Decomposition of halogenated methanes in oxygen-free gas mixtures by the use of a silent electric discharge

A silent electric discharge was applied to decompose halogenated methanes including CCl4, CHCl3, CFCl3, CF2Cl2 and CF3Cl, in argon-containing gas mixtures. The decompositions of the target compounds were studied in static reactors at a fixed electric field and room temperature. The reaction products were analyzed by FT-IR spectroscopy, gas chromatography and UV spectrophotometry. The results demonstrated, that the radical-type decomposition of chlorofluoromethanes led to products formed by realignment of the halogen atoms. The decomposition of CCl4 was faster than that of the cholorofluoromethanes, and produced perchloroethane and chlorine. CHCl3 exhibited the highest decomposition rate and produced a large variety of products.     

Fluorinated natural products: the biosynthesis of fluoroacetate and 4-fluorothreonine in Streptomyces cattleya

Organofluorine compounds are rare in Nature, with only a handful known to be produced by some species of plant and two microorganisms. Consequently, the mechanism of enzymatic carbon-fluorine bond formation is poorly understood. The bacterium Streptomyces cattleya biosynthesises fluoroacetate and 4-fluorothreonine as secondary metabolites and is a convenient system to study the biosynthesis and enzymology of fluorometabolite production. Using stable-isotope labelled precursors it has been shown that there is a common intermediate in the biosynthesis of the fluorometabolites, which has recently been identified as fluoroacetaldehyde. Studies with cell-free extracts of S. cattleya have identified two enzymes, an aldehyde dehydrogenase and a threonine transaldolase, that are involved in the biotransformation of fluoroacetaldehyde to fluoroacetate and 4-fluorothreonine.     

Screening of organic halogens and identification of chlorinated benzoic acids in carbonaceous meteorites

The occurrence of halogenated organic compounds measured as a sum parameter and the evidence of chlorinated benzoic acids in four carbonaceous meteorites (Cold Bokkeveld, Murray, Murchison and Orgueil) from four independent fall events is reported. After AOX (Adsorbable organic halogen) and EOX (Extractable organic halogen) screening to quantify organically bound halogens, chlorinated organic compounds were analyzed by gas chromatography. AOX concentrations varying from 124 to 209 microg Cl/g d.w. were observed in carbonaceous meteorites. Ion chromatographic analysis of the distribution of organically bound halogens performed on the Cold Bokkeveld meteorite revealed that chlorinated and brominated organic compounds were extractable, up to 70%, whereas only trace amounts of organofluorines could be extracted. Chlorinated benzoic acids have been identified in carbonaceous meteorite extracts. Their presence and concentrations raise the question concerning the origin of halogenated, especially chlorinated, organic compounds in primitive planetary matter.     

Structure elucidation of four possible biogenic organohalogens using isotope exchange mass spectrometry

The molecular structures of four unknown bioaccumulating halogenated compounds, C10H6N2Br3Cl3, C10H6N2Br4Cl2, C10H6N2Br5Cl, and C10H6N2Br6 were characterized using isotope exchange positive chemical ionization (IE-PCI) mass spectrometry (MS) and identified by comparison to synthesized standards. NH3 and ND3 were used as reagent gases for the IE-PCI-MS experiment. The shift in mass of the quasimolecular ion between the NH3 and ND3 PCI obtained spectra indicated the number of exchangeable hydrogens attached to the two nitrogen atoms in C10H6N2Br4Cl2, and thus the type of amines present (primary, secondary, or tertiary). 19 compounds (13 amines of varying degree of substitution; six containing no nitrogen) were used as reference compounds and controls in the experiment to validate the IE-PCI technique. The results of the IE-PCI-MS indicated the presence of two tertiary amine functional groups. The molecular structures of the four hexahalogenated compounds were then proposed to be 1,1'-dimethyl-3,3',4,-tribromo-4',5,5'-trichloro-2,2'-bipyrrole, 1,1'-dimethyl-3,3',4,4'-tetrabromo-5,5'-dichloro-2,2'-bipyrrole, 1,1'-dimethyl-3,3',4,4',5-pentabromo-5'-chloro-2,2'-bipyrrole, and 1,1'-dimethyl-3,3',4,4',5,5'-hexabromo-2,2'-bipyrrole and subsequently synthesized. Comparison of retention times and electron capture negative ionization (ECNI) full scans on various gas chromatography (GC) columns between the synthesized bipyrroles and the corresponding unknown compounds in biota indicated that three of the unknown compounds--possible marine natural products--were the proposed halogenated dimethyl bipyrroles. The placement of the halogen atoms on the fourth compound, C10H6N2Br3Cl3 could not be unequivocally determined since the synthesized standard could not be fully characterized.     

Anaerobic decomposition of halogenated aromatic compounds

Halogenated compounds constitute one of the largest groups of environmental pollutants, partly as a result of their widespread use as biocides, solvents and other industrial chemicals. A critical step in degradation of organohalides is the cleavage of the carbon?halogen bond. Reductive dehalogenation is generally the initial step in metabolism under methanogenic conditions, which requires a source of reducing equivalents, with the halogenated compound serving as an electron acceptor. Dehalogenation is greatly influenced by alternate electron acceptors; e.g. sulfate frequently inhibits reductive dehalogenation. On the other hand, a number of halogenated aromatic compounds can be degraded under different electron-accepting conditions and their complete oxidation to CO(2) can be coupled to processes such as denitrification, iron(III)-reduction, sulfate reduction and methanogenesis. Reductive dehalogenation was the initial step in degradation not only under methanogenic, but also under sulfate- and iron(III)-reducing conditions. Dehalogenation rates were in general slower under sulfidogenic and iron-reducing conditions, suggesting that dehalogenation was affected by the electron acceptor. The capacity for dehalogenation appears to be widely distributed in anoxic environments; however, the different substrate specificities and activities observed for the halogenated aromatic compounds suggest that distinct dehalogenating microbial populations are enriched under the different reducing conditions. Characterization of the microbial community structure using a combination of biomolecular techniques, such as cellular fatty acid profiling, and 16 S rRNA fingerprinting/sequence analysis, was used to discern the distinct populations enriched with each substrate and under each electron-accepting condition. These combined techniques will aid in identifying the organisms responsible for dehalogenation and degradation of halogenated aromatic compounds.     

Halogen production from aqueous tropospheric particles

Box model studies have been performed to study the role of aqueous phase chemistry with regard to halogen activation for marine and urban clouds and the marine aerosol as well. Different chemical pathways leading to halogen activation in diluted cloud droplets and highly concentrated sea salt aerosol particles are investigated. The concentration of halides in cloud droplets is significantly smaller than in sea-salt particles, and hence different reaction sequences control the overall chemical conversions. In diluted droplets radical chemistry involving OH, NO(3), Cl/Cl(2)(-)/ClOH(-), and Br/Br(2)(-)/BrOH(-) gains in importance and pH independent pathways lead to the release of halogens from the particle phase whereas the chemistry in aerosol particles with high electrolyte concentrations is controlled by non-radical reactions at high ionic strengths and relatively low pH values.For the simulation of halogen activation in tropospheric clouds and aqueous aerosol particles in different environments a halogen module was developed including both gas and aqueous phase processes of halogen containing species. This module is coupled to a base mechanism consisting of RACM (Regional Atmospheric Chemistry Mechanism) and the Chemical Aqueous Phase Radical Mechanism CAPRAM 2.4 (MODAC-mechanism). Phase exchange is described by the resistance model by Chemistry of Multiphase Atmospheric Systems, NATO ASI Series, 1986.It can be shown that under cloud conditions the bromine atom is mainly produced by OH initiated reactions, i.e. its concentration maximum is reached at noon. In contrast, the concentration level of chlorine atoms is linked to NO(3) radical chemistry leading to a smaller amplitude between day and night time concentrations.The contribution of radical processes to halogen atom formation in the particle phase is evident, e.g. by halogen atoms which undergo direct phase transfer. Furthermore, the application of the multiphase model for initial concentrations for sea-salt aerosols shows that the particle phase can act as a main source of halogen containing molecules (Cl(2), BrCl, Br(2)) which are photolysed in the gas phase to yield halogen atoms (about 70% of all Cl sources and more than 99% for Br).     

Halogenated compounds in a dated sediment core of the Teltow Canal, Berlin: time related sediment contamination

To study the recent contamination history of DDT (1,1,1-trichloro-2,2-bis(chlorophenyl)ethane) and its metabolites, as well as methoxychlor (1,1,1-trichloro-2,2-bis(p-methoxyphenyl)ethane), chlorfenson (4-chlorophenyl-p-chlorobenzenesulfonate), and further halogenated aromatics, a sediment core was collected from the Teltow Canal in Berlin (Germany). The sampling site is located nearby a former industrial point source, where recently analyses on pre-samples have indicated high concentrations of halogenated organic compounds. The deposition time of the investigated sediments was determined by gamma-spectrometrical dating. Pollution trends of selected contaminants were attributed to a time period between 5 and 10 years. Concentration profiles reflect not only the recent pollution history of these compounds, but also the time-depending effects of the ban, restriction and termination of DDT-production in the German Democratic Republic (GDR). DDT and other chlorinated aromatic compounds were produced onsite until the late 1980s. Maximum values of 133 mg kg(-1) (dry weight) for p,p'-DDD (1,1-dichloro-2,2-bis(chlorophenyl)ethane) and approximately 100 mg kg(-1) (dry weight) for p,p'-DDMS (1-chloro-2,2-bis(chlorophenyl)ethane), main metabolites of the anaerobic degradation of DDT, were determined. The occurrence of all selected contaminants, most of which have been banned more than 10 years ago, demonstrate recent contamination pathways, and the necessity of a continuous long-term monitoring of the affected environment.     

Ability of bacterial biphenyl dioxygenases from Burkholderia sp. LB400 and Comamonas testosteroni B-356 to catalyse oxygenation of ortho-hydroxychlorobiphenyls formed from PCBs by plants

Capacity of enzymes of the biphenyl/chlorobiphenyl pathway, especially biphenyl dioxygenase (BPDO) of two polychlorinated biphenyls (PCB) degrading bacteria, Burkholderia sp. LB400 and Comamonas testosteroni B-356, to metabolize ortho-substituted hydroxybiphenyls was tested.,These compounds found among plant products of PCB metabolism, are carrying chlorine atoms on the hydroxyl-substituted ring. The abilities of His-tagged purified LB400 and B-356 BPDOs to catalyze the oxygenation of 2-hydroxy-3-chlorobiphenyl, 2-hydroxy-5-chlorobiphenyl and 2-hydroxy-3,5-dichlorobiphenyl were compared. Both enzyme preparations catalyzed the hydroxylation of the three chloro-hydroxybiphenyls on the non-substituted ring. Neither LB400 BPDO nor B-356 BPDO oxygenated the substituted ring of the ortho-hydroxylated biphenyl. The fact that metabolites generated by both enzymes were identical for all three hydroxychlorobiphenyls tested; exclude any other mode of attack of these compounds by LB400 BPDOs than the ortho-meta oxygenation.     

The use of PLS algorithms and quantum chemical parameters derived from PM3 hamiltonian in QSPR studies on direct photolysis quantum yields of substituted aromatic halides

The Partial Least-Squares (PLS) method was used to further study Quantitative Structure-Property Relationship (QSPR) for photohydrolysis quantum yields of selected aromatic halides. The cluster of substituted bromobenzenes and iodobenzenes was further grouped into two clusters, substituted bromobenzenes and substituted iodobenzenes, for which QSPRs were obtained, respectively. The QSPRs obtained by PLS are more significant than those obtained in previous studies. The studies showed that only when the compounds belonging to different groups are studies separately, inherent relationships between molecular properties and their structure characteristics can be revealed. It can be generally concluded that the photohydrolysis quantum yields of the substituted aromatic halides are dependent on the overall characters of the molecules, the characters of the carbon–halogen bonds to be broken in the photolysis, and the character of the halogen atoms to be replaced in the photolysis. Electronegativity has great relevance to the photohydrolysis processes of the compounds. Substituted aromatic halides with large average molecular polarizability and molecular weight values tend to have low photolysis quantum yields.     

Analysis of halogenated polycyclic aromatic hydrocarbons in urban air, snow and automobile exhaust

Urban air, snow and automobile exhaust samples were extensively cleaned up by open column liquid chromatography. The appropriate fractions were analysed for halogenated polycyclic aromatic hydrocarbons (XPAH) by gas chromatography/negative chemical ionization mass spectrometry (GC/NCIMS). XPAH were found in all three sample types. A urban air sample was found to contain chlorinated pyrenes, fluoranthenes and benzopyrene and brominated pyrenes and fluoranthenes. Furthermore, the concentration of 1-chloropyrene in that air sample was estimated to be 10 pg/m³. XPAH were also found in snow samples taken in the vicinity of a motor-way. Ethylene dibromide and ethylene dichloride, are probably the source of the halogen atoms in the XPAH detected in car exhaust.     

Bromination of 2-methoxydiphenyl ether to an average of tetrabrominated 2-methoxydiphenyl ethers

Brominated 2-phenoxyanisoles (2-methoxydiphenyl ethers, 2-MeO-BDEs) are a class of halogenated natural products, produced by algae and sponges. Especially two tetrabrominated isomers, i.e. 2′-MeO-BDE 68 (BC-2) and 6-MeO-BDE 47 (BC-3), have also been frequently determined in environmental and food samples. In addition, 2-MeO-BDEs are under discussion as metabolites of polybrominated diphenyl ethers (PBDEs). In this study, we synthesized the backbone 2-methoxydiphenyl ether and brominated it to an average degree of four bromine substituents. The reaction mixture only contained one major product (∼90%) along with three further MeO-BDEs and ∼5% hydroxylated BDEs. In all likelihood, the HO-BDEs were formed in a side reaction by cleavage of the methoxy group. The major MeO-BDE was identified as 6′-methoxy-2,3′,4,4′-tetrabromodiphenyl ether (6′-MeO-BDE-66). The HO-BDEs were separated by KOH/n-hexane partitioning, and the resulting 2-MeO-BDEs were fractionated by means of high-speed counter-current chromatography (HSCCC). Due to the excellent enrichment facilities of HSCCC, some 15 MeO-BDEs, mainly present at traces only, could be detected in 26 fractions, and eight of them could be characterized by nuclear magnetic resonance spectroscopy (NMR). Only two of the compounds - 2′-MeO-BDE 68 and 6-MeO-BDE 123 - had been characterized as natural products while the prominent halogenated natural product 6-MeO-BDE 47 was not detected at all in the reaction product. The “non-natural” 2-MeO-BDEs may be useful internal standards in trace analysis.     

Destruction of halogenated hydrocarbons with solvated electrons in the presence of water

Model halogenated aromatic and aliphatic hydrocarbons and halogenated phenols were dehalogenated in seconds by solvated electrons generated from sodium in both anhydrous liquid ammonia and ammonia/water solutions. The minimum sodium required to completely dehalogenate these model compounds was determined by increasing the Na/substrate ratio until halogen loss was complete. Minimum sodium consumptions were determined in both anhydrous liquid ammonia and with a (5, 20, 50-fold molar excess of water per mole of halide). While more Na was consumed in the presence of water, these dehalogenations were still efficient when a 50-fold water excess was present. Dehalogenation is faster than competiting reactions with water. CCl4 and CH3CCl3 in the presence of a stoichiometric deficiency of sodium produced only CH4 and CH3CH3 and recovered CCl4 or CH3CCl3, respectively. No partially dechlorinated products were detected, indicating dechlorination was diffusion controlled. Na consumption per chlorine removed (as NaCl) was lower than that of Li, K or Ca and this advantage increased in the presence of water. Na consumption was lower using Na chunks instead of a thin Na mirror. Chloroaromatic compounds gave the parent aromatic hydrocarbon and aminated products in anhydrous ammonia but aminated products did not form when water was present.     

TiO2光催化技术处理饮用水微污染及杀灭微生物的研究

光催化处理饮用水微量污染物以及在饮用水消毒和杀菌方面的研究是近年来研究的热点.本文论述了 TiO2光催化处理饮用水中的微量卤代物、腐殖质、微生物代谢产物,以及杀灭细菌、真菌和病毒等微生物的研究进展.探讨了光催化杀灭微生物的作用机制,最后对该研究领域的发展方向提出建议和展望.     

Boiling points of halogenated organic compounds

The normal boiling points of a number of halogenated organic compounds have been compiled from experimental measurements over three decades. Some of these chemicals have not been reported in the literature. The substances listed are halogenated aliphatic hydrocarbons, halogenated aliphatic ethers, halogenated ring (cyclic) hydrocarbons and other related compounds.     

Radiocarbon content of synthetic and natural semi-volatile halogenated organic compounds

Some halogenated organic compounds, such as polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs) and polybrominated diphenyl ethers (PBDEs), have been suggested to have natural sources but separating these compounds from their commercially synthesized counterparts is difficult. Molecular-level 14C analysis may be beneficial since most synthetic compounds are manufactured from petrochemicals (14C-free) and natural compounds should have "modern" or "contemporary" 14C levels. As a baseline study, we measured, for the first time, the 14C abundance in commercial PCB and PBDE mixtures, a number of organochlorine pesticides, as well as one natural product 2-(3',5'-dibromo-2'-methoxyphenoxy)-3,5-dibromoanisole. The latter compound was isolated from a marine sponge and is similar in structure to a PBDE. All of the synthetic compounds were 14C-free except for the pesticide toxaphene. which had a modern 14C abundance, as did the brominated natural compound. The result for toxaphene was not surprising since it was commercially synthesized by the chlorination of camphene derived from pine trees. These results suggest that measuring the 14C content of halogenated organic compounds may be quite useful in establishing whether organic compounds encountered in the environment have natural or synthetic origins (or both) provided that any synthetic counterparts derive from petrochemical feedstock.     

Halogenated organic compounds in archived whale oil: a pre-industrial record

To provide additional evidence that several halogenated organic compounds (HOCs) found in environmental samples are natural and not industrially produced, we analyzed an archived whale oil sample collected in 1921 from the last voyage of the whaling ship Charles W. Morgan. This sample, which pre-dates large-scale industrial manufacture of HOCs, contained two methoxylated polybrominated diphenyl ethers (MeO-PBDEs), five halogenated methyl bipyrroles (MBPs), one halogenated dimethyl bipyrrole (DMBP), and tentatively one dimethoxylated polybrominated biphenyl (diMeO-PBB). This result indicates, at least in part, a natural source of the latter compounds.     

Bacterial degradation of chlorophenols: pathways, biochemica, and genetic aspects

Chlorophenols belong to the group of toxic and persistent to microbial attack xenobiotics. Nevertheless, due to the adaptation microorganisms acquire the ability to use chlorophenols as the sole source of carbon and energy. The present review describes the diversity of aerobic pathways for the utilization of halogenated phenols by bacteria with the emphasis on the main reactions and intermediates formed, enzymes responsible for these reactions and their genetic basis. Taking into account (i) the fact that enzymes degrading chlorophenols are similar to the ones involved in the conversion of other (chloro)aromatic compounds and (ii) that present numerous publications describing the properties of separated enzymes or encoding their genes are published, this review was planned as the attempt to present both, the most general and specific aspects in chlorophenols degradation with the emphasis on the literature of the last ten years.     

Identification of phase II in vivo metabolites of alkyl-anthracenes in rainbow trout (Oncorhynchus mykiss)

Metabolism of xenobiotics is a two-step process that increases the polarity of compounds to facilitate their excretion. In previous work, the major in vitro phase I metabolites of alkyl-anthracenes by rainbow trout (Oncorhynchus mykiss) CYP enzymes were shown to be predominantly ring hydroxylated metabolites. Here, we present the first report on the identification of in vivo phase II metabolites of alkyl-anthracenes in juvenile rainbow trout. Bile was collected from trout injected with individual alkyl-anthracenes with, in some cases, a co-injection of β-naphthoflavone (BNF). Some samples were digested with the β-glucuronidase enzyme to confirm the presence of glucuronide conjugates. The metabolites were separated using a water-acetonitrile gradient on a HPLC system equipped with a C₁₈ column and a UV-diode array detector. Trout with endogenous and BNF-induced enzymes produced the same metabolites, but higher concentrations of metabolites were detected after enzyme induction. Alkyl-anthracenes were metabolized predominantly on the rings as evidenced by the UV spectral analysis. Likewise, mass spectrometry and UV spectral analysis confirmed a predominance of glucuronide conjugates for all systems investigated.