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Exercise may worsen NO2 toxicity.

Exercise may worsen NO2 toxicity

Last year the Environmental Protection Agency reported onstudies indicating that even healthy people who exercise vigorously at smog-ozone levels previously thought to be safe may suffer adverse respiratory effects (SN: 6/28/86, p.405). Now researchers at Los Alamos (N.M.) National Laboratory report animal data showing that exercise following exposure to nitrogen dioxide (NO2), another component of photochemical smog, can worsen that pollutant's respiratory toxicity.

After being trained over a 15-day period to run on a treadmillfor 8 minutes per day, rats were exposed to a single "sublethal' dose of NO2--at a concentration of 25 to 150 parts per million (ppm) for up to 30 minutes. An hour later, one group of animals in each exposure group then made a last treadmill run. The rest were exposed to a 5 percent concentration of carbon dioxide (CO2), to stimulate the same deep breathing the exercising animals were getting.

Though all six exercising rats that had been exposed to 150ppm NO2 were dead within 6 hours of running, none of the nonexercising (CO2-exposed) controls was. Even those exercising animals that had been exposed to as little as 25 ppm NO2 for 15 minutes had four times more damage to lung tissues than did controls. "These results indicate that exercise following NO2 inhalation can potentiate the severity of the toxic response,' say Bruce E. Lehnert, Doug M. Stavert and coworkers. And that raises some provocative occupational-health concerns, they add, since many people are exposed to comparable acute NO2 exposures in the workplace--as welders, miners, firefighters or grain-silo fillers.

Stavert notes that his NO2 studies were conducted in themorning--the rat's normal sleep period. However, he told SCIENCE NEWS, "I wouldn't expect any major [toxicological] differences to be found if we changed [the rats' biological clocks] so that their sleep/wake cycles corresponded with those of the human.'
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Title Annotation:nitrogen dioxide
Author:Raloff, Janet
Publication:Science News
Date:Mar 14, 1987
Words:310
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