Click our logo for the Sierra Club homepage.
Printer-friendly version Share:  Share this page on FacebookShare this page on TwitterShare this page by emailShare this page with other services

Sierra Club Conservation Policies

Gasoline Additive: MTBE


MTBE (Methyl Tertiary Butyl Ether) is widely used as a gasoline additive. It is used to enhance engine performance, improve combustion efficiency, and to reduce emissions of air pollutants.

MTBE also is a water pollutant. It is water-soluble and has been detected in groundwater in thousands of communities. MTBE in even minute amounts causes the water to taste and smell offensive. The health effects of direct exposure to MTBE are not well known, although initial laboratory tests indicate it is a carcinogen.

Since MTBE has provided improvements in air quality, but degradation to water quality, we favor a rapid phase out, but not an immediate ban. This approach is intended to preserve the air quality benefits while eliminating the water quality degradation. Additionally, we propose an elimination of the oxygenate requirement for gasoline along with an improvement in the existing gasoline performance standards. This should allow different gasoline formulations to continue to provide improvements in air quality while not doing so at the expense of water quality, public health or the environment.

The following Interim Guidance has been developed to address the immediate health and environmental concerns of MTBE. This is merely a first step in attempting to fix a short-term problem. A longer-term solution will require a much more comprehensive approach.

1. MTBE should be phased out as a gasoline additive as soon as possible. California is on track to have a phase out by December 2002. A national phase out should occur on a similar timetable.

Discussion: MTBE is added to gasoline for a number of different reasons. It is used to raise octane levels. Motor vehicles require a minimum octane level to operate properly. MTBE has been used as a replacement for tetraethyl lead when that substance was banned as a fuel additive to increase octane levels. The phase out and eventual prohibition of adding tetraethyl lead to gasoline was responsible for a major improvement of public health and the environment. That its replacement is still problematic should be one of the lessons learned while establishing acceptable standards for chemicals that may be used to replace MTBE.

An alternative solution that avoids the need for such additives is to promote the use of vehicles that do not require high octane fuels. It should be noted that using a fuel with a higher-octane level than the minimum recommended by the manufacture generally does not improve engine performance.

MTBE is also used as an oxygenate to make the gasoline burn cleaner and reduce tailpipe air emissions. ReFormulated Gasoline (RFG) is required in serious ozone non-attainment areas and other areas that have "opted in" to require the use of RFG to reduce pollution from gasoline burning engines. Areas that exceed carbon monoxide standards require even higher oxygenate levels and these are called oxy fuels.

Gasoline is not an ideal fuel. It consists of a mixture of liquid organic (fossil-derived) chemicals. Many of these are Volatile Organic Compounds (VOC's) which react in the presence of oxides of nitrogen, heat, and sunlight to produce ground level ozone (smog). In addition, some of these chemicals are Hazardous Air Pollutants (HAPs). An example is benzene, a known carcinogen. When combusted, gasoline produces a variety of air pollutants such as nitrogen oxides, carbon monoxide, particulate matter (smoke and soot), and numerous HAPs such as polycyclic organic materials (POMs) and formaldehyde which are carcinogens. It also produces carbon dioxide, a major contributor to global warming.

The physical and chemical properties of MTBE are such that releases to the environment through spills, leaks, or mishandling usually result in the rapid contamination of surface and ground water. The rapid transfer through soil means that MTBE will contaminate groundwater in incidents where gasoline does not. In addition, MTBE, unlike gasoline, is readily water soluble, making it extremely difficult to remove.

Although the health effects of direct exposure to MTBE are not well known, initial laboratory tests indicate it is a carcinogen. The presence of MTBE in water is readily detectable: a very small amount imparts a strong smell and taste of turpentine. Its presence in groundwater or surface water is unacceptable. The health and environmental risks it poses to drinking water supplies more than justify a rapid phase-out.

In addition to an oxygenate, RFG requires a performance standard that reduces the HAPs and VOC's in gasoline from evaporative and tailpipe emissions. There are a variety of gasoline formulations that are cleaner burning and produce less evaporative and tailpipe emissions.

2. The Clean Air Act should be modified to remove the current oxygenate requirement in RFG and oxy fuels.

Discussion: In older vehicles, the addition of an oxygenate promoted more complete combustion and lower air emissions. Over the last twenty years substantial improvement in combustion technology and emissions controls have been introduced incremental phases. Since the 1994 model year all vehicles are required to have optimized combustion to an extent that oxygenates have negligible effects. As the existing fleet of motor vehicles continues to turn over, the air quality improvements that can be expected from the already obsolete oxygenate requirement will continue to diminish.

The oxygenate requirement causes an additional problem. It has become an obstacle limiting the ability to maximize the total evaporative and tailpipe emissions from gasoline that could be accomplished by using different formulations without a prescribed oxygenate requirement.

Another oxygenate in common use is Ethanol. It is the chemical name for the ingredient of interest in vodka, and other fermented beverages. It also is an air pollutant. When combusted it produces additional pollutants some of which are HAPs such as acetaldehyde.

3. There should be an immediate crackdown on leaking underground and aboveground storage tanks, spills, pipelines and other mishandling that results in releases of gasoline or its additives to the environment.

Discussion: MTBE is released into the environment primarily through mishandling or "accidents": spills, leaks, pipe ruptures, improper transfers and overfilling.

The airborne MTBE also comes from fuel transfer operations such as filling up the vehicle, transfer from delivery truck to gas pumps, and throughout the process. With proper transfer technology the smell gasoline or its additives should be negligible to nonexistent.

Airborne emissions of MTBE are a relatively minor contributor to groundwater or drinking water contamination as compared to mishandling.

4. Entities that are responsible for releases of gasoline to the environment should be subjected to heavy fines and penalties AND held strictly liable for cleanup and damages. If it is legally or physically impossible to determine responsible parties, appropriate state or federal funds should be used for immediate response to water quality problems.

Discussion: Those that cause environmental problems should be held accountable. However, legal loopholes and other impediments often make it is very difficult, if not impossible to hold the responsible party accountable for a gasoline spill.

In those cases where no responsible party can be determined or legally held accountable, the Leaking Underground Storage Treatment (LUST) Trust Fund can be used to help address this problem. The LUST program is a federally funded program that is applicable to states. Some states have their own LUST or similar programs. These programs should be adequately funded. Furthermore, the criteria should be expanded to allow states to use these funds to prevent and cleanup leaks from aboveground sources.

It is important that leaks or spills be cleaned up as quickly as possible. While surface water contamination is unacceptable; ground water contamination is even more serious and difficult to clean up.

State and local governments must immediately evaluate the adequacy of their inspection, training and management programs. Increased monitoring should be done or whatever measures are necessary to prevent and mitigate any problems. Activists can play a major role in making sure this happens locally.

5. The phase out of MTBE should not result in any net loss of the air quality benefits presently associated with its use as a gasoline additive.

Discussion: MTBE has provided improvements in air quality. For this reason we do not favor an immediate ban, but rather call for an improvement in the existing gasoline performance standards. This should allow different gasoline formulations to continue to provide improvements in air quality while not doing so at the expense of public health or the environment.

The reduction of VOCs and HAPs from gasoline itself must be preserved in any new RFG not containing MTBE. Other ether-based fuel oxygenates such as ETBE, TAME, and DIPE are of potentially greater concern because these substances have similar physical and chemical characteristics to MTBE. Although various refiners are already using them, we don't know their toxicity for lack of data.

Furthermore, there should be no backsliding in reducing the air emissions from mobile sources. There should be no increases in benzene or other known carcinogens in new gasoline formulations.

The value of oxygenates in gasoline continues to diminish as fleet turnover continues. Thus air pollution reduction attributed to oxygenates continues to become even more overstated as newer vehicles replace older ones.

We support the increased use of improved combustion control technology in newer vehicles and improved gasoline formulations that reduce air emissions. Furthermore, we support the widespread use of motor vehicle Inspection and Maintenance (I&M) programs that make certain all systems are functioning properly.

6. The Sierra Club does not specifically endorse the use of any specific gasoline additives. If additives are still required to replace MTBE, appropriate research should establish beforehand the health and environmental effects of any additives, so the experiences with MTBE will not be repeated.

Discussion: If it were not for the oxygenate requirement for gasoline in certain non-attainment areas, gasoline could be reformulated to reduce the evaporative and tailpipe emissions without the need for additives such as MTBE. Combustion control technology has essentially eliminated the value of adding oxygenates to gasoline to preserve and make further gains in air quality improvements.

7. MTBE should not be used in 2-cycle engines or in any type of watercraft.

Discussion. Two-cycle gasoline engines are highly inefficient and heavy emitters of pollutants, including MTBE. Gasoline with MTBE as an additive should not be used in watercraft engines, since the likelihood of water contamination is high.

The above are short-term responses to the problems of MTBE. Over the long-term, the use of gasoline or other petroleum derivatives as fuel must be phased out along with the single occupancy of internal combustion powered vehicles in sprawling urban centers.

The Sierra Club has advocated many changes in energy policies designed to reduce the use of fossil fuels. This is consistent with the club's important work on addressing Global Climate Change. Carpooling to avoid sole use of a conventional vehicle designed for multiple occupancy is an obvious first step. Over the long term, the internal combustion engines fueled by gasoline or other petroleum derivatives must be phased out and replaced by new technology with a goal of zero emissions transportation technologies. Clearly, more cars, more highways, poor public transit contribute to the pollution problem from mobile sources. The Sprawl campaign is attempting the address these problems. Changes in transportation policies, zoning and other measures provide possible components to a more effective long-term solution of which MTBE in groundwater is just the tip of the iceberg.

Sierra Club® and "Explore, enjoy and protect the planet"® are registered trademarks of the Sierra Club. © 2014 Sierra Club.
The Sierra Club Seal is a registered copyright, service mark, and trademark of the Sierra Club.