By Marianne Metzger
Per- and polyfluoroalkyl substances (referred to as PFAS or forever chemicals) are the latest emerging contaminants being found in drinking water across the United States as well as throughout the world. There are over 4,500 of these chemicals that have been identified and are being used in hundreds of products all over the planet. While these chemicals are not new and have been in use since the 1940s, their prevalence in our drinking water first came to light after the third Unregulated Contaminant Monitoring Rule (UCMR). This rule required monitoring of six perfluorinated compounds from 2013-2016 in public water supplies, to determine the level of occurrence for possible future regulation. With the advancement of testing methods and increased monitoring across the country, significant contamination has been uncovered.
Testing methods
US EPA Method 537, first released in 2009, was designed to test for perfluorinated alkyl acids, which are carbon chains that are fully fluorinated. This method was utilized in the UCRM3 for the detection of six compounds named in the rule. Additionally, this method could also detect another eight compounds that were not included in this rule. Under the UCMR3, the minimum reporting levels for these compounds was in the parts per billion ranges (0.01–0.06 µg/L). At that time, there were much higher detection levels than what current testing methods can now accomplish.
US EPA Method 537.1 (released in 2018) is able to detect both perfluorinated and polyfluorinated alkyl substances, including a total of 18 PFAS compounds. Polyfluorinated compounds are carbon chains that have at least one carbon atom that is not fully fluorinated. This method allows for detection levels in the range of 0.5–6.5 ng/L (part per trillion), so detection levels are much lower, with a majority of labs reporting down to two ng/L (ppt). The latest method introduced is US EPA Method 533, released in 2019, which covers a total of 25 PFAS contaminants. This newer method focuses on shorter chain PFAS, those that have chain lengths of four to 12 carbon atoms (see Table 1). All these methods utilize liquid chromatography with tandem mass spectrometry (LC/MS/MS), an analytical instrument that uses liquid chromatography to separate individual compounds and the mass spectrometers to accurately measure complex mixtures for individual compounds based upon molecular weight (see Image 1).
There are a couple of notable differences between the methods. First, not all the compounds covered in US EPA 537 are included in US EPA Method 533, so both methods may be needed, depending on the PFAS compounds. The biggest difference is the extraction process: US EPA 537 and 537.1 employ a polystyrene divinyl benzene (SDVB) solid-phase extraction (SPE) cartridge while US EPA 533 uses weak anion exchange (WAX) SPE cartridge. Another major difference is that US EPA 533 uses extracted internal standards as part of isotopic dilution quantification, while US EPA 537 methods do not. The use of isotopic dilutions reduces matrix interferences and reduces overall uncertainty that is associated with PFAS analysis. Other differences include the preservative used and the holding times. In US EPA 537, trizma is used, while ammonium acetate is used to preserve 533 samples. Holding time for US EPA 533 allows for 28 days to extraction and another 28 day to run after extraction, while US EPA 537 has a holding time of 14 days to extraction with 28 days to analyze.
Sample collection
With the prevalence of these contaminants in the products that are used in our everyday lives, sample collection is more difficult that just filling up a sample container. It’s possible to inadvertently contaminate a sample simply by what the sample collector is wearing. It’s also important to note that due to these chemicals being measured at such trace levels (typically in the part per trillion range) it doesn’t take much to skew results.
Pre-planning sample site
Before collecting samples, it’s important to do some pre-planning to help ensure the samples accurately reflect actual levels of contamination. If possible, visit the site prior to the sample collection to determine if there are any potential sources of PFAS in close proximity to the sampling point. When visiting the site be on the lookout for PFAS-containing products/materials, such as a deck that may be treated for water resistance or Teflon pans in a kitchen, cosmetic products in a bathroom. If possible, have any PFAS-containing materials removed from the sampling area prior to collection to reduce possible cross-contamination. If there are significant sources of PFAS in the area that cannot be easily removed (such as stain-treated carpet, furniture or decks), consider using a field reagent blank to determine if these sources are contributing to what is detected in the water sample, if anything.
Pre-planning—sampler
For those collecting the sample, there are also many things to consider to properly plan. Specifically, the use of products that may contain PFAS compounds: things like lotions, dental floss, cosmetics and certain clothing and footwear, should be avoided. First, let’s tackle clothing. Any clothes that are stain-resistant or water-resistant are obvious sources of PFAS but consider any clothing that has been washed using a fabric softener, which also may be a source of PFAS. It’s recommended that clothing intended to wear for sampling be washed without fabric softener, perhaps even washed a couple times to fully remove any remaining contaminants. Carefully consider the footwear to be worn, as many are treated to be waterproof and may contain PFAS.
If samples are to be collected outdoors, take care in selecting any sunscreens or insect repellents, as these often contain PFAS chemicals. It is strongly suggested one use something that is all natural or organic. Finally, these samples should be shipped cold; some blue ice or ice packs may contain PFAS, so it’s best to avoid using these when collecting samples. If possible, use a source of wet ice that is known to be PFAS-free. It can be difficult to determine if ice is PFAS-free, so use Ziploc® bags for sample bottles to prevent any possible cross-contamination that could occur. Additionally, when preparing for sampling, do not bring any Teflon tubing or tape that may be used for other field sampling, as well as any notebooks, Sharpie pens, plastic clipboards or binders or any food or drink, except water or hydration drinks.
Field reagent blanks
Field reagent blanks (FRB) are intended to take into account sample handling and the environment surrounding the sampling area that may contribute to cross-contamination of water samples. For FRB samples, two bottles are sent, one an empty sample bottle (preserved as it would be for a regular water sample) and the second bottle filled with lab-grade water that is known to be PFAS-free. Once the sample is collected, prepare the FRB. Take the filled bottle of reagent-grade water and pour into one of the sample bottles; some labs will already have the empty bottle labeled as a field reagent blank, but if it’s not, it should be labeled as such. These samples should always be collected and only analyzed when there is a detection of PFAS in the actual sample. Keep in mind that many labs will typically charge these as a separate sample, thus doubling the cost of analysis. These samples are, however, very helpful in determining accurate results.
Sample collection
Once all the planning is done, collect the sample. Before collecting the sample, wash hands thoroughly with soap and water and put on a new pair of nitrile gloves. If collecting multiple samples, wear a fresh pair of gloves for every sample. If collecting other samples at the same time, collect the PFAS sample first and keep samples separate, as some sample containers may contain Teflon. Remove the aerator from the faucet (if present) and let the water run for one to three minutes, until the temperature stabilizes. Use only bottles provided by the laboratory, as they are clean and preserved with trizma, as written in the testing method. When filling the sample bottle, take care not to touch the top of the bottle to the faucet, which may have Teflon tape or thread paste. It is also important to not set the bottle cap down when filling the bottle; once the sample bottle is filled, cap securely and agitate the bottle to help dissolve the preservative. If using ice that is of unknown quality, place sample bottle in zipper bag to protect from potential cross-contamination; using two bags will add extra protection.
If shipping samples, consider chilling the sample before shipping, as samples need to arrive at the laboratory at 10°C or less; depending on the season and sample location, chilling samples may be required. When shipping samples to a laboratory, plan ahead and check with whatever carrier is to be used so the sample gets shipped overnight the same day the sample is collected. It is best to ship the samples later in the day, keeping them cool before shipping. Make sure to not meet the cutoff for the same-day overnight shipping, as it can vary based upon the carrier and location.
Conclusion
PFAS testing continues to increase as more contamination sources are uncovered from manufacturing plants, military bases, airports and landfills. In addition to being found in municipal water supplies, PFAS is also being found in private wells, wreaking havoc on homeowners. In some instances, homeowners are being supplied bottled water while seeking a more permanent solution. In other areas, they are installing POU treatment equipment, like under-the-counter RO systems. In some cases, polluters are paying for systems while in others, it has largely been left up to the homeowner to seek treatment to protect themselves from contaminated drinking water. There are several variables when testing for PFAS, so understanding the testing is the first step.
About the author
Marianne R. Metzger has spent a majority of her career working for a couple of laboratories in a variety of capacities from Technical Support Representative to Vice President of Sales. Most recently she has joined ResinTech Inc. to head up their new laboratory services division. Metzger has presented at several National and Regional Water Quality Conferences about water-testing topics and has contributed several articles to pertinent trade publications within the water treatment industry. In addition to working for laboratories, she also serves as the Executive Director of the Eastern Water Quality Association, where she assists the Board of Directors in developing membership through education.
About the company
ResinTech Inc. is a globally recognized leader in the field of ion exchange. The company manufactures a broad range of IX resins, carbons and selective adsorbents used in water and wastewater treatment. ResinTech’s world-renowned technical support team uses its proprietary MIST-X technology software to perform complex ion-exchange simulations and the company’s state-of-the-art laboratory offers complete water and resin testing capabilities. The company’s Filterworks Division manufactures POU water filtration cartridges and ultra-pure lab water systems, while a Resource Recovery division provides off-site resin regeneration and RO membrane restoration services.