News & Updates

ATDSR Releases Risk-Level Guidance for PFAS Water Contamination Levels November 13, 2018

The Agency for Toxic Substances and Disease Registry (ATSDR) has released guidance on minimal risk levels (MRLs) for water contamination by per- and polyfluoroalkyl substances (PFAS). This will precede a final report from the agency.

Following the ATSDR’s Toxicological Profile for Perfluoroalkyls Draft for Public Comment, released in June 2018, this new guidance pertains to MRLs for for perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), perfluorohexane sulfonic acid (PFHxS), and perfluorononanoic acid (PFNA), the four chemicals in the PFAS family that have been garnering the most scrutiny. The MRL screening values released in the initial public draft report can be converted into drinking water concentrations for adults and children based on mathematical equations and information about a person’s body weight and how much water a person drinks each day. When ATSDR uses an average adult’s or child’s weight and water intake to convert these MRLs into drinking water concentrations, the individual concentrations (also referred to as environmental media evaluation guides) are:

  • PFOA: 78 ppt (adult) and 21 ppt (child)
  • PFOS: 52 ppt (adult) and 14 ppt (child)
  • PFHxS: 517 ppt (adult) and 140 ppt (child)
  • PFNA: 78 ppt (adult) and 21 ppt (child)

These concentration numbers are of a different utility than the Health Advisories (HAs) or Maximum Contaminant Levels (MCLs) that are meant to indicate the potential occurrence of health impacts. (Observers will recall the outcry about the much lower concentrations inferred from the ATSDR report released in June 2018 as compared to those HAs adopted by the Environmental Protection Agency.) In sum, these individual concentrations are used to compare to concentrations in drinking water to determine if further evaluation is needed at a particular site.

Issues surrounding co-exposure (exposure to multiple PFAS substances) still exist, but these concentration numbers do provide further guidance to public utilities and other important actors in studying the nature and extent of contamination in water at a site.

To learn more about PFAS and the anticipated ATSDR report, please contact:

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