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METHYL TERTIARY BUTYL ETHER [15], [22]
CASRN: 1634044

Update: October 1992

Current Massachusetts Regulatory Limit
ORSGL = 0.07 mg/L.

Federal Regulatory Limit
The U.S. EPA has not published an MCL for methyl tertiary butyl ether.

Basis for Criteria
The The ORSGL is based on the RfD derived below and assumes that a 70 kg adult ingests 2 L/day of water. A relative source contribution factor of 20% and a 10-fold uncertainty factor to account for potential carcinogenicity are incorporated into the final value.

RfD: 0.1 mg/kg/day
UF: 1000 (10 = interspecies; 10 = intraspecies; 10 = subchronic to chronic)

Critical Effects
Robinson et al. (1990) conducted an oral toxicity study in which Sprague-Dawley rats were exposed via gavage to MTBE. This study included fourteen-day (subacute) and ninety day (subchronic) components, which were well done, included controls, a sufficient numbers of animals of both sexes and an adequate number of endpoints. The authors of the study concluded that there were no significant pathophysiological changes observed at doses below those inducing anesthesia (1200 mg/kg). This observation would result in the identification of a NOAEL of 900 mg/kg. ORS chose the next lowest dose as the NOAEL (100 mg/kg) for two primary reasons: (1) a previous inhalation study done by Greenough et al. indicates that effects may be observed at lower doses; and (2) the study by Robinson et al. is the only available oral study.

Cancer Assessment: C (tentative)
Although ORS believes there is suggestive evidence that MTBE may be a possible human carcinogen, there is much uncertainty over the strength of the available data. ORS has therefore tentatively classified MTBE as a possible human carcinogen.

Class
VOC

Analytical Information
PQL
: 10 ug/L

Analytical Methods
524.2

PQLs and analytical methods may have been updated since this guidance value was last revised. Updated analytical methods for drinking water and their associated PQLs may be found at http://www.epa.gov/safewater/methods/methods.html.

Other Regulatory Data
Any Health Advisories, Reference Doses (RfDs), cancer assessments or Cancer Potency Factors (CPFs) referenced in this document pertain to the derivation of the current guidance value. Updated information may be obtained from the following sources:

Health Advisories - The U.S. EPA provides guidance for shorter-term exposures for chemicals based on their non-cancer effects. Current health advisories may be more current than those used to derive MCLs and may be found at http://www.epa.gov/safewater/methods/methods.html.

RfDs, cancer assessments and CPFs - For specific information pertaining to derivation of drinking water criteria, consult the Federal Register notice that announces the availability of the most current guidance for that chemical. In addition, information on other current RfDs and CPFs as well as cancer assessments for specific chemicals may be found in the U.S. EPA Integrated Risk Information System (IRIS) at http://www.epa.gov/iris/. Please note that the information in IRIS may differ from that used in the derivation process as published in the Federal Register notice.

References
Greenough, R.J., P. McDonald, P. Robinson et al. 1980. Methyl tertiary-butyl ether (Driveron) three-month inhalation toxicity in rats (unpublished material). Prepared for Chemische Werke Huls AG, West Germany, by Inversek Research International. TSCATS/303353. EPA/OTS No. 86-870000172.

Robinson et al. 1990. Fourteen and Ninety-Day Oral Toxicity Studies of Methyl Tertiary Butyl Ether in Sprague-Dawley Rats. J. Amer. Coll. Toxicol. 9:525-539.


[15] The health-based guideline for MTBE was reviewed by ORS in 2000.

[22] The secondary MCL for MTBE is based on the Drinking Water Advisory set by EPA and is based on taste and odor considerations.