Firefighting foam contains more branched PFOA than anticipated

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A new study has revealed there may be a significant underestimation of a specific type of PFAS "forever chemical" in the environment.

Researchers from UNSW Sydney found that branched perfluorooctanoic acid (PFOA) was more prevalent than expected in firefighting foam. PFOA is classified as a human carcinogen by the International Agency for Research on Cancer.

Firefighting foams have historically been composed of Per- and poly-fluoroalkyl substances, known collectively as PFAS, which have been linked to environmental and health issues because they can take hundreds or even thousands of years to naturally break down.

Low traces of PFAS are believed to now be present in more than 99% of the global population and there are growing concerns about the level of contamination in water supplies, including drinking water.

In a paper published in Water Research, the UNSW team led by Professor Denis O'Carroll, Professor Naresh Kumar, Professor Michael Manefield and Dr. Matthew Lee, showed that concentrations of branched PFOA in firefighting foam would double after time in the environment.

The researchers conducted what is known as a TOPA—a total oxidizable precursor assay—which simulates the oxidation process that helps create regulated PFAS naturally in the environment, but at a much faster speed.

"[We took] the firefighting foam and put it through a test to mimic what would happen to those chemical compounds in the environment. And we found that this branched PFOA was actually an important product of that process," said Prof. O'Carroll, from UNSW's School of Civil and Environmental Engineering.

"PFOA also exists in a linear form, but people have not really been looking or analyzing the amount of branched PFOA. But in our samples we found that about 50% was linear and 50% was branched after TOPA."

Safe drinking limits

The Australian government recently proposed updating its drinking water guideline, suggesting an acceptable level of 200 nanograms per liter for PFOA. However, in April 2024, the United States Environmental Protection Agency set its drinking water concentration limits for PFOA at just 4 nanograms per liter.

In April, a UNSW-led international study assessed the levels of PFAS contamination in surface and ground water around the globe and found that much of our global source water exceeded PFAS safe drinking limits.

Forever chemicals have been linked in some studies to adverse health outcomes, such as lower birth weight in babies, higher levels of cholesterol, reduced kidney function, thyroid disease, altered sex hormone levels, reduced vaccine response, and liver, kidney, and testicular cancers.

While PFAS have been linked to many of these health outcomes, they haven't necessarily been shown to cause them.

But Prof. O'Carroll says the research from UNSW, which also included work by Dr. Jun Sun, shows that more studies need to be done to properly identify the levels of as many potentially dangerous chemicals as possible.

"PFAS is actually a group of nearly 14,000 synthetic chemicals, but in Australia the authorities measure, monitor and advise on just three of them," he said.

"We can identify in this paper that branched PFOA is likely to be more pervasive in the environment than currently anticipated. But then there are 14,000 other ones we could also be measuring.

"What I think this research shows, more broadly, is that we should be analyzing for more than just a few of these PFAS that are out there and compiling a more holistic picture to help address the problems."

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Decreasing toxicity of PFAS

The researchers have simultaneously been working on developing new catalysts that are able to break down PFAS chemicals.

This novel process is a form of reductive defluorination using a type of eco-friendly chemical reducing agent called zero-valent metals (ZVMs) in conjunction with vitamin B12 and its analogs.

Promisingly, a number of the various branched PFOA chemicals identified in the analysis of the firefighting foam degraded within 10 days when treated with zero-valent zinc and vitamin B12.

"We already know the linear PFOA is very difficult to break down using traditional methods, but we have shown with this new process that the branch PFOA more easily degrades using the new process we have developed," said Prof. Kumar, from UNSW's School of Chemistry.

"So if we are showing that 50% of the PFAS chemicals are actually branch PFOA then that is potentially positive.

"According to some models, the estimated initial step in the reductive defluorination of PFOA would take eight years just with zero-valent zinc, but in our tests the majority of the branched isomers degraded within 10 days using a system including vitamin B12.

"But it's important to understand there is not just one single PFAS in the firefighting foam, or other sources such as non-stick frying pans, clothing, cosmetics, insecticides.

"There is a mixture of things, but the branch version of PFOA is formed from PFAS precursors via environmental conditions.

"It is essential to recognize that effective remediation of PFAS will necessitate treatment combinations, as it is improbable for any single technology to produce environmentally benign products."

More information: Jun Sun et al, Characterization of PFOA isomers from PFAS precursors and their reductive defluorination, Water Research (2024). DOI: 10.1016/j.watres.2024.122717

Journal information: Water Research

Provided by University of New South Wales