by Wildfires in parts of the Western US could transform a harmless form of chromium into its cancer-causing counterpart – putting first responders and surrounding communities at risk, according to a new study.
The research, published Tuesday in the journal Nature Communications, identified high levels of the hazardous metal chromium hexafluoride, or chromium-6, at specific types of burn sites along California’s North Coast.
Also known as “the Erin Brockovich chemical,” chromium-6 came into the public eye in the 1990s after Brockovich – then a legal aid – determined it was contaminating drinking water and making residents sick. Hinkley, Calif.
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 burned.
Rather, soils and plants at these sites were rich in naturally occurring trivalent chromium – chromium-3 – an essential nutrient that helps the human body break down glucose.
Although chromium-6 can also occur naturally in the environment, this toxic form of the metal often pollutes communities through runoff and wastewater from industrial processes.
Smoke plumes from wildfires are known to carry dangerous pollutants such as aerosols, gases and fine particulate matter, but the researchers looked at whether the same could be said for heavy metals, and what the risk might be. there for firefighters and those who live downwind.
“In the complex mix of gases and particles that wildfires emit as smoke and leave behind as dust, heavy metals such as chromium have been overlooked,” said senior author Scott Fendorf, a professor in the School of Sustainability Stanford University Doerr, in a. statement.
Laboratory experiments carried out by Australian researchers in 2019 have already shown that chromium-6 can form rapidly from chromium-3 in surface soils that are located on fire.
This transformation occurs through a process known as oxidation — or in this case, a reaction between chromium and atmospheric oxygen in which electrons are lost.
Because that process is slow at low temperatures, “it doesn’t happen efficiently,” said Fendorf, who is also a senior fellow at the Stanford Woods Institute for the Environment, The Hill.
“But when you start heating the samples in this wildfire situation, it causes that reaction,” he said. “And so, you have changed from the benign form to the highly toxic form.”
With that in mind, Fendorf and his colleagues decided to test the theory that wildfires could leave soils contaminated with chromium-6 in their place.
The scientists focused their attention on the North Coast of California, where they identified four recently burned ecological preserves containing chromium-rich rocks, such as serpentinite.
While the southern Nevada Sierra tends to have more granite and less chromium content, the northern Sierra has more serpentine — California’s state rock, Fendorf noted.
“When you bring the wildfire through, that results in the production of much higher levels of chromium-6,” he said.
The four research sites – Pepperwood Preserve, White Rock Preserve, Modini Preserve and Sylvia McLaughlin Natural Reserve – all burned partially or completely during the Kincade or Hennessey fires, which occurred in November 2019 and September 2020 respectively, of according to the study.
Lead author Alandra Lopez, a postdoctoral scholar in Earth system science at Stanford’s Doerr School, collected soil from these sites and then separated out the smallest particles that are sensitive to wind transport.
She then measured the levels of chromium-6 in this ultra-fine dust from burned and unburned areas, and collected data on local fire intensity, prevailing soil conditions, underlying geology and ecosystem characteristics.
In chromium-rich sites where vegetation was fueled by long-term high-heat fires, the scientists found that toxic chromium concentrations 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 that additional metals are also present,” Lopez said in a statement.
This is necessary, she said, “to more accurately characterize the overall threats that wildfires pose to human health.”
As far as these potential threats are concerned, the authors said they believe that exposure to toxic chromium from fire has the most acute impact on first responders and people who live near the blazes.
Compared to exposure to chromium-6 through contaminated drinking water, as he discovered in Hinkley with Brockovich, Fendorf emphasized that “inhalation is much worse”.
“Toxicologists are very clear about that,” he said. “If you had the choice, you’d drink it before you breathed it. And it’s not that they recommend either.”
The extent of the threat also varies based on the plants that are pushing the fire, according to Fendorf.
For example, grasslands don’t produce temperatures high enough to create enough chromium-6, but shrubs and tree canopies provide plenty of heat, he explained.
Even after the fires end, strong winds could expose nearby populations to fine particles of chromium-laced soil, the researchers noted.
The risk of inhaling airborne chromium-6 is likely to decrease after the first heavy rain, which can wash the metal underground, according to Fendorf.
But in a high-elevation environment like the US West, which is facing increased and prolonged droughts due to climate change, there could be exposed risks for those rebuilding and regrowing burned areas, he warned.
While chromium is the toxin Fendorf is most interested in because of “the radical transformation that occurs,” he said he is also concerned about other metals, such as manganese, certain forms of iron, nickel and cadmium.
While emphasizing the need for more research on wildfire-related heavy metal exposure, Fendorf noted that wearing an N95 at such a burn site may be beneficial for now.
Fendorf said he and his team are now creating predictive maps, so firefighters have more awareness of where they might encounter fine particulate matter and where they might face exposure risk. also chromium-6.
He and his colleagues have been preparing for the past two years to deploy active monitoring devices that can monitor contaminants in the midst of a fire, but the number of such conflagrations during this period is small.
Ed Burton, who led the 2019 research on the transformation of chromium-3 to chromium-6, credited the new study with showing that “wildfires cause a significant change in the chemistry of chromium in fire-affected soil.”
“Significantly, the authors show that newly formed hexavalent chromium can persist in surface soil and ash for many months after wildfires,” said Burton, professor of environmental geochemistry and mineralogy at Southern Cross University in Australia. The Hill in an email.
As well as describing the potential health risks for those exposed to soil particles or ash, he highlighted his “particular concern” about the impacts of these findings on Western USA.
The region may be at particular risk because “large areas of land are naturally rich in soil chromium and because wildfires appear to be increasing in intensity and frequency due to climate change,” said Burton, who he was involved in the Stanford study.
Dimitrios Alexakis, a professor of geology and geochemistry at the University of West Attica in Greece, also described a “wide global threat of metal born from wildfire dust and smoke to humans,” resulting from the combination of these blazes and chromium-rich soils.
“This study shows an unrecognized human health threat related to 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 the spread of toxins from burnt vegetation and the impact of fire ground contamination on human health.
The Stanford study, he noted, could help “offer fresh perspectives on the reasons behind the elevated health risks associated with exposure to wildfire smoke compared to pollution from other sources.”
Understanding how environmental factors contribute to the formation of chromium-6 in a fire could help scientists devise predictive tools to mitigate exposure risk and guide policymaking, according to Alexakis.
As more research on the topic emerges, the Stanford team emphasized that the findings will be applicable not only to California’s North Coast, but to fire-prone areas with metal-rich landscapes around the world.
“With wildland fires 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,” said the authors.
Geologies higher in chromium are found in both the Pacific and Mediterranean rim areas, as are other parts of Europe, Australia, South Africa and Brazil, according to the study.
“There are areas on every continent that are relatively high risk, so it’s not a small point,” Fendorf said. “It’s really a broad problem.”
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