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Lungs hurt most by ozone-acid synergy.

Lungs hurt most by ozone-acid synergy

The federal air-quality standard for ozone--the primary irritant in smog-- was developed primarily from human health-effects data showing that the chemical might aggravate existing respiratory problems. But new research by scientists at the University of California at Davis suggests the current ozone standard (SN:6/28/86, p.405) may be based on studies that underestimate the pollutant's real-world risk. The Davis researchers have shown in rats that ozone's effects on health are magnified in the presence of acidic air-pollution aerosols such as sulfuric acid and ammonium sulfate. And most researchers agree that people are more likely to encounter ozone in the presence of acidic aerosols than by itself.

Though the level of aerosols used in this study was 100 times higher than what tends to occur outdoors, Davis's Darren Warren says a study now under way is using concentrations of both ozone and an acid aerosol--in this case, sulfuric acid--typical of southern California pollution. "And we have preliminary data showing that these ozone and aerosol concentrations also cause a synergistic effect,' he told SCIENCE NEWS.

Unlike ozone, acid aerosols are not governed by national air-quality standards. In fact, studies by the Davis researchers and others have shown that at urban levels, acid aerosols alone do not cause noticeable lung damage. But reasoning that the acids might exacerbate the respiratory risk posed by their smoggy companions--such as ozone-- the Davis team began comparing lung damage in rats caused by ozone alone and by ozone together with otherwise nondamaging levels of acid aerosols.

In the July TOXICOLOGY AND APPLIED PHARMACOLOGY, Warren, Daniel Guth and Jerold Last report that ammonium sulfate, the most common acidic aerosol in smog, indeed interacts synergistically with ozone at concentrations of ozone common in the Los Angeles basin--0.2 parts per million in air. The two most sensitive biochemical indicators of this effect were elevations in the protein content of lavage (material washed from the lung) and the rate at which lung tissue increased its synthesis of collagen.

Exposure to ozone and ammonium sulfate elevated lavage-protein content 26 percent above the level found in animals exposed to ozone only. According to Warren, elevated lavage-protein content signals inflammation--one sign of ozone damage. Exposure to both pollutants elevated collagen synthesis 22 percent above the increase caused by ozone alone. Collagen synthesis rate can be a clue to developing ozone toxicity, since fibrosis of the lung--an excess of connective tissue such as collagen--occurs in advanced stages of ozone toxicity. Finally, the number of fibroblasts--cells that make collagen--was three times higher in lung tissue of rats that had been exposed to both pollutants than in those exposed to just ozone.

According to David McKee of Research Triangle Park, N.C., project officer for the Environmental Protection Agency's ozone air-quality review, this synergism and the type of lung effects reported by the Davis group "are of sufficient importance to raise a flag of concern. It really is worth paying attention to.'
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Author:Raloff, Janet
Publication:Science News
Date:Aug 9, 1986
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