Photodegradative fate and potential phototoxic products of bromocarbazoles and chlorocarbazoles in water

Abstract

Bromocarbazoles and chlorocarbazoles are emerging environmental contaminants that have been reported to be persistent and possessing dioxin-like toxicity; however, their photodegradative fate in water is unknown. The photodegradation of 3-bromocarbazole, 3-chlorocarbazole, and 3,6-dichlorocarbazole was determined in ultrapure water. They proceeded by direct photolysis and followed first-order kinetics. The rate constants (k) were 0.4838, 0.3454, and 0.4422 h corresponding to half-lives (t ) 1.81, 2.01, and 1.62, while the quantum yields (Ф) were 0.232, 0.180, and 0.295 respectively. The maximum wavelengths of absorption (λ) were in the near ultraviolet region (295, 296, 299, and 301 nm) implying these compounds are likely to degrade slowly under sunlight in natural aquatic environment. The molar extinction coefficients (ε) determined in acetonitrile were 18,573, 17,028, 13,385, and 14,010 L mol cm, respectively, the latter being 3,6-dibromocarbazole. A bathochromic shift was observed with halogen addition on their respective mono-substituted congeners. Bromocarbazoles were observed to degrade faster in water than chlorocarbazoles. In addition, photodegradation was estimated to proceed faster in summer than in winter, in natural water system at 50° N latitude. In the absence of light, hydrolytic degradation occurred but proceeded very slowly. Hexahydroxybenzene and trihydroxycarbazole were positively identified as the likely photoproducts with the former being a known toxic compound. Dehalogenation, oxidative cleavage, hydroxylation, and hydrolysis are suggested as the major photodegradation mechanisms in water, yielding phototoxic products that may be of enhanced toxicity than the parent compounds.

Laccase–mediator co-immobilized doped-HKUST-1 cellulose composite beads and their application for the biodegradation of carbazole

“…Compared with a low concentration of carbazole, the degradation rate of the high concentration carbazole was significantly weaker because a high concentration of carbazole would poison the active sites of laccase in the Lac@Ce-GMA-Cu-DA@AS biocatalyst, resulting in the deactivation of laccase. 42 The degradation rate of carbazole catalyzed by the Lac@Ce-GMA-Cu-DA@AS beads at different concentrations of the substrate reached more than 85% after 8 h, suggesting that the Lac@Ce-GMA-Cu-DA@AS biocatalyst possesses favorable tolerance to the substrate and is not susceptible to the toxic effects of a high substrate concentration. Thus, the promising catalytic performance of Lac@Ce-GMA-Cu-DA@AS offers great potential for water treatment applications.…”

Towards improved drinking water safety: the use of in vitro bioassays to optimize treatment processes and assess chemical hazards

“…Natural sunlight irradiation, for instance, plays an important role in transforming MPs and dissolved organic matter in other water environments such as open storage of reclaimed water and in natural surface waters due to natural processes (e.g., photolysis) (Bahnmüller et al, 2014;Tixier et al, 2002;Wang et al, 2021). At the same time, phototoxic products may also be formed during the photolysis of organic contaminants such as dioxin-like bromocarbazoles and chlorocarbazoles (Mumbo et al, 2017) and pharmaceutical mixtures (Wang and Lin, 2014). In short, while identification of the compounds inducing the AhR activity was not in the scope of the current study, the higher AhR bioactivities detected in the basin samples compared to the preceding sampling points provide interesting insight into the presence of AhR-inducing chemical hazards in the basins.…”

Polyhalogenated Carbazoles in Sediments of Lower Laurentian Great Lakes and Regional Perspectives

“…Since discoveries of significant quantities of polyhalogenated carbazoles (PHCZs) in sediments of Lake Michigan, , the occurrence of PHCZs in soils, − sediments, − water, , and biota − from various regions of the world has been reported. Recent studies on their sources, , transformation, − and toxicity − have also increased our understanding of the behavior of these compounds in the environment. Recent reports of PHCZs in drinking water raise concerns about their effects on public health. , Together, the results of these studies indicate a need for more focused studies on this chemical group of emerging concern.…”