For much of the 20th century, asbestos was viewed as the "miracle mineral" due to its various desirable properties. It was fire-resistant, non-corrosive, chemical-resistant, and made a great insulator. Further, it could be added to just about anything. Industrialization of the mining process allowed for asbestos fibers to be ground so small that the mineral could be sprinkled into anything from joint compound to cigarette filters.
However, by the late 1970s, it was painfully apparent that asbestos was hazardous - that it led to various lung diseases, including asbestosis, mesothelioma, and lung cancer.
What many don't quite understand, however, is why asbestos can lead to these conditions. The answer may be a bit surprising.
One of the things that makes asbestos fibers so dangerous is their size. To put it in perspective, when looked at side by side under a microscope, a strand of fiberglass insulation looks like a tree trunk when next to an asbestos fiber. The asbestos fiber, conversely, looks like a tiny whisker left behind in the sink after shaving.
The asbestos fibers of most concern are around three to five microns in length - that's three to five millionths of a meter. This is rather amazing when one thinks of the fact that the diameter of a human hair is approximately 100 microns.
Because of their small size, these fibers can bypass the body's natural defense mechanisms. Large particles and fibers may get caught in nose hair, or become embedded in the mucous lining the nose and throat. If the particle happens to get by these barriers, the hairlike cells in the respiratory epithelium work to constantly move particles back up the respiratory tract, where they can be swallowed or expectorated.
Again, because asbestos fibers can be so small, they can many times dance right around these barriers. If they do, they follow down the bronchial tubes and end up in the alveoli cells, the small air sacs at the end of the respiratory tree that are responsible for transferring oxygen from the lung to the blood.
It is here that the asbestos fibers can do real damage.
Because the body views the fiber as a foreign body, it attempts to destroy it by sending out cells known as macrophages. Macrophages are cells that target certain invading bodies and break them down. However, in the case of the asbestos fiber, the macrophage is unable to do its job. The very characteristics that made asbestos so desirable in building materials also prevents it from being digested by the body's defenses.
The length of the fiber is a key detriment to the macrophage. A longer fiber will cause damage to the macrophage as the macrophage tries to envelop the asbestos fiber. The macrophage cell wall becomes punctured by the fiber. The damaged cell releases acidic digestive enzymes which will damage lung tissue. Cytokines are also released which is an immune system messenger or signaler. The body, still sensing the presence of the fiber, cytokines, and damaged alveolus releases more macrophages, which still are unable to remove the foreign body. This cycle repeats itself for years and years until finally the macrophage activity leads to significant scarring of the alveoli walls. This scarring prevents the transfer of oxygen from the lung to the blood.
This scarring of the alveoli continues until the individual has what is known as asbestosis - a chronic and debilitating disease that leaves its victims constantly struggling for oxygen. Asbestosis many times can lead to lung cancer, which oftentimes leads to death.
Thus, ironically, it is the body's own defense mechanisms that damage the body, not the asbestos fiber itself.
It should be noted that there is a dose-response relationship between asbestos and resulting diseases such as asbestosis and lung cancer. This means that the greater the exposure to asbestos, the more likely it is that a disease will develop.
Also, there is a latency period between exposure and onset of disease. The time period between exposure and onset of symptoms can be anywhere from 20 to 50 years. This is how long the body sometimes takes to finally scar the alveoli to the point that they are no longer able to function.
When intact, asbestos containing building materials do not present a risk. It is when the materials are disturbed - crushed, torn, or broken - that asbestos fibers are released. All of this underscores how important it is to test for asbestos prior to disturbing building materials, and to leave asbestos abatement to those who specialize in doing it safely and lawfully.
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