Long-term smog exposure deadly, study finds
CTV.ca News Staff
Published Wednesday, March 11, 2009 11:50PM EDT
Every summer, hospital emergency rooms fill with people developing breathing problems during suddenly hot and smoggy days. Now, scientists are finding that long-term exposure to even low levels of the ozone in smog boosts death risk.
Lorraine LeBlanc, whose lungs are already damaged by disease, can tell when air pollution levels are high without even looking outside -- her breathing becomes even more strained.
"I get worried," she tells CTV News. "I know it's going to make my lungs worse and that's something I don't need. They're bad enough as it is."
The study out of the U.S. found that people who lived in areas with the highest concentrations of ground-level ozone had a 25 to 30 per cent greater annual risk of dying from respiratory diseases compared with people from area with the lowest levels of the pollutant.
Ground-level ozone forms when nitrogen dioxide from car tailpipes, coal-fired power plants and other industries collides with oxygen in the presence of sunlight.
It's different from fine particulate matter, the tiny particles of pollutants emitted by factories, cars, and power plants. That element of air pollution tends to be more concentrated at its source.
Ground-level ozone, on the other hand, can be found in higher concentration in suburbs and rural areas downwind of cities, because ozone takes time to form as it travels along the wind.
While it's not news that "smog days" - those summer days when hot weather and pollution combine to create extra hazy days - can cause health problems, this study is the first to look at the long-term impact of ozone.
"What this study says is that to protect the public's health, we can't just reduce the peaks, we must also reduce long-term, cumulative exposure," says Dr. George Thurston, a professor in the Department of Environmental Medicine at NYU School of Medicine, who directed the air pollution exposure assessment part of the study.
The study analyzed data on about 450,000 people who were followed from 1982 to 2000 as part of an American Cancer Society study. Over that period 118,777 people in the study died.
The researchers looked at how the study subjects died and then compared them to air pollution levels in 96 cities, making sure to control for other risk factors for lung disease, such as age, smoking status and weight.
The researchers estimate that the risk of dying from respiratory diseases, such as emphysema, pneumonia and chronic obstructive pulmonary disease, rises four per cent for every 10 parts-per-billion increase in exposure to ozone.
The findings are published in the New England Journal of Medicine.
Dr. Ted Boadway, the Canadian Medical Association's technical advisor on health and the environment, says the study is a "a very exciting piece of science."
"What it does for the first time is it quantifies the actual effect of increases of ozone levels on death rates," he tells CTV News.
One of the study authors, Daniel Krewski, the director of the McLaughlin Centre for Population Health Risk Assessment at the University of Ottawa, says the results are probably applicable to Canada, because ozone levels in some areas in Canada, such as southern Ontario, are comparable to those in many of the U.S. cities studied.
"Now that we have information that long-term, low-level ozone exposure is of concern for population health, it's important that we take that information into account in the next update of the Canada-wide standards for ozone," he told CTV.
With ozone levels set to rise again this summer, when abundant sunshine contributes to the chemical processes that form ozone in the atmosphere, Krewski says the focus should be on controlling the sources of air pollution.
"At the individual level, it's difficult to sort of take personal precautionary measures, because once you're outdoors, ozone is ubiquitous in ambient air and you will be exposed," he explained.
"I think the solution to the problem really is to focus on the source of ozone exposure, reduce the exposures lower, to reduce the risk."
With a report from CTV's medical specialist Avis Favaro and producer Elizabeth St. Philip