Asbestos is a group of six naturally occurring fibrous metamorphic minerals: chrysotile, tremolite, actinolite, amosite, crocidolite and anthophyllite. Of the hydrous magnesium silicate variety, asbestos has long been used for a variety of industrial and commercial purposes. Once viewed as a "miracle mineral," asbestos was commonly used as an insulator. Resistant to heat and fire and high in tensile strength, asbestos was used for insulation in buildings, automobile parts and the shipbuilding trades. Miners, harvesting the hazardous mineral on a daily basis, were most at risk of developing mesothelioma because of the amount of direct asbestos exposure they faced.
The health hazards associated with asbestos have been known since the late nineteenth century, though they were ignored for the purpose of business prosperity. A result of increased public awareness and growing health concerns, asbestos was finally regulated under section 112 of the Clean Air Act in 1970.
Asbestos Types and Associated Fibres
Six minerals are defined as "asbestos" including: chrysotile, amosite, crocidolite, tremolite, anthophyllite and actinolite.
Chrysotile, CAS No. 12001-29-5, is obtained from serpentine rocks which are common throughout the world. Its idealized chemical formula is Mg3(Si2O5)(OH)4. Chrysotile fibers are curly as opposed to fibers from amosite, crocidolite, tremolite, actinolite, and anthophyllite which are needlelike.Chrysotile, along with other types of asbestos, has been banned in dozens of countries and is only allowed in the United States and Europe in very limited circumstances. Chrysotile has been used more than any other type and accounts for about 95% of the asbestos found in buildings in America. Applications where chrysotile might be used include the use of joint compound. It is more flexible than amphibole types of asbestos; it can be spun and woven into fabric. The most common use is within corrugated asbestos cement roof sheets typically used for outbuildings, warehouses and garages. It is also found as flat sheets used for ceilings and sometimes for walls and floors. Numerous other items have been made containing chrysotile including brake linings, cloth behind fuses (for fire protection), pipe insulation, floor tiles, and rope seals for boilers.
Amosite, CAS No. 12172-73-5, is a trade name for the amphiboles belonging to the Cummingtonite - Grunerite solid solution series, commonly from Africa, named as an acronym from Asbestos Mines of South Africa. One formula given for amosite is Fe7Si8O22(OH)2. It is found most frequently as a fire retardant in thermal insulation products and ceiling tiles.
Crocidolite, CAS No. 12001-28-4 is an amphibole found primarily in southern Africa, but also in Australia. It is the fibrous form of the amphibole riebeckite. One formula given for crocidolite is Na2Fe2+3Fe3+2Si8O22(OH)2.
Notes: chrysotile commonly occurs as soft friable fibers. Asbestiform amphibole may also occur as soft friable fibers but some varieties such as amosite are commonly straighter. All forms of asbestos are fibrillar in that they are composed of fibers with widths less than 1 micrometer that occur in bundles and have very long lengths. Asbestos with particularly fine fibers is also referred to as "amianthus". Amphiboles such as tremolite have a crystal structure containing strongly bonded ribbonlike silicate anion polymers that extend the length of the crystal. Serpentine (chrysotile) has a sheetlike silicate anion which is curved and which rolls up like a carpet to form the fiber.
Chrysotile asbestos - Also called white asbestos, chrysotile asbestos is viewed to be the safest of the six because it is less friable (less brittle / likely to produce airborne microbes) and therefore less likely to be inhaled. More than 95% of asbestos used today is of the chrysotile variety. Some early evidence suggested that chrysotile asbestos did not pose a health hazard even when inhaled, though more recent animal studies have dispelled this myth. Chrysotile is the only type of asbestos classed as a serpentine mineral (fibers making up chrysotile are of a curled variety).
The remaining five types of asbestos are amphibole minerals, meaning that they are made up of straight, needle-like fibers.
- Tremolite asbestos - Tremolite asbestos is not often used industrially, though it was sometimes found in certain commercial products such as talcum powder.
- Actinolite asbestos - Like tremolite, actinolite asbestos is not often used industrially. Airborne actinolite asbestos fibers are easily inhaled and severely damaging to the lungs.
- Amosite asbestos - Also called brown asbestos, amosite asbestos is used for a variety of commercial purposes such as pipe and cement sheet insulation.
- Crocidolite asbestos - Also called blue asbestos, crocidolite asbestos viewed as the most dangerous of the six.
- Anthophyllite asbestos - Like tremolite and actinolite, anthophylite asbestos is not often used industrially, though it can occasionally be found in certain types of vermiculite (natural minerals that expand with the application of heat).
Source: Mesothelioma Research Foundation Of America www.mesorfa.org
- When asbestos fibers are inhaled, most fibers are expelled, but some can become lodged in the lungs and remain there throughout life. Fibers can accumulate and cause scarring and inflammation. Enough scarring and inflammation can affect breathing, leading to disease.
- People are more likely to experience asbestos-related disorders when they are exposed to high concentrations of asbestos, are exposed for longer periods of time, and/or are exposed more often.
- Inhaling longer, more durable asbestos fibers (such as tremolite and other amphiboles) contributes to the severity of asbestos-related disorders.
- Exposure to asbestos, including tremolite, can increase the likelihood of lung cancer, mesothelioma, and non-malignant lung conditions such as asbestosis (restricted use of the lungs due to retained asbestos fibers) and changes in the lung lining.
- Changes in the lining of the lungs (pleura) such as thickening, plaques, calcification, and fluid around the lungs (pleural effusion) may be early signs of asbestos exposure. These changes can affect breathing more than previously thought. Pleural effusion can be an early warning sign for mesothelioma (cancer of the lining of the lungs).
- Most cases of asbestosis or lung cancer in workers occurred 15 years or more after the person was first exposed to asbestos.
- Most cases of mesothelioma are diagnosed 30 years or more after the first exposure to asbestos.
- Mesothelioma has been diagnosed in asbestos workers, family members, and residents who live close to asbestos mines.
- Health effects from asbestos exposure may continue to progress even after exposure is stopped.
- Smoking or cigarette smoke, together with exposure to asbestos, greatly increases the likelihood of lung cancer.
Source: Agency for Toxic Substances and Disease Registry, www.atsdr.cdc.gov/asbestos
Conditions Associated with Asbestos
Asbestosis is a serious, progressive, long-term disease of the lungs. Asbestosis is not a cancer. Inhaling asbestos fibers that irritate and inflame lung tissues, causing the lung tissues to scar, causes asbestosis. The scarring makes it hard to breathe and difficult for oxygen and carbon dioxide pass through the lungs. Asbestosis generally progresses slowly. The latency period for the onset of asbestosis is typically 10-20 years after the initial exposure. The disease can vary from asymptomatic (no symptoms) to disabling and potentially fatal.
Signs and Symptoms of asbestosis can include:
- Shortness of breath is the primary symptom
- A persistent and productive cough (a cough that expels mucus)
- Chest tightness
- Chest pain
- Loss of appetite
- A dry, crackling sound in the lungs while inhaling.
Persons with significant exposure to asbestos are at risk for developing various types of pleural (lining of the lungs) abnormalities. These abnormalities include pleural plaques, pleural thickening, pleural calcification, and pleural mesothelioma.
Mesothelioma is a rare cancer which may affect the lining of the lungs (pleura) or the abdominal contents (peritoneum). Most mesotheliomas are caused by exposure to asbestos.
Lung cancer is a malignant tumor that invades and obstructs the lung's air passages. Cigarette smoking greatly increases the likelihood of a person developing lung cancer as the result of asbestos exposure. The most common symptoms of lung cancer are cough, wheezing, unexplained weight loss, coughing up blood, and labored breathing. Other symptoms of lung cancer include shortness of breath, persistent chest pain, hoarseness, and anemia. People who develop these symptoms do not necessarily have lung cancer, but they should consult a physician for advice.
Source: Agency for Toxic Substances and Disease Registry, www.atsdr.cdc.gov/asbestos
Asbestos Exposure and Your Work
Many people have come into contact with asbestos fibers through their jobs (occupational exposure). Some of the work environments or occupations in which workers are now or were exposed in the past include:
- Asbestos product manufacturing (insulation, roofing, building, materials)
- Automotive repair (brakes & clutches)
- Construction sites
- Maritime operations
- Mining operations
- Offshore rust removals
- Oil refineries
- Power plants
- Sand or abrasive manufacturers
- Shipyards / ships / shipbuilders
- Steel mills
Individuals who have worked in the above work environments and occupations should consult with a physician with expertise in the evaluation and management of asbestos-related lung disease.
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