oh, sure, they can produce microplastics after you take the food out. but you aren't going to get plastic dust in your lettuce
the most common plastics used in packaging are pet, polypropylene, and polyethylene, which have exceptional elongation at break. when you scratch them, you don't produce microplastics; you produce a burr on the surface
that's a good point about the tap water, and you're probably right about polystyrene yogurt cups and tupperware, though i still think you won't find any evidence of it unless you do the experiment yourself
the most common plastics used in packaging are pet, polypropylene, and polyethylene, which have exceptional elongation at break. when you scratch them, you don't produce microplastics; you produce a burr on the surface