Perfluoro (PFAS) is a group of substances that contains PFOS, PFOA and GenX. Perfluoro substances often occur as pollution in ground water and drinking water. Recently, cases of perluoro pollution have risen concerns about possible health effects. In 2016, RIVM has determined a Health-Based Guidance Value for PFOA. RIVM has now developed a method to determine the risk of a PFAS mixture based on this threshold limit value.