Recent News on PFOA/PFOS in Drinking Water


Substantial amounts of new information on PFOA and PFOS, including scientific insights and potential regulatory schemes, were released between October and December 2023. As all who study this topic are aware, the EPA posted a new proposed MCL for drinking water in the spring of 2023. That value was virtually at the limit of analytical detection assays (most commonly high-performance liquid chromatography coupled with tandem mass spectrometry), or possibly below that concentration (4 ppt) in some circumstances.

Considerable disagreement exists within the scientific community about whether such a low concentration is necessary to prevent adverse human and environmental outcomes. Hundreds of organizations and over 1,000 individuals submited comments on the EPA proposal. Many took issue with the quality of some of the published papers relied upon by EPA, and others disagreed with the way EPA interpreted the existing data.

In a three-day meeting of scientists held in Washington, DC, from October 17 to 19 by the not-for-profit groups TERA (Toxicology Excellence for Risk Assessment) and ISRTP (International Society for Regulatory Toxicology and Pharmacology), approximately 20 quality papers on PFAS were presented. The papers addressed why the drinking water limits proposed by the EPA were up to 100,000-fold lower than those promulgated in other countries, such as Canada and Australia. It was concluded that, in light of the recent epidemiology and toxicological information, the EPA should reexamine the proposed 4 ppt value.

It was noted by one or more presenters that the cost to homeowners impacted by PFAS-contaminated water utilities could be an additional $250 per month to treat for PFAS going forward if the MCL of 4 ppt was promulgated.

Lastly, on December 1, the International Agency for Research on Cancer (IARC) classified PFOA as carcinogenic to humans (Group 1) and PFOS as possibly carcinogenic to humans (Group 2B). That view was based on what the IARC considered ‘sufficient evidence for cancer in experimental animals and strong mechanistic evidence (for epigenetic alterations and immunosuppression) in exposed humans’. This comes after publication of a major review paper by Steenland et al. (2023), which evaluated 20+ epidemiology studies and concluded that there was weak or inadequate evidence that either chemical was a carcinogen in any organ. These many factors will need to be weighed by EPA, Office of Management and Budget, and the regulated community in the coming months.

Our firm has been studying this class of chemicals for several years. Paustenbach and Associates holds that the evidence that PFOA/PFOS in drinking water is a hazard at concentrations below 250-500 ppt deserves further study. We recognize that the World Health Organization has identified 100 ppt as a reasonable goal. We have considerable experience conducting risk assessments on chemicals and contaminated or potentially contaminated sites of national importance.

We have offered testimony in more than 400 depositions and 30+ trials over the years where we presented our risk analyses. In the cases for which we were retained, we applied exposure science and the health risk assessment methodology embraced by the National Academies of Science to characterize the possible risks. Over the years, we have conducted more than 1,000 risk assessments. Please contact Dr. David Brew at or 307-395-0599 to learn more about our expertise.