Right now the cytotoxic effects are the only effects confirmed in humans I believe.
We are consuming microplastics at an alarming rate, it's found in our stomach, brain, lungs and blood. Fish and drinking water are the two largest sources of human ingestion of microplastics.
If carcinogenic then it would likely be pretty substantial.
Yes. It's an assumption but the higher the exposure generally means higher chances of issues. Such is true for most things, especially other cytotoxic materials.