Washington, July 24 - Ozone levels deemed safe can be taxing for healthy lungs, according to new research.

'The National Ambient Air Quality Standard (NAAQS) for ozone was recently revised to set lower limits for ozone concentrations,' said Edward Schelegle, University of California-Davis (UC-D).

'Specifically, we found that 6.6 hours exposure to mean ozone concentrations as low as 70 parts per billion have a significant negative effect on lung function, even though the current NAAQS standards allow ozone concentrations to be up to 75 parts per billion (ppb) over an eight-hour period.'

To test whether mean ozone concentrations above and below the new standard tax lung function, Schelegle and colleagues recruited 31 healthy non-smoking individuals.

They participated in 6.6-hour sessions during which they were exposed to ozone at 60, 70, 80 or 87 ppb or filtered air while undergoing six 50-minute bouts of moderate exercise followed by 10-minute breaks.