PFAS Risk Assessment For PFHxA and PFDA – Impact On Business

Apr 24, 2023 | Environmental, PFAS, Toxic Tort

Last year, we wrote regarding the EPA’s efforts to publish a comprehensive PFAS risk assessment for the PFAS chemical PFHxS, which they did in February 2022 in draft form. In April 2022, the EPA finalized its study and also published a draft toxicological review for PFDA. The findings and dose response information contained in the toxicity assessments are important for businesses with current or legacy uses of PFHxA and PFDA to pay attention to, and PFHxA and PFDA considerations must enter into the equation for any compliance programs in order to avoid significant financial disruption.

PFAS Risk Assessment for PFHxA

The EPA’s PFHxA toxicity assessment provides a great deal of discussion regarding the available scientific literature and information  to support the EPA’s ultimate conclusions as to toxicity and a Reference Dose for PFHxA.

The EPA examined human epidemiological studies and animal studies. The human epidemiological studies provided the EPA with only a “limited” ability to draw conclusions as to PFHxA as a causative agent for several human health issues. The limited number of studies, the low confidence interval stated in the studies, and the inability to measure exposure to PFHxA in the studies were all factors that inhibited the EPA in its assessment. The EPA found the animal studies (which were limited to oral ingestion studies) to be more persuasive, and it concluded that the studies support a conclusion that PFHxA can cause hepatic, developmental, hematopoietic, and endocrine effects in humans with proper levels of exposure. For all other effects considered, including carcinogenicity, the EPA determined that the available information was inadequate or inconclusive to find correlative impact.

The toxicity assessment for PFHxA concludes that the evidence supports a reference dose of 5×10^-4 milligrams per kilogram bodyweight per day (mg/kg-day), which represents the most that an adult could consumer of PFHxA over a lifetime without the risk of health effects (the EPA defines a reference dose as follows: “a reference dose is an estimate of the amount of a chemical a person can ingest daily over a lifetime (chronic RfD) or less (subchronic RfD) that is unlikely to lead to adverse health effects in humans.”). This is much less stringent than the EPA’s GenX RfD (3×10^-6 mg/kg-day), stricter than the RfD for PFBA (0.001 mg/kg-day) and similar to the RfD for PFBS (3×10^-4 mg/kg-day).

PFAS Risk Assessment for PFDA

The draft IRIS for PFDA concludes that PFDA can cause liver, immune, developmental and reproductive effects in humans, but there is inadequate information to assess carcinogenicity. Similar to the IRIS for PFHxS, the EPA found much of the human studies to date to be inconclusive standing alone, but supplemented with existing animal studies, the EPA was able to draw its conclusions. Based on the studies examined, the EPA’s draft IRIS  sets an overall lifetime organ-specific reference dose (osRfD) of 4×10^-10 milligrams per kilogram bodyweight per day (mg/kg-day) for PFDA.

Public comment on the draft IRIS will be open until June 9, 2023.

Impact of PFAS Risk Assessment On Businesses

It should be noted that the PFAS risk assessments for PFHxA and PFDA was conducted under the EPA’s Integrated Risk Information System (IRIS) Program, which has undertaken to assess and publish five different PFAS toxicological assessments – PFHxA, PFBA, PFHxS, PFNA, and PFDA. The IRIS assessments could factor in to the EPA’s site remediation, waterway remediation, and Toxic Substances Control Act (TSCA) chemicals review.

The immediate and short-term impact of the PFHxA and PFDA PFAS toxicity assessments are that they are merely harbingers of much more significant regulatory action, enforcement action and litigation. The EPA’s toxicity assessments are not binding regulations; however, the EPA fully intends to utilize the toxicity assessments as support for conclusions that it will soon draw with respect to drinking water regulations, CERCLA designations, RCRA designations, and a number of other regulatory frameworks under which the EPA is addressing PFAS issues. The risk assessments also provide other federal level agencies with scientific support and references for potential future regulatory action for exposure sources other than drinking water.


Companies with current or legacy uses of PFHxA or PFDA (or any of the PFAS types being evaluated under the IRIS program) must understand that the non-binding nature of the risk assessments cannot simply be ignored. The results in the assessments will inform future regulatory action with respect to those chemicals. As such, compliance programs absolutely must take into consideration all avenues of risk from current or past use of the chemicals. Failing to do so could result in considerable financial disruption that could have been avoided with careful planning.

CMBG3 Law is following judicial, legislative, administrative, and scientific developments relating to PFAS. More information about the services we can provide, including risk assessments, to ensure your business is ready for any intersection with these substances can be found on our PFAS Litigation page.

Our attorneys have been at the forefront of PFAS issues, including giving presentations as to the future waves of litigation stemming from PFAS issues. For more information, please contact the Chair of our PFAS – Toxic Torts Team: John Gardella.


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