Over the past decade, about 67 million gallons of fire retardants have been dumped in wildfires across California, according to the U.S. Forest Service.

If you’ve ever wondered what’s in the bright red paste used to protect houses and hills, one new study out of USC offers clues beyond what manufacturers show on their official data sheets. Most concerning is that researchers found heavy metals in the products they tested, raising questions about how retardants may contribute to the spread of metals like cadmium and chromium in the environment.

An air tanker drops fire retardant behind a house as the Grubbs Fire burns in the Palermo area of ​​Oroville, California, July 3, 2024.

The main points to remember

After a wildfire has ravaged an area, it is not uncommon to see an increase in heavy metals in waterways once rains fall on bare surfaces. One such case occurred after the station fire in 2009, when high levels of cadmium were detected in runoff water when the rainy season finally arrived.

And although metals can come from natural resources like rocks and soils, or from burned vegetation, USC researchers found evidence of heavy metals in 14 different flame retardants they purchased and tested.

“Unfortunately, Phos-Chek LC-95… contained potentially concerning concentrations of a few heavy metals, including chromium, cadmium and vanadium,” said Daniel McCurry, associate professor of civil and environmental engineering at USC, and a co-author on the paper. “This isn’t really smoking gun, but it at least suggests that it’s entirely possible that these extinguishers are contributing to the metal release observed after fires.”

Phos-Chek LC-95 is one of the USDA approved retarders used today and is just one of many variations manufactured by Perimeter Solutions. The company never responded to LAist’s request for comment.

The authors give three possible reasons for the presence of metals:

1. That they are included in the product as a corrosion inhibitor
2. That the phosphate ore used in the product could be contaminated
3. The metal tanks in which the product is stored leak into the mixture

Full disclosure: I am thanked for my “helpful discussion” in the acknowledgments section of the article. I contacted McCurry in 2019 to ask if we should be concerned about the contents of flame retardants. McCurry, curious, continued his research with co-authors Marella Schammel and Samantha Gold.

“This is a truly important contribution to the literature. Start thinking about different sources of metal contamination after fires,” said Lauren Magliozzi of the University of Colorado Boulder, whose research has focused on the topic. It is not associated with research.

Heavy metals can accumulate in ecosystems, posing a threat to organisms large and small as they move up the food chain. For example, from algae to benthic invertebrates to fish, whose endocrine systems can be affected.

“We really don’t want this acute metal toxicity to break down any of these different networks in our ecosystem, because then we start to worry about ecosystem collapse,” Magliozzi said.

Government agencies recognize the risk posed by phosphates used in water retardant products and are working to prevent falls near waterways, according to the U.S. Forest Service and Cal Fire.

“We recognize that fire retardants are generally safe in the quantities applied in a given area. For sensitive areas such as waterways and endangered species habitats, we limit the use of fire retardants,” a said Linnea Edmeier, public information officer at Cal Fire. “While Cal Fire prioritizes safety and environmental protection, we also recognize the critical role of fire retardants in fighting fires.”

A blimp drops fire retardant on the Line Fire as it burns near homes September 10, 2024 in Running Springs, California.

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Gina Ferazzi

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Los Angeles Times via Getty Images

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Limitations of the study

As is often the case with studies, this one is limited in scope.

Researchers highlight a variation of Phos-Chek, but not the version used throughout California by Cal Fire, according to the agency. They said it was because Perimeter Solutions refused to provide samples.

Although LC-95 is approved for use by the Forest Service, it is unclear how often and whether it is used in California.

To further our understanding of how retardants may contribute to contamination, more data on metal concentrations in streams before and after fires needs to be collected.

“We don’t really have a direct A-to-B connection between metals in fire extinguishers and metals released from wildfires,” McCurry said.

He added that they might be able to use unique isotope signatures in both the flame retardants they test and the heavy metals they measure in the field, which could help them quantify the share contamination due to the retarder.