On June 9, 2021, the Organisation for Economic Co-operation and Development (OECD) published a report that revises terminology for per- and polyfluoroalkyl substances (PFASs), gives practical recommendations on how to use that terminology, and recognizes open questions that warrant future consideration.

In 2011, Buck et al. were the first to publish an article that gave a clear structural definition on PFAS covering 200 individual substances. Two recent developments have motivated the OECD/UNEP Global PFC Group to review the PFASs terminology, including the definition of Buck et al.: 1) In 2018, the OECD/UNEP Global PFC Group compiled a new list of PFASs potentially present on the global market comprising 4730 CAS numbers. Some of these substances lack a -CF3 group in their molecular structure, which, according to the definition by Buck et al., is a characteristic of PFAS. And, 2) advancements of non-targeted analytical techniques have made identification of many unknown substances possible.

Therefore, the OECD now recommends the following broadened definition: “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.” With that definition, the OECD aims to recognize the diversity of PFASs comprising chemicals with many different molecular structures and properties. At the same time, this definition should be easy to implement, allowing even non-experts to distinguish PFASs and non-PFASs. To assist stakeholders, the report also “provides practical guidance to governments and other stakeholders on how to use the PFAS terminology” and “a standardized approach for systematic characterization of different PFASs based on molecular structural traits that will allow stakeholders to make their own categorization in a coherent and consistent manner.”

The last chapter of the report highlights four major areas that warrant further development including “a centralized PFAS nomenclature database/platform” and “further work on the characterization and reporting of polymers.” There are ongoing projects concerning PFAS including a publicly available database covering 742 toxicity studies on 29 PFASs published in April 2021 (FPF reported). In addition, a discussion concerning the polymer registration under REACH is currently ongoing (FPF reported and here).



OECD (2021). “Reconciling Terminology of the Universe of Per- and Polyfluoroalkyl Substances: Recommendations and Practical Guidance.” OECD Series on Risk Management (pdf).

Buck et al. (2011). ”Perfluoroalkyl and polyfluoroalkyl substances in the environment: Terminology, classification, and origins.” Integrated Environmental Assessment and Management.