How asbestos fibers enter the lungs
Asbestos is a term for a group of fibrous minerals, forms of magnesium silicate. All forms of asbestos are considered dangerous, and capable of causing cancer. The six most common are amosite, chrysotile, crocidolite, and the fibrous varieties of tremolite, actinolite, and anthophyllite. Asbestos minerals consist of fibers that are easily separable. Individual fibers are extremely small and fine, light enough to be carried in the air. Amphibole forms of asbestos, whose fibers are straight, are more likely to cause disease than chrysotile, whose fibers are curved.
In the course of mining, manufacturing and installing products using asbestos, fibers are dislodged and become airborne. Workers have described mining and factory environments where the air was white with asbestos, and their clothes and hair were covered within the fine white fibers. Asbestos workers cannot avoid inhaling the airborne fibers, especially when ventilation is poor, and protective apparatus is insufficient or lacking.
Most fibers are cleared from the lungs within hours of inhalation. Coughing carries them to the throat in a layer of mucus, where they are either spit out, or swallowed, and make their way out of the body.
How asbestos fibers damage the lungs
Some inhaled asbestos fibers reach the lungs, and progress into the alveoli, the tiny pockets within the lung where oxygen passes into the bloodstream. The fibers may remain for years, even the rest of a person's life. Amphibole asbestos fibers, which are longer and straighter than chrysotile fibers, tend to remain in the lung the longest.
Asbestos fibers tend to move toward the lower portion of the lungs. In autopsies, most asbestos disease of the lungs is seen the bottom lobes of the lungs and on the surface of the diaphragm, the large muscle that moves the lungs in breathing, which sits just under the lungs.
Asbestos fibers that remain in the lungs can cause mesothelioma, lung cancer, and asbestosis. All three are serious, fatal diseases, and all of them develop very slowly. The first symptoms of mesothelioma may not show up for 15, sometimes for as long as 30 or 40 years after the victim's exposure to asbestos. By the time symptoms are troublesome enough for a victim to seek medical attention the disease may have progressed so far that the victim life expectancy will be measured in months.
Asbestos fibers work their way through the lungs into the lung, or pleural, cavity. There they invade the mesothelium, the thin, moist, flexible tissue that lines the cavity. Mesothelioma specialists have two theories about how asbestos in the pleural cavity causes mesothelioma. One theory is that as the asbestos fibers migrate through the pleural cavity, they enter tissue walls and irritate tissues. The irritated cells respond by forming scar tissue. The mesothelial cells show an inflammatory immune response, scarring, and eventually the uncontrolled proliferation of cells that is the hallmark of cancer.
The second theory focuses on events at a molecular level, speculating that asbestos fibers interact with individual mesothelial cells, interfering with their cell division, or possibly damaging the cell's DNA during mitosis, or cell division. The part of the DNA that regulates the cells' growth and reproduction is damaged, so that reproduction is no longer controlled. Cells begin to reproduce wildly. This uncontrolled cell growth creates the thickened cancerous tissue and eventually begins to invade other organs.
The American Lung Association notes that almost all lung cancers are caused by external irritants that cause cancerous changes in cells. Like the mesothelium in the chest cavity, tissues in the lung are vulnerable to the cancer-causing effects of asbestos. Most lung cancer caused by asbestos inhalation starts in the lining of the bronchi, the tubes that lead from the windpipe into each lung. Lung cancer caused by asbestos exposure can also begin in the windpipe itself, the bronchioles, smaller tubes which branch off from the bronchi, or in the alveoli.
Lung cancer is also slow-growing, and there may be a latency of years between asbestos exposure and the first symptoms. Changes in the lung may in fact have begun almost as soon as a person is exposed to asbestos. Soon after exposure begins, a few abnormal cells may appear in the lining of the bronchi. If the exposure continues, more abnormal cells will appear. These cells may be on their way to becoming cancerous.
Workers with long exposure asbestos have 3 to 4 times greater risk of developing lung cancer than workers who have not been exposed to asbestos. Asbestos workers who smoke increase their risk of getting lung cancer by a factor of 50 to 100.
Asbestos Fibers Implicated in More Cancers
The International Agency Research on Cancer, IARC, which is a constituent organization of the World Health Association, recently reported that asbestos is implicated in still other types of cancer. Sufficient evidence has established that asbestos can cause cancers of the larynx, and ovarian cancer.
In the United Kingdom women exposed to asbestos during World War II when they manufactured gas masks have experienced an increased rate of ovarian cancer. Researchers have since demonstrated that of women who are exposed to asbestos have asbestos fibers accumulated in their ovaries. For cancer of the larynx, any exposure to asbestos was found to increase the risk of developing this deadly cancer, and the higher exposure, the higher the risk.
The mechanisms by which asbestos fibers cause cancers is complex, involving interactions between the mineral fibers and vulnerable cells in the affected organs. Crystalline asbestos fibers are very long-lived; once they lodge in human tissues, they may stay there for decades. Their reactivity to cells, their size, especially their surface area, and their surface chemistry all contribute to their potential to cause harm.
Although a causal linkage between asbestos exposure and colorectal cancer is not confirmed, increasing evidence links exposure to this cancer as well.
Asbestosis is caused by asbestos fibers that irritate the lung cells, causing the growth of scar-like tissue in the lungs and in the pleural membrane that surrounds the lungs. The scar tissue is thicker and less flexible than normal lung tissue, and cannot expand and contract as easily. Breathing becomes more difficult and painful for the affected person. People with asbestosis have shortness of breath, often accompanied by a cough. The scar-like tissue also compromises blood flow to the lung, forcing the heart to pump harder, which causes it to enlarge. Asbestosis is a serious, painful disease which can cause disability or death.