Methyl tertiary-butyl ether: MTBE
MTBE came into wide use as a gasoline additive in 1992, when amendments to the US Clean Air Acts of 1990 (CAA) mandated the use of cleaner-burning, "reformulated" gasoline in those areas of the country with the highest levels of air pollution. Although the CAA does not specify which additive must be used, many oil refiners identified MTBE as the most cost-effective option (1).

At the time of the CAA amendment, environmental advocates supported the requirement and its potential for air quality improvement. However, MTBE's chemical properties and the poor repair of thousands of underground gasoline storage tanks across the country now pose a threat to drinking water supplies nationwide (2).

The past two years have witnessed efforts by a number of state legislatures to phase out or limit the use of MTBE due to its effects on groundwater. According to the Renewable Fuels Association, at least 14 states have enacted phase-out bans or limitations on the sale of gasoline containing MTBE (3). However, some critics of these plans note that ethanol, the most likely candidate for replacing MTBE, is not without its own drawbacks, and could lead to a spike in gas prices due to the high cost of transporting the corn-based additive.

The pump and treat system employed in Pascoag. This system, including a pump to remove the water from the ground, air strippers to remove the contaminant from the evaporated material, and carbon filters to clean the water directly, is, according to RIDEM, of the type commonly used to clean up similar contaminations.

Scientific Uncertainty
To date, there have been no conclusive studies to indicate whether MTBE is harmful to human health. Several independent studies have found that rats developed tumors when exposed to very high doses of the chemical . However, the long-term effects of relatively low-level exposure, such as that experienced by many Pascoag residents, are unknown. Based on the current scientific data, the EPA has not adopted health advisory limits on MTBE levels in drinking water. However, EPA has issued a secondary drinking water standard of 20-40 parts per billion of MTBE in drinking water, based on taste and odor concerns. The Rhode Island Department of Health chose to adopt 40 parts per billion as its MTBE advisory level.

The lack of scientific certainty about the risk of MTBE exposure contributed to a sense of confusion and frustration among Pascoag residents. Given the lack of concrete scientific date, the only information that HEALTH offered relating to possible health effects stated that "MTBE smells and taste bad. Strong odors often nauseate people and cause stress." (see HEALTH's MTBE handout.)

For more information about MTBE, visit:

• the EPA's MTBE homepage at http://www.epa.gov/mtbe/
• the Agency for Toxic Substances and Disease Registry MTBE fact sheet at http://www.atsdr.cdc.gov/tfacts91.html

For more information on the health effects of MTBE, visit:

• the University of California 1999 study "An Evaluation of the Scientific Peer-Reviewed Research and Literature on the Human Health Effects of MTBE, its Metabolites, Combustion Products and Substitute Compounds"
  http://www.tsrtp.ucdavis.edu/mtberpt/vol2.pd

1. http://www.epa.gov/ost/drinking/mtbefact.pdf Accessed July, 2002
2. http://pubs.acs.org/hotartcl/est/2000/research/0666-00may_pankow.pdf
Accessed July, 2002
3.http://www.bioproducts-bioenergy.gov/news/recentArticles/August2002Article.asp Accessed August, 2002

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