We have a lot of defenses to make sure large molecules don't make it into the bloodstream so if those polymers start making it through, we'd have much bigger problems. Microplastics are a special case because they're very chemically inert, but they're still filtered out by the kidneys. Any cellulose or lignin would be too.

To be honest, after reading some of these microplastics papers I'm starting to suspect most of them are bullshit. Plastics are everywhere in a modern lab and rarely do these papers have proper controls, which I suspect would show that there is a baseline level of microplastic contamination in labs that is unavoidable. Petri dishes, pipettes, microplates, EVERYTHING is plastic, packaged in plastic, and cleaned using plastic tools, all by people wearing tons of synthetic fibers.

We went through this same nonsense when genetic sequencers first became available until people got it into their heads that DNA contamination was everywhere and that we had to be really careful with sample collection and statistical methods.

> One of the most lethal professions of old was baker, because of all the flour dust inhaled.

Pretty much anything that is small enough to irritate the lungs will cause the same effect, especially at professional exposure levels (or worse, like silicosis). Pre-industrial agricultural workers and miners frequently suffered from pneumoconiosis from dust inhalation too, for example.