Ozone: an overview of its toxicity in man and animals

Ozone is one of the most toxic and ubiquitous air pollutants. This review focuses on the toxic effects of ozone in animals and on the similarities and disimilarities between the toxic effects in animals and humans. The molecular basis for the toxicity of ozone is discussed, based on the vigorous oxidizing properties of ozone. Despite the existence of anatomical differences between human, subhuman primate, and dog lungs versus common experimental rodent lungs, the anatomical lesion of ozone inhalation occurs at the functionally equivalent site of the junction between the conducting airway and the respiratory region. Ciliated cells of the upper airways and the type 1 cell of the centriacinar region are most affected. Type 2 cell proliferation is a hallmark of ozone toxicity. A wide variety of biochemical and physiological changes have been noted in several animal species and in humans. Considerable evidence for a free-radical-mediated or lipid peroxide-mediated toxicity is evident, especially in the induction of the glutathione peroxidase system and the protective effects of vitamins C and E. Ozone appears to be a weak mutagen and to produce chromosomal abnormalities. Defects in defense against airborne infection are present in animals, which are more susceptible to airborne infection after ozone exposure. Epidemiological studies, however, fail to detect increased respiratory infections in humans due to ozone. Despite the variety of toxic effects, few qualitative differences between species are apparent; rather, quantitative differences do occur. Ozone may thus be an ideal compound for quantitative extrapolation of toxicity from animals to humans.