I think the guy that needs a blood or plasma transfusion is going to be much better off with it (even with the PFAS), than without.

The people that received your blood have most likely "destroyed" alot of their own which most likely also contained PFAS thats why they need yours. No need to deliberately throw away perfectly good blood.

It depends on the need for the blood, I guess. Getting a nanogram of PFAS is preferable to dying from blood loss. The nanogram of PFAS increases you chance of dying 5% sooner by 20%, whereas losing all your blood through a wound guarantees a 100% chance of dying in the next 20 minutes. (All made up numbers, but you can see the risk/reward balance.)

I wouldn't be surprised that in 5 years, there's a little drop down when you go to donate blood that asks if you're a firefighter, ski wax technician, factory worker or lived in certain contaminated zip codes. You select it, and they exclude you.

You're never concentrating the PFAS, so at worst you're bringing poor sap's new PFAS concentration closer to your own pre-transfusion levels.

So the question is whether they need the blood more than you did pre-transfusion. If they did, then you're still commiting a net positive. If not, then it serves them right for requesting a blood donation despite needing it less than did an individual who was ready to donate their own.

Unless the blood is going to research, in which case it is a net positive regardless.