They just found them in 50% of artery blockages, so we should probably keep looking so we can finally ban materials that degrade into them.

There is a new process for treating wastewater sludge that destroys the microfibers, so that is good news at least. I think it may be expensive, of course. It is called “hydrothermal carbonization”. Basically put the sludge in a giant pressure-cooker and the heat breaks the plastics into carbon and some water-soluble residual molecules which can go back to the start of the wastewater treatment plant to be biodegraded. But like others say, the main source in general is tires - not sure if they know whether tire microplastics are the main source in agricultural land though.