Pace® has been conducting sampling of environmental matrices for PFAS testing since 2013. Today, we employ more than 40 field sampling teams around the country. In addition, Pace® is a US EPA-approved UCMR laboratory and has sampled and tested thousands of samples during UCMR 3, 4, and 5 You could say we know a thing or two about sampling for emerging contaminants like PFAS.
While we and our clients always strive to avoid cross-contamination caused during sampling, especially when sampling for PFAS, this issue has taken on renewed relevance with the finalization of the National Primary Drinking Water Regulations (NPDWR) for PFAS. With federally enforceable Maximum Contaminant Levels (MCLs) set as low as 4 parts per trillion (ppt) and non-enforceable Maximum Contaminant Level Goals (MCLGs) set at zero, it’s more important than ever to avoid sample cross-contamination.
But is cross-contamination as much of an issue as it’s made out to be? Earlier this year, I gave a presentation on how to avoid sample cross-contamination. In this webinar, I also shared some discoveries from my analysis of the data from our PFAS laboratories. I’ll hit a few of the highlights in this post, but the webinar is also available on-demand.
Watch: Is PFAS Sample Cross-Contamination Caused by Sampling?
What is Sample Cross-Contamination?
Cross-contamination refers to the unintentional contamination of environmental samples that can occur in the field during sample collection due to the presence of PFAS in many materials we wear and use during sampling.
Given the prevalence of PFAS in the consumer goods we use every day, contamination can come from any number of sources, including:
- Sharpies used to mark samples or collection documents
- Waterproof gear worn during sampling
- Sunscreen
- Insect repellant
- Cosmetics
- Laundry detergents and softeners used on clothes worn during sampling
- Precipitation, e.g., rain, during sampling, especially if downwind from a PFAS source
- Sampling equipment, e.g., fluorinated plastics or Teflon® tape
- Water used to clean equipment
- Waterproof notebooks
- Packaging from food consumed or carried on-site
How is Sample Cross-Contamination Assessed?
Sampling cross-contamination is assessed using blanks. The most common type of blank is the Field Reagent Blank (FRB), also referred to as a Field Blank (FB). However, three types of blanks may be used, so we’ll cover all of them here.
Field Reagent Blank (FRB)/ Field Blank (FB) – These terms are synonymous. FRBs or FBs are a sample of PFAS-free water that is opened and poured into a sample container at the sampling site. The purpose of this type of blank is to check for potential contamination that typically occurs during the sampling process. As mentioned, this is the most common type of blank and is used to validate that field sampling did not cause cross-contamination.
Equipment Blank - This is a sample of PFAS-free water that is collected while doing the final rinse of sampling equipment after washing before and between sampling points to check for potential contamination from the equipment itself.
Trip Blank – This sample is used to validate that samples and containers were not cross-contaminated enroute to the field and the laboratory. Laboratory PFAS-free water in a PFAS container accompanies the containers during transportation to the site and back again to the laboratory but is never opened or exposed to the sampling environment.
Are Blanks Required?
.png?width=398&height=398&name=Cross%20Contamination%20(5).png)
The answer to this question isn’t always a clear yes or no. Field reagent blanks are written into the protocols for the EPA’s PFAS drinking water test methods – 533 and 537.1. For example, Section 8.4 of EPA Method 533 states: Each sample set must include an FRB. A sample set is defined as samples collected from the same site and at the same time. The same lot of preservative must be used for the FRBs as for the field samples.
However, the fact that field blanks are written into a method doesn’t necessarily mean field blanks are always required or warranted. Remember, field blanks only determine whether detected contamination is likely to have come from the sampling process itself. If no PFAS are detected in an actual sample, running a field blank that also returns a non-detect isn’t going to provide any value.
Due to the relatively low prevalence of cross-contamination (see the section below on “What the Data Shows”) and because PFAS sample analysis is one of the more expensive tests, we often suggest our clients limit the frequency of field blanks in their first round of sampling. Of course, this assumes every effort is made to avoid sample cross-contamination. If you are concerned about lax field sampling protocols, including a field blank in the first round may be warranted.
As always, remember to check with your state authorities to see what is required. Many states have specific sampling protocols and may require field blanks. Here are links to a few of them: New Hampshire, New Jersey, California, New York, Michigan.
As is the case for all field QC practices, we suggest clients carefully consider all ramifications when developing their sampling plans. Ultimately, all environmental sampling and training is meant to minimize cross-contamination regardless of the contaminants of concern and those practices are also applicable to PFAS.
What the Data Shows
To assess how much of an issue cross-contamination is for our clients, I went back to data from a recent 6-month period. I chose to use data that did not come from projects initiated by the EPA’s Fifth Unregulated Compound Monitoring Program (UCMR 5). UCMR 5 has a reporting limit of 4 ppt, whereas our non-UCMR 5 projects are typically 2 ppt. This resulted in a total of 14,074 data points, of which 9186 were analyzed using EPA 533 and 4,888 using EPA 537.1.
The data show that our clients and our Pace® samplers are good at minimizing cross-contamination. Out of 14,074 data points, only 111 (0.79%) showed detections at or above the reporting limit of 2 ppt. Here’s a breakdown of the compounds in those 111 samples:
- PFPeA – 6%
- PFOS – 5%
- PFOA – 8%
- PFHxS – 7%
- PFBS – 7%
- PFBA – 8%
- 6:2 FTS – 34%
- PFNA - <1%
- HDPO-DA - <1%
PFOA has federally enforceable limits, so let’s put that one into real numbers. Nine of the FRBs had detections for PFOA – a pretty low hit rate. At 34%, 6:2 FTS is a bit of an outlier, but it’s a common compound in products like laundry detergent and not yet regulated.
Have Questions?
We fielded more questions than I expected in the webinar, so clearly, people are interested in this topic. I’ve also responded personally to a dozen or so inquiries we didn’t get a chance to answer during the session. In a future post, I’ll share some of that Q&A. In the meantime, if you have specific questions about sample cross-contamination, don’t hesitate to reach out to us.
