How PFAS are defined by different organisations

In July 2021, five countries published their intention to propose a REACH restriction for PFAS based on the assessment of the information collected. The PFAS Registry of Intentions (RoI) by Denmark, Germany, the Netherlands, Norway and Sweden provided a definition of PFAS that they are using to gather additional data during the second consultation. Most fluorinated gases are covered by the PFAS definition used, but its interpretation has some ambiguities that will no doubt be resolved as the RoI process continues and the final scope of the restriction process becomes clearer.  However, for the RoI data collection it is assumed that all fluorinated gases (with at least a CF₂ group) are included to ensure more complete data. See the press release EFCTC ready to continue assisting in building robust and comprehensive data sets for the PFAS Registry of Intentions for a REACH restriction.

The RoI definition is slightly different to that used by the OECD in its latest guidelines about PFAS terminology and other PFAS definitions also are being used for different purposes.

PFAS Registry of Intentions (RoI) Scope Definition

For the scope of the current consultation the following has been selected:

X-(-CF2-)_n-X’ with n ≥ 1 and X, X’ not being H (thus including X-CF₃) meaning fluorinated substances that contain at least one aliphatic carbon atom that is both, saturated and fully fluorinated, i.e. any chemical with at least one perfluorinated methyl group (-CF₃) or at least one perfluorinated methylene group (-CF₂-), including branched fluoroalkyl groups and substances containing ether linkages, fluoropolymers and side chain fluorinated polymers.

BUT for the RoI data collection it is assumed that all fluorinated gases (with at least a CF₂ group) are included to ensure more complete data.

OECD Revised PFAS Definition

The OECD has issued new guidance document about PFAS, Reconciling Terminology of the Universe of Per- and Polyfluoroalkyl Substances: Recommendations and Practical Guidance. This report summarizes recent efforts by the OECD/UNEP Global PFC Group between June 2018 and

March 2021 in reviewing the universe and terminology of per- and polyfluoroalkyl substances (PFASs) to provide recommendations and practical guidance to all stakeholders with regard to the terminology of PFASs. It has a revised PFAS definition.

The intention of the revision of the PFAS definition is not to expand the PFAS universe, but to comprehensively reflect it. More concretely, the rationale behind the revision is to have a general PFAS definition that is coherent and consistent across compounds from the chemical structure point of view and is easily implementable for distinguishing between PFASs and non-PFASs, also by non-experts.

PFASs are defined as fluorinated substances that contain at least one fully fluorinated methyl or methylene carbon atom (without any H/Cl/Br/I atom attached to it), i.e. with a few noted exceptions, any chemical with at least a perfluorinated methyl group (–CF₃) or a perfluorinated methylene group (–CF₂–) is a PFAS.

This definition excludes several fluorinated gases such as R-32, R-23, CF3I, R-152a, R-22.

The OECD guideline notes that “As PFASs are a chemical class with diverse molecular structures and physical, chemical and biological properties, it is highly recommended that such diversity be properly recognized and communicated in a clear, specific and descriptive manner. The term “PFASs” is a broad, general, non-specific term, which does not inform whether a compound is harmful or not, but only communicates that the compounds under this term share the same trait for having a fully fluorinated methyl or methylene carbon moiety.”

Other PFAS definitions also are being used for different purposes

According to the OECD guidelines, individual users may define their own PFAS working scope for a specific activity according to their specific needs by combining this general definition of PFASs with additional considerations (e.g. specific properties, use areas). For example, the US Interstate Technology & Regulatory Council (ITRC) used a working scope of “CnF2n+1”(n>2) in making its own PFAS fact sheets.

The US EPA has a provisional (not official) definition for proposed PFAS Reporting Rule under TSCA, which is “For the purposes of this proposed action, the structural definition of PFAS includes per- and polyfluorinated substances that structurally contain the unit R-(CF₂)-C(F)(R′)R″. Both the CF₂ and CF moieties are saturated carbons and none of the R groups (R, R′ or R″) can be hydrogen. It should be noted that this structural definition of PFAS is a working definition which has been used by EPA's Office of Pollution Prevention and Toxics when identifying PFAS on the TSCA Inventory. This definition may not be identical to other definitions of PFAS used within EPA and/or other organizations.”