Everybody living in an industrialized centre is aware of the fact that, whenever air pollution exceeds certain limits, cars may not be used. What local authorities generally check is the quantity of PM-10 (i.e. particulate matter the size of 10 microns) suspended in the air, but, unfortunately, there is a dust a quarter that size, called PM-2.5, that is considerably more dangerous, and, as a rule, the smaller the particles, the more treacherous they are.
A Belgian group working at the University of Leuven demonstrated that inorganic particles the size of 100 nm cross the alveolar barrier and enter the blood stream a minute after they have been inhaled. An hour later that dust is found in the liver. It was also demonstrated by British researchers that the curve describing the incidence of cardiovascular diseases follows very closely the fluctuations of concentration of PM-2.5 in the air. Not so for the larger and less aggressive PM-10.
Silicosis and asbestosis, two forms of lung fibrosis respectively induced by the inhalation of particles of silica and asbestos, have been known for a long time to affect people working under particular environmental conditions.
Pleural mesothelioma can be caused by asbestos, but other fine particulates, for example talc, can be responsible for that disease. Both asbestos and talc are still used in some industrial procedures and too often very little precautions are taken against their aggression.
Tobacco smoke is also dangerous, as it is the carrier of fine inorganic particles fallen on tobacco leaves during their growth and their drying process, and practically impossible to get rid of.
Once the particles enter the alveoli, the lungs behave like any other organ and react against their presence with a mild inflammation whose chronic consequence can be a granulomatosis, a fibrosis or, later, a cancer. Most particles, in particular the smallest ones, though, do not stop in the lung tissue, but settle in the pleura or are carried away by the blood to reach other organs, where they trigger reactions similar to those occurring in the other tissues.

Pleural asbesthosis.
Iron-proteinate has deposited on the asbesthos particle.