, and the specific adsorption mechanisms are van der Waals force, π-π, hydrogen bonding, and nonspecific hydrophobic interactions. The adsorption reaction of PHCZs by SPM is endothermic, and the amount of adsorption increases with increasing temperature, oscillation velocity, and decrease in pH. HA may reduce the adsorption sites of hydroxyl, carbonyl, amide groups, and π-π bonds on SPM for PHCZs, while the SPM@HA conjugates can provide new sites for the adsorption of PHCZs. According to the experimental findings of this study, SPM plays a significant role in contaminant transport. As a result, when conducting environmental investigations of PHCZs and even other hydrophobic contaminants, we must fully consider the level of contaminants present in SPM to reveal the ecological risks accurately.

Degradation of 1,3,6,8-tetrabromocarbazole by sulfidated zero-valent iron activated peroxydisulfate: Mechanistic insight and transformation pathways

Polyhalogenated carbazoles (PHCZs) are a kind of emerging contaminants which have widespread distribution, strong potential persistence, high bioaccumulation, and dioxin-like toxicity. In this study, we used sulfidated zero-valent iron (S-ZVI) synthesized by ball-milling to activate peroxydisulfate (PDS) for the degradation of 1,3,6,8-tetrabromocarbazole (1,3,6,8-BCZ). The initial 1 mg/L 1,3,6,8-BCZ was degraded by 92.9 % within 30 min in S-ZVI/PDS system. The pseudo-first-order rate constant was estimated as high as 0.182 min−1. Electron paramagnetic resonance (EPR) study and quenching experiments results revealed that •OH, 1O2, O2•−, and SO4•− played roles in the degradation of 1,3,6,8-BCZ, with their contribution percentages of 32.8 %, 32.5 %, 24.8 % and 9.9 %, respectively. By further density functional theory (DFT) calculations, radical addition by •OH and 1,4-cycloaddition by 1O2 were suggested as the dominant channels for 1,3,6,8-BCZ degradation, while O2•− exerted an indirect synergistic influence. Based on the identification of intermediates and analysis of Fukui indices, 1,3,6,8-BCZ degraded through three degradation pathways, namely hydroxylation, debromination, and C–N bond cleavage. The S/Fe molar ratio, S-ZVI dosage, PDS dosage, reaction temperature, initial pH, and water matrices had influences on the degradation in 1,3,6,8-BCZ, result in a great toxicity reduction. Overall, this research developed an effective and feasible approach for the treatment of PHCZs, and which gave deep insights into the vital roles and synergistic effects of various reactive species based on the combination of experimental study and theoretical calculation.

Polyhalogenated carbazoles in indoor dust from Hangzhou, China

Carbazoles (CZ) and polyhalogenated carbazoles (PHCZs), showing dioxin-like toxicity, have gained increasing attention in recent years as novel persistent organic pollutants. However, the occurrence of these chemicals in indoor dust from China remains not well known. In this study, CZ and 11 chloro/bromo CZs were analyzed in indoor dust samples collected from residential houses in rural (n = 51) and urban (n = 55) regions of Hangzhou, China. CZ was detected in all indoor dust samples, with the concentrations of 0.81–18 ng/g (mean 5.4 ng/g). All 11 measured PHCZs were detected in indoor dust samples, showing the detection frequency of 7.3–96 %. This means that general populations had wide exposure to CZ and PHCZs through indoor dust ingestion. 3,6-dichlorocarbzole (36-CCZ) and 3,6-dibromocarbazole (36-BCZ) were the predominant PHCZs in indoor dust, having comparable mean concentrations of 1.2 ng/g, followed by 3-monobromocarbazole (3-BCZ; mean 0.66 ng/g, range < LOD–2.1 ng/g) and 1,3,6-tribromocarbazole (136-BCZ; 0.36 ng/g, < LOD–1.0 ng/g). Indoor dust concentrations of 3-BCZ, 36-BCZ, and 1,3,6,8-tetrabromocarbazole in urban regions were significantly (p ≤ 0.01–0.035) higher than that in rural regions. Daily intakes (DIs) of CZ and PHCZs through indoor dust ingestion were estimated for general Chinese population. Among PHCZs, 36-CCZ and 36-BCZ (mean 1.4–3.4 pg/kg bw/day) had the highest mean DIs, followed by 3-BCZ (0.77–1.9 pg/kg bw/day) and 136-BCZ (0.42–1.0 pg/kg/day). To our knowledge, this is the first study reporting the concentrations of CZ and PHCZs in indoor dust from China, which contributes to the better understanding of the sources of human exposure to CZ and PHCZs.

Hydroxylation and dechlorination of 3,3',4,4'-tetrachlorobiphenyl (CB77) by rat and human CYP1A1s and critical roles of amino acids composing their substrate-binding cavity.

Cytochrome P450 (CYP) monooxygenases play critical roles in determining the toxicity of polychlorinated biphenyls (PCBs) in mammals. Hydroxylation of PCBs by these enzymes leads to increased water solubility, promoting the elimination of PCBs from the body. The CYP1 family is mainly responsible for metabolizing PCBs that exhibit a dioxin-like toxicity. Although the dioxin-like PCB 3,3',4,4'-tetrachlorobiphenyl (CB77) is abundant in the environment and accumulates in organisms, information on CB77 metabolism by CYP1A1s is limited. In this study, recombinant rat CYP1A1 metabolized CB77 to 4'-hydroxy (OH)-3,3',4,5'-tetrachlorobiphenyl (CB79) and 4'-OH-3,3',4-trichlorobiphenyl (CB35), whereas human CYP1A1 produced only 4'-OH-CB79. Rat CYP1A1 exhibited much higher metabolizing activity than human CYP1A1 because CB77 was stably accommodated in the substrate-binding cavity of rat CYP1A1 and was close to its heme. In a rat CYP1A1 mutant with two human-type amino acids, the production of 4'-OH-CB79 decreased, whereas that of the dechlorinated metabolite 4'-OH-CB35 increased. These results are explained by a shift in the CB77 positions toward the heme. This study provides insight into the development of enzymes with high metabolizing activity and clarifies the structural basis of PCB metabolism, as dechlorination contributes to a drastic decrease in dioxin-like toxicity.

Determination of PCDD/F and DL-PCB pollution levels, source appointment and risk assessment of surface sediments in dam lakes in Istanbul, Türkiye.

The current situation of the water resources of Istanbul, which is one of the important metropolises of Europe, should be known and constantly monitored by the reasons of the rapid increase in the city population, the acceleration of production-related industrial activities, the expansion of the city with construction activities, and the decrease in precipitation. The purpose of this study was to reveal the situations of surface sediments collected from Istanbul water reservoirs in terms of PCDD/Fs and DL-PCBs, to identify possible sources, and to conduct their ecological risk assessment. Total PCDD/Fs and DL-PCBs concentrations varied between 28.13 and 457.4pg/g (average 136.8pg/g) and 12.19-340.1pg/g (average 72.09pg/g). The corresponding TEQ values of PCDD/Fs and DL-PCBs were between 0.53 and 5.37pg TEQ/g (average 2.23pg TEQ/g) and 0.02-0.44pg TEQ/g (average 0.12pg TEQ/g), respectively. Octachlorodibenzo-p-dioxin (OCDD) is the dominant congener by constituting about 75% of the total PCDD/Fs on average, while congener distributions of DL-PCBs showed the dominance of PCB-118 and PCB-105. The sediments taken from Kazandere dam have the lowest pollution levels for both PCDD/Fs and DL-PCBs. The highest PCDD/F and DL-PCB amounts were measured in sediments of Alibey and Elmalı dams (closest to highly populated settlements of Istanbul), which are most affected by the air pollution caused by the traffic, commercial/industrial combustion (like waste incineration facility) and combustion for residential heating. Almost all the sediments have total dioxin-like toxicity levels higher than the safe threshold level (with two exceptions) of 0.85pg TEQ/g dw, proposed for ecological risk. Health risk assessment shows that levels of dioxin-like compounds would result in a total intake of 0.33pg TEQ/kg bw/day even in the worst-case scenario, not exceeding the tolerable daily intake value of 1pg TEQ/kg bw/day. Among exposure pathways, consumption of fish constitutes almost all the total intake, while contributions of other pathways are minimal.

Polyhalogenated carbazoles (PHCZs) induce cardiotoxicity and behavioral changes in zebrafish at early developmental stages

Polyhalogenated carbazoles (PHCZs) are widely present in the environment, and their health risks are of increasing concern. Available studies primarily confirm their dioxin-like toxicity mechanism based on biomarkers, such as aryl hydrocarbon receptor (AHR) and CYP1A1, while few studies have investigated their actual toxic effects at the level of individual organisms. In the present study, the developmental toxicity of two typical PHCZs with a high detection rate and high concentration in the environment (3,6-dichlorocarbazol (3,6-DCCZ) and 3,6-dibromocarbazole (3,6-DBCZ)) was investigated based on a fish embryo acute toxicity test (FET, zebrafish) and transcriptomics analysis. The 96 h LC50 values of 3,6-DCCZ and 3,6-DBCZ were 0.636 mg/L and 1.167 mg/L, respectively. Both tested PHCZs reduced the zebrafish heart rate and blocked heart looping at concentrations of 0.5 mg/L or higher. The swimming/escaping behavior of zebrafish larvae was more vulnerable to 3,6-DBCZ than 3,6-DCCZ. Transcriptomics assays showed that multiple pathways linked to organ development, immunization, metabolism and protein synthesis were disturbed in PHCZ-exposed fish, which might be the internal mechanism of the adverse effects. The present study provides evidence that PHCZs cause cardiac developmental toxicity and behavioral changes and improves our understanding of their health risks.