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PFAS Chemical Lists and Tiered Testing Methods Descriptions

EPA and NIH researchers are working together to use new chemical testing approach methods to test 150 PFAS chemicals. The testing is quickly generating toxicity, toxicokinetic and other types of data to help inform decisions made about the potential health effects of PFAS. 

These new approach methods screen for potential liver, developmental neurotoxicity, developmental toxicity, immunotoxicity, and mitochondrial toxicity as well as help to better predict the disposition and excretion of PFAS from the body. Results from the new approach methods testing will be used to prioritize (tier) PFAS for risk assessment, provide support for gap-filling approaches such as chemical read-across, and to inform further testing. The testing being done is using a combination of innovative methods and high-throughput in vitro assays.

PFAS Chemical Lists

EPA researchers have curated multiple lists of PFAS chemicals that have been developed by the Agency and the international community.  The various PFAS lists are available on the CompTox Chemicals Dashboard. A subset of ~430 PFAS have been commercially procured by the Agency as part of a PFAS chemical library to support the development of analytical methods, environmental monitoring and toxicity testing.

EPA filtered several publicly available PFAS lists to exclude most high (>500) and low (<50) molecular weight compounds, aromatic compounds, metal-containing compounds, and chemicals with a low ratio of fluorine to carbon. There are three PFAS lists, which encompass EPA’s entire PFAS Chemical Library. These lists are published on EPA’s Computational Toxicology Chemicals Dashboard.

  • EPAPFASINV 
    List contains the entire 430 PFAS chemicals in the current inventory found to be soluble in DMSO. 
  • EPAPFAS75S1
    A subset of the 430 PFAS Library, the list contains 74 unique chemicals (75 samples) prioritized for testing by researchers to generate data to inform read-across approaches.
  • EPAPFASINSOL
    List of 43 chemicals procured but found to be insoluble in DMSO at 5mM or lower.  All or some subset of these 43 chemicals may be available in neat form. 

Tiered Testing Methods

EPA and NIH researchers are working together to use new chemical testing approach methods to test 150 PFAS chemicals. The testing will quickly generate toxicity, toxicokinetic and other types of data to help inform decisions made about the potential health effects of PFAS. 

These new approach methods screen for liver, developmental neurotoxicity, developmental toxicity, immunotoxicity, and mitochondrial toxicity as well as to better predict the disposition and excretion of PFAS from the body.

Results from the new approach methods testing can be used to help prioritize (tier) PFAS for risk assessment, provide support for gap-filling approaches such as chemical read-across, and to inform further testing. The testing being done is using a combination of innovative methods and high-throughput in vitro assays detailed in the table below.

Toxicological Response
Assay
Assay Endpoints
Purpose

Hepatotoxicity

3D HepaRG assay

Cell death and transcriptomics

Measure cell death and changes in important biological pathways

Developmental Toxicity

Zebrafish embryo assay

Lethality, hatching status and structural defects

Assess potential teratogenicity

Immunotoxicity

Bioseek Diversity Plus

Protein biomarkers across multiple primary cell types

Measure potential disease and immune responses

Mitochondrial Toxicity

Mitochondrial membrane potential and respiration (HepaRG)

Mitochondrial membrane potential and oxygen consumption

Measure mitochondrial health and function

Developmental Neurotoxicity

Microelectrode array assay (rat primary neurons)

Neuronal electrical activity

Impacts on neuron function

Endocrine Disruption

ACEA real-time cell proliferation assay (T47D)

Cell proliferation

Measure ER activity

General Toxicity

Attagene cis- and trans- Factorial assay (HepG2)

Nuclear receptor and transcription factor activation

Activation of key receptors and transcription factors involved in hepatotoxicity

 

High-throughput transcriptomic assay (multiple cell types)

Cellular mRNA

Measures changes in important biological pathways

High-throughput phenotypic profiling (multiple cell types)

Nuclear, endoplasmic reticulum, nucleoli, golgi, plasma membrane, cytoskeleton, and mitochondria morphology

Changes in cellular organelles and  general morphology

Toxicokinetic Parameter

Assay

Assay Endpoints

Purpose

Intrinsic hepatic clearance

Hepatocyte stability assay (primary human hepatocytes)

Time course metabolism of parent chemical

Measure metabolic breakdown by the liver

Plasma protein binding

Ultracentrifugation assay

Fraction of chemical not bound to plasma protein

Measure amount of free chemical in the blood