In a press release published on November 14, 2018, the U.S. Environmental Protection Agency (EPA) informed that it is “seeking public input on draft toxicity assessments for GenX chemicals and perfluorobutane sulfonic acid (PFBS).” ‘GenX chemicals’ stands collectively for the hexafluoropropylene oxide (HFPO) dimer acid (CAS 13252-13-6) and its ammonium salt (CAS 62037-80-3). The draft toxicity assessment for PFBS (CAS 375-73-5) also covers a related compound, potassium perfluorobutane sulfonate (CAS 29420-49-3).

The fact sheet concomitantly released by EPA explains that “GenX is a trade name for a technology that is used to make high-performance fluoropolymers (e.g., some non-stick coatings) without the use of perfluorooctanoic acid” (PFOA, CAS 335-67-1), whereas “PFBS is a replacement chemical for PFOS” (perfluorooctanesulfonate, CAS 1763-23-1). Although both PFOA and PFOS “have been voluntarily phased out by industry,” they are “still persistent in the environment” (FPF reported). The fact sheet further informs that “GenX chemicals have been found in surface water, groundwater, finished drinking water, rainwater, and air emissions in some areas,” while “PFBS has been identified in the environment and consumer products, including surface water, wastewater, drinking water, dust, carpeting and carpet cleaners, floor wax, and food packaging.” Therefore, “people can be potentially exposed to GenX chemicals and PFBS through a number of different pathways, including drinking water, inhaling air, and consuming food wrapped in PFAS [(per- and polyfluoroalkyl substances)] containing products” (FPF reported). EPA noted, however, that food packaging falls under the responsibility of the U.S. Food and Drug Administration (FDA).

With regard to health effects, EPA summarized that for GenX chemicals “animal studies have shown health effects in the kidney, blood, immune system, developing fetus, and especially in the liver following oral exposure.” Further, “the data are suggestive of cancer.” For PFBS, “animal studies have shown health effect on the thyroid, reproductive organs and tissues, developing fetus, and kidney following oral exposure.” EPA further stated that “the thyroid and kidney are particularly sensitive to PFBS” and that “the data are inadequate to evaluate cancer.”

Based on the collected data, EPA proposed to set the chronic oral reference dose (RfD) at 0.01 mg/kg-day for PFBS and at 0.00008 mg/kg-day for GenX chemicals. For both PFOA and PFOS, chronic RfDs are set at 0.00002 mg/kg-day. Thus, this preliminary assessment suggests that PFBS “is less toxic than GenX chemicals, PFOA, and PFOS,” and that GenX chemicals “are less toxic than PFOA and PFOS.” EPA cautioned, however, that “these draft values may change in response to public comments.” Further, EPA pointed out that “toxicity is only one piece of information that public officials consider when determining whether there is a risk to public health,” as “other factors, such as exposure, must also be considered.”

Public comments on these draft toxicity assessments will be accepted for 60 days after publication of the Federal Register Notice already submitted by EPA.

Read more

EPA (November 14, 2018). “EPA seeks public input on draft toxicity assessments for PFAS chemicals.

EPA (November 14, 2018). “GenX and PFBS draft toxicity assessments.

EPA (November 14, 2018). “Fact sheet: Draft toxicity assessments for GenX chemicals and PFBS.(pdf)

Vince Winkel (November 14, 2018). “GenX: Exposure study results released in Wilmington.WHQR

Steve DeVane (November 14, 2018). “EPA seeks input on draft GenX guidelines.The Fayetteville Observer

Kelly Franklin and Lisa Martin Jenkins (November 15, 2018). “EPA releases draft toxicological profiles for two PFASs.Chemical Watch

Anna Reade (November 16, 2018). “EPA finds replacements for toxic ‘Teflon’ chemicals toxic.EcoWatch


EPA (November 2018). “Human health toxicity values for hexafluoropropylene oxide (HFPO) dimer acid and its ammonium salt (CASRN 13252-13-6 and CASRN 62037-80-3) also known as ‘GenX chemicals.’(pdf)

EPA (November 2018). “Human health toxicity values for perfluorobutane sulfonic acid (CASRN 375-73-5) and related compound potassium perfluorobutane sulfonate (CASRN 29420-49-3).(pdf)

Federal Register (November 2018). “Request for public review and comment: Draft human toxicity assessments for hexafluorpropylene oxide dimer acid and its ammonium salt (GenX chemicals) and for perfluorobutane sulfonic acid (PFBS) and related compound potassium perfluorobutane sulfonate.” Prepublication of Federal Register Notice EPA-HQ-OW-2018-0614. (pdf)