Implications of an MTBE odor study for setting drinking water standards

In early 2001, the US Environmental Protection Agency is expected to adopt a secondary maximum contaminant level (SMCL) for methyl tertiary butyl ether (MTBE) in drinking water. This article presents the first and only consumer study to determine the odor threshold of MTBE in drinking water. A protocol, based on the American Society for Testing and Materials method E679-91, was augmented to address concerns raised by interested stakeholders. The study, which was conducted according to the final odor threshold protocol, used a panel of 57 consumers and yielded an odor threshold for MTBE in drinking water of 15 μg/L. The 15 μg/L threshold is the geometric mean of the individual thresholds for each of the 57 consumers. This consumer panel threshold is consistent with the trained panel thresholds reported from five other taste and/or odor studies, which ranged from 13.5 to 45.5 μg/L. Consequently, the authors recommend using the methodology presented in this article as the scientific basis for establishing the federal SMCL for MTBE and other organic chemicals in drinking water.