by Wildfires in parts of the western U.S. may be transforming a benign form of chromium into its carcinogenic counterpart, potentially endangering first responders and surrounding communities, according to a new study.
The research, published Tuesday in the journal Nature Communications, identified high levels of the dangerous metal hexavalent chromium, or chromium-6, at specific types of burn sites along California’s northern coast.
Also known as “the Erin Brockovich chemical,” chromium-6 came to public attention in the 1990s after Brockovich, then a paralegal, discovered that it contaminated drinking water and sickened residents of Hinkley, California.
This toxic compound, which increases the risk of cancer when inhaled or ingested, was not present at the sites of interest for the study before they were burned.
Rather, the soils and plants of these places were rich in natural trivalent chromium (chromium-3), an essential nutrient that helps the human body break down glucose.
While chromium-6 can also exist naturally in the environment, this toxic form of the metal most commonly contaminates communities through runoff and wastewater from industrial processes.
Smoke plumes from wildfires are known to carry dangerous pollutants such as aerosols, gases and fine particles, but researchers wondered if the same could be said for heavy metals and what the risk might be to firefighters and those They reside downwind.
“In the complex mix of gases and particles that wildfires spew out as smoke and leave behind as dust, heavy metals such as chromium have been largely overlooked,” the lead author said in a paper. Scott Fendorf, professor at the Doerr School of Sustainability at Stanford University. statement.
Laboratory experiments conducted by Australian researchers in 2019 had already shown that chromium-6 could form rapidly from chromium-3 in burned surface soils.
This transformation occurs through a process known as oxidation or, in this scenario, a reaction between chromium and atmospheric oxygen in which electrons are lost.
Because that process is slow at low temperatures, “it effectively doesn’t happen,” Fendorf, who is also a senior researcher at the Stanford Woods Institute for the Environment, told The Hill.
“But when you start heating the samples during, in this case, wildfires, that reaction occurs,” he said. “And just like that, you’ve transformed from the benign form to the truly toxic one.”
With that in mind, Fendorf and his colleagues decided to test the theory that wildfires could leave soil contaminated with chromium-6 in their place.
Scientists turned their attention to the northern coast of California, where they identified four recently burned ecological reserves containing chromium-rich rocks, such as serpentinite.
While the southern Sierra Nevada tends to have more granite and less chromium content, the northern Sierra has more serpentinite, California’s state rock, Fendorf noted.
“When a wildfire occurs, much higher levels of chromium-6 are produced,” he said.
All four research sites (Pepperwood Preserve, White Rock Preserve, Modini Preserve and Sylvia McLaughlin Natural Reserve) burned partially or completely during the Kincade or Hennessey fires, which occurred respectively in November 2019 and September 2020, according to the study.
Lead author Alandra López, a postdoctoral researcher in Earth system sciences at Stanford’s Doerr School, collected soil from these sites and then separated out the smaller particles that are most sensitive to wind transport.
He then measured chromium-6 levels in this ultrafine dust from burned and unburned areas, while also collecting data on local fire severity, prevailing soil conditions, underlying geology, and ecosystem traits.
At chromium-rich sites where vegetation fueled long-lasting fires at high temperatures, scientists found that concentrations of toxic chromium were 6.5 times higher than those in unburned areas.
“Our study suggests that much more attention should be paid to wildfire-modified chromium, and we assume there will be additional metals as well,” Lopez said in a statement.
Doing so, he added, is necessary “to further characterize the overall threats that wildfires pose to human health.”
When it comes to these potential threats, the authors said they believe fire-induced toxic chromium exposure has the most acute impacts on first responders and people living near fires.
Compared to exposure to chromium-6 through contaminated drinking water, as Brockovich discovered in Hinkley, Fendorf noted that “inhalation is much worse.”
“Toxicologists are very clear about it,” he said. “If you had the choice, you would want to drink it before breathing it. And it’s not that they suggest either.”
According to Fendorf, the extent of the threat also varies depending on the plants fueling the fire.
Grasslands, for example, don’t produce temperatures high enough to create a lot of chromium-6, but shrubs and tree canopies do provide enough heat, he explained.
Even after the fires end, strong winds could expose nearby populations to fine soil particles containing chromium, the researchers said.
According to Fendorf, most of the risk associated with inhaling airborne chromium-6 will likely subside after the first big rains, which can wash the metal underground.
But in an arid environment like the western United States, which faces increasing and prolonged droughts due to climate change, exposure risks could persist for those rebuilding and revegetating burned areas, he warned.
While chromium has been the toxin of most interest to Fendorf because of “the radical transformation that takes place,” he said he is also concerned about other metals, such as manganese, certain forms of iron, nickel and cadmium.
Fendorf highlighted the need for more research on heavy metal exposure related to wildfires and noted that, for the time being, wearing an N95 at such a burn site could be beneficial.
Fendorf said he and his team are now creating predictive maps, so firefighters have more awareness of where they might encounter fine particles and where they might also face the risk of exposure to chromium-6.
He and his colleagues have been preparing for the past two years to deploy active monitoring devices that are capable of monitoring contaminants in the middle of a fire, but such conflagrations have been minimal during this period.
Ed Burton, who led the 2019 research into the transformation of chromium-3 to chromium-6, credited the new study for showing “that wildfires cause a dramatic change in chromium chemistry in fire-impacted soil.” “.
“Significantly, the authors show that newly formed hexavalent chromium can persist on the soil surface and in ash for many months after wildfires,” Burton, a professor of environmental geochemistry and mineralogy, told The Hill in an email. at Southern Cross University in Australia.
In addition to describing the potential health risks to those exposed to soil particles or ash, he highlighted his “particular concern” about the impacts of these findings in the western United States.
The region could be at particular risk because “large areas of land are naturally rich in chromium and because wildfires appear to be increasing in severity and frequency due to climate change,” said Burton, who was not involved in the Stanford study.
Dimitrios Alexakis, professor of geology and geochemistry at the University of Western Attica in Greece, also described “a broad global threat to humans from metals generated in dust and smoke from forest fires,” arising from the combination of these fires and soils rich in chrome.
“This study demonstrates an underrecognized threat to human health associated with the geology and severity of the fire,” he told The Hill in an email.
Alexakis, who was also not involved in this research, has studied both the dispersion of toxins from burned vegetation and the impacts of land pollution caused by fires on human health.
He noted that the Stanford study could help offer “new insights into the reasons behind the increased health risks associated with exposure to wildfire smoke compared to pollution from other sources.”
According to Alexakis, understanding how environmental factors contribute to the creation of chromium-6 through fire could also help scientists design predictive tools to mitigate exposure risk and guide policymaking.
As more research is developed on the topic, the Stanford team noted that the results will be applicable not only to the northern California coast, but to fire-prone areas with metal-rich landscapes around the world.
“As wildfires are expected to increase in frequency and severity in many geographic regions due to a combination of climate change and past fire management, post-fire dust emissions are likely to increase,” the authors stated. .
Both the Pacific basin and the Mediterranean areas have geologies with higher chromium content, as do other parts of Europe, Australia, South Africa and Brazil, according to the study.
“Each continent has areas that are at fairly high risk, so it’s not a small point,” Fendorf said. “It’s really a widely distributed problem.”
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