Formation of strong airway irritants in terpene/ozone mixtures

The American Society for Testing and Materials (ASTM) mouse bioassay, which quantifies airway irritation from reduction in the respiratory rate, was u sed to find evidence for the formation of highly irritating substances in r eactions of ozone with terpenes (common indoor volatile organic compounds ( VOCs)). No-observed-effect-levels (NOELs) and concentration-effect relation ships were established for ozone, (+)-alpha-pinene and R-(+)-limonene, isop rene, and some of their major reaction products. Reaction mixtures of exces s terpene and ozone considerably below their NOEL concentrations resulted i n significant upper airway irritation. The reduction of the respiratory rat e was from 30% to about 50%, lowest for the alpha-pinene and highest for th e isoprene mixture. Chemical analysis of reaction mixtures by conventional methods showed that readily identified stable products and residual reactan ts at the concentrations found could not account for the observed reduction s of the respiratory rate, assuming additivity of the reaction products. Th e results suggest that, in addition to known irritants (formaldehyde, acrol ein, methacrolein, methyl vinylketone), one or more strong airway irritant( s) of unknown structure(s) were formed. Future indoor air quality (IAQ) gui delines for unsaturated VOCs (e.g., terpenes) and their emission from build ing products may require the consideration of reactions with oxidants, like ozone. Similarly, effects of ozone-emitting equipment should be re-evaluat ed.