Kat, is this for commercial or residential? For commerical look out for the Green label. The Green Label Plus program symbolizes the carpet industry's commitment to a better environment for living, working, learning and healing.
It was recenlty introduced by the Carpet and Rug Institute.
Green Floors is known for it green carpet, low VOC etc - http://www.greenfloors.com/HP_RC_Index.htm
There are also carpets made of wool, jute, seagrass and other natural fibers. They are naturally greener than synthetic materials. Plus, they harbor fewer chemicals and have lower toxicity. Also pay attention to the carpet padding. At least one company makes recycled cotton padding, which is way better than the standard petroleum-based stuff.
We just installed Smart Strand upstairs with an eco-friendly pad and wool on the stairs.
Yes they are called Hardwood....or tile.
Indoor air quality is indeed compromised by carpet...check out this article I wrote.
I am in agreement with KMS on this as well. Carpet, regardless of how Eco it is will support all sorts of bacteria, mold, and dust mites after just a few months. Read this information from HGTV however if you choose to go this route. http://www.hgtvremodels.com/interiors/choosing-eco-friendly-carpet/index.html
I would also suggest that you purchase a book written by Jeffery May called "My House is Killing Me" Its paperback about three hundred pages or so. You will take an entirely different stance when designing and living in your home after reading it. Some info may be a bit over the top, but if you take into consideration what the author is trying to tell you, you will find other ways to do things.
To have a "carpet" feel in some areas of our home we have large area rugs. Most of these are 100% wool...some are even some vintage Persian. With quality rugs such as those the "tufts" of the rug are knotted and "tied" to the weft and warp and there is no "need" for the adhesives found in most carpets.
The beauty of these "rugs" is they can be easily removed form the home for a deeper cleaning than any carpet could ever have.
Thanks to you all for your valuable and insightful comments about "clean" carpets. I have informed the homeowner of her various options and she was very pleased. Should any of you contractors want work in the Raleigh/Durham NC area let me know! It would be a privilege to refer your services to homeowners! Enjoy your weekend!