Compared with the other examples you gave, I think one of the differences with micro- and nanoplastic and their growing bioaccumulation, is that if/when we discover that some level of concentration of it causes noticeable issues, it will be very hard to reverse, and it will be globally abundant (i.e. throughout the entire food chain). We'll be stuck with the problem for a very very long time.

It's not like we'll be able to just outlaw it and be done with the issue after a few years. So for this specific polluant, it feels right that we should be cautious and look for solutions as quickly as we can.