Metals in Wildfire\nSuppressants

Frequent and severe wildfires have led to increased application\nof fire suppression products (long-term fire retardants, water enhancers,\nand Class A foams) in the American West. While fire suppressing products\nused on wildfires must be approved by the U.S. Forest Service, portions\nof their formulations are trade secrets. Increased metals content\nin soils and surface waters at the wildland-urban interface has been\nobserved after wildfires but has primarily been attributed to ash\ndeposition or anthropogenic impact from nearby urban areas. In this\nstudy, metal concentrations in several fire suppression products (some\napproved by the U.S. Forest Service, and some marketed for consumer\nuse) were quantified to evaluate whether these products could contribute\nto increased metal concentrations observed in the environment postfire.\nLong-term fire retardants contained concentrations of toxic metals\n(V, Cr, Mn, Cu, As, Cd, Sb, Ba, Tl, and Pb) 4–2,880 times greater\nthan drinking water regulatory limits, and potentially greater than\nsome aquatic toxicity thresholds when released into the environment.\nWater enhancers and Class A foams contained some metals, but at lower\nconcentrations than fire retardants. Based on these concentrations\nand retardant application records, we estimate fire retardant application\nin the U.S. contributed approximately 380,000 kg of toxic metals to\nthe environment between 2009 and 2021.