The US federal government and chemical makers have long concealed the contents of pink wildfire suppressants widely spread by firefighting aircraft to contain blazes, but new test results provide alarming answers – the substances are rife with cadmium, arsenic, chromium and other toxic heavy metals.
The suppressants are a “major” source of toxic pollution that causes heavy-metal levels to spike in the environment, and the products themselves contain metal levels up to 3,000 times above drinking water limits, the peer-reviewed research found.
The government and chemical makers have claimed up to 20% of aerial suppressants’ contents are “trade secrets” and exempt from public disclosure, so while there has been suspicion of the substances’ toxicity, the study is the first to confirm the metals’ presence.
It also highlights the tension between protecting human health and property from wildfires by spraying highly toxic substances – about 440m gallons were sprayed between 2009 and 2021, the study noted.
“As rates of aerial fire retardant application have grown, likely so too have loadings of toxic metals released into the environment from their use, a trend which may intensify if wildfire frequency and intensity continues to increase,” the University of Southern California authors wrote.
The suppressants are a mix of water, fertilizer, and undisclosed ingredients, while the pink color comes from added dye to show firefighters where it has been sprayed. Metals are likely used as anti-corrosion agents to prevent the plane’s tankers from disintegrating, they authors wrote. The mix works by coating vegetation and lowering the amount of oxygen that could fuel the fire.
The substance was dropped by as many as 25 aircraft daily to contain the devastating Los Angeles wildfires, and photos from it vividly convey the trade off, showing homes and property covered in hot pink suppression.
The metal levels in the suppressants meet federal guidelines and the authors were initially most worried about environmental contamination, but the heavy use in residential areas this year raises a new set of concerns, Daniel McCurry, one of the study’s co-authors, told the Guardian.
“Are the hazardous waste thresholds the appropriate bar for these to clear, or, if they’re being used in a massive scale in populated neighborhoods, do we need to get stricter on permissible concentrations of toxic compounds?” McCurry asked.
Although metal pollution has been documented in the wake of wildfires, previous research has largely ignored the possibility that it stems from undisclosed suppressant ingredients. The USC researchers started with two pieces of “circumstantial evidence” that pointed to the possibility – an internal federal report that detailed metal use, and a state of Washington environmental violation notice that revealed the potential for toxic metal pollution.
The authors tested 10 types of commonly used commercial suppressants and confirmed they contained high levels of toxic metals.
Researchers then checked state and federal records to determine where suppressants were spread between 2009 and 2021, as well as metal levels in the environment, and showed that the data tracked with their testing’s findings.
The producer of one of the suppressants has said a new generation of the product is “greener”, McCurry said, but he added “until we are able to come across some of this material and test it, we really don’t know”.
