Some wildfire suppressants contain heavy metals and could contaminate the environment
In fire-prone areas, water isn’t the only thing used to quell blazes. Wildland firefighters also apply chemical or synthetic suppressants. Researchers reporting in ACS’ Environmental Science & Technology Letters explored whether these suppressants could be a source of elevated metal levels sometimes found in waterways after wildfires are extinguished. Several products they investigated contained high levels of at least one metal, including chromium and cadmium, and could contribute to post-fire increases in the environment.
“Wildfires are associated with the release of toxic heavy metals to the environment, but until now, it was assumed that these metals came from natural sources like soil,” says Daniel McCurry, principal investigator of the study. “We now know that fire retardants may contribute to these metal releases.”
Wildfire suppressant products, which are intended to inhibit fire activity before and after water evaporates, include fire retardants, water enhancers and foams. As wildfires have become more frequent and severe, larger volumes of water along with chemical and synthetic suppressants — sprayed from the ground and dropped from planes — have been required to extinguish them. Although manufacturers identify most of the active ingredients in suppressants, some components are proprietary. In addition, previous researchers have observed increased concentrations of potentially toxic metals in soil and streams after wildfires. So, McCurry and colleagues at the University of Southern California wondered if the suppressants contain metals and could contaminate the environment.
The researchers tested samples from 14 fire suppression products sold by commercial retailers. They analyzed samples for 10 metals that have known toxicity or are regulated by the U.S. Environmental Protection Agency (EPA). Every product contained at least one metal with a concentration that exceeded the EPA’s Maximum Contaminant Level regulations for drinking water. In particular, the two suppression products classified as fire retardants contained eight metals (chromium, cadmium, arsenic, lead, vanadium, manganese, antimony and thallium) that greatly exceeded the EPA’s drinking water regulations. And one of the retardants exceeded California’s hazardous waste regulations for three of those metals. The researchers say these results indicate the potential for fire retardants to contaminate the aquatic environment and potentially drinking water, if these products enter bodies of waters.
From the volume of fire retardants dropped on wildfires in the U.S. between 2009 and 2021, the researchers determined that the total amount of metals applied was variable year to year but generally increased over time. And for one Southern California wildfire, they estimate that the increased concentration of cadmium in a nearby stream could be explained by 31% of the reported fire retardant used to contain the fire. They say these results show that fire suppression activities could contribute to elevated metal levels in the environment but that more work is needed to determine potential risks to human and environmental health.
The authors acknowledge funding from the U.S. National Science Foundation (NSF), an NSF Graduate Research Fellowship, and a University of Southern California Graduate School and Women in Science and Engineering Fellowship.
The paper’s abstract will be available on Oct. 30 at 8 a.m. Eastern time here: http://pubs.acs.org/doi/abs/10.1021/acs.estlett.4c00727
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Journal
Environmental Science & Technology Letters
Article Title
Metals in Wildfire Suppressants
Article Publication Date
30-Oct-2024
Toxic metals found in wildfire suppressants
New research estimates 850,000 pounds of heavy metals have been released into the environment in the Western US from 2009-2021
A team of researchers from the USC Viterbi of School of Engineering’s Sonny Astani Department of Civil and Environmental Engineering have tested several wildfire suppressants, estimating in a paper in Environmental Science and Technology Letters, that these materials have released approximately 850,000 pounds of toxic metals into the environment in the Western United States from 2009-2021.
Previously, researchers in the field found increased concentrations of heavy metals in the local waterways following wildfires. The new paper by the researchers at USC Viterbi, might explain why. The USC research team believes this to be the first paper to quantify environmental metal toxicity from fire suppression products.
Materials used to address wildfires including fire retardants, water enhancers and foams, all have to be approved by the U.S. Forest Service, says Daniel McCurry, Associate Professor of Civil and Environmental Engineering at the USC Viterbi School of Engineering and the corresponding author on the paper. McCurry explains that the Fire Service approves materials after they pass a series of evaluations including for effectiveness and corrosion potential (as the fire suppressant is held in metal tanks). However, says McCurry, the companies that produce the materials that extinguish fires are allowed to keep up to 20 percent of their product composition proprietary as long as the products pass Forest Service evaluation.
McCurry and co-authors PhD student Marella Schammel and undergraduate student Samantha Gold, purchased fire suppressant materials, and using an inductively-coupled plasma mass spectrometer quantified elements that are known contaminants: vanadium, chromium, manganese, copper, arsenic, cadmium, antimony, barium, thallium and lead.
They then, using their measured concentrations combined with publicly available data on suppressant application rates, estimated the quantity of heavy metals that have been dropped in the Western U.S. over the last decade.
The findings:
- In the fire suppressant products tested, at least 8 metals were present at concentrations above the USEPA drinking water maximum contaminant level
- Approximately 1 million gallons of retardant were dropped in intrusions that entered surface waters.
- Phos-Chek LC-95 W, a clear version of the pinkish-red material often seen in footage discharged from planes, was found to have the greatest concentrations of most heavy metals. (The researchers go so far to note that Phos-Chek LC-95W could even be classified as “hazardous waste according to federal and CA regulations”) “
- An estimated 380,000 kg or ~1 million pounds of heavy metals are believed to have been released into the environment in the Western U.S. from 2009-2021
The lead author of the study, Environmental Engineering PhD student Marella Schammel said, “I think what surprised me most was the array of metals we found. Some of them make sense as they're used as corrosion inhibitors (chromium and cadmium) or are known contaminants in phosphate ores (arsenic, among others) used in the active ingredient of the retardant. But others, like vanadium - which there's a ton of in Phos-Chek - were definitely unexpected.”
Next steps:
The team plans to continue this research and to directly test soil and waterways prior to, and after wildfire season.
Journal
Environmental Science & Technology Letters
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Metals in Wildfire Suppressants
Article Publication Date
30-Oct-2024
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