Issue Date: February 4, 2008
MTBE Solubility Concerns
In response to Jonathan Targett's letter, methyl tert-butyl ether (MTBE) is indeed far less toxic than benzene, but it is also far more soluble in water (46 g/L) (C&EN, Dec. 10, 2007, page 2). As a result, it spreads in groundwater from gas station leaks faster and farther than benzene.
A gasoline leak in Port Hueneme, Calif., resulted in an MTBE plume covering 36 acres, whereas the plume of benzene, toluene, ethylbenzene, and xylenes (BTEX) covered only 9 acres. The Environmental Protection Agency drinking water advisory limit for MTBE is 20-40 µg/L; it is tasteable at 40 µg/L. A gas station leak in my own community resulted in MTBE being above the EPA advisory limit in several domestic wells, but BTEX was not. The latter is also readily metabolized by soil microorganisms. MTBE-utilizing organisms were not detected until 1994, though they are now common and even used commercially to remediate MTBE in groundwater.
Ethanol, of course, has replaced MTBE not so much for smog reduction as because it is a renewable fuel produced from crop feedstocks—possibly increasing the cost of foods produced from corn, including beef and pork.
Theodore Chase Jr.
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