I use my microwave for my RA4 chemicals. Same one that I use for my food. The containers I use are only used for chemistry.
I don't worry about fumes / vapours. Microwaves aren't sealed units. Otherwise they would be a pressure cooker and you would probably have stream burns every time you opened it up.
They vent the air out the back. Or in my case, into the venting for my range fan.