The Effects of Ozone on Human Health

14. In considering the health effects of ozone, the Panel have been guided by the conclusions of the Department of Health's Advisory Group on the Medical Aspects of Air Pollution Episodes, who considered the evidence with respect to this pollutant in their first report. The effects of high concentrations of ozone may be noticeable as a slight irritation of the eyes and nose. These effects are a particular problem on the sunny western seaboard of the United States and most experimental and medical studies have therefore taken place there. Attention has been paid especially to effects on the lung, since these could be responsible for both short term, acute, and longer term, chronic, damage to health. Studies both on human volunteer subjects and on experimental animals have shown that exposure to very high concentrations (500 ppb and 1000 ppb) for several hours leads to damage to the airway lining followed by an inflammatory reaction.This is associated with a transient increase in the liability of the airways to react abnormally to various stimuli such as breathing cold air - so-called airway hyperresponsiveness. This syndrome is familiar to many as the tickly cough that often accompanies a viral infection and may be provoked, for example, by exertion. In addition, there is evidence that at lower levels of exposure, down to about 120 ppb for one hour, changes may occur in the airways of people that increase their sensitivity to inhaled allergens such as pollen. It has been shown that greater responses occur with longer periods of exposure to ozone. The Panel have concluded from these studies that exposures to concentrations of around 100 ppb and above for several hours may lead to airway inflammation in some susceptible people and that this inflammation has the potential to cause short term respiratory symptoms. Additionally, exposure out-of-doors on warm days may well last for a number of hours. These facts have led the Panel to recommend a Standard which is based on a running 8-hour average ozone concentration.
15. Other studies have considered the effect of ozone exposure on measurements of lung function - that is, tests of breathing ability. These studies have included children and both healthy and asthmatic adults, and have examined the effects of exercise which, since it causes deeper and faster breathing, increases exposure. In general they have shown that there is wide variability between individuals in their responsiveness to ozone. Rather surprisingly however, people with asthma seem to be no more susceptible than those without. Nevertheless, both experimental studies and studies of children exposed to ambient ozone concentrations in summer camps in the United States have shown that measurable decrements in lung function may occur on exposure to concentrations of ozone greater than about 100 ppb. The evidence suggests strongly that these effects are only transient and that, with repeated exposure, the airways become resistant to ozone. The Panel found no evidence that exposure to the levels of ozone that are encountered in the United Kingdom are likely to lead to long term damage to the respiratory system. Nevertheless they felt that this aspect needs to be kept under review. Such review will be carried out by the Department of Health's Committee on the Medical Effects of Air Pollutants.
16. These findings are not surprising, since ozone is a powerful oxidising agent, able to release free oxygen radicals during chemical reactions. Such radicals are also an important component of the body's natural defences against invading bacteria, being released by cells as part of the inflammatory reaction. Being toxic to bacteria, oxygen radicals also have the capacity to damage normal tissue in the vicinity, and the body has natural antioxidant defences which act to neutralise them. Thus, inhalation of ozone up to a certain concentration is likely to be within the capacity of the lungs of most individuals to cope with, while higher concentrations may lead to local tissue responses.