Formation and chlorination of carbazole, phenoxazine, and phenazine

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.

Unintended polyhalogenated carbazole production during advanced oxidation of coking wastewater

Polyhalogenated carbazoles (PHCZs) are emerging as dioxin-like global pollutants, yet their environmental origins are not fully understood. This study investigates the application of the Fenton process in coking wastewater treatment, focusing on its dual role in carbazole removal and unintended PHCZ formation. The common halide ions (Cl- and Br-) in coking wastewater, especially Br- ions, exerted a notable impact on carbazole removal. Particularly, the influence of Br- ions was more significant, not only enhancing carbazole removal but also shaping the congener composition of PHCZ formation. Elevated halide ion concentrations were associated with the heightened formation of higher halogenated carbazoles. The Fenton reagent dosage ratio was identified as a crucial factor affecting the congener composition of PHCZs and their toxic equivalency value. The coexisting organic substance (i.e., phenol) in coking wastewater was observed to inhibit PHCZ formation, likely through competitive reactions with carbazole. Intriguingly, ammonium (NH4+) facilitated the generation of higher and mixed halogenated carbazoles, possibly due to the generation of nitrogen-containing brominating agents with stronger bromination capacity. This study underscores the importance of a comprehensive assessment, considering both substrate removal and potential byproduct formation, when employing the Fenton process for saline wastewater treatment.

Development of a three-dimensional porous ionic liquid-chitosan-graphene oxide aerogel for efficient extraction and detection of polyhalogenated carbazoles in sediment samples

The three-dimensional porous ionic liquid-chitosan-graphene oxide aerogel (IL-CS-GOA) monolithic adsorbent with a through-hole structure was prepared using natural chitosan (CS) as the skeletal framework, graphene oxide (GO) as the support to provide mechanical strength, and ionic liquid (IL) as the porogen and modifier. The resulting IL-CS-GOA demonstrated a fluffy and porous structure with various pore sizes and excellent regeneration capability (over six cycles). Its specific surface area exceeded that of CS-GOA and IL-GOA by more than 7 times, enhancing its polyhalogenated carbazoles (PHCZs) adsorption capacity. Within 5 min, IL-CS-GOA (1.0 mg) exhibited adsorption amounts of 539 ng mg-1 for 3-bromocarbazole (3-BCZ), 716 ng mg-1 for 2,7-dibromocarbazole (2,7-BCZ), and 798 ng mg-1 for 1,3,6,8-tetrabromocarbazole (1,3,6,8-BCZ), showcasing its rapid mass transfer and high adsorption capabilities. IL-CS-GOA was utilized as the adsorbent for glass dropper extraction (GDE) in conjunction with gas chromatography-mass spectrometry (GC-MS/MS), to develop a highly efficient and accurate method for determining PHCZs in sediments. Under optimal conditions, the established method exhibited a wide linear range (0.4-250 ng g-1, r ≥ 0.9990), low detection limits (0.04-0.24 ng g-1), and satisfactory recoveries (80.5 %-93.8 %), enabling the accurate and rapid detection of PHCZs in sediment samples. This study presents a novel approach for creating three-dimensional porous aerogels, introduces a new form of sample pretreatment using GDE with a monolithic adsorbent, and offers a new method for the determination of PHCZs in environmental matrices.

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.

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.

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.

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.

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.

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.

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.

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.

Bromination mechanisms of aromatic pollutants: formation of Br2 and bromine transfer from metallic oxybromides

Bromination mechanisms of aromatic pollutants assume a chief contribution in the observed yields and pattern's distribution of a wide array of dioxin-like toxicants. However, salient features of the governing pathways remain largely speculative. This study presents detail mechanistic insights into two commonly discussed routes; namely: surface-assisted conversion of HBr into Br₂ and direct bromine transfer from oxybromides into a benzene ring. Utilizing iron surfaces, as structural representative of the metallic content in electronic wastes, results from density functional theory calculations portray accessible reactions into the successive dissociative adsorption of HBr over the Fe(100) surface and the subsequent evolution of gas phase bromine molecules. Activation energies for HBr uptake by the plain iron surface reside in the range of 129-182 kJ/mol. Over an oxygen pre-covered surface, dissociative adsorption of HBr leading to bromine molecules requires significantly lower activation energies (45-78 kJ/mol). Likewise, bromination of a benzene ring into a monobromobenzene molecule over Fe(100)_O*Br* (i.e., an oxybromide) configuration ensues with an opening activation energy of ~ 165 kJ/mol. Adsorption of a phenyl radical over an iron-oxybromide forms a phenolate moiety that subsequently desorbs from the surface into a phenoxy radical. Reaction pathways presented herein shall be useful in the ongoing efforts to comprehend the formation and bromination routes of the notorious bromine-bearing pollutants in real scenarios, such as, these encountered in the open burning and primitive thermal recycling of electronic wastes.

Remediation of PAHs contaminated industrial soils by hypochlorous acid: performance and mechanisms

Polycyclic aromatic hydrocarbons (PAHs) mainly originate from incomplete combustion of organic substances and are carcinogenic, mutagenic and teratogenetic, posing a high risk to the ecosystem and human health. The remediation of soils contaminated with PAHs has aroused wide public concern. In this study, hypochlorous acid (HOCl) was applied to realize PAHs removal from industrial contaminated soil with an extremely high degradation efficiency of 93.33% when the initial chlorine concentration was 5000 mg L⁻¹. The degradation behavior of PAHs by HOCl oxidation was investigated in detail. Parameters including chlorine dosage, pH and temperature that had effects on the degradation process were evaluated systematically. The removal of PAHs was followed well with the pseudo-first-order kinetic model. It is found that HOCl and OH˙ were major contributors to the degradation products of chlorinated and oxygenated PAHs. This research provided an easy-operating and energy-saving way to realize the remediation of PAHs contaminated industrial soil practically with high efficiency.

An extremely high degradation efficiency of 93.3% was realized for PAHs in contaminated industrial soil by HOCl oxidation.

On the formation chemistry of brominated polycyclic aromatic hydrocarbons (BrPAHs)

Brominated polycyclic aromatic hydrocarbons (BrPAHs) have been consistently detected in various environmental matrices, and measured at alarming rates in stack emissions. However, formation mechanisms and bromination patterns of BrPAHs remain unclear. This contribution constructs detailed mechanistic pathways for the synthesis of selected BrPAHs (namely bromine-bearing naphthalene, acenaphthylene, anthracene, and phenanthrene). Mapped-out pathways follow the Bittner-Howard's route in the hydrogen abstraction acetylene addition (HACA) mechanism, in which a second C₂HBr molecule is added to the first one. Constructed kinetic model portrays temperature-dependent profiles of major and minor species. Direct loss of an H atom from the acetylenic fragment appears to be more important at elevated temperatures, when compared with further addition of C₂HBr cuts or ring-cyclization reactions. The occurrence of closed-shell Diels-Alder pathway should be inhibited owing to sizable enthalpic barriers. Fukui Indices for electrophilic substitutions (f^-1) establish bromination' s pattern of selected BrPAHs. The diradical character of BrPAHs coupled with electron-deficient C(Br) sites, render BrPAHs as potent precursors for the formation of environmentally persistent free radicals (EPFRs). Findings reported herein shall be useful in comprehending the formation chemistry of BrPAHs, a less-investigated category of toxicants in thermal systems.

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 of chlorinated and brominated polycyclic aromatic hydrocarbons from electric arc furnace for steelmaking

Chlorinated and brominated polycyclic aromatic hydrocarbons (Cl/Br-PAHs) are persistent organic pollutants with potential carcinogenic toxicities that are even higher than those of their parent PAH congeners. Current knowledge of Cl/Br-PAH sources and emission characteristics is lacking. Electric arc furnace (EAF) steelmaking is a potential source for Cl/Br-PAHs, considering that preheating of raw materials before they enter the EAF could produce suitable conditions for Cl/Br-PAHs formation. In this field study, we identified EAFs as an important source of Cl/Br-PAHs and clarified their emission concentrations, fingerprints by gas chromatography coupled with high-resolution magnetic mass spectrometry. Potential formation mechanisms of Cl/Br-PAHs were also proposed. The mass concentration ranges for Σ₁₈Cl-PAHs and Σ₁₈Br-PAHs in stack gas were 25.85-4191 ng Nm^-3 and 1.02-341 ng Nm^-3, respectively. The variation of concentration indicated that the steel scrap composition greatly affected the production of Cl/Br-PAHs. The congener ratios including 6-chlorobenzo [a]pyrene/3-chlorofluoranthene and 1-chloroanthracene/1-chloropyrene could be used to estimate the influence of industrial sources on Cl-PAH occurrences in the air. Ring structure growth was the dominant formation pathway for Cl/Br-PAHs, distinctly different from dioxin formation mechanisms dominated by precursor dimerization and chlorination.

Role of hypobromous acid in the transformation of polycyclic aromatic hydrocarbons during chlorination

Hypobromous acid (HOBr), a highly reactive active species, can be formed and impact reaction processes with organic pollutants in source water during chlorination disinfection of the water containing bromide (Br-). In this study, we investigated the transformation kinetics of 10 parent polycyclic aromatic hydrocarbons (PAHs) and formation mechanisms of transformation products in the presence of Br- during chlorination. The results indicated that HOBr can accelerate the processes of electrophilic substitution (ES) and single electron transfer (ET) reactions in PAHs, and the second-order rate constants of HOBr are 10²-10³ times higher than those of hypochlorous acid (HOCl) with PAHs. HOBr was more conductive to induce ES reactions than HOCl. In water containing Br-, HOBr and HOCl dominate the reaction processes with PAHs, although other active bromine species may still affect reaction processes. In terms of transformation products, higher reactivity of HOBr results from faster formation of oxygenated PAHs (OPAHs) and halogenated PAHs (HPAHs) than HOCl. As an example of 3 model PAHs, anthracene transforms faster to its oxygenated products at a higher concentration, while pyrene and fluorene transform faster to halogenated products. These fundamental results were essential to understanding the transformation kinetics of PAHs and the formation of toxic disinfection by-products in the presence of Br-.

Theoretical Calculation on the Reaction Mechanisms, Kinetics and Toxicity of Acetaminophen Degradation Initiated by Hydroxyl and Sulfate Radicals in the Aqueous Phase

The •OH and SO₄^•− play a vital role on degrading pharmaceutical contaminants in water. In this paper, theoretical calculations have been used to discuss the degradation mechanisms, kinetics and ecotoxicity of acetaminophen (AAP) initiated by •OH and SO₄^•−. Two significant reaction mechanisms of radical adduct formation (RAF) and formal hydrogen atom transfer (FHAT) were investigated deeply. The results showed that the RAF takes precedence over FHAT in both •OH and SO₄^•− with AAP reactions. The whole and branched rate constants were calculated in a suitable temperature range of 198–338 K and 1 atm by using the KiSThelP program. At 298 K and 1 atm, the total rate constants of •OH and SO₄^•− with AAP were 3.23 × 10⁹ M⁻¹ s⁻¹ and 4.60 × 10¹⁰ M⁻¹ s⁻¹, respectively, considering the diffusion-limited effect. The chronic toxicity showed that the main degradation intermediates were harmless to three aquatic organism, namely, fish, daphnia, and green algae. From point of view of the acute toxicity, some degradation intermediates were still at harmful or toxic level. These results provide theoretical guidance on the practical degradation of AAP in the water.

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.

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.

Formation of polybrominated dibenzofurans (PBDFs) and polybrominated diphenyl ethers (PBDEs) from oxidation of brominated flame retardants (BFRs)

Brominated aromatic rings constitute main structural entities in virtually all commercially deployed brominated flame retardants (BFRs). Oxidative decomposition of BFRs liberates appreciable quantities of bromobenzenes (BBzs). This contribution reports experimental measurements for the generation of notorious polybrominated dibenzofurans (PBDFs) and polybrominated diphenyl ethers (PBDEs) from oxidation of monobromobenzene (MBBz). In the light of developed product profiles, we map out reaction pathways and report kinetic parameters for PBDFs and PBDEs formation from coupling reactions of MBBz molecule and its derived ortho-bromophenoxy (o-BPhxy) radical using quantum chemical calculations. The identification and quantitation of product species involve the use of gas chromatograph - triple quadrupole mass spectrometer (GC-QQQMS) operating in the multiple reaction monitoring (MRM) mode. Bimolecular reactions of MBBz and o-BPhxy result in the generation of twelve pre-PBDF intermediates, of which four can also serve as building blocks for the synthesis of PBDEs. These four intermediates are denoted as pre-PBDE/pre-PBDF, with the remaining eight symbolised as pre-PBDF. The resonance-stabilised structure of the o-BPhxy radical accumulates more spin density character on its phenoxy O atom (30.9 %) in reference to ortho-C and para-C sites. Thus, the formation of the pre-PBDE/pre-PBDF structures via O/o-C couplings advances faster as it requires lower activation enthalpies (79.2 - 84.9 kJ mol^-1) than the pre-PBDF moieties, which arise via pairing reactions involving o-C(H or Br)/o-C(H or Br) sites (97.2 - 180.2 kJ mol^-1). Kinetic analysis indicates that, the O/o-C pre-PBDE/pre-PBDF adducts self-eject the out-of-plane H atoms to produce PBDEs, rather than undergo a three-step mechanism forming PBDFs. However, experimental measurements demonstrate PBDEs appearing in lower yields as compared to those of PBDFs; presumably due to H- and Br-induced conversion of the PBDEs into PBDFs following a simple ring-closure reaction. High reaction temperatures facilitate loss of ortho Br atom from PBDEs, followed by cyclisation step to generate PBDFs. PBDFs are observed in a narrow temperature range of 700-850 °C, whereas PBDEs form between 550-850 °C. Since formation mechanisms of PBDFs and polybrominated dibenzo-p-dioxins (PBDDs) are typically only sensitive to the bromination at ortho positions, the results reported herein apply also to higher brominated isomers of BBzs.

Thermochemical formation of dioxins promoted by chromium chloride: In situ Cr- and Cl-XAFS analysis

Chromium is commonly found in the flue gases and ashes of Municipal Solid Waste Incineration. It has been reported as an active catalyst for the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) during de novo tests, yet its specific mode of action has remained unclear. This study aims to identify the effects of chromium chloride on the formation of PCDD/F and other chloro-aromatics and to elucidate the underlying reaction mechanisms. A series of de novo tests, conducted over a wide range of temperature (from 250 to 550 °C) and for four different oxygen contents (0, 5, 10, 20 %), confirmed the promoting effect of CrCl₃ on the PCDD/F formation. In situ X-ray Absorption Fine Structure (XAFS) spectroscopy was applied to investigate the behavior of CrCl₃ during heating, describing the entire picture of CrCl₃-promoted formation pathways of dioxins. The effect of oxygen was studied by measuring XAFS spectra on samples heated at different oxygen concentrations. According to these spectra, chromium compounds play two key roles during dioxins formation: (a) chlorinating carbon, using chlorine derived from conversion of CrCl₃ into Cr₂O₃, and further oxidation to Cr(VI), and (b) facilitating oxidative destruction of the carbon matrix, while reducing Cr(VI) to Cr₂O₃.

Mechanistic aspects of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) formation from chlorine bleaching of non-wood pulp

Chlorine bleaching of non-wood pulp can produce and release polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) into environment. In this study, a series of chlorination experiments were conducted to explore the source, formation pathway and formation kinetics of Cl_1-8DD/Fs during the chlorine bleaching of wheat straw pulp. The ¹³C isotope-labeling experiment verified that PCDD/Fs could not be formed from the chlorination of phenols in pulp. Above 80% of the observed PCDFs originated from the direct chlorination of dibenzofuran (DBF) in unbleached wheat straw pulp, while approximately 60% of the observed PCDDs came from the chlorination of nonextractable precursors in the pulp. The yield of total PCDFs was 2 orders of magnitude higher than that of total PCDDs. The kinetic study indicated that DBF was more easily chlorinated than dibenzo-p-dioxin (DBD) in the pulp solution. Pseudo-first-order reaction kinetic equations fitted the formation and degradation of PCDD/Fs well. The direct chlorination of DBD/F primarily preferred a selective pattern at the 2 position, followed by the 8, 7 and 3 positions. A higher content of DBF in unbleached pulp led to a higher yield of 2,3,7,8-Cl₄DF. Finally, the practical implication for dioxin formation control was discussed.

Mechanistic formation of hazardous molecular heterocyclic amines from high temperature pyrolysis of model biomass materials: cellulose and tyrosine

Background

Research inventories on the co-pyrolysis of major biomass components such as cellulose with amino acid materials is scarce in literature despite the fact that such studies are critical in understanding toxic product relations from high temperature cooking, combustion of bio-fuels, cigarette smoking and forest fires. This paper explores, quantitatively, the yields of heterocyclic nitrogenated molecular reaction products of grave mutagenetic concern from the co-pyrolysis of model biomass materials; tyrosine and cellulose. Research has established that heterocyclic amines such as isocyanates are mutagens as well precursors for asthma, and other respiratory disorders.

Methods

An equimassic mixture of tyrosine and cellulose (50 ± 2 mg) by weight were pyrolyzed in a tubular quartz reactor in flowing nitrogen at 1 atm. Besides, varying combinations of tyrosine and cellulose in the ratios 3:1 and 1:3 were also explored for comparison. The reaction time was set at 2 s so as to simulate combustions events in nature. The pyrolysate was collected over 5 mL dichloromethane and characterized using a gas chromatograph coupled to a mass spectrometer detector.

Results

Evidently, it was noted that 1-methylindazole was released in high yields at 300 °C, constituting ~ 300 µg in the entire pyrolysis temperature range (200–700 °C). Nonetheless, isoindazole gave the highest yield ~ 730 µg while 1-naphthyl isocyanate gave a total yield of ~ 336 µg in the same temperature range. Remarkably, the change in char yield between 300 and 450 °C for the pyrolysis of 25% tyrosine in 75% cellulose was found to be ~ 48% whereas the change in char yield for the pyrolysis of 75% tyrosine in 25% cellulose was 49%.

Conclusion

The char and tar yields considered important residues of biomass burning have been reported in this study and found to be consistent with other research output in literature. The striking similarities of % yield of char across all temperatures for various combinations was the most significant observation in this investigation—char yield was independent of the mixing ratio during pyrolysis. From a mechanistic standpoint, it was noted that tyrosine inhibited cellulose based nitrogenated products. Thus N-products dominated the O-products.

Method development for analyzing ultratrace polyhalogenated carbazoles in soil and sediment

In the past few years, polyhalogenated carbazoles (PHCZs) have been of increasing concern because their structure is similar to that of legacy POPs. In the present study, an analytical method, including intensive cleanup and fractionation procedures in combination with instrumental parameters, was developed to determine ultratrace polyhalogenated carbazoles (PHCZs) in soil and sediment. The eluting sorbents, volume and packing of the column were optimized. Our results showed that 5 g of florisil and 4 g of silica gel under 150 mL of hexane/DCM = 3:1 presented good performance in terms of recovery and repeatability. GC-HRMS, GC-MS/MS (EI-MRM) and GC-MS (EI-SIM) were applied to compare the performance of PHCZ analysis. For sensitivity, EI-MRM presents method detection limits comparable to those of GC-HRMS and much lower than those of EI-SIM. Regarding selectivity, GC-HRMS performed better than the other two techniques since GC-HRMS can reduce interference from perfluorokerosene (PFK) and DDX (DDT, DDE, and DDD) due to its high resolution. GC-HRMS was then further optimized by shortening the run time and modifying the SIM ion. The final method was successfully applied to determine PHCZs in soil and sediment, and the target compounds had almost 100% detection frequency in the samples. The ubiquitous presence of PHCZ in soil and sediment calls for a further investigation of its source, distribution and degradation in the environment.

Oxidation pathways, kinetics and branching ratios of chloromethyl ethyl ether (CMEE) initiated by OH radicals and the fate of its product radical: an insight from a computational study

The OH-initiated oxidation reactions of chloromethyl ethyl ether (CH2ClOCH2CH3) have been presented by using quantum calculation methods. The Minnesota functional (M06-2X) of the density functional theory method along with a polarization and diffuse 6-311++G(d,p) basis set is chosen for optimization and frequency calculations for H-abstractions from CH2ClOCH2CH3 molecules by OH radicals. Furthermore, the CCSD(T) method along with the same basis set is used for energy refinement of all optimized structures to obtain more accurate energies of the species. Our thermo-chemical calculation results show that the C˙HClOCH2CH3 product radical is more stable, corresponding to hydrogen atom abstraction from the -CH2Cl site, than others while the energy profile results indicate that the H-atom abstracted from the -OCH2 site follows the minimum energy path compared to other channels. The rate constants are computed using canonical transition state theory (CTST) within the temperature range of 250-450 K at 1 atm. The overall rate constant (at 298 K) for the abstraction reactions is found to be consistent with the earlier reported rate constant. The percentage branching ratios of different abstraction channels and the lifetime of chloromethyl ethyl ether are also given herein. We further investigated the unimolecular decomposition pathways of the CH2ClOCH(O˙)CH3 radical and found that unimolecular C-C bond scission is the kinetically and thermodynamically more feasible pathway compared to other unimolecular decomposition reactions.

New insight into the formation of polyhalogenated carbazoles: Aqueous chlorination of residual carbazole under bromide condition in drinking water

Although polyhalogenated carbazoles (PHCZs) have been increasingly detected in aquatic environments, studies on their source and formation are extremely scarce. After investigation of PHCZs and carbazole in drinking water, an overlooked formation route of chloro/bromo-CZs was now proposed as aqueous chlorination of residual carbazole under bromide condition. Four groups of PHCZ, including mono-, di-, tri-, and tetra-halogenated groups, were identified in chlorinated drinking water, and the mechanism of the formation of the four groups of PHCZs was proposed. Twenty-six PHCZ congeners, including chloro-, bromo-, and chlorobromo-mixed species, were thoroughly studied and it was revealed for the first time the four groups of PHCZs shifted from chlorinated to being more brominated with increasing bromide level. The speciation of the four groups of PHCZs was modeled. It was revealed that the shift of PHCZs from chlorinated to being more brominated was caused by the reactivity differences between HOCl and HOBr in reactions forming PHCZs. Furthermore, this study revealed that the species numbers and concentrations of PHCZs formed in chlorination were much higher than those in chloramination, and the formation of PHCZs was decreased by ∼50% with an increase of pH from 6.0 to 9.0. This study of the variety of PHCZs in chlorinated water is an important step toward revealing the occurrence of PHCZs in aquatic environments.

Deposition and Source Identification of Nitrogen Heterocyclic Polycyclic Aromatic Compounds in Snow, Sediment, and Air Samples from the Athabasca Oil Sands Region

Polycyclic aromatic compounds (PACs) can have multiple sources in the Athabasca Oil Sands Region (AOSR). The current study was designed to identify and explore the potential of nitrogen heterocyclic PACs (NPACs) as source indicators in snowpack, lake sediment and passive air samples from the AOSR during 2014-2015. Source samples including petroleum coke (petcoke), haul road dust, and unprocessed oil sands were also analyzed. Samples were analyzed using comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry, and liquid chromatography-high resolution Orbitrap mass spectrometry. Over 200 NPACs were identified and classified into at least 24 isomer groups, including alkylated carbazoles, benzocarbazoles, and indenoquinolines. Levels of NPACs in environmental samples decreased with distance from the main developments and with increasing depth in lake sediments but were detected within 50 km from the major developments. The composition profiles of several NPAC isomer classes, such as dimethylcarbazoles, showed that petcoke had a distinct distribution of NPACs compared to the haul road dust and unprocessed oil sands ores and was the most similar source material to near-field environmental samples. These results suggest that petcoke is a major contributing source for the identified NPACs and that these compounds have the potential to be used as source indicators for future research in the AOSR.

Mechanism and kinetics studies of the atmospheric oxidation of p,p'-Dicofol by OH and NO3 radicals

As an effective organochlorine pesticide, Dicofol has been extensively applied in more than 30 countries for protecting over 60 different crops. Considering its large consumption and potential adverse effect on human health (endocrine disrupting and carcinogenicity), the fate of Dicofol sprayed into the air is of public concern. In this study, we conducted a comprehensive study on the reaction mechanisms of p,p'-Dicofol with OH and NO₃ radicals using DFT method. Comparing the abstrations by OH and NO₃ radical, OH and NO₃ radical addition reactions are predominant due to the lower potential barriers and stronger heat release. The phenolic substances (P1P5), epoxides (P11 and P15), dialdehyde (P13) and other species (P8, P9, P10 and P14) are generated by OH additions and their subsequent reactions while OH abstraction reactions produce DCBP, P7 and chlorphenyl radical. Particularly, NO₃ additions and their subsequent reactions yield dialdehydes (P16 and P17) and 2,8-DCDD, which is the first report of the generation of dioxin from atmospheric oxidation of p,p'-Dicofol. Additionally, based on the structure optimization and energy calculation, rate constants and Arrhenius formulas of the elementary reactions of p,p'-Dicofol with OH and NO₃ radicals were obtained over the temperature range of 280-380 K and at 1 atm. The rate constants for the reactions of p,p'-Dicofol with OH and NO₃ radicals are 1.51 × 10^-12 and 8.88 × 10^-14 cm³ molecule^-1 s^-1, respectively. The lifetime (τ_Total) of p,p'-Dicofol determined by the reactions of OH and NO₃ radical is 5.86 h, indicating a potential long-range transport in the atmosphere.

A Thermochemical Parameters and Theoretical Study of the Chlorinated Compounds of Thiophene

This contribution sets out to compute thermochemical and geometrical parameters of the complete series of chlorinated isomers of thiophene based on the accurate chemistry model of CBS-QB3. Herein, we compute standard entropies, standard enthalpies of formation, standard Gibbs free energies of formation, and heat capacities. Our calculated enthalpy values agree with available limited experimental values. The DFT-based reactivity descriptors were used to elucidate the site selectivity for the chlorination sequence of thiophene. The relative preference for chlorination was found to be in accord with the thermodynamic stability trends inferred based on the H scale. Calculated Fukui indices predict a chlorination sequence to ensue as follows: 2-chloro → 2,5-dichloro → 2,3,5-trichloro → 2,3,4,5-tetrachlorothiophene.

Occurrence of carbazoles in dust and air samples from different locations in Germany

9H-carbazole is generated from incomplete combustion of diverse fossil fuels and biomass, in tobacco smoke and from industrial processes, while halogenated carbazoles have natural and anthropogenic sources. We analyzed 9H-carbazole and 14 halogenated carbazoles in dust samples from 14 schools, 13 daycare centers, and 13 residences, as well as 5 indoor air samples from residences in Munich, Germany. Overall, we present first data of various carbazoles in different indoor environments without visible combustion sources. The median (95th percentile) values of the halogenated analytes mainly detected in the entire study group were 10.3ng/g (308ng/g) for 9H-carbazole, 13.3ng/g (735ng/g) for 3,6-dichloro-9H-carbazole, 6.2ng/g (159ng/g) for 1,3,6-tribromo-9H-carbazole, and 1.2ng/g (21.1ng/g) for 2,7-dibromo-9H-carbazole. For most of the target analytes, the highest concentrations were observed in dust samples from schools, and the lowest were found in residences. In the air samples, all analytes were found only at low levels, with median values of 7.7pg/m³ for 9H-carbazole and 6.1pg/m³ for 2,3,6,7-tetrachloro-9H-carbazole. For 9H-carbazole, "typical" and "high" non-dietary intake of children through dust ingestion using median and 95th percentile values were calculated to be 0.03ng/kg b.w. and 1.1ng/kg b.w. daily, respectively. Due to limited toxicological information and exposure data for other relevant pathways (e.g., dietary intake), the risk assessment is inconclusive. Nevertheless, there are indications that 9H-carbazole has carcinogenic properties and that halogenated carbazoles have dioxin-like toxicities. Therefore, further research is essential.

Quantum calculation on night-time degradation of 2-chloroethyl ethyl ether (CH3CH2OCH2CH2Cl) initiated by NO3 radical

A dual-level quantum chemical calculations have been carried out on the initiation of night-time degradation of 2-chloroethyl ethyl ether (CH3CH2OCH2CH2Cl) via H-abstraction by NO3 radical. Within the scope of density functional theory, the electronic structure of all the species involved in the titled reaction has been optimized at M06-2X functional along with 6-31[Formula: see text]G(d,p) basis set. A higher level of couple cluster CCSD(T) method in conjunction with 6-311[Formula: see text]G(d,p) basis set has been used for the refined energy of the species. All minima and saddle states involved in the reaction channel have been characterized on the potential energy surface (PES). From PES, it is confirmed that H-abstraction from methylene (–CH2–) of ethyl (CH3CH2–) part of CH3CH2OCH2CH2Cl follows the minimum energy path. The rate constants (individual and overall) of the titled reaction are obtained using Canonical Transition State Theory (CTST) over the temperature range of 250–350[Formula: see text]K. The atmospheric lifetime and radiative efficiency of the titled molecule have also been estimated, amounting to 0.23 years and 0.024 years, respectively. The Global Warming Potentials of the 2-chloroethyl ethyl ether in 20 years, 100 years and 500 years time horizon were found to be 0.13, 0.04 and 0.01, respectively.

Thermal Oxidation Degradation of 2,2',4,4'-Tetrabromodiphenyl Ether over LiαTiOx Micro/Nanostructures with Dozens of Oxidative Product Analyses and Reaction Mechanisms

Flowerlike Li_αTiO_x micro/nanostructures were successfully synthesized to degrade 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) at 250-350 °C. The pseudo-first-order kinetics rate constant of the reaction at 300 °C was in the range of 0.034-0.055 min^-1. The activation energy was as low as 39.9-48.1 kJ/mol. The excellent performance attained over Li_αTiO_x was attributed to Li dopant having the electron-donating effect, which enhanced the oxygen species mobility. The oxidative reaction was believed to be the dominant degradation pathway following the Mars-van Krevelen mechanism, being accompanied by the weak hydrodebromination occurrence generating the trace mono- to tri-BDEs. More than 70 types of oxidation products containing diphenyl ether backbone, single-benzene rings, and ring-opened products were detected by GC-MS with derivatization, ESI-FT-ICR-MS, and ion chromatography. An increase in the number of ring-cracked oxidative products under prolonged reaction was observed by ESI-FT-ICR-MS analysis according to the van Krevelen diagram. In the oxidative reaction, a series of oxidative products, such as OH-tri-BDEs and OH-tetra-BDEs, first formed via the nucleophilic O^2- attack and subsequently transformed into dibromophenol, tribromophenol, and benzenedicarboxylic and benzoic acids, etc. They could be further attacked by electrophilic O₂^- and O^- and completely cracked to small molecules such as formic, acetic, propionic, and butyric acids.

Mechanism and Rate of Thermal Decomposition of Hexachlorocyclopentadiene and Its Importance in PCDD/F Formation from the Combustion of Cyclodiene Pesticides

Thermal decomposition of hexachlorocyclopentadiene (HCCP) has been studied in inert gas and under oxidative conditions in a silica flow reactor at a residence time of 5.0 s between 690 and 923 K and 1 atm pressure. Pyrolysis was initiated by Cl bond fission to form pentachlorocyclopentadienyl radical; two such radicals then combined to undergo a series of intramolecular rearrangements and Cl fissions, producing principally octachloronaphthalene (8ClNP) and Cl₂. This process has been studied by quantum chemical calculation, and a reaction potential energy surface has been developed. The rate constant of initial Cl atom fission has been calculated by canonical variational transition state theory as k = 1.45 × 10¹⁵ exp(-222 ± 9 kJ mol^-1/RT) s^-1 between 500 and 2000 K. A minimal kinetic model was developed to model the decomposition and major products. Oxidative decomposition was studied in nitrogen with O₂ contents of 1, 6, 12, and 20 mol %. Increasing O₂ to 6-8% increased the rate of decomposition of HCCP and decreased the yield of 8ClNP. Above 823 K, hexachlorobenzene (HCB) and CO became major products. The oxidative reaction has also been studied quantum chemically. At high O₂ content (>∼10%), the rate of decomposition of HCCP declined as did yields of 8ClNP and HCB, but CO yields increased.

Highly Elevated Levels and Particle-Size Distributions of Environmentally Persistent Free Radicals in Haze-Associated Atmosphere

Levels and particle-size distributions of environmentally persistent free radicals (EPFRs) in haze-associated atmospheric particulate matter (PM) have not been highlighted, even though they may enter the human body along with PM and adversely affect human health. This study quantified the levels of EPFRs in airborne PM with different aerodynamic diameters (d_ae) using electron paramagnetic resonance (EPR) spectroscopy. EPR spectra showed a single, unstructured signal from persistent semiquinone radicals. The average concentration of EPFRs in the airborne PM during haze events was 2.18 × 12²⁰ spins/g (range: 3.06 × 10¹⁹-6.23 × 10²⁰ spins/g), approximately 2 orders of magnitude higher than that reported previously in the US atmosphere. Particle-size distributions of EPFRs in four different PM fractions (d_ae > 10 μm, 10 μm < d_ae < 2.5 μm, 2.5 μm <d_ae < 1 μm, d_ae < 1 μm) indicated the highest levels of EPFRs in the PM fraction with d_ae < 1 μm, with average 1/e lifetime of 59.2 days. A significant occurrence of EPFRs in PM samples collected from coal-burning activities (1.52 × 10²² spins/g), automobile exhaust (3.0 × 10²² spins/g), and biomass burning activities (1.14 × 10²² spins/g) was detected, which may be potential primary sources of EPFRs in airborne PM. The results in this study may help to understand the sources and potential risks of EPFRs in airborne fine particles.

Characterization of the reactivity and chlorinated products of carbazole during aqueous chlorination

Carbazole in source water is a potential precursor for toxic chlorocarbazoles in drinking water when chlorine is used as a disinfection agent in drinking water treatment plants. However, the reactivity of carbazole and the specific structures and predominant analogues of chlorocarbazoles produced during aqueous chlorination remain unknown. In this study, the aqueous chlorination of carbazole was performed to characterize its reactivity and the chlorinated products. Chlorocarbazoles generated from carbazole were identified by a comprehensive two-dimensional gas chromatography-mass spectrometry method, and their molecular structures were predicted by the Fukui index of electrophilic attack, f^-1(r). As a result, the comprehensive chlorination pathway of carbazole was extrapolated with a total of nine chlorocarbazoles identified, including two monochlorocarbazoles (3-chlorocarbazole and 1-chlorocarbazole), four dichlorocarbazoles (3,6-dichlorocarbazole, 1,6-dichlorocarbazole, 1,3-dichlorocarbazole and 1,8-dichlorocarbazole), two trichlorocarbazoles (1,3,6-trichlorocarbazole and 1,3,8-trichlorocarbazole) and one tetrachlorocarbazole (1,3,6,8-tetrachlorocarbazole). The f^-1(r) value indicates that the C1, C3, C6 and C8 atoms of carbazole were the favored positions for electrophilic attack, with the C3 and C6 atoms being the predominant sites for chlorine substitution. 3-Chlorocarbazole, 3,6-dichlorocarbazole, 1,3,6-trichlorocarbazole and 1,3,6,8-tetrachlorocarbazole were the major analogues of each chlorocarbazole group; however, the production of minor analogues such as 1-chlorocarbazole and 1,6-dichlorocarbazole should not be overlooked. The chlorination of carbazole was a pseudo first order reaction with a reaction rate of 0.1836 nmol/(L· h) and half-life of 3.77 h (pH = 6.4, Cl₂ = 4.7 mg/L), and the chlorination rate of carbazole was approximately 5 times faster than that of an known chlorination precursor pyrene. These results showed that Fukui index was efficacious to predict the chlorination sites of aromatic compounds, and that carbazole is readily transformed into toxic chlorocarbazoles in drinking water treatment plants that use chlorine as a disinfection agent.

Studies on the formation of formaldehyde during 2-ethylhexyl 4-(dimethylamino)benzoate demethylation in the presence of reactive oxygen and chlorine species

In order to protect the skin from UV radiation, personal care products (PCPS) often contain chemical UV-filters. These compounds can enter the environment causing serious consequences on the water ecosystems. The aim of this study was to examine, the effect of different factors, such as UV light, the presence of NaOCl and H₂O₂ on the formaldehyde formation during popular UV filter, 2-ethylhexyl 4-(dimethylamino)benzoate (ODPABA) demethylation. The concentration of formaldehyde was determined by VIS spectrophotometry after derivatization. The reaction mixtures were qualitatively analyzed using GC/MS chromatography. The highest concentration of formaldehyde was observed in the case of ODPABA/H₂O₂/UV reaction mixture. In order to describe two types of demethylation mechanisms, namely, radical and ionic, the experimental results were enriched with Fukui function analysis and thermodynamic calculations. In the case of non-irradiated system containing ODPABA and NaOCl, demethylation reaction probably proceeds via ionic mechanism. As it was established, amino nitrogen atom in the ODPABA molecule is the most susceptible site for the HOCl electrophilic attack, which is the first step of ionic demethylation mechanism. In the case of irradiated mixtures, the reaction is probably radical in nature. The results of thermodynamic calculations showed that abstraction of the hydrogen from N(CH₃)₂ group is more probable than from 2-ethylhexyl moiety, which indicates higher susceptibility of N(CH₃)₂ to the oxidation.

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

Polyhalogenated carbazoles (PHCZs) have been increasingly detected in the environment. Their similarities in chemical structure with legacy pollutants and their potential toxicity have caused increasing concern. In this work, 112 Ponar grab and 28 core sediment samples were collected from Lakes Michigan, Superior, and Huron, and a total of 26 PHCZs were analyzed along with unsubstituted carbazole using gas chromatography coupled with single- or triple-quadrupole mass spectrometry. Our results show that the total accumulation of PHCZs in the sediments of the upper Great Lakes is >3000 tonnes, orders of magnitude greater than those of polychlorinated biphenyls (PCBs) and decabromodiphenyl ether (BDE209). The 27 individual analytes differ in spatial distribution and temporal trend. Our results showed that PHCZs with substitution patterns of -Br_2-5, -Cl_1-2Br_2-4, or having iodine, were more abundant in sediment of Lake Michigan deposited before 1900 than those deposited more recently, implying a natural origin. Some "emerging" PHCZs have been increasingly deposited into the sediment in recent decades, and deserve further environmental monitoring and research. Other PHCZs with low halogen substitution may form from in situ dehalogenation of PHCZs having more halogens. Anthropogenic sources of PHCZs may exist, particularly for the emerging and low molecular mass congeners.

Formation of environmentally-persistent free radicals (EPFR) on α-Al2O3 clusters

This study explores the role of alumina clusters assume an important role in catalyzing formation of notorious environmental persistent free radicals (EPFRs).

Decomposition of selected chlorinated volatile organic compounds by ceria (CeO2)

Guided by recent experimental measurements, this study theoretically investigates the initial steps operating in the interactions of ceria surface CeO₂(111) with three CVOC model compounds, namely chloroethene (CE), chloroethane (CA) and chlorobenzene (CB).

Polyhalogenated carbazoles in sediments from Lake Tai (China): Distribution, congener composition, and toxic equivalent evaluation

Polyhalogenated carbazoles (PHCZs) have attracted mounting environmental concerns since they were recently discovered in sediments and soil. Current knowledge on their occurrence, environmental behavior and fate remains very limited in general. In the present study, 11 PHCZ congeners were screened in surface sediments of Lake Tai, an important freshwater system located in the Yangtze River Delta, China. Total concentrations of PHCZs (∑PHCZs) ranged up to 15.8 ng/g dry weight (median: 1.54 ng/g dw), rivaling those of polybrominated diphenyl ethers (∑PBDEs, 0.07-15.9 ng/g dw) in the same sediments. The PHCZ congener composition profiles revealed a dominance of 3,6-dichlorocarbazole and 3,6-dibromocarbazole with comparable concentrations. These two dominant congeners differed in spatial distribution patterns in Lake Tai, indicating different sources or origins. Potential toxic effects associated with the levels of PHCZs in the sediments were evaluated via the toxic equivalent (TEQ) approach. The TEQs of PHCZs in Lake Tai sediments ranged up to 1.36 pg TEQ/g dw. As the first report on the occurrence of PHCZs in an Asian waterbody, our findings suggest that PHCZs should be given more attention during environmental monitoring and risk assessments of hazardous chemicals, as they may represent another group of persistent organic pollutants with dioxin-like effects and wide distributions.

Synergetic inhibition of PCDD/F formation from pentachlorophenol by mixtures of urea and calcium oxide

Chlorophenols are structurally similar to PCDD/Fs and have been considered as highly potential precursors for PCDD/Fs formation. The suppressing effects of PCDD/F formation from pentachlorophenol (PCP) were investigated on various mass ratios of CaO and urea. The total concentration of 2,3,7,8-PCDD/Fs, mostly dominated by OCDD, was determined to be 48.58-10186ng/mg in inhibitor-reaction systems, being much lower than that in blank reaction system (75654ng/mg). Interestingly, compared with pure CaO and urea reaction system, the concentration and TEQ of formed 2,3,7,8-PCDD/Fs in mixed urea/CaO reaction system were lower, especially with 5-20% urea reaction systems being respectively at decrease by 96.5-99.4% and 99.2-99.7%. The suppression efficiency of TEQ in 5-20% urea reaction systems could be always approximately 100% under 250-350°C. These results suggested that mixed inhibitors, especially 5-20% urea inhibitors, have a synergetic inhibition effect for PCDD/Fs formation from PCP. Mixed inhibitor generated several intermediates, involving CO2, H2O, NH3, Ca(OH)2, CaCO3, HNCO, biuret and ammelide. The complex between PCP and Ca, N-doped species, lower chlorinated phenols and benzenediol, and organic acids were also determined. Synergetic inhibition mechanism may be attributed to accelerated facilitation of acid-base reaction and N doping. The decomposition of PCP itself also contributes to prevent PCDD/Fs formation.

Synergetic inhibition of thermochemical formation of chlorinated aromatics by sulfur and nitrogen derived from thiourea: Multielement characterizations

Nitrogen and sulfur (N/S)-containing compounds inhibit the formation of polychlorinated dibenzo-p-dioxins (PCDDs) and furans (PCDFs) in thermal processes. However, few studies have examined the inhibition mechanisms of N/S-containing compounds. In the present study, we focused on thiourea [(NH2)2CS] as such a compound and investigated its inhibition effects and mechanisms. The production of PCDD/Fs, polychlorinated biphenyls (PCBs), and chlorobenzenes (CBzs) were inhibited by >99% in the model fly ash in the presence of 1.0% thiourea after heating at 300 °C. Experimental results using real fly ash series were indicative of the thermal destruction of these chlorinated aromatics by thiourea. Multielement characterization using K-edge X-ray absorption fine structures of copper, chlorine, sulfur, nitrogen, and carbon revealed three possible inhibition paths, namely, (a) sulfidization of the copper catalyst to CuS, Cu2S, and CuSO4; (b) blocking the chlorination of carbon via the reaction of chlorine with N-containing compounds to generate ammonium chloride and other minor compounds; and (c) changing the carbon frame involved in attacking the carbon matrix by sulfur and nitrogen. Thus, thiourea plays a role as a sulfur and nitrogen donor to achieve multiple and synergistic inhibition of chlorinated aromatics. Our results suggest that other N/S-containing inhibitors function based on similar mechanisms.

Quantitative determination of ultra-trace carbazoles in sediments in the coastal environment

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

A DFT study on dihydropyrazine annulated linear polyacenes: aromaticity, stability and HOMO–LUMO energy modulation

Linear polyacene (LPA) mimics containing up to 34 rings have been designed by annulating dihydropyrazine units to LPA cores and they showed enhanced aromatic character than the LPA due to significant mixing of the N-lone pairs with the carbon π-orbitals.