Increased Cancer Risk Linked to Wildfires Amid Worsening Impacts of Climate Change

Increased Cancer Risk Linked to Wildfires Amid Worsening Impacts of Climate Change

Fact-checked May 23, 2022 by Vivianna Shields, a journalist and fact-checker with experience publishing on health and wellness topics.

As climate change worsens and wildfires become more common around the world, a new study has found that long-term exposure to such fires may increase the risk of developing certain types of cancer.

The study, published inThe lancetfound that people who lived within 20 to 50 kilometers of a wildfire had an increased risk of developing lung and brain cancer.

Wildfires, the study found, release a complex mix of harmful pollutants into the environment that have known impacts on outdoor air quality and can contaminate water, soil and terrestrial environments and even indoor spaces. In addition, many of the pollutants produced by such fires are known human carcinogens – including polycyclic aromatic hydrocarbons, benzene, formaldehyde, phenols and heavy metals.

“If we really want to understand the overall health impacts of these events, we also need to consider the long-term health effects,” Scott Weichenthal, an associate professor in the Department of Epidemiology, Biostatistics and Occupational Medicine at McGill University and the study’s senior author, tellsThe health.“Our results suggest that an increase in cancer risk may be one of these effects.”

As the world grapples with the worsening impacts of natural disasters linked to climate change, here is a closer look at the health impacts of wildfires.

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Forest fires and cancer risk

Most studies on the health effects of wildfires have focused on short-term damage to the lungs and heart, which often contribute to conditions such as asthma and heart disease. However, little is known about the long-term health effects of wildfires, including their potential contribution to cancer risk.

To understand the broader impacts of such natural disasters, researchers conducted a population-based observational study that included analyzes of more than 2 million people observed over a median period of 20 years. To do this, the researchers used data from the 1996 Canadian Census of Health and Environment Cohort, a group of people whose cancer incidence and death rates were monitored between 1996 and 2015.

Specifically, researchers tracked whether people exposed to wildfires developed lung and brain cancers, as well as three types of blood cancers - non-Hodgkin's lymphoma, multiple myeloma and leukemia.

To measure exposure to wildfires, researchers looked for people who lived within 20 or 50 kilometers of wildfires in the past three, five and 10 years. Because most wildfires in Canada occur in the same areas each year, many of those once exposed have had some level of chronic exposure.

The study found that those who lived within 30 miles of wildfires in the past 10 years had a 10% higher risk of developing brain cancer and a 4.9% higher risk of developing lung cancer than those who were not chronically exposed. The research is one of the first to support a link between exposure to wildfires and cancer risk.

“We looked at the types of chemicals that are known to be released in fires,” Weichenthal said. “Using this list of chemicals, we identified cancers that were associated with these chemicals.”

Compared to unexposed people, each group the researchers measured had an increased risk of developing brain and lung cancer. Depending on how far the person lived from the fire and how long they were exposed to the fire, they were 3.6% to 4.9% more likely to develop lung cancer and 6.4% to 10% more likely to develop brain cancer than unexposed people. There were no links between exposure to wildfires and any type of blood cancer that the researchers tracked.

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Impact of the study results

While the findings are indeed concerning, researchers say there are many things individuals can do to protect themselves from exposure to air pollution from wildfires.

“A simple mask can be very, very helpful in filtering out these particles,” said Loren Wold, a professor of physiology and cell biology at the Ohio State University College of Medicine, who was not involved in the studyThe health.

“A typical N95 mask filters out a lot of particulate matter,” Wold explained, referring to particles released in wildfires and other pollution sources that are less than 2.5 micrometers in size. Using high-efficiency particulate matter (HEPA) filters in your home can also help filter out these particles, also called PM2.5, from indoor air, Wold said.

It's also important to pay attention to wildfire warnings in your area, said Éric Lavigne, a research scientist at Health Canada and an associate professor at the University of OttawaThe health.

“Public health officials typically have alert systems in place and ensure messages are sent to the population,” Lavigne said. Many warnings include instructions to stay indoors whenever possible, avoid physical activity and stay indoors in a cool place. “These are the things I would say to someone on an individual level,” Lavigne said.

However, Lavigne also said that these increased risks for individuals are relatively small, especially compared to other risk factors such as smoking. But exposure to wildfires affects so many people around the world that even a small risk of cancer is a concern, he said.

“Although these risks are small, they can affect millions of people,” Lavigne said. This is especially true, the researchers noted, as wildfires increase in frequency and severity due to climate change.

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What's next?

Although this study is the first of its kind to examine wildfire exposure and cancer risk, it also raises many very important questions.

First of all, it is not clear why the researchers did not find an increased risk of developing blood cancer in any of the blood cancers examined in the study. It could be that an association really doesn't exist, Wold said, or that an even longer-term study would be needed to see an association.

Lavigne said it's also possible there weren't enough cases of these cancers in the study to identify a correlation.

In addition, the researchers saw no connection between particularly high levels of exposure to forest fires and a greater increased risk of cancer. This does not necessarily mean that stronger forest fires would not further increase the risk of cancer, warned Weichenthal. It could simply be that the methods used in this study, which determined risk groups based on the size of the area burned nearby, did not effectively capture the impact of more severe wildfires.

“There are probably improvements in the way we think about wildfire attribution,” Weichenthal said.

Another limitation of the current study is that it did not examine what pollutants from the wildfires people were exposed to, Lavigne said. Future research should investigate what substances might be behind these revealed results, Lavigne added.

Still, Wold said the study, in which he was not involved, was "exceptionally well done" and provided important insights into the long-term effects of exposure to wildfires.

“I think we're very concerned about the acute impacts, the very short-term impacts,” Wold said. “Thinking about the long-term impact is very, very striking.”

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