As you may have heard, EPA today announced its proposed PFAS rule. It includes an MCL for PFOA and PFOS at 4 ppt, individually, and a hazard index of 1.0 (unitless) for GenX, PFBS, PFNA, and PFHxS, as a mixture: Compound Proposed MCLG Proposed MCL (enforceable levels) PFOA Zero 4.0 ppt (also expressed as ng/L) PFOS Zero 4.0 ppt PFNA 1.0 (unitless) Hazard Index 1.0 (unitless) Hazard Index PFHxS PFBS HFPO-DA (GenX) More details: Per- and Polyfluoroalkyl Substances (PFAS) US EPA NSF/ANSI 53 and 58 have recently published with updated PFAS values as well. Best, Monica NSF Confidential