A recent US study has conclusive evidence on the deadly nature of fine particulate matter in the air. These unseen particles, mostly emitted by the combustion of fossil fuels, are cutting our lives shorter by increasing the chances of lung cancer and heart disease. We review the global scientific evidence on these tiny killers
PACKED off. A stunning US study has clinched the battle of evidence on what tiny particles in the air, mostly emitted by the combustion of fossil fuels do to human health. The industry had refused to admit the mounting scientific evidence that had emerged till now. But this study has come up with conclusive evidence. And has practically put the debate to rest.
A mere increase of 10 microgrammes per cubic metre (g/cum) of fine particles (smaller than 2.5 microns or PM2.5) can increase the risk of lung cancer by 8 per cent, cardiopulmonary deaths by 6 per cent and all deaths by 4 per cent. This shocking news was broken by a recent study published in the Journal of American Medical Association (JAMA).
Sixteen years, about 500,000 people and 116 metropolitan areas. That's what it took the researchers to come up with the findings. The analysis is based on data collected by the American Cancer Society (ACS) as part of the cancer prevention study II, an ongoing prospective mortality study of approximately 1.2 million adults.
"The findings of this study provide the strongest evidence to date that long-term exposure to air pollution, common to many metropolitan areas in the US, is an important risk factor for cardiopulmonary and lung cancer mortality," says Arden Pope, professor of economics at the Brigham Young University and co-author of the study. "To understand how air pollution might increase the risk for lung cancer, we first had to account for the effects of smoking on lung cancer risk," Pope adds.
The study has evoked strong response in the US. These findings come at a time when the George Bush administration attempts to dilute fuel effciency norms for vehicles. Environmental groups have seized on the new findings as support for their position that tough enforcement is still needed.
Allen Dearry, a scientist at the National Institute of Environmental Health Sciences, which partly funded the study, called it "the best epidemiologic evidence that we have so far that associates this type of exposure to lung cancer death."
John Kirkwood, president and CEO of the American Lung Association, said the study adds urgency to the need for the US Environment Protection Agency (USEPA) to immediately implement stringent new rules to curb fine particle emissions.
"This research dramatically underscores the urgent need for USEPA to limit the emission of these cancer causing particles," said Kirkwood. "The scientific evidence keeps mounting."
Pope teamed with Harvard researchers to report similar risks associated with cardiopulmonary mortality and fine particulate matter in two studies published in the mid-1990s. Automobile and manufacturing industry groups attacked the research as faulty science and their scorn grew when the USEPA used the studies as the basis for tightening particulate pollution standards in 1997 (see box: The business...). In addition to the new insights into lung cancer risk, Pope believes the new study's main contribution is putting to rest many of the detractors' claims.
Many US cities at present exceed that standard, though particulate air pollution levels have fallen considerably since 1979, the earliest year covered by the current study. According to the study, from 1979 to 1983, the annual average was 24 g/cum in New York City, 27 g/cum in Los Angeles, 23 g/cum in Chicago and 26 g/cum in Washington DC. The levels have come down over the years, and in 1999-2000 the annual average was 16 g/cum in New York, 20 g/cum in Los Angeles, 18 g/cum in Chicago and 15 g/cum in Washington, DC.
Despite this improvement, the study shows that current US levels of fine particulate matter air pollution are still high enough to be associated with a significantly increased risk of cancer and cardiopulmonary deaths.
In a way the study isn't saying anything new. It only reinforces what worldwide research in recent years was coming around: particulates are a big threat to human health.