Mixtures of Volatile Organic Compounds: Detection of Odor, Nasal Pungency, and Eye Irritation
Thresholds for detection of odor, nasal pungency (irritation), and eye irritation were measured for single volatile organic compounds (VOCs) (1-propanol, 1-hexanol, ethyl acetate, heptyl acetate, 2-pentanone, 2-heptanone, toluene, ethyl benzene, and propyl benzene) and certain mixtures of them (two three-component mixtures, two six-component mixtures and one nine-component mixture). Nasal pungency was measured in persons lacking a functional sense of smell to avoid interference from olfaction. The results showed the existence of various degrees of stimulus agonism (additive effects) in the three sensory channels. Such agonism increased with the complexity of the mixtures and with the lipophilicity of their components. Eye irritation even showed synergistic stimulus agonism for the most lipophilic (one of the six-component) and the most complex (the nine-component) mixtures. The results indicate that complex chemical environments may enable chemosensory, and particularly irritative, detection when single VOCs lie far below their individual thresholds. Even the present rather rudimentary state of knowledge of how lipophilicity influences detection of single VOCs and how it and complexity (number of components) influence detection of mixtures would presumably allow refinement of a measure such as total mass (or concentration) of volatile organic compounds (TVOC) into a much more meaningful index that we might call the perceptually weighted level of VOCs, or PWVOC. Such an index, like the index dB(A) for sound, could make an otherwise strictly physical measurement at least somewhat predictive of human responses.