Tale of Two Isomers: Complexities of Human Odor Perception forcis- andtrans-4-Methylcyclohexane Methanol from the Chemical Spill in West Virginia

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 for individuals with prior exposure compared to naïve subjects. Individual trans-4-MCHM odor threshold concentrations vary by more than a factor of 100. The cis-4-MCHM isomer has approximately a 2000-fold higher odor threshold concentration, different descriptors, and an even wider individual response range.

Toxicity Assessment of 4-Methyl-1-cyclohexanemethanol and Its Metabolites in Response to a Recent Chemical Spill in West Virginia, USA

“…The crude MCHM also has a different ratio of cis- and trans-MCHM isomers compared to the standard 4-MCHM used in this study, 8 with different odor thresholds. 49 Isomers and their metabolites may have different activities, leading to different toxicity, which require further investigation. According to the previous study of the Eastman Company, crude MCHM seems to be less toxic than 4-MCHM with a weaker effect on dermal irritation and skin sensitization.…”

Identification and characterization of phenylacetonitrile as a nitrogenous disinfection byproduct derived from chlorination of phenylalanine in drinking water

“…According to the logistic regression, a 0.6 mg/L GC-O concentration corresponds to the odor threshold, based on a threshold definition of 0.5 probability of detection (Fig. S3) (Gallagher and Cuppett, 2007;Gallagher et al, 2015). The GC-O OTC analysis result showed that the inhalation threshold for phenylacetonitrile was approximately 0.2 ppt-v, which corresponded to an injected concentration of 0.6 mg/L on the GC-O (Gallagher et al, 2015).…”

Important Considerations for Estimating Odor Threshold Concentrations of Contaminants Found in Water Supplies

“…This same challenge applies to comparing odor thresholds of chemicals in water. Gallagher et al () provided an application of psychophysical measurements to a chemical mixture that ultimately caused serious aesthetic problems in a drinking water supply, pointing out both the strengths and challenges in conducting such evaluations. This work illustrates the fact that setting chemical‐specific standards based on odor thresholds can be challenging (AWWA Taste and Odor Committee , Young et al ).…”