ATSDR Finalizes PFAS Tox Profile, May Signal More Stringent Criteria

We are actively monitoring the dynamic regulatory landscape with regard to per and polyfluorinated alkyl substances (PFAS). Technically sound and up-to-date toxicological information is critical to developing health-based regulatory criteria and risk-based solutions. We have analyzed the recently published to ATSDR Toxicological Profile for PFAS, which may signal more stringent regulatory criteria to come.

The Agency for Toxic Substance and Disease Registry (ATSDR) recently released the final Toxicological Profile for PFAS. The document reviewed the toxicological literature for 12 PFAS compounds and developed Minimal Risk Levels (MRLs) wherever possible. MRLs represent the daily human exposure that is likely to be without risk of noncarcinogenic effects. Following review of the toxicological data, ATSDR determined that there was sufficient data to develop MRLs for only four PFAS for intermediate (15-364 days) oral exposures:

• PFOA (perfluorooctanoic acid): 3×10-6 mg/kg-day
• PFOS (perfluorooctane sulfonic acid): 2×10-6 mg/kg-day
• PFHxS (perfluorohexane sulfonic acid): 2×10-6 mg/kg-day
• PFNA (perfluorononanoic acid): 3×10-6 mg/kg-day

Although publishing the final Toxicological Profile for PFAS represents a step forward in understanding the toxicology of PFAS, there remain significant data gaps. The absence of chronic MRLs, as well as MRLs for inhalation identify the need for additional research. In comparison, USEPA provided the following chronic (>7 yr exposure) reference doses (RfDs) in their 2014 Health Advisory:

• PFOA: 2×10-5 mg/kg-day
• PFOS: 2×10-5 mg/kg-day

Generally, sensitivity increases with exposure duration and, therefore, the RfDs (which are for >7 yrs exposure) should be lower than the MRLs (which are for <1 yr exposure). However, ATSDR’s MRLs are an order of magnitude lower than USEPA’s RfDs.

If the MRLs are used to calculate tapwater screening levels using the same method as the USEPA Health Advisory, the following screening levels are calculated (based on a hazard quotient of 1):

• PFOA: 11 ng/L
• PFOS: 7 ng/L
• PFHxS: 7 ng/L
• PFNA: 11 ng/L

These screening levels are substantially less than the current USEPA Health Advisory of 70 ng/L and are for intermediate exposures. It is expected that screening levels protective of chronic exposures would be lower.

Additionally, USEPA provided updated toxicity reviews and RfDs for three additional PFAS chemicals through its Provisional Peer-Reviewed Toxicity Value (PPRTV) program in April of this year, as follows:

• PFBS (Perfluorobutane Sulfonic Acid): 3×10-4 mg/kg-day
• Perfluorobutanesulfonate: 3×10-4 mg/kg-day
• Potassium Perfluorobutane Sulfonate: 3×10-4 mg/kg-day

These RfDs are unchanged from the previous values, which indicates that the current Regional Screening Levels (RSLs) for these three PFAS chemicals will not change. USEPA is currently working on updating its toxicity values for PFAS chemicals. We will continue to monitor the scientific literature to keep pace with the state of the science of PFAS toxicology.

Based on this information, our experts offer consultation, advocacy, and technology to clients preparing to meet more stringent criteria, including site-specific risk-based solutions (e.g., pathway elimination, engineering controls, site-specific risk assessments) and treatment technologies capable of meeting stringent, health-based regulatory criteria.