Investigating PFAS: Key concerns for sampling programs
November 10, 2021
November 10, 2021
What does it take to assess and evaluate these emerging contaminants? Sampling and laboratory requirements are important.
If you’re reading this, you’re probably already aware of per- and polyfluoroalkyl substances (PFAS). Perhaps you’ve read about PFAS in the news or through your work. In any case, I’ll give you a brief primer. As discussed in my previous blog, PFAS are emerging contaminants with beneficial uses in consumer and industrial products but with many drawbacks. Those include their impact on the environment and the health of people, plants, and animals.
PFAS are found in a variety of natural environments. They are increasingly found around military sites, airports, firefighting training facilities, landfills, production facilities, wastewater treatment plants, and in run-off from fire incidents and where biosolids may have been applied. If you know or think that you have a PFAS-impacted site, the first step is to zero in on the likely location of highest impacts. The next step involves conducting a site investigation to establish if PFAS are present at your site through collection and analysis of samples.
This is where it can get complicated. PFAS are found in many commercial products, including the equipment and supplies used to collect environmental samples. Since laboratory-detection limits are so low, it’s important to have a sampling program that produces defensible data and avoids cross-contamination where possible.
If you don’t carefully plan how you sample or what equipment you use to sample, you could end up with cross-contamination and/or biased results. It is also possible to have low-biased data, as some equipment adsorbs PFAS. Both high- and low-biased data would make it tough to assess your site properly and to find suitable next steps, such as remediation.
There are some great resources that can guide you through the dos and don’ts of PFAS sampling, including these two:
Let’s walk through some of the more important concerns when implementing a PFAS sampling program.
PFAS are found in many commercial products, including the equipment and supplies used to collect environmental samples.
When PFAS are contaminants of interest, it’s best to follow standard environmental sampling, with some extra considerations. It’s important to take the time to plan the field program and to follow strict sampling protocols. This may include training for those conducting the sampling, as well as the use of a daily questionnaire to track that sampling personnel are following the protocols put in place.
Because lab analysis of PFAS is conducted on the nanogram scale, removing potential cross-contamination sources is important to avoid biased results.
It’s key to include sampling and field-quality assurance plans in the sampling program as checks for potential cross-contamination and/or false positives. This is done by incorporating quality assurance samples such as field duplicates, field blanks, and equipment blanks.
If the PFAS source at a site is known or suspected, begin by sampling locations upgradient of the source and moving toward the source. Likewise, consider starting at your property limit downgradient of the source (as appropriate) and move upgradient in the direction of the source. The goal is to begin with samples expected to have low-to-no PFAS and work toward areas that have higher concentrations, to limit potential cross-contamination between sampling locations.
Health and safety are still the top priority. Selecting the right personal protective equipment (PPE), such as steel toe boots, is important. If you expect your PPE contains PFAS and there is no alternative, standard practice is to proceed with using it but to be mindful of how it is used—and to make sure it doesn’t contact the samples. Many of the sampling guidance resources available provide a list of PPE that may contain PFAS as well as some options.
When it comes to specific sampling materials and supplies, the rule of thumb is that any material or equipment that contacts the sample medium should be PFAS-free. If you feel uncertain about the potential for PFAS in your materials or equipment, collect and analyze an equipment blank—aka PFAS-free water collected after contact with materials/equipment—to confirm presence or absence of PFAS.
For example, low density polyethylene is an option if the laboratory results show that there are no PFAS in the equipment blank. It’s preferable, however, to use products made from high density polyethylene (HDPE), or others such as stainless steel and PVC.
When it comes to laboratory sample containers for either liquid or solid samples, select polypropylene or HDPE. Make sure that the container is unlined. Many liners used in sampling containers contain Teflon, which can lead to PFAS cross-contamination. Avoid glass containers (because of the adsorption of PFAS), as well as certain plastic bags (because of PFAS introduced during the manufacturing process).
When it comes to decontamination, it is fine to use conventional procedures for cleaning. However, it should also include additional rinsing with PFAS-free water following cleaning with PFAS-free cleaning reagents. Although some sampling guidance resources suggest a methanol cleaning step, not all jurisdictions follow that practice.
Labs can provide PFAS-free water for cleaning. If a large volume of water is needed, costs can multiply. If that’s the case, you can use other sources, such as commercially available deionized water or municipal tap water—if they’re verified as PFAS-free through testing. When decontaminating equipment, it’s important to clean between use but also prior to any use, since you don’t know how well it was cleaned previously.
After sample collection, store samples below 10°C. When selecting materials to keep the samples cold, don’t use the blue ice or chemical gel ice packs. Instead, use conventional ice, double bagged in PFAS-free bags.
If you suspect that samples have high PFAS concentrations, such as when sampling aqueous film-forming foam, clearly identify and segregate these samples during storage and shipping. Flagging high-concentration samples also allows the lab to properly prepare for those samples.
Also, remember to submit samples on time! Analytical laboratories are busy with more and more samples for PFAS testing. The standard extraction time is 14 days. If samples are submitted late, the lab may not have time to extract the sample within the time limit.
Our knowledge of PFAS keeps evolving as we conduct more studies to better understand these contaminants. So, it’s important to stay up to date on changes such as sampling guidance, laboratory methods, and evaluation practices (such as guidelines and standards). The processes or methods that were applied as part of a previous investigation may no longer be the right process or method.
Keep an eye out for other PFAS blogs from our team. We are excited to share our expertise on these emerging contaminants.