SAN DIEGO — Extended exposure to wildfire smoke may increase the risk of several types of cancer, according to a study presented Tuesday at an American Association for Cancer Research meeting.
The research, not yet peer-reviewed, found that people who were exposed to higher levels of wildfire smoke over the previous three years were at increased risk of lung, colorectal, breast, bladder and blood cancers. The study was based on a long-term database following more than 91,000 people.
As wildfires worsen and increase in frequency due to climate change, the research’s lead author suggested the smoke may emerge as a key driver of cancers. The work adds to a growing body of evidence of the harm associatedwith wildfires, ranging from increased risk of acute health harms such as asthma, to cardiovascular risks such as heart disease or stroke. A study in the Lancet Planetary Healthfound long-term exposure to wildfires may be linked to an increased risk of brain and lung tumors.
The latest study suggests that at current levels of smoke exposure, 19 lung cancer cases in every 100,000 individuals per year could be attributed to wildfires, said Shuguang Leng, a molecular cancer epidemiologist at the University of New Mexico Comprehensive Cancer Center and the senior author of the study.
As cigarette smoking has decreased, but wildfire activity is expected to increase, it could mean “wildfire smoke may emerge as an increasingly important driver of cancer burden in the United States,” Leng said. And that could also change the kinds of lung cancers that people have. Some lung cancers, he said, are more likely to be driven by cigarette smoking, but others are more often caused by air pollution.
“That will affect screening. That will affect treatment,” Leng said.
The study could not prove that wildfires caused the increased cancer risk. But exposure to the carcinogens found in wildfire smoke could help spark new cancers or cause inflammation that could favor the growth of tumors.
Leng and colleagues calculated that for every step up in wildfire smoke exposure, the risk of several cancers increased. One key measure of wildfire smoke exposure is the concentration of ultrafine airborne particles less than 2.5 micrometers in diameter, roughly a thirtieth of the diameter of a human hair.
When exposure to these tiny particles increases by 1 microgram per liter over a three-year-period, cancer risk markedly increases. Leng compared the increase in exposure to experiencing one week of wildfire smoke per month over a three-year-period. This level of exposure was associated with a doubled risk of lung cancer, colorectal cancer and breast cancer, as well as a 249 percent greater risk of bladder cancer and a 63 percent greater risk of blood cancers.
Leng said that this increase in risk for lung cancer was roughly similar to the increased risk of low-to-moderate smoking.
With nearly 78 percent of the United States covered by abnormally dry or drought conditions, concerns are mounting that the coming wildfire season could be particularly bad.
As of late April, the worst droughts are affecting the Intermountain West, Plains and South. In parts of these regions, the National Interagency Fire Center has highlighted above-average fire potential in the months ahead. There have already been big fires in Nebraska, Oklahoma and Florida.
A forming El Niño and very warm seas in the North Pacific may help trigger more thunderstorms across the West this summer, which come with lightning that can spark fires.
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