EPA Publishes Toxicological Review of PFHxS, a Biologically Persistent PFAS

A final toxicological review of perfluorohexanesulfonic acid (PFHxS) and its related salts conducted by EPA’s Integrated Risk Information System (IRIS) program finds that exposure to these substances is likely to cause thyroid and immune effects in humans. PFHxS and its related salts are per- and polyfluoroalkyl substances, or PFAS, human-made compounds known for their persistence in the environment. According to the report, exposure to PFHxS likely causes decreased thyroid hormones, or thyroid toxicity, as well as immunotoxicity in humans. The main evidence supporting immune effects related to PFHxS exposure includes “decreased antibody responses to vaccination against tetanus or diphtheria in children,” EPA explains. The report also describes evidence from studies suggesting that exposure to PFHxS may cause other adverse health effects in humans’ hepatic, neurodevelopmental, and cardiometabolic systems.

A recent report on exposures to PFAS among firefighters and others involved in the response to the 2023 Maui wildfires describes PFHxS as “one of the most biologically persistent PFAS.” According to the report, which was authored by individuals from NIOSH’s Division of Field Studies and Engineering, the highest blood serum concentrations of PFHxS were detected among firefighters.

EPA’s new IRIS report notes that PFHxS has been used in aqueous film-forming foam for fire suppression and in water- and stain-protective coatings for carpets, paper, packaging, and textiles. According to the agency, PFHxS may also be found in some industrial fluids and in consumer products like electronics.

The IRIS toxicological review of PFHxS and related documents are available from the EPA website.

Related: An article published in the March 2022 issue of The Synergist focuses on the challenges in researching and managing exposure to PFAS. Another article published later that year explores how PFAS complicate product stewards' efforts to plan ahead.