While the Drexlerian nanoassembler/nanofactory concept appears to be pollution-free (except perhaps for heat), I have to wonder what all those materials and all their itty-bitty parts break down into when exposed to the chaotic environment.

Do the breakdown byproducts cause problems along the lines that're starting to be reported for buckytubes and buckyballs? Are there good, reliable methods available to prevent such breakdown and/or scavenge the byproducts out of the environment before damage is done?

Or is nanotech going to be limited to clean-room conditions?

Since the material and procedural developments in Nanoscience is by, ëfrom-top-to-downí approach (reference: Feynmanís concepts), early-predictions on hazardous environmental-impacts may be unnecessary and misleading. That is, the regulations for the Environmental-friendliness of Nanoscience-developments; has to be a time to time proceeding only.