Effects of chronic ozone (O₃) exposure on vocal-fold mucosa in bonnet monkeys

Effects of ambient ozone (O₃) on the respiratory tract have been frequently reported. However, little is known regarding possible effects of chronic exposure to O₃ on the larynx or on vocal-fold mucosa. In this study, six bonnet monkeys were exposed to 1 ppm O₃ 8 h per day, 5 days per week, for 3 months. Three of the monkeys' larynges were examined 4 h after exposure, and three were examined 9 months after exposure. Tissues were subjected to histological staining and morphometric quantification. Results revealed increased thickness of epithelial and connective tissue components of vocal-fold mucosa in the 4-h group and connective tissue changes that persisted in mucosa examined 9 months after exposure. Additional changes indicative of hyperplasia and disorganization of epithelial and connective tissue, as well as disruption of glands and vessels, were also noted in tissues examined at both postexposure intervals. Implications of the data for the larynx and voice quality in humans exposed to similar environmental toxins are discussed.