Asbestos

More modern uses of asbestos go back to the end of the 19th century, after the discovery of major deposits of asbestos in Canada. Johns Manville, who later was associated with a major asbestos company named after him in the United States, discovered deposits of this mineral and expanded their use. An early use of asbestos was to replace dried dung as wrapping around boilers for insulation. Ironically, in the 20th century Manville would die of a mesothelioma. The increasing use of asbestos began in the 1920s and 1930s with peak use around the world in the mid-1970s [1]. Eventually

some 3-4000 products would be made using asbestos. In the United States about 775,000 tons of asbestos were used at its peak, whereas the most recent figures suggest that slightly more than 1,000 tons of raw asbestos are now imported. Asbestos in finished products is not counted as part of the amount of asbestos being brought into any country and is, therefore, unaccounted for. The use of asbestos has markedly decreased around the world; currently over 50 countries have totally banned the use of asbestos [3]. Presently the major producers of asbestos include Russia, Kazakhstan, China, and Brazil [1]. While traditionally Canada has been in the top-five worldwide producers of asbestos, there was a major political change in 2012, which led to the announcement that all the Canadian asbestos mines that were still left, in the province of Quebec, would be shut down and that Canada would cease to be an exporter of asbestos fiber. There are steps being taken to end any use of asbestos in Quebec as well. As this is being written the Brazilian Supreme Court is considering the national issue of a ban on asbestos in that country. In addition to the mining of asbestos, the countries with the greatest current use of this material include China, Russia, India, and Brazil [1]. Because of perceived differences, which may in fact not be true, for the different fiber types, virtually all countries have stopped using any of the amphiboles, so the current worldwide controversy over the use of asbestos relates to the continuing use of chrysotile asbestos alone. Unfortunately, a small number of countries with commercial interests in the use of asbestos have for decades blocked its listing under the Rotterdom Conventions as a hazardous material. Because of its potentially useful characteristics, such as being a good insulator for both hot and cold, not conducting electricity, being resistant to acids, and being relatively easy to manipulate and add to other materials, asbestos was widely used in a large range of products in the past [4]. It has been estimated that between 3000 and 4000 different products containing asbestos were found at one time in the United States, but the diminished use has now limited the materials that are likely to contain asbestos through such things as roofing felts and automotive friction products. The wide range of products in which asbestos could be found, or was considered

for use, includes traditional construction materials, automotive products, filtering agents, cutting boards for specialty jewelry use, phonographic records, filters on cigarettes, and paper wrappers around other tobacco products. Over time, in some countries that have not totally eliminated the use of asbestos, limitation after limitation has been put in place that minimizes the use of asbestos. Because of its former widespread use, many individuals with a long list of job titles have been exposed to asbestos. Of special note would be those in the construction trades, shipyard workers, auto mechanics, and many others. Major exposures to asbestos occur through occupational and environmental exposures. It is important to note that asbestos fibers were not always contained in the workplace. In addition to the direct handling of asbestos, exposures occurred to workers who worked in the vicinity of those using it, resulting in bystander exposure. Fibers would also work their way home, giving rise to familial exposure. Neighborhoods surrounding asbestos utilizing facilities could lead to neighborhood exposure, such as that occurring near mines, factories, and shipyards. 14.4 How Does Asbestos Enter the Body?The major routes of entry for asbestos into the body are inhalation and ingestion, with minor exposure via the skin. While the ingestion of asbestos may relate to fibers of virtually any size, the issues relating to inhalation are more complex. 14.4.1 Inhalation

Only fibers of a respirable size will enter the respiratory system [5]. There are both mechanical and biological efforts by which the body attempts to keep asbestos from entering the body or eliminating it after its entry. This begins in the nose with large particles, including fibers, being trapped in nasal hairs and then in the upper airway, which is lined with ciliated epithelium and mucous-producing cells. In the mucociliary escalator, mucous traps the materials, with the cilia then beating upward and forcing the materials out to prevent entry into the lung, ultimately being swallowed and eliminated.