Methyl-tert-butyl ether (MTBE) has been used as an octane enhancer of automobile gasoline since the late 1970s' in the United States. MTBE has also been added to most high-octane gasoline in Japan. Since ground water is easily contaminated by MTBE due to gasoline leakage from underground tanks, MTBE may affect human health via drinking water. In this article, we have collected data concerning MTBE toxicity and information on MTBE risk assessment. MTBE induced hepatic and renal toxicity in rodents. The no observed adverse effect levels (NOAELs) of non-cancer endpoints for continuous long-term exposure were considered to be 259 mg·m-3 for inhalation route and 100 mg·kg-1·day-1 for oral route. High dose MTBE exposure caused certain tumors (Leydig cell tumor, lymphoma and/or leukemia, renal cell tumor, hepatocellular adenoma) in rodents. However, there is some controversy regarding extrapolation of the rodents' carcinogenic effects by MTBE to humans. This issue has not yet been clearly resolved. The US EPA Drinking Water Advisory recommended a tolerable contamination range of 20 to 40 μg·l-1 or below in drinking water based on the safety evaluation and organoleptic properties, and analyzed the margin of exposure (MOE) for the general population. For more accurate risk assessment of MTBE, it is necessary to conduct exposure surveys more widely and to examine the mechanism of carcinogenic effects.
