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EPA’s Final Human Health Toxicity Assessment for PFAS GenX Chemicals

EPA’s Final Human Health Toxicity Assessment for PFAS GenX Chemicals Background Image

On October 25, 2021, the Environmental Protection Agency (“EPA”) released a final human health toxicity assessment for two PFAS substances — hexafluoropropylene oxide dimer acid and its ammonium salt — also known as “GenX chemicals.” The assessment, included in EPA’s PFAS Strategic Roadmap as a key action, provides detailed information on the toxicity of the chemicals and is a “step” in establishing a national drinking water health advisory1 for the chemicals.

What is “GenX”?

GenX chemicals are part of a larger group of chemicals referred to as per- and polyfluoroalkyl substances or “PFAS.” GenX is a trade name for the processing aid technology developed by DuPont in 2009 to make fluoropolymers without the use of another PFAS substance known as perfluorooctanoic acid (“PFOA”). DuPont took this step as part of its agreement to phase out and cease production of PFOA, which has been linked to other health issues. Like some other PFAS chemicals, GenX chemicals have been widely used in manufacturing sectors and numerous products, including food packaging, laptops, paint, cleaning products, and nonstick coatings. GenX chemicals have been found in surface water, groundwater, drinking water, and air, and EPA has flagged them for having bio-persistence concerns — meaning they remain in the environment for extended periods of time.

What did EPA’s Assessment Conclude?

EPA’s toxicity assessment concludes that oral ingestion of GenX chemicals through drinking water has potential adverse health effects on the hepatic, hematological, renal, reproductive, and immune systems. It also notes that oral exposure to GenX chemicals has been linked to liver and pancreatic cancer. As a result of the assessment, EPA established chronic and subchronic reference doses (“RfDs”) for GenX chemicals.

An RfD is “an estimate of the concentration or dose of a substance . . . to which a human population (including sensitive subgroups) can be exposed that is likely to be without an appreciable risk of deleterious effects during a lifetime.”1 An RfD is not a standard itself, but a piece of information that can be combined with specific exposure information to inform health-based national standards, clean-up levels at local sites, and non-regulatory advisory levels.2 RfDs can be used to develop health protective levels based on oral exposure for chemicals in drinking water, ambient water, and soil. For example, RfDs can be combined with exposure information in risk assessments which can lead to the development of regulatory standards for drinking water under the Safe Drinking Water Act (SDWA), as well as human health water quality criteria for permitting discharges into ambient waters or to assess the potential risk of pollutants in biosolids under the Clean Water Act (CWA).

RfDs are also used in risk assessments under other laws including the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) and the Resource Conservation and Recovery Act (RCRA) to develop cleanup levels for contaminated soil and groundwater.

For GenX chemicals, the chronic RfD is 0.000003 mg/kg/day and for subchronic is it is 0.00003 mg/kg/day. EPA previously published toxicity assessments for three other PFAS: PFOA, perfluorooctane sulfonate (“PFOS”), and perfluorobutane sulfonic acid (“PFBS”). The final chronic RfD for GenX chemicals is approximately 10 times lower than for PFOA or PFOS. However, EPA has noted that it is currently reevaluating toxicity information for these two chemicals. In comparison to PFBS, which EPA recently finalized a toxicity assessment for, the chronic RfD for GenX chemicals is 100 times lower.


EPA’s efforts to tackle PFAS continue to unfold rapidly. Although EPA’s toxicity assessment is not a binding regulation, nor is it enforceable, it demonstrates yet one more step towards EPA’s plan of setting regulatory standards and levels that include GenX chemicals. EPA’s assessment can be used to develop standards under a wide range of statutes, and EPA has noted that it plans to develop drinking water health advisories for PFAS chemicals that have final EPA toxicity assessments, including for GenX chemicals and PFBS, in Spring 2022.

Once EPA has set an enforceable regulatory standard, the agency will then have enforcement power to pursue those companies that it believes have contributed to GenX environmental contamination. EPA can proceed with enforcement actions and pursue responsible parties for remediation costs, which can be significant. Businesses that have some exposure to GenX chemicals, whether through the use of goods containing the chemicals or through its operations, should pay close attention to the toxicity assessment and, in particular, EPA’s RfDs.

The PFAS Taskforce

V&E’s PFAS Taskforce is dedicated to helping our clients navigate the emerging and complex law and regulations that may be used to address PFAS and related chemicals. By actively tracking and analyzing the different federal and state regulatory approaches to addressing PFAS — whether in water, groundwater, soil, and air — and engaging with the evolving scientific understanding of PFAS substances, we can help our clients build short- and long-term strategies to address potential liability, remediation, and litigation concerns regarding these emerging contaminants. Drawing upon the significant capabilities in our cross-office environmental team, V&E’s PFAS Taskforce is on hand to provide practical and tailored guidance for our clients as they prepare for the shifting PFAS landscape.

1 A health advisory provides information on contaminants, such as PFAS, that are known to occur, or are anticipated to occur, in drinking water and that cause human health effects. Although EPA’s health advisories are non-enforceable, they do provide technical information to state agencies and public health officials on the health effects of contaminated drinking water alongside analytical methodologies and the potential technologies available to treat such contamination.

2 EPA, Human Health Toxicity Values for Hexafluoropropylene Oxide (HFPO) Dimer Acid and Its Ammonium Salt (CASRN 13252-13-6 and CASRN 62037-80-3) at 30 (Oct. 2021). 

3 See generally EPA, Technical Fact Sheet: Human Health Toxicity Assessment for GenX Chemicals (Oct. 2021).

This information is provided by Vinson & Elkins LLP for educational and informational purposes only and is not intended, nor should it be construed, as legal advice.