U.S. smog limit permits subtle lung damage

This week, weather forecasters in Washington, D.C., issued their first ozone alerts of the year. Announcing the arrival of “code orange” weather, an unhealthy confluence of heat and pollution, they advised people with respiratory problems to stay indoors and avoid exercise.

However, even robust individuals may suffer temporary, subtle damage—leaky lungs—by breathing ozone concentrations below those needed to trigger such alerts, according to a European study reported this week in Toronto at the American Thoracic Society meeting.

The study indicates that even in regions meeting the U.S. air-quality standard for ozone, “there’s a potential risk to human health,” contends study leader Alfred Bernard of the Catholic University of Louvain in Brussels, Belgium. As such, he told Science News, the current U.S. ozone limits appear to offer “no margin of safety.”

For the past several years, Bernard’s team has been developing blood assays of CC16, a protein produced by the cells that form the lungs’ outer barrier. Explains Bernard, detection of CC16 in the blood serves as a sensitive indicator that this barrier has been breached.

Lungs appear to rely on the protein as an antioxidant to fend off damage from free radicals, he says. In animals, he’s found, strains producing the most CC16 suffer the least damage from ozone.

His team has now used its new assay to gauge ozone effects in 24 healthy cyclists; each participated in two tests at various times in July. These young adults pedaled down Italian roads at a brisk clip for 2 hours. Researchers at the University of Parma then supplied Bernard’s lab with blood that they had collected before and after each cyclist’s exertions.

CC16 concentrations in the blood increased during exercise. The changes went in lockstep with increasing outdoor ozone—beginning on days when ozone was just 0.07 parts per million (ppm) in air, Bernard reports. The current U.S. ozone limit is 0.08 ppm averaged over 8 hours. During the 25 percent of days when ozone was highest, the cyclists’ blood contained up to 50 percent more leaked protein than during the 25 percent of days when airborne ozone was lowest.

The researchers also exposed an especially sensitive strain of mice to the same ozone conditions. After exercise, the animals exhibited a comparable release of CC16 into blood and a similarly inappropriate movement of a different protein from blood into the lungs.

The lung’s leaky barrier can repair itself quickly once ozone exposures subside. However, Bernard now worries that during the leaky period, people may face an increased vulnerability to invasion by bacteria and asthma-provoking pollutants. The risk would be proportional to the ozone dose.

A report of these new findings on the cyclists and animals will appear in the June Environmental Health Perspectives.

Though earlier laboratory studies by others had shown that lung leakiness could occur at relatively low concentrations of ozone, “it’s always important to see that the same thing happens in the real world,” notes pulmonologist William S. Beckett of the University of Rochester (N.Y.) School of Medicine. These “well-done” studies confirm just that, he says.

The leakiness that Bernard’s team is studying “is important because it’s an indication that there’s a biological effect—even at very low concentrations of ozone,” says David J. McKee of the Environmental Protection Agency in Research Triangle Park, N.C. Moreover, he notes, the new assay sounds less unpleasant for the participant than past techniques, such as lavage—”injecting a saline solution into the lungs and then suctioning it out.”

However, McKee argues, low-level leakiness may present no clinical harm, “unless it is repeated throughout a summer or throughout life. Then, you can develop chronic effects”—such as inflammation or scarring of lung tissue.

Beckett says that the direction of the trend Bernard reports is worrisome. Moreover, he maintains, it suggests that “paradoxically, the people who are most likely to be affected by ozone may be the healthiest, most robust individuals”—those with the stamina to exercise despite unhealthy air.

Concerned that other groups—perhaps grannies or babies—might be even more sensitive, Bernard’s team is now beginning a study of lung leakiness from ozone, which will include different age groups and European countries.

Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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