In fire-prone areas, water isn’t the only thing used to quell blazes. Wildland firefighters also apply chemical or synthetic suppressants. Researchers reporting in ACS’ Environmental Science & Technology Letters explored whether these suppressants could be a source of elevated metal levels sometimes found in waterways after wildfires are extinguished. Several products they investigated contained high levels of at least one metal, including chromium and cadmium, and could contribute to post-fire increases in the environment.
“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,” says Daniel McCurry, principal investigator of the study. “We now know that fire retardants may contribute to these metal releases.”
Wildfire suppressant products, which are intended to inhibit fire activity before and after water evaporates, include fire retardants, water enhancers and foams. As wildfires have become more frequent and severe, larger volumes of water along with chemical and synthetic suppressants — sprayed from the ground and dropped from planes — have been required to extinguish them. Although manufacturers identify most of the active ingredients in suppressants, some components are proprietary. In addition, previous researchers have observed increased concentrations of potentially toxic metals in soil and streams after wildfires. So, McCurry and colleagues at the University of Southern California wondered if the suppressants contain metals and could contaminate the environment.
The researchers tested samples from 14 fire suppression products sold by commercial retailers. They analyzed samples for 10 metals that have known toxicity or are regulated by the U.S. Environmental Protection Agency (EPA). Every product contained at least one metal with a concentration that exceeded the EPA’s Maximum Contaminant Level regulations for drinking water. In particular, the two suppression products classified as fire retardants contained eight metals (chromium, cadmium, arsenic, lead, vanadium, manganese, antimony and thallium) that greatly exceeded the EPA’s drinking water regulations. And one of the retardants exceeded California’s hazardous waste regulations for three of those metals. The researchers say these results indicate the potential for fire retardants to contaminate the aquatic environment and potentially drinking water, if these products enter bodies of waters.
From the volume of fire retardants dropped on wildfires in the U.S. between 2009 and 2021, the researchers determined that the total amount of metals applied was variable year to year but generally increased over time. And for one Southern California wildfire, they estimate that the increased concentration of cadmium in a nearby stream could be explained by 31% of the reported fire retardant used to contain the fire. They say these results show that fire suppression activities could contribute to elevated metal levels in the environment but that more work is needed to determine potential risks to human and environmental health.
The authors acknowledge funding from 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.
The paper’s abstract will be available on Oct. 30 at 8 a.m. Eastern time here: http://pubs.acs.org/doi/abs/10.1021/acs.estlett.4c00727
###
The American Chemical Society (ACS) is a nonprofit organization chartered by the U.S. Congress. ACS’ mission is to advance the broader chemistry enterprise and its practitioners for the benefit of Earth and all its people. The Society is a global leader in promoting excellence in science education and providing access to chemistry-related information and research through its multiple research solutions, peer-reviewed journals, scientific conferences, e-books and weekly news periodical Chemical & Engineering News. ACS journals are among the most cited, most trusted and most read within the scientific literature; however, ACS itself does not conduct chemical research. As a leader in scientific information solutions, its CAS division partners with global innovators to accelerate breakthroughs by curating, connecting and analyzing the world’s scientific knowledge. ACS’ main offices are in Washington, D.C., and Columbus, Ohio.
Registered journalists can subscribe to the ACS journalist news portal on EurekAlert! to access embargoed and public science press releases. For media inquiries, contact newsroom@acs.org.
Note: ACS does not conduct research but publishes and publicizes peer-reviewed scientific studies.
Follow us: X, formerly Twitter | Facebook | LinkedIn | Instagram
