In fire-prone areas, water isn't the only thing used to put out flames. Wildland firefighters also use chemicals or synthetics to put out fires. The researchers investigated whether these products could be the cause of the high concentrations of metals sometimes found in waterways after a wildfire has been extinguished. Several products studied contained elevated levels of at least one metal, including chromium and cadmium, and may contribute to increased metal concentrations in the environment after the fires.
« Wildfires are associated with the release of toxic heavy metals into the environment, but until now these metals were assumed to come from natural sources such as soil “, explains Daniel McCurry, principal investigator of the study. “We now know that flame retardants can contribute to these metal releases.”
Flame retardants, which are intended to inhibit fire activity before and after water evaporates, include flame retardants, water enhancers and foams. As wildfires become more frequent and more severe, it is necessary to use larger volumes of water as well as chemicals and synthetics to extinguish them, whether sprayed from the ground or dropped by plane.
Although manufacturers identify most of the active ingredients in removal products, some components are proprietary. Additionally, researchers have previously observed increased concentrations of potentially toxic metals in soil and waterways after wildfires. So McCurry and his colleagues at the University of Southern California wondered whether the removal products contained metals and could contaminate the environment.
Researchers tested samples of 14 fire suppression products sold by commercial retailers. They analyzed the samples for 10 metals known to be toxic or regulated by the U.S. Environmental Protection Agency (EPA).
Each product contained at least one metal whose concentration exceeded the EPA's maximum contamination limits for drinking water. In particular, the two suppression products classified as flame retardants contained eight metals (chromium, cadmium, arsenic, lead, vanadium, manganese, antimony, and thallium) whose concentration far exceeded EPA drinking water regulations . And one of the retarders exceeded California's hazardous waste regulations for three of those metals. According to the researchers, these results indicate that flame retardants can contaminate the aquatic environment and potentially drinking water, if these products enter water bodies.
Using the volume of fire retardants applied to wildfires in the United States between 2009 and 2021, the researchers determined that the total amount of metals applied varied from year to year, but generally increased with time. For a forest fire in Southern California, they estimate that the increase in cadmium concentration in a nearby stream could be explained by 31% of the flame retardants used to contain the fire. These results show that firefighting activities could contribute to elevated levels of metals in the environment, but that additional work is needed to determine potential risks to human health and the environment.
Article : « Metals in Wildfire Suppressants » – DOI: 10.1021/acs.estlett.4c00727
