Atmospheric and potable water exposures to methyl tert-butyl ether (MTBE)

This paper presents information on the ways in which people can be exposed to methyl tert-butyl ether (MTBE) via air and water and on the distribution of doses that can result from those exposures. Data on concentrations of MTBE in air were complied for 15 different occupational, commuting, or residential exposure categories, and concentrations in potable water were complied from five states in the MTBE-using areas of the United States. Based on these concentrations and characteristics of the exposed populations, average daily and lifetime average doses were estimated. Both the concentration data and several of the population characteristics were estimated as distributions rather than as point values so that the numbers of people exposed at various levels could be estimated. Arithmetic mean occupational doses via air were in the range of 0.1 to 1.0 mg/kg-day, while doses from residential exposures, commuting, and refueling were in the range of 0.0004 to 0.006 mg/kg-day. Lifetime doses for workers were in the range 0.01 to 0.1 mg/kg-day. The cumulative dose distribution for the entire population of the MTBE-using regions of the United States was estimated by combining the distributions of doses and the numbers of people in each exposure category. In the MTBE-using areas, arithmetic mean doses via air were estimated to be 0.0053 and 0.00185 mg/kg-day for the chronic and lifetime cases, respectively. Approximately 98.5% of the population living in MTBE-using regions uses water with concentrations affected only by atmospheric deposition, if at all, and too low to be detected with current methods (< 2 micrograms/liter). The remaining population uses water with an estimated geometric mean concentration of 0.36 microgram/liter, an arithmetic mean concentration of 49 micrograms/l, and a 95th percentile concentration of 64 micrograms/liter. Doses via ingestion, inhalation, and dermal absorption were included. The estimated arithmetic mean dose for the population exposed via water was 1.4 x 10(-3) mg/kg-day.