Causes of Mesothelioma
Mesothelioma is a highly aggressive cancer that is difficult to both diagnose and treat. Between two and three thousand cases of malignant mesothelioma are diagnosed each year in America, and these figures are projected to increase throughout the next decade.
What Causes Mesothelioma?
An overwhelming body of scientific and medical evidence has proven that malignant mesothelioma is caused by asbestos exposure. Currently, there is no other proven cause for this disease.
Asbestos is a naturally-occurring fibrous mineral that was widely used in industrial, commercial, and domestic products throughout the twentieth century. Asbestos was touted for its durability, fire resistance, and excellent insulating properties, and was used in several thousand different manufactured "asbestos products," including construction materials, household appliances, and brake linings. Because asbestos use was so widespread, millions of Americans have been exposed to the toxic material, which has led to the development of malignant mesothelioma among thousands of Americans.
How Does Asbestos Exposure Cause Mesothelioma?
Internal organs and body cavities are covered by a thin tissue membrane called the mesothelium. This lining covers the thoracic cavity (where it is called the pleura), the heart sac (where it is known as the pericardium), and the abdominal cavity (where it is called the peritoneum). The mesothelium offers both support and protection for organs and body cavities and provides a source of lubrication that helps organ function and health.
Mesothelioma develops in the linings of organs and body cavities, typically in the pleura, pericardium, or peritoneum. In very rare cases, mesothelioma may develop in the lining of the testicles, known as the tunica vaginalis.
The exact method by which asbestos causes mesothelioma is still being researched, but medical professionals offer four different theories:
- Asbestos causes irritation and inflammation of mesothelial cells, which results in irreversible scarring, cellular damage, and eventually cancer.
- Asbestos fibers enter cells and disrupt the function of cellular structures that are essential for normal cell division, causing cellular changes that lead to cancer.
- Asbestos causes the production of free radicals. These molecules damage DNA, and cause cells to mutate and become cancerous.
- The presence of asbestos causes cells to produce oncoproteins. These molecules cause mesothelial cells to ignore normal cellular division restraints, and this can lead to the development of cancer.
The element that ties each theory together is the fact that asbestos results in cellular damage, which causes cells to lose control over their own cycles of normal division and begin dividing uncontrollably. Healthy cells follow cycles of cell division that ensure tissues and organs do not grow beyond normal size - in cancer cells, these restraints are lost.
In cases of mesothelioma, the result is that membranes in the affected location begin to thicken, and fluid builds up in the spaces between membrane layers. As cancer cells continue to divide and pile on top of one another, tumors begin to form. The uncontrolled division of cancer cells results in the impaired function of the body's organs and systems (primarily due to factors such as internal pressure caused by the growth of tumors, and the reduction of essential nutrients for organs).
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The six recognized asbestos minerals, which are considered silicates (molecules that include silicon and oxygen), include:
- Chrysotile - (Also known as white or green asbestos, from the Greek word meaning "fine, silky hair") Appears as curly, whitish fibers and constitutes 95 percent of the asbestos in use. Chrysotile is mined throughout the world, but most of the United State's chrysotile supply comes from Canada, Africa, and former USSR. Scientists believe this to be the least toxic of all asbestos forms.
- Crocidolite - (Also known as riebeckite or blue asbestos) Composed of straight fibers, most crocidolite comes from southern Africa and Australia. It is believed to be the most toxic form of all asbestos minerals.
- Amosite - (Also known as cummingtonite-grunerite or brown asbestos) The trade name "amosite" is an acronym for Asbestos Mines of South Africa, after the Amosa mines. Amosite is also straight in shape, but brittle in structure and excellent for use in heat insulation.
- Anthophyllite - This form of asbestos is brittle, white, and contains various forms of iron. It has been found to have excellent resistance to chemicals and heat.
- Tremolite - In rough form, tremolite appears white and chalky. Tremolite can also be naturally found in other mineral forms aside from asbestiform. It has been the major ingredient in industrial and commercial talc.
- Actinolite - Typically prismatic, flat in structure, and elongated. Actinolite also comes in forms other than asbestiform and has poor resistance to chemicals.
The last five amphibole (which translates to "ambiguous" in Greek) types have a slightly more complex crystal structure than chrysotile and are not used as extensively in commercial products as chrysotile. Due to their structure, amphiboles tend to stay in the lungs longer than chrysotile and are more likely to cause illness because of this factor. Some hypothesize very small contaminations of amphibole fibers within chrysotile are most to blame for cancer deaths caused by asbestos exposure.
Asbestiform minerals are found in serpentine and ultramafic rock. These rocks are located throughout the United States, especially near mountainous regions. California is exceptionally bountiful in asbestos, where the mineral can be found in at least 44 of the state's 58 counties (some geologists report asbestos is found in 50 of the 58 counties). Asbestos fibers especially form near fault zones, where temperature, pressure, and time have transformed the molecules into the asbestiform crystals.
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The term "asbestos" has been given to six naturally occurring mineral fibers that have been used for commercial purposes. It can be found in hundreds of countries on just about every continent. These fibers belong to two separate mineral groups, known as serpentine and amphibole.
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| A Detailed Diagram of Where Asbestos Can Be Found in the Home |
The U.S. Bureau of Mines has listed more than 100 mineral fibers as "asbestos-like" fibers, but the United States government only regulates the six aforementioned forms (primarily due to effective lobbying on behalf of the asbestos and stone industries).
These very fine fibers are separable, hundreds of times thinner than human hairs, and too small to be seen with the naked eye. The Occupational Safety and Health Administration (OSHA) defines fibers of concern as at least five micrometers long and at least three times as long as their diameters. For a frame of reference, mineralogists work with fibers as much as a thousand times as long as their diameters.
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Over the course of the past century, millions of innocent people have been exposed to asbestos, a class of fibrous minerals known to cause a variety of cancers.
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| Once asbestos is inhaled it can lodge itself within the body's organs causing cells to mutate and become cancerous. |
For many decades asbestos was considered an acceptable source of insulation, and thousands of materials made from asbestos were widely applied in industrial and domestic settings.
Asbestos was found in countless products on the commercial market, in many factories, homes and public structures, and in a myriad of industries, such as railway production, shipbuilding, and energy production.
For information about at-risk workplaces and products, please see Occupations at Risk for Asbestos Exposure and Products Containing Asbestos.
Of the millions of people who have been exposed to asbestos in the United States alone, thousands have developed life-threatening illnesses, many of which are aggressive cancers. Each year, approximately 10,000 Americans die from diseases caused by exposure to asbestos.
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