An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

EPA and Partners Describe a Chemical Category Prioritization Approach to Select 75 PFAS for Testing using New Approach Methods

Published February 26, 2019

Per- and polyfluoroalkyl substances (PFAS) are a large group of chemicals that are widely used in industrial and consumer applications. Examples include perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), and hexafluoropropylene oxide dimer acid (HFPO–DA, one of several ‘GenX chemicals’). These chemicals have attracted the interest of researchers, regulators, and the public due to their widespread occurrence and persistence in the environment.

There is evidence that exposure to certain PFAS can lead to adverse effects in wildlife and humans. While some PFAS, such as PFOA and PFOS, have extensive amounts of human epidemiological, exposure, and toxicity data, there is little toxicity and exposure information for much of the other chemicals in the group that could be used to inform decisions about their safety.

Traditional approaches to generate toxicity information are resource intensive, so researchers are using new approach methods, including in vitro high-throughput toxicity testing and toxicokinetic testing, to inform PFAS hazard characterization and further testing.

EPA scientists are collaborating with the National Toxicology Program (NTP), headquartered at the National Institute of Environmental Health Sciences (NIEHS), to develop a risk-based approach for conducting toxicity testing for PFAS to inform human health assessments. EPA and NTP/NIEHS published a brief commentary article in Environmental Health Perspectives which describes how the first set of 75 PFAS chemicals were selected for testing.

The overarching goals for this selection focused on two main objectives:

  1. maximizing information to support read-across within structure-based groupings; and
  2. capturing the structural diversity across all the PFAS of interest to EPA.

Factors considered in the selection included:

  • Interest to EPA scientists and regulators based primarily on incidence and/or magnitude of occurrence or potential exposures across the United States; membership within targeted PFAS structural categories;
  • structural diversity;
  • availability of in vivo toxicity data;
  • ability to purchase commercially; and
  • high-throughput screening testability.

The list of the first set of 75 chemicals selected for targeted testing is available here.

The selected PFAS chemicals are currently undergoing testing using the new approach methods including zebrafish, microelectrode arrays, and high-throughput screening. These methods screen chemicals for potential liver toxicity, developmental neurotoxicity, developmental toxicity, immunotoxicity, and mitochondrial toxicity.

The results from high-throughput toxicity testing and toxicokinetic testing will continue to inform subsequent in vivo testing, risk assessment efforts, and the selection of new sets of PFAS for future testing. EPA and NTP/NIEHS are currently selecting an additional 75 PFAS for testing from the expanded PFAS screening library that now contains 430 unique substances.

EPA’s PFAS research efforts are part of the Agency’s PFAS Action Plan that was announced on February 14, 2019. This historic plan responds to extensive public interest and input the EPA has received. The Action Plan represents the first time the EPA has built a national, multi-media, multi-program, research, management, and risk communication plan to address an emerging chemical of concern like PFAS. The Action Plan identifies both short-term solutions for addressing PFAS chemicals and long-term strategies that will help provide the tools and technologies states, tribes, and local communities need to clean up sites and provide clean and safe drinking water to their residents.

More information about EPA’s PFAS research is available here.  Lists of the EPA PFAS chemical library and the 75 PFAS selected for tiered toxicity testing are available on the EPA CompTox Chemicals Dashboard (the entire library is available here and the 75 selected PFAS is available here).