See chapter 3.3 of "Discovery and quantification of plastic particle pollution in human blood" https://www.sciencedirect.com/science/article/pii/S016041202...

There’s already a well known correlation between heart disease and gum disease. One of the hypothesis is that plaque creating bacteria from the mouth end up in the bloodstream and create plaque in the heart. It wouldn’t be a big stretch to suggest that microplastics could take the same route to reach the heart.

Plastic is commonly found in canned food and drink. The foods are boiled inside plastic lined containers to ensure safety. Feed is sometimes ground up human waste aka moldy bread with plastic that's been ground up that the animals eat.

Here are more ways you can ingest them. https://www.earthday.org/you-are-what-you-eat-plastics-in-ou... Apples and carrots were not expected to be the most contaminated.

Some bits of plastic are very small far smaller I think than even that of a virus particle. Since nano-plastics are not alive I'd say there's nothing to stop it from entering through bowels if it's eaten.

You probably get some plastic entering your bloodstream every time you get a flu shot, just from the disposable syringe. (Yes, it's IM not IV, but it will migrate.)