On October 3, 2025, California’s Office of Environmental Health Hazard Assessment (OEHHA) announced the development of a public health goal (PHG) for perfluorohexane sulfonic acid (PFHxS) in drinking water, thereby determining the level of PFHxS that does not pose a significant risk to health and setting the foundation for an enforceable maximum contaminant level (MCL) for PFHxS under California’s Safe Drinking Water Act. The move marks a key step toward potential state-level regulation of PFHxS, following the federal government’s recent decision to rescind national drinking-water standards for certain PFAS (see 5/14/2025 post).

California’s initiative underscores its continued commitment to advance independent PFAS regulation despite shifting federal oversight. Although PHGs themselves are not regulatory, they are a prerequisite to enforceable drinking-water standards and may carry significant implications for regulated entities. The establishment of an MCL could trigger new reporting, treatment, and litigation risks for industries associated with PFHxS contamination. OEHHA’s initiative follows the State Water Resources Control Board’s (Water Board) May 2025 announcement of its intent to promulgate an enforceable MCL for PFHxS, citing widespread detections across the state. According to the Water Board, 130 public water systems serving approximately 9.7 million Californians have reported PFHxS concentrations at or above 2 parts per trillion (ppt).

Once finalized, the PHG for PFHxS will guide the Water Board’s rulemaking to set a corresponding MCL “as close as is technologically and economically feasible” to the PHG, as required under California law. OEHHA’s assessment will incorporate toxicological data from both human and animal studies, evaluating potential adverse health effects such as thyroid toxicity. The agency is currently accepting public comments through November 3, 2025, before releasing a draft assessment for peer review.