Known as the “eternal chemicals,” per- and polyfluoroalkyl substances (PFAS) are compounds that impact our daily lives. Waterproof, durable and long lasting, PFAS are commonly used to repel water and grease. The chemicals are found in Teflon™ coated pans, fast food wrappers and even in the firefighting industry.
Although PFAS have many useful applications, they have been shown to be highly toxic, causing damage to the human body and ecosystems. And now they are integrated into society.
Even though PFAS are extremely prevalent in today’s environment, there are few ways to clearly identify them. Joe Charbonnet, a researcher and assistant professor in the Department of Civil, Construction, and Environmental Engineering at Iowa State University, is creating a way for scientists around the world to communicate the characteristics of compounds they encounter using l one of the main methods for identifying PFAS – high-resolution mass spectrometry.
“PFAS are present in ScotchGard™, popcorn bags and similar finished surfaces. They all consist of a carbon bonded to multiple fluorine atoms as part of their chemical structure,” Charbonnet said. “This project aims to develop a clearer way for scientists to communicate when they have discovered a new PFAS.These are a big concern in the world right now because they are toxic, they last a long time and they accumulate in our body, making it a very urgent area of research.
There are over 6,000 known types of PFAS. Sometimes the structure of PFAS makes it easy to identify. But sometimes it’s a little more complicated.
“It can be very clear – sometimes scientists can say, ‘I know exactly what the structure of the compound is’ in a test, and those are the easy cases,” Charbonnet said. “But that’s not the case for the most part.”
By using a strictly pure “example” molecule called a certified analytical reference standard, the scientist can test the sampled PFAS against another PFAS that has already been discovered. This is one of the clearest ways to identify a compound with confidence: if the compounds match, it is almost certain that the PFAS the scientist brought is the same compound in the lab. But of the more than 6,000 PFAS in existence, less than 100 of them have a certified exact match to compare. Due to the high reliability but low availability of this comparison method, scientists have developed new ways to identify compounds that appear to be PFAS.
One of the additional methods of identifying a potential PFAS is called high-resolution mass spectrometry, which is a tool used to help determine the structure and qualities of a chemical. Some molecules can be made of the same atoms, but when they are arranged differently, they become different molecules. The high-resolution mass spectrometer separates molecules into smaller pieces, allowing scientists to see which atoms are bound together. Seeing certain atoms bond together gives scientists insight into the structure of the chemical, which can increase their certainty of identifying what type of PFAS it might be, if any.
“By fragmenting these molecules, we can learn what their structure is. And the better the fragmentation, the more certain you can be that it’s the chemical you think it is,” Charbonnet said.
Since mass spectrometry is a very effective method for identifying compounds, it is important to ensure that scientists using this method all record their data in the same way. Charbonnet has created a solution to this exact problem – a framework to help scientists sift through the data they have gathered from mass spectrometry and structure-matching studies. Charbonnet and his colleagues from three continents have devised a chart showing the different results researchers can get from a high-resolution mass spectrometry experiment. The table determines the degree of confidence a scientist can have in their PFAS identification, organized from most confident to least. The more boxes checked, the more confident scientists can be that their proposed PFAS structure is accurate. The first level starts with the clearest method, a successfully matched structure using the reference matching method. Charbonnet compares the ladder to catching a getaway car.
“A level five ID might be the molecular equivalent of saying ‘the bank robber escaped in a blue sedan’, while level one provides an exact molecular structure, something like ‘the bank robber got away’. escaped in a blue 2008 Nissan Sentra with Nevada license plate ANF-53B and a broken left taillight.’ You’re much more likely to catch the bad guy,” Charbonnet said.
Confidence scales like that of Charbonnet have already existed, in particular for spectrometry studies. But when PFAS began to be studied extensively, researchers found gray areas in the rules for characterizing the chemical.
“It’s really important that we speak to each other clearly when we say we’ve found something new or found something mischaracterised,” Charbonnet said. “Using this framework, everyone can understand how confident you are that you’ve found what you’ve found. Because there are some great tools you can use with PFAS, we felt the need to define more clearly the confidence of the identification.
“In the public space, we care a lot about PFAS, especially right now. These are compounds that we know are toxic, we know are harmful to humans and ecosystems, so we are concerned about ways to identify them and where they come from, and how to get rid of them. So by communicating more clearly when we find these compounds, we become more aware of the types of chemicals we are exposed to,” Charbonnet said. “This table helps to specifically clarify the context of PFAS and the strength of your evidence when using these types of tools.”
Charbonnet’s research was published this month in Environmental Science & Technology Letters, a prestigious journal highlighting environmental research.