Types of Asbestos
Asbestos refers to six unique substances that belong to the serpentine and amphibole mineral families. These terms do not refer to mineral descriptions but to a broad term that refers to unique fibers. According to the Toxic Substances Control Act (TSCA), the asbestiform varieties of the following minerals are classified as asbestos:
This classification was adopted by the U.S. Environmental Protection Agency (EPA) in 1976. The TSCA granted the EPA permission to regulate these six types of asbestos, and they have since been banned in 52 countries.
However, hundreds of other asbestos-like minerals have since been recognized by the U.S. Bureau of Mines, yet they are not restricted or regulated. Erionite and taconite are two minerals that contain asbestiform fibers with the potential to cause serious health problems.
All of the identified forms of asbestos are recognized as human carcinogens that can cause asbestosis, malignant mesothelioma, lung cancer, ovarian cancer, laryngeal cancer and other serious diseases. The EPA has abandoned projects that strive to identify which asbestos fiber types are the most toxic, citing that the overall regulation of asbestos and asbestiform minerals is a more pressing priority.
Chrysotile is the only type of asbestos that is from the serpentine family and is known as white asbestos. These fibers are curly and are comprised of sheets of crystals.
Throughout industrial history, more than 95 percent of all asbestos used around the world was of the chrysotile variety. In many countries where other types of asbestos have been banned, the “controlled use” of chrysotile is still permitted. Despite the numerous studies that have proven chrysotile's carcinogenity, this exemption is the result of a long lobbying history by those in the asbestos industry.
In a study on 181 railroad workers exposed primarily to chrysotile asbestos, there were 14 mesothelioma deaths - which constituted 34 percent of cancer deaths in the study. Another study that followed 8,391 chrysotile-exposed members of the Finnish Locomotive Drivers' Association between the years 1953 and 1991 found a fourfold risk of mesothelioma. And a study on workers in an asbestos manufacturing facility - which used 99 percent chrysotile asbestos - recorded 17 mesothelioma fatalities, composing 4.3 percent of all deaths.
The other five types of asbestos are classified in the amphibole category. Amosite (brown asbestos) and crocidolite (blue asbestos) are considered the most commercially valuable types. Anthophyllite, tremolite and actinolite are the other non-commercial forms of amphibole asbestos. All amphibole fibers are straight and longer than chrysotile fibers, and studies suggest it may take less exposure to amphibole asbestos to cause mesothelioma than chrysotile asbestos.
Amosite, also known as cummingtonite-grunerite, originated in Africa. This form of asbestos was used heavily in the following industrial products:
- Cement sheets
- Pipe insulation
- Thermal insulation
- Roofing products
Amosite is similar in composition to anthophyllite but has higher iron content. Because it was especially resistant to sea water, amosite was commonly used to insulate ships. This form of asbestos is considered highly carcinogenic. In a study on 230 workers from an amosite manufacturing factory, researchers found 14 asbestosis deaths, five mesothelioma deaths, 25 lung cancer deaths, five gastrointestinal cancers, and 43 cancers overall.
Crocidolite is also found in Africa (as well as Australia and Bolivia), and is typically regarded as the most dangerous form of asbestos. Crocidolite varies in shade from gray-blue to leek-green. These fibers are stronger than chrysotile and are very heat-resistant. This type of asbestos is a harsher and more brittle form of the mineral, which is why it was not commonly used in many commercial products. Because of its tolerance to heat, it was used to insulate steam engines and make pipe insulation products. The mining town of Wittenoom, Australia is one of most prominent examples of the health risks of working with crocidolite. Of the roughly 6,500 men and 500 women who worked in or around the blue asbestos mine between 1943 and 1966, more than 1,000 have died of asbestos-related diseases and approximately 85 have passed away from mesothelioma. Exposure studies estimate as many as 700 mesothelioma cases could develop among former workers of Wittenoom by the year 2020.
Anthophyllite is one of the less common variations of asbestos. It was primarily mined in Finland until 1974. It generally has a lower tensile strength than other forms of asbestos. The fibers are brittle and white with a chain-like appearance. Mesothelioma has also been found to occur in workers exposed to the anthophyllite type of asbestos. A study on 736 miners and millers from two anthophyllite mines reported four cases of mesothelioma when 0.1 was expected, and an excess of lung cancer was also recorded.
Tremolite commonly appears in the form of blade-shaped crystals and is white or grayish in color. It was not used industrially, but it was found as a contaminant in certain talcum powders. Tremolite is commonly found in vermiculite ore, and it also appears in a number of metamorphic rocks. Much of the asbestos at the infamous Libby, Montana mine was tremolite. Tremolite has also been a contaminant of whitewash powders. The process of mixing the tremolite-contaminated whitewash product has been known to cause pleural mesothelioma, or cancer of the lining of the lungs. Numerous studied have confirmed that exposure to tremolite can cause asbestosis, lung cancer and mesothelioma cancer.
Actinolite is more resistant to acids and possess a harsh and brittle texture, making it less flexible than other types of asbestos. Even though actinolite was not used commercially, it can be found as a contaminant in chrysotile and vermiculite. As a result, actinolite can be found in some vermiculite- and chrysotile-containing products, including sheet gaskets, packing products, brakes and dryer felt. Because actinolite was a contaminant and not a primary component of asbestos-containing products, exclusive studies on the health effects of actinolite exposure are limited. In one case report, a railroad welder developed asbestosis from using asbestos-covered electrodes contaminated with actinolite.
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