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Ozone saps toads' immune systems

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10:36am, February 1, 2005
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The ozone in smog can impair immunity in human lungs. A laboratory study now indicates that the pollutant can do the same in toads.

Michael R. Dohm and his colleagues at the University of Hawaii at Hilo placed cane toads (Bufo marinus), collected locally, into a chamber for 4 hours with air containing 0.2 to 0.8 part per million (ppm) ozone. That's well above the 0.01 ppm ozone concentration typical of Hilo. But it's within the range of exposures in many major cities worldwide and the air that drifts downwind from them.

At various intervals over the 2 days following the ozone exposure, Dohm's team collected macrophages from the amphibians' lungs and tested them for ozone damage. Macrophages are immune cells that, among other roles, engulf bacteria and other microscopic particles.

Although ozone didn't affect the number or viability of lung macrophages, it severely impaired the cells' capacity to engulf particles. "Nearly 40 percent of cells failed to [engulf any] particles when the toads were exposed to ozone," the scientists report in the January Environmental Toxicology and Chemistry. Many of the rest of the ozone-exposed macrophages collected only a single particle. During the next day, most of the cells had recovered their appetites and once again engulfed many particles.

What this means, the researchers conclude, is that ozone "may be a significant and now commonplace stressor of wildlife populations." Through immunological suppression, the pollutant may contribute to the perplexing worldwide decline of amphibian species (SN: 4/15/00, p. 247: Colossal study shows amphibian woes), say Dohm and his colleagues.

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