Abstract  Retene (7-isopropyl-1-methylphenanthrene) causes blue sac disease (BSD) in early life stages of fish, an effect similar to that of 2,3,7,8-tetrachlorodibenzo(p)dioxin. The signs of BSD include cytochrome P450 (CYP1A) induction, edema, hemorrhaging, and craniofacial deformities, indicating membrane damage, circulatory failure, and impaired development. To test if the underlying cause was oxidative stress, rainbow trout (Oncorhynchus mykiss) larvae were exposed to waterborne retene or to known prooxidants (paraquat, t-butyl hydroperoxide, and carbon tetrachloride) in the presence or absence of vitamin E, an antioxidant. Fish exposed to retene showed an increased prevalence of BSD, reduced tissue concentrations of vitamin E and total glutathione, and a lower percentage of glutathione in a reduced form. Coexposure to vitamin E reduced the prevalence of BSD and restored tissue concentrations of vitamin E, but it did not affect retene uptake or tissue concentrations of glutathione. These responses are consistent with oxidative stress as a mode of action of retene. However, retene did not affect whole-body lipid peroxide concentrations, and prooxidants did not affect the prevalence of BSD and had only minimal effects on tissue glutathione and vitamin E. Possible explanations for these conflicting results include prooxidant exposures were insufficient to generate oxidative stress; lipid peroxidation may not be measurable in whole-body homogenates of retene-exposed fish if effects are localized to endothelial cells, where CYP1A enzymes are most induced; or retene may have an alternate mode of action (e.g., adduction of retene metabolites to lipids, protein, or DNA).

Abstract  Zonguldak bituminous coal, Tuncbilek and Soma-Merkez lignites were each separated into two sub-fractions, coal rich and mineral matter rich, using a centrifugal float-sink separation technique in heavy media. An isopropyl alcohol (IPA)-carbon tetrachloride (CCl4) mixture and a zinc chloride (ZnCl2) solution, with a specific gravity of 1.40 g cm(-3) at 25 degrees C were used as dense medium liquids. The addition of surface active agents (Triton X-100 and Brij-35) to the zinc chloride solution improved the removal of minerals. The recovery and purity of the final product (float) obtained from the heavy media separation depend on such parameters as the density of the medium, rotor speed and centrifugation time. The separation efficiency of each coal differed significantly. Particle size distributions of the coals and their float and sink fractions were analysed using a Laser Particle Size Analyser. A Scanning Electron Microscope (SEM) was used to interpret the liberation of minerals from the coal particles. (C) 1998 Elsevier Science B,V. All rights reserved.

Abstract  Selectivities to carbon monoxide higher than 90% for conversions of methane greater than 10% were obtained from the partial oxidation of methane on stoichiometric strontium hydroxyapatite (SrHAp1.67) at 873 K during 6 h on stream. However, the activities decreased gradually with increasing the time-on-stream to 78 h due to the transformation of the apatite to Sr-3(PO4)(2). With small quantities of tetrachloromethane (TCM) added to the feedstream, the high selectivity to CO was retained while the conversion suffered a marked decrease with increasing the times-on-stream. In the presence of TCM the catalytic solid consists of a complex mixture of hydroxyapatite, chlorapatite, phosphate and chloride, each of which contributes dissimilarly to the catalytic process.

Abstract  The polyoxomolybdates encapsulated PAni hybrid materials are prepared by interfacial polymerisation. In P12MPA, the crystal structure of 12MPA is not modified on doping with PAni, However, P11MPA have the polycrystallinity due to the presence of vanadium in the dopant molecule. Though, the hybrids prepared by interfacial polymerisation are in emaraldine salt form, there is a blue shift in the absorption spectra due to dopant induced decrease in conjugation length and over-oxidation. Interfacially polymerised PAniPOM hybrid materials are exposed with various concentrations of vapours of different volatile organic compounds (VOC) Such as acetone, methanol, chloroform and carbon tetrachloride. The oxidising VOCs like acetone and methanol on exposure to PAni decrease the resistivity by hydrogen bonding with the redox cites of the polymer. Among these two, the sensitivity towards acetone is more in PAni and its hybrids which can be linked with the vapour pressure of the analyte. Due to the weak acidic characteristics of chlorinated hydrocarbons which are reducing vapours, the resistivity of PAni and its hybrids increases on exposure to chloroform and CCl4. Here, the chlorinated hydrocarbons interact with the redox sites of PAni and reduce it to base form. Bridging of polymer chains is also proposed for the reduction of conductivity oil exposure to the analyte. The sensitivity is higher for the reducing analytes than that of the oxidising one. (C) 2009 Elsevier B.V. All rights reserved

Abstract  BIOSIS COPYRIGHT: BIOL ABS. Determination of the degradation potentials for a mixture of eight organic trace contaminants (benzene, toluene, o-xylene, naphthalene, tetrachloromethane, 1,1,1-trichloroethane, trichloroethene, tetrachloroethene) has been made by specially developed in situ microcosms under aerobic and anaerobic aquifer conditions. The developed in situ microcosms allowed for determination of the degradation potentials in the aquifer as represented by the combined groundwater and sediment and by the groundwater only. Six out of eight microcosms functioned hydraulically well as determined by means of a hydraulic tracer. Control experiments showed that the in situ microcosms were not as determined by means of a hydraulic tracer. Control experiments showed that the in situ microcosms were not subject to unaccounted losses of the contaminants except from sorption to sediment in the beginning of the experiments. All compounds were studied at initial concentrations of approximately 120 mug/l

Abstract  The experimental in situ aquifer biorestoration site at Moffett Field, California, is a small, confined, sand and gravel aquifer, interspersed with layers of silts and clays. Laboratory sorption and solids characterization studies were carried out on core material recovered from in and around the aquifer zone. Equilibrium (distribution coefficient K(d)) and nonequilibrium (effective pore-diffusion coefficient D(p)) sorption parameters, estimated from batch experiments, were used in one-dimensional simulations of the breakthrough of three halogenated organic compounds: trichloroethylene (TCE), carbon tetrachloride (CT), and vinyl chloride (VC). Three types of transport models were used: equilibrium partitioning, spherical diffusion, and equivalent first-order diffusion. The hydrodynamic parameters (dispersion coefficient and porc water velocity) were determined previously using field-scale tracer tests. Simulations reconfirmed the theory that while an accurate K(d) value is required for each compound. it is sufficient, for similar compounds, to measure the rate parameters for one compound. then calculate these parameters for the other compounds. Although the simulations were generally successful, difficulty in estimating the field particle size, and a lack of understanding of field-scale heterogeneities, limited the accuracy of the simulations and the potential for model verification.

Abstract  The widespread use of chlorofluorocarbons (CFCs) as refrigerants, aerosols and foam insulation gases has led to their ubiquitous presence in modern landfills. Landfill leachates may have concentrations of CFC11, CFC12 and CFC113 thousands of times higher than in uncontaminated surface and groundwaters. Such great disparity offers a means of using CFCs as tracers of environmental contamination by landfill leachate. The threshold at which diluted leachate can be detected is around 0.1-1%, compared with 10-50% for conventional indicators such as COD, CI- or NH4+. A single, systematic survey may establish the extent and pattern of a leachate plume, whereas conventional indicators must rely on monitoring continued over many years to establish trends rising above background. This paper presents results from just such a survey conducted at a landfill site in Yorkshire, England. There were clear impacts on surface water courses and shallow groundwater, whereas an upward hydraulic gradient protected deeper groundwater beneath the site. Selective degradation of CFC11 was observed in groundwaters.

Abstract  Biotransformation of carbon tetrachloride (CT) was examined with an anaerobic enrichment culture grown on dichloromethane as the sole organic carbon and energy source. The principal products from [C-14]-CT included chloroform (17%), carbon disulfide (21%), and CO2 (21%). When cyanocobalamin was added along with CT, the percentage converted to CO2 increased almost 3-fold (59%), while CS2 decreased somewhat (11%), and virtually none of the CT (<1%) was reduced to chloroform. Carbon monoxide was a major transformation product (12-27%) in autoclaved cultures and in live cultures that received high levels of CT (up to 52 mg/L). Adding cyanocobalamin also increased the rate of CT transformation in live cultures by at least 10-fold, but had a minor effect on the rate of CT use in autoclaved cultures. Accelerated rates of transformation by live cultures were sustained for as long as 200 days, with hydrogen serving as the electron donor. Cyanocobalamin, hydroxocobalamin, and methylcobalamin were equally effective, while a 3-week lag period was required before adenosylcobalamin started to enhance CT transformation. Because of their high cost, the feasibility of using cobalamins will depend on the amount required. We observed significant enhancement in CT transformation at concentrations up to 340 mu M, with cobalamin levels as low as 10 mu M.

Abstract  The rate of solvent extraction of chromium(III) in aqueous nitrate solutions which contained 2-thenoyltrifluoroacetone(Htta), acetate buffer and ascorbic acid has been studied. The aqueous solution prepared was left standing for varying time intervals before agitation with chloroform. The chromium(III) complex extracted was then measured. The amount of chromium(III) extracted was larger when hydrated Cr3+ was initially present in the aqueous solution than when chromium(III) was produced by reduction of chromium(VI) in the aqueous solution. The extracted complex was assumed to be tris(thenoyltrifluoroacetonato)chromium(III) by spectrophotometry. This was quite different from extraction with acetylacetone which formed the extractable complex more rapidly when the chromium(III) was produced by reduction of chromium(VI) than when it was initially added in the form of hydrated Cr3+. The extraction with Htta proceeded more quickly when complex formation with this extractant took place in the aqueous phase followed by chloroform extraction than when the extractant is initially present in the chloroform and the aqueous solution containing chromium(III) was immediately agitated with the solvent.

Abstract  Polyacrylonitrile- and rayon-based activated carbon fibers (ACFs) subject to heat treatment were investigated by means of elemental analyzer, and X-ray photoelectron spectroscopy (XPS). The total ash content of all ACFs was also analyzed. The adsorption of benzene, carbon tetrachloride and water vapor on ACFs was determined to shed light on the role of surface chemistry on gas adsorption. Results show that different precursors resulted in various elemental compositions and imposed diverse influence upon surface functionalities after heat treatment. The surface of heat-treated ACFs became more graphitic and hydrophobic. Three distinct peaks due to C, N, and O atoms were identified by XPS, and the high-resolution revealed the existence of several surface functionalities. The presence of nitride-like species, aromatic N-imines, or chemisorbed nitrogen oxides was found to be of great advantage to adsorption of water vapor or benzene, but the pyridine-N was not. Unstable complexes on the surface would hinder the fibers from adsorption of carbon tetrachloride. The rise in total ash content or hydrogen composition was of benefit to the access of water vapor. Modifications of ACFs by heat treatment have effectively improved adsorption performance. (c) 2006 Elsevier B.V. All rights reserved.

Abstract  Montmorillonites modified with carbon deposits were reported to be promising catalysts of NO reduction with ammonia (SCR). The influence of different preparation methods on structural, textural and sorption properties were discussed. Three preparation methods were considered, differing in the pretreatment of the clay preceding the introduction of carbon precursor (polymer soluble in water). The structure was studied by XRD, texture by sorption of argon, benzene and carbon tetrachloride and surface composition by XPS. The obtained nanocomposites had different textural properties, depending on pretreatment. XPS, TPD and textural data suggest different mechanisms of formation of nanocomposites on untreated and acidic pretreated clays. The introduction of carbon deposits influenced hydrophilic properties. The number of ammonia sites changed after each preparative step: acidic pretreatment, pillaring and the formation of carbon deposits. (C) 2004 Elsevier B.V. All rights reserved.

Abstract  This study presents an experiment which characterizes reductive dechlorination of tetra chloroethylene (PCE) by green rusts (GRs) in the presence of Pt using a batch reactor system. Relative to GR alone, the rate of PCE reduction in GR suspensions was greatly enhanced with the addition of Pt(IV) (95% of PCE was removed in 30 h). PCE was mostly transformed to a nonchlorinated byproduct, acetylene rather than trichloroethylene, and the carbon mass recovery was 98% at the last sampling point. The reduction of PCE was four times faster for GR-F(Pt) than for GR-CO3(Pt), mainly due to the higher Fe(II) content of GR-F The estimated kinetic rate Constants of GR-CI(Pt) increased significantly (i.e., 0.17, 0.21, and 1.01 h(-1), respectively) with an incremental addition of Pt from 0.5 to 2 mM. X-ray diffraction analysis showed the transformation of GR to magnetite as an oxidation product. X-ray photoelectron spectroscopy analysis revealed that the oxidation was coupled to the reduction of Pt (IV to 0) on the GR surfaces. The scanning electron microscope with energy dispersive spectrometer measurement showed the formation of Pt particles on the surfaces of GRs modified with the Pt(IV).

Abstract  The paper presents a process for the obtaining of the MALTOL (I) and CYCLOTEN (II) compounds of a purity higher than 99% by separation from wood tar as follows: (1) steaming of the I + II mixture (preferably in the presence of the ammonium sulphate in order to increase the amount of involved compounds); (2) L/L selective extraction of the I + II mixture in the aqueous phase steamed at two pH values (with chloroform at pH = 7 and carbon tetrachloride at pH << 1); (3) separation of the I and II compounds from the I + II mixture based on the insolubility of the pirylium salt (I H + Cl-) in chloroform; (4) purification of the isolated I-II compounds. Because the steaming technique is used on a large scale for the obtaining of finite wood tar the process also allows the purification of the industrial waters which may be recycled or drained (after a biological treatment); the result is an oily secondary product which may be further processed to obtain other compounds.

Abstract  Biodegradation of chloroform (CF) was examined in a methanogenic enrichment culture grown on dichloromethane (DCM) as the sole organic carbon and energy source, with and without the addition of supplemental cyanocobalamin. In the absence of cyanocobalamin, the principal products of [C-14] CF biodegradation were (CO2)-C-14 and [C-14]DCM. The extent of CF reduction to DCM increased significantly when CF was biodegraded in the presence of a large amount of DCM. The addition of cyanocobalamin enhanced CF biodegradation in two ways. First, the rate of CF biodegradation increased approximately 10-fold. Second, the metallocofactor increased the extent of CF oxidation to CO2 and virtually eliminated the accumulation of DCM. These effects were not observed in autoclaved cultures supplemented with cyanocobalamin. When cyanocobalamin was added to viable cultures, as much as 10% of the [C-14]CF transformed accumulated as C-14-labeled carbon monoxide. This suggested that the oxidation of CF to CO2 proceeds via net hydrolysis to CO. CF levels as high as 2.2 mM were readily transformed, without accumulation of DCM, at cyanocobalamin to CF molar ratios of 3-5%. Although the organism or consortium responsible for CF biodegradation was not identified, prior work with DCM suggests that acetogenic bacteria are involved.

Abstract  Toxicity and exposure evaluations remain the two of the key components of human health assessment. While improvement in exposure assessment relies on a better understanding of human behavior patterns, toxicity assessment still relies to a great extent on animal toxicity testing and human epidemiological studies. Recent advances in computer modeling of the dose-response relationship and distribution of xenobiotics in humans to important target tissues have advanced our abilities to assess toxicity. In particular, physiologically based pharmacokinetic (PBPK) models are among the tools than can enhance toxicity assessment accuracy. Many PBPK models are available to the health assessor, but most are so difficult to use that health assessors rarely use them. To encourage their use these models need to have transparent and user-friendly formats. To this end the Agency for Toxic Substances and Disease Registry (ATSDR) is using translational research to increase PBPK model accessibility, understandability, and use in the site-specific health assessment arena. The agency has initiated development of a human PBPK tool-kit for certain high priority pollutants. The tool kit comprises a series of suitable models. The models are recoded in a single computer simulation language and evaluated for use by health assessors. While not necessarily being state-of-the-art code for each chemical, the models will be sufficiently accurate to use for screening purposes. This article presents a generic, seven-compartment PBPK model for six priority volatile organic compounds (VOCs): benzene (BEN), carbon tetrachloride (CCl(4)), dichloromethane (DCM), perchloroethylene (PCE), trichloroethylene (TCE), and vinyl chloride (VC). Limited comparisons of the generic and original model predictions to published kinetic data were conducted. A goodness of fit was determined by calculating the means of the sum of the squared differences (MSSDs) for simulation vs. experimental kinetic data using the generic and original models. Using simplified solvent exposure assumptions for oral ingestion and inhalation, steady-state blood concentrations of each solvent were simulated for exposures equivalent to the ATSDR Minimal Risk Levels (MRLs). The predicted blood levels were then compared to those reported in the National Health and Nutrition Examination Survey (NHANES). With the notable exception of BEN, simulations of combined oral and inhalation MRLs using our generic VOC model yielded blood concentrations well above those reported for the 95th percentile blood concentrations for the U.S. populations, suggesting no health concerns. When the PBPK tool kit is fully developed, risk assessors will have a readily accessible tool for evaluating human exposure to a variety of environmental pollutants.

Abstract  A convenient new chemical actinometer was developed to measure the spectral output of laboratory ultraviolet (UV) light sources over the wavelength range of 260-330 nm. It can also be used to measure solar UV irradiance (< or =325 nm). The actinometer is based on the photoreduction of aqueous carbon tetrachloride (CT) to chloroform (CF) in the presence of acetone (the chromophore) and 2-propanol (the reductant). In all cases, CT disappearance (and CF formation) followed zero-order kinetics over 95% of the reaction. The slope of the linear decay curve forms the basis of the new actinometer, which was calibrated using ferrioxalate actinometry. Quantum yields were measured at 10 nm intervals and were found to be uniform throughout the range of 260-300 nm. As expected, quantum yields gradually decreased to zero asthe wavelength was increased from 300 to 340 nm. The high quantum yields (approximately 150), low sensitivityto room light, and the straightforward determination of [CT] and [CF] by gas chromatography offer significant advantages over some other chemical actinometers, which might require the preparation and purification of light-sensitive compounds in a darkened environment and long exposure times.

Abstract  [1] An in situ gas chromatograph (GC) instrument on a balloonborne package is described in detail and data from seven science deployments are presented. This instrument, the Lightweight Airborne Chromatograph Experiment (LACE), operates on the Observations of the Middle Stratosphere (OMS) in situ gondola and has taken data from the upper troposphere to near 32 km with a vertical resolution of better than 300 m. LACE chromatography has been developed to measure halon-1211, the chlorofluorocarbons (CFC-11, CFC-113, CFC-12), nitrous oxide (N2O), and sulfur hexafluoride (SF6) every 70 s and methyl chloroform (CH3CCl3), carbon tetrachloride (CCl4), hydrogen (H-2), methane (CH4), and carbon monoxide (CO) every 140 s. In the introduction we present scientific motivation for choosing this suite of molecules and for the use of faster sample rates resulting in unprecedented vertical resolution from an in situ GC. Results from an intercomparison with the Airborne Chromatograph for Atmospheric Trace Species (ACATS-IV) instrument are shown to quantitatively connect this LACE data set to the complementary data set generated on board the NASA ER-2 aircraft.

Abstract  Efficient design of zero-valent metal permeable 'barriers' for the reduction of organohalides requires information regarding the pertinent reaction rates as well as an understanding of the resultant distribution of products. In this study, the pathways and kinetics for reaction of polychlorinated ethanes with Zn(0) have been examined in batch reactors. Reductive p-elimination was the only route through which hexachloroethane (HCA), 1,1,1,2-tetrachloroethane (1,1,1,2-TeCA), 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA), 1,1,2-trichloroethane (1,1,2-TCA) and 1,2-dichloroethane (1,2-DCA) reacted. Pentachloroethane (PCA) reacted via concurrent reductive beta-elimination (93%) and hydrolysis (7%). As previously demonstrated, 1,1,1-trichloroethane (1,1,1-TCA) and 1,1-dichloroethane (1,1-DCA) reacted predominantly via reductive a-elimination. Attempts to correlate BET surface area-normalized rate constants (k(SA-BET)) with one-electron reduction potential (E-1) met with limited success, as HCA, PCA, 1,1,1,2-TeCA, and 1,1,1-TCA reacted at nearly identical rates despite substantial differences in E-1 values. Comparison of the pseudo-first-order rate constants (k(obs)) for these species with rate constants (k(L)a) obtained from a correlation for mass transfer to suspended particles revealed that the reaction of these species was mass transfer limited even though reaction rates were unaffected by mixing speed. Calculations suggest that mass transfer limitations may also play a role in the design of treatment systems for highly reactive species, with overall rate constants predicted to increase with flow velocity. (C) 1999 Elsevier Science B,V. All rights reserved.

Abstract  Magnetite nanoparticles (MNPs) are ubiquitous components of the subsurface environment, and increasing attention has been paid to MNPs due to their highly reductive and heterogeneous catalysis reactivity for the degradation of organic contaminants. However, most previous research studies neglected the generation of reactive oxygen species (ROS) by MNPs, which plays an important role in the transformation of contaminants. In this paper, we investigated the activation of persulfate (PS) by MNPs for the degradation of 2,4,4'-CB (PCB28), a selected model compound, and the underlying mechanism was elucidated. The results indicated that the PS can be activated by MNPs efficiently for the degradation of PCB28 at neutral pH. Electron paramagnetic resonance (EPR) technique was used to detect and identify the radical species in these processes. The mechanism of the activation of PS by MNPs was that superoxide radical anion (Of) generated by MNPs could activate the PS to produce more sulfate radicals (SO4 center dot-), which favored the degradation of PCB28. The conclusion was further confirmed by quenching studies with the addition of superoxide dismutase (SOD). The effects of Fe(II) and pH on the degradation of PCB28 by PS/MNPs as well as the generation of ROS by MNPs were also studied. Both sorbed Fe(11) on MNPs surface and increased pH led to production of more Of -, which activated the PS to give more SO4 center dot- to degrade PCB28. In addition, increasing the oxygen concentration in the reaction solution favored the generation of O-2(center dot-) as well as the degradation of PCB28. The findings of this study provide new insights into the mechanism of heterogeneous catalysis based on MNPs and the reactivity of MNPs toward environmental contaminants. (C) 2012 Elsevier B.V. All rights reserved.

Abstract  Compound specific isotope analysis (CSIA) has been applied to monitor bioremediation of groundwater contaminants and provide insight into mechanisms of transformation of chlorinated ethanes. To date there is little information on its applicability for chlorinated methanes. Moreover, published enrichment factors (ε) observed during the biotic and abiotic degradation of chlorinated alkanes, such as carbon tetrachloride (CT); 1,1,1-trichloroethane (1,1,1-TCA); and 1,1-dichloroethane (1,1-DCA), range from -26.5‰ to -1.8‰ and illustrate a system where similar C-Cl bonds are cleaved but significantly different isotope enrichment factors are observed. In the current study, biotic degradation of chloroform (CF) to dichloromethane (DCM) was carried out by the Dehalobacter containing culture DHB-CF/MEL also shown to degrade 1,1,1-TCA and 1,1-DCA. The carbon isotope enrichment factor (ε) measured during biodegradation of CF was -27.5‰ ± 0.9‰, consistent with the theoretical maximum kinetic isotope effect for C-Cl bond cleavage. Unlike 1,1,1-TCA and 1,1-DCA, reductive dechlorination of CF by the Dehalobacter-containing culture shows no evidence of suppression of the intrinsic maximum kinetic isotope effect. Such a large fractionation effect, comparable to those published for cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC) suggests CSIA has significant potential to identify and monitor biodegradation of CF, as well as important implications for recent efforts to fingerprint natural versus anthropogenic sources of CF in soils and groundwater.

Abstract  BIOSIS COPYRIGHT: BIOL ABS. 1,1,2-Trichloroethylene (TCE), 1,1-dichloroethylene, cis and trans-1,2-dichloroethylene and tetrachloroethylene (PCE), at concentrations of 20 ppm in aqueous solutions were rapidly hydrodechlorinated to ethane (in a few minutes), on the surface of palladized iron in batch experiments that were performed in closed vials. No intermediate reaction products such as 1,1-dichloroethylene, 1,2-dichloroethylenes and vinyl chloride were detected at concentrations 1 ppm either in the headspace or in solution. The chloromethanes, CCl4, CHCl3 and CH2Cl2 were also dechlorinated to methane on palladized iron; the CCl4 was dechlorinated in a few minutes, the CHCl3, in less than an hour and the CH2Cl2, in 4-5 h. These results indicate that an above-ground treatment method can be designed for the treatment of groundwater contaminated with low molecular weight chlorinated hydrocarbons.

Abstract  In a recent publication (Moggridge, 2012), it was shown that a simple equation could be used to accurately predict the mutual diffusion coefficients in a wide range of non-ideal binary mixtures from their tracer diffusion coefficients and a thermodynamic correction factor. The physical basis of the equation is that dynamic concentration fluctuations in the liquid mixture result in a reduction of the mean thermodynamic correction factor relative to the hypothetical case in which no such fluctuations occur. Here, the analysis is extended to cases where strong molecular association occurs, in the form of dimerisation of a polar species, mixed with a non-polar component. This requires a modification of the average molecular mobility part of the predictive equation for mutual diffusivity, in the form of doubling the tracer diffusivity of the dimerised species - on the basis that each labelled molecule which moves carries with it a second unlabelled molecule of the same species. In this paper, it is demonstrated that such a modified equation is valid for four alcohol-non polar mixtures, in which the alcohol is close to fully dimerised beyond a mole fraction of about 0.2. It is of significance that the form of the thermodynamic correction factor required in these systems remains unchanged, raising the possibility of its more general validity for non-ideal liquid mixtures. The prediction of mutual diffusion coefficients from tracer diffusivities has practical implications, particularly where measurement of the mutual diffusion coefficient is difficult; tracer diffusivities can be easily measured by pulsed field gradient NMR or estimated using molecular simulation calculations. (c) 2012 Elsevier Ltd. All rights reserved.

Abstract  Observations of methane, CFC-11, and ozone losses are used along with insights from models and observations regarding interrelationships between tracers to develop a semi-empirical framework for evaluating global ozone depletion potentials. Direct measurements of some hydrochlorofluorocarbons including HCFC-22 in the Arctic lower stratosphere are also used to evaluate the local ozone depletion potentials there. This approach assumes that all of the observed ozone destruction in the contemporary atmosphere is due to chlorine and that the depletion is proportional to the local relative chlorine release. It is shown that the global ozone depletion potentials for compounds with relatively long stratospheric lifetimes such as HCFC-22 and HCFC-142b are likely to be larger than those generally predicted by gas phase chemical models, due largely to the importance of lower stratospheric ozone losses that are not simulated in gas phase studies. The analysis presented suggests that the globally averaged efficiency for ozone depletion by HCFC-22 is as much as a factor of 2 larger than some gas phase model estimates. For compounds with short stratospheric lifetimes such as (CCl4). and (CH3CCl3), on the other hand, gas phase models likely overestimate the ozone depletion potentials for the present-day stratosphere. Observations of polar ozone loss and reactive halogen radical abundances also imply that the globally averaged ozone depletion potentials for brominated species for the contemporary stratosphere could be as much as 1.5–3 times greater than some gas phase model predictions, depending upon lower stratospheric loss processes.

Abstract  BIOSIS COPYRIGHT: BIOL ABS. The bacterial transition-metal coenzymes vitamin B12 (Co), coenzyme F430 (Ni), and hematin (Fe) catalyzed the reductive dechlorination of polychlorinated ethylene and benzenes, whereas the electron-transfer proteins four-iron ferredoxin, two-iron ferredoxin, and azurin (Cu) did not. For vitamin B12 and coenzyme F430, reductive dechlorination rates for different classes of perchlorinated compounds had the following order: carbon tetrachloride tetrachloroethylene hexachlorobenzene. For hematin, the order of reductive dechlorination rates was carbon tetrachloride hexachlorobenzene tetrachloroethylene. Within each class of compounds, rates of dechlorination decreased with decreasing chlorine content. Regio- and stereospecificity were observed in these reactions. In the reductive dechlorination of trichloroethylene, cis-1,2-dichloroethylene was the predominant product formed with vitamin B12, coenzyme F430, and hematin. Pentachlorobenzene and pentachloroph