Key points
- Per- and Polyfluoroalkyl Substances (PFAS) are harmful chemicals, which don’t break down naturally in the environment.
- While new technologies claim to destroy 99.99 per cent of PFAS, this doesn’t always account for the emission of airborne particles.
- An international team of researchers has devised new analytical methods to help prevent harmful emissions.
Getting rid of Per- and Polyfluoroalkyl Substances (PFAS) is one of the greatest environmental challenges of our time. This group of 15,000 human-made chemicals doesn’t break down naturally, leaching into soils and waterways and accumulating in the environment.
High levels of PFAS can have serious health impacts on humans, animals and plants. That’s why cleaning them up is a high priority for governments, industries and communities around the world.
Currently, the most promising way of disposing of PFAS is to expose them to high temperatures. A range of technologies can be used to do this. But in the process, harmful airborne particles can form, including potent greenhouse gases.
Now, an international team of researchers is working on new methods to identify these airborne particles and ensure they don’t escape into the environment.
Breaking the strongest bonds in chemistry
Dr Jens Blotevogel, a Principal Research Scientist at Australia’s national science agency CSIRO, explained that the carbon-fluorine bonds found in PFAS are some of the strongest known in chemistry.
This is what prevents PFAS from degrading naturally in the environment, requiring specialised treatment to remove and destroy them. The most promising solutions include burning matter containing PFAS inside a specialised hazardous waste incinerator, or vaporising the contaminants, leaving soil structure intact so it can be reused, a process called thermal desorption.
“When we put PFAS-impacted materials in a kiln to destroy them, the aim is to break them down into relatively harmless end products, like carbon dioxide and fluorine,” Dr Blotevogel said.
“PFAS start to break down at temperatures between 200°C and 700 °C. They go into the gas phase, forming tens or even hundreds of intermediary compounds.
“Most of these intermediaries are short-lived, but some can form even stronger bonds that require temperatures of around 1000°C to fully break down.
“If these PFAS fragments escape into the atmosphere, they can travel vast distances, and many are harmful greenhouse gases.”
The good news is that these intermediaries can be avoided altogether, if treated correctly. Before they can leave the smokestack, they must go through a scrubber, which uses water to capture fluorine emissions so that only steam is emitted.
Global research for a global problem
The facilities that destroy PFAS are held to standards that require the elimination of 99.99 per cent or more of the chemicals. But while scientists have developed a lot of techniques over the years to identify and quantify PFAS in solids and water, more research is needed to analyse gaseous forms.
Dr Blotevogel has been working with colleagues from the Colorado School of Mines, North Carolina State University, University of Notre Dame, the U.S. Environmental Protection Agency, the U.S. Navy, Helmholtz Centre for Environmental Research and York University.
A key focus of these efforts has been to identify the gases formed by existing and emerging PFAS destruction technologies and come up with ways to measure them.
“In order to know how much PFAS has been destroyed, you need to use an arsenal of techniques to measure what’s formed in the solid, liquid and gas phases,” Dr Blotevogel said.
“This presents a real challenge, even with our current methods, requiring multiple lines of evidence, lab experiments and theoretical insights to ensure we can get rid of the desired amount of PFAS.
“Our goal is to have a combination of real-time methods which can tell us what chemicals are being formed during combustion, supported by regular emissions testing with a focus on those harmful intermediaries.”
As countries around the world invest billions of dollars in cleaning up PFAS-contaminated sites, understanding what happens to these chemicals during destruction is becoming just as important as removing them from soil and water.
By gaining new insights and developing novel techniques to analyse airborne byproducts, researchers hope to ensure that solutions designed to protect communities and ecosystems don’t create new problems elsewhere.
“If we do this right, we can destroy PFAS safely and effectively,” Dr Blotevogel said.