MTBE and other oxygenates: Environmental sources, analysis, occurrence, and treatment

The production and use of fuel oxygenates has increased dramatically since the early 1990s due to federal and state regulations aimed to improve air quality. Currently, methyl tert-butyl ether (MTBE) is the most widely used oxygenate in gasoline, followed by ethanol. Widespread use of oxygenates in gasoline has been accompanied by widespread release of these materials into the environment. This manuscript provides a review of environmental sources of MTBE and alternative oxygenates, analytical methods available for their detection in environmental samples, their occurrence in the environment with a focus on groundwater, and treatment methods for their removal from gasoline-contaminated water. Accidental gasoline releases from underground storage tanks and pipelines are the most significant point sources of oxygenates in groundwater. Because of their polar characteristics, oxygenates migrate through aquifers with minimal retardation, raising great concerns nationwide of their potential for reaching drinking water sources. As a group, fuel oxygenates present distinct analytical and sample preparation issues. Conventional procedures for the analysis of gasoline constituents have been shown to be insensitive for fuel oxygenates, and ether hydrolysis to alcohol under acidic conditions has led to a reassessment of conventional handling techniques for groundwater samples. An evaluation of MTBE's occurrence in drinking water sources over time in three states showed that the frequency of MTBE detection since 1999 appears to be stabilizing in groundwater and slightly decreasing over time in surface water. Recent studies have demonstrated the effectiveness of conventional treatment technologies and the promise of emerging technologies for MTBE removal from contaminated media. However, the removal from water of tert-butyl alcohol (TBA), an impurity in MTBE-blended fuels and an MTBE breakdown product, can be problematic using some conventional technologies such as air stripping and granular activated carbon. These limitations may generate additional problems for water purveyors, regulators, and site managers.