[cyberax]

The difference between teflon and PFAS is in the hydrophilic "head".

Basically, teflon consists just of long chains of carbon atoms saturated with fluorine. They are extremely chemically resistant, and they appear to be biologically inert. Even if you heat the teflon past its decomposition temperature, you simply get pieces of the hydrocarbon chain as a result. They are nasty, but they are not persistent pollutants.

PFAS are different. They also consist of a chain of carbons with fluorine atoms attached to them. But they also have a hydrophilic "head" attached to them at the beginning of the chain. This hydrophilic head allows PFAS to function as surfactants, and it also makes them biologically active. The body can't do anything with the hydrocarbons saturated with fluorine, but the head provides a "handle" that can be used to absorb the PFAS into cell membranes where it can stay and cause all kinds of issues.