Concrete is normally stained with a muriatic acid solution.
I have done it myself and can tell you, you will never wear the clothes you wore staining in polite society again. It is worse than working with straight bleach! It burns through the clothes so fast that I would not need much research to figure it to be very nasty stuff.
That being said, the concrete eats it up and once stained, it doesn't appear to pose much of a problem, at least not to the naked eye, ear or skin and you would seal it as well.
Finding a good clear sealer with no VOCs can be challenging. Something happens when you get all the proper environmental things in place: the product isn't as nice looking.
- Some waterbased, low VOC sealers might not be compatible with the traditional acid stains.
- The manufacturers can help you out with this.
If you don't have concrete yet, and you can do your color as an integral mix, you will have a very nice product, or if you can, use a surface "flash hardener" that stains the top 1/32" of an inch while the concrete is wet.
If you already have your concrete, try using the soy based stain, "SoyCrete" sold at Living Green in Culver City. I'm experimenting with that now, but have no long term data to report. I like the looks, though. Try it, I think the worst that can happen is that it will fade. Most concrete stain does fade a bit anyway.
Sherman Williams has a low VOC concrete stain and they also can give excellent customer education to determine if it is the product you want. Call the company directly to find the right person to talk to. They have the data and have finish products that pass some of the toughest standards in the country.
For more information:
Read "What is the most reliable, user-friendly, low-VOC, water-based concrete stain available?" a Q&A answered by Joel Hirshberg.