All Fiber Types Cause Mesothelioma
There are various types of asbestos fibers, but all types, including Chrysotile, cause mesothelioma. Many experts have testified that Chrysotile fibers, like those found in friction and clutch products, cause mesothelioma. Indeed, virtually every group of scientists that has examined the question has found that reliable data show a causal relationship between Chrysotile asbestos and mesothelioma. Reports from various international and national agencies have confirmed this fact. This includes reports prepared by the 1997 Helsinki Conference, the American Cancer Society, the World Health Organization (“WHO”), the World Trade Organization (“WTO”), the Occupational Safety and Health Administration (“OSHA”), the National Institute for Occupational Safety and Health (“NIOSH”), the Environmental Protection Agency (“EPA”), the Consumer Products Safety Commission (“CPSC”) and the U.S. Department of Health and Human Services.
Mineralogy of Asbestos
According to the U.S. Geological Survey (USGS) asbestos is a generic name given to the fibrous variety of six naturally occurring minerals used in numerous asbestos-containing products. Asbestos is found in many places around the world, with the largest commercial mines in Canada, South Africa, Russia, and China.
Asbestos is composed of bundles of extremely long and thin fibers that can be easily separated from one another. The distinguishing characteristics of asbestos are that it is fibrous, resistant to heat and chemicals, has a high tensile strength, is flexible and has low electrical conductivity.
Asbestos minerals crystallize in fibrous forms with a range of chemical compositions. The minerals that crystallize as asbestos differ in gross appearance with different fiber sizes, shapes, colors and textures visible in hand specimens. They are divided into two main groups – amphiboles and serpentines. The amphibole group contains crocidolite, amosite, anthophyllite, tremolite and actinolite. Chrysotile is the only type of asbestos in the serpentine group. Crocidolite, amosite and chrysotile are the most important types of asbestos used historically. Crocidolite and amosite fibers are straight and needle-like while chrysotile fibers have a curly shape. Optical or electron microscopes other analytic instruments are used to identify specific asbestos types.
Amphiboles and Serpentines
The minerals called asbestos appear in fibrous forms with a range of chemical compositions. Asbestos can be divided into two main groups – amphiboles and serpentines. The amphibole group contains several types of asbestos including crocidolite, amosite, anthophyllite, tremolite and actinolite. Chrysotile is the only type of asbestos in the serpentine group. Amphiboles are classified by the amount of sodium, calcium, magnesium and iron they contain. Both amphiboles and serpentines minerals can have nonfibrous forms which are not considered to be asbestos.
Crocidolite, Amosite and Chrysotile
Crocidolite, amosite and chrysotile are the most important types of asbestos used historically. Tremolite may be found as a contaminant in other fibers or industrial minerals such as vermiculite and talc. All types of asbestos can be broken down mechanically into small fiber bundles consisting of individual thin fibers.
Crocidolite and amosite fibers are straight and needle-like while chrysotile fibers have a curly shape. This common shape or morphology is described by the aspect ratio which is the ratio between the length of the fiber versus its width. Typically, asbestos fibers have an aspect ratio of 3 to 1 or greater.
Crocidolite or blue asbestos is a cobalt blue to lavender blue variety of the mineral riebeckite and is particularly resistant to chemicals such as acids, alkalis and solvents. Amosite or brown asbestos is a trade name for the yellowish gray to dark brown variety of minerals belonging to the cummingtonite-grunerite solid solution series. Amosite fibers are very strong, somewhat coarse and were often added as a strengthening or binding agent in thermal insulation materials.
Chrysotile or white asbestos is the most abundant form of asbestos. It may appear white to grayish green with a silky luster. Chrysotile fibers can be over 10 cm in length and are very flexible. Chrysotile can be woven into various textiles such as asbestos cloth, felt and yarn.
The fiber bundle structure of asbestos is most evident in chrysotile which exhibits a well-defined unit fiber comprised of tightly rolled up sheets forming the fibers. The crystal structures of amphiboles exhibit a gradual transition from a blocky to asbestiform shape.
The mechanical separation of asbestos, i.e. defiberizing or opening, creates morphologic changes such as breaking up fiber bundles, bending and splitting the ends of fibers. Resistance to thermal degradation in asbestos is related to dehydration reaction of the water contained in the asbestos minerals.
The tensile strength of amosite and crocidolite is comparable to chrysotile. However, chrysotile retains its tensile strength to a higher temperature than the amphiboles. Asbestos fibers are nearly insoluble in water, but prolonged exposure to water, especially at high temperature, can lead to leaching of some elements. Chrysotile dissolves in acids more easily than the amphiboles, but both resist deterioration in alkali solutions.
In general, the electrical resistivity of chrysotile is lower than the amphiboles, but all asbestos fibers have high electrical resistivity. This property has been widely exploited in electrical insulation applications. Other bulk physical properties of asbestos including surface area and charge, adsorption and chemical bonding determine its suitability for commercial use.
U.S. Geological Survey Fact Sheet FS-012-01 “Some Facts About Asbestos” by Robert L. Virta (March 2001).
Substances Profiles: Asbestos CAS No. 1332-21-4 in Report on Carcinogens, Eleventh Edition.