Terpene/ozone Reaction Products (tops). Dependence of Irritation on Reaction Time and Relative Humidity

Earlier, we reported the formation of unidentified strong irritants in reaction mixtures of terpenes and ozone. The identified products included aldehydes, ketones and carboxylic acids. Here we report the effects of relative humidity and reaction time on irritant formation in our flow reaction system using limonene and isoprene. Upper airway irritation was measured in mice (via reduction of respiratory rate) using ca. 5 and 35% relative humidity and long and short reaction times. Maximum irritation was observed for low humidity/short time reaction mixtures for both terpenes and the combination of high humidity and long reaction time gave the least irritation. In order to estimate the comparative irritation of limonene/ozone mixtures, we studied irritation effects at four ozone concentrations using low humidity/short time conditions holding other parameters constant. The mixture containing limonene/ozone at 46/0.5 ppm exhibited an irritation effect, which was the same magnitude as that of pure limonene. INDEX TERMS Indoor air chemistry, Ozone, Terpene, Mouse bioassay, Upper airway irritation INTRODUCTION We have suggested that terpene/ozone reaction products (α-pinene, R-(+)-limonene, ozone) include unidentified, potent airway irritants (Wolkoff et al., 1999, Clausen et al., 2001, Wilkins et al., 2001). Reaction time and relative humidity are the two of the most interesting reaction parameters with respect to the formation of highly irritating (and thus chemically reactive) products indoors. Formation of ozonides and peroxides during ozone reactions of terpenes has been reported (Griesbaum et al., 1998, Sauer et al., 1999, Hewitt and Kok, 1991). We investigated the effect of increased relative humidity and reaction time on irritant concentration using the mouse bioassay. In order to estimate the irritation potency of the limonene/ozone reaction mixture relative to known irritants, ozone concentration was varied and the respiratory rate was monitored. METHODS Materials O3 was generated photochemically as described earlier (Wolkoff et al., 1999). The age of the reaction mixture was determined by the transport time through the flow tube reactor and exposure chamber. For the low humidity experiments, medicinal grade air was used to evaporate the terpene. Pure oxygen at ca. 0.5 l/min was irradiated and added to the terpene stream to give a total flow of ca. 17 l/min (Clausen et al., 2001). For high humidity experiments the medicinal air was bubbled through warm water (ca. 30° C) to give final * Contact author email: [email protected] Proceedings: Indoor Air 2002