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Can Fire Smoke Cause Lung Cancer?

Q: How does wildfire smoke affect lung cancer risk? And how does this compare to things like secondhand cigarette smoke?

When smoke from wildfires in the summer of 2020 turned the sky of the San Francisco Bay Area red, Dr. Kari Nadeau, a physician and scientist at Stanford University, to the people who were most vulnerable. She worried about the workers of local wineries running to protect their harvest; and the children who lived near refineries and inhaled pollutants every day.

During that August, September and October, she watched air quality routinely reach unhealthy levels for anyone without a mask. At the time, Dr. Nadeau said in a public panel that being outside and breathing that air was comparable to smoking seven cigarettes a day.

But now she said she believes the health effects of inhaling heavy wildfire smoke are likely worse. “At least cigarettes have filters,” says Dr. Nadeau, director of the Sean N. Parker Center for Allergy and Asthma Research at Stanford University.

While cigarette smoke, even secondhand, is proven to cause lung cancerwildfire smoke is not. Some recent, limited studies published in recent years have found correlations between people exposed to wildfire smoke and lung cancer. But none have proven causation, the scientists who conducted those studies said, and much more research is needed.

“We don’t know much about the long-term health effects of wildfires,” said Scott Weichenthal, an assistant professor in the department of epidemiology, biostatistics, and occupational health at McGill University in Montreal. Until recently, fires were studied as one-time disasters, he said, and we don’t understand how severe, sometimes recurring, short-term smoke exposure can affect the health of people on the road.

Experts do know that, even in the short term, particulate pollution from wildfires — including tiny bits of ash, dust and soot — can exacerbate heart problems, decrease lung function and worsen asthma. In this way, smoke from forest fires can affect health in the same way as diesel exhaust or smoke from cigarettes.

Wildfire smoke can also contain heavy metals such as lead and arsenic, and dangerous chemicals such as benzene and formaldehyde gas, all of which are present in cigarette smoke and can cause cancer.

“There’s plenty of evidence that we shouldn’t look the other way,” said Dr. nadeau.

To understand how the air you breathe can affect lung cancer risk, scientists say it’s essential to understand what harmful things are in the air, how much of it is present, and how long you’re exposed to it.

For example, according to the Centers for Disease Control and Prevention, exposure to secondhand cigarette smoke, at work or at home, may increase a non-smoker’s risk of lung cancer by 20 to 30 percent.

However, calculating the health risks of wildfires is much more challenging. What the smoke contains and the potential health risks it may pose depend in part on what the fire consumed. Smoke from burning trees and vegetation, for example, poses different dangers than those from burning houses, cars, electronics or tool sheds.

Wildfire smoke is also temperamental; it literally blows away with the wind. The harmful substances that fires bring can be volatile and difficult to characterize, said Dr. Weichenthal. And it can be challenging to measure the extent to which people are exposed.

But as wildfires increase due to climate change, get bigger and spread faster, researchers have recently begun to focus on people exposed to smoke and fire for extended periods of time. For example, experts at the University of California, Davis, are tracking survivors of the 2018 campfire in Butte County, California. And at McGill University, Dr. Weichenthal was part of a team that analyzed about two decades of Canadian public health records to better understand the health effects of wildfires, motivated in part by record fire years in Ontario and British Columbia.

“It shouldn’t be shocking to us that we would see some kind of increased risk of cancer in these places,” he said. “We know that the chemicals released are carcinogenic.”

The study of Dr. Weichenthal, who was… published in The Lancet in Mayfound that those who lived within about 30 miles of a wildfire in the past decade were about 5 percent more likely to develop lung cancer and 10 percent more likely to develop brain tumors than people who lived further away.

Although the study had some limitations, said Dr. Weichenthal, these findings are “important because so many people can be exposed.”

To date, the best evidence we have that lung cancer is associated with smoke from wildfires comes from firefighter studies. At the height of the fire season, tens of thousands of them work long shifts day in and day out, often without masks.

In a study published in 2019Kathleen Navarro, who researches workplace safety issues for firefighters at the National Institute for Occupational Safety and Health, estimates with her colleagues that short-season firefighters spend at least seven weeks a year on the front lines for five to 25 years. working, would increase their risk of dying from lung cancer by 8 to 26 percent as a result of smoke exposure. Firefighters working twice as long each year, they calculated, would have a 13 to 43 percent increased risk of dying from lung cancer during the same period.

“But there’s still a lot unknown about what happens cumulatively, throughout each season,” said Dr. Navarro, who worked as a Hotshot firefighter in Oregon in 2019. She noted that the federal government is monitoring and analyzing cancer trends and risk factors more closely among firefighters in the United States. A national register for firefighter health will open this fall.

Even without evidence that wildfires in the public cause lung cancer, said Dr. Nadeau that there is enough evidence to seek more protective policies and take security measures.

“We should let this be a catalyst to be even better prepared to adapt to wildfires and climate change,” she said. And if smoke is noticeable: “You have to evacuate. You shouldn’t just keep waiting. Smoke itself is a hazard to avoid.”

Molly Peterson is an investigative journalist based in Los Angeles who focuses on the intersections of climate, catastrophe and public health.

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