26 October 2021

PFAS Strategic Roadmap: EPA Releases Human Health Toxicity Assessment for “GenX” PFAS Chemicals

The U.S. Environmental Protection Agency (EPA or Agency) has released its final human health toxicity assessments for a subgroup of PFAS chemicals known as GenX (i.e., hexafluoropropylene oxide dimer acid and its ammonium salt). GenX is the trade name for a set of chemicals intended to replace another PFAS chemical called PFOA (perfluorooctanoic acid).

EPA’s health toxicity assessment provides hazard identification and dose-response information and derives chronic and subchronic oral reference doses (RfD) for exposure to GenX. A reference dose is the Agency’s estimate of the amount of a chemical a person can ingest daily over a lifetime (the chronic reference dose) or less (the subchronic reference dose) that is unlikely to cause adverse human health effects.

The final subchronic reference dose for GenX published by EPA is 0.00003 (3 x 10-5) mg/kg-day, and the final chronic reference dose is 0.000003 (3 x 10-6) mg/kg-day. EPA’s chronic reference dose for GenX is considerably lower than its proposed number (from November 2018) and those published for other PFAS compounds:

PFAS Chemical Chronic Reference Dose (mg/kg-day)
GenX (final RfD, 2021) 0.000003
GenX (proposed RfD, 2018) 0.00008
PFBS (final RfD, 2021) 0.0003
PFOA (final RfD, 2016) 0.00002
PFOS (final RfD, 2016) 0.00002


Note, however, that the Agency is reevaluating its human health toxicity assessments for both PFOS and PFOA and may lower those numbers in a future publication. Also, as described in EPA’s PFAS Strategic Roadmap, the Agency will use this GenX human health toxicity assessment to develop future health advisories — nonenforceable drinking water standards that can be used to help Tribal, state, and local governments assess human health effects in those communities. EPA has said that it anticipates publishing health advisories for GenEx by spring 2022.