New method has potential to manage 'forever chemicals'

Scientists at UNSW Sydney have devised a method that has the potential to manage the PFAS that contaminate water and do not break down in the human body.

Per- and poly-fluoroalkyl substances (PFAS) are known as ‘forever chemicals’ because they are notoriously resistant to degradation. Due to their stable chemical structure, PFAS — which are found in thousands of variants — are used in oil- and grease-resistant food packaging, non-stick cookware, cosmetics, clothing and firefighting foams.

These chemicals have become widespread, infiltrating water sources and soil. With recent reports revealing that many global water resources exceed the drinking limits of PFAS, concerns over their environmental and health impacts have escalated.

The chemical is so resistant to degradation that people all over the world are likely to have low levels of PFAS in their bodies. “PFAS is such a robust chemical that it cannot be degraded within the human body,” said Professor Naresh Kumar from UNSW. “And that has become a concern.”

Despite ongoing efforts to develop ways of degrading PFAS, current methods are limited by a lack of efficient, scalable and environmentally friendly processes.

In seeking to tackle this problem, the team of scientists from UNSW’s School of Chemistry designed a catalyst system that can activate a reaction to break down common types of branched PFAS. The new method, developed by Kumar with Dr Jun Sun and recently published in the journal Water Research, could potentially be used for more efficient and sustainable PFAS remediation in the future.

“Owing to its robust nature, simple application and cost-effectiveness, the new system we have developed shows successful PFAS remediation in the lab, which we hope to eventually test at a larger scale,” said Sun, first author of the paper.

Due to the chemicals’ potential risks and their durability, many regulatory bodies have tightened PFAS regulations and set precautionary drinking water limits, including in Australia.

“The pressing need for effective PFAS remediation has driven the investigation into a wide array of treatment methods, spanning from physical separation processes to advanced destruction techniques, all which have their limitations,” Sun said.

Current processes used to reduce PFAS

PFAS is a fluorinated chemical bound by strong carbon-fluoride (C-F) bonds, which are famously hard to break.

An existing method to remove PFAS from water and soil works by absorbing PFAS onto carbon material. “So if you’ve got a pad of activated carbon and you pass water through it, you can absorb PFAS onto the activated carbon, but you then have to burn it to destroy the PFAS or safely store it,” Kumar said.

This is laborious, inefficient and not good for the environment. Also, while physical separation techniques such as this offer potential for isolating PFAS, they do not actually destroy the chemical, ultimately exacerbating the management challenges associated with PFAS-contaminated waste.

Another method uses a strong oxidising agent to break PFAS apart. However, this process requires aggressive chemicals that break PFAS down into smaller structures, which can become even harder to remove completely.

“There is an ongoing need to come up with an energy-efficient and environmentally friendly way to remove PFAS from water,” Sun said. “The method we have developed is a type of reductive defluorination, which decreases the toxicity of PFAS by breaking the strong C-F bonds of branched PFAS.”

Developing an effective catalyst

Nano zero-valent metals (nZVMs) are a type of eco-friendly chemical-reducing agent that scientists have used for decades in the treatment of groundwater and soil contaminated with chlorinated compounds, using a dechlorination process.

Despite their effectiveness elsewhere, there has been a lack of research into the use of nZVMs to break down PFAS, largely due to the lack of appropriate catalysts required to activate the reaction.

Previous studies indicate that PFAS can be degraded using nano zero-valent zinc and the naturally occurring catalyst vitamin B12, a water-soluble vitamin present in our daily diet. But again, the process is slow and inefficient.

“Inspired by the fact that B12 has the potential to catalyse this reaction, we wanted to synthesise a catalyst that mirrors the unique ring shape of B12, which we did using a structure known as a porphyrin ring,” Sun said.

Testing their method out on two common types of PFAS — branched PFOS and PFOA — Kumar and Sun mixed the PFAS chemicals with nZVMs and the porphyrin ring in a buffer solution and measured the breakdown of the PFAS.

The results from this latest study revealed that within five hours, approximately 75% of the fluoride had been released from branched PFOS and PFOA, significantly reducing the amount of PFAS within the solution. Meanwhile, a B12-based catalyst system only showed less than 8% defluorination within five hours.

Potential for large-scale application

Further research is needed before the method could be applied at scale, but the team fully intend to take their discovery further.

“The next step for us is to really try this on a pilot scale to see if this can be done out of the laboratory on a real sample,” Kumar said. “Then we’d like to try it out in a real water purification system or sites which are contaminated with PFAS.”

The researchers are also exploring how to scale up the process in an environmentally friendly way by incorporating the catalyst into an electrode.

“We hope to try this method out on linear PFAS, not just branched types,” Sun said. “But we’re already one step closer to solving a widespread environmental problem.”

Kumar and Sun worked alongside Prof Denis O’Carroll, Prof Michael Manefield and Dr Matthew Lee from the UNSW School of Civil and Environmental Engineering. Their research was funded by a $3 million grant from the Australian Research Council in 2019.

Image credit: iStock.com/onuma Inthapong