Experimental Studies on the Concentrations of Subjectively Equivalent Irritation for Odorants

Abstract

Discussion of non-olfactory “irritation”, which is caused by the excitement of the trigeminal nerve, has important implications for odor pollution. The main purpose of this study is to work out the mechanisms for the generation of non-olfactory irritation, and the sensory characteristics of the perceived irritation. Concentrations of subjectively equivalent irritation (CE) of 16 odorous compounds were measured by the sensory test. The relations between the CE and the physicochemical properties of the compounds were shown and discussed. It was found that the CE of dissociated compounds is much lower than that of undissociated compounds. And among the dissociated compounds, the acidic ones have a lower CE than the basic compounds. The CE of acrolein, which is an unsaturated compound, was the lowest among all the compounds used in this experiment. The delay time, i.e. time until the sensation of irritation after inhaling, was longer for acrolein gas than for other gases. Therefore, the mechanism for generating sensory irritation by the acrolein gas may be different from that of other gases. From analysis on the basis of relation to some physicochemical properties, it was concluded that the electrophilic reactivity of the acrolein molecule may be related to the generation of sensory irritation. In the case of dissociated compounds, the CE is related to the dissociation constants of the compounds. In other words, the larger the acidic and basic dissociation constants (Ka and Kb) are, the lower the CE becomes. Key Words : Sensory test, Odorous irritant, Concentration for subjectively equivalent irritation, Physicochemical properties, Dissociation constant