Not really. For many things there is no "safe" level, eg. airborne PM2.5 pollution or lead.
What you say is a bit of a common sense rule of thumb usually used for stuff we digest and poop out.
So that may rule out microplastics, which was shown to cross into tissue (including lungs) which means it would accumulate. And definitely nanoplastic, as those enter even individual cells and screw up their mechanics.
I wouldn't be surprised if in a few years we would consider no safe level of micro/nanoplastic exposure. Maybe we would already if not for the interests of manufacturers and oil industry.
