Most experts agreed that “all PFAS” should not be grouped together

An expert panel was convened to provide insight and guidance on per- and polyfluoroalkyl substances (PFAS) grouping for the purposes of protecting human health from drinking water exposures, and how risks to PFAS mixtures should be assessed. Most experts agreed that “all PFAS” should not be grouped together; persistence alone is not sufficient for grouping PFAS for the purposes of assessing human health risk, and that the definition of appropriate subgroups can only be defined on a case-by-case manner. Most panellists agreed that it is inappropriate to assume equal toxicity/potency across the diverse class of PFAS. The results of the expert panel discussions and findings are reported in a July 2022 paper “Grouping of PFAS for human health risk assessment: Findings from an independent panel of experts” [1].

Independent experts compiled information to address: how PFAS should be defined for purposes of human health risk assessment and regulatory decision making; how PFAS should be grouped to inform potential mixtures effects; and what information is most technically sound and feasible to inform potential human health risks to exposure to PFAS in drinking water.

Most expert panellists agreed that the USEPA TSCA [2] definition and approach for grouping PFAS is pragmatic and generally is a good starting place for human health risk assessment. However, some panellists were concerned about the exclusion of some PFAS categories in the TSCA definition. The USEPA working definition eliminates many of the pharmaceutical and agricultural chemicals that would be otherwise defined as a PFAS based on the OECD (2021) definition [3], due to the formation of trifluoracetic acid as a degradation product. USEPA references trifluoracetic acid [TFA] as “a well-studied non PFAS”, although TFA belongs to the PFAS family according to the OECD definition.

The expert panel was asked whether and how PFAS mixtures in drinking water should be assessed for human health risks – as a single homogenous group or divided into different subgroups. Experts generally agreed that use of a broad definition for PFAS (i.e., “all PFAS”) should not be considered as a group for the purposes of risk assessment. Persistence was generally not deemed scientifically valid way to group “all PFAS” for the purposes of assessing human health risk specifically for drinking water exposures. It was acknowledged that toxicity, bioaccumulation, toxicokinetics, and exposure profiles would vary among PFAS and therefore, those characteristics should be considered when assessing human health risk. Grouping all PFAS together as “persistent” was not supported as practical nor appropriate for assessing human health.

In conclusion, most experts agreed that “all PFAS” should not be grouped together, persistence alone is not sufficient for grouping PFAS for the purposes of assessing human health risk, that subgroups are appropriate, and that the nature and definition of the subgroups can only be defined on a situation-dependent and case-by-case manner. No single grouping strategy was agreed on that would be sufficient for all regulatory or public health risk assessment purposes. Most panellists agreed that it is inappropriate to assume equal toxicity/potency across the diverse class of PFAS for human health risk assessment.

Explanatory note: The experts also discussed in detail how mixtures of PFAS should be assessed for human health effects. For substances relevant to EFCTC, TFA is a breakdown product of some HFCs and HFOs, and TFA has distinct chemical, physical and biological properties when compared to other longer chain PFAS, and it has been extensively studied, including its potential effects due to the use and emissions of HFCs and HFOs.

 

References 

[1] Grouping of PFAS for human health risk assessment: Findings from an independent panel of experts, J.K. Anderson, R.W. Brecher, I.T. Cousins, J. DeWitt, H. Fiedler, K. Kannan, C.R. Kirman, J. Lipscomb, B. Priestly, R. Schoeny, J. Seed, M. Verner, S.M. Hays, Regulatory Toxicology and Pharmacology 134 (2022) 105226, https://doi.org/10.1016/j.yrtph.2022.105226, open access paper.

[2] US EPA, National PFAS Testing Strategy: Identification of Candidate Per- and Polyfluoroalkyl Substances (PFAS) for Testing.

[3] OECD, 2021. Reconciling Terminology of the Universe of Per- and Polyfluoroalkyl Substances: Recommendations and Practical Guidance, OECD Publishing, Paris, Risk Management No 61, 2021