In reality no one can say for certain, but a lot of research is pointing to long term exposure being bad. The problem is that the research to determine how bad will take decades (and has been going on for decades at this point). Right now it’s being used as the boogeyman for every sort of ill from causing cancer, infertility, issues with lactation, liver failure, high cholesterol, thyroid disease, and auto-immune disorders. Basically the preliminary research says that it at least in part impacts all of these things, we just don’t know how much.
On the flip side bacon also causes cancer and high cholesterol at some level. That’s not to make light of the situation, but it does give some credence to your earlier statement.
The thing people are missing in these discussions is what are they willing to live without if we don’t use these chemicals. Going without non-stick cookware is literally the tip of the iceberg. How do we feel about cars, furniture, and mattresses being more flammable because they don’t have the fire retarding forever chemicals? How do we feel about stain resistance, oil resistance, water resistance, and slip resistance in everything including shoes, umbrellas, clothes, oven mitts, jackets, and more? How do we feel about needing to clean everything including clothes, appliances, and floors more often. How about in industry where it’s used as a fume suppressant so smelly chemicals don’t waft as far or fire fighting foams the next time an electric car catches on fire? This stuff is even in the wrapping of your food so the it doesn’t go through the packaging and cause a mess as easily.
Dupont coined the phrase “Better Living Through Chemistry” and that chemistry is PFAS. It’s in your clothes when you buy them, it’s in your detergent when you clean them, it’s in the cleaner that you wipe your washer off with, it’s in the floor sealant of the laundry room that washer is in, it’s in the gloves you wear while cleaning that laundry room, it’s in the carpet in the room next to the laundry room, and the list goes on and on.
Dropping PFAS chemicals fully would probably send us back to the 1960’s or we’ll end up replacing it with something just as bad that we don’t know the effects of yet.
You can’t have it needed in some stuff and critically dangerous if it’s a bio-accumulating chemical that virtually never breaks down. To reduce it enough to not be a hazard world wide you would functionally have to stop using it everywhere.
I haven’t seen any definitive results on dangerous health levels, 4.4 ng/kg might be it, but then other studies show people with mg/L of blood concentration. Overall the effects of exposure seem to depend on more than just the concentration, such as health status, exposure duration, magnitude of exposure, and how lucky you got with the genetic lottery. Even then we are fairly certain it is bad, we just don’t know what or how specifically. I would also throw caution at any study using ng as a serious measurement here, especially over prolonged exposure. The problem with measuring on such a low level is that you have far too much uncertainty to claim any true accuracy, at best these studies are guessing when they throw out numbers. Hell, the EPA just came out with a standardized method for analyzing PFAS last year.
At those levels of exposure you’re probably getting it just from eating commercially grown fruits and vegetables, because it can bio-accumulate in those as well.