Ok, I admit that may have been a little bit of hyperbole. But I expect in such a scenario some (very expensive, wide reaching) mitigations might be put in place

Ok, I admit that may have been a little bit of hyperbole. But I expect in such a scenario some (very expensive, wide reaching) mitigations might be put in place such as banning the relevant types of plastic and introducing some kind of specially targeted filtering/treatment in fresh water supplies in areas where that's logistically/politically possible (assuming an effective system for it can be found).