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Ozone causes 20% of lung deaths, study suggests

 Toronto Star, March 11, 2009

Joseph Hall

Health Reporter

 Long-term exposure to ozone in Toronto may be responsible for about 20 per cent of all lung-related deaths in the city, a massive new American study on health risks of the common air pollutant suggests.

 And the study, which looked at data tracking 450,000 people over 18 years, suggests the current emphasis on peak ozone days as the smog component's major health danger ignores the serious, cumulative perils that breathing it over a lifetime impose.

 "It's not just the peaks you should worry about, it's the cumulative, entire ozone season that's important too," says George Thurston, a professor off environmental medicine at New York University medical school.

 "So we can't just sort of hide in our homes on the peak days and avoid the adverse effects of ozone says Thurston, who directed the air pollution portion of the study.

 That paper, released in the New England Journal of Medicine, does not look at Canadian cities, but York University air pollution expert Geoff Harris says Toronto's ozone levels are roughly in line with those found in many large U.S cities in the northeast.

In New York and Washington, for example, ozone increased the risk of dying of any respiratory ailment — from cancers to a severe asthma attack — by about 25 per cent.

That means about 20 per cent of respiratory deaths in these centres can be directly attributable to a long-term exposure to the pollutant, which along with fine airborne particles is one of the two major components of smog.

In smog-bound cities such as Los Angeles — hot, sunny and hemmed in by mountains — the increased death risk rises to 50 per cent.

While ozone in the upper reaches of the atmosphere help protect the Earth from the sun's punishing ultraviolet rays, its ground-level counterpart poses serious health risks.

Ground level ozone is created by a set of complex chemical reactions set in motion by sunlight reacting with nitrogen dioxide and fine particle pollutants emitted by cars, factories and coal fired generating plants. The resulting triple oxygen molecule (O3) is volatile, and can react with the vulnerable surface of the lung, breaking down the tissue and causing a host of pulmonary conditions.

It is especially dangerous for those people who suffer from pre-existing pulmonary conditions such as emphysema. It is these people smog alerts, both in the United States and Canada, are meant to target.

Some 90 per cent of Ontario's smog originates in the United States, particularly from coal-fired power plants in the Ohio Valley.

"As a result, 19 of 20 monitored sites in Ontario cannot currently meet the Canada-Wide Standards for ozone," according to a provincial web site.

The study is the first to tease out the relative contribution ozone exposure contributes to deaths due to smog.

Death rates from particle pollution, says Thurston are typically related to cardiac problems. But the lung risks from ozone were not known, says Kenneth Maybee, head of environmental issues at the Canadian Lung Association.

Maybee says the study will give more ammunition to groups like his to argue for more stringent pollution standards.

Toronto Public Health estimates air pollution in general accounts for about 1,700 premature deaths in the city and 6,000 hospital admissions each year. Those death figures include acute fatalities due to high pollution days, as well as estimates of the toll taken by long-term exposures. Health officials have no statistics, however, on the precise number of people dying of respiratory ailments in the city each year.

"While some pollutants are coming down (however), ozone is without a doubt increasing on an average basis every year in our city," says Monica Campbell, manager of the environmental protection office with the department.

For its data, Thurston's group mined a massive, cancer-tracking study carried out between 1982 and 2000 in 96 U.S. cities.

For more information read "Choking us to death:the air pollution crisis and its effects on bicycle couriers (1999)"

Long-Term Ozone Exposure and Mortality – New England Journal of Medicine , March 12, 2009

Study links smog exposure to premature death – New York Times, March 12, 2009

Ozone causes 20% of lung deaths, study suggests -  Toronto Star, March 11, 2009

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