^ This is correct. PP and PE account for more than 2/3 of microplastics and are biologically completely inert, which only leaves physical tissue irritation to get an effect (like e.g. the very different Asbestos fibers do). Another 10 % is PET where it is not as easy to tell (because it is a much more complex plastic than PE and PP), however, I have not seen any credible evidence that PET is biologically active (e.g. as an EDC) except for a few bacteria which apparently digest it. As far as I know even the monomers of PET aren't endocrine disrupting, which is overall a rare property in plastics (the monomers of many plastics are pretty nasty stuff and so if the process control is bad, there is a good chance that precursor chemicals end up unbound in the finished plastic).

Overall this means ~80 % or so of microplastics are pretty much what parent says: biologically inert dust.