This standard is based largely on scientific data documenting the effects of short-term exposure on lung function in humans. Because ozone can damage cells, prolonged or repeated exposures may be a risk factor for lung cancer. Another public health concern is that prolonged exposure to ozone may damage the cells that line the airways, leading to functional changes in the components of the respiratory tract.
Mucous flow is critical to a defense mechanism called mucociliary clearance.
Other studies in this project investigated possible changes in lung function, structure, and biochemistry, and are being published as other Parts of Research Report Number 65. Harkema and Morgan and their colleagues used a video recording technique to measure the speed of mucous flow in different regions of the nasal cavities of rats exposed to 0, 0.12, 0.50, or 1.0 ppm ozone for six hours per day, five days per week, for 20 months. The investigators used specific stains and a technique called image analysis to determine the effect of ozone exposure on mucous content, and light and electron microscopy to study cellular changes in the epithelial cell layer. The investigators found that the effects of ozone on both nasal function and structure in laboratory rats were dependent on dose. Mucous flow rates decreased in nasal tissue isolated from rats exposed to 0.5 and 1.0 ppm ozone.