It doesn’t have to be an identical material, just one that has similar properties in attracting and holding contaminants.

So if you're studying slices of e.g. brain to look for microplastic particles, what would be a material with similar properties, that you would then go through the same steps of preserving, preparing, slicing, mounting, etc.?

I'm genuinely curious. Are there standard widely used stand-in materials for animal flesh, for plant materials, etc.?