In a laboratory setting, presumably you could makeq conditions clean enough to grow a cell culture that is free from micro plastics. But that isn’t going to tell you much about systemic effects like in an organ or body.
Maybe you could breed mice in a clean room. Not sure what the generational half life of microplastics is…
The alternative you could probably test is levels of Microplastics. Grow a number of colonies with varying levels of microplastics and compare between them.