So I especially noticed this press release that just arrived: "Super-Strong, High-Tech Material Found to be Toxic to Aquatic Animals by Researchers at MU and USGS"
CNTs are microscopically thin cylinders of carbon atoms that can be hundreds of millions of times longer than they are wide, but they are not pure carbon. Nickel, chromium and other metals used in the manufacturing process can remain as impurities. Deng and his colleagues found that these metals and the CNTs themselves can reduce the growth rates or even kill some species of aquatic organisms. The four species used in the experiment were mussels (Villosa iris), small flies’ larvae (Chironomus dilutus), worms (Lumbriculus variegatus) and crustaceans (Hyalella azteca).A space elevator, if it can ever be built, would likely be built on an base in the ocean, for a few reasons. First, you want to built it very near the equator because you get maximum centrifugal force there (an elevator is basically a taut string hanging off a spinning object), and because few storms cross the equator, and if the elevator was ever severed and fell back to Earth you'd want to avoid killing people. (After all, the thing has a mass of about 105 kg, or over 100 tons at the Earth's surface.)
“One of the greatest possibilities of contamination of the environment by CNTs comes during the manufacture of composite materials,” said Hao Li, associate professor of mechanical and aerospace engineering at MU. “Good waste management and handling procedures can minimize this risk. Also, to control long-term risks, we need to understand what happens when these composite materials break down.”
I don't have a copy yet of the above paper, so I don't know at what concentration they found CNTs to be toxic. It's a big ocean, after all. Still, you might not want to have carbon nanotubes flaking off it, or big pieces falling off and dissolving in the ocean. Maybe you coat the CNT ribbon with some polymer or something, but that adds mass and reduces your strength-to-density ratio.
And if these are toxic to marine animals, what about other animals, including human animals? I honestly don't know. I do seem to see a relatively steady stream of press releases about nanotechnology safety, and my (mostly uninformed) impression is that this area is understudied and behind the curve of nanotech R&D. I'm not even sure about nanoparticles in sunscreens, to be honest -- information like this isn't completely reassuring.
At the very least, environmental groups will likely have another target when/if a space elevator is ever seriously proposed.
We might never get off this damned planet.