The California wildfires have burned tens of thousands of acres in recent weeks. Therefore, suppression strategies beyond just spraying the blazes with water have been necessary.

Videos showing airplanes and helicopters unleashing vast clouds of red or pink suppressants onto the fires have been commonplace in news reports.

While these retardants are effective, and many of the California fires are nearing full containment, they may be significantly costing the environment.

A recent study published in the Environmental Science and Technology Letters found that many fire retardants contain toxic metals. These include chromium and cadmium in amounts exceeding regulatory limits for drinking water.

These metals may linger in the environment after a fire has been suppressed and have been detected following blazes before.

“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,” Principal Investigator Daniel McCurry said in a press release. “We now know that fire retardants may contribute to these metal releases.”

Hundreds of Tons of Toxic Metals May Have Been Released

The researchers, who initially published their findings in October, set out to learn more about why metal content in soil and surface waters tends to rise after a wildfire affects the area.

According to the study, the rise in metals has historically been attributed to ash or the impact of nearby urban areas.

But, the researchers found that fire suppression products, including some approved by the U.S. Forest Service, contain several toxic metals at high levels.

“At least eight, and in some cases all ten, examined metals were present above the detection limit in all evaluated fire suppression products,” the study stated.

However, according to CBS News, the Forest Service’s fire retardant manufacturer, Perimeter, claimed that McCurry’s research was on a formula the Forest Service no longer uses.

Aerial fire suppressants are often a mixture of water and ammonium phosphate. While the complete formula is a trade secret, many fire suppressants have a corrosion inhibitor. This ensures the foam doesn’t harm their storage containers. Although the exact inhibitors are not public knowledge, they might contain the widely used aluminum corrosion inhibitors chromium and cadmium.

The study found that, from 2009 to 2021, fire suppression released over 380,000 kilograms of toxic metals into the environment. That’s equivalent to over 400 tons.

Researchers found that the metal levels exceeded safe drinking standards. If these retardants leak into bodies of water, there may be health risks.

According to the Centers for Disease Control and Prevention, chromium is tied to cancer development. Ingestion of the metal may also cause irritation and ulcers.

Despite Toxic Metal Risk, Fire Suppressants Play Key Role

Despite the potential toxic metal risks tied to some fire suppressants, they play a vital role in fighting fires. Due to their effectiveness, mitigating the toxicity risks is unlikely to have a simple solution. The fire-suppressing abilities of these retardants far outpaces that of simple water application.

They coat the plant life they land on, helping to make it inflammable and less likely to burn. This can be key in containing and fighting wildfires and can be effective for longer than just dropping water.

The suppressants are dyed a bright color so firefighters can easily see what areas have had suppressants applied.

But, concerns surrounding the release of these toxic metals and their environmental impact may grow as more suppressants become necessary. The toxic metals study noted that the frequency of wildfires has grown over the years and is expected to continue to grow in years to come.

Editor Lindsay Donaldson contributed to this article.