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A trichloroethene (TCE)-dechlorinating community (CANAS) maintained in a completely mixed flow reactor was established from a semi-batch enrichment culture (ANAS) and was monitored for 400 days at a low solids retention time (SRT) under electron acceptor limitation. Around 85% of TCE supplied to CANAS (0.13 mmol d-1) was converted to ethene at a rate of 0.1 mmol d-1, with detection of low production rates of vinyl chloride (6.8 × 10-3 mmol d-1) and cis-dichloroethene (2.3 × 10-3 mmol d-1). Two distinct Dehalococcoides mccartyi strains (ANAS1 and ANAS2) were stably maintained at 6.2 ± 2.8 × 108 cells mL-1 and 5.8 ± 1.2 × 108 cells mL-1, respectively. Electron balance analysis showed 107% electron recovery, in which 6.1% were involved in dechlorination. 16 S rRNA amplicon sequencing revealed a structural regime shift between ANAS and CANAS while maintaining robust TCE dechlorination due to similar relative abundances of D. mccartyi and functional redundancy among each functional guild supporting D. mccartyi activity. D. mccartyi transcriptomic analysis identified the genes encoding for ribosomal RNA and the reductive dehalogenases tceA and vcrA as the most expressed genes in CANAS, while hup and vhu were the most critical hydrogenases utilized by D. mccartyi in the community.

Electrokinetics is being applied in combination with common insituremediation technologies, e.g. permeable reactive barriers, bioremediation and in-situ chemical oxidation, to overcome experienced limitations in remediation of chlorinated ethenes in low-permeable subsurface soils. The purpose of this review is to evaluate state-of-theart for identification of major knowledge gaps to obtain robust and successful field-implementations. Some of the major knowledge gaps include the behavior and influence of induced transient changes in soil systems, transport velocities of chlorinated ethenes, and significance of site-specific parameters on transport velocities, e.g. heterogeneous soils and hydrogeochemistry. Furthermore, the various ways of reporting voltage distribution and transport rates complicate the comparison of transport velocities across studies. It was found, that for the combined EK-techniques, it is important to control the pH and redox changes caused by electrolysis for steady transport, uniform distribution of the electric field etc. Specifically for electrokinetically enhanced bioremediation, delivery of lactate and biodegrading bacteria is of the same order of magnitude. This review shows that enhancement of remediation technologies can be achieved by electrokinetics, but major knowledge gaps must be examined to mature EK as robust methods for successful remediation of chlorinated ethene contaminated sites. • EK-combined techniques overcome transport limitations experienced in low-permeable soils. • EK velocity of PCE and TCE is of comparable size to supplied reactants. • In EK-BIO, transport velocity of lactate and biodegrading bacteria are in the same order of magnitude. • General knowledge on the dependency of EK transport velocity on soil type is lacking. • Identified knowledge gaps must be filled in for robust and successful field-implementations. [ABSTRACT FROM AUTHOR]

Groundwater pollution by chlorinated compounds is one of the most common environmental issues affecting urban areas, especially for those with a huge industrial vocation. Even if Rome is not an industrial city, this kind of contamination has been recently started to be detected in the groundwater. In order to better evaluate the presence and distribution of chlorinated solvents in groundwater in the eastern sector of Rome, a sampling survey in the monitoring network of the city has been conducted. First preliminary results, deriving from samples collected in wells mainly located in public green areas in a previous investigation survey, seem to show how the species tetrachloroethylene, trichlorethylene and all their degradation pathway can be associated more with point source of contamination with locally very high concentration values. On the contrary, the detection of trichloromethane and 1,1,2-trichloroethane, which have been found in the new data collection at low concentration in several of the investigated wells, could suggest a diffuse occurrence of these compounds. Unfortunately, even if the presented results represent a good starting point for further evaluations, the preliminary status of this research cannot allow to clearly understand the source of contamination and declare the possible diffusion of these two compounds. [ABSTRACT FROM AUTHOR]

Abstract Thermal proteome profiling (TPP) is increasingly applied in eukaryotes to investigate protein-ligand binding through protein melting curve shifts induced by the presence of a ligand. In anaerobic bacteria, identification of protein-substrate interactions is a major challenge. We applied TPP to Sulfurospirillum multivorans , which is able to use trichloroethene as electron acceptor for growth, to investigate the interaction of its tetrachloroethene reductive dehalogenase PceA with trichloroethene. Several modifications in the protocol (e.g., incubation under anaerobic conditions; increasing the temperature range up to 97 °C) extended the protein detection range and allowed the investigation of oxygen-sensitive proteins. Enzymatic reductive dehalogenation was prevented by omitting the electron donor during incubations. This enabled detecting the interaction of PceA with trichloroethene and confirmed that trichloroethene is a substrate of this enzyme. Interestingly, a putative response regulator showed a similar trend, which is the first biochemical hint for its proposed role in trichloroethene respiration. We proved that our TPP approach facilitates the identification of protein-substrate interactions of strictly anaerobic reductive dehalogenases and probably their regulators. This strategy can be used to identify yet unknown substrate specificities and possible signal-sensing proteins, and therefore has the potential to elucidate one of the unresolved fields in research on organohalide-respiring bacteria. Significance The assessment of enzyme-substrate or protein-ligand interactions in organohalide-respiring bacteria is a fundamental challenge. Thermal proteome profiling (TPP) allows elucidating proteome-wide thermal stability changes relying on the sensitivity of modern mass spectrometry. This gives access to the identification of interactions not detectable with other methods. In this TPP study, we demonstrate the interactions of a chlorinated substrate with a reductive dehalogenase and potentially with a response regulator, thereby supporting the response regulator's function in organohalide respiration. The strategy might also be applied to identify yet unknown substrates of other enzymes in bacteria which are difficult to investigate or for which only low amounts of biomass are available. The assessment of enzyme-substrate interactions, which might enable conclusions about enzyme specificities, represents a new application for TPP. Graphical abstract Unlabelled Image Highlights • Thermal proteome profiling (TPP) was modified for analyzing bacterial oxygen-sensitive enzymes. • Protein-trichloroethene interactions in organohalide-respiring Sulfurospirillum multivorans were identified. • Interaction of the tetrachloroethene reductive dehalogenase with trichloroethene was confirmed. • A first hint for the interaction of a response regulator and a chlorinated ethene was provided. [ABSTRACT FROM AUTHOR]

The probability distributions of total potential doses of disinfection byproducts and volatile organic compounds via ingestion, inhalation, and dermal exposure were estimated with Monte Carlo simulations, after conducting physiologically based pharmacokinetic model simulations to takes into account the differences in availability between the three exposures. If the criterion that the 95th percentile estimate equals the TDI (tolerable daily intake) is regarded as protecting the majority of a population, the drinking water criteria would be 140 (trichloromethane), 66 (bromodichloromethane), 157 (dibromochloromethane), 203 (tribromomethane), 140 (dichloroacetic acid), 78 (trichloroacetic acid), 6.55 (trichloroethylene, TCE), and 22 μg/L (perchloroethylene). The TCE criterion was lower than the Japanese Drinking Water Quality Standard (10 μg/L). The latter would allow the intake of 20% of the population to exceed the TDI. Indirect inhalation via evaporation from water, especially in bathrooms, was the major route of exposure to compounds other than haloacetic acids (HAAs) and accounted for 1.2–9 liter-equivalents/day for the median-exposure subpopulation. The ingestion of food was a major indirect route of exposure to HAAs. Contributions of direct water intake were not very different for trihalomethanes (30–45% of TDIs) and HAAs (45–52% of TDIs). [ABSTRACT FROM AUTHOR]

Column studies were conducted to investigate the influence of benzene or toluene on the dechlorination of perchloroethene (PCE) and trichloroethene (TCE) in columns packed with zerovalent iron (ZVI) in order to simulate a permeable reactive barrier (PRB). Enhancive and inhibitive influences of benzene and toluene, respectively, on PCE and TCE reduction were observed within 10-80 pore volumes (PV) that flowed through the columns. However, such influences dissipated when the flow-through volume increased above 80 PV. The presence of benzene increased the mean dechlorination kobs of PCE and TCE by 7% and 6%, respectively; in contrast, the presence of toluene decreased the mean dechlorination kobs of PCE and TCE by 21% and 10%, respectively. We presumed that the more competitive adsorption between benzene and toluene in comparison to PCE and TCE on the ZVI particle surface might have caused the disparate influences. With a lower affinity for ZVI, benzene has no substantial influence on PCE and TCE adsorption on the ZVI particle surface. However, toluene has a higher affinity for ZVI and could compete with PCE and TCE by contacting the ZVI particle surface. Moreover, given benzene's higher polarity, it could also benefit electron transfer from ZVI to PCE and TCE. [ABSTRACT FROM AUTHOR]

The objective of this study was to examine the sensor response characteristics of three commercial Internet of Things (IoT) compatible metal oxide (MOx) sensors in preparation for the development of field-scale sensor networks for the real-time monitoring of volatile organic compounds (VOCs) in indoor environments located in proximity to brownfield sites. Currently, there is limited examination of such sensor responses to relevant mixtures of target VOCs, such as the common petrochemicals benzene, toluene, ethylbenzene, and xylene (BTEX), as well as chlorinated aliphatic hydrocarbon (CAH) contaminants such as tetrachloroethylene (PCE) and trichloroethylene (TCE) which are frequently associated with deterioration of indoor air quality. To address this, a study of three commercial metal oxide (MOx) sensors (SGP30, BME680, and CCS811) was undertaken to examine the sensor response characteristics of individual components as well as mixtures of each of the target BTEX and CAH chemicals over relevant indoor air concentrations within the operating range of the MOx sensors (0−6000 ppb). Our investigation revealed similar response patterns to those previously reported for the thick film MOx sensor to most individual target VOCs, however, response trends for mixtures were more difficult to discern. In general, the MOx sensors we examined demonstrated similar magnitude responses to the CAHs as BTEX compounds indicating reliable detection of CAHs.

Laboratory batch experiments were performed to assess the impacts of temperature and mineralogy on the abiotic dechlorination of tetrachloroethene (PCE) or trichloroethene (TCE) due to the presence of ferrous minerals in natural aquifer clayey soils under anaerobic conditions. A combination of x-ray diffraction (XRD), magnetic susceptibility, and ferrous mineral content were used to characterize each of the 3 natural soils tested in this study, and dechlorination at temperatures ranging from 20 to 55 °C were examined. Results showed that abiotic dechlorination occurred in all 3 soils examined, yielding reduced gas abiotic dechlorination products acetylene, butane, ethene, and/or propane. Bulk first-order dechlorination rate constants (k bulk ), scaled to the soil:water ratio expected for in situ conditions, ranged from 2.0 × 10 − 5 day − 1 at 20 °C, to 32 × 10 − 5 day − 1 at 55 °C in the soil with the greatest ferrous mineral content. For the generation of acetylene and ethene from PCE, the reaction was well described by Arrhenius kinetics, with an activation energy of 91 kJ/mol. For the generation of coupling products butane and propane, the Arrhenius equation did not provide a satisfactory description of the data, likely owing to the complex reaction mechanisms associated with these products and/or diffusional mass transfer processes associated with the ferrous minerals likely responsible for these coupling reactions. Although the data set was too limited to determine a definitive correlation, the two soils with elevated ferrous mineral contents had elevated abiotic dechlorination rate constants, while the one soil with a low ferrous mineral content had a relatively low abiotic dechlorination rate constant. Overall, results suggest intrinsic abiotic dechlorination rates may be an important long-term natural attenuation component in site conceptual models for clays that have the appropriate iron mineralogy. [ABSTRACT FROM AUTHOR]

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Vapor intrusion (VI) is the migration of subsurface vapors, including radon and volatile organic compounds (VOCs), from the subsurface to indoor air. The VI exposure pathway extends from the contaminant source, which can be impacted soil or groundwater, to indoor air-exposure points. VOC contaminants of concern typically include halogenated solvents as well as petroleum hydrocarbons. Radon, a colorless radioactive gas that is released by radioactive decay of radionuclides in rock and soil, migrates into homes through VI in a similar fashion to VOCs. This project focused on the performance of permanent versus temporary sub-slab sampling ports for the determination of VI of halogenated VOCs and radon into an unoccupied house. VOC and radon concentrations measured simultaneously in soil gas using collocated temporary and permanent ports appeared to be independent of the type of port. The variability between collocated temporary and permanent ports was much less than the spatial variability between different locations within a single residential duplex. Post sampling leak test results suggested that the temporary SSP desiccation and cracking of the clay portion of the seal were not as detrimental to the port seal performance as would have been expected, this suggests that the Teflon tape portion of the seals served an important function. Pre and post sampling leak tests are advisable when temporary ports are used to collect a time-integrated sample. These results suggest that temporary sub-slab sampling ports can provide data equivalent to that collected from a permanent sub-slab sampling port. [ABSTRACT FROM PUBLISHER]

Selection of effective groundwater remediation scenarios is a complex issue that requires understanding of contaminants' transport processes. The effectiveness of cleanup measures may be verified by fate and transport numerical modeling. The goal of this work was to present the usefulness of fate and transport modeling for planning, verification and fulfillment of effective groundwater remediation methods. Selection methodology was developed, which is based on results of numerical flow and transport modeling. A field site located in south-east Poland was selected as a case study, in which groundwater contamination of trichloroethene and tetrachloroethene was detected. The results indicated that 'pump and treat' was the most effective among the studied remediation methods, followed by permeable reactive barrier and in situ chemical oxidation. Natural attenuation-based remediation was demonstrated to be the least suitable, as it requires the longest time to reach predefined remediation goals, principally due to low sorption capacity and unfavorable hydrogeochemical conditions for biodegradation. Fate and transport numerical modeling allowed simulating different remediation strategies, and thus the decision-making process was facilitated. [ABSTRACT FROM AUTHOR]

Vapor degreasing with the chlorinated solvents trichloroethylene, 1,1,1-trichloroethane, and perchloroethylene is a historically important source of environmental release and contamination. After describing how a vapor degreaser works and the solvents used, we provide a brief history of vapor degreasing in the United States, focusing on specific time periods. The practice originated in about 1930 and was quickly adopted, including by key manufacturers. Its use grew rapidly, particularly during World War II. However, it wasn't until about 1976 with the passage of RCRA that commercial waste haulers became available. During an interim period after the passage of RCRA disposal of liquid spent solvents and sludges was to landfills, thereby simply moving the location of the eventual contamination. Finally, we discuss the most common types of vapor degreaser releases to the environment and some ways that they can be identified. Understanding how a release occurred can help in allocating liability or developing a conceptual model for site remediation. [ABSTRACT FROM PUBLISHER]

Radiation induced dechlorination of trichloroethylene (TCE) and tetrachloroethylene (PCE) in aqueous solutions containing the active carbon (AC) or cupric oxide (CuO) as the modifiers was studied. The obtained results were compared to the previously studied dechlorination of polychlorinated biphenyls (PCBs). Both modifiers were found to decrease the efficiency of dechlorination. The AC modifier acts mainly via adsorption of the aliphatic (unlike the aromatic) hydrocarbons and the CuO oxide mainly inhibits the mineralization of the perchloroethylene. The results presented in this paper will be also helpful for the studies of the impact of chlorinated hydrocarbons on the membrane permeability of living cells. [ABSTRACT FROM AUTHOR]

The photocatalytic decomposition of trichloroethylene (TCE) and tetrachloroethylene (PCE) in water was studied. TCE and PCE were present in water at very low concentrations of about 15 μg/dm3. This concentration level corresponds to the one occasionally occurring in groundwater. Results of this research confirmed usefulness of the photocatalytic process for successful removal of low-concentrated TCE and PCE from water. Removal of trichloroethylene and tetrachloroethylene from water can be achieved by application of the photocatalytic process over titanium dioxide. It was confirmed that both suspended and immobilized modes of the photocatalytic process give comparable results. Therefore it is recommended to employ the immobilized system as more beneficial from the economical point of view. Presented studies revealed that very low amounts of TCE and PCE can be removed from water using the photocatalytic process. This method could be than applied for purification of groundwater occasionally polluted with the small amounts of TCE and PCE. [ABSTRACT FROM AUTHOR]

Dehalobacter restrictus strain PER-K23 (DSM 9455) is the type strain of the species Dehalobacter restrictus. D. restrictus strain PER-K23 grows by organohalide respiration, coupling the oxidation of H to the reductive dechlorination of tetra- or trichloroethene. Growth has not been observed with any other electron donor or acceptor, nor has fermentative growth been shown. Here we introduce the first full genome of a pure culture within the genus Dehalobacter. The 2,943,336 bp long genome contains 2,826 protein coding and 82 RNA genes, including 5 16S rRNA genes. Interestingly, the genome contains 25 predicted reductive dehalogenase genes, the majority of which appear to be full length. The reductive dehalogenase genes are mainly located in two clusters, suggesting a much larger potential for organohalide respiration than previously anticipated. [ABSTRACT FROM AUTHOR]

Simulated groundwater solutions contaminated with trichloroethylene (TCE) and tetrachloroethylene (PCE) were treated in a flow-through reactor equipped with ultrasound (US) and ultraviolet light (UV) sources. The treatment process was operated using UV or US individually, and UV and US concurrently (UVUS). The solutions contaminated with TCE or PCE were exposed to UV light emitted from Hg-arc lamps surrounding the quartz reactor vessel, and to acoustic waves from a US horn located at the bottom of the reactor vessel. The rate constants () of photolysis by UV, sonolysis by US, and photosonolysis by UVUS were evaluated using a mathematical model in conjunction with a nonlinear regression analysis. The removal efficiencies () for the UV, US, and UVUS treatments were also determined. For TCE, the US rate constant () and the UV rate constant () yield the theoretical additive rate constant () of , whereas the observed UVUS rate constant () is . Furthermore, the efficiency of the US treatment () and of the UV treatment () gives the theoretical additive efficiency () of 0.706, whereas the observed UVUS efficiency () is 0.741. For PCE, and are 0.324 and , respectively, whereas and are 0.894 and 0.948, respectively. The results suggest that the combined effect of UV and US on the decomposition of TCE and PCE is likely synergistic. [ABSTRACT FROM AUTHOR]

Abstract: Numerical simulations were conducted to evaluate the efficacy of in situ field scale chemical oxidation (ISCO) (with permanganate) for trichloroethylene (TCE) and tetrachloroethylene (PCE) DNAPL in eight idealized heterogeneous porous media sites. The goal of this work was to study the effects of DNAPL source zone remediation at the site scale utilizing a high-resolution three-dimensional numerical model. The model results demonstrated that both dissolution (no treatment) and treatment were unable to completely deplete DNAPL mass or boundary mass flux for any of the sites over a 10 year period. Performance was highly variable due to competition with oxidizable organic aquifer materials, manganese dioxide (rind) formation, DNAPL architecture, and geologic characteristics. When compared to dissolution only, DNAPL mass depletion at the end of treatment ranged from adverse impacts to a three-fold improvement, but diminished with post-treatment monitoring. Similarly, the relative reduction in boundary mass flux varied between unity and a factor of two at the termination of treatment, but at 10 years ranged from a 10-fold reduction to adverse impacts. During the post-treatment phase of the simulations, most of the benefits achieved during active treatment were negated due to dissolution tailing. [Copyright &y& Elsevier]

Predicting the fate of chlorinated ethenes in groundwater requires the solution of equations that describe both the transport and the biodegradation of the contaminants. Here, we present a model that accounts for (1) transport of chlorinated ethenes in flowing groundwater, (2) mass transfer of contaminants between mobile groundwater and stationary biofilms, and (3) diffusion and biodegradation within the biofilms. Equations for biodegradation kinetics account for biomass growth within the biofilms, the effect of hydrogen on dechlorination, and competitive inhibition between vinyl chloride and cis-dichloroethene. The overall model consists of coupled, non-linear, partial differential equations; solution of such a model is challenging and requires innovative numerical algorithms. We developed and tested two new numerical algorithms to solve the equations in the model; these are called system splitting with operator splitting (SSOS) and system splitting with Picard iteration (SSPI). We discuss the conditions under which one of these algorithms is superior to the other. The contributions of this paper are as follows: first, we believe that the mathematical model presented here is the first transport model that also accounts for diffusion and non-linear biodegradation of chlorinated ethenes in biofilms; second, the SSOS and SSPI are new computational algorithms developed specifically for problems of transport, mass transfer, and non-linear reaction; third, we have identified which of the two new algorithms is computationally more efficient for the case of chlorinated ethenes; and finally, we applied the model to compare the biodegradation behavior under diffusion-limited, metabolism-limited, and hydrogen-limited (donor-limited) conditions. [ABSTRACT FROM AUTHOR]

Photolysis, sonolysis, and photosonolysis of common groundwater contaminants, namely 1,1,1-trichloroethane, trichloroethylene, and tetrachloroethylene, were investigated using a flow-through photosono reactor system. Simulated groundwater containing the chlorinated volatile organic compounds (VOCs) was exposed to ultraviolet light (UV), ultrasonication (US), and UV and US concurrently (UVUS), without a photo catalyst. VOC removal efficiencies of the UV, US, and UVUS treatment processes were computed from the VOC concentrations in influent and effluent of the reactor. The process using UVUS exhibited larger degradation efficiencies than that with UV and US separately in most cases; however, statistical analysis showed that the UVUS treatment efficiency is likely to be additive of the UV and US treatment efficiencies. The results also showed that the increase of the detention time from 26 to 60 min had no significant effect on the VOC removal efficiencies in these processes. [ABSTRACT FROM AUTHOR]

Photocatalytic oxidation of trichloroethylene (TCE) and tetrachloroethylene (PCE) in air had been carried out with TiO2 film alone and Au/TiO2 film. On the TiO2 film TCE and PCE were converted mainly into toxic COCl2, while COCl2 free TEC and PCE oxidation could be achieved with Au/TiO2. [ABSTRACT FROM AUTHOR]

Column experiments were conducted to evaluate the effect of pore velocity on the extent of biodegradation of cis-dichloroethene ( cis-DCE) during transport in porous media. Columns were filled with homogeneous glass beads and inoculated with a culture capable of complete dechlorination of tetrachloroethene to ethene. A constant concentration of cis-DCE was maintained in the columns’ influent. Three different pore velocities were tested in duplicate, subjecting each column to a constant velocity. At high flow velocity, degradation of cis-DCE to ethene was nearly complete within the residence time of the columns. However, at medium and low flow velocities, incomplete dechlorination was observed. After 7 weeks, DNA was harvested from the columns to determine differences in the microbial populations. Results suggest that Dehalococcoides sp. were present in higher quantities in the high-velocity columns, consistent with the observed dechlorination. These results suggest that, at contaminated groundwater sites, heterogeneity of groundwater velocity may be one factor that contributes to heterogeneous distribution of biological activity. [ABSTRACT FROM AUTHOR]

Photocatalytic oxidation of trichloroethylene (TCE) and tetrachloroethylene (PCE) in air had been carried out with TiO2 film alone and Au/TiO2 film. On the TiO2 film TCE and PCE were converted mainly into toxic COCl2, while COCl2 free TEC and PCE oxidation could be achieved with Au/TiO2. [ABSTRACT FROM AUTHOR]

Abstract: Extracellular hydroxyl radical ( OH) production via quinone redox cycling in Trametes versicolor, grown in a chemically defined medium, was investigated to degrade trichloroethylene (TCE), perchloroethylene (PCE), 1,2,4- and 1,3,5-trichlorobenzene (TCB). The activity of the enzymes catalyzing the quinone redox cycle, quinone reductase and laccase, as well as the rate of OH production, estimated as the formation of thiobarbituric acid reactive substances (TBARS) from 2-deoxyribose, increased rapidly during the first 2–3days and then remained at relatively constant levels. Under quinone redox cycling conditions, TCE degradation was concomitant to TBARS production and chloride release, reaching a plateau after 6h of incubation. Similar results were obtained in PCE, 1,2,4- and 1,3,5-TCB time course degradation experiments. The mole balance of chloride release and 1,2,4-TCB and TCE degraded suggests that these chemicals were almost completely dechlorinated. Experiments using [13C]-TCE confirmed unequivocal transformation of TCE to 13CO2. These results are of particular interest because PCE and 1,3,5-TCB degradation in aerobic conditions has been rarely reported to date in bacterial or fungal systems. [Copyright &y& Elsevier]

Abstract: To assist in the design of enhanced reductive dechlorination systems for in situ remediation of chlorinated solvent source zones, the software BUCHLORAC (BUffering of deCHLORination ACidity) was developed to predict the amount of buffer required to maintain the groundwater pH in a DNAPL treatment zone within the optimal range for dechlorinating bacteria. Reductive dechlorination is an acid-forming process with hydrochloric acid and organic acids typically building up in the treatment zone. Remediation of source zones is associated with such extensive localized dechlorination that it may be common for the soils'' natural buffering capacity to be exceeded. As groundwater acidification may inhibit the activity of dechlorinating microorganisms and thus slow or stall the remediation process, sufficient alkalinity must be present to maintain a near-neutral pH. BUCHLORAC is a Windows Graphical Interface based on an abiotic geochemical model that is implemented through the program PHREEQC. BUCHLORAC allows users to estimate the buffer requirements for their specific operating and design conditions including, for example, site water chemistry, mineralogy, amount of chlorinated solvent to be degraded, design inhibition pH, and type of organic substrate and buffering additive. [Copyright &y& Elsevier]

Chlorinated solvents such as perchloroethylene (PCE) and trichloroethylene (TCE) continue to be significant groundwater contaminants throughout the USA. In many cases efficient bioremediation of aquifers contaminated with these chemicals requires the addition of exogenous microorganisms, specifically members of the genus Dehalococcoides (DHC). This process is referred to as bioaugmentation. In this study a fed-batch fermentation process was developed for producing large volumes (to 3,200 L) of DHC-containing consortia suitable for treating contaminated aquifers. Three consortia enriched from three different sites were grown anaerobically with sodium lactate as an electron donor and PCE or TCE as an electron acceptor. DHC titers in excess of 1011 DHC/L could be reproducibly obtained at all scales tested and with all three of the enrichment cultures. The mean specific DHC growth rate for culture SDC-9™ was 0.036 ± 0.005 (standard error, SE)/h with a calculated mean doubling time of 19.3 ± 2.7 (SE) h. Finished cultures could be concentrated approximately tenfold by membrane filtration and stored refrigerated (4°C) for more that 40 days without measurable loss of activity. Dehalogenation of PCE by the fermented cultures was affected by pH with no measurable activity at pH <5.0. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes the potential of using gamma radiation technology to degrade trichloroethylene (TCE) and perchloroethylene (PCE) wastewater. The experimental method is divided into two parts: (1) using the γ-ray to irradiate the TCE and PCE solution, the dose-rate is 10Gy/minute, the irradiation dosage is 0–2.5kGy and (2) self-making the UV irradiation system, the tube specification is 254nm and 6W, and turning on 8 tubes at the same time to make the irradiation. The efficiency of degradation ratio for γ-ray is better than UV in the range of 0.1–250ppm; for example, as for the concentration of 0.1ppm, when TCE is degraded to D 90 and T 90, the γ-ray only needed 46.7Gy and took about 4.67 minutes, but UV needed to take about 28.1 minutes. The dose-concentration equations of TCE and PCE are: TCE: y=44.58+8.832x, R 2=0.999; and PCE: y=81.33+12.81x, R 2=0.997. We verified that the radiation technology is able to effectively degrade the organic chlorine wastewater without yielding the secondary pollution, and the TCE and PCE that degraded by using γ-ray will be reached US-EPA and Taiwan Effluent Standard (5ppb). [Copyright &y& Elsevier]

Laboratory experiments are conducted to determine the liquid-liquid phase separation behavior of six three-component systems with each system comprised of a common alcohol (namely ethanol, isopropanol, or methanol), water, and one of two engineered dense nonaqueous phase liquids (DNAPLs) manufactured by the 3M™ Corporation (namely methoxy-nonafluorobutane (HFE-7100) or ethoxy-nonafluorobutane (HFE-7200)). The experimental results are presented on ternary phase diagrams and compared against available published experimental data where tetrachloroethylene (PCE) and (or) trichloroethylene (TCE) is the dense nonaqueous phase liquid (DNAPL). Results show that the two engineered fluids exhibit similar phase separation behavior in the presence of the same alcohol. Furthermore, these engineered fluids exhibit similar phase separation behavior to that of PCE, but relatively dissimilar phase separation behavior to that of TCE. [ABSTRACT FROM AUTHOR]

Two of three water-distribution systems that have historically supplied drinking water to family housing at U.S. Marine Corps Base Camp Lejeune, North Carolina, were contaminated with volatile organic compounds (VOCs). Scientific data relating to the harmful effects of VOCs on a child or fetus are limited. Therefore, the U.S. Agency for Toxic Substances and Disease Registry (ATSDR) is conducting an epidemiological study to evaluate potential associations between in utero and infant (up to 1 year of age) exposures to VOCs in contaminated drinking water at Camp Lejeune and specific birth defects and childhood cancers. The study includes births that occurred during the period 1968–1985 to women who were pregnant while they resided in family housing at Camp Lejeune. To support the epidemiological study, water-modeling techniques are being used to reconstruct historical conditions of groundwater flow, contaminant fate and transport, and the distribution of drinking water contaminated with VOCs. Results for this phase of the study indicate that PCE concentrations in drinking water, delivered to the Tarawa Terrace housing area, exceeded the current maximum contaminant level for PCE of 5 micrograms per liter (μg/L) for 346 months—November 1957–February 1987; the maximum simulated PCE concentration in Tarawa Terrace drinking water was 183 μg/L during March 1984 compared to a measured concentration of 215 μg/L during February 1985. [ABSTRACT FROM AUTHOR]

Abstract: The variability of stable carbon isotope fractionation upon reductive dechlorination of tetra- and trichloroethene by several microbial strains was investigated to examine the uncertainties related to the in situ application of compound specific isotope analysis (CSIA) of chlorinated ethenes. Carbon isotope fractionation was investigated with a set of microorganisms representative for the currently known diversity of dehalorespirers: Dehalococcoides ethenogenes strain 195, Desulfitobacterium sp. strain Viet1, Desulfuromonas michiganensis and Geobacter lovleyi sp. strain SZ and compared to the previous reports using Sulfurospirillum spp. and Desulfitobacterium sp. strain PCE-S. Carbon isotope fractionation of tetrachloroethene (PCE) and trichlorethene (TCE) was highly variable ranging from the absence of significant fractionation to carbon isotope fractionation (εC) of 16.7 and 3.5–18.9 for PCE and TCE, respectively. Fractionation of both compounds by D. ethenogenes strain 195 (PCE: εC=6.0; TCE: εC=13.7) was similar to the literature data for mixed cultures containing Dehalococcoides spp. D. michiganensis (PCE: no significant fractionation; TCE: εC=3.5) and G. lovleyi sp. strain SZ (PCE no significant fractionation; TCE: εC=8.5) generated the lowest fractionation of all studied strains. Desulfitobacterium sp. strain Viet1 (PCE: εC=16.7) gave the highest enrichment factor for PCE. [Copyright &y& Elsevier]

In situ chemical oxidation (ISCO) using permanganate has been increasingly applied to deplete mass from dense nonaqueous-phase liquid (DNAPL) source zones. However, uncertainty in the performance of ISCO on DNAPL contaminants is partially attributable to a limited understanding of interactions between the oxidant, subsurface hydrology, and DNAPL mass transfer, resulting in failure to optimize ISCO applications. To investigate these interactions, a factorial design experiment was conducted using one-dimensional flow through tube reactors to determine how groundwater velocity, permanganate concentration, and DNAPL type affected DNAPL mass depletion rates. DNAPL mass depletion rates were found to increase with increasing groundwater velocity, or increasing oxidant concentration. An interaction occurred between the two factors, where high oxidant concentrations had little impact on mass depletion rates at high velocities. High oxidant concentration systems experienced gas generation. Mass depletion rates were fastest at high velocities, but required additional oxidant mass and pore volume addition to achieve complete mass depletion. Lower-velocity systems were more efficient with respect to oxidant mass and pore volume requirements, but mass depletion rates were reduced. [ABSTRACT FROM AUTHOR]

Bioremediation by reductive dehalogenation of groundwater contaminated with tetrachloroethene (PCE) or trichloroethene (TCE) is generally carried out through the addition of a fermentable electron donor such as lactate, benzoate, carbohydrates or vegetable oil. These fermentable donors are converted by fermenting organisms into acetate and hydrogen, either of which might be used by dehalogenating microorganisms. Comparisons were made between H2 and acetate on the rate and extent of reductive dehalogenation of PCE. PCE dehalogenation with H2 alone was complete to ethene, but with acetate alone it generally proceeded only about half as fast and only to cis-1,2-dichloroethene (cDCE). Additionally, acetate was not used as an electron donor in the presence of H2. These findings suggest the fermentable electron donor requirement for PCE dehalogenation to ethene can be reduced up to 50% by separating PCE dehalogenation into two stages, the first of which uses acetate for the conversion of PCE to cDCE, and the second uses H2 for the conversion of cDCE to ethene. This can be implemented with a recycle system in which the fermentable substrate is added down-gradient, where the hydrogen being produced by fermentation effects cDCE conversion into ethene. The acetate produced is recycled up-gradient to achieve PCE conversion into cDCE. With the lower electron donor usage required, potential problems of aquifer clogging, excess methane production, and high groundwater chemical oxygen demand (COD) can be greatly reduced. [Copyright &y& Elsevier]

This study may be the first investigation to be performed into the potential benefits of recycling industrial waste in controlling contaminants in leachate. Batch reactors were used to evaluate the efficacy of waste steel scrap and converter slag to treat mixed contaminants using mimic leachate solution. The waste steel scrap was prepared through pre-treatment by an acid-washed step, which retained both zero-valent iron site and iron oxide site. Extensive trichloroethene (TCE) removal (95%) occurred by acid-washed steel scrap within 48 h. In addition, dehalogenation (Cl− production) was observed to be above 7.5% of the added TCE on a molar basis for 48 h. The waste steel scrap also removed tetrachloroethylene (PCE) through the dehalogenation process although to a lesser extent than TCE. Heavy metals (Cr, Mn, Cu, Zn, As, Cd, and Pb) were extensively removed by both acid-washed steel scrap and converter slag through the adsorption process. Among salt ions (NH, NO, and PO), PO was removed by both waste steel scrap (100% within 8 h) and converter slag (100% within 20 min), whereas NO and NHwere removed by waste steel scrap (100% within 7 days) and converter slag (up to 50% within 4 days) respectively. This work suggests that permeable reactive barriers (PRBs) with waste steel scrap and converter slag might be an effective approach to intercepting mixed contaminants in leachate from landfill. [ABSTRACT FROM AUTHOR]

The influence of seepage velocity and groundwater temperature on the dechlorination rates of trichloroethylene (TCE) and tetrachloroethylene (PCE) by zero-valent iron (Fe0) were investigated by running laboratory column tests at seepage velocities ranging from 31 to 1,884 m/year at temperatures of 10 and 23°C. By increasing the seepage velocity from 31 to 1,884 m/year at 10°C, there were approximately seven- and nine-fold increases in the normalized dechlorination rate constants (kSA) of TCE and PCE, respectively. Similarly, a four-fold increase in the kSA of TCE and PCE was also observed at 23°C when increasing the seepage velocity from 103 to 1,183 m/year. Raising the groundwater temperature from 10 to 23°C at a given seepage velocity resulted in 2.7 and 1.1 times increases in the TCE kSA and PCE kSA, respectively. With the application of the Arrhenius equation, activation energies of 70.3 kJ/mol for TCE and 38.6 kJ/mol for PCE dechlorination were determined, indicating domination of the electron transfer process over the mass transfer as a major rate-limiting step of the dechlorination reactions by Fe0. [ABSTRACT FROM AUTHOR]

Abstract: Surfactants are widely used for the remediation of groundwater contaminated with chlorinated solvents. The reuse of surfactants is quite important for the economic feasibility of the remediation process. Pervaporation with a polydimethylsiloxane membrane was conducted to simultaneously separate trichloroethylene (TCE) and tetra-chloroethylene (PCE) from waste solution of the non-ionic surfactant Tween 80. The effects of key process variables on the removal efficiency were investigated. Membrane thickness between 200 µm and 300 µm did not affect the pervaporation performance. Organic flux did not increase above the flow rate of 100 mL/min. The increase of feed concentration and temperature led to large organic flux. Selectivity was reduced significantly with temperature due to the increase in thermal motion of polymer. The reduction of flux was small below 1.0 wt% surfactant (Tween 80) in feed solution. Flux and selectivity of TCE were higher than those of PCE because an extramicellar portion of TCE was higher than that of PCE. In simultaneous pervaporation of TCE and PCE, flux and selectivity declined due to the competitive sorption of TCE and PCE. However, the reduction percentage in flux and selectivity was less than 10% with 1:1 ratio of TCE/PCE. With operation during 100 h, over 95% of TCE and 90% of PCE were simultaneously removed from 0.5 wt% of Tween 80 solution with TCE and PCE of 1,000 ppm. From the present results, which gave a high efficiency in the simultaneous removal of chlorinated solvents, this process could be a practical alternative for surfactant reuse. [Copyright &y& Elsevier]

Abstract: Surface modification of zero-valent iron (ZVI) to enhance its reduction rates for chlorinated ethanes and ethenes has recently attracted great attention. In this research, the enhancement of perchloroethylene (PCE) reduction by ZVI in the presence of sorbed micelles of the cationic surfactant hexadecyltrimethylammonium (HDTMA) was examined in a series of laboratory column tests with varying flow rates and input PCE concentrations. Model simulations using HYDRUS-1D showed that the overall pseudo first-order rate constants for PCE reduction by ZVI increased by a factor of four in the presence of sorbed HDTMA admicelles. The increase in reduction rate was attributed to a higher distribution coefficient (K d) for contaminant sorption on surfactant-modified ZVI (SM-ZVI) compared to untreated ZVI. Modeling results also showed that in the presence of HDTMA admicelles 58–100% of PCE reduction occurred via hydrogenolysis. In contrast, only 12–25% PCE underwent hydrogenolysis when HDTMA was absent. The significant increase in TCE production during PCE reduction by SM-ZVI verified a shift in reaction pathway previously observed in batch studies, most likely from β-elimination to hydrogenolysis. Although this shift in reaction pathway resulted in a higher accumulation of TCE, the combined concentrations of chlorinated hydrocarbons in the effluent were 1.5–5 times lower when SM-ZVI rather than unmodified ZVI was used. [Copyright &y& Elsevier]

Abstract: The structural and sorptive characteristics of the high-surface-area carbonaceous material (HSACM) isolated from soils were investigated. The HSACM contents in soils were first identified by the organic petrology method. A novel isolation method using acid demineralization, base extraction, and ZnBr2 floatation sequential steps was developed to extract the HSACM from soil. The differences in structural and sorptive characteristics with the HSACM and the intact soil were investigated using nitrogen adsorption isotherms and trichloroethylene (TCE) sorption isotherms at low concentrations (0 to about 2mg/L) both with and without tetrachloroethylene (PCE) as the cosolute. It was found that HSACM possesses a much higher specific surface area and pore volume as well as a smaller pore size than the original soil. Moreover, the sorption of TCE to HSACM is noticeably more nonlinear and competitive than to the original soil. A small amount of highly adsorptive HSACM is largely responsible for the nonlinear soil sorption of a single solute at very low concentrations. [Copyright &y& Elsevier]

Tetrachloroethylene (PCE) and trichloroethylene (TCE) are among the most ubiquitous chlorinated contaminants or compounds found in the subsurface environment. A recent site groundwater investigation focused on the underground storage tanks, that found elevated aqueous PCE, TCE, and their degradation byproducts. These chlorinated ethylenes are not commonly found at gas vender stations in Taiwan. The purpose of this monitoring work is to investigate and verify contamination sources in the vicinity of the gas vender station. Measurements of dissolved oxygen content, redox potential, and various cations as well as anions were conducted on the site. The results indicate that the underground environment remains in reducing conditions, but not strictly in anaerobic conditions. Since the sulfate concentration remains at around the background level and the dissolved iron stays below the detection limit, the sulfate and iron reduction are not prominent. Based on the cone penetration geological testing results, a less permeable silt and clay interbed locates at 4.5–6 m below ground surface. The upper aquifer is less permeable than the lower aquifer with one to two orders of magnitudes in hydraulic conductivity. PCE and TCE concentrations are relatively high in the upper aquifer as opposed to the other halocarbons. Though their concentrations are high in the upper aquifer, the extents of contamination plums are similar in both aquifers due to the attribution of advection effects. PCE and TCE are microbiologically transformed to less chlorinated compounds as dichloroethylene (DCE) isomers and vinyl chloride (VC) in this investigative finding. Among these DCE isomers, cis-DCE is the dominant species. The plum of cis-DCE is consistent with that of TCE, while the plume of 1,1-DCE exists in a significantly less extent. The accumulation of vinyl chloride is insignificant for the investigated groundwater that might be resulted from the slightly oxidizing environment where further oxidation of VC might take place. However, further investigation needs to be carried out to verify the complete degradation of VC for the public health’s protection due to its toxicity. [ABSTRACT FROM AUTHOR]

Many different degradation reactions of chlorinated hydrocarbons are possible in natural groundwaters. In order to identify which degradation reactions are important, a large number of possible reaction pathways must be sorted out. Recent advances in ab initio electronic structure methods have the potential to help identify relevant environmental degradation reactions by characterizing the thermodynamic properties of all relevant contaminant species and intermediates for which experimental data are usually not available, as well as provide activation energies for relevant pathways. In this paper, strategies based on ab initio electronic structure methods for estimating thermochemical and kinetic properties of reactions with chlorinated hydrocarbons are presented. Particular emphasis is placed on strategies that are computationally fast and can be used for large organochlorine compounds such as 4,4′-DDT [ABSTRACT FROM AUTHOR]

The ability of chitin fermentation products to promote tetrachloroethene (PCE) reduction was evaluated in a continuous-flow column system to identify how different electron donors affect reductive dechlorination. Natural chitin fermentation products were initially used to support PCE reduction. Acetate (3.5 mM) was the dominant fermentation product, followed by propionate (0.1 mM), butyrate (0.1 mM), and hydrogen (100 nM). After chlorinated ethene concentration profiles reached pseudo steady state, the ability of individual fermentation products (acetate, acetate+propionate, propionate, or formate) to support PCE reduction was evaluated. None of the fermentation products tested stimulated dechlorination as well as the suite generated from chitin (kPCE=6.9 day-1); however, acetate-stimulated PCE dechlorination the best (kPCE=5.3 day-1), followed by formate (kPCE=2.4 day-1), acetate+propionate (kPCE=1.8 day-1), and propionate (kPCE=1.2 day-1). Similar trends were observed for the PCE daughter products trichloroethene and dichloroethene. Free energies of individual fatty acid reactions were calculated and shown to be useful predictors of dechlorination performance, except for the case of acetate+propionate. Hence, acetate is the dominant fatty acid controlling dechlorination in the chitin-enhanced system, propionate appears to have an inhibitory effect when present with acetate alone, and other unidentified nutrients produced during chitin fermentation likely contribute to dechlorination activity as well. [ABSTRACT FROM AUTHOR]

Long-term (e.g., 5–15 years) groundwater concentration versus time records were compiled from 47 near-source zone monitoring wells at 23 chlorinated solvent sites (52 total records). Chlorinated volatile organic compound (CVOC) concentrations decreased significantly in most of the 52 temporal records, with a median reduction in concentration of 74%. A statistical method based on a Mann–Kendall analysis also showed that most sites had statistically significant decreasing concentration trends over time. Median point decay rate constants (kpoint) values were calculated for nine sites containing tetrachloroethene (PCE); 13 sites containing trichloroethene (TCE); two sites containing cis-1,2-dichloroethene (DCE); and six sites containing 1,1,1-trichloroethane (TCA). The TCA sites had the highest kpoint values (0.34/year) followed by PCE, DCE, and TCE (0.23/year, 0.16/year, and 0.11/year, respectively) (equal to decay half-lives of 2.0, 3.0, 4.3, and 6.1 years, respectively). If the median point decay rates from these sites are maintained over a 20 year period, the resulting reduction in concentration will be similar to the reported reduction in source zone concentrations achieved by active in situ source remediation technologies (typical project length: 1–2 years). [ABSTRACT FROM AUTHOR]

The application of zero-valent iron (Fe0) in the funnel-and-gate permeable reactive barrier (PRB) installed at the Vapokon site, Denmark, was conducted in 1999 to remediate the groundwater contaminated by chlorinated aliphatic hydrocarbons (CAHs). Over the past 4 years, except in September 2002 and January 2003, about 92.4–97.5% CAH removal could be achieved with the PRB. Although there was a continuous decrease in total alkalinity (90.3%), calcium (81.7%), and sulfate (69.2%) ions in the groundwater crossing the PRB, probably caused by mineral precipitation and resulting in 0.88% porosity loss per year, no noticeable deterioration of the barrier’s performance was observed between March 2000, and August 2003. Instead, climatic variation in the barrier’s performance on CAH dechlorination was examined. The dechlorination rates in the cold season (January 2003 and March 2000) were generally smaller than those in the hot season (August 2003, September 2000, and September 2001). Besides, 1,2-dichloroethane and dichloromethane, which were proven to be not treatable by Fe0, could also be removed with the PRB, thereby suggesting enhancement from Fe0 adsorption or microbial degradation. [ABSTRACT FROM AUTHOR]

Laboratory experiments were conducted to investigate the abiotic interactions of soybean oil (SoyOil) and chlorinated ethene (CE) nonaqueous phase liquids (NAPLs). The mixed NAPL density and interfacial tension behaved ideally, as predicted by the volume ratio. The mixed NAPL viscosity increased exponentially from that of the pure CE to that of pure SoyOil as the volume fraction increased. The measured contact angle was highly variable and was unpredictable as a function of the volume composition of the mixed NAPL. The physical property effects indicate that the mobilization of residual CE NAPLs because of SoyOil injection is unlikely. Equilibrium dissolution of CEs from the NAPL mixtures behaved linearly as a function of the mole fraction. Dissolved SoyOil in simulated groundwater enhanced the dissolution of trichloroethene (TCE) during flow tests, increasing the effluent TCE concentration from 141 to 202 mg/L. The ready intermingling of the CE dense nonaqueous phase liquids (DNAPLs) and SoyOil indicate that such interactions may be significant at sites where vegetable oil is injected into DNAPL source areas to enhance in situ anaerobic bioremediation. [ABSTRACT FROM AUTHOR]

The biodegradability of chlorinated methanes, chlorinated ethanes, chlorinated ethenes, chlorofluorocarbons (CFCs), chlorinated acetic acids, chlorinated propanoids and chlorinated butadienes was evaluated based on literature data. Evidence for the biodegradation of compounds in all of the compound categories evaluated has been reported. A broad range of chlorinated aliphatic structures are susceptible to biodegradation under a variety of physiological and redox conditions. Microbial biodegradation of a wide variety of chlorinated aliphatic compounds was shown to occur under five physiological conditions. However, any given physiological condition could only act upon a subset of the chlorinated compounds. Firstly, chlorinated compounds are used as an electron donor and carbon source under aerobic conditions. Secondly, chlorinated compounds are cometabolized under aerobic conditions while the microorganisms are growing (or otherwise already have grown) on another primary substrate. Thirdly, chlorinated compounds are also degraded under anaerobic conditions in which they are utilized as an electron donor and carbon source. Fourthly, chlorinated compounds can serve as an electron acceptor to support respiration of anaerobic microorganisms utilizing simple electron donating substrates. Lastly chlorinated compounds are subject to anaerobic cometabolism becoming biotransformed while the microorganisms grow on other primary substrate or electron acceptor. The literature survey demonstrates that, in many cases, chlorinated compounds are completely mineralised to benign end products. Additionally, biodegradation can occur rapidly. Growth rates exceeding 1 d-1 were observed for many compounds. Most compound categories include chlorinated structures that are used to support microbial growth. Growth can be due to the use of the chlorinated compound as an electron donor or alternatively to the use of the chlorinated compound as an electron acceptor (halorespiration). Biodegradation linked to growth is important, since under such conditions, rates of degradation will increase as the microbial population (biocatalyst) increases. Combinations of redox conditions are favorable for the biodegradation of highly chlorinated structures that are recalcitrant to degradation under aerobic conditions. However, under anaerobic conditions, highly chlorinated structures are partially dehalogenated to lower chlorinated counterparts. The lower chlorinated compounds are subsequently more readily mineralized under aerobic conditions. [ABSTRACT FROM AUTHOR]

The objective of this research is to investigate the intrinsic biodegradation potential of the municipal solid waste (MSW) landfill ecosystem for chlorinated aliphatic hydrocarbons (CAHs). The research was conducted in two complementary systems: simulated landfill bioreactors and batch degradation experiment in serum bottles. Refuse samples excavated from a MSW landfill were tested in laboratory bioreactors operated with leachate recirculation and gas collection. Tetrachloroethene (PCE) and trichloroethene (TCE) were added to reactors and maintained at 20 μM each in leachate to simulate the long-term exposure of refuse microorganisms to CAHs in landfills. Anaerobic microbial cultures were derived from reactors at two different stages of refuse decomposition: active refuse decomposition stage representing young landfills and maturation phase representing aged landfills. These cultures were tested in serum bottles for their abilities to biodegrade target CAHs. Results of this study show that MSW landfills have an intrinsic reductive dechlorination capacity for PCE and TCE. The decomposition of refuse also enhanced reductive dechlorination in this study. This research suggests the potential to develop engineering strategies to promote chlorinated solvent degradation concurrently with refuse decomposition in MSW landfills. [ABSTRACT FROM AUTHOR]

On-line solid phase extraction (SPE) coupled with reversed phase high performance liquid chromatography (PRHPLC-DAD) detection was developed for the determination of tetrachloroethene (PCE), trichloroethylene (TCE), and the metabolites [cis-1,2-dichloroethene (cis-DCE), trans-1,2-dichloroethene (trans-DCE)] in ground waters. The PCE, TCE, and their metabolites were directly concentrated and cleaned-up on the cartridge, and separated by a C18 column with UV at 210 nm. Five sorbents (C8, C18, PLRP-S, PRP-1, and Bond-Elut Env) were evaluated to concentrate these compounds. The recoveries of the compounds were significantly improved by the addition of 10% (v/v) acetonitrile (ACN) to the sample before loading. When a 50 mL sample spiked with 1 µg/L was loaded onto PLRP-S sorbent, the recoveries of the compounds ranged from 66.7% to 104.5%. The determination of these compounds was possible with detection limits less than 0.05 µg/L. The method was compared with a gas chromatography (GC) for the determination of TCE, and good agreement was achieved between both methods. The TCE and its metabolites in ground waters were determined from industrial sites in Salisbury, South Australia to characterize the distribution and assess potential remediation of TCE. [ABSTRACT FROM AUTHOR]