A new study involving 23 healthy, young adults shows that a 2-hour exposure to high levels of ozone can lead to physiological changes associated with cardiovascular ailments, according to an article published online in Circulation, a journal of the American Heart Association.
Although participants reported no physical symptoms, tests revealed evidence of vascular inflammation, a potential reduced ability to dissolve artery-blocking blood clots, and changes in the autonomic nervous system that controls the heart’s rhythm.
The physiological changes observed during these one-time, short-term exposures were temporary, but suggest how acute exposure can lead to death for those with existing cardiovascular problems, and how long-term exposure may contribute to cardiovascular disease.
Good Ozone. Bad Ozone.
Depending on where in the atmosphere it’s found, ozone is both helpful and harmful.
High above in the stratosphere, ozone (03) protects life on earth from the Sun’s harmful ultraviolet rays (UV-b). Here, it’s produced naturally when oxygen (O2) reacts with UV-b. But because O3 is instable, it decays back to O2 rather quickly. The resulting equilibrium is responsible for what is commonly called the “ozone layer.”
At ground level, ozone is an air pollutant and a key ingredient of urban smog, harmful to both plants and animals. Ground-level ozone is not emitted directly but created by a chemical reaction between oxides of nitrogen (NOx), and volatile organic compounds (VOC) in the presence of sunlight. Vehicle exhaust, industrial emissions, and chemical solvents are among the largest souces of NOx and VOCs.
Ground-level ozone is created when pollutants from vehicles, power plants, industry, chemical solvents and consumer products react in the presence of sunlight. Recent epidemiology studies have reported associations between acute exposure to ozone and death but little was known about the underlying pathophysiological pathways responsible.
Researchers exposed the volunteers, ages 19 to 33, to 0.3 parts per million (ppm) of ozone. While the dose was higher than the EPA’s eight-hour ozone standard of 0.076 ppm, a person breathing 0.3 ppm for two hours receives roughly the same amount of ozone as does a person breathing the lower 0.076 ppm for eight hours.
Test subjects underwent two controlled exposures — one to clean air and one to ozone-polluted air — at least two weeks apart. During each exposure, participants alternated 15-minute periods of stationary cycling and rest.
None of the participants reported physical symptoms after breathing air or ozone. However, tests conducted immediately following and the morning after ozone inhalation showed significant ozone-induced vascular changes compared to clear-air exposure, including:
- An increase in blood levels of interleukin 1beta, a signature marker of inflammation that appears to play a key role in heart disease.
- A decrease in plasminogen activator inhibitor 1 and plasminogen, components that play an important role in dissolving blood clots that may form along arterial walls.
- A change in heart rhythm, indicating altered autonomic nervous system control of heart rate.
Epidemiology studies have also associated acute exposure to another ubiquitous air pollutant, particulate matter (PM), with death in elderly people with cardiovascular disease. Particulate matter is tiny airborne particles that can be inhaled into the lungs.
Controlled exposure studies of both humans and animals have described PM-induced changes that are very similar to those described in this ozone study, suggesting that both pollutants may be causing death by affecting similar pathways, the researchers said.
The World Health Organization estimates 2 million people worldwide, mostly elderly people with cardiovascular disease, die because of acute exposure to air pollution. The EPA puts the yearly U.S. toll at 40,000-50,000 deaths.
“People can take steps to reduce their ozone exposure, but a lot of physicians don’t realize this,” said Robert B. Devlin, Ph.D., the study’s lead author and senior scientist at the U.S. Environmental Protection Agency’s (EPA) National Health and Environmental Effects Research Laboratory in Research Triangle Park, N.C.
To learn more about air quality, ozone levels, and how you can limit your exposure, visit the EPA website, airnow.gov.
