asbestos, silica, etc. How do they cause cancer?

I understand how ionizing radiation can damage DNA. I understand how certain reactive molecules can do the same. I understand how this damage can lease to tumorigenesis.

I do not understand how certain small particles cause cancer. Off the top of my head (and after a quick look around my lab), these substances have carcinogenic dust:

asbestos
silica
celite 454 (I’m not sure exactly what this is…DE and other stuff?)
molecular sieves (I’m not sure of the composition of this either)

Does anyone know why they are so bad to breathe?

As I understand it, abestos “dust” is nothing more than a whole lot of little tiny slivers. These slivers get into the lungs, and stick there. Ever have a splinter in your finger? Think of a couple of lungs full of them. :eek:
I do not about the other items listed.

I used to process claims settlements for asbestos lung disease and mesothelioma. What I recall of it is that it’s the straight needle-like forms of asbestos that are most harmful. Crocidolite is just about the most common form of this - there’s also a somewhat curly form known as chrysotile. The chrysotile tends to get caught in mucus in the sinuses and upper respiratory region before it has a chance to get into the lungs. The needle-like shapes manage to slip by these defenses and it’s believed that the never-ending physical irritation of the sharp fibers leads to scar tissue and cancer.

Silica (ie: fiberglass molecular sieves and Celite) is also looking to be harmful for the same reasons. Silica particles may well cause mesotheliona, but the interim disease would be called silicosis, as opposed to asbestosis.

Simple answer is that they do not cause cancer. Cancer is more common in smokers who are exposed to asbestos.

This site from the Canadian Lung Association is a good summary and explanation (of what I already knew/suspected),

the exact mechanism is not known. However from here is an educated hypothesis
from http://www.madsci.org/posts/archives/nov2000/975481424.Me.r.html

“When the asbestos is in someone’s lungs, the body sends its immune system
cells or white blood cells (WBCs) to attack it. The body’s WBCs create
particles that are toxic to cells, especially free radicals. When the body
is fighting off bacteria, this is good. The free radicals kill the
bacteria, the WBCs gobble up the rest of the bacterial debris, and then
go away. However, when asbestos gets into the lungs, the white blood cells
keep making free radicals. The free radicals slowly damage the cells that
are around the asbestos. Some of this damage includes damage to the DNA
that cause mutations in cancer-causing genes. Apparently, these mutations
eventially result in cancer in some people who are exposed to asbestos.”

Hmm, I guess that makes sense to me. Sounds like it could work that way for the other things I mentioned as well. Thanks all for your responses.

A newer hypothesis involves the “sc” phrase. When the body is regularly attacked by an irritant, stem cells start propagating to replace the damaged cells. Over time (and many generations of less-than-perfect cell division), this propagation gets out of control and you get cancer. Linky-

http://www.hopkinsmedicine.org/Press_releases/2004/11_22_04.html

Re: silica, celite, molecular sieves

Celite is just silica. Molecular sieves include not only Si oxide, but also Al & Mg.

MSDS:
http://www.uiowa.edu/~chemsafe/MSDS/Celite.htm
http://www.ecompressedair.com/msds/molecularsieve.shtml