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second day of exposure (Hackney et al., 1975b). A group of young male volunteers were exposed at 0.5 ppm for 2 h. There were only minimal effects on the first day. However, when the exposure was repeated on the next day, 5 of 7 subjects showed significant effects. Twenty subjects were exposed to ozone at 0.5 ppm for 6 h (Kerr et al., 1975). Medium exercise on a bicycle ergometer (100 W at 60 rpm) was used. The subjects experienced dry cough and chest discomfort after exposure. Chest discomfort ranged from tightness on full inspiration to generalized chest pain that was accentuated by exercise, cough, and irritation of the nose and throat. Significant changes from control values were reported for several lung-function tests (specific airway conductance, pulmonary resistance, FVC, and forced expiratory volume in 3 s).

There has been some suggestion that ozone at low concentrations may be carcinogenic or mutagenic in man. Chromosomal abnormalities have been produced in plants and animals, sometimes after low ozone exposures (0.2 ppm for 5 h) (Zelac et al., 1971). Minor chromosomal abnormalities have also been observed in the circulating lymphocytes of humans who have been exposed experimentally at 0.5 ppm for 6–10 h (Merz et al., 1975). So far, however, there is no convincing evidence that ozone at low concentrations causes cancer or congenital malformations in man.


Mittler et al. (1956) reported LC50s for 3-h exposures to ozone as follows:


21 ppm


21.8 ppm


34.5 ppm


36 ppm

Guinea pigs:

51.7 ppm

Svirbely and Saltzman (1957) reported LC50s for 4-h exposures as follows:


2.1–9.9 ppm


7.2–12.3 ppm


15.8 ppm

Diggle and Gage (1955) investigated toxicity in rats and mice after 4-h exposures to ozone and concluded that the LC50 was around 10–12 ppm. Generally, lethal exposures to ozone are accompanied by dyspnea and lethargy, and autopsy reveals lung edema.

Eye effects of ozone exposure were studied in rabbits by Mettier et al. (1960) and Hine et al. (1960). Exposure of rabbits for 1.9–2.8 ppm for 4 h produced no ocular effects, and exposure at 2 ppm 4 h/d was also without eye effects.

Morphologic changes have been reported in the respiratory tracts of animals as a result of exposure to ozone at 0.2–0.25 ppm. Cats were exposed at 0.25, 0.5, and 1.0 ppm for 4.7–6.6 h (Boatman et al., 1974). At all three concentrations, there was considerable

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