EVALUATION OF 13-WEEK INHALATION TOXICITY STUDY ON METHYL T-BUTYL ETHER (MTBE) IN FISCHER-344 RATS

Methyl-t-butyl ether (MTBE) is widely used as an octane enhancing agen t in gasoline. A 13-week inhalation study was conducted in Fischer 344 rats to provide information on potential target organs and toxicity o f MTBE, and to ascertain a no-observed-adverse-effect level (NOAEL) fo r MTBE. Male and female Fischer 344 rats were exposed to target doses of MTBE vapor of 0, 800, 4000 and 8000 ppm for 6 h a day, 5 days per w eek for 13 weeks: MTBE produced no mortalities. At 8000 ppm, males and females showed a decrease in body weights compared to controls. The o nly notable effect on clinical observation was ataxia at 8000 ppm, whi ch was apparent during the first 4 weeks of treatment. Mild hematologi cal and clinical chemistry changes were observed in the 8000 ppm group . At 8080 ppm, animals showed increased serum levels of corticosteroid s, which suggest some stress-like effect. At necropsy, there were no t reatment-related gross lesions. Absolute and relative organ weights (l iver, adrenals and kidneys) were increased in both sexes at 4000 and 8 000 ppm, but there were no microscopic lesions in these tissues with t he exception of the kidney. Microscopic examination of other tissues r evealed no effects with the exception that at 8000 ppm, male rats show ed: mild increased size of hyaline droplets within the kidney, mild in crease in hemosiderosis in the spleen and higher incidence of hyperpla sia in the lymph nodes. The highest NOAEL was judged at 800 ppm. (C) 1 997 John Wiley & Sons, Ltd.