“If fire retardant is applied near waterways or is washed into these areas with rain, there is the potential for it to directly affect fish and other aquatic creatures and indirectly by promoting algal blooms by increasing nutrients in water,” said associate professor Tina Bell from the University of Sydney.
Dr Bell was involved in a study on the effect of one of the retardants, Phos-Chek, on vegetation in eastern Victoria in 2005.
There is the potential for it to directly affect fish and other aquatic creatures.
Tina Bill, University of Sydney
Fire retardants are essentially fertilisers, containing ammonium mixed with thickeners and corrosion inhibitors to prevent damage to the aircraft that drop them.
Retardants coat vegetation in a chemical residue that prevents or slows down ignition, until it is removed by rain or erosion.
They are sprayed strategically to create a barrier to slow a fire’s spread, working for up to 18 hours or more.
Firefighting foams – known as Class A foams – are also deployed by the Rural Fire Service to smother bushfires that are already alight.
They are considered much safer than some of the Class B foams used on fuel and chemical fires, which have historically contained toxic PFAS compounds.
One of the main fire retardants used by the NSW Rural Fire Service is Phos-Chek, known for its characteristic red pigment, which is used by pilots to track where it has been sprayed.
While the RFS would not confirm the volumes nor the formulations of the products it has used this season, sources told the Herald that Phos-Chek has been sprayed liberally around the state.
“Unfortunately, very little research has been done in Australia on the immediate and longer term effects of fire retardants on plant and animal communities,” Dr Bell said.
“Most of it has been done in the US and Canada where the ecosystems are quite different.”
The Phos-Chek brand was pioneered by chemical giant Monsanto in the 1960s but since 2018 has been owned by US-based Perimeter Solutions.
The general manager of Phos-Chek Australia, Darren Webb, said the product was an important tool in the arsenal for firefighters.
“The retardant is like putting a bulldozer through the vegetation … without those harsh environmental effects,” he said. “You can construct that [containment] line a lot quicker and get in there early enough before it’s got time to spread.”
Mr Webb stressed that Phos-Chek had been through an exhaustive approval process by the US Forest Service deeming it safe for use, relied on by Australian firefighting authorities.
“It’s absolutely been closely examined,” he said.
Mr Webb said the manufacturer endorsed a policy among both Australian and US fire authorities to avoid applying Phos-Chek in close proximity to waterways.
But he said that it was a matter of “weighing up the risk and benefit” when it came to using retardants in water catchment areas, because allowing the total incineration of vegetation posed its own risks.
“The ash, the sludge can come down the side of the catchment area into the waterway and create its own issues – as compared to trying to stop it coming into a catchment area [with the retardant],” Mr Webb said.
Of additional concern have been performance-enhancing additives in Phos-Chek retardants that are trade secret and exempt from public disclosure. Mr Webb said the additives had been fully disclosed to US regulatory authorities.
Dr Bell’s study found that Phos-Chek did not have a large impact on vegetation in the area tested, but did result in the death of some individual plants.
“This is not an environmentally-friendly product but if you look at it from the point of view of using it as a tool to help ground crews manage fire containment lines, there are certainly good reasons for it to be used at certain times, ” she said.
About 120 tonnes of a Phos-Chek formulation known as D75R was dropped on the devastating Caledonia fires in Victoria’s Alpine National Park in 1998.
At the time The Age reported that residents had observed an unusual oily sludge coming down a river catchment supplying 9000 people.
It was followed by more than a year of “widespread complaints” of “severe rashes, itching, sores, insomnia and eye irritations”.
The CSIRO was subsequently commissioned to investigate. Its report noted the additives in the Phos-Chek retardant were “potentially harmful” but their exact impact was unclear because state agencies would not share water quality data collected.
However the report concluded that the health risks were minimal, while the risk of not using retardant to control intense bushfires was “very high”.
Carrie Fellner is an investigative reporter for The Sydney Morning Herald.