Wildfire suppressants dumped nearly a million pounds of toxic metals into the West U.S.

Companies supplying the USFS with wildfire suppressants may have been hiding various heavy metals present in their formula, according to an ongoing study.

Materials used in suppressants, including fire retardants, water enhancers, and foams, all have to be approved by the U.S. Forest Service, according to Associate Professor of Civil and Environmental Engineering Daniel McCurry, a co-author of the study. However, the companies supplying the suppressants don’t have to disclose up to 20% of their product formulas, keeping them “trade secrets” under law.

Researchers from the USC’s Sonny Astani Department of Civil and Environmental Engineering discovered much of the “trade secrets” could be toxic heavy metals. The team tested numerous wildfire suppressants and found they have released ~850,000 pounds of toxic metals into the environment in the Western United States from 2009-2021.

“Increased metals content in soils and surface waters at the wildland-urban interface has been observed after wildfires but has primarily been attributed to ash deposition or anthropogenic impact from nearby urban areas,” an introductory paper into the ongoing research said. ” In this study, metal concentrations in several fire suppression products (some approved by the U.S. Forest Service, and some marketed for consumer use) were quantified to evaluate whether these products could contribute to increased metal concentrations observed in the environment postfire.”

Researchers estimated the heavy metal amounts by purchasing the fire suppressant materials themselves and used equipment called inductively-coupled plasma mass spectrometers. They found several contaminants in the materials, including:

• vanadium
• chromium
• manganese
• copper
• arsenic
• cadmium
• antimony
• barium
• thallium
• lead

They estimated the quantity of heavy metals that have been dropped in the Western U.S. over the last decade by using contaminant measurements and publicly available data on suppressant application rates.

The researchers concluded that at least 8 of the contaminants were present at concentrations above EPA drinking water contaminant levels and that 1 million gallons of dropped retardant later entered surface waters.

Additionally, a clear version of the pinkish-red material often seen in fire retardant air drops called “Phos-Chek LC-95 W” was found to have the greatest amount of heavy metals. Researchers even went as far as to note the material could be classified as “hazardous waste” under federal and California regulations.

“I think what surprised me most was the array of metals we found,” said the study’s lead author, Environmental Engineering  PhD student Marella Schammel.

“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.”

Researchers will continue studying how the toxic materials interacted with the environment by directly testing soil and waterways prior to and after the wildfire season.