Dan,
I'm glad you brought that Treeworkers Lung thing up, it has been on my mind too, lately. It is not such a far flung conclusion that people like arborists, carpenters, stone masons, farmers, any one who has been in contact with contamints in the air their whole working lives, more than likely have lungs full of these fine dust particles.
Now that I'm older, it makes you think about the amount of fine sawdust particles, not to mention the dust from chippers and stump grinders that have gotten into the lungs and stayed there because of repeated and constant exposure to the same situation day in and day out.
I consider myself fit for my age, but find I have to take more frequent "breather " breaks to get a job done if it is strenious on the lungs. I can't help but think my lungs have got more than their share of tree dust in them, causing me to slow down a little.
Larry