As wildfires rage with growing frequency and intensity, the destruction left behind is only part of the story. Beneath the flames lies a largely unstudied consequence, the potential release of natural radionuclides stored in vegetation and soil. Produced by cosmic rays or from natural radioactive materials found within the Earth's crust, such as uranium, thorium, potassium and their decay products, these radionuclides occur naturally in the environment. When radionuclides occurring in the environment are altered by wildfires, the impacts to both ecosystems and human health are largely unknown underscoring the importance of research to better understand the potential risks.
Normally dispersed in trace amounts, radionuclides can be concentrated in smoke particulate matter and carried in smoke and ash before returning to earth through rain, snow and wind. As wildfires become more frequent and severe, scientists all over the world are looking to better understand the lasting environmental impacts. This research will help close the critical knowledge gap, and identify which radionuclides are present, how much is being released, and how far their impacts extend into the air we breathe, the water we drink, and the soil that sustains us.
At Canadian Nuclear Laboratories (CNL), the radioecology team is taking a leading role in pursuit of better understanding Canada's evolving wildfire season. In partnership with Environment and Climate Change Canada (ECCC), Natural Resources Canada (NRCan), Health Canada (HC), Canadian Forces Base Garrison Petawawa (CFB Garrison Petawawa), and academic and Indigenous partners, the team is exploring how wildfires mobilize radionuclides across ecosystems. Funded by Atomic Energy of Canada Limited's Federal Nuclear Science and Technology (FNST) Work Plan, the research consists of program planning, design, methodology testing, and review processes to understand how radionuclides move through air, soil, water, and vegetation during and after fires.
This three-year study, lead by research and development officer Stephanie Walsh, will be the first of its size and scope in Canada, referred to as the Impact of Wildfires on the Enrichment, Mobilization and Distribution of Radionuclides in the Environment which officially launched in April 2025.
Fun fact about the team: Over the years, the Radioecology Team has logged thousands of kilometers collecting environmental samples, from the west coast to the east coast, the Arctic, the Great Lakes of southern Ontario and many places in between, to study how radionuclides move through Canadian environments.
"There are radionuclides everywhere in the environment, naturally distributed in vegetation and soils at very low levels," explains Walsh. "When wildfires occur, that balance changes. Combusting vegetation and soils release these materials in potentially concentrated amounts that can be transported atmospherically, as well as through erosion and runoff events."
This summer marked the project's first field activities. The radioecology team focused on procuring new air-sampling equipment, testing methods, and building partnerships to prepare for next season. While Walsh's team has long studied terrestrial and aquatic systems sampling vegetation, soil, and aquatic species measuring airborne radionuclides is a new frontier for them.
"Using air filters for data collection is new for our team," says Walsh. "We spent much of this summer learning about the equipment, refining our methodology, and taking advantage of smoky days here in the Ottawa Valley to practice collecting and processing samples." Those early trials will help the team mobilize quickly for the next wildfire season, to capture meaningful data from wildfires in regions across the country.
Designed as a national-scale study, the program will deploy to select wildfire events across Canada between May and October. "Sadly, we know we'll find uncontrolled and unplanned fires across the country next year," Walsh notes. "We're building this research program to respond in a way that we can act quickly and gather this data safely no matter where fires breakout next season."
Through collaboration with ECCC, HC, and NRCan's Canadian Forest Service, CNL will work with wildfire experts on project design and analyze archived air-filter samples collected during past wildfires via ECCC's National Air Pollution Surveillance Network (NAPS). These samples spanning regions from east to west will be studied over the winter to build a national database and guide field sampling next summer.
To further prepare for next year's season, the radioecology team established a partnership with CNL's neighbour, CFB Garrison Petawawa, leveraging already scheduled, controlled burns, to refine study techniques in a safe and controlled environment, ahead of next year's wildfire season. Preparing with the support of CFB Garrison Petawawa will provide a safe environment to calibrate equipment before deployment to active wildfire zones. The team also plans to expand collaborations with academic researchers, Indigenous communities, and regional experts working in fire-affected areas.
By year three, the project aims to model how radionuclides move through different ecosystems, measuring concentrations both near and far from burn sites.
"Wildfires change how radionuclides behave in the environment," says Walsh. "They can be carried long distances in smoke and later settle through rain or surface runoff. We want to know how far those effects extend and how factors like soil type, vegetation, and fire severity influence that movement."
The data will help regulators and policymakers develop stronger environmental safety guidelines and wildfire response strategies. It could also enable scientists to forecast how certain landscapes will respond to future fires, linking wildfire intensity, ecosystem type, and radiological transport patterns.
As Canada prepares for another unpredictable wildfire season, the research team will spend the winter refining methods and analyzing archived samples to build the first national picture of how radionuclides behave during and after fires. Those insights will inform next summer's fieldwork and help identify the ecosystems most at risk.
"It's complex work," Walsh reflects, "but in a country increasingly defined by its fire seasons, it's essential. Each data point brings us closer to understanding the multidisciplinary consequences of wildfires and to protecting the air, water, and land Canadians depend on. Every wildfire tells a story, and by listening closely through the science, the data, and the land itself we can better understand and protect the environment and the communities living within it."
This research is funded by Atomic Energy of Canada Limited's (AECL) Federal Nuclear Science & Technology (FNST) Work Plan, which connects federal organizations, departments, and agencies to the nuclear science expertise and facilities we have at Chalk River Laboratories.
Under the FNST Work Plan, researchers at Canadian Nuclear Laboratories (CNL) carry out projects to support the Canadian government's core responsibilities and priorities across the areas of health, safety and security, energy, and the environment.
