The Office of Environmental Health Hazard Assessment has announced that it is proposing a notification level for perfluorobutane sulfonic acid, one of the chemicals in the PFAS category. As OEHHA's announcement reads:

[OEHHA proposes a] notification level (NL) ... of 0.5 parts per billion (ppb), based on thyroid toxicity, for perfluorobutane sulfonic acid (PFBS) in drinking water. PFBS is a member of a large class of chemicals known as per- and poly-fluoroalkyl substances (PFAS) that are used in numerous commercial products for their water- and stain-repellent properties. An NL is the concentration of an unregulated drinking water contaminant that does not pose a significant health risk but warrants notification when exceeded.

The technical support document for this recommendation can be found at https://oehha.ca.gov/media/downloads/water/chemicals/nl/pfbsnl121820.pdf