A probabilistic assessment of household exposures to MTBE from drinking water

The oxygenate methyl tertiary butyl ether (MTBE) has been added to reformul ated gasoline in the U.S. to meet national ambient air quality standards. A lthough MTBE has provided significant health benefits in terms of reduced c riteria and toxic air pollutants, detections of MTBE in some groundwater an d drinking water sources have raised concerns about potential environmental contamination and human exposures. In this paper, we examine the frequency and concentration of MTBE detections in drinking water sources in Californ ia from 1995 to 1999, and provide a preliminary analysis of the distributio n of household exposures to MTBE from water-related activities. Using publi shed data on the toxicity and possible cancer hazard posed by MTBE, we esti mate the likely cancer and non-cancer risks for the general population in C alifornia from past and potential future MTBE exposures. More highly expose d subgroups were also addressed. Our findings indicate that less than 2% of all sampled drinking water sources in California had detectable levels of MTBE in 1999, with average MTBE drinking water concentrations ranging from 0.09 to 4.9 ppb for this year. Both the detection rate for MTBE and average MTBE concentrations have remained relatively stable since 1995, despite in creased sampling of drinking water sources in California. The probabilistic exposure analysis suggests that drinking water exposures to MTBE are unlik ely to pose a significant health risk for the general population or more hi ghly exposed individuals in California.