The purpose of this paper is to relate the well-established organoleptic reactions of consumers to crude 4-methylcyclohexanemethanol (MCHM) to the likely reactions of consumers to methyl t-butyl ether (MTBE) in drinking water and to determine best estimates of threshold, recognition and detection concentrations for MTBE. On January 9, 2014, a spill of “Crude” MCHM into the Elk River in West Virginia caused an intense “licorice” odor in the water supply for 300,000 people. Panel studies employed ASTM E679-04, which has been used to determine hundreds of odor thresholds in water. The consumer panel estimated that the odor threshold and odor recognition concentrations for Crude MCHM in water were 0.55 and 7.4 ppb, respectively. Two estimates of the odor objection concentrations were 7.7 and 9.5 ppb (McGuire et al. 2014). The population served by the Elk River supply in 2014 complained about the presence of MCHM in their tap water well below 10 ppb, which was the limit of analytical detection for the compound during the initial phase of the contamination event. There have been several studies of the odor threshold concentration of MTBE. The most widely regarded is a consumer panel study published by Stocking et al. (2001) which estimated the MTBE odor threshold at 15 ppb. Determining how consumers may have recognized or objected to the presence of low levels of MTBE in actual drinking water is difficult because there have been few studies published that actually linked MTBE concentrations to consumer responses. There are, however, several data sets and anecdotal information, which confirm a threshold odor concentration of 15 ppb for MTBE and suggest recognition and objection levels. These data and the experiences determined by the study of MCHM organoleptic responses of consumers, strongly suggest that a reported low threshold concentration for MTBE in water is incorrect. In 1993, a research facility released a report that claimed the flavor threshold concentration of MTBE was between 0.04 and 0.06 ppb.

Estimates of threshold, recognition and objection concentrations for crude 4-methylcyclohexanol and methyl t-butyl ether in water

253rd National Meeting (2017)

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