Ozone Damages Lab Rats’ Lungs, but Not Seriously
In the most comprehensive laboratory study of the long-term health effects of smog, rodents exposed to large doses of ozone for nearly a lifetime suffered some mild to moderate changes in their lungs but no serious damage or loss of breathing ability, a team of scientists reported today.
Some researchers say the results suggest that ozone--a caustic gas that is the main ingredient of the Los Angeles Basin’s smog--could have some long-term health effects but probably is not inflicting chronic lung problems on most residents of polluted cities.
Rats exposed to concentrations much higher than found in the most polluted part of the basin suffered moderate nose lesions and congestion, and lung scarring described by the scientists as minor. At low concentrations subtle cellular changes occurred in the rats’ lungs.
But in all cases, the animals’ breathing ability, or lung function, was not impaired, leading the researchers to theorize that the rats’ lungs built up tolerance to the pollutant after prolonged exposure.
“Some of the most striking effects of prolonged ozone exposure were observed in the nose,” said the report to be released today by the Massachusetts-based Health Effects Institute, which is funded by the U.S. Environmental Protection Agency and the auto industry. “Prolonged exposure to ozone had mild to moderate effects on other regions of the respiratory tract.”
The findings seem to support the need for urban areas to meet the federal health standard for ozone--which the Los Angeles region has been struggling to do for two decades--but provide little evidence that the standard needs strengthening, as some environmental advocates have long maintained.
“The study is very encouraging in that we do not have a big sleeping dragon ready to wake up when it comes to chronic ozone exposure in human beings,” said toxicologist Robert Phalen, who directs UC Irvine’s Air Pollution Health Effects Laboratory. “I feel a little comforted. It looks like current standards are adequate.”
*
The four-year study, hailed by a reviewing panel of scientists as “carefully designed and well executed,” leaves many unanswered questions, since human lungs are more sensitive to air pollutants than those of rodents.
Unlike the healthy rats in the study, many people suffer asthma and other breathing disorders that are aggravated by ozone. And while 20 months of inhaling ozone is nearly a lifetime for a rodent, it isn’t long for a human, and it might take longer exposures or larger volumes for the pollutant to wear down lungs.
“Rats are more resistant to the effects of air pollution than humans are,” said Kent Pinkerton, a specialist in respiratory cell biology at the UC Davis School of Veterinary Medicine who was one of the project’s 11 researchers. “In some ways, it is a challenge to extrapolate this work to the human health effects.”
For decades, it has been widely known that the Los Angeles Basin’s smog can cause temporary health problems such as shortness of breath and coughing. But scientists have long grappled with whether it prematurely ages lungs and causes chronic respiratory disease.
“This is a landmark study that will increase our knowledge and understanding, but this study, as valuable as it was, did not give any definitive answer,” said Morton Lippmann, a New York University Medical Center professor of environmental medicine.
About 135 million people live in metropolitan areas that violate the federal health standard for ozone, but the only area classified as “extreme” is the region that includes Los Angeles, Orange, Riverside and San Bernardino counties. Ozone forms when hydrocarbons and nitrogen oxides from vehicles, industrial plants and solvents are trapped near the ground and react with sunlight.
The findings already are triggering debate among lung doctors and toxicologists, since previous animal and human studies have shown more troubling impacts on public health.
In a landmark 1987 study, UCLA scientists reported that Glendora residents lost twice as much lung function every year as residents of Tucson, which has no ozone pollution problem. In other research, Olympic cyclists put in smog chambers experienced reduced athletic ability.
“This rodent study has limitations and you have to be cautious in giving it undue weight because there are other studies that indicate more (lung damage) is going on than what this study suggests,” said Dr. Henry Gong, a USC medical professor and chief of environmental health services at Rancho Los Amigos Medical Center in Downey who has researched ozone’s effects.
“This doesn’t change my mind either way,” he said. “I wouldn’t change how I treat my patients based on this.” Gong said he finds the lung abnormalities, while slight, still troubling.
The new report combines the findings of eight projects by Harvard’s School of Public Health, UC Davis and other universities under direction of the Health Effects Institute.
Most of the rats’ nose and lung abnormalities occurred at very high ozone concentrations--0.5 parts per million and 1 p.p.m. The nation’s peak concentration, in the San Gabriel Valley, has hovered around 0.3 p.p.m. in the past few years.
The rodents experienced few effects at 0.12 p.p.m.--the current national health standard, which the Los Angeles Basin violates once every three days, on average.
In the tests, the rats inhaled the ozone-polluted air for 20 months--equivalent to 50 human years--six hours a day, five days per week. They were exposed to only a single pollutant, unlike people, who breathe a brew of chemicals.
“The results of an extensive battery of tests indicated that ozone exposure had little or no effect on overall pulmonary function,” the review panel said in an accompanying report.
But in an unusual finding, cells in a localized but vital section where gases flow into the lung were altered by the low ozone concentration that is considered safe under the federal health standard.
The abnormalities, though, seemed minor and protective in nature: Normal cells were replaced with thicker ones, similar to a callous forming on a hand, and there was no detected effect on the rats’ breathing, said Pinkerton, who conducted the cellular tests with UC Davis pulmonary medicine professor Jerold Last.
“I’m relieved we are not seeing many changes at the low concentration,” Pinkerton said, “I am concerned, though, if one comes away from the study saying there is absolutely no effect at that concentration. There is an anatomical change, and we don’t really know if it is a good or a bad effect.”
At the high concentrations, “mild to moderate” lesions in the rats’ lungs are similar to bronchiolitis in humans, which usually has no symptoms, the scientists reported. If the scarring had been severe or occurred at a lower dose, it would have signaled a clear danger for humans.
* SMOG PLAN DISPUTE: EPA backs California bid to be freed from U.S. smog plan. A3
