What’s in a number? Understanding reported PFAS concentrations

PFAS. These are the “forever chemicals” that everyone, from the Environmental Working Group to the Daily Show, is talking about. PFAS are a large family of per- and polyfluoroalkyl compounds found in fire-fighting foams, frying pans, water and stain-resistant clothing, floss, food-wrappers, and more. These chemicals are rapidly gaining the attention of the general public and regulators across the globe. In January 2020, the PFAS Action Act was passed by the United States (US) House of Representatives (H.R. 535). This act proposed that certain PFAS be classified as hazardous substances. This declaration would lead to an enforceable maximum contaminant level (MCL) for certain PFAS in the US. While PFAS concentrations are not yet broadly regulated nationally in North America, federal guidelines exist in both Canada and the US, and different states have moved to adopt their own, more conservative concentration levels. These levels can be as low as 5.1 parts per trillion (ppt) for perfluorooctanoic acid (PFOA)—or approximately five drops of water in 20 Olympic-sized swimming pools (in California)! What are the implications of creating regulations that enforce numbers that are this low?

If lower concentrations for PFAS are to become enforceable, we will need new and improved laboratory methods to test for these compounds. The US Environmental Protection Agency (EPA) released a new method for analyzing PFAS in drinking water (EPA Method 533) in December 2019, as an update to the previous method available (EPA Method 537.1). EPA Method 533 measures up to 29 PFAS compounds (11 more than EPA Method 537.1) and includes the use of a more rigorous analytical technique (isotope dilution) to make the method more suitable for complex water samples. US EPA laboratory methods go through extensive quality assurance and quality control (QA/QC) review to ensure that the methods are accurate, precise, and robust. The minimum reporting levels presented from the development of the US EPA methods ranged from 0.53 to 14 ppt. As such, reporting levels from the laboratory are very close to many of the proposed guidelines, which means that uncertainties in measurement will have a large impact on the interpretation of the data.

For example, let’s say that you and some friends wanted to measure the thickness of your new phone, but all you had was a ruler with centimeter increments. You and your friends might end up with a large variety of measured thicknesses for this new phone. How would you decide which measurement was the most accurate? How much more confidence would you have if you had a ruler with millimeter increments? This is a potential issue that we may run into with the analysis of PFAS concentrations.

While a total of 29 PFAS can be measured using US EPA methods, PFAS is a huge family of compounds with thousands of different species—including long-chain PFAS (with more carbon molecules) that are not measured by the current analytical methodology. There is evidence that these longer-chain PFAS can be transformed in the environment to the stable forms of PFAS—such as PFOA and perfluorooctane sulfonic acid (PFOS). So, if these longer-chain PFAS are not measured, you might not capture the full PFAS burden at a site in your measurements. What’s more, since PFAS concentrations are sometimes reported as a sum of all analyzed PFAS, it is important to understand which PFAS were analyzed and compare “apples” to “apples.” Analyzing for the full suite recommended by the US EPA will provide a better outlook on the PFAS present at any given site, but sampling programs will need to stay flexible to keep up with future developments in analytical methods and regulations.

As analytical methods improve and the reporting levels decrease, we will start to see more detections of PFAS from environmental water samples. But it’s important to note that there are many different factors within the environment that can introduce bias or background concentrations of PFAS. Since PFAS can be found in many common items, using water-repellent clothing during sampling activities, consuming pre-packaged food items or fast food, applying certain personal care products, or collecting samples with equipment or containers with Teflon components may all impact the integrity of a PFAS sample. Trip, field, and equipment blanks are critical checks to confirm that sampling procedures are not having an impact on the collected samples. There are some general guidance documents available [1][2][3] but consultation with knowledgeable technical staff familiar with PFAS projects will help implement procedures that are properly adjusted when sampling for PFAS.

In short, the key considerations one must make before reacting to a reported PFAS concentration are:

• Review the analytical procedure and QA/QC results from the laboratory
• Understand the number of different PFAS included in the analytical procedure, especially if PFAS is reported as a sum
• Investigate the field sampling procedures and blank sample concentrations to understand if background sources of PFAS have been captured during sampling

Taking the time to consider these factors will facilitate making defensible conclusions about PFAS concentrations.

[1] Eurofins (2019). PFAS Sampling Protocol.

[2] California State Water Quality Control Board (2019). Per- and Polyfluoroalkyl Substances (PFAS) Sampling Guidelines.

[2] Michigan State, Department of Environment, Great Lakes, and Energy. PFAS Sampling Guidance.