Abstract  The effects of nine solvents of different nature on the concurrent chlorination of tetrachloroethene and 1,2-dichloroethane were studied. The ratio of the rate constants for the radical chlorination of substrates in nonaromatic solvents was shown to depend on the solubility constant. Solvation of chlorine radicals by solvents of this sort is not specific. The effect of aromatic solvents is associated with the formation of the donor-acceptor complexes of aromatic molecules with chlorine radicals, which are the chlorination agents in radical chlorination. The relative activation parameters of the rate constants for the radical chlorination of tetrachloroethene and 1,2-dichloroethane were determined. These parameters were shown to follow the isokinetic dependence for all solvents studied.

Abstract  Anaerobic sequencing batch reactors (ANSBRs) typically have not been used to treat wastewater, possibly because of the potential rapid acidification that may occur with batch feeding of an anaerobic reactor. To investigate ANSBR capabilities, a simulation model was developed and experimentally validated. The model explicitly considers different microbial populations in an anaerobic community, predicts formation and consumption of intermediate products as a function of hydrogen partial pressure, predicts system pH, and considers inhibition caused by pH and hydrogen partial pressure. Simulation model results agreed well with experimental results from three separate tests using a laboratory-scale ANSBR receiving glucose. Experimental and simulation results indicated that, for the same organic loading rate, reactor performance improved with a slower fill cycle. The model may be used to rapidly identify other opportunities to improve the capability of ANSBRs to treat a variety of wastewater types.

Abstract  This study investigated the effect of cation type, ionic strength, and pH on the performance of an anionic monorhamnolipid biosurfactant for solubilization and removal of residual hexadecane from sand. Three common soil cations, Na+, Mg2+, and Ca2+, were used in these experiments and hexadecane was chosen to represent a nonaqueous phase liquid (NAPL) less dense than water. Results showed that hexadecane solubility in rhamnolipid solution was significantly increased by the addition of Na+ and Mg2+. Addition of up to 0.2 mM Ca2+ also increased hexadecane solubility. For Ca2+ concentrations greater than 0.2 mM there was little effect on hexadecane solubility due to competing effects of calcium-induced rhamnolipid precipitation and enhanced hexadecane solubilization. Efficiency of NAPL solubilization can be expressed in terms of molar solubilization ratios (MSR). The results showed that MSR values for hexadecane in rhamnolipid solutions increased 7.5-fold in the presence of 500 mM Na+, and 25-fold in the presence of 1 mM Mg2+. The presence of cations also reduced the interfacial tension between rhamnolipid solutions and hexadecane. For example, an increase in Na+ from 0 to 800 mM caused a decrease in interfacial tension from 2.2 to 0.89 dyn cm(-1). Similarly, decreasing pH caused a reduction in interfacial tension. The lowest interfacial tension value observed in this study was 0.02 dyn cm(-1) at pH 6 in the presence of 320 mM Na+. These conditions were also found to be optimal for removal of hexadecane residual from sand columns, with 58% of residual removed within three pore volumes. The removal of residual NAPL from the packed columns was primarily by mobilization, even though solubilization was significantly increased in the presence of Na+. (C) 1998 Elsevier Science B.V.

Abstract  Recent interest in norvitamin B-12-derivatives, homologues of complete vitamin B-12-derivatives, lacking the methyl group at carbon 176, stems from the identification of the corrinoid cofactor of the tetrachloroethene reductive dehalogenase of Sulfurospirillum multivorans as 176-nor-pseudovitamin B-12. Here we report the partial synthesis of the corrinoid Co alpha Co beta-dicyano-176-norcobinamide by condensation of cobyric acid and 2-aminoethanol. In addition, the partial synthesis of crystalline Co-alpha-aquo-Co-beta-cyanocobyric acid by acid catalyzed hydrolysis of vitamin B-12 is detailed, improving the method and the isolation procedure worked out earlier by Bernhauer et al. The solution structure of Co alpha Co beta-dicyano-176-norcobinamide was studied by spectroscopy and was compared with that of the homologue Co alpha Co beta-dicyanocobinamide. The title compound, Co alpha Co beta-dicyano-176-norcobinamide, represents the dicyano-form of a potential biosynthetic precursor of the 176-nor-B-12-derivatives, such as 176-nor-pseudovitamin B-12.

Abstract  In this paper the tradeoff between process control and cost-effectiveness for PERL-type process flows is investigated. Three aspects are considered: (1) whether a surface pre-treatment (for example special cleans and/or oxidation) prior to the deposition of the Al2O3-based rear-side passivation stack has to be added to the flow; (2) the quantification of the impact on cell parameters of skipping the rear-side polishing and/or the Al2O3 deposition; and (3) the possibility of replacing Al paste with PVD Al for rear side metallization. It is found that: (1) SPM-like cleans or thermal oxidation prior to Al2O3 deposition are useful steps to guarantee a stable Al2O3-based passivation process. (2) The efficiency drops by more than 1% by skipping the polishing, but only approximate to 0.15% by removing the Al2O3 from the passivation stack. Therefore, while rear-side polishing appears to be a necessary step for PERC/PERL technologies, the insertion of Al2O3 in the passivation stack could be traded off for a reduced production cost, depending on the (company-specific) details of cost-calculations. (3) Replacing Al paste with PVD Al for rear side metallization results in a deteriorated reflectance. The effect is larger for thinner passivation stacks. Although less advantageous in term of material costs with respect to PVD Al, screen-printed Al would therefore be the preferred choice for PERL cells featuring thin passivation stacks. (C) 2013 Elsevier B.V. All rights reserved.

Abstract  The absorption of tetrachloroethylene - the VOC - in di-ethyl-hexyl-adipate - the solvent - was carried out as an example of gaseous waste treatment. Two gas-liquid contactors were used: a column provided with as structured Sulzer EX (R) packing and a microstructured falling-film absorber provided with thin vertical channels, manufactured by the Institut fur Mikrotechnik Mainz (IMM). The overall transfer coefficient of VOC, K(G)a, was calculated from the absorption efficiency of the various runs carried out, allowing comparison of the two gas-liquid contactors. Due to the high solubility of the considered VOC, mass transfer was shown to be mainly controlled by gas-side transfer rates. Transfer coefficient K(G)a of the two absorbers were found to be comparable, but with gas and liquid velocity in the microstructured absorber from one to two orders of magnitude below those in the column, expressing the high transfer performance offered by the microsystem. Moreover, the thickness of the liquid film in the channels was below 100 mu m, much lower than that in a structured packing near 500 mu m. This shows that lower liquid flow rates can be used for efficient absorption in the microsystem. It is shown that contrary to conventional structured packing, the designed contact specific area in the microabsorber strictly corresponds to the interfacial G/L surface. This enables more compact and to miniaturize G/L contactors to be designed. (C) 2010 Elsevier Ltd. All rights reserved.

Abstract  Upward water flow can arrest the downward migration of dense, nonaqueous phase liquids (DNAPLs) through rough-walled fractures provided that a sufficient hydraulic gradient exists. An exact analytical solution to predict the arresting gradient demonstrates that there is little difference between the gradient required to arrest DNAPL migration near the top of the fracture, and the gradient required to arrest migration once DNAPL has extended to the bottom of the fracture. Laboratory experiments involving the migration of tetrachloroethylene (PCE) through two samples of fractured limestone demonstrate the ability of upward water flow to arrest downward DNAPL migration under both wetting and drainage conditions. It is suggested that upward gradients can be generated beneath contaminated regions of the subsurface to provide a ''hydraulic bottom.'' A hydraulic bottom at a site would protect against potential downward mobilization of DNAPL in response to the application of aggressive remediation technologies such as surfactant flooding, alcohol flooding, and steam flooding. Upward gradients applied during drilling may also protect against downward mobilization of DNAPL in the formation while drilling through source zones.

Abstract  Chlorinated hydrocarbons enter aquifers by various ways. Bacteria found in ground water transform the dissolved compounds into one or more intermediate compounds, then into a final compound that is sometimes not biodegradable. Biotransformation of tetrachloroethylene (PCE) to trichloroethylene (TCE), dichloroethylene (DCE), and vinyl chloride (VC) by a reductive dehalogenation process catalyzed by microorganisms has been observed in aquifers and laboratory columns under methanogenic conditions. The pathway for conversion includes the replacement of a chlorine atom by a hydrogen atom. The quantification of these conversion and migration processes of parent and intermediate compounds is achieved by mole balance equations of respective compounds, Michaelis-Menten kinetic equations, and stoichiometric relations. Following a simplification of the general model for a column experiment, a numerical solution is obtained by using a finite difference scheme to provide estimates of mole fractions of parent and intermediate compounds. The numerical results show a favorable match with experimental data. A significant sensitivity to model parameters, particularly the rate constants of parent compounds, is discovered. It is concluded that biotransformation processes can be satisfactorily quantified by first-order rate expressions.

Abstract  This paper describes laboratory studies conducted to evaluate the impact of varying environmental conditions (dense nonaqueous phase liquid (DNAPL) type and mass, and properties of the subsurface porous media) and design features (oxidant type and load) on the effectiveness and efficiency of in situ chemical oxidation (ISCO) for destruction of DNAPL contaminants. Porous media in 160 mL zero-headspace reactors were employed to examine the destruction of trichloroethylene and perchloroethylene by the oxidants potassium permanganate and catalyzed hydrogen peroxide. Measures of oxidation effectiveness and efficiency include (1) media demand (mg-oxidant/kg-porous media), (2) oxidant demand (mol-oxidant/mol-DNAPL), (3) reaction rate constants for oxidant and DNAPL depletion (min(-1)), (4) the percent (%) DNAPL destroyed, and (5) the relative treatment efficiency, i.e., the rate of oxidant depletion versus rate of DNAPL destruction. While an obvious goal of ISCO for DNAPL treatment is high effectiveness (i.e., extensive contaminant destruction), it is also important to focus on oxidation efficiency, or to what extent the oxidant is utilized for contaminant destruction instead of competing side reactions, for improved cost effectiveness and/or treatment times. Results indicate that DNAPL contaminants can be treated both effectively and efficiently under many environmental and design conditions. In some cases, DNAPL treatment was more effective and efficient than dissolved/sorbed phase treatment. In these experiments, permanganate was a more effective oxidant, however catalyzed hydrogen peroxide treated contaminants more efficiently (e.g., less oxidant required per mass contaminant treated). Results also indicate that oxidation treatment goals can be dictated by environmental conditions, and that specific treatment goals can dictate remediation design parameters (e.g., faster contaminant destruction was realized in catalyzed hydrogen peroxide systems, whereas greater contaminant destruction occurred in permanganate systems).

Abstract  A new simple and reliable method combining an acetonitrile partitioning extractive procedure followed by dispersive solid-phase cleanup (QuEChERS) with dispersive liquid-liquid microextraction (DLLME) and further gas chromatography mass spectrometry analysis was developed for the simultaneous determination of bisphenol A (BPA) and bisphenol B (BPB) in canned seafood samples. Besides the great enrichment factor provided, the final DLLME extractive step was designed in order to allow the simultaneous acetylation of the compounds required for their gas chromatographic analysis. Tetrachloroethylene was used as extractive solvent, while the acetonitrile extract obtained from QuEChERS was used as dispersive solvent, and anhydride acetic as derivatizing reagent. The main factors influencing QuEChERS and DLLME efficiency including nature of QuEChERS dispersive-SPE sorbents, amount of DLLME extractive and dispersive solvents and nature and amount of derivatizing reagent were evaluated. DLLME procedure provides an effective enrichment of the extract, allowing the required sensitivity even using a single quadropole MS as detector. The optimized method showed to be accurate (>68 % recovery), reproducible (<21 % relative standard deviation) and sensitive for the target analytes (method detection limits of 0.2 μg/kg for BPA and 0.4 μg/kg for BPB). The screening of several canned seafood samples commercialized in Portugal (total = 47) revealed the presence of BPA in more than 83 % of the samples with levels ranging from 1.0 to 99.9 μg/kg, while BPB was found in only one sample at a level of 21.8 μg/kg.

Abstract  The influence of softeners in pigment printing on print quality has been investigated. Two softeners have been selected - one based on esters of fatty acids, and the other, based on silicone microemulsion. The influence of the quantity of softener applied on water absorption, on the stability of textile printing on the organic solvent C2Cl4 has been tested. More stable films, with improved elasticity, have been obtained with the softener based on silicone microemulsion. The softener based on esters of fatty acids increases water absorption, but with a less stable polymere film. This is reflected in fabric hand, and the choice of softeners will primarily depend upon the intended end-use of the printed textile product.

Abstract  This report examines sorption of low ppb levels of organic solutions by polytetrafluoroethylene (PTFE), rigid polyvinyl chloride (PVC), and stainless steel 304 and 316 well casings. Nineteen organics were selected, including several munitions and chlorinated solvents. Compounds were selected to offer a range of physical properties, such as solubility in water, octanol/water partition coefficient, and molecular structure. When these results were compared with the results from a similar study conducted at ppm levels, the rate and extent of sorption by PTFE and PVC were the same as seen previously For almost all analytes. There were no losses of any compounds associated with stainless steel. At these low levels (ppm and ppb), the rate of diffusion within the polymer (PVC and PTFE) is independent of concentration. Only with PFTE are the rates rapid enough to be of concern when monitoring for some contaminants in ground water. Tetrachloroethylene was the compound PTFE sorbed the most rapidly. The study showed that PVC well casings are suitable for monitoring low levels (ppm and ppb) of organics.

Abstract  Packed towers are the most widely used air-stripping technique for removal of volatile organic chemicals (VOCs) from contaminated water. Hydraulic jets are an alternative air stripping process. The jets increase the air-water surface area per volume of water to be treated by creating a high powered spray. The turbulent conditions within the jets allow the VOCs within the liquid phase to be released to the gas phase. The compounds then can be removed from the gas phase by sorption on activated carbon or by other technologies, This paper reports the results of a research project to evaluate the feasibility of using hydraulic jets to remove VOCs from water. Lumped mass transfer coefficients (k) for nine VOCs were determined experimentally. The mass transfer coefficients were plotted against their respective Henry's Law Constants (H(a)) and an equation, k = 0.506 + 0.14*Log(H(a)), was developed to estimate the mass transfer coefficient (for a specific configuration) for a VOC with a known H(a). Design equations for the removal of VOCs by hydraulic jets also were developed. The concentrations-of VOCs such as benzene and tetrachloethylene were reduced to acceptable levels using the jets. Hydraulic jets require more power than packed towers for removing benzene and tetrachloroethylene. However, hydraulic jets are resistant to fouling by waters high in iron or biological growths.

Abstract  A preliminary examination of a simple and rapid screening method for quantifying a range of toxic organohalides directly in aqueous solution based on their electrocatalytic reduction with a metalloporphyrin catalyst is described. Homogenous catalysis is described as well as heterogeneous catalysis using precipitated cobalt(II) tetraphenylporphine ((TPP)Co) at a graphite foil electrode which permitted the sensitive detection of a wide range of different organohalides, including a number of chemically diverse industrial pollutants such as 1,2,3,4,5,6-hexachlorocyclohexane (lindane) and carbon tetrachloride, representative of haloalkane compounds, haloalkenes such as perchloroethylene, and aromatics, such as 2,4-dichlorophenoxyacetic acid, pentachlorophenol, and the insecticide DDT. The coordinating effect of solvent on the thermodynamics of the Co(II)/(I) electrode reaction is used to practical advantage to build an amperometric detector that is insensitive to interference from oxygen, a parameter that varies considerably in environmental samples. Devices also appear relatively insensitive to the ionic composition of the analyte sample, The work provides the basis for developing a prototype sensor for screening toxic organohalogen pollutants for use in environmental monitoring situations.

Abstract  Systemic decrease of dopaminergic cells, such as in Parkinson's disease may produce visual alterations in humans. Zn order to show possible pattern electroretinogram (PERG) spatial tuning function (STE) alterations due to impaired dopaminergic transmission in humans, we studied a group of Parkinson's disease patients before and during treatment with the dopamine precursor, levodopa, and compared theirperformances with those of an age-matched control group. Moreover, in order to exclude the possible involvement of motor disabilities to produce PERG alterations, we also investigated PERC responses in post-traumatic parkinsonian patients who exhibited motor abnormalities as a consequence of focal lesions of basal ganglia, in the absence of systemic dopaminergic degeneration. Our results showed a clear decrease of PERG responses in Parkinson's disease patients particularly at medium spatial frequency range (2.7-4.0 cycles/degree) with a substantial preservation of responses at low frequencies. Levodopa therapy reversed these alterations in Parkinson's disease patients, resulting in the recovery of a normal tuning function shape. In contrast to Parkinson's disease, the tuning function appeared to be preserved in post-traumatic parkinsonian patients. Our results clearly establish a relationship between retinal alteration in PD patients and dopaminergic retinal function. (C) 1998 Elsevier Science Ireland Ltd.

Abstract  The mass transfer rate from residual dense non-aqueous phase liquids (DNAPLs) to the mobile aqueous phase is an important parameter for the efficiency of surfactant-enhanced remediation through solubilization of this type of contamination. The mass transfer kinetics are highly dependent on the dimensionality of the system. In this study, irregularly shaped residual TCE saturations in two-dimensional saturated flow fields were flushed with a 2% polyoxyethylene sorbitan (20) monooleate (POESMO) solution until complete removal had been achieved. A numerical model was developed and used for the simulation of the various surfactant-flushing experiments with different initial saturation patterns and flow rates. Through optimization against in situ concentration and saturation data, a phenomenological power-law model for the relationship between the mass transfer rate from the DNAPL to the mobile aqueous phase on the one hand and the residual DNAPL saturation and the flow velocity on the other hand was derived. The obtained mass transfer rate parameters provide a reasonable fit to the experimental data, predicting the cleanup time and the general saturation and concentration pattern quite well but failing to predict the concentration curves at every individual sampling port. The obtained mass transfer rate model gives smaller values for the predicted mass transfer rate but shows a comparable dependence on water flow and saturation as in earlier published one-dimensional column experiments with identical characteristics for porous medium, DNAPL and surfactant. Mass transfer rate predictions were about one order of magnitude lower in the 2-D flow cell experiment than in 1-D column experiments. These results give an indication for the importance of dimensionality during surfactant remediation.

Abstract  Many common organic pollutants are characterized by low solubilities and high interfacial tensions; these characteristics combine to render pump-and-treat processes ineffective. Surfactants can dramatically increase the solubility of organic compounds in groundwater and lower their interfacial tensions; both effects theoretically can greatly increase the extraction efficiency of pump-and-treat systems. Lowering of interfacial tensions can result in movement of dense contaminants downward in an aquifer, potentially contaminating underlying layers. Increasing a pollutant's solubility increases the fraction of pollutant present as dissolved phase, increasing the efficiency of extraction using a modified pump-and-treat technique. Thus we propose that a surfactant solution intended for extraction of dense organic liquids should be optimized for solubilization, with a minimal reduction of interfacial tensions. The results of porous media experiments comparing the extraction efficiency of over 100 surfactants indicate that solubilization ability is the most important factor; although both the extent of reduction of interfacial tension and the tendency to form spontaneous emulsions must also be considered. Using a suitable surfactant mixture, a pool of tetrachloroethylene can be extracted from a lab-scale saturated porous media model in 7 to 14 pore volumes, depending upon the geometry of the contamination. Mass balance calculations indicate complete removal of the contaminant and analysis of sand samples at the conclusion of the experiment indicates less than 1 milligram of contaminant remains. In contrast, concentrations of the effluent average only 6 ppm when distilled water is used for flushing, producing no measurable reduction in the volume of the pool in 14 pore volumes. These experiments suggest that utilizing surfactants to increase the solubility of dense organic pollutants can be an effective and relatively inexpensive way of in situ remediation of contaminated aquifers.

Abstract  The purpose of this research was to better understand the interactions between biodegradable and nonbiodegradable synthetic organic chemicals (SOCs) during bioregeneration of biologically active granular activated carbon (GAC) columns. Continuous-flow GAC bioregeneration experiments were conducted at different empty-bed contact times (EBCTs) using mixtures of a biodegradable (benzene or toluene) and a nonbiodegradable (perchloroethylene or carbon tetrachloride) SOC. The GAC was pre-equilibrated with respect to each combination of SOCs to facilitate the study of bioregeneration. If no dissolved oxygen limitations occurred in the bioregeneration experiments, the effluent biodegradable SOC concentration decreased over time and then remained low, after which the effluent nonbiodegradable SOC concentration also decreased because of the increased availability of adsorption sites on the GAC. Pre- and postexperimental GAC loadings show a marked decrease in the biodegradable SOC loading as well as an increase in the nonbiodegradable SOC loading. Greater degrees of bioregeneration were found for higher SOC equilibrium concentrations and longer EBCTs. Bioregeneration ranged from 28.8 to 45.5% of the initial biodegradable SOC loading after 13-17 days. These results illustrate an increase in GAC adsorption capacity for nonbiodegradable SOCs through bioregeneration of GAC containing biodegradable SOCs.

Abstract  Background Occupational scientists agree there are hazards associated with dry-cleaning, but no dry-cleaning owners and workers concur? Knowledge of owners' and workers' perceptions can help guide intervention efforts to reduce worker exposure. To better understand these issues, a qualitative study was conducted using focus group methodology and constant comparative analysis. Methods Two owner and four worker focus groups were held. Results Findings suggest that overall, health and safety issues were not of great concern. Owners were primarily concerned with the economic impact of regulations. Workers did express some anxiety about solvent exposure and burns, but most felt that these hazards were "just part of the job. "Also, other than the installation of air-conditioning in the shops and the provision of health benefits, workers could not think of ways health and safety on the job could be improved. Conclusions These findings will be used to develop comprehensive safety and health interventions (e.g., engineering plus education and training) in dry-cleaning shops. Am. J. Ind. Med. 35:112-123, 1999. Published 1999 Wiley-Liss, Inc.dagger

Abstract  A study of different methods for cleaning copper components to improve electrical conductivity of Cu/Ag glue joints is presented. Copper samples were cleaned with three different methods: (i) wet chemical cleaning with tetrachloroethylene, (ii) discharge cleaning with an oxygen plasma, and (iii) subsequent discharge cleaning with oxygen and hydrogen plasmas. Discharge cleaning was performed in a low-pressure weakly-ionized plasma created with a RF generator of the output power of 200 W and the frequency of 27.12 MHz. The concentration of impurities on the copper surface was determined by Auger electron spectroscopy (AES) depth profiling. Cleaning with oxygen plasma caused effective removal of organic impurities, but the oxygen concentration on the surface was increased. Additional cleaning with hydrogen plasma effectively reduced the oxide film, so the copper surface became virtually free of any impurities. The electrical resistance of the joints between the components treated by different methods showed that the contact resistance is decreased with increasing copper surface cleanliness. (C) 2003 Elsevier Science Ltd. All rights reserved.

Abstract  Thermal neutron logging is used to determine water content by measuring the elastic scattering due to hydrogen present in rocks and soils. The response of a thermal neutron device is also affected by the radiative capture of thermal neutrons by all elements. Chlorine has a large capture cross section in comparison to other elements usually found in aquifers; therefore, theory predicts that thermal neutron devices should respond to the presence of chlorinated solvents. Thermal neutron logging performed during a controlled release of perchloroethylene (PCE) confirmed that these methods can be used successfully to detect and monitor chlorinated solvents in the subsurface. To quantify the field results, a series of laboratory tests assessed the response of a neutron moisture probe used in the field experiments. These tests show that this device is very sensitive to the presence of chlorine and provide a basis for converting its response into an apparent PCE saturation. These saturation values compare favorably with PCE saturations obtained from core samples.

Abstract  Perchloroethylene, the most widely used solvent in dry cleaning, is toxic to the liver, kidneys and central nervous system and may be a human carcinogen. An exposure assessment was carried out in 69 dry-cleaning shops using perchloroethylene in Tehran city, Iran. The 8-h time weighted average (TWA) breathing zone air samples and end-exhaled air samples were obtained from 179 workers who worked as the job titles included machine operator (n=71), presser (n=63) and counter area (clerk) (n=45). The mean perchloroethylene concentrations in breathing zone air were 11.5 ppm, 9.6 ppm and 7.2 ppm respectively. The mean perchloroethylene concentrations in end-exhaled air of the same participants in Saturday morning (prior to shift of workweek) were 1.7 ppm, 1.5 ppm and 1.1 ppm, but in Thursday evening (end of shift at end of workweek) were 2.4 ppm, 2.0 ppm and 1.5 ppm respectively. This study found that, the mean perchloroethylene concentrations in breathing zone air and end-exhaled air in the dry-cleaning workers were lower than the TLV (25 ppm) and BEI (5 ppm) recommended by ACGIH. Regression analysis showed that the concentration of perchloroethylene in breathing zone air (TWA) was highly and significantly correlated with the concentration of perchloroethylene in end-exhaled air in Saturday morning with a regression equation Y=0.147X + 0.031, (r=0.99, p<0.001) and also in Thursday evening with a regression equation Y=0.201X + 0.072 (r=0.98, p<0.001) where X is the concentration of perchloroethylene in breathing zone air and Y is that the concentration of perchloroethylene in end-exhaled air. The results also showed the potential utility of measuring the concentration of perchloroethylene in end-exhaled air as a method for assessing relative exposure in dry cleaning shops which use it.

Abstract  Absorption fields are soil-based onsite installations designed to infiltrate, drain, filter or biochemically renovate water. A critical component in absorption field development is determination of the soil's ability to transmit water. Two of the most important in-situ methodologies for measuring water transmission in absorption fields are the Perc Test, which determines Perc Time (PT) in an open borehole or pit, and the Constant Head Well Permeameter (CHWP), which determines field-saturated hydraulic conductivity (K-fs) in an open borehole. Although both methods have important features, they also have deficiencies that can impair their use in absorption field investigations. Features of the Perc Test include simplicity, intuitive measurements (decline in water ponding depth, H, with time, t), and inclusion of PT criteria in most absorption field design specifications and regulatory codes. Critical deficiencies of the Perc Test include its empirical nature (absence of theoretical foundation), lack of standardization, and strong dependence of PT on borehole/pit dimensions, water ponding depth and antecedent soil properties. Features of the CHWP include a solid theoretical foundation, formal accounting for borehole dimensions, water ponding depth and soil properties, and recognition that K-fs controls long-term water acceptance rates. A critical deficiency of the CHWP is the absence of K-fs criteria from many absorption field specifications and codes. This study develops a unified Perc-CHWP analysis and application protocol that maintains the features of the Perc and CHWP tests, but circumvents the deficiencies. The unified analysis combined numerical optimization with piece-wise analytical integration of a falling-head CHWP equation; and it yielded accurate estimates of PT and K-fs using H vs. t data obtained from numerical simulations, laboratory experiments, and field-based Perc Tests. The unified Perc-CHWP methodology improves measurement of water transmission in absorption field investigations by providing: physically based PT values required by many design specifications and regulatory codes; K-fs values required for estimation of long-term water acceptance rates; and functionally linked PT-K-fs data pairs that are accurate and based on rigorous borehole infiltration theory. Crown Copyright (C) 2015 Published by Elsevier B.V. All rights reserved.

Abstract  The dehydrochlorination of pentachloroethane to tetrachloroethylene was investigated to gain insight into mechanisms of hexachloroethane reduction as well as structure-reactivity relationships for polyhalogenated alkanes. Although the absence of deuterium exchange excludes the possibility of an (E1CB)R mechanism, several factors suggest the transition state possesses considerable carbanion character: the reaction is insensitive to buffer catalysis, exhibits a moderately large solvent kinetic isotope effect, and only displays a neutral mechanism at low pH. Though our results cannot rule out a stepwise (E1CB)I or (E1CB)ip sequence, we believe CHCl2CCl3 reacts via a concerted mechanism based on a comparison of its dehydrohalogenation kinetics with proton-exchange rates for CHCl3 and CHCl2CF3. Pentachloroethane reported in the reduction of hexachloroethane to tetrachloroethylene is unlikely to result from carbanion protonation. Rather, it may be diagnostic of free-radical reduction mechanisms. Because pentachloroethane reacts relatively rapidly, future studies of hexachloroethane reduction should consider whether pentachloroethane represents a reaction intermediate instead of dismissing it as a minor side product.

Abstract  Laboratory experiments and numerical simulations in homogeneous porous media were used to investigate the influence of porous medium wettability on the formation and growth of preferential dissolution pathways, dissolution fingers, during nonaqueous phase liquid (NAPL) dissolution. As the porous medium became increasingly NAPL-wet, dissolution fingers grew wider and slower. This result was observed in physical experiments with 0% and 100% NAPL-wet conditions and confirmed with numerical simulations at these and intermediate wettabilities. A previously derived expression for an upscaled mass transfer rate coefficient that accounts for the growth of dissolution fingers was used to quantify the effect of fingering on overall NAPL removal rates. For the test cases evaluated, NAPL dissolution fingering controlled the overall rate of NAPL dissolution after the dissolution front moved 4 cm, in 0% NAPL-wet conditions and 18 cm in 100% NAPL-wet conditions. Thus, even in completely NAPL-wet media dissolution fingering may control the overall rate of NAPL dissolution after relatively short travel distances. The importance of NAPL dissolution fingering in heterogeneous systems with spatially varying NAPL saturations, though, remains an important question for future work. (c) 2008 Elsevier Ltd. All rights reserved.