PFAS testing methods, decoded
PFAS results are only valid if the right EPA method was run for your matrix (drinking water, wastewater, soil, etc.). Here's how the main methods differ and how to find a lab accredited to run them.
The methods
Choose for drinking-water PFAS testing when you want a long-established, widely accepted method. Uses external standard calibration (with surrogates). Good default for finished drinking water; pair with Method 533 to cover short-chain PFAS not in 537.1.
Choose for drinking water when you need short-chain PFAS (e.g., PFBA, PFBS, GenX-related) and isotope-dilution data quality. Complements 537.1; many labs run both to capture the full 29-analyte combined list.
Choose for environmental/non-potable matrices: wastewater (NPDES), groundwater/surface water, soil, sediment, biosolids/sewage sludge, landfill leachate, and fish tissue. The current single-method standard for multi-matrix environmental PFAS work.
Largely historical; generally use 537.1 instead. May be referenced in older datasets or specific legacy programs. Not the best choice for new drinking-water projects.
A screening-level option for aqueous environmental samples under RCRA/SW-846 programs. For rigorous, multi-matrix, or compliance-leaning environmental PFAS work, Method 1633 is now the preferred choice.
How to choose the right method
Pick the method by your matrix first, then by data-quality needs. DRINKING WATER (tap, well, finished/treated water): use EPA Method 537.1 (18 PFAS, includes GenX) and/or EPA Method 533 (25 PFAS, short-chain focus, isotope dilution). Together they cover 29 unique PFAS, and both are EPA-approved for compliance monitoring under the PFAS National Primary Drinking Water Regulation. For a home/well drinking-water test, a lab certified for 537.1 and/or 533 is what you want. Method 537 (the original 2009, 14 analytes) is mostly historical -- prefer 537.1. NON-POTABLE / ENVIRONMENTAL samples (wastewater, surface water, groundwater, soil, sediment, biosolids/sludge, landfill leachate, fish tissue): use EPA Method 1633/1633A (40 PFAS, isotope dilution, multi-matrix; finalized Dec 2024 and proposed for CWA approval but not yet nationally mandated). For aqueous-only environmental screening under RCRA/SW-846, Method 8327 (24 PFAS, external standard) exists but is generally superseded by 1633 for serious work. Quick rule: drinking water = 533 + 537.1; everything else (soil/sludge/wastewater/tissue) = 1633.
How to find a PFAS-accredited lab
For DRINKING WATER PFAS testing, use a state-certified drinking-water laboratory: start at EPA's drinking-water lab certification page, which links to each state's certification program and lists of state-certified labs (EPA: 'Contact Information for Certification Programs and Certified Laboratories for Drinking Water'). Confirm the lab holds certification specifically for EPA Method 537.1 and/or 533 for the PFAS analytes you care about. For ENVIRONMENTAL/non-potable PFAS (soil, wastewater, biosolids, tissue), look for a lab accredited under TNI/NELAP for the relevant method (e.g., 1633, 8327) -- search the TNI LAMS (Laboratory Accreditation Management System) by lab name, state, accreditation body, and field of accreditation, and verify the specific PFAS analytes/method are listed in their scope. Always verify (1) the exact method, (2) the matrix, and (3) the specific analytes are on the lab's current accreditation/certification scope before sampling, since scopes change (e.g., many accreditation bodies added PFAS fields of accreditation effective Jan 1, 2025).
- TNI LAMS - National Environmental Laboratory Accreditation Management System (search for NELAP-accredited labs by name, state, accreditation body, and field of accreditation, including PFAS), National searchable database of TNI/NELAP-accredited environmental laboratories; filter for PFAS methods/analytes and matrices.
- NELAP Accreditation Bodies - The NELAC Institute (TNI), List of state and third-party NELAP accreditation bodies; useful for verifying a lab's accrediting authority and scope.
- EPA - Contact Information for Certification Programs and Certified Laboratories for Drinking Water, EPA hub linking to each state's drinking-water lab certification program and its list of state-certified drinking-water labs (use to find labs certified for Methods 537.1/533).
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Sources: https://www.epa.gov/dwanalyticalmethods/comparing-epa-analytical-methods-pfas-drinking-water · https://www.epa.gov/pfas/epa-pfas-drinking-water-laboratory-methods · https://www.epa.gov/dwanalyticalmethods/method-533-determination-and-polyfluoroalkyl-substances-drinking-water-isotope · https://www.epa.gov/sites/default/files/2019-12/documents/method-533-815b19020.pdf · https://www.epa.gov/water-research/epa-drinking-water-research-methods · https://cfpub.epa.gov/si/si_public_file_download.cfm?p_download_id=537290&Lab=NERL · https://www.epa.gov/cwa-methods/cwa-analytical-methods-and-polyfluorinated-alkyl-substances-pfas · https://www.epa.gov/system/files/documents/2024-12/method-1633a-december-5-2024-508-compliant.pdf · https://www.epa.gov/hw-sw846/sw-846-test-method-8327-and-polyfluoroalkyl-substances-pfas-liquid-chromatographytandem · https://www.epa.gov/sites/default/files/2019-06/documents/method_8327_executive_summary.pdf · https://www.epa.gov/dwlabcert/contact-information-certification-programs-and-certified-laboratories-drinking-water · https://lams.nelac-institute.org/search · https://nelac-institute.org/content/NELAP/accred-bodies.php
Information only, not legal or technical advice. Method scopes and regulatory status change; confirm the appropriate method and a lab's current accreditation with the lab and the relevant authority before sampling.
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