Evaluation of airborne sensory irritants for setting exposure limits or guidelines: A systematic approach

Sensory irritation of eyes and upper airways is an important endpoint for setting occupational exposure limits (OELs) and indoor air guidelines. Sensory irritants cause a painful burning, stinging and itching sensation. Controlled chamber studies are the "golden standard" for evaluations. Well conducted workplace studies offer another possibility. For generalization, the number of participants and their age, smoking, gender, and prior exposure, experience and mood has to be considered. Exposure assessments have to be reliable and exposure duration sufficiently long to establish time-response relationships. A potential confounding by odour has to be assessed. For workplace exposures, mixed exposure and healthy worker effects have to be evaluated. The "Alarie test" is the only validated animal bioassay for prediction of sensory irritation in humans. The mouse bioassay uses the trigeminal reflex-induced decrease in the respiratory rate. The 50% decrease (RD₅₀) has been correlated with OELs set for sensory irritants; predicted OELs for sensory irritants are 0.03xRD₅₀. Evaluation of the bioassay comprises the number of mice and the strain, the reliability of the exposure concentrations and exposure-response relationships, and the similar mode-of-action in mice and humans. These approaches can be used for quality assurance of reported data to set air quality guidelines.