Article pubs.acs.org/est
Tale of Two Isomers: Complexities of Human Odor Perception for cisand trans-4-Methylcyclohexane Methanol from the Chemical Spill in West Virginia Daniel L. Gallagher,*,† Katherine Phetxumphou,† Elizabeth Smiley,† and Andrea M. Dietrich†,‡ †
Civil and Environmental Engineering 413 Durham Hall, Virginia Tech, 1145 Perry Street, MC 0246, Blacksburg, Virginia 24061, United States ‡ Food Science and Technology, Virginia Tech, 360 Duck Pond Drive, MC 0924, Blacksburg, Virginia 24061, United States S Supporting Information *
ABSTRACT: Application of gas chromatography with mass spectrometric and human olfactory “sniffer” detectors reveals the nature of odorous chemicals from an industrial chemical spill. Crude 4-methylcyclohexane methanol (4-MCHM) spilled in a river and then contaminated drinking water and air for over 300000 consumers living in West Virginia. Olfactory gas chromatography allows investigators to independently measure the odor of chemical components in a mixture. Crude 4-MCHM is comprised of several major cyclohexane components, four of which have distinct isomer pairs. The cis- and trans-4-MCHM isomers are the only components to have distinct odors at the concentrations used in this study. The trans-4-MCHM is the dominant odorant with descriptors of “licorice” and “sweet”. Trans-4-MCHM has an air odor threshold concentration of 0.060 ppb-v (95% CI: 0.040−0.091). The odor threshold concentrations are not influenced by gender or age but are lower by a factor of 5 ̈ subjects. Individual trans-4for individuals with prior exposure compared to naive MCHM odor threshold concentrations vary by more than a factor of 100. The cis-4MCHM isomer has approximately a 2000-fold higher odor threshold concentration, different descriptors, and an even wider individual response range.
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INTRODUCTION Chemical Spill in Charleston, WV. On the morning of January 9, 2014, West Virginia (WV) residents living near the Freedom Industries tank farm complained of licorice odors in the air. This prompted the WV Department of Environmental Protection to investigate and discover that approximately 10000 gallons (37800 L) of crude 4-methylcyclohexane methanol (MCHM) leaked and drained into the nearby Elk River.1,2 The WV American Water drinking water treatment plant (DWTP) was located 2.4 km downstream of the leaking tank in the city of Charleston, which is WV’s largest city and located in densely populated Kanawha County. By the afternoon of January 9, WV American Water announced that contaminated Elk River water was processed into drinking water and delivered to over 300000 consumers in Charleston, Kanawha County, and eight other counties.1,3,4 A licorice odor was acknowledged at the DWTP and complaints of strong licorice odors from drinking water were reported to government officials by residents living throughout Charleston and Kanawha County.4 Radio, television, and social media provided news about the spill and its pervasive drinking water contamination. By 6:00 PM on January 9, WV Governor Tomblin, in conjunction with WV American Water, issued “do-not-use orders”1 and notified consumers that tap water was not safe to use for drinking, cooking, cleaning, bathing, or washing.3 During the next day, © 2014 American Chemical Society
concentrations of 4-MCHM leaving the DWTP were 750− 2400 μg/L (see Table S1 of the Supporting Information for concentrations and timeline).5 Schools, businesses, and government offices closed for several days. Drinking water in bottles and from trucks was provided to consumers by the government. Home owners were instructed to flush and purge contaminated water from homes.6 The “do-not-use orders” were lifted for some consumers 4 days after the spill; within a week, all “donot-use-orders” were lifted.1 Concentrations of 4-MCHM leaving the DWTP were below the detection limit of 0.5 μg/ L from January 14−19, but 2−5 μg/L concentrations were detected January 20−30.7 Even though the water was declared to meet drinking water quality, public confidence was low because of lingering licorice odors. Hundreds of people went to the hospital reporting symptoms of nausea, headaches, itching, sore throat, vomiting, eye irritation, rash, abdominal pain, and diarrhea that may have been associated with exposure.2,6 Two weeks following the spill, a survey found concentrations of 50 yr age < 50 yr
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0.041 (0.019−0.086)
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0.066 (0.041−0.107)
1.2 × 1002 (1.1 × 1000 − 1.4 × 1004) 1.3 × 10−01 (2.2 × 10−02 − 7.5 × 10−01) 1.9 × 1006 (4.5 × 10−05 − 7.7 × 1016) 3.4 × 1002 (9.7 × 10−01 − 1.2 × 1005) 9.1 × 1000 (3.5 × 10−02 − 2.4 × 1003) 6.3 × 10−01 (9.7 × 10−02 − 4.1 × 1000) 8.9 × 1003 (2.4 × 10−02 − 3.3 × 1009)
subject groups
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RESULTS The crude MCHM at 1000 mg/L was characterized by the GCO-MS and revealed that the mixture was comprised of ten distinct cyclohexane components with four isomer pairs. A compound identified as cyclohexane methanol (probability match 59%) was the first to elute, followed by trans-4-MCHM then cis-4-MCHM. 4-MCHM was followed by two isomers of methyl-4-methylcyclohexanecarboxylate (probability match 66.8% and 63.41%), two unknown isomers of low concentration and low (
