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Study: wildfires can leave behind 'dangerous levels' of carcinogen

A fire burns in a forest full of green trees with white and grey smoking filling the top left of the photo.
Flick/NPS Climate Change Response

If hexavalent chromium sounds familiar to you, it’s probably thanks to the 2000 legal thriller Erin Brockovich, which dramatizes a fight against contaminated water. But now, researchers say that wildfires can leave the carcinogen behind.

Trivalent chromium, a relatively safe form of the element, is found naturally in metal-rich geologies across our region – and around the world. But heat from intense wildfires can transform it into its dangerous hexavalent form.

In a recent paper, Stanford University scientists found dangerous levels in dirt and ash that persisted after fires – for many months in some cases.

Coauthor Scott Fendorf said he and his fellow researchers were trying to measure what was on the ground. But, he added, “it's really hard to imagine … if we're finding [particles] in the residual ash, in fine particulate matter that those same particles weren't also airborne during the fire.”

Fendorf said researchers don't know how far those particles might travel. “So, is it something that you have to worry about within a mile of the main part of the fire, the front of the fire? Ten miles? 100 miles? 1,000 miles? That's all yet to be determined.”

The findings have changed Fendorf’s behavior around smoke. He now takes additional precautions, like wearing an N95 mask if he has to be out in it. Given that less intense fire is much less likely to produce hexavalent chromium, he said the findings lend support to wider use of prescribed fires.

“Controlled burns are really going to be a key way, maybe the only way, really, that I can think of on a large scale to mitigate the impacts of these, of these big fires,” he said.

This story was produced by the Mountain West News Bureau, a collaboration between Wyoming Public Media, Nevada Public Radio, Boise State Public Radio in Idaho, KUNR in Nevada, KUNC in Colorado and KANW in New Mexico, with support from affiliate stations across the region. Funding for the Mountain West News Bureau is provided in part by the Corporation for Public Broadcasting.

Hey everyone! I’m Murphy Woodhouse, Boise State Public Radio’s Mountain West News Bureau reporter.

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