Table 2.

Definitions of PFAS included in analysis

Definition	Formal definition verbatim from organization	Informal interpretation
Buck et al. (2011)	“Aliphatic substances containing one or more C atoms on which all the H substituents present in the nonfluorinated analogues from which they are notionally derived have been replaced by F atoms, in such a manner that PFASs contain the perfluoroalkyl moiety CnF2n+1–.”	Compounds that contain at least one carbon atom that is bound to three fluorine atoms (-CF3). The structure must be saturated with no double or triple bonds (the only definition with this restriction).
OECD (2018)	“PFASs, including perfluorocarbons, that contain a perfluoroalkyl moiety with three or more carbons (i.e. –CnF2n–, n ≥ 3) or a perfluoroalkylether moiety with two or more carbons (i.e. –CnF2nOCmF2m−, n and m ≥ 1).”	Compounds with at least three carbons on which all of the hydrogens have been replaced by a fluorine atom, so as to form a three-carbon unit with the subunits of (-CF2-). It also includes compounds with an oxygen placed between two carbon atoms on which all of the hydrogens have been replaced by a fluorine atom, so as to form a carbon-oxygen-carbon unit with the subunits (-CF2OCF2-)
OECD (2021)	“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.”	Compounds containing at least one carbon that has three fluorine atoms attached (–CF3). Also includes compounds that have at least one carbon attached to two fluorine atoms (-CF2-). In both cases, the carbon atom cannot be attached to a hydrogen, chlorine, or bromine atom. It still includes compounds whose carbon-fluorine units are attached together by an oxygen (-CF2OCF2-). These structures can contain rings or be arranged in a chain
Glüge et al. (2020)	In addition to substances containing CnF2n+1, where n ≥ 1, it also “includes (i) substances where a perfluorocarbon chain is connected with functional groups on both ends, (ii) aromatic substances that have perfluoroalkyl moieties on the side chains, and (iii) fluorinated cycloaliphatic substances. Additionally, “polymeric PFAS with the –CF2– moiety and non-polymeric PFAS with the –CF2–CF2– moiety … [excluding] non-polymeric substances that only contain a –CF3 or –CF2– moiety, with the exception of perfluoroalkylethers and per- and polyfluoroalkylether-based substances. For these two PFAS groups, substances with a –CF2OCF2– or –CF2OCFHCF2– moiety are also included.”	Does not include compounds with a single –CF2– or –CF3, but can include compounds with two or more –CF2– or –CF3 groups. Compounds can contain rings or be arranged in a chain. Also includes compounds that contain two carbon atoms next to each other, each containing at least two fluorine atoms (–CF2–CF2–). The two fluorinated carbons can be attached together by an oxygen atom (–CF2OCF2– or –CF2OCFHCF2–).
TURA (2021a)	“Those PFAS that contain a perfluoroalkyl moiety with three or more carbons (e.g., –CnF2n–, n ≥ 3; or CF3–CnF2n–, n ≥ 2) or a perfluoroalkylether moiety with two or more carbons (e.g., –CnF2nOCmF2m− or –CnF2nOCmFm–, n and m ≥ 1).”	Key to this definition is that the compound must contain a string of at least three carbon atoms, each containing two or more fluorine atoms. Perfluoroalkylethers are compounds that contain two –CF2– groups connected by an oxygen. Includes linear, branched, cyclic compounds and aromatic rings
TURA (2021b)	“Certain PFAS not otherwise listed includes those PFAS that contain a perfluoroalkyl moiety with three or more carbons (e.g., –CnF2n–, n ≥ 3; or CF3–CnF2n–, n ≥ 2) or a perfluoroalkylether moiety with two or more carbons (e.g., –CnF2nOCmF2m− or –CnF2nOCmFm, n and m ≥ 1), wherein for the example structures shown the dash (−) is not a bond to a hydrogen and may represent a straight or branched structure, that are not otherwise listed.”	Clarifies that in TURA 2021a the (−) does not include a bond to hydrogen
U.S. EPA OPPT (2021)	“… 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).”	Compounds that contain a string of two adjacent carbon atoms, with one of them containing at least two fluorine atoms and the other containing at least one fluorine atom, and neither carbon bound to a hydrogen
≥1 Fully Fluorinated Carbona	Organic chemicals containing “at least one fully fluorinated carbon atom.”	A compound with at least one carbon on which all of the hydrogen atoms have been replaced by fluorine atoms. The number of bonds on the carbon is not specified
All Organofluorineb	All organic compounds containing at least one fluorine atom should be classified as PFAS.	Any compound whose structure contains a carbon attached to a fluorine atom

^aAuthorities whose legislation defines PFAS as a class of fluorinated organic chemicals containing at least one fully fluorinated carbon atom (WA, VT, ME, CA, NDAA).

^bNGOs that advocate for broader definitions of PFAS to include all organofluorines.