Understanding Final MCL’s for PFAS and How to Navigate

Decades of research show mixtures of different chemicals can have additive health effects, even if the individual chemicals are each present at lower levels. This means that low levels of multiple PFAS that individually would not likely result in adverse health effects may pose health concerns when combined in a mixture. The Hazard Index is a long-established approach that EPA regularly uses, for example in the Superfund program, to determine the health concerns associated with exposure to chemical mixtures. EPA’s Hazard Index Maximum Contaminant Level (MCL) is set at 1 and applies to any mixture containing two or more of PFNA, PFHxS, PFBS, and HFPO-DA (known as “GenX chemicals). These PFAS can often be found together in different mixtures and research shows that exposure to mixtures of these chemicals may have additive health impacts.