Women's lung cancer risk raised hugely by soot

Study author "not sure that there's any safe level" of particulate matter in air
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The following article was originally published by Environmental Health News

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Nonsmoking women who live many years in communities polluted with fine particles have an elevated risk of lung cancer, according to new research.

The study, which is the largest to date to examine the link, adds to mounting evidence that chronic exposure to soot may raise the risk of lung cancer, particularly among nonsmokers.

“The results are dramatic in the sense that there appears to be a substantial effect of being close to air pollution in terms of risk for cancer,” said Dr. Norman Edelman, a senior medical advisor with the American Lung Association who was not involved in the study.

All particle sizes linked to risk of lung cancer

Led by Harvard University researchers, the study estimated exposures of 103,650 U.S. women to three sizes of airborne particulates. They calculated how many women contracted cancer—2,155—between 1994 and 2010 and analyzed the pollution levels near their homes for the previous six years.

All sizes of particle pollution, particularly the smallest, or PM2.5, were linked to an increased risk of lung cancer. For every small (10-microgram per cubic metre) increase in PM2.5, the risk of lung cancer increased 37 percent among nonsmoking women or women who had quit smoking at least 10 years earlier, according to the study, which was published online in the journal Environmental Health Perspectives.

[PM2.5 means particulate matter less than 2.5 micrometres in diameter, about one-quarter the diameter of a human hair; a micrometre is one-millionth of a metre–GS]

Nonsmokers valuable study subjects

“Once you restrict to nonsmokers—people not getting bombarded with cigarette smoke—these associations do get much stronger,” said senior author Francine Laden, a Harvard professor of environmental epidemiology.

The sources of the pollutants varied. Although the research suggested that traffic played a role in the higher cancer risk, the finding was not scientifically significant because too few women in the study lived near major roads.

Spewed by trucks, buses, cars, factories, and fires, fine particles can penetrate deep into lungs, raising people’s risks of respiratory problems and heart attacks.

More than 46 million Americans, or almost 15 percent, live in areas with unhealthful year-round levels of fine-particle pollution, according to the American Lung Association. U.S. areas with the highest levels include the Los Angeles region, California’s Central Valley, Chicago, and Houston.

In the new study, about half of the women lived in the Northeast.

Latest study to link lung cancer to fine particles

The research doesn’t prove air pollution causes lung cancer. But it is the latest of multiple human-health studies that have linked fine particles to lung cancer. Such studies prompted the International Agency for Research on Cancer to classify particulate matter as carcinogenic to humans last year.

Lung cancer is the leading cause of cancer death, killing about 160,000 Americans every year. Almost 90 percent of lung cancers are attributed to cigarette smoking, but an estimated 16,000 to 24,000 nonsmokers die of lung cancer every year in the United States, according to the American Cancer Society.

[The Canadian Medical Association estimates that Canada’s air pollution is responsible for 21,000 premature deaths, 92,000 emergency-room visits, and 620,000 doctor-office trips every year, and that air pollution–related sickness and death in Canada costs us more than $8 billion a year.–GS]

Length of study both praised and panned

The researchers didn’t have personal exposure for the women. Instead, they estimated their exposures by plugging local air-quality data into models that took into account how close the women lived to major roads, as well as nearby industries and weather conditions.

Edelman of the American Lung Association said the study’s strength was that it looked at a period of six years of exposure instead of a snapshot in time.

However, one researcher said the study didn’t look far enough back in the women’s past. Previous exposures may be more important because cancer can develop over a period of decades.

The study uses “more or less current exposure to categorize long-term response,” said Fred Lipfert, an environmental engineer formerly of the Brookhaven National Laboratory who has published multiple articles on air pollution and health.

Indoor pollution not measured

“The other problem I have? The words indoor air don’t appear anywhere,” Lipfert said.

Indoor sources of particulates include cigarette smoke, cooking, wood burners, and kerosene heaters. The researchers don’t know how often the women’s windows were closed or how much time they spent outdoors, Laden said.

Laden agreed that past exposures are important, but the scientists were limited by the data. Particulates were not routinely measured a decade or two ago. “Ideally, we would have exposure data for 20 years back,” she said.

Nevertheless, it’s “pretty certain that air pollution, specifically particulates, is a very important hazard,” Laden said. “We’re not sure that there’s any safe level.”

Comments (3) Add New Comment
Dr Dorothy L Robinson
Your illustration is misleading – passenger cars are NOT a major source of PM2.5 pollution. Environment Canada reported that in 2012, 37.4% of PM2.5 were emitted by home firewood burning, compared to 7.8% for transportation and 4.1% from the oil and gas industry http://www.ec.gc.ca/indicateurs-indicators/default.asp?lang=en&n=58DE4720-1

In Sydney, The NSW EPA Emissions inventory for 2008 reported that woodheaters emit 5,457 tonnes of PM2.5 in Sydney, compared to 1,552 tonnes from on-road vehicles, 1,935 from industry, 952 from off-road vehicles and 184 tonnes from other sources http://woodsmoke.3sc.net/syd

A study of PM2.5 pollution in Utah reported that wood stoves and fireplaces, coupled with exhaust from cooking grills, make up the biggest contributor to the area’s winter pollution problem — roughly the same amount as all the emissions in the Salt Lake Valley from engines powered by gas and diesel http://www.sltrib.com/sltrib/news/56427415-78/utah-pollution-winter-wood...

Pollution from burning wood in stoves, fireplaces and elsewhere was noted in 2009 to be the top cancer risk in Oregon's air, http://www.oregonlive.com/environment/index.ssf/2009/07/pollution_from_b...

Woodsmoke contains several known human carcinogens, including benzene, benzo[a]pyrene and formaldehyde and has been nominated to the US National Toxicology Program Report on Carcinogens.
http://ntp.niehs.nih.gov/?objectid=C3265922-AFC1-098A-6BDE6B05F18DE4AC#W...

Burning 10 kg of wood in a modern Australian heater produces more benzo[a]pyrene than in the smoke from 270,000 cigarettes and more benzene and formaldehyde than in the smoke of 60,000 cigarettes.

It is also noteworthy that the risk in this study was even higher when restricted to the most prevalent subtype, adenocarcinomas, which have been linked to woodsmoke exposure http://www.ncbi.nlm.nih.gov/pubmed/15139478 and http://www.ncbi.nlm.nih.gov/pubmed/16002925

With a single wood stove emitting more PM2.5 pollution per year than 1,000 passenger cars, and the finding in this paper that risks with roadway proximity were less consistent, it would be more appropriate to illustrate articles about PM2.5 pollution and cancers with the major source of PM2.5 pollution in many residential areas – woodsmoke http://www.energyjustice.net/content/dirty-wood-heaters
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Martin Dunphy
Dr. Robinson:

Thanks for your post. Unfortunately, this article, which we merely posted with permission, only mentions wood smoke once, near the bottom, and has no information about that source of PN2.5 pollution.
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Alan Smith
Urban smoke has been known as a cause of lung cancer for centuries---long before vehicles and industry (as we know it today) came on the scene. That residential wood smoke causes cancer has never been in question as chimney sweeps, before the days of protective measures could develop lung and skin cancer. The British Cancer Society confirmed these findings a decade before it was realized that the much milder cigarette smoke could cause the same diseases. Interestingly the graph relating lung cancer rates to residential smoke is linear and on extrapolation does not go to zero which means that there is no safe exposure. alforcleanair@yahoo.ca Red Deer Alberta
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