I have a Studor mini vent connected to the plumbing in a 1st floor bathroom vanity. The plumbing works fine, but, there is a very fowl oder coming from the vent. I assume the mini vent needs to be replaced. Are the gases toxic or danagerous to breathe until I can get this changed?

Are the gases toxic or danagerous to breathe
I wouldn't think so, not at the rate it is entering your home.
To change the AAV (Studor) vent should be a simple matter. Unscrew the old one and screw in a new one. Don't even have to turn the water off.

Toxic and dangerous but it won't kill you. Sooner the better with that new studor. Like Harold says, easy to do