Olfactory adaptation, threshold shift and recovery at low levels of exposure to methyl isobutyl ketone (MIBK).

The anatomic position of olfactory receptors renders them vulnerable to airborne pollutants. Chamber inhalation studies have shown dose-dependent olfactory adaptation and temporary olfactory threshold perception shift for particular inhaled substances. The present study was undertaken to examine olfactory perception threshold (OPT) and adaptation of healthy subjects exposed for 7h to MIBK. Volunteers (n = 4) were exposed in an inhalation chamber to MIBK at concentrations of 20 ppm and 40 ppm. For each of 6 exposure days, OPT for MIBK and PM-Carbinol were determined once before exposure and at 3 successive intervals following exit. Exhaled air samples were taken at regular intervals during and after exposure. Perceived odor intensity and symptoms were ascertained through a questionnaire filled out hourly. On all days, post-exposure OPT-MIBK at chamber exit was significantly higher than pre-exposure, representing a ninefold increase in concentration; recovery was dose-dependent and not complete 95 min. after exit. No threshold shift was observed for OPT-PM-Carbinol. Perceived odor intensity was high when entering the chamber, but diminished with time, stabilizing after approximately 2 hours. Symptoms of nose, eye or throat irritation and headache were present in some subjects. The findings of this study suggest that at these levels of MIBK, there is olfactory adaptation during exposure and a transient OPT shift for the inhaled substance. Persons exposed professionally or environmentally to certain organic solvents may suffer temporary smell loss which hinders odor detection.