Okay, maybe I'm being something of an alarmist, but one really can't ignore stuff like this outright:
Carbon Nanotubes That Look Like Asbestos, Behave Like Asbestos
New study shows inhaling long, thin carbon nanotubes may result in asbestos-like health effects.
This is the head and sub-head of an article on The Project on Emerging Nanotechnologies website. It's based on a paper published in the journal Nature Nanotechnology that reports on a study done that indicates that carbon nanotubes, introduced into the body (the tests were conducted on mice), have an asbestos-like pathogenicity.
Remember asbestos? If it got into your lungs, you were pretty much toast. Asbestos fibers were long, thin fibers very much like carbon-nanotubes.
Go here to read the PEN article: http://www.nanotechproject.org/news/archive/mwcnt/
Go here to read the abstract of the Nature Nanotechnology article: http://www.nature.com/nnano/journal/v3/n7/abs/nnano.2008.111.html
I was turned onto this by a post on the Cozy Beehive. (In the same post there's some love for Thomson components-- which are NOT carbon composite!)
Why am I bothering with this? I'm not a huge fan of carbon composites in general. Now I'm not a "Luddite" but sometimes I think we humans have a tendency to do things because we can (Times like this I'm always reminded of the joke about why dogs lick their balls...)
We've created this wonderful amazing material, but what is the net effect of its creation and disposal? I mean, c'mon-- go Google "snapped carbon steerer" or some variation and you'll doubtless turn up plenty of scary reading material. And that's just for steerers-- not handlebars, forks, seatposts and even frames.
I'll mention this again-- do carbon composite materials degrade into healthful fertilizer when they're disposed of? Or do they shed harmful component chemicals and dangerous particulate matter?
I know I'm just scratching the surface and not touching on other toxic manufacturing processes involved in the manufacture of metal alloy bicycles and components.
Still... I guess it's good to ask questions, right?