Due to growing public concern over the presence of per- and polyfluoroalkyl substances (PFAS) in groundwater, surface water, soils, and other environmental matrices, there is an urgent need to establish standardized analytical methods for PFAS in environmental media. The over-arching goal of this project is to establish a standardized analytical method for PFAS in a variety of environmental matrices including groundwater, surface water, soils, sediment, landfill leachate, municipal wastewater, tissue, and biosolids (i.e., municipal wastewater treatment plant residuals). The work is being conducted as a joint effort by the U.S. Department of Defense (DoD) and the Environmental Protection Agency (EPA) and is designed to provide data on the accuracy and precision of the method in aqueous matrices (wastewater, surface waters, groundwaters, landfill leachate), solids (soil, sediment, biosolids), and fish and clam tissues.
The two primary objectives of this project are to complete a single-laboratory validation study and a multi-laboratory validation study to move towards the goal of establishing a standardized analytical method for PFAS in these additional matrices. The focus of the single- and multiple-laboratory validation studies is to generate the necessary data to document the precision and accuracy of the analytical method for quantitation of PFAS in environmental media.
The draft EPA Office of Water Method 1633: Analysis of Per- and Polyfluoroalkyl Substances (PFAS) in Aqueous, Solid, Biosolids, and Tissue Samples by LC-MS/MS is now available and the results of the single-laboratory validation study are available in the Study Report.
The laboratory validation study will be conducted in two stages as detailed below:
Single-Laboratory Validation Study (Stage 1)
- The first stage is a single-laboratory validation study, which must be completed before embarking on the second stage. Following completion of the single-laboratory validation study, a thorough statistical analysis of the results will be conducted. Based on the analysis of results, and consultation with the commercial laboratory, some adjustments to the standard operating procedure (SOP) for the analytical method may be made. Also, a holding time study will be initiated during Stage 1. This stage of the study is complete.
Multiple-Laboratory Validation Study (Stage 2)
- After any necessary adjustments have been made to the SOP for the analytical method, the multiple-laboratory validation study will be initiated. The multiple-laboratory validation study will include both State and commercial laboratories. The participating commercial laboratories will be accredited by the DoD Environmental Laboratory Accreditation Program (ELAP) for PFAS analysis in aqueous, and/or solid, media. It is expected that a total of ten laboratories will participate in the study. Following completion of the multiple-laboratory validation study, a thorough statistical analysis of the results will be conducted.
Upon completion of both stages of the study, the results of the statistical analysis, and the data validation report will be turned over to EPA so that it can be considered for establishment of a new, standardized method for PFAS.
Single-Laboratory Validation Study
The analytical SOP used for this study was developed in cooperation with chemists at the EPA, the U.S. Navy, and a commercial analytical laboratory, SGS-AXYS in British Columbia, Canada. The method utilizes liquid chromatograph-tandem mass spectrometry (LC-MS/MS) in multiple reaction monitoring mode. The method included sample preparation and sample analysis procedures for aqueous, solid, and tissue matrices.
The study was designed to demonstrate the efficacy of the method using PFAS-spiked environmental samples. In addition to the method SOP, the Study Plan included interim quality assurance and quality control criteria. Extracts for aqueous matrices were prepared via solid-phase extraction (SPE) followed by carbon clean-up. Extracts for soil, sediment, biosolids, and tissue matrices were prepared via solvent extraction, followed by SPE and carbon clean up. Analyte concentrations were determined using either an isotope dilution or extracted internal standard (EIS) quantification schemes; both of which utilize isotopically labeled compounds that are added to the samples prior to extraction. Injection internal standards (IISs), referred to as non-extracted internal standards (NISs) in EPA Method 1633, also were used to determine EIS recoveries and provide a general indicator of overall analytical quality. The method includes 40 target analytes, 24 EIS compounds, and 7 IIS compounds. The isotope dilution and EIS quantification schemes correct the analyte results for the measured recovery. Analytes were quantified and reported as their acid form.
The efficacy of the method was evaluated using a mean matrix spike interim recovery criterion of 70–130% of the spike concentration after correcting for native sample concentrations. Mean matrix spike recoveries for groundwater and surface water, with the exception of NMeFOSAA in surface water, were within criterion. For wastewater, this criterion was met for 37 target analytes, the exceptions being PFDoS, NMeFOSAA, and NEtFOSAA. For landfill leachate, nine analytes did not meet the criterion: PFDoS, NMeFOSAA, ADONA, PFMBA, NFDHA, 9Cl-PF3ONS, PFEESA, and 5:3FTCA.
For soils and sediment, the criterion was met for all 40 analytes. For biosolids, four analytes did not meet the recovery criterion: PFDOS, PFMPA, NFDHA, and 3:3FTCA. For tissues, matrix spike recoveries for PFDOS, NMeFOSE, NEtFOSE, HFPO-DA, 5:3FTCA, and 7:3FTCA were outside the criterion.
The data generated during the study also demonstrated that the interim criteria for the mass calibration, mass calibration verification, initial calibration (ICAL), and initial demonstration of capability can be routinely achieved. The study method requirements for instrument blanks, calibration verifications, instrument sensitivity checks (ISCs), and qualitative standard analyses were consistently met, with few exceptions. Failure to meet the 70–130% EIS recovery criteria proved to be inconsequential with respect to analyte recoveries. Because of this, it is recommended that the acceptance criteria for standards be adjusted accordingly. A criterion of 50–150% is recommended for EIS recoveries in instrument blanks, calibration verifications, ISCs, and qualitative standards.
The initial precision and recovery (IPR), method detection limit (MDL), lower limit of quantitation verification (LOQVER), ongoing precision and recovery (OPR), and matrix spike results were evaluated to determine if any target analytes should be eliminated for a particular matrix type. Tissue matrix sample results indicate that use of this method for the determination of NMeFOSE and NEtFOSE is inaccurate This is demonstrated through the consistently low recoveries of their associated EIS compounds and the low method analyte responses. These analytes, in particular, demonstrated that there is a limitation to the adjustments that can be made from the EIS recovery. When EIS recoveries fell below 10%, method analyte recoveries were over adjusted, resulting in recoveries well over 150%. This suggests that the lower limit of acceptable EIS recoveries should be set near or at 10%. With respect to IIS recoveries, study data indicate IIS recoveries routinely can meet a 50–150% criteria.
Given the success of the method in the Single-Laboratory Validation Study, the EPA published the method as draft EPA Method 1633 in September 2021. The method is now being tested further in a multi-laboratory validation study that will be completed in 2022.
Completion of this effort will provide the DoD and other organizations with much needed standardized analytical methods for determining PFAS concentrations in groundwater, surface water, soils, sediment, landfill leachate, municipal wastewater, tissue, and biosolids.