Perfluoroalkyl and polyfluoroalkyl substances in the environment: terminology, classification, and origins

Abstract

The primary aim of this article is to provide an overview of perfluoroalkyl and polyfluoroalkyl substances (PFASs) detected in the environment, wildlife, and humans, and recommend clear, specific, and descriptive terminology, names, and acronyms for PFASs. The overarching objective is to unify and harmonize communication on PFASs by offering terminology for use by the global scientific, regulatory, and industrial communities. A particular emphasis is placed on long-chain perfluoroalkyl acids, substances related to the long-chain perfluoroalkyl acids, and substances intended as alternatives to the use of the long-chain perfluoroalkyl acids or their precursors. First, we define PFASs, classify them into various families, and recommend a pragmatic set of common names and acronyms for both the families and their individual members. Terminology related to fluorinated polymers is an important aspect of our classification. Second, we provide a brief description of the 2 main production processes, electrochemical fluorination and telomerization, used for introducing perfluoroalkyl moieties into organic compounds, and we specify the types of byproducts (isomers and homologues) likely to arise in these processes. Third, we show how the principal families of PFASs are interrelated as industrial, environmental, or metabolic precursors or transformation products of one another. We pay particular attention to those PFASs that have the potential to be converted, by abiotic or biotic environmental processes or by human metabolism, into long-chain perfluoroalkyl carboxylic or sulfonic acids, which are currently the focus of regulatory action. The Supplemental Data lists 42 families and subfamilies of PFASs and 268 selected individual compounds, providing recommended names and acronyms, and structural formulas, as well as Chemical Abstracts Service registry numbers.

Figure 1

Synthesis, by electrochemical fluorination, of building blocks leading to PFOS, PFOA, and derivatives.

Figure 2

Synthesis, by telomerization, of building blocks leading to fluorotelomer alcohols.

Figure 3

Perfluoroalkyl carboxylic acids and fluorotelomer (FT) derivatives synthesized from perfluoroalkyl iodides (PFAIs), exemplified for a starting PFAI with 8 C atoms. N.B. Names and acronyms for substance families are indicated. Those for the specific compounds shown can be found in the Supplemental Data.

Figure 4

Classification hierarchy of environmentally relevant perfluoroalkyl and polyfluoroalkyl substances (PFASs).

Figure 5

Aerobic biotransformation pathways for 8:2 fluorotelomer alcohol (8:2 FTOH). Adapted from Wang et al. (2009).

Figure 6

Simplified atmospheric degradation scheme for 8:2 fluorotelomer derivatives. Free-radical and transient molecular intermediates are shown in boxes with a dashed outline, while the starting compounds, the more stable molecular intermediates, and the final products are shown in boxes with a solid outline, their acronyms being indicated in bold type. An arrow on the chart often implies several elementary steps: i.e., certain intermediates are omitted.

Figure 7

Perfluoroalkane sulfonamido derivatives synthesized from perfluoroalkane sulfonyl fluorides (PASFs), exemplified for a starting PASF with 8 C atoms. N.B. Names and acronyms for substance families are indicated. Those for the specific compounds shown can be found in the Supplemental Data.

Figure 8

Transformation pathways for perfluoroalkane sulfonamido derivatives. Adapted from Olsen et al. and Olsen et al. .

Figure 9

Oxetane-based fluorinated polymers.