Few pollutants perfuse ecosystems like per- and polyfluoroalkyl substances (PFASs). Understanding their environmental and public health impact involves detecting and measuring the concentrations of more than 3,000 chemicals, not all of which are fully identified. There is already monitoring for some PFASs, but this isn’t nearly enough. Advanced sample preparation workflows and instrumentation are expanding the scope of PFAS detection efforts. Carrie McDonough, an environmental chemist at Stony Brook University, who has been collaborating with Agilent to develop workflows for PFAS analysis, explains recent developments that are improving our understanding of these chemicals.
What are PFASs and why are they so concerning?
PFAS is a term that encompasses a wide range of chemicals that all have a perfluorinated carbon chain. These chemicals have been designed to be excellent, stable surfactant type molecules for application in products like cosmetics, non-stick cookware, and fire-extinguishing aqueous film-forming foams. They can also be produced as byproducts during complex, often messy, manufacturing processes.
Environmental release of PFASs can be a problem because they're remarkably persistent. We usually describe a PFAS as not being degradable on a geological timescale, which means that — at least as far as we know — some of these substances just don't go away. PFOA (perfluorooctanoic acid) and PFOS (perfluorooctanesulfonate) are subtypes of PFAS, which are already regulated, but more needs to be done to address the problem.
Can any PFAS be broken down?
Although thousands of types of PFAS, including precursor molecules, can in some ways be degraded, many form similarly persistent perfluorinated final products, or final products that look structurally like PFOA or PFOS.
The persistence of these chemicals is scary, especially with mounting evidence that shows PFASs are clearly a pressing global health issue.
Why has research largely focused on PFOA and PFOS, and how is this changing?
A decade ago, most labs in this space tested for PFOS and PFOA structures. That’s largely because they are among the most persistent and bio-accumulative compounds, meaning they’re widespread in the environment and are going to be prominent in samples, including human blood.
Now, thanks to surrogate methods that allow us to indirectly measure total PFAS concentrations, we know that there are thousands of organic fluorine compounds that are not being captured by the previously narrow focus on PFOS/PFOA and related compounds. There are a lot of methods being developed now that allow labs to target 15 to 40 compounds, or more.
Why is it important to look at these other organic fluorine compounds?
There are a number of reasons. PFOS and PFOA are already regulated and, for the most part, aren’t included in household products anymore. But people are still exposed to PFASs that may accumulate in the body. We don't necessarily know which PFASs people are being exposed to, and that's really important for toxicity risk assessment.
We also need to study these compounds to truly understand PFASs’ environmental impact.
How do we test for these other compounds?
Through non-target screening and advanced analytical techniques. In non-target screening, we're expanding our analytical capabilities beyond just the compounds that have analytical standards. This allows us to look for compounds that we may not have seen before or compounds that are not well described in the literature.
There are multiple ways to do this, all of which involve collecting as much data as possible and then querying for structures of interest, either expected or unexpected.
What type of instruments do you use in your screenings?
Sensitive instruments are important. The quadrupole time of flight mass spectrometer (Q-TOF-MS) is a good example. It provides highly accurate mass measurements while also fragmenting compounds, allowing you to differentiate between isomers and other compounds that might share the same mass. It’s really becoming the workhorse instrument for rapidly analysing complex mixtures.
I see a lot of exciting work happening in the clever and agile development of workflows. I’ve been working with Agilent because their software allows me to modify everything in my lab’s workflows. There's a high learning curve, but we can really make the exact workflow needed for the questions that we’re trying to ask.
Are there tradeoffs to this broader screening?
When you start broadening your compound list, you may start to have an issue with sensitivity to detect specific items. Fortunately, there are a lot of tools that you can use to get around that, things like better sample preparation techniques, iterative analysis, using large volume injection, and more.
However, broad screening is important. While studying chemical oceanography in graduate school, I saw how pollutants move around the globe. I was struck by the fact that pollution is a global issue. Pollutants don't care about boundaries. If anyone is producing persistent pollutants, they're going to end up all over the place — and PFASs are the best example of that.