Abstract  Purge-and-trap combined with high-resolution gas chromatography and detection by mass spectrometry was evaluated for the analysis of 27 volatile organic compounds (VOCs) in marine water samples down to ng l(-1) concentration levels. The target compounds included chlorinated alkanes and alkenes, monocyclic aromatic hydrocarbons and chlorinated monocyclic aromatic hydrocarbons and covered a wide range of VOCs of environmental interest. Limits of detection ranged from 0.15 ng l(-1) to 6.57 ng l(-1) for all VOCs, except for dichloromethane (41.07 ng l(-1)), chloroform (19.74 ng l(-1)), benzene (22.05 ng l(-1)) and 1,4-dichlorobenzene (20.43 ng l(-1)). Precision and accuracy were determined at a concentration level of 25.97 to 66.68 ng l(-1). Besides method validation, emphasis was put on quality control and assessment during routine determination of VOCs in marine water samples. Analytical quality control charts were plotted for all VOCs and a standard addition test was performed, as proposed by the QUASIMEME (Quality Assurance of Information in Marine Environmental Monitoring Programmes in Europe) working group. The analytical charts were incorporated in a working scheme containing guidelines to be applied during routine determinations, ensuring the long time reliability of the analytical method. Results yielded by the QUASIMEME interlaboratory exercise on organohalogen measurements in seawater are presented. The exercise was attended by seven out of eight laboratories who agreed to participate. Samples taken along the Scheldt estuary, from Breskens (The Netherlands) to Temse (Antwerp, Belgium) were analysed according to the developed technique. Concentrations as low as 0.33 ng l(-1) (1,2-dichloropropane) were detected near the mouth of the river Scheldt, while concentrations up to 326 ng l(-1) for tetrachloroethene and 461 ng l(-1) for cyclohexane were found in the vicinity of Antwerp.

Abstract  Exposure to perchlorethylene, especially for dry cleaning workers and for people living near dry cleaning shops, could lead to several diseases and disorders. This study examines the value of solid-phase microextraction (SPME) for sampling perchlorethylene in the atmosphere of dry cleaning shops. Carboxen/polydimethylsiloxane (CAR/PDMS) in 0.5-cm retracted mode was selected. There were no significant differences between sampling rates at different temperatures (range of 20 to 30 °C) and air velocities (2 to 50 cm/s). On the opposite, relative humidity (RH) had a significant effect on sampling rates. Method reproducibility was realized in the laboratory and field conditions and was 6.2 % and 7 to 11 %, respectively. Repeatability was also determined as 8.9 %. Comparison of the results according to the American Industrial Hygiene Association exposure assessment strategy showed the SPME sampler yields more conservative results in comparison with traditional standard method.

Abstract  This work presents the results of an assessment of the existence and concentration of 13 volatile organic compounds (VOCs) in groundwaters from 14 hydrological basins in Sicily (25,710 km(2)). On the basis of hydrological, hydrogeochemical and geological studies, 324 sampling points were selected. All groundwater sampled were collected twice, from October to December 2004 and from February to May 2005, and were analysed to determine the concentration and spatial distribution of the VOCs in the aquifers. The need to analyze a large number of samples in a short space of time so as to obtain quantitative analyses in trace concentration levels spurred us to create a new analytical method, both simple and sensitive, based on HS-SPME/GC/MS. The concentrations of VOCs measured in industrial and intensive agricultural unconfined aquifers were greater than those found in other aquifers. Tetrachloroethylene, chloroform, trichloroethylene and 1,2-dichloropropane were the most frequently detected VOCs. However, they exceeded the guideline values proposed by the EU in only three aquifers located near to industrial and intense agricultural areas. (C) 2008 Elsevier Ltd. All rights reserved.

Abstract  We demonstrated adsorption and reduction of cobalamin(III) (Co(III)) on nano-mackinawite (nFeS) surface and their impact on reductive dechlorination of tetrachloroethene (PCE). The adsorption of Co(III) on the nFeS surface followed Langmuir isotherm and the reduction of Co(III) provided different reactive surface chemical species on nFeS surface. Content of Fe(2+)S on nFeS surface decreased (45.9-14.5%) as Fe(2+)S was oxidized to Fe(3+)S and Fe(3+)O coupled with the surface reduction of Co(III) to cobalamin(II) (Co(II)). S(2-) and S(n)(2-) contents on the nFeS surface also decreased by 48.5% and 82.3%, respectively during the formation of sulfidecobalamin(II) (≡S(2-)Co(II)) by the reactive surface sulfur. PCE was fully degraded in nFeSCo(III) suspension at pH 8.3 in 120 h. The dechlorination kinetic rate constant of PCE in the nFeSCo(III) suspension (k(FeSCo(III))=0.188±0.003 h(-1)) was 145 times greater than that in nFeS suspension, showing a potential role of ≡S(2-)Co(II) as an electron transfer mediator to shuttle electrons for the enhanced reductive dechlorination. PCE was transformed to acetylene and 1,3-butadiene as major products via reductive β-elimination and isomerization reactions, respectively. The experimental findings can provide basic knowledge to identify a reaction mechanism for the enhanced reductive dechlorination of chlorinated organic by biogeochemical reactions possibly observed in natural reducing environments.

Abstract  Tetrakis-(4-sulfonatophenyl)porphyrin cobalt was identified as a highly-active reductive dechlorination catalyst for chlorinated ethylenes. Through batch reactor kinetic studies, degradation of chlorinated ethylenes proceeded in a step-wise fashion with the sequential replacement of Cl by H. For perchloroethylene (PCE) and trichloroethylene (TCE), the dechlorination products were quantified and the C₂ mass was accounted for. Degradation of the chlorinated ethylenes was found to be first-order in substrate. Dechlorination trials with increasing catalyst concentration showed a linearly increasing pseudo first-order rate constant which yielded rate laws for PCE and TCE degradation that are first-order in catalyst. The dechlorination activity of this catalyst was compared to that of another water-soluble cobalt porphyrin under the same reaction conditions and found to be comparable for PCE and TCE.

Abstract  In this study, nanoscale zero-valent iron (NZVI) particles were synthesized and utilized to integrate with surfactant and electrokinetics for the remediation of perchloroethylene (PCE). The average particle diameter and specific surface area of the lab-synthesized iron particles were 109.3 nm and 129.7 m2 g-1, respectively. Experiments were performed in a glass sandbox to simulate the transport and degradation of PCE in the aquifer. The results of the transport tests revealed that the PCE concentrations at the bottom layer was higher than those at the mid and upper layers, and that the surfactant Tween 80 showed its conspicuous mobilization for PCE in the aquifer. As the results of the degradation tests showed, NZVI activity could be promoted by electrokinetics that enhanced the remediation performance of PCE contaminated groundwater by the NZVI reactive barrier. Chlorinated byproducts were not detected during the degradation tests, that is, PCE was completely dechlorinated by NZVI in the reactive barrier. The information collected from this study will be useful for further application of the NZVI reactive barrier system to remediate the aquifers contaminated by the chlorinated solvents.

Abstract  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.

Abstract  Dechlorination of pentachlorophenol (PCP) by zero-valent iron (Fe-0) and palladium (Pd)/iron (Fe) bimetallic nanoparticles (NPs) immobilized in nylon 6,6/PEG membranes was investigated at room temperature. Pd/Fe bimetallic NPs were synthesized by two different approaches, sequential and simultaneous reduction of trivalent iron (Fe3+) and divalent palladium (Pd2+) ions. Pd/Fe NPs prepared by simultaneous reduction showed a much smaller particle size, only 30 nm in average, and significantly higher reactivity toward PCP dechlorination than the other two materials. Almost 85% PCP removal within 45 min was qualified in terms of both phenol emergence and chlorine ion release. In contrast, dechlorination efficiency by Pd/Fe NPs immobilized by sequential reduction was insignificant. Iron oxides between Fe-0 and Pd-0 during the sequential reduction process impeded their effective contact, and enhanced PCP sorption on membranes. Spectra of X-ray photoelectron spectroscopy confirmed the existence of both Fe-0 and iron oxide on the surface of these three NPs. This investigation has revealed that Pd/Fe NPs immobilized by simultaneous reduction may serve as a suitable medium for in situ remediation, even though it is difficult to avoid the formation of iron oxides.

Abstract  Landfill gas (LFG) was upgraded to pure methane using the adsorption and absorption processes. Different toxic compounds like aromatics and chlorinated compounds were removed using granular activated carbon. The activated carbon adsorbed toxic trace components in the following order: carbon tetrachloride > toluene > chloroform > xylene > ethylbenzene > benzene > trichloroethylene [asymptotic to] tetrachloroethylene. After removing all trace components, the gas was fed to absorption apparatus for the removal of carbon dioxide (CO sub(2)). Two alkanolamines, monoethanol amine (MEA) and diethanol amine (DEA) were used for the removal of CO sub(2) from LFG. The maximum CO sub(2) loading is obtained for 30 wt.% MEA which is around 2.9 mol L super(- 1) of absorbent solution whereas for same concentration of DEA it is around 1.66 mol L super(- 1) of solution. 30 wt% MEA displayed a higher absorption rate of around 6.64 x 10 super(- 5) mol L super(- 1) min super(- 1). DEA displayed a higher desorption rate and a better cyclic capacity as compared to MEA. Methane obtained from this process can be further used in the natural gas network for city.

Abstract  The presence of chlorinated hydrocarbons such as trichloroethylene [CAS 79-01-6] and tetrachloroethylene [CAS 127-18-4] in marine fuels, including gas oil, can lead to accelerated corrosion to fuel pumps, valves and, ultimately, catastrophic engine failures. The two chlorinated compounds mentioned previously are used extensively as highly effective degreasers of metal parts in the automotive and other metal-working industries. The presence of these compounds in marine fuels can arise from cross-contamination of blending fuels with cutter stocks of unregulated quality, or illegal disposal of chemical waste in fuel. A practical gas chromatographic approach has been successfully developed for the accurate measurement of these compounds using a five-port planar microfluidic device configured as a Deans switch for multidimensional gas chromatography (MDGC) with a flame ionization detector (FID).

Abstract  Biological degradation of 12 chlorinated aliphatic compounds (CACs) was assessed in bench‐top reactors and in serum bottle tests. Three continuously mixed daily batch‐fed reactor systems were evaluated: anaerobic, aerobic, and sequential‐anaerobic‐aerobic (sequential). Glucose, acetate, benzoate, and phenol were fed as growth substrates to both the anaerobic and aerobic systems. Methane and toluene were also added to the aerobic systems to induce cometabolic degradation of the feed CACs. The anaerobic culture degraded seven of the feed CACs. The specialized aerobic cultures degraded all but three of the highly chlorinated CACs. The sequential system outperformed either of the other systems alone by degrading 10 of the feed CACs: chloroform, carbon tetrachloride, 1,1‐dichloroethane, 1,1,1‐trichloroethane, hexachloroethane, 1,1‐dichloroethylene, trans‐1,2‐dichloroethylene, trichloroethylene, perchloroethylene, and 1,2,3‐trichloropropane, plus the anaerobic metabolites: dichloromethane and cis‐1,2‐dichloroethylene. Sequential treatment did not show significant removal of 2‐chloropropene, or 1,1‐dichloropropene. Cultures from each of the reactors were used in bottle tests to determine relative CAC degradation rates. Maximum degradation rates observed for individual CACs ranged from 20 to 150 μg per gram volatile suspended solids per day.

Abstract  A series of batch tests were performed and the impacts of environmental conditions and phase change on the sorption of volatile organic compounds (VOCs) were investigated. Benzene, trichloroethylene, tetrachloroethylene, and ethylbenzene were selected as target VOCs. Sorption of VOCs onto tire powder was well demonstrated by a linear-partitioning model. Water-tire partition coefficients of VOCs (not tested in this study) could be estimated using a logarithmic relationship between observed water-tire partition coefficients and octanol-water partition coefficients of the VOCs tested. The target VOCs did not seem to compete with other VOCs significantly when sorbed onto the tire powder for the range of concentrations tested. The influence of environmental conditions, such as pH and ionic strength also did not seem to be significant. Water-tire partition coefficients of benzene, trichloroethylene, tetrachloroethylene, and ethylbenzene decreased as the sorbent dosage increased. However, they showed stable values when the sorbent dosage was greater than 10 g/L. Air-tire partition coefficient could be extrapolated from Henry's law constants and water-tire partition coefficient of VOCs.

Abstract  BIOSIS COPYRIGHT: BIOL ABS. The use of granular iron for in situ degradation of dissolved chlorinated organic compounds is rapidly gaining acceptance as a cost-effective technology for ground water remediation. This paper describes the first field demonstration of the technology, and is of particular importance since it provides the longest available record of performance (five years). A mixture of 22% granular iron and 78% sand was installed as a permeable "wall" across the path of a contaminant plume at Canadian Forces Base, Borden, Ontario. The major contaminants were trichloroethene (TCE, 268 mg) and tetrachloroethene (PCE, 58 mg/L). Approximately 90% of the TCE and 86% of the PCE were removed by reductive dechlorination within the wall, with no measurable decrease in performance over the five year duration of the test. Though about 1% of the influent TCE and PCE appeared as dichloroethene isomers as a consequence of the dechlorination of TCE and PCE, these also degraded within the iron-sand m

Abstract  BIOSIS COPYRIGHT: BIOL ABS. This paper develops a generalized kinetic model for two-phase systems involving reactions in one phase with product partitioning into a second phase, and applies it to the reductive dehalogenation of trichloroethylene using two systems. The generalized approach can be used for a variety of catalyst choices, including zero-valent metals. With vitamin B12, the model includes specific reaction pathways for the reductive dehalogenation of TCE combined with the partitioning of reactants, intermediates, and products between the gas and liquid phases. The model has been used to study the effect of various parameters on the process effectiveness, which otherwise are very difficult to conceive through experimental analysis. In the case of zero-headspace system with zero-valent iron, sorption effects are included to incorporate the partitioning onto the solid surface. A new parameter, 'fractional active site concentration' is introduced to incorporate the differences in reactive

Abstract  This paper reports comprehensive studies on the mixed assembly of bis-(trialkoxybenzamide)-functionalized dialkoxynaphthalene (DAN) donors and naphthalene-diimide (NDI) acceptors due the cooperative effects of hydrogen bonding, charge-transfer (CT) interactions, and solvophobic effects. A series of DAN as well as NDI building blocks have been examined (wherein the relative distance between the two amide groups in a particular chromophore is the variable structural parameter) to understand the structure-dependent variation in mode of supramolecular assembly and morphology (organogel, reverse vesicle, etc.) of the self-assembled material. Interestingly, it was observed that when the amide functionalities are introduced to enhance the self-assembly propensity, the mode of co-assembly among the DAN and NDI chromophores no longer remained trivial and was dictated by a relatively stronger hydrogen-bonding interaction instead of a weak CT interaction. Consequently, in a highly non-polar solvent like methylcyclohexane (MCH), although kinetically controlled CT-gelation was initially noticed, within a few hours the system sacrificed the CT-interaction and switched over to the more stable self-sorted gel to maximize the gain in enthalpy from the hydrogen-bonding interaction. In contrast, in a relatively less non-polar solvent such as tetrachloroethylene (TCE), in which the strength of hydrogen bonding is inherently weak, the contribution of the CT interaction also had to be accounted for along with hydrogen bonding leading to a stable CT-state in the gel or solution phase. The stability and morphology of the CT complex and rate of supramolecular switching (from CT to segregated state) were found to be greatly influenced by subtle structural variation of the building blocks, solvent polarity, and the DAN/NDI ratio. For example, in a given D-A pair, by introducing just one methylene unit in the spacer segment of either of the building blocks a complete change in the mode of co-assembly (CT state or segregated state) and the morphology (1D fiber to 2D reverse vesicle) was observed. The role of solvent polarity, structural variation, and D/A ratio on the nature of co-assembly, morphology, and the unprecedented supramolecular-switching phenomenon have been studied by detail spectroscopic and microscopic experiments in a gel as well as in the solution state and are well supported by DFT calculations.

Abstract  The performance of electrophoretic displays is strongly dependent on the stability of the electrophoretic suspension in the device. In this manuscript, to obtain the stable electrophoretic suspension, the titanium dioxide grafted with poly [N-(p-vinyl benzyl) phthalimide] (TiO2-g-PVBP) composite particles were prepared via radical polymerization. The obtained TiO2-g-PVBP composite particles were fully characterized. The results showed that PVBP was grafted onto TiO2 surface by chemical bonding. The composite particles with the effective diameter of 300 nm can monodisperse stably in tetrachloroethylene due to the long-chain polymer PVBP, which can provide each TiO2 particle with steric stabilization. The zeta potential and electrophoretic mobility of the composite particles were 30.3 mV and 4.69 x 10(-6) cm(2)/Vs, respectively, without charge control agent. With the stable electrophoretic suspension containing the prepared composite particles, the matrix electrophoretic display prototype with good performance operated at 9 V was demonstrated.

Abstract  In this paper we present the remediation possibilities of a trichloroethylene contaminated site of a former metalworking plant in Hungary, where high TCE concentration (150 mu g/L to 35.000 mu g/L) was detected in the groundwater Lab-scale experiments were performed to compare the potential bioremediation technology-alternatives eg.: enhanced biodegradation; pump & treat by UV irradiation (photodegradation); in situ chemical oxidation (ISCO) applying different oxidants (KMnO4, Na2S2O8 and H2O2). The lab-scale experiments showed in all cases reduction of the TCE-concentration of the water Comparing the removal efficacy and concerning the time requirement ISCO was the most effective in laboratory studies.

Abstract  The compositions of bacterial groundwater communities of three sites contaminated with chlorinated ethenes were analyzed by pyrosequencing their 16S rRNA genes. For each location, the entire and the active bacterial populations were characterized by independent molecular analysis of the community DNA and RNA. The sites were selected to cover a broad range of different environmental conditions and contamination levels, with tetrachloroethene (PCE) and trichloroethene (TCE) being the primary contaminants. Before sampling the biomass, a long-term monitoring of the polluted locations revealed high concentrations of cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC), which are toxic by-products of the incomplete bacterial degradation of PCE and TCE. The applied pyrosequencing technique enabled known dechlorinators to be identified at a very low detection level (<0.25%) without compromising the detailed analysis of the entire bacterial community of these sites. The study revealed that only a few species dominated the bacterial communities, with Albidiferax ferrireducens being the only highly prominent member found at all three sites. Only a limited number of OTUs with abundances of up to 1% and high sequence identities to known dechlorinating microorganisms were retrieved from the RNA pools of the two highly contaminated sites. The dechlorinating consortium was likely to be comprised of cDCE-assimilating bacteria (Polaromonas spp.), anaerobic organohalide respirers (mainly Geobacter spp.), and Burkholderia spp. involved in cometabolic dechlorination processes, together with methylotrophs (Methylobacter spp.). The deep sequencing results suggest that the indigenous dechlorinating consortia present at the investigated sites can be used as a starting point for future bioremediation activities by stimulating their anaerobic and aerobic chloroethene degradation capacities (i.e. reductive dechlorination, and metabolic and cometabolic oxidation).

Abstract  Density measurements are frequently associated to specific requirements to evaluate the quality of a process or to determine mass and/or volume of the material. Certified reference liquids can be used to assure metrological traceability of density measurements to the SI with uncertainty lower than 0.005%. This paper presents the new approach of INRIM to set density standards. The procedure involved accurate density determinations of some reference liquids which were supported by gas-chromatography coupled with mass spectrometry (GC-MS) in order to assess their homogeneity and short-term stability. GC-MS analyses on tetrachloroethylene and trichloroethylene were carried out before and after density measurements. Samples that had undergone to variations in density value showed also different gas-chromatographic profiles. In the same time, samples that had not undergone to density variations kept similar gas-chromatographic profiles. The results support the approach of combining independent methods in order to set physico-chemical properties of reference materials.

Abstract  Chlorinated volatile organic compounds (CVOCs) are hazardous and potent environmental pollutants. Catalytic combustion has been regarded as one of the most promising technologies to eliminate CVOCs emissions. CH2Cl2 is difficult to be oxidized among CVOCs. A catalyst with high activity for CVOCs oxidation is desirable. In this paper, CrOx/Al2O3 catalysts with different Cr contents were prepared using a deposition-precipitation method and tested for CH2Cl2 oxidation. The highest activity was obtained over the catalyst with 18% Cr content, with a complete oxidation of CH2Cl2 at 350 degrees C. Characterization results indicated that both high oxidation state Cr species (Cr(VI) species) and crystalline Cr2O3 existed in the CrOx/Al2O3 catalysts, and the average valence of Cr species in the catalysts decreased with Cr content. It was found that the reaction rate for CH2Cl2 oxidation increased with increasing average valence of Cr, which indicated that high oxidation state Cr species were probably the active phase for the reaction. (C) 2011 Elsevier B.V. All rights reserved.

Abstract  Simulated groundwater solutions contaminated with trichloroethylene (TCE) and tetrachloroethylene (PCE) were treated in a flow-through reactor equipped with ultrasound (US) and ultraviolet light (UV) sources. The treatment process was operated using UV or US individually, and UV and US concurrently (UVUS). The solutions contaminated with TCE or PCE were exposed to UV light emitted from Hg-arc lamps surrounding the quartz reactor vessel, and to acoustic waves from a US horn located at the bottom of the reactor vessel. The rate constants (k) of photolysis by UV, sonolysis by US, and photosonolysis by UVUS were evaluated using a mathematical model in conjunction with a nonlinear regression analysis. The removal efficiencies (E) for the UV, US, and UVUS treatments were also determined. For TCE, the US rate constant (k(us) 0.016 +/- 0.010 min(-1)) and the UV rate constant (k(uv) = 0.076 +/- 0.004 min(-1)) yield the theoretical additive rate constant (k(ad)) of 0.092 min(-1), whereas the observed UVUS rate constant (k(uvus)) is 0.110 +/- 0.002 min(-1). Furthermore, the efficiency of the US treatment (E-us = 0.299) and of the UV treatment (E-uv = 0.664) gives the theoretical additive efficiency (E-ad) of 0.706, whereas the observed UVUS efficiency (E-uvus) is 0.741. For PCE, k(ad) and k(uvus) are 0.324 and 0.698 min(-1), respectively, whereas E-ad and E-uvus are 0.894 and 0.948, respectively. The results suggest that the combined effect of UV and US on the decomposition of TCE and PCE is likely synergistic. DOI: 10.1061/(ASCE)EE.1943-7870.0000590. (C) 2012 American Society of Civil Engineers.

Abstract  Perchloroethylene and trichloroethylene are two particular organochloro compounds, are often used for dry-cleaning. In the present study the excretion of urinary Perchloroethylene and trichloroethylene were evaluated as biomarkers of exposure to these compounds. The mean value of Perchloroethylene in breathing zone and the total Perchloroethylene uptake during the work shift of the three groups of dry-cleaning workers according to the capacity of the dry-cleaning machine (8, 12 and 18 kg) were 31.04, 50.87 and 120.99 mg m(-3) and 11.46, 22.6 and 41.6 μg L(-1), respectively, which were significantly greater than the occupationally nonexposed groups. A good correlation (r = 0.907) between the mean values of Perchloroethylene in breathing zone and the urinary concentrations was observed.

Abstract  BACKGROUND: The current paradigm for the assessment of the health risk of chemical substances focuses primarily on the effects of individual substances for determining the doses of toxicological concern in order to inform appropriately the regulatory process. These policy instruments place varying requirements on health and safety data of chemicals in the environment. REACH focuses on safety of individual substances; yet all the other facets of public health policy that relate to chemical stressors put emphasis on the effects of combined exposure to mixtures of chemical and physical agents. This emphasis brings about methodological problems linked to the complexity of the respective exposure pathways; the effect (more complex than simple additivity) of mixtures (the so-called 'cocktail effect'); dose extrapolation, i.e. the extrapolation of the validity of dose-response data to dose ranges that extend beyond the levels used for the derivation of the original dose-response relationship; the integrated use of toxicity data across species (including human clinical, epidemiological and biomonitoring data); and variation in inter-individual susceptibility associated with both genetic and environmental factors.

METHODS: In this paper we give an overview of the main methodologies available today to estimate the human health risk of environmental chemical mixtures, ranging from dose addition to independent action, and from ignoring interactions among the mixture constituents to modelling their biological fate taking into account the biochemical interactions affecting both internal exposure and the toxic potency of the mixture.

RESULTS: We discuss their applicability, possible options available to policy makers and the difficulties and potential pitfalls in implementing these methodologies in the frame of the currently existing policy framework in the European Union. Finally, we suggest a pragmatic solution for policy/regulatory action that would facilitate the evaluation of the health effects of chemical mixtures in the environment and consumer products.

CONCLUSIONS: One universally applicable methodology does not yet exist. Therefore, a pragmatic, tiered approach to regulatory risk assessment of chemical mixtures is suggested, encompassing (a) the use of dose addition to calculate a hazard index that takes into account interactions among mixture components; and (b) the use of the connectivity approach in data-rich situations to integrate mechanistic knowledge at different scales of biological organization.

Abstract  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 decrease in DNAPL removal accompanied a decrease in the effective DNAPL-water interfacial area, likely owing to obstruction of these interfaces resulting from oxidation by-products. Fracture aperture distribution, oxidant type, and oxidant activation all affected overall treatment effectiveness, and DNAPL dissolution mass transfer controlled the overall treatment process. DOI: 10.1061/(ASCE)EE.1943-7870.0000466. (C) 2012 American Society of Civil Engineers.

Abstract  Four expanded granular sludge bed (EGSB) bioreactors were seeded with a mesophilically-grown granular sludge and operated in duplicate for mesophilic (37 °C; R1 & R2) and low- (15°; R3 & R4) temperature treatment of a synthetic volatile fatty acid (VFA) based wastewater (3 kg COD m(-3) d(-1)) with one of each pair (R1 & R3) supplemented with increasing concentrations of trichloroethylene (TCE; 10, 20, 40, 60 mg l(-1)) and one acting as a control. Bioreactor performance was evaluated by % COD removal efficiency and % biogas methane (CH(4)) content. Quantitative Polymerase Chain Reaction (qPCR) was used to investigate the methanogenic community composition and dynamics in the bioreactors during the trial, while specific methanogenic activity (SMA) and toxicity assays were utilized to investigate the activity and TCE/dichloroethylene (DCE) toxicity thresholds of key trophic groups, respectively. At both 37 °C and 15 °C, TCE levels of 60 mg l(-1) resulted in the decline of % COD removal efficiencies to 29% (Day 235) and 37% (Day 238), respectively, and in % biogas CH(4) to 54% (Day 235) and 5% (Day 238), respectively. Despite the inhibitory effect of TCE on the anaerobic digestion process, the main drivers influencing methanogenic community development, as determined by qPCR and Non-metric multidimensional scaling analysis, were (i) wastewater composition and (ii) operating temperature. At the apical TCE concentration both SMA and qPCR of methanogenic archaea suggested that acetoclastic methanogens were somewhat inhibited by the presence of TCE and/or its degradation derivatives, while competition by dechlorinating organisms may have limited the availability of H(2) for hydrogenotrophic methanogenesis. In addition, there appeared to be an inverse correlation between SMA levels and TCE tolerance, a finding that was supported by the analysis of the inhibitory effect of TCE on two additional biomass sources. The results indicate that low-temperature anaerobic digestion is a feasible approach for the treatment of TCE-containing wastewater.