PFAS (per- and polyfluoroalkyl substances) are a group of substances that are characterised by the presence of at least one per- or polyfluoalkyl chain that is connected to different functional groups[1]. Many PFAS substances play a vital role across a range of application use sectors. However, some members of the PFAS group are characterised by long environmental persistence, the potential for toxic effects on humans and the potential for bioaccumulation. The strength of the C-F bond, one of the strongest chemical bonds, is often a significant contributor to the environmental persistence of PFAS substances.
Typically, a PFAS requires a structure containing a –C n F 2n – (n ≥ 3) chain moiety[2]. Variation in the length of this chain can result in significantly different physicochemical properties that in turn alter the behaviour of the substance in terms of persistence, toxicity and bioaccumulation. Some long-chain PFAS compounds, for example perfluorooctyl sulphonic acid (PFOS) and perfluorooctanoic acid (PFOA), have been recognised as Substances of Very High Concern (SVHC) as a result of their persistence, bioaccumulation and toxicity properties and regulations are already in place to control or limit their use.
The REACH regulation governs the registration, evaluation, authorization and restriction of chemical substances in the EEC. Currently, 5 countries (Norway, Sweden, Denmark, Germany and the Netherlands) are involved in a review of the REACH regulations with a view to restricting the use of PFAS and have provided a new definition of PFAS substances for the purposes of collecting usage data. Under this initial definition, many substances having one or more -CF2- or -CF3 groups would be categorised as being a PFAS. Although this initial definition is not necessarily representative of what will ultimately be used to define the scope of any regulation going forward, the definition is very broad and appears to include substances ranging from polymers such as PTFE to anaesthetics used in medical surgery to volatile HFCs and HFOs (F-Gases) used in refrigeration and medical propellant applications.
The F-Gases used in refrigeration and related sectors are volatile substances that rapidly partition into the atmosphere where they are subject to degradation mechanisms that are not available to the more traditional PFAS substances. The F-Gases are typically broken down in the atmosphere in a period of days to years depending on the specific substance. Atmospheric degradation of most F-Gases leads to carbon dioxide and fluoride, both abundant natural substances. Some may also degrade to some degree to trifluoroacetic acid (TFA), a long-lived substance that is produced both naturally and from anthropogenic activities. The ecological impact of TFA generation from current and projected atmospheric F-Gas degradation has been the subject of a number of published studies and the United Nations Environmental Program (UNEP) judged that the current low concentration of TFA produced by the degradation of F-Gases is not a risk to human health or to the environment[3].
As a group, the F-Gases of commercial interest display a range of relatively short atmospheric lifetimes ranging from a few days to several years. The uses and management of F-Gases are already monitored and controlled in Europe through the European MAC Directive and the F-Gas Regulations 517/2014 [4] and elsewhere by the Kigali amendment to the Montreal Protocol.
Koura supports regulation of PFAS materials on the basis of their persistence, bioaccumulation and ecotoxicity properties and recommends that the volatile HFCs/HFOs be recognised as a distinct group having short atmospheric lifetimes, minimal potential for bioaccumulation and low toxicity. A blanket approach to regulation that takes no account of the variety of properties exhibited within the broad potential PFAS grouping is disproportionate and risks sacrificing the benefits associated with use of many of the substances for little or no environmental or safety benefit.