Thanks rastus2 and rru2, I have a primitive understanding of...

Thanks rastus2 and rru2, I have a primitive understanding of this and each time I learn a little more. I remember Nick's discussion about the size of the molecule and that it couldn't get into the smaller part of the lungs. This made me realize that I knew little about the molecule's size, and had no idea how small the pockets in the lung get. In short I am out of my depth.

I have been trying to follow these discussions because I think this is a significant area where I should look into pushing back my lack of knowledge. Takes me back to my chem lab days. I am content to see that both of you have the idea that the exposure is much less than one cancer in a million it seems. This seems to be a very slight risk and, as you pointed out, the risk from coal plants is much greater.

Thank you both for your detailed and well reasoned responses. They are much appreciated.

toto