Inhalation- The Primary Path of Exposure:

The primary access path for asbestos fibers is the respiratory system. Fibers released into the air are inhaled by the subjects where they are carried into the deepest recesses of the lungs. Asbestos fibers that are locked into heavier particles of plaster, concrete or paint are often expelled through coughing and rarely reach deeply enough into the lungs. From studies conducted in the early to mid-20th century, most of which were post-mortem examinations, it became apparent that pleural asbestos disease tended to accumulate near the bottom lobes of the lungs, in the gutter of the thoracic cavity and on the surface of the diaphragm.

Microscopic examination of biopsy or autopsy tissue samples revealed that in many cases the asbestos fibers were no longer located in the alveoli of the lungs but rather in the intrapleural space or within the mesothelial lining of that space. This was described by many physicians as a “clearing” of the lungs, but despite the benign sounding label, this process held serious and potentially fatal implications for the subject.

The clearing of the lungs is directly connected to the two primary theories about how injury is caused by asbestos. The first theory postulates that the asbestos fibers pierce the tissue walls of the pleural space (and sometimes the peritoneal space via the stomach or the diaphragm) and cause tissue damage which creates an inflammatory immune response. The second theory states that the asbestos fibers are so small that they begin to interact with mesothelial cells at a molecular level, interrupting cell replication and/or damaging the cellular DNA during mitosis, or cell division.