Plastic fragments of which size are considered to be microplastics?

Player #17763543, I agree. I did choose 5.0mm because it was the smallest size. I think 0.5 would been more correct.

I have a hard time considering anything 5 mm in length (about the size of a green pea) as being "micro." Not that they're not a problem, but they could have come up with a better name.