Abstract  Pt-loaded MCM-41 catalysts modified with phosphorus acids at various SUP ratios were prepared. Phosphoric acid molecules may react with surface Si-OH groups, which prevented the direct attack of H2PtCl4 on mesostructure and improved the structural stability of Pt-loaded catalysts. Ammonia temperature-programmed desorption (NH3-TPD) indicated that P-MCM-41 samples possessed weak Bronsted acidities, and the Bronsted acidities on P-MCM-41 decreased with the incorporation of Pt, depending on the phosphoric acid loading. The interaction of Pt with phosphoric species resulted in the change of Pt oxidation state and the Bronsted acidity strength. The results of catalytic combustion of trichloroethylene over these catalysts showed that the modification with phosphoric acid endowed the catalysts with good catalytic performance of high trichloroethylene conversion and absence of tetrachloroethylene. The combination of Bronsted acidities and oxidation state Pt would propose a novel catalytic material suitable for the combustion of chlorinated volatile organic compounds. Carbon deposit over acid sites resulted in the deactivation of Pt/P-MCM-41 catalysts, and the deactivated catalysts were recovered at 500 degrees C in air. (C) 2008 Elsevier B.V. All rights reserved.

Abstract  The partition of 1-pyrenemethanol (PyM) between the external medium and AOT/water reverse micelles formed in several organic solvents has been measured and compared with its partition between bulk solvents. The organic solvents employed were n-heptane, cyclohexane, isooctane, dodecane, benzene, chlorobenzene, toluene, and tetrachloroethylene. The partition of PyM in AOT/water/nonpolar solvent reverse micelles is dominated by the free energy of the probe in the external solvent. To evaluate the stability of the probe in micelles dispersed in different solvents, the micellar data were referred to a common (water) solvent. A weakly positive correlation was obtained for the partition of the probe between the different micelles and water. Furthermore, the polarity sensed by PyM is higher in AOT/alkane/water that in AOT/aromatic solvent/water reverse micelles. These results can be explained in terms of two driving forces whose relative importance is determined by the characteristics of the solute and the external solvent. One of them, solvation of the surfactant head by the polar group of PyM, will be disfavored by polar solvents. The second one, interaction of the aromatic part of the micelle associated PyM molecules with the external solvent, would be determined by the solvent/probe affinity, measured by the solvent/water partition constant.

Abstract  We constructed a multispecies biofilm model for simultaneous reduction of trichloroethene (TCE) and nitrate (NO3-) in the biofilm of a H2-based membrane biofilm reactor (MBfR). The one-dimensional model includes dual-substrate Monod kinetics for a steady-state biofilm with multiple solid and dissolved components. The model has five solid components: autotrophic denitrifying bacteria (ADB), heterotrophic denitrifying bacteria (HDB), Dehalococcoides (DHC), inert biomass (IB), and extracellular polymeric substances (EPS). The model has eight dissolved components: NO3-, TCE, dichloroethene (DCE), vinyl chloride (VC), ethene, hydrogen (H2), substrate-utilization-associated products (UAP), and biomass-associated products (BAP). We used this model to simulate a bench-scale experiment in a H2-based MBfR. The model simulated the trends well: almost complete removal of nitrate, incomplete reduction of TCE, and almost no accumulation of DCE and VC. To gain insight into reductive dehalogenation in a H2-based MBfR, we also simulated the concentrations of nitrate, TCE, DCE, VC, and ethene in the reactor effluent while varying the influent nitrate concentration. Simultaneous low concentrations of nitrate and the three chlorinated ethenes can occur as long as the influent ratio of NO3- to TCE is not too large, so that DHC are a significant fraction of the biofilm.

Abstract  Chlorinated ethenes such as tetrachloroethene and trichloroethene have been widely used as dry-cleaning and degreasing solvents. Under anaerobic conditions, microorganisms reduce these parent compounds to less-chlorinated daughter products such as cis-1,2-dichloroethene (cDCE), and often further to ethene. This process can be stalled at cDCE, due to insufficient supply of reductants and/or inadequate microbial-community composition. Recently, a novel bacterium, Polaromonas sp. JS666, was isolated that is able to aerobically oxidize cDCE as sole carbon and energy source. As such, it is a promising candidate for use as a subsurface, bioaugmentation agent at sites where anaerobic bioremediation is inappropriate or has stalled and cDCE has migrated to, and accumulated within, aerobic zones, or where it is practical to impose aerobic conditions.

Abstract  A kinetic model is presented for the catalytic hydrodehalogenation of chlorinated ethylenes using Pd and H-2 under water treatment conditions, All five chlorinated ethylenes, including tetrachloroethylene (PCE) and vinyl chloride, were completely removed from tap water within 10 minutes at room temperature by 0.5 g of 0.5% Pd on alumina and 0.1 atm H-2. Ethane accounted for 55-85% of the mass balance in these systems, Ethene was a reactive intermediate whose maximum concentration accounted for less than about 5% of the initial substrate, Palladium on granular carbon was also an effective catalyst, although ethane yield for PCE was somewhat lower than with Pd-alumina (55% versus 85%). The transformation of PCE was first order with respect to both substrate and amount of metal, with a half-life of t(1/2) = 9 min for 0.055 mu mole Pd (583 mu g of 1% Pd on powdered activated carbon), Addition of similar to 10 mg/L of nitrite to the water decreased the rate constant by about 50%. The nitrite concentration decreased by about 25% over the course of the reaction, Addition of nitrate or sulfate had smaller effect on the rate of PCE transformation; chloride had no effect, The presence of oxygen greatly reduced the amount of ethane produced regardless of the catalyst support, Bisulfide poisoned the catalyst.

Abstract  This study evaluates the efficiency of a full-scale, 81 m-wide permeable reactive barrier (PRB) configured by injection of dairy whey in the downgradient region of a contaminant source zone to enhance the in situ biodegradation of high concentrations (102 to 103 mu g/L) of chlorinated ethenes (CEs). Ten biannual whey injections were completed in a 3.5-year pilot phase and 1.5-year operational phase. Improved and sustained dechlorination was observed at extraction/injection and downgradient wells in the fully-operational phase, when dried whey masses were increased from 13.6 kg to 230-360 kg, whey slurry volumes were increased from 2300 L to 307,000-480,000 L, and extraction/injection well loops were employed for the application of whey. At extraction/injection wells, CEs decreased to low ( less than or equal to 10 mu g/L) or undetectable levels. At downgradient wells, average trichloroethene concentrations decreased, by as much as 100% (from less than or equal to 384.2 during the pilot phase to less than or equal to 102.6 mu g/L during the operational phase), while average cis-dichloroethene concentrations decreased by as much as 57.5% (from less than or equal to 6466.1 to less than or equal to 4912.2 mu g/L). Downgradient vinyl chloride averages either increased by as much as 63.8% (from less than or equal to 859.6 to less than or equal to 1407.9 mu g/L) or decreased by 64.0% (from 1375.4 to 880 mu g/L). Downgradient ethene + ethane averages increased by as much as 73.2% (from less than or equal to 1145.3 to less than or equal to 1347.1 mu g/L). On the basis of the 2008 average market price, the estimated material cost of whey is $1.96/kg organic carbon or, for the configuration of an 81 m PRB by biannual application of 300 kg whey, $325/year. Carbon substrate cost comparisons and implications for efficient in situ treatment design are discussed.

Abstract  We estimated the distribution of chlorinated aliphatic hydrocarbons (CAHs) from groundwater samples collected along three transects in a sand aquifer. Trichloroethylene (TCE) leaked and contaminated the aquifer probably more than a decade before we collected the measurements. The data show significant concentrations of TCE, cis-1,2-dichloroethylene (c-DCE), vinyl chloride (VC), and ethene. We attributed DCE, VC, and ethene to the reductive dehalogenation of TCE. The CAH concentrations varied significantly with depth and correlate with sulfate and methane concentrations. Anoxic aquifer conditions exist with methane present at relatively high concentrations at depth. High concentrations of TCE correspond with the absence of methane or low methane concentrations, whereas products of TCE dehalogenation are associated with higher methane concentrations and low sulfate concentrations. Indications are that the dechlorination of TCE and DCE to VC and ethene is associated with sulfate reduction and active methanogenesis. TCE dechlorination to DCE is likely occurring under the less reducing conditions of sulfate reduction, with further reductions to VC and ethene occurring under methanogenic conditions. We estimated that about 20% of TCE has dechlorinated to ethene. The analysis of the data enhanced our knowledge of natural in situ transformation and transport processes of CAHs.

Abstract  Various technologies have been used for the treatment and remediation of areas contaminated by BTEX (benzene, toluene, ethylbenzene and xylenes), which are organic compounds that are of particular concern due to their toxicity. Potential applications of synthetic zeolites for environmental fieldwork have also been reported worldwide. In this work, a hexadecyltrimethyl ammonium (HDTMA) surfactant-modified synthetic zeolite was investigated for its efficiency in removing BTEX from aqueous solutions. Three surfactant-modified zeolites were synthesized, with amounts of surfactant corresponding to 50%, 100%, and 200% of the total cation-exchange capacity (CEC) of the synthetic zeolite Y. The results of the BTEX adsorption experiments onto both synthetic zeolite and surfactant-modified zeolites (SMZ) showed that the SMZ-100 (zeolite modified with surfactant levels at 100% of CEC) was the most efficient modified zeolite for BTEX removal. Kinetics studies indicated that the multicomponent adsorption equilibrium was reached within 6 h and followed pseudo-second-order kinetics. The Langmuir, Freundlich, Redlich-Peterson and Temkin models were used to evaluate the BTEX adsorption capacity by SMZ-100. The Temkin model was found to be suitable for all BTEX compounds in a multicomponent system. Regeneration cycles of the modified zeolite were also performed, and the results showed that the adsorbent could be used efficiently in as many as four adsorption cycles, except for benzene.

Abstract  Background concentrations, emission rates, and trends in emission rates for five trace gases are inferred for the northeastern United States from continuous atmospheric observations at Harvard Forest in central New England for 1996-1998. Mixing ratios of gases regulated by the Montreal Protocol (CFC-11 (CCl3F), CFC-12 (CCl2F2), CFC-113 (CCl2F-CClF2), CH3CCl3, and halon-1211 (CBrClF2)) are referenced to CO and PCE (perchloroethylene, tetrachloroethene, C2Cl4) to determine their urban/industrial source strengths and to test existing estimates of U.S. emissions. Despite the full imposition by 1996 of the Montreal Protocol ban on production by developed countries, our data show that significant releases to the atmosphere continue and that only emissions of CFC-12 and CH(3)CC(l)3 declined in the region during this period. A broader historical and geographical study of emissions reveals that from 1986 to 1996 the international treaty has reduced U. S. emissions of CFC-11, CFC-12, CFC-113, and CH3CCl3 by 87%, 70%, 93%, and 87%, respectively, but current trends suggest persistent emissions for many years following.

Abstract  Nanoscale Pd/Fe bimetallic particles were synthesized and used to hydrodechlorinate 2,4-dichlorophenol. 2,4-dichlorophenol was transformed to phenol with a small amount of 2-chlorophenol and 4-chlorophenol produced. The reaction pathway and reaction rate constants for each step have been determined. The effects of various Pd bulk loadings in the bi-metals, temperatures and pH conditions on the hydrodechlorination of 2,4-dichlorophenol were examined. The results showed that higher Pd bulk loadings, higher temperatures and weak acid conditions are beneficial to the catalytic dechlorination of 2,4-dichlorophenol.

Abstract  THIO, used in the production of pesticides, polymers, and pharmaceuticals, and as a food additive, was tested for developmental toxicity in Sprague-Dawley rats (25/group) and New Zealand White rabbits (15-26/group). THIO was given po in corn oil to rats (0, 20, 35, or 50 mg/kg/day; gestational days (gd) 6-15) or rabbits (0, 10, 30 or 40 mg/kg/day; gd 6-19). Maternal body wt., food and water consumption (rats) were recorded. On gd 20 (rats) or 30 (rabbits), maternal organs and fetuses were weighed, and fetuses were examined for malformations (external, visceral, and skeletal). In rats, maternal body wt. change and food consumption were depressed in all THIO-treated groups on gd. 6-9. Gravid uterine wt. was decreased, and relative maternal liver wt. was increased at 50 mg/kg/day; kidney wt. was unaffected. Increased postimplantation loss and incidence of external malformations, and decreased live litter size were observed at 50 mg/kg/day. Female fetal body wt. was decreased at 35 mg/kg/day. In rabbits, maternal food intake tended to be lower, and body wt. change was decreased at 30 and 40 mg/kg/day on gd 12-15. Gravid uterine wt., liver and kidney wt. were unaffected. Postimplantation loss, litter size, average fetal body wt. and morphological development were unaffected. In summary, for rats, 20 mg/kg/day THIO was the low observed adverse effect level (LOAEL) for maternal toxicity, based on transient decreases in maternal wt. gain and food intake. A maternal no observed adverse effect level (NOAEL) was not determined. The developmental NOAEL in rats was 20 mg/kg/day; clear evidence of developmental toxicity was seen at greater than or equal to 35 mg/kg/day. In rabbits, the maternal NOAEL was 10 mg/kg/day. Maternal toxic effects at greater than or equal to 30 mg/kg/day were minor. The developmental NOAEL was greater than or equal to 40 mg/kg/day.

Abstract  The Report on Carcinogens (RoC) is a scientific and public health document mandated by Congress in 1978. The RoC identifies and discusses substances, chemicals, mixtures, or exposure circumstances (collectively called substances) that may pose a cancer hazard to human health and to which persons in the United States are exposed. Nominations to the RoC go through a rigorous review process with multiple opportunities for public comment. The RoC is a compilation of substance profiles and each new edition replaces the previous one. Each substance profile in the RoC identifies a substance as known or reasonably anticipated to be a human carcinogen and provides information on (1) the scientific evidence that supports the listing (human epidemiological studies, cancer studies in experimental animals, and toxicokinetic, genotoxic, and mechanistic data), (2) the potential for human exposure, such as data on use, production, environmental occurrence, occupational exposure, and exposure to the general population, and (3) current Federal regulations to limit exposure.

Abstract  Methyl tert-butyl ether (MTBE) was detected in source water used by 8.7 percent of randomly selected community water systems (CWSs) in the United States at concentrations that ranged from 0.2 to 20 micrograms per liter (Ág/L). The Random Survey conducted by the U.S. Geological Survey, in cooperation with the Metropolitan Water District of Southern California and the Oregon Health & Science University, was designed to provide an assessment of the frequency of detection, concentration, and distribution of MTBE, three other ether gasoline oxygenates, and 62 other volatile organic compounds (VOCs) in ground- and surface-water sources used for drinking-water supplies. The Random Survey was the first of two components of a national assessment of the quality of source water supplying CWSs sponsored by the American Water Works Association Research Foundation. A total of 954 CWSs were selected for VOC sampling from the population of nearly 47,000 active, self-supplied CWSs in all 50 States, Native American Lands, and Puerto Rico based on a statistical design that stratified on CWS size (population served), type of source water (ground and surface water), and geographic distribution (State). At a reporting level of 0.2 Ág/L, VOCs were detected in 27 percent of source-water samples collected from May 3, 1999 through October 23, 2000. Chloroform (in 13 percent of samples) was the most frequently detected of 42 VOCs present in the source-water samples, followed by MTBE. VOC concentrations were generally less than 10 Ág/L--95 percent of the 530 detections--and 63 percent were less than 1.0 Ág/L. Concentrations of 1,1-dichloroethene, tetrachloroethene, trichloroethene, vinyl chloride, and total trihalomethanes (TTHMs), however, exceeded drinking-water regulations in eight samples. Detections of most VOCs were more frequent in surface-water sources than in ground-water sources, with gasoline compounds collectively and MTBE individually detected significantly more often in surface water. Use of personal and commercial motorized watercraft on surface-water bodies that are drinking-water sources is probably the reason for the elevated detections of gasoline contaminants relative to ground water. MTBE detections demonstrated a seasonal pattern with more frequent detections in surface water in summer months, which is consistent with seasonal watercraft use. The detection frequency of most VOCs was significantly related to urban land use and population density. Detections of any VOC, non-trihalomethane compounds, gasoline compounds collectively, the specific gasoline compounds benzene, toluene, ethylbenzene, and xylenes (BTEX), MTBE, solvents, and refrigerants were significantly greater in areas with more than 60 percent urban land use and (or) population density greater than 1,000 people per square mile than in source waters from less urbanized or lower population-density areas. MTBE detections were five times more frequent in source waters from areas with high MTBE use than in source waters from low or no MTBE use, but, unlike other gasoline compounds, MTBE detections were not significantly related to the density of gasoline storage tanks near drinking-water sources.

Abstract  In recent years physiologically based pharmacokinetic models have come to play an increasingly important role in risk assessment for carcinogens. The hope is that they can help open the black box between external exposure and carcinogenic effects to experimental observations, and improve both high-dose to low-dose and interspecies projections of risk. However, to date, there have been only relatively preliminary efforts to assess the uncertainties in current modeling results. In this paper we compare the physiologically based pharmacokinetic models (and model predictions of risk-related overall metabolism) that have been produced by seven different sets of authors for perchloroethylene (tetrachloroethylene). The most striking conclusion from the data is that most of the differences in risk-related model predictions are attributable to the choice of the data sets used for calibrating the metabolic parameters. Second, it is clear that the bottom-line differences among the model predictions are appreciable. Overall, the ratios of low-dose human to bioassay rodent metabolism spanned a 30-fold range for the six available human/rat comparisons, and the seven predicted ratios of low-dose human to bioassay mouse metabolism spanned a 13-fold range. (The greater range for the rat/human comparison is attributable to a structural assumption by one author group of competing linear and saturable pathways, and their conclusion that the dangerous saturable pathway constitutes a minor fraction of metabolism in rats.) It is clear that there are a number of opportunities for modelers to make different choices of model structure, interpretive assumptions, and calibrating data in the process of constructing pharmacokinetic models for use in estimating “delivered” or “biologically effective” dose for carcinogenesis risk assessments. We believe that in presenting the results of such modeling studies, it is important for researchers to explore the results of alternative, reasonably likely approaches for interpreting the available data—and either show that any conclusions they make are relatively insensitive to particular interpretive choices, or to acknowledge the differences in conclusions that would result from plausible alternative views of the world.

Abstract  Toluene and 5 aliphatic chlorinated hydrocarbons of wide industrial use were injected into the air space of fertilized chicken eggs at 2,3 and 6 days of incubation. The embryotoxicity was evaluated as survival and death incidences after 14 days of incubation, and also the the weights and lengths of the embryo were recored. The approximate LD50 value for trichloroethylene and trichlorethanes varied between 50 and 100 μmol/egg while for toluene, tetrachlorethylene and methylene chloride it was over 100 μmol/egg. Macroscopic malformations of various kinds were produced with doses of 5–100 μmol/egg. The teratogenic potential of the tested compounds decreased in the following order: 1,1,1-trichloroethane > trichloroethylene > methylene chloride, tetrachloroethylene, 1,1,2-trichloroethane > toluene > olive oil control.

Abstract  The U.S. Geological Survey, in cooperation with the U.S. Department of the Army Environmental and Natural Resources Management Office of the U.S. Army Signal Center and Fort Gordon, Georgia, assessed the groundwater, soil gas, and soil for contaminants at the Vietnam Armor Training Facility (VATF) at Fort Gordon, from October 2009 to September 2010. The assessment included the detection of organic compounds in the groundwater and soil gas, and inorganic compounds in the soil. In addition, organic contaminant assessment included organic compounds classified as explosives and chemical agents in selected areas. The assessment was conducted to provide environmental contamination data to the U.S. Army at Fort Gordon pursuant to requirements of the Resource Conservation and Recovery Act Part B Hazardous Waste Permit process. Four passive samplers were deployed in groundwater wells at the VATF in Fort Gordon. Total petroleum hydrocarbons were detected above the method detection level at all four wells. The only other volatile organic compounds detected above their method detection level were undecane and pentadecane, which were detected in two of the four wells sampled. Soil-gas samplers were deployed at 72 locations in a grid pattern across the VATF. Total petroleum hydrocarbons were detected in 71 of the 72 samplers (one sampler was destroyed in the field and not analyzed) at levels above the method detection level, and the combined mass of benzene, toluene, ethylbenzene, and total xylene was detected above the detection level in 31 of the 71 samplers that were analyzed. Other volatile organic compounds detected above their respective method detection levels were naphthalene, 2-methyl-naphthalene, tridecane, 1,2,4-trimethylbenzene, and perchloroethene. Subsequent to the soil-gas survey, four areas determined to have elevated contaminant mass were selected and sampled for explosives and chemical agents. No detections of explosives or chemical agents above their respective method detection levels were found at any of the sampling locations. The same four locations that were sampled for explosives and chemical agents were selected for the collection of soil samples. A fifth location also was selected on the basis of the elevated contaminant mass of the soil-gas survey. No metals that exceeded the Regional Screening Levels for Industrial Soils as classified by the U.S. Environmental Protection Agency were detected at any of the five VATF locations. The soil samples also were compared to values from the ambient, uncontaminated (background) levels for soils in South Carolina, as classified by the South Carolina Department of Health and Environmental Control. Because South Carolina is adjacent to Georgia and the soils in the coastal plain are similar, these comparisons are valid. No similar values are available for Georgia to use for comparison purposes. The metals that were detected above the ambient background levels for South Carolina, as classified by the South Carolina Department of Health and Environmental Control, include aluminum, arsenic, barium, beryllium, calcium, chromium, copper, iron, lead, magnesium, manganese, nickel, potassium, sodium, and zinc.

Abstract  Reductive capacities of soil minerals and soil for Cr(VI) and chlorinated ethylenes were measured and characterized to provide basic knowledge for in-situ and ex-situ treatment using these natural reductants. The reductive capacities of iron-bearing sulfide (pyrite), hydroxide (green rust; GR(SO4)), and oxide (magnetite) minerals for Cr(VI) and tetrachloroethylene (PCE) were 1-3 orders of magnitude greater than those of iron-bearing phyllosilicates (biotite, vermiculite, and montmorillonite). The reductive capacities of surface soil collected from the plains of central Texas were similar and slightly greater than those of iron-bearing phyllosilicates. The reductive capacity of iron-bearing soil minerals for Cr(VI) was roughly 3-16 times greater than that for PCE, implying that Cr(VI) is more susceptible to being reduced by soil minerals than is PCE. GR(SO4) has the greatest reductive capacity for both Cr(VI) and PCE followed by magnetite, pyrite, biotite, montmorillonite, and vermiculite. This order was the same for both target compounds, which indicates that the relative reductive capacities of soil minerals are consistent. The reductive capacities of pyrite and GR(SO4) for chlorinated ethylenes decreased in the order: trichloroethylene (TCE) > PCE > cis-dichloroethylene (c-DCE) > vinyl chloride (VC). Fe(II) content in soil minerals was directly proportional to the reductive capacity of soil minerals for Cr(VI) and PCE, suggesting that Fe(II) content is an important factor that significantly affects reductive transformations of target contaminants in natural systems.

Abstract  The Kirkwood-Buff integrals and the volume-corrected preferential solvation parameters for the first solvation shell are reported for binary mixtures of 1,4-dioxane with many organic solvents. They are calculated from reported thermodynamic data at the temperatures for which these data are available. The co-solvents include n-hexane, n-heptane, e-hexane, methyl-e-hexane, benzene, toluene, ethylbenzene, methanol, ethanol, 1-propanol, 2-propanol, c-pentanol, 1,2-ethanediol, acetic acid, dichloromethane, chloroform, tetrachloromethane, 1,2-dichloroethane, 1,2-dibromoethane, trichloroethene, tetrachloroethene, bromochlorotrifluoroethane (halothane), hexafluorobenzene, acetonitrile, triethylamine, piperidine, formamide, N,N-dimethylformamide, dimethyl sulfoxide, and tetramethylene sulfone (sulfolane). The derived preferential solvation parameters of these mixtures are discussed in terms of the interactions that take place. (C) 2006 Elsevier B.V. All rights reserved.