National Water-Quality Assessment Program
By Patty Toccalino
Oregon Health & Science University
There are differing views amongst scientists regarding the potential health effects of methyl tert-butyl ether (MTBE). Numerous summaries on the health effects of MTBE have been compiled by federal [1-8], state [9-12], and international [13,14] agencies. After the introduction of oxygenated fuels containing MTBE, there were reports of acute human-health effects such as nausea, dizziness, and headaches by people exposed to fuel vapors in air. However, these symptoms have not been clearly linked to MTBE exposure [1-3,7,11,12]. The human-health effects of long-term inhalation or oral exposures to MTBE are unknown [3,15], although several reports indicate that chronic noncancer health effects are not likely to result under the intermittent, low-level exposures experienced by humans [4-6], such as inhaling vapors when refueling automobiles. There are no published findings on the carcinogenicity of MTBE in humans [6,11,16], but MTBE has been shown to cause cancer in rats and mice exposed at high levels via inhalation or gavage (MTBE introduced to the stomach using a tube) over their lifetimes [2,3,8,17]. There has been considerable scientific discussion regarding the relevance of these animal cancer study results to humans [10,11], and a range of conclusions has been drawn regarding the carcinogenicity of MTBE. The National Toxicology Program does not recommend listing MTBE in its Report on Carcinogens . The International Agency for Research on Cancer classifies MTBE as a Group 3 carcinogen (that is, not classifiable as to its carcinogenicity to humans) . In contrast, other agencies have not formally classified MTBE as to its carcinogenicity to humans, but they have published reports indicating that MTBE should be regarded as posing a potential carcinogenic risk to humans based on animal cancer data [5,6,8,10,11]. Although the U.S. Environmental Protection Agency (USEPA) concludes that "MTBE poses a potential for human carcinogenicity at high doses" based on animal data, these animal data "do not support confident, quantitative estimation of risk at low exposure" . Therefore, USEPA's Office of Water has based its drinking-water guidance on taste and odor thresholds (20 to 40 µg/L) in humans, which are several thousand times lower than the exposure levels in which cancer or noncancer effects were observed in animal tests . For more information about the potential health effects of MTBE, contact your state drinking-water agency [20,21].
1. Agency for Toxic Substances and Disease Registry, 1996, Toxicological profile for methyl t-butyl ether (MTBE): Atlanta, GA, U.S. Department of Health and Human Services, Public Health Service, August 1996, 268 p., http://atsdr1.atsdr.cdc.gov/toxprofiles/tp91.html.
2. Health Effects Institute, 1996, The potential health effects of oxygenates added to gasoline. A review of the current literature. A special report of the Institute's oxygenates evaluation committee: Cambridge, MA, Health Effects Institute, April 1996, http://www.healtheffects.org/Pubs/oxysum.htm.
3. National Institute of Environmental Health Sciences, 2002, MTBE (in gasoline): National Institute of Environmental Health Sciences, March 13, 2002, Accessed December 1, 2002, 2002, at URL http://www.niehs.nih.gov/external/faq/gas.htm.
4. National Research Council, 1996, Toxicological and performance aspects of oxygenated motor vehicle fuels: Washington, D.C., National Academy Press, 160 p.
5. National Science and Technology Council, 1996, Interagency assessment of potential health risks associated with oxygenated gasoline: Washington, DC, National Science and Technology Council, Committee on Environment and Natural Resources, February 1996, http://www.ostp.gov/NSTC/html/MTBE/mtbe-top.html.
6. Office of Science and Technology Policy, 1997, Interagency assessment of oxygenated fuels: Washington, DC, Office of Science and Technology Policy, National Science and Technology Council, Executive Office of the President of the United States, June 1997, 264 p., http://www.epa.gov/oms/regs/fuels/ostpfin.pdf.
7. U. S. Environmental Protection Agency, 1994, Health risk perspectives on fuel oxygenates: Washington, DC, U. S. Environmental Protection Agency, Office of Research and Development, EPA 600/R-94/217, December 1994, 16 p., http://www.epa.gov/ncea/pdfs/mtbe/oxyrisk.pdf.
8. U. S. Environmental Protection Agency, 1997, Drinking water advisory: Consumer acceptability advice and health effects analysis on methyl tertiary-butyl ether (MTBE): Washington, DC, U. S. Environmental Protection Agency, Office of Water, EPA-822-F-97-009, December 1997, 48 p., http://www.epa.gov/waterscience/drinking/mtbe.pdf.
9. California Department of Health Services, 2000, Final statement of reasons, primary maximum contaminant level for methyl tert-butyl ether, Title 22, California Code of Regulations: Sacramento, CA, California Department of Health Services, R-8-99, February 2000, 23 p., http://www.dhs.cahwnet.gov/ps/ddwem/chemicals/MTBE/4-17-00MTBESOR.PDF.
10. California Environmental Protection Agency, 1999, Public health goal for methyl tertiary butyl ether (MTBE) in drinking water: Sacramento, CA, California Environmental Protection Agency, Pesticide and Environmental Toxicology Section, Office of Environmental Health Hazard Assessment, March 1999, 124 p., http://www.oehha.ca.gov/water/phg/pdf/mtbe_f.pdf.
11. Froines, J.R., Collins, M., Fanning, E., McConnell, R., Robbins, W., Silver, K., Kun, H., Mutialu, R., Okoji, R., Taber, R., Tareen, N., and Zandonella, C., 1998, An evaluation of the scientific peer-reviewed research and literature on the human health effects of MTBE, its metabolites, combustion products and substitute compounds. In: Health and environmental assessment of MTBE: report to the Governor and legislature of the state of California as sponsored by SB 521. Volume II: human health effects: Davis, CA, University of California Toxic Substances Research & Teaching Program, November 1998, 267 p., http://www.tsrtp.ucdavis.edu/.
12. New Jersey Department of Environmental Protection, 1996, Water for the 21st century: the vital resource: New Jersey statewide water supply plan, chapter VI, 46 p.
13. International Agency for Research on Cancer, 1999, Some chemicals that cause tumours of the kidney or urinary bladder in rodents and some other substances: IARC monographs on the evaluation of carcinogenic risks to humans: France, IARC Press, v. 73, 674 p.
14. World Health Organization, 1998, Environmental health criteria, No. 206: Methyl tertiary-butyl ether: Geneva, Switzerland, World Health Organization, 199 p.
15. U. S. Environmental Protection Agency, 1995, Proceedings of the conference on MTBE and other oxygenates: a research update. Conference summary session seven: Research Triangle Park, NC, U.S. Environmental Protection Agency, National Center for Environmental Assessment, EPA/600/R-95/134, August 1995, 274 p., http://www.epa.gov/ncea/pdfs/mtbe/0850-A.pdf.
16. Agency for Toxic Substances and Disease Registry, 1997, Methyl tert-butyl ether (MTBE) CAS# 1634-04-4 ToxFAQs: Atlanta, GA, U. S. Department of Health and Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry, September 1997, 2 p., http://atsdr1.atsdr.cdc.gov/tfacts91.pdf.
17. California Department of Health Services, 2001, Proposed Regulations, California Code of Regulations, Title 22, Chapter 15, Section 64468.2. health effects language - volatile organic chemicals: Sacramento, CA, California Department of Health Services, R-16-01, April 12, 2001, 26 p., http://www.dhs.cahwnet.gov/ps/ddwem/publications/Regulations/R-16-01-RegTxt.pdf.
18. National Toxicology Program, 2002, 10th report on carcinogens: Research Triangle Park, NC, National Toxicology Program, National Institute of Environmental Health Sciences, National Institutes of Health, U.S. Department of Health and Human Services, 2002, http://ehp.niehs.nih.gov/roc/.
19. U. S. Environmental Protection Agency, 1997, Drinking water advisory: Consumer acceptability advice and health effects analysis on methyl tertiary-butyl ether (MTBE), fact sheet: Washington, DC, U. S. Environmental Protection Agency, Office of Water, EPA-822-F-97-009, December 1997, 4 p., http://www.epa.gov/waterscience/drinking/mtbefact.pdf.
20. Association of State Drinking Water Administrators, 2002, State drinking water program pages: Association of State Drinking Water Administrators, November 25, 2002, Accessed December 24, 2002, 2002, at URL http://www.asdwa.org/state.html.
21. Stoner, S., 2000, Federal-State Toxicology and Risk Assessment Committee (FSTRAC): state water contacts list, contacts for state surface water, groundwater and drinking water standards: New York, New York State Department of Environmental Conservation, August 2, 2000, 10 p., http://www.epa.gov/ost/fstrac/water2.pdf.
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