Asbestos (Greek: inextinguishable) is the common name of a number of naturally occurring, hydrated silicate minerals that possess a crystalline structure and low thermal conductivity. They are incombustible in air and separable into filaments. These minerals occur as extremely thin flexible fibers having great tensile strength and thermal stability, and they can be spun into yarn and made into textiles. There are some 3000 recorded uses of asbestos including ‘‘fireproof’’ textiles, paper and boards, clutch and brake linings, asbestos cement sheets and pipes, flooring and roofing products, electrical and thermal insulating materials, coatings, and heat shields.
The term asbestos was first used mineralogically in the middle of the 19th century with regard to a fibrous amphibole mineral discovered in the Italian Alps. The six major types of asbestos in use fall into two major groups: serpentine, having a layered silicate structure, and amphibole, having an SiO4 chain structure. Chrysotile (white asbestos) is the sole member of the serpentine group. Chrysotile asbestos accounts for over 90 % of the world’s asbestos production. Of the five members of the amphibole group, crocidolite (blue asbestos) and amosite (brown asbestos) are widely used commercially and tremolite and actinolite less so (Table 1).
Asbestos has been known and used in small amounts for thousands of years, but it was not widely used prior to the latter part of the 19th century [3]. Asbestos was first mined in the Quebec, Canada, chrysotile fields in 1878, followed by Russia in 1885 and South Africa in 1906.
Within 20 years of the first industrial production of asbestos, the public health hazards associated with asbestos started to come to light. Between 1890 and 1895, 16 out of 17 workers in a French asbestos weaving factory had died; by 1899, 11men who had worked in an asbestos spinning factory in the United Kingdom had died at aboutthe age of 30, having spent the whole of their working lives in this occupation (cording). The last of these deaths was reported to the Departmental Committee for Compensation for Industrial Diseases (U. K.) in 1906; this was the first recorded case of the disease that has become known as asbestosis [5]. The first complete description of asbestosis appeared in 1927 [6], [7]. Asbestosis and other asbestos-related diseases are treated in detail in Chapter 9.
The widespread commercial use of asbestos over the past 100 years has led to its uncontrolled distribution throughout much of the industrialized world and its appearance in the general environ ment. The concentration of asbestos fibers in the urban atmosphere is actually in the lower part of the range 10 – 100 ng/m3 , but this can rise substantially in certain locations [8–12]. For example, in the vicinity of factories using asbestos, concentrations of asbestos fibers in the external atmosphere up to 5000 ng/m3 have been reported. In buildings where asbestos is being worked with or damaged, the concentration of asbestos in the air can be as high as 800 ng/m3 [11], [13], [14]. Low concentrations of asbestos are also found in water, beverages, and pharmaceutical and other medical products [9], [11], [15–23].
All commercial asbestos minerals are hydrous silicates of either the serpentine or the amphibole group. The serpentine minerals, which include chrysotile, have relatively simple chemical formulas; e.g., for chrysotile it is Mg3[Si2O5](OH)4. (See Figs. 1,2,3) Amphiboles have a widely varying nature and they are best considered by the general formula A0-1X2Y5Z8O22(OH, F)2; the substituents are: A ¼ sodium or potassium; X ¼ sodium or calcium; Y ¼ magnesium, iron, or aluminum; Z ¼ aluminum or silicon. It is not uncommon that small amounts of elements such as chromium, nickel, and titanium occur; usually many other elements are present in trace amounts. Minerals can have wide ranges of composition but still possess their characteristic structure and general formulas.