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At least 937 records · Page 52Linked to original sources
PubMed2000

Potential artifact formation of dioxins in ball clay during supercritical fluid extraction.

Earlier surveys indicate that meat, fish and dairy products are the principal source of polychlorinated dibenzo-p-dioxin (PCDD) exposure in the diet. A recent finding by others of PCDDs in chickens that consumed a feed containing PCDD led to the finding of ball clay, an anti-caking agent, as the source. Supercritical fluid extraction (SFE) was studied as a means to isolate PCDDs from commercial ball clays using GC-electron capture detection (muECD) as a means to screen for these contaminants. The finding of ng/g amounts and recoveries >100% in several samples of ball clay containing octachlorodibenzo-p-dioxin (OCDD) suggested that PCDD may form artifactually as a result of analysis. Studies on pentachlorophenol (PCP) fortified ball clay were carried out by SFE and soxhlet extraction and the results compared. The values obtained by SFE were considered more problematic. The results obtained from ball clay suggest that precautions need to be exercised when using SFE to analyze for dioxins in solid samples containing chlorophenols.

Animal Feed↗
PubMed1990

Use of polymeric sorbents for the off-line preconcentration of priority pollutant phenols from water for high-performance liquid chromatographic analysis.

The use of porous polymeric minicolumns for the determination of phenols from the U.S. Environmental Priority Pollutant List was studied. For the off-line preconcentration of priority pollutant phenols from water by solid-phase extraction, minicolumns packed with 1,4-di(methacryloyloxymethyl)naphthalene-divinylbenzene copolymer and Amberlite XAD-4 were used. In order to compare the sorption properties of these polymeric sorbents, the recoveries and breakthrough volumes of phenol, p-nitrophenol, 2,4-dinitrophenol, o-chlorophenol, o-nitrophenol, 2,4-dimethylphenol, 4-chloro-m-cresol, 4,6-dinitro-o-cresol, 2,4-dichlorophenol, 2,4,6-trichlorophenol and pentachlorophenol were studied.

Acrylates↗
PubMed1983

Occurrence of low- and high-chlorinated phenols in municipal sewage before and after passing through biological treatment plants.

Four biological treatment plants for municipal sewage, situated at different locations, were examined for their chlorophenol content and their ability to degrade these compounds. A routine method for the analysis of both low- and high-chlorinated phenols was developed, based on gas chromatography with electron-capture detection (GC-ECD). The method was evaluated by comparing the GC-ECD results with those obtained by combined gas chromatography-mass spectrometry with selected-ion monitoring of the molecular ions of the specific phenols. The total phenol content, determined by GC-ECD showed a good correlation with the phenol number, obtained by using the 4-aminoantipyrine method.

Chemical Phenomena↗
PubMed1997

Determination of phenolic pollutants in drinking water by capillary electrophoresis in the sample stacking mode.

A method for the determination of phenol, chlorophenols and nitrophenols at levels below those allowed by international legislation in water from the public supply is proposed. Ten of the compounds studied are included on the USA Environmental Protection Agency priority list of aquatic pollutants. Samples are concentrated off-line on cross-linked polystyrene and subsequently subjected to capillary electrophoresis using the sample stacking procedure to remove the matrix. The recoveries afforded by the off-line concentration process and the behaviour of the phenols in relation to sample stacking injection were examined.

Chlorophenols↗
PubMed1999

Nonaqueous capillary electrophoresis equipped with amperometric detection for analysis of chlorinated phenolic compounds.

Nonaqueous capillary electrophoresis (NACE) equipped with amperometric detection has been developed for separation and detection of an 11-member model mixture of chlorinated phenolic compounds. With triacetyl-beta-cyclodextrin (TACD) as a novel selectivity selector, acetonitrile proved to be an excellent solvent for this water-insoluble cyclodextrin derivative. Resolution of the analytes was achieved by using an optimized acetonitrile medium consisting of 500 mM acetic acid, 10 mM sodium acetate, 12 mM TACD and 50 mM tetrabutylammonium perchlorate. Separation of analytes was attributed to differential electrostatic and/or inductive interactions of the analytes with the TACD/TBA+ complex and charged tetrabutylammonium phases. A simple end-column amperometric detector (Pt vs. Ag/AgCl, poised at +1.6 V) in conjunction with NACE was used to analyze chlorophenols. Amperometric detection of such target compounds in acetonitrile-based media offers high sensitivity and alleviates electrode fouling compared to aqueous buffers. The detection limits obtained, ranging from 30 nM to 500 nM, are 3-8-fold lower than those obtained with aqueous buffers.

Chlorophenols↗
PubMed2000

On-line coupling of subcritical water extraction with high-performance liquid chromatography via solid-phase trapping.

Although ambient water is very polar and cannot dissolve many organic species, water at elevated temperatures behaves like a polar organic solvent. Thus, subcritical water has been proven to be an effective extraction fluid for several classes of organic compounds. While solvent trapping was used to collect the extracted analytes in most of previous subcritical water extractions, sorbent trapping has also been developed for subcritical water extraction. In this study, an on-line system for subcritical water extraction and high-performance liquid chromatography (HPLC) was built and tested. A sorbent trap was used as the interface between subcritical water extraction and HPLC. Several shut-off valves have been utilized to switch the system from one mode to another (e.g., from the extraction mode to HPLC mode). The coupling technique of subcritical water extraction and HPLC eliminates the liquid-liquid extraction used in solvent trapping subcritical water extraction and provides higher sensitivity. Compared to the off-line system reported in an earlier work, the operation of this on-line system is even easier. Some peak broadening occurred after the coupling the water extraction with HPLC for the analytes studied. The performance of this on-line system was evaluated by the extraction and determination of caffeine, nitrotoluenes, polychlorinated biphenyls, chlorophenols and anilines.

Aniline Compounds↗
PubMed2001

The spinning disc reactor--studies on a novel TiO2 photocatalytic reactor.

A new type of photocatalytic reactor, the spinning disc reactor (SDR), was used to degrade aqueous solutions of 4-chlorophenol and salicylic acid. The efficiency of the photocatalytic process depends on the type of UV source used. Lamps supplying shorter wavelength UV radiation are more efficient than those whose emissions lay mainly in the near UV region. The method used to coat the disc of the SDR does not meet its operational requirements. The characteristics of the turbulent liquid films produced in the SDR reduce the influence of mass transfer over the overall photocatalytic process.

Catalysis↗
PubMed2002

Thermolysis of 2,4,6-trichlorophenol chemisorbed on aluminium oxides as example of fly ash mediated surface catalysis reaction in PCDD/PCDF formation.

The influence of aluminium cation as a strong electrophilic centre on the thermolysis of chlorophenols chemisorbed on Al(OH)3 surface was investigated. If thermolysis is carried out at 300 degrees C the spontaneous rupture of the bond between aluminium and oxygen of phenol takes place in the temperature range of 260-280 degrees C. The thermolysis of chlorophenoxy aluminium compounds occurs through homolytic and heterolytic bond cleavage. In the case of heterolytic cleavage the leaving chlorophenoxy anion causes a simultaneous formation of the aluminium cation, which is the driving force for the rearrangement of the unstable intermediate. By homolytic cleavage of the Al-O bond the chlorophenoxy radical is formed. The isolation of reaction products of the thermolysis of the system AI(OH)3/2,4,6-trichlorophenol gave five isomers of dimeric compounds of resonance stabilised 2,4,6-trichlorophenoxy radical. The compounds are stable in nonaqueous, aprotic solution, but they are very sensitive to acid catalysis. They quickly transform into aromatic hydroxydiphenyl ethers. The process of dechlorination and aromatisation of cyclohexadienone dimers gives PCDD/PCDF.

Adsorption↗
PubMed2002

Kinetic modeling of fenton oxidation of phenol and monochlorophenols.

A kinetic model, consisting of 28 reactions, was proposed to understand the key mechanism of the Fenton oxidation of phenol and o-, m-, and p-chlorophenols. Particular attention is paid to the interactions of the organic intermediates with the Fe species. The proposed model reasonably predicts the decomposition kinetics and by-product formation for the different phenols at widely varying levels of Fe2+, H2O2, and the phenols. For the phenols and intermediates, change in concentrations with time was predicted within 20-30% deviation from the measured data. The single model predicts the overall kinetics of Fenton oxidation of all the tested phenols by adjusting the rate constant of hydroxyl radical for each phenol. Sensitivity analysis indicates that the key reactions are those that directly govern the levels of OH radical and Fe2+. Both the model prediction and the experimental results show that the decomposition rate could be complicated particularly by the availability of Fe2+. Understanding the interactions of the organic intermediates with Fe2+ is thus of critical importance to improve the decomposition performance.

Chlorophenols↗
PubMedDate not supplied

Comparison of 2,4,6-trichlorophenol conversion to PCDD/ PCDF on a MSWI-fly ash and a model fly ash.

We performed experiments on two different matrices with 2,4,6-trichlorophenol as precursor to Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD)/F. A municipal solid waste incinerators (MSWI) and a model fly ash were spiked in two different ways. The experiments demonstrated a three times higher formation potential of the trichlorophenol to PCDD on MSWI fly ash compared with the model fly ash used. For both fly ashes the PCDD yield was higher when gaseous trichlorophenol was fed continuously compared to mixing the fly ashes prior to the experiments with the total amount of the precursor. Despite dilution of the fly ashes tenfold with an inactive matrix the conversion of the chlorophenol was very high.

Benzofurans↗
PubMed2003

Aerobic degradation of 2,4,6-TCP content in ECF bleached effluent.

Elemental chlorine-free (ECF) bleach effluents from kraft mill are characterised by: a chemical organic demand/biological organic demand (COD/BOD(5)) ratio of 4, chlorophenol content with low chlorine substitution, and toxicity. The effect of increasing the concentration of 2,4,6-trichlorophenol (2,4,6-TCP) content in ECF bleaching sequence effluent on the degradative activity of bacterial communities present in an aerobic system treatment was studied. An aerobic lagoon (AL) was used as a typical secondary treatment of kraft-mill effluent. AL displays a high performance of BOD(5) degradation (up to 90%); however, only 40% of the COD was removed. Simultaneously, the AL system shows a high ability to biodegrade 2,4,6-TCP up to 237 mg/l day. Kinetic parameters of the 2,4,6-TCP biodegradation by aerobic bacteria were determined. The K(s) and K(i) values were 34.3 and 50 mg/l 2,4,6-TCP, respectively. Moreover, the tolerance of aerobic bacteria was observed up to 1.3 g/l 2,4,6-TCP.

Bacteria, Aerobic↗
PubMed2000

Modeling the kinetics of UV/hydrogen peroxide oxidation of some mono-, di-, and trichlorophenols.

The decomposition of a number of chlorophenols (CPs), namely 2-CP, 2, 4-dichlorophenol and 2,4,6-trichlorophenol, has been studied in aqueous solution by UV-catalyzed oxidation with H(2)O(2) under UV radiation emitted by a 125-W medium pressure Hg lamp in an immersion well-type quartz photoreactor, and the organic-bound chlorine has been converted into the environmentally harmless inorganic chloride. For oxidant/CP mole ratios between 1:1 and 16:1, the reaction kinetics were modeled and the corresponding rate constants found by periodically measuring the remaining CP, hydrogen peroxide and converted chloride in solution. A theoretical model for the degradation pathway is proposed expressing the rate as a linear function of the concentrations of CP and oxidant. The rate constants for the pseudo-first order approximation of the CP degradation were compared. H(2)O(2), when combined with UV, is an effective photoactivated oxidant. The photodegradation order in terms of the initial rate of CPs destruction was: Cl(3).Ph>/=Cl(2).Ph>Cl.Ph.

Chlorophenols↗
PubMed2002

Dechlorination of chlorinated phenols by catalyzed and uncatalyzed Fe(0) and Mg(0) particles.

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.

Catalysis↗
PubMed1999

Detoxifying chlorine rich gas streams using solid supported nickel catalysts.

Catalytic hydrogen treatment is presented as a viable low energy means of treating/detoxifying concentrated chlorinated gas streams to generate recyclable raw materials. Nickel (1.5% w/w and 15.2%) loaded silica and nickel (2.2% w/w) exchanged Y zeolite catalysts have been used to hydrotreat a range of chlorophenols (CPs), dichlorophenols (DCPs), trichlorophenols (TCPs) and pentachlorophenol (PCP) over the temperature interval 473 K</=T</=573 K. In every instance the nickel catalysts were 100% selective in cleaving the chlorine component from the ring, leaving the aromatic nucleus and hydroxyl substituent intact. The effects of varying process time and temperature are considered in terms of phenol yield and the ultimate partitioning of chlorine in the parent organic and product inorganic hosts. Chlorine removal rates, hydrodechlorination selectivity and apparent activation energies are also provided. Prolonged exposure of the catalysts to the concentrated chlorine gas streams resulted in an irreversible loss of activity which is related to the total concentration of chlorine that had been hydroprocessed. Hydrodechlorination proceeds via irreversible stepwise and/or concerted routes as is illustrated for the treatment of 2,3,5-TCP. Increasing the nickel content was found to raise the overall detoxification efficiency while the use of a zeolite support introduced spatial constraints which had a strong bearing on process selectivity.

Catalysis↗
PubMed2003

An inducible Streptomyces gene cluster involved in aromatic compound metabolism.

Streptomyces setonii (ATCC 39116) is a thermophilic soil actinomycete capable of degrading single aromatic compounds including phenol and benzoate via the ortho-cleavage pathway. Previously, a 6.3-kb S. setonii DNA fragment containing a thermophilic catechol 1,2-dioxygenase (C12O) gene was isolated and functionally overexpressed in Escherichia coli (An et al., FEMS Microbiol. Lett. 195 (2001) 17-22). Here the 6.3-kb S. setonii DNA fragment was shown to be organized into two putative divergently transcribed gene clusters with six complete and one incomplete open reading frames (ORFs). The first cluster with three ORFs showed homologies to previously known benA, benB, and benC, implying it is a part of the benzoate catabolic operon. The second cluster revealed an ortho-cleavage catechol catabolic operon with three translationally coupled ORFs (in order): catR, a putative LysR-type regulatory gene; catB, a muconate cycloisomerase gene; catA, a C12O gene. Each of these individually cloned ORFs was expressed in E. coli and identified as a distinct protein. The expression of the cloned S. setonii catechol operon was induced in Streptomyces lividans by specific single aromatic compounds including catechol, phenol, and 4-chlorophenol. A similar induction pattern was also observed using a luciferase gene-fused reporter system.

Base Sequence↗
PubMed1997

On-line supported liquid membrane-liquid chromatography with a phenol oxidase-based biosensor as a selective detection unit for the determination of phenols in blood plasma.

The potential of on-line combination of supported liquid membrane extraction and column liquid chromatography with a phenol oxidase-based biosensor as a selective detection unit has been investigated for the determination of phenols in human plasma. The phenols are selectively extracted into a porous PTFE (polytetraflouroethene) membrane impregnated with a water-immiscible organic solvent and further into an alkaline acceptor phase. Via an ion-exchange interface, the analytes are transferred to a reversed-phase column where they are separated and detected using the biosensor. No sample pretreatment before the extraction, except centrifugation, is made. Due to the high selectivity both in the extraction and in the detection steps and to the fact that the demands on the chromatographic separation are low, a quick separation using an eluent with a low concentration of organic modifier can be made, without affecting the biosensor response. Detection limits below the 50 microg/l level in blood plasma were obtained for the three model compounds, phenol, p-cresol and 4-chlorophenol.

Biosensing Techniques↗
PubMed1999

Defluvibacter lusatiae gen. nov., sp. nov., a new chlorohenol-degrading member of the alpha-2 subgroup of proteobacteria.

The two Gram-negative bacterial strains S1 and S4 were isolated from activated sludge of an industrial waste water treatment plant and exhibited a stable capability to degrade 2,4-dichlorophenol, 4-chloro-2-methylphenol, 4-chlorophenol and phenol. The cells were short rods with a polar flagellum, being mesophilic, strictly aerobic, oxidase-positive, and chemoorganotrophic. They utilized a range of amino acids, but only a restricted number of carbohydrates. Reassociation experiments with DNA from strains S1 and S4 revealed high interstrain similarity, indicating, that both strains belong to the same species. The phylogenetic position was determined by comparison of the almost complete 16S rDNA sequence of strain S1 with sequences of related bacteria. Strain S1 clustered with members of the alpha-2 subgroup of the Proteobacteria by forming a separate lineage within the radiation of Mesorhizobium, Phyllobacterium and Sinorhizobium. Both strains can be differentiated from members of related taxa by a set of physiological and chemotaxonomic properties including the ability to grow with norvaline, L-tryptophan, putrescine, glutarate and malonate, and by the presence of spermidine as major polyamine and of 12:0 3OH as fatty acid. Strain S1 is described as type strain of a new species and assigned to a new genus with the proposed name Defluvibacter lusatiae.

Base Sequence↗
PubMed1998

Screening of xenobiotic compounds degrading microorganisms using biosensor techniques.

A screening device based on microorganisms immobilised onto a Clark-type oxygen electrode was used to monitor the potential of these microorganisms for the degradation and detection of xenobiotic compounds especially their chlorinated derivatives. The sensitivity and specificity of various species of Pseudomonas, Sphinomonas, Ralstonia, Rhodococcus were characterised in relation to xenobiotic compounds by using biosensor techniques. The following groups of xenobiotics were subjects of investigation: chlorophenols, chlorobenzoates, 2,4-D, PCB, dibenzofurane and their putative intermediates. Using this simple setup it proved possible to screen microbial strains for their potential to catabolize aromatic and chloroaromatic compounds under oxygen consumption. In a kinetic regime, a reproducible signal was obtained within minutes. Based on these results the sensor technique was a suitable method for the rapid characterization of microorganisms and allowed to gather information about the substrate spectrum.

2,4-Dichlorophenoxyacetic Acid↗