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Risk Anal

Title:		Route-to-route extrapolation of the toxic potency of MTBE
Author(s):		Dourson ML; Felter SP;
Address:		"Toxicology Excellence for Risk Assessment, Cincinnati, Ohio 45223, USA"
Journal Title:		Risk Anal
Year:		1997
Volume:		17
Issue:		6
Page Number:		717 - 725
DOI:		10.1111/j.1539-6924.1997.tb01278.x
ISSN/ISBN:		0272-4332 (Print) 0272-4332 (Linking)
Abstract:		"MTBE is a volatile organic compound used as an oxygenating agent in gasoline. Inhalation from fumes while refueling automobiles is the principle route of exposure for humans, and toxicity by this route has been well studied. Oral exposures to MTBE exist as well, primarily due to groundwater contamination from leaking stationary sources, such as underground storage tanks. Assessing the potential public health impacts of oral exposures to MTBE is problematic because drinking water studies do not exist for MTBE, and the few oil-gavage studies from which a risk assessment could be derived are limited. This paper evaluates the suitability of the MTBE database for conducting an inhalation route-to-oral route extrapolation of toxicity. This includes evaluating the similarity of critical effect between these two routes, quantifiable differences in absorption, distribution, metabolism, and excretion, and sufficiency of toxicity data by the inhalation route. We conclude that such an extrapolation is appropriate and have validated the extrapolation by finding comparable toxicity between a subchronic gavage oral bioassay and oral doses we extrapolate from a subchronic inhalation bioassay. Our results are extended to the 2-year inhalation toxicity study by Chun et al. (1992) in which rats were exposed to 0, 400, 3000, or 8000 ppm MTBE for 6 hr/d, 5 d/wk. We have estimated the equivalent oral doses to be 0, 130, 940, or 2700 mg/kg/d. These equivalent doses may be useful in conducting noncancer and cancer risk assessments"
Keywords:		Absorption Air Pollutants/metabolism/pharmacokinetics/*toxicity/urine Animals Automobiles Carcinogens/metabolism/pharmacokinetics/*toxicity Databases as Topic Environmental Exposure Female Gasoline Humans Male Methyl Ethers/metabolism/pharmacokinetics/*to;
Notes:		"MedlineDourson, M L Felter, S P eng 1998/02/17 Risk Anal. 1997 Dec; 17(6):717-25. doi: 10.1111/j.1539-6924.1997.tb01278.x"