The primary purpose of the pink dye is simply to help firefighters and pilots be accurate in creating and identifying lines of retardant.
“Essentially, it lets pilots see where lines are dropped,” Horn said. “If it was clear, they wouldn’t know where the retardant lines are.”
Phos-Chek can fade over time in sunlight and be washed off with water, so it does not permanently stain a landscape.
Neptune Aviation, a Montana-based air tanker company, is among the services currently delivering fire retardant to areas affected by the fires. The company contracts with the U.S. Forest Service and California Department of Forestry and Fire Protection (Cal Fire).
Nic Lynn, Neptune Aviation’s vice president of operations, said three of the company’s air tankers are in use in Southern California. The planes use designated, government-established air tanker bases, he explained.
“We go to those pre-established tanker bases, where they mix the retardant and pump it into the airplanes. Kind of think of us like we’re a dump truck. We’ll carry the product from A to B,” he said.
Neptune Aviation has conducted at least 93 missions and delivered more 280,000 gallons of retardant to combat the fires, Lynn added.
To protect ecosystems, the Forest Service and the Department of the Interior require planes to avoid dropping fire retardant within 300 feet of waterways (ground deliveries must also avoid waterways). Some exceptions can be made, however, including if “potential damage to natural resources outweighs possible loss of aquatic life,” according to the Forest Service.
The primary environmental concern associated with the retardant is the presence of heavy metals. A study last year suggested that one version of Phos-Chek had higher levels of metals like cadmium and chromium than is considered safe according to regulatory thresholds. Heavy metals are not directly added to the product but may come from naturally occurring impurities.
Horn, however, said that the version of Phos-Chek being dropped in California is “a different product from years ago.”
Yifang Zhu, a professor of environmental health sciences at the University of California, Los Angeles Fielding School of Public Health, said the benefits of using fire retardants outweigh the risks.
“There’s very little evidence showing there are serious long-term health effects associated with it” for people, Zhu said.
She added that the immediate health risks posed by wildfire smoke, which contains high levels of particulate matter, are more severe than potential concerns linked to the fire retardant.
Exposure to smoke pollution can cause a range of respiratory and cardiovascular issues, such as difficulty breathing, bronchitis or heart attacks, according to the Environmental Protection Agency.