The US Environmental Protection Agency (EPA) released on November 2 the final version of its fifth Contaminant Candidate List (CCL 5) that significantly expands the draft CCL’s definition of per- and polyfluoroalkyl substances (PFAS). The new definition, which EPA revised following a year-long public comment and review process, may implicate thousands of individual PFAS chemicals for future regulation under the Safe Drinking Water Act.
In a press release announcing its new action, EPA described its pre-publication release of CCL 5 as “strengthen[ing] EPA’s commitment to protect public health from impacts of PFAS and support[ing] the Agency’s decision-making for potential future regulations of PFAS.” 
The CCL is a list of contaminants not currently subject to national drinking water regulations, but which are known or anticipated to occur in public water systems and may therefore require future regulation under the Safe Drinking Water Act (SDWA). EPA is required to compile and publish a new candidate list every five years. In doing so, the agency must consider data on the occurrence of contaminants in public water systems, consult with the scientific community and solicit feedback from the public. After publishing the CCL, EPA must initiate a separate rulemaking process with further opportunity for public comment if it decides to move forward with regulating a contaminant on the list.
Based on EPA’s review of data and information submitted during the comment period, the agency revised the class definition of PFAS in its draft CCL 5 to add several PFAS subtypes that include thousands of distinct chemicals. While inclusion of a chemical on the CCL is not determinative of future regulation under the SDWA, it is the first step in the regulatory process and inclusion is often a harbinger of future action to restrict or otherwise regulate usage.
EPA’s inclusion of a class definition of PFAS on the CCL 5 is therefore a milestone in the ongoing discourse over appropriate regulation of PFAS chemicals—as a class or individually. Although EPA has stated that this revised and expanded class definition of PFAS is limited to this CCL 5 listing, the action should be considered in the context of other moves that EPA has made in recent years to quickly and assertively regulate PFAS categorically, even as data implicating toxicology, usage and fate and transport is being collected and studied.
This action is consistent with EPA’s broader PFAS strategy, outlined in the “PFAS Strategic Roadmap” published in October 2021, which laid out a comprehensive approach for researching, restricting, and remediating PFAS that extends well beyond EPA’s current regulation of just the two most well-studied PFAS chemicals, perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS).
Those who may be affected by regulation of other PFAS chemicals, including many that are currently not considered harmful to human health or the environment, should stay up to date with these developments and consider how best to prepare for future regulation.
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 In addition to the group of PFAS chemicals, the Final CCL 5 includes the additional substances identified in the 2021 draft CCL list, for a total of 69 chemicals or chemical groups and 12 microbes. The remaining 68 chemicals/chemical groups include two non-PFAS chemical groups (cyanotoxins and disinfection byproducts (DBPs)) and 66 chemicals (including 1,4-dioxane, which EPA had deferred advancing for rulemaking for under CCL 4).