Behind the paper: fast-tracking the fight against “forever chemicals” in drinking water

We talk to Mr. Deepak Timalsina, a predoctoral graduate student of Bioanalytical Chemistry in the Department of Chemistry, and Dr. Michael Zhuo Wang, a tenured Professor and doctoral research advisor in the Department of Pharmaceutical Chemistry, School of Pharmacy, at the University of Kansas about their recently published PLOS Water paper “Achieving sub-part per trillion trace level PFAS quantification in drinking water using an optimized fast flow solid-phase extraction and UPLC-MS/MS method“

What motivated you to explore the topic and decide on this research question?

PFAS has become one of the most urgent environmental and public health concerns of our time. These man-made synthetic chemicals are found in everyday products such as non-stick cookware, clothes, textiles, food wrappers, and drinking water. Unfortunately, most PFAS do not break down in the environment and hence accumulate in the ecosystem, including soil, animals, and humans, hence dubbed as “forever chemicals”. Multiple studies have found that nearly all people in the United States have PFAS in their blood and nearly half of the drinking water systems in the United States have detectable PFAS. Regulatory agencies and public health authorities such as the US EPA, WHO, and EU have now set strict limits on PFAS in drinking water. However, existing methods to analyze PFAS are too slow and do not have enough sensitivity to detect them at the extremely low levels in drinking water. In this context, we had a simple yet urgent question: how can we fast-track a rapid and sensitive method for detecting trace-level PFAS in drinking water in our fight against these harmful “forever chemicals”?

Could you talk us through how you designed your study?

To tackle those challenges, we focused on how we can efficiently concentrate and extract the low-concentration PFAS from drinking water. Our strategy relied on two key analytical technologies: Fast-Flow Solid Phase Extraction (SPE) and Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry (UPLC-MS/MS). We systematically evaluated and optimized critical sample preparation steps, such as concentration via nitrogen drying, syringe filtration, elution volume, and most importantly, SPE flow rate. We tested whether we could increase the SPE flow rate and drastically reduce the sample processing time from hours to minutes. We also evaluated the larger starting sample volume to push the detection limit even lower, while maintaining analytical performance criteria. Ultimately, we validated our optimized Fast-Flow SPE workflow to detect and quantify forty PFAS compounds in real-world tap water samples.

Did you encounter any challenges during your study?

Detecting PFAS at this low level is like finding a few grains of sand in the Olympic-size swimming pool. The UPLC-MS/MS system is a highly sensitive analytical instrument widely used for environmental chemical monitoring and pharmaceutical drug analysis, but it still has a long way from sub-part per trillion (sub-ppt) trace-level PFAS detection. Hence preconcentration of a large volume of a water sample becomes necessary, but it can also lead to concentration of interfering molecules and low extraction recovery of PFAS compounds. Substantial loss of some neutral PFAS compounds during the solvent drying process is another roadblock that requires us to further investigate the cause. Another unexpected challenge is the realization that the lower limit of quantification for the optimized Fast-Flow SPE method is not determined by preconcentration or extraction recovery, rather by the presence of background trace-level PFAS in the blank pure water obtained from commercial vendors.    

What did you find most striking or surprising about your results?

The most surprising finding is just how fast the optimized method became without sacrificing the analytical performance. A 500-mL sample, if processed using the standard method, requires 100 min to just load the sample onto SPE cartridge, but it can now be processed in 6-8 minutes. A 4-L sample, which would have taken 800 minutes, can now take only about 60 minutes to process. With the optimized Fast-Flow SPE method, we achieved striking analytical detection limit down to sub-ppt levels (as low as 0.01 ppt) for some PFAS, which is one of the lowest reported in the literature. Another worrying surprise is that many regulated PFAS compounds are found in our tap water, attesting to the gravity of the PFAS environmental crisis and how it can hit close to home.  

How could this research be used, and who might benefit?

We hope our optimized Fast-Flow SPE workflow will be an enabling tool for:

• Regulatory and monitoring agencies: As stricter regulations are proposed,  simple, reliable, and cost-effective analytical methods are required to implement the new PFAS limits in drinking water.
• Water treatment facilities: Fast, sensitive, and affordable PFAS detection will reduce the cost of compliance and support effective remediation plans.
• Public health officials: Fast, sensitive, and affordable PFAS detection will expand PFAS monitoring and remediation, ultimately benefiting the general public.
• Researchers studying PFAS: This method serves as the basis for expanding to environmental water samples, e.g., river, lake, and ground water, to allow trace-level PFAS detection to help understand how PFAS moves through the ecosystem.

What Further questions remain?

Collecting and shipping large quantities of water from source to analytical labs are still time-consuming and costly. Alternatively, water samples can be collected and the contained PFAS adsorbed to light-weight portable devices on the spot with negligible loss. Then these devices can be conveniently shipped to labs for PFAS analysis. Questions remain as to whether these loss-free adsorbents and cleverly engineered portable devices can be developed.

Why did you choose PLOS Water as a venue for your article?

PLOS Water focuses on the global water challenges and open access science with a worldwide readership and audience. PFAS contamination is not limited to one place, rather, it is a worldwide issue affecting the global ecosystem and public health. Publishing in an open-access journal ensures that scientists, policymakers, water utilities, and other concerned stakeholders have access to our findings, which is critical when research has a direct impact on environmental monitoring and public health. By publishing in PLOS Water with open access, we are perfectly positioned to fast-track our discoveries to assist in the fight against the monumental PFAS crisis.

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