A class of chemicals known as per- and polyfluoroalkyl substances (PFAS) are ubiquitous in the environment. Found in products such as nonstick pans and waterproof apparel, they often end up in wastewater and break down slowly, if at all. More than 15,000 of the synthetic substances exist, and exposure to them can adversely affect human health and the environment.

Diana Aga, Ph.D., director of the University at Buffalo’s Research and Education in eNergy, Environment and Water (RENEW) Institute, and graduate student Karla Ríos-Bonilla study these chemicals and their effects. Together with collaborators, they published a study supported in part by NIEHS showing that exposure to a mixture of PFAS chemicals was more toxic than exposure to just one. Now, they are working to develop a test able to quantify short and ultrashort PFAS, which are challenging to detect in environmental samples using conventional analytical methods.

“The new approach allows us to analyze for a wider range of PFAS using one method, which is typically achieved using multiple techniques, to gain a comprehensive picture of the different PFAS in environmental samples,” Aga said.

The traditional method

The molecular structure of PFAS includes carbon chains in which fluorine atoms have replaced hydrogen atoms. Some PFAS have long chains, whereas others have short and ultrashort ones.

Researchers typically use a technique called liquid chromatography with tandem mass spectrometry (LC-MS/MS) to separate and identify PFAS in a sample. According to Ríos-Bonilla, separation of PFAS is achieved by introducing a concentrated sample into a column filled with a material that interacts with the different PFAS forms at varying strengths. A mixture of water and organic solvent, which is capable of dissolving other substances, flows through the column, moving the various PFAS out of the column at different rates, and depending on their physicochemical properties, results in their separation.

She says the technique wastes a lot of solvent and takes a long time to analyze. Most importantly, short and ultrashort chain PFAS do not significantly interact with the material in the column, and they are neither separated nor detected by LC-MS.

This is a significant limitation of current methods that could have implications for human health, says Aga, because PFAS with chain lengths of less than four carbons are the ones likely to escape granular-activated carbon filters used for drinking water treatment.

“Short and ultrashort chain PFAS just go through the liquid chromatography column and don't interact with what's inside,” said Ríos-Bonilla. “That's why you cannot separate or see them.”

A new technique

To solve the problem, Ríos-Bonilla, Aga, and their collaborator Luis Colón, Ph.D., of the University at Buffalo, are using substances with different properties to separate the PFAS. Specifically, they are using supercritical fluid chromatography (SFC) carbon dioxide that behaves like a hybrid between a gas and a liquid. The process takes less time and uses less solvent, making it a more efficient and environmentally friendly alternative to the conventional LC-MS/MS. Ideally, scientists could use LC-MS/MS and SFC-MS/MS as complementary techniques to separate a wide range of PFAS in environmental and biological samples.

“That's the goal,” said Ríos-Bonilla. “If I'm looking at a wastewater sample, the comprehensive analysis would allow me to see many more PFAS that are not currently being monitored.”

Future applications

If Ríos-Bonilla can perfect the technique, the scientific community could eventually apply it more widely to identify more than just PFAS.

“I would like to see the SFC-MS/MS technique used more as a routine analysis for PFAS, but also for antibiotics, pharmaceuticals, and antivirals,” Ríos-Bonilla said. “It could allow more communities to assess the contaminants in their water or be more aware of the variety of chemicals affecting them.”