U.S. EPA WORKING DEFINITION FOR PFAS EXCLUDES TFA
The U.S. EPA has recently published its PFAS strategic roadmap [1] and National PFAS testing strategy [2]. This uses a working definition that provides focus on PFAS of concern based on their persistence and potential for presence in the environment and human exposure. According to the EPA, trifluoroacetic acid (TFA) is a well-studied non-PFAS. TFA is found naturally - over 200 million tonnes are in the oceans and it is also formed as by-product of the degradation of some HFCs and HFOs.
A range of PFAS working definitions are being used by different organisations for a specific activity according to their specific needs by combining this general definition of PFASs with additional considerations (see PFAS – A RANGE OF DEFINITIONS ARE BEING USED BY DIFFERENT ORGANISATIONS - Fluorocarbons).
The U.S. EPA uses a narrower definition than the OECD or the REACH restriction proposal call for evidence, to develop a starting list of PFAS, to be used in developing its national PFAS testing strategy.
“The chemical substances were filtered for those that met the working definition of a PFAS used by EPA’s Office of Pollution Prevention and Toxics (OPPT), which administers TSCA (Toxic Substances Control Act): a structure that contains the unit R-CF2-CF(R')(R''), where R, R', and R'' do not equal "H" and the carbon-carbon bond is saturated (note: branching, heteroatoms, and cyclic structures are included).
The working definition identifies chemicals with at least two adjacent carbon atoms, where one carbon is fully fluorinated and the other is at least partially fluorinated. This working definition provides focus on PFAS of concern based on their persistence and potential for presence in the environment and human exposure. For example, chemicals with (-CF2-) that are not (-CF3) are expected to degrade in the environment and most substances with only one terminal carbon (-CF3) are expected to degrade to trifluoroacetic acid, which is a well-studied non-PFAS.” [3]
Explanatory Note: Some F-gases with a terminal CF3 group do form TFA (HFC-125) when they breakdown, or only form a very low yield of TFA (most HFOs and HCFOs). See Published evidence supports very low yields of TFA from most HFOs and HCFOs - Fluorocarbons
References
[1] available at PFAS Strategic Roadmap: EPA’s Commitments to Action 2021—2024
[2] Identification of Candidate Per- and Poly-fluoroalkyl Substances (PFAS) for Testing October 2021, U.S. Environmental Protection Agency, available at National PFAS Testing Strategy (epa.gov)
[3] see page 5 of reference 2