Asbestos refers to a family of magnesium-silicate mineral fibers. In the past, asbestos was used widely for insulation because it does not conduct heat well and it is resistant to melting or burning. As the link between asbestos and mesothelioma has become well known, the use of this material has decreased. However, up to 8 million Americans may already have been exposed to asbestos.
According to the United States Environmental Protection Agency, as many as 733,000 schools and public buildings in the country contain asbestos insulation. As many as 10% to 15% of schools in the United States may contain asbestos insulation. People who may be at risk for occupational asbestos exposure include some miners, factory workers, insulation manufacturers, rail-road workers, ship builders, gas mask manufacturers and construction workers, particularly those involved with installing insulation. Several studies have shown that family members of people exposed to asbestos at work have an increased risk of developing mesothelioma, because asbestos fibers are carried home on the clothes of the workers.
There are 2 main forms of asbestos-- serpentine and amphiboles. Serpentine fibers are curly and pliable. Chrysotile is the only type of serpentine fiber and it is the most widely used form of asbestos. Amphiboles are thin, rod-like fibers of which there are 5 main types-crocidolite, amosite, anthrophylite, tremolite and actinolyte. Amphiboles (particularly crocidolite) are considered to be the most carcinogenic (cancer-causing). However, even the more commonly used chrysotile fibers have been associated with malignant (cancerous) mesotheliomas and should be considered dangerous as well.
It may be that asbestos causes cancer by physically irritating cells rather than by a chemical effect. When fibers are inhaled, most are cleared in the nose, throat, trachea or bronchi. Fibers are cleared by sticking to mucus inside the air passages and being coughed up or swallowed. The long, thin, fibers are less readily cleared, and they may reach the ends of the small airways and penetrate into the pleural lining of the lung and chest wall. These fibers may then directly injure mesothelial cells of the pleura, and eventually cause mesothelioma.
Asbestos fibers can also damage cells of the lung and result in asbestosis (formation of scar tissue in the lung), and lung cancer. The risk of lung cancer among people exposed to asbestos is increased by 7 times, compared with the general population. Indeed, asbestosis, mesothelioma and lung cancer are the 3 most frequent causes of death and disease among people with heavy asbestos exposure. Peritoneal mesothelioma, which forms in the abdomen, may result from coughing up and swallowing inhaled asbestos fibers. Cancers of the larynx, pancreas, esophagus, colon and kidney have also been linked to asbestos exposure, but the increased risk is not as great as with lung cancer.
Although the risk of developing mesothelioma rises with the amount of asbestos exposure, it is clear that genetic factors also play a role in determining who develops the disease. This explains why not all persons exposed to high levels of asbestos dust develop mesothelioma.
(Inputs from www.mesothelioma.com and www.mesothelioma.org)
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