UC San Diego

This two-part investigation assessed the effects of 1-h exposures to methyl tertiary-butyl ether (MTBE) at an ambient concentration of 1.7 ppm on healthy adults. In one part, four subjects participated in a pharmacokinetic study of blood levels of MTBE. Concentration in blood rose 20-fold from baseline to 17 mg/L by the end of exposure and declined to one half that level at 40 min after exposure. In another part, 43 subjects participated in a double-blind study of reactions to exposures to MTBE (1.7 ppm), to a mixture of 17 volatile organic compounds (VOCs) (7.1 ppm), and to air. Subjects rated symptoms (e.g., irritation, headache, mental fatigue), their mood, and various environmental attributes (e.g., odor, air quality, temperature), and also took computerized performance tests during exposures. Measures of eye irritation (e.g., tear-film breakup, eye redness) and nasal inflammation (i.e., measurement of polymorphonuclear neutrophilic leukocytes, PMNs) were taken before and after exposure as objective correlates of symptoms. Although subjects could perceive differences among the exposures via odor and air quality, they showed no increase in symptoms in response to MTBE and VOCs over those to air. The only significant objective effect comprised a time-by-agent interaction in number PMNs due principally to an increase in PMNs after exposure to VOCs. The level was higher 18-24 h after exposure than immediately after lt. Because the subjects' ratings replicated effects found previously (e.g., time dependence in irritation judgments, effect of gender on rated odor intensity and pleasantness, and thermal comfort), it would appear that the absence of differential effects of MTBE on symptoms can be accepted at face value.