PFAS (poly- and perfluoroalkyl substances) are chemicals that are not or hardly biodegradable, some more dangerous than others. This is why they remain in the environment and in our body. They are synthetic substances produced in the chemical industry and are not naturally present in our environment.
They are often used for waterproof products such as raincoats, or as a layer of grease or dust-repellent, for example on pans.
Especially PFOS, one type of PFAS, has been known since the 3M scandal in Zwijndrecht, but PFAS is a whole “family” of chemicals. Read more about it in this article.