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MTBE/Oxygenates

The National Exposure Research Laboratory (NERL) staff has been conducting research on MTBE exposure issues utilizing a wide variety of measurement methods and exposure scenarios for several years.

Summary List:

Evaluation of MTBE Environmental Fate and Transport

Characterizing emissions from engines using MTBE-gasoline

Human exposure to MTBE

Outputs on MTBE Research

Research conducted by NERL:

Evaluation of MTBE Environmental Fate and Transport

Fate and transport studies for MTBE plumes from four Long Island leaking underground storage tank sites are being conducted in collaboration with the New York State Department of Environmental Conservation (NYSDEC). The efforts have focused on determining the factors which influence the qualitative and quantitative reasons for observed plume behavior. Models have been used to verify qualitative conceptualizations concerning the sites and to assess the ability of existing models to simulate MTBE plume behavior.

MTBE: Is A Little Bit OK?

James W. Weaver
Ecosystems Research Division
National Exposure Research Laboratory
United States Environmental Protection Agency
Athens, Georgia 30605

Matthew C. Small
Underground Storage Tank Program Office
Region 9
United States Environmental Protection Agency
San Francisco, California 94105

Abstract

Methyl tertiary butyl ether (MTBE) has been used as a gasoline additive to serve two major purposes. First, MTBE was used as an octane-enhancer to replace organic lead, beginning in about 1979. Beginning in about 1992, MTBE was also used as a fuel oxygenate additive to meet requirements of the Clean Air Act Amendments (CAAA) of 1990. Generally, the amount of MTBE used for octane enhancement was lower than that required to meet CAAA requirements. An unintended consequence of using MTBE to address air quality issues has been widespread groundwater contamination. The decision to use certain amounts of MTBE or other chemicals as gasoline additives is the outcome of economic, regulatory, policy, political, and scientific cons iderations. Decision makers ask questions such as "How do ground water impacts change with changing MTBE content? How many wells would be impacted? and What are the associated costs?" These questions are best answered through scientific inquiry, but many different approaches could be developed. Decision criteria include time, money, comprehensiveness, and complexity of the approach. Because results must be communicated to a non-technical audience, there is a trade-off between the complexity of the approach and the ability to convince economists, lawyers and policy makers that the results make sense.

The questions on MTBE content posed above were investigated using transport models, a known release scenario and varying gasoline compositions. A set of simulations was performed that assumed 3% (octane enhancement) and 11% (CAAA) MTBE in gasoline. The results were that ground water concentrations would be reduced in proportion to the reduction of MTBE in the fuel. Plume lengths, though, would not be proportionately reduced. One implication of these results was that the concentrations would be reduced, but the number of impacted wells would remain similar. Because simulations included emplacement of the gasoline, dissolution from contact with flowing ground water and transient transport in the aquifer, a common sense explanation of the results was difficult to construct. A simpler model was then used for the purpose of explaining to policy makers why the plume length reductions were less than proportionate to the reduction of the amount of MTBE. The model was simple enough (one-dimensional, steady state, constant source concentration) so that the effect of each term of the transport equation on plume length could be easily shown. The weight of evidence from using multiple models, direct explanations from the transport equation, and field observation, should provide a sufficient basis for policy makers to understand scientifically how gasoline composition affects ground water impacts.

Presented at the National Ground Water Association's 2002 Petroleum Hydrocarbons and Organic Chemicals in Ground Water®: Prevention, Assessment, and Remediation, November 6 - 8, Atlanta, Georgia, pp 206-219

MTBE: Is A Little Bit OK? (PDF format, 67K)

 

Diving of MTBE Plumes

James W. Weaver
Ecosystems Research Division
National Exposure Research Laboratory
United States Environmental Protection Agency
Athens, Georgia

Abstract

MTBE and other petroleum hydrocarbons can "dive" into aquifers because of infiltration of surface water, stratigraphy, and pumping wells. An example is given that illustrates plume diving from a site in New York, where a sand pit caused increased infiltration directly over a contaminant plume. The plume was shown to be pushed downward in direct proportion to the amount of infiltrating water. The paper describes an approach to assessing plume diving at sites by outlining important factors to consider.

LUSTLine: A Report on Federal & State Programs to Control Leaking Underground Storage Tanks, New England Interstate Water Pollution Control Commission, Lowell, MA, November 2000, Bulletin 36, pp. 12-15.

Diving of MTBE Plumes (PDF format, 38K)

 

A Screening Approach to Simulation of Aquifer Contamination by Fuel Hydrocarbons (BTEX and MTBE)

James W. Weaver
Ecosystems Research Division
National Exposure Research Laboratory
United States Environmental Protection Agency
Athens, Georgia

Randall J. Charbeneau
Center for Research in Water Resources
The University of Texas at Austin
Austin, Texas

Abstract
Subsurface contamination by light nonaqueous phase liquids (LNAPLs) is a common occurrence as evidenced by more than 397,000 confirmed releases from underground storage tanks across the United States (USEPA, 2000). Because of generally limited resources, common biodegradation of contaminants, and programmatic policies, there is an emphasis on risk-based corrective action for these releases. This approach implies a predictive modeling capability. This chapter describes data from a set of LNAPL case studies, drawn from underground storage tank program files from state environmental agencies and the U.S. Department of Defense. These illustrate data availability under realistic conditions. Against this background, a simplified model for exposure assessment is described. This model is called the Hydrocarbon Spill Screening Model (HSSM). The mathematical basis of the model is given, and the underlying assumptions are discussed. Application of the model to a field site is described. This case has extensive data set that was analyzed to generate input parameter values for the model. The approach included an estimate of mass of contaminants, the location of center of mass, and the gasoline volume. By treating the model inputs as fitting parameters, order-of-magnitude matches to these data sets were achieved. The model provides a means of completing the conceptualization of each site by providing a plausible source and transport scenario, which may not be directly observed from site data.

Weaver, J.W. and R. J. Charbeneau, A Screening Approach to Fuel Hydrocarbon Spill Assessment, Groundwater Contamination by Organic Pollutants: Analysis and Remediation, ASCE Manuals and Reports on Engineering Practice No. 100, American Society of Civil Engineers, 2000, 41-78.

A Screening Approach to Simulation of Aquifer Contamination by Fuel Hydrocarbons (BTEX and MTBE) (PDF format, 422K)

Characteristics of Gasoline Releases in the Water Table Aquifer of Long Island

James W. Weaver
Ecosystems Research Division
National Exposure Research Laboratory
United States Environmental Protection Agency
960 College Station Road
Athens, Georgia 30605

Joseph E. Haas
New York State Department of Environmental Conservation
SUNY Building 40
Stony Brook, New York 11790

Charles B. Sosik
Environmental Assessments and Remediation
225 Atlantic Ave
Patchogue, New York 11792

Abstract
The aquifers of Long Island serve as the sole-source drinking water supply for approximately 3 million people. About 20 percent of this population obtain drinking water directly from the water table aquifer (Upper Glacial) whereas the remainder obtain their drinking water from deeper aquifers (Magothy and Lloyd). High population density assures a large number of gasoline stations and numerous fuel releases which directly impact the water table aquifer. Thin surface soils overlie the coarse sands and gravels of the Upper Glacial aquifer through this area, leaving the aquifer particularly vulnerable to contamination. This paper summarizes observations from four gasoline release cases investigated by the New York State Department of Environmental Conservation with input from U.S. Environmental Protection Agency. The sites chosen for study are ones where data collection efforts had generated a well-characterized plume. Since all the sites are on Long Island, they share some common general characteristics, namely similar climate and geology. Differences in observed plumes result from the differences in timing and volume of the releases, prior release history and the chemical properties of benzene, toluene, ethylbenzene, and xylene (BTEX) and Methyl tert-butyl ether (MTBE), rather than dramatic hydrogeologic variation among the sites.

At the East Patchogue and Riverhead sites, the MTBE plume is moving as a pulse ahead of the benzene and other plumes. This appears largely due to high ground water velocity and high recharge rate causing relatively rapid dissolution of MTBE from the gasoline. In contrast at the Uniondale and Lindenhurst sites, the MTBE plume is continuous with the source. Although the ground water velocity and recharge rate at these locations are also high, the releases are positively dated to a later time than either East Patchogue or Riverhead. Thus the Uniondale and Lindenhurst plumes have had roughly ten years less time to evolve. Qualitative differences between the plume configurations seem mostly related to the differing release times. Common characteristics of the detached plumes are longer in situ times, lack of observed free product, and unpaved surfaces. The attached plumes share the opposite characteristics.

In addition to the high ground water velocity, a reason for the long length of some of the plumes is the vertical characterization used at these sites. Vertical characterization avoids 1) averaging contaminant distributions over the arbitrarily long screen lengths and thus reducing maximum concentrations, 2) missing the down gradient edge of a plunging plume and 3) possible confusion presented by the presence of possible contaminant contributions from other sources. Vertical characterization at each of these sites showed that plume plunging in response to recharge was common. Vertical plume delineation is critical for these sites, because each of the BTEX and MTBE plumes show evidence of diving. Averaging vertical concentrations, as would implicitly occur in a screened well, generates artificially short, high gradient plumes. At East Patchogue averaging eliminated chromatographic separation of BTEX and eliminated MTBE concentrations above the action level of 50 µg/l.

Weaver, J.W., J.E. Haas, C.B. Sosik, 1999, Characteristics of Gasoline Releases in the Water Table Aquifer of Long Island, Proceedings of 1999 Petroleum Petroleum Hydrocarbons and Organic Chemicals in Ground Water, API/NGWA, Houston, Texas, November 17-19.

Characteristics of Gasoline Releases in the Water Table Aquifer of Long Island (PDF format, 42K)

 

Application of the Hydrocarbon Spill Screening Model to Field Sites

James W. Weaver
Ecosystems Research Division
National Exposure Research Laboratory
United States Environmental Protection Agency
Athens, Georgia

Abstract
The Hydrocarbon Spill Screening Model, HSSM, was developed for estimating the impacts of petroleum hydrocarbon contamination on subsurface water resources. The model simulates the release of the hydrocarbon at the ground surface, formation of lens in the capillary fringe, dissolution of constituents of the gasoline, and transport to a receptor in the aquifer. Field data from two case histories were used to develop input parameter sets for HSSM. In one case there were aqueous concentration data from an extensive monitoring network. In the second case the monitoring network was small, but the date and volume of the release could be estimated. Both of these cases have features that are well suited for testing of the model. In both cases the model was able to reproduce the trends in the data set and the concentrations to within an order of magnitude.

Weaver, J.W, 1996, Application of the Hydrocarbon Spill Screening Model to Field Sites, Procedings of Non-Aqueous Phase Liquids (NAPLs) in Subsurface Environment: Assessment and Remeidation, ed. L. Reddi, American Society of Civil Engineers, Washington, D.C., November 12-14, pp. 788-799.

Application of the Hydrocarbon Spill Screening Model to Field Sites (PDF format, 121K)

See http://www.epa.gov/ada/research/patchogue.html for more information about the gasoline release which occurred at East Patchogue, Long Island, New York.

 

Analysis of the Gasoline Spill at East Patchoque, New York

James W. Weaver
Ecosystems Research Division
National Exposure Research Laboratory
United States Environmental Protection Agency
960 College Station Road
Athens, Georgia 30605

Joseph E. Haas
New York State Department of Environmental Conservation
SUNY Building 40
Stony Brook, New York 11790

John T. Wilson
Subsurface Protection and Remediation Division
National Risk Management Research Laboratory
919 Kerr Lab Drive
Ada, Oklahoma 74820
(580) 436-8545 

Abstract
Gasoline containing methyl tert-butyl ether (MTBE) was released from a service station in East Patchogue, Long Island, New York. The resulting plume of contaminated ground water was over 1800 m (6000 feet) long, and resulted in the closing of private water supply wells. Data from a three-dimensional monitoring network were used to estimate the mass and position of the center of mass of benzene, toluene, ethylbenzene, xylenes and MTBE contaminant plumes. The monitoring network was sampled on three occasions so temporal information on the evolution of the plume was available. By estimating the moments of the contaminant distributions for each of the sample rounds, the loss of mass of each contaminant was estimated, as was the rate of migration of the center of mass. An estimate of the volume of gasoline released was made from plausible estimates of the gasoline composition. DBP Methods Development and MTBE Exposure study Drinking Water Exposures to MTBE will be investigated during a Nationwide sampling study to determine concentration and frequency of occurrence of MTBE, along with 50 high priority disinfection by-products (DBP), in drinking water samples from representative water utility plants in several regions across the U.S. The environmental fate of MTBE in these drinking water distribution systems will also be determined.

Weaver, J.W, J.T. Haas, and J.T. Wilson, 1996, Analysis of the gasoline spill at East Patchogue, New York, Procedings of Non-Aqueous Phase Liquids (NAPLs) in Subsurface Environment: Assessment and Remeidation, ed. L. Reddi, American Society of Civil Engineers, Washington, D.C., November 12-14, pp. 707-718.

Analysis of the Gasoline Spill at East Patchogue, New York (PDF format, 150K)

See http://www.epa.gov/ada/research/patchogue.html for more information about the gasoline release which occurred at East Patchogue, Long Island, New York.

 

Characterizing emissions from engines using MTBE-gasoline

Engine and tailpipe emissions research has focused on both outboard engines and light duty passenger vehicles for several different blends of gasoline containing MTBE. These tests were conducted over a wide range of temperature conditions and are designed to capture both evaporative and tailpipe emissions.

 

Emissions from Two Outboard Engines Operating on Reformulated Gasoline Containing MTBE

Peter A. Gabele
U.S. Environmental Protection Agency,
Environmental Characterization & Apportionment Branch,
Mail Drop 46
Research Triangle Park
North Carolina 27711

Steven M. Pyle
U.S. Environmental Protection Agency
Environmental Chemistry Branch
944 E. Harmon Ave.
Mail Drop ECB
Las Vegas, Nevada 89119

Abstract
Air and water pollutant emissions were measured from two 9.9 HP outboard engines: a two-stroke Evinrude and its four-stroke Honda counterpart. In addition to the measurement of regulated air pollutants, speciated organic pollutants and particulate matter emissions were determined. Aqueous samples were analyzed for MTBE (methyl tert-butyl ether) and BTEX (benzene, toluene, ethyl-benzene, and xylene) emission rates. Compared to the four-stroke engine, the two-stroke had dramatically higher levels of toxic organic and particulate matter emissions. The organic material emitted from the two-stroke engine resembles the test gasoline due to the predominance of unburned fuel. Emission rates for PM10 (particulate matter with a diameter of 10 mm or less) are equal to those for PM2.5 , implying that emitted particles are all in the respirable range. Aqueous emissions from the two-stroke are also higher: the two-stroke, BTEX and MTBE emissions are, on average, 5 and 24 times higher, respectively, and 3-10 percent of the MTBE fed to the engine is emitted to the water. Aqueous emission rates, expressed in brake-specific units, tend to increase with decreasing engine load, as do the atmospheric emission rates.

Citation: Gabele, P. Environ. Sci. Technol. 2000, 34, 368.

 

Characterization of Emissions from Malfunctioning Vehicles Fueled with Oxygenated Gasoline-MTBE Fuel - Part I

Fred Stump, Silvestre Tejada, and David Dropkin
U.S. Environmental Protection Agency
Environmental Characterization & Apportionment Branch
Research Triangle Park
North Carolina 27711

Colleen Loomis
Clean Air Vehicle Technology Center, Inc.
Research Triangle Park
North Carolina 27709

Abstract

Two vehicles, a 1993 4-cylinder Chevrolet Cavalier and a 1993 6-cylinder Ford Taurus, were tested using three different fuels - a winter grade fuel containing 11.3% methyl tertiary butyl ether (MTBE), a winter grade fuel (base fuel) without MTBE, and a summer grade fuel without MTBE. Vehicle tests were conducted at ambient temperatures of 75° (with summer grade fuel only), 20°, 0°, and -20°F. The vehicles were first tested under a normal mode (vehicles were tuned to manufacturers specifications) and then tested under two simulated malfunction modes - 1) the oxygen (O2) sensor was disconnected and 2) the exhaust gas recirculating valve (EGR) was disconnected and plugged. The malfunction modes were not tested simultaneously. The vehicles were tested on the Urban Dynamometer Driving Schedule (UDDS) of the Federal Test Procedure (FTP). Two high speed REPO5 test cycles were run after each of the UDDS tests. The exhaust emissions determined were particulate matter (PM2.5 and PM10), gaseous total hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx), speciated (individual) hydrocarbons, MTBE, and speciated aldehydes.

The UDDS hydrocarbon emissions from both vehicles increased as test temperatures decreased. Under normal mode, the HC emissions at 20°F tripled, the CO emissions more than doubled, while the NOx changed only slightly when the vehicles were tested at -20°F. HC emissions with the MTBE fuel were on the average 9-14% less than those with the base fuel. The Cavalier emitted on the average 12% less CO with the MTBE fuel than with the base fuel while the Taurus, 5% more CO with the MTBE fuel. The Cavalier HC, CO, and NOx emissions on the average increased 235%, 489% and -8%, respectively with the base fuel and 226%, 483% and -27%, respectively with the MTBE fuel over the normal mode emissions when the oxygen sensor was disconnected at the winter test temperatures. The Taurus HC, CO, and NOx emissions on the average increased 216%, 347% and 55% with the base fuel and 91%, 138% and 52% respectively with the MTBE fuel. Disconnecting the EGR had a minimal impact on the HC and CO emissions but a significant one on NOx emissions. The Cavalier NOx emissions increased 81% and 148% with the base and MTBE fuel respectively over those of the normal mode, while those of the Taurus increased 31% and 41% respectively.

The emissions of such toxic compounds benzene and 1,3-butadiene tended to increase as the testing temperature decreased. Disconnecting the O2 sensor generally increased the emissions of the toxic compounds, while the fuel containing MTBE reduced some toxic compound emissions. The measured emissions of formaldehyde and acetaldehyde did not show trend associated with changes of test temperatures, modes or fuels used in this study.

Particulate emissions were mostly PM2.5 particles. Particulate emissions correlated very well (R2 > 0.920) with HC emissions for every vehicle-fuel-malfunction mode combinations. Particle emissions increased 4-5 times when the test temperature was decreased from 20°F to -20°F. Both vehicles emitted more particles with the base fuel than with the MTBE at all test conditions. Taurus particle emissions ranged 13-73 mg/mi with the base fuel and 6-34 mg/mi with the MTBE fuel. The Taurus particulate emissions were 2-3 times greater than those of the Cavalier. Maximum particulate emissions were obtained when the oxygen sensor was disconnected. Particle emissions with a disconnected EGR differed only slightly from normal mode emissions for both vehicles.

Characterization of Emissions from Malfunctioning Vehicles Fueled with Oxygenated Gasoline-MTBE Fuel - Part I

 

Characterization of Emissions from Malfunctioning Vehicles Fueled with Oxygenated Gasoline-Ethanol (E-10) Fuel - Part II

Fred Stump, Silvestre Tejada, and David Dropkin
U.S. Environmental Protection Agency
Environmental Characterization & Apportionment Branch
Research Triangle Park
North Carolina 27711

Colleen Loomis and Christy Park
Clean Air Vehicle Technology Center, Inc.
Research Triangle Park
North Carolina 27709

Abstract

Five vehicles (a 1987 Ford Taurus, a 1996 Chrysler Concord, a 2001 Ford Focus, a 1993 Buick Regal, and a 2001 Dodge Intrepid) were tested using three different fuels: (1) winter grade (E-10) fuel containing 10% (vol.) 200 proof ethanol, (2) winter grade (WG) fuel without any ethanol or oxygen containing compounds, and (3) summer grade (SG) fuel without oxygenates. Vehicle emissions were characterized at test temperatures of 75 ( SG fuel only), 40, 20, 0, and - 20°F. The vehicles were tested in the conditions in which they were obtained from either a private individual or a vehicle rental service. They were also tested in a simulated malfunction mode in which the oxygen sensor was disconnected (O2 mode). The vehicles were tested using the Urban Dynamometer Driving Schedule (UDDS) of the Federal Test Procedure (FTP). Four IM240 test cycles were run after each of the UDDS tests and the exhaust particulate matter (PM2.5 and PM10), from the four IM240 driving cycles were collected on single filters. The gaseous emissions were collected and analyzed for total hydrocarbons (THC), carbon monoxide (CO), oxides of nitrogen (NO and NO2), speciated hydrocarbons, speciated aldehydes, ethanol, methanol, 2-propanol, methyltertiarybutyl ether (MTBE), and ethyltertiarybutyl ether (ETBE).

Hydrocarbon emissions generally increased as test temperature decreased for all vehicles, fuels, and test modes. The E-10 fuel generally reduced vehicular CO emissions. The trend for carbon monoxide and oxides of nitrogen emissions showed a general increase in emission rates as the testing temperatures decreased. When the O2 sensor was disabled (O2 mode), the trend showed increasing carbon monoxide and oxides of nitrogen emissions.

The emissions of such toxic compounds as benzene and 1,3-butadiene tended to increase as the testing temperatures decreased. Disconnecting the O2 sensor generally increased the emissions of these toxic compounds when compared with the no malfunction (NM) mode emissions. The E-10 fuel generally reduced 1,3-butadiene emissions. The measured emissions of formaldehyde and acetaldehyde from the test vehicles showed a general increase in emissions as test temperature decreased, when operating in the malfunction mode, and when testing with E- 10 fuel.

The PM2.5 and PM10 particulate emission rates were comparable at all test conditions. The particulate emissions from both vehicles followed the HC emission trend and increased as the test temperature decreased. The E-10 fuel generally reduced particulate emissions from the test vehicles. Disconnecting the oxygen sensor generally increased particulate emissions.

Characterization of Emissions from Malfunctioning Vehicles Fueled with Oxygenated Gasoline-Ethanol (E-10) Fuel - Part II (PDF format, 1.9M) EPA Report #: EPA-600/R-01-053.

 

Characterization of Emissions from Malfunctioning Vehicles Fueled with Oxygenated Gasoline-Ethanol (E-10) Fuel - Part III

Fred Stump, David Dropkin and Silvestre Tejada
U.S. Environmental Protection Agency
Environmental Characterization & Apportionment Branch
Research Triangle Park
North Carolina 27711

Colleen Loomis and Christy Park
Clean Air Vehicle Technology Center, Inc.
Research Triangle Park
North Carolina 27709

Abstract

Five vehicles (a 1987 Ford Taurus, a 1996 Chrysler Concord, a 2001 Ford Focus, a 1993 Buick Regal, and a 2001 Dodge Intrepid) were tested using three different fuels: (1) winter grade (E-10) fuel containing 10% (vol.) 200 proof ethanol, (2) winter grade (WG) fuel without any ethanol or oxygen containing compounds, and (3) summer grade (SG) fuel without oxygenates. Vehicle emissions were characterized at test temperatures of 75 ( SG fuel only), 40, 20, 0, and -20 oF. The vehicles were tested in the conditions in which they were obtained from either a private individual or a vehicle rental service. They were also tested in a simulated malfunction mode in which the oxygen sensor was disconnected (O2 mode). The vehicles were tested using the Urban Dynamometer Driving Schedule (UDDS) of the Federal Test Procedure (FTP). Four IM240 test cycles were run after each of the UDDS tests and the exhaust particulate matter (PM2.5 and PM10), from the four IM240 driving cycles were collected on single filters. The gaseous emissions were collected and analyzed for total hydrocarbons (THC), carbon monoxide (CO), oxides of nitrogen (NO and NO2 ), speciated hydrocarbons, speciated aldehydes, ethanol, methanol, 2-propanol, methyltertiarybutyl ether (MTBE), and ethyltertiarybutyl ether (ETBE).

Hydrocarbon emissions generally increased as test temperature decreased for all vehicles, fuels, and test modes. The E-10 fuel generally reduced vehicular CO emissions. The trend for carbon monoxide and oxides of nitrogen emissions showed a general increase in emission rates as the testing temperatures decreased. When the O2 sensor was disabled (O2 mode), the trend showed increasing carbon monoxide and oxides of nitrogen emissions.

The emissions of such toxic compounds as benzene and 1,3-butadiene tended to increase as the testing temperatures decreased. Disconnecting the O2 sensor generally increased the emissions of these toxic compounds when compared with the no malfunction (NM) mode emissions. The E-10 fuel generally reduced 1,3-butadiene emissions. The measured emissions of formaldehyde and acetaldehyde from the test vehicles showed a general increase in emissions as test temperature decreased, when operating in the malfunction mode, and when testing with E-10 fuel.

The PM2.5 and PM10 particulate emission rates were comparable at all test conditions. The particulate emissions from both vehicles followed the HC emission trend and increased as the test temperature decreased. The E-10 fuel generally reduced particulate emissions from the test vehicles. Disconnecting the oxygen sensor generally increased particulate emissions.

Characterization of Emissions from Malfunctioning Vehicles Fueled with Oxygenated Gasoline-Ethanol (E-10) Fuel - Part III (PDF format, 700K)

 

 

Human exposure to MTBE

The principal focus of the human exposure research on MTBE has been on the development of dermal and breath measurement technologies and their application in pilot scale projects. The focus of the various human exposure projects include exposure to MTBE will showering with MTBE contaminated water and exposure to MTBE during vehicle refueling operations.

 

Human Exposure to Methyl Tertiary-Butyl Ether (MTBE) While Bathing with Contaminated Water

Lance A. Wallace
Human Exposure and Atmospheric Sciences Division
National Exposure Reserach Laboratory
555 National Center
Reston, VA 20192

Abstract
Because MTBE is now the most common contaminant of ground water in the United States, a possible source of human exposure is bathing in contaminated water. This exposure may occur through inhalation or absorption through the skin. Some inhalation studies have been carried out, but no published studies have reported on potential uptake of MTBE through the skin. Therefore one goal of this study will be to measure as directly as possible the absorption of MTBE through the skin, using volunteers taking full-immersion baths while wearing full-face masks to prevent inhalation. A second goal will be to calculate the fraction of MTBE exhaled following inhalation exposure only. Using the information from the inhalation study, it may be possible to estimate the relative contribution of the inhalation and dermal pathways during normal baths. A continuous real-time air analyzer and a continuous real-time water analyzer will be used to determine air, water, and breath concentrations and thereby close the mass balance. Breath and blood samples will be analyzed for MTBE and its metabolite, tertiary-butyl alcohol (TBA)

Controlled Short-Term Dermal and Inhalation Exposure to MTBE and Dibromochloromethane (PDF format, 219K)- presentation at the International Society of Exposure Analysis (ISEA) Conference in Vancouver, BC on August 11-15, 2002.

Inhalation and Dermal Exposure to MTBE using Continuous Breath Analysis

Lance A. Wallace
Human Exposure and Atmospheric Sciences Division
National Exposure Reserach Laboratory
555 National Center
Reston, VA 20192

Abstract
In this study, which is coordinated with the study above, a new continuous breath analyzer will be used to measure MTBE and TBA in the breath of the volunteers exposed to MTBE either in baths or in showers. Based on previous studies using this methodology for chloroform, which found a very strong effect of the water temperature on dermal absorption, the same subjects will take baths or showers in water at two temperatures (35 and 40 C). Blood flow to the skin is suspected of causing the increased absorption at higher temperatures, and attempts will be made to measure or estimate this quantity to test the hypothesis previously published by scientists associated with this group of experimenters. The results of these two studies will be analyzed with a view to developing or evaluating models of the uptake, distribution, and excretion of MTBE in contaminated water.

Controlled Short-Term Dermal and Inhalation Exposure to MTBE and Dibromochloromethane (PDF format, 219K) - presentation at the International Society of Exposure Analysis (ISEA) Conference in Vancouver, BC on August 11-15, 2002.

Alveolar Breath Sampling and Analysis to Assess Exposures to methyl Tertiary Butyl Ether (MTBE) During Motor Vehicle Refueling

Andrew B. Lindstrom and Joachim D. Pleil
Human Exposure and Atmospheric Sciences Division
National Exposure Research Laboratory
79 Alexander Drive
Research Triangle Park, NC 27711

Abstract
Methyl tertiary butyl ether (MTBE) is added to gasoline (15% by volume) in many areas of the U.S. to help control carbon monoxide emissions from motor vehicles. In this study we present a sampling and analytical methodology that can be used to assess consumers' exposures to MTBE that may result from routine vehicle refueling operations. The method is based on the collection of alveolar breath samples using evacuated one-liter stainless steel canisters and analysis using a gas chromatograph-mass spectrometer equipped with a patented, valveless, cryogenic preconcentrator.

To demonstrate the utility of this approach, a series of breath samples was collected from two individuals (the person pumping the fuel and a nearby observer) immediately before and for 65 min after a vehicle was refueled with premium grade gasoline. Results demonstrate low levels of MTBE in both subjects breaths before refueling, and levels that increased by a factor of 35 to 100 after the exposure. Breath elimination models fitted to the post exposure measurements incidate that the half-life of MTBE in the first physiological compartment was between 1.3 and 2.9 min. Analysis of the resulting models suggests that breath elimination of MTBE during the 64 min monitoring period was approximately 115 Fg for the refueling subject while it was only 30 Fg for the nearby observer. This analysis also shows that the post exposure breath elimination of other gasoline constituents was consistent with previously published observations.

Lindstrom, A.B. and J.D. Pleil, 1996. Alveolar Breath Sampling and Analysis to Assess Exposures to Methyl Tertiary Butyl Ether (MTBE) During Motor Vehicle Refueling, Journal of the Air and Waste Management Association, 46:676-682

Controlled methyl tertiary butyl ether (MTBE) exposure to humans through dermal, ingestion, and inhalation routes and the resultant biomarker tertiary butyl alcohol (TBA) as measured in exhaled breath and venous blood

Joachim D. Pleil and Maribel Colon
Human Exposure and Atmospheric Sciences Division
National Exposure Research Laboratory
79 Alexander Drive
Research Triangle Park, NC 27711

James D. Prah and Martin W. Case
Human Studies Division
National Health and Environmnetal Effects Research Laboratory
Highway 54
Research Triangle Park, NC 27711

David L. Ashley
Center for Disease Control and Prevention
NCEH/EHLS
Atlanta, GA

Abstract
Methyl tertiary butyl ether (MTBE) is commonly used as a gasoline additive to boost octane and to reduce carbon monoxide (CO) and ozone precursor emissions from automobiles in non-attainment areas. It is blended into the U.S. gasoline supply at an average concentration of about 2% and in areas of non-attainment at about 15%. There is a potential for appreciable human exposure to MTBE through domestic water use when gasoline enters the water table through a surface spill or leaking underground storage tanks, or through ambient exposure when the public refuels vehicles. Due to the peculiar odor noticeable even at trace levels, the anecdotal reports of short-term health effects, and the potential for a long term cancer risk, there is concern in the general public over MTBE exposure and mandated usage. The State of California, for instance, is phasing out the use of MTBE in its fuel supply due to public concern.

This study is a collaborative effort among EPA's National Exposure Research Laboratory (NERL) and National Health and Environmental Effects Laboratory (NHEERL), and the Centers for Disease Control (CDC) of the Dept. of Health and Human Resources; NHEERL provides human subjects and exposure scenarios, NERL performs breath sampling and analyses, and CDC performs blood analyses. We are studying the uptake and elimination of MTBE through time course monitoring of dermal, ingestion, and inhalation exposures to MTBE in blood and breath. Additionally, we monitor the appearance and persistence of tertiary butyl alcohol (TBA) as a biomarker for MTBE exposure. Initial experiments show that the blood and breath data track well qualitatively. TBA production has a modest lag time and its levels persists over many hours during the post-exposure period despite the rapid decay of the MTBE levels. We find that the blood/breath ratio for both MTBE and TBA are not a constant value as is often assumed from in vitro measurements, but vary with time and conditions suggesting that a breath measurement may not be a simple surrogate for the circulating (venous) blood concentration.

Pleil, J.D., J.D. Prah, D. Ashley, M. Case, and M. Colon, 1999 Controlled methyl tertiary butyl ether (MTBE) exposure to humans through dermal, ingestion, and inhalation routes and the resultant biomarker tertiary butyl alcohol (TBA) as measured in exhaled breath and venous blood, EPA/NIEHS Workshop on Applying Biomarker Research, Chapel Hill, NC, August 1999.

 

Outputs on MTBE research:

Physiologicaly based pharmacokinetic model for dermal absorption of methyl tertiary butyl ether

Teresa L. Leavens, Martin W. Case and James D. Prah
Human Studies Division
National Health and Environmnetal Effects Research Laboratory
Highway 54
Rsearch Triangle Park, NC 27711

Joachim D. Pleil
Human Exposure and Atmospheric Sciences Division
National Exposure Research Laboratory
79 Alexander Drive
Research Triangle Park, NC 27711

David L. Ashley
Center for Disease Control and Prevention
NCEH/EHLS
Atlanta, GA

Abstract
Dermal Exposure to the oxygenated fuel additive methyl tertiary-butyl ether (MTBE) occurs from contact with contaminated groundwater sources during daily activities such as bathing and showering. The purpose of this research was to develop a physiologically based pharmacokinetic model for dermal absorption of MTBE. Compartments in the model included alveolar space, arterial and venous blood, brain, fat, gastrointestinal tract, kidney, liver, rapidly perfused tissues, skin, and slowly perfused tissues. Metabolism of MTBE to tertiary butyl alcohol (TBA) was assumed to occur only in the liver, and elimination was assumed to occur via exhalation of MTBE and TBA and urinary elimination of TBA. Absorption of MTBE through skin was described by well-stirred compartments for exposure media, skin, and blood that perfused the skin, with equilibrium between the media and skin compartments and the skin and blood compartments. Predictions from the model were compared with data on blood and exhaled breath concentrations of MTBE and TBA in male subjects whose arms were submerged in water containing MTBE for one hour. The model overpredicted the absorption of MTBE from water in blood, shown by predictions of a more rapid increase in blood concentrations and higher peak concentrations of MTBE than experimentally observed values. The parameters to which the peak blood concentration of MTBE was most sensitive included permeability, thickness, and surface area of skin; blood flow to skin; and alveolar ventilation. In addition the predicted blood concentrations versus time indicated the compartmental model for dermal absorption is not appropriate for MTBE, and a distributed model may more accurately predict dermal absorption of MTBE into the blood. Ultimately the dermal model will be used to predict the relative contributions of various routes of exposure to total body burden of MTBE and TBA in humans exposed environmentally to MTBE.

Leavens, T.L., J.D. Pleil, M.W. Case, D.L. Ashley, and J.D. Prah, 2000. Physiologicaly based pharmacokinetic model for dermal absorption of methyl tertiary butyl ether", Society of Toxicology Annual Meeting, Philadelphia, PA, March 2000.

Breath measurement and models to assess VOC dermal absorption in water

Victor S. Fan and Timothy J.Buckley
Johns Hopkins University
School of Hygiene and Public Health
Department of Environmental Health Sciences
Baltimore, MD 21205

Maribel Colon and Joachim D. Pleil
Human Exposure and Atmospheric Sciences Division
National Exposure Research Laboratory
79 Alexander Drive
Research Triangle Park, NC 27711

 

Abstract
Dermal exposure to volatile organic compounds (VOCs) in water results from environmental contamination of surface, ground-, and drinking waters. This exposure occurs both in occupational and residential settings. Compartmental models incorporating body burden measurements have been developed to estimate VOC exposure through pathways of inhalation and ingestion. This modeling approach is needed for the dermal pathway as well because VOC dermal exposure in water can be significant. We present preliminary results of alveolar breath measurements as a biomarker for VOC dermal exposure.

Models were developed from VOC dermal uptake and breath concentration measurements collected in a laboratory-based human in vivo study. Subjects placed their hand and forearm into a sealed 2-liter plexiglass cylinder containing 100, 100, 100, and 400 g/L of chloroform, toluene, 1,1,1-trichloroethane (111TCA) and methyl t-butyl ether (MTBE) in water, respectively, for one hour. The amount of dermal uptake was determined by measuring the change in water concentration from the beginning to the end of the exposure period. Concentrations of target VOCs in breath were measured before, during and after exposure in order to establish the concentration time-course associated with dermal uptake. Breath samples were collected via a single-breath exhalation procedure into Summa canisters. Breath sample analysis was conducted using a gas chromatography/mass spectrometry detector (GC/MS).

This study develops mathematical, compartmental models to estimate VOC dermal exposure with body burden as a biomarker. This modeling approach is an effective and practical tool for field researchers to more fully characterize the population exposure distribution.

Fan, V.S., T.J. Buckley, M. Colon, and J.D. Pleil, 2000 Breath measurement and models to assess VOC dermal absorption in water, American Industrial Hygiene Conference and Exposition, Orlando FL, May 2000.

Evaluation of methyl tert-butyl ether (MTBE) as an interference on commercial breath-alcohol analyzers

Timothy J. Buckley
Johns Hopkins University
School of Hygiene and Public Health
Department of Environmental Health Sciences
Baltimore, MD 21205

Joachim D. Pleil
Human Exposure and Atmospheric Sciences Division
National Exposure Research Laboratory
79 Alexander Drive
Research Triangle Park, NC 27711

James R. Bowyer
ManTech Environmental Technology
2 Triangle Drive
Research Triangle Park, NC 27709

J. Michael Davis
National Center for Environmental Assessment
Rsearch Triangle Park, NC 27709

Abstract
Anecdotal reports suggest that high environmental or occupational exposures to the fuel oxygenate methyl tert-butyl ether (MTBE) may result in breath concentrations that are sufficiently elevated to cause a false positive on commercial breath-alcohol analyzers. We evaluated this possibility in vitro by establishing a response curve for simulated breath containing MTBE in ethanol. Two types of breath-alcohol analyzers were evaluated. One analyzer's principle of operation involves in situ wet chemistry (oxidation of ethanol in a potassium dichromate solution) and absorption of visible light. The second instrument uses a combination of infrared absorption and an electrochemical sensor. Both types of instruments are currently used, although the former method represents older technology while the latter method represents newer technology. The response curve was evaluated over a breath concentration range thought to be relevant to high-level environmental or occupational exposure (0-100 PPM-V). Results indicate that MTBE positively biases the response of the older technology Breathalyzer when evaluated as a single constituent or in combination with ethanol. We conclude that a false positive is possible on this instrument if the MTBE exposure is very high, recent with respect to testing, and occurs in combination with ethanol consumption. The interference can be identified on the older technology instrument by a time dependent increase in the instrument response that does not occur for ethanol alone. In contrast, the newer technology instrument using infrared and electrochemical detectors did not respond to MTBE at lower levels (0-10 PPM-V), and at higher levels (>20 PPM-V) the instrument indicated an "interference" or "error". For this instrument, a false positive does not occur even at high MTBE levels in the presence of ethanol.

Buckley, T.J., J.D. Pleil, J.R. Bowyer and J.M. Davis, Evaluation of methyl tert-butyl ether (MTBE) as an interference on commercial breath-alcohol analyzers, Forensic Sci. Int., v. 123, No. 2-3, pp. 111-118, December 2001.

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