A much better metric would be to classify the plastic found into major types (polyamides, polyesters, polyethylene, polypropylene, polystyrene, polyurethane, et

A much better metric would be to classify the plastic found into major types (polyamides, polyesters, polyethylene, polypropylene, polystyrene, polyurethane, etc) and then to quantify how much (either in mass or weighted also by surface area) there is of each type. All of these factors will have a big impact on how dangerous or safe the microplastics are. In fact, microplastic counts often do not even separate out cellulose based fibers such as Rayon. Then you are talking about a "plastic" which is safe enough to be used for sausage casings, it's just wood pulp which has been broken down and spun into fibers. The research into microplastics is very much in its infancy, like early research into disease transmission talking about the deadly "miasma".