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Anaerobic bioremediation is rarely an effective strategy to treat chlorinated ethenes such as trichloroethene (TCE) in acidic aquifers because partial dechlorination typically results in accumulation of daughter products. Methanotrophs have the capability of oxidizing TCE and other chlorinated volatile organic compounds (CVOCs) to non-toxic products, but their occurrence, diversity, and biodegradation capabilities in acidic environments are largely unknown. This study investigated the impacts of different methane (CH4) concentrations and the presence of CVOCs on the community of acidophilic methanotrophs in microcosms prepared from acidic aquifer samples collected upgradient and downgradient of a mulch barrier installed to promote in-situ anaerobic CVOC biodegradation in Maryland, USA. The ability of indigenous methanotrophs to biodegrade CVOCs was also evaluated. Results of stable isotope probing (SIP) and Next Generation Sequencing (NGS) showed that the microbial communities in the microcosms varied by location and were affected by both CH4 concentration and the presence of different CVOCs, many of which were biodegraded by the indigenous methanotrophs. Data indicate the likelihood of aerobic cometabolic degradation of CVOCs downgradient of the mulch barrier designed for anaerobic treatment. The study extends the overall knowledge of acidophilic methanotrophs in groundwater and shows that these bacteria have significant potential for degrading CVOCs even at low CH4 concentrations. [ABSTRACT FROM AUTHOR]

The application of Monitored Natural Attenuation (MNA) technology has been widespread, while there is a paucity of data on groundwater with multiple co-contaminants. This study focused on high permeability, low hydraulic gradient groundwater with co-contamination of benzene, toluene, ethylbenzene, and xylenes (BTEX), chlorinated aliphatic hydrocarbons (CAHs), and chlorinated aromatic hydrocarbons (CPs). The objective was to investigate the responses of microbial communities during natural attenuation processes. Results revealed greater horizontal variation in groundwater microbial community composition compared to vertical variation. The variation was strongly correlated with the total contaminant quantity (r = 0.722, p < 0.001) rather than individual contaminants. BTEX exerted a more significant influence on community diversity than other contaminants. The assembly of groundwater microbial communities was primarily governed by deterministic processes (βNTI < −2) in high contaminant concentration zones, while stochastic processes (|βNTI| < 2) dominated in low-concentration zones. Moreover, the microbial interactions shifted at different depths indicating the degradation rate variation in the vertical. This study makes fundamental contribution to the understanding for the effects of groundwater flow and material fields on indigenous microbial communities, which will provide a scientific basis for more precise adoption of microbial stimulation/augmentation to accelerate the rate of contaminant removal. [Display omitted] • Groundwater microbial community composition vary more horizontally. • Contaminants concentration correlate more with microbial community than their risk. • BTEX impacts community diversity more than CAHs in multi-contaminated groundwater. • Stochasticity increases progressively with decreasing contamination. • Groundwater microbial interactions vary across different depths. [ABSTRACT FROM AUTHOR]

Significant challenges remain for the remediation of chlorinated-solvent plumes in groundwater, such as trichloroethene (TCE) and tetrachloroethene (PCE). A novel slow-release permanganate gel (SRP-G) technique may show promise for the in-situ treatment (remediation) of chlorinated contaminant plumes in groundwater. A series of laboratory experiments were conducted to characterize the primary physical factors that influence SRP-G gelation processes to optimize SRP-G performance for plume treatment. Specifically, experiments were conducted to quantify gel zeta potential, particle size distribution, and viscosity to determine SRP-G gelation characteristics and processes. These experiments tested various concentrations of two SRP-G amendment solutions (NaMnO 4 and KMnO 4) prepared with 30-wt.% and 50-wt.% colloidal silica to determine such influences on zeta potential, particle size distribution, and viscosity. The results of this study show that SRP-G solutions with low zeta potential and relatively high pH favor more rapid SRP-G gelation. The concomitant interaction of the predominantly negatively charged colloidal silica particles and the positively charged dissociated cations (Na+ and K+) in the SRP-G solution had the effect of stabilizing charge imbalance via attraction of particles and thereby inducing a greater influence on the gelation process. Gel particle size distribution and changes in viscosity had a significant influence on SRP-G solution gelation. The addition of permanganate (NaMnO 4 or KMnO 4) increased the average particle size distribution and the viscosity of the SRP-G solution and decreased the overall gelation time. SRP-G amendments (NaMnO 4 or KMnO 4) prepared with 50-wt.% colloidal silica showed more effective gelation (and reduced gelation time) compared to SRP-G amendments prepared with 30-wt.% colloidal silica. Under the conditions of these experiments, it was determined that both the 7-wt.% NaMnO 4 solution and 90 mg/L KMnO 4 solution using 50-wt.% colloidal silica would be the optimal injection SRP-G solution concentrations for this in-situ treatment technique. [Display omitted] • Slow-release permanganate gel (SRP-G) solution was unstable at low zeta potential and relatively high pH. • Increase in permanganate concentration caused decreasing gelation time for the SRP-G solution. • Gelation time decreased with increases in SRP-G solution viscosity. • SRP-G solution is a promising technique for in-situ chlorinated plume treatment in aquifers. [ABSTRACT FROM AUTHOR]

Per- and poly fluoroalkyl substances (PFASs) are often encountered with nonaqueous phase liquid (NAPL) in the groundwater at fire-fighting and military training sites. However, it is unclear how PFASs affect the dechlorination performance of sulfidized nanoscale zerovalent iron (S-nFe 0 ), which is an emerging promising NAPL remediation agent. Here, S-nFe 0 synthesized with controllable S speciation (FeS or FeS 2 ) were characterized to assess their interactions with PFASs and their dechlorination performance for trichloroethylene NAPL (TCE-NAPL). Surface-adsorbed PFASs blocked materials' reactive sites and inhibited aqueous TCE dechlorination. In contrast, PFASs-adsorbed particles with improved hydrophobicity tended to enrich at the NAPL-water interface, and the reactive sites were re-exposed after the PFASs accumulation into the NAPL phase to accelerate dechlorination. This PFASs-induced phenomenon allowed the materials to present a higher reactivity (up to 1.8-fold) with a high electron efficiency (up to 99%) for TCE-NAPL dechlorination. Moreover, nFe 0 -FeS 2 with a higher hydrophobicity was more readily enriched at the NAPL-water interface and more reactive and selective than nFe 0 -FeS, regardless of coexisting PFASs. These results unveil that a small amount of yet previously overlooked coexisting PFASs can favor selective reductions of TCE-NAPL by S-nFe 0 , highlighting the importance of materials hydrophobicity and transportation induced by S and PFASs for NAPL remediation.

OBJECTIVES: The etiology of male breast cancer (MBC) is largely unknown but a causal role of exposure to organic solvents has been suggested. Previous studies on occupational risk factors of breast cancer were often restricted to women who are frequently exposed to lower levels and at a lower frequency than men. We investigated the association between MBC and occupational exposure to petroleum and oxygenated and chlorinated solvents in a multicenter case-control study of rare cancers in Europe. METHODS: The study included 104 MBC cases and 1901 controls. Detailed lifetime work history was obtained during interviews, together with sociodemographic characteristics, medical history and lifestyle factors. Occupational exposures to solvents were estimated from a job-exposure matrix. Odds ratios (OR) and their 95% confidence intervals (CI) were calculated using unconditional logistic regression models. RESULTS: Lifetime cumulative exposure to trichloroethylene >23.9 ppm years was associated with an increased MBC risk, compared to non-exposure [OR (95% CI): 2.1 (1.2–4.0); P trend

OBJECTIVES: This study investigated the associations between occupational exposures to solvents and metals and fixed airflow obstruction (AO) using post-bronchodilator spirometry. METHODS: We included 1335 participants from the 2002–2008 follow-up of the Tasmanian Longitudinal Health Study. Ever-exposure and cumulative exposure-unit (EU) years were calculated using the ALOHA plus job exposure matrix (JEM). Fixed AO was defined as post-bronchodilator forced expiratory volume in one second (FEV1)/forced vital capacity (FVC)

Abstract Biodegradation of 1,4-dioxane was examined in packed quartz and soil column flow-through systems. The inhibitory effects of co-contaminants, specifically trichloroethene (TCE), 1,1-dichloroethene (1,1-DCE), and copper (Cu2+) ions, were investigated in the columns either with or without bioaugmentation with a 1,4-dioxane degrading bacterium Pseudonocardia dioxanivorans CB1190. Results indicate that CB1190 cells readily grew and colonized in the columns, leading to significant degradation of 1,4-dioxane under oxic conditions. Degradation of 1,4-dioxane was also observed in the native soil (without bioaugmentation), which had been previously subjected to enhanced reductive dechlorination treatment for co-contaminants TCE and 1,1-DCE. Bioaugmentation of the soil with CB1190 resulted in nearly complete degradation at influent concentrations of 3–10 mg L−1 1,4-dioxane and a residence reaction time of 40–80 h, but the presence of co-contaminants, 1,1-DCE and Cu2+ ions (up to 10 mg L−1), partially inhibited 1,4-dioxane degradation in the untreated and bioaugmented soil columns. However, the inhibitory effects were much less severe in the column flow-through systems than those previously observed in planktonic cultures, which showed near complete inhibition at the same co-contaminant concentrations. These observations demonstrate a low susceptibility of soil microbes to the toxicity of 1,1-DCE and Cu2+ in packed soil flow-through systems, and thus have important implications for predicting biodegradation potential and developing sustainable, cost-effective technologies for in situ remediation of 1,4-dioxane contaminated soils and groundwater. Graphical abstract Image 1 Highlights • Biodegradation of 1,4-dioxane was examined in packed column flow-through systems. • Degradation of 1,4-dioxane is inhibited by co-contaminants 1,1-DCE and Cu2+. • Inhibitory effects of co-contaminants are much less severe in the column than in planktonic systems. • Bioaugmentation with Pseudonocardia dioxanivorans CB1190 is effective in degrading 1,4-dioxane in the soil column. [ABSTRACT FROM AUTHOR]

Solvent alleged that chlorinated benzene contamination detected in Solvent's offsite groundwater recovery wells was 98% due to releases from the neighboring Olin chlorobenzene production facility and only 2% due to Solvent's nearby chlorinated benzene production facility. However, Solvent's position was complicated by the fact that it had acknowledged that its operations had impacted site contamination levels. Solvent's position was that the onsite contamination was partially due to Olin, but it faced an uphill struggle because the New York State Department of Environmental Conservation (NYSDEC) had assigned Solvent responsibility for the Hot Spot cleanup at the Olin site. However, Solvent was able to recover virtually the entire amount of its Hot Spot costs attributable to chlorinated benzenes from Olin, as well as the full percentage of allocation they requested from Olin for the Solvent site through the useof chemical tracers such as benzene hexachloride (BHC). [ABSTRACT FROM AUTHOR]

Objectives The etiology of male breast cancer (MBC) is largely unknown but a causal role of exposure to organic solvents has been suggested. Previous studies on occupational risk factors of breast cancer were often restricted to women who are frequently exposed to lower levels and at a lower frequency than men. We investigated the association between MBC and occupational exposure to petroleum and oxygenated and chlorinated solvents in a multicenter case-control study of rare cancers in Europe. Methods The study included 104 MBC cases and 1901 controls. Detailed lifetime work history was obtained during interviews, together with sociodemographic characteristics, medical history and lifestyle factors. Occupational exposures to solvents were estimated from a job-exposure matrix. Odds ratios (OR) and their 95% confidence intervals (CI) were calculated using unconditional logistic regression models. Results Lifetime cumulative exposure to trichloroethylene >23.9 ppm years was associated with an increased MBC risk, compared to non-exposure [OR (95% CI): 2.1 (1.2-4.0), P trend <0.01). This increase in risk persisted when only exposures that occurred ≥10 years before diagnosis were considered. In addition, a possible role for benzene and ethylene glycol in MBC risk was suggested, but no exposure-response trend was observed. Conclusions These findings add to the evidence of an increased risk of breast cancer among men professionally exposed to trichloroethylene and possibly to benzene or ethylene glycol. Further studies should be conducted in populations with high level of exposure to confirm our results. [ABSTRACT FROM AUTHOR]

Objectives This study investigated the associations between occupational exposures to solvents and metals and fixed airflow obstruction (AO) using post-bronchodilator spirometry. Methods We included 1335 participants from the 2002-2008 follow-up of the Tasmanian Longitudinal Health Study. Ever-exposure and cumulative exposure-unit (EU) years were calculated using the ALOHA plus job exposure matrix (JEM). Fixed AO was defined as post-bronchodilator forced expiratory volume in one second (FEV1)/forced vital capacity (FVC) <0.7 and FEV1/FVCLCO) was combined with FEV1/FVC<0.7 to define fixed AO plus low DLCO. Multinomial regressions were used to estimate associations adjusting for possible confounders. Results Ever-exposure to metals was associated with fixed AO [relative risk (RR) 1.71, 95% CI 1.03-2.85] and fixed AO lower limit of normal (RR 1.67, 95% CI 1.00-2.78). Women had lower cumulative EU years to chlorinated solvents [mean 20.9, standard deviation (SD) 13.4] than men (mean 28.6, SD 36.9). However, the risk of developing fixed AO and fixed AO plus low DLCO associated with each cumulative EU year of chlorinated solvents were higher among women than men (RR 1.08 versus 0.99, P-value for effect measure modification=0.006; RR 1.08 versus 1.00, P-value for effect measure modification=0.02). Conclusions We have shown ever-exposure to metals and chlorinated solvents are important risk factors for fixed AO. The effects for solvents were strongest among women. Preventive strategies need to be followed to reduce these exposures at the workplace. [ABSTRACT FROM AUTHOR]

Characterization of dense non-aqueous phase liquid (DNAPL) source zones in limestone aquifers/bedrock is essential to develop accurate site-specific conceptual models and perform risk assessment. Here innovative field methods were combined to improve determination of source zone architecture, hydrogeology and contaminant distribution. The FACT™ is a new technology and it was applied and tested at a contaminated site with a limestone aquifer, together with a number of existing methods including wire-line coring with core subsampling, FLUTe® transmissivity profiling and multilevel water sampling. Laboratory sorption studies were combined with a model of contaminant uptake on the FACT™ for data interpretation. Limestone aquifers were found particularly difficult to sample with existing methods because of core loss, particularly from soft zones in contact with chert beds. Water FLUTe™ multilevel groundwater sampling (under two flow conditions) and FACT™ sampling and analysis combined with FLUTe® transmissivity profiling and modeling were used to provide a line of evidence for the presence of DNAPL, dissolved and sorbed phase contamination in the limestone fractures and matrix. The combined methods were able to provide detailed vertical profiles of DNAPL and contaminant distributions, water flows and fracture zones in the aquifer and are therefore a powerful tool for site investigation. For the limestone aquifer the results indicate horizontal spreading in the upper crushed zone, vertical migration through fractures in the bryozoan limestone down to about 16–18 m depth with some horizontal migrations along horizontal fractures within the limestone. Documentation of the DNAPL source in the limestone aquifer was significantly improved by the use of FACT™ and Water FLUTe™ data. [ABSTRACT FROM AUTHOR]

A permeable reactive barrier, consisting of both zero valent iron (ZVI) and a biodegradable organic carbon, was evaluated for the remediation of 1,1,2-trichloroethane (1,1,2-TCA) contaminated groundwater. During an 888 day laboratory column study, degradation rates initially stabilized with a degradation half-life of 4.4 ± 0.4 days. Based on the accumulation of vinyl chloride (VC) and limited production of 1,1-dichloroethene (1,1-DCE) and 1,2-dichloroethane (1,2-DCA), the dominant degradation pathway was likely abiotic dichloroelimination to form VC. Degradation of VC was not observed based on the accumulation of VC and limited ethene production. After a step reduction in the influent concentration of 1,1,2-TCA from 170 ± 20 mg L − 1 to 39 ± 11 mg L − 1 , the degradation half-life decreased 5-fold to 0.83 ± 0.17 days. The isotopic enrichment factor of 1,1,2-TCA also changed after the step reduction from − 14.6 ± 0.7‰ to − 0.72 ± 0.12‰, suggesting a possible change in the degradation mechanism from abiotic reductive degradation to biodegradation. Microbiological data suggested a co-culture of Desulfitobacterium and Dehalococcoides was responsible for the biodegradation of 1,1,2-TCA to ethene. [ABSTRACT FROM AUTHOR]

The analysis of crude oil using laser-based analytical techniques such as laser-induced breakdown spectroscopy (LIBS) has become of great interest to various specialists in different fields such as geology, petro-chemistry and environmental science. In this work, a detailed study is presented wherein the implementation of an efficient and simple LIBS technique to identify the elemental constituents of crude oil and to distinguish between different grades of petroleum crude oil is discussed. Laser-induced plasma (LIP) technique has been used in this work for direct measurements of atomic, ionic and molecular species in dry crude oil samples with API gravities ranging between 18 and 36. The technique was implemented using the first harmonic of a pulsed Nd-YAG laser source. Atomic and molecular emission bands were observed, consisting of characteristic spectral lines of atoms and diatomic molecular bands, namely from C, H, Si, Na, Ca, Mg, AL, Fe, Ti, Mo, C 2 and CN. The intensities of high-resolution spectral lines for some atoms and molecules of elements such as Ca, Na, Fe, Mo, C 2 and CN were evaluated at different wavelengths along the obtained spectra. The molecular bands and the elemental spectral lines were used to assess the possibility of adopting the LIBS technique in differentiating between crude oil samples with different American Petroleum Institute (API) gravity values. The results indicate the presence of a distinct correlation between the API gravity values of the various oil samples and the spectral line intensities of the elements and some molecular radical constituents. In addition, the possibility of identifying the API gravity values of unknown oil samples is also indicated. [ABSTRACT FROM AUTHOR]

Microbial bioelectrochemical systems, which use solid-state cathodes to drive the reductive degradation of contaminants such as the chlorinated hydrocarbons, are recently attracting considerable attention for bioremediation applications. So far, most of the published research has focused on analyzing the influence of key (bio)electrochemical factors influencing contaminant degradation, such as the cathode potential, whereas only few studies have examined the potential impact of mass transport phenomena on process performance. Here we analyzed the performance of a flow-through bioelectrochemical reactor, continuously fed with a synthetic groundwater containing trichloroethene at three different linear fluid velocities (from 0.3 m d −1 to 1.7 m d −1 ) and three different set cathode potentials (from −250 mV to −450 mV vs. the standard hydrogen electrode). The obtained results demonstrated that, in the range of fluid velocities which are characteristics for natural groundwater systems, mass transport phenomena may strongly influence the rate and extent of reductive dechlorination. Nonetheless, the relative importance of mass transport largely depends on the applied cathode potential which, in turn, controls the intrinsic kinetics of biological reactions and the underlying electron transfer mechanisms. [ABSTRACT FROM AUTHOR]

The production of chlorinated solvents such as tetrachloroethylene and tetrachloromethane has resulted in large stockpiles of unintentionally produced persistent organic pollutants (POPs) including high content of hexachlorobenzene (HCB waste). HCB waste of 15,000 t arising from the production of chlorinated solvents at the Kalush factory in Ukraine was landfilled. In 2008, it was discovered that HCB and other pollutants were escaping from the landfill into local environment including the Sapogi-Limnytsia Rivers, tributaries of the Dniester River. This showed that the HCB waste was not appropriately contained and represented a threat to the Dniester River basin. A Presidential Decree of Ukraine was therefore issued requiring remediation of the site and excavation of the waste. Between 2010 and 2013, approximately 29,445 t of HCB waste and associated contaminated soil was excavated and exported to various EU countries for incineration. This excavation revealed that these wastes can corrode through their drums within a few decades with release of pollutants. Other sites at which chlorinated solvents were produced should therefore be assessed for possible similar pollution. Despite the remediation efforts and the excavation of the landfill, the Kalush area remains a POP-contaminated site requiring further assessment. A part of the waste was exported to Poland and is stored close to the Baltic Sea and is treated in an incinerator with small capacity over a time frame of years. This case and recent similar cases reveal that the control of POP waste for destruction even in EU countries needs to be improved. [ABSTRACT FROM AUTHOR]

A binary catalytic system, siderite-catalyzed hydrogen peroxide (H 2 O 2 ) coupled with persulfate (S 2 O 8 2− ), was investigated for the remediation of trichloroethene (TCE) contamination. Batch experiments were conducted to investigate reaction mechanisms, oxidant decomposition rates, and degradation products. By using high performance liquid chromatography (HPLC) coupled with electron paramagnetic resonance (EPR), we identified four radicals (hydroxyl (HO ), sulfate (SO 4 − ), hydroperoxyl (HO 2 ), and superoxide (O 2 − )) in the siderite-catalyzed H 2 O 2 –S 2 O 8 2− system. In the absence of S 2 O 8 2− (i.e., siderite-catalyzed H 2 O 2 ), a majority of H 2 O 2 was decomposed in the first hour of the experiment, resulting in the waste of HO . The addition of S 2 O 8 2− moderated the H 2 O 2 decomposition rate, producing a more sustainable release of hydroxyl radicals that improved the treatment efficiency. Furthermore, the heat released by H 2 O 2 decomposition accelerated the activation of S 2 O 8 2− , and the resultant SO 4 − was the primary oxidative agent during the first two hours of the reaction. Dichloroacetic acid was for the first time detected as a degradation product. The results of this study indicate a new insight to the reaction mechanism for the catalytic binary H 2 O 2 –S 2 O 8 2− oxidant system, and the delineation of radicals and the discovery of the chlorinated byproduct provide useful information for efficient treatment of chlorinated-solvent contamination in groundwater. [ABSTRACT FROM AUTHOR]

The presence of trichloroethylene (TCE) dense non-aqueous phase liquid (DNAPL) in the subsurface can generate a dissolved phase plume in groundwater. This study developed an alkaline activated sodium persulfate (SPS) sustained release oxidation rod (alkaline SPS SR-Rod) for long-term in situ chemical oxidation accelerated treatment of TCE dissolved from TCE DNAPL, by creating a greater concentration gradient at the TCE DNPL boundary. The dissolution of TCE DNAPL (1 mL) in water (280 mL) generated ~700 mg L−1, with a volumetric mass transfer coefficient (k L a) of 0.0187 d−1. The alkaline SPS SR-Rod system had a k L a of 0.013 d−1 for TCE dissolution at early stage, and thereafter aqueous TCE concentration remained below ~10 mg L−1 over 60 d of reaction. An SPS SR-Rod life-span of 186 d, for 90% of SPS released from the rod, was estimated. In the soil-water system, aqueous TCE was maintained < 3 mg L− 1 throughout the reaction and the soil oxidant demand was determined to be ~4 g-SPS/kg-soil in the alkaline SPS SR-Rod system. These results revealed that the use of the alkaline SPS SR-Rod can be effective as a method of treating dissolved TCE released from DNAPL contamination, and thereby accelerating TCE DNAPL removal. [Display omitted] • An alkaline activated sodium persulfate (SPS) sustained-release rod was prepared. • The rod was formulated with a SPS/paraffin wax/NaOH at a weight ratio of 6/1/1. • The rod was effective in treating aqueous TCE released from TCE DNAPL. • The life-span of the rod was estimated to be 186 d, with 90% of SPS released. • The soil oxidant demand was ~4 g-SPS/kg-soil in the soil-water system. [ABSTRACT FROM AUTHOR]

Aquitards contaminated by chlorinated solvents may act as a secondary source slowly releasing contaminants into adjacent aquifers, thus severely hampering the remediation of groundwater systems. Accurate predicting the long-term exchange of solvents between aquifers and aquitards can more effectively guide site management and remediation. This study presented a general analytical model for the back-diffusion of chlorinated solvents through multilayer aquitards. This model considers the slow advection and local degradation of dissolved constituents in natural aquitards and the dynamic depletion of dense nonaqueous phase liquid (DNAPL) source zone in aquifers. Transient solutions for the proposed multilayer model were derived using Duhamel's Theorem, the separation of variables method, and the transfer matrix method, verified against experimental and numerical concentration data. Results reveal that advection in aquitards can significantly shorten the trailing time of chlorinated solvent plumes, and highly adsorptive soils may reduce this effect in layered aquitards. The previous no-degradation model is no longer applicable to predict the back-diffusion behavior of chlorinated solvents when the extent and rate of solvent degradation are large, giving a "strong-effect zone". Based on numerous example simulations and data fitting, the forecast functions for the back-diffusion onset time and plume trailing time were proposed, greatly facilitating remediation decisions and risk assessment of chlorinated-solvent contaminated sites. [Display omitted] • Analytical solutions for chlorinated solvent migration in heterogeneous aquitards. • Role of slow advection and local degradation in back-diffusion behaviors. • Forecast functions for the back-diffusion onset time and plume trailing time. • Some advice for management and remediation of the DNAPL-contaminated site. [ABSTRACT FROM AUTHOR]

• Analytical model considering remediation of both NAPL source and downgradient contaminant plume. • Contaminant-dependent retardation factors for contaminant and degradation byproduct. • Effects of contaminant-dependent retardation factors on plume migration are investigated. • Developed model is applied to illustrate the effectiveness of various remedial efforts. The contamination of groundwater aquifers by chlorinated solvents is a water-resource issue of great importance worldwide. Such contaminants are difficult to treat because they are often released as dense non-aqueous phase liquids (DNAPLs). Research shows that the application of remediation technologies to both the NAPL source and dissolved plume can lead to more efficient remediation, rather than to either alone. In these remediation efforts, analytical models that evaluate behavior and fate of contaminants do provide a better understanding of the performance of these remedial technologies. To the best of our knowledge, there exist no analytical model of simulating the plume migration of multiple contaminants with capabilities of accounting for both NAPL source and plume remediation simultaneously and different retardation for original chlorinated solvent contaminant and its degradation byproducts. In this study, we present a new analytical model for remediating both NAPL source and downgradient contaminant plume in groundwater at sites contaminated with chlorinated solvents and their degradation products with different retardation factors as well as considering both NAPL source and plume remediation simultaneously. A source model that accounts for the depletion of mass by the processes of dissolution or first-order decay reactions, corresponding with the removal or destruction of the source mass, is coupled to a plume reactive transport model. The source model is accounted for by relating source mass to the flux-averaged source discharge concentration through a power function. The developed analytical model considers 1-D advection, 3-D dispersion, first-order decay reactions and ingrowth as well as linear isothermal equilibrium sorption. The proposed analytical solution was derived through successive application of the Laplace transform in time and the double finite Fourier cosine transform regarding y and z. The correctness of the analytical model and its auxiliary FORTRAN computer program code are proved by showing excellent agreements between the simulated plume concentrations of all contaminants obtained from the derived analytical model and from a semi-analytical model available in the literature. Application of the proposed analytical solutions illustrates that the use of identical retardation factors for all contaminants may lead to underestimation or overestimation of the mobility of the contaminants, in cases when the retardation factors of the individual contaminants are greatly different from the identical retardation factor value adopted in all contaminants. From the experiments on six scenarios corresponding six remedial treatments, we found out that both the enhanced source decay and partial removal of source mass are main controlling factors at reducing the concentrations of all the contaminants, whereas plume decay leads to effective reduction in the concentrations of PCE, however, rather it causes unfavorable increases of the concentrations of the degradation byproducts. Ultimately, the developed model is used to better understand the impacts of various possible combinations of remedial efforts and management decisions on remediation of the subsurface contamination and quantify the benefit of a certain remediation decision. [ABSTRACT FROM AUTHOR]

A novel approach to compound-specific stable chlorine isotope analysis is presented to overcome many of the major drawbacks of existing methods. Contemporary methods often require either several laborious off-line procedures prior to isotope analysis or complicated mathematical data calculations and evaluation schemes to derive the chlorine isotope ratios from the mass spectra. In contrast to previous methods, our on-line setup was based on the use of gas chromatography-negative chemical ionization mass spectrometry. The ion traces of35Cl−(m/z 35) and37Cl−(m/z 37) were recorded to directly determine the isotopic ratios of chlorine. The chlorine fragments were obtained from each specific chlorinated compound using the appropriate energy and an optimized acquisition mode, and the method completely avoided isobaric interferences. The principle and the mechanism of this approach were presented and explained using trichloroethene. Optimization of the gas chromatography-negative chemical ionization mass spectrometry parameters and method validation were achieved using chlorinated alkenes, chlorinated benzenes, and organochlorine pesticides. The sensitivity of the method over previous methods was significantly improved, and the ultra-trace injection amounts of 0.4–473.5 pmol resulted in standard deviations (1σ) ranging from 0.55‰–2.15‰. The present study suggested that the gas chromatography-negative chemical ionization mass spectrometry method offered an innovative approach to compound-specific chlorine isotope analysis, and it could facilitate the application of compound-specific stable chlorine isotope analysis in environmental fields. [ABSTRACT FROM PUBLISHER]

A sustainable in-well vapor stripping system is designed as a cost-effective alternative for remediation of shallow chlorinated solvent groundwater plumes. A solar-powered air compressor is used to inject air bubbles into a monitoring well to strip volatile organic compounds from a liquid to vapor phase while simultaneously inducing groundwater circulation around the well screen. An analytical model of the remediation process is developed to estimate contaminant mass flow and removal rates. The model was calibrated based on a one-day pilot study conducted in an existing monitoring well at a former dry cleaning site. According to the model, induced groundwater circulation at the study site increased the contaminant mass flow rate into the well by approximately two orders of magnitude relative to ambient conditions. Modeled estimates for 5 h of pulsed air injection per day at the pilot study site indicated that the average effluent concentrations of dissolved tetrachloroethylene and trichloroethylene can be reduced by over 90% relative to the ambient concentrations. The results indicate that the system could be used cost-effectively as either a single- or multi-well point technology to substantially reduce the mass of dissolved chlorinated solvents in groundwater. [ABSTRACT FROM AUTHOR]

A detailed field-scale investigation of processes controlling the architecture, persistence and dissolution of a 20 to 45 year old trichloroethene (TCE) dense non-aqueous phase liquid (DNAPL) source zone located within a heterogeneous sand/gravel aquifer at a UK industrial site is presented. The source zone was partially enclosed by a 3-sided cell that allowed detailed longitudinal/fence transect monitoring along/across a controlled streamtube of flow induced by an extraction well positioned at the cell closed end. Integrated analysis of high-resolution DNAPL saturation ( S n ) (from cores), dissolved-phase plume concentration (from multilevel samplers), tracer test and permeability datasets was undertaken. DNAPL architecture was determined from soil concentration data using partitioning calculations. DNAPL threshold soil concentrations and low S n values calculated were sensitive to sorption assumptions. An outcome of this was the uncertainty in demarcation of secondary source zone diffused and sorbed mass that is distinct from trace amounts of low S n DNAPL mass. The majority of source mass occurred within discrete lenses or pools of DNAPL associated with low permeability geological units. High residual saturation ( S n > 10–20%) and pools ( S n > 20%) together accounted for almost 40% of the DNAPL mass, but only 3% of the sampled source volume. High-saturation DNAPL lenses/pools were supported by lower permeability layers, but with DNAPL still primarily present within slightly more permeable overlying units. These lenses/pools exhibited approximately linearly declining S n profiles with increasing elevation ascribed to preferential dissolution of the uppermost DNAPL. Bi-component partitioning calculations on soil samples confirmed that the dechlorination product cDCE (cis-dichloroethene) was accumulating in the TCE DNAPL. Estimated cDCE mole fractions in the DNAPL increased towards the DNAPL interface with the uppermost mole fraction of 0.04 comparable to literature laboratory data. DNAPL dissolution yielded heterogeneous dissolved-phase plumes of TCE and its dechlorination products that exhibited orders of magnitude local concentration variation. TCE solubility concentrations were relatively localised, but coincident with high saturation DNAPL lens source areas. Biotic dechlorination in the source zone area, however, caused cDCE to be the dominant dissolved-phase plume. The conservative tracer test usefully confirmed the continuity of a permeable gravel unit at depth through the source zone. Although this unit offered significant opportunity for DNAPL bypassing and decreased timeframes for dechlorination, it still transmitted a significant proportion of the contaminant flux. This was attributed to dissolution of DNAPL–mudstone aquitard associated sources at the base of the continuous gravel as well as contaminated groundwater from surrounding less permeable sand and gravel horizons draining into this permeable conduit. The cell extraction well provided an integrated metric of source zone dissolution yielding a mean concentration of around 45% TCE solubility (taking into account dechlorination) that was equivalent to a DNAPL mass removal rate of 0.4 tonnes per annum over a 16 m 2 cell cross sectional area of flow. This is a significant flux considering the source age and observed occurrence of much of the source mass within discrete lenses/pools. We advocate the need for further detailed field-scale studies on old DNAPL source zones that better resolve persistent pool/lens features and are of prolonged duration to assess the ageing of source zones. Such studies would further underpin the application of more surgical remediation technologies. [ABSTRACT FROM AUTHOR]

Dechlorination reaction of 1,3-dichloropropane, a contaminant solvent, was investigated by electrochemical reduction in aqueous medium using a Ni(tmc)Br2complex, known as effective catalyst in dehalogenation reactions. The catalytic activity of the complex was first investigated by cyclic voltammetry and flow homogeneous redox catalysis using a graphite felt as working electrode. A total degradation of 1,3-dichloropropane was obtained after 5h of electrolysis with a substrate/catalyst ratio of 2.3. The concentration of chloride ions determined by ion chromatography analysis showed a dechlorination yield of 98%. The complex was then immobilized on the graphite felt electrode in a Nafion®film. Flow heterogeneous catalytic reduction of 1,3-dichloropropane was then carried out with the [Ni(tmc)]Br2-modified Nafion®electrode. GC analyses underlined the total degradation of the substrate in only 3.5h with a substrate/catalyst ratio of 100. A dechlorination yield of 80% was obtained, as seen with ion chromatography analyses of chloride ion. Comparison of both homogeneous and heterogeneous reactions highlighted the interest of the [Ni(tmc)]Br2-modified Nafion®electrode that led to a higher stability of the catalyst with a turnover number of 180 and a higher current efficiency. [ABSTRACT FROM AUTHOR]

Background Exposure to dichloromethane (DCM or methylene chloride - CH2Cl2) in paint strippers continues to be an avoidable source of morbidity and mortality. DCM has been under regulatory scrutiny by occupational and consumer product agencies since the identification of its carcinogenicity in the mid-1980s. Methods We investigated two independent workplace incidents that resulted in three cases of DCM intoxication from paint stripper use. Results Each incident investigated resulted in a fatality. A third worker suffered obtundation requiring hospitalization and intubation. Conclusions The continued occurrence of fatalities and other serious injuries due to DCM-containing paint strippers in the United States calls for a re-evaluation of existing regulatory strategies. Am. J. Ind. Med. 56:907-910, 2013. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

A laboratory-scale study with a sand column was designed to simulate trichloroethylene (TCE) pollution in the aquifer environment with three-section controlled-release potassium permanganate (CRP) barriers. The main objective of this study was to evaluate the feasibility of CRP barriers in remediation of TCE in aquifers in a long-term and controlled manner. CRP particles with a 1:3 molar ratio of KMnO4 to steadric acid showed the best controlled-release properties in pure water, and the theoretical release time was 138.5 days. The results of TCE removal in the test column indicated that complete removal efficiency of TCE in a sand column by three-section CRP barriers could be reached within 15 days. The molar ratio of KMnO4 to TCE in the three-section CRP barriers was 16:1, which was much lower than 82:1 as required when KMnO4 solution is used directly to achieve complete destruction of TCE. This result revealed that the efficiency of CRP for remediation of TCE was highly improved after encapsulation. [ABSTRACT FROM AUTHOR]

The cytotoxic effects of 4 industrially important chlorinated organic solvents, dichloromethane (DCM), 1,2-dichloroethane (DCE), trichloroethylene (TCE), and tetrachloroethylene (PERC) in vitro, were investigated. Jurkat T cells were exposed to the solvents individually for 72 hours and changes in reactive oxygen species (ROS) formation, cell proliferation, intracellular free calcium concentration ([Ca2+]), and caspase-3 activity were measured. There was a concentration-dependent increase in the ROS formation and intracellular free [Ca2+] following exposure to each of the solvents. This was accompanied by a decrease in the cell proliferation. Solvent potency decreased in the following order: PERC > TCE > DCM > DCE. Caspase-3 activity was increased in a concentration-dependent manner by TCE and PERC but was not significantly altered by DCM or DCE. n-Acetyl-l-cysteine pretreatment showed that changes in the intracellular free [Ca2+] and caspase-3 activity were independent of ROS formation. However, increased ROS formation did play a causal role in the decreased cell proliferation observed. [ABSTRACT FROM AUTHOR]

Chlorinated solvents are the most prevalent organic contaminants in groundwater because of their extensive and widespread use as cleaning agents and metal degreasers, and they have become a significant threat to groundwater supplies. Groundwater contamination by chlorinated solvents has proven difficult and costly to remedy because of the physicochemical properties of the solvents. This study was conducted to examine the effectiveness of treating contaminated groundwater containing chlorinated solvents using air stripping, advanced oxidation, and activated carbon adsorption processes. The results showed that the stripping instrument could effectively transfer chlorinated solvents into the gas phase within several minutes at an airflow rate of and a temperature of 298 K. The residual chlorinated solvents were further oxidized into harmless by-products by the subsequent process, and the off-gas generated from the previously-mentioned processes were collected and absorbed by four types of activated carbon [i.e., Shanghai coconut, Shanghai fruit, Taixi coal () and Taixi ZJ-15 (cylinder)]. Shanghai coconut exhibited the greatest adsorption capacity, at . Two types of contaminated groundwater containing chlorinated solvents from contaminated sites were successfully treated by the coupled process at bench scale with the effluent concentrations of chlorinated solvents complying with the target values standard for groundwater regulated by the Dutch Ministry of Public Housing. Overall, the study found that the proposed coupled process is a viable method for efficiently and effectively remediating shallow contaminated groundwater containing chlorinated solvents in southern China. [ABSTRACT FROM AUTHOR]

This work focuses on chloroform (CF) cometabolism by a butane-grown aerobic pure culture ( Rhodococcus aetherovorans BCP1) in continuous-flow biofilm reactors. The goals were to obtain preliminary information on the feasibility of CF biodegradation by BCP1 in biofilm reactors and to evaluate the applicability of the pulsed injection of growth substrate and oxygen to biofilm reactors. The attached-cell tests were initially conducted in a 0.165-L bioreactor and, then, scaled-up to a 1.772-L bioreactor. Glass cylinders were utilized as biofilm carriers. The continuous supply of growth substrate (butane), which led to the attainment of the highest CF degradation rate (8.4 mg day m), was compared with four schedules of butane and oxygen pulsed feeding. The pulsed injection technique allowed the attainment of a ratio of CF mass degraded per unit mass of butane supplied equal to 0.16 mg mg, a value 4.4 times higher than that obtained with the continuous substrate supply. A procedure based on the utilization of integral mass balances and of average concentrations along the bioreactors resulted in a satisfactory match between the predicted and the experimental CF degradation performances, and can therefore be utilized to provide a guideline for optimizing the substrate pulsed injection schedule. [ABSTRACT FROM AUTHOR]

Abstract: The long-term impact of source-zone remediation efforts was assessed for a large site contaminated by trichloroethene. The impact of the remediation efforts (soil vapor extraction and in-situ chemical oxidation) was assessed through analysis of plume-scale contaminant mass discharge, which was measured using a high-resolution data set obtained from 23years of operation of a large pump-and-treat system. The initial contaminant mass discharge peaked at approximately 7kg/d, and then declined to approximately 2kg/d. This latter value was sustained for several years prior to the initiation of source-zone remediation efforts. The contaminant mass discharge in 2010, measured several years after completion of the two source-zone remediation actions, was approximately 0.2kg/d, which is ten times lower than the value prior to source-zone remediation. The time-continuous contaminant mass discharge data can be used to evaluate the impact of the source-zone remediation efforts on reducing the time required to operate the pump-and-treat system, and to estimate the cost savings associated with the decreased operational period. While significant reductions have been achieved, it is evident that the remediation efforts have not completely eliminated contaminant mass discharge and associated risk. Remaining contaminant mass contributing to the current mass discharge is hypothesized to comprise poorly accessible mass in the source zones, as well as aqueous (and sorbed) mass present in the extensive lower-permeability units located within and adjacent to the contaminant plume. The fate of these sources is an issue of critical import to the remediation of chlorinated-solvent contaminated sites, and development of methods to address these sources will be required to achieve successful long-term management of such sites and to ultimately transition them to closure. [Copyright &y& Elsevier]

Abstract: The coupling adsorption and degradation of trichloroethylene (TCE) through dechlorination using synthetic granular activated carbon and zerovalent iron (GAC–ZVI) composites was studied. The GAC–ZVI composites were prepared from aqueous Fe2+ solutions by impregnation with and without the use of a PEG dispersant and then heated at 105°C or 700°C under a stream of N2. Pseudo-first-order rate constant data on the removal of TCE demonstrates that the adsorption kinetics of GAC is similar to those of GAC–ZVI composites. However, the usage of GAC–ZVI composites liberated a greater amount of Cl than when ZVI was used alone. The highest degree of reductive dechlorination of TCE was achieved using a GAC–ZVI700P composite (synthesized using PEG under 700°C). A modified Langmuir–Hinshelwood rate law was employed to depict the behavior of Cl liberation. As a result, a zero-order Cl liberation reaction was observed and the desorption limited TCE degradation rate constant decreased as the composite dosage was increased. The GAC–ZVI composites can be employed as a reactive GAC that is not subject to the limitations of using GAC and ZVI separately. [Copyright &y& Elsevier]

Abstract: The effectiveness of permanganate for in situ chemical oxidation of organic liquid (trichloroethene) trapped in lower-permeability (K) zones located within a higher-permeability matrix was examined in a series of flow-cell experiments. The permanganate solution was applied in both continuous and pulsed-injection modes. Manganese-oxide precipitation, as confirmed by use of SEM-EDS, occurred within, adjacent to, and downgradient of the lower-K zones, reflective of trichloroethene oxidation. During flow interruptions, precipitate formed within the surrounding higher-permeability matrix, indicating diffusive flux of aqueous-phase trichloroethene from the lower-K zones. The impact of permanganate treatment on mass flux behavior was examined by conducting water floods after permanganate injection. The results were compared to those of water-flood control experiments. The amount of water flushing required for complete contaminant mass removal was reduced for all permanganate treatments for which complete removal was characterized. However, the nature of the mass-flux-reduction/mass-removal relationship observed during water flooding varied as a function of the specific permanganate treatment. [ABSTRACT FROM AUTHOR]

Oxygen used for flight crews and for extra-hospital therapies is kept in vacuum containers and maintained as liquid phase (LOX) until use; by using this procedure, the weight of the breathing apparatus is reduced, thus extending breathing oxygen availability and improving safety by using atmosphere pressure sampler. On the other hand, because of its low boiling point (-183°C), during storage and distribution, LOX shows continuous evaporation with a constant increase in pollutant concentration obtained in the LOX production. Therefore, LOX is subjected to a strict quality control to evaluate the contamination levels from production until its use. In this study, an analytical procedure has been optimised to measure the main LOX contaminants (freon, chlorinated solvents, light hydrocarbons, CO2, CO, and N2O) based on a single technique (GC-MS) and two chromatographic columns (Poraplot Q/HT and HP-Plot molecular sieve 5 A). The proposed method is an improvement in terms of time as well cost of analysis and selectivity with respect to the present methods based on three chromatographic techniques (GC-ECD, GC-FID, GC-HID) and four different columns. [ABSTRACT FROM AUTHOR]

In situ chemical oxidation with persulfate anion is a viable technique for remediation of groundwater contaminants such as trichloroethylene (TCE). An accelerated reaction using to destroy TCE can be achieved via chemical activation with ferrous ion to generate sulfate radicals . The column study presented here simulates persulfate oxidation of TCE in porous media (glass beads and a sandy soil). Initial experiments were conducted to investigate persulfate transport in the absence of TCE in the column. The persulfate flushing exhibited a longer residence time and revealed a moderate persulfate interaction with soils. In TCE treatment experiments, the results indicate that the water or persulfate solution would push dissolved TCE from the column. Therefore, the effluent TCE concentration gradually increased to a maximum when about one pore volume was replaced with the flushing solution in the column. The presence of Fe2+ concentration within the column caused a quick drop in effluent TCE concentration and more TCE degradation was observed. When a TCE solution was flushing through the soil column, breakthrough of TCE concentration in the effluent was relatively slow. In contrast, when the soil column was flushed with a mixed solution of persulfate and TCE, persulfate appeared to preferentially oxidize soil oxidizable matter rather than TCE during transport. Hence, persulfate oxidation of soil organics may possibly reduce the interaction between TCE and soil (e.g., adsorption) and facilitate the transport of TCE through soil columns resulting in faster breakthrough. [Copyright &y& Elsevier]

Abstract: An extensive site-characterization project was conducted at a large chlorinated-solvent contaminated Superfund site in Tucson, AZ. The project consisted of several components, including traditional site-characterization activities, tracer tests, laboratory experiments conducted with core material collected from the site, and mathematical modeling. The primary focus of the work presented herein is the analysis of induced-gradient contaminant elution tests conducted in a source zone at the site, investigation of the potential occurrence of immiscible liquid in the saturated zone, characterization of the relationship between mass flux reduction and mass removal, and evaluation of the impact of source-zone management on site remediation. The results of the present study, along with those of prior work, indicate that immiscible liquid is likely present in the saturated zone at the site source zones. Extensive tailing and rebound was observed for the contaminant-elution tests, indicating nonideal transport and mass-transfer behavior. The elution data were analyzed with a source-zone-scale mathematical model, and the results indicated that nonideal immiscible-liquid dissolution was the primary cause of the observed behavior. The time-continuous relationship between mass flux reduction and mass removal associated with the plume-scale pump-and-treat operation exhibited an initial large drop in mass flux with minimal mass removed, followed by a period of minimal mass flux reduction and a second period of large reduction. This behavior reflects the impact of both source-zone and aqueous-plume mass removal dynamics. Ultimately, a greater than 90% reduction in mass flux was achieved for a mass removal of approximately 50%. The influence of source-zone management on site remediation was evaluated by conducting two predictive simulations, one for which the source zones were controlled and one for which they were not. A plume-scale model was used to simulate the composite contaminant concentrations associated with groundwater extracted with the pump-and-treat system, which were compared to measured data. The information generated from this study was used to enhance the site conceptual model, help optimize operation of the pump-and-treat system, and evaluate the utility of source-zone remediation. [Copyright &y& Elsevier]

Abstract: Block copolymers are increasingly being applied in areas such as transfection, membrane sealing, site-specific targeting, and bionanoengineering yet there is a relative paucity of assays available for simple, stable and reproducible colorimetric determination of copolymer concentration in solution. We have focused on improving the accuracy and reproducibility of a modified version of the Stewart biphasic colorimetric assay for quantitative determination of Pluronic (poloxamer) and Tetronic (poloxamine) macromolecules. The optimized assay achieved linear response ranges in chloroform for commonly used copolymers such as poloxamine 904 (20–300μg/ml), poloxamine 908 (10–400μg/ml), poloxamer 402 (20–400μg/ml), and poloxamer 407 (10–400μg/ml). Variation in the type of chlorinated solvent used significantly increased assay sensitivity, presumably through macromolecular reorientation, affording increased access for copolymer–ferrothiocyanate complexation. This was found to be optimally favored by the planar geometry of the solvent cis 1,2-dichloroethylene. For application to biological systems copolymer–protein interactions were for the first time determined and were found to be dependent on the fraction of hydrophobic constituents of the block copolymers and protein type. For instance serum albumin was found to interact with copolymers of low hydrophilic–lipophilic balance values and poly(propylene oxide) contaminants, whereas this interaction was not significant with the relatively hydrophilic IgG. In such systems the colorimetric assay directly determines the fraction of unbound (free) copolymer in the presence of proteins. [Copyright &y& Elsevier]

Abstract: In situ chemical oxidation (ISCO) is a technology used for groundwater remediation. This laboratory study investigated the use of the oxidant sodium persulfate for the chemical oxidation of trichloroethylene (TCE) at near ambient temperatures (10, 20 and 30°C) to determine the influence of pH (pH=4, 7 and 9) on the reaction rate (i.e., pseudo-first-order rate constants) over the range of temperatures utilized. TCE solutions (60mgl−1; 0.46mM) were prepared in phosphate buffered RO water and a fixed persulfate/TCE molar ratio of 50/1 was employed in all tests. Half-lives of TCE degradation at 10, 20 and 30°C (pH 7) were 115.5, 35.0 and 5.5h, respectively. Maximum TCE degradation occurred at pH 7. Lowering system pH resulted in a greater decrease in TCE degradation rates than increasing system pH. Radical scavenging tests used to identify predominant radical species suggested that the sulfate radical predominates under acidic conditions and the hydroxyl radical ( OH) predominates under basic conditions. In a side by side comparison of TCE degradation in a groundwater vs. unbuffered RO water it was demonstrated that when the system pH is buffered to near neutral pH conditions due to the presence of natural occurring groundwater constituents that the TCE degradation rate is higher than in unbuffered RO water where the system pH dropped from 5.9 to 2.8. The results of this study suggest that in a field application of ISCO, pH should be monitored and adjusted to near neutral if necessary. [Copyright &y& Elsevier]

Abstract: The aerobic cometabolic biodegradation of a mixture of chlorinated aliphatic hydrocarbons (CAHs) including vinyl chloride (VC), cis- and trans-1,2-dichloroethylene (cis-DCE, trans-DCE), trichloroethylene (TCE), 1,1,2-trichloroethane (1,1,2-TCA) and 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA) was investigated at both 25 and 17°C by means of bioaugmented and non-bioaugmented sediment-groundwater slurry microcosm tests. The goals of the study were (i) to study the long-term aerobic biodegradation of a CAH mixture including a high-chlorinated solvent (1,1,2,2-TeCA) generally considered non-biodegradable in aerobic conditions; (ii) to investigate the efficacy of bioaugmentation with two types of internal inocula obtained from the indigenous biomass of the studied site; (iii) to identify the CAH-degrading bacteria. VC, methane and propane were utilized as growth substrates. The non-bioaugmented microcosms were characterized, at 25°C, by an average 18-day lag-time for the direct metabolism of VC (accompanied by the cometabolism of cis- and trans-DCE) and by long lag-times (36–264 days) for the onset of methane or propane utilization (associated with the cometabolism of the remaining CAHs). In the inoculated microcosms the lag-phases for the onset of growth substrate utilization and CAH cometabolism were significantly shorter (0–15 days at 25°C). Biodegradation of the 6-CAH mixture was successfully continued for up to 410 days. The low-chlorinated solvents were characterized by higher depletion rates. The composition of the microbial consortium of a propane-utilizing microcosm was determined by 16s rDNA sequencing and phylotype analysis. To the best of our knowledge, this is the first study that documents the long-term aerobic biodegradation of 1,1,2,2-TeCA. [Copyright &y& Elsevier]

The effectiveness of whey as an electron donor that stimulates bioremediation and enhances dissolution of trichloroethene (TCE) dense non-aqueous phase liquid (DNAPL) was investigated. Laboratory experiments were conducted to evaluate increased mass transfer of TCE from the DNAPL to the aqueous phase in abiotic batch microcosms amended with several concentrations of whey, and in abiotic columns using high- and low-concentration whey mixtures. The effective solubility of TCE was a factor of 6 higher in microcosms amended with 10% w/w whey compared to 1% w/w whey or nanopure water. Increased aqueous-phase concentrations of TCE were a function of both the concentration of whey and time. In the columns, a factor of 5 increase in TCE concentrations was observed in the effluent during amendment with 10% w/w whey compared to potable water and 1% w/w whey. A field study involving three whey injections was performed at a site that had been actively undergoing bioremediation in a residual source area using lactate for 5 years. Results of the field test show a factor of 3 increase in total molar concentrations of chloroethenes and ethene following injection of 10% w/w whey compared to 5% lactate. In addition, complete dechlorination of TCE to ethene continued. [ABSTRACT FROM AUTHOR]

This research investigated the feasibility of an electrochemical reductive dechlorination method for removing carbon tetrachloride (CT) from contaminated waters. Reaction rates and Faradaic current efficiencies were measured for CT dechlorination in small flow-through reactors utilizing bare and silicone polymer coated nickel cathodes. CT dechlorination resulted in near stoichiometric production of methane. Rates of CT reduction were found to follow a first-order kinetic model for all CT concentrations investigated. CT disappearance was limited by its reaction rate, and the performance of the reactor could be approximated with an ideal plug-flow reactor model. Destruction half-life values for CT with the bare nickel electrode ranged from 3.5 to 5.8?min for electrode potentials ranging from -652 to -852?mV with respect to the standard hydrogen electrode (SHE). The apparent electron transfer coefficient for CT reduction was only 0.06. The low transfer coefficient can be attributed to oxides coating the electrode surface that contributed to mass transfer resistance for CT reduction. Faradaic current efficiencies for CT reduction were found to decline with decreasing electrode potential. This can be attributed to an electron transfer coefficient for water reduction of 0.33 that was significantly greater than that for CT reduction. Faradaic current efficiencies could be increased by 100-360% by coating the electrode with a silicone polymer. In addition to decreasing the rate of water reduction by acting as hydrophobic mass transfer barrier, the polymer coating resulted in small increases in CT reaction rates. The energy cost per volume of water treated was strongly dependent on the electrode potential, but only weakly dependent on the influent CT concentration over the range of practical interest. The energy costs for reductive dechlorination appear to be lower than the carbon costs for adsorptive treatment of CT. This indicates that low current efficiencies at low CT concentrations are not a significant obstacle for developing a practical treatment process. The main impediment to electrochemical treatment for removing CT from water is the slow reaction rate that requires large reactors for obtaining sufficient hydraulic detention time to meet effluent water standards. [ABSTRACT FROM AUTHOR]

This article presents an approach for modeling the dissolution process of single component dense non-aqueous phase liquids (DNAPL), such as tetrachloroethene and trichloroethene, in a biologically reactive porous medium. In the proposed approach, the overall transport processes are conceptualized as three distinct reactions. Firstly, the dissolution (or dissolving) process of a residual DNAPL source zone is conceptualized as a mass-transfer limited reaction. Secondly, the contaminants dissolved from the DNAPL source are allowed to partition between sediment and water phases through a rate-limited sorption reaction. Finally, the contaminants in the solid and liquid phases are allowed to degrade by a set of kinetic-limited biological reactions. Although all of these three reaction processes have been researched in the past, little progress has been made towards understanding the combined effects of these processes. This work provides a rigorous mathematical model for describing the coupled effects of these three fundamental reactive transport mechanisms. The model equations are then solved using the general-purpose reactive transport code RT3D (Clement, 1997). [ABSTRACT FROM AUTHOR]

Approximately 25, 000–35, 000 dry cleaning facilities currently operate in the U.S. The release of perchloroethylene and other solvents from these establishments represents a major source of soil and groundwater contamination. The manner in which dry cleaning solvents escape from dry cleaning plants is, for all practical purposes, identical for chlorinated and petroleum hydrocarbon solvents and is related to one of the following events: the catastrophic failure of a component of the dry cleaning system, the improper installation, operation or maintenance of the dry cleaning equipment or a combination of all of these causes. Acceptable customs, codes and regulations can also dictate what is authorized for operation of a dry cleaning facility in a particular community, geographic area during a particular time frame. Environmental litigation dealing with the origin of a solvent release from dry cleaners tends to focus on the design and manufacture of dry cleaning industry machines such as washers, washer extractors, tumblers, solvent filters, water separators, stills and spotting boards. A thorough analysis of the daily operations of dry cleaners often reveals that poor maintenance, failure to follow the manufacturer''s instructions and the actions of the operator are the most likely causes of soil and groundwater pollution. In order to forensically evaluate the most probable origins of a solvent release and to examine issues regarding liability, a thorough understanding of the history of dry cleaning and a detailed analysis of the operation and maintenance of the dry cleaning equipment are necessary. The discovery of solvent plumes in the vicinity of dry cleaning plants may suggest that the solvent source is the dry cleaning plant; however, the presence of these plumes does not necessarily indicate that the dry cleaning equipment was defectively designed or manufactured. A thorough review of the type of equipment used over the life of the dry cleaning plant and verifiable solvent mileage records frequently indicates that operators of the plant have disposed of solvent and contaminated solids into the municipal sewer or on ground surfaces. [Copyright &y& Elsevier]

The effect of trichloroethylene (TCY) was investigated to determine whether repeated exposure alters the pharmacokinetics of some drugs. Sprague-Dawley rats were given intraperitoneal injections of TCY (5 mmol/kg) in corn oil once daily for 3 days, while the control group received only corn oil. Four hours after the last dose, theophylline, quinidine, or pentobarbital were administered. Blood samples were collected at appropriate intervals for drug analyses. There was a small decrease in plasma clearance of theophylline, with no change in volume of distribution (V[sub d] ) as compared with controls. For quinidine, the elimination half-life was unchanged, and the V[sub d] was decreased by 40%. The clearance of pentobarbital was decreased by 40% in male rats, but not in the females. Nonetheless, the duration of the sleeping time for both sexes was remarkably prolonged as compared with the control group. There was a decrease in the cytochrome P-450 content only in male rats. In conclusion, exposure to TCY causes changes in some drug kinetics, probably resulting from differential effects on the drug-metabolizing enzymes.Copyright © 2001 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

The occurrence of twelve chlorinated and brominated volatile compounds was investigated by a HRGC (High Resolution Gas Chromatography) device with a dynamic purge (PTI, Chrompack) in the water of the river Seine under dry conditions and under contrasting hydrological regimes, according to three longitudinal profiles from upstream to downstream of the Paris urban centre. Our results showed an obvious rise of the solvent concentrations in the river Seine water along the profiles. The total chlorinated solvent concentration, which was below 1 μg L$^-1$ upstream of Paris, reached a maximum value of 8 μg L$^-1$ dowstream of the urban centre in December 1994. This corresponded to a flux of around 300 kg d$^-1$. This contamination originated in successive waste inputs, both domestic and industrial, from the Paris main sewers. The losses by evaporation from the river were taken into account for the estimation of the waste. The waste inputs represented about 85 to 97% of the total chlorinated solvent flux observed downstream of Paris. During the two first sampling sessions, dichloromethane represented 67% of the inputs. Though the hydrological regime plays a part both in the waste dilution and in the losses by evaporation processes, other factors such as the industrial activities or the ambient temperature may have a major influence upon the river contamination. [ABSTRACT FROM AUTHOR]