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Water contamination from chemicals such as the potentially hazardous MTBE, a difficult-to-remove gasoline additive, is becoming a concern from coast to coast.

But as this ScienCentral News video reports, researchers at Purdue University may have found a way to eliminate this and other chemicals from water using sound waves.


Just what is MTBE?

Methyl tertiary butyl ether, or MTBE, is a chemical that’s added to gasoline in order to reduce carbon monoxide emissions and the resultant air pollution. Originally introduced in the late 1970’s, MTBE is also designed to prevent engine "knocking." Combustion engines rely on precise timing to burn their fuel correctly, with the highest efficiency and most power. Abnormal combustion of fuel causes engine parts to move at the wrong time, sometimes colliding and causing a sound known as a knock. A fuel’s octane rating is a measure of its knocking tendency; MTBE gives fuel a higher octane rating. (Lead was used in this capacity until it was found to be toxic to humans.)

MTBE not only improves octane ratings, but also reduces harmful emissions by allowing the combustion of the fuel to go further toward completion. We know that depriving a fire of oxygen will cause it to go out. And the same happens when fuel in an engine runs out of oxygen: combustion stops and the incompletely burned fuel produces carbon monoxide. MTBE provides extra oxygen to the reaction in an engine, burning more of it and reducing the amount of carbon monoxide produced.

So what’s the problem?

As often turns out with things that seem too good to be true, there’s a catch. In 1992, residents of Fairbanks, Alaska started reporting health problems they felt resulted from MTBE: headaches, coughing, nausea, and nose and throat burning. After studying their complaints, the state of Alaska suspended their oxygenated fuel program at the end of the year.

Since then, most studies of MTBE’s health effects have focused on inhalation of the chemical, like the 1994 Interagency Assessment of Oxygenated Fuels , commissioned by the Environmental Protection Agency. These reports have found that inhalation of MTBE vapors is not likely very dangerous to humans, as it is less of a threat than vapors of conventional gasoline. But they have not examined the effects of ingesting MTBE through contaminated water. This is where the real danger may lie, and is part of the inspiration for Dr. Hua’s work.

In 1994, the U. S. Geological Survey found very high concentrations of MTBE in drinking water supplies near Reno, Nevada, where MTBE was never even used in gasoline. This led to investigations into MTBE’s persistence in the environment.

MTBE can get into groundwater via several routes. Most obviously, leaking underground and aboveground fuel storage tanks and pipelines, as well as fuel spills from tankers, allow reformulated gasoline into water. However, simple fuel spills at consumer gas pumps, auto accidents, and improper disposal of "old" gasoline from lawnmowers and the like can be washed into storm drains after rainfall, polluting public waterways. Emissions from older engines and simple evaporation can lead to MTBE mixing with water in the atmosphere and dirtying regular rainfall as well.

While these scenarios involve contamination of water with gasoline rather than just MTBE, it’s important to point out that MTBE’s structure makes it very attracted to water, unlike gasoline. It can be carried away from the gasoline and much farther afield, which explains the discovery of MTBE in Reno. This property also makes it very difficult and expensive to remove from water, just as it’s much easier to mix sugar into water than to separate it out again. MTBE also takes longer to decompose in the environment than other gasoline components, though it can evaporate rather easily from surface waters.

The National Research Council’s 1999 report, Ozone-Forming Potential of Reformulated Gasoline, casts doubt on the usefulness of these reformulated, oxygenating gasolines at reducing air pollution. While MTBE reduces some air contaminants, there are some it doesn’t affect and others it can even increase. Limiting overall emissions from vehicles themselves leads to a much greater improvement in air quality. The EPA, in a 1999 Blue Ribbon Panel Report, outlined recommendations for the reduction of MTBE in gasoline to protect drinking water yet still help with air quality.






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