Even if R410 and R22 are carcinogins, they are used in a closed system and are required by the EPA to be recovered. A leak will cause a release in the atmosphere. Home AC units rarely leak if installed properly. They can go 40 years or more without leaking because the compressor is sealed. Auto air conditioners are another story.
Here is the scoop on R410A:
http://www.honeywell.com/sites/docs/...fdc1e6517d.pdf
One story, I always like to tell is that water can be harmful. Too much water can be dangerous. You drown. This is also a fun read.
Dihydrogen monoxide hoax