title: Subtleties of human exposure and response to chemical mixtures from spills.
abstract: Worldwide, chemical spills degrade drinking water quality and threaten human health through ingestion and inhalation. Spills are often mixtures of chemicals; thus, understanding the interaction of chemical and biological properties of the major and minor components is critical to assessing human exposure. The crude (4-methylcyclohexyl)methanol (MCHM) spill provides an opportunity to assess such subtleties. This research determined the relative amounts, volatilization, and biological odor properties of minor components cis- and trans-methyl-4-methylcyclohexanecarboxylate (MMCHC) isomers and major components cis- and trans-4-MCHM, then compared properties and human exposure differences among them. (1)H nuclear magnetic resonance and chromatography revealed that the minor MMCHC isomers were about 1% of the major MCHM isomers. At typical showering temperature of 40 °C, Henry's law constants were 1.50 × 10(-2) and 2.23 × 10(-2) for cis- and trans-MMCHC, respectively, which is 20-50 fold higher than for 4-MCHM isomers. The odor thresholds were 1.83 and 0.02 ppb-v air for cis- and trans-MMCHC, which were both described as predominantly sweet. These data are compared to the higher 120 ppb-v air and 0.06 ppb-v odor thresholds for cis- and trans-4-MCHM, for which the trans-isomer had a dominant licorice descriptor. Application of a shower model demonstrated that while MMCHC isomers are only about 1% of the MCHM isomers, during showering, the MMCHC isomers are 13.8% by volume (16.3% by mass) because of their higher volatility. Trans-4-MCHM contributed about 82% of the odor because of higher volatility and lower odor threshold, trans-MMCHC, which represents 0.3% of the mass, contributed 18% of the odor. This study, with its unique human sensory component to assess exposure, reaffirmed that hazard assessment must not be based solely on relative concentration, but also consider the chemical fate, transport, and biological properties to determine the actual levels of exposure across different media.
authors.affiliation: Civil and Environmental Engineering, 413 Durham Hall, MC0246, 1145 Perry Street, Virginia Tech, Blacksburg, VA 24061, USA. Electronic address: katphet@vt.edu.
authors.forename: Katherine
authors.initials: K
authors.lastname: Phetxumphou
authors.affiliation: Civil and Environmental Engineering, 413 Durham Hall, MC0246, 1145 Perry Street, Virginia Tech, Blacksburg, VA 24061, USA. Electronic address: andread@vt.edu.
authors.forename: Andrea M
authors.initials: AM
authors.lastname: Dietrich
authors.affiliation: Chemistry, Hahn Hall South, MC004C, Virginia Tech, Blacksburg, VA 24061, USA. Electronic address: nmrns@vt.edu.
authors.forename: Narasimhamurthy
authors.initials: N
authors.lastname: Shanaiah
authors.affiliation: Civil and Environmental Engineering, 413 Durham Hall, MC0246, 1145 Perry Street, Virginia Tech, Blacksburg, VA 24061, USA. Electronic address: esmiley@vt.edu.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Smiley
authors.affiliation: Civil and Environmental Engineering, 413 Durham Hall, MC0246, 1145 Perry Street, Virginia Tech, Blacksburg, VA 24061, USA. Electronic address: dang@vt.edu.
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Gallagher
mesh_terms: D000388:Air; D016902:Air Pollution, Indoor / Q000032:analysis*; D045424:Complex Mixtures; D003510:Cyclohexanes / Q000032:analysis; D004781:Environmental Exposure / Q000032:analysis*; D015386:Hazardous Substances; D006801:Humans; D007536:Isomerism; D009812:Odorants / Q000032:analysis*; D013696:Temperature; D014835:Volatilization; D014867:Water; D014874:Water Pollutants, Chemical / Q000032:analysis*; D060753:Water Quality; D014881:Water Supply / Q000592:standards*
chemical_list: D045424:Complex Mixtures; D003510:Cyclohexanes; D015386:Hazardous Substances; D014874:Water Pollutants, Chemical; D014867:Water; C000607184:4-methylcyclohexanemethanol
keywords: Chemical spill; Henry's law; Mixtures; Odors; Water-atmosphere partitioning