ESTIMATION OF RESPIRATORY IRRITANCY FROM INHALED METHYL TERTIARY BUTYL ETHER IN MICE

The Clean Air Act Amendments require the use oi oxygenated fuels in th e winter months to reduce carbon monoxide levels in areas of the count ry that exceed national health standards for carbon monoxide. Methyl t ertiary butyl ether (MTBE, CAS number 1634-044) is the most widely use d fuel additive for this purpose. During implementation, people in a f ew areas oi the country reported nose, eye, and throat irritation. To evaluate the potential for MTBE to produce symptoms indicative of sens ory irritation, mice were tested using a standard bioassay. Concentrat ion-response data obtained from 1-h exposures to MTBE between 300 and 30,000 mg/m(3) revealed that slight to severe sensory irritation occur red with exposure to all concentrations. At the highest concentration both sensory and pulmonary irritation was observed, indicative or acut e lung injury. However, lung lavage protein and lactate dehydrogenase measurements did not support this contention. Respiratory rate was pre dicted by linear interpolation to be decreased by 50% (RD50) at 16,600 mg/m(3) MTBE. Some experts suggest that 3% of the RD50 (in this case 500 mg/m(3)) would not cause significant sensory (i.e., discomforting) irritation. Since this estimate is at least an order of magnitude gre ater than typical peak atmospheric exposure levels during refueling, t he data would suggest that few healthy individuals would experience se nsory irritation during transient exposures to MTBE.