About Asbestos

Asbestos describes any of a group of minerals that can be fibrous, many of which are metamorphic and are hydrous magnesium silicates. These minerals, together with their occurrences, uses, and associated hazards, have been discussed in detail by Guthrie and Mossman (1993).

The name is derived for its historical use in lamp wicks; the resistance of asbestos to fire has long been exploited for a variety of purposes. Asbestos was used in fabrics such as Egyptian burial cloths and Charlemagne's tablecloth (which according to legend, he threw in a fire to clean). Asbestos occurs naturally in many forms (see below); it is mined from metamorphic rocks.

When asbestos is used for its resistance to fire or heat, the fibers are often mixed with cement or woven into fabric or mats. Asbestos is used in brake shoes and gaskets for its heat resistance, and in the past was used on electric oven and hotplate wiring for its electrical insulation at elevated temperature, and in buildings for its flame-retardant and insulating properties, tensile strength, flexibility, and resistance to chemicals. The inhalation of some kinds of asbestos fibers, however, can cause various serious illnesses, including cancer. Many uses of asbestos are banned in many countries.

Types of asbestos and associated fibres

White asbestos

Chrysotile, CAS No. 12001-29-5, is obtained from serpentine rocks. Chrysotile is the type most often used industrially in the United States. There is evidence that this type of asbestos is harmful, although not perhaps as harmful as other forms (refer to UK Health & Safety Commission report Asbestos: Effects on health of exposure to asbestos, 1985). One formula given for Chrysotile is Mg₃(Si₂O₅)(OH)₄.

Brown asbestos

Amosite, CAS No. 12172-73-5, is a trade name for the amphibole known as Grunerite, from Africa, named as an acronym from Asbestos Mines of South Africa. One formula given for Amosite is Fe₇Si₈O₂₂(OH)₂.

Blue asbestos

Riebeckite, CAS No. 12001-28-4, also known under the variety name of Crocidolite, is an amphibole from Africa and Australia. It is the fibrous form of the amphibole riebeckite. Blue asbestos is commonly thought of as the most dangerous type of asbestos (see above and below). One formula given for Crocidolite is Na₂Fe²+₃Fe³+₂Si₈O₂₂(OH)₂.

Diseases caused by asbestos

As early as 1898 the Chief Inspector of Factories of the United Kingdom reported to Parliament in his Annual Report about the "evil effects of asbestos dust". He reported the "sharp, glass like nature of the particles" when allowed to remain in the air in any quantity, "have been found to be injurious, as might have been expected" (Report of the Select Committee 1994). In 1906 a British Parliamentary Commission confirmed the first cases of asbestos deaths in factories in Britain and recommended better ventilation and other safety measures. In 1918 a US insurance company produced a study showing premature deaths in the asbestos industry in the United States. In 1926 the Massachusetts Industrial Accidents Board processed the first successful compensation claim by a sick asbestos worker. Many American injuries from asbestos exposure came from shipbuilders working during World War II.

The problem with asbestos arises when the fibers become airborne and are inhaled. Because of the size of the fibers, the lungs cannot expel them. [Casarrett & Doull's Toxicology (2001), pp 520-522]

Diseases caused by asbestos include:

• Asbestosis – A lung disease first found in naval shipyard workers, asbestosis is a scarring of the lung tissue from an acid produced by the body's attempt to dissolve the fibers. [8] The scarring may eventually become so severe that the lungs can no longer function. The latency period (the time it takes for the disease to develop) is often 10-20 years.
  
  
  
• Mesothelioma – A cancer of the mesothelial lining of the lungs and the chest cavity, the peritoneum (abdominal cavity) or the pericardium (a sac surrounding the heart). It is believed that mesothelioma is caused by generation of reactive oxygen species (ROS) by the asbestos fibers. There is also some evidence to suggest that simian virus 40 (SV40) works together with asbestos in the development of malignant mesothelioma. Asbestos exposure is linked to at least 50% of patients developing malignant mesothelioma. Malignant mesothelioma has a peak incidence 35-45 years after asbestos exposure. Median survival for patients with malignant mesothelioma is 11 months. Asbestos has a synergistic effect with tobacco smoking in the causation of pleural mesothelioma.
  
  
  
• Cancer – Cancer of the larynx has been linked to asbestos. Some studies suggest that asbestos exposure is linked to a slightly increased risk of stomach, pharyngeal, and colorectal cancer.

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