Researchers have known for years that toxic heavy metal levels in soil and water can jump in the wake of wildfires. But a new academic paper suggests that substances used to control wildfires could be contributing to that issue.
“If you have a hillside and it burns and then you wait until the first storm comes to flush that hillside, and you measure heavy metals in a creek or a river downhill from there, you see these huge spikes repeatedly in cadmium and chromium and things like that,” said Daniel McCurry, a civil and environmental engineering associate professor at the University of Southern California and co-author of the paper published in Environmental Science & Technology Letters. “This has been pretty widely studied, but until now, everyone studying it assumed it was a purely natural phenomenon.”
He and his fellow researchers studied the toxic contents in a number of fire suppression products, including one – PhosChek LC-95W – that he said is likely all but identical to the slurry often dropped from planes and seen painting hillsides red near fires.
“It contained, to me, a pretty surprisingly high concentration of chromium, cadmium, and vanadium, among other metals,” he said.
Click the links above for information from federal agencies on the potential risks of each of the elements.
The paper estimated that nearly 840,000 pounds of toxic metals may have been dropped on Western fires between 2009 and 2021. While the heavy metal contents were concerning, McCurry said “they would have to drop like 747s full of this stuff” into drinking water sources “to make a big difference.”
“I'm not a toxicologist, but I think this is more likely to be an ecological health risk than a human health risk,” he added.
In response to a request for comment on the paper, the U.S. Forest Service said that retardant “is extensively tested by the Forest Service, including effectiveness, environmental consultations and risk assessments, mammalian and aquatic safety, and corrosion.”
“Heavy metals are not added to retardants as corrosion inhibitors,” the written statement concluded. “But may be present as naturally occurring impurities in the retarding salts (which come from the same source as crop fertilizers).”
If that is in fact the source of the heavy metals, McCurry said “that's a pretty easy fix.”
“Just find a less contaminated source,” he added.
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.
