MTBE is an acronym for Methyl Tertiary Butyl Ether. Almost all gasoline currently produced in the USA contains MTBE. You will be quite lucky to find any gasoline in the USA that does not contain MTBE. To understand why it is used, here is some chronological history:

Many years ago, gasoline producers used small amounts of Tetra Ethyl Lead (TEL) as a gasoline additive because it was a very economical way to increase the octane rating of gasoline. Since lead is hazardous to human health, the federal EPA banned the use of TEL in gasoline (about 10-15 years ago).

Banning the use of TEL forced gasoline producers to increase the amount of benzene in gasoline in order to raise the octane rating of their gasoline. Since long term chronic exposure to benzene is carcinogenic, the federal EPA subsequently required gasoline producers to drastically lower the amount of benzene in gasoline.

At about the same time, the EPA mandated that gasoline be reformulated and that the ReFormulated Gasoline (RFG) must contain oxygenates (i.e., chemical compounds containing oxygen) such as MTBE or other ethers or alcohols ... because oxygenates helped reduce the pollutants emitted from automotive tailpipes. Almost all gasoline producers in the USA chose to use MTBE as their required oxygenate and because it also enhanced the octane rating of their gasolines. In other words, it was the federal EPA's requirement that RFG (reformulated gasoline) contain oxygenates that led to the widespread use of MTBE.

Leaks in the underground gasoline storage tanks at many gasoline filline stations led to MTBE finding its way into underground water aquifers. MTBE can be detected in water by taste and odor even at very, very low concentrations (i.e., parts per billion or even less) and the taste/odor is quite unpleasant. To the best of my knowledge, to date there have been no comprehensive, scientific epidemiology studies made to determine if such low concentrations of MTBE constitute a health hazard. Nonetheless, the unpleasant taste and odor of MTBE in drinking water supplies forced the politicians (especially so in California) to try and ban the use of MTBE ... hence the stickers that you see at gasoline filling stations about MTBE presenting a risk to the environment.

In my opinion, MTBE will probably be completely banned in the near future ... and gasoline producers will probably replace it with ethyl alcohol or some other oxygenate. Then, some years later, the EPA will find something of concern about alcohol or any other oxygenate ... and will ban their use. And so on and so on.

Milton Beychok
(Visit me at www.air-dispersion.com)