The association is that long term mortality rates in the pilot population are no higher than in the general population. If exposure to toxic fumes are such a pressing issue then surely we would see higher cancer rates in pilots. Since this is not the case then I conclude that exposure to these fumes in isolated cases are not affecting the long term health of the majority of pilots.
As I said above, I do agree that fumes enter into the cockpit at times. I also accept that some individuals are more susceptible to these fumes. I am saying that the majority of pilots work their entire career with no ill effects from these isolated events.
Oh and smoking is Bad.