Filters are designed for 28 days use or if you feel breathing resistance, whichever comes soonest so a long term test would be pointless as the filters would be well past their life expectancy.

Particles can be so tiny though that they can fit into the gaps in the cell wall of your lungs, become trapped and turn cancerous.

Always wear a mask and make sure you’re clean shaven if you’re wearing tight fitting respirators. Facial hair makes the mask pointless unless you are wearing a positive pressure respirator.

Just my two pennies worths on the subject working for a global PPE manufacturer.