General Information on How to Interpret Field Blank Data from Water Analysis for PFAS

I had my water tested for PFAS, what is the field blank and what can I make of that information? Hopefully this short article can shed some light on this important quality control measure and what it might mean in regard to your test results.

What is the purpose of a Field Blank:

"A Field Blank (FB) is collected to verify that the sampling environment does not introduce PFAS and cross-contaminate samples during the sampling event. For the analysis of aqueous matrices, the field blank is collected by pouring PFAS-free reagent water that is stored in an acceptable sample container for PFAS sampling into an empty, clean sample container at the sampling site. The sample containers and supplies to process a field blank should be prepared and provided by the laboratory prior to the sampling event. The field blank is treated the same throughout field and laboratory procedures." (Per- and Polyfluoroalkyl Substances (PFAS) Sampling Guidelines for Non-Drinking Water CALIFORNIA STATE WATER QUALITY CONTROL BOARD DIVISION OF WATER QUALITY, September 2020)

"FIELD REAGENT BLANK (FRB) – An aliquot of reagent water that is placed in a sample container in the laboratory and treated as a sample in all respects, including shipment to the sampling site, exposure to sampling site conditions, storage, preservation, and all analytical procedures. The purpose of the FRB is to determine if method analytes or other interferences are present in the field environment." (EPA Method 537.1 for analysis of PFAS in drinking water)

What does EPA Method 537.1 say about Field Blanks:

"8.3. FIELD REAGENT BLANKS (FRB) 8.3.1. A FRB must be handled along with each sample set. The sample set is composed of samples collected from the same sample site and at the same time. At the laboratory, fill the field blank sample bottle with reagent water and preservatives, seal, and ship to the sampling site along with the sample bottles. For each FRB shipped, an empty sample bottle (no preservatives) must also be shipped. At the sampling site, the sampler must open the shipped FRB and pour the preserved reagent water into the empty shipped sample bottle, seal and label this bottle as the FRB. The FRB is shipped back to the laboratory along with the samples and analyzed to ensure that PFAS were not introduced into the sample during sample collection/handling. 8.3.2.The same batch of preservative must be used for the FRBs as for the field samples. 8.3.3. The reagent water used for the FRBs must be initially analyzed for method analytes as a LRB (using the same lot of sample bottles as the field samples) and must meet the LRB criteria in Section 9.3.1 prior to use. This requirement will ensure samples are not being discarded due to contaminated reagent water or sample bottles rather than contamination during sampling." (EPA Method 537.1)

9.3.1. LABORATORY REAGENT BLANK (LRB) – An LRB is required with each extraction batch (Sect. 3.6) to confirm that potential background contaminants are not interfering with the identification or quantitation of method analytes. If more than 20 Field Samples are included in a batch, analyze an LRB for every 20 samples. If the LRB produces a peak within the retention time window of any analyte that would prevent the determination of that analyte, determine the source of contamination and eliminate the interference before processing samples. 537.1-21 Background contamination must be reduced to an acceptable level before proceeding. Background from method analytes or other contaminants that interfere with the measurement of method analytes must be below 1/3 of the MRL (minimum reporting level). Blank contamination is estimated by extrapolation, if the concentration is below the lowest CAL standard. This extrapolation procedure is not allowed for sample results as it may not meet data quality objectives. If the method analytes are detected in the LRB at concentrations equal to or greater than this level, then all data for the problem analyte(s) must be considered invalid for all samples in the extraction batch. Because background contamination is a significant problem for several method analytes, maintaining a historical record of LRB data is highly recommended. (EPA Method 537.1)

What one Laboratory Organization says about the need for Field Blanks in PFAS testing:

"The sole purpose of the field reagent blank, also called field blank, is to provide evidence that the sampling activity itself did not cause PFAS contamination of the sample(s). Since many sampling materials usually taken into the field contain PFAS, and we’re testing samples to reporting limits of 2 ppt or ng/L, the potential to cause contamination during sampling is an important consideration. Materials such as clothing, boots, field notebooks, personal care products, and paper food packaging are all known sources of PFAS. Current PFAS sampling guidance is full of common-sense safeguards as well as restrictive requirements about materials that contain PFAS. They also document the use of field reagent blanks and other field QC samples as an important way to validate the analytical data. This is a fundamental way to help remove any doubts about the testing, proving to yourself, your consumers, and regulators that the field sampling activity did not cause contamination." https://f.hubspotusercontent40.net/hubfs/6835044/ENV_PFAS/FAQ_PFAS_Field%20Reagent%20Blanks_9-11-20.pdf

What EPA Says About Reviewing the Field Blank Data from PFAS analysis:

"Evaluation of field blanks that were prepared from reagent water shown to be clean in the laboratory and using the same lot of containers used for field sample collection can help the reviewer determine the extent of any PFAS contamination during sampling." "Field blank results can help a data reviewer evaluate the impact of potential sources of measurement bias." "If method and instrument blanks meet acceptance criteria but field and trip blanks do not, the data reviewer must decide if the data is usable, how it should be qualified, and/or if resampling is warranted." You should read and understand the entire document referenced here as it is critical to the review of PFAS data: (https://www.epa.gov/sites/default/files/2019-05/documents/technical_brief_pfas_data_review_final_19apr19-508_compliant.pdf)

How can a Laboratory, End Data User or Client Go About Interpreting Test Results from a Field Blank from a PFAS Analysis:

1st: Understand the purpose of the field blank. (see above, the labs definition for the Field Blank or any Quality Assurance Project Plan related to your sampling)

2nd: Review the test results of the field blank analysis, if provided in the test report. Make sure your laboratory does steps 2-7 and follows any requirements for a field blank.

3rd: Check for contamination by comparing the concentrations of PFAS compounds detected in the field blank to the acceptable levels or detection limits specified by the applicable regulatory agency, in the test method used for the analysis or in any QAPP. If concentrations exceed these levels, it suggests contamination during sampling, handling or analysis.

4th: Determine the impact of contamination on the accuracy and reliability of the test results for the actual field samples. If contamination is high or exceeds an established acceptance level in the field blank it may cast doubt on the usability of the test results obtained from the actual field samples collected alongside the field blank.

5th: If the are concerns or questions regarding the interpretation of the results, the analysis or the usability of the test results, seek someone to consult with (e.g., laboratory that analyzed your sample, consultant). They can provide clarification and guidance on the significance of the field blank test result and if there is a need or requirement for corrective action during sampling or at the laboratory to try and eliminate the source of the contamination. Perhaps the associated test results need only be appropriately qualified by the laboratory or there could be a need to recollect your field samples and reanalyze them.

6th: If corrective action is needed (it very likely will be required at the lab), then it is recommended that the laboratory perform root cause analysis as part of the corrective action process. The role of the corrective action taken should again be to eliminate or minimize the source(s) of contamination in future sampling, handling and analysis. You don't want to collect or have more samples analyzed if the source of the contamination id not rectified. The corrective action may require a host of actions be taken to do this. The effectiveness of the corrective action needs to be verified by the laboratory at some point.

7th: The laboratory needs to document not only the field blank results, any data review of the field blank, interpretations, and any corrective actions taken. If it is not documented it was not done, is the age old adage in the lab business.

Hopefully, this simple and short article can give you some insights into what should occur when field blank result for PFAS analysis are evaluated. This knowledge should give you a better understanding of this vital quality control measure and how it relates to your test results.

P.S. - This article is not meant to endorse any given laboratory, but I highly encourage the use of an accredited laboratory for such testing.