ADAPTATION TO OZONE - DURATION OF EFFECT

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Abstract
The effects of repeated exposure to the oxidant air pollutant ozone is a matter of considerable concern for persons who live in areas with high air pollution rates. Repeated ozone exposure induces an adaptative response whereby subsequent ozone exposure induces little or no pulmonary function change. The time course and persistence of this adaptation was determined in 24 subjects. Subjects were studied for 125 min while they exercised intermittently. They were exposed to filtered air for 1 day and then in the next week for 5 consecutive days to 0.5 ppm ozone. After the 5th day, subjects were randomly assigned to return for one more ozone exposure at 1, 2 or 3 wk. The greatest decrement in FEV1 [1 s forced expiratory volume] occurred on the 2nd day of exposure. The number of consecutive ozone exposures required to produce adaptation varied 2-5 days. Persistence of adaptation in ozone-sensitive subjects (initial decrease in FEV1 > 10%) showed marked individual variability but the duration of adapatation was shortest for more sensitive subjects. Adaptation on the average lasted less than 2 wk, being as short as 7 days and as long as 20 days. More sensitive subjects required more daily sequential exposures in order to adapt.