"Doesn't lime carry with it similar respiratory risks"
Depends on the type of lime.
"DE powder is crushed diatoms and therefore the silica, alumina, and iron oxide are all contained together within the tiny bits of diatom shell that make up the powder" Yes they say there is to be some diatoms (hard shell algae) but they don't state the amount.
"Therefore, the health risks of each of them as individual substances don't necessarily apply."
If that is what you believe that is fine with me.
I know what diatoms are, thanks :)
I am pretty sure that it is ALL diatoms. I don't think it has filler in it, at least if you buy 100% food grade diatomaceous earth, all the MSDS and product info I could find indicate that is exactly what it is. The diatom shells themselves are what contains silica (primary) alumina, calcium, iron oxide, etc...
Therefore assessing the health impacts of DE by evaluating the risks associated with it's individual components, which are not 'free' for you to be exposed to, but instead 'locked up' in the shell of the diatoms, is not good science. It's like evaluating health impacts of DDT by saying, "well carbon isn't bad for you and neither is hydrogen, and they put chlorine in our water so DDT must be OK." (point being, DDT is horrible for you but is made up of only carbon, hydrogen and chlorine).
It doesn't work that way, it's not just "something I believe".
EDIT TO ADD: it is also highly unlikely that normal human metabolism would break down the diatom shells so that any of the above mentioned substances (aluminum, iron oxide, etc.) would be bioavailable in any way within your body. If it goes in as a diatom shell, it will come out as a diatom shell. There are no data I can find indicating any health risks to eating it in small quantities. In addition, the type of silica that food grade DE is comprised of is almost all (>99%) amorphus silica, and less then 0.5% crystalline silica. Crystalline silica is quite harmful when breathed in, however amorphus silica doesn't carry with it this additional risk (obviously inhalation of any dust is bad).
Edited by PDXcluck - 5/3/12 at 4:06pm