https://medium.com/p/2587fc2d6932 In a recent study conducted by researchers from the University of Campania Luigi Vanvitelli in Italy, a surprising discovery was made: microplastics were found within arterial plaques. These tiny plastic particles, measuring less than 5 millimeters in length, were present in approximately 60% of the plaques removed from patients with atherosclerosis
It seems weird to specify half a dang centimeter, I assumed "microplastics" would be invisible to the naked eye, right?
A micron is 1/1000th of a mm, so while sort of visible, they can aggregate and form bigger particles. Usually they define a microplastic particle as being from 1–1000 μm (0.001 mm to 1 mm) some argue it should be 1-5000 μm, but to me anything beyond 1 mm isn't microplastic, just plain old plastic chunks.
That sounds a lot more normal, much more like what I'd expect.