Explore the different types of PFAS tests and see how they continue to evolve.
Current Environment Protection Agency (EPA) methods for targeted PFAS sample testing can quantify up to 40 PFAS. While PFAS with maximum contamination limits are currently included in these methods, there is great concern for the thousands of potential PFAS that are not screened and quantified. Therefore, the ability for laboratories to provide analytical tests that are complementary to the EPA methods currently offered is of great importance. It would provide a more holistic picture of how much PFAS contamination exists in aqueous, solid, and gas samples.
Additional testing methods for PFAS in aqueous samples
Expanded analyte testing methods
Currently, drinking water methods published by the EPA for the analysis of PFAS only examine 18 analytes (Method 537.1) and 25 analytes (Method 533). These methods use liquid chromatography-tandem mass spectrometry (LC-MS/MS) to analyse samples that are concentrated beforehand via solid phase extraction (SPE). The combination of pre-concentration and LC-MS/MS allows for very precise and accurate measurements of targeted PFAS. To screen more PFAS compounds beyond those included in the EPA methods, it is possible to develop LC-MS/MS methods that quantify 70 total PFAS analytes and more, while keeping the same accuracy and limit-of-detection (LOD) that the EPA methods achieve. Expanded analyte methods can be great tools to provide more specifics about additional types of PFAS in drinking water. However, they still lack the ability to screen for many other PFAS compounds that can potentially be found in a drinking water sample.
Total Organic Fluorine (TOF) PFAS screening
EPA methods for the analysis of PFAS in drinking water can be described as targeted analysis, meaning that only a relatively small set of PFAS are screened and quantified. TOF is a non-specific analysis that produces an estimate of the total fluorine content from fluorine-containing organic substances. Consequently, TOF does not provide specifics about which PFAS are in the sample, nor is it selective to only PFAS. Additionally, the detection limit of TOF is commonly in the parts per billion (ppb) range, which is well above the regulatory limits of some PFAS (e.g., PFOA with 4 parts per trillion (ppt) maximum contamination limit). Therefore, TOF can be seen as a complementary analysis to the EPA drinking water methods when there is concern that PFAS beyond those screened in the EPA method are present.
Total Oxidisable Precursor (TOP) assay
TOP analysis combines the benefits of the broader screening approach seen in TOF with the sensitivity of current EPA methods for PFAS analysis. This method works by oxidising PFAS that are not normally detectable by EPA drinking water methods and converting them to products that are part of the targeted analysis, with a ppt limit of detection. Compared to TOF screening, TOP has a much lower limit of detection and can offer more specificity for what other potential PFAS are in samples. However, because the analytical method is still targeted analysis, TOP analysis can still miss PFAS that are oxidised to products with carbon chains shorter than 4 carbons or greater than 14 carbons. Ultimately, TOP assays are growing in popularity as they give complementary data to traditional EPA methods and help give a bigger picture of whether the EPA method is underreporting the total PFAS concentration in a sample.
Ultra-short chain PFAS analysis
Current EPA methods used for analysis of PFAS in drinking water can only analyse PFAS with carbon chain lengths of four carbons or greater. Ultra-short chain PFAS are not only produced and used in products around the globe, but they can also be common by-products of larger PFAS as they break down in the environment. Ultra-short chain PFAS are of growing concern due to the difficulty of current water treatment systems capturing ultra-short chain PFAS. These systems are meant to capture longer chain PFAS such as perfluorooctanoic acid (PFOA). Additionally, ultra-short chain PFAS are more mobile through the environment than longer chain PFAS, leading to the potential to contaminate water and end-sources more quickly.
This combination of mobility and persistence has led to large observed concentrations of TFA in aqueous samples. For example, a white paper published by Eurofins studied the concentration of ultra-short chain PFAS in juices and drinks, and elevated levels of trifluoroacetic acid (TFA) were found in some orange juices with concentrations as high as 84,000 ppt. Due to the prevalence of ultra-short chain PFAS across a variety of aqueous and solid samples, specific detection methods are being developed to quantify these compounds. The team at DOD Labs has developed an analytical method to test five ultra-short chain PFAS down to 156 ppt.
Soil testing by EPA 1633A
While PFAS in drinking water is concerning due to the direct impact it has on those consuming water, another sample matrix that is becoming increasingly investigated is soil. PFAS can enter the environment in many ways, and a prevalent means is diffusion through soil. While PFAS can diffuse through the soil into our water systems, they can also be retained and accumulate in the soil. Currently, labs can follow EPA Method 1633A to test for 40 PFAS analytes in soil down to the low ppt levels. Performing soil testing can be greatly beneficial. It can be used to screen if certain sites near landfills or facilities that use firefighting foam have large levels of PFAS contamination. It can commonly accumulate in the soil and leach into our water systems. Analysing soil can also help form an understanding of whether agricultural and residential land for growing produce is PFAS-free.
Air testing by other test methods (OTM)
While there are many analytical methods in development to test for PFAS in aqueous and solid samples, PFAS in air emissions are becoming more prevalent. There can be many sources of PFAS in the air, ranging from chemical manufacturing to thermal incineration. There are two methods that are commonly used to sample and quantify PFAS in air: OTM-45 and OTM-50. OTM-45 tests for 50 semi-volatile and condensable PFAS from stationary sources. For example, in a chemical stack from a manufacturing plant that uses PFAS, emissions can be tracked by sub-sampling part of the gas stream and using OTM-45 to analyse for ionic and covalent PFAS. OTM-45 uses a robustly designed sampling system with multiple filters and cold traps to accurately quantify the 50 targeted analytes. It also ensures that minimal breakthrough occurs in the sampling train.
OTM-50 is another sampling method, which tests for 30 specific volatile PFAS analytes that are known industrial chemicals or byproducts of thermal destruction. This method commonly uses canisters under a vacuum to draw in gases from stationary sources over time, and the resulting gas container is then analysed. Overall, OTM-45 and OTM-50, along with other air testing methods, are important tools for quantifying PFAS emissions in air and can be vital for source tracking PFAS contamination in our environment.
DOD Labs (DODlabs.com) is a full-service analytical laboratory specialising in PFAS, water, soil, and air testing. Utilising EPA-validated methodologies, we support environmental monitoring programmes and help organisations meet evolving regulatory requirements with confident, defensible, precise data.
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