Reductive transformation of carbamazepine by abiotic and biotic processes.

The antiepileptic drug carbamazepine (CBZ) is ubiquitously present in the anthropogenic water cycle and is therefore of concern regarding the potable water supply. Despite of its persistent behavior in the aquatic environment, a redox dependent removal at bank filtration sites with anaerobic aquifer passage was reported repeatedly but not elucidated in detail yet. The reductive transformation of CBZ was studied, using abiotic systems (catalytic hydrogenation, electrochemistry) as well as biologically active systems (column systems, batch degradation tests). In catalytic hydrogenation CBZ is gradually hydrogenated and nine transformation products (TPs) were detected by liquid chromatography high-resolution mass spectrometry. 10,11-Dihydro-CBZ ((2H)-CBZ) was the major stable product in these abiotic, surface catalyzed reduction processes and turned out to be not a precursor of the more hydrogenated TPs. In the biotic reduction processes the formation of (2H)-CBZ alone could not explain the observed CBZ decline. There, also traces of (6H)-CBZ and (8H)-CBZ were formed by microbes under anaerobic conditions and four phase-II metabolites of reduced CBZ could be detected and tentatively identified. Thus, the spectrum of reduction products of CBZ is more diverse than previously thought. In environmental samples CBZ removal along an anaerobic soil passage was confirmed and (2H)-CBZ was determined at one of the sites.

Sunlight photolysis of benzotriazoles - Identification of transformation products and pathways.

Benzotriazoles (BTs) are widely used corrosion inhibitors, incompletely removed in municipal wastewater treatment. The photochemical fate of the three BTs 1H-benzotriazole (1H-BT), 4-methyl-1H-benzotriazole (4Me-BT) and 5-methyl-1H-benzotriazole (5Me-BT) and of three microbial metabolites, was studied under simulated sunlight (290-800 nm) at neutral pH in aqueous solution for 24 h. The half-life, the quantum yield and the reaction rate were determined and a total of 36 photolysis products were detected and identified using liquid chromatography-high resolution-mass spectrometry. The half-lives of all six BTs were in the range of 6-24 h under the experimental conditions. Though the quantum yields were comparatively low (0.0007-0.0021), the environmental half-lives ranged from 2.4 to 8 d, suggesting that sunlight photolysis is still a relevant degradation process of BTs in surface waters. The photolysis pathway of 1H-BT under simulated sunlight differed from that suggested for UV-radiation, in that aminophenol is formed directly rather than via aniline. Similar pathways were found for the other BTs, except for 4-hydroxy-1H-benzotriazole (4OH-BT). Most identified transformation products of the BTs showed a high reactivity and appear not to persist in the environment. Upon co-photolysis of BTs with dissolved organic matter (DOM), however, series of reaction products were determined by Fourier transform - ion cyclotron resonance - mass spectrometry (FTICR-MS) which are formed by reaction of photolysis intermediates of the BTs with DOM.

Electrochemistry Combined with LC-HRMS: Elucidating Transformation Products of the Recalcitrant Pharmaceutical Compound Carbamazepine Generated by the White-Rot Fungus Pleurotus ostreatus.

Transformation products (TPs) of environmental pollutants must be identified to understand biodegradation processes and reaction mechanisms and to assess the efficiency of treatment processes. The combination of oxidation by an electrochemical cell (EC) with analysis by liquid chromatography-high-resolution mass spectrometry (LC-HRMS) is a rapid approach for the determination and identification of TPs generated by natural microbial processes. Electrochemically generated TPs of the recalcitrant pharmaceutical carbamazepine (CBZ) were used for a target screening for TPs formed by the white-rot fungus Pleurotus ostreatus. EC with LC-HRMS facilitates detection and identification of TPs because the product spectrum is not superimposed with biogenic metabolites and elevated substrate concentrations can be used. A group of 10 TPs formed in the microbial process were detected by target screening for molecular ions, and another 4 were detected by screening on the basis of characteristic fragment ions. Three of these TPs have never been reported before. For CBZ, EC with LC-HRMS was found to be more effective than software tools in defining targets for the screening and faster than nontarget screening alone in TP identification. EC with LC-HRMS may be used to feed MS databases with spectra of possible TPs of larger numbers of environmental contaminants for an efficient target screening.

Reductive Dehalogenation of Oligocyclic Phenolic Bromoaromatics by Dehalococcoides mccartyi Strain CBDB1.

Dehalococcoides mccartyi strains transform many halogenated compounds and are used for bioremediation. Such anaerobic transformations were intensively studied with chlorinated and simply structured compounds such as chlorinated benzenes, ethenes, and ethanes. However, many halogenated oligocyclic aromatic compounds occur in nature as either naturally produced materials or as part of commercial products such as pharmaceuticals, pesticides, or flame retardants. Here, we demonstrate that the D. mccartyi strain CBDB1 reductively debrominated two oligocyclic aromatic phenolic compounds, tetrabromobisphenol A (TBBPA) and bromophenol blue (BPB). The strain CBDB1 completely converted TBBPA to bisphenol A and BPB to phenol red with a stepwise removal of all bromide substituents. Debromination (but no cell growth) was detected in the cultures cultivated with TBBPA. In contrast, strain CBDB1 grew when interacting with BPB, demonstrating that this substrate was used as an electron acceptor for organobromine respiration. High doses of BPB delayed debromination and inhibited growth in the early cultivation phase. A higher toxicity of TBBPA compared with that of BPB might be due to the higher lipophilicity of TBBPA. Mass spectrometric analyses of whole-cell extracts demonstrated that two proteins encoded by the reductive dehalogenase homologous genes CbdbA1092 and CbdbA1503 were specifically induced by the used oligocyclic compounds, whereas others (e.g., CbdbA84 (CbrA)) were downregulated.