When wildfires rage in the western United States (and other parts of the world), the most attention is paid to the destructive power of fire and clouds of smoke that affect air quality. New research has added a new problem to that list: airborne microbes can dock a trip with smoke and infect firefighters and people who live on fire from the wind.
In an article published in Science, researchers Leda Kobziar and George Thompson examined existing research and modeled how bacterial and fungal cells can spread through devastating smoke. Smoke-related health risks such as asthma and bronchitis, as well as some smoke-related infections, are already well documented, according to the researchers. Valley Fever, for example, is a fungal infection common among fire fighters in the wild, and studies show correlations between forest fire events and spikes in bacterial infections in the western United States. However, the prevalence of microbes in smoke plumes has so far only been little formally investigated.
For their assessment, Kobziar and Thompson focused on fungal and bacterial cells, also known as bioaerosols, and studied how they can survive and spread in devastating smoke. While feathers can get incredibly hot – too hot for a microbe to survive – they also vary widely depending on what is burning, how the fire behaves, and how the smoke mixes with the air. Because of this variability, bioaerosols could be drawn into the air and survive.
In the air, smoke can be a surprisingly habitable place for these organisms. Carbon is one of the byproducts of fires, and carbon particles in the cloud can provide “temporary habitat for soil microbes,” the researchers write. In addition, the dead plants and particles sucked into the smoke can protect the bioaerosols from the sun’s UV rays, which would normally destroy them, and water vapor in the smoke prevents them from drying out.
So how many bacteria and fungal cells could be floating around in devastating smoke? Kobziar’s estimate is in the trillions.
“It’s really unknown at this point,” she told the Los Angeles Times. “The variety of microbes we’ve found is really mind-boggling.”
No previous studies have assessed bioaerosol levels in forest fire smoke, but she and Thompson cite a study that focused on mandatory burns. Even these low-intensity fires produced smoke with microbial numbers five times that of normal air. In their assessment, they modeled how bioaerosols could travel in plumes of smoke and found that they have the potential to spread hundreds of kilometers from the fire. After all, they write, these organisms are deposited before the wind – or inhaled by humans.
For Kobziar and Thompson, the evaluation is a clear indicator that more research is needed. Climate change is contributing to forest fire seasons around the world becoming longer and more devastating. With more smoke in the sky, scientists fear the risk of airborne infections could increase.
“We have more questions than answers at this point,” Thompson said.
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