Long-term ozone exposure linked to higher death risk

March 12th, 2009 - 4:31 pm ICT by IANS  

Washington, March 12 (IANS) Long-term exposure to ground-level ozone, a component of smog, may result in increased risk of death from respiratory ailments, according to a new study throughout the US.
Ozone, a gas made up of three oxygen atoms - forms a protective layer from the sun’s ultraviolet radiation when located in the Earth’s upper atmosphere. However, that same gas is toxic at ground level where it can be breathed by humans.

Ground level ozone is formed through a complex chemical reaction in sunlight between nitrogen oxides (NOx), commonly spewed from vehicle exhaust, and industrial factory emissions.

The study found that for every 10 parts-per-billion (ppb) increase in ozone level, there is a four percent increase in risk of death from respiratory causes, primarily pneumonia and chronic pulmonary obstructive pulmonary disease.

The study analysed the risk of death for both ozone and fine particulate matter, two of the most prevalent components of air pollution. It followed nearly 450,000 people for two decades and covered 96 metropolitan regions in the US.

University of California-Berkeley (UC-B) researchers found that people living in areas with the highest concentrations of ozone, such as the Los Angeles metropolitan area and California’s Central Valley, had a 25 to 30 percent greater annual risk of dying from respiratory diseases compared with people from regions with the lowest levels of the pollutant.

“This is the first time we’ve been able to connect chronic exposure to ozone, one of the most widespread pollutants in the world, with the risk of death,” said Michael Jerrett, UC-B associate professor of environmental health sciences.

“World Health Organisation data indicate that about 240,000 people die each year from respiratory causes in the United States,” said Jerrett, who led the study.

“Even a four percent increase can translate into thousands of excess deaths each year. Globally, some 7.7 million people die from respiratory causes, so worldwide the impact of ozone pollution could be very large,” he said.

The findings come a year after the US Environmental Protection Agency (EPA) strengthened its National Ambient Air Quality Standards for ground-level ozone from an annual average of 80 ppb to 75 ppb to reflect growing evidence of the harmful health effects of ozone.

A month after the EPA released its new standards, a National Research Council report concluded that premature deaths related to ozone exposure of less than 24 hours are more likely among those with pre-existing diseases, said an UC-B release.

These findings were published in Thursday’s issue of the New England Journal of Medicine.

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