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Chemacal Summary Methyl-Tert-Butyl Ether- Microsoft Internet Explorer Page 5 of 13 1 Air - MTBE is not expected to persist in the atmosphere because of its rapid reaction with hydroxyl radicals The rate constant for this reaction is 2 84 x 10-12 cm3/molecule-sec at 25oC (HSDB 1994) . MTBE does not absorb light of greater than 210 nm, therefore, direct photolysis by UV absorption is ' not expected to be environmentally significant. Atmospheric half-lives of 3 0 days in polluted air and 6.1 days in noti- polluted air have been calculated (U.S EPA 1993a) ' 2 Soil - MTBE is expected to volatilize rapidly from soil surfades (U S. EPA 1993a) MTBE released in subsoils as a result of leaks from underground storage tanks may be persistent There is little evidence that MTBE is susceptible to either aerobic ' or anaerobic biodegradation (U.S. EPA 1993a) 3. Writer - MTHF In e.npeot:ed to vol at:i l i zn from surfaGc watetrg (U S EPA 1993a) . Volatilization half-lives of MTBE from streams, rivers and lakes were estimated to be 2 5 h, 9 5 h and 3,296 h (137 days) , respectively (U S EPA 1993a) MTBE is not expected to hydrolyze, photolyze, or be adsorbed to sediments or suapanded paxtiaulate !natter (HODD 1004) ' 4. Biota - Bioconcentration factors (BCF) of 1 5 and 1 4 were reported for Japanese carp exposed to 10 and 80 mg/L MTBE (U S. EPA 1993a) . Bi000naontration faotorc of 3 70 and 1 56 were estimated from regression equations based on Kow values ' (U S EPA 1993a) . These BCFs indicate a low potential for bioconcentration !Back to TOC( IV. HUMAN HEAL'T'H ErFE CTS A Pharmacokinetics I1. Absorption - Animal studies have shown that MTBE is rapidly absorbed following oral or inhalation exposures. Bioavailability following dermal exposure is reported to be 39% or less than that ' fvL ULdl expusuLes (U.S EPA 1993x) 2 Distribution - Animal studies indicate that MTBE is rapidly distributed in the blood to all parts of the body including ' the brain. Peak blood levels occur within 15 min of i p injection, and highest tissue levels were reported to occur in the liver and kidneys (U.S EPA 1993a) . 3 Metabolism - The major metabolites of MTBE are tertiary butyl alcohol (TBA) and formaldehyde (U 5 EPA 1993a) The formaldehyde is likely further metabolized to formic acid and carbon dioxide, with the possible formation of methanol as well ' 2-Methyl--1, 2-propanediol and A-hydroxyisobutyric acid have also been identified in the urine of MTBE-exposed animals. 4 Excretion - Animal studies have shown that MTBE is rapidly excreted following oral or inhalation exposures (U.S EPA 1993a) Following oral exposures, MTBE is eliminated mainly in expired air (46-69%) with smaller amounts excreted in the urine (11-36%) . Following inhalation exposures, most MTBE and metabolites are excreted in the urine (53-72%) with smaller amounts in expired air (17-22%) (U S EPA 1993a) B. Acute Effects Friday, August 16, 1996 4 25 PM