Microplastics are everywhere, even in the precipitation.
The plastic bits you can see in your
raised bed soil are at least discernable.
You could,with a lot of work, sift them out.
Some fungi seem to be able to break down some plastics and mealworms are noted to able to break down Styrofoam.
I don't know of any plants that are noted for their ability to break down plastic.
I have an urban lot where the house burned down,was pushed into its own cellar, and coveted with fill dirt.
I minimize contamination by building raised
lasagna beds for annuals, and planting perennials directly in the ground.