PCE Concentrations Research Articles

Spatiotemporal variability of tetrachloroethylene in residential indoor air due to vapor intrusion: a longitudinal, community-based study

The migration of volatile contaminants from groundwater and soil into indoor air is a potential health threat at thousands of contaminated sites across the country. This phenomenon, known as vapor intrusion, is characterized by spatial and temporal heterogeneity. This study examined short-term fluctuations in concentrations of tetrachloroethylene (PCE) in the indoor air of residential homes due to vapor intrusion in a community in San Antonio, Texas, that sits atop an extensive, shallow plume of contaminated groundwater. Using a community-based design, we removed potential indoor sources of PCE and then collected twelve 3-day passive indoor air samples in each of the 20 homes. Results demonstrated a one-order-of-magnitude variability in concentration across both space and time among the study homes, although all measured concentrations were below risk-based screening levels. We found that within any given home, indoor concentrations increase with the magnitude of the barometric pressure drop (P=0.048) and humidity (P<0.001), while concentrations decrease as wind speed increases (P<0.001) and also during winter (P=0.001). In a second analysis to examine sources of spatial variability, we found that indoor air PCE concentrations between homes increase with groundwater concentration (P=0.030) and a slab-on-grade (as compared with a crawl space) foundation (P=0.028), whereas concentrations decrease in homes without air conditioners (P=0.015). This study offers insights into the drivers of temporal and spatial variability in vapor intrusion that can inform decisions regarding monitoring and exposure assessment at affected sites.

Biodegradation of tetrachloroethylene-rich synthetic wastewater in anaerobic hybrid reactor

In this study, the anaerobic hybrid reactor (AHR) was used for the treatment of synthetic wastewater containing tetrachloroethylene (PCE) by systematic increment in the influent PCE and chemical oxygen demand (COD) concentrations. According to the acclimatization study, 99.95 ± 0.07% of PCE and 98.26 ± 0.46% of COD removals were obtained at an influent PCE and COD concentrations of 50mg/l and 2,000 mg/l, respectively. The maximum yield coefficient (Ym) was found to be 0.055 mg biomass/mg COD, while the maximum specific substrate as COD (qm S) and co-substrate as PCE (qm CS) utilization rates were found to be 570 mg COD/g volatile suspended solids (VSS)/d and 15.83 mg PCE/g VSS/d, respectively, during the bio-kinetics study. The optimum hydraulic retention time for the maximum PCE removal was observed to be 18 h. The results of this study broadly indicated that the AHR has the high potentiality for the treatment of wastewater containing high concentration of PCE.

Biodegradation of perchloroethylene and chlorophenol co-contamination and toxic effect on activated sludge performance

This study investigated the effects of PCE and 2-CP co-contamination on growth of microbial community in terms of enzymatic activity and microbial diversity in activated sludge. Results showed that the activities of three key enzymes (dehydrogenase, phosphatase and urease) decreased significantly when PCE (in the range of 5–150mg/L) was mixed with 2-CP (in the range of 25–150mg/L). Especially, activity of dehydrogenase decreased by more than 93% as the concentration of PCE and 2-CP both reached 150mg/L. PCR–DGGE revealed that short-term exposure with PCE and 2-CP did not lead to shift in the microbial community structure, while clone library demonstrated a significant change in the microbial diversity after long-term exposure. As the population of Alphaproteobacteria and Gamaproteobacteria decreased, with Actinobacteria eventually disappeared, species including Firmicutes, Bacteroidetes and Synergistetes became dominating groups. This study demonstrated that co-contamination with PCE and 2-CP affected the performance of activated sludge in a significant way.

Field Evidence of Dissolution and Degradation Rates Enhancement During ISCR and ENA Treatments of Chlorinated Solvents

AbstractThis article presents field tests comparing two methods of treatment of chlorinated solvents undertaken at the same site. The site is an automobile factory where two chlorinated solvents (CS) plumes were identified. At the first source, in situ chemical reduction (ISCR) was applied, while at the second one, enhanced natural attenuation (ENA) was used. A set of specific multilevel sampling wells were installed approximately 20 m downgradient of the sources to estimate the efficiency of the treatments. The presence of a low‐permeability layer (source 1) or a thick oil lens (source 2) in the top part of the aquifer prevented the CS from reaching the bottom of the aquifer. These layers led to difficulties treating the contamination. At the ISCR and ENA treatment zones, the concentrations of tetrachloroethene (PCE) and trichloroethene (TCE) did not change significantly, while the concentration of metabolites (cis‐1,2‐DCE, vinyl chloride, and ethene) significantly increased 50 to 150 days after treatment. Due to high concentration of CS in the source zone, a mass balance calculation, including chlorine, was possible. It showed that around 1 to 2 percent of the injected products were used to reduce the CS. A detailed analysis and 1D analytical modeling of CS concentrations showed that the treatment led to a large (two to three times) increase in dissolution of the organic phase. This explains why, despite an efficient treatment, the PCE and TCE concentrations remained virtually unchanged. Degradation rates also increased due to the treatment. Due to some differences in the source‐zone chemistry, it was not possible to differentiate between the ISCR and ENA efficiencies. © 2013 Wiley Periodicals, Inc.

Biodegradable poly(carbonate‐ether)s with thermoresponsive feature at body temperature

AbstractNovel biodegradable poly(carbonate‐ether)s (PCEs) with lower critical solution temperature (LCST) at body temperature were synthesized by copolymerization of CO2 and ethylene oxide (EO) under double metal cyanide (DMC) catalyst. The PCEs showed carbonate unit (CU) content of 1.0–42.4 mol % and molecular weight of 2.7–247 kg/mol, which exhibited reversible thermoresponsive feature in deionized water with LCST in a broad window from 21.5 to 84.1 °C. The LCST was highly sensitive to the CU content and the molecular weight of PCEs, and it showed a linear relation with CU content for PCEs with similar molecular weight. In particular, aqueous solution of PCE with a 26.0 mol % of CU showed an LCST around 36.1 °C, which was very close to the body temperature. Interestingly, it was found that the phase transition behavior changed with PCE concentration. For PCE with Mn of 2.7 kg/mol and CU content of 30.0 mol %, the LCST increased from 21.5 to 36.7 °C when the PCE concentration changed from 10 to 1 g/L. Dynamic light scattering indicated that the phase transition was possibly due to a coil‐to‐globule transition. The thermoresponsive biodegradable PCE with LCST at body temperature is promising for biomedical applications, especially for in vivo applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

A two and half-year-performance evaluation of a field test on treatment of source zone tetrachloroethene and its chlorinated daughter products using emulsified zero valent iron nanoparticles

A field test of emulsified zero valent iron (EZVI) nanoparticles was conducted at Parris Island, SC, USA and was monitored for two and half years to assess the treatment of subsurface-source zone chlorinated volatile organic compounds (CVOCs) dominated by tetrachloroethene (PCE) and its chlorinated daughter products. Two EZVI delivery methods were used: pneumatic injection and direct injection. In the pneumatic injection plot, 2180 L of EZVI containing 225 kg of iron (Toda RNIP-10DS), 856 kg of corn oil, and 22.5 kg of surfactant were injected to remedy an estimated 38 kg of CVOCs. In the direct injection plot, 572 L of EZVI were injected to treat an estimated 0.155 kg of CVOCs. After injection of the EZVI, significant reductions in PCE and trichloroethene (TCE) concentrations were observed in downgradient wells with corresponding increases in degradation products including significant increases in ethene. In the pneumatic injection plot, there were significant reductions in the downgradient groundwater mass flux values for PCE (>85%) and TCE (>85%) and a significant increase in the mass flux of ethene. There were significant reductions in total CVOC mass (86%); an estimated reduction of 63% in the sorbed and dissolved phases and 93% reduction in the PCE DNAPL mass. There are uncertainties in these estimates because DNAPL may have been mobilized during and after injection. Following injection, significant increases in dissolved sulfide, volatile fatty acids (VFA), and total organic carbon (TOC) were observed. In contrast, dissolved sulfate and pH decreased in many wells. The apparent effective remediation seems to have been accomplished by direct abiotic dechlorination by nanoiron followed by biological reductive dechlorination stimulated by the corn oil in the emulsion.

Reductive dechlorination of chlorinated hydrocarbons as non-aqueous phase liquid (NAPL): Preliminary investigation on effects of cement doses

The reactivities of various types of iron mixtures to degrade chlorinated hydrocarbons (PCE, TCE and 1,1,1-TCA) in the form of non-aqueous phase liquids were investigated. The iron mixtures included a mixture of Fe(II) and Portland cement (Fe(II)-C), a mixture of Fe(II), Fe(III) and Ca(OH)2 (Fe(II/III)-L), and a mixture of Fe(II), Fe(III), Ca(OH)2, and Portland cement (Fe(II/III)-C). When the same amount of Fe(II) was used, Fe(II)-C was more reactive with chlorinated ethylenes (i.e. PCE and TCE) than Fe(II/III)-L. The reductive pathway for high concentrations of total PCE (i.e. above solubility) with Fe(II)-C was determined to be a combination of two-electron transfer, β-elimination and hydrogenolysis. Increasing the cement dose from 5% to 10% in Fe(II)-C did not affect PCE dechlorination rates, but it did favor the β-elimination pathway. In addition, when Fe(II/III)-C with 5%C was used, PCE dechlorination was similar to that by Fe(II)-C, but this mixture did not effectively degrade TCE. A modified second-order kinetic model was developed and shown to appropriately describe degradation of TCE at high concentrations. Fe(II/III)-L effectively degraded high concentrations of 1,1,1-TCA at rates that were similar to those obtained with Fe(II)-C using 10% C. Moreover, both increasing cement doses and the presence of Fe(III) increased dechlorination rates of 1,1,1-TCA, which was mainly through the hydrogenolysis pathway. The reactivity of Fe(II/III)-L was strongly dependent on the target compound (i.e. less reactivity with TCE, more with 1,1,1-TCA). Therefore, Fe(II/III)-L could be a potential mixture for degrading 1,1,1-TCA, but it should be modified to degrade TCE more effectively.

Assessment of Chemical Oxidation for Treatment of DNAPL in Fractured Sandstone Blocks

Laboratory experiments were performed in discretely-fractured sandstone blocks to evaluate the use of chemical oxidants to treat residual dense nonaqueous phase liquid (DNAPL) tetrachloroethene (PCE). Persulfate (chelated ferrous iron and alkaline activated) and permanganate oxidants were evaluated. Results showed that the maximum DNAPL mass removal rates ranged from 4,700 mg/L/day by using permanganate, to 2,600 mg/L/day by using chelated iron activated persulfate, to 480 mg/L/day by using alkaline activated persulfate. The rate of DNAPL mass removal rapidly declined over the 10 to 60 day application period, limiting DNAPL mass removal rates to only 2 to 20% of the residual DNAPL present on the fractures. The permanganate experiment was terminated after 10 days owing to plugging of the fracture. In the persulfate-treated fractures, substantial rebound in dissolved PCE concentrations were observed after persulfate addition ceased. Use of interfacial tracers in the persulfate experiments showed that the ...

Effect of chloroethene concentrations and granular activated carbon on reductive dechlorination rates and growth of Dehalococcoides spp.

This study focused on the investigation of (i) the tetrachloroethene (PCE) toxicity threshold of a reductively dechlorinating mixed culture containing Dehalococcoides spp., (ii) the adsorption of PCE on different types of granular activated carbon (GAC), and (iii) the bioavailability and reductive dechlorination in the presence of GAC. The abundance of Dehalococcoides spp. detected by quantitative real-time polymerase chain reaction (qPCR) was found to increase by 2–4 orders of magnitude during degradation of PCE. No degradation occurred at dissolved concentrations beyond 420μM (70mg/L). Different adsorption isotherms were determined for thermally and chemically activated carbons. The addition of GAC to biological assays reduced the dissolved PCE concentration below the toxicity threshold. The combination of microbial reductive dechlorination with GAC adsorption proved to be a promising method for remediation of groundwater contaminated by high concentrations of chloroethenes.

Reductive dechlorination of tetrachloroethene by two compost samples with different maturity

This study sets up microcosms using two types of compost samples, bagasse/manure compost, and yard-trimming compost with different maturity, to evaluate their capacity for reductive dechlorination of tetrachloroethene (PCE). The experimental results show that less matured compost samples could reduce 300μM of PCE to ethene within 180days of incubation. Decreasing initial PCE concentration and removing dissolved oxygen from the solution could enhance reducing efficiency. The solution remains near neutral pH throughout the experiment, and ethene emerged when the redox potential dropped to below −150mV. Different microbial inhibition agents, such as 2-bromoethanesulfonic acid and sodium molybdate 2-hydrate, exhibit different effects on the dechlorination efficiency. The potential advantages of using compost to remove PCE are discussed. Overall, due to their high carbon content, diverse microbial activity, high buffer capacity, and complex physical structure, compost samples could serve as suitable media for dechlorinating PCE.

Anticancer activity of persimmon ( Diospyros kaki L.) calyx extracts on human cancer cells

Natural products are the source of numerous therapeutic agents. Recent progress in the discovery of drugs from natural products has resulted in development of compounds for use in cancer treatment. Results from this study demonstrated that methanolic extracts of persimmon calyx (PCE) have cytotoxic effects in human cancer cells. Through MTT reduction assay, lactate dehydrogenase release assay, morphological assay, and colony formation assay, highly cytotoxic effects were demonstrated in human cancer cells treated with various concentrations of PCE. As expected, PCE inhibited growth of HT-29 cells in a dose-dependent manner. In particular, 500 µg/ml of PCE showed 31.1% inhibition against HT-29 cells. Interestingly, characteristics of apoptosis, including chromatin condensation and sharking, were shown to occur in HT-29 cells 24 h after treatment with 500 µg/ml of PCE. In addition, PCE also showed cytotoxic activity against HeLa and PANC-1 cells, as well as HT-29 cells. These results indicate that PCE contains bioactive materials and that it is a potential candidate for use as a chemotherapeutic agent against human cancer cells. Key words: Natural products, persimmon calyx, cytotoxic effects, cancer cells, apoptosis.

Risk of breast cancer following exposure to tetrachloroethylene-contaminated drinking water in Cape Cod, Massachusetts: reanalysis of a case-control study using a modified exposure assessment

BackgroundTetrachloroethylene (PCE) is an important occupational chemical used in metal degreasing and drycleaning and a prevalent drinking water contaminant. Exposure often occurs with other chemicals but it occurred alone in a pattern that reduced the likelihood of confounding in a unique scenario on Cape Cod, Massachusetts. We previously found a small to moderate increased risk of breast cancer among women with the highest exposures using a simple exposure model. We have taken advantage of technical improvements in publically available software to incorporate a more sophisticated determination of water flow and direction to see if previous results were robust to more accurate exposure assessment.MethodsThe current analysis used PCE exposure estimates generated with the addition of water distribution modeling software (EPANET 2.0) to test model assumptions, compare exposure distributions to prior methods, and re-examine the risk of breast cancer. In addition, we applied data smoothing to examine nonlinear relationships between breast cancer and exposure. We also compared a set of measured PCE concentrations in water samples collected in 1980 to modeled estimates.ResultsThirty-nine percent of individuals considered unexposed in prior epidemiological analyses were considered exposed using the current method, but mostly at low exposure levels. As a result, the exposure distribution was shifted downward resulting in a lower value for the 90th percentile, the definition of "high exposure" in prior analyses. The current analyses confirmed a modest increase in the risk of breast cancer for women with high PCE exposure levels defined by either the 90th percentile (adjusted ORs 1.0-1.5 for 0-19 year latency assumptions) or smoothing analysis cut point (adjusted ORs 1.3-2.0 for 0-15 year latency assumptions). Current exposure estimates had a higher correlation with PCE concentrations in water samples (Spearman correlation coefficient = 0.65, p < 0.0001) than estimates generated using the prior method (0.54, p < 0.0001).ConclusionsThe incorporation of sophisticated flow estimates in the exposure assessment method shifted the PCE exposure distribution downward, but did not meaningfully affect the exposure ranking of subjects or the strength of the association with the risk of breast cancer found in earlier analyses. Thus, the current analyses show a slightly elevated breast cancer risk for highly exposed women, with strengthened exposure assessment and minimization of misclassification by using the latest technology.

A self-standing, UV-cured polymer networks-reinforced plastic crystal composite electrolyte for a lithium-ion battery

We demonstrate a facile approach to fabrication of a self-standing plastic crystal composite electrolyte for a lithium-ion battery, wherein UV (ultraviolet)-cured ethoxylated trimethylolpropane triacrylate (ETPTA) networks are incorporated into a plastic crystal electrolyte (PCE, 1 M lithium bis-trifluoromethanesulphonimide (LiTFSI) in succinonitrile (SN)). An ETPTA monomer having trifunctional groups is successfully crosslinked within a very short UV-exposure time of 20 s without using any solvent, leading to the formation of a self-standing, transparent, and non-sticky plastic crystal composite electrolyte (X-PCCE). Owing to the introduction of the UV-cured ETPTA networks, the X-PCCE is capable of providing unprecedentedly robust mechanical strength even at a high concentration of PCE (i.e., ETPTA/PCE = 15/85%, w/w), along with affording high ionic conductivity. In contrast, a conventional plastic crystal composite electrolyte (F-PCCE) comprising polyvinylidenefluoride-co-hexafluoropropylene (PVdF-HFP) and PCE is difficult to be fabricated as a self-standing film and easily deformed by weak external stress. Notably, the X-PCCE shows significant improvement in electrochemical stability and interfacial resistance toward lithium metal electrodes. Ionic conductivities of the X-PCCE and the F-PCCE are examined as a function of temperature and discussed under consideration of the interaction between SN, LiTFSI, and polymers in the plastic crystal composite electrolytes.

Isolation and characterization of tetrachloroethylene- and cis-1,2-dichloroethylene-dechlorinating propionibacteria

Two rapidly growing propionibacteria that could reductively dechlorinate tetrachloroethylene (PCE) and cis-1,2-dichloroethylene (cis-DCE) to ethylene were isolated from environmental sediments. Metabolic characterization and partial sequence analysis of their 16S rRNA genes showed that the new isolates, designated as strains Propionibacterium sp. HK-1 and Propionibacterium sp. HK-3, did not match any known PCE- or cis-DCE-degrading bacteria. Both strains dechlorinated relatively high concentrations of PCE (0.3 mM) and cis-DCE (0.52 mM) under anaerobic conditions without accumulating toxic intermediates during incubation. Cell-free extracts of both strains catalyzed PCE and cis-DCE dechlorination; degradation was accelerated by the addition of various electron donors. PCE dehalogenase from strain HK-1 was mediated by a corrinoid protein, since the dehalogenase was inactivated by propyl iodide only after reduction by titanium citrate. The amounts of chloride ions (0.094 and 0.103 mM) released after PCE (0.026 mM) and cis-DCE (0.05 mM) dehalogenation using the cell-free enzyme extracts of both strains, HK-1 and HK-3, were stoichiometrically similar (91 and 100%), indicating that PCE and cis-DCE were fully dechlorinated. Radiotracer studies with [1,2-¹⁴C] PCE and [1,2-¹⁴C] cis-DCE indicated that ethylene was the terminal product; partial conversion to ethylene was observed. Various chlorinated aliphatic compounds (PCE, trichloroethylene, cis-DCE, trans-1,2-dichloroethylene, 1,1-dichloroethylene, 1,1-dichloroethane, 1,2-dichloroethane, 1,2-dichloropropane, 1,1,2-trichloroethane, and vinyl chloride) were degraded by cell-free extracts of strain HK-1.

Adaptation of a Constructed Wetland to Simultaneous Treatment of Monochlorobenzene and Perchloroethene

Mixed groundwater contaminations by chlorinated volatile organic compounds (VOC) cause environmental hazards if contaminated groundwater discharges into surface waters and river floodplains. Constructed wetlands (CW) or engineered natural wetlands provide a promising technology for the protection of sensitive water bodies. We adapted a constructed wetland able to treat monochlorobenzene (MCB) contaminated groundwater to a mixture of MCB and tetrachloroethene (PCE), representing low and high chlorinated model VOC. Simultaneous treatment of both compounds was efficient after an adaptation time of 2½ years. Removal of MCB was temporarily impaired by PCE addition, but after adaptation a MCB concentration decrease of up to 64% (55.3 μmol L−1) was observed. Oxygen availability in the rhizosphere was relatively low, leading to sub-optimal MCB elimination but providing also appropriate conditions for PCE dechlorination. PCE and metabolites concentration patterns indicated a very slow system adaptation. However, under steady state conditions complete removal of PCE inflow concentrations of 10–15 μmol L−1 was achieved with negligible concentrations of chlorinated metabolites in the outflow. Recovery of total dechlorination metabolite loads corresponding to 100%, and ethene loads corresponding to 30% of the PCE inflow load provided evidence for complete reductive dechlorination, corroborated by the detection of Dehalococcoides sp.

Field study of biostimulation and bioaugmentation for remediation of tetrachloroethene in groundwater

AbstractA pilot field study was conducted for remediation of a tetrachloroethene (PCE)‐contaminated site in Manhattan, Kansas. Prior to the pilot study, the PCE concentration in groundwater at the pilot‐study area was about 15 mg/L (91 µM). Nutrient solution comprising soy oil methyl esters (SOME), lactate, and yeast extract was added in the pilot‐study area for biostimulation on August 18, 2005 (day 0). Potassium bromide (KBr) was added in the nutrient solution as a tracer. PCE was converted to dichloroethene (DCE) under these conditions. KB‐1, a consortium of Dehalococcoides, and a second dose of nutrient solution were added on day 56. After addition of KB‐1, both PCE and DCE concentrations decreased. Nutrients were again injected on day 197 (with KBr). On day 348, cheese whey was injected. Soluble nutrients and KB‐1 migrated downstream, affecting PCE and DCE concentrations at downgradient wells; however, KB‐1 moved slower than the aqueous phase. The total chlorinated ethenes (CEs) decreased by about 80 percent in the pilot‐study area due to bioremediation. Biodegradation of CEs continued for several months after the addition of nutrients. A portion of the insoluble SOME was retained in the vicinity of the injection wells and provided a long‐time source of nutrients and electron donors that supported degradation of PCE. A mixture of SOME and soluble substrates worked effectively in this study. © 2011 Wiley Periodicals, Inc.

Enhanced Dechlorination of Tetrachloroethylene by Zerovalent Silicon in the Presence of Polyethylene Glycol under Anoxic Conditions

The combination of zerovalent silicon (Si(0)) with polyethylene glycol (PEG) is a novel technique to enhance the dechlorination efficiency and rate of chlorinated hydrocarbons. In this study, the dechlorination of tetrachloroethylene (PCE) by Si(0) in the presence of various concentrations of PEG was investigated under anoxic conditions. Several surfactants including cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and Tween 80 were also selected for comparison. Addition of SDS and Tween 80 had little effect on the enhancement of PCE dechlorination, while CTAB and PEG significantly enhanced the dechlorination efficiency and rate of PCE by Si(0) under anoxic conditions. The Langmuir-Hinshelwood model was used to describe the dechlorination kinetics of PCE and could be simplified to pseudo-first-order kinetics at low PCE concentration. The rate constants (k(obs)) for PCE dechlorination were 0.21 and 0.36 h(-1) in the presence of CTAB and PEG, respectively. However, the reaction mechanisms for CTAB and PEG are different. CTAB could enhance the apparent water solubility of PCE in solution containing Si(0), leading to the enhancement of dechlorination efficiency and rate of PCE, while PEG prevented the formation of silicon dioxide, and significantly enhanced the dechlorination efficiency and rate of PCE at pH 8.3 ± 0.2. In addition, the dechlorination rate increased upon increasing PEG concentration and then leveled off to a plateau when the PEG concentration was higher than 0.2 μM. The k(obs) for PCE dechlorination by Si(0) in the presence of PEG was 106 times higher than that by Si(0) alone. Results obtained in this study would be helpful in facilitating the development of processes that could be useful for the enhanced degradation of cocontaminants by zerovalent silicon.

Application of a New Vertical Profiling Tool (ESASS) for Sampling Groundwater Quality During Hollow‐Stem Auger Drilling

A new tool called ESASS (Enhanced Screen Auger Sampling System) was developed by the U.S. Geological Survey. The use of ESASS, because of its unique U.S. patent design (U.S. patent no. 7,631,705 B1), allows for the collection of representative, depth‐specific groundwater samples (vertical profiling) in a quick and efficient manner using a 0.305‐m long screen auger during hollow‐stem auger drilling. With ESASS, the water column in the flights above the screen auger is separated from the water in the screen auger by a specially designed removable plug and collar. The tool fits inside an auger of standard inner diameter (82.55 mm). The novel design of the system constituted by the plug, collar, and A‐rod allows the plug to be retrieved using conventional drilling A‐rods. After retrieval, standard‐diameter (50.8 mm) observation wells can be installed within the hollow‐stem augers. Testing of ESASS was conducted at one waste‐disposal site with tetrachloroethylene (PCE) contamination and at two reference sites with no known waste‐disposal history. All three sites have similar geology and are underlain by glacial, stratified‐drift deposits. For the applications tested, ESASS proved to be a useful tool in vertical profiling of groundwater quality. At the waste site, PCE concentrations measured with ESASS profiling at several depths were comparable (relative percent difference &lt;25%) to PCE concentrations sampled from wells. Vertical profiling with ESASS at the reference sites illustrated the vertical resolution achievable in the profile system; shallow groundwater quality varied by a factor of five in concentration of some constituents (nitrate and nitrite) over short (0.61 m) distances.

Enhanced reductive dechlorination of tetrachloroethene by nano-sized zero valent iron with vitamin B 12

We demonstrated that the addition of vitamin B 12 can significantly enhance the reductive dechlorination of tetrachloroethene (PCE) by nano-sized zero valent iron (nZVI). A remarkable reductive dechlorination of PCE (0.25 ± 0.01 h −1) was observed in nZVI suspension (0.05 g/24 mL) with 0.5 mM vitamin B 12 in 6 h, while no significant reductive dechlorination of PCE was observed in the nZVI suspension without vitamin B 12. Vitamin B 12r of which central metal is Co 2+ was identified as predominant specie during the dechlorination of PCE. The dechlorination kinetic rate constant of PCE in nZVI/vitamin B 12 system was significantly dependent on the suspension pH and concentrations of vitamin B 12, nZVI, and PCE. An enhancement in PCE dechlorination kinetic (0.180 ± 0.006–0.709 ± 0.004 h −1) due to the formation of hydroxovitamin B 12r was observed by increasing the suspension pH (5–9). The dechlorination kinetic rate constant of PCE increased proportionally (0.0010 ± 0.0009–1.3660 ± 0.2940 h −1) as the concentration of vitamin B 12 increased (5 nM to 5 mM). As the concentration of nZVI increased by 50 times (0.01–0.50 g), the dechlorination kinetic increased approximately 137 times (0.007 ± 0.001–0.961 ± 0.182 h −1). However, the dechlorination kinetic decelerated (0.184 ± 0.010–0.039 ± 0.006 h −1) as PCE concentration increased (0.005–1.0 mM). This study provides basic understanding on the role of vitamin B 12/vitamin B 12r as an electron mediator in the enhanced reductive dechlorination of PCE by nZVI occasionally observed in remediation sites.

Dehalorespiration Model That Incorporates the Self-Inhibition and Biomass Inactivation Effects of High Tetrachloroethene Concentrations

In the vicinity of dense nonaqueous phase liquid (DNAPL) contaminant source zones, aqueous concentrations of tetrachloroethene (PCE) in groundwater may approach saturation levels. In this study, the ability of two PCE-respiring strains (Desulfuromonas michiganensis and Desulfitobacterium strain PCE1) to dechlorinate high concentrations of PCE was experimentally evaluated and depended on the initial biomass concentration. This suggests high PCE concentrations permanently inactivated a fraction of biomass, which, if sufficiently large, prevented dechlorination from proceeding. The toxic effects of PCE were incorporated into a model of dehalorespirer growth by adapting the transformation capacity concept previously applied to describe biomass inactivation by products of cometabolic TCE oxidation. The inactivation growth model was coupled to the Andrews substrate utilization model, which accounts for the self-inhibitory effects of PCE on dechlorination rates, and fit to the experimental data. The importance of incorporating biomass inactivation and self-inhibition effects when modeling reductive dechlorination of high PCE concentrations was demonstrated by comparing the goodness-of-fit of the Andrews biomass inactivation and three alternate models that do capture these factors. The new dehalorespiration model should improve our ability to predict contaminant removal in DNAPL source zones and determine the inoculum size needed to successfully implement bioaugmentation of DNAPL source zones.