Toxic metals found in wildfire suppressants

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.