Methyl Tertiary Butyl Ether (MTBE)
Since MTBE was incorporated in the mid-1980s into gasoline mixtures as an antiknock replacement for aromatics and as an "oxygenator" to reduce carbon monoxide emissions, it has increasingly appeared in groundwater due to spills of reformulated gasoline and leaking underground storage tanks at gasoline stations. It is highly water soluble and its appearance typically marks the leading front of a contamination plume. The molecular weight of MTBE (C5H12O) is 88.15.
In terms of noncarcinogenic effects, it has low oral toxicity, but at the gasoline pump and in the automobile, symptoms such as airway and eye irritation have been reported. In water, MTBE has a noticeable odor at 20 to 40 µg/L (U.S. Environmental Protection Agency, 1997). Though MTBE is not mutagenic/genotoxic, exposure to high levels by inhalation (8000 ppm) or by ingestion (1000 mg/kg) was associated with the development of lymphoma and leukemia, as well as liver, renal, and testicular cancers in rodents (Burleigh-Flayer et al., 1992; Belpoggi et al., 1995).
The relevance of these cancers to human health is not clear, but "weight of evidence suggests that MTBE is an animal carcinogen." "Concentrations in the range of 20 to 40 µg/L are about 20,000 to 100,000 (or more) times lower than the range of exposure levels in which cancer or non-cancer effects were observed in rodent tests." (U.S. Environmental Protection Agency, 1997). Thus, the USEPA says "protection of the water source from unpleasant taste and odor will also protect consumers from potential (MTBE) health effects."
MTBE is adsorbed onto activated carbon similar to chloroform, but with a use rate of 2-3 times that of chloroform, i.e., the life of the activated carbon may be only 1/2 to 1/3 of that for chloroform when MTBE will begin to break through. For concentrations of MTBE greater than 100 µg/L or parts per billion, pretreatment with an atmospheric air stripping system with repressurization is recommended prior to activated carbon adsorption.