Adsorption Isotherms for Methyl Tert-Butyl Ether and Other Fuel Oxygenates on Two Bituminous-Coal Activated Carbons

Methyl tert-butyl ether (MTBE) is frequently used as a gasoline additive to reduce carbon monoxide emissions from vehicles. Alternative fuel oxygenates are also used separately or in conjunction with MTBE including ethyl tert-butyl ether (ETBE), tert-amyl methyl ether (TAME), diisopropyl ether (DIPE), tert-butyl alcohol (TBA), and ethanol (EtOH). Granular activated carbon (GAC) sorption is a proven technology for the removal of the ether oxygenates while the alcohols are not well adsorbed. In this research, Freundlich and Langmuir isotherms coefficients were developed based on linearized forms of the models for MTBE, ETBE, TAME, and DIPE (R2>0.97) on two common bituminous coal GACs:Calgon F400 and F600. No significant adsorption of either TBA or EtOH was observed on these carbons. The relative capacities on both Calgon F400 and F600 were DIPE>TAME>ETBE>MTBE>TBA, EtOH.     

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.     

Novel Bifunctional Aluminum for Oxidation of MTBE and TAME

The transformation of methyl tert-butyl ether (MTBE) and tert-amyl methyl ether (TAME) using bifunctional aluminum in the presence of dioxygen (O2) has been examined. Bifunctional aluminum, prepared by sulfating zero-valent aluminum with sulfuric acid, is an innovative extension of zero-valent metal technology. It has a dual functionality of simultaneously decomposing both reductively and oxidatively degradable contaminants. Bifunctional aluminum is capable of utilizing dioxygen through a reductive activation process to degrade oxygenates at ambient temperature and pressure where oxygenates are stable. The reductive activation of dioxygen is a new concept for oxygenate treatments for which most of oxidative technologies require strong oxidants. Results indicate that aluminum serves as a reductant to create favorable reducing conditions while sulfur-containing species, generated by the sulfation of aluminum at the metal surface, are considered to act as active sites. MTBE and TAME underwent similar parallel reaction pathways where the oxidation occurred on both sides of ether linkage. The oxidation of MTBE produced primarily tert-butyl alcohol, tert-butyl formate, methyl acetate, and acetone while tert-amyl alcohol, tert-amyl formate, methyl acetate, methyl ethyl ketone, and acetone accounted for 71.7% of the TAME lost. A postulated mechanism rationalizing the oxidation of oxygenates by bifunctional aluminum is proposed.     

Performance Assessment of a New Type of Membrane Bioreactor under Steady State and Transient Operating Conditions

Methyl-t-butyl ether (MTBE) is an additive to gasoline that serves as an oxygenate to increase the octane rating and improve combustion efficiency. Assessment of MTBE biodegradation under aerobic conditions was performed in lab-scale biomass concentrator reactors (BCRs). These reactors were bench-scale microcosms that retain and concentrate biomass thereby enabling biodegradation to sub-μg/L level. The BCRs were run under low hydraulic retention times with a synthetically prepared feed containing 500??μg/L of several oxygenates, MTBE, diisopropyl ether (DIPE), ethyl-t-butyl ether (ETBE), t-amyl methyl ether (TAME), t-amyl alcohol (TAA), and the primary gasoline constituents benzene, toluene, ethyl benzene, and p-xylene (BTEX). The BCRs were effective in the removal of the aforementioned contaminants to concentrations lower than the targeted 5??μg/L, which is below the U.S. Environmental Protection Agency (EPA) taste and odor threshold of 20–40??μg/L. Reactor performance was also evaluated under shock loading and intermittent feeding (starvation tests) of the contaminants of concern to evaluate the reactor’s robustness in recovering from such stresses. The BCRs were found to be highly resilient to fluctuations in substrate and flow conditions.     

Charge-transfer chromatographic study of the complex formation of some steroidal drugs with carboxymethyl-gamma-cyclodextrin

Methyl tert-butyl ether (MTBE) is a widely used gasoline oxygenate. Two other ethers, ethyl tert-butyl ether (ETBE) and tert-amyl methyl ether (TAME), are also used in reformulated gasoline. Inhalation is a major route for human exposure to MTBE and other gasoline ethers. The possible adverse effects of MTBE in humans are a public concern and some of the reported symptoms attributed to MTBE exposure appear to be related to olfactory sensation. In the present study, we have demonstrated that the olfactory mucosa of the male Sprague-Dawley rat possesses the highest microsomal activities, among the tissues examined, in metabolizing MTBE, ETBE, and TAME. The metabolic activity of the olfactory mucosa was 46-fold higher than that of the liver in metabolizing MTBE, and 37- and 25-fold higher, respectively, in metabolizing ETBE and TAME. No detectable activities were found in the microsomes prepared from the lungs, kidneys, and olfactory bulbs of the brain. The observations that the metabolic activity was localized exclusively in the microsomal fraction, depended on the presence of NADPH, and was inhibitable by carbon monoxide are consistent with our recent report on MTBE metabolism in human and mouse livers (Hong et al., 1997) and further confirm that cytochrome P450 enzymes play a critical role in the metabolism of MTBE, ETBE, and TAME. The apparent K(m) and Vmax values for the metabolism of MTBE, ETBE, and TAME in rat olfactory microsomes were very similar, ranging from 87 to 125 microM and 9.8 to 11.7 nmol/min/mg protein, respectively. Addition of TAME (0.1 to 0.5 mM) into the incubation mixture caused a concentration-dependent inhibition of the metabolism of MTBE and ETBE. Coumarin (50 microM) inhibited the metabolism of these ethers by approximately 87%. Further comparative studies with human nasal tissues on the metabolism of these ethers are needed in order to assess the human relevance of our present findings.     

Degradation of MTBE and Related Gasoline Oxygenates in Aqueous Media by Ultrasound Irradiation

Gasoline oxygenates [methyl tert-butyl ether (MTBE), di-isopropyl ether, ethyl tert-butyl ether, and tert-amyl methyl ether] in aqueous media are readily decomposed upon ultrasonic irradiation (665 kHz). The optimal instrumental settings for the production of reactive radical species employing a specific reactor were determined using dosimetry. Since hydroxyl radical is generally believed to be the predominant reactive species leading to the ultrasonically induced degradation of organic substrates in aqueous media, a terephthalate dosimeter was employed to selectively determine the yields of hydroxyl radicals. The decomposition of the gasoline oxygenates and the primary decomposition products of MTBE were compared in the presence of different saturating gases (O2, N2, and Ar). The observed decomposition rates for the oxygenates were similar under Ar and O2 saturated conditions, but significantly slower under nitrogen saturated conditions. The observed decomposition rates for a number of the primary decomposition products of MTBE are significantly slower under N2 and O2 saturation relative to Ar saturation. All the gasoline oxygenates in this study were degraded by more than 98% within 3 h of ultrasonic irradiation under O2 saturation with half-lives of 21–25 min.     

Primary care: detection of women with alcohol use disorders

DNA damage of human leukemia (HL-60) cells caused by methyl tert-butyl ether (MTBE), a new gasoline additive, and its metabolites tert-butyl alcohol (TBA), a-hydroxyisobutyric acid (HIBA) and formaldehyde was determined by single cell gel electrophoresis (SCGE), with release of lactate dehydrogenase as an indicator for evaluating its cytotoxicity. Results showed that MTBE, TBA and HUBA at levels of 1 to 30 mmol/L could cause DNA damage in a dose-dependent pattern. Formaldehyde at level of 5 mumol/L could cause DNA damage, but at a higher level could decrease DNA migration. It suggested that MTBE and its metabolites could have genotoxicity, however, with doses causing genotoxic effects, no cytotoxic effect by MTBE, TBA and HIBA was observed, but formaldehyde presented obvious cytotoxic effect.     

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.     

Biodegradation Kinetics of MTBE in Laboratory Batch and Continuous Flow Reactors

Methyl tert-butyl ether (MTBE) biodegradation was investigated using a continuously stirred tank reactor with biomass retention (porous pot reactor) operated under aerobic conditions. MTBE was fed to the reactor at an influent concentration of 150 mg/L (1.70 mM). An identical reactor was operated as a killed control under the same conditions. Operation of these reactors demonstrated that removal of MTBE was biological and suggests that biomass retention is critical for effective degradation. MTBE removal exceeded 99.99% when the volatile suspended solids concentration in the reactor was above 600 mg/L. Batch experiments conducted using mixed liquor from the porous pot reactor indicated that the individual rates of biodegradation of MTBE and tert-butyl alcohol (TBA) increase with increasing initial concentration. When batch tests were later repeated, the MTBE degradation rates were found to have increased while the TBA degradation rates remained constant. All batch tests confirmed that the degradation rate of TBA governed the overall degradation rate (degradation rate of both MTBE and TBA). The presence of TBA at lower concentrations did not affect the rate of MTBE degradation; however, higher concentrations of TBA did reduce the rate of MTBE biodegradation.     

Degradation of MTBE Intermediates using Fenton’s Reagent

In a previous study, the chemical oxidation of methyl tert-butyl ether (MTBE) at low concentrations in water using Fenton’s reagent (FR) was investigated. At certain reaction conditions the process achieved 99.99% degradation of MTBE but it did not result in complete MTBE mineralization. In the present study, the major intermediate by-products generated during the reaction, such as tert-butyl formate (TBF), tert-butyl alcohol (TBA), methyl acetate, and acetone were separately used as parent contaminants and treated under the same reaction conditions initially used for MTBE (i.e., pH of the water, molar ratio of pollutant to FR) in order to compare their degradability by hydroxyl radicals generated from Fenton’s reaction. The results were compatible with the second order reaction rate constants for the reaction of hydroxyl radicals with each contaminant commonly available in the literature. The comparison of the degradation kinetics for each intermediate by-product provided information that aims at unveiling the limiting step(s) of the entire MTBE degradation pathway. In this context, it was found that (1) TBA was generated by reactions subsequent to those that produced TBF, (2) acetone was originated by at least three independent pathways involving direct hydroxyl radical attack on MTBE, TBF, and TBA, and (3) methyl acetate was formed exclusively from MTBE.     

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.     

Comparison of Liquid and Gas-Phase Photooxidation of MTBE: Synthetic and Field Samples

The feasibility of photooxidation treatment of methyl tert-butyl ether (MTBE) in water was investigated using two systems: (1) a slurry falling film photoreactor and (2) an integrated air stripping with gas phase photooxidation system. Methyl tert-butyl ether-contaminated synthetic water and field samples from contaminated sites were used for these studies. Using a TiO2 slurry (0.1 g/L; Degussa P25) flowing down at a rate of up to 0.26 L/min over the inner surface of a glass tube surrounding a 1-kW medium pressure mercury lamp, more than 99% of MTBE in the synthetic samples, initially at 1 mg/L, was degraded within 90 min. The major degradation products from MTBE were tert-butyl alcohol, tert-butyl formate, and small amounts of acetone. However, the degradation of MTBE and its byproducts in contaminated groundwater samples was hindered significantly by dissolved metals such as Fe2+, chloride ions, and aromatic organic species. Integrating air stripping with gas-phase photocatalysis is an an effective alternative that would not be affected by the water chemistry. The reaction rates for MTBE degradation in the gas phase are orders of magnitude faster than in aqueous solution.     

Vitamin E in therapy of rheumatic diseases]

Methyl t-butyl ether (MTBE) and ethyl t-butyl ether (ETBE) are commonly used in unleaded gasoline to increase the oxygen content of fuel and to reduce carbon monoxide emissions from motor vehicles. This study was undertaken to investigate: (1) the effect of administration to rats of ETBE and its metabolite, t-butanol, on the induction and/or inhibition of hepatic P450 isoenzymes; (2) the oxidative metabolism of MTBE and ETBE by liver microsomes from rats pretreated with selected P450 inducers and purified rat P450(s), (2B1, 2E1, 2C11, 1A1). ETBE administration by gavage at a dose of 2 ml/kg for 2 days induced hepatic microsomal P4502E1-linked p-nitrophenol hydroxylase and the P4502B1/2-associated PROD and 16beta-testosterone hydroxylase, verified by immunoblot experiments. t-Butanol treatments at doses of 200 and 400 mg/kg i.p. for 4 days did not alter any liver microsomal monoxygenases. Both MTBE and ETBE were substrates for rat liver microsomes and were oxidatively dealkylated to yield formaldehyde and acetaldehyde, respectively. The dealkylation rates of both MTBE and ETBE were increased c. fourfold in phenobarbital (PB)-treated rats. In rats pretreated with pyrazole, an inducer of 2E1, only the demethylation of MTBE was increased (c. twofold). When the oxidations of MTBE and ETBE were investigated with purified P450(s) in a reconstituted system, it was found that P4502B1 had the highest activities towards both solvents, whereas 1A1 and 2C1 were only slightly active; P4502E1 had an appreciable activity on MTBE but not against ETBE. Metyrapone, a potent inhibitor of P450 2B, consistently inhibited both the MTBE and ETBE dealkylations in microsomes from PB-treated rats. Furthermore, 4-methylpyrazole (a probe inhibitor of 2E1) and anti-P4502E1 IgG showed inhibition, though modest, only on MTBE demethylation, but not on ETBE deethylation. Inhibition experiments have also suggested that rat 2A1 may exert an important role in MTBE and ETBE oxidation. Taken together, these results indicate that 2B1, when expressed, is the major enzyme involved in the oxidation of these two solvents and that 2E1 may have a role, although minor, in MTBE demethylation. The implications of these data for MTBE and ETBE toxicity remain to be established.     

Performance and Cost Evaluations of Synthetic Resin Technology for the Removal of Methyl Tert-Butyl Ether from Drinking Water

This study investigated the performance of synthetic carbonaceous resin technology for the treatment of methyl tert-butyl ether (MTBE) contaminated waters using rapid small-scale column tests (RSSCTs). The RSSCTs were conducted using Ambersorb 563 carbonaceous resin (Rohm and Haas Corp., Philadelphia, Pa.) under multisolute conditions of typical municipal water source, soluble fuel components or additive/by-product, and MTBE. Specifically, one RSSCT column run was conducted with groundwater from Arcadia Wellfield, Santa Monica, Calif., with tert-butyl alcohol (TBA) and MTBE, while the other RSSCT column run was performed with surface water from Lake Perris, Calif., with benzene, toluene, p-xylene (BTX) and MTBE. The results obtained were compared to RSSCTs performed using PCB coconut shell granulated activated carbon (GAC) (Calgon Corp., Philadelphia, Pa.). The adsorbent comparisons indicate that the performance (as characterized by indicators such as carbon usage rates or integrated column capacity) of the Ambersorb 563 synthetic resin in multisolute conditions of TBA or BTEX with MTBE in typical municipal water source is significantly superior to that of the coconut shell PCB GAC. Cost comparison for the coconut shell GAC and synthetic resin system was also performed. Under multisolute conditions of typical municipal water source, flow rates, and influent MTBE concentrations, the cost of the resin system, for most of the scenarios evaluated, is demonstrated to be significantly lower than the complementary GAC system under the costing procedure used. Further, when soluble fuel components such as BTX or fuel additives/byproducts such as TBA were present along with MTBE, the predicted higher adsorbent usage rates for the coconut shell GAC were translated into significantly higher treatment costs relative to the synthetic carbonaceous resin system.     

Regulation of tumour cell fatty acid oxidation by n-6 polyunsaturated fatty acids

The aim of this study was to evaluate acute effects of ethyl tert-butyl ether (ETBE) in man after short-term exposure. ETBE may in the future replace methyl tert-butyl ether, a widely used oxygenate in unleaded gasoline. Eight healthy male volunteers were exposed to ETBE vapor for 2 h at four levels (0, 5, 25, and 50 ppm) during light physical exercise. The subjects rated irritative symptoms, discomfort, and central nervous system effects in a questionnaire. Ocular (eye redness, tear film break-up time, conjunctival epithelial damage, and blinking frequency), nasal (acoustic rhinometry and analysis of inflammatory markers and cells in nasal lavage fluid), and pulmonary (peak expiratory flow, forced expiratory volume in 1 s, forced vital capacity, vital capacity, and transfer factor) measurements were performed. Significantly increased ratings of solvent smell (p = 0.001, repeated-measures ANOVA) were seen during exposures and correlated to exposure levels. Furthermore, significantly elevated ratings of discomfort in throat and airways were seen during and after 50 ppm compared to the control exposure (p = 0.02). Increased nasal swelling (p = 0.001) and blinking frequency (p = 0.01) were noted at all exposure levels, but their magnitudes were not related to exposure levels. A slightly impaired pulmonary function was seen at 25 and 50 ppm, since forced vital capacity (p = 0.02) and vital capacity (p = 0.04) differed significantly from the clean air exposure. Although the impairments seemed to fall within normal inter- and intraindividual variation and have no clinical relevance as such, it cannot be excluded that other individuals may react more severely than eight healthy male volunteers in this study.     

Treatment of MTBE-Contaminated Water in Fluidized Bed Bioreactor

Methyl tertiary-butyl ether (MTBE) biodegradation was evaluated in a laboratory-scale granular activated carbon (GAC)-based fluidized bed bioreactor system. The reactor was operated in seven distinct phases during which the MTBE loading rate, hydraulic retention time, cocontaminant loading [butyl, toluene, ethylbenzene, and xylene (BTEX) and tertiary-butyl alcohol (TBA)] and temperature were varied. The reactor was able to treat MTBE to less than 20 ug/L at 25°C and total organic carbon (TOC) loading rates between 0.01 and 1.1 kg/m3 of expanded GAC bed per day (kg/m3?day). Net biomass yield in the reactor under high loading conditions was approximately 0.55 g of total suspended solids (TSS) per gram of TOC consumed. This high yield under the higher loading rates necessitated that biomass be removed from the reactor to control bed expansion. At a loading rate of 1.5 kg/m3?day, MTBE effluents exceeded 20 ug/L. Reactor performance decreased as the reactor temperature was reduced from 25 to 15°C, but even at the lower temperatures MTBE removal efficiency exceeded 99%. Methyl tertiary-butyl ether treatment efficiency was not affected by the addition of TBA or BTEX under the conditions evaluated. Results of this study demonstrate that fluid bed bioreactors inoculated with an appropriate microbial culture can efficiently treat MTBE-contaminated water.     

Methyl tert butyl ether systemic toxicity

In male F344 rats exposed in a chronic inhalation study to methyl tertiary butyl ether (MTBE) a treatment related increase in severity of chronic nephropathy and mortality and an increase in hyaline droplets in the kidney were noted. Liver weights were increased in both rats and mice but no histological lesions other than hypertrophy are seen. Transient CNS effects but no indications of permanent nervous system effects were noted. MTBE is not a reproductive or developmental hazard. MTBE is rapidly absorbed. MTBE with some metabolite, tertiary butyl alcohol (TBA) and a little CO2 are excreted in the air. The urinary excretion products in animals are TBA metabolites, while in humans the urinary excretion products are MTBE and TBA. A comparison of the systematic responses of the possible metabolites TBA and formaldehyde indicate that they are not responsible for toxicity associated with MTBE, except that TBA may be partially responsible for the kidney effects reported. Animals and humans are similar in the uptake and excretion though with some differences in metabolism of MTBE. This supports the use of the animal data as a surrogate for humans.     

Effects of Ethanol versus MTBE on Benzene, Toluene, Ethylbenzene, and Xylene Natural Attenuation in Aquifer Columns

The increased use of ethanol as a replacement for the gasoline oxygenate, methyl tert-butyl ether (MTBE), may lead to indirect impacts related to natural attenuation of benzene, toluene, ethylbenzene, and the three isomers of xylene (BTEX compounds). Ethanol could enhance dissolved BTEX mobility by exerting a cosolvent effect that decreases sorption-related retardation. This effect, however, is concentration dependent and was not observed when ethanol was added continuously (at 1%) with BTEX to sterile aquifer columns. Nevertheless, a significant decrease in BTEX retardation was observed with 50% ethanol, suggesting that neat ethanol spills in bulk terminals could facilitate the migration of pre-existing contamination. MTBE (25 mg/L influent) was not degraded in biologically active columns, and it did not affect BTEX degradation. Ethanol (2 g/L influent), on the other hand, was degraded rapidly and exerted a high demand for nutrients and electron acceptors that could otherwise have been used for BTEX degradation. Ethanol also increased the microbial concentration near the column inlet by one order of magnitude relative to columns fed BTEX alone or with MTBE. However, 16S-ribosomal ribonucleic acid sequence analyses of dominant denaturing gradient gel electrophoresis bands identified fewer species that are known to degrade BTEX when ethanol was present. Overall, the preferential degradation of ethanol and the accompanying depletion of oxygen and other electron acceptors hindered BTEX biodegradation, which suggests that ethanol could increase the length of BTEX plumes.     

Co-Occurrence of MTBE and Benzene, Toluene, Ethylbenzene, and Xylene Compounds at Marinas in Large Reservoir

Methyl tert-butyl ether (MTBE) is released into the environment as one of some gasoline components, not as a pure compound. Benzene, toluene, ethylbenzene, and xylene (BTEX) compounds are major volatile constituents found in gasoline and are water soluble and mobile. This study focused on the occurrence of MTBE with BTEX compounds in several marinas in Lake Texoma, which is a large reservoir located on the Oklahoma and Texas border. During a monitoring period from June 1999 to July 2001, MTBE and BTEX were detected in 28 and 5% of samples analyzed, respectively. Methyl tert-butyl ether co-occurred with BTEX compounds in 15% of lake water samples when detectable MTBE was present. The relatively low co-occurrence (15%) of MTBE with BTEX compounds is primarily due to the volume percentage in gasoline mixtures and physicochemical properties such as water solubility and Henry’s law constant. Toluene was the most commonly co-occurring BTEX with MTBE. Values of the ratios of the BTEX concentration to the MTBE concentration generally increase with depth of water.     

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.