ATMOSPHERIC AND POTABLE WATER EXPOSURES TO METHYL TERT-BUTYL ETHER (MTBE)

This paper presents information an the ways in which people can be exp osed to methyl tert-butyl ether (MTBE) via air and water and on the di stribution of doses that can result from those exposures. Data on conc entrations of MTBE in air were compiled for 15 different occupational, commuting, or residential exposure categories, and concentrations in potable water were compiled from five states in the MTBE-using areas o f 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 populat ion characteristics were estimated as distributions rather than as poi nt values so that the numbers of people exposed at various levels coul d 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-da y. The cumulative dose distribution for the entire population of the M TBE-using regions of the United States was estimated by combining the distributions of doses and the numbers of people in each exposure cate gory. In the MTBE-using areas, arithmetic mean doses via air were esti mated 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 M TBE-using regions uses water with concentrations affected only by atmo spheric deposition, if at all, and too low to be detected with current methods (<2 mu g/liter). The remaining population uses water with an estimated geometric mean concentration of 0.36 mu g/liter, an arithmet ic mean concentration of 49 mu g/l, and a 95th percentile concentratio n of 64 mu g/liter. Doses via ingestion, inhalation, and dermal absorp tion were included, The estimated arithmetic mean dose for the populat ion exposed via water was 1.4 x 10(-3) mg/kg-day. (C) 1997 Academic Pr ess.