Multiple spatial correspondence effects on dual-task performance.

Three dual-task experiments were conducted to examine whether the underadditive interaction of the Simon effect and stimulus onset asynchrony (SOA) on Task 2 performance is due to decay. The experiments tested whether the reverse Simon effect obtained with an incompatible stimulus–response (S-R) mapping would show an overadditive interaction with SOA, as predicted by R. De Jong, C.-C. Liang, and E. Lauber's (1994) dual-process model. Tone or letter identification tasks with vocal or keypress responses were used as Task 1. Task 2 was keypresses to arrow direction (or letter identity in Experiment 1). For all experiments, the normal Simon effect showed an underadditive interaction with SOA, but the reverse Simon effect did not show an overadditive interaction. The results imply that the dual-process model is not applicable to the dual-task context. Multiple correspondence effects across tasks implicate an explanation in terms of automatic S-R translation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Adsorption and Abiotic Transformation of Methyl tert-Butyl Ether through Acidic Catalysts

The fuel additive methyl tert-butyl ether (MTBE) is sometimes considered to be a recalcitrant compound in groundwater. Due to MTBE’s relatively poor adsorption and low volatility, interest is growing in new remediation methods which provide an alternative to using activated carbon or stripping techniques. This study addresses the abiotic degradation (hydrolysis) of MTBE to the intermediate tert-butanol (TBA). Two selected materials with acidic properties were shown to hydrolyze MTBE in batch tests at moderate pH values. The sorption of MTBE and TBA was estimated with Freundlich isotherms. Isotherms and TBA formation were used to calculate MTBE degradation. In another experiment, TBA was degraded aerobically by microorganisms. Since TBA seems to be more easily available as a carbon source to microorganisms than MTBE, the catalytic transformation of MTBE to TBA and methanol could enhance the natural attenuation of MTBE.     

Aerobic and Cometabolic MTBE Biodegradation at Novato and Port Hueneme

Methyl tert-butyl ether (MTBE), a gasoline oxygenate additive, is present in groundwater aquifers at the Department of Defense Housing Facility, Novato, Calif. (Novato), and the Naval Base Ventura County, Port Hueneme, Calif. (Port Hueneme). A microcosm study was conducted to examine and compare the potential for and performance of aerobic, anaerobic, and aerobic cometabolic MTBE biodegradation processes using soils and groundwater collected from the Novato and Port Hueneme sites. Propane and butane were tested as the cometabolic growth substrates. Nitrogen requirements were tested by preparing microcosms with and without nitrate as a nitrogen source. The results of this study demonstrated the potential for aerobic MTBE biodegradation and mineralization at both sites. In the commingled, or upgradient, portion of the Novato plume, nitrate enhanced aerobic MTBE biodegradation; in the absence of nitrate or under anaerobic conditions, MTBE degradation was insignificant. Downgradient, where the groundwater was impacted only by MTBE, the MTBE was readily degraded with and without nitrate addition and without other external nutrient amendments. Mineralization studies showed that MTBE was mineralized at both sites, with maximum recoveries approaching 80% of the radiolabeled carbon added to the microcosms. In the downgradient, MTBE-only portions of both sites, the addition of propane and butane to stimulate cometabolic MTBE degradation provided negligible improvement over direct oxidation under aerobic conditions. Furthermore, when nitrate was not present, propane and butane were not degraded and the residual propane and butane in the bottles appeared to inhibit the MTBE degradation; this inhibition was most pronounced in the Port Hueneme microcosms where MTBE degradation all but ceased in the presence of residual propane and butane. In the upgradient, commingled Novato plume, propane plus nitrate-fed microcosms outperformed the aerobic, nitrate-fed microcosms; this was the only condition where cometabolism enhanced MTBE degradation over direct aerobic oxidation.     

Effect of fluorochromes on bacterial surface properties and interaction with granular media

Simple, efficient, and safe tagging methods are desired in short-term microbial transport studies such as in the study of filtration systems for water and wastewater treatment. Suitability of selected fluorochromes as bacterial tagging agents in transport studies was evaluated on the basis of stability of stained cells and the effect of staining on bacterial surface characteristics and interaction with granular media. Surface properties were characterized by zeta potential and microbial adhesion to hydrocarbons. The effect of staining on interactions between bacteria and porous media was evaluated in terms of removal of bacteria in batch adsorption tests using sand coated with aluminum hydroxide to enhance adsorption. The DNA-specific fluorochrome 4',6-diamidino-2-phenylindole (DAPI) had generally negligible effects on bacterial surface properties and interaction with sand, as indicated in batch adsorption tests using pure cultures (Escherichia coli or Acinetobacter sp.) and wastewater bacteria. Cells stained with DAPI were stable for 48 h at 4 or 20 degrees C. Other nucleic acid fluorochromes tested had different but significant effects on bacterial cells and produced less stable fluorescence. Since transport through porous media is modulated by surface properties, it may be concluded based on these results that the choice of fluorochromes is critical in microbial transport studies. DAPI appeared to be a promising tagging agent. Time dependence of fluorescence of stained cells may limit the use of fluorochrome-tagged cells in long-term transport studies.     

Model for In Situ Perchloroethene Dechlorination via Membrane-Delivered Hydrogen

A one-dimensional contaminant fate and transport model was developed to simulate reductive dechlorination of perchloroethene (PCE) in an anaerobic aquifer supplied with hydrogen via a gas-permeable membrane curtain. The model predicted that providing hydrogen at transfer rates equal to the reducing-equivalent demand associated with the groundwater PCE flux would mineralize 75% of the PCE-bound chlorine to chloride and, furthermore, that 0.55 moles of chloride would be released per mole of hydrogen transferred. Supplying higher hydrogen transfer rates was predicted to result in slightly lower dechlorination efficiencies and significantly lower dechlorination yields due to greater methanogenic growth and concomitant displacement of dehalorespirers away from the hydrogen-supply membranes. The model also predicted that high hydrogen-utilizing biomass concentrations would develop near the membranes, resulting in minimal hydrogen dispersal. Model predictions were qualitatively similar to results attained in experimental soil column studies; however, incorporation of homoacetogenesis and acetate utilization by dehalorespirers, as well as hydrogen production via fermentation of biomass decay products, would have improved agreement between model simulations and experimentally observed dechlorination performance.     

Evidence for Phytodegradation of MTBE from Coupled Bench-Scale and Intermediate-Scale Tests

This paper presents methodologies and demonstrates the need to couple bench-scale and intermediate tree-scale experiments, to fully understand the transport and fate of organic contaminants, specifically methyl tert butyl ether (MTBE), in mature trees. Bench-scale experiments showed MTBE to be optimally taken up by small poplar saplings with a transpiration stream concentration factor of approximately 1, little or no degradation in soils and, nearly 100±20% recovery in the coupled water-plant-air system, indicating no measurable phytodegradation at the bench-scale. A large 14?ft tree chamber was designed to evaluate MTBE transport and fate through intermediate-scale (12?ft tall) poplar trees. Abiotic MTBE volatilization tests conducted in the tree chamber showed 100±20% MTBE mass recovery, thereby demonstrating the integrity of the large chamber and its air monitoring technique. In contrast, replicate intermediate-scale experiments conducted with large (12?ft) trees irrigated with a known mass of MTBE showed a deficit of MTBE mass recovery (65±20%) in replicate soil-tree-air systems monitored over a 2-week period. More significantly, tert butyl alcohol (TBA), a degradation product of MTBE, was detected in increasing concentrations in leaf biomass while MTBE concentrations in leaf biomass decreased as the experiment progressed. The MTBE mass recovery deficit, coupled with the detection of increasing TBA in leaf biomass, provides preliminary evidence of MTBE degradation in mature trees.     

Effect of BTEX on Degradation of MTBE and TBA by Mixed Bacterial Consortium

Methyl tert-butyl ether (MTBE) contamination in groundwater often coexists with benzene, toluene, ethylbenzene, and xylene (BTEX) near the source of the plume. Tertiary butyl alcohol (TBA) is a prevalent intermediate of MTBE degradation. Therefore, there is a significant potential for interference of MTBE and TBA degradation by the presence of BTEX whether treatment is in situ or ex situ. In this study, the effect of BTEX on the degradation of MTBE and TBA was examined using a mixed bacterial culture enriched on MTBE and BTEX. In batch studies, the presence of BTEX did not have a significant effect on MTBE degradation, but did have a slight effect on TBA degradation. Under continuous flow conditions, all compounds degraded simultaneously. Normalizing rates to the MTBE loading to the reactor indicates that BTEX may assist in the development of the biomass for TBA and overall MTBE degradation. Using denaturing gradient gel electrophoresis, several diverse organisms were identified, two of which showed very high similarity with PM1, a known MTBE degrader.     

Alternative Sorbents for Removing MTBE from Gasoline-Contaminated Ground Water

The objective of this work is to provide a preliminary screening of the effectiveness of alternative sorbents for treating ground water contaminated with methyl tert-butyl ether (MTBE). Sorbents studied include synthetic carbonaceous resins, porous graphitic carbon, C18 silicas, and acrylic resins. Activated carbon was also tested for comparison purposes. Bottle point isotherms show that porous graphitic carbon and two synthetic carbonaceous resins have a greater capacity for MTBE than activated carbon. However, the required addition of a wetting agent to suspend and activate the porous graphitic carbon makes this sorbent unsuitable for drinking water purposes. The synthetic carbonaceous resins tested were found to have capacities three to five times greater than activated carbon at an MTBE concentration of 1 mg∕L. The application of the Dubinin-Astakov isotherm to data for the synthetic carbonaceous resins suggests that the mechanism of adsorption is micropore filling. Additional bisolute experiments with m-xylene as a representative gasoline contaminant indicate that the m-xylene is preferentially sorbed, depleting the micropore volume available for MTBE sorption. The extent of this competitive adsorption was directly predicted from measured concentrations of the monoaromatic hydrocarbon.     

A set-intersection model of letter recognition in the spatial probe task.

Proposes a dual-process model involving 2 interacting identification processes. The set-intersection model can explain the predominance of mislocations, but, contrary to independent dual-process models, predicts that mislocations and intrusions can be affected by the same variable. Results of 2 experiments conducted with 24 undergraduates support the set-intersection model but are difficult to explain using independent dual-process models. Computer simulations comparing a single-process identification model to the set-intersection model isolated the advantages of a new identification process in the set-intersection model. Only the set-intersection model successfully reproduced the results of the 2 experiments. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Biodegradation of the gasoline oxygenates methyl tert-butyl ether, ethyl tert-butyl ether, and tert-amyl methyl ether by propane-oxidizing bacteria

Several propane-oxidizing bacteria were tested for their ability to degrade gasoline oxygenates, including methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), and tert-amyl methyl ether (TAME). Both a laboratory strain and natural isolates were able to degrade each compound after growth on propane. When propane-grown strain ENV425 was incubated with 20 mg of uniformly labeled [14C]MTBE per liter, the strain converted > 60% of the added MTBE to 14CO2 in < 30 h. The initial oxidation of MTBE and ETBE resulted in the production of nearly stoichiometric amounts of tert-butyl alcohol (TBA), while the initial oxidation of TAME resulted in the production of tert-amyl alcohol. The methoxy methyl group of MTBE was oxidized to formaldehyde and ultimately to CO2. TBA was further oxidized to 2-methyl-2-hydroxy-1-propanol and then 2-hydroxy isobutyric acid; however, neither of these degradation products was an effective growth substrate for the propane oxidizers. Analysis of cell extracts of ENV425 and experiments with enzyme inhibitors implicated a soluble P-450 enzyme in the oxidation of both MTBE and TBA. MTBE was oxidized to TBA by camphor-grown Pseudomonas putida CAM, which produces the well-characterized P-450cam, but not by Rhodococcus rhodochrous 116, which produces two P-450 enzymes. Rates of MTBE degradation by propane-oxidizing strains ranged from 3.9 to 9.2 nmol/min/mg of cell protein at 28 degrees C, whereas TBA was oxidized at a rate of only 1.8 to 2.4 nmol/min/mg of cell protein at the same temperature.