Results of long-term experimental studies on the carcinogenicity of methyl tert-butyl ether.

Methyl-tert-butyl ether (MTBE) was submitted to long-term carcinogenicity bioassays on Sprague-Dawley rats. The test compound was delivered in olive oil by stomach tube (gavage), at the doses of 1000, 250, and 0 mg/kg b.w. to groups of 60 males and 60 females, once daily, 4 times weekly, for 104 weeks. All animals were kept under control until spontaneous death. MTBE was found to cause in males an increased incidence of Leydig cell testicular tumors in the group treated with the higher dose, and in females a dose-related increase of leukemias, an increase of dysplastic proliferations of lymphoreticular tissues, and also an increase of uterine sarcomas at the lower tested dose. On the basis of the presented data, MTBE must be considered a potential carcinogen.