Researchers in Sweden and the United States have identified two metabolites of the fuel oxygenate MTBE in humans. Other than tertiary butyl alcohol (TBA) these are believed to be the first metabolites of MTBE characterized in humans. The research was a collaboration between CIIT and three Swedish institutes: the National Institute for Working Life, the Karolinska Institute (both in Solna), and University Hospital (Uppsala).
The findings are important because of the widespread use of MTBE (methyl tertiary butyl ether) as a fuel additive. It is combined with gasoline during winter months to provide extra oxygen and make the fuel burn more cleanly, thus reducing air pollution. MTBE has been shown to cause kidney and liver tumors in some rodents at high exposure levels.
In this study four adult males were exposed to MTBE by mouth (inhaled) for two hours at 50 parts per million. During exposure the men rode an exercise bike and were monitored for heart rate and other factors every 20 seconds. Both urine and blood samples were taken and analyzed. Both metabolites identified as HBA (a-hydoxyisobutyric acid) and MPD (2-methyl-1,2-propanediol) were found in the urine as measured by nuclear magnetic resonance spectroscopy conducted at CIIT.
While the two metabolites had been seen before in similar tests on rodents, this is the first time they have been observed in humans. The European investigators are using these data to develop a model to study the dose effects for MTBE in humans. Understanding the relationship between MTBE effects in rodents and humans is essential for evaluating potential human health risk based on rodent bioassay data.
The findings appear in the September 20th issue of Chemical Research in Toxicology. [Nihlén, A., Sumner, S., Löf, A., and Johanson, G. (1999). 13C-Labeled Methyl tertiary-Butyl Ether (13C2-MTBE): Toxicokinetics and Characterization of Urinary Metabolites in Humans.]
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Contact: Bob Nellis
nellis@ciit.org
919-558-1310
CIIT - Chemical Industry Institute of Toxicology
17-Sep-1999