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Trichloroethylene (TCE), a widespread environmental contaminant, has been linked to congenital heart defects. Abnormal regulation of Connexin 43 is closely associated with various cardiac diseases. However, it is yet to be established how Cx43 responds to environmental pollutants. Here, we aim to explore the role of Cx43 in TCE-induced cardiac toxicity using H9C2 cardiomyocytes. EdU incorporation assay and cell cycle analysis revealed that increased number of TCE-treated cells entered into the S stage, indicating that TCE exposure provoked cell proliferation. Additionally, compromised mitochondrial function was observed in TCE-treated cells, and inhibition of mitochondrial permeability transition pore (mPTP) with Cyclosporin A or eliminating mitochondrial ROS by MitoQ alleviated the TCE-induced cardiac toxicity. Importantly, TCE exposure increased the protein expression levels of Cx43 and stimulated the recruitment of Cx43 to the mitochondria. TCE exposure disrupted canonical Wnt signal pathway, resulting in downregulation of antioxidant genes and β-catenin. The adverse effects of TCE on Wnt signal pathway activation, mitochondrial function and cell proliferation were efficiently counteracted by either Cx43 knockdown or pharmaceutical activator of Wnt signaling, CHIR-99021. Taken together, our results for the first time revealed that dysregulation of Cx43 mediates TCE-induced heart defects via mitochondrial dysfunction and Wnt signaling inhibition, suggesting that Cx43 can be a potential molecular marker or therapeutic target for cardiac diseases caused by environmental pollutants., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Chlorinated ethenes (CEs) are common and persistent contaminants of soil and groundwater. Their degradation is mostly driven by a process of bacterial reductive dechlorination (also called organohalide respiration) in anaerobic conditions. This study summarizes the outcomes of the long-term in-situ application of glycerol for the enhanced reductive dechlorination of CEs on a highly contaminated site. Glycerol injection resulted in an almost immediate increase in the abundance of fermentative Firmicutes, which produce essential sources of carbon (acetate) and electrons (H 2 ) for organohalide-respiring bacteria (OHRB) and change groundwater conditions to be suitable for OHRB growth. The decreased redox potential of groundwater promoted also the proliferation of sulfate-reducing bacteria, which compete for electron donors with OHRB but at the same time support their growth by producing essential corrinoids and acetate. A considerable increase in the abundance of OHRB Dehalococcoides, concurrently with vinyl chloride (VC) reductase gene levels, was revealed by real time polymerase chain reaction (qPCR) method. Consistent with the shifts in bacterial populations, the concentrations of pollutants tetrachloroethylene and trichloroethylene decreased during the monitoring period, with rising levels of cis-1,2-dichloroethylene, VC, and most importantly, the final CE degradation products: ethene and ethane. Our study implies the importance of syntrophic bacterial interactions for successful and complete CE degradation and evaluates glycerol as convenient substrate to enhance reductive dechlorination and as an effective source of electrons for OHRB., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Diffusion, sorption-desorption, and biodegradation influence chlorinated solvent storage in, and release (mass flux) from, low-permeability media. Although bioenhanced dissolution of non-aqueous phase liquids has been well-documented, less attention has been directed towards biologically-mediated enhanced diffusion from low-permeability media. This process was investigated using a heterogeneous aquifer cell, packed with 20-30 mesh Ottawa sand and lenses of varying permeability (1.0 × 10 -12 -1.2 × 10 -11  m 2 ) and organic carbon (OC) content (<0.1%-2%), underlain by trichloroethene (TCE)-saturated clay. Initial contaminant loading was attained by flushing with 0.5 mM TCE. Total chlorinated ethenes removal by hydraulic flushing was then compared for abiotic and bioaugmented systems (KB-1® SIREM; Guelph, ON). A numerical model incorporating coupled diffusion and (de)sorption facilitated quantification of bio-enhanced TCE release from low-permeability lenses, which ranged from 6% to 53%. Although Dehalococcoides mccartyi (Dhc) 16S rRNA genes were uniformly distributed throughout the porous media, strain-specific distribution, as indicated by the reductive dehalogenase (RDase) genes vcrA, bvcA, and tceA, was influenced by physical and chemical heterogeneity. Cells harboring the bvcA gene comprised 44% of the total RDase genes in the lower clay layer and media surrounding high OC lenses, but only 2% of RDase genes at other locations. Conversely, cells harboring the vcrA gene comprised 50% of RDase genes in low-permeability media compared with 85% at other locations. These results demonstrate the influence of microbial processes on back diffusion, which was most evident in regions with pronounced contrasts in permeability and OC content. Bioenhanced mass transfer and changes in the relative abundance of Dhc strains are likely to impact bioremediation performance in heterogeneous systems., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Catalyzed H 2 O 2 propagations (CHP) have demonstrated great potential in the remediation of chlorinated aliphatic hydrocarbons (CAHs) like trichloroethene (TCE) contaminated groundwater. However, the importation of highly unstable H 2 O 2 into subsurface environment remains challenging. In this work, the in-situ H 2 O 2 generation reaction between glucose oxidase (GOD) and glucose was applied in combination with Fe(II) to form the modified Fenton system (GMFs) and its performance in TCE oxidative degradation was investigated. The influence of reactant concentration as well as environmental factors like temperature and pH on the kinetics of TCE oxidation in GMFs were studied. At optimized conditions, about 78% TCE were removed within 8 h in GMFs, which remained effective over the temperature range of 15-30 °C and pH range of 3.6-6.0 (in acetate buffer). The in-situ H 2 O 2 and OH generation capacity of GMFs were further investigated to elucidate their functional mechanism on TCE oxidation. Intermediate and product analysis indicated the near-complete release of chloride ion by TCE oxidation with few organic chlorinated intermediates detected. This work reveals the potential of GMFs for CAHs contaminated groundwater remediation through in-situ generation of reactive oxygen species., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

This study evaluated the biological removal of trichloroethylene (TCE) by Rhodococcus opacus using airlift bioreactor under continuous operation mode. The effect of inlet TCE concentration in the range 0.12-2.34 g m -3 on TCE removal has studied for 55 days. During the continuous bioreactor operation, a maximum of 96% TCE removal was obtained for low inlet TCE concentration, whereas the highest elimination capacity was 151.2 g m -3 h -1 for the TCE loading rate of 175.0 g m -3 h -1 . The carbon dioxide (CO 2 ) concentration profile from the airlift bioreactor revealed that the degraded TCE has primarily converted to CO 2 with a fraction of organic carbon utilized for bacterial growth. The artificial neural network (ANN) based model was able to successfully predict the performance of the bioreactor system using the Levenberg-Marquardt (LM) back propagation algorithm, and optimized biological topology is 3:12:1. The prediction accuracy of the model was high as the experimental data were in good agreement (R 2  = 0.9923) with the ANN predicted data. Overall, from the bioreactor experiments and its ANN modeling, the potential strength of R. opacus in TCE biodegradation is proved., Competing Interests: Declaration of competing interest The authors declare that they have no conflict of interest between authors or any institute or funding agencies., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Identifying co-metabolic TCE oxidation in polluted groundwater is challenging due to lack of indicative by-products. This challenge may theoretically be resolved if the oxidation process can be characterized by a distinct dual isotope enrichment. In this work, we aimed to explore the carbon and chlorine isotope effects associated with TCE oxidation by a variety of oxygenases. These included pure strains and enrichment cultures of methane, toluene and ammonia oxidizers, as well as experiments with crude extracts. Isotope effects determined for TCE oxidation by toluene and ammonia oxidizers were mostly in line with expected values for epoxidation mechanism (ϵ 13 C -11.0 ± 0.7 to -24.8 ± 0.2‰ and ϵ 37 Cl +0.9 ± 0.5 to +1.0 ± 0.4‰), whereas, the methanotrophs resulted in distinctively different isotope effects (ϵ 13 C -2.4 ± 0.4 to -3.4 ± 0.8‰ and ϵ 37 Cl -1.8 ± 0.2 to -2.9 ± 0.9‰). It is suggested that in TCE oxidation by methanotrophs, substrate binding rather than bond cleavage is rate limiting, leading to this unexpected isotope effect. On the environmental level, our results imply that the oxidative process can be differentiated if catalyzed by toluene and ammonia oxidizers or by methanotrophs. Additionally, the oxidative process can be distinguished from the reductive one. However, using dual isotope analysis in the field may result in an under-estimation of the overall co-metabolic process if methanotrophs are to be excluded due to low isotope effects., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Electrochemical removal of chlorinated ethenes in groundwater plumes may potentially overcome some of the challenges faced by current remediation technologies. So far, studies have been conducted in simplified settings of synthetic groundwater and inert porous matrices. This study is a stepwise investigation of the influence of field-extracted groundwater, sandy sediment and groundwater aquifer temperatures on the removal of an aged partially degraded contamination of tetrachloroethylene (PCE) at a typical groundwater flow rate. The aim is to assess the potential for applying electrochemistry at contaminated sites. At a constant current of 120 mA, pH and conductivity were unaffected downgradient the electrochemical zone. Major groundwater species were reduced and oxidized. Some minerals deposited, others dissolved. Hydrogen peroxide, a strong oxidant, was formed in levels up to 5 mg L -1 with a limited distribution into the sandy sediment. Trichloromethane was formed, supposedly by oxidation of organic matter in the sandy sediment in the presence of chloride. The more realistic the settings, the higher the PCE removal, bringing concentrations down to 7.8 ± 2.3 μg L -1 . A complete removal of trichloroethylene and cis-1,2-dichloroethylene was obtained. The results suggest that competing reactions related to the natural complex hydrogeochemistry are insignificant in terms of affecting the electrochemical degradation of PCE and chlorinated intermediates., Competing Interests: Declaration of competing interest None., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Deteriorated environmental conditions during the bioremediation of trichloroethene (TCE)-polluted groundwater cause decreased treatment efficiencies. This study assessed the effect of applying immobilized Clostridium butyricum (a hydrogen-producing bacterium) in silica gel on enhancing the reductive dechlorination efficiency of TCE with the slow polycolloid-releasing substrate (SPRS) supplement in groundwater. The responses of microbial communities with the immobilized system (immobilized Clostridium butyricum and SPRS amendments) were also characterized by the metagenomics assay. A complete TCE removal in microcosms was obtained within 30 days with the application of this immobilized system via reductive dechlorination processes. An increase in the population of Dehalococcoides spp. was observed using the quantitative polymerase chain reaction (qPCR) analysis. Results of metagenomics assay reveal that the microbial communities in the immobilized system were distinct from those in systems with SPRS only. Bacterial communities associated with TCE biodegradation also increased in microcosms treated with the immobilized system. The immobilized system shows a great potential to promote the TCE dechlorination efficiency, and the metagenomics-based approach provides detailed insights into dechlorinating microbial community dynamics. The results would be helpful in designing an in situ immobilized system to enhance the bioremediation efficiency of TCE-contaminated groundwater., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

ISCO using activated sodium persulphate is a widely used technology for treating chlorinated solvent source zones. In sensitive areas, however, high groundwater sulphate concentrations following treatment may be a drawback. In situ biogeochemical transformation, a technology that degrades contaminants via reduced iron minerals formed by microbial activity, offers a potential solution for such sites, the bioreduction of sulphate and production of iron sulphides that abiotically degrade chlorinated ethenes acting as a secondary technology following ISCO. This study assesses this approach in the field using hydrochemical and molecular tools, solid phase analysis and geochemical modelling. Following a neutralisation and bioaugmentation, favourable conditions for iron- and sulphate-reducers were created, resulting in a remarkable increase in their relative abundance. The abundance of dechlorinating bacteria (Dehalococcoides mccartyi, Dehalobacter sp. and Desulfitobacterium spp.) remained low throughout this process. The activity of iron- and sulphate-reducers was further stimulated through application of magnetite plus starch and microiron plus starch, resulting in an increase in ferrous iron concentration (from

The effectiveness of using gamma poly-glutamic acid (γ-PGA) as the primary carbon and nitrogen sources to bioremediate trichloroethene (TCE)-contaminated groundwater was studied in this pilot-scale study. γ-PGA (40 L) solution was injected into the aquifer via the injection well (IW) for substrate supplement. Groundwater samples were collected from monitor wells and IW and analyzed for TCE and its byproducts, geochemical indicators, dechlorinating bacteria, and microbial diversity periodically. Injected γ-PGA resulted in an increase in total organic carbon (TOC) (up to 9820 mg/L in IW), and the TOC biodegradation caused the formation of anaerobic conditions. Increased ammonia concentration (because of amine release from γ-PGA) resulted in the neutral condition in groundwater, which benefited the growth of Dehalococcoides. The negative zeta potential and micro-scale diameter of γ-PGA allowed its globule to distribute evenly within soil pores. Up to 93% of TCE removal was observed (TCE dropped from 0.14 to 0.01 mg/L) after 59 days of γ-PGA injection, and TCE dechlorination byproducts were also biodegraded subsequently. Next generation sequence (NGS) analyses were applied to determine the dominant bacterial communities. γ-PGA supplement developed reductive dechlorinating conditions and caused variations in microbial diversity and dominant bacterial species. The dominant four groups of bacterial communities including dechlorinating bacteria, vinyl chloride degrading bacteria, hydrogen producing bacteria, and carbon biodegrading bacteria., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Trichloroethylene (TCE) is one of the most ubiquitous halogenated organic compounds of concerns of carcinogens in groundwater in Taiwan. Bioremediation has been recognized as a cost-effective approach in reducing TCE concentration. Five pilot-scale wells were constructed to monitor TCE concentrations in contaminated groundwater. With injection of EOS ® , TCE was effectively degraded to 42%-93% by the end of 175 days. The biostimulation with EOS ® was useful in establishing a micro-site anaerobic but with limited contribution. Dilution of the aquifer movement also caused the TCE reduction among injection and monitoring wells. The degradability was affected by the location and the proximity from the injection well. TCE concentrations found to be negatively correlated with the associated Dehalococcoides spp. and functional genes levels. Dhc concentration of 10 8 copies L -1 caused the initial 40% of TCE degradation. The well with the optimal degradation owned tceA of 10 9  cells L -1 . T-RFLP results indicate the wells with the superior TCE degradability also performed the highest Shannon index number (means the highest diversity), which occurred on the same day that Dhc levels started to enlarge. Desulfovibrio desulfuricans and Desulfuromonas chloroethenica were predominant species identified in the T-RFLP fingerprint profile. In brief, a variety of different factors including well locations, geochemical indicators, and microbial contribution were useful to explain the site-specific optimal TCE remediation approach. The consistence among TCE degradation, Dhc growing pattern, functional gene levels, and the dynamics of the microbial community structure present the novelty of this study., (Copyright © 2019. Published by Elsevier Ltd.)

Zero-valent iron nanoparticles (ZVIN) have found applications in many strategies for on-site soil and groundwater decontamination. A number of studies have reported the prospective utilization of ZVIN in the reduction of chlorinated organic compounds such as dense non-aqueous phase liquids (DNAPLs) in groundwater. Due to their bioaccumulation and carcinogenesis, DNAPLs in groundwater are a human health hazard and pose environmental risks. Therefore, decontamination of these contaminants is necessary. This study presents the in-situ remediation of trichloroethylene (TCE), perchloroethene (PCE), and 1,2-dichloroethene (1,2-DCE) DNAPLs through the direct injection of polyethylenimine (PEI)-coated ZVIN (PEI-ZVIN composite materials) to facilitate the reduction of contaminants in low-permeability media. A field test was conducted at the premises of a petrochemical company, situated in the Miaoli County of Northern Taiwan that discharged significant amounts of DNAPLs. After in-situ injection and one-day of reaction with groundwater contaminants, ZVIN was further characterized to examine its efficacy in the reduction of pollutants. After the direct injection of PEI-ZVIN, a notable reduction in the concentration of DNAPLs was recorded with conversion from toxic to non-toxic substances. Use of resistivity image profiling (RIP) technique suggested similar conductivity data for the PEI-coated ZVIN suspension and groundwater samples. X-ray absorption near edge structure (XANES) and X-ray absorption fine structure (EXAFS) studies depicted that the oxidation of ZVIN and PEI-ZVIN was occurring after the reductive reaction with contaminated groundwater. The reacted samples had bond distance values of 1.98, 2.00, 1.96, and 1.94 Å. Combining floating surface-coated ZVIN and RIP technique seems promising and environmentally attractive., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Dehalococcoides spp. were extensively studied and applied to in-situ trichloroethylene (TCE) remediation since it is the only genus that can reduce TCE to harmless ethene completely. However, this technology was hindered because of the requirement of electron donor (i.e. hydrogen or fermentable organic substrate). Considering the spontaneous electric field and in-situ hydrogen production capacity of tourmaline, this mineral was used as an environmental-friendly bio-promoter for dechlorinating mixed culture containing Dehalococcoides spp. in this work. Research results showed that biodegradation of TCE and the intermediates were both significantly improved by tourmaline. The first-order TCE degradation rate coefficient increased from 0.0125 h -1 for the tourmaline-free system to 0.0306 h -1 for the system combined with 5 g L -1 tourmaline, and ethene production increased by 36%. The outstanding TCE-degrading ability in the tourmaline-bacteria system without the addition of fermentative electron donor (i.e. methanol) indicated that tourmaline could also produce electron donor to support dechlorinating bacteria. Tourmaline could have direct electric biostimulatory effect and indirect enhanced effect associated with water-derived H 2 production in the electric field of tourmaline. Meanwhile, PCR-DGGE analysis exhibited that tourmaline could accelerate the succession of a bacterial, dechlorinating community. The distinctive effects of tourmaline on bacteria were related to its stable electric properties. Therefore, tourmaline could be continuously used in the bioremediation. The present study provided a safe, convenient and persistent alternative to the commonly used enhancement approaches for anaerobic reductive dechlorination process., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

An environmental isolate Comamonas testosteroni strain RF2, which has been found to cometabolize trichloroethene (TCE) in the presence of phenol and sodium lactate as growth substrates, was tested to investigate its capacity for degrading 1,2-cis-dichloroethene (cDCE), 1,2-trans-dichlorothene (tDCE), and 1,1-dichloroethene (1,1DCE). Degradation assays were performed for single DCEs, as well as for a mixture of DCEs with TCE, which resembled contaminated plume in groundwater. RF2 was capable of efficiently removing all three dichloroethenes (DCEs) at the initial aqueous concentrations of 6.01 mg L -1 for cDCE, 3.80 mg L -1 for tDCE and 0.65 mg L -1 for 1,1DCE, with a removal efficiency of 100% for cDCE, 65.8% for tDCE, and 46.8% for 1,1DCE. Furthermore, complete removal of TCE, cDCE and 1,1DCE (122.5 μg L -1 , 84.3 μg L -1 and 51.4 μg L -1 , respectively) was observed in a mixture sample that also contained 72.33 μg L -1 of tDCE, which was removed to the amount of 72.3%. Moreover, degradation of cDCE (6.01 mg L -1 ) led to a 93.8% release of inorganic chloride, and 2,2-dichloroacetaldehyde was determined as the first intermediate of cDCE transformation. The findings of this study suggest that the strain RF2 exhibits the potential to remediate groundwater contaminated with less chlorinated ethenes., (Copyright © 2017. Published by Elsevier Ltd.)

Carbon tetrachloride (CT) and chloroform (CF) were transformed in batch reactor experiments conducted with anaerobic dechlorinating cultures and supernatant (ADC + S) harvested from continuous flow reactors. The Evanite (EV) and Victoria/Stanford (VS) cultures, capable of respiring trichloroethene (TCE), 1,2-cis-dichloroethene (cDCE), and vinyl chloride (VC) to ethene (ETH), were grown in continuous flow reactors receiving an influent feed of saturated TCE (10 mM; 60 mEq) and formate (45 mM; 90 mEq) but no CT or CF. Cells and supernatant were harvested from the chemostats and inoculated into batch reactors at the onset of each experiment. CT transformation was complete following first order kinetics with CF, DCM and CS 2 as the measurable transformation products, representing 20-40% of the original mass of CT, with CO 2 likely the unknown transformation product. CF was transformed to DCM and likely CO 2 at an order of magnitude rate lower than CT, while DCM was not further transformed. An analytical first order model including multiple key reactions effectively simulated CT transformation, product formation and transformation, and provided reasonable estimates of transformation rate coefficients. Biotic and abiotic treatments indicated that CT was mainly transformed via abiotic processes. However, the presence of live cells was associated with the transformation of CF to DCM. In biotic tests both TCE and CT were simultaneously transformed, with TCE transformed to ETH and approximately 15-53% less CF formed via CT transformation. A 14-day exposure to CF (CF max  = 1.4 μM) reduced all rates of chlorinated ethene respiration by a factor of 10 or greater., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

1,2,3-Trichloropropane (TCP) is an emerging groundwater pollutant and suspected human carcinogen. TCP, a recalcitrant contaminant, has been detected in the subsurface near TCP manufacture facilities and many superfund sites. Considering the toxicity and the occurence of TCP, there is a need to seek for cost-effective treatment technologies for TCP-contaminated sites. This paper investigated TCP biodegradation by propane-oxidizing bacteria (PrOB) which are known to express propane monooxygenase (PrMO). PrMO can cometabolically degrade many different contaminants. Four PrOB, Rhodococus jostii RHA1, Mycobacterium vaccae JOB5, Rhodococcus rubber ENV425 and one isolate Sphingopyxis sp. AX-A were examined for their ability to degrade TCP. All the four PrOB resting cells were able to degrade TCP. Strain JOB5 exhibited the best TCP degradation ability (v initial = 9.7 ± 0.7 μg TCP (mg protein) -1 h -1 ). No TCP was degraded in the presence of acetylene (an inhibitor for PrMO), suggesting that PrMO might be responsible for TCP degradation. Furthermore, competitive inhibition was observed between propane and TCP, and between trichloroethylene (TCE) and TCP., (Copyright © 2016. Published by Elsevier Ltd.)

Bench-scale microcosms with wetland plant roots were investigated to characterize the microbial contributions to contaminant degradation of trichloroethene (TCE) with ammonium. The batch system microcosms consisted of a known mass of wetland plant roots in aerobic growth media where the roots provided both an inoculum of root-associated ammonium-oxidizing microorganisms and a microbial habitat. Aqueous growth media, ammonium, and TCE were replaced weekly in batch microcosms while retaining roots and root-associated biomass. Molecular biology results indicated that ammonium-oxidizing bacteria (AOB) were enriched from wetland plant roots while analysis of contaminant and oxygen concentrations showed that those microorganisms can degrade TCE by aerobic cometabolism. Cometabolism of TCE, at 29 and 46 μg L(-1), was sustainable over the course of 9 weeks, with 20-30 mg L(-1) ammonium-N. However, at 69 μg L(-1) of TCE, ammonium oxidation and TCE cometabolism were completely deactivated in two weeks. This indicated that between 46 and 69 μg L(-1) TCE with 30 mg L(-1) ammonium-N there is a threshold [TCE] below which sustainable cometabolism can be maintained with ammonium as the primary substrate. However, cometabolism-induced microbial deactivation of ammonium oxidation and TCE degradation at 69 μg L(-1) TCE did not result in a lower abundance of the amoA gene in the microcosms, suggesting that the capacity to recover from TCE inhibition was still intact, given time and removal of stress. Our study indicates that microorganisms associated with wetland plant roots can assist in the natural attenuation of TCE in contaminated aquatic environments, such as urban or treatment wetlands, and wetlands impacted by industrial solvents., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

The anaerobic biotransformation of trichloroethylene (TCE) can be affected by competing electron acceptors such as Fe (III). This study assessed the role of Fe (III) reduction on the bioenhanced dissolution of TCE dense non-aqueous phase liquid (DNAPL). Columns were set up as 1-D diffusion cells consisting of a lower DNAPL layer, a layer with an aquifer substratum and an upper water layer that is regularly refreshed. The substrata used were either inert sand or sand coated with 2-line ferrihydrite (HFO) or two environmental Fe (III) containing samples. The columns were inoculated with KB-1 and were repeatedly fed with formate. In none of the diffusion cells, vinyl chloride or ethene was detected while dissolved and extractable Fe (II) increased strongly during 60 d of incubation. The cis-DCE concentration peaked at 4.0 cm from the DNAPL (inert sand) while it was at 3.4 cm (sand+HFO), 1.7 cm and 2.5 cm (environmental samples). The TCE concentration gradients near the DNAPL indicate that the DNAPL dissolution rate was larger than that in an abiotic cell by factors 1.3 (inert sand), 1.0 (sand+HFO) and 2.2 (both environmental samples). This results show that high bioavailable Fe (III) in HFO reduces the TCE degradation by competitive Fe (III) reduction, yielding lower bioenhanced dissolution. However, Fe (III) reduction in environmental samples was not reducing TCE degradation and the dissolution factor was even larger than that of inert sand. It is speculated that physical factors, e.g. micro-niches in the environmental samples protect microorganisms from toxic concentrations of TCE., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Reductive dechlorination of chlorinated ethenes is inhibited by acidification and by the presence of Fe (III) as a competitive electron acceptor. Synergism between both factors on dechlorination is predicted as reductive dissolution of Fe (III) minerals is facilitated by acidification. This study was set-up to assess this synergism for two common aquifer Fe (III) minerals, goethite and ferrihydrite. Anaerobic microbial dechlorination of trichloroethylene (TCE) by KB-1 culture and formate as electron donor was investigated in anaerobic batch containers at different solution pH values (6.2-7.2) in sand coated with these Fe minerals and a sand only as control. In the absence of Fe, lowering substrate pH from 7.2 to 6.2 increased the time for 90% TCE degradation from 14±1d to 42±4d. At pH 7.2, goethite did not affect TCE degradation time while ferrihydrite increased the degradation time to 19±1d compared to the no Fe control. At pH 6.2, 90% degradation was at 78±1 (ferrihydrite) or 131±1d (goethite). Ferrous iron production in ferrihydrite treatment increased between pH 7.2 and 6.5 but decreased by further lowering pH to 6.2, likely due to reduced microbial activity. This study confirms that TCE is increasingly inhibited by the combined effect of acidification and bioavailable Fe (III), however no evidence was found for synergistic inhibition since Fe reduction did not increase as pH decreases. To the best of our knowledge, this is the first study where effect of pH and Fe (III) reduction on TCE was simultaneously tested. Acid Fe-rich aquifers need sufficient buffering and alkalinity to ensure swift degradation of chlorinated ethenes., (Copyright © 2014. Published by Elsevier Ltd.)

Biodegradation of trichloroethene (TCE) near a Dense Non Aqueous Phase Liquid (DNAPL) can enhance the dissolution rate of the DNAPL by increasing the concentration gradient at the DNAPL-water interface. Two-dimensional flow-through sand boxes containing a TCE DNAPL and inoculated with a TCE dechlorinating consortium were set up to measure this bio-enhanced dissolution under anaerobic conditions. The total mass of TCE and daughter products in the effluent of the biotic boxes was 3-6 fold larger than in the effluent of the abiotic box. However, the mass of daughter products only accounted for 19-55% of the total mass of chlorinated compounds in the effluent, suggesting that bio-enhanced dissolution factors were maximally 1.3-2.2. The enhanced dissolution most likely primarily resulted from variable DNAPL distribution rather than biodegradation. Specific dechlorination rates previously determined in a stirred liquid medium were used in a reactive transport model to identify the rate limiting factors. The model adequately simulated the overall TCE degradation when predicted resident microbial numbers approached observed values and indicated an enhancement factor for TCE dissolution of 1.01. The model shows that dechlorination of TCE in the 2D box was limited due to the short residence time and the self-inhibition of the TCE degradation. A parameter sensitivity analysis predicts that the bio-enhanced dissolution factor for this TCE source zone can only exceed a value of 2 if the TCE self-inhibition is drastically reduced (when a TCE tolerant dehalogenating community is present) or if the DNAPL is located in a low-permeable layer with a small Darcy velocity., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Batch and column experiments were conducted with eucalyptus mulch and commercial compost to evaluate suitability of highly organic natural media to support anaerobic decomposition of trichloroethylene (TCE) in groundwater. Experimental data for TCE and its dechlorination byproducts were analyzed with Hydrus-1D model to estimate the partitioning and kinetic parameters for the sequential dechlorination reactions during TCE decomposition. The highly organic natural media allowed development of a bioactive zone capable of decomposing TCE under anaerobic conditions. The first order TCE biodecomposition reaction rates were 0.23 and 1.2d(-1) in eucalyptus mulch and compost media, respectively. The retardation factors in the eucalyptus mulch and compost columns for TCE were 35 and 301, respectively. The results showed that natural organic soil amendments can effectively support the anaerobic bioactive zone for remediation of TCE contaminated groundwater. The natural organic media are effective environmentally sustainable materials for use in permeable reactive barriers., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Using inoculum from a microcosm study that exhibited aerobic transformation of cis-1,2-dichloroethene (cDCE) and trichloroethene (TCE) commensurate with biodegradation of monoaromatic compounds, enrichment cultures were developed by providing benzene, chlorobenzene (CB), dichlorobenzene (DCB) isomers and 1,2,4-trichlorobenzene as carbon and energy sources. Isolates that grow on benzene, CB, 1,2-DCB and 1,3-DCB were identified as Rhodococcus, Ralstonia, Variovorax and Ralstonia spp., respectively. Cometabolic transformation of cDCE and TCE by resting cells was demonstrated. Transformation capacities (T(c)=0.47-1.0 μg TCE mg(-1)biomass; 1.3-5.3 μg cDCE mg(-1)biomass), transformation yields (T(y)=0.18-0.27 μg TCE mg(-1)substrate; 0.46-2.1 μg cDCE mg(-1)substrate), and pseudo-first-order cometabolic degradation rate constants (0.00081-0.0031 L mg TCE(-1)d(-1); 0.0012-0.030 L mg cDCE(-1)d(-1)) for resting cells grown on benzene, CB, 1,2-DCB and 1,3-DCB were generally lower in comparison to phenol and toluene-grown isolates. Cometabolic transformation of cDCE and TCE also occurred while the cultures concurrently consumed their growth substrate (T(c)(')=0.15-0.33 μg TCE mg(-1)biomass; 4.9-11 μg cDCE mg(-1)biomass; T(y)(')=0.06-0.11 μg TCE mg(-1)substrate; 1.7-4.6 μg cDCE mg(-1)substrate), a condition that is more likely to be encountered in situ compared to cometabolic transformations by resting cells. This study is the first to report transformation rates, capacities, and yields for cometabolism of cDCE and TCE during aerobic growth on benzene, CB, 1,2-DCB and 1,3-DCB. This type of information is needed to predict the potential for natural attenuation when these compounds occur as co-contaminants., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Microbial reductive dechlorination of trichloroethene (TCE) and perchloroethene (PCE) in the vicinity of their dense non-aqueous phase liquid (DNAPL) has been shown to accelerate DNAPL dissolution. A three-layer diffusion-cell was developed to quantify this bio-enhanced dissolution and to measure the conditions near the DNAPL interface. The 12 cm long diffusion-cell setup consists of a 5.5 cm central porous layer (sand), a lower 3.5 cm DNAPL layer and a top 3 cm water layer. The water layer is frequently refreshed to remove chloroethenes at the upper boundary of the porous layer, while the DNAPL layer maintains the saturated chloroethene concentration at the lower boundary. Two abiotic and two biotic diffusion-cells with TCE DNAPL were tested. In the abiotic diffusion-cells, a linear steady state TCE concentration profile between the DNAPL and the water layer developed beyond 21 d. In the biotic diffusion-cells, TCE was completely converted into cis-dichloroethene (cis-DCE) at 2.5 cm distance of the DNAPL. Dechlorination was likely inhibited up to a distance of 1.5 cm from the DNAPL, as in this part the TCE concentration exceeded the culture's maximum tolerable concentration (2.5mM). The DNAPL dissolution fluxes were calculated from the TCE concentration gradient, measured at the interface of the DNAPL layer and the porous layer. Biotic fluxes were a factor 2.4 (standard deviation 0.2) larger than abiotic dissolution fluxes. This diffusion-cell setup can be used to study the factors affecting the bio-enhanced dissolution of DNAPL and to assess bioaugmentation, pH buffer addition and donor delivery strategies for source zones., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Iron (Fe) nanoparticles are increasingly being employed for the remediation of Chlorinated Aliphatic Hydrocarbon (CAH) contaminated sites. However, these particles have recently been reported to be cytotoxic to bacterial cells, and may therefore have a negative impact on exposed microbial communities. The overall objective of this study was to investigate the impact of Fe nanoparticles on the biodegradation of CAHs by an indigenous dechlorinating bacterial community. Also, to determine the most appropriate combination and/or application of bimetallic (Ni/Fe) nanoparticles and dechlorinating bacteria for the remediation of CAH contaminated sites. Addition of Fe nanoparticles to groundwater collected from a CAH contaminated site in Derby, UK, led to a decrease in the oxidation-reduction potential (ORP) and an increase in pH. The biological degradation rate of TCE was observed to progressively decrease in the presence of increasing Fe nanoparticle concentrations; which ranged from 0.01 to 0.1 gL(-1), and cease completely at concentrations of 0.3 gL(-1) or above. Concentrations greater than 0.3 gL(-1) led to a decline in viable bacterial counts and the inhibition of biological sulphate reduction. The most appropriate means of combining bimetallic (Ni/Fe) nanoparticles and indigenous dechlorinating bacteria was to employ a two step process: initially stimulating the biodegradation of TCE using acetate, followed by the addition of bimetallic nanoparticles to degrade the remaining cis-1,2-DCE and VC., (2010. Published by Elsevier Ltd. All rights reserved.)

Trichloroethylene is a toxic and recalcitrant groundwater pollutant. Palladium nanoparticles bio-precipitated on Shewanella oneidensis were encapsulated in polyurethane, polyacrylamide, alginate, silica or coated on zeolites. The reactivity of these bio-Pd beads and zeolites was tested in batch experiments and trichloroethylene dechlorination followed first order reaction kinetics. The calculated k-values of the encapsulated catalysts were a factor of six lower compared to non-encapsulated bio-Pd. Bio-Pd, used as a catalyst, was able to dechlorinate 100 mgL(-1) trichloroethylene within a time period of 1h. The main reaction product was ethane; yet small levels of chlorinated intermediates were detected. Subsequently polyurethane cubes empowered with bio-Pd were implemented in a fixed bed reactor for the treatment of water containing trichloroethylene. The influent recycle configuration resulted in a cumulative removal of 98% after 22 h. The same reactor in a flow through configuration achieved removal rates up to 1059 mg trichloroethylene g Pd(-1)d(-1). This work showed that fixed bed reactors with bio-Pd polyurethane cubes can be instrumental for remediation of water contaminated with trichloroethylene.

Batch and column experiments were performed to evaluate the transport, growth and dechlorination activity of Dehalococcoides sp. (DHC) during bioaugmentation for chlorinated ethenes. Batch experiments showed that the reductive dechlorination of trichloroethene (TCE), cis-1,2-dichloroethene (DCE), and vinyl chloride (VC), as well as growth of the DHC, were well described by the Monod kinetic model. The measured maximum utilization rate coefficients for TCE, DCE, and VC were 1.3x10(-12), 5.2x10(-13), and 1.4x10(-12)mmol Cl(-) (cellh)(-1), respectively. Results of the column experiments showed that dechlorination occurred throughout the length of the column, and that extractable DHC concentrations associated with the soil phase throughout the column were negligible relative to the aqueous phase concentrations. Dechlorination rates relative to aqueous DHC concentrations in the column were approximately 200-times greater than in the batch experiments. Additional batch experiments performed using column effluent water confirmed this result. Incorporation of these enhanced dechlorination kinetics in the transport model provided a reasonable prediction of the column data. Overall results of this study suggest that aqueous phase (as opposed to soil phase) DHC concentrations can be used to estimate dechlorination activity in saturated soils, and DHC dechlorination activity in porous media may be substantially greater than DHC dechlorination activity measured in batch experiments.

Modeling of cometabolic kinetics is important for better understanding of degradation reaction and in situ application of bio-remediation. In this study, a model incorporated cell growth and decay, loss of transformation activity, competitive inhibition between growth substrate and non-growth substrate and self-inhibition of non-growth substrate was proposed to simulate the degradation kinetics of phenol and trichloroethylene (TCE) by Pseudomonas putida. All the intrinsic parameters employed in this study were measured independently, and were then used for predicting the batch experimental data. The model predictions conformed well to the observed data at different phenol and TCE concentrations. At low TCE concentrations (<2 mg l(-1)), the models with or without self-inhibition of non-growth substrate both simulated the experimental data well. However, at higher TCE concentrations (>6 mg l(-1)), only the model considering self-inhibition can describe the experimental data, suggesting that a self-inhibition of TCE was present in the system. The proposed model was also employed in predicting the experimental data conducted in a repeated batch reactor, and good agreements were observed between model predictions and experimental data. The results also indicated that the biomass loss in the degradation of TCE below 2 mg l(-1) can be totally recovered in the absence of TCE for the next cycle, and it could be used for the next batch experiment for the degradation of phenol and TCE. However, for higher concentration of TCE (>6 mg l(-1)), the recovery of biomass may not be as good as that at lower TCE concentrations.

The widespread use of tetrachloroethene (PCE) and trichloroethene (TCE) as dry cleaning solvents and degreasing agents for military and industrial applications has resulted in significant environmental contamination worldwide. Anaerobic biotransformation of PCE and TCE through reductive dechlorination frequently lead to the accumulation of dichloroethenes (DCEs), thus limiting the use of reductive dechlorination for the biotransformation of the compounds. In this study, seven bacteria indigenous to contaminated sites in Africa were characterized for DCE degradation under aerobic conditions. The specific growth rate constants of the bacterial isolates ranged between 0.346-0.552 d(-1) and 0.461-0.667 d(-1) in cis-DCE and trans-DCE, respectively. Gas chromatographic analysis revealed that up to 75% of the compounds were degraded within seven days with the degradation rate constants ranging between 0.167 and 0.198 d(-1). The two compounds were also observed to be significantly degraded, simultaneously, rather than sequentially, when present as a mixture. Phylogenetic analysis of the 16S rRNA gene sequences of the bacterial isolates revealed their identity as well as their relation to other environmentally-important bacteria. The observed biodegradation of DCEs may contribute to PCE and TCE removal at the aerobic fringe of groundwater plumes undergoing reductive dechlorination in contaminated sites.

This study developed single-well, gas-sparging tests for assessing the feasibility of in situ aerobic cometabolism of trichloroethene (TCE) and cis-1,2-dichloroethene (cis-DCE) using propane and methane as growth substrates. Tests were performed in groundwater contaminated with TCE (100-400 microg l(-1)) and cis-DCE (20-60 microg l(-1)). A series of gas-sparging tests was performed by first sparging ("bubbling") gas mixtures in a well fitted with a "straddle" packer and then periodically sampling groundwater from the same well to develop concentration profiles and to estimate transformation rate coefficients. Evidence that gas-sparging of propane (or methane) and oxygen had stimulated organisms expressing a propane (or methane) monooxygenase enzyme system and the capability to transform TCE and cis-DCE included: (1) the transformation of sparged ethylene and propylene to their corresponding cometabolic by-products, ethylene oxide and propylene oxide, (2) the transformation of both cis-DCE and TCE in the propane-sparged well, (3) the transformation of cis-DCE in the methane-sparged well, and (4) the inhibition of ethylene and propylene transformations in the presence of acetylene, a known monooxygenase inactivator. At a well sparged with propane, first-order rate coefficients for propane utilization and ethylene and propylene transformation were similar, ranging from 0.007 to 0.010 h(-1). At the well sparged with methane, the propylene first-order transformation rate coefficient was 0.028 h(-1), a factor of 1.8 and 1.6 greater than methane and ethylene, respectively. The results demonstrated that gas-sparging tests are a rapid, low-cost means of assessing the potential for the in situ aerobic cometabolism of cis-DCE and TCE.

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 (epsilonC) of 16.7 and 3.5-18.9 for PCE and TCE, respectively. Fractionation of both compounds by D. ethenogenes strain 195 (PCE: epsilonC=6.0; TCE: epsilonC=13.7) was similar to the literature data for mixed cultures containing Dehalococcoides spp. D. michiganensis (PCE: no significant fractionation; TCE: epsilonC=3.5) and G. lovleyi sp. strain SZ (PCE no significant fractionation; TCE: epsilonC=8.5) generated the lowest fractionation of all studied strains. Desulfitobacterium sp. strain Viet1 (PCE: epsilonC=16.7) gave the highest enrichment factor for PCE.

The white-rot fungus Trametes versicolor degraded trichloroethylene (TCE), a highly oxidized chloroethene, and produced 2,2,2-trichloroethanol and carbon dioxide as the main products of degradation, based on the results obtained using [13C]-TCE as the substrate. For a range of concentrations of TCE between 2 and 20 mg l(-1), 53% of the theoretical maximum chloride expected from complete degradation of TCE was observed. Laccase was shown to be induced by TCE, but did not appear to play a role in TCE degradation. Cytochrome P-450 appears to be involved in TCE degradation, as evidenced by marked inhibition of degradation of TCE in the presence of 1-aminobenzotriazole, a known inhibitor of cytochrome P-450. Our results suggested that chloral (trichloroacetaldehyde) was an intermediate of the TCE degradation pathway. The results indicate that the TCE degradation pathway in T. versicolor appears to be similar to that previously reported in mammals and is mechanistically quite different from bacterial TCE degradation.

A microcosm study was conducted to evaluate dechlorination of trichloroethene (TCE) to ethene and survival of dechlorinating bacteria after a thermal treatment in order to explore the potential for post-thermal bioremediation. Unamended microcosms containing groundwater and aquifer material from a contaminated site dechlorinated TCE to cis-1,2-dichloroethene (cDCE), while lactate-amended microcosms dechlorinated TCE to cDCE or ethene. A thermal treatment was simulated by heating a sub-set of microcosms to 100 degrees C for 10d followed by cooling to 10 degrees C over 150 d. The heated microcosms demonstrated no dechlorination when unamended. However, when amended with lactate, cDCE was produced in 2 out of 6 microcosms within 300 d after heating. Dechlorination of TCE to cDCE thus occurred in fewer heated (2 out of 12) than unheated (10 out of 12) microcosms. In unheated microcosms, the presence of dechlorinating microorganisms, including Dehalococcoides, was confirmed using nested PCR of 16S rRNA genes. Dechlorinating microorganisms were detected in fewer microcosms after heating, and Dehalococcoides were not detected in any microcosms after heating. Dechlorination may therefore be limited after a thermal treatment in areas that have been heated to 100 degrees C. Thus, inflow of groundwater containing dechlorinating microorganisms and/or bioaugmention may be needed for anaerobic dechlorination to occur after a thermal treatment.

The objective of this study is to find metal ions that enhance the ozone decomposition of chlorinated organic substances in acetic acid. Although the pseudo-first order degradation rate constant for 2,4-DCP by ozone in acetic acid in addition of Ca2+, Mg2+, Al3+ and Fe2+ were almost the same as that with no metal ion, the degradation rate in addition of Mn2+ and Fe3+ were 2.4 and 4.5 times as high as that with no metal ion, respectively. The presence of Fe3+ enhanced the degradation of 2,4-DCP by ozone in acetic acid because Fe3+-phenolate complex which have high reactivity with ozone was produced by the reaction between 2,4-DCP and Fe3+ in acetic acid.

Groundwater, used in this study, contaminated predominantly with aromatic compounds, was biologically treated in a fluidized-bed reactor (FBR) with immobilized cells. The aromatics were completely decomposed, while cis-1,2-dichloroethylene (cis-DCE) and trichloroethylene (TCE) were decomposed only approximately 20% and 5%, respectively. In these studies a significant improvement of the decomposition efficiency for chlorinated ethylenes was achieved by utilizing cometabolism. Methanol (MeOH) and toluene were used as the substrate in the case of one-stage reactor (Single Reactor). MeOH (187 mg l(-1)) increased the decomposition efficiency up to 40% and 60% for cis-DCE and TCE, respectively, while toluene (20 mg l(-1)) increased the decomposition efficiency of cis-DCE to 92% and the decomposition efficiency of TCE to 76%. In the case of two-stage reactor system (Reactor 1 and Reactor 2), MeOH and methane (CH4) were used as the substrate. In this system, cells grown on MeOH or CH4 in the Reactor 1 were continuously fed into Reactor 2 and groundwater was fed into Reactor 2 only. When MeOH (384 mg l(-1) d(-1)) was used as substrate the decomposition efficiency of cis-DCE and TCE were 60% and 70%, respectively. Similar decomposition efficiency was observed for a small amount of CH4 (19.3 mg l(-1) d(-1)).

The effects of cross-substrate interaction to the performance of a gas-phase biotrickling filter for treating a mixture of volatile organic compounds (VOCs), including three structural heterologous in acetone, toluene, and trichloroethylene, were investigated. The biotrickling filter was inoculated with microbial consortium containing at least seven bacterial species utilizing either acetone or toluene, or both, as their carbon sources. In the performance study, the column operating under variable conditions typifying the waste gas emission from the microelectronics fabrication processes achieved a total hydrocarbon (THC) removal efficiency in excess of 85% and a mineralization capacity over 50% for THC mass loading as high as 36.2 g-CH4 m-3h-1. The cross-substrate effects were examined by correlating the relative changes in the mass removal of each substrate with the biodegradative capability of the microbial consortium. The degradation of trichloroethylene was primarily due to co-metabolism by the toluene-oxidizing enzymes, but the results also indicated that trichloroethylene partially induced its own degradation. Concentration increases in acetone appeared to cause a diauxie effect that suppressed degradation of toluene and trichloroethylene, and shifted the microbial population toward the selective acetone-degraders. No irrecoverable toxicity or inhibitory effects were observed throughout the experiments. These results suggest that the relative VOC concentration in the waste gas mixture is a factor as important as the biodegradative function of the microbial consortium, and thus should be carefully evaluated to satisfy the treatment objectives., (copyright 2004 Elsevier Ltd.)

Trichloroethylene (TCE) is one of the most prevalent environmental contaminants, and it poses an expensive remediation problem. Phytoremediation has been investigated as a potential tool for the removal of TCE from ground water and soil, and has shown promise in preliminary trials. However, the fate of TCE in plants is largely unknown. Radiolabel studies showed that once taken up and transformed, most of the TCE is incorporated into plant tissue as a non-volatile, un-extractable residue. We describe here an assay for TCE transformation by poplar suspension cells. Using this assay, it was shown that two different activities contribute to the fixation of TCE by poplar cells, one associated with cell walls and insoluble residues, the other associated with a high molecular weight, heat labile fraction of the cell extract. It appears that plant enzymes catalyze some of the transformations.

The industrial solvent trichloroethylene (TCE) is among the most ubiquitous chlorinated compounds found in groundwater contamination. The objective of this study was to develop a biobarrier system containing oxygen-organic releasing material to enhance the aerobic cometabolism of TCE in situ. The oxygen-organic material, which contains calcium peroxide and peat, is able to release oxygen and primary substrates continuously upon contact with water. Batch experiments were conducted to design and identify the components of the oxygen-organic releasing material, and evaluate the oxygen and organic substrate (presented as COD equivalent) release from the designed oxygen-organic material. The observed oxygen and chemical oxygen demand (COD) release rates were approximately 0.0246 and 0.052 mg/d/g of material, respectively. A laboratory-scale column experiment was then conducted to evaluate the feasibility of this proposed system for the bioremediation of TCE-contaminated groundwater. This system was performed using a series of continuous-flow glass columns including a soil column, an oxygen-organic material column, followed by two consecutive soil columns. Aerobic acclimated sludges were inoculated in all three soil columns to provide microbial consortia for TCE biodegradation. Simulated TCE-contaminated groundwater with a flow rate of 0.25 l/day was pumped into this system. Effluent samples from each column were analyzed for TCE and other indicating parameters (e.g., pH, dissolved oxygen). Results show that the decreases in TCE concentrations were observed over a 4-month operating period. Up to 99% of TCE removal efficiency was obtained in this passive system. Results indicate that the continuously released oxygen and organic substrates from the oxygen-organic materials enhanced TCE biotransformation. Thus, the biobarrier treatment scheme has the potential to be developed into an environmentally and economically acceptable remediation technology.

The photocatalytic oxidation of high levels of volatile chlorinated organic compounds in gas phase has been studied using a specially designed photoreactor. The influence of light intensity, initial water vapour concentration, temperature, inlet contaminant concentration and flow rate on destruction efficiency has been investigated. The performance of the titanium catalyst was strongly affected by the presence of water in the air stream. Experiments have been most successfully conducted at room temperature, low initial contaminant concentrations, low flow rates and high light intensities. Several by-products have been detected performing photocatalytic degradation of trichloroethylene (TCE) and tetrachloroethylene (PCE). No catalyst deactivation was observed.

Investigation on the degradability of tetrachloroethene was performed using fresh and mechanically-biologically pretreated household waste. The corresponding metabolites were determined and the experimental conditions were characterized by the concentrations of methane, organic acids, sulfate and nitrate as well as by pH and redox potential. Furthermore, sorption studies on the substances in different wastes were carried out. With pretreated waste the degradation efficiency was much higher than with fresh waste. On the other hand, the fresh waste showed higher sorption capacity for the chlorinated compounds.

Risk assessments for vinyl chloride (VC) and trichloroethylene (TCE) are presented as examples of approaches for incorporating chemical-specific pharmacokinetic and mechanistic information into a more scientifically plausible cancer risk assessment. For VC, the evidence regarding mode of action includes direct reaction of a metabolite with DNA, resulting in DNA adducts and mistranscription, and cross-species target-tissue correspondence of a rare tumor type. Risk estimates for human exposure to VC predicted with a physiologically-based pharmacokinetic (PBPK) model and the linearized multistage (LMS) model were lower than those currently used in environmental decision-making by a factor of 30 to 50, and were more consistent with human epidemiological data. For TCE, there is evidence of increased cell proliferation due to receptor interaction or cytotoxicity in every instance in which tumors are observed, and the tumors typically represent an increase in the incidence of a commonly observed, species-specific lesion. Virtually safe exposure estimates for human exposure to TCE predicted with a PBPK model and a margin of exposure (MOE) approach were higher than those obtained by the conventional LMS approach by roughly a factor of 100. The MOE approach is recommended as an alternative to the LMS approach for chemicals with a carcinogenic mode of action which entails increased cell proliferation, leading to the expectation of a highly nonlinear cancer dose-response.