It’s a scene that’s become engrained in the narrative of wildfire management in the American West. As a plane swoops at a low altitude over a forlorn ridgetop enveloped in smoke, it releases a striking ribbon of fire retardant, saturating the hillside with a vibrant pink hue. Enthusiastic onlookers often respond with cheers, captivated by the aerial display of firefighting expertise.
The U.S. Forest Service, alongside various emergency response agencies, deploys tens of millions of gallons of fire retardant each year. This mainly consists of an ammonium phosphate-based mixture known as Phos-Chek, strategically applied around wildfires to coat flammable vegetation and curtail the relentless advance of flames.
However, insights from a recent study conducted by researchers at the University of Southern California have unveiled alarming findings regarding this popular fire suppressant. The research reveals that a notable variety is contaminated with toxic heavy metals, estimating that roughly 850,000 pounds of these hazardous chemicals have been emitted into the environment since 2009. According to Daniel McCurry, an associate professor of civil and environmental engineering at USC and one of the study’s primary authors, the ecological repercussions of using such retardants warrant deeper investigation, and there’s substantial justification for seeking a more environmentally friendly alternative.
The implications of these findings contribute to longstanding apprehensions voiced by environmental advocates concerning the impact of aerial fire suppressant applications. Nonetheless, fire officials staunchly defend the strategy, asserting that the life-saving benefits of mitigating fire spread significantly outweigh the potential ecological risks. As climate change catalyzes increasingly severe wildfires, the discourse surrounding this issue is poised to deepen.
“There is a distinctly observable trend indicating an upward trajectory in both the frequency and severity of wildfires, and I anticipate that the strategies for managing these infernos will continue to incorporate aerial firefighting for the foreseeable future,” McCurry remarked.
Orange County Fire Authority Chief Brian Fennessy recognized the downsides associated with the use of fire retardants, particularly the adverse effects on aquatic life that may occur if the chemicals enter water systems. However, he firmly stated, “there’s simply no substitute for retardant when it comes to combating wildfires.”
The sticky substance outperforms water due to its ability to cling to vegetation, retaining its flame-retardant properties even after drying. Fennessy noted that if his teams were deprived of the use of retardants, “I think you’d see fires get bigger — that’s the basic answer.”
“I believe there’s a necessary tradeoff and balance to maintain, and as every situation presents its unique challenges, it’s crucial that these considerations are actively discussed,” Fennessy continued.
In their pivotal study, published in Environmental Science & Technology Letters, McCurry and his colleagues scrutinized 14 different fire suppressants they purchased on the open market after manufacturers declined to supply samples. Alarmingly, each of these substances contained no fewer than eight heavy metals. The specific variety identified as Phos-Chek LC-95W exhibited what McCurry described as “potentially alarming” levels of multiple metals, including chromium, cadmium, and vanadium. He further emphasized that this particular formulation could potentially be categorized as hazardous waste under federal and California regulations.
Research indicates that chronic exposure to these heavy metals has been associated with severe health issues such as cancer, along with kidney and liver diseases in humans. However, the possible ramifications for environmental health, especially considering the potential contamination of waterways by these retardants, raise even more pressing concerns.
McCurry characterized the retardant tested by his team as the colorless variant of the flashy pink Phos-Chek typically dispensed from aircraft. Notably, the pink formulation, known as LC-95A, is unavailable for consumers to purchase.
Perimeter Solutions, the manufacturer behind Phos-Chek, responded to these findings by distinguishing between their products, asserting that LC-95W is not deployed in aerial applications. The company maintained that all Phos-Chek retardants utilized in aerial firefighting are rigorously evaluated by the Forest Service, which mandates thorough testing to ensure compliance with stringent safety standards.
Despite this, the Forest Service acknowledged its limited, albeit rare, use of Phos-Chek LC-95W in aerial firefighting. The agency clarified that this formulation has been cleared for both aerial and terrestrial applications after successfully passing a series of safety examinations, including a toxicity leaching test configured by the Environmental Protection Agency, designed to ascertain the extent of any toxic substances released into a landfill.
These findings contribute to an existing body of knowledge concerning heightened heavy metal concentrations in aquatic ecosystems following nearby wildfires. For example, after the devastating Station fire swept through the Angeles National Forest in 2009, researchers documented cadmium levels in the Arroyo Seco that were up to 1,000 times greater than usual.
“There are numerous hypotheses that seek to explain the sources of these metals, and this new study introduces another layer to the discussion,” explained Josh West, a professor of earth sciences and environmental studies at USC, who was not directly involved in McCurry’s research but provided insights prior to its publication.
Additional investigation is needed to fully ascertain the degree to which retardants infiltrate waterways and their contribution to elevated metal concentrations, West stated. It’s plausible that retardants represent one of multiple contributing factors. His own research has indicated that metals from air pollution can settle on vegetation and subsequently leach into soil and water systems upon combustion.
McCurry’s team is dedicated to advancing understanding regarding whether the heavy metals present in retardants filter down into groundwater or run off into streams. One approach being employed involves collecting soil samples from the San Gabriel Mountains, applying Phos-Chek, conducting controlled burns in laboratory settings, and utilizing a rainfall simulator designed by students to assess the movement of these metals.
Additionally, the researchers are working to clarify the sources of heavy metal concentrations detected in streams post-wildfires by employing unique isotopic markers to link the chemicals back to either retardants or alternative origins.
To investigate the Phos-Chek formulation that is not commercially accessible, McCurry’s team has visited burn sites, including areas affected by the Post fire near Gorman and the Highland fire near Aguanga, to collect soil samples treated with retardant for subsequent analysis of metal content.
Andy Stahl, the executive director of Forest Service Employees for Environmental Ethics, articulated that the study substantiates longstanding fears regarding the presence of heavy metals in Phos-Chek, concerns that had previously relied on circumstantial evidence. A Washington air tanker base was cited by the state Department of Ecology in 2016 for contravening limits on cadmium, chromium, and vanadium according to its waste discharge permit. A report issued by the Forest Service acknowledged it could not dismiss the potential for heavy metal impurities within the retardant.
With a history of legal actions against the Forest Service regarding its retardant practices dating back to 2003, Stahl’s group has prompted the agency to establish buffer zones surrounding habitats home to vulnerable species and waterways where retardant use would be curtailed unless public safety was at imminent risk.
The most recent litigation took place in 2022 when the nonprofit filed a lawsuit in U.S. District Court in Montana after uncovering that the Forest Service had dropped over 1 million gallons of retardant in these exclusion zones between 2012 and 2019.
The lawsuit sought to halt the agency’s aerial retardant use until it secured a Clean Water Act permit addressing discharges into waterways, a process estimated by the EPA to require two and a half years.
Though the judge mandated that the Forest Service must obtain the relevant permit, he permitted the continuation of retardant drops in the interim due to their critical importance in safeguarding lives and property.
During the legal proceedings, an anonymous individual left behind hundreds of pages of documents, including what appeared to be an EPA list of contaminated air tanker bases, on the front porch of FSEEE’s attorney in Missoula, Montana. Accompanying this was a letter, allegedly authored by a long-serving Forest Service employee, asserting that the presence of heavy metals such as cadmium and chromium in Phos-Chek is “one of the worst kept secrets of the retardant industry.”
The existence of heavy metals in these retardants may introduce new regulatory complexities for the EPA as it drafts the Clean Water Act permit for the Forest Service, Stahl noted, adding that his organization is considering whether subsequent legal action is necessary in light of the findings.
“We’re introducing a potentially significant volume of toxic heavy metals every time retardant is deployed, regardless of where it’s applied within the watershed,” he concluded.
How do manufacturers differentiate their fire retardant products, and why is transparency regarding their use important?
**Interview with Daniel McCurry, Associate Professor of Civil and Environmental Engineering at USC, on Heavy Metals in Fire Retardants**
**Editor:** Thank you for joining us today, Professor McCurry. Your recent study uncovered some alarming findings about the fire retardant Phos-Chek and its heavy metal content. Can you give us a brief overview of what prompted this research?
**Daniel McCurry:** Thank you for having me. We were motivated to investigate the chemical composition of fire suppressants after reports indicating their increasing usage in wildfire management. As wildfires become more severe and frequent due to climate change, it’s vital to understand what goes into the products we rely on—especially those that could have a long-term impact on our environment.
**Editor:** Your study found that products like Phos-Chek LC-95W contain multiple heavy metals. Can you elaborate on the significance of these findings?
**Daniel McCurry:** Certainly. We found that every fire suppressant we tested contained at least eight heavy metals, including chromium, cadmium, and vanadium—all of which are potentially hazardous. The significant concern is that these metals can leach into soil and waterways, posing severe health risks to both ecosystems and human populations. Chronic exposure to these substances is linked to serious health issues, including cancer and organ damage.
**Editor:** Fire officials, like Orange County Fire Authority’s Chief Brian Fennessy, argue that the benefits of using retardants outweigh the ecological risks. How do you respond to this perspective?
**Daniel McCurry:** It’s an important debate. While it’s undeniable that fire retardants can help protect life and property during wildfires, the ecological consequences cannot be ignored. Our study suggests that as we continue to rely on these substances, we need to seek safer alternatives or at least mitigate the potential harm by improving the formulations currently in use. It’s crucial to strike a balance between saving lives and protecting our environment.
**Editor:** You mentioned that Phos-Chek LC-95A is widely used in aerial applications, while LC-95W contains heavy metals. Is there a clear distinction made by manufacturers about when and how these products are used?
**Daniel McCurry:** Yes, the manufacturers, including Perimeter Solutions, differentiate between their products. They assert that LC-95W is rarely used in aerial firefighting. However, our study highlights the need for transparency regarding which formulations are used in which contexts, and the potential risks associated with them. This information is crucial for both fire officials and the public to make informed decisions.
**Editor:** What steps are you and your team taking to further investigate the extent of contamination from these retardants?
**Daniel McCurry:** We are conducting field studies, collecting soil and water samples from burn sites treated with retardants to analyze metal concentrations. We’re also using ecological models to better understand the movement of these metals in the environment, especially in relation to runoff into waterways. Our goal is to determine how severely these retardants contribute to metal pollution post-wildfire.
**Editor:** Thank you for sharing your insights, Professor McCurry. It’s clear that ongoing research into fire management strategies and their environmental impact is crucial as we face more frequent wildfires.
**Daniel McCurry:** Thank you for having me. It’s a pressing issue, and the dialogue is essential. We need collaborative efforts to develop effective, environmentally friendly firefighting tools that can protect both our communities and ecosystems.
