Dear Editor,
Summer is here, and wildfires are burning in Montana. Wildland firefighting seems to be replete with ubiquitous images: a hand crew in yellow shirts, packs slung low on their backs; smoke billowing around a hazy mountaintop; a swath of pink mist issuing from a plane.
The pink substance is fire retardant, used to slow the spread of fire and reduce its intensity. In a 2024 study by the University of Southern California, the most used retardant, called Phos-Chek, was found to be rich in lead, arsenic, cadmium, chromium and other metals toxic to life. Some of the elements are present in a high enough concentration that the mixture could “legally be classified as hazardous waste under both federal and CA regulations,” the study states.
The Forest Service drops over a million and a half gallons of retardant every year in Montana. BLM and other agencies that fight fire use it as well.
Retardant comes in different forms, but the most common is a sludge containing the fertilizer ammonium polyphosphate, which sticks to vegetation and reacts with cellulose when heated to form a sheath of nonflammable char. The product that the Forest Service drops from planes is Phos-Chek LC-95A, manufactured by the company Perimeter Solutions. The researchers were only able to test LC-95W, a colorless version approved for ground application; the aerial pink stuff isn’t available for the public to purchase. It contained up to thousands of times the limit for drinking water and several times the limit for hazardous waste of several toxic metals, especially chromium and cadmium.
All in all, the researchers estimated that, assuming the pink retardant is composed the same as the colorless version, around 840,000 pounds of hazardous metals were dropped on the U.S. between 2009 and 2021. Perimeter Solutions denies that the makeups of the two solutions are the same, and asserts that the aerial variety isn’t harmful to the environment. But increased levels of toxic metal have long been noticed in soil after a wildfire. The USC researchers showed that the amount of cadmium recorded in the soil after a particular fire roughly predicted the volume of retardant that was dropped, based on the concentration they measured in the lab.
During the 2017 Lolo Peak Fire near Missoula, which burned 54,000 acres, the Forest Service dropped more than 200,000 gallons of retardant. Using the concentration reported in the study, this corresponds to 375 pounds of metal released into the environment.
Simon Nathans
Bozeman, Montana
