Volatile Organic Compounds (VOC)

Background

From about 1992 to 2006, large volumes of fuel oxygenates were used in gasoline in certain areas of the United States (U.S.).  Fuel oxygenates are volatile organic compounds that contain oxygen and are used to increase oxygen content in fuels.  Most fuel oxygenates that were used in the U.S. are alkyl ethers such as methyl tert-butyl ether (MTBE), the most commonly used oxygenate.  In the U.S., MTBE was first added to gasoline in 1979 as an octane booster to replace tetraethyl lead.  In 1990, the Clean Air Act (CAA) Amendments mandated that oxygen be added to gasoline in areas of the U.S. where certain air-quality standards were not attained.  Oxygen allows more complete and clean burning of gasoline in engines. 

The CAA Amendments greatly expanded the use of MTBE in the U.S.  Although the CAA Amendments did not specify which oxygenate must be added to gasoline to achieve the oxygen requirement, MTBE was the most widely and frequently used.  To meet the oxygen requirements of the CAA Amendments, gasoline contained between 11 and 15% percent MTBE by volume in non-attainment areas.  In addition to the areas mandated for oxygen use by the CAA Amendments, some areas of the United States chose to voluntarily use MTBE in gasoline or had additional local laws requiring oxygenate use. 

In 1998, MTBE was used in more than 80 percent of oxygenated gasoline and in 1999 about 30 percent of gasoline sold in the U.S. was oxygenated.  In 1998, almost 12 billion liters of MTBE were produced in the U.S. and from 1993 to 1998 MTBE was the second most produced organic chemical in the U.S.  In 2005, the Energy Policy Act removed the oxygen requirement from gasoline and by September 2006 MTBE use in gasoline has declined considerably.

The physical and chemical properties of MTBE allow it to reach ground water faster and travel further than other common gasoline constituents.  Compared to other gasoline compounds MTBE has a high water solubility, low sorption to organic matter, a long half-life, and a tendency to partition from air to water.  Collectively, these properties make MTBE the most significant gasoline constituent with respect to water quality.

MTBE has been widely detected in ground water and drinking water resources.  In a recent survey conducted by the U. S. Geological Survey (USGS) on the occurrence of volatile organic compounds in ground water from aquifers across the U.S., MTBE was the third most frequently detected chemical and the second most frequently detected chemical in ground water from public wells. The USGS has conducted numerous surveys of the occurrence of MTBE and other fuel oxygenates in ground water, source water, and drinking water across the Nation.  The data from these surveys provide insights into the quality of ground water and water used for human consumption with regard to the occurrence of contaminants like MTBE. 

Bibliography Content

The USGS has developed a bibliography of pertinent reports, journal articles, and books on the occurrence of MTBE and other gasoline oxygenates in water and other environmental media.  The content in this bibliography represents only those publications on MTBE and other gasoline oxygenates authored or co-authored by USGS personnel.  This limitation was imposed because of the large volume of written material that exists on MTBE and the many areas of science and engineering that the material encompasses.  The resources in this MTBE bibliography primarily characterize the environmental occurrence of MTBE in ground water and ground water used as a source of drinking water and the environmental behavior and fate of MTBE.  Every effort has been made to include only materials that have been published as USGS reports or in recognized scientific journals.

Search Methodology

The Oxygenate Bibliography is searchable using a keyword search. The initial word search should begin with the oxygenate acronym(s) (e.g. the acronym for methyl tert-butyl ether is MTBE).  Topics that aid in further defining the search include transformation, transfer, and transport processes, environmental occurrences and miscellaneous. Each topic has a listing of searchable keywords to facilitate a search.  References may appear under more than one of the keyword searches.

In addition, the Oxygenate Bibliography is searchable using a free text search. The free text search locates references only if the search word is contained within the citation. Citations for publications from a particular year or author can by retrieved using the free text search (for example, search for 1998 or Moran)

In addition, the full bibliography can be viewed as follows: sorted by author | or sorted by publication date

USGS Gasoline Oxygenates Bibliography Search

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List bibliography by author || List bibliography by date

Updates to the Oxygenate Bibliography

The bibliography will be updated periodically. Suggestions for new listings or other comments are appreciated. Please submit them to Joshua Valder using this comment form.