As I have written previously, PFOA is not naturally occurring. It is very useful and stable, and as a result, very low concentrations are found throughout the environment - in a few places, higher levels that may be harmful.
The 2019 meeting of the Society of Environmental Toxicology and Chemistry (SETAC) demonstrated the dilemma facing government agencies globally - a wide divergence on the safety assessment of these fluorinated chemistries, making communication with the public extremely difficult. To cite just one example, PFOA estimates its safe dose by government agencies vary by around 750-fold.
This diversity of opinion is the result of two issues. First, the determination of PFOA’s safe dose depends, in part, on establishing its first toxic effect, referred to as its critical effect. This determination is not straightforward and government agencies, even within the US, disagree. Second, PFOA’s half-life, the time required to eliminate it from humans, is generally much longer than that measured in experimental animals; this longer half-life for humans lowers its safe dose estimate. Because these estimates are based on human observational studies where all sources of PFOA exposure may not have been carefully identified, government agencies faced additional uncertainty.
A recent peer-reviewed study by myself and co-author Bernard Gadagbui [1] (2021) focused directly on the half-life of PFOAs utilized the sole human clinical study on PFOA. The bottom line of this research was that:
- PFOA half-life estimates vary widely among human observational studies. They cannot all be correct.
- Differences in these estimates are most likely due to varying degrees of unmeasured PFOA exposures among studies.
- PFOA half-life of ~1.5 years appears to be most reliable since background exposures were subtracted from the estimate.
- The sole human clinical study estimated a PFOA half-life of ~200 days (~0.5 years).
- Thus, a range in the PFOA half-life appears to lie between 0.5 and 1.5 years, rather than the currently used values of all more than two years. Using a half-life from this range would raise existing regulatory safe levels if all other parameters stay the same.
Safe or low-risk doses for PFOA and related chemicals used in regulations remain widely disparate and contentious due to disagreements in the methods underlying the reported “science.” Recent scientific findings may reduce some of this disparity and harmonize or at least make more consistent government regulations. Legislative efforts ahead of this scientific resolution are premature.
Source: The Dilemma of Perfluorooctanoate (PFOA) Human Half-life Regulatory Toxicology and Pharmacology DOI: 10.1016/j.yrtph.2021.105025
Michael Dourson
Michael L. Dourson, PhD, DABT, FATS, FSRA -- "America's Toxicologist" -- is a member of the American Council on Science and Health Board of Scientific Advisors. He has a PhD in toxicology from the University of Cincinnati, College of Medicine, and is a board-certified toxicologist (i.e., DABT) serving as the Director of Science at the 501c3 environmental science NGO, Toxicology Excellence for Risk Assessment (TERA). Prior to this, he was Senior Advisor in the Office of the Administrator at the US EPA. Before this, he was a Professor in the Risk Science Center at the University of Cincinnati, College of Medicine and also worked at TERA and US EPA.
