Dropping fire retardant solutions from planes is a crucial strategy in wildfire fighting, but some experts are concerned about their impact on the environment, including aquatic ecosystems.
Once dropped, these retardants leave a rust-coloured or pinkish liquid coating on roads, roofs, and vegetation. This technique, commonly used since the mid 20th century, helps fire crews contain blazes by depriving flames of oxygen, explains Jen Baron, a postdoctoral researcher at the University of British Columbia’s Centre for Wildfire Coexistence.
Since 2009, the B.C. Wildfire Service has relied on Phos-Chek LC-95A, a widely used retardant from Perimeter Solutions, a global manufacturer of firefighting products headquartered in the U.S. Its main ingredient, ammonium polyphosphate, is a common fertilizer.
Additives, like iron oxide, give the retardant its signature red colour, helping crews to see where it has been dropped.
The exact chemical composition of the retardant is, however, unknown.
“There isn’t a ton of research on retardant environmental impacts, but they’re generally assumed to be safe for people and for the environment,” Baron says.
However, she points out that there are restrictions on their use near waterways because ammonia and phosphate can be dangerous for aquatic ecosystems.
“If the retardant directly enters a water system, this can result in die-off of fish species,” Baron said. Many fish species and amphibians are very sensitive to ammonia salts and the retardant’s chemicals can also cause algae blooms that can affect water quality and turbidity, she added.
B.C. Wildfire confirmed in an email to CBC News and Radio-Canada that it has a policy “not to release or drop fire retardant where it can enter a body of water.” The service added that Phos-Chek LC-95A is diluted before use, with nearly 90 per cent of the retardant solution comprised of water.
A document about Phos-Chek use from the B.C. Ministry of Environment and Climate Change Strategy says “when precautions and guidelines are followed correctly, there is minimal risk to the environment”.
Restrictions, but also accidents
But accidents do happen and retardant impacts are little known, says Uldis Silins, a professor of forest hydrology at the University of Alberta, who’s been studying watersheds in the Canadian Rockies for more than 20 years.
In 2020, Silins and his team had the chance to study long-term effects of retardants, after Phos-Chek LC-95-A was accidentally dumped over North Racehorse Creek in southwest Alberta.
Crews were combating a small fire during a time of “particularly high hazard” and accidentally hit a 100-metre stretch of the waterway, Silins says. The quantity dropped was unknown, but “pretty significant,” he added.
A year later, the research team found phosphorus-enriched sediments six kilometres downstream from the spill.
This “challenged the conventional understanding that these retardants just flush out of the ecosystem and disappear after a while,” said Madelyn Lux, one of Silins’s students, who led the research published in Environmental Science & Technology.
“Instead, we found that they can be stored long term and they can move downstream,” she added.
With climate change fuelling more frequent and intense wildfires, Silins says we should expect retardant use to increase and warns accidents are inevitable.
Balancing risks
In 2022, the use of ammonium polyphosphate retardants in the U.S. wound its way to court when the American non-profit group Forest Service Employees for Environmental Ethics sued the U.S. Forest Service for discharging retardant in waterways without the necessary permits.
A judge ruled the Forest Service had violated the country’s Clean Water Act by using those retardants without a permit — but confirmed the substance could still be used with a permit in order to save lives and properties.
In Canada, keeping track of retardant use is difficult. Silins notes that Canadian agencies do not document increasing use at a federal scale like the U.S. Forest Service does.
Data from B.C. Wildfire show that the largest volumes of retardant were applied during the province’s worst wildfire seasons, in 2017, 2018, 2021 and 2023.
When asked about the amount of fire retardants used domestically, Environment and Climate Change Canada (ECCC) referred CBC News/Radio-Canada to provincial and territorial fire agencies.
In an email, ECCC stated that “the risk that fire retardants could pose to the environment and aquatic life is probably less important than those of extreme wildfires.”
Hydrologist Silins echoes this, pointing out that retardant misapplications remain rare and their impacts on watersheds are not on the scale of the effects of severe wildfires — including water quality deterioration, changes in hydrological regime, erosion of sediments and turbidity.
“These are very well documented now,” he said.
Evelyne Thiffault, an associate professor at Laval University’s department of wood and forest science in Quebec City emphasizes that retardants are used only in specific situations where public safety is at risk.
“Even with these products, we see all the impacts that wildfires have. We had Jasper burned down last year, we see all the people who are evacuated. Without retardants, it would be even worse,” Thiffault said.
“If we removed this product from our toolbox, we would end up in catastrophic situations,” she added.
Push for more research
But Silins says studying retardants like Phos-Chek remains crucial, especially because their specific chemical composition is proprietary and therefore unknown.
In 2024, a study published in Environmental Science & Technology Letters revealed that the Phos-Chek LC-95A uncoloured version contained toxic metals like chromium, arsenic and lead.
“As we learn more and we find out more about the formulation of those retardants, we may see some change in their composition,” Silins believes.
Researchers are also working on alternatives, such as options using cellulose fibre, which could offer “biosourced options with less impacts on the ecosystems,” Thiffault says.
Perimeter Solutions, the multinational company behind Phos-Chek, maintains that its product has been “rigorously tested.” In a statement to CBC News/Radio-Canada, the company states that “like any other product, it must be applied according to established guidelines, including avoidance of dropping over waterways.”
