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Query: EC:3.4.15.1 (ACE)
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Laboratory studies using chemical concentrations comparable to those found in nature have provided considerable knowledge of microbial transformations in nature. Although the number of studies performed is increasing rapidly, the effects of low substrate levels on growth, enzyme induction, enzyme activity, and the use of mixtures of substrates have not yet been clarified. Likewise, studies at low concentrations in seawater are lacking. This paper describes a study of the rates of degradation of chlorophenols 4-chlor-2-methylphenol, 2,4-dichlorophenol (2,4-DCP), and 2,4,6-trichlorophenol at concentrations ranging from 2 to 18 micrograms/liter. The compounds were tested separately, in a mixture, and in waste water containing other organics. The obtained rates of 2,4-DCP in seawater were comparable to those found in fresh water. Also, the rates were in general agreement with a kinetic model proposed for degradation of chlorophenols. The rates of degradation of chlorophenols in the mixture were comparable to those found when tested separately. In the waste, very low rates were observed. It is suggested that this might be explained by a toxic effect, caused by other substances in the waste water, on the microorganisms considered to be active in degrading the chlorophenols at low concentrations.
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PMID:Biodegradability of chlorophenols and mixtures of chlorophenols in seawater. 273 14

In this study, we investigated the potential for reductive dechlorination of chlorophenols by municipal sewage sludge acclimated to 2,4-dichlorophenol (2,4-DCP) and 3,4-dichlorophenol (3,4-DCP). The optimal temperature and pH for dechlorination of 2,4,6-trichlorophenol (2,4,6-TCP) were 30 degrees C and 7.2. Dechlorination of 2,4,6-TCP was inhibited by sulfate, nitrate, or ferric (III), but was increased by manganese (IV) except that product of 2,4-DCP was accumulated. Organic substrates such as pyruvate or acetate did not influence dechlorination of 2,4,6-TCP, but increased dechlorination of 2,4-DCP; nevertheless lactate showed no influence on dechlorination. When glucose was added as substrate, only 20% of 2,4,6-TCP dechlorination was found. Addition of methanogenesis inhibitor 2-bromoethane sulfonate did not influence dechlorination, but addition of eubacteria inhibitor vancomycin showed no dechlorination activity at the first few days, and finally complete transformation and accumulation of 2,4-DCP occurred. Because mixed culture was from Di-Hwa Wastewater Treatment Plant, adding the same water as culture medium was found to increase the dechlorination of 2,4,6-TCP and its product 2,4-DCP. Dechlorination by adding wastewater of Petroleum Corporation was also increased, especially for 2,4-DCP product, but only 7% of 2,4,6-TCP dechlorination was found after incubation with Hou-Chin river water for 14 days.
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PMID:[Reductive dechlorination of chlorophenols by an anaerobic mixed culture]. 798 80

The co-immobilization and the culture of anaerobic and aerobic communities was tested for the mineralization of 2,4,6-trichlorophenol (2,4,6-TCP). At first, the anaerobic microorganisms (aggregated into granules) were cultivated in an upflow anaerobic sludge blanket (UASB) reactor, in a continuous mode, with glucose, propionate, acetate (COD loading rate = 0.5-2.0 g COD/l per day, ratio 1:1:1) and 2,4,6-TCP (2,4,6-TCP loading rate = 25-278 micromol/l per day) as substrates. 2,4,6-TCP was degraded into 2,4-DCP and 4-CP, but it was not mineralized because of the low degradation rates of 4-CP. Furthermore, the highest loading rates of 2,4,6-TCP (>126 micromol/l per day) caused the inhibition of the strains degrading the propionate. The granules were therefore tested in association with the aerobic community. They were immobilized in kappa-carrageenan/gelatin [2% (w/w) of each polymer] gel beads and cultivated in a reactor, on their own (to test the influence of the gel), and then with the aerobic community, under anaerobic and air-limited conditions, respectively. The results showed that (1) the gel did not influence the activity of the granules, (2) the anaerobic and aerobic communities could be easily co-immobilized in gel beads and cultivated in a reactor, (3) the mineralization of 2,4,6-TCP (2,4,6-TCP loading rate = 10-506 micromol/l per day), its intermediates of degradation and the other substrates [glucose + acetate + propionate (ratio 1:1:1) = COD loading rate = 500 mg COD/l per day] could be obtained under air-limited conditions if the culture parameters were strictly controlled [airflow = 36-48 vvd (volume of air/volume of liquid in the reactor per day), pH value at around 7.5]. Finally, the gel did not retain its structure during the whole culture (263 days) in the air-limited reactor, but the anaerobic and aerobic communities retained their activities and worked together for the mineralization.
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PMID:Degradation of 2,4,6-trichlorophenol (2,4,6-TCP) by co-immobilization of anaerobic and aerobic microbial communities in an upflow reactor under air-limited conditions. 1154 32

Uncatalyzed, and palladium-catalyzed Fe(0) and Mg(0) systems were examined for their efficiencies of dechlorination of 2.86 mM 4-chlorophenol (4-CP), 2.52 mM 2,6-dichlorophenol (2,6-DCP), 3.03 mM 2,4,6-trichlorophenol (2,4,6-TCP), and 2.48 mM pentachlorophenol (PCP) in 50/50 (v/v) 2-propanol/water under room temperature and pressure conditions. Previous investigators have found that PCP is extremely recalcitrant under these conditions. In this investigation, complete dechlorination of 5.0 ml of 2.48 mM PCP was observed for 1.0 g of 2659 ppm Pd/Mg (20 mesh) after 48 h. The only detectable products were cyclohexanol and cyclohexanone at 25% yield. No other chlorinated or otherwise products were observed by mass spectral analysis. It is hypothesized that volatile low molecular weight species were formed from the Pd/Mg dechlorination of PCP. Under conditions of equal surface area (0.0786 m2), the approximate order of PCP dechlorination power of these systems followed as 2659 ppm Pd/Mg>319 ppm Pd/Mg>Mg approximately 4856 ppm Pd/Fe>Fe. Degradation of the other chlorinated phenols by all metallic systems was more facile than PCP.
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PMID:Dechlorination of chlorinated phenols by catalyzed and uncatalyzed Fe(0) and Mg(0) particles. 1177 95

In this study, a wall-jet flow cell with a GRC (graphite reinforced by carbon) electrode was designed for the amperometric detection of phenol and chlorophenols in liquid chromatography. The voltammetric responses of these analytes at the GRC electrodes are very similar to those at conventional glassy carbon electrodes. As the GRC electrodes were made of the same materials as commercially available mechanical pencil leads, they exhibit the advantages of low cost, simple surface renewability, lower residual current, and good electrode-to-electrode reproducibility, and thus can be used as disposable-type electrodes. Chromatographic separations of phenol, o-chlorophenol (o-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP), and pentachlorophenol (PCP) were achieved with an ODS column using a mobile phase containing a mixture of CH3CN and H20 (40:60) containing 25 mM L-(+)tartaric acid (pH = 4.5). Amperometric detections were based on the electrochemical oxidation of these compounds around +0.9 V vs. Ag/AgCl. Under the optimized conditions, linear calibrations were obtained in a range up to 100 microM for phenol, o-CP, 2,4-DCP, 2,4,6-TCP, and 200 microM for PCP, with the correlation coefficients r2 of 0.9992, 0.9997, 0.9986, 0.9992, and 0.9968, respectively. The chromatographic detection limits for the tested analytes were obtained at pmol levels.
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PMID:Use of disposable GRC electrodes for the detection of phenol and chlorophenols in liquid chromatography. 1203 23

An assessment of the toxicity of three chlorophenol compounds (2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP) and pentachlorophenol (PCP)), individually and in combinations, was made in deionised water, soil extracts and soils using the lux-marked microbial biosensors: Escherichia coli HB101 pUCD607 and Pseudomonas fluorescens 10586r pUCD607. These biosensors responded to the bioavailable fraction of pollutants enabling a rapid and ecologically relevant toxicity test. Toxicity interaction responses of pollutant mixtures were predicted after individual compounds were assessed. Synergistic interactions were observed in the response of P. fluorescens to all combinations of chlorophenols tested, while the toxicity response of E. coli varied with the matrices tested. Soil characteristics influenced the toxicity response when compared with aqueous solutions. These results highlight the significance of interactive factors and physicochemical parameters when evaluating toxicity. To develop an understanding of pollution derived hazard assessment in soils we need to integrate a wide spectrum of parameters.
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PMID:Evaluation of interactive toxicity of chlorophenols in water and soil using lux-marked biosensors. 1219 88

The equilibrium and kinetics of chlorophenol (CP) sorption by chitosan, poly D-glucosamine, were studied under simulated groundwater conditions. Lower temperature, from 25 degrees C to 15 degrees C and then 5 degrees C, markedly decreased the adsorption rates by a factor of 30-53% and 7-22%. Comparison between two types of chitosan, flakes and highly swollen beads, demonstrated that the maximum pentachlorophenol (PCP) uptake capacities in Langmuir and Freundlich models depend on the specific surface area of the particle. Low temperature (5 degrees C) significantly increased the PCP uptake capacity in comparison to higher temperatures (15 degrees C and 25 degrees C). PCP uptake capacity was halved at pH levels higher than 6.5, and NaCl concentrations greater than 1% blocked PCP sorption almost completely. Of five kinds of chlorophenols, i.e. 2,4,6-trichlorophenol (2,4,6-TCP), 3,4-dichlorophenol (3,4-DCP), 2,3-dichlorophenol (2,3-DCP), 2,6-dichlorophenol (2,6-DCP), 3-monochlorophenol (3-MCP), TCP had the maximum sorption efficiency on flake-type chitosan, followed by DCPs, and finally MCP (the three kinds of DCP, with the same elemental compositions, achieved similar sorption performances).
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PMID:Removal of chlorophenols from groundwater by chitosan sorption. 1560 85

This study describes a comparative degradation of various chlorophenols by electro-Fenton method. Chloride released and reaction intermediate products were determined by ionic chromatography (IC) and gas chromatography/mass spectrometry (GC/MS). Using pentachlorophenol (PCP) as the model compound, we investigated the effects of cell voltage, electrolyte concentration and pH to optimize the degradation conditions. It was noted that the addition of small quantities of Fe3+ or Fe2+ significantly accelerated the degradation rate. Under the optimal conditions, electro-Fenton method was used to treat various chlorophenols including PCP, 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP) and their mixture aqueous solutions. Their pseudo first-order degradation rate constants at the first stages were calculated and compared, which gave the following sequence: 2,4-DCP>2,4,6-TCP>PCP>4-CP. The relationship between the chlorine content and degradation rate was discussed and compared with other advanced oxidation processes. Finally, we proposed the degradation pathways of different chlorophenols.
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PMID:Comparison treatment of various chlorophenols by electro-Fenton method: relationship between chlorine content and degradation. 1572 32

Chlorophenol (CP) toxins are classified as probable human carcinogens and are known to undergo bioactivation to generate benzoquinone (BQ) electrophiles that react covalently with biopolymers. Recently, we characterized the ability of pentachlorophenol (PCP) to react covalently with deoxyguanosine (dG) following treatment with horseradish peroxidase (HRP)/H2O2 or myeloperoxidase to yield a C8-dG oxygen (O)-adduct that suggested the intermediacy of the pentachlorophenoxyl radical in covalent bond formation [Dai, J., Wright, M. W., and Manderville, R. A. (2003) Chem. Res. Toxicol. 16, 817-821]. Investigations currently focus on a wider range of CP substrates (PCP, 2,4,6-trichlorophenol (2,4,6-TCP), 2,4,5-TCP, and 2,4-dichlorophenol (2,4-DCP)) to establish their reactivity toward dG and duplex DNA (calf thymus (CT)) following activation by HRP/H2O2, as a representative peroxidase system. Our data show that chlorophenoxyl radicals may either react directly with dG and CT-DNA to form C8-dG O-adducts in an irreversible process or couple to yield 1,4-BQ electrophiles that react with dG to afford adducts of the benzetheno variety. These results are the first to establish the in vitro relevance of C8-dG O-adducts of phenolic toxins. The 1H NMR chemical shifts and reactivity of the benzetheno adducts favor 4' '-hydroxy-1,N2-benzetheno-dG adduct assignment, which is in contrast to other literature which has assigned the 1,4-BQ-dG adduct as 3' '-hydroxy-1,N2-benzetheno-dG. Overall, the results from this current study have provided new insights into peroxidase-mediated activation of CP substrates and have strengthened the hypothesis that direct reactions of phenoxyl radicals with DNA contribute to peroxidase-driven toxic effects of phenolic xenobiotics.
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PMID:Role of phenoxyl radicals in DNA adduction by chlorophenol xenobiotics following peroxidase activation. 1583 38

A procedure for the determination of 2-(2,4-dichlorophenoxy)-5-chlorophenol (Triclosan) and two possible transformation compounds, 2,4-dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP), in sludge from sewage treatment plants (STP) and sediments is presented. Extraction was performed using an acetone:methanol (1:1) mixture under the action of a microwave field. The centrifuged supernatant was diluted with a NaOH aqueous solution and twice extracted with n-hexane for removing neutral and basic interferences. The aqueous layer was acidified and processed as a waste water sample. After concentration analytes were silylated and determined by gas chromatography with tandem mass spectrometry (GC-MS/MS). Influence of experimental conditions on the yield of the extraction process and on the efficiency of the further clean-up step was thoroughly evaluated. Performance of MS/MS detection in comparison to single MS is described. Under final working conditions quantification limits between 0.4 and 0.8 ng/g and recoveries from 78% to 106% were obtained. The method was applied to the analysis of several sludge and sediment samples. Only low levels of TCS were detected in some of the sediments; however, all three compounds were found in sludge samples at concentrations ranging from 7 to 316 ng/g, in the case of chlorophenols, and from 420 to 5400 ng/g, for Triclosan.
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PMID:Microwave assisted extraction followed by gas chromatography with tandem mass spectrometry for the determination of triclosan and two related chlorophenols in sludge and sediments. 1603 53


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