[Report] Synthetic Report on Understanding Side-Chain Fluoroianted Polymers and Their Life Cycle

By OECD
December 1, 2022

Per- and polyfluoroalkyl substances (PFASs) comprise a class of synthetic compounds that have attracted much public attention since the early 2000s, when the persistence, hazards and ubiquitous occurrence of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) started to be reported and recognized. Since then, research and risk management measures have expanded from these two PFASs to a wide range of PFASs. To date, research has primarily focused on understanding the identity, life cycle, hazard, occurrence and exposure, and risk of non-polymeric PFASs. This has informed development of many risk management measures at the national and international level. To ensure the sound management of the entire class of PFASs, it is equally important to understand polymeric PFASs, which include side-chain fluorinated polymers (SCFPs), fluoropolymers and perfluoropolyethers (Buck et al., 2011; Fiedler et al., 2019). This report summarizes efforts by the OECD/UNEP Global PFC Group, between July 2021 and April 2022, in synthesizing publicly available scientific and technical information on the life cycle of SCFPs, which are polymers with a non-fluorinated polymer backbone and with substructures that meet the OECD PFAS definition (hereafter referred to as “PFAS moieties”) on the side chains. The report provides a comprehensive overview on the chemical identities of SCFPs that have been on the global market, including a non-exhaustive list of 103 SCFPs and 42 monomers (Chapter 2). Based on the generic chemical structures identified, these SCFPs can be categorized according to the types of PFAS moieties present on the side chains, including n:2 fluorotelomers (CnF2n+1CH2CH2−), perfluoroalkanesulfonyl fluoride (PASF)-derivatives [CnF2n+1S(O)2−], perfluoroalkanoyl fluoride (PACF)derivatives [CnF2n+1C(O)−; CnF2n+1CH2−] and perfluoropolyethers (PFPEs; containing a moiety such as −CF2−O−CF2− in the fluorinated side chains), with varied fluorinated carbon chain lengths. Another way of categorizing the SCFPs can be according to the structural repeating units in the polymer backbone, with some simplifications, including acrylates {e.g., [−CH2−CH(C(O)ORF)−]n}, ethoxylates {e.g., [−O−CH2−CH2−]n}, oxetanes {e.g., [−CH2−C(CH3)(CH2OCH2RF)−CH2−O−]n}, silicones {e.g., [−Si(CH2CH2RF)−O−Si(CH2CH2RF)−]n} and urethanes {e.g., [−NH−C(O)−O−]n}, where RF is used to represent a fluorinated carbon chain moiety. In this report, the four chapters on the life cycle of different SCFPs are separated according to structural repeating units in the polymer backbone, specifically: acrylates and urethanes (Chapter 3), oxetanes (Chapter 4), silicones (Chapter 5), and ethoxylates (Chapter 6). In each chapter, the analysis focuses on the production and use of respective SCFPs, presence of other PFASs in the commercial formulations, degradation of SCFPs during use and end-oflife treatment, environmental releases of SCFPs, and other PFASs present in the commercial formulations, followed by a summary of critical knowledge and data gaps and options for a way forward. Chapter 7 focuses on overarching conclusions and recommendations. The key messages of chapters 3-6 are summarized at the start of each chapter. The report comes with an Annex comprising five spreadsheets providing information on: substances identities, use information, PFAS-impurity studies, degradation studies and SCFP release.

Compared to many non-polymeric PFAS, SCFPs and their known and unknown degradation products have received comparatively little attention from scientists and regulators, despite their manifold industrial uses and high volumes, their propensity to release non-polymeric PFAS, and their potential environmental and health impacts. Overall, a wide range of information on the chemical identities of SCFPs, other PFASs present therein, historical and ongoing production and use, degradation of SCFPs, and release of SCFPs and associated non-polymeric PFASs is identified in the public domain and has been synthesized in this report. Despite the many knowledge and data gaps identified, the following can be concluded from the information synthesized here: A wide range of SCFPs have been produced and used in many different applications, with at least some SCFPs at high volumes (up to tens of thousands of tonnes/year). Many non-polymeric PFASs may be present in the commercial SCFP formulations, sometimes at percentage levels. During the production, use and disposal of SCFPs and SCFP-treated products, substantial amounts of SCFPs and associated non-polymeric PFASs may have been released. It is well expected that SCFPs can degrade and form non-polymeric PFASs, including PFCAs and/or PFSAs, in the environment and biota. Thus, many SCFPs are acting as long-term significant sources to the global burden of non-polymeric PFASs including PFCAs and PFSAs. Concerted action by all stakeholders is needed to address SCFPs in an efficient and effective manner. This includes identifying, making funding available and conducting research on those critical knowledge and data gaps that are most relevant for soundly regulating/managing SCFPs in different jurisdictions, building on the gaps identified in the respective chapters above. When addressing critical knowledge and data gaps, to increase efficiency, the following concerted action may be taken: (i) investigating additional information that is available in safety data sheets and patents (but was not actively searched and considered in this analysis due to time and resource constraints); (ii) working with manufacturers to enable open access to information that has been generated by them (and made available to specific regulators), but has not been made publicly available; and (iii) regularly gathering newly available public information and synthesizing them to further increase the knowledge base on SCFPs. In parallel to action on critical knowledge and data gaps, concerted action may be taken to develop, facilitate and promote national and international stewardship programmes and regulatory approaches to reduce emissions of SCFPs and related PFASs and to work toward global elimination, where appropriate and technically feasible.

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