Wildfires can unlock toxic metals from soil, Stanford study shows

ByStephanie Sierra and Timothy Didion KGO logo
Wednesday, December 13, 2023
Wildfires can unlock toxic metals from soil: study
Stanford study shows intense heat from wildfires can transform natural elements in soil into Chromium 6, a toxic metal believed to cause cancer.

SAN FRANCISCO (KGO) -- Teams fighting the raging wildfires that sweep through California are trained for potentially deadly risks. But now, researchers at Stanford's Doerr School of Sustainability believe they may have to add one more to the list: toxic metals.

"A big part of the findings of our study are to alert first responders to the hazards that are there," says Scott Fendorf, Ph.D. a professor of Earth System Science, and co-author of the study.

He and the Stanford team analyzed soil samples from wildfire ravaged areas in Northern California. They found that the intense heat from those fires can transform natural elements in the soil into Chromium 6, a toxic metal believed to cause cancer.

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"As we heat up the minerals in the soil, in many cases the soils have toxic metals in them and specifically in this case, chromium, that gets transformed from a fairly benign form to one that becomes very toxic. And that is in the very small particulate matter," Prof. Fendorf explains.

And that particulate matter could be a key threat, if it carries the metals into the air and ultimately the lungs of firefighters and others. Dr. Sharon Chinthrajah, M.D., treats and researches breathing issues at Stanford Medicine's Sean Parker Center for Asthma and Allergy Research.

"That's smaller than a strand of your hair in diameter. And so that's why it's so inflammatory and concerning because we're talking about things that are so small that they can travel far right on wind currents. And particularly when we inhale, it can actually travel to the farthest branches of your respiratory tract system. And then and then essentially get embedded there, or absorbed there and cause inflammatory reactions, says Dr. Chinthrajah.

MORE: Stanford study examines health risks associated with exposure to wildfire smoke pollution

Professor Fendorf says the study was not designed to trace airborne metals. But he believes the discoveries so far should raise an alarm.

"Given what we're seeing in the on the surface of the soils, the land, there is no way that you can have this fine particulate matter that isn't also being transported in the air," he argues.

He says the metals are contained in specific types of plants and soils. And identifying them could help create a kind of threat map, to warn both fire fighters and also cleanup crews when they're working in a high-risk area. And ultimately, help better protect them from the toxic metal threat.

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