When Good Fuel Additives Go Bad - MTBE

Clara Broten

by Clara Broten

Some History

In the 1990s, concern about ground level ozone and carbon monoxide from vehicles was increasing, along with the rising levels of air pollution in large cities. Additives were found to oxygenate gasoline to make it burn better and reduce both the smog forming pollutants (e.g. nitrous oxide) and the toxics (e.g. benzene) in car exhaust. The US Clean Air Act of 1990 required the use of oxygenated gasoline, called reformulated gasoline, in areas with air pollution problems.

One of the additives was methyl tertiary-butyl ether,MTBE. MTBE was initially used to increase the octane of gasoline in the 1980s, and after the Clean Air Act, higher amounts were used to oxygenate gasoline. By 2000 MTBE was the leading gasoline additive in the States.

Water Contamination

MTBE dissolves easily in water and leakage from gasoline storage facilities is common. Since MTBE is a suspected carcinogen, its presence in ground water was worrying. In 1996 MTBE was found in two wellfields that supplied drinking water to Santa Monica California at 618 and 86 ppb. The wellfields were shut down, cutting 50% of the city’s water supply and forcing it to purchase water. By 2000, the EPA was sounding alarms about MTBE in ground water, and attempting to have it replaced with ethanol in gasoline.

In the meantime, on the Canadian side of the border, alarm bells were also sounding about MTBE even though it was not in widespread use here. Most gasoline containing MTBE in Canada was produced for export to the United States. By 2001, only Irving Oil and North Atlantic Refining were still producing gasoline containing MTBE in Canada and only North Atlantic Refining planned to keep selling this gasoline in Canada.

In 2001, Environment Canada required the reporting of both MTBE use and spills. These reports revealed MTBE in groundwater in 250 locations in every province in Canada including 6 locations in PEI used as drinking water sources, three of which were later cleared of contamination.

However, out of the 23 companies responding, only 3 regularly tested for MTBE in ground water 80% of the contamination discovered was reported by two of those companies. Other sites with MTBE contamination across Canada may be undiscovered due to lack of testing.

Concentrations of MTBE in groundwater ranged from 1 part per billion (ppb) in Clinton, BC to 59 million ppb in Come by Chance, NF. The majority of contamination reports came from British Columbia but this may be a result of the limited number of companies doing tests.

Unfortunately, the effects of MTBE on the environment have not been fully tested, and the US EPA has not set a ‘safe’ drinking water level. Most people can’t detect it by odor or taste at 20-to-40 ppb or less. Much of the testing on the effects of MTBE has been on inhaled MTBE, not ingested. Breathing large amounts for a short term can cause nervous system reactions varying from hyperactivity to convulsions in animals. Long term exposure to large amounts of MTBE in the air may cause kidney damage or cancer in animals. The EPA states that effects on humans of long or short term exposures are unknown. Health Canada says that existing studies are not suitable for creating a drinking water standard due to flaws in the test procedures.

While there have been no human studies on ingestion of MTBE, high levels of MTBE in gasoline in the US have caused complaints of headaches, eye irritation, and cough.  Ingestion studies in animals conducted in the 1990s seem somewhat inconsistent in results with the no observed adverse effect level (NOAEL) varying from 100 mg/kg body weight to 716 mg/kg body weight. High doses do seem to indicate a carcinogenic effect in most studies, according to Health Canada.


Current Status

In the United States during the early part of the decade, more and more states were banning the use of gasoline containing MTBE. As of 2007, 25 states had full or partial bans of MTBE, and some extend that ban to other oxygenates as well. In 2005 most American oil companies stated that they were going to stop using MTBE as of 2006.

The bans of MTBE in the US have had an economic impact in Canada. In 1999, Methanex, a British Columbia producer of methanol (a raw component of MTBE) filed a suit under NAFTA as a result of the California ban. They lost the case in August 2005.  It’s interesting that in a similar NAFTA case by Ethyl Corporation against the Canadian government, Canada settled out of court and rescinded the ban on Ethyl’s product MMT, another fuel additive.

Current information on MTBE in gasoline in Canada is difficult to find, most likely because it has been phased out. As of 2003 only one company was continuing to sell gasoline containing MTBE in Canada. As well, despite the failure of Canada’s initial attempt to ban MMT, a manganese based replacement for lead in gasoline, in 2004 indications were that all oil and gas companies were phasing it out of their fuels (Sierra Club of Canada, 2004).

New Additives

In the USA the EPA has been encouraging the use of ethanol as a replacement additive to oxygenate gasoline. In Canada the Federal Ethanol Expansion Program (EEP) was launched in 2003 to increase the use of ethanol in fuels from approximately 7% to a planned 35% in 2010 Ontario has mandated 5% ethanol in gasoline as of 2007. Manitoba reduces the tax on gasohol containing 10% ethanol. Starting in 2010, Alberta is also requiring gasoline to contain 5% ethanol, and diesel to contain 2% ethanol.

Ethanol has its own problems in terms of environmental impact and there are real concerns about the use of valuable food crop land to produce raw material for ethanol. Further, it is extremely unlikely that enough biofuel to completely replace gasoline could be produced.  However, processes that use the refuse from food agriculture (e.g. the straw from wheat) are showing some promise of producing enough ethanol to work as a gasoline additive.

Oil and gas companies continue to add their own proprietary additives to their products, such as Shell’s new ‘nitrogen enriched’ gasoline. Although this claims to improve engine efficiency by cleaning out ‘gunk’ from other fuels, there are concerns that this may produce more nitrous oxide in exhaust. NO and NO2 are greenhouse gases. The long-term effects on the environment of these new proprietary additives remain to be seen.


Main Sources

Bellamy, J., Guthrie, J., & Groves, S. (2003). Use and Releases of MTBE in Canada. Oil, Gas and Energy Branch, Environment Canada.

US Environmental Protection Agency. (2007, Sept 13). Methyl Tertiary Butyle Ether (MTBE),http://www.epa.gov/mtbe/

Office of Pollution Prevention and Toxics, Enironmental Protection Agency. (1994, August). Chemicals In The Environment: Methyl-Tert-Butyl Ether, www.epa.gov/chemfact/f_mtbe.txt

Health Canada. (2006, July). Methyl Tertiary-Butyl Ether (MTBE) – Guidelines for Canadian Drinking Water Quality: Guideline Technical Document. www.hc-sc.gc.ca/ewh-semt/pubs/water-eau/mtbe/index-eng.php


[From Watershed Sentinel, Nov/Dec 2009]

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