Fire Suppressants Found to Contain Toxic Metals, Raising Environmental Concerns

In fire-prone regions, the battle against wildfires involves more than just water; chemical and synthetic suppressants play a crucial role in quelling blazes. A recent study published in *Environmental Science & Technology Letters* by researchers at the University of Southern California has uncovered concerning findings about these fire suppressants. They discovered that several of these products contain elevated levels of toxic metals, including chromium and cadmium, which could contribute to increased metal concentrations in waterways after wildfires are extinguished.

"Wildfires are associated with the release of toxic heavy metals to the environment, but until now, it was assumed that these metals came from natural sources like soil," explains Daniel McCurry, the principal investigator of the study. This revelation suggests that fire retardants themselves may be a source of these harmful metals.

Fire suppression products, which are designed to inhibit fire activity before and after water evaporates, include fire retardants, water enhancers, and foams. With wildfires becoming increasingly frequent and severe, there is a growing need for larger volumes of water and these chemical suppressants, which are sprayed from both the ground and aircraft to combat the flames.

While manufacturers typically disclose most active ingredients in these suppressants, some components remain proprietary. Previous studies have documented increased concentrations of potentially toxic metals in soil and streams following wildfires, prompting McCurry and his team to investigate the possible contamination from suppressants.

The researchers analyzed samples from 14 commercially available fire suppression products, testing for 10 metals known for their toxicity or regulated by the U.S. Environmental Protection Agency (EPA). Alarmingly, every product contained at least one metal at concentrations exceeding the EPA's Maximum Contaminant Level regulations for drinking water. Notably, two products classified as fire retardants were found to contain eight metals—chromium, cadmium, arsenic, lead, vanadium, manganese, antimony, and thallium—well above the EPA's safe limits. One of the retardants even exceeded California's hazardous waste regulations for three of these metals.

These findings highlight the potential for fire retardants to contaminate aquatic environments and drinking water sources if they enter nearby bodies of water. An analysis of the volume of fire retardants used in the U.S. from 2009 to 2021 indicated a variable but generally increasing trend in the total amount of metals applied. For one wildfire in Southern California, researchers estimated that 31% of the observed cadmium concentration in a nearby stream could be attributed to the fire retardant used during the incident.

While these results demonstrate that fire suppression activities could elevate metal levels in the environment, the researchers stress that further investigation is necessary to assess the potential risks to human and environmental health. This study was supported by the U.S. National Science Foundation (NSF), an NSF Graduate Research Fellowship, and a University of Southern California Graduate School and Women in Science and Engineering Fellowship.