Turn on the tap and you would hope that the water coming out is safe for use and consumption. But what if it isn’t? What about the hazards we either aren’t looking for or that evade detection and treatment? Per- and polyfluoroalkyl substances (PFAS) are one such family of chemicals. Widely prized for their surfactant and flame-retardant properties, PFAS came into common use in the 1950s in a host of everyday items. However, evidence has shown these so-called “legacy” PFAS are potentially harmful to health. Analysts have consequently been looking to detect them in consumer products such as drinking water, and manufacturers have moved away from their use. It doesn’t, however, change the fact that we need substances with the properties offered by these chemicals. Consequently, so-called GenX chemicals that fulfill these roles have come into use despite many unanswered questions around their safety.
We spoke to Dr Katherine C. Hyland from SCIEX, about sources of PFAS that are contaminating our water system, the hazards posed to consumers and the outlook for detection and prevention strategies.
Karen Steward (KS): How do PFAS enter drinking water? If they are in water sources, such as reservoirs, rivers and aquifers, are they harmful to the environment too?
Katherine Hyland (KH): Let’s talk about point sources vs. diffuse sources. Point sources are discrete entries of pollutants into the environment from an identifiable conveyance, such as a wastewater outfall or an industrial dumping site. Diffuse, or nonpoint source, is a large, often combined, entry of pollutants that is harder to identify as a single-entry point. This includes runoff or atmospheric deposition. PFAS enter the water supply through many point and diffuse sources, making it challenging to pinpoint a “primary” entry mode, so let’s cover a few examples.
PFAS are constituents of a wide range of products such as paper products, packaging, textiles, waterproofing materials, Teflon manufacturing, industrial surfactants, protective coatings and firefighting foams (or aqueous film-forming foam [AFFF]). From these uses, PFAS are likely to end up in waste dumps, sewage water and the general environment. Wastewater effluent represents a major point source of PFAS into the environment. A PFAS cycle could look something like this: One might sit on a stain-resistant textile sofa. The PFAS from that sofa would transfer to one’s pants. Washing those pants would carry the chemicals into the wastewater stream.
It is also conceivable that solid waste, such as food packaging or textiles, might end up in a landfill. Landfill leachate is a diffuse pollutant source which happens when precipitation onto the exposed landfill washes into the environment, carrying with it the residues and contaminants from all the landfilled items.
In the case of AFFF, it has been very well documented that firefighting training operations, common to military bases, often result in copious amounts of the firefighting foams laden with PFAS draining into the surrounding soil, surface water, or seeping into groundwater systems. This is an extreme example of a point source of PFAS entry. Yet, these instances represent only a few possible examples of routes of PFAS into water sources and the environment.
While it has long been known that the “legacy” PFAS such as perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are tremendously persistent as well as bioaccumulative/bioconcentrating, it seems that the field is continuously evolving to learn more about the actual harmful effects that are posed. For example, PFOS is highly toxic (acute) to honeybees, it has been detected in tissues of wild birds and fish, in surface water and sediment, in wastewater treatment plant effluent, sewage sludge and in landfill leachate.
KS: Do PFAS that enter the drinking water system reach the consumer or do the water treatment processes remove these substances?
KH: Conventional drinking water or wastewater treatment does not remove PFAS from the water stream. No doubt, there are select treatment processes that will remove PFAS but there are issues even with these. For example, filtration through granular activated carbon (GAC) during some drinking water treatment has been shown to remove long-chain PFAS. Yet, the possibility for desorption or breakthrough, particularly of short-chain species, is a concern, as is regeneration or disposal of used GAC.
The media continues to refer to these substances as “forever chemicals” due to their extreme level of persistence. PFAS are highly unlikely to be broken down or degraded in the environment by either chemical or biological pathways. During engineered treatment processes, this becomes important because traditional wastewater treatment plants (WWTPs) operate using biological secondary treatment. Live bacteria are cultivated in the treatment train which serve to biologically breakdown organic carbon constituents in the water. The biological “sludge” is then clarified out of the water. Because of the resistance to breakdown that PFAS exhibit, they will not be broken down in the sludge treatment and can continue along the treatment train. This means water effluent from WWTPs represents significant sources of PFAS to the environment. But, there’s even more to consider: PFAS compounds can sorb to the solid phase of the sludge during treatment and clarification. Ultimately, this means that those compounds can be removed from the liquid effluent stream but remain unchanged in the solid waste stream (biosolids sludge).
KS: What techniques are best suited to detecting PFAS in drinking water? Are there currently any unmet needs in PFAS detection?
KH: When PFAS analysis first became a necessary task, challenges faced were not unlike those for any new analyte or compound class. There was a lack of commercially available standards and instrumentation of the time was not very sensitive. However, over the last few decades, huge advances in technology and application strategies have been realized. Today, there are numerous native and isotopically labeled PFAS standards commercially available and the sensitivity of modern mass spectrometers has lowered detection limits down into the ng/L range and lower.
Today, a suite of different PFAS classes beyond just PFOS and PFOA exists. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) techniques can multiplex these and large panels of other PFAS analytes. While these techniques are considered the gold standard for PFAS analysis, it must now be expanded and built upon to encompass the latest analytical needs for the expanded understanding of PFAS as a broad suite of potentially hundreds or thousands of individual analytes. The use of triple quadrupole MS techniques, which primarily leverage multiple reaction monitoring (MRM) detection strategies, achieves incomparable sensitivity, selectivity, accuracy and precision in quantitative analyses of PFAS.
Other techniques are occasionally employed to answer specific questions. For example, particle-induced gamma-ray emission spectroscopy to measure the total fluorine (F) in an environmental sample. Knowing the mass balance difference between the total fluorine present in the sample and how much of the known, targeted PFAS comprise that total fluorine profile can help point to PFAS that may be present that are not already known, characterized or included in targeted methods.
When we consider these “other” PFAS chemicals beyond the panel of “legacy” analytes, we should also realize that high-resolution MS (HRMS) techniques such as liquid chromatography quadrupole time-of-flight tandem mass spectrometry (LC-QTOF-MS/MS) are also a critical tool in characterizing novel PFAS structures and compound classes present in the environment. HRMS has led researchers to discover hundreds or even thousands of new PFAS species that could be impacting humans and the environment.
KS: What are the biggest challenges faced by analysts in the accurate detection and quantification of PFAS? Are any of these challenges specific to detection in drinking water?
KH: The challenges of today’s PFAS analysts are different from the challenges of the past. As instrumentation becomes more sensitive, and lower and lower detection limits become the goal, background PFAS levels due to environmental ubiquity represent a major analytical obstacle. What this means is that the presence of PFAS is so universal in products in our environment that being able to measure the low levels that are relevant becomes challenging. Sample contamination during preparation and analysis or originating from analytical instrumentation can vastly impact the ability to achieve sensitive and accurate quantification. However, in recognition of this, several analytical procedures have become common practice for the LC-MS/MS analysis of PFAS. For instance, all polytetrafluoroethylene (PTFE) components of the LC system are typically swapped with alternative stainless-steel components to avoid leaching of PFAS from the PTFE. There is also the addition of a small reverse-phase delay column upstream of the LC autosampler, which will retard any PFAS coming from the LC system away from the analytical peak, allowing the analytical peak to be consistently and accurately integrated during quantitative data processing.
Additionally, there is this increasing awareness of the novel, uncharacterized, and precursor PFAS that fall outside of the original legacy species. This presents a new challenge, in that MRM based analytical methods are inherently targeted methods, meaning that it is only possible to detect the analytes for which you have a pre-established method developed. Employing HRMS is one solution to this challenge, which allows for the detection of unknown species. Leveraging the ability to detect high resolution and high accuracy precursor and fragment masses also allows researchers to characterize the structures and properties to define and study new PFAS.
KS: Where do you feel the responsibility lies to clean up PFAS environmental contamination and how could it best be done?
KH: I hope that PFAS analysis techniques will take a forensic perspective to accurately pinpoint the source of PFAS contamination and those associated with it. With current information making us wary of PFAS impact on humans, animals and the ecosystem, it is the responsibility of corporations to be transparent and responsible with how they treat the chemicals and products they produce.
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Dr Katherine Hyland was speaking to Dr Karen Steward, Science Writer for Technology Networks.